Regulation of the MAP kinase cascade in PC12 cells: B‐Raf activates MEK‐1 (MAP kinase or ERK kinase) and is inhibited by cAMP

FEBS Letters

Peraldi, P.²  Calleja, V.²  Van Obberghen, E.²  Calothy, G.¹  Frödin, M.²  Scimeca, J.-C.²  Barnier, J.V.¹  Filloux, C.² 

[1] CNRS URA 1443, Institut Curie, Université Paris II, 91905 Orsay Cédex, France;INSERM U 145, Faculté de Médecine, 06107 Nice Cédex 2, France

关键词: cAMP;    B-Raf;    MAP kinase;    MEK;    p21ras;    PC12 cell;    MAP kinase;    mitogen-activated protein kinase;    MEK;    MAP kinase or ERK kinase;    CPT-cAMP;    8-(4-chlorophenylthio)-cyclic-AMP;    NGF;    nerve growth factor;    MBP;    myelin basic protein;    PMA;    phorbol 12-myristate 13-acetate;    PKA;    cAMP-dependent protein kinase;    PKC;    protein kinase C;   

DOI  :  10.1016/0014-5793(94)01376-C

学科分类：生物化学/生物物理

来源: John Wiley & Sons Ltd.

【 摘 要 】

In PC12 cells, cAMP stimulates the MAP kinase pathway by an unknown mechanism. Firstly, we examined the role of calcium ion mobilization and of protein kinase C in cAMP-stimulated MAP kinase activation. We show that cAMP stimulates p44^mapk independently of these events. Secondly, we studied the role of B-Raf in this process. We observed that NGF, PMA and cAMP induce the phosphorylation of B-Raf as well as an upward shift in its electrophoretic mobility. We show that B-Raf is activated following NGF and PMA treatment of PC12 cells, and that it can phosphorylate and activate MEK-1. However, cAMP inhibits B-Raf autokinase activity as well as its ability to phosphorylate and activate MEK-1. This inhibition is likely to be due to a direct effect since we found that PKA phosphorylates B-Raf in vitro. Further, we show that B-Raf binds to p21^ras, but more important, this binding to p21^ras is virtually abolished with B-Raf from PC12 cells treated with CPT-cAMP. Hence, these data indicate that the PKA-mediated phosphorylation of B-Raf hampers its interaction with p21^ras, which is responsible for the PKA-mediated decrease in B-Raf activity. Finally, our work suggests that in PC12 cells, cAMP stimulates MAP kinase through the activation of an unidentified MEK kinase and/or the inhibition of a MEK phosphatase.

【 授权许可】

Unknown