title: Modulation of integrin antagonist signaling by ligand binding of the heparin-binding domain of vitronectin to the alphaVbeta3 integrin.
abstract: The interaction between the arginine glycine and aspartic acid motif (RGD) of integrin ligands such as vitronectin and the integrin receptor alphaVbeta3 in mediating cell attachment has been well described. Similarly, the ability of disintegrins, small RGD containing peptides, to inhibit cell attachment and other cellular processes has also been studied extensively. Recently, we characterized a second site of interaction between vitronectin and its integrin partner. We determined that amino acids within the heparin-binding domain of vitronectin bind to a cysteine loop (C-loop) region of beta3 and that this interaction is required for the positive effects of alphaVbeta3 ligand occupancy on IGF-I signaling in smooth muscle cells. In this study we examine the signaling events activated following ligand binding of disintegrins to the alphaVbeta3 and the ability of these signals to be regulated by binding of the heparin-binding domain of vitronectin. We demonstrate that disintegrin ligand binding activates a series of events including the sequential activation of the tyrosine kinases c-Src and Syk. This leads to the activation of calpain and the cleavage of the beta3 cytoplasmic tail. Addition of vitronectin or a peptide homologous to the heparin-binding domain inhibited activation of this pathway. Our results suggest that the signaling events that occur following ligand binding to the alphaVbeta3 integrin reflects a balance between the effects mediated through the RGD binding site interaction and the effects mediated by the heparin binding site interaction and that for intact vitronectin the effect of the heparin-binding domain predominates.
authors.affiliation: Division of Endocrinology, Department of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7170, USA. laura_maile@med.unc.edu
authors.forename: Laura A
authors.initials: LA
authors.lastname: Maile
authors.forename: Ariel W
authors.initials: AW
authors.lastname: Aday
authors.forename: Walker H
authors.initials: WH
authors.lastname: Busby
authors.forename: Ravi
authors.initials: R
authors.lastname: Sanghani
authors.forename: Umadevi
authors.initials: U
authors.lastname: Veluvolu
authors.forename: David R
authors.initials: DR
authors.lastname: Clemmons
mesh_terms: D000818:Animals; D001665:Binding Sites; D000081247:CSK Tyrosine-Protein Kinase; D019483:Disintegrins / Q000378:metabolism; D006493:Heparin; D039302:Integrin alphaVbeta3 / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D008024:Ligands; D032389:Myocytes, Smooth Muscle / Q000378:metabolism; D011485:Protein Binding; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D015398:Signal Transduction; D013552:Swine; D000072377:Syk Kinase; D019096:Vitronectin / Q000378:metabolism*; D019061:src-Family Kinases
chemical_list: D019483:Disintegrins; D039302:Integrin alphaVbeta3; D047908:Intracellular Signaling Peptides and Proteins; D008024:Ligands; D019096:Vitronectin; D006493:Heparin; D011505:Protein-Tyrosine Kinases; D000081247:CSK Tyrosine-Protein Kinase; D000072377:Syk Kinase; D019061:src-Family Kinases