Raf-1 is activated by the p38 mitogen-activated protein kinase inhibitor, SB203580.
SB203580 (4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imi dazole) is widely used as a specific inhibitor of p38 mitogen-activated protein kinase (MAPK). Here, we report that SB203580 activates the serine/threonine kinase Raf-1 in quiescent smooth muscle cells in a dose-dependent fashion. The concentrations of SB203580 required lie above those necessary to inhibit p38 MAPK and we were unable to detect basal levels of active p38 MAPK. SB203580 does not directly activate Raf-1 in vitro, and fails to activate Ras, MEK, and ERK in intact cells. In vitro, however, SB203580-stimulated Raf-1 activates MEK1 in a coupled assay. We conclude that activation of Raf-1 by SB203580 is not mediated by an inhibition of p38 MAPK, is Ras-independent, and is uncoupled from MEK/ERK signaling.
Department of Surgery, University of Washington, Seattle 98195-6410, USA. kalmes@u.washington.edu
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Clowes
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D016475:3T3 Cells; D000818:Animals; D001011:Aorta; D000077214:Becaplermin; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism / Q000502:physiology; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007093:Imidazoles / Q000378:metabolism / Q000494:pharmacology*; D007213:Indomethacin / Q000494:pharmacology; D048369:MAP Kinase Kinase 1; D051379:Mice; D020929:Mitogen-Activated Protein Kinase Kinases; D020928:Mitogen-Activated Protein Kinases; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects; D015689:Oncogene Protein p21(ras) / Q000378:metabolism; D010215:Papio; D010766:Phosphorylation / Q000187:drug effects; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D011233:Precipitin Tests; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism*; D020574:Proto-Oncogene Proteins c-sis; D011725:Pyridines / Q000378:metabolism / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects; D048051:p38 Mitogen-Activated Protein Kinases
D004791:Enzyme Inhibitors; D007093:Imidazoles; D010982:Platelet-Derived Growth Factor; D020574:Proto-Oncogene Proteins c-sis; D011725:Pyridines; D000077214:Becaplermin; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; C482127:Map2k1 protein, mouse; D020929:Mitogen-Activated Protein Kinase Kinases; D015689:Oncogene Protein p21(ras); C093642:SB 203580; D007213:Indomethacin