Ceramide and cyclic adenosine monophosphate (cAMP) induce cAMP response element binding protein phosphorylation via distinct signaling pathways whilehaving opposite effects on myeloid cell survival

The role of ceramide as a second messenger is a subject of great interest, particularly since it is implicated in signaling in response to inflammator y cytokines. Ceramide induces apoptosis in both cytokine-dependent MC/9 cel ls and factor-independent U937 cells. Elevation of cyclic adenosine monopho sphate (cAMP) levels inhibits apoptosis induced by ceramide and several oth er treatments. One target of cAMP-mediated signaling is the transcription f actor CREB (cAMP response element binding protein), and recently CREB phosp horylation at an activating site has been shown to also be mediated by a ca scade involving p38 mitogen-activated protein kinase (MAPK), one of the str ess-activated MAP kinases. Because no role for p38 MAPK in apoptosis has be en firmly established, we examined the relationship between p38 MAPK and CR EB phosphorylation under various conditions. Ceramide, or sphingomyelinase, like tumor necrosis factor-alpha (TNF-alpha) or the hematopoietic growth f actor, interleukin-3 (IL-3), was shown to activate p38 MAPK, which in turn activated MAPKAP kinase-2, Each of these treatments led to phosphorylation of CREB (and the related factor ATF-1). A selective p38 MAPK inhibitor, SB2 03580, blocked TNF-alpha- or ceramide-induced CREB phosphorylation, but had no effect on the induction of apoptosis mediated by these agents, The prot ective agents cAMP and IL-3 also led to CREB phosphorylation, but this effe ct was independent of p38 MAPK, even though IL-3 was shown to activate both p38 MAPK and MAPKAP kinase-2. Therefore, the opposing effects on apoptosis observed with cAMP and IL-3, compared with ceramide and TNF-alpha could no t be explained on the basis of phosphorylation of CREB, In addition, becaus e SB203580 had no effect of TNF-alpha or ceramide-induced apoptosis, our re sults strongly argue against a role for p38 MAPK in the induction of TNF-al pha- or ceramide-induced apoptosis, (C) 1999 by The American Society of Hem atology.