Abbreviations used: bFGF, basic fibroblast growth factor; CPT-cAMP, 4-(8-chlorophenylthio)cyclic AMP; EGF, epidermal growth factor; ERK, extracellular signal-regulated kinase; GST, glutathione S-transferase; JNK, c-Jun N-terminal kinase; NGF, nerve growth factor; PACAP, pituitary adenylyl cyclase-activating peptide 1–38; PAGE, polyacrylamide gel electrophoresis; PI, phosphatidylinositol; SDS, sodium dodecyl sulfate; zVAD-FMK, benzyloxycarbonyl-Val-Ala-dl-Asp fluoromethyl ketone.
Abstract: Neurotrophic factors prevent apoptosis of PC12 cells in serum-free medium. The present study determines whether neurotrophic factors can prevent ceramide-induced apoptosis in PC12 cells and investigates the role that c-Jun N-terminal kinase (JNK) activation may play in this system. Ceramide-induced apoptosis was inhibited by nerve growth factor, basic fibroblast growth factor, pituitary adenylyl cyclase-activating peptide, 4-(8-chlorophenylthio)cyclic AMP, and the caspase inhibitor benzyloxycarbonyl-Val-Ala-dl-Asp fluoromethyl ketone (zVAD-FMK). It was surprising that inhibition of extracellular signal-regulated kinase and/or phosphatidylinositol 3-kinase did not markedly block the protective effects exerted by neurotrophic factors against ceramide-induced apoptosis, suggesting that neurotrophic factors can promote survival independently of these signaling pathways. Treatment of PC12 cells with ceramide resulted in a time-dependent increase in JNK activity. However, neither neurotrophic factors nor zVAD-FMK attenuated ceramide-stimulated JNK activation. Further experiments indicated that ceramide-induced apoptosis in PC12 cells requires new protein synthesis, and that nerve growth factor and zVAD-FMK can prevent apoptosis after JNK activity has been detected. These results indicate that ceramide-induced JNK activation is an early event and may be required for the expression of essential components of the apoptotic machinery. It is anticipated that neurotrophic factors inhibit ceramide-induced apoptosis by affecting signaling events downstream of JNK activation.