Structural analysis of the role of the beta 3 subunit of the alpha V beta 3 integrin in IGF-I signaling.
The disintegrin echistatin inhibits ligand occupancy of the alpha V beta 3 integrin and reduces Insulin-like growth factor I (IGF-I) stimulated migration, DNA synthesis, and receptor autophosphorylation in smooth muscle cells. This suggests that ligand occupancy of the alpha V beta 3 receptor is required for full activation of the IGF-I receptor. Transfection of the full-length beta 3 subunit into CHO cells that have no endogenous beta 3 and do not migrate in response to IGF-I was sufficient for IGF-I to stimulate migration of these anchorage dependent cells. In contrast, transfection of either of two truncated mutant forms of beta 3 (terminating at W(715) or E(731)) or a mutant with substitutions for Tyr(747) Tyr(759) (YY) into either CHO or into porcine smooth muscle cells did not restore the capacity of these cells to migrate across a surface in response to IGF-I. This effect was not due to loss of IGF-I receptor autophosphorylation since the response of the receptor to IGF-I was similar in cells expressing either the full-length or any of the mutant forms of the beta 3 subunit. Echistatin reduced IGF-I receptor phosphorylation in cells expressing the full-length or the YY mutant forms of beta 3 subunit, but it had no effect in cells expressing either of two truncated forms of beta 3. A cell-permeable peptide homologous to the C-terminal region of the beta 3 subunit (amino acids 747-762) reduced IGF-I stimulated migration and receptor autophosphorylation of non-transfected porcine smooth muscle cells. These results demonstrate that the full-length beta 3 with intact tyrosines at positions 747 and 759 is required for CHO cells to migrate in response to IGF-I. Furthermore, a region of critical amino acids between residues 742-762 is required for echistatin to induce its regulatory effect on receptor phosphorylation. Since the IGF-I receptor does not bind to alpha V beta 3 the results suggest that specific but distinct regions of the beta 3 subunit interact with intermediary proteins to facilitate IGF-I stimulated cell migration and echistatin induced inhibition of IGF-I signal transduction.
CB# 7170, Division of Endocrinology, University of North Carolina, Chapel Hill, NC 27599-7170, USA.
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Maile
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Badley-Clarke
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Clemmons
D000595:Amino Acid Sequence; D000818:Animals; D015703:Antigens, CD / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D016466:CHO Cells; D002465:Cell Movement; D006224:Cricetinae; D003593:Cytoplasm / Q000378:metabolism; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D015870:Gene Expression; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D039661:Integrin beta3; D036341:Intercellular Signaling Peptides and Proteins; D008969:Molecular Sequence Data; D010455:Peptides / Q000378:metabolism / Q000494:pharmacology; D010766:Phosphorylation; D010980:Platelet Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D019030:Receptors, Vitronectin / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*
D015703:Antigens, CD; D039661:Integrin beta3; D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; D010980:Platelet Membrane Glycoproteins; D019030:Receptors, Vitronectin; C057986:echistatin; D007334:Insulin-Like Growth Factor I; D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496050:PTK2 protein, human