Primary ovarian cancer cultures are resistant to Fas-mediated apoptosis

Objectives. Fas, a primary mediator of cellular apoptosis, is expressed by the normal ovarian epithelium. We analyzed the levels of Fas and soluble Fa s (sFas) expression in ovarian cancer tissue and determined the susceptibil ity of primary ovarian cancer cell (CSOC) cultures to Fas-mediated apoptosi s. Methods. Fas mRNA levels were detected by RT-PCR, and Fas protein levels we re determined by immunohistochemistry and Western blot analysis. Secreted s Fas levels were measured by ELISA. Localization of Fas to the cell surface was demonstrated by flow cytometry. The effect of Fas on cell proliferation was measured by MTT assay. Results. Intense Las staining was detected on the cell surface and in the c ytoplasm of ovarian carcinoma specimens. We also found that mean levels of sFas, which can function as a Fas agonist, were significantly increased in 18 sera from cancer patients (0.98 ng/ml) compared to those of 8 healthy in dividuals (0.61 ng/ml, P = 0.004). Fas mRNA and protein were expressed in a ll primary ovarian cancer cell cultures. Despite abundant Fas expression, C SOC cultures were significantly less sensitive to Fas-mediated apoptosis (1 1.3%) than primary cultures of normal ovarian epithelial cells (HOSE) (50.0 %) (P = 0.00001). The sFas level in CSOC-conditioned medium was minimal (0. 07 ng/ml) and not significantly different from that of HOSE-conditioned med ium (0.09 ng/ml). The small amount of sFas secreted by CSOC does not likely account for the observed resistance to Fas-mediated apoptosis. Conclusion. Decreased sensitivity to Fas-mediated apoptosis could contribut e to ovarian tumorigenesis through resistance to cytotoxic T lymphocyte-med iated cytotoxicity and may play a role in ovarian tumorigenesis. (C) 1999 A cademic Press.