Activation of Fas ligand/receptor system kills ovarian cancer cell lines by an apoptotic mechanism.

The majority of ovarian cancers originate from the surface epithelium of the ovary and from inclusion cysts derived from the epithelium that becomes sequestered in the stroma. To identify naturally occurring ligands that could activate mechanisms by which these ovarian neoplasms could be eliminated, we have examined the ability of anti-Fas mAb to induce apoptosis in two cell lines, HEY and Caov-3, derived from ovarian carcinomas of surface epithelial origin. Treatment of each cell line with anti-Fas mAb caused chromatin condensation, nuclear segmentation, and apoptotic body formation, indicative of apoptosis. Furthermore we have shown that anti-Fas mAb activates the sphingomyelin-ceramide signal transduction pathway. Sphingomyelin levels were measured by normal-phase high-performance liquid chromatography interfaced with electrospray mass spectrometry. The six most abundant sphingomyelin species identified in Caov-3 cells were 34:1 (d18:1/16:0), 36:1 (d18:1/18:0), 40:1 (d18:1/22:0), 41:1 (d18:1/23:0), 42:1 (d18:1/24:0), and 42:2 (d18:1/24:1). Treatment of Caov-3 cells for 30 min caused a 40% decrease in the total sphingomyelin content. Specifically three of these species, 34:1, 40:1, and 42:2, were reduced to 44, 70, and 54% of control values, respectively. The decrease was attributed to the hydrolysis of sphingomyelin. Treatment of these cell lines with ceramide, a product of sphingomyelin hydrolysis, using a cell-permeable synthetic ceramide analogue C2-ceramide, also caused the above cells to undergo apoptosis. Thus, the Fas ligand/receptor system, acting through the sphingomyelin-ceramide pathway, provides a mechanism by which ovarian surface epithelial cancer cells can be induced to undergo apoptosis.