title: IGF-I stimulates intestinal muscle cell growth by activating distinct PI 3-kinase and MAP kinase pathways.
abstract: Insulin-like growth factor I (IGF-I), acting via its cognate receptor, plays an autocrine role in the regulation of growth of intestinal muscle cells. In the present study the signaling pathways mediating the growth effects of IGF-I were characterized in cultured human intestinal smooth muscle cells. Growth induced by a maximally effective concentration of IGF-I (100 nM), measured as [3H]thymidine incorporation, was only partially inhibited by LY-294002 [phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor] or PD-98059 [mitogen-activated protein (MAP) kinase kinase (MEK) inhibitor] (86 +/- 7% and 35 +/- 6% inhibition, respectively) alone but was abolished by the two combined (114 +/- 18% inhibition), implying the participation of both pathways. IGF-I elicited time- and concentration-dependent increases in PI 3-kinase activity. This effect was inhibited only by LY-294002 (89 +/- 12%). IGF-I elicited time- and concentration-dependent phosphorylation of p44/p42 MAP kinase and increased MAP kinase activity. These effects were inhibited only by PD-98059 (78 +/- 9% and 98 +/- 7%, respectively). We conclude that in human intestinal muscle cells IGF-I activates distinct PI 3-kinase and MAP kinase signaling pathways, which act in conjunction to mediate growth.
authors.affiliation: Department of Medicine, Medical College of Virginia Campus, Virginia Commonwealth University, Richmond, Virginia 23298-0711, USA.
authors.forename: J F
authors.initials: JF
authors.lastname: Kuemmerle
authors.forename: T L
authors.initials: TL
authors.lastname: Bushman
mesh_terms: D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D002867:Chromones / Q000494:pharmacology; D004247:DNA / Q000096:biosynthesis; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007583:Jejunum / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D007700:Kinetics; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D009025:Morpholines / Q000494:pharmacology; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013936:Thymidine / Q000378:metabolism; D013997:Time Factors
chemical_list: D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002867:Chromones; D004247:DNA; D004791:Enzyme Inhibitors; D005419:Flavonoids; D007334:Insulin-Like Growth Factor I; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D013936:Thymidine; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one