Ceramide influences neurite outgrowth and neuroblastoma cell apoptosis regulated by novel protein kinase C isoforms

We have previously seen that protein kinase C (PKC) epsilon induces neurite outgrowth and that PKCdelta and PKCtheta elicit apoptosis in neuroblastoma cells. In this study we investigate the effects of cell-permeable C-2-ceramide on these events in SK-N-BE(2) neuroblastoma cells. C-2-ceramide abolishes neurite formation induced by overexpression of PKCepsilon and, in cells overexpressing PKCdelta or PKCtheta, ceramide treatment leads to apoptosis. Exposure to C-2-ceramide also suppressed neurite outgrowth induced by retinoic acid, but ceramide did not abrogate neurite induction by treatment with the ROCK inhibitor Y-27632, demonstrating that C-2-ceramide is not a general inhibitor of neurite outgrowth. The neurite-suppressing effect occurs independently of cell-death. Furthermore, C-2-ceramide relocated PKCepsilon and the isolated regulatory domain of PKCepsilon from the cytosol to the perinuclear region. In contrast, neither the localization of PKCdelta nor of PKCtheta was affected by C-2-ceramide. Taken together, the data indicate that the neurite-inhibiting effect of C-2-ceramide treatment may be caused by a re-localization of PKCepsilon and thus identify a functional consequence of ceramide effects on PKCepsilon localization.