Coupling of the insulin-like growth factor-I receptor tyrosine kinase to Gi2 in human intestinal smooth muscle: Gbetagamma -dependent mitogen-activated protein kinase activation and growth.
Endogenous insulin-like growth factor-1 (IGF-I) stimulates growth of cultured human intestinal smooth muscle by activating distinct mitogen-activated protein (MAP) kinase-dependent and phosphatidylinositol 3-kinase-dependent signaling pathways. In Rat1 and Balb/c3T3 fibroblasts and in neurons the IGF-I receptor is coupled to an inhibitory G protein, G(i), which mediates G(beta)gamma-dependent MAP kinase activation. The present study determined whether in normal human intestinal smooth muscle cells the IGF-I receptor activates a heterotrimeric G protein and the role of G protein activation in mediating IGF-I-induced growth. IGF-I elicited IGF-I receptor tyrosine phosphorylation, resulting in the specific activation of G(i2). G(beta)gamma subunits selectively mediated IGF-I-dependent MAP kinase activation; G(alpha)i2 subunits selectively mediated IGF-I-dependent inhibition of adenylyl cyclase activity. IGF-I-stimulated MAP kinase activation and growth were inhibited by pertussis toxin, an inhibitor of G(i)/G(o) activation. Cyclic AMP inhibits growth of human intestinal muscle cells. IGF-I inhibited both basal and forskolin-stimulated cAMP levels. This inhibition was attenuated in the presence of pertussis toxin. IGF-I stimulated phosphatidylinositol 3-kinase activation, in contrast to MAP kinase activation, occurred independently of G(i2) activation. These data suggest that IGF-I specifically activates G(i2), resulting in concurrent G(beta)gamma-dependent stimulation of MAP kinase activity and growth, and G(alpha)i2-dependent inhibition of cAMP levels resulting in disinhibition of cAMP-mediated growth suppression.
Kuemmerle
J F
JF
Departments of Medicine and Physiology, Medical College of Virginia of Virginia Commonwealth University, Richmond, Virginia 23298, USA. jkuemmerle@hsc.vcu.edu
Murthy
K S
KS
D037361:Adenylate Cyclase Toxin; D000262:Adenylyl Cyclases / Q000378:metabolism; D002455:Cell Division; D002478:Cells, Cultured; D002867:Chromones / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D051960:GTP-Binding Protein alpha Subunit, Gi2; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism*; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism; D006801:Humans; D007335:Insulin-Like Growth Factor II / Q000378:metabolism; D007413:Intestinal Mucosa / Q000378:metabolism*; D020935:MAP Kinase Signaling System; D009025:Morpholines / Q000494:pharmacology; D009130:Muscle, Smooth / Q000378:metabolism*; D037342:Pertussis Toxin; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D013997:Time Factors; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D037361:Adenylate Cyclase Toxin; D002867:Chromones; D004791:Enzyme Inhibitors; D005419:Flavonoids; C118981:G-protein Beta gamma; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D009025:Morpholines; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins; D010566:Virulence Factors, Bordetella; D005576:Colforsin; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D007335:Insulin-Like Growth Factor II; D000242:Cyclic AMP; D037342:Pertussis Toxin; D019869:Phosphatidylinositol 3-Kinases; D011505:Protein-Tyrosine Kinases; D017526:Receptor, IGF Type 1; C498015:GNAI2 protein, human; D051960:GTP-Binding Protein alpha Subunit, Gi2; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D020962:Heterotrimeric GTP-Binding Proteins; D000262:Adenylyl Cyclases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one