title: Cloning and characterization of PHIP, a novel insulin receptor substrate-1 pleckstrin homology domain interacting protein.
abstract: Insulin receptor substrate-1 (IRS-1) protein is a major substrate of the insulin receptor tyrosine kinase and is essential for transducing many of the biological effects of insulin including mitogenesis, gene expression, and glucose transport. The N terminus of IRS-1 contains a pleckstrin homology (PH) domain that is critical for recognition and subsequent phosphorylation of IRS-1 by the activated insulin receptor. Here we report the isolation of a novel protein, PHIP (PH-interacting protein), which selectively binds to the PH domain of IRS-1 in vitro and stably associates with IRS-1 in vivo. Importantly, mutants of the IRS-1 PH domain that disrupt the PH fold fail to bind to PHIP. Anti-phosphotyrosine immunoblots of PHIP revealed no discernible insulin receptor-regulated phosphorylation, suggesting that PHIP is not itself a substrate of the insulin receptor. In contrast to full-length PHIP, overexpression of the PH-binding region of PHIP has a pronounced inhibitory effect on insulin-induced IRS-1 tyrosine phosphorylation levels. Furthermore, expression of this dominant-negative PHIP mutant leads to a marked attenuation of insulin-stimulated mitogen-activated protein kinase activity. We conclude that PHIP represents a novel protein ligand of the IRS-1 PH domain that may serve to link IRS-1 to the insulin receptor.
authors.affiliation: Departments of Biology and Pathology and Molecular Medicine, McMaster University, Hamilton, Ontario, Canada.
authors.forename: J
authors.initials: J
authors.lastname: Farhang-Fallah
authors.forename: X
authors.initials: X
authors.lastname: Yin
authors.forename: G
authors.initials: G
authors.lastname: Trentin
authors.forename: A M
authors.initials: AM
authors.lastname: Cheng
authors.forename: M
authors.initials: M
authors.lastname: Rozakis-Adcock
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D002460:Cell Line; D003001:Cloning, Molecular; D018076:DNA, Complementary; D004789:Enzyme Activation; D006801:Humans; D007328:Insulin / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008969:Molecular Sequence Data; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats; D017386:Sequence Homology, Amino Acid; D014443:Tyrosine / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D018076:DNA, Complementary; C526292:IRS1 protein, human; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; C526296:Irs1 protein, rat; C418612:PHIP protein, human; D010750:Phosphoproteins; D014443:Tyrosine; D020928:Mitogen-Activated Protein Kinases