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

TY - JOUR

T1 - Regulation of the MAP kinase cascade in PC12 cells: B-Raf activates MEK-1 (MAP kinase or ERK kinase) and is inhibited by cAMP.

AU - Peraldi, P

AU - Frödin, M

AU - Barnier, J V

AU - Calleja, V

AU - Scimeca, J C

AU - Filloux, C

AU - Calothy, G

AU - Van Obberghen, E

N1 - Keywords: Animals; Calcium-Calmodulin-Dependent Protein Kinases; Cyclic AMP; Enzyme Activation; MAP Kinase Kinase 1; Mitogen-Activated Protein Kinase 3; Mitogen-Activated Protein Kinase Kinases; Mitogen-Activated Protein Kinases; PC12 Cells; Phosphorylation; Protein-Serine-Threonine Kinases; Protein-Tyrosine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-raf; Rats; Thionucleotides

PY - 1995

Y1 - 1995

N2 - 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 p44mapk 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 p21ras, but more important, this binding to p21ras 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 p21ras, 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.

AB - 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 p44mapk 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 p21ras, but more important, this binding to p21ras 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 p21ras, 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.

M3 - Journal article

C2 - 7835430

SN - 0014-5793

VL - 357

SP - 290

EP - 296

JO - FEBS Letters

JF - FEBS Letters

IS - 3

ER -