Alpha-thrombin-mediated phosphatidylinositol 3-kinase activation through release of Gbetagamma dimers from Galphaq and Galphai2.
Chinese hamster embryonic fibroblasts (IIC9 cells) express the Galpha subunits Galphas, Galphai2, Galphai3, Galphao, Galpha(q/11), and Galpha13. Consistent with reports in other cell types, alpha-thrombin stimulates a subset of the expressed G proteins in IIC9 cells, namely Gi2, G13, and Gq as measured by an in vitro membrane [35S]guanosine 5'-O-(3-thio)triphosphate binding assay. Using specific Galpha peptides, which block coupling of G-protein receptors to selective G proteins, as well as dominant negative xanthine nucleotide-binding Galpha mutants, we show that activation of the phosphatidylinositol 3-kinase/Akt pathway is dependent on Gq and Gi2. To examine the role of the two G proteins, we examined the events upstream of PI 3-kinase. The activation of the PI 3-kinase/Akt pathway by alpha-thrombin in IIC9 cells is blocked by the expression of dominant negative Ras and beta-arrestin1 (Phillips-Mason, P. J., Raben, D. M., and Baldassare, J. J. (2000) J. Biol. Chem. 275, 18046-18053, and Goel, R., Phillips-Mason, P. J., Raben, D. M., and Baldassare, J. J. (2002) J. Biol. Chem. 277, 18640-18648), indicating a role for Ras and beta-arrestin1. Interestingly, inhibition of Gi2 and Gq activation blocks Ras activation and beta-arrestin1 membrane translocation, respectively. Furthermore, expression of the Gbetagamma sequestrant, alpha-transducin, inhibits both Ras activation and membrane translocation of beta-arrestin1, suggesting that Gbetagamma dimers from Galphai2 and Galphaq activate different effectors to coordinately regulate the PI 3-kinase/Akt pathway.
Goel
Reema
R
Department of Pharmacological and Physiological Sciences, St. Louis University Medical School, St. Louis, Missouri 63104, USA.
Phillips-Mason
Polly J
PJ
Gardner
Alice
A
Raben
Daniel M
DM
Baldassare
Joseph J
JJ
D000244:Adenosine Diphosphate / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D019390:Arrestins / Q000378:metabolism; D015153:Blotting, Western; D002462:Cell Membrane / Q000378:metabolism; D006224:Cricetinae; D018076:DNA, Complementary / Q000378:metabolism; D019281:Dimerization; D004789:Enzyme Activation; D005347:Fibroblasts / Q000378:metabolism; D051960:GTP-Binding Protein alpha Subunit, Gi2; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000737:chemistry*; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000737:chemistry*; D044387:GTP-Binding Protein beta Subunits / Q000737:chemistry*; D044388:GTP-Binding Protein gamma Subunits / Q000737:chemistry*; D005799:Genes, Dominant; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D018613:Microscopy, Confocal; D008954:Models, Biological; D009154:Mutation; D010455:Peptides / Q000737:chemistry; D037342:Pertussis Toxin / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D011518:Proto-Oncogene Proteins / Q000737:chemistry*; D012266:Ribose / Q000737:chemistry; D015398:Signal Transduction; D013917:Thrombin / Q000737:chemistry / Q000378:metabolism*; D015293:Transducin / Q000378:metabolism; D014162:Transfection; D019820:Xanthine / Q000378:metabolism; D000071557:beta-Arrestins
D019390:Arrestins; D018076:DNA, Complementary; C118981:G-protein Beta gamma; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D010455:Peptides; D011518:Proto-Oncogene Proteins; D000071557:beta-Arrestins; D019820:Xanthine; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D000244:Adenosine Diphosphate; D012266:Ribose; D037342:Pertussis Toxin; D019869:Phosphatidylinositol 3-Kinases; D013917:Thrombin; D051960:GTP-Binding Protein alpha Subunit, Gi2; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D015293:Transducin