title: Insulin-like growth factor-I-stimulated insulin receptor substrate-1 negatively regulates Src homology 2 domain-containing protein-tyrosine phosphatase substrate-1 function in vascular smooth muscle cells.
abstract: Vascular smooth muscle cells maintained in normal (5.6 mm) glucose respond to insulin-like growth factor-I (IGF-I) with increased protein synthesis but do not proliferate. In contrast, hyperglycemia alters responsiveness to IGF-I, resulting in increased SHPS-1 phosphorylation and assembly of a signaling complex that enhances MAPK and phosphatidylinositol 3-kinase pathways. Hyperglycemia also reduces the basal IRS-1 concentration and IGF-I-stimulated IRS-1-linked signaling. To determine if failure to down-regulate IRS-1 alters vascular smooth muscle cell (VSMC) responses to IGF-I, we overexpressed IRS-1 in VSMCs maintained in high glucose. These cultures showed reduced SHPS-1 phosphorylation, transfer of SHP-2 to SHPS-1, and impaired Shc and MAPK phosphorylation and cell proliferation in response to IGF-I. In vitro studies demonstrated that SHPS-1 was a substrate for type I IGF receptor (IGF-IR) and that IRS-1 competitively inhibited SHPS-1 phosphorylation. Exposure of VSMC cultures to a peptide that inhibited IRS-1/IGF-IR interaction showed that IRS-1 binding to IGF-IR impairs SHPS-1 phosphorylation in vivo. IRS-1 also sequestered SHP-2. Expression of an IRS-1 mutant (Y1179F/Y1229F) reduced IRS-1/SHP-2 association, and exposure of cells expressing the mutant to the inhibitory peptide enhanced SHPS-1 phosphorylation and SHP-2 transfer. This result was confirmed by expressing an IRS-1 mutant that had both impaired binding to IGF-IR and to SHP-2 IGF-I increased SHPS-1 phosphorylation, SHP-2 association with SHPS-1, Shc MAPK phosphorylation, and proliferation in cells expressing the mutant. We conclude that IRS-1 is an important factor for maintaining VSMCs in the non-proliferative state and that its down-regulation is a component of the VSMC response to hyperglycemic stress that results in an enhanced response to IGF-I.
authors.affiliation: Department of Medicine, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599, USA.
authors.forename: Yashwanth
authors.initials: Y
authors.lastname: Radhakrishnan
authors.forename: Walker H
authors.initials: WH
authors.lastname: Busby
authors.forename: Xinchun
authors.initials: X
authors.lastname: Shen
authors.forename: Laura A
authors.initials: LA
authors.lastname: Maile
authors.forename: David R
authors.initials: DR
authors.lastname: Clemmons
mesh_terms: D000818:Animals; D000943:Antigens, Differentiation / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D005947:Glucose / Q000494:pharmacology; D006801:Humans; D055504:Insulin Receptor Substrate Proteins / Q000235:genetics / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology; D051379:Mice; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D009154:Mutation; D032389:Myocytes, Smooth Muscle / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects / Q000502:physiology; D011485:Protein Binding; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11 / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017526:Receptor, IGF Type 1 / Q000235:genetics / Q000378:metabolism*; D011971:Receptors, Immunologic / Q000235:genetics / Q000378:metabolism*; D055765:Shc Signaling Adaptor Proteins; D013312:Stress, Physiological / Q000187:drug effects / Q000502:physiology; D013549:Sweetening Agents / Q000494:pharmacology; D013552:Swine
chemical_list: D000943:Antigens, Differentiation; C526292:IRS1 protein, human; D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; C501922:Sirpa protein, mouse; D011971:Receptors, Immunologic; C501920:SIRPA protein, human; D055765:Shc Signaling Adaptor Proteins; C501924:Sirpa protein, rat; D013549:Sweetening Agents; C519530:insulin-like growth factor-1, mouse; C548904:insulin-like growth factor-1, rat; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1; C516724:PTPN11 protein, human; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; C516725:Ptpn11 protein, mouse; D005947:Glucose