Modulation of proliferation and chemosensitivity by procathepsin D and itspeptides in ovarian cancer

Since the presence of precursors (pro-forms) of the aspartyl endoprotease, cathepsin D, appears to be linked with tumor progression, their presence wa s examined in sera and tumor tissues of ovarian cancer patients. The role o f cathepsin D pro-forms was further assessed in the dysregulated proliferat ion and chemoresistance observed in advanced ovarian cancer. Cathepsin D wa s isolated from sera of ovarian cancer patients (n = 20) and normal volunte ers (n = 11), as well as from solubilized normal ovarian epithelium (n = 8) and ovarian epithelial tumor tissue (n = 12). The specific molecular forms of cathepsin D were analyzed in these samples by Western immunoblot. Multi ple circulating molecular weight forms of cathepsin D were identified in ov arian cancer patients ranging from 24 to 60 kDa, while in normal controls, a major band was observed at 34 kDa in all samples and minor bands correspo nding to 27 and 48 kDa were detected in approximately half of the controls. To assess its consequences on ovarian cancer, the 52-kDa protein was immun oprecipitated from culture medium of an exponentially growing ovarian tumor cell line and was further purified by reverse-phase high-pressure liquid c hromatography. Its effect on proliferation was assayed by determining cell doubling times and their chemosensitivity was measured in a standard cytoto xicity assay using cisplatin. In addition, decapeptides corresponding to th e pro-portion of cathepsin D were analyzed in parallel. Procathepsin D and one decapeptide, peptide 2, as well as IGF-II (as a known positive) increas ed cell proliferation, with doubling times of 28.4, 28.8, and 30.3 h, respe ctively, versus untreated UL-1 cells (36.4 h). Procathepsin D treatment of UL-1 tumor cells significantly increased the cisplatin LD50 (74.9 mu g/ml) over untreated (33.9 mu g/ml) as well as IGF-II-treated (38.8 mu g/ml) cell s. Peptide 2 also showed a significant increase in LD50 (69.5 mu g/ml) comp ared to untreated and peptide 1-treated cells (37.1 mu g/ml). There are sev eral unique forms of cathepsin D expressed and accumulated by ovarian tumor s and these forms are detectable in the sera of those with ovarian cancer. The presence of these procathepsin D can increase the proliferation of thes e tumor cells, while decreasing their sensitivity to chemotherapeutic agent s. While procathepsin D and IGF-II both enhance proliferation, only procath epsin D (and peptide 2) appears to modulate chemosensitivity, suggesting a separate receptor or pathway for this consequence. (C) 1999 Academic Press.