title: Blocking ligand occupancy of the alphaVbeta3 integrin inhibits insulin-like growth factor I signaling in vascular smooth muscle cells.
abstract: Blocking alphaVbeta3 integrin occupancy results in attenuation of the cellular migration response to insulin-like growth factor I (IGF-I). To determine whether integrin antagonists alter other IGF-I-stimulated biologic actions, quiescent smooth muscle cells (SMCs) were exposed to echistatin and their ability to respond to IGF-I was determined. Echistatin (10(-7) M) inhibited IGF-I-stimulated DNA synthesis by 80%, and the protein synthesis response also was inhibited. Therefore blocking occupancy of alphaVbeta3 inhibited multiple target cell actions of IGF-I. To determine whether blocking alphaVbeta3 occupancy could alter IGF-I receptor-mediated signal transduction, the ability of IGF-I to stimulate phosphorylation of insulin receptor substrate-1 (IRS-1) was analyzed. A 10-min exposure to 100 ng/ml of IGF-I resulted in a substantial increase in phosphorylated IRS-1, and echistatin (10(-7) M) blocked the IGF-I-induced IRS-1 phosphorylation response. Echistatin also attenuated downstream signaling because the capacity of the p85 subunit of phosphatidylinositol-3 kinase (PI-3 kinase) to bind to IRS-1 was blocked. In contrast, exposure of SMCs to vitronectin (1.0 micrograms/cm2) or thrombospondin (0.25 micrograms/cm2), two known ligands for alphaVbeta3, resulted in enhancement of the IGF-I-stimulated IRS-1 response. To determine whether these effects were caused by alterations in receptor kinase activity, the IGF-I receptor was immunoprecipitated and then analyzed for phosphotyrosine. Echistatin (10(-7) M) significantly reduced IGF-I-stimulated tyrosine phosphorylation of the IGF-I receptor beta subunit. We conclude that occupancy of the alphaVbeta3 integrin is necessary for IGF-I to fully activate the kinase activity of the IGF-I receptor and phosphorylate IRS-1. Activation of the alphaVbeta3 receptor results in an interaction with the IGF-I signal transduction pathway, which modulates SMCs responsiveness to IGF-I.
authors.affiliation: Department of Medicine, University of North Carolina School of Medicine, Chapel Hill, NC 27599, USA.
authors.forename: B
authors.initials: B
authors.lastname: Zheng
authors.forename: D R
authors.initials: DR
authors.lastname: Clemmons
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D002465:Cell Movement / Q000187:drug effects; D016326:Extracellular Matrix Proteins / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D036341:Intercellular Signaling Peptides and Proteins; D008024:Ligands; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D019000:Phosphotyrosine / Q000032:analysis; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D019030:Receptors, Vitronectin / Q000037:antagonists & inhibitors*; D015398:Signal Transduction / Q000187:drug effects; D013552:Swine; D019699:Thrombospondins / Q000494:pharmacology; D013936:Thymidine / Q000378:metabolism; D019096:Vitronectin / Q000494:pharmacology
chemical_list: D016326:Extracellular Matrix Proteins; D055504:Insulin Receptor Substrate Proteins; D007334:Insulin-Like Growth Factor I; D036341:Intercellular Signaling Peptides and Proteins; D008024:Ligands; D019384:Nucleic Acid Synthesis Inhibitors; D010455:Peptides; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D019000:Phosphotyrosine; D010982:Platelet-Derived Growth Factor; D019030:Receptors, Vitronectin; D019699:Thrombospondins; D013936:Thymidine; D019096:Vitronectin; C057986:echistatin