Human Osteoclast-Derived Cathepsin

This invention relates to newly identified polynucleotides, polypeptides encoded by such polynucleotides, the use of such polynucleotides and polypeptides, as well as the production of such polynucleotides and polypeptides. More particularly, the polypeptide of the present invention is a human osteoclast-derived cathepsin (Cathepsin O). The invention also relates to inhibiting the action of such polypeptide and to assays for identifying inhibitors of the polypeptide.

Bone resorption involves the simultaneous removal of both the mineral and the organic constituents of the extracellular matrix. This occurs mainly in an acidic phagolysosome-like extracellular compartment covered by the ruffled border of osteoclasts. Barron, et al., J. Cell Biol., 101:2210-22, (1985). Osteoclasts are multinucleate giant cells that play key roles in bone resorption. Attached to the bone surface, osteoclasts produce an acidic microenvironment between osteoclasts and bone matrix. In this acidic microenvironment, bone minerals and organic components are solubilized. Organic components, mainly type-I collagen, are thought to be solubilized by protease digestion. There is evidence that cystsine proteinases may play an important role in the degradation of organic components of bone. Among cystsine proteinases, cathepsins B, L, N, and S can degrade type-I collagen in the acidic condition. Etherington, D. J. Biochem. J., 127, 685-692 (1972). Cathepsin L is the most active of the lysosomal cysteine proteases with regard to its ability to hydrolyze azocasein, elastin, and collagen.

Cathepsins are proteases that function in the normal physiological as well as pathological degradation of connective tissue. Cathepsins play a major role in intracellular protein degradation and turnover, bone remodeling, and prohormone activation. Marx, J. L., Science. 235:285-286 (1987). Cathepsin B, H, L and S are ubiquitously expressed lysosomal cysteine proteinases that belong to the papain superfamily. They are found at constitutive levels in many tissues in the human including kidney, liver, lung and spleen. Some pathological roles of cathepsins include an involvement in glomerulonephritis, arthritis, and cancer metastasis. Sloan, B. F., and Honn, K. V., Cancer Metastasis Rev., 3:249-263 (1984). Greatly elevated levels of cathepsin L and B mRNA and protein are seen in tumor cells. Cathepsin L mRNA is also induced in fibroblasts treated with tumor promoting agents and growth factors. Kane, S. E. and Gottesman, M. M. Cancer Biology, 1:127-136 (1990).

In vitro studies on bone resorption have shown that cathepsins L and B may be involved in the remodelling of this tissue. These lysosomal cysteine proteases digest extracellular matrix proteins such as elastin, laminin, and type I collagen under acidic conditions. Osteoclast cells require this activity to degrade the organic matrix prior to bone regeneration accomplished by osteoblasts. Several natural and synthetic inhibitors of cysteine proteinases have been effective in inhibiting the degradation of this matrix.

The isolation of cathepsins and their role in bone resorption has been the subject of an intensive study. OC-2 has recently been isolated from pure osteoclasts from rabbit bones. The OC-2 was found to encode a possible cysteine proteinase structurally related to cathepsins L and S. Tezuka, K., et al., J. Biol. Chem., 269:1106-1109, (1994).

An inhibitor of cysteine proteinases and collagenase, Z-Phe-Ala-CHN.sub.2 has been studied for its effect on the resorptive activity of isolated osteoclasts and has been found to inhibit resorption pits in dentine. Delaisse, J. M. et al., Bone, 8:305-313 (1987). Also, the effect of human recombinant cystatin C, a cysteine proteinase inhibitor, on bone resorption in vitro has been evaluated, and has been shown to significantly inhibit bone resorption which has been stimulated by parathyroid hormone. Lerner, U. H. and Grubb Anders, Journal of Bone and Mineral Research, 7:433-439, (1989). Further, a cDNA clone encoding the human cysteine protease cathepsin L has been recombinantly manufactured and expressed at high levels in E. coli in a T7 expression system. Recombinant human procathepsin L was successfully expressed at high levels and purified as both procathepsin L and active processed cathepsin L forms. Information about the possible function of the propeptide in cathepsin L folding and/or processing and about the necessity for the light chain of the enzyme for protease activity was obtained by expressing and purifying mutant enzymes carrying structural alterations in these regions. Smith, S. M. and Gottesman, M. M., J. Bio Chem., 264:20487-20495, (1989). There has also been reported the expression of a functional human cathepsin S in Saccharomyces cerevisiae and the characterization of the recombinant enzyme. Bromme, D. et al., J. Bio Chem., 268:4832-4838 (1993).

In accordance with one aspect of the present invention, there is provided a novel mature polypeptide which is a osteoclast-derived cathepsin as well as fragments, analogs and derivatives thereof. The human osteoclast-derived cathepsin of the present invention is of human origin.

In accordance with another aspect of the present invention, there are provided polynucleotides (DNA or RNA) which encode such polypeptides.

In accordance with still another aspect of the present invention, there is provided a procedure for producing such polypeptide by recombinant techniques.

In accordance with yet a further aspect of the present invention, there is provided an antibody which inhibits the action of such polypeptide.

In accordance with yet another aspect of the present invention, there are provided antagonists to such polypeptides, e.g., a small molecule inhibitor which may be used to inhibit the action of such polypeptide, for example, in the treatment of metastatic tumors and osteoporosis.

In accordance with still another aspect of the present invention, there is provided a procedure for developing assay systems to identify inhibitors of the polypeptide of the present invention.

These and other aspects of the present invention should be apparent to those skilled in the art from the teachings herein.

The following drawings are meant only as illustrations of specific embodiments of the present invention and are not meant as limitations in any manner.

FIG. 1 shows the polynucleotide sequence and corresponding deduced amino acid sequence for cathepsin O. The cathepsin O shown is the predicted precursor form of the protein where approximately the first 15 amino acids represent the leader sequence and the first 115 amino acids are the prosequence. The standard three letter abbreviation has been used for the amino acid sequence.

FIG. 2 is an illustration of the amino acid homology of cathepsin O to other human cathepsins and rabbit OC-2.

In accordance with one aspect of the present invention, there is provided an isolated nucleic acid (polynucleotide) which encodes for the mature polypeptide having the deduced amino acid sequence of FIG. 1 (SEQ ID NO:2) or for the mature polypeptide encoded by the cDNA of the clone deposited as ATCC Deposit No. 75671 on Feb. 9, 1994.

A polynucleotide encoding a polypeptide of the present invention may be obtained from a cDNA library derived from human osteoclastoma cells, placenta, kidney or lung. The polynucleotide described herein was isolated from a cDNA library derived from human osteoclastoma cells. The cDNA insert is 1619 base pairs (bp) in length and contains an open reading frame encoding a protein 329 amino acids in length of which approximately the first 15 amino acids represent the leader sequence and first 115 amino acids represent the prosequence. Thus, the mature form of the polypeptide of the present invention consists of 214 amino acids after the 115 amino acid prosequence (which includes the approximately 15 amino acid leader sequence) is cleaved. The polypeptide encoded by the polynucleotide is structurally related to human cathepsin S with 56% identical amino acids and 71% similarity over the entire coding region. It is also structurally related to rabbit OC-2 cathepsin with 94% identical amino acids and 97% similarity over the entire coding region. The polypeptide may be found in lysosomes of, or extracellularly near, osteoclasts.

The polynucleotide of the present invention may be in the form of RNA or in the form of DNA, which DNA includes cDNA, genomic DNA, and synthetic DNA. The DNA may be double-stranded or single-stranded, and if single stranded may be the coding strand or non-coding (anti-sense) strand. The coding sequence which encodes the mature polypeptide may be identical to the coding sequence shown in FIG. 1 (SEQ ID NO:1) or that of the deposited clone or may be a different coding sequence which coding sequence, as a result of the redundancy or degeneracy of the genetic code, encodes the same, mature polypeptide as the DNA of FIG. 1 (SEQ ID NO:2) or the deposited cDNA.

The polynucleotide which encodes for the mature polypeptide of FIG. 1 (SEQ ID NO:2) or for the mature polypeptide encoded by the deposited cDNA may include: only the coding sequence for the mature polypeptide; the coding sequence for the mature polypeptide and additional coding sequence such as a leader or secretory sequence or a proprotein sequence; the coding sequence for the mature polypeptide (and optionally additional coding sequence) and non-coding sequence, such as introns or non-coding sequence 5' and/or 3' of the coding sequence for the mature polypeptide.

Thus, the term "polynucleotide encoding a polypeptide" encompasses a polynucleotide which includes only coding sequence for the polypeptide as well as a polynucleotide which includes additional coding and/or non-coding sequence.

The present invention further relates to variants of the hereinabove described polynucleotides which encode for fragments, analogs and derivatives of the polypeptide having the deduced amino acid sequence of FIG. 1 (SEQ ID NO:2) or the polypeptide encoded by the cDNA of the deposited clone. The variant of the polynucleotide may be a naturally occurring allelic variant of the polynucleotide or a non-naturally occurring variant of the polynucleotide. The present invention also relates to polynucleotide probes constructed from the polynucleotide sequence of FIG. 1 or a segment of the sequence of FIG. 1 (SEQ ID NO:2) amplified by the PCR method, which could be utilized to screen an osteoclast cDNA library to deduce the polypeptide of the present invention.

Thus, the present invention includes polynucleotides encoding the same mature polypeptide as shown in FIG. 1 (SEQ ID NO:2) or the same mature polypeptide encoded by the cDNA of the deposited clone as well as variants of such polynucleotides which variants encode for a fragment, derivative or analog of the polypeptide of FIG. 1 (SEQ ID NO:2) or the polypeptide encoded by the cDNA of the deposited clone. Such nucleotide variants include deletion variants, substitution variants and addition or insertion variants.

As hereinabove indicated, the polynucleotide may have a coding sequence which is a naturally occurring allelic variant of the coding sequence shown in FIG. 1 (SEQ ID NO:1) or of the coding sequence of the deposited clone. As known in the art, an allelic variant is an alternate form of a polynucleotide sequence which may have a substitution, deletion or addition of one or more nucleotides, which does not substantially alter the function of the encoded polypeptide.

The present invention also includes polynucleotides, wherein the coding sequence for the mature polypeptide may be fused in the same reading frame to a polynucleotide sequence which aids in expression and secretion of a polypeptide from a host cell, for example, a leader sequence which functions as a secretory sequence for controlling transport of a polypeptide from the cell. The polypeptide having a leader sequence is a preprotein and may have the leader sequence cleaved by the host cell to form the mature form of the polypeptide. The polynucleotides may also encode for a proprotein which is the mature protein plus additional 5' amino acid residues. A mature protein having a prosequence is a proprotein and may in some cases be an inactive form of the protein. Once the prosequence is cleaved an active mature protein remains.

Thus, for example, the polynucleotide of the present invention may encode for a mature protein, or for a protein having a prosequence or for a protein having both a presequence (leader sequence) and a prosequence.

The polynucleotides of the present invention may also have the coding sequence fused in frame to a marker sequence which allows for purification of the polypeptide of the present invention. The marker sequence may be a hexa-histidine tag supplied by a pQE-9 vector to provide for purification of the mature polypeptide fused to the marker in the case of a bacterial host, or, for example, the marker sequence may be a hemagglutinin (HA) tag when a mammalian host, e.g. COS-7 cells, is used. The HA tag corresponds to an epitope derived from the influenza hemagglutinin protein (Wilson, I., et al., Cell, 37:767 (1984)).

The present invention further relates to polynucleotides which hybridize to the hereinabove-described sequences if there is at least 50% and preferably 70% identity between the sequences. The present invention particularly relates to polynucleotides which hybridize under stringent conditions to the hereinabove-described polynucleotides. As herein used, the term "stringent conditions" means hybridization will occur only if there is at least 95% and preferably at least 97% identity between the sequences. The polynucleotides which hybridize to the hereinabove described polynucleotides in a preferred embodiment encode polypeptides which retain substantially the same biological function or activity as the mature polypeptide encoded by the cDNA of FIG. 1 or the deposited cDNA.

The deposits referred to herein will be maintained under the Budapest Treaty on the International Recognition of the Deposit of Microorganisms for the purposes of Patent Procedure. These deposits are provided merely as a convenience and are not an admission that a deposit is required under 35 U.S.C. .sctn.112. The sequence of the polynucleotides contained in the deposited materials, as well as the amino acid sequence of the polypeptides encoded thereby, are incorporated herein by reference and are controlling in the event of any conflict with the description of sequences herein. A license may be required to make, use or sell the deposited materials, and no such license is hereby granted.

The present invention further relates to a cathepsin O polypeptide which has the deduced amino acid sequence of FIG. 1 (SEQ ID NO:2) or which has the amino acid sequence encoded by the deposited cDNA, as well as fragments, analogs and derivatives of such polypeptide.

The terms "fragment," "derivative" and "analog" when referring to the polypeptide of FIG. 1 (SEQ ID NO:2) or that encoded by the deposited cDNA, means a polypeptide which retains essentially the same biological function or activity as such polypeptide. Thus, an analog includes a proprotein which can be activated by cleavage of the proprotein portion to produce an active mature polypeptide.

The polypeptide of the present invention may be a recombinant polypeptide, a natural polypeptide or a synthetic polypeptide, preferably a recombinant polypeptide.

The fragment, derivative or analog of the polypeptide of FIG. 1 (SEQ ID NO:2) or that encoded by the deposited cDNA may be (i) one in which one or more of the amino acid residues are substituted with a conserved or non-conserved amino acid residue (preferably a conserved amino acid residue) and such substituted amino acid residue may or may not be one encoded by the genetic code, or (ii) one in which one or more of the amino acid residues includes a substituent group, or (iii) one in which the mature polypeptide is fused with another compound, such as a compound to increase the half-life of the polypeptide (for example, polyethylene glycol), or (iv) one in which the additional amino acids are fused to the mature polypeptide, such as a leader or secretory sequence or a sequence which is employed for purification of the mature polypeptide or a proprotein sequence. Such fragments, derivatives and analogs are deemed to be within the scope of those skilled in the art from the teachings herein.

The polypeptides and polynucleotides of the present invention are preferably provided in an isolated form, and preferably are purified to homogeneity.

The term "isolated" means that the material is removed from its original environment (e.g., the natural environment if it is naturally occurring). For example, a naturally-occurring polynucleotide or polypeptide present in a living animal is not isolated, but the same polynucleotide or DNA or polypeptide, separated from some or all of the coexisting materials in the natural system, is isolated. Such polynucleotide could be part of a vector and/or such polynucleotide or polypeptide could be part of a composition, and still be isolated in that such vector or composition is not part of its natural environment.

The present invention also relates to vectors which include polynucleotides of the present invention, host cells which are genetically engineered with vectors of the invention and the production of polypeptides of the invention by recombinant techniques.

Host cells are genetically engineered (transduced or transformed or transfected) with the vectors of this invention which may be, for example, a cloning vector or an expression vector. The vector may be, for example, in the form of a plasmid, a viral particle, a phage, etc. The engineered host cells can be cultured in conventional nutrient media modified as appropriate for activating promoters, selecting transformants or amplifying the cathepsin O genes. The culture conditions, such as temperature, pH and the like, are those previously used with the host cell selected for expression, and will be apparent to the ordinarily skilled artisan.

The polynucleotide of the present invention may be employed for producing a polypeptide by recombinant techniques. Thus, for example, the polynucleotide sequence may be included in any one of a variety of expression vehicles, in particular vectors or plasmids for expressing a polypeptide. Such vectors include chromosomal, nonchromosomal and synthetic DNA sequences, e.g., derivatives of SV40; bacterial plasmids; phage DNA; yeast plasmids; vectors derived from combinations of plasmids and phage DNA, viral DNA such as vaccinia, adenovirus, fowl pox virus, and pseudorabies. However, any other plasmid or vector may be used as long as it is replicable and viable in the host.

As hereinabove indicated, the appropriate DNA sequence may be inserted into the vector by a variety of procedures. In general, the DNA sequence is inserted into appropriate restriction endonuclease sites by procedures known in the art. Such procedures and others are deemed to be within the scope of those skilled in the art.

The DNA sequence in the expression vector is operatively linked to an appropriate expression control sequence(s) (promoter) to direct mRNA synthesis. As representative examples of such promoters, there may be mentioned: LTR or SV40 promoter, the E. coli. lac or trp, the phage lambda P.sub.L promoter and other promoters known to control expression of genes in prokaryotic or eukaryotic cells or their viruses. The expression vector also contains a ribosome binding site for translation initiation and a transcription terminator. The vector may also include appropriate sequences for amplifying expression.

In addition, the expression vectors preferably contain a gene to provide a phenotypic trait for selection of transformed host cells such as dihydrofolate reductase or neomycin resistance for eukaryotic cell culture, or such as tetracycline or ampicillin resistance in E. coli.

The vector containing the appropriate DNA sequence as hereinabove described, as well as an appropriate promoter or control sequence, may be employed to transform an appropriate host to permit the host to express the protein. As representative examples of appropriate hosts, there may be mentioned: bacterial cells, such as E. coli, Salmonella typhimurium; Streptomyces; fungal cells, such as yeast; insect cells such as Drosophila and Sf9; animal cells such as CHO, COS or Bowes melanoma; plant cells, etc. The selection of an appropriate host is deemed to be within the scope of those skilled in the art from the teachings herein.

More particularly, the present invention also includes recombinant constructs comprising one or more of the sequences as broadly described above. The constructs comprise a vector, such as a plasmid or viral vector, into which a sequence of the invention has been inserted, in a forward or reverse orientation. In a preferred aspect of this embodiment, the construct further comprises regulatory sequences, including, for example, a promoter, operably linked to the sequence. Large numbers of suitable vectors and promoters are known to those of skill in the art, and are commercially available. The following vectors are provided by way of example. Bacterial: pQE70, pQE60, pQE-9 (Qiagen) pBs, phagescript, psiX174, pBluescript SK, pBsKS, pNH8a, pNH16a, pNH18a, pNH46a (Stratagene); pTrc99A, pKK223-3, pKK233-3, pDR540, pRIT5 (Pharmacia). Eukaryotic: pWLneo, pSV2cat, pOG44, pXT1, pSG (Stratagene) pSVK3, pBPV, pMSG, pSVL (Pharmacia). However, any other plasmid or vector may be used as long as it is replicable and viable in the host.

Promoter regions can be selected from any desired gene using CAT (chloramphenicol transferase) vectors or other vectors with selectable markers. Two appropriate vectors are pKK232-8 and pCM7. Particular named bacterial promoters include lacI, lacZ, T3, T7, gpt, lambda P.sub.R, P.sub.L and trp. Eukaryotic promoters include CMV immediate early, HSV thymidine kinase, early and late SV40, LTRs from retrovirus, and mouse metallothionein-I. Selection of the appropriate vector and promoter is well within the level of ordinary skill in the art.

In a further embodiment, the present invention relates to host cells containing the above-described construct. The host cell can be a higher eukaryotic cell, such as a mammalian cell, or a lower eukaryotic cell, such as a yeast cell, or the host cell can be a prokaryotic cell, such as a bacterial cell. Introduction of the construct into the host cell can be effected by calcium phosphate transfection, DEAE-Dextran mediated transfection, or electroporation (Davis, L., Dibner, M., Battey, I., Basic Methods in Molecular Biology, 1986)).

The constructs in host cells can be used in a conventional manner to produce the gene product encoded by the recombinant sequence. Alternatively, the polypeptides of the invention can be synthetically produced by conventional peptide synthesizers.

Mature proteins can be expressed in mammalian cells, yeast, bacteria, or other cells under the control of appropriate promoters. Cell-free translation systems can also be employed to produce such proteins using RNAs derived from the DNA constructs of the present invention. Appropriate cloning and expression vectors for use with prokaryotic and eukaryotic hosts are described by Sambrook et al., Molecular Cloning: A Laboratory Manual, Second Edition, (Cold Spring Harbor, N.Y., 1989), the disclosure of which is hereby incorporated by reference.

Transcription of a DNA encoding the polypeptides of the present invention by higher eukaryotes is increased by inserting an enhancer sequence into the vector. Enhancers are cis-acting elements of DNA, usually about from 10 to 300 bp, that act on a promoter to increase its transcription. Examples include the SV40 enhancer on the late side of the replication origin (bp 100 to 270), a cytomegalovirus early promoter enhancer, a polyoma enhancer on the late side of the replication origin, and adenovirus enhancers.

Generally, recombinant expression vectors will include origins of replication and selectable markers permitting transformation of the host cell, e.g., the ampicillin resistance gene of E. coli and S. cerevisiae TRP1 gene, and a promoter derived from a highly-expressed gene to direct transcription of a downstream structural sequence. Such promoters can be derived from operons encoding glycolytic enzymes such as 3-phosphoglycerate kinase (PGK), .alpha. factor, acid phosphatase, or heat shock proteins, among others. The heterologous structural sequence is assembled in appropriate phase with translation initiation and termination sequences, and preferably, a leader sequence capable of directing secretion of translated protein into the periplasmic space or extracellular medium. Optionally, the heterologous sequence can encode a fusion protein including an N-terminal identification peptide imparting desired characteristics, e.g., stabilization or simplified purification of expressed recombinant product.

Useful expression vectors for bacterial use are constructed by inserting a structural DNA sequence encoding a desired protein together with suitable translation initiation and termination signals in operable reading phase with a functional promoter. The vector will comprise one or more phenotypic selectable markers and an origin of replication to ensure maintenance of the vector and to, if desirable, provide amplification within the host. Suitable prokaryotic hosts for transformation include E. coli, Bacillus subtilis, Salmonella typhimurium and various species within the genera Pseudomonas, Streptomyces, and Staphylococcus, although others may also be employed as a matter of choice.

As a representative but nonlimiting example, useful expression vectors for bacterial use can comprise a selectable marker and bacterial origin of replication derived from commercially available plasmids comprising genetic elements of the well known cloning vector pBR322 (ATCC 37017). Such commercial vectors include, for example, PKK223-3 (Pharmacia Fine Chemicals, Uppsala, Sweden) and GEM1 (Promega Biotec, Madison, Wis., U.S.A.). These pBR322 "backbone" sections are combined with an appropriate promoter and the structural sequence to be expressed.

Following transformation of a suitable host strain and growth of the host strain to an appropriate cell density, the selected promoter is derepressed by appropriate means (e.g., temperature shift or chemical induction) and cells are cultured for an additional period.

Cells are typically harvested by centrifugation, disrupted by physical or chemical means, and the resulting crude extract retained for further purification.

Microbial cells employed in expression of proteins can be disrupted by any convenient method, including freeze-thaw cycling, sonication, mechanical disruption, or use of cell lysing agents, such methods are well-known to those skilled in the art.

Various mammalian cell culture systems can also be employed to express recombinant protein. Examples of mammalian expression systems include the COS-7 lines of monkey kidney fibroblasts, described by Gluzman, Cell, 23:175 (1981), and other cell lines capable of expressing a compatible vector, for example, the C127, 3T3, CHO, HeLa and BHK cell lines. Mammalian expression vectors will comprise an origin of replication, a suitable promoter and enhancer, and also any necessary ribosome binding sites, polyadenylation site, splice donor and acceptor sites, transcriptional termination sequences, and 5' flanking nontranscribed sequences. DNA sequences derived from the SV40 viral genome, for example, SV40 origin, early promoter, enhancer, splice, and polyadenylation sites may be used to provide the required nontranscribed genetic elements.

Cathepsin O is recovered and purified from recombinant cell cultures by methods used heretofore, including ammonium sulfate or ethanol precipitation, acid extraction, anion or cation exchange chromatography, phosphocellulose chromatography, hydrophobic interaction chromatography, hydroxyapatite chromatography and lectin chromatography. It is preferred to have low concentrations (approximately 0.1-5 mM) of calcium ion present during purification (Price, et al., J. Biol. Chem., 244:917 (1969)). Protein refolding steps can be used, as necessary, in completing configuration of the mature protein. Finally, high performance liquid chromatography (HPLC) can be employed for final purification steps.

The polypeptides of the present invention may be naturally purified products expressed from a high expressing cell line, or a product of chemical synthetic procedures, or produced by recombinant techniques from a prokaryotic or eukaryotic host (for example, by bacterial, yeast, higher plant, insect and mammalian cells in culture). Depending upon the host employed in a recombinant production procedure, the polypeptides of the present invention may be glycosylated with mammalian or other eukaryotic carbohydrates or may be non-glycosylated. Polypeptides of the invention may also include an initial methionine amino acid residue.

The sequences of the present invention are also valuable for chromosome identification. The sequence is specifically targeted to and can hybridize with a particular location on an individual human chromosome. Moreover, there is a current need for identifying particular sites on the chromosome. Few chromosome marking reagents based on actual sequence data (repeat polymorphism's) are presently available for marking chromosomal location. The mapping of DNAs to chromosomes according to the present invention is an important first step in correlating those sequences with genes associated with disease.

Briefly, sequences can be mapped to chromosomes by preparing PCR primers (preferably 15-25 bp) from the cDNA. Computer analysis of the cDNA is used to rapidly select primers that do not span more than one exon in the genomic DNA, thus complicating the amplification process. These primers are then used for PCR screening of somatic cell hybrids containing individual human chromosomes. Only those hybrids containing the human gene corresponding to the primer will yield an amplified fragment.

PCR mapping of somatic cell hybrids is a rapid procedure for assigning a particular DNA to a particular chromosome. Using the present invention with the same oligonucleotide primers, sublocalization can be achieved with panels of fragments from specific chromosomes or pools of large genomic clones in an analogous manner. Other mapping strategies that can similarly be used to map to its chromosome include in situ hybridization, prescreening with labeled flow-sorted chromosomes and preselection by hybridization to construct chromosome specific-cDNA libraries.

Fluorescence in situ hybridization (FISH) of a cDNA clone to a metaphase chromosomal spread can be used to provide a precise chromosomal location in one step. This technique can be used with cDNA as short as 500 or 600 bases; however, clones larger than 2,000 bp have a higher likelihood of binding to a unique chromosomal location with sufficient signal intensity for simple detection. FISH requires use of the clone from which the EST was derived, and the longer the better. For example, 2,000 bp is good, 4,000 is better, and more than 4,000 is probably not necessary to get good results a reasonable percentage of the time. For a review of this technique, see Verma et al., Human Chromosomes: a Manual of Basic Techniques. Pergamon Press, N.Y. (1988).

Once a sequence has been mapped to a precise chromosomal location, the physical position of the sequence on the chromosome can be correlated with genetic map data. (Such data are found, for example, in V. McKusick, Mendelian Inheritance in Man (available on line through Johns Hopkins University Welch Medical Library). The relationship between genes and diseases that have been mapped to the same chromosomal region are then identified through linkage analysis (coinheritance of physically adjacent genes).

Next, it is necessary to determine the differences in the cDNA or genomic sequence between affected and unaffected individuals. If a mutation is observed in some or all of the affected individuals but not in any normal individuals, then the mutation is likely to be the causative agent of the disease.

With current resolution of physical mapping and genetic mapping techniques, a cDNA precisely localized to a chromosomal region associated with the disease could be one of between 50 and 500 potential causative genes. (This assumes 1 megabase mapping resolution and one gene per 20 kb).

Comparison of affected and unaffected individuals generally involves first looking for structural alterations in the chromosomes, such as deletions or translocations that are visible from chromosome spreads or detectable using PCR based on that cDNA sequence. Ultimately, complete sequencing of genes from several individuals is required to confirm the presence of a mutation and to distinguish mutations from polymorphisms.

The present invention is directed to inhibiting cathepsin O in vivo by the use of antisense technology. Antisense technology can be used to control gene expression through triple-helix formation or antisense DNA or RNA, both of which methods are based on binding of a polynucleotide to DNA or RNA. For example, the 5' coding portion of the polynucleotide sequence, which encodes for the mature polypeptide of the present invention, is used to design an antisense RNA oligonucleotide of from 10 to 40 base pairs in length. A DNA oligonucleotide is designed to be complementary to a region of the gene involved in transcription (triple helix--see Lee et al, Nucl. Acids Res., 6:3073 (1979); Cooney et al, Science, 241:456 (1988); and Dervan et al, Science, 251:1360 (1991), thereby preventing transcription and the production of cathepsin O. The antisense RNA oligonucleotide hybridizes to the mRNA in vivo and blocks translation of an mRNA molecule into the cathepsin O (antisense--Okano, J. Neurochem., 56:560 (1991); Oligodeoxynucleotides as Antisense Inhibitors of Gene Expression, CRC Press, Boca Raton, Fla. (1988)).

Alternatively, the oligonucleotides described above can be delivered to cells by procedures in the art such that the anti-sense RNA or DNA may be expressed in vivo to inhibit production of cathepsin O in the manner described above.

Antisense constructs to cathepsin O, therefore, inhibit the action of cathepsin O and may be used for treating certain disorders, for example, osteoporosis, since bone resorption is slowed or prevented. These antisense constructs may also be used to treat tumor metastasis since elevated levels of cathepsins are found in some tumor cells, and cathepsin L mRNA and protein is increased in ras-transformed fibroblasts. Further, there is evidence that metastatic B16 melanomas all upregulate cathepsin B compared with non-metastatic tumors.

The polypeptides, their fragments or other derivatives, or analogs thereof, or cells expressing them can be used as an immunogen to produce antibodies thereto. These antibodies can be, for example, polyclonal or monoclonal antibodies. The present also includes chimeric, single chain and humanized antibodies, as well as Fab fragments, or the product of an Fab expression library. Various procedures known in the art may be used for the production of such antibodies and fragments.

Antibodies generated against the polypeptide corresponding to a sequence of the present invention or its in vivo receptor can be obtained by direct injection of the polypeptide into an animal or by administering the polypeptide to an animal, preferably a nonhuman. The antibody so obtained will then bind the polypeptide itself. In this manner, even a sequence encoding only a fragment of the polypeptide can be used to generate antibodies binding the whole native polypeptide. Such antibodies can then be used to isolate the polypeptide from tissue expressing that polypeptide. For preparation of monoclonal antibodies, any technique which provides antibodies produced by continuous cell line cultures can be used. Examples include the hybridoma technique (Kohler and Milstein, 1975, Nature, 256:495-497), the trioma technique, the human B-cell hybridoma technique (Kozbor et al., 1983, Immunology Today 4:72), and the EBV-hybridoma technique to produce human monoclonal antibodies (Cole, et al., 1985, in Monoclonal Antibodies and Cancer Therapy, Alan R. Liss, Inc., pp. 77-96).

Techniques described for the production of single chain antibodies (U.S. Pat. No. 4,946,778) can be adapted to produce single chain antibodies to immunogenic polypeptide products of this invention.

Antibodies specific to the cathepsin O may further be used to inhibit the biological action of the polypeptide by binding to the polypeptide. In this manner, the antibodies may be used in therapy, for example, to treat cancer since cathepsin L mRNA and protein is increased in ras-transformed fibroblasts and after addition of phorbol esters and growth factors. Also, osteoporosis may be treated with these antibodies since bone resorption by cathepsin O is prevented.

Further, such antibodies can detect the presence or absence of cathepsin O and the level of concentration of cathepsin O and, therefore, are useful as diagnostic markers for the diagnosis of disorders such as high turnover osteoporosis, Paget's disease, tumor osteolysis, or other metabolic bone disorders. Such antibodies may also function as a diagnostic marker for tumor metastases.

The present invention is also directed to antagonists and inhibitors of the polypeptides of the present invention. The antagonists and inhibitors are those which inhibit or eliminate the function of the polypeptide.

Thus, for example, an antagonist may bind to a polypeptide of the present invention and inhibit or eliminate its function. The antagonist, for example, could be an antibody against the polypeptide which eliminates the activity of cathepsin O by binding to cathepsin O, or in some cases the antagonist may be an oligonucleotide. An example of an inhibitor is a small molecule inhibitor which inactivates the polypeptide by binding to and occupying the catalytic site, thereby making the catalytic site inaccessible to a substrate, such that the biological activity of cathepsin O is prevented. Examples of small molecule inhibitors include but are not limited to small peptides or peptide-like molecules.

In these ways, the antagonists and inhibitors may be used to treat bone disease, such as osteoporosis by preventing cathepsin O from functioning to break down bone. The antagonists and inhibitors may also be used to treat metastatic tumors since cathepsins play a role in increasing metastatic tumor growth.

The antagonists and inhibitors may be employed in a composition with a pharmaceutically acceptable carrier, including but not limited to saline, buffered saline, dextrose, water, glycerol, ethanol and combinations thereof. Administration of cathepsin inhibitors are preferably systemic. Intraperitoneal injections of the cysteine proteinase inhibitor leupeptin (0.36 mg/kg body weight) and E-64 (0.18 mg/kg body weight) in rats were able to decrease serum calcium and urinary excretion of hydroxyproline. Delaisse et al., BBRC, 125:441-447 (1984). A direct application on areas of bone vulnerable to osteoporosis such as the proximal neck of the femur may also be employed.

The present invention also relates to an assay for identifying the above-mentioned small molecule inhibitors which are specific to Cathepsin O and prevent it from functioning. Either natural protein substrates or synthetic peptides would be used to assess proteolytic activity of cathepsin O, and the ability of inhibitors to prevent this activity could be the basis for a screen to identify compounds that have therapeutic activity in disorders of excessive bone resorption. Maciewicz, R. A. and Etheringtin, D. J., BioChem. J. 256:433-440 (1988).

A general example of such an assay for identifying inhibitors of cathepsin O utilizes peptide-based substrates which are conjugated with a chromogenic tag. An illustrative example of such a peptide substrate has the X-(Y).sub.n -Z, wherein X represents an appropriate amino protecting group such as acetyl, acetate or amide, Y is any naturally or non-naturally occurring amino acid which in combination forms a substrate which cathepsin O recognizes and will cleave in the absence of an inhibitor, n represents an integer which may be any number, however, which is usually at least 20, and Z represents any chromogenic or flourogenic tag, for example, para-nitroanelide or n-methyl coumarin, which upon cleavage of the Y group by the cathepsin O can be monitored for color production. If the potential inhibitor does not inhibit cathepsin O and the substrate (Y group) is cleaved, Z has a corresponding change in configuration, which change allows fluorescence to be detected by a fluorimeter in the case of a flourogenic tag and color to be detected by a spectrophotometer in the case of a chromogenic tag. When the inhibitor successfully inhibits cathepsin O from cleaving the substrate, the Y group is not cleaved and Z does not have a change in configuration and no fluorescence or color is detectable which indicates that the inhibitor has inhibited the action of cathepsin O.

The present invention will be further described with reference to the following examples; however, it is to be understood that the present invention is not limited to such examples. All parts or amounts, unless otherwise specified, are by weight.

In order to facilitate understanding of the following examples, certain frequently occurring methods and/or terms will be described.

"Plasmids" are designated by a lower case p preceded and/or followed by capital letters and/or numbers. The starting plasmids herein are either commercially available, publicly available on an unrestricted basis, or can be constructed from available plasmids in accord with published procedures. In addition, equivalent plasmids to those described are known in the art and will be apparent to the ordinarily skilled artisan.

"Digestion" of DNA refers to catalytic cleavage of the DNA with a restriction enzyme that acts only at certain sequences in the DNA. The various restriction enzymes used herein are commercially available and their reaction conditions, cofactors and other requirements were used as would be known to the ordinarily skilled artisan. For analytical purposes, typically 1 .mu.g of plasmid or DNA fragment is used with about 2 units of enzyme in about 20 .mu.l of buffer solution. For the purpose of isolating DNA fragments for plasmid construction, typically 5 to 50 .mu.g of DNA are digested with 20 to 250 units of enzyme in a larger volume. Appropriate buffers and substrate amounts for particular restriction enzymes are specified by the manufacturer. Incubation times of about 1 hour at 37.degree. C. are ordinarily used, but may vary in accordance with the supplier's instructions. After digestion the reaction is electrophoresed directly on a polyacrylamide gel to isolate the desired fragment.

Size separation of the cleaved fragments is performed using 8 percent polyacrylamide gel described by Goeddel, D. et al., Nucleic Acids Res., 8:4057 (1980).

"Oligonucleotides" refers to either a single stranded polydeoxynucleotide or two complementary polydeoxynucleotide strands which may be chemically synthesized. Such synthetic oligonucleotides have no 5' phosphate and thus will not ligate to another oligonucleotide without adding a phosphate with an ATP in the presence of a kinase. A synthetic oligonucleotide will ligate to a fragment that has not been dephosphorylated.

"Ligation" refers to the process of forming phosphodiester bonds between two double stranded nucleic acid fragments (Maniatis, T., et al., Id., p. 146). Unless otherwise provided, ligation may be accomplished using known buffers and conditions with 10 units of T4 DNA ligase ("ligase") per 0.5 .mu.g of approximately equimolar amounts of the DNA fragments to be ligated.

Unless otherwise stated, transformation was performed as described in the methods of Graham, F. and Van Der Eb, A., Virology, 52:456-457 (1973).

The DNA sequence encoding for cathepsin O (ATCC #75671) is initially amplified using PCR oligonucleotide primers corresponding to the 5' and 3' end of the DNA sequence to synthesize insertion fragments. The 5' oligonucleotide primer has the sequence 5' GCTAAGGATCCTGGGGGCTCAAGGTT 3' (SEQ ID NO:3) contains a Bam H1 restriction enzyme site followed by 15 nucleotides of cathepsin O coding sequence starting from the codon following the methionine start codon; the 3' sequence, 5' GCTAATCTAGATCACATCTTGGGGAA 3' (SEQ ID NO:4) contains complementary sequences to XbaI site, and the last 12 nucleotides of cathepsin O coding sequence. The restriction enzyme sites correspond to the restriction enzyme sites on the bacterial expression vector pQE-9 (Qiagen Inc., 9259 Eton Ave., Chatsworth, Calif. 91311). The plasmid vector encodes antibiotic resistance (Amp.sup.r), a bacterial origin of replication (ori), an IPTG-regulatable promoter/operator (P/O), a ribosome binding site (RBS), a 6-histidine tag (6-His) and restriction enzyme cloning sites. The pQE-9 vector was digested with Bam HI and XbaI and the insertion fragments were then ligated into the vector maintaining the reading frame initiated at the bacterial RBS. The ligation mixture was then used to transform the E. coli strain m15/rep4 (available from Qiagen under the trademark m15/rep4). M15/rep4 contains multiple copies of the plasmid pREP4, which expresses the lacI repressor and also confers kanamycin resistance (Kan.sup.r). Transformants are identified by their ability to grow on LB plates containing both Amp and Kan. Clones containing the desired constructs were grown overnight (O/N) in liquid culture in either LB media supplemented with both Amp (100 .mu.g/ml) and Kan (25 .mu.g/ml). The O/N culture is used to inoculate a large culture at a ratio of 1:100 to 1:250. The cells were grown to an optical density of 600 (O.D..sup.600) between 0.4 and 0.6. IPTG ("Isopropyl-B-D-thiogalacto pyranoside") was then added to a final concentration of 1 mM. IPTG induces by inactivating the lacI repressor, clearing the P/O leading to increased gene expression. Cells were grown an extra 3-4 hours. Cells were then harvested by centrifugation. The cell pellet was solubilized in the chaotropic agent 6 molar guanidine-HCL and 50 mM NaPO.sub.4 pH 8.0. After clarification, solubilized cathepsin O was purified from this solution by chromatography on a Nickel-Chelate column under conditions that allow for tight binding by proteins containing the 6-His tag. (Hochuli, E. et al., Genetic Engineering, Principle & Methods, 12:87-98 Plenum Press, New York (1990)). Cathepsin O (95% pure) was eluted from the column in 6 molar guanidine-HCL, 150 mM NaPO.sub.4 pH 5.0.

.sup.35 S!-labeled sense or antisense riboprobes generated from a partial cDNA clone of Cathepsin O were used as part of a Northern blot analysis to probe cryosections of osteoclastoma tissue, which demonstrated a single mRNA species, and spleen tissue. Current Protocols in Molecular Biology, Vol. 2, Ausubel et al., editors, section 14.3. Total RNA was isolated from osteoclastoma tissue and spleen. The RNA was electrophoresed on a formaldehyde agarose gel, and transferred to nitrocellulose. Following pre-hybridization, the blot was hybridized overnight with either sense or antisense 32P!-labeled riboprobe at 2.times.106 cpm/ml at 42.degree. C. Following stringent washes (0.2.times.SSC at 65.degree. C.), the blots were exposed to x-ray film. When used in in situ hybridization on sections of osteoclastoma tissue, specific, high level expression was observed in the osteoclasts; some expression was observed in mononuclear cells, but the stromal cells and osteoblasts did not express the mRNA for Cathepsin O at detectable levels. When sections of spleen tissue were used for in situ hybridization, no expression of Cathepsin O was observed. These data indicate that the mRNA for Cathepsin O is expressed at high levels in osteoclasts, and appears to be selectively expressed in these cells.

Antibodies were prepared against synthetic peptides from the Cathepsin O sequence, from regions sufficiently dissimilar to other members of the cathepsin family to allow specific analysis of Cathepsin O in Western blots. The antibodies were affinity purified and used to probe Western blots of osteoclastoma tissue. Synthetic peptides (AIDASLTSFQFYSK (SEQ ID NO:5) and YDESCNSDNLN (SEQ ID NO:6)) were prepared based upon the predicted sequence of Cathepsin O (corresponding to amino acids 248-261 and 265-275 in FIG. 1). The regions were chosen because of lowest identity to other members of the cathepsin family. The peptides were conjugated to Keyhole Limpet Hemocyanin with glutaraldehyde, mixed with adjuvant, and injected into rabbits. Immune sera was affinity purified using the immobilized peptide. Drake et al., Biochemistry, 28:8154-8160 (1989).

Tissue samples were homogenized in SDS-PAGE sample buffer and run on a 14% SDS-PAGE. The proteins were transferred to nitrocellulose, followed by blocking in bovine serum albumin. Immunoblotting was carried out with affinity purified anti-peptide antibodies, followed by alkaline phosphatase conjugated second antibody and visualization with a chromogenic substrate. Molecular mass determination was made based upon the mobility of pre-stained molecular weight standards (Rainbow markers, Amersham). Antibodies to two different peptides recognized a major band of approximately 29 kDa and a minor band of approximately 27 kDa. The immunoreactivity could be competed by the peptides used to generate the antibodies, confirming the specificity of the signal. This indicates that the mRNA for Cathepsin O is actually expressed in the tissue, and produces a protein with a size consistent with that of a fully processed Cathepsin O (assuming processing similar to related cathepsins).

Numerous modifications and variations of the present invention are possible in light of the above teachings and, therefore, within the scope of the appended claims, the invention may be practiced otherwise than as particularly described.