title: The AP-1 complex regulates intracellular localization of insulin receptor substrate 1, which is required for insulin-like growth factor I-dependent cell proliferation.
abstract: The activation of the insulin/insulin-like growth factor I (IGF-I) receptor and the subsequent tyrosine phosphorylation of insulin receptor substrates (IRSs) are key initial events in a variety of insulin/IGF bioactivities, including mitogenesis. It has been reported that IRS-1 associates with intracellular membrane compartments, and this localization is believed to be important for insulin/IGF signal transduction. However, the molecular mechanisms underlying IRS-1 localization remain unclear. Here we show that in L6 myoblasts, IRS-1 associates with μ1A of the ubiquitously expressed AP-1 complex, which packages cargo proteins into clathrin-coated vesicles derived from intracellular membranes. While wild-type IRS-1 was predominantly localized to vesicular structures, IRS-1 mutants lacking three YXXΦ motifs responsible for binding to μ1A were mislocalized to the mannose-6-phosphate receptor-positive structures, suggesting that AP-1-dependent transport to peripheral vesicles is inhibited in these mutants. Furthermore, deletion of AP-1 binding sites in IRS-1 impaired IGF-I-induced cell proliferation, accompanied by reduced tyrosine phosphorylation of IRS-1 and its association with phosphoinositide (PI) 3-kinase. These data demonstrate the importance of AP-1-dependent localization of IRS-1 in mediating IGF-I-stimulated signaling and maximum mitogenic response.
authors.affiliation: Department of Animal Sciences, The University of Tokyo, Bunkyo-ku, Tokyo, Japan.
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Yoneyama
authors.forename: Masao
authors.initials: M
authors.lastname: Matsuo
authors.forename: Kazumi
authors.initials: K
authors.lastname: Take
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Kabuta
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Chida
authors.forename: Fumihiko
authors.initials: F
authors.lastname: Hakuno
authors.forename: Shin-Ichiro
authors.initials: S
authors.lastname: Takahashi
mesh_terms: D033961:Adaptor Protein Complex 1 / Q000378:metabolism*; D033983:Adaptor Protein Complex mu Subunits / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002462:Cell Membrane / Q000378:metabolism; D049109:Cell Proliferation; D004261:DNA Replication; D055785:Gene Knockdown Techniques; D057809:HEK293 Cells; D006801:Humans; D055504:Insulin Receptor Substrate Proteins / Q000737:chemistry / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000502:physiology*; D008969:Molecular Sequence Data; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D011499:Protein Processing, Post-Translational; D021122:Protein Subunits; D021381:Protein Transport; D051381:Rats; D059008:Time-Lapse Imaging
chemical_list: C438883:AP1M1 protein, human; D033961:Adaptor Protein Complex 1; D033983:Adaptor Protein Complex mu Subunits; C526292:IRS1 protein, human; D055504:Insulin Receptor Substrate Proteins; D021122:Protein Subunits; D007334:Insulin-Like Growth Factor I; D019869:Phosphatidylinositol 3-Kinases