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

We have previously seen that protein kinase C (PKC) ε induces neurite outgrowth and that PKCδ and PKCθ 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 PKCε and, in cells overexpressing PKCδ or PKCθ, 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 PKCε and the isolated regulatory domain of PKCε from the cytosol to the perinuclear region. In contrast, neither the localization of PKCδ nor of PKCθ 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 PKCε and thus identify a functional consequence of ceramide effects on PKCε localization.