Ceramide-induced apoptosis in cortical neurons is mediated by an increase in p38 phosphorylation and not by the decrease in ERK phosphorylation

Ceramide, the central molecule of the sphingomyelin pathway, serves as a se cond messenger for cellular functions ranging from proliferation and differ entiation to growth arrest and apoptosis. In this study we show that c(2)-c eramide induces apoptosis in primary cortical neuron cultures and that this effect correlates with differential modulation of mitogen-activated protei n kinase (MAPK) cascades. Phosphorylation of extracellular signal-regulated kinases (ERKs) and their upstream activators MAPK kinases (MEKs), as measu red by immunoblotting is rapidly decreased by c(2)-ceramide. However, the M EK inhibitor PD98059 alone does not induce apoptosis and in combination wit h c(2)-ceramide it does not modify c(2)-ceramide-induced apoptosis. Treatme nt with c(2)-ceramide increases p38 and c-jun N-terminal kinase (JNK) phosp horylation before and during caspase-3 activation. The p38 inhibitor SB2035 80 partially protects cortical neurons against ca-ceramide-induced apoptosi s, implicating the p38 pathway in this process. The c(2)-ceramide treatment also increases levels of c-jun, c-fos and p53 mRNA in primary cortical neu ron cultures, but this is independent of p38 activation. Our study further elucidates the time-courses of MAPK cascade modulation, acid of c-jun, c-fo s and p53 activation during c(2)-ceramide-induced neuronal apoptosis. It re veals that one of the activated kinases, p38, is necessary for this apoptos is.