US 5,871,961 AGrant
Nucleic Acids Encoding CR2 Polypeptides, Vector and Transformed Cell Thereof, and Expression Thereof
Issue Date:1999-02-16
•44 Claims
•2 Drawing Sheets
Abstract
Early-induced genes by interleukin-2 (IL-2) have various DNA sequences. This patent describes a polyribonucleotide with a nucleotide segment encoding amino acids 1-60 of SEQ. ID No: 4, antibody binding homologues thereof, antibody binding fragments thereof at least 5 amino acids long, and fusion proteins thereof, alleles or naturally occurring mutants of the polyribonucleotide, and anti-sense polyribonucleotides thereof. Also provided are proteins, homologues, fragments, fusion proteins, vectors, transfected hosts, animal models, probes, and other related technology.
Metadata
Assignee
- Trustees of Dartmouth College
Inventors
- Kendall A. Smith
- Carol Beadling
Application Information
Application Number:US 4613791
Filing Date:1995-06-05
Priority Date:1991-11-20
Art Unit:182
Classifications
IPC:
C12N 1512C12N 1562C12N 1564
Field of Search:
53643523.5;24.5;24.32;23.1;24.33;69.169.1
Patent Drawings (2 sheets)
Description
BACKGROUND OF THE INVENTION
Mammalian cell growth, differentiation, and migration are directed by hormones and specific protein ligands, often termed cytokines. In particular, cells comprising the neuro-endocrine, hematopoietic and the immune/inflammatory systems are known to be governed by cytokines. Cytokines, like other ligands, interact with cells by means of specific receptors, usually expressed on the cell surface.
A fundamental problem confronting biomedical scientists is to discern how signals are transduced through ligand receptors and how these signals determine the response of the cell. Many ligands influence their target cells by stimulating the expression of specific genes. However, the genes signaled by most cytokines remain largely unknown owing to the complexity of cellular biochemistry. Moreover, the gene products that are vital for performing different cellular processes are often only expressed transiently, and/or in very low concentrations so that they are difficult to detect, isolate and characterize.
Interleukin-2 (IL-2) is a cytokine that is critical for the immune system: it directs the proliferation and differentiation of T lymphocytes (T-cells), B lymphocytes (B-cells), and natural killer (NK) cells. Just how IL-2 signals these cellular events in the various types of target cells remains unknown. A few genes have been identified that are expressed as a result of IL-2 stimulation of T cells. These include the cellular proto-oncogenes c-fos, c-myb, c-myc, pim-1, and c-raf-1. However, exactly how many and what other genes are expressed as a result of IL-2/IL-2 receptor interaction remains unknown.
Since the discovery of DNA cloning, methods have become available to isolate specific genes expressed by cells. However, it has been difficult to devise new methods to isolate and clone all or most of the genes expressed by a cell activated by a given ligand, a task that must be done before one can understand how the ligand directs the cell to perform specific functions. In addition, methods of identifying a particular gene or genes stimulated early on after ligand receptor activation have not been easily forthcoming as the number of genes stimulated by receptor activation from which a particular gene must be selected is usually quite large.
Therefore, what is needed are methods to select and enrich only for those genes stimulated by a given ligand. Ideally, these methods should detect those genes expressed in low concentrations, as well as those expressed at high concentrations.
SUMMARY OF THE INVENTION
This invention pertains to complementary deoxyribonucleic acid (cDNA) libraries enriched in clones containing genes induced by ligand stimulation of a cell having a corresponding receptor for the ligand, and to methods of producing the same. This invention also relates to the genes which are expressed immediately or early on as a consequence of such a ligand-receptor interaction, and to methods of identifying these genes.
In the method of producing a cDNA library enriched in ligand-inducible genes, a cellular ligand receptor on a cell is activated with a ligand, for a predetermined period of time, to induce expression of those genes expressed as a result of ligand-receptor binding. Useful ligands include any of those which can activate a specific cellular receptor. These include natural or synthetic ligands for the receptor. Ligands include cytokines such as the interleukins, cellular growth factors, colony stimulating factors, hormones, peptides, antibodies, and receptor-binding fragments thereof.
The cells are activated with the ligand in the presence of labelled RNA precursors. These precursors are incorporated into RNA synthesized by the cell in response to receptor activation. Labelled precursors are used in order to distinguish newly transcribed RNA from unlabelled, preexisting RNA. Preferred labelled RNA precursors include 6-thioguanine, 4-thiouridine, and tritiated uridine.
Activation is also carried out in the presence of a substance which enhances the level of RNA in a cell. Preferred substances include the protein synthesis inhibitors, cycloheximide and puromycin. Other useful substances include cyclic 3',5'-adenosine monophosphate (cAMP), analogs of cAMP such as dibutyryl cAMP, and other molecules which increase the intracellular level of cAMP. The labelled RNA is then separated from the unlabelled RNA and used to prepare cDNA. The cDNA is cloned into host cells to provide a cDNA library of cDNA-containing clones. This library is then screened for clones containing ligand-inducible genes.
In one embodiment of the invention, the screening step includes probing the cDNA library with a DNA probe constructed from total cellular RNA or mRNA derived from (1) a ligand-induced cell and from (2) an uninduced cell. The library is probed under conditions such that the probe hybridizes specifically with a complementary cDNA sequence in the library. The selecting step includes selecting those clones containing sequences that hybridize only with probes constructed from ligand-induced mRNA or total RNA.
By following the method of the invention, eight clones containing ligand-induced genes have been identified. These genes have been named Cytokine Response (CR) genes 1-8. CR genes 1-3, 5, 6, and 8 are novel. CR4 is identical to a gene reported as SATB-1 (Dickinson, L. A. et al. (1992) Cell 70:631-645), for Special AT-rich Binding protein 1, which binds selectively to the nuclear matrix/scaffold-associating region of DNA. CR7, also identified using the method of the invention, is identical to the putative proto-oncogene, pim 1, a known IL-2-induced gene. The nucleic acid sequences of these CR genes, i.e., CR genes 1-6 and 8 are set forth in SEQ ID NOs:1, 3, 5, 7, 9, 11, and 13 and FIGS. 1-7. The amino acid sequences encoded by these CR genes are set forth in SEQ ID NOs.:2, 4, 6, 8, 10, 12, and 14 as well as in SEQ ID NOs:1, 3, 5, 7, 9, 11, and 13 and FIGS. 1-7.
The present invention, therefore, also pertains to a CR1 polypeptide, preferably a substantially pure preparation of a CR1 polypeptide, or a recombinant CR1 polypeptide. In preferred embodiments, the CR1 polypeptide has an amino acid sequence at least 60%, 80%, 90% or 95% homologous to the amino acid sequence in SEQ ID NO:2; the polypeptide has an amino acid sequence essentially the same as the amino acid sequence in SEQ ID NO:2; the polypeptide is at least 5, 10, 20, 50, 100, or 150 amino acids in length; the polypeptide comprises at least 5, preferably at least 10, more preferably at least 20, more preferably at least 50, 100, or 150 contiguous amino acids from SEQ ID NO:2. In further preferred embodiments, a protein homologous to SEQ ID NO:2 has a molecular weight of about 22 kilodaltons (kD), e.g. in the range of 15-30 kD.
In a preferred embodiment, a polypeptide having at least one biological activity of the CR1 polypeptide may differ in amino acid sequence from the sequence in SEQ ID NO:2, but such differences result in a modified polypeptide which functions in the same or similar manner as native CR1 protein or which has the same or similar characteristics of the native CR1 protein. Such a peptide can include at least 1, 2, 3, or 5, and preferably 10, 20, and 30, amino acid residues from residues 1-202 of SEQ ID NO:2.
In yet other preferred embodiments, the CR1 polypeptide is a recombinant fusion protein which includes a second polypeptide portion, e.g., a second polypeptide having an amino acid sequence unrelated to a protein represented by SEQ ID NO:2, e.g., the second polypeptide portion is glutathione-S-transferase, e.g., the second polypeptide portion is a DNA binding domain, e.g., the second polypeptide portion is a polymerase activating domain, e.g. the fusion protein is functional in a two-hybrid assay.
Yet another aspect of the present invention concerns an immunogen comprising a CR1 polypeptide in an immunogenic preparation, the immunogen being capable of eliciting an immune response specific for the CR1 polypeptide; e.g., a humoral response, e.g. an antibody response; e.g. a cellular response. In preferred embodiments, the immunogen comprises an antigenic determinant, e.g., a unique determinant, from a protein represented by SEQ ID NO:2. A further aspect of the present invention features an antibody preparation specifically reactive with an epitope of the CR1 immunogen.
Another aspect of the present invention provides a substantially pure nucleic acid having a nucleotide sequence which encodes a CR1 polypeptide. In preferred embodiments: the encoded polypeptide has at least one biological activity; the encoded polypeptide has an amino acid sequence at least 60%, 80%, 90% or 95% homologous to the amino acid sequence in SEQ ID NO:2; the encoded polypeptide has an amino acid sequence essentially the same as the amino acid sequence in SEQ ID NO:2; the encoded polypeptide is at least 5, 10, 20, 50, 100, or 150 amino acids in length; the encoded polypeptide comprises at least 5, preferably at least 10, more preferably at least 20, more preferably at least 50, 100, or 150 contiguous amino acids from SEQ ID NO:2.
In a preferred embodiment, the encoded polypeptide having at least one biological activity of the CR1 polypeptide may differ in amino acid sequence from the sequence in SEQ ID NO:2, but such differences result in a modified polypeptide which functions in the same or similar manner as the native CR1 or which has the same or similar characteristics of the native CR1.
In yet other preferred embodiments, the encoded CR1 polypeptide is a recombinant fusion protein which includes a second polypeptide portion, e.g., a second polypeptide having an amino acid sequence unrelated to a protein represented by SEQ ID NO:2, e.g., the second polypeptide portion is glutathione-S-transferase, e.g. the second polypeptide portion is a DNA binding domain, e.g., the second polypeptide portion is a polymerase activating domain, e.g., the fusion protein is functional in a two-hybrid assay.
Furthermore, in certain preferred embodiments, the subject CR1 nucleic acid includes a transcriptional regulatory sequence, e.g. at least one of a transcriptional promoter or transcriptional enhancer sequence, operably linked to the CR1 gene sequence, e.g., to render the CR1 gene sequence suitable for use as an expression vector.
In yet a further preferred embodiment, the nucleic acid which encodes a CR1 polypeptide of the invention hybridizes under stringent conditions to a nucleic acid probe corresponding to at least 12 consecutive nucleotides of SEQ ID NO:1; more preferably to at least 20 consecutive nucleotides of SEQ ID NO:1; more preferably to at least 40 consecutive nucleotides of SEQ ID NO:1. In yet a further preferred embodiment, the CR1 encoding nucleic acid hybridizes to a nucleic acid probe corresponding to a subsequence encoding at least 4 consecutive amino acids, more preferably at least 10 consecutive amino acid residues, and even more preferably at least 20 amino acid residues between residues 1-202 of SEQ ID NO:2.
In preferred embodiments: the nucleic acid sequence includes at least 1, 2, 3 or 5, and preferably at least 10, 20, 50, or 100 nucleotides from the region of SEQ ID NO:1 which encodes amino acid residues 1-202 of SEQ ID NO:2; the encoded peptide includes at least 1, 2, 3, 5, 10, 20, or 30 amino acid residues from amino acid residues 1-202 of SEQ ID NO:2.
The present invention also pertains to a CR2 polypeptide, preferably a substantially pure preparation of a CR2 polypeptide, or a recombinant CR2 polypeptide. In preferred embodiments, the CR2 polypeptide has an amino acid sequence at least 60%, 80%, 90% or 95% homologous to the amino acid sequence in SEQ ID NO:4; the polypeptide has an amino acid sequence essentially the same as the amino acid sequence in SEQ ID NO:4; the polypeptide is at least 5, 10, 20, 50, 100, or 150 amino acids in length; the polypeptide comprises at least 5, preferably at least 10, more preferably at least 20, more preferably at least 50, 100, or 150 contiguous amino acids from SEQ ID NO:4. In further preferred embodiments, a protein homologous to SEQ ID NO:4 has a molecular weight of about 6 kilodaltons (kD), e.g. in the range of 5-15 kD.
In a preferred embodiment, a polypeptide having at least one biological activity of the CR2 polypeptide may differ in amino acid sequence from the sequence in SEQ ID NO:4, but such differences result in a modified polypeptide which functions in the same or similar manner as native CR2 protein or which has the same or similar characteristics of the native CR2 protein. Such a peptide can include at least 1, 2, 3, or 5, and preferably 10, 20, and 30, amino acid residues from residues 1-60 of SEQ ID NO:4.
In yet other preferred embodiments, the CR2 polypeptide is a recombinant fusion protein which includes a second polypeptide portion, e.g., a second polypeptide having an amino acid sequence unrelated to a protein represented by SEQ ID NO:4, e.g., the second polypeptide portion is glutathione-S-transferase, e.g., the second polypeptide portion is a DNA binding domain, e.g., the second polypeptide portion is a polymerase activating domain, e.g., the fusion protein is functional in a two-hybrid assay.
Yet another aspect of the present invention concerns an immunogen comprising a CR2 polypeptide in an immunogenic preparation, the immunogen being capable of eliciting an immune response specific for the CR2 polypeptide; e.g. a humoral response, e.g. an antibody response; e.g. a cellular response. In preferred embodiments, the immunogen comprises an antigenic determinant, e.g. a unique determinant, from a protein represented by SEQ ID NO:4. A further aspect of the present invention features an antibody preparation specifically reactive with an epitope of the CR2 immunogen.
Another aspect of the present invention provides a substantially pure nucleic acid having a nucleotide sequence which encodes a CR2 polypeptide. In preferred embodiments: the encoded polypeptide has at least one biological activity; the encoded polypeptide has an amino acid sequence at least 60%, 80%, 90% or 95% homologous to the amino acid sequence in SEQ ID NO:4; the encoded polypeptide has an amino acid sequence essentially the same as the amino acid sequence in SEQ ID NO:4; the encoded polypeptide is at least 5, 10, 20, 50, 100, or 150 amino acids in length; the encoded polypeptide comprises at least 5, preferably at least 10, more preferably at least 20, more preferably at least 50, 100, or 150 contiguous amino acids from SEQ ID NO:4.
In a preferred embodiment, the encoded polypeptide having at least one biological activity of the CR2 polypeptide may differ in amino acid sequence from the sequence in SEQ ID NO:4, but such differences result in a modified polypeptide which functions in the same or similar manner as the native CR2 protein or which has the same or similar characteristics of the native CR2 protein.
In yet other preferred embodiments, the encoded CR2 polypeptide is a recombinant fusion protein which includes a second polypeptide portion, e.g., a second polypeptide having an amino acid sequence unrelated to a protein represented by SEQ ID NO:4, e.g. the second polypeptide portion is glutathione-S-transferase, e.g., the second polypeptide portion is a DNA binding domain, e.g., the second polypeptide portion is a polymerase activating domain, e.g., the fusion protein is functional in a two-hybrid assay.
Furthermore, in certain preferred embodiments, the subject CR2 nucleic acid includes a transcriptional regulatory sequence, e.g. at least one of a transcriptional promoter or transcriptional enhancer sequence, operably linked to the CR2 gene sequence, e.g., to render the CR2 gene sequence suitable for use as an expression vector.
In yet a further preferred embodiment, the nucleic acid which encodes a CR2 polypeptide of the invention hybridizes under stringent conditions to a nucleic acid probe corresponding to at least 12 consecutive nucleotides of SEQ ID NO:3; more preferably to at least 20 consecutive nucleotides of SEQ ID NO:3; more preferably to at least 40 consecutive nucleotides of SEQ ID NO:3. In yet a further preferred embodiment, the CR2 encoding nucleic acid hybridizes to a nucleic acid probe corresponding to a subsequence encoding at least 4 consecutive amino acids, more preferably at least 10 consecutive amino acid residues, and even more preferably at least 20 amino acid residues between residues 1-60 of SEQ ID NO:4.
In preferred embodiments: the nucleic acid sequence includes at least 1, 2, 3 or 5, and preferably at least 10, 20, 50, or 100 nucleotides from the region of SEQ ID NO:3 which encodes amino acid residues 1-60 of SEQ ID NO:4; the encoded peptide includes at least 1, 2, 3, 5, 10, 20, or 30 amino acid residues from amino acid residues 1-60 of SEQ ID NO:4.
The present invention further pertains to a CR3 polypeptide, preferably a substantially pure preparation of a CR3 polypeptide, or a recombinant CR3 polypeptide. In preferred embodiments, the CR3 polypeptide has an amino acid sequence at least 60%, 80%, 90% or 95% homologous to the amino acid sequence in SEQ ID NO:6; the polypeptide has an amino acid sequence essentially the same as the amino acid sequence in SEQ ID NO:6; the polypeptide is at least 5, 10, 20, 50, 100, or 150 amino acids in length; the polypeptide comprises at least 5, preferably at least 10, more preferably at least 20, more preferably at least 50, 100, or 150 contiguous amino acids from SEQ ID NO:6. In further preferred embodiments, a protein homologous to SEQ ID NO:6 has a molecular weight of about 88 kilodaltons (kD), e.g. in the range of 80-95 kD.
In a preferred embodiment, a peptide having at least one biological activity of the CR3 polypeptide may differ in amino acid sequence from the sequence in SEQ ID NO:6, but such differences result in a modified protein which functions in the same or similar manner as native CR3 protein or which has the same or similar characteristics of the native CR3 protein. Such a peptide can include at least 1, 2, 3, or 5, and preferably 10, 20, and 30, amino acid residues from residues 1-358 of SEQ ID NO:6.
In yet other preferred embodiments, the CR3 polypeptide is a recombinant fusion protein which includes a second polypeptide portion, e.g., a second polypeptide having an amino acid sequence unrelated to a protein represented by SEQ ID NO:6, e.g., the second polypeptide portion is glutathione-S-transferase, e.g., the second polypeptide portion is a DNA binding domain, e.g., the second polypeptide portion is a polymerase activating domain, e.g., the fusion protein is functional in a two-hybrid assay.
Yet another aspect of the present invention concerns an immunogen comprising a CR3 polypeptide in an immunogenic preparation, the immunogen being capable of eliciting an immune response specific for said CR3 polypeptide; e.g. a humoral response, e.g. an antibody response; e.g. a cellular response. In preferred embodiments, the immunogen comprises an antigenic determinant, e.g. a unique determinant, from a protein represented by SEQ ID NO:6. A further aspect of the present invention features an antibody preparation specifically reactive with an epitope of the CR3 immunogen.
Another aspect of the present invention provides a substantially pure nucleic acid having a nucleotide sequence which encodes a CR3 polypeptide. In preferred embodiments: the encoded polypeptide has at least one biological activity; the encoded polypeptide has an amino acid sequence at least 60%, 80%, 90% or 95% homologous to the amino acid sequence in SEQ ID NO:6; the encoded polypeptide has an amino acid sequence essentially the same as the amino acid sequence in SEQ ID NO:6; the encoded polypeptide is at least 5, 10, 20, 50, 100, or 150 amino acids in length; the encoded polypeptide comprises at least 5, preferably at least 10, more preferably at least 20, more preferably at least 50, 100, or 150 contiguous amino acids from SEQ ID NO:6.
In a preferred embodiment, the encoded polypeptide having at least one biological activity of the CR3 polypeptide may differ in amino acid sequence from the sequence in SEQ ID NO:6, but such differences result in a modified polypeptide which functions in the same or similar manner as the native CR3 protein or which has the same or similar characteristics of the native CR3 protein.
In yet other preferred embodiments, the encoded CR3 polypeptide is a recombinant fusion protein which includes a second polypeptide portion, e.g., a second polypeptide having an amino acid sequence unrelated to a protein represented by SEQ ID NO:6, e.g., the second polypeptide portion is glutathione-S-transferase, e.g., the second polypeptide portion is a DNA binding domain, e.g., the second polypeptide portion is a polymerase activating domain, e.g., the fusion protein is functional in a two-hybrid assay.
Furthermore, in certain preferred embodiments, the subject CR3 nucleic acid includes a transcriptional regulatory sequence, e.g. at least one of a transcriptional promoter or transcriptional enhancer sequence, operably linked to the CR3 gene sequence, e.g., to render the CR3 gene sequence suitable for use as an expression vector.
In yet a further preferred embodiment, the nucleic acid which encodes a CR3 polypeptide of the invention hybridizes under stringent conditions to a nucleic acid probe corresponding to at least 12 consecutive nucleotides of SEQ ID NO:5; more preferably to at least 20 consecutive nucleotides of SEQ ID NO:5; more preferably to at least 40 consecutive nucleotides of SEQ ID NO:5. In yet a further preferred embodiment, the CR3 encoding nucleic acid hybridizes to a nucleic acid probe corresponding to a subsequence encoding at least 4 consecutive amino acids, more preferably at least 10 consecutive amino acid residues, and even more preferably at least 20 amino acid residues between residues 1-358 of SEQ ID NO:6.
In preferred embodiments: the nucleic acid sequence includes at least 1, 2, 3 or 5, and preferably at least 10, 20, 50, or 100 nucleotides from the region of SEQ ID NO:5 which encodes amino acid residues 1-358 of SEQ ID NO:6; the encoded peptide includes at least 1, 2, 3, 5, 10, 20, or 30 amino acid residues from amino acid residues 1-358 of SEQ ID NO:6.
The present invention still further pertains to a CR4 polypeptide, preferably a substantially pure preparation of a CR4 polypeptide, or a recombinant CR4 polypeptide. In preferred embodiments, the CR4 polypeptide has an amino acid sequence at least 60%, 80%, 90% or 95% homologous to the amino acid sequence in SEQ ID NO:8; the polypeptide has an amino acid sequence essentially the same as the amino acid sequence in SEQ ID NO:8; the polypeptide is at least 5, 10, 20, 50, 100, or 150 amino acids in length; the polypeptide comprises at least 5, preferably at least 10, more preferably at least 20, more preferably at least 50, 100, or 150 contiguous amino acids from SEQ ID NO:8. In further preferred embodiments, a protein homologous to SEQ ID NO:8 has a molecular weight of about 83 kilodaltons (kD), e.g. in the range of 75-90 kD.
In a preferred embodiment, a polypeptide having at least one biological activity of the CR4 polypeptide may differ in amino acid sequence from the sequence in SEQ ID NO:8, but such differences result in a modified polypeptide which functions in the same or similar manner as native CR4 protein or which has the same or similar characteristics of the native CR4 protein. Such a peptide can include at least 1, 2, 3, or 5, and preferably 10, 20, and 30, amino acid residues from residues 1-763 of SEQ ID NO:8.
In yet other preferred embodiments, the CR4 polypeptide is a recombinant fusion protein which includes a second polypeptide portion, e.g., a second polypeptide having an amino acid sequence unrelated to a protein represented by SEQ ID NO:8, e.g., the second polypeptide portion is glutathione-S-transferase, e.g., the second polypeptide portion is a DNA binding domain, e.g., the second polypeptide portion is a polymerase activating domain, e.g., the fusion protein is functional in a two-hybrid assay.
Yet another aspect of the present invention pertains to an immunogen comprising a CR4 polypeptide in an immunogenic preparation, the immunogen being capable of eliciting an immune response specific for the CR4 polypeptide; e.g. a humoral response, e.g. an antibody response; e.g. a cellular response. In preferred embodiments, the immunogen comprises an antigenic determinant, e.g. a unique determinant, from a protein represented by SEQ ID NO:8. A further aspect of the present invention features an antibody preparation specifically reactive with an epitope of the CR4 immunogen.
Another aspect of the present invention provides a substantially pure nucleic acid having a nucleotide sequence which encodes a CR4 polypeptide. In preferred embodiments: the encoded polypeptide has at least one biological activity; the encoded polypeptide has an amino acid sequence at least 60%, 80%, 90% or 95% homologous to the amino acid sequence in SEQ ID NO:8; the encoded polypeptide has an amino acid sequence essentially the same as the amino acid sequence in SEQ ID NO:8; the encoded polypeptide is at least 5, 10, 20, 50, 100, or 150 amino acids in length; the encoded polypeptide comprises at least 5, preferably at least 10, more preferably at least 20, more preferably at least 50, 100, or 150 contiguous amino acids from SEQ ID NO:8.
In a preferred embodiment, the encoded polypeptide having at least one biological activity of the CR4 polypeptide may differ in amino acid sequence from the sequence in SEQ ID NO:8, but such differences result in a modified polypeptide which functions in the same or similar manner as the native CR4 protein or which has the same or similar characteristics of the native CR4 protein.
In yet other preferred embodiments, the encoded CR4 polypeptide is a recombinant fusion protein which includes a second polypeptide portion, e.g., a second polypeptide having an amino acid sequence unrelated to a protein represented by SEQ ID NO:8, e.g., the second polypeptide portion is glutathione-S-transferase, e.g. the second polypeptide portion is a DNA binding domain, e.g., the second polypeptide portion is a polymerase activating domain, e.g., the fusion protein is functional in a two-hybrid assay.
Furthermore, in certain preferred embodiments, the subject CR4 nucleic acid includes a transcriptional regulatory sequence, e.g., at least one of a transcriptional promoter or transcriptional enhancer sequence, operably linked to the CR4 gene sequence, e.g., to render the CR4 gene sequence suitable for use as an expression vector.
In yet a further preferred embodiment, the nucleic acid which encodes a CR4 polypeptide of the invention hybridizes under stringent conditions to a nucleic acid probe corresponding to at least 12 consecutive nucleotides of SEQ ID NO:7; more preferably to at least 20 consecutive nucleotides of SEQ ID NO:7; more preferably to at least 40 consecutive nucleotides of SEQ ID NO:7. In yet a further preferred embodiment, the CR4 encoding nucleic acid hybridizes to a nucleic acid probe corresponding to a subsequence encoding at least 4 consecutive amino acids, more preferably at least 10 consecutive amino acid residues, and even more preferably at least 20 amino acid residues between residues 1-763 of SEQ ID NO:8.
In preferred embodiments: the nucleic acid sequence includes at least 1, 2, 3 or 5, and preferably at least 10, 20, 50, or 100 nucleotides from the region of SEQ ID NO:7 which encodes amino acid residues 1-763 of SEQ ID NO:8; the encoded peptide includes at least 1, 2, 3, 5, 10, 20, or 30 amino acid residues from amino acid residues 1-763 of SEQ ID NO:8.
Another aspect of the present invention pertains to a CR5 polypeptide, preferably a substantially pure preparation of a CR5 polypeptide, or a recombinant CR5 polypeptide. In preferred embodiments, the CR5 polypeptide has an amino acid sequence at least 60%, 80%, 90% or 95% homologous to the amino acid sequence in SEQ ID NO:10; the polypeptide has an amino acid sequence essentially the same as the amino acid sequence in SEQ ID NO:10; the polypeptide is at least 5, 10, 20, 50, 100, or 150 amino acids in length; the polypeptide comprises at least 5, preferably at least 10, more preferably at least 20, more preferably at least 50, 100, or 150 contiguous amino acids from SEQ ID NO:10. In further preferred embodiments, a protein homologous to SEQ ID NO:10 has a molecular weight of about 28 kilodaltons (kD), e.g. in the range of 20-35 kD.
In a preferred embodiment, a polypeptide having at least one biological activity of the CR5 polypeptide may differ in amino acid sequence from the sequence in SEQ ID NO:10, but such differences result in a modified polypeptide which functions in the same or similar manner as native CR5 protein or which has the same or similar characteristics of the native CR5 protein. Such a peptide can include at least 1, 2, 3, or 5, and preferably 10, 20, and 30, amino acid residues from residues 1-258 of SEQ ID NO:10.
In yet other preferred embodiments, the CR5 polypeptide is a recombinant fusion protein which includes a second polypeptide portion, e.g., a second polypeptide having an amino acid sequence unrelated to a protein represented by SEQ ID NO:10, e.g., the second polypeptide portion is glutathione-S-transferase, e.g. the second polypeptide portion is a DNA binding domain, e.g., the second polypeptide portion is a polymerase activating domain, e.g., the fusion protein is functional in a two-hybrid assay.
Yet another aspect of the present invention concerns an immunogen comprising a CR5 polypeptide in an immunogenic preparation, the immunogen being capable of eliciting an immune response specific for the CR5 polypeptide; e.g. a humoral response, e.g. an antibody response; e.g. a cellular response. In preferred embodiments, the immunogen comprises an antigenic determinant, e.g. a unique determinant, from a protein represented by SEQ ID NO:10. A further aspect of the present invention features an antibody preparation specifically reactive with an epitope of the CR5 immunogen.
Another aspect of the present invention provides a substantially pure nucleic acid having a nucleotide sequence which encodes a CR5 polypeptide. In preferred embodiments: the encoded polypeptide has at least one biological activity; the encoded polypeptide has an amino acid sequence at least 60%, 80%, 90% or 95% homologous to the amino acid sequence in SEQ ID NO:10; the encoded polypeptide has an amino acid sequence essentially the same as the amino acid sequence in SEQ ID NO:10; the encoded polypeptide is at least 5, 10, 20, 50, 100, or 150 amino acids in length; the encoded polypeptide comprises at least 5, preferably at least 10, more preferably at least 20, more preferably at least 50, 100, or 150 contiguous amino acids from SEQ ID NO:10.
In a preferred embodiment, the encoded polypeptide having at least one biological activity of the CR5 polypeptide may differ in amino acid sequence from the sequence in SEQ ID NO:10, but such differences result in a modified polypeptide which functions in the same or similar manner as the native CR5 protein or which has the same or similar characteristics of the native CR5 protein.
In yet other preferred embodiments, the encoded CR5 polypeptide is a recombinant fusion protein which includes a second polypeptide portion, e.g., a second polypeptide having an amino acid sequence unrelated to a protein represented by SEQ ID NO:10, e.g., the second polypeptide portion is glutathione-S-transferase, e.g., the second polypeptide portion is a DNA binding domain, e.g., the second polypeptide portion is a polymerase activating domain, e.g. the fusion protein is functional in a two-hybrid assay.
Furthermore, in certain preferred embodiments, the subject CR5 nucleic acid includes a transcriptional regulatory sequence, e.g., at least one of a transcriptional promoter or transcriptional enhancer sequence, operably linked to the CR5 gene sequence, e.g., to render the CR5 gene sequence suitable for use as an expression vector.
In yet a further preferred embodiment, the nucleic acid which encodes an CR5 polypeptide of the invention hybridizes under stringent conditions to a nucleic acid probe corresponding to at least 12 consecutive nucleotides of SEQ ID NO:9; more preferably to at least 20 consecutive nucleotides of SEQ ID NO:9; more preferably to at least 40 consecutive nucleotides of SEQ ID NO:9. In yet a further preferred embodiment, the CR5 encoding nucleic acid hybridizes to a nucleic acid probe corresponding to a subsequence encoding at least 4 consecutive amino acids, more preferably at least 10 consecutive amino acid residues, and even more preferably at least 20 amino acid residues between residues 1-258 of SEQ ID NO:10.
In preferred embodiments: the nucleic acid sequence includes at least 1, 2, 3 or 5, and preferably at least 10, 20, 50, or 100 nucleotides from the region of SEQ ID NO:9 which encodes amino acid residues 1-258 of SEQ ID NO:10; the encoded peptide includes at least 1, 2, 3, 5, 10, 20, or 30 amino acid residues from amino acid residues 1-258 of SEQ ID NO:10.
The present invention further pertains to a CR6 polypeptide, preferably a substantially pure preparation of a CR6 polypeptide, or a recombinant CR6 polypeptide. In preferred embodiments, the CR6 polypeptide has an amino acid sequence at least 60%, 80%, 90% or 95% homologous to the amino acid sequence in SEQ ID NO:12; the polypeptide has an amino acid sequence essentially the same as the amino acid sequence in SEQ ID NO:12; the polypeptide is at least 5, 10, 20, 50, 100, or 150 amino acids in length; the polypeptide comprises at least 5, preferably at least 10, more preferably at least 20, more preferably at least 50, 100, or 150 contiguous amino acids from SEQ ID NO:12. In further preferred embodiments, a protein homologous to SEQ ID NO:12 has a molecular weight of about 17 kilodaltons (kD), e.g. in the range of 15-25 kD.
In a preferred embodiment, a polypeptide having at least one biological activity of the CR6 polypeptide may differ in amino acid sequence from the sequence in SEQ ID NO:12, but such differences result in a modified polypeptide which functions in the same or similar manner as native CR6 protein or which has the same or similar characteristics of the native CR6 protein. Such a peptide can include at least 1, 2, 3, or 5, and preferably 10, 20, and 30, amino acid residues from residues 1-159 of SEQ ID NO:12.
In yet other preferred embodiments, the CR6 polypeptide is a recombinant fusion protein which includes a second polypeptide portion, e.g., a second polypeptide having an amino acid sequence unrelated to a protein represented by SEQ ID NO:12, e.g., the second polypeptide portion is glutathione-S-transferase, e.g., the second polypeptide portion is a DNA binding domain, e.g., the second polypeptide portion is a polymerase activating domain, e.g. the fusion protein is functional in a two-hybrid assay.
Yet another aspect of the present invention concerns an immunogen comprising a CR6 polypeptide in an immunogenic preparation, the immunogen being capable of eliciting an immune response specific for the CR6 polypeptide; e.g. a humoral response, e.g. an antibody response; e.g. a cellular response. In preferred embodiments, the immunogen comprises an antigenic determinant, e.g. a unique determinant, from a protein represented by SEQ ID NO:12. A further aspect of the present invention features an antibody preparation specifically reactive with an epitope of the CR6 immunogen.
Another aspect of the present invention provides a substantially pure nucleic acid having a nucleotide sequence which encodes a CR6 polypeptide. In preferred embodiments: the encoded polypeptide has at least one biological activity; the encoded polypeptide has an amino acid sequence at least 60%, 80%, 90% or 95% homologous to the amino acid sequence in SEQ ID NO:12; the encoded polypeptide has an amino acid sequence essentially the same as the amino acid sequence in SEQ ID NO:12; the encoded polypeptide is at least 5, 10, 20, 50, 100, or 150 amino acids in length; the encoded polypeptide comprises at least 5, preferably at least 10, more preferably at least 20, more preferably at least 50, 100, or 150 contiguous amino acids from SEQ ID NO:12.
In a preferred embodiment, the encoded polypeptide having at least one biological activity of the CR6 polypeptide may differ in amino acid sequence from the sequence in SEQ ID NO:12, but such differences result in a modified polypeptide which functions in the same or similar manner as the native CR6 protein or which has the same or similar characteristics of the native CR6 protein.
In yet other preferred embodiments, the encoded CR6 polypeptide is a recombinant fusion protein which includes a second polypeptide portion, e.g., a second polypeptide having an amino acid sequence unrelated to a protein represented by SEQ ID NO:12, e.g., the second polypeptide portion is glutathione-S-transferase, e.g., the second polypeptide portion is a DNA binding domain, e.g., the second polypeptide portion is a polymerase activating domain, e.g., the fusion protein is functional in a two-hybrid assay.
Furthermore, in certain preferred embodiments, the subject CR6 nucleic acid includes a transcriptional regulatory sequence, e.g. at least one of a transcriptional promoter or transcriptional enhancer sequence, operably linked to the CR6 gene sequence, e.g., to render the CR6 gene sequence suitable for use as an expression vector.
In yet a further preferred embodiment, the nucleic acid which encodes an CR6 polypeptide of the invention hybridizes under stringent conditions to a nucleic acid probe corresponding to at least 12 consecutive nucleotides of SEQ ID NO:11; more preferably to at least 20 consecutive nucleotides of SEQ ID NO:11; more preferably to at least 40 consecutive nucleotides of SEQ ID NO:11. In yet a further preferred embodiment, the CR6 encoding nucleic acid hybridizes to a nucleic acid probe corresponding to a subsequence encoding at least 4 consecutive amino acids, more preferably at least 10 consecutive amino acid residues, and even more preferably at least 20 amino acid residues between residues 1-159 of SEQ ID NO:12.
In preferred embodiments: the nucleic acid sequence includes at least 1, 2, 3 or 5, and preferably at least 10, 20, 50, or 100 nucleotides from the region of SEQ ID NO:11 which encodes amino acid residues 1-159 of SEQ ID NO:12; the encoded peptide includes at least 1, 2, 3, 5, 10, 20, or 30 amino acid residues from amino acid residues 1-159 of SEQ ID NO:12.
The present invention still further pertains to a CR8 polypeptide, preferably a substantially pure preparation of a CR8 polypeptide, or a recombinant CR8 polypeptide. In preferred embodiments, the CR8 polypeptide has an amino acid sequence at least 60%, 80%, 90% or 95% homologous to the amino acid sequence in SEQ ID NO:14; the polypeptide has an amino acid sequence essentially the same as the amino acid sequence in SEQ ID NO:14; the polypeptide is at least 5, 10, 20, 50, 100, or 150 amino acids in length; the polypeptide comprises at least 5, preferably at least 10, more preferably at least 20, more preferably at least 50, 100, or 150 contiguous amino acids from SEQ ID NO:14. In further preferred embodiments, a protein homologous to SEQ ID NO:14 has a molecular weight of about 45 kilodaltons (kD), e.g. in the range of 35-50 kD.
In a preferred embodiment, a polypeptide having at least one biological activity of the CR8 polypeptide may differ in amino acid sequence from the sequence in SEQ ID NO:14, but such differences result in a modified polypeptide which functions in the same or similar manner as native CR8 protein or which has the same or similar characteristics of the native CR8 protein. Such a peptide can include at least 1, 2, 3, or 5, and preferably 10, 20, and 30, amino acid residues from residues 1-412 of SEQ ID NO:14.
In yet other preferred embodiments, the CR8 polypeptide is a recombinant fusion protein which includes a second polypeptide portion, e.g., a second polypeptide having an amino acid sequence unrelated to a protein represented by SEQ ID NO:14, e.g., the second polypeptide portion is glutathione-S-transferase, e.g., the second polypeptide portion is a DNA binding domain, e.g., the second polypeptide portion is a polymerase activating domain, e.g., the fusion protein is functional in a two-hybrid assay.
Yet another aspect of the present invention pertains to an immunogen comprising a CR8 polypeptide in an immunogenic preparation, the immunogen being capable of eliciting an immune response specific for said CR8 polypeptide; e.g. a humoral response, e.g. an antibody response; e.g. a cellular response. In preferred embodiments, the immunogen comprises an antigenic determinant, e.g. a unique determinant, from a protein represented by SEQ ID NO:14. A further aspect of the present invention features an antibody preparation specifically reactive with an epitope of the CR8 immunogen.
Another aspect of the present invention provides a substantially pure nucleic acid having a nucleotide sequence which encodes a CR8 polypeptide. In preferred embodiments: the encoded polypeptide has at least one biological activity; the encoded polypeptide has an amino acid sequence at least 60%, 80%, 90% or 95% homologous to the amino acid sequence in SEQ ID NO:14; the encoded polypeptide has an amino acid sequence essentially the same as the amino acid sequence in SEQ ID NO:14; the encoded polypeptide is at least 5, 10, 20, 50, 100, or 150 amino acids in length; the encoded polypeptide comprises at least 5, preferably at least 10, more preferably at least 20, more preferably at least 50, 100, or 150 contiguous amino acids from SEQ ID NO:14.
In a preferred embodiment, the encoded polypeptide having at least one biological activity of the CR8 polypeptide may differ in amino acid sequence from the sequence in SEQ ID NO:14, but such differences result in a modified polypeptide which functions in the same or similar manner as the native CR8 protein or which has the same or similar characteristics of the native CR8 protein.
In yet other preferred embodiments, the encoded CR8 polypeptide is a recombinant fusion protein which includes a second polypeptide portion, e.g., a second polypeptide having an amino acid sequence unrelated to a protein represented by SEQ ID NO:14, e.g., the second polypeptide portion is glutathione-S-transferase, e.g., the second polypeptide portion is a DNA binding domain, e.g., the second polypeptide portion is a polymerase activating domain, e.g. the fusion protein is functional in a two-hybrid assay.
Furthermore, in certain preferred embodiments, the subject CR8 nucleic acid includes a transcriptional regulatory sequence, e.g., at least one of a transcriptional promoter or transcriptional enhancer sequence, operably linked to the CR8 gene sequence, e.g., to render the CR8 gene sequence suitable for use as an expression vector.
In yet a further preferred embodiment, the nucleic acid which encodes a CR8 polypeptide of the invention hybridizes under stringent conditions to a nucleic acid probe corresponding to at least 12 consecutive nucleotides of SEQ ID NO:13; more preferably to at least 20 consecutive nucleotides of SEQ ID NO:13; more preferably to at least 40 consecutive nucleotides of SEQ ID NO:13. In yet a further preferred embodiment, the CR8 encoding nucleic acid hybridizes to a nucleic acid probe corresponding to a subsequence encoding at least 4 consecutive amino acids, more preferably at least 10 consecutive amino acid residues, and even more preferably at least 20 amino acid residues between residues 1-412 of SEQ ID NO:14.
In preferred embodiments: the nucleic acid sequence includes at least 1, 2, 3 or 5, and preferably at least 10, 20, 50, or 100 nucleotides from the region of SEQ ID NO:13 which encodes amino acid residues 1-412 of SEQ ID NO:14; the encoded peptide includes at least 1, 2, 3, 5, 10, 20, or 30 amino acid residues from amino acid residues 1-412 of SEQ ID NO:14.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a histogram showing the level of DNA synthesis (as the incorporation of .sup.3 H!-thymidine in PBMN cells treated with CHX, OKT3 or OKT3 and CHX.
FIG. 2 shows CR8 expression in the following cytokine-dependent cell lines: the IL-2-dependent human T cell line Kit 225; the IL-3-dependent mouse pro-B cell line Ba/F3; and the IL-2-dependent mouse T cell line CTLL2.
DETAILED DESCRIPTION OF THE INVENTION
By combining several different procedures, a cDNA library can be constructed which is enriched in clones containing genes whose expression is induced by activation of a cellular ligand-specific receptor. This enriched library can facilitate identification and characterization of ligand-activated genes that are triggered immediately and/or early on after receptor activation (e.g., 2 to 4 hours after the ligand binds to its receptor). Such genes may play a role in stimulating growth phase transitions and subsequent clonal expansion of a particular cell type.
The method of the invention can be used to create cDNA libraries of the genes induced by activation of a variety of different cellular receptors. The receptors can be cytoplasmic, nuclear, or cell-surface receptors, and include receptors for cytokines, hormones, factors, and peptides. For example, cytokines such as the interleukins (e.g., IL-1 and IL-2), cellular growth factors (e.g., platelet-derived growth factor (PDGF), epidermal growth factor (EGF), fibroblast growth factor (FGF), insulin-like growth factor (IGF)), colony stimulating factors (e.g., multiplication stimulating activity), and hormones (e.g., insulin, somatomedin C, and steroid hormones are useful as activators of certain cellular receptors.
The ligand used to activate the receptor can be the natural ligand recognized by the receptor or a synthetic analog. Alternatively, an antibody specific for the receptor and capable of activating the receptor can be used.
The receptor is activated by a ligand or other activation for a predetermined length of time and at a concentration necessary to activate the receptor. This activation is carried out in the presence of labelled RNA precursors which are incorporated into the RNA synthesized by the cell in response to receptor activation. Thus, the RNA transcribed is labelled so as to be distinguished from preexisting RNA which is not labelled.
Some labels (such as radiolabels) can be employed to monitor the newly synthesized RNA. Useful radiolabelled RNA precursors for such purposes include .sup.3 H!-uridine. Other labels may be used to separate newly transcribed RNA from unlabelled RNA. For example, RNA synthesized from thiol-labelled RNA precursors specifically adheres to phenylmercury agarose (Woodford et al. (1988) Anal. Biochem. 1781:166-172). RNA newly synthesized in response to receptor activation can be separated from preexisting RNA in the cell; all RNA molecules expressed prior to ligand-activation pass through the phenylmethyl mercury column, leaving only the newly synthesized, thiol-(SH--) labelled RNA attached to the agarose via a covalent bond between the mercury and sulfur. The thiol-labelled RNA molecules are then eluted from the column by reducing the Hg-S bond with an excess of 2-mercaptoethanol.
To augment the expression of immediate/early ligand-activated genes which may be difficult to identify because of the large number of downstream genes turned on at a later time, a substance that enhances the level of RNA is added to the culture medium during the ligand stimulation (see, e.g., Cochran et al. (1983) Cell 33:939-947). Useful substances include those compounds that stabilize RNA and/or that block translation, thereby blocking feedback inhibition of these genes by a later gene product. Such activity may potentiate the magnitude of the RNA expressed as well as the duration of the life of the RNA. Examples of such useful substances include cyclohexamide (CHX), which inhibits protein synthesis at the level of RNA-ribosome complexing and may stabilize polysomal RNA, and puromycin, which inhibits translation by causing premature dissociation of the peptide-mRNA-ribosome complex.
cAMP is another useful substance which enhances the level of RNA. Increased levels of cAMP, or analogs or agents that elevate cAMP levels, such as forskolin, dibutyryl AMP, and isobutylmethyl xanthene, are known to inhibit cell growth, proliferation, and inositol phospholipid turnover. In addition, elevated levels of cAMP completely inhibit IL-2-stimulated T-cell proliferation (Johnson et al. (1988) Proc. Natl. Acad. Sci. (USA) 85:6072-6076).
The labelled RNA transcribed consequent to receptor activation in the presence of the substance which enhances RNA levels is then purified from the cytoplasm of the cells. Purification can be accomplished by extracting total cellular RNA from a cell homogenate or fraction thereof, isolating mRNA therefrom, for example, using a poly U or polydT! column, and then separating the labelled RNA from the unlabelled RNA. Separation can be accomplished, for example, using the phenylmethyl mercury agarose protocol described above. Of course, other known methods of separating the newly synthesized RNA from the preexisting can also be used.
The cDNA libraries can be prepared from the separated labelled RNA by standard techniques. For example, the labelled RNA may be reversed transcribed into cDNA, using oligodT! primers. The cDNA is then ligated into appropriate vectors using established recombinant DNA techniques. A cDNA library is then constructed by methods well known in the art in prokaryotic or eukaryotic host cells that are capable of being transfected by the vectors.
Prokaryotic systems most commonly utilize E. coli as host, although other bacterial strains such as Bacillus, Pseudomonas, or other Gram-positive or Gram-negative prokaryotes can also be used. When such prokaryotic hosts are employed, operable control systems compatible with these hosts are ligated to the cDNA fragments and disposed on a suitable transfer vector which is capable of replication in the bacterial host cell. Backbone vectors capable of replication include phage vectors and plasmid vectors, as is known in the art. Common plasmid vectors include those derived from pBR322 and the pUC series. One such useful vector which is commercially available is the plasmid pBluescriptTIISK+ (Stratagene, La Jolla, Calif.). Charon lambda phage is a frequently employed phage vector. Control sequences obligatorily include promoter and ribosome binding site encoding sequences, and a variety of such controls are available in the art, such as the beta-lactamase (pencillinase) and lactose (lac) promoter systems (see, e.g., Chang et al. (1977) Nature 198:106), and the tryptophan (trp) promoter systems (Goeddel et al. (1980) Nucleic Acids Res. 8:4057). Composite promoters containing elements of both the trp and lac promoter systems are also available in the art.
Eukaryotic microbes, such as laboratory strains of Saccharomyces cerevisiae, or Baker's yeast, can also be used for expression. A number of yeast control systems and vectors are available, including those which are promoters for the synthesis of glycolytic enzymes (see, e.g., Hess et al. (1968) Biochem. 17:4900). Yeast vectors employing the 2 micron origin of replication are suitable as transfer vectors (see, e.g., Broach (1982) Meth. Enzym. 101:307).
Tissue cultures of insect cell lines, or cell lines immortalized from mammalian or other higher organisms have also been used as recombinant hosts. Such cell lines include chinese hamster ovary (CHO), Vero, HeLa, and COS cells. In general, the COS cell system is used for transient expression, while CHO cells typically integrate transformed DNA into the chromosome. Suitable mammalian vectors are generally based on viral origins of replication and control sequences. Most commonly used are the simian virus 40 (SV40) promoters and replicons (see Fiers et al. (1978) Nature 273:113) and similar systems derived from Adenovirus 2, bovine papilloma virus, and avian sarcoma virus.
The ligand-activated genes are then screened in the library using any one of several different methods. One method involves differential hybridization with cDNA probes constructed from mRNA derived from ligand-activated cells and unactivated cells. Another method includes hybridization subtraction, whereby cDNA from ligand-activated cells is hybridized with an excess of mRNA from unactivated cells to remove RNA molecules common to both. Alternatively, cDNA probes can be made from the same pool of thiol-selected mRNA used to make the cDNA library, as these sequences are highly enriched for ligand-induced molecules. One can prepare cDNA probes from mRNA extracted from cells treated with drugs that block the biologic response to the particular cytokine (e.g., rapamycin blocks the proliferative response of T cells to IL-2, and cyclosporin A and FK506 block the T-cell response to activation via the T-cell antigen receptor). Results from probing with the cDNA made from drug-inhibited cells can then be compared to results from probes made from cells not inhibited by these drugs.
The marked superinduction observed for a number of the genes using a substance, such as CHX, which enhances RNA levels is crucial in enabling their detection by differential hybridization, as it has been estimated that differential hybridization is only effective in the detection of relatively high-abundance RNAs expressed at a level of greater than 500 copies per cell. Therefore, the superinduction increases that level of expression of low-abundance RNAs above the threshold of detection by differential screening. In addition, the approximately 10-fold enrichment for newly synthesized RNA afforded by the thiol-labelling procedure further heightens the efficacy of the cloning procedure. Thus, the combination of superinduction and thiol-labelling of RNA significantly enhances the sensitivity of differential screening, and provides a cloning strategy which has the capacity to detect messages normally present in relatively low abundance (i.e., less than 100 copies/cell).
After the initial screening of the cDNA library, all clones isolated as tentatively positive must be corroborated as truly ligand-activated. This can be accomplished by isolating the cDNA insert from each cloned plasmid, and then employing this cDNA to probe RNA from ligand-activated cells by Northern blot analysis.
Then, to identify each gene, the cDNA can be subjected to sequence analysis. Searches of the GenBank (Los Alamos, N.Mex.) and EMBL (Heidleberg, Germany) data bases can be made of even partial sequences to identify known sequences such as pim-1, a previously characterized, IL-2 induced gene.
A number of methods can be used to characterize the novel ligand-enhanced genes and begin to determine their functional roles in, for example, signal transduction. DNA sequence analysis of the cDNA of the mRNA transcript can predict the coding region for the gene product and the amino acid sequence. From the amino acid sequence, the gene product can be placed into one of several categories of proteins, such as DNA-binding proteins, kinases, phosphatases, transmembrane proteins, or secreted products. These categories then will predict certain obvious functions and characteristics to be examined.
For example, the mechanism whereby IL-2 binding to its heterodimeric p55/p75 receptor on the cell surface activates specific gene expression is not well understood. The 75 kD component of the IL-2 receptor, which is responsible for signal transduction, does not exhibit sequence homologies indicative of previously characterized functional domains. However, the involvement of protein phosphorylation in the IL-2 response has been indicated by the activation of IL-2R-associated kinases, including the tyrosine kinase p56.sup.lck, as well as the cytoplasmic serine/threonine kinase c-raf-1 in early IL-2-mediated transmembrane signalling. In addition, a number of proteins, including the IL-2R p75, are rapidly phosphorylated in response to IL-2. The hydrolysis of phosphatidylinositol glycan is also stimulated by IL-2, resulting in the formation of the putative second messengers myristylated diacylglycerol and inositol phosphate-glycan. Analysis of the regulatory elements governing expression of the immediate-early genes described in the present study will be useful in the further characterization of the secondary biochemical messengers activated by the IL-2 receptor.
Other methods helpful in determining the functional relevance of the IL-2-induced genes include examining T-cells for their expression in response to triggering of other receptors.
One such receptor is the T-cell antigen receptor. Seminal studies of the T-cell system have demonstrated that T-cell activation occurs as a two-step process. Quiescent cells are initially stimulated through engagement of the antigen receptor, which provides the cells with the capacity to produce and respond to IL-2. Subsequently, the interaction of IL-2 with its cell-surface receptor drives progression through the G.sub.1 to the S phase of the cell cycle. Transmembrane signalling through both the T-cell antigen receptor has been shown to trigger the heightened expression of a number of genes, including c-fos, c-myc and c-raf-1 (Reed et al. (1986) Proc. Nat. Acad. Sci. USA 83:3982-3986; Dautry et al. (1988) J. Biol. Chem. 263:17615-17620; and Zmuidzinas et al. (1991) Mol. Cell. Biol. 11:2794-2803). By comparison, in the case of the c-myb gene, the induction is unique to the IL-2 signalling pathway (Stern et al. (1986) Science 233:203-206). Therefore, to categorize the novel IL-2-induced genes with regard to their patterns of induction by these two receptor pathways, the sensitivity of the genes to T-cell receptor stimulation can be determined.
Additional methods that can be used to categorize the genes isolated include screening for expression by proliferating versus non-proliferating cells, for tissue-specific expression, and for expression in response to different cytokines and hormones. Genes that are expressed exclusively by proliferating cells are obvious candidates for functioning to promote cell growth. Other genes may be important for signaling differentiation and would be expected to be tissue-specific or activated only by a restricted family of similar ligands.
An additional means of elucidating the mechanisms of IL-2-mediated transmembrane signalling is provided by the varied effects of elevated cAMP on IL-2-induced gene expression. The diverse responses of the genes to cAMP suggest that the IL-2 signalling pathways responsible for their induction must bifurcate at a point prior to intersection with the cAMP regulated pathways. One potential mechanism of cAMP action may involve regulation of protein phosphorylation, as cAMP is an activator of protein kinase A, and elevations of intracellular cAMP inhibit IL-2-inducted phosphorylation events. In addition, as cAMP blocks IL-2-stimulated cell cycle progression at a point in early G.sub.1, cAMP sensitivity is a useful tool with which to dissect IL-2-mediated signal transduction pathways involved in cell cycle progression.
A likely function of the immediate/early gene products is the governing of subsequent DNA replication and cell division. Previously characterized IL-2 induced genes encode kinases (c-raf-1, pim-1) and DNA binding proteins (c-fos, c-myc, c-myb). Further sequence analysis of the novel genes will determine whether the proteins they encode contain conserved domains which would implicate similar functions. However, since IL-2 stimulates cellular differentiation as well as division, and has been shown to induce the expression of a number of genes which do not per se perform a direct role in cell cycle progression, a functional correlation between the expression of the novel genes and cell cycle transit should be demonstration.
Indirectly, cAMP sensitivity is suggestive of involvement in G.sub.1 progression. The demonstration of induction of the genes by other growth factors, as well as heightened expression in transformed cell lines would further support this notion. A more direct approach, utilizing antisense oligonucleotides, will make it possible to determine whether specific blockage of expression of any of these genes is sufficient to prevent cell cycle progression. Similarly, it will be possible to determine whether the immediate early gene products exert cell cycle control through the induction of expression of late genes, as has been demonstrated for regulation of the PCNA/cyclin, DNA polymerase A and cdc2 genes by the c-myb and c-myc gene products. Interestingly, the IL-2-induced expression of the PCNA/cyclin and DNA topoisomerase II gene in late G.sub.1 is specifically inhibited by cAMP, so that cAMP sensitivity of immediate early gene expression can provide a useful indicator of which genes play a role in regulating late gene expression. If, like the previously characterized cell cycle regulatory cdc2/CDC28 and cyclin genes, the novel IL-2 induced genes are highly conserved, then it may ultimately be possible to isolate yeast homologs of the clones and perform deletional analyses to further define the functions of the gene products.
Ultimately, the definitive assignment of a given gene product to a particular function within a cell depends upon a series of different approaches, including determining intracellular location, and determining the consequences of blocking the expression of the gene either by mRNA antisense methods or by homologous recombination methods. All of the methods necessary for these studies exist as prior art and therefore, given the identification of a given gene as activated by a ligand such as the cytokine IL-2 is possible to characterize each gene product.
By following the method of the invention, eight clones containing ligand-induced genes have been identified. At least six of these ligand-induced genes are novel and have been named Cytokine Response (CR) genes 1-3, 5, 6 and 8. CR4 is identical to a gene reported as SATB-1 (Dickinson, L. A. et al. (1992) Cell 70:631-645), for Special AT-rich Binding protein 1, which binds selectively to the nuclear matrix/scaffold-associating region of DNA. CR7 is identical to the putative proto-oncogene, pim 1, a known IL-2-induced gene. The nucleic acid sequences of these CR genes, i.e., CR genes 1-6 and 8, are set forth in SEQ ID NOs: 1, 3, 5, 7, 9, 11, and 13 (these sequences are also shown in FIGS. 1-7). The amino acid sequences encoded by these CR genes are set forth in SEQ ID NOs.: 2, 4, 6, 8, 10, 12, and 14 (these sequences are also shown in FIGS. 1-7) as well as in SEQ ID NOs: 1, 3, 5, 7, 9, 11, and 13. Table I provides several characteristics of the CR genes.
The regulatory region of all of the CR genes can be used to construct assays to identify the relevant cis-acting DNA response elements, the trans-acting factors responsible for transcriptional activation leading to CR gene expression, and the biochemical signalling for pathways triggered by IL-2 (the ligand) that activate the transcriptional activating factors. These assays can be used to identify novel agents or drugs that either suppress or activate CR gene expression. Such novel agents or drugs can be used immunosuppressives, immunostimulants, or anti-cancer agents.
The immediate-early CR genes and gene products can be used to construct assays to determine which biochemical and molecular events, initiated by the ligand-receptor stimulation, promote progression to the intermediate and late stages of cell cycle progression that are responsible for DNA synthesis and replication. These assays can be used to identify novel agents and drugs that either suppress or promote these processes. With the capacity to generate large quantities of the CR gene products, the three-dimensional structures of the products can be determined by conventional methods, such as x-ray crystallography and nuclear magnetic resonance. From this information, novel agents or drugs can be identified using computer analysis of the chemical structures, that interact with the CR gene product. These agents can then be developed as therapeutics.
The regulation of CR1 expression is notable in that it is rapidly and transiently induced by IL-2, and mRNA expression is suppressed by elevated intracellular cAMP, which also suppresses IL-2-promoted G.sub.1 progression. There are already available pharmaceuticals that elevate intracellular cAMP, such as aminophylline and theophylline. Therefore, it is now possible to determine how these agents function to inhibit CR1 expression and to identify novel agents that act similarly, but may have particular pharmacologic advantages.
The CR1 gene includes 2406 nucleotides (shown in SEQ ID NO:1 and FIG. 1) and encodes a protein of 202 amino acids (about 22 kDa) (shown in SEQ ID NO:2 and FIG. 1) that shares sequence homology to two other recently reported genes, GOS8 and BL-34, both of which are induced to high levels of expression by mitogens. The nucleotide sequence of the CR1 gene is about 58% homologous to the nucleotide sequence of the GOS8 gene (Siderovski, D. P. et al. (1994) DNA and Cell Biology 13:125-147), which was isolated from a PHA-induced T cell library. At the protein level, CR1 is about 51.2% homologous to GOS8. In addition, the nucleotide sequence of the CR1 gene is about 58% homologous to the nucleotide sequence of the BL34 gene (Hong, J. X. et al. (1993) J. Immunol. 150:3895-3904), which was isolated from a Staph A-activated B cell cDNA library. At the protein level, CR1 is about 48.0% homologous to BL34. The homology of CR1 with BL-34 is of particular interest, in that BL-34 is expressed only by activated B cells, is preferentially expressed in vivo by B cells in lymph node germinal centers, and is overexpressed in B cell malignancies. As predicted from its amino acid sequence which contains neither a hydrophobic leader sequence nor a transmembrane region, CR1 is an intracellular protein. Also, the CR1 protein includes no sequences consistent with other functional motifs or domains, such as found for DNA binding proteins, kinases, phosphatases, or linker molecules. The sequences for the gene (SEQ. ID No: 1), protein (SEQ ID No: 2), and protein coding region of the gene (SEQ. ID No: 27) for CR1, the underlined being the protein coding region of the gene, are provided below in Table II.
The CR2 gene includes 1283 nucleotides (shown in SEQ ID NO:3 and FIG. 2) and encodes a small, intracellular protein of 60 amino acids (about 6.6 kDa)(shown in SEQ ID NO:4 and FIG. 2). The CR2 gene is the only CR gene for which there are no homologies to known gene products. Elevated cAMP suppresses, but does not abolish CR2 gene expression. The sequences for the gene (SEQ. ID No: 3), protein (SEQ. ID No: 4), and protein coding region of the gene (SEQ ID No: 28) for CR2, the underlined being the protein coding region of the gene (SEQ. ID No: 28), are provided below in Table III.
The CR3 gene includes 2451 nucleotides (shown in SEQ ID NO:5 and FIG. 3) and encodes a protein of 378 amino acids (about 41.5 kDa) (shown in SEQ ID NO:6 and FIG. 3). This protein is homologous to G-coupled, 7 transmembrane-spanning receptors of the prostaglandin family. The receptor for prostacyclin (PGI.sub.2) is most homologous (about 70%) (See Boie, Y. et al. (1994) J. Biol. Chem. 269:12173-12178) to the CR3 protein. PGI.sub.2 is a labile metabolite of arachidonic acid produced via the cyclooxygenase pathway, and plays a major physiological role as a potent mediator of vasodilation and inhibitor of platelet activation. It is primarily expressed in the kidney with lower levels of mRNA also observed in the lung and the liver. In the kidney the PGI.sub.2 receptor is thought to play an important role in renal blood flow, renin release, and glomerular filtration rate. By comparison, CR3 is maximally expressed by leukocytes, placenta, testes, ovary and small intestine, and at lower levels by spleen, thymus and prostate, but not by kidney or liver. Therefore, CR3 most likely plays a regulatory role in cellular proliferation and/or inflammation. Elevated cAMP suppresses CR3 expression early on after IL-2 stimulation, but not at later time intervals.
Because the CR3 encodes a protein that is a member of a family of 7 transmembrane spanning receptors, it is likely that this receptor is coupled to cytoplasmic GTP-binding proteins (G proteins) that are known to activate or suppress the generation of cAMP. Therefore, the CR3 gene product provides a new receptor that can allow the manipulation of cellular functions that are controlled by biochemical pathways signaled by the receptor. The CR3 gene and gene product can be used in assays for identifying ligands that trigger the receptor. These ligands can be used to modulate cellular proliferation and inflammation. The sequences for the gene (SEQ. ID No: 5), protein (SEQ. ID No: 6), and protein coding region of the gene (SEQ. ID No: 29) corresponding to CR3, the underlined being the protein coding region of the gene (SEQ. ID No: 29), are shown in Table IV below.
The CR4 gene includes 2946 nucleotides (shown in SEQ ID NO:7 and FIG. 4) and encodes a protein of 763 amino acids (about 85.9 kDa) (shown in SEQ ID NO:8 and FIG. 4). The sequence of this gene is identical to a gene reported as SATB-1 (Dickinson, L. A. et al. (1992) Cell 70:631-645), for Special AT-rich Binding protein 1, which binds selectively to the nuclear matrix/scaffold-associating region of DNA. It is expressed exclusively in the thymus and activated peripheral T cells. CR4 is the only CR gene also activated by the TCR. In addition, elevated cAMP actually stimulates CR4 gene expression.
Because the CR4 gene product binds to special AT-rich regions of DNA known to associate with proteins in the nuclear mating, CR4 is most likely a novel nuclear matrix protein. The nuclear matrix proteins are known to influence the structure of DNA, facilitating transcription of specific genes in particular differentiated tissues. Because the expression of CR4 is restricted to thymocytes and activated T cells, it is likely that CR4 plays an important role in T cell maturation, differentiation or proliferation. Therefore, novel agents that modify CR4 gene expression or CR4 function have the potential to be useful to manipulate the T cell immune response. Thus, CR4 can be used in an assay to identify such novel agents which can be used, for example, to treat transplant recipients by, for example, inhibiting the recipient's T cell immune response. These agents can also be used to stimulate the T cell immune response in immunosuppressed subjects, e.g., AIDS patients. The sequences for the gene (SEQ. ID No: 7), protein (SEQ. ID No: 8), and protein coding region of the gene (SEQ. ID No: 30) for CR4, the underlined being the protein coding region of the gene, are shown in Table V below.
The CR5 gene includes 2020 nucleotides (shown in SEQ ID NO:9 and FIG. 5) and encodes a protein of 258 amino acids (about 28 kDa) (shown in SEQ ID NO:10 and FIG. 5). In the middle of the open reading frame of the CR5 protein is about a 100 amino acid region that has sequence homology (about 25-35%) to src homology 2 (SH2) domains (Waksman, G. et al. (1993) Cell 72:779-790), found in many proteins that bind to phosphotyrosine residues, e.g., kinases, substrates, linking molecules, and transcription factors. On either side of this SH2 domain the amino acid sequence is very rich in proline residues. Analysis of CR5 protein expression by different tissues reveals a high level of expression in heart, placenta, lung, liver skeletal muscle and kidney. CR5 protein expression is induced by the proliferation-promoting cytokines IL-2, IL-3, IL-4, IL-5, but not by IL-6. Also, CR5 protein expression is induced by IFN-.beta. and elevated intracellular cAMP, both of which antagonize IL-2 promoted proliferation. CR5 protein has been found to interact with a subunit of the RNA polymerase II preinitiation complex, termed RNA polymerase II elongation factor SIII, p15 subunit. Garret, K. P. et al. (1994) Proc. Natl. Acad. Sci. USA 91:5237-5241. The p15 subunit of this RNA polymerase II elongation factor is known to be responsible for promoting the elongation of transcripted mRNA molecules. Therefore, CR5 appears to function as a ligand-stimulated factor that facilitates mRNA expression by promoting the full elongation of mRNA transcripts. This phenomenon promises to be a novel way in which ligand-receptor systems can regularly promote gene expression. Previously, attention has focused almost entirely on this initiation of transcription, not the elongation of transcripts that were prematurely truncated. Accordingly, novel agents or drugs that modify CR5 gene expression or CR5 function have the potential to provide new ways to alter ligand-stimulated gene expression and thereby alter cellular function. The sequences for the gene (SEQ. ID No: 9), protein (SEQ. ID No: 10), and protein coding region of the gene (SEQ. ID No: 33) for CR5, the underlined being the protein coding region of the gene (SEQ. ID No: 33), are shown in Table VI below.
The CR6 gene includes 1066 nucleotides (shown in SEQ ID NO:11 and FIG. 6) and encodes protein of 159 amino acids (about 17.5 kDa) (shown in SEQ ID NO:12 and FIG. 6). This gene belongs to a family of small nuclear-localizing gene products. Two other members of this family, GADD45 and MyD118, have been identified. GADD45 was cloned from human fibroblasts induced by UV irradiation (Papathanasiou, M. A. et al. (1991) Mol. Cell Biol. 11(2):1009-1016). This protein is regulated by p53 and suppresses growth of cells by binding to PCNA, a co-factor required for DNA polymerase .delta. activity. (Smith, M. L. et al. (1994) Science 266:1376-1380). MyD118 was cloned from M1D+ myeloid precursors following induction of terminal differentiation and growth arrest by IL6. Abdollahi, A. et al. (1991) Oncogene 6:165-167. At the nucleotide level, CR6 is about 65% homologous to GADD45. At the protein level, CR6 is about 54% homologous to GADD45. At the nucleotide level, CR6 is about 66% homologous to MyD118. At the protein level, CR6 is about 53% homologous to MyD118. The CR6 protein is expressed only in testes, ovary and prostate, and its expression is suppressed by elevated cAMP.
By analogy to it's homology to GADD45 and MyD118, the CR6 gene product most likely plays a role in DNA replication. Thus far, experiments have indicated that CR6 expression is not induced by agents that damage DNA, such as UV light. Moreover, CR6 does not bind to PCNA. However, CR6 does promote DNA replication in vitro, and it is likely to be a novel CD-factor necessary for DNA replication. Therefore, the CR6 gene product can be used to identify inhibitors of DNA replication which can be used as anti-proliferative agents, e.g., in the treatment of cancer. The SEQ. ID No: 11, SEQ. ID No: 12, and SEQ. ID No: 31, corresponding to the gene, protein and protein coding DNA sequences of CR6, the underlined corresponding to the protein coding region of the gene (SEQ. ID No: 31), are shown in Table VII below.
The CR7 gene includes 2400 nucleotides and encodes a protein of 313 amino acids (about 34 kDa). The CR7 gene is identical to the putative proto-oncogene, pim-1, which has been reported to be over-expressed in about 50% of Moloney murine leukemia virus (MuLV)-induced T cell lymphomas. See Selten, G. et al. (1986) Cell 46:603-611 for the nucleotide and amino acid sequence of pim-1) Pim-1 is known to be an IL-2-induced gene and is a serine/threonine-specific protein kinase involved in T cell lymphomagenesis. The CR7 gene includes a 2400 nucleotide DNA (SEQ. ID No: 25), encoding a protein of 313 amino acids (about 34 kD) of SEQ. ID No: 26. The gene (SEQ. ID No: 25), protein (SEQ. ID No: 26), protein coding region of the gene (SEQ. ID No: 35), and the DNA sequence complementary to the gene sequence (SEQ. ID No: 34), the underlined being the protein coding region of the gene, are shown in Table VIII below.
The CR8 gene includes 2980 nucleotides (shown in SEQ ID NO:13 and FIG. 7) and encodes (via a 3.2 kb mRNA transcript) a protein of 412 amino acids (about 45 kDa) (shown in SEQ ID NO:14 and FIG. 7). There is significant sequence homology (40-45%) within an N-terminal 58 amino acid residue region to transcription factors that have a basic-Helix-Loop-Helix (bHLH) motif. The protein encoded by the bHLH region of the gene has been expressed in E. coli and has been found to bind to a hexanucleotide predicted by the binding specificity of other bHLH proteins. See Feder, J. et al. (1993) Mol. Cell Biol. 13(1):105-113. The N-terminal basic region binds to DNA and the HLH region serves as a protein dimerization motif. From the sequence of the bHLH region, CR8 fits into a class by itself. It shares most homology with Drosophila transcription repressors of the hairy family. However, CR8 lacks amino acid residues in the basic region and a C-terminal WRPW motif, characteristic for hairy proteins. CR8 also binds to Class B E-box sites (CACGTC/CATGTG), as do the c-myc family of bHLH proteins, rather than to Class C sites (CAGCCG) preferred by hairy-related family members. CR8 is ubiquitously expressed in all tissues examined except placenta. Its expression is induced by cytokines such as IL-2 and IL-3, which stimulate cellular proliferation, and also by IFN.beta. and elevated cAMP, which antagonize proliferation.
Because CR8 contains a bHLH domain, it is most likely a protein that binds to DNA and modifies gene expression, either by activation or by suppression. Since CR8 binds to class B E-bax sequences, which the proto-oncogene c-myc family members also bind, it is likely that CR8 modifies the expression of genes important for the intermediate and late phases of ligand-promoted cell cycle progression. It follows that CR8 is a prime candidate for the development of new assays to discover agents that modify cellular function by either enhancing or suppressing CR8 gene expression or CR8 function. The CR8 gene and its gene product are described in further detail below in Example VII. The CR8 gene includes a 2980 nucleotide fragment of SEQ. ID NO: 13, which encodes (via a 3.2 Kb mRNA transcript) a protein of 412 amino acids (about 45 kD) of SEQ. ID NO: 14. The SEQ. ID No: 13, SEQ. ID No: 14, and SEQ. ID No: 32, corresponding to the gene, protein, and protein coding gene sequences, are shown in Table IX below.
In summary, of the eight CR genes isolated using the thiol-selected IL-2-induced cDNA library, two are DNA binding proteins, one is a newly recognized transmembrane receptor, one contains an SH2 domain, one is homologous to a newly recognized family of small proteins that regulate cellular proliferation, and another is a serine/threonine kinase already known to be IL-2-induced, and to be over-expressed in MuLV-induced T cell lymphomas. Allowing for redundancies, a conservative estimate is that there are still about 40-50 novel genes induced by IL-2 which can be isolated using the method of the present invention.
Accordingly, the present invention pertains to an isolated nucleic acid comprising the nucleotide sequence encoding one of the subject CR proteins, e.g., CR1, CR2, CR3, CR4, CR5, CR6, and CR8, and/or equivalents of such nucleic acids. The term "nucleic acid" as used herein is intended to include fragments and equivalents. The term "equivalent" as used herein refers to nucleotide sequences encoding functionally equivalent CR proteins or functionally equivalent peptides which retain other activities of an CR protein such as described herein. Equivalent nucleotide sequences include sequences that differ by one or more nucleotide substitutions, additions or deletions, such as allelic variants; and, therefore, include sequences that differ from the nucleotide sequence CR proteins shown in any of SEQ ID NOs:2, 4, 6, 8, 10, 12, and 14 due to the degeneracy of the genetic code. Equivalents also include nucleotide sequences that hybridize under stringent conditions (i.e., equivalent to about 20.degree.-27.degree. C. below the melting temperature (T.sub.m) of the DNA duplex formed in about 1M salt) to the nucleotide sequence of the presently claimed CR proteins represented in SEQ ID NOs:2, 4, 6, 8, 10, 12, and 14. In one embodiment, equivalents further include nucleic acid sequences derived from and evolutionarily related to, a nucleotide sequences shown in any of SEQ ID NOs:1, 3, 5, 7, 9, 11, and 13. Moreover, it is explicitly contemplated by the present invention that, under certain circumstances, it may be advantageous to provide homologs of the subject CR proteins which have at least one biological activity of a CR protein. Such homologs of the subject CR proteins can be generated by mutagenesis, such as by discrete point mutation(s) or by truncation. For instance, mutation can give rise to homologs which retain substantially the same, or merely a subset, of the biological activity of the CR protein from which it was derived. Alternatively, antagonistic forms of the protein can be generated which are able to inhibit the function of the naturally occurring form of the CR protein.
A protein has CR biological activity if it has one or more of the following properties: (1) its expression is regulated by ligand-receptor stimulation; and (2) it participates in ligand-receptor modification of cellular function, e.g. proliferation, differentiation, programmed cell death.
As used herein, the term "gene" or "recombinant gene" refers to a nucleic acid comprising an open reading frame encoding a CR protein of the present invention, including both exon and (optionally) intron sequences. A "recombinant gene" refers to nucleic acid encoding a CR protein and comprising CR encoding exon sequences, though it may optionally include intron sequences which are either derived from a chromosomal CR gene or from an unrelated chromosomal gene. The term "intron" refers to a DNA sequence present in a given CR gene which is not translated into protein and is generally found between exons.
As used herein, the term "transfection" means the introduction of a nucleic acid, e.g., an expression vector, into a recipient cell by nucleic acid-mediated gene transfer. "Transformation", as used herein, refers to a process in which a cell's genotype is changed as a result of the cellular uptake of exogenous DNA or RNA, and, for example, the transformed cell expresses a recombinant form of the CR protein of the present invention or where anti-sense expression occurs from the transferred gene, the expression of a naturally-occurring form of the CR protein is disrupted.
As used herein, the term "vector" refers to a nucleic acid molecule capable of transporting another nucleic acid to which it has been linked. One type of preferred vector is an episome, i.e., a nucleic acid capable of extra-chromosomal replication. Preferred vectors are those capable of autonomous replication and/expression of nucleic acids to which they are linked. Vectors capable of directing the expression of genes to which they are operatively linked are referred to herein as "expression vectors". In general, expression vectors of utility in recombinant DNA techniques are often in the form of "plasmids" which refer to circular double stranded DNA loops which, in their vector form are not bound to the chromosome. In the present application, "plasmid" and "vector" are used interchangeably as the plasmid is the most commonly used form of vector. However, the invention is intended to include such other forms of expression vectors which serve equivalent functions and which become known in the art subsequently hereto.
"Transcriptional regulatory sequence" is a generic term used throughout the specification to refer to DNA sequences, such as initiation signals, enhancers, and promoters, which induce or control transcription of protein coding sequences with which they are operably linked. In preferred embodiments, transcription of a recombinant CR gene is under the control of a promoter sequence (or other transcriptional regulatory sequence) which controls the expression of the recombinant gene in a cell-type in which expression is intended. The recombinant gene can also be under the control of transcriptional regulatory sequences which are the same or which are different from those sequences which control transcription of the naturally-occurring form of the CR proteins.
As used herein, the term "tissue-specific promoter" means a DNA sequence that serves as a promoter, i.e., regulates expression of a selected DNA sequence operably linked to the promoter, and which effects expression of the selected DNA sequence in specific cells of a tissue. The term also covers so-called "leaky" promoters, which regulate expression of a selected DNA primarily in one tissue, but cause expression in other tissues as well.
As used herein, a "transgenic animal" is any animal, preferably a non-human mammal, e.g. a rat, a mouse or pig, in which one or more of the cells of the animal includes a transgene. The transgene is introduced into the cell, directly or indirectly by introduction into a precursor of the cell, by way of deliberate genetic manipulation, such as by microinjection or by infection with a recombinant virus. The language "genetic manipulation" does not include classical cross-breeding, or in vitro fertilization, but rather is directed to the introduction of a recombinant DNA molecule. This molecule can be integrated within a chromosome, or it may be extrachromosomally replicating DNA. In the transgenic animals described herein, the transgene causes cells to express a recombinant form of one or more of the subject CR proteins, or alternatively, to disrupt expression of one or more of the naturally-occurring forms of the CR genes.
As used herein, the term "transgene" refers to a nucleic acid sequence which is partly or entirely heterologous, i.e., foreign, to the animal or cell into which it is introduced, or, is homologous to an endogenous gene of the animal or cell into which it is introduced, but which is designed to be inserted, or is inserted, into the animal's genome in such a way as to alter the genome of the cell into which it is inserted (e.g., it is inserted at a location which differs from that of the natural gene or its insertion results in a knockout). A transgene can include one or more transcriptional regulatory sequences and any other nucleic acid, such as introns, that may be necessary for optimal expression of a selected nucleic acid.
As is well known, genes for a particular polypeptide may exist in single or multiple copies within the genome of an individual. Such duplicate genes may be identical or may have certain modifications, including nucleotide substitutions, additions or deletions, which all still code for polypeptides having substantially the same activity. The term "DNA sequence encoding a CR protein" refers to one or more genes within a particular individual. Moreover, certain differences in nucleotide sequences may exist between individual organisms, which are called alleles. Such allelic differences may or may not result in differences in amino acid sequence of the encoded polypeptide yet still encode a protein with the same biological activity.
"Cells," "host cells" or "recombinant host cells" are terms used interchangeably herein. Such terms refer not only to the particular subject cell but to the progeny or potential progeny of such a cell. Because certain modifications may occur in succeeding generations due to either mutation or environmental influences, such progeny may not, in fact, be identical to the parent cell, but are still included within the scope of the term as used herein.
A "chimeric protein" or "fusion protein" is a fusion of a first amino acid sequence encoding one of the subject CR proteins with a second amino acid sequence defining a domain foreign to and not substantially homologous with any domain of the subject CR protein. A chimeric protein may present a foreign domain which is found (albeit in a different protein) in an organism which also expresses the first protein, or it may be an "interspecies", "intergeneric", etc. fusion of protein structures expressed by different kinds of organisms.
The language "evolutionarily related to", with respect to nucleic acid sequences encoding CR proteins, refers to nucleic acid sequences which have arisen naturally in an organism, including naturally occurring mutants. This language also refers to nucleic acid sequences which, while derived from a naturally occurring CR nucleic, have been altered by mutagenesis, as for example, combinatorial mutagenesis, yet still encode polypeptides which have at least one activity of a CR protein.
In one embodiment, the nucleic acid is a cDNA encoding a peptide having at least one activity of a subject CR proteins. Preferably, the nucleic acid is a cDNA molecule comprising at least a portion of the nucleotide sequence represented in one of SEQ ID NOs: 1, 3, 5, 7, 9, 11, and 13. A preferred portion of these cDNA molecules includes the coding region of the gene.
Preferred nucleic acids encode a CR protein comprising an amino acid sequence at least 60% homologous, more preferably 70% homologous and most preferably 80%, 90%, or 95% homologous with an amino acid sequence shown in one of SEQ ID NOs:2, 4, 6, 8, 10, 12, or 14. Nucleic acids which encode polypeptides having an activity of a subject CR protein and having at least about 90%, more preferably at least about 95%, and most preferably at least about 98-99% homology with a sequence shown in one of SEQ ID NOs:2, 4, 6, 8, 10, 12, or 14 are also within the scope of the invention. The term "homology" refers to sequence similarity between two peptides or between two nucleic acid molecules. Homology can be determined by comparing a position in each sequence which may be aligned for purposes of comparison. When a position in the compared sequence is occupied by the same base or amino acid, then the molecules are homologous at that position. The degree of homology between sequences is a function of the number of matching or homologous positions shared by the sequences.
Another aspect of the invention provides a nucleic acid which hybridizes under high or low stringency conditions to a nucleic acid which encodes a peptide having all or a portion of an amino acid sequence shown in SEQ ID NO:2, SEQ ID NO:4, SEQ ID NO:6, SEQ ID NO:8, SEQ ID NO:10, SEQ ID NO:12 or SEQ ID NO:14. Appropriate stringency conditions which promote DNA hybridization, for example, 6.0.times.sodium chloride/sodium citrate (SSC) at about 45.degree. C., followed by a wash of 2.0.times.SSC at 50.degree. C., are known to those skilled in the art or can be found in Current Protocols in Molecular Biology, John Wiley & Sons, N.Y. (1989), 6.3.1-6.3.6. For example, the salt concentration in the wash step can be selected from a low stringency of about 2.0.times.SSC at 50.degree. C. to a high stringency of about 0.2.times.SSC at 50.degree. C. In addition, the temperature in the wash step can be increased from low stringency conditions at room temperature, about 22.degree. C., to high stringency conditions at about 65.degree. C.
Nucleic acids, having a sequence that differs from the nucleotide sequence shown in any of SEQ ID NOs:1, 3, 5, 7, 9, 11, and 13 due to degeneracy in the genetic code are also within the scope of the invention. Such nucleic acids encode functionally equivalent peptides (i.e., a peptide having a biological activity of a CR protein) but differ in sequence from the sequence shown in said sequence listings due to degeneracy in the genetic code. For example, a number of amino acids are designated by more than one triplet. Codons that specify the same amino acid, or synonyms (for example, CAU and CAC each encode histidine) may result in "silent" mutations which do not affect the amino acid sequence of the CR protein. However, it is expected that DNA sequence polymorphisms that do lead to changes in the amino acid sequences of the subject CR proteins will exist among vertebrates. One skilled in the art will appreciate that these variations in one or more nucleotides (up to about 3-5% of the nucleotides) of the nucleic acids encoding polypeptides having an activity of an CR protein may exist among individuals of a given species due to natural allelic variation. Any and all such nucleotide variations and resulting amino acid polymorphisms are within the scope of this invention.
Fragments of the nucleic acids encoding the active portion of the presently claimed CR proteins are also within the scope of the invention. As used herein, a fragment of the nucleic acid encoding the active portion of a CR protein refers to a nucleic acid having fewer nucleotides than the nucleotide sequence encoding the entire amino acid sequence of a CR protein but which nevertheless encodes a peptide having a biological activity of the CR proteins described herein. Nucleic acid fragments within the scope of the present invention include those capable of hybridizing under high or low stringency conditions with nucleic acids from other species for use in screening protocols to detect CR homologs, as well as those capable of hybridizing with nucleic acids from human specimens for use in detecting the presence of a nucleic acid encoding one of the subject CR proteins, including alternate isoforms, e.g. mRNA splicing variants. Nucleic acids within the scope of the invention can also contain linker sequences, modified restriction endonuclease sites and other sequences useful for molecular cloning, expression or purification of recombinant forms of the subject CR proteins.
A nucleic acid encoding a peptide having an activity of an CR protein can be obtained from mRNA present in any of a number of eukaryotic cells. Nucleic acids encoding CR proteins of the present invention can also be obtained from genomic DNA obtained from both adults and embryos. For example, a gene encoding a CR protein can be cloned from either a cDNA or a genomic library in accordance with protocols herein described, as well as those generally known to persons skilled in the art. A cDNA encoding one of the subject CR proteins can be obtained by isolating total mRNA from a cell, e.g. a mammalian cell, e.g. a human cell, including tumor cells. Double stranded cDNAs can then be prepared from the total mRNA, and subsequently inserted into a suitable plasmid or bacteriophage vector using any one of a number of known techniques. The gene encoding the CR protein can also be cloned using established polymerase chain reaction techniques in accordance with the nucleotide sequence information provided by the invention. The nucleic acid of the invention can be DNA or RNA. Preferred nucleic acids are the cDNAs represented by the sequences shown in SEQ ID NOs:1, 3, 5, 7, 9, 11, and 13.
This invention also provides expression vectors containing a nucleic acid encoding a peptide having an activity of an CR protein, operably linked to at least one transcriptional regulatory sequence. The language "operably linked" refers to linkage of the nucleotide sequence to a regulatory sequence in a manner which allows expression of the nucleotide sequence. Regulatory sequences are art-recognized and are selected to direct expression of the peptide having an activity of a CR protein. Accordingly, the language "transcriptional regulatory sequence" includes promoters, enhancers and other expression control elements. Such regulatory sequences are described in Goeddel; Gene Expression Technology: Methods in Enzymology 185, Academic Press, San Diego, Calif. (1990). The design of the expression vector may depend on such factors as the choice of the host cell to be transformed and/or the type of protein desired to be expressed. In one embodiment, the expression vector includes a recombinant gene encoding a peptide having an activity of a subject CR protein. Such expression vectors can be used to transfect cells and thereby produce proteins or peptides, including fusion proteins or peptides, encoded by nucleic acids as described herein. Moreover, such vectors can be used as a part of a gene therapy protocol to reconstitute the function of, or alternatively, abrogate the function of one of the subject CR proteins in a cell in which a CR protein is misexpressed.
Another aspect of the present invention concerns recombinant forms of the subject CR proteins which are encoded by genes derived from eukaryotic organisms, e.g. mammals, e.g. humans, and which have at least one biological activity of a CR protein. The term "recombinant protein" refers to a protein of the present invention which is produced by recombinant DNA techniques, wherein generally DNA encoding the subject CR protein is inserted into a suitable expression vector which is in turn used to transform a host cell to produce the heterologous protein. Moreover, the phrase "derived from", with respect to a recombinant gene encoding the recombinant CR protein, includes within the meaning of "recombinant protein" those proteins having an amino acid sequence of a native CR protein of the present invention, or an amino acid sequence similar thereto which is generated by mutations including substitutions and deletions (including truncation) of a naturally occurring CR protein of a organism. Recombinant proteins preferred by the present invention, in addition to native CR proteins, are at least 60% homologous, more preferably 70% homologous and most preferably 80% homologous with an amino acid sequence shown in one of SEQ ID NOs:2, 4, 6, 8, 10, 12, or 14. Polypeptides having an activity of the subject CR proteins and having at least about 90%, more preferably at least about 95%, and most preferably at least about 98-99% homology with a sequence of either in SEQ ID NO:2, 4, 6, 8, 10, 12, or 14 are also within the scope of the invention.
The present invention further pertains to recombinant forms of the subject CR proteins which are encoded by genes derived from an organism and which have amino acid sequences evolutionarily related to a CR protein of either SEQ ID NO:2, 4, 6, 8, 10, 12, or 14. The language "evolutionarily related to", with respect to amino acid sequences of the present recombinant CR proteins, refers to CR proteins having amino acid sequences which have arisen naturally, as well as mutational variants of CR proteins which are derived, for example, by combinatorial mutagenesis. Preferred evolutionarily derived CR proteins are at least 60% homologous, more preferably 70% homologous and most preferably 80% homologous with an amino acid sequence shown in either SEQ ID NO:2, SEQ ID NO:4, SEQ ID NO:6, SEQ ID NO:8, SEQ ID NO:10, SEQ ID NO:12 or SEQ ID NO:14. Polypeptides having at least about 90%, more preferably at least about 95%, and most preferably at least about 98-99% homology with a sequence shown in any of SEQ ID NOs:2, 4, 6, 8, 10, 12, or 14 are also within the scope of the invention.
The present invention further pertains to methods of producing the subject CR proteins. For example, a host cell transfected with a nucleic acid vector directing expression of a nucleotide sequence encoding the subject CR protein can be cultured under appropriate conditions to allow expression of the peptide to occur. The peptide can be secreted and isolated from a mixture of cells and medium containing the recombinant CR peptide. Alternatively, the peptide can be retained cytoplasmically and the cells harvested, lysed and the protein isolated. A cell culture includes host cells, media and other byproducts. Suitable media for cell culture are well known in the art. The recombinant CR peptide can be isolated from cell culture medium, host cells, or both using techniques known in the art for purifying proteins including ion-exchange chromatography, gel filtration chromatography, ultrafiltration, electrophoresis, and immunoaffinity purification with antibodies specific for such peptide. In a preferred embodiment, the recombinant CR protein is a fusion protein containing a domain which facilitates its purification.
This invention also pertains to a host cell transfected to express a recombinant form of at least one of the subject CR proteins. The host cell can be any prokaryotic or eukaryotic cell. Thus, a nucleotide sequence derived from the cloning of the CR proteins of the present invention, encoding all or a selected portion of a protein, can be used to produce a recombinant form of a CR protein via microbial or eukaryotic cellular processes. Ligating the polynucleotide sequence into a gene construct, such as an expression vector, and transforming or transfecting into hosts, either eukaryotic (yeast, avian, insect or mammalian) or prokaryotic (bacterial cells), are standard procedures used in producing other well-known proteins, e.g. insulin, interferons, human growth hormone, IL-1, IL-2, and the like. Similar procedures, or modifications thereof, can be employed to prepare recombinant CR proteins, or portions thereof, by microbial means or tissue-culture technology in accordance with the subject invention.
A recombinant CR gene can be produced by ligating nucleic acid encoding a subject CR protein, or a portion thereof, into a vector suitable for expression in either prokaryotic cells, eukaryotic cells, or both. Expression vectors for production of recombinant forms of the subject CR proteins include plasmids and other vectors. For instance, suitable vectors for the expression of a CR protein include plasmids of the types: pBR322-derived plasmids, pEMBL-derived plasmids, pEX-derived plasmids, pBTac-derived plasmids and pUC-derived plasmids for expression in prokaryotic cells, such as E. coli.
A number of vectors exist for the expression of recombinant proteins in yeast. For instance, YEP24, YIP5, YEP51, YEP52, pYES2, and YRP17 are cloning and expression vehicles useful in the introduction of genetic constructs into S. cerevisiae (see, for example, Broach et al. (1983) in Experimental Manipulation of Gene Expression, ed. M. Inouye Academic Press, p. 83, incorporated by reference herein). These vectors can replicate in E. coli due the presence of the pBR322 ori, and in S. cerevisiae due to the replication determinant of the yeast 2 micron plasmid. In addition, drug resistance markers such as ampicillin can be used.
The preferred mammalian expression vectors contain both prokaryotic sequences to facilitate the propagation of the vector in bacteria, and one or more eukaryotic transcription units that are expressed in eukaryotic cells. The pcDNAI/amp, pcDNAI/neo, pRc/CMV, pSV2gpt, pSV2neo, pSV2-dhfr, pTk2, pRSVneo, pMSG, pSVT7, pko-neo and pHyg derived vectors are examples of mammalian expression vectors suitable for transfection of eukaryotic cells. Some of these vectors are modified with sequences from bacterial plasmids, such as pBR322, to facilitate replication and drug resistance selection in both prokaryotic and eukaryotic cells. Alternatively, derivatives of viruses such as the bovine papilloma virus (BPV-1), or Epstein-Barr virus (pHEBo, pREP-derived and p205) can be used for transient expression of proteins in eukaryotic cells. The various methods employed in the preparation of the plasmids and transformation of host organisms are well known in the art. For other suitable expression systems for both prokaryotic and eukaryotic cells, as well as general recombinant procedures, see Molecular Cloning A Laboratory Manual, 2nd Ed., ed. by Sambrook, Fritsch and Maniatis (Cold Spring Harbor Laboratory Press: 1989) Chapters 16 and 17. In some instances, the recombinant CR protein can be expressed using a baculovirus expression system. Examples of such baculovirus expression systems include pVL-derived vectors (such as pVL1392, pVL1393 and pVL941), pAcUW-derived vectors (such as pAcUW1), and pBlueBac-derived vectors (such as the .beta.-gal containing pBlueBac III).
When expression of a portion of one of the subject CR proteins is desired, i.e. a truncation mutant, it may be necessary to add a start codon (ATG) to the oligonucleotide fragment containing the desired sequence to be expressed. It is well known in the art that a methionine at the N-terminal position can be enzymatically cleaved by the use of the enzyme methionine aminopeptidase (MAP). MAP has been cloned from E. coli (Ben-Bassat et al. (1987) J. Bacteriol. 169:751-757) and Salmonella typhimurium and its in vitro activity has been demonstrated on recombinant proteins (Miller et al. (1987) PNAS 84:2718-1722). Therefore, removal of an N-terminal methionine, if desired, can be achieved either in vivo by expressing CR-derived polypeptides in a host which produces MAP (e.g., E. coli or CM89 or S. cerevisiae), or in vitro by use of purified MAP (e.g., procedure of Miller et al., supra).
Alternatively, the coding sequences for the polypeptide can be incorporated as a part of a fusion gene including a nucleotide sequence encoding a different polypeptide. This type of expression system can be useful under conditions where it is desirable to produce an immunogenic fragment of a CR protein. The nucleic acid sequences corresponding to the portion of a subject CR protein to which antibodies are to be raised can be incorporated into a fusion gene construct which includes coding sequences for a late vaccinia virus structural protein to produce a set of recombinant viruses expressing fusion proteins comprising a portion of the CR protein as part of the virion. It has been demonstrated with the use of immunogenic fusion proteins utilizing the Hepatitis B surface antigen fusion proteins that recombinant Hepatitis B virions can be utilized in this role as well. Similarly, chimeric constructs coding for fusion proteins containing a portion of a CR protein and the poliovirus capsid protein can be created to enhance immunogenicity of the set of polypeptide antigens (see, for example, EP Publication No: 0259149; and Evans et al. (1989) Nature 339:385; Huang et al. (1988) J. Virol. 62:3855; and Schlienger et al. (1992) J. Virol. 66:2).
The Multiple Antigen Peptide system for peptide-based immunization can also be utilized to generate an immunogen, wherein a desired portion of a subject CR protein is obtained directly from organo-chemical synthesis of the peptide onto an oligomeric branching lysine core (see, for example, Posnett et al. (1988) JBC 263:1719 and Nardelli et al. (1992) J. Immunol. 148:914). Antigenic determinants of the subject CR proteins can also be expressed and presented by bacterial cells.
In addition to utilizing fusion proteins to enhance immunogenicity, fusion proteins can also facilitate the expression of proteins, such as any one of the CR proteins of the present invention. For example, a CR protein of the present invention can be generated as a glutathione-S-transferase (GST-fusion protein). Such GST fusion proteins can enable easy purification of the CR protein, such as by the use of glutathione-derivatized matrices (see, for example, Current Protocols in Molecular Biology, eds. Ausabel et al. (N.Y.: John Wiley & Sons, 1991)).
Techniques for making fusion genes are known to those skilled in the art. Essentially, the joining of various DNA fragments coding for different polypeptide sequences is performed in accordance with conventional techniques, employing blunt-ended or stagger-ended termini for ligation, restriction enzyme digestion to provide for appropriate termini, filling-in of cohesive ends as appropriate, alkaline phosphatase treatment to avoid undesirable joining, and enzymatic ligation. In another embodiment, the fusion gene can be synthesized by conventional techniques including automated DNA synthesizers. Alternatively, PCR amplification of gene fragments can be carried out using anchor primers which give rise to complementary overhangs between two consecutive gene fragments which can subsequently be annealed to generate a chimeric gene sequence (see, for example, Current Protocols in Molecular Biology, eds. Ausubel et al. John Wiley & Sons: 1992).
Another aspect of the invention pertains to isolated peptides having an activity of one of the subject CR proteins. In preferred embodiments, a biological activity of a CR protein includes: promotion of cell cycle progression (e.g., CR1); ligand-receptor signalling (e.g., CR3); cellular maturation, differentiation, and proliferation (e.g., CR4); enhancement or suppression of DNA replication (e.g., CR5, CR6); promotion of mRNA transcription by stimulating elongation of mRNA transcription (e.g., CR5, CR6); and transcriptional activation and repression (e.g., CR8). Other biological activities of the subject CR proteins are described herein or will be reasonably apparent to those skilled in the art. A polypeptide having at least one biological activity of the subject CR proteins may differ in amino acid sequence from the sequence shown in either SEQ ID NO:2, 4, 6, 8, 10, 12, or 14, but such differences result in a modified polypeptide which functions in the same or similar manner as the native CR or which has the same or similar characteristics of the native CR protein. Various modifications of a CR protein of the present invention to produce these and other functionally equivalent peptides are described in detail herein. The terms peptide, protein, and polypeptide are used interchangeably herein.
The present invention also pertains to isolated CR proteins which are isolated from, or otherwise substantially free of other cellular proteins normally associated with the CR protein. The language "substantially free of other cellular proteins" (also referred to herein as "contaminating proteins") or "substantially pure, substantially pure preparation, or purified preparations" are defined as encompassing CR protein preparations having less than 20% (by dry weight) contaminating protein, and preferably having less than 5% contaminating protein. Functional forms of the subject CR proteins can be prepared, for the first time, as purified preparations by using a cloned gene as described herein. As used herein, the term "purified", when referring to a peptide or DNA or RNA sequence, that the indicated molecule is present in the substantial absence of other biological macromolecules, such as other proteins. The term "purified" as used herein preferably means at least 80% by dry weight, more preferably in the range of 95-99% by weight, and most preferably at least 99.8% by weight, of biological macromolecules of the same type present (but water, buffers, and other small molecules, especially molecules having a molecular weight of less than 5000, can be present). The term "pure" as used herein preferably has the same numerical limits as the term "purified". "Isolated" and "purified" do not encompass either natural materials in their native state or natural materials that have been separated into components (e.g., in an acrylamide gel) but not obtained either as pure (e.g. lacking contaminating proteins, or chromatography reagents such as denaturing agents and polymers, e.g. acrylamide or agarose) substances or solutions.
The term "isolated" as also used herein with respect to nucleic acids, such as DNA or RNA, refers to molecules separated from other DNAs, or RNAs, respectively, that are present in the natural source of the macromolecule. For example, an isolated nucleic acid encoding one of the subject CR proteins preferably includes no more than 1 0 kilobases (kb) of nucleic acid sequence which naturally immediately flanks that particular CR gene in genomic DNA, more preferably no more than 5 kb of such naturally occurring flanking sequences, and most preferably less than 1.5 kb of such naturally occurring flanking sequence. The term isolated as used herein also refers to a nucleic acid or peptide that is substantially free of cellular material, viral material, or culture medium when produced by recombinant DNA techniques, or chemical precursors or other chemicals when chemically synthesized. Moreover, an "isolated nucleic acid" is meant to include nucleic acid fragments which are not naturally occurring as fragments and would not be found in the natural state.
Furthermore, isolated peptidyl portions of the subject CR proteins can also be obtained by screening peptides recombinantly produced from the corresponding fragment of the nucleic acid encoding such peptides. In addition, fragments can be chemically synthesized using techniques known in the art such as conventional Merrifield solid phase f-Moc or t-Boc chemistry. For example, a CR protein of the present invention can be arbitrarily divided into fragments of desired length with no overlap of the fragments, or preferably divided into overlapping fragments of a desired length. The fragments can be produced (recombinantly or by chemical synthesis) and tested to identify those peptidyl fragments which can function as either agonists or antagonists of a CR protein activity, such as by microinjection assays.
The structure of the subject CR proteins can be modified for such purposes as enhancing therapeutic or prophylactic efficacy, or stability (e.g., ex vivo shelf life and resistance to proteolytic degradation in vivo). Such modified peptides, when designed to retain at least one activity of the naturally-occurring form of the protein, are considered functional equivalents of the CR proteins described in more detail herein. Such modified peptide can be produced, for instance, by amino acid substitution, deletion, or addition.
Moreover, it is reasonable to expect that an isolated replacement in CR proteins of the invention of a leucine with an isoleucine or valine, an aspartate with a glutamate, a threonine with a serine, or a similar replacement of an amino acid with a structurally related amino acid (i.e. conservative mutations) will not have a major effect on the biological activity of the resulting molecule. Conservative replacements are those that take place within a family of amino acids that are related in their side chains. Genetically encoded amino acids are divided into four families: (1) acidic=aspartate, glutamate; (2) basic=lysine, arginine, histidine; (3) nonpolar=alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine, tryptophan; and (4) uncharged polar=glycine, asparagine, glutamine, cysteine, serine, threonine, tyrosine. Phenylalanine, tryptophan, and tyrosine are sometimes classified jointly as aromatic amino acids. In similar fashion, the amino acid repertoire can be grouped as (1) acidic=aspartate, glutamate; (2) basic=lysine, arginine histidine, (3) aliphatic=glycine, alanine, valine, leucine, isoleucine, serine, threonine, with serine and threonine optionally be grouped separately as aliphatic-hydroxyl; (4) aromatic=phenylalanine, tyrosine, tryptophan; (5) amide=asparagine, glutamine; and (6) sulfur-containing=cysteine and methionine. (see, for example, Biochemistry, 2nd ed., Ed. by L. Stryer, W H Freeman and Co.: 1981). Whether a change in the amino acid sequence of a peptide results in a functional CR homolog can be readily determined by assessing the ability of the variant peptide to produce a response in cells in a fashion similar to the wild-type CR protein or peptide. Peptides in which more than one replacement has taken place can readily be tested in the same manner.
Another aspect of the invention pertains to an antibody or antibody preparation specifically reactive with at least one epitope of at least one of the subject CR proteins. For example, by using immunogens derived from the present CR proteins, based on the cDNA sequences, anti-protein/anti-peptide antisera or monoclonal antibodies can be made by standard protocols (See, for example, Antibodies: A Laboratory Manual ed. by Harlow and Lane (Cold Spring Harbor Press: 1988)). A mammal such as a mouse, a hamster or rabbit can be immunized with an immunogenic form of the peptide (e.g., CR protein or an antigenic fragment which is capable of eliciting an antibody response). Techniques for conferring immunogenicity on a protein or peptide include conjugation to carriers or other techniques well known in the art. An immunogenic portion of the subject CR proteins can be administered in the presence of adjuvant. The progress of immunization can be monitored by detection of antibody titers in plasma or serum. Standard ELISA or other immunoassays can be used with the immunogen as antigen to assess the levels of antibodies. In a preferred embodiment, the subject antibodies are immunospecific for antigenic determinants of the CR proteins of the present invention, e.g. antigenic determinants of a protein represented by one of SEQ ID NOs:2, 4, 6, 8, 10, 12, or 14 or a closely related human or non-human mammalian homolog (e.g. 90 percent homologous, more preferably at least 95 percent homologous). In yet a further preferred embodiment of the present invention, the anti-CR protein antibodies do not substantially cross react (i.e. react specifically) with a protein which is: e.g. less than 90 percent homologous to one of SEQ ID NOs:2, 4, 6, 8, 10, 12, or 14; e.g. less than 95 percent homologous with one of SEQ ID NOs:2, 4, 6, 8, 10, 12, or 14; e.g. less than 98-99 percent homologous with one of SEQ ID NOs:2, 4, 6, 8, 10, 12, or 14. The language "not substantially cross react" means that the antibody has a binding affinity for a non-homologous protein which is less than 10 percent, more preferably less than 5 percent, and even more preferably less than 1 percent, of the binding affinity for a protein of SEQ ID NOs:2, 4, 6, 8, 10, 12, or 14.
Following immunization, anti-CR antisera can be obtained and, if desired, polyclonal anti-CR antibodies isolated from the serum. To produce monoclonal antibodies, antibody producing cells (lymphocytes) can be harvested from an immunized animal and fused by standard somatic cell fusion procedures with immortalizing cells such as myeloma cells to yield hybridoma cells. Such techniques are well known in the art, an include, for example, the hybridoma technique (originally developed by Kohler and Milstein, (1975) Nature, 256: 495-497), the human B cell hybridoma technique (Kozbar et al., (1983) Immunology Today, 4: 72), and the EBV-hybridoma technique to produce human monoclonal antibodies (Cole et al., (1985) Monoclonal Antibodies and Cancer Therapy, Alan R. Liss, Inc. pp. 77-96). Hybridoma cells can be screened immunochemically for production of antibodies specifically reactive with a CR protein of the present invention and monoclonal antibodies isolated from a culture comprising such hybridoma cells.
The term "antibody" as used herein is intended to include fragments thereof which are also specifically reactive with one of the subject CR proteins. Antibodies can be fragmented using conventional techniques and the fragments screened for utility in the same manner as described above for whole antibodies. For example, F(ab').sub.2 fragments can be generated by treating antibody with pepsin. The resulting F(ab').sub.2 fragment can be treated to reduce disulfide bridges to produce Fab' fragments. Antibodies of the present invention are further intended to include bispecific and chimeric molecules having an anti-CR portion.
Both monoclonal and polyclonal antibodies (Ab) directed against CR or CR variants, and antibody fragments such as Fab' and F(ab').sub.2, can be used to block the action of a CR proteins and allow the study of the role of the particular CR protein of the present invention in cell signalling.
The nucleotide sequence determined from the cloning of the subject CR proteins from a human cell line allows for the generation of probes designed for use in identifying CR homologs in other human cell types, as well as CR homologs from other animals. For instance, the present invention also provides a probe/primer comprising a substantially purified oligonucleotide, wherein the oligonucleotide comprises a region of nucleotide sequence which hybridizes under stringent conditions to at least 10 consecutive nucleotides of sense or anti-sense sequence of one of SEQ ID NOs: 1, 3, 5, 7, 9, 11, or 13, or naturally occurring mutants thereof. In preferred embodiments, the probe/primer further comprises a label group attached thereto and is able to be detected, e.g. the label group is selected from the group consisting of radioisotopes, fluorescent compounds, enzymes, and enzyme co-factors. Such probes can be used as a part of a test kit for measuring a level of an CR nucleic acid in a sample of cells from a patient; e.g. measuring a CR mRNA level; e.g. determining whether a genomic CR gene has been mutated or deleted.
In addition, nucleotide probes can be generated from the cloned sequence of the subject CR proteins, which allow for histological screening of intact tissue and tissue samples for the presence of a CR mRNA. Use of probes directed to CR mRNAs, or to genomic CR sequences, can be used for both predictive and therapeutic evaluation of allelic mutations which might be manifest in a variety of disorders including cancer, immunodeficiencies, autoimmune disorders, developmental abnormalities, infectious diseases, toxic damage due to irradiation, chemicals, and other noxious compounds or natural products. Used in conjunction with anti-CR antibody immunoassays, the nucleotide probes can help facilitate the determination of the molecular basis for a developmental disorder which may involve some abnormality associated with expression (or lack thereof) of a CR protein. For instance, variation in CR synthesis can be differentiated from a mutation in the CR coding sequence.
Also, the use of anti-sense techniques (e.g. microinjection of antisense molecules, or transfection with plasmids whose transcripts are anti-sense with regard to a CR mRNA or gene sequence) can be used to investigate the normal cellular function of each of the novel CR proteins, e.g. in cell signalling. Such techniques can be utilized in cell culture, but can also be used in the creation of transgenic animals.
Furthermore, by making available purified and recombinant CR proteins, the present invention facilitates the development of assays which can be used to screen for drugs which are either agonists or antagonists of the normal cellular function of the subject CR proteins, or of their role in cell signalling.
In another aspect, the invention features transgenic non-human animals which express a recombinant CR gene of the present invention, or which have had one or more of the subject CR gene(s), e.g. heterozygous or homozygous, disrupted in at least one of the tissue or cell-types of the animal.
In another aspect, the invention features an animal model for disorders related to cell signalling, which has a CR allele which is mis-expressed. For example, a mouse can be bred which has a CR allele deleted, or in which all or part of one or more CR exons are deleted. Such a mouse model can then be used to study disorders arising from mis-expressed CR genes.
This invention is further illustrated by the following examples which in no way should be construed as being further limiting. The contents of all cited references (including literature references, issued patents, published patent applications, and co-pending patent applications) cited throughout this application are hereby expressly incorporated by reference.
EXAMPLES
Example I
Construction of cDNA Library Containing Clones of Ligand-Induced Genes
Human peripheral blood mononuclear cells (PBMCs) were isolated by Ficoll/Hypaque discontinuous centrifugation, and cultured at 10.sup.6 cells/ml in complete medium comprised of RPMI 1640 (GIBCO Laboratories, Grand Island, N.Y.) supplemented with 10% heat-inactivated (56.degree. C., 30 min) calf serum (Sterile Systems, Inc., Logan, Utah), 50 mg/ml L-glutamine, and 50 units/ml penicillin. T-cells were activated by stimulation of the CD3 component of the T-cell receptor complex with an anti-CD3 reactive monoclonal antibody (OKT3, 1:10,000 dilution, Ortho Pharmaceuticals, Raritan, N.J.) in the presence of absence of 10 mg/ml CHX, and DNA synthesis was monitored at 48-52 hr by adding 0.5 mCi .sup.3 H!-thymidine to 200 ml aliquots of cell cultures in 96-well microtiter plates. Cultures were harvested onto glass fiber filters, radioactivity was counted by liquid scintillation, and .sup.3 H!-thymidine incorporation was calculated as cpm/10.sup.4 cells/hr.
IL-2R-positive T-cell blasts were prepared by stimulation of PBMCs with OKT3 for 3 days, after which the cells were washed and replaced in culture for an additional 11 days in the presence of 500 pM IL-2. The cells were subsequently washed and placed in culture in the absence of IL-2 for 36 hr, followed by a 12 hr stimulation with 50 ng/ml phorbol 12, 13 dibutyrate (PdBu) to augment high-affinity IL-2R expression. Cells were washed free of PdBU and placed in culture for 12 hr prior to restimulation. Such treatment enabled the generation of a G.sub.0 /G.sub.1 -synchronized cell population, made up of greater than 90% T8-positive T lymphocytes (Gullberg et al. (1986) J. Exp. Med. 163:270-284).
Human IL-2R-positive T-cell blasts were cultured in the presence of 1 nM IL-2, 10 mg/ml CHX, 250 mM 4-thiouridine (Sigma Chemical Co., St. Louis, Mo.) and 2.5 mCi/ml 5,6-.sup.3 H!-uridine (48 Ci/mmole, Amersham, Arlington Heights, Ill.) for 2 hr. CHX was included in the 2 hr IL-2 stimulation of the IL-2R-positive, G.sub.0 /G.sub.1 -synchronized human T-cells from which the cDNA library was generated in order to isolate immediate-early genes, and also to possibly superinduce the expression of low-abundance messages. Total RNA was isolated essentially as described by Caligiuri et al. ((1989) J. Exp. Med. 171:1509-1526), and the 4-thiouridine-labelled RNA purified by passage over a phenylmercury agarose column as described by Woodford et al. ((1988) Anal. Biochem. 171:166-172). The cells were labelled with 4-thiouridine during stimulation, to enable isolation of only those transcripts which were synthesized during the period of IL-2 and CHX treatment (Stetler et al. (1984) Proc. Nat. Acad. Sci. (USA) 81:1144-1148) and Woodford et al. ((1988) Anal. Biochem. 171:166-172). Fractionation of total cellular RNA resulted in a 10-fold enrichment for newly-synthesized transcripts.
This thiol-selected RNA was used in the synthesis of Not-1 primer/adapter-primed cDNA, utilizing the Riboclone cDNA Synthesis System (Promega, Madison, Wis.) according to manufacturers instructions. After addition of EcoRI adapters (Promega), Not-1 digestion, and size selection for fragments greater than 500 base pairs (bp), the cDNA was ligated directionally into an EcoRI- and Not-1-digested pBluescript II SK+ plasmid vector (Stratagene, La Jolla, Calif.), followed by transformation into Epicurian Coli XL-1 Blue competent cells (Stratagene). A cDNA library of approximately 10,000 clones resulted.
Example II
Screening of cDNA Library for Clones Containing Ligand-Induced Genes
About 10% of the cDNA library was then screened using radiolabelled cDNA probes made from mRNA isolated from T-cells induced with IL-2 or from uninduced cells as follows. Single-stranded .sup.32 P!-labelled cDNA probes were prepared from poly(A).sup.+ RNA isolated from human T-cell blasts stimulated for 2 hr with medium (unstimulated probe), or 1 nM IL-2 and 10 mg/ml CHX (stimulated probe). Total cellular RNA was prepared as described by Caligiuri et al. ((1989) J. Exp. Med. 171:1509-1526), and poly(A).sup.+ RNA was isolated by three passages over an oligo-dT-cellulose column (5 Prime-3 Prime, West Chester, Pa.). First strand cDNA synthesis was performed with an oligo-dT 12-18 primer (United States Biochemical Corp., Cleveland, Ohio), using the Riboclone cDNA Synthesis System (Promega, Madison, Wis.) according to manufacturers instructions, with the exception of dCTP at a final concentration of 35 mM and the addition of 2.5 mCi/ml .sup.32 P!-dCTP. Hybridization was carried out for 72-96 hr at 42.degree. C. in 50% formamide, with a final probe concentration of approximately 2.times.10.sup.6 cpm/ml (W. M. Strauss, in Current Protocols in Molecular Biology, (1989) pp. 6.3.1-6.3.6). Subsequent to hybridization, filters were washed repeatedly at 62.degree. C. in 0.1.times.SSC (1.times.SSC=0.15M NaCl, 0.015M sodium citrate, pH 7.0), 0.1% SDS and placed on film (Kodak XAR-5) with Dupont Cronex intensifying screens overnight at -70.degree. C. The initial screening yielded 18 putative positive clones which exhibited differential hybridization to the stimulated and unstimulated probes after three independent screens. These clones were isolated for further characterization by Northern Blot analysis.
Total cellular RNA was isolated by the guanidine thiocyanate method described by Caligiuri et al. (ibid.), and denatured in glyoxal and DMSO. The RNA was fractionated on a 1% agarose gel in 0.01M NaH.sub.2 PO.sub.4 with 0.5 mg/ml ethidium bromide (Selden, Current Protocols in Molecular Biology, (1989) pp. 4.9.5-4.9.8). To estimate sizes of RNA transcripts, a 0.24-9.5 kb RNA ladder (Bethesda Research Laboratories, Gaithersburg, Md.) was run alongside the cellular RNA samples. After visualization under ultraviolet light, the RNA was transferred to nitrocellulose by capillary transfer in 10.times.SSC. Plasmids were purified from the clones of interest, and the Not-1- and EcoRI-excised inserts .sup.32 P!-labelled with random primers. Hybridization was carried out in 50% formamide at 42.degree. C. for 48-72 hr, followed by repeated washes in 0.1.times.SSC, 0.1% SDS at 56.degree.-62.degree. C. (Selden, ibid.). Filters were exposed to Kodak XAR-5 film with Dupont Cronex intensifying screens, and specific bands quantitated with an EC densitometer (EC Apparatus Corp., St. Petersburg, Fla.).
In as much as CHX was included in both the library and probe preparation, it was essential to verify that the differential expression of putative clones observed upon colony screening was not due solely to the effects of this drug. In addition, determination of the sizes and patterns of induction of the RNA transcripts was necessary to enable estimation of the redundancy of the clones. Therefore, Northern blot analysis was performed with RNA isolated from human IL-2R-positive T-cell blasts stimulated with either CHX or IL-2 alone, or with a combination of the two agents.
Hybridization of the RNA with probes generated from the inserts of each of the 18 putative clones resulted in the identification of 4 clones that were solely CHX-induced. For the remaining 14 clones, the induction by the combination of IL-2 and CHX could not be accounted for by the effects of CHX alone. Based upon the patterns of induction and approximate sizes of the RNA transcripts, 8 readily distinguishable and apparently unique IL-2-induced genes were discerned, as partial sequences, among these 14. These are described in Table X.
The original designations of the CR clones are included in parentheses in the left-hand column of Table II. The original designations are used herein to refer to the partial sequences shown in the column second from the left in Table II. As shown in Table II and in FIGS. 8A-8H, three of the genes, CR1, CR3, and CR5, were induced by IL-2 alone, while five of the genes, CR2, CR4, CR6, CR7, and CR8, were induced by both CHX and IL-2. In several instances, the combination of IL-2 and CHX resulted in a marked synergistic induction.
Example III
Kinetic Analysis of IL-2-Induced Gene Expression
The temporal expression of the novel, IL-2-induced genes was determined by Northern blot analysis, using RNA isolated from human IL-2R-positive T-cell blasts after IL-2 stimulation in the presence or absence of CHX. Northern blots were prepared with 15 mg total RNA isolated from G.sub.0 /G.sub.1 -synchronized human T-cells stimulated for 0, 0.5, 1, 2, 4, or 8 hours with 1 nM IL-2 or IL-2+10 mg/ml CHX. Filters were probed with the cDNA inserts of the IL-2-induced clones.
As shown in FIGS. 9A-9H, two of the genes, 1A8 (FIG. 9A) and 10D6 (FIG. 9B), exhibited rapid induction, reaching peak levels within 1-4 hr of IL-2 stimulation and returning to basal levels after 8 hr, while the other six clones (FIGS. 9C-9H) remained at elevated levels for at least 8 hr after IL-2 treatment. The magnitude of IL-2 induction of steady state RNA levels of the clones ranged from an approximately 5-fold elevation of clone 11B2 (FIG. 9F) to a greater than 50-fold stimulation of clone 10F9 (FIG. 9E) during the interval examined. These results are also summarized in Table II. Several of the clones were superinduced by CHX, with an increase observed in both the magnitude and duration of the IL-2 response.
The kinetics of induction of previously characterized IL-2-responsive genes have been found to range from those such as c-fos, which are rapidly and transiently induced within minutes of IL-2 stimulation (Dautry et al. (1988) J. Biol. Chem. 263:17615-17620), to those which remain at elevated levels through G.sub.1 to S phase entry (Sabath et al. (1990) J. Biol. Chem. 265:12671-12678).
Example IV
Sequence Analysis of Clones Containing Ligand-Induced Genes
To verify the redundancy of the clones as estimated from Northern analysis, as well as to determine the identities of the genes, the cDNA clones were subjected to sequence analysis.
Plasmids were isolated from the clones of interest essentially as described by Kraft et al. ((1988) Biotechniques 6:544-547), and vector primers were used to sequence the termini of the cDNA inserts, employing the Sequenase 2.0 dideoxy sequencing kit (United States Biochemical, Cleveland, Ohio). Approximately 200 bases of sequence were attained from each end of the inserts. These partial sequences are described in Table II. Searches of the GenBank and EMBL data bases were performed with the FASTA program as described by Pearson et al. ((1988) Proc. Natl. Acad. Sci. (USA) 85:2444-2448).
The combination of sequence and Northern analyses revealed that the 14 putative IL-2-induced clones consisted of 8 unique genes, three of which, 1A8, 11B2, and 13E2, were isolated three times each. Searches of the GenBank and EMBL data bases with the partial sequences enabled the identification of one clone, 11E6, as pim-1, a previously characterized IL-2-induced gene (Dautry et al. (1988) J. Biol. Chem. 263:17615-17620; and Kakut-Houri et al. (1987) Gene 54:105-111) which encodes a 33 kD cytoplasmic kinase (Telerman et al. (1988) Mol. Cell. Biol. 8:1498-1503).
Thus, by utilizing the method of the invention seven unique IL-2 induced genes were cloned, representing novel human genes. These clones were identified after screening only approximately 800 library colonies, and thus, it is estimated that as many as 80 additional novel IL-2-induced genes remain to be detected in the 10,000-clone library.
To determine the complete sequences of these clones described in Table II the original partial cDNAs were used as probes to screen a second cDNA library. It is standard procedure to use partial cDNA inserts identified by an initial screen of a cDNA library to make radiolabeled cDNA probes to screen a second library to obtain clones with the portions missing in the initial cDNA clones. This was done, briefly, as follows: a second cDNA library was prepared from mRNA obtained from human T cells stimulated for two hours with interleukin-2 in the presence of cycloheximide by cloning into the .lambda.gt-10 phage vector using standard methods. (Sambrook, J. et al. Molecular Cloning: A Laboratory Manual (Cold Spring Harbor Laboratory Press, New York, 1989) pp. 2.82-2.122).
This second cDNA library was then screened using as probes each of the cDNA fragments obtained from the first, thiol-selected cDNA library. Candidate clones that corresponded to the correct size according to the mRNA were then subcloned and sequenced. The complete cDNA sequences (and the predicted amino acid sequences) of seven out of eight of these clones are set forth in SEQ ID NOs:1-14 and FIGS. 1-7. The complete cDNA sequence (and the predicted amino acid sequence) of the eighth clone was determined to be identical to that of the IL-2 induced gene pim-1. The nucleotide sequence as well as the predicted amino acid sequence of pim-1 are set forth at page 605 in Selten, G. et al. (1986) Cell 46:603-611.
Example V
Determination of Sensitivity of IL-2-Induced Gene Expression
As a further means of characterizing the regulation of expression of these genes, the sensitivity of induction to the known IL-2 functional antagonist was investigated. Human IL-2R-positive T-cell blasts were stimulated with IL-2 in the absence or presence of 0.5 mM dibutyryl-cAMP, a concentration of the membrane-permeant cAMP analog sufficient to inhibit IL-2-mediated G.sub.1 progression without adversely affecting cellular viability. The effect of an equivalent molar amount of sodium butyrate, which does not inhibit the IL-2 response, was also tested to control for the actions of free butyric acid.
Northern blots were prepared as follows: Human IL-2R-positive T cells were treated with 1 nM IL-2 alone or in combination with 0.5 mM dibutyryl cAMP or sodium butyrate (NaBt) for 1, 2, or 4 hours. Filters were prepared with 15 mg total RNA and hybridized with cDNA inserts or the IL-2 induced clones.
These analyses demonstrate that the IL-2 induction of one gene, 1A8 (FIG. 10A) is markedly inhibited when the intracellular level of cAMP is raised by the addition of dibutyryl cAMP, whereas the expression of two others, 10D6 (FIG. 10B) and 13E2 (FIG. 10C), is augmented approximately 3-fold. By comparison, the expression of five of the genes was not affected by elevated cAMP (FIGS. 10D-10H). Thus, the sequences in clone 1A8 may be involved in T-cell proliferation. The fact that not all genes were sensitive to cAMP indicated that the observed results were not due to non-specific effects, and furthermore that the previously documented down-regulation of IL-2R binding capacity by cAMP (Johnson et al. (1990) J. Immunol. 145:1144-1151) could not account for the inhibition of gene expression.
Example VI
Determination of Role of T-cell Receptor Activation in the Stimulation of Expression of IL-2-Induced Genes
In order to determine if activation of the T-cell receptor mediates the stimulation of expression of cytokine IL-2-induced genes, the following study was performed. Northern blots were prepared from 20 mg total cellular RNA isolated from human peripheral blood mononuclear cells (PBMCs) stimulated with a monoclonal antibody (OKT3) specific to the CD3 component of the T-cell antigen receptor complex. Blots were probed with cDNA inserts of the IL-2-induced clones. Data was determined as the mean.+-.SEM (n=6).
By isolation of RNA at early time intervals, it was possible to identify those genes which were induced by T-cell receptor triggering in the absence of IL-2 effects. As shown in FIGS. 11A-11H, only one of the genes, 10D6 exhibited heightened levels of expression after 2 hr of T-cell receptor activation, while the seven others were apparently insensitive to this stimulus. Two of the clones, 1F5 and 11B2, were undetectable, even after seven days of autoradiographic exposure of the Northern blots. Two other genes, 11E6 and 13E2, were expressed at relatively high levels regardless of the stimulus; activation with anti-CD3 did not induce RNA expression beyond the level observed by culture in medium alone. Identical results were obtained after 1 and 4 hr of stimulation.
To determine whether the cells were actually activated via CD3, aliquots of the cells were left in culture for 52 hr in the presence of 10 mg/ml CHX, alone, OKT3 alone, or OKT3+CHX, after which cell cycle progression was monitored by .sup.3 H!-thymidine incorporation into RNA.
As shown in FIG. 12, the cells were sufficiently stimulated by anti-CD3. Thus, the T-cell receptor-induced expression of only one of the genes was comparable to that seen with IL-2 stimulation, while the expression of the seven others was unique to the IL-2 signaling pathway. Thus, the methods described herein to identify IL-2-induced gene successfully selected and enriched for these genes that are highly specific for cytokine (IL-2) activation.
Of the 8 IL-2 induced G.sub.1 progression genes reported here, only one appears to also be induced during the T cell receptor-mediated competence phase of the cell cycle. Thus, while several genes such as c-fos, c-myc and c-raf-1 are known to be induced during both the initial G.sub.0 -G.sub.1 and subsequent G.sub.1 -S phase transitions, the expression of a number of IL-2-stimulated genes is unique to the latter event. In addition, the immediate-early genes reported here appear to define a class distinct from the IL-2-induced genes isolated by Sabath et al. ((1990) J. Biol. Chem. 265:12671-12678). These investigators utilized a differential screening procedure to isolate genes expressed at the G.sub.1 /S phase boundary in a murine T helper clone which was stimulated with IL-2 for 20 hr in the absence of protein synthesis inhibitors. In this case, the expression of only 3 of the 21 clones isolated was inhibited by CHX, while the remainder were insensitive to this agent. This pattern of regulation markedly contrasts with the CHX superinduction observed with the immediate-early IL-2-induced genes described here. Moreover, these observations indicate that IL-2 stimulates a complex program of gene expression, ranging from those genes induced very early in G.sub.1 through those subsequently expressed at the G.sub.1 /S phase transition.
Example VII
Cloning and Analysis of CR8
As described above, the CR8 gene encodes a novel basic helix-loop-helix (bHLH) protein. While the CR8 transcript is ubiquitously expressed in many tissues, it is induced by IL-2 as well as by IL-3 in cytokine-dependent lymphoid cell lines. In an IL-2-dependent human T cell line Kit 225, the CR8 transcript is induced not only by IL-2, but also by interferon b and forskolin, which elevates intracellular cAMP. The bHLH domain of CR8 shows the highest structural homology to a Drosophila transcriptional repressor hairy. The recombinant CR8 protein binds preferentially to the Class B E-box DNA sequence (CACGTG), which is found in the promoter/enhancer regions of a number of genes associated with cell growth and differentiation, suggesting that CR8 may regulate the transcription of such genes.
The cloning of the full-length cDNA for CR8 is described in detail herein. The predicted amino acid sequence revealed that CR8 contains a helix-loop-helix (HLH) domain, characteristic for transcription factors. The HLH domain is a dimerization motif characterized by the two amphipathic .alpha.-helices separated by a nonhelical loop of variable length (Davis, R. L. et al.(1990) Cell 60:733-746). Most of the HLH family members possess a cluster of basic amino acid residues immediately N-terminal to the HLH region basic helix-loop-helix (bHLH)!, which are required for site-specific DNA binding, while others lack the basic region and function as negative regulators of DNA binding (Benezra, R. et al. (1990) Cell 61:49-59; Ellis, H. M. et al. (1990) Cell 61:27-38; Garrell, J. et al. (1990) Cell 61:39-48.22,28). A wide variety of developmental processes are regulated by HLH proteins; the MyoD family of myogenic transcription factors directly induce the expression of muscle-specific genes, thereby functioning as master regulators of muscle cell lineage specification (reviewed in (Edmonson, D. G. et al. (1993) J. Biol. Chem. 268:755-758; Weintraub, H. (1993) Cell 75:1241-1244)). The crucial role of the bHLH protein encoded by the tal-l/SCL gene in hematopoiesis, originally discovered as a chromosomal breakpoint in leukemia (Begley, C. G. et al. (1989) Proc. Natl. Acad Sci. USA 86:10128-10132; Chen, G. et al. (1990) EMBO J. 9:415-424; Finger, L. et al. (1989) Proc. Natl. Acad. Sci. USA 86:5039-5043), is illustrated by the absence of blood formation in tal-l null mutant mice (Shivdasani, R. A. et al. (1995) Nature 373:432-434).
The regulation of immunoglobulin (Ig) gene expression has been extensively studied, and has been shown to be controlled by numerous transcription factors that recognize specific DNA sequences in the Ig enhancers (Kadesch, T. (1992) Immunol. Today 13:31-36). Recent reports on E2A null mutant mice that lack mature B cells clearly depict the impact of these bHLH proteins on B cell development (Bain, G. et al. (1994) Cell 79:885-892; Zhuang, Y. et al. (1994) Cell 79:875-884). Genetic analysis of neural cell fate and sex determination in Drosophila provided in vivo evidence for interaction between bHLH proteins (reviewed in (Jan, Y. N. et al. (1993) Cell 75:827-830)). For instance, bHLH proteins encoded by daughterless (da) and the achaete-scute complex (AS-C) heterodimerize and positively regulate sensory organ formation. On the other hand, the genes encoding negative regulators such as hairy and extramacrochaetae are required to control the appropriate pattern of neural precursor distribution. Moreover, because cell differentiation is often associated with the suppression of proliferation, some HLH proteins have also been implicated in the regulation of cell growth. One of the most extensively studied may be Myc, a bHLH protein encoded by the c-myc oncogene (reviewed in Marcu, K. B. et al. (1992) Annu. Rev. Biochem. 61:809-860). The negative regulator Id proteins which inhibit differentiation by forming inactive heterodimers with bHLH proteins, thereby may be required for proliferation. For example, the level of Id expression is higher in undifferentiated proliferating cells (Benezra, R. et al. (1990) Cell 61:49-59). Also, antisense oligonucleotide against Id mRNA inhibits re-entry to the cell cycle (Barone, M. V. et al. (1994) Proc. Natl. Acad. Sci. USA 91:4985-4988; Hara, E. et al. (1994) J. Biol. Chem. 269:2139-2145), and cell cycle progression is accelerated in Id2 stable transfectant cell lines (Ivarone, A. et al. (1994) Genes & Dev 8:1270-1284).
The following Materials and Methods were used in this Example:
Cell Culture and Reagents:
Human T cells were prepared as described previously (Beadling, C. et al. (1993) Proc. Natl. Acad. Sci. USA 90:2719-2723); in short, peripheral blood mononuclear cells were cultured in RPMI 1640 supplemented with 10% (v/v) heat-inactivated fetal calf serum (FCS) and antibiotics in the presence of OKT3 (Ortho Pharmaceuticals) for 3 days, then for an additional 11 days in the presence of IL-2 (Takeda Chemical). The cells were subsequently removed from of IL-2 for 36 hr, followed by a 12 hr stimulation with phorbol-12, 13-dibutyrate (Sigma) to augment the expression of high-affinity IL-2 receptor. Such treatment enabled the generation of a G0/G1-synchronized cell population, comprised of >90% CD8+ T lymphocytes (Gullberg, M. et al. (1986) J. Exp. Med. 163:270-284). Kit 225 is an IL-2-dependent human T cell line (Hori, T. et al. (1987) Blood 70:1069-1072). Ba/F3 and CTLL2 are mouse cell lines dependent on IL-3 and IL-2, respectively. Both Kit 225 and CTLL2 were maintained in RPMI1640 supplemented with 10% (v/v) FCS and 500 pM recombinant human IL-2. Ba/F3 was maintained in RPMI1640 supplemented with 10% (v/v) FCS and 5% (v/v) conditioned medium from fibroblasts transfected with mouse IL-3 as a source of IL-3. Recombinant mouse IL-3 was purchased from Genzyme. Before using for experiments, cell lines were made quiescent by growth factor deprivation for 72 hr for Kit 225, 12 hr for Ba/F3 and 2 hr for CTLL2.
Forskolin was obtained from Sigma. Human interferon (IFN) .beta. was from GIBCO BRL. Proliferation was monitored by measuring the incorporation of .sup.3 H-methyl!thymidine (Amersham) into ten thousand cells incubated with indicated reagents in 200 fl for 24 hr at 37.degree. C. The culture was pulsed with 0.5 fCi .sup.3 H!thymidine for the last 4 hr prior to harvest.
Northern Hybridization:
Total cellular RNA was isolated by RNAzolB (Tel-Test) and fractionated on a 1.2% agarose formaldehyde gel. RNA was visualized with ethidium bromide. After electrophoresis, RNA was transferred and fixed to Hybond-N+ nylon membrane (Amersham) with 40 mM NaOH. Multiple Tissue Northern Blot membranes were purchased from Clontech. Membranes were hybridized with the radiolabeled probe for 3 hr to overnight at 65.degree. C. in Rapid-Hyb hybridization solution (Amersham), washed twice with 2.times.SSC/0.1% SDS (1.times.SSC=150 mM NaCl/15 mM sodium citrate, pH 7.0) at room temperature for 15 min, once with 0.5.times.SSC/0.1% SDS at 60.degree. C. for 15 min and subjected to autoradiography.
cDNA Library Screening:
The .lambda.gt10 cDNA libraries were constructed and screened according to the standard molecular biology procedure (Sambrook, J., E. F. Fritsch, and T. Maniatis. 1989. Molecular Cloning: A Laboratory Manual, Second Edition. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.). Poly(A)+ RNA was isolated from IL-2-stimulated normal human T cells prepared as above and cDNA synthesis was primed with both oligo(dT)12-18 and random hexamers. The recombinant phages were screened with radiolabeled CR8 insert. For mouse CR8, a.lambda.gt10 cDNA library from IL-2-stimulated mouse splenocytes were screened with human CR8 insert under low-stringency condition.
Sequence Analysis:
CR8 cDNA sequence was analyzed by the fluorescence-based dideoxynucleotide termination method (Taq DyeDeoxy.TM. Terminator Cycle Sequencing Kit, Perkin Elmer) on the Applied Biosystems Model 373A DNA sequencer. Consensus sequences were constructed and analyzed with the help of the University of Wisconsin GCG software package. The BLAST algorithm from the National Center for Biotechnology Information (NCBI) was also employed for nucleotide and amino acid sequence homology search (Altschul, S. F. et al. (1990) J. Mol. Biol. 215:403-410).
Preparation of Recombinant Proteins:
The recombinant CR8 protein with histidine-tag was prepared using the Xpress.TM. System (Invitrogen) according to the manufacturer's protocol. cDNA corresponding to the CR8 bHLH domain was obtained by PCR. The sequences of the primers, 5'-GGGGTCTACCAGGGATGTAC-3' (SEQ ID NO:15) for the 5' side, and 5'-GTAAACCACTCTGCAGGGCAATGA-3' (SEQ ID NO:16) for the 3' side, were slightly different from the final consensus sequence for CR8, but the difference did not affect the core bHLH motif. The PCR product was cloned into pT7Blue T-vector (Novagen) and subsequently into pRSET-A vector at BamHI and HindIII sites. Constructs were confirmed by DNA sequencing. The protein was overexpressed in JM109 at 37.degree. C. in the presence of isopropylthio-b-D-galactoside (IPTG) by infecting the bacteria with M13 phages that contain the T7 RNA polymerase gene. The cells were lysed with 100 fg/ml lysozyme in native binding buffer (20 mM sodium phosphate, pH 7.8, 500 mM NaCl), the lysate was loaded on a ProBond.TM. Ni2+ column, and the recombinant protein was eluted with native-imidazole elution buffer (20 mM sodium phosphate, pH 6.0, 500 mM NaCl, 500 mM imidazole). The protein was then dialyzed against lysis buffer (50 mM Tris-HCl, pH 7.5, 150 mM NaCl, 1 mM EDTA, 10% glycerol, 0.1% Triton X-100, 1 mM DTT) and concentrated on a Microcon 10 (Amicon). To confirm the purity and the quantity, the protein was fractionated on a 12% SDS-polyacrylamide gel with protein standards of known concentrations and visualized by silver staining. The recombinant protein corresponding to the bHLH domain of da was supplied by Dr. Michael Caudy (Cornell University Medical College).
Mobility Shift Assay:
The oligonucleotide probes used for the electrophoretic mobility shift assay (EMSA) are as follows: the Class A site used was the CACCTG hexamer (CAGGTG for the opposite strand) from the T5 promoter region of the Drosophila AS-C (Villares, R. et al. (1987) Cell 550:415-424) (5'-GATCGTAGTCACGCAGGTGGGATCCCTA-3' (SEQ ID NO:17) and 5'-GATCTAGGGATCCCACCTGCGTGACTAC-3' (SEQ ID NO:18) for the opposite strand), the Class B site was the CACGTG hexamer from the USF binding site in the adenovirus major late promoter (Gregor, P. D. et al. (1990) Genes & Dev. 4:1730-1740) (5'-GATCGGTGTAGGCCACGTGACCGGGTGT-3' (SEQ ID NO:19) and 5'-GATCACACCCGGTCACGTGGCCTACACC-3') (SEQ ID NO:20), the Class C site was the CACGCG hexamer (CGCGTG for the opposite strand) from the AS-C T5 promoter (5'-GATCGGCAGCCGGCACGCGACAGGGCC-3' (SEQ ID NO:21) and 5'-GATCGGCCCTGTCGCGTGCCGGCTGCC-3') (SEQ ID NO:22), and the N-box (CACNAG) was the double hexamer sequence from the Enhancer of split E(spl)! m8 promoter (Klimbt, C. et al. (1989) EMBO J. 8:203-210) (5'-GATCACGCCACGAGCCACAAGGATTG-3' (SEQ ID NO:23) and 5'-GATCCAATCCTTGTGGCTCGTGGCGT-3' (SEQ ID NO:24). One strand of the oligonucleotide was labeled with g-32P!ATP by T4 polynucleotide kinase, hybridized with three times excess of the opposite strand, and purified using MERmaid oligonucleotide purification kit (BIO 101). 150 ng of the protein was allowed to bind to 50,000 cpm (equivalent to 0.5 ng in a typical experiment) of the labeled probe for 15 min at room temperature in 20 mM Hepes, pH 7.6, 50 mM KCl, 10 mM DTT, 5% glycerol, 0.5 mM EDTA and 0.3 mg/ml BSA. Two microgram of poly(dI-dC) was added to each 20 fl reaction as on-specific DNA. Samples were analyzed on a 5% native polyacrylamide gel and visualized by autoradiography.
Regulation of CR8:
CR genes were originally defined in IL-2 stimulated normal human T cells. To examine CR8 expression in cytokine-dependent cell lines, the level of CR8 expression was measured by Northern hybridization in the IL-2-dependent human T cell line Kit 225, the IL-3-dependent mouse pro-B cell line Ba/F3, and the IL-2-dependent mouse T cell line CTLL2. The results of this experiment are illustrated in FIGS. 13A-13C. In FIG. 13A, RNA was isolated from quiescent normal human T cells (lanes 1 and 2), IL-2-dependent human T cell line Kit 225 (lanes 3 and 4), IL-3-dependent mouse pro-B cell line Ba/F3 (lanes 5 and 6) and IL-2-dependent mouse T cell line CTLL2 (lanes 7 and 8) left untreated (lanes 1, 3, 5, and 7) or stimulated with 500 pM recombinant human IL-2 (lanes 2, 4, and 8) or 10 U/ml recombinant mouse IL-3 (lane 6) for 2 hr at 37.degree. C. The amount of the growth factor used in the experiment was sufficient to induce maximal .sup.3 H!thymidine incorporation. Ten microgram of total RNA was analyzed on formaldehyde/agarose gel and hybridized with either human (lanes 1 to 4) or mouse (lane 5 to 8) CR8 cDNA.
As shown in FIG. 13A, a single 3.2 kb species hybridized to the cDNA probe, and in all three cell lines tested, the level of CR8 was clearly augmented when the cells were stimulated with their respective growth factors. Correlation between the level of CR8 and that of DNA synthesis was in the presence of growth-inhibitory agents was also examined. In this regard, increases in cytoplasmic cAMP are known to inhibit the growth of many cell types, including lymphocytes (Johnson, K. W. et al. (1988) Proc. Natl. Acad. Sci. USA 85:6072-6076). IFNs also exert antiproliferative activity on many cell types (Pestka, S. et al. (1987) Annu. Rev. Biochem. 56: 727-777). Therefore, Kit 225 was stimulated with IL-2, IFN .beta., or forskolin, which increases cytoplasmic cAMP by activating adenylate cyclase, either alone or in combination. IL-2-dependent .sup.3 H!thymidine incorporation was inhibited by IFNb and forskolin in Kit 225 cells in a dose-dependent fashion (FIG. 13B). FIG. 13B demonstrates that IFN.beta. and forskolin inhibit IL-2-dependent .sup.3 H!thymidine incorporation by Kit 225 cells. Ten thousand quiescent Kit 225 cells were incubated with indicated reagents in 200 fl for 24 hr at 37.degree. C. The culture was pulsed with .sup.3 H!thymidine for the last 4 hr to monitor the DNA synthesis. (.sup..cndot.), IL-2 only (500 pM); (.diamond.), IL-2 500 pM+varying concentrations of IFNb (U/ml); (o), IL-2 500 pM+varying concentrations of forskolin (fM). While forskolin was capable of reducing the IL-2-dependent .sup.3 H!thymidine incorporation almost to the basal level, IFN.beta.-mediated inhibition never exceeded 70% of the maximal incorporation in several independent experiments. The expression of CR8 was compared with that of c-myc, an IL-2-inducible immediate-early gene that encodes a bHLH protein and is implicated for cell proliferation (Marcu, K. B. et al. (1992) Annu. Rev. Biochem. 61:809-860).
FIG. 13C shows the effect of antiproliferative agents on the expression of CR8 and c-myc transcripts in Kit 225. Quiescent Kit 225 cells were left untreated (lane 1) or incubated with 500 pM IL-2 (lane 2), 1000 U/ml IFNb (lane 3), 100 fM forskolin (lane 4), 500 pM IL-2+1000 U/ml IFNa (lane 5) or 500 pM IL-2+100 fM forskolin (lane 6) for 2 hr at 37.degree. C. and 15 fg of total RNA was analyzed. The same membrane was probed with CR8 and c-myc. As shown in FIG. 13C, CR8 transcripts were moderately induced, not only by IL-2, but also by IFN.beta. or forskolin alone. Furthermore, the simultaneous stimulation of quiescent Kit 225 cells with IL-2 and IFN.beta., or IL-2 and forskolin, did not suppress the IL-2-induced expression of CR8 transcripts. In contrast, IL-2-induction of c-myc expression was substantially inhibited in the presence of forskolin, while IFN.beta. did not significantly reduce IL-2-promoted c-myc expression.
Cloning of CR8:
The original human CR8 clone isolated from the thiol-selected library had a 1.5 kb insert, while the full-length mRNA transcript was estimated to be 3.2 kb from Northern blotting experiments. As the CR8 clone did not have a long open reading frame, two full-length cDNA clones of human CR8 were isolated from a .lambda.gt10 human T cell cDNA library after two rounds of screening with cDNA fragments of the CR8 clone. These two clones were fully sequenced on both strands, and the amino acid sequence was deduced (FIG. 14). In FIG. 14, the asterisk denotes the stop codon. In-frame termination codon in the 5'-untranslated region, the nucleotide sequences used for PCR and the polyadenylation signal are underlined. The amino acid residues in the bHLH region are double-underlined. When the final consensus cDNA sequence of 2970 bp (excluding the poly(A) stretch) was screened against the nonredundant nucleotide databases using the NCBI BLAST E-mail server (GenBank release 86.0), no known genes in the database shared significant homology with CR8 except for nine EST sequences (Adams, M. D. et al. (1991) Science 252:1651-1656.). CR8 has an open reading frame of 412 amino acids, with an in-frame termination codon at position 198 followed by Met at position 240 in a reasonable context for translation initiation (CGCCATGG) (Kozak, M. (1986) Cell 44:283-292). The MOTIFS program in the GCG package predicted the presence of an HLH motif in CR8.
A mouse CR8 cDNA fragment corresponding to nt 388 to 2720 of the human sequence was also isolated from a .lambda.gt10 mouse cDNA library by comparison of CR8 with other bHLH Proteins. The protein database search with the putative peptide sequence revealed that CR8 shares homology with the bHLH proteins encoded by Drosophila hairy gene and the enhancer of split complex E(spl)-C! of neurogenic genes. FIGS. 15A-15B show a sequence comparison of CR8 and other HLH proteins. Protein alignments were made to maximize homology within the bHLH domain. Amino acids conserved among most HLH proteins are shaded. The proline residues in the basic region and the arginine residues at position 13 ("R13") are boxed. The boxed alanine residue in MyoD is the one whose substitution to proline abrogated the DNA binding and muscle-specific gene activation activity of MyoD (Davis, R. L. et al. (1990) Cell 60:733-746). h!, human; D!, Drosophila melanogaster; r!, rat; and m!, mouse. Sources for sequences: hairy, (Rushlow, C. A. et al. (1989) EMBO J. 8:3095-3103); Enhancer of split E(spl)!m7, (Klimbt, C. et al. (1989) EMBO J. 8:203-210); deadpan (dpn), (Bier, E. et al. (1992) Genes & Dev 6:2137-2151); HES-1, (Sasai, Y. et al. (1992) Genes & Dev 6:2620-2634); daughterless (da), (Caudy, M. et al. (1988) Cell 55:1061-1067); E12 and E47, (Murre, C. et al. (1989) Cell 56:777-783); MyoD, (Davis, R. L. et al. (1987) Cell 51:987-1000); Tal-1, (Begley, C. G. et al. (1989) Proc. Natl. Acad. Sci. USA 86:10128-10132); USF, (Gregor, P. D. et al. (1990) Genes & Dev 4:1730-1740); Max, (Blackwood, E. M. et al. (1991) Science 251:1211-1217); N-myc, (Slamon, D. J. et al. (1986) Science 232:768-772); L-myc, (Kaye, F. et al. (1988) Mol. Cell. Biol. 8:186-195); c-myc, (Gazin, C. et al. (1984) EMBO J. 3:383-387); extramacrochaetae (emc), (Ellis, H. M. et al. (1990) Cell 61:27-38; Garrell, J. et al. (1990) Cell 61:39-48) and Id1, (Benezra, R. et al. (1990) Cell 61:49-59).
When CR8 was aligned with other bHLH proteins (FIGS. 15A-15B), it was clear that most of the residues conserved throughout the family were present in CR8. Taken together with the result of the MOTIFS program, it was concluded that CR8 is a bHLH protein. The amino acid sequence of the 58-residue bHLH domain of CR8 showed 40% identity to hairy, 41% to E(spl)m7, and 45% to one of their mammalian counterparts HES-1. This degree of amino acid identity accounts well for the failure to detect any significant homology to any known bHLH proteins at the nucleotide sequence level. The amino acid sequence for human and mouse CR8 was 100% identical in the bHLH domain.
FIG. 15B shows a sequence comparison of CR8 and hairy-related bHLH. Conserved amino acids are shaded. Note that HES-2, 3 and 5 proteins do not align perfectly in the hairy-related homology region (HRHR)-2. Sources for sequences: HES-2, (Ishibashi, M. et al. (1993) Eur. J. Biochem. 215:645-652); HES-3, (Sasai, Y. et al. (1992) Genes & Dev 6:2620-2634); HES-5, (Akazawa, C. et al. (1992) J. Biol. Chem. 267:21879-21885); human hairy-like (HHL), (Feder, J. N. et al. (1994) Genomics 20:56-61); Drosophila melanogaster hairy h(m)!, (Rushlow, C. A. et al. (1989) EMBO J. 8:3095-3103); Drosophila virilis hairy h(v)!, (Wainwright, S. M. et al. (1992) Mol. Cell. Biol. 12:2475-2483); Tribolium hairy h(T)!, (Sommer, R. J. et al. (1993) Nature 361:448-450); E(spl)m5 and m8, (Klimbt, C. et al. (1989) EMBO J. 8:203-210); E(spl)m3, b/A, g/B, and d/C, (Deldakis, C. et al. (1992) Proc. Natl. Acad. Sci. USA 89:8731-8735; Knust, E. et al. (1992) Genetics 132:505-518). As shown in FIG. 15B, the amino acid sequence of the bHLH region of CR8 is aligned with hairy, bHLH proteins of the E(spl)-C, deadpan (dpn) and their mammalian homologs (the term "hairy-related bHLH proteins" refer to them collectively). Among all the bHLH proteins described thus far, CR8 is the only one with a proline residue in the basic region, other than the hairy-related bHLH proteins. However, while the position of the proline residue is strictly conserved throughout the hairy-related bHLH proteins, in CR8 it is offset N-terminally by two residues. CR8 and hairy-related bHLH proteins are different in the C-terminus as well; all the hairy-related bHLH proteins terminate with a specific Trp-Arg-Pro-Trp (WRPW) motif, which is absent in CR8. Nevertheless, CR8 showed appreciable homology to other hairy-related bHLH proteins in the region immediately C-terminal to the bHLH domain, which has been shown previously to be rich in hydrophobic residues, and proposed to form two more .alpha.-helices in bHLH proteins of the E(spl)-C (43). This region is referred to herein as the "hairy-related homology region (HRHR)-2", the HRHR-1 being the bHLH domain. The region N-terminal to the bHLH domain and the C-terminal half of the CR8 protein are rich in proline (8 proline residues between positions 1 and 30, 22 between 310 and 405). Notably, there are no known proteins in the data bases that share homologies to these most N-terminal and C-terminal regions of CR8.
Tissue Distribution of CR8 Transcripts:
Murre et al. ((1989) Cell 58:537-544) categorized bHLH proteins based upon their tissue distribution. While proteins such as MyoD and AS-C gene products show a cell-type specific expression, others such as E12/E47 and da are fairly ubiquitously expressed. The tissue distribution of CR8 was analyzed using a Multiple Tissue Northern blot. CR8 transcripts of the expected size (3.2 kb) were detected in all tissues examined except placenta (see FIG. 16). FIG. 16 demonstrates that the Multiple Tissue Northern Blot membranes (Clontech; each lane contains 2 fg poly(A)+ RNA from indicated human tissue) were hybridized with human CR8 probe.
The expression of CR8 in peripheral blood leukocytes was unexpected, in that CR8 is not expressed by quiescent T cells. This may reflect much higher sensitivity of Multiple Tissue Northern blot prepared from poly(A)+ RNA compared to our previous Northern blots, which used total RNA. Alternatively, the contribution of other leukocytes such as B cells, NK cells, monocytes and granulocytes that were not present in the original T cell preparations could account for CR8 expression by the peripheral blood leukocytes.
DNA-Binding Activity of CR8:
The canonical bHLH binding sequence is called the E-box, CANNTG, originally identified in the immunoglobulin heavy chain enhancer (Ephrussi, A. et al. (1985) Science 227:134-140). Many bHLH proteins were later divided into two mutually exclusive classes, depending on whether they bind to the Class A sites (CAGCTG/CACCTG) or the Class B sites (CACGTG/CATGTG) (Dang, C. V. et al. (1992) Proc. Natl. Acad. Sci. USA 89:599-602). The presence of an arginine residue at position 13 ("R13", see FIG. 15A) in the basic region, which CR8 contains, is considered to be the key structural criterion that defines Class B binding specificity. However, despite the presence of "R13", hairy-related bHLH proteins are reported to prefer noncanonical binding sites such as the N-box (CACNAG) (Akazawa, C. et al. (1992) J. Biol. Chem. 267:21879-21885; Sasai, Y. et al. (1992) Genes & Dev 6:2620-2634; Tietze, K. et al. (1992) Proc. Natl. Acad. Sci. USA 89:6152-6156) or the Class C (CACGCG) sites (Ohsako, S. et al. (1994) Genes & Dev 8:2743-2755; Van Doren, M. et al. (1994) Genes & Dev 8:2729-2742.). Therefore, the binding of CR8 to all of these sites was tested.
Since it is well documented that the bHLH domain is sufficient to determine its DNA binding specificity (Pognonec, P. et al. (1994) Mol. Cell. Biol. 11:5125-5136), the bHLH domain of CR8 (CR8 bHLH) expressed in E. coli was employed for this study. A histidine-tag was added to facilitate the purification of the recombinant protein. While most of the recombinant protein localized in inclusion bodies, there was still enough soluble protein in the cytoplasm, thereby enabling its purification under native conditions using a Ni.sup.2+ column. A single band of protein was detected at the expected size (16.6 kD with the histidine-tag) by silver staining. EMSA was carried out using this recombinant protein.
FIG. 17A is an EMSA shows binding of recombinant bHLH proteins to the radiolabeled probes. CR8 bHLH protein strongly binds to the Class B (CACGTG, lane 3) and the Class C (CACGCG, lane 4) sites, and weakly to the N box (CACNAG, lane 5) sequence but not to the Class A (CACCTG, lane 2) site. Binding of the bHLH region of da protein to the Class A site is shown as control (lane 1). As shown in FIG. 17A, CR8 bHLH bound to the Class B and the Class C probes, but only weakly to the N-box probe, and not at all to the Class A probe. However, the control da bHLH protein effectively recognized and bound to the same Class A probe.
To examine the relative binding affinity, a large excess of non-labeled oligonucleotide was added to the reaction as competitor. FIG. 17B shows competition of the binding of CR8 bHLH to the Class B sites. 0.5 ng of the radiolabeled Class B probe was incubated with CR8 bHLH in the absence (lane 1) or the presence (lanes 2 to 7) of either 25 ng (50-fold excess; lanes 2, 4 and 6) and 250 ng (500-fold excess; lanes 3, 5 and 7) of unlabeled competitors. FIG. 17B demonstrates that the binding of CR8 bHLH to the radiolabeled Class B site can be abolished partially by a 50-fold excess, and completely by a 500-fold excess of Class B site (lanes 2 and 3), while a 500-fold excess of Class C site only partially displaced CR8 bHLH from the labeled Class B probe (lanes 4 and 5) and the N-box sequence did not affect the binding at all (lanes 6 and 7). Thus, since all these experiments were done in the absence of other HLH proteins, it appears that CR8 bHLH bound to the Class B sequence as a homodimer with the highest affinity.
The CR8 gene encodes a novel bHLH protein that appears to fit into a class by itself. Other than c-myc, CR8 is the first bHLH-containing protein found to be induced by cytokines. Also, from its predicted amino acid sequence, CR8 clearly contains a bHLH motif most closely related to the hairy family, but the amino acid sequence of the basic region differs from other hairy-related proteins: the position of the proline residue is N-terminal to the defining proline of the hairy-related proteins, and CR8 lacks the C-terminal WRPW sequence found in all other hairy-related-related proteins. These differences in the amino acid sequence, especially of the basic region, most likely account for the unique binding specificity of the CR8 bHLH domain. Instead of preferring Class C sites according to the other hairy-related family members (Ohsako, S. et al. (1994) Genes & Dev 8:2743-275572; Van Doren, M. et al. (1994) Genes & Dev 8:2729-2742), CR8 binds preferentially to Class B sites.
The identification of CR8 as a bHLH protein, thereby functioning, most likely, as a regulator of subsequent gene expression stimulated by IL-2, provides a link between the immediate biochemical events triggered by cytokine receptors and the subsequent events of proliferation and/or differentiation. Thus far, IL-2 has been found to activate the serine/threonine kinase proto-oncogene Raf-1 (Turner, B. et al. (1991) Proc. Natl. Acad. Sci. USA 88:1227-1231;Zmuidzinas, A. et al. (1991) Mol. Cell Biol. 11:2794-2803) and the tyrosine-specific kinases JAK 1 and JAK 3 (Beadling, C. et al. (1994) EMBO J. 13:5605-5615; Miyazaki, T. et al. (1994) Science 266:1045-1047; Russell, S. M. et al. (1994) Science 266:1042-1045).
From the results described herein comparing the effects of IFNa and forskolin on CR8 and c-myc gene expression, the regulation of these two bHLH genes is clearly distinct. It is also of interest that although IFN.beta. antagonizes IL-2-promoted cell cycle progression, it promotes the expression of both CR8 and c-myc. Indeed, induction of c-myc by IFN.beta. was unexpected, as it was previously reported to be suppressed by IFNs (Einat, M. et al. (1985) Nature 313:597-600). The bHLH region of CR8 is most homologous to that of hairy and the bHLH proteins of the E(spl)-C. In Drosophila, the hairy-related bHLH proteins function as transcriptional repressors, and this activity requires the basic DNA binding region, as well as the interaction with a non-HLH protein termed groucho (gro) via the C-terminal WRPW motif (Paroush, Z. et al. (1994) Cell 79:805-815). Although mammalian homologues of gro have been identified (Stifani, S. et al. (1992) Nat. Genet. 2:119-127), they are not likely to interact with CR8 because CR8 lacks the WRPW motif.
The results described herein indicate that CR8 recombinant protein binds to Class B E-box sites as a homodimer. This result is consistent with the predictions from DNA-bHLH protein co-crystals (Ferr-D'Amar, A. R. et al. (1994) EMBO J. 13:180-189; Ferr-D'Amar, A. R. et al. (1993) Nature 363:38-45). However, it is noteworthy in that CR8 is the first bHLH vertebrate protein without a leucine zipper (LZ) motif found to bind Class B sites. Protein dimerization is more selective than DNA binding, but currently no rules are available that predict the dimerization preference of any given HLH proteins. Even so, a Class A-binding protein seems to form DNA binding heterodimers only with other Class A proteins, and a bHLH protein with a LZ does not form heterodimers with those without LZs (Blackwood, E. M. et al. (1991) Science 251:1211-1217; Prendergast, G. C. et al. (1991) Cell 65:395-407). Therefore, if CR8 does form heterodimers, the most likely partner is a class B-binding bHLH protein without a LZ.
Although CR8 is most homologous to hairy in its bHLH domain, its preference for Class B E-box binding sites rather than class C sites, and its lack of a C-terminal WPRW motif, clearly sets CR8 apart and does not predict necessarily that CR8 may act as a transcriptional repressor as do hairy-related proteins. Recently, Id proteins that lack a basic region have been shown to favor proliferation, presumably by forming heterodimers with differentiation inducing bHLH proteins, thereby preventing DNA binding and transcriptional activation of genes that program differentiation (Barone, M. V. et al. (1994) Proc. Natl. Acad. Sci. USA 91:4985-4988; Hara, E. et al. (1994) J. Biol. Chem. 269:2139-2145; Iavarone, A. et al. (1994) Genes & Dev 1270-1284). Therefore, CR8 could promote proliferation by suppressing differentiation by either of these transcriptional repressor mechanisms. Alternatively, CR8 could also activate transcription like the bHLH-LZ Myc family.
Equivalents
Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents of the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the following claims.
Claims
We claim:
1. A substantially pure polynucleotide, comprising a nucleic acid selected from the group consisting of (A) a sense nucleotide segment encoding amino acids 1-60 of SEQ ID No: 4, alleles thereof, antibody binding fragments thereof at least 10 amino acids long and fusion proteins thereof; (B) nucleotide segments which are anti-sense to segments in (A); and (C) primers/probes at least 20 consecutive nucleotides long complementary to the segments of (A) and (B).
2. The polynucleotide of claim 1, wherein the primers/probes comprise at least 20 consecutive nucleotides of the sense nucleotide segment.
3. The polynucleotide of claim 1, wherein the sense nucleotide segment encodes a fusion protein comprising (A) and an additional polynucleotide.
4. The polynucleotide of claim 1, comprising a nucleic acid selected from the group consisting of a sense nucleotide segment and alleles thereof encoding a polypeptide selected from the group consisting of amino acids 1-60 of SEQ. ID No: 4, its antibody binding, fragments thereof at least 10 amino acids long, and fusion proteins thereof.
5. The polynucleotide of claim 1, wherein the nucleic acid comprises an anti-sense nucleotide segment.
6. The polynucleotide of claim 1, wherein the nucleic acid comprises an allele, or encodes and antibody binding fragment.
7. The polynucleotide of claim 1, wherein the nucleotide segment encodes an antibody binding fragment at least 20 amino acids long.
8. The polynucleotide of claim 1, comprising (A) primer/probes of at least 20 consecutive nucleotides of the nucleic acid segment encoding a polypeptide selected from the group consisting of amino acids 1-60 of SEQ. ID No: 4, and antibody binding fragments thereof; (B) alleles encoding amino acids 1-60 of SEQ. ID No: 4 or antibody binding fragments thereof at least 10 amino acids long; or (C) antisense polynucleotides thereof.
9. The polynucleotide of claim 1, wherein the nucleotide segment comprises at least 20 consecutive nucleotides of SEQ. ID No: 3.
10. The polynucleotide of claim 1, wherein the nucleic acid is selected from the group consisting of (A) nucleotide segment selected from the group consisting of SEQ. ID No: 3, SEQ. ID No: 28, and alleles thereof; (B) nucleic acids encoding fusion proteins comprising nucleotide segments and alleles of the segments encoding amino acids 1-60 of SEQ. ID No: 4; (C) primers/probes at least 20 consecutive nucleotides long complementary to the segments in (A) and (B); and (D) nucleotide segments which are anti-sense to the nucleotide segments in (A), (B) or (C).
11. The polynucleotide of claim 10, wherein the nucleic acid comprises SEQ. ID No: 1.
12. The polynucleotide of claim 10, wherein the nucleic acid comprises SEQ. ID No: 28.
13. The polynucleotide of claim 1, wherein the nucleic acid encodes amino acids 1-60 of SEQ. ID No: 4.
14. The polynucleotide of claim 3, wherein the nucleic acid comprises an additional polynucleotide encoding a polypeptide substantially unrelated to amino acids 1-258 of SEQ. ID No: 10.
15. The polynucleotide of claim 13, wherein the additional polynucleotide comprises a nucleic acid selected from the group consisting of (A) sense nucleotide segments and alleles thereof encoding amino acids 1-202 of SEQ. ID No: 2, 1-358 of SEQ. ID No: 6, 1-763 of SEQ. ID No: 8, 1-258 of SEQ ID NO: 10, 1-159 of SEQ. ID No: 12, 1-412 of SEQ. ID No: 14, 1-313 of SEQ. ID No: 26, polymerase activating polypeptide, c-raf, c-fos, c-myc, c-myb, and pim-1, and antibody binding fragments thereof at least 10 amino acids long; and (B) probes/primers at least 12 consecutive nucleotides long complementary to nucleotide segments in (A).
16. The polynucleotide of claim 15, wherein the additional polynucleotide comprises a nucleic acid segment selected from the group consisting of sense and anti-sense segments and alleles thereof of SEQ. ID No: 1, SEQ. ID No: 5, SEQ. ID No: 7, SEQ. ID No: 9, SEQ. ID No: 11, SEQ. ID No: 13, SEQ. ID No: 25, nucleic acid segments encoding polymerase activating polypeptide, c-raf, c-fos, c-myc, c-myb, and pim-1; probes/primers at least 12 consecutive nucleotides long complementary to the sense and anti-sense segments and alleles thereof; and fragments thereof at least 20 nucleotides long.
17. The polynucleotide of claim 1, being a DNA.
18. The polynucleotide of claim 1, being an RNA.
19. The polynucleotide of claim 1, wherein the nucleic acid comprises a probe/primer, and the probe/primer comprises a nucleotide sequence at least 20 consecutive nucleotides long complementary to the sense or anti-sense nucleotide segments.
20. A composition, comprising the polynucleotide of claim 1, and a diluent or carrier.
21. The composition of claim 20, where the diluent or carrier comprises a pharmaceutically acceptable diluent or carrier.
22. A vector, comprising the polynucleotide of claim 1, linked in reading frame thereto.
23. A composition, comprising the vector of claim 22, and a carrier or diluent.
24. A vector comprising the polyribonucleotide of claim 4, linked in reading frame thereto.
25. The vector of claim 24, comprising an expression vector.
26. A host cell transfected with the vector of claim 22.
27. A host cell transfected with the vector of claim 25.
28. A cell culture, comprising the hose cell of claim 26.
29. A cell culture, comprising the host cell of claim 27.
30. A method for producing a polypeptide, comprising culturing a host cell of claim 27, in an expression medium, under conditions effective to express the polypeptide; and separating the polypeptide from the cells.
31. The method of claim 30, wherein the polypeptide is further separated from the medium.
32. A method for producing a polypeptide, comprising culturing a host cell of claim 26, in an expression medium, under conditions effective to express the polypeptide; and separating the polypeptide from the cells.
33. The method of claim 32, wherein the polypeptide is further separated from the medium.
34. A DNA, having a nucleotide sequence complementary to the polynucleotide of claim 1.
35. A RNA, having a polynucleotide sequence corresponding to the DNA of claim 34.
36. A composition, comprising the DNA of claim 34, and a carrier or diluent.
37. A composition, comprising the RNA of claim 35, and a carrier or diluent.
38. A vector, comprising the DNA of claim 34 linked thereto.
39. A host cell, transfected with the vector of claim 38.
40. A cell culture, comprising a host cell comprising a vector comprising the probe/primer of claim 19.
41. A composition, comprising the probe/primer of claim 19, and a carrier or diluent.
42. A vector, comprising the probe/primer of claim 19 linked thereto.
43. A host cell, transfected with the vector of claim 42.
44. A hybridization kit, comprising the polynucleotide of claim 5, and instructions for its use.
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