NEUROTROPHIC FACTORS PREVENT CERAMIDE-INDUCED APOPTOSIS DOWNSTREAM OFC-JUN N-TERMINAL KINASE ACTIVATION IN PC12 CELLS

Neurotrophic factors prevent apoptosis of PC12 cells in serum-free med ium, The present study determines whether neurotrophic factors can pre vent ceramide-induced apoptosis in PC12 cells and investigates the rol e that c-Jun N-terminal kinase (JNK) activation may play in this syste m. Ceramide-induced apoptosis was inhibited by nerve growth factor, ba sic fibroblast growth factor, pituitary adenylyl cyclase-activating pe ptide, 4- (8-chlorophenylthio) cyclic AMP, and the caspase inhibitor b enzyloxycarbonyl-val-Ala-DL-Asp fluoromethyl ketone (zVAD-FMK). It was surprising that inhibition of extracellular signal-regulated kinase a nd/or phosphatidylinositol 3-kinase did not markedly block the protect ive effects exerted by neurotrophic factors against ceramide-induced a poptosis, suggesting that neurotrophic factors can promote survival in dependently of these signaling pathways. Treatment of PC12 cells with ceramide resulted in a time-dependent increase in JNK activity. Howeve r, neither neurotrophic factors nor zVAD-FMK attenuated ceramide-stimu lated JNK activation. Further experiments indicated that ceramide-indu ced apoptosis in PC12 cells requires new protein synthesis, and that n erve growth factor and zVAD-FMK can prevent apoptosis after JNK activi ty has been detected. These results indicate that ceramide-induced JNK activation is an early event and may be required for the expression o f essential components of the apoptotic machinery. It is anticipated t hat neurotrophic factors inhibit ceramide-induced apoptosis by affecti ng signaling events downstream of JNK activation.