A NOVEL PROTEASE HOMOLOG DIFFERENTIALLY EXPRESSED IN BREAST AND OVARIAN-CANCER

Background: Using differential display (DD), we discovered a new membe r of the serine protease family of protein-cleaving enzymes, named pro tease M. The gene is most closely related by sequence to the kallikrei ns, to prostate-specific antigen (PSA), and to trypsin. The diagnostic use of PSA in prostate cancer suggested that a related molecule might be a predictor for breast or ovarian cancer. This, in turn, led to st udies designed to characterize the protein and to screen for its expre ssion in cancer. Materials and Methods: The isolation of protease M by DD, the cloning and sequencing of the cDNA, and the comparison of the predicted protein structure with related proteins are described, as a re methods to produce recombinant proteins and polyclonal antibody pre parations. Protease M expression was examined in mammary, prostate, an d ovarian cancer, as well as normal cells and tissues. Stable transfec tants expressing the protease M gene were produced in mammary carcinom a cells. Results: Protease M was localized by fluorescent in situ hybr idization analysis to chromosome 19q13.3, in a region to which other k allikreins and PSA also map. The gene is expressed in the primary mamm ary carcinoma lines tested but not in the corresponding cell lines of metastatic origin. It is strongly expressed in ovarian cancer;tissues and cell lines. The enzyme activity could not be established, because of difficulties in producing sufficient recombinant protein, a common problem with proteases. Transfectants were selected that overexpress t he mRNA, but the protein levels remained very low. Conclusions: Protea se M expression (mRNA) may be a useful marker in the detection of prim ary mammary carcinomas, as well as primary ovarian cancers. Other medi cal applications are also likely, based on sequence relatedness to try psin and PSA.