Ceramide induces cell death in the human prostatic carcinoma cell lines PC3 and DU145 but does not seem to be involved in Fas-mediated apoptosis

Treatment of cells with synthetic C2-ceramide has been reported to induce a poptosis in several cell systems, and endogenously formed ceramide has been proposed to act as a second messenger, activating signaling pathways which contribute to the execution of apoptotic cell death after Fas ligation or tumor necrosis factor receptor-1 ligation. In this study, we examined the e ffect of exogenously administered C2-ceramide on the human prostatic carcin oma cell lines PC3 (Fas-sensitive) and DU145 (Fas-resistant). In both cell lines, C2-ceramide induced cell death in a dose-dependent manner, whereas a structural analog, C2-dihydroceramide, did not. The pan-caspase inhibitor zVAD-fmk did not prevent C2-ceramide-induced cell death but did prevent C2- ceramide-induced DNA fragmentation, indicating that apoptotic and non-apopt otic mechanisms are involved in C2-ceramide-induced death. Interestingly, c ycloheximide prevented C2-ceramide-induced DNA fragmentation, indicating th at ceramide-induced apoptosis in PC3 and DU145 requires new protein synthes is. In addition, because cycloheximide converts Fas-resistant DU145 to Fas- sensitive as assessed by DNA fragmentation, ceramide does not seem to play a major role in the Fas-mediated pathway in this cell line. We also determi ned the levels of endogenous sphingomyelin after Fas ligation in PC3. No de crease of sphingomyelin levels could be detected after Fas activation. We c onclude that sphingomyelinase-generated ceramide does not play a role in Fa s-mediated apoptosis in PC3, and that there are fundamental differences in the mechanisms of cell death induced by C2-ceramide and Fas ligation.