Stimulation of the ERK pathway by GTP-loaded Rap1 requires the concomitant activation of Ras, protein kinase C, and protein kinase A in neuronal cells.
The small GTPases Ras or Rap1 were suggested to mediate the stimulatory effect of some G protein-coupled receptors on ERK activity in neuronal cells. Accordingly, we reported here that pituitary adenylate cyclase-activating polypeptide (PACAP), whose G protein-coupled receptor triggers neuronal differentiation of the PC12 cell line via ERK1/2 activation, transiently activated Ras and induced the sustained GTP loading of Rap1. Ras mediated peak stimulation of ERK by PACAP, whereas Rap1 was necessary for the sustained activation phase. However, PACAP-induced GTP-loading of Rap1 was not sufficient to account for ERK activation by PACAP because 1) PACAP-elicited Rap1 GTP-loading depended only on phospholipase C, whereas maximal stimulation of ERK by PACAP also required the activity of protein kinase A (PKA), protein kinase C (PKC), and calcium-dependent signaling; and 2) constitutively active mutants of Rap1, Rap1A-V12, and Rap1B-V12 only minimally stimulated the ERK pathway compared with Ras-V12. The effect of Rap1A-V12 was dramatically potentiated by the concurrent activation of PKC, the cAMP pathway, and Ras, and this potentiation was blocked by dominant-negative mutants of Ras and Raf. Thus, this set of data indicated that GPCR-elicited GTP loading of Rap1 was not sufficient to stimulate efficiently ERK in PC12 cells and required the permissive co-stimulation of PKA, PKC, or Ras.
Bouschet
Tristan
T
UPR 9023 CNRS, CCIPE-141, Rue de la Cardonille, 34094 Montpellier Cedex, France.
Perez
Virgili
V
Fernandez
Céline
C
Bockaert
Joël
J
Eychene
Alain
A
Journot
Laurent
L
D000818:Animals; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004789:Enzyme Activation; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism; D016716:PC12 Cells; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D015398:Signal Transduction; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism*; D018631:ras Proteins / Q000378:metabolism*
D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D020928:Mitogen-Activated Protein Kinases; D020827:rap1 GTP-Binding Proteins; D018631:ras Proteins