Activation of the sphingomyelinase ceramide signal transduction pathway ininsulin-secreting beta-cells - Role in cytokine-induced beta-cell death

mediate interleukin-1-induced beta-cell death (Welsh, N: Interleuken-1 beta -induced ceramide and diacylglycerol generation may lead to activation of t he c-Jun NH2-terminal kinase and the transcription factor ATF-2 in the insu lin-producing cell line RINm5F. J Biol Chem 271: 8307-8312, 1996). In this report, we have examined this pathway in more detail. Culture of beta-TC3 c ells with 25 mu mol/l ceramide analogs (N-acetyl- and N-hexanoylsphingosine ) for 72 h did not significantly affect glucose- and carbachol-induced insu lin secretion. Dihydroceramide (N-acetyl- or N-hexanoylsphinganine), a stru cturally similar analog, had no effect on agonist-induced secretion. Howeve r, ceramide analogs both time- and dose-dependently decreased cell viabilit y, while the dihydroceramide analog had no effect. The ceramide effect on c ell viability mimicked the effect of the cytokines TNF-alpha, IL-1 beta, an d IFN-gamma, reported stimulators of sphingomyelin hydrolysis. Cytokines, h owever, failed to stimulate sphingomyelin metabolism. Furthermore, using tw o different methods to quantitate ceramide, cytokines failed to cause an in crease in beta-cell ceramide content versus unstimulated or time-matched ve hicle controls. Taken together, these data suggest that although ceramide a nalogs mimic the cytotoxic effect of cytokines, activation of the sphingomy elin/ceramide signaling pathway is not involved in cytokine-induced beta-ce ll death.