Primary ovarian cancer cultures are resistant to Fas-mediated apoptosis.
OBJECTIVE
Fas, a primary mediator of cellular apoptosis, is expressed by the normal ovarian epithelium. We analyzed the levels of Fas and soluble Fas (sFas) expression in ovarian cancer tissue and determined the susceptibility of primary ovarian cancer cell (CSOC) cultures to Fas-mediated apoptosis.


METHODS
Fas mRNA levels were detected by RT-PCR, and Fas protein levels were determined by immunohistochemistry and Western blot analysis. Secreted sFas 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 Fas staining was detected on the cell surface and in the cytoplasm 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 individuals (0.61 ng/ml, P = 0.004). Fas mRNA and protein were expressed in all primary ovarian cancer cell cultures. Despite abundant Fas expression, CSOC cultures were significantly less sensitive to Fas-mediated apoptosis (11.3%) 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 medium (0. 09 ng/ml). The small amount of sFas secreted by CSOC does not likely account for the observed resistance to Fas-mediated apoptosis.


CONCLUSIONS
Decreased sensitivity to Fas-mediated apoptosis could contribute to ovarian tumorigenesis through resistance to cytotoxic T lymphocyte-mediated cytotoxicity and may play a role in ovarian tumorigenesis.
Department of Obstetrics and Gynecology, The Burns and Allen Research Institute, Los Angeles, California, 90048, USA.
R L
RL
Baldwin
H
H
Tran
B Y
BY
Karlan
D017209:Apoptosis; D017077:Culture Media, Conditioned; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008875:Middle Aged; D010051:Ovarian Neoplasms / Q000473:pathology*; D018124:Receptors, Tumor Necrosis Factor / Q000096:biosynthesis / Q000502:physiology*; D014407:Tumor Cells, Cultured; D019014:fas Receptor / Q000096:biosynthesis / Q000502:physiology*
D017077:Culture Media, Conditioned; D018124:Receptors, Tumor Necrosis Factor; D019014:fas Receptor