title: Role of p85 subunit of phosphatidylinositol-3-kinase as an adaptor molecule linking the insulin receptor to insulin receptor substrate 1.
abstract: After insulin stimulation of cells, signaling complexes are formed, containing the insulin receptor (IR), insulin receptor substrate-1 (IRS-1), and phosphatidylinositol-3-kinase. To study the nature of these complexes, we employed purified IR, recombinant IRS-1, antibodies to IR and IRS-1, and fusion proteins containing the two SH2 domains of p85. In intact cells, insulin increased tyrosine phosphorylation of both the IR and IRS-1. Both of these proteins were immunoprecipitated with antibodies to p85. Also, fusion proteins containing the two SH2 domains of p85 directly precipitated both the IR and IRS-1. Next, these signaling complexes were reconstituted in vitro with purified IR, recombinant IRS-1, and the two SH2 domains of p85. In the presence of both SH2 domains of p85, the IR associated with IRS-1. Other data, both in intact cells and in vitro, demonstrated that N- and C-terminal SH2 domains of p85 had preferential binding affinities for the IR and IRS-1, respectively. Studies with an IR mutant truncated in the C terminus indicated that the C-terminal phosphotyrosines of the IR play a major role in interacting with the SH2 domains of p85. In conclusion, both in vivo and in vitro data support a role for p85 in directly linking the IR to IRS-1 via its SH2 domains. The formation of these complexes, therefore, may provide a mechanism for the translocation to the plasma membrane of phosphatidylinositol-3-kinase and other molecules that are involved in IR signaling.
authors.affiliation: Department of Medicine, Mount Zion Medical Center/University of California, San Francisco 94115, USA.
authors.forename: V
authors.initials: V
authors.lastname: Sánchez-Margalet
authors.forename: I D
authors.initials: ID
authors.lastname: Goldfine
authors.forename: K
authors.initials: K
authors.lastname: Truitt
authors.forename: J
authors.initials: J
authors.lastname: Imboden
authors.forename: C K
authors.initials: CK
authors.lastname: Sung
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000235:genetics; D002846:Chromatography, Affinity; D018076:DNA, Complementary / Q000235:genetics; D006801:Humans; D007328:Insulin / Q000378:metabolism; D055504:Insulin Receptor Substrate Proteins; D008114:Liver Neoplasms, Experimental / Q000473:pathology; D046911:Macromolecular Substances; D058619:Maltose-Binding Proteins; D051379:Mice; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins / Q000737:chemistry*; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D011487:Protein Conformation; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D051381:Rats; D011972:Receptor, Insulin / Q000737:chemistry*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000302:isolation & purification; D015398:Signal Transduction; D014407:Tumor Cells, Cultured
chemical_list: D002352:Carrier Proteins; D018076:DNA, Complementary; C526292:IRS1 protein, human; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; C526296:Irs1 protein, rat; D046911:Macromolecular Substances; D058619:Maltose-Binding Proteins; D010750:Phosphoproteins; D011993:Recombinant Fusion Proteins; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D011972:Receptor, Insulin