title: Expression of the human beta3 integrin subunit in mouse smooth muscle cells enhances IGF-I-stimulated signaling and proliferation.
abstract: Optimal stimulation of signal transduction and biological functions by IGF-I in porcine smooth muscle cells (pSMC) requires ligand occupancy of the alphaVbeta3 integrin. Binding of heparin-binding domain (HBD) of vitronectin (VN) to the cysteine loop (C-loop) region of beta3 is required for pSMC to respond optimally to IGF-I stimulation. Mouse smooth muscle cells (mSMC), which express a form of beta3 whose sequence within the C-loop region is different than porcine or human beta3, do not respond optimally to IGF-I, and IGF-I stimulated beta3 and SHPS-1 phosphorylation which are necessary for optimal IGF-I signaling were undetectable. VN also had no effect on IGF-I stimulated the cell proliferation. In contrast, when human beta3 (hbeta3) was introduced into mSMC, there was an enhanced VN binding in spite of an equivalent amount of total beta3 expression, and IGF-I-dependent beta3, and SHPS-1 phosphorylation were detected. In addition, there was enhanced IGF-I-stimulated Shc association with SHPS-1, Shc tyrosine phosphorylation, Shc and Grb2 association, and MAP kinase activation leading to increased cell proliferation. These enhancements could be further augmented by adding a peptide containing the HBD of VN. To determine if these changes were mediated by the C-loop region of beta3, an antibody that reacts with that region of beta3 was utilized. The addition of the hbeta3 C-loop antibody abolished VN-induced enhancement of IGF-I signaling and IGF-I-stimulated cell proliferation. These results strongly support the conclusion that optimal SMC responsiveness to IGF-I requires ligand interaction with the C-loop domain of hbeta3.
authors.affiliation: Department of Medicine, University of North Carolina, School of Medicine, Chapel Hill, North Carolina, USA.
authors.forename: Gang
authors.initials: G
authors.lastname: Xi
authors.forename: Laura A
authors.initials: LA
authors.lastname: Maile
authors.forename: Sung-Eun
authors.initials: SE
authors.lastname: Yoo
authors.forename: David R
authors.initials: DR
authors.lastname: Clemmons
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001011:Aorta / Q000166:cytology; D049109:Cell Proliferation / Q000187:drug effects*; D002478:Cells, Cultured; D016895:Culture Media, Serum-Free; D051380:GRB2 Adaptor Protein / Q000378:metabolism; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D039661:Integrin beta3 / Q000737:chemistry / Q000378:metabolism*; D008024:Ligands; D020935:MAP Kinase Signaling System / Q000502:physiology; D051379:Mice; D008969:Molecular Sequence Data; D032389:Myocytes, Smooth Muscle / Q000187:drug effects* / Q000378:metabolism; D010766:Phosphorylation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011971:Receptors, Immunologic / Q000378:metabolism; D055765:Shc Signaling Adaptor Proteins; D015398:Signal Transduction / Q000187:drug effects*; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; D014443:Tyrosine / Q000378:metabolism; D019096:Vitronectin / Q000737:chemistry / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D016895:Culture Media, Serum-Free; D051380:GRB2 Adaptor Protein; D039661:Integrin beta3; D008024:Ligands; C501922:Sirpa protein, mouse; D011971:Receptors, Immunologic; C528024:SHC1 protein, human; D055765:Shc Signaling Adaptor Proteins; C528034:Shc1 protein, mouse; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; D019096:Vitronectin; D014443:Tyrosine; D007334:Insulin-Like Growth Factor I