Galpha12 stimulates c-Jun NH2-terminal kinase through the small G proteins Ras and Rac.
The pertussis toxin (PTX) insensitive heterotrimeric G protein G12 has been implicated in mitogenesis and transformation, but its direct effectors remain unknown. To define potential signaling pathways utilized by G12, we expressed an activated mutant of its alpha subunit, Galpha12(Q229L), in HEK293 cells and examined its effects on Ras and mitogen-activated protein kinases (MAPKs). Transient expression of activated Galpha12 increased the percentage of Ras in the active, GTP-bound state, stimulated c-Jun NH2-terminal kinase (JNK) activity, and enhanced the transcriptional activity of c-Jun. Dominant negative Ras (N17Ras) inhibited Galpha12-mediated JNK activation in NIH3T3 cells but failed to do so in HEK293 cells. In contrast, dominant negative Rac (N17Rac1) inhibited JNK activation by Galpha12 in HEK293 cells as well as three other cell lines. In 1321N1 cells, where thrombin stimulates G12-dependent mitogenesis, coexpression of N17Rac1 or a dominant negative mutant of MEKK1 (MEKKDelta(K432M)) inhibits c-Jun/AP-1 sensitive reporter gene expression stimulated by thrombin or Galpha12. These data demonstrate that the alpha subunit of the heterotrimeric G protein G12, like tyrosine kinase growth factor receptors, activates Ras and recruits a signal transduction pathway involving the small GTP-binding protein Rac that leads to JNK activation.
Collins
L R
LR
Department of Pharmacology, University of California at San Diego, La Jolla, California 92093-0636, USA.
Minden
A
A
Karin
M
M
Brown
J H
JH
D016475:3T3 Cells; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002455:Cell Division; D002460:Cell Line; D002522:Chlorocebus aethiops; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000096:biosynthesis / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases; D007668:Kidney; D048728:MAP Kinase Kinase Kinase 1; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000096:biosynthesis / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D009419:Nerve Tissue Proteins / Q000096:biosynthesis / Q000378:metabolism; D017354:Point Mutation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D014162:Transfection; D020744:rac GTP-Binding Proteins; D018631:ras Proteins / Q000378:metabolism*
D009419:Nerve Tissue Proteins; D011994:Recombinant Proteins; D017346:Protein Serine-Threonine Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048728:MAP Kinase Kinase Kinase 1; C482576:MAP3K1 protein, human; C482578:Map3k1 protein, mouse; D019204:GTP-Binding Proteins; D020744:rac GTP-Binding Proteins; D018631:ras Proteins