RESUMO
The mitogen-activated protein kinase p38 plays a critical role in inflammation, cell cycle progression, differentiation, and apoptosis. The activity of p38 is stimulated by a variety of extracellular stimuli, such as the proinflammatory cytokine tumor necrosis factor alpha (TNF-alpha), and subjected to regulation by other intracellular signaling pathways, including the cyclic AMP (cAMP) pathway. Yet the underlying mechanism by which cAMP inhibits p38 activation is unknown. Here we show that the induction of dynein light chain (DLC) by cAMP response element-binding protein (CREB) is required for cAMP-mediated inhibition of p38 activation. cAMP inhibits p38 activation via the protein kinase A-CREB pathway. The inhibition is mediated by the CREB target gene Dlc, whose protein product, DLC, interferes with the formation of the MKK3/6-p38 complex, thereby suppressing p38 phosphorylation activation by MKK3/6. The inhibition of p38 activation by cAMP leads to suppression of NF-kappaB activity and promotion of apoptosis in response to TNF-alpha. Thus, our results identify DLC as a novel inhibitor of the p38 pathway and provide a molecular mechanism by which cAMP suppresses p38 activation and promotes apoptosis.
Assuntos
Proteínas de Transporte/metabolismo , Proteína de Ligação ao Elemento de Resposta ao AMP Cíclico/metabolismo , AMP Cíclico/metabolismo , Proteínas de Drosophila/metabolismo , Proteínas Quinases p38 Ativadas por Mitógeno/antagonistas & inibidores , Animais , Apoptose/efeitos dos fármacos , Proteínas de Transporte/genética , Linhagem Celular , Proteínas Quinases Dependentes de AMP Cíclico/metabolismo , Proteínas de Drosophila/genética , Dineínas , Ativação Enzimática , Humanos , Sistema de Sinalização das MAP Quinases , Camundongos , Modelos Biológicos , NF-kappa B/metabolismo , Células NIH 3T3 , Fosforilação , Interferência de RNA , Ratos , Transcrição Gênica , Fator de Necrose Tumoral alfa/farmacologia , Proteínas Quinases p38 Ativadas por Mitógeno/metabolismoRESUMO
JNK has been suggested to be proapoptotic, antiapoptotic, or have no role in apoptosis depending on the cell type and stimulus used. The precise mechanism of JNK action, under conditions when it promotes cell survival, is not entirely clear. Here, we report that JNK is required for IL-3-mediated cell survival through phosphorylation and inactivation of the proapoptotic Bcl-2 family protein BAD. IL-3 withdrawal-induced apoptosis is promoted by inhibition of JNK but suppressed by expression of a constitutively active JNK. JNK phosphorylates BAD at threonine 201, thereby inhibiting BAD association with the antiapoptotic molecule BCL-X(L). IL-3 induces BAD phosphorylation at threonine 201, and replacement of threonine 201 by alanine generates a BAD mutant, which promotes IL-3 withdrawal-induced apoptosis. Thus, our results provide a molecular mechanism by which JNK contributes to cell survival.
