title: Frap-dependent serine phosphorylation of IRS-1 inhibits IRS-1 tyrosine phosphorylation.
abstract: We have previously shown that interferon-alpha (IFN alpha)-dependent tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1) is impaired by serine phosphorylation of IRS-1 due to the reduced ability of serine phosphorylated IRS-1 to serve as a substrate for Janus kinase 1 (JAK1). Here we report that FKBP12-rapamycin-associated protein (FRAP) is a physiologic IRS-1 kinase that blocks IFN alpha signaling by serine phosphorylating IRS-1. We found that both FRAP and insulin-activated p70 S6 kinase (p70(s6k)) serine phosphorylated IRS-1 between residues 511 and 772 (IRS-1(511-772)). Importantly, only FRAP-dependent IRS-1(511-772) serine phosphorylation inhibited by 50% subsequent JAK1-dependent tyrosine phosphorylation of IRS-1. Furthermore, treatment of U266 cells with the FRAP inhibitor rapamycin increased IFN alpha-dependent tyrosine phosphorylation by twofold while reducing constitutive IRS-1 serine phosphorylation within S/T-P motifs by 80%. Taken together, these data indicate that FRAP, but not p70(s6k), is a likely physiologic IRS-1 serine kinase that negatively regulates JAK1-dependent IRS-1 tyrosine phosphorylation and suggests that FRAP may modulate IRS-dependent cytokine signaling.
authors.affiliation: Department of Animal Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
authors.forename: M E
authors.initials: ME
authors.lastname: Hartman
authors.forename: M
authors.initials: M
authors.lastname: Villela-Bach
authors.forename: J
authors.initials: J
authors.lastname: Chen
authors.forename: G G
authors.initials: GG
authors.lastname: Freund
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins; D002460:Cell Line; D006801:Humans; D020104:Immunophilins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D055504:Insulin Receptor Substrate Proteins; D016898:Interferon-alpha / Q000494:pharmacology; D053613:Janus Kinase 1; D010750:Phosphoproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor); D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D051381:Rats; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D012694:Serine / Q000737:chemistry; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D014443:Tyrosine / Q000737:chemistry
chemical_list: D002352:Carrier Proteins; C526292:IRS1 protein, human; D055504:Insulin Receptor Substrate Proteins; D016898:Interferon-alpha; C526296:Irs1 protein, rat; D010750:Phosphoproteins; D014443:Tyrosine; D012694:Serine; D017853:Phosphotransferases (Alcohol Group Acceptor); C546842:MTOR protein, human; C546845:mTOR protein, rat; D011505:Protein-Tyrosine Kinases; C507904:JAK1 protein, human; C507906:Jak1 protein, rat; D053613:Janus Kinase 1; D019893:Ribosomal Protein S6 Kinases; D058570:TOR Serine-Threonine Kinases; D020104:Immunophilins; D020123:Sirolimus