Phosphatidylinositol 3-kinase is required for insulin-like growth factor-I-induced vascular smooth muscle cell proliferation and migration.
Insulin-like growth factor-I (IGF-I) plays an important role in regulating vascular smooth muscle cell (VSMC) proliferation and directed migration. The mitogenic and chemotactic actions of IGF-I are mediated through the IGF-I receptor, but how the activation of the IGF-I receptor leads to these biological responses is poorly understood. In this study, we examined the role of phosphatidylinositol 3-kinase (PI3 kinase) in mediating the mitogenic and chemotactic signals of IGF-I. IGF-I treatment resulted in a significant increase in phosphotyrosine-associated PI3 kinase activity in cultured primary VSMCs. To determine whether insulin receptor substrate (IRS)-1, -2, or both are involved in IGF-I signaling in VSMCs, cell lysates were immunoprecipitated with either an anti-IRS-1 or an anti-IRS-2 antibody, and the associated PI3 kinase activity was determined. IGF-I stimulation resulted in a significant increase in IRS-1- but not IRS-2-associated PI3 kinase activity, suggesting that IGF-I primarily utilizes IRS-1 to transmit its signal in VSMCs. The IGF-I-induced increase in IRS-I-associated PI3 kinase activity was concentration dependent. At the maximum concentration (50 ng/mL), IGF-I induced a 60-fold increase. This activation occurred within 5 minutes and was sustained at high levels for at least 6 hours. IGF-I also caused a concentration-dependent and long-lasting activation of protein kinase B (PKB/Akt). Inhibition of PI3 kinase activation by LY294002 or wortmannin abolished IGF-I-stimulated VSMC proliferation and reduced IGF-I-directed VSMC migration by approximately 60%. These results indicate that activation of PI3 kinase is required for both IGF-I-induced VSMC proliferation and migration.
Duan
C
C
Department of Biology, University of Michigan, Ann Arbor, Mich. 48109-1048, USA. cduan@umich.edu
Bauchat
J R
JR
Hsieh
T
T
D000818:Animals; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002465:Cell Movement / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D055504:Insulin Receptor Substrate Proteins; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology / Q000502:physiology*; D047908:Intracellular Signaling Peptides and Proteins; D009131:Muscle, Smooth, Vascular / Q000166:cytology* / Q000187:drug effects; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D010750:Phosphoproteins / Q000502:physiology; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D013552:Swine; D013997:Time Factors
D055504:Insulin Receptor Substrate Proteins; D007334:Insulin-Like Growth Factor I; D047908:Intracellular Signaling Peptides and Proteins; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt