p42/mitogen-activated protein kinase as a converging target for different growth factor signaling pathways: use of pertussis toxin as a discrimination factor.
Mitogen-activated protein (MAP) kinase is a 42-kDa serine/threonine-specific protein kinase that requires phosphorylation on both tyrosine and threonine residues for activity. This enzyme is rapidly and transiently activated in quiescent cells after addition of various agonists, including insulin, epidermal growth factor, platelet-derived growth factor, and phorbol esters. We show here that addition of the growth factors thrombin or basic fibroblast growth factor to CCL39 fibroblasts rapidly induces tyrosine phosphorylation of the p42 MAP kinase protein and concomitantly stimulates MAP kinase enzymatic activity. To elucidate the signaling pathways utilized in this activation, we took advantage of the sensitivity of CCL39 cells to the toxin of bordetella pertussis, which ADP-ribosylates two Gi proteins in this cell system. We show that pretreatment of cells with the toxin inhibited thrombin stimulation of MAP kinase by greater than 75% but had no detectable effect on the stimulation induced by basic fibroblast growth factor. We also demonstrate that these two growth factors that synergize for mitogenicity are able to cooperate in activation of MAP kinase and that this synergism is partially sensitive to pertussis toxin. Finally, we describe a 44-kDa protein, the tyrosine phosphorylation of which appears to be coregulated with p42 MAP kinase. We conclude that p42 MAP kinase (and the pp44 protein) are at or are downstream from a point of convergence of two different receptor-induced signaling pathways and might well play a key role in integrating those signals.
L'Allemain
G
G
Department of Microbiology, University of Virginia Health Sciences Center, Charlottesville 22908.
Pouyssegur
J
J
Weber
M J
MJ
D000818:Animals; D002460:Cell Line; D006224:Cricetinae; D004789:Enzyme Activation / Q000187:drug effects; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology; D019950:Mitogen-Activated Protein Kinase 1; D037342:Pertussis Toxin; D010766:Phosphorylation / Q000187:drug effects; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases; D015398:Signal Transduction / Q000187:drug effects; D013917:Thrombin / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D014443:Tyrosine / Q000378:metabolism; D010566:Virulence Factors, Bordetella / Q000494:pharmacology*
D010982:Platelet-Derived Growth Factor; D010566:Virulence Factors, Bordetella; D016222:Fibroblast Growth Factor 2; D014443:Tyrosine; D004815:Epidermal Growth Factor; D037342:Pertussis Toxin; D011494:Protein Kinases; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D019950:Mitogen-Activated Protein Kinase 1; D013917:Thrombin