151
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Kerouz NJ, Hörsch D, Pons S, Kahn CR. Differential regulation of insulin receptor substrates-1 and -2 (IRS-1 and IRS-2) and phosphatidylinositol 3-kinase isoforms in liver and muscle of the obese diabetic (ob/ob) mouse. J Clin Invest 1997; 100:3164-72. [PMID: 9399964 PMCID: PMC508530 DOI: 10.1172/jci119872] [Citation(s) in RCA: 217] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Intracellular insulin signaling involves a series of alternative and complementary pathways created by the multiple substrates of the insulin receptor (IRS) and the various isoforms of SH2 domain signaling molecules that can interact with these substrates. In this study, we have evaluated the roles of IRS-1 and IRS-2 in signaling to the phosphatidylinositol (PI) 3-kinase pathway in the ob/ob mouse, a model of the insulin resistance of obesity and non-insulin-dependent diabetes mellitus. We find that the levels of expression of both IRS-1 and IRS-2 are decreased approximately 50% in muscle, whereas in liver the decrease is significantly greater for IRS-2 (72%) than for IRS-1 (29%). This results in differential decreases in IRS-1 and IRS-2 phosphorylation, docking of the p85alpha regulatory subunit of PI 3-kinase, and activation of this enzyme in these two insulin target tissues. In ob/ob liver there is also a change in expression of the alternatively spliced isoforms of the regulatory subunits for PI 3-kinase that was detected at the protein and mRNA level. This resulted in a 45% decrease in the p85alpha form of PI 3-kinase, a ninefold increase in the AS53/p55alpha, and a twofold increase in p50alpha isoforms. Thus, there are multiple alterations in the early steps of insulin signaling in the ob/ob mouse, with differential regulation of IRS-1 and IRS-2, various PI 3-kinase regulatory isoforms, and a lack of compensation for the decrease in insulin signaling by any of the known alternative pathways at these levels.
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Affiliation(s)
- N J Kerouz
- Research Division, Joslin Diabetes Center, and Department of Medicine, Harvard Medical School, Boston, Massachusetts 02215, USA
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152
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Mothe I, Delahaye L, Filloux C, Pons S, White MF, Van Obberghen E. Interaction of wild type and dominant-negative p55PIK regulatory subunit of phosphatidylinositol 3-kinase with insulin-like growth factor-1 signaling proteins. Mol Endocrinol 1997; 11:1911-23. [PMID: 9415396 DOI: 10.1210/mend.11.13.0029] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
In a first series of experiments done in the yeast two-hybrid system, we investigated the nature of protein-protein interaction between the regulatory subunit of phosphatidylinositol 3-kinase (PI 3-kinase), p55PIK, and several of its potential signaling partners. The region between the Src homology 2 (SH2) domains of p55PIK bound to the NH2 terminus region of p110alpha, as previously shown for p85alpha. Moreover, we found that the insulin-like growth factor-1 receptor (IGF-IR) bound to p55PIK; the interaction occurred at the receptor tyrosine 1316 and involved both p55PIK SH2 domains. Interaction between p55PIK and IGF-IR was seen not only in the yeast two-hybrid system, but also using in vitro binding and coimmunoprecipitation of lysates from IGF-1 stimulated 293 cells overexpressing p55PIK. Further, IGF-I stimulation of these cells led to tyrosine phosphorylation of p55PIK. In 293 cells association of p55PIK with insulin receptor substrate-1 and with IGF-IR was dependent on PI 3-kinase, since it was increased by wortmannin, an inhibitor of PI 3-kinase. Further, by deleting amino acids 203-217 of p55PIK inter-SH2 domain, we engineered a p55PIK mutant unable to bind to the p110alpha catalytic subunit of PI 3-kinase. This mutant had a dominant-negative action on insulin-stimulated glucose transport, since insulin's effect on Glut 4 myc translocation was inhibited in adipocytes expressing mutant p55PIK. Importantly, this dominant-negative mutant was more efficient than wild type p55PIK in associating to IGF-IR and insulin receptor substrate-1 in 293 cells. Taken together, our results show that p55PIK interacts with key elements in the IGF-I signaling pathway, and that these interactions are negatively modulated by PI 3-kinase itself, providing circuitry for regulatory feedback control.
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Affiliation(s)
- I Mothe
- Institut National de la Santé et de la Recherche Médicale U145, Nice, France
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153
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Hill MM, Clark SF, James DE. Insulin-regulatable phosphoproteins in 3T3-L1 adipocytes form detergent-insoluble complexes not associated with caveolin. Electrophoresis 1997; 18:2629-37. [PMID: 9527493 DOI: 10.1002/elps.1150181419] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Whole body glucose homeostasis is dependent on the action of insulin. In muscle and adipose tissues, insulin stimulates glucose uptake by inducing the translocation of vesicles containing the glucose transporter GLUT4 to the cell surface. While the mechanisms of insulin-regulated GLUT4 translocation are not fully understood, some signaling intermediates have been implicated in this process. Interestingly, some of these intermediates, including IRS-1 and PI3K, have been localised to the same intracellular membrane fraction as the GLUT4 storage pool, designated here as the high-speed pellet (HSP) fraction. This raises the possibility that many of the downstream insulin signaling intermediates may be located within close proximity to intracellular GLUT4. The goal of this study was to test this hypothesis in 3T3-L1 adipocytes. A large proportion of adipocyte phosphoproteins co-fractionated in the HSP fraction. In an attempt to resolve insulin-regulatable phosphoproteins, we subjected 32P-labeled subcellular fractions to two-dimensional gel electrophoresis (2-DE). Insulin reproducibly stimulated the phosphorylation of 12 spots in the HSP fraction. Most of the HSP phosphoproteins were insoluble in the nonionic detergent Triton X-100, whereas integral membrane proteins such as GLUT4 and intracellular caveolin were soluble under the same conditions. These results suggest that insulin-regulatable phosphoproteins in adipocytes may be organized in microdomains within the cell and that this assembly may act as an efficient conductor of the signaling proteins to rapidly facilitate downstream biological responses. Further study is required to establish the molecular basis for these detergent-insoluble signaling complexes.
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Affiliation(s)
- M M Hill
- Centre for Molecular and Cellular Biology, Department of Physiology and Pharmacology, University of Queensland, St. Lucia, Australia
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154
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Abstract
Insulin receptor substrate (IRS) proteins are key regulators of basic functions such as cellular growth and metabolism. They provide an interface between multiple receptors and a complex network of intracellular signaling molecules. Two members of this family (IRS-1 and IRS-2) have been identified previously. In this investigation, we analyzed a mouse expressed sequence tag clone that proved to be a new member of the IRS family. Sequence analysis of this clone and comparison with the sequences deposited in GenBank demonstrates this protein may be the murine homolog of rat IRS-3, recently purified and cloned from rat adipocytes. Accordingly, we have named our protein mouse IRS-3. The expressed sequence tag clone contains the complete coding sequence of 1485 bp, encoding a protein of 495 amino acids. Sequence alignment with the other members of the IRS family shows that this protein contains pleckstrin homology and phosphotyrosine-binding domains that are highly conserved. In addition, there is conservation of many tyrosine phosphorylation motifs responsible for interactions with downstream signaling molecules containing SH2 domains. The murine IRS-3 messenger RNA (2.4 kilobases in length) is expressed in many tissues, with highest levels in liver and lung. Mouse IRS-3 is highly expressed in the first part of the embryonic life, when IRS-1 messenger RNA is barely detectable. Unlike the genes encoding IRS-1 and IRS-2, the IRS-3 gene contains an intron (344 bp in length) in the region between the pleckstrin homology and the phosphotyrosine-binding domains. Fluorescent in situ hybridization localized the mouse IRS-3 gene on the telomeric region of chromosome 5G2. Cloning of the murine IRS-3 gene will make it possible to apply genetic approaches to elucidate the physiological role of this new member of the IRS family of proteins.
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Affiliation(s)
- S Sciacchitano
- Diabetes Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-1829, USA
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155
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Burks DJ, Pons S, Towery H, Smith-Hall J, Myers MG, Yenush L, White MF. Heterologous pleckstrin homology domains do not couple IRS-1 to the insulin receptor. J Biol Chem 1997; 272:27716-21. [PMID: 9346913 DOI: 10.1074/jbc.272.44.27716] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Pleckstrin homology (PH) domains occur in many signaling proteins, including substrates for the insulin receptor tyrosine kinase (IRS proteins). Based on the hypothesis that PH domains may have a common function such as membrane targeting we tested the ability of PH domains from other signaling molecules to link IRS-1 to the insulin receptor. Chimeric IRS-1 proteins containing a homologous PH domain derived from other IRS proteins (IRS-2 or Gab-1) were tyrosine phosphorylated normally in response to insulin. In contrast, heterologous PH domains from the beta-adrenergic receptor kinase, phospholipase Cgamma, or spectrin failed to mediate tyrosine phosphorylation of chimeric IRS-1 proteins, even in cells expressing high levels of insulin receptor. Moreover, IRS-1 proteins containing heterologous PH domains did not bind phosphorylated NPEY motifs derived from the insulin receptor, suggesting that the presence of these structures interfered with the function of the adjacent PTB binding domain. Thus, tyrosine phosphorylation of IRS-1 by the insulin receptor specifically requires a PH domain derived from IRS proteins.
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Affiliation(s)
- D J Burks
- Research Division, Joslin Diabetes Center, and the Department of Medicine, Harvard Medical School, Boston, Massachusetts 02215, USA
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156
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Ogihara T, Isobe T, Ichimura T, Taoka M, Funaki M, Sakoda H, Onishi Y, Inukai K, Anai M, Fukushima Y, Kikuchi M, Yazaki Y, Oka Y, Asano T. 14-3-3 protein binds to insulin receptor substrate-1, one of the binding sites of which is in the phosphotyrosine binding domain. J Biol Chem 1997; 272:25267-74. [PMID: 9312143 DOI: 10.1074/jbc.272.40.25267] [Citation(s) in RCA: 129] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Insulin binding to its receptor induces the phosphorylation of cytosolic substrates, insulin receptor substrate (IRS)-1 and IRS-2, which associate with several Src homology-2 domain-containing proteins. To identify unique IRS-1-binding proteins, we screened a human heart cDNA library with 32P-labeled recombinant IRS-1 and obtained two isoforms (epsilon and zeta) of the 14-3-3 protein family. 14-3-3 protein has been shown to associate with IRS-1 in L6 myotubes, HepG2 hepatoma cells, Chinese hamster ovary cells, and bovine brain tissue. IRS-2, a protein structurally similar to IRS-1, was also shown to form a complex with 14-3-3 protein using a baculovirus expression system. The amount of 14-3-3 protein associated with IRS-1 was not affected by insulin stimulation but was increased significantly by treatment with okadaic acid, a potent serine/threonine phosphatase inhibitor. Peptide inhibition experiments using phosphoserine-containing peptides of IRS-1 revealed that IRS-1 contains three putative binding sites for 14-3-3 protein (Ser-270, Ser-374, and Ser-641). Among these three, the motif around Ser-270 is located in the phosphotyrosine binding domain of IRS-1, which is responsible for the interaction with the insulin receptor. Indeed, a truncated mutant of IRS-1 consisting of only the phosphotyrosine binding domain retained the capacity to bind to 14-3-3 protein in vivo. Finally, the effect of 14-3-3 protein binding on the insulin-induced phosphorylation of IRS-1 was investigated. Phosphoamino acid analysis revealed that IRS-1 coimmunoprecipitated with anti-14-3-3 antibody to be weakly phosphorylated after insulin stimulation, on tyrosine as well as serine residues, compared with IRS-1 immunoprecipitated with anti-IRS-1 antibody. Thus, the association with 14-3-3 protein may play a role in the regulation of insulin sensitivity by interrupting the association between the insulin receptor and IRS-1.
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Affiliation(s)
- T Ogihara
- Third Department of Internal Medicine, Faculty of Medicine, University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113, Japan
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157
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Albert S, Twardzik T, Heisenberg M, Schneuwly S. Isolation and characterization of the droPIK57 gene encoding a new regulatory subunit of phosphatidylinositol 3-kinase from Drosophila melanogaster. Gene 1997; 198:181-9. [PMID: 9370280 DOI: 10.1016/s0378-1119(97)00313-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Mammalian phosphatidylinositol 3-kinase (PI 3-kinase) plays an important role in the regulation of various cellular, receptor tyrosine kinase-mediated processes, such as mitogenesis and transformation. PI 3-kinase is composed of a 110-kDa catalytic subunit and a regulatory subunit of 85 kDa or 55 kDa. We have cloned a gene for a regulatory subunit from Drosophila melanogaster, named droPIK57, from head-specific cDNA libraries. The droPIK57 gene encodes a protein containing two SH2 domains with significant sequence homology to those in p85 and p55. Like the p55 subunits, DroPIK57 is missing the SH3 domain and the bcr homology region of the p85 subunit. The short N-terminus as well as the C-terminus of the DroPIK57 protein show no identity to the known PI 3-kinase subunits, suggesting that it is a new member in the family of regulatory subunits. In-situ hybridization and Northern blot analysis indicate a widespread function of this gene during embryogenesis and in the CNS.
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Affiliation(s)
- S Albert
- Theodor-Boveri-Institut für Biowissenschaften, Lehrstuhl für Genetik, Universität Würzburg, Germany
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158
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Burfoot MS, Rogers NC, Watling D, Smith JM, Pons S, Paonessaw G, Pellegrini S, White MF, Kerr IM. Janus kinase-dependent activation of insulin receptor substrate 1 in response to interleukin-4, oncostatin M, and the interferons. J Biol Chem 1997; 272:24183-90. [PMID: 9305869 DOI: 10.1074/jbc.272.39.24183] [Citation(s) in RCA: 103] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
In addition to a role in response to insulin and insulin-like growth factors, insulin receptor substrate 1 (IRS-1) is phosphorylated in response to IL-4, the interferons (IFNs) and oncostatin M (OSM). Here mutant cell lines lacking JAK1, JAK2, or Tyk2 were used to determine the role(s) of the Janus kinase (JAK) family of protein-tyrosine kinases in IRS-1 phophorylation. 32D cells, which do not express IRS proteins, were analyzed for any requirement for these proteins in response to the IFNs. For the mutant human fibrosarcoma cell lines, phosphorylation of IRS-1 through the insulin-like growth factor receptor is independent of JAK1, JAK2, or Tyk2. In contrast, phosphorylation of IRS-1 mediated by the Type I IFNs, IL-4, and OSM is JAK-dependent. For the alphabeta-IFNs, activation of IRS-1 is dependent on JAK1 and Tyk2, consistent with the interdependence of these kinases in the IFN-alphabeta response. Neither IRS-1 nor IRS-2 was detectably activated by IFN-gamma. Consistent with this, activation of neither IRS proteins appears to be an absolute requirement for an antiproliferative or an antiviral response to the IFNs. For IL-4 and OSM phosphorylation of IRS-1 in the human fibrosarcoma cells is largely dependent on JAK1 but can also be mediated through Tyk2 or JAK2. Activation of phosphatidylinositol 3'-kinase in response to IL-4 and OSM, at least, was also JAK-dependent. The JAKs are, therefore, required not only for STAT activation but also for the activation, through a variety of different types of cytokine receptor, of an additional signaling pathway(s) through IRS-1 and phosphatidylinositol 3'-kinase.
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Affiliation(s)
- M S Burfoot
- Imperial Cancer Research Fund, 44 Lincoln's Inn Fields, London WC2A 3PX, United Kingdom
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159
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Domin J, Pages F, Volinia S, Rittenhouse SE, Zvelebil MJ, Stein RC, Waterfield MD. Cloning of a human phosphoinositide 3-kinase with a C2 domain that displays reduced sensitivity to the inhibitor wortmannin. Biochem J 1997; 326 ( Pt 1):139-47. [PMID: 9337861 PMCID: PMC1218647 DOI: 10.1042/bj3260139] [Citation(s) in RCA: 201] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The generation of phosphatidylinositide 3-phosphates has been observed in a variety of cellular responses. The enzymes that mediate synthesis are the phosphoinositide 3-kinases (PI3-Ks) that form a family of structurally diverse enzymes with distinct substrate specificities. In this paper, we describe the cloning of a novel human PI3-K, namely PI3-K-C2 alpha, which contains a C-terminal C2 domain. This enzyme can be assigned to the class II PI3-Ks, which was defined by characterization of the Drosophila 68D enzyme and includes the recently described murine enzymes m-cpk and p170. Despite the overall similarity in the amino acid sequence of the murine and human enzymes, which suggests that they are encoded by closely related genes, these molecules show marked sequence heterogeneity at their N-termini. Biochemical analysis of recombinant PI3-K-C2 alpha demonstrates a restricted lipid substrate specificity. As reported for other members of this class, the enzyme only phosphorylates PtdIns and PtdIns4P when the lipids are presented alone. However, when lipids were presented together with phosphatidylserine acting as a carrier, phosphorylation of PtdIns(4,5)P2 was also observed. The catalytic activity of PI3-K-C2 alpha is refractory to concentrations of wortmannin and LY294002 which inhibit the PI3-K activity of other family members. The comparative insensitivity of PI3-K-C2 alpha to these inhibitors suggests that their use should be reevaluated in the study of PI3-Ks.
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Affiliation(s)
- J Domin
- Ludwig Institute for Cancer Research, London, U.K
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160
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Shepherd PR, Navé BT, Rincon J, Nolte LA, Bevan AP, Siddle K, Zierath JR, Wallberg-Henriksson H. Differential regulation of phosphoinositide 3-kinase adapter subunit variants by insulin in human skeletal muscle. J Biol Chem 1997; 272:19000-7. [PMID: 9228082 DOI: 10.1074/jbc.272.30.19000] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The role of phosphoinositide 3-kinase (PI 3-kinase) in insulin signaling was evaluated in human skeletal muscle. Insulin stimulated both antiphosphotyrosine-precipitable PI 3-kinase activity and 3-O-methylglucose transport in isolated skeletal muscle (both approximately 2-3-fold). Insulin stimulation of 3-O-methylglucose transport was inhibited by the PI 3-kinase inhibitor LY294002 (IC50 = 2.5 microM). The PI 3-kinase adapter subunits were purified from muscle lysates using phosphopeptide beads based on the Tyr-751 region of the platelet-derived growth factor receptor. Immunoblotting of the material adsorbed onto the phosphopeptide beads revealed the presence of p85alpha, p85beta, p55(PIK)/p55gamma, and p50 adapter subunit isoforms. In addition, p85alpha-NSH2 antibodies recognized four adapter subunit variants of 54, 53, 48, and 46 kDa, the latter corresponding to the p50 splice variant. Serial immunoprecipitations demonstrated that these four proteins were associated with a large proportion of the total PI 3-kinase activity immunoprecipitated by p85alpha-NSH2 domain antibodies. Antibodies to p85beta, p55(PIK)/p55gamma, and the p50 adapter subunit also immunoprecipitated PI 3-kinase activity from human muscle lysates. A large proportion of the total cellular pool of the 53-kDa variant, p50, and p55(PIK) was present in antiphosphotyrosine immunoprecipitates from unstimulated muscle, whereas these immunoprecipitates contained only a very small proportion of the cellular pool of p85alpha, p85beta, and the 48-kDa variant. Insulin greatly increased the levels of the 48-kDa variant in antiphosphotyrosine immunoprecipitates and caused smaller -fold increases in the levels of p85alpha, p85beta, and the 53-kDa variant. The levels of p50 and p55(PIK) were not significantly changed. These properties indicate mechanisms by which specificity is achieved in the PI 3-kinase signaling system.
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Affiliation(s)
- P R Shepherd
- Department of Biochemistry, University College London, Gower Street, London WC1E 6BT, United Kingdom.
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161
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Smith-Hall J, Pons S, Patti ME, Burks DJ, Yenush L, Sun XJ, Kahn CR, White MF. The 60 kDa insulin receptor substrate functions like an IRS protein (pp60IRS3) in adipose cells. Biochemistry 1997; 36:8304-10. [PMID: 9204876 DOI: 10.1021/bi9630974] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The 60 kDa insulin receptor substrate in rat adipocytes that binds to the PI-3 kinase displays several functional characteristics in common with the IRS proteins; so we propose the name pp60(IRS3) to distinguish it from other tyrosine phosphorylated proteins of similar size. During insulin stimulation, p85 associated with pp60(IRS3) more rapidly than with IRS-1 or IRS-2. In mice lacking IRS-1, p85 associated more strongly with pp60(IRS3) than with IRS-2, suggesting that pp60(IRS3) provides an alternate pathway in these cells. Synthetic peptides containing two phosphorylated YMPM motifs displace pp60(IRS3) and IRS-1 from alphap85 immune complexes, suggesting that pp60(IRS3), like IRS-1, engages both SH2 domains in p85. Moreover, pp60(IRS3) binds to immobilized peptides containing a phosphorylated NPXY motif, suggesting that it contains a PTB domain with similar specificity to that in IRS-1. The cloning of pp60(IRS3) will reveal a new member of the IRS protein family which mediates insulin receptor signals in a narrow range of tissues.
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Affiliation(s)
- J Smith-Hall
- Joslin Diabetes Center and Department of Medicine, Harvard Medical School, Boston, Massachusetts 02215, USA
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162
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Esposito DL, Blakesley VA, Koval AP, Scrimgeour AG, LeRoith D. Tyrosine residues in the C-terminal domain of the insulin-like growth factor-I receptor mediate mitogenic and tumorigenic signals. Endocrinology 1997; 138:2979-88. [PMID: 9202243 DOI: 10.1210/endo.138.7.5281] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
We investigated cellular proliferation, the transforming activity, and activation of known signal transduction pathways in NIH-3T3 cells stably expressing insulin-like growth factor-I receptors (IGF-IRs) with amino acid substitutions in the carboxy(C)-terminal domain. The mutant receptors contained substitutions of both tyrosines 1250 and 1251 with phenylalanine and histidine (amino acids present in the analogous positions in the insulin receptor), as well as phenylalanine 1310 replaced by tyrosine (IsY clones) to resemble the placement of tyrosine residues in the C-terminal domain of the insulin receptor. As a control for the IsY clones, a second mutant receptor was expressed with a substitution of phenylalanine 1310 with tyrosine only (DBY clones). Clones expressing IGF-IRs with the IsY substitutions had a significantly slower rate of growth compared with cells expressing an equivalent number of wild-type IGF-IRs (NWT). In contrast, the DBY clones showed relatively normal growth rates. Cells with wild-type IGF-IR demonstrated a transformed phenotype in soft agar assays. The IsY clones lost the transforming ability of the wild type IGF-IR, whereas DBY clones formed colonies. IGF-I-stimulated autophosphorylation of the IGF-IR and tyrosine phosphorylation of IRS-1 and SHC, known substrates in the IGF-IR signal transduction pathway, were studied. Mutated IGF-IRs (IsY and DBY) did not alter the IGF-I-induced tyrosine phosphorylation of these proteins. Furthermore, the mutated IGF-IRs did not alter Grb2 association with phosphorylated IRS-1 and SHC. IGF-I stimulation of Crk-II phosphorylation, a novel substrate of the IGF-IR, was similar in cells expressing mutated and wild-type IGF-IRs. IGF-I-induced activation of phosphatidylinositol (PI) 3'-kinase was equivalent in cells expressing either mutant or wild-type IGF-IRs. These data suggest that the IGF-IR mediates, at least in part, cellular proliferation and increased transforming ability through its C-terminal domain. The exact postreceptor signaling pathway(s) involved have yet to be fully elucidated.
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Affiliation(s)
- D L Esposito
- Diabetes Branch, NIDDK, NIH, Bethesda, Maryland 20892-1770, USA
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163
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Sawka-Verhelle D, Baron V, Mothe I, Filloux C, White MF, Van Obberghen E. Tyr624 and Tyr628 in insulin receptor substrate-2 mediate its association with the insulin receptor. J Biol Chem 1997; 272:16414-20. [PMID: 9195949 DOI: 10.1074/jbc.272.26.16414] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
In addition to the pleckstrin homology domain and the phosphotyrosine binding domain in insulin receptor substrate (IRS)-1 and IRS-2, a region between amino acids 591 and 786 in IRS-2 (IRS-2-(591-786)) binds to the insulin receptor. Based on peptide competition studies, this region interacts with the phosphorylated regulatory loop of the insulin receptor; we designate this region the kinase regulatory loop binding (KRLB) domain. Two tyrosine residues in the KRLB domain at positions 624 and 628 are crucial for this interaction. Phosphorylation of tyrosine residues in the KRLB domain by the insulin receptor inhibits the binding to the receptor. These results reveal a novel mechanism regulating the interaction of the insulin receptor and IRS-2 that may distinguish the signal of IRS-2 from IRS-1.
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164
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Domin J, Waterfield MD. Using structure to define the function of phosphoinositide 3-kinase family members. FEBS Lett 1997; 410:91-5. [PMID: 9247130 DOI: 10.1016/s0014-5793(97)00617-0] [Citation(s) in RCA: 183] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Affiliation(s)
- J Domin
- Ludwig Institute for Cancer Research, London, UK
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165
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Ho LK, Liu D, Rozycka M, Brown RA, Fry MJ. Identification of four novel human phosphoinositide 3-kinases defines a multi-isoform subfamily. Biochem Biophys Res Commun 1997; 235:130-7. [PMID: 9196049 DOI: 10.1006/bbrc.1997.6747] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Phosphoinositide (PI) 3-kinases have critical roles in diverse cellular signalling processes and in protein trafficking. This suggests that like other intracellular signalling molecules, e.g., phospholipase C and protein kinase C, there might be a large family of PI 3-kinase isoforms with the individual members having discrete signalling roles. Reverse transcription-polymerase chain reaction methods, using degenerate oligonucleotide primers against the lipid kinase consensus region, revealed eight sequences from human cDNA containing a high degree of identity to the family of PI 3-kinases. The sequences obtained included the previously described p110 alpha, p110 beta, and p110 gamma isoforms and HsVps34. Additionally, we have identified four novel sequences which are related to PI 3-kinases. Three of the novel sequences would appear to form a distinct sub-family of PI 3-kinases. We report the expression of these novel PI 3-kinases in human tissues and in cells derived from normal breast.
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Affiliation(s)
- L K Ho
- Section of Cell Biology and Experimental Pathology, Institute of Cancer Research, Haddow Laboratories, Sutton, Surrey, United Kingdom
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166
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Weinkove D, Leevers SJ, MacDougall LK, Waterfield MD. p60 is an adaptor for the Drosophila phosphoinositide 3-kinase, Dp110. J Biol Chem 1997; 272:14606-10. [PMID: 9169420 DOI: 10.1074/jbc.272.23.14606] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The mammalian phosphoinositide 3-kinases (PI3Ks) p110alpha, beta, and delta form heterodimers with Src homology 2 (SH2) domain-containing adaptors such as p85alpha or p55(PIK). The two SH2 domains of these adaptors bind to phosphotyrosine residues (pY) found within the consensus sequence pYXXM. Here we show that a heterodimer of the Drosophila PI3K, Dp110, with an adaptor, p60, can be purified from S2 cells with a pYXXM phosphopeptide affinity matrix. Using amino acid sequence from the gel-purified protein, the gene encoding p60 was cloned and mapped to the genomic region 21B8-C1, and the exon/intron structure was determined. p60 contains two SH2 domains and an inter-SH2 domain but lacks the SH3 and breakpoint cluster region homology (BH) domains found in mammalian p85alpha and beta. Analysis of the sequence of p60 shows that the amino acids responsible for the SH2 domain binding specificity in mammalian p85alpha are conserved and predicts that the inter-SH2 domain has a coiled-coil structure. The Dp110.p60 complex was immunoprecipitated with p60-specific antisera and shown to possess both lipid and protein kinase activity. The complex was found in larvae, pupae, and adults, consistent with p60 functioning as the adaptor for Dp110 throughout the Drosophila life cycle.
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Affiliation(s)
- D Weinkove
- Ludwig Institute for Cancer Research, 91 Riding House Street, London W1P 8BT, United Kingdom
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167
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Duménil G, Rubini M, Dubois G, Baserga R, Fellous M, Pellegrini S. Identification of signalling components in tyrosine kinase cascades using phosphopeptide affinity chromatography. Biochem Biophys Res Commun 1997; 234:748-53. [PMID: 9175787 DOI: 10.1006/bbrc.1997.6702] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Various methods are now available to identify the molecular partners of the component of a signal transduction pathway. Some interactions, however, can be technically difficult to detect because they depend upon transient tyrosine phosphorylation. Here, we present a simple affinity chromatography approach based on synthetic phosphopeptides to purify potential partners of phosphotyrosine-containing proteins. With this approach, we confirm the previously characterized interaction between Grb2 and the EGF receptor, and we identify novel partners of the IGF-1 receptor and of the JAK proteins. Methenyltetrahydrofolate synthetase (MTHFS) was identified as a potential mediator of IGF-1R dependent transformation. P85alpha, the regulatory subunit of PI3 kinase, was identified as one of four proteins recruited by a phosphopeptide mimicking a motif conserved in all JAK family members.
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Affiliation(s)
- G Duménil
- Unité INSERM 276, Institut Pasteur, Paris, France.
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168
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Ogihara T, Shin BC, Anai M, Katagiri H, Inukai K, Funaki M, Fukushima Y, Ishihara H, Takata K, Kikuchi M, Yazaki Y, Oka Y, Asano T. Insulin receptor substrate (IRS)-2 is dephosphorylated more rapidly than IRS-1 via its association with phosphatidylinositol 3-kinase in skeletal muscle cells. J Biol Chem 1997; 272:12868-73. [PMID: 9139749 DOI: 10.1074/jbc.272.19.12868] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Insulin receptor substrate (IRS)-2 is structurally and functionally similar to IRS-1. Indeed, stimulation with insulin or insulin-like growth factor I led to the rapid tyrosine phosphorylation of both IRS-1 and IRS-2, which in turn activated phosphatidylinositol (PI) 3-kinase in L6 cells and rat skeletal muscle. However, IRS-2 was rapidly dephosphorylated (3-10 min after the addition of insulin/insulin-like growth factor I), whereas IRS-1 phosphorylation continued for at least 60 min. The time courses of the PI 3-kinase activity associated with IRS-1 and IRS-2 paralleled the tyrosine phosphorylation of these proteins. Preincubation with sodium orthovanadate, an inhibitor of protein tyrosine phosphatase, blocked the rapid dephosphorylation of IRS-2, suggesting the involvement of tyrosine phosphatase. The activation of PI 3-kinase apparently plays an important role in the rapid dephosphorylation of IRS-2, as IRS-2 dephosphorylation was inhibited markedly by suppressing PI 3-kinase activity with wortmannin or overexpression of the dominant negative p85 subunit of PI 3-kinase, which cannot bind the p110 catalytic subunit. In addition, platelet-derived growth factor stimulation prior to insulin stimulation decreased IRS-associated PI 3-kinase and significantly inhibited the dephosphorylation of IRS-2. Taken together, these observations suggest that IRS-2 plays a unique role in mediating the signals from the insulin receptor to downstream molecules and that this effect is more transient than that of IRS-1. Tyrosine phosphatase and IRS-associated PI 3-kinase activity thus contribute to the rapid dephosphorylation of IRS-2.
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Affiliation(s)
- T Ogihara
- Third Department of Internal Medicine, Faculty of Medicine, University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113, Japan
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169
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Vanhaesebroeck B, Welham MJ, Kotani K, Stein R, Warne PH, Zvelebil MJ, Higashi K, Volinia S, Downward J, Waterfield MD. P110delta, a novel phosphoinositide 3-kinase in leukocytes. Proc Natl Acad Sci U S A 1997; 94:4330-5. [PMID: 9113989 PMCID: PMC20722 DOI: 10.1073/pnas.94.9.4330] [Citation(s) in RCA: 351] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Phosphoinositide 3-kinases (PI3Ks) are a family of lipid kinases that have been implicated in signal transduction through tyrosine kinase- and heterotrimeric G-protein-linked receptors. We report herein the cloning and characterization of p110delta, a novel class I PI3K. Like p110alpha and p110beta, other class I PI3Ks, p110delta displays a broad phosphoinositide lipid substrate specificity and interacts with SH2/SH3 domain-containing p85 adaptor proteins and with GTP-bound Ras. In contrast to the widely distributed p110alpha and beta, p110delta is exclusively found in leukocytes. In these cells, p110alpha and delta both associate with the p85alpha and beta adaptor subunits and are similarly recruited to activated signaling complexes after treatment with the cytokines interleukin 3 and 4 and stem cell factor. Thus, these class I PI3Ks appear not to be distinguishable at the level of p85 adaptor selection or recruitment to activated receptor complexes. However, distinct biochemical and structural features of p110delta suggest divergent functional/regulatory capacities for this PI3K. Unlike p110alpha, p110delta does not phosphorylate p85 but instead harbors an intrinsic autophosphorylation capacity. In addition, the p110delta catalytic domain contains unique potential protein-protein interaction modules such as a Pro-rich region and a basic-region leucine-zipper (bZIP)-like domain. Possible selective functions of p110delta in white blood cells are discussed.
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Affiliation(s)
- B Vanhaesebroeck
- Ludwig Institute for Cancer Research, 91 Riding House Street, London W1P 8BT, United Kingdom
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170
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Stephens LR, Eguinoa A, Erdjument-Bromage H, Lui M, Cooke F, Coadwell J, Smrcka AS, Thelen M, Cadwallader K, Tempst P, Hawkins PT. The G beta gamma sensitivity of a PI3K is dependent upon a tightly associated adaptor, p101. Cell 1997; 89:105-14. [PMID: 9094719 DOI: 10.1016/s0092-8674(00)80187-7] [Citation(s) in RCA: 462] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Two highly similar, PtdIns(4,5)P2-selective, G beta gamma-activated PI3Ks were purified from pig neutrophil cytosol. Both were heterodimers, were composed of a 101 kDa protein and either a 120 kDa or a 117 kDa catalytic subunit, and were activated greater than 100-fold by G beta gammas. Peptide sequence-based oligonucleotide probes were used to clone cDNAs for the p120 and p101 species. The cDNA of p120 is highly related to p110 gamma, while the cDNA of p101 is not substantially related to anything in current databases. The proteins were expressed in and purified from insect and mammalian cells. They bound tightly to one another, both in vivo and in vitro, and in so doing, p101 amplified the effect of G beta gammas on the PI3K activity of p120 from less than 2-fold to greater than 100-fold.
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Affiliation(s)
- L R Stephens
- Department of Signalling, The Babraham Institute, Cambridge, United Kingdom
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171
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Inukai K, Funaki M, Ogihara T, Katagiri H, Kanda A, Anai M, Fukushima Y, Hosaka T, Suzuki M, Shin BC, Takata K, Yazaki Y, Kikuchi M, Oka Y, Asano T. p85alpha gene generates three isoforms of regulatory subunit for phosphatidylinositol 3-kinase (PI 3-Kinase), p50alpha, p55alpha, and p85alpha, with different PI 3-kinase activity elevating responses to insulin. J Biol Chem 1997; 272:7873-82. [PMID: 9065454 DOI: 10.1074/jbc.272.12.7873] [Citation(s) in RCA: 117] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Phosphatidylinositol 3-kinase (PI 3-kinase) is stimulated by association with a variety of tyrosine kinase receptors and intracellular tyrosine-phosphorylated substrates. We isolated a cDNA that encodes a 50-kDa regulatory subunit of PI 3-kinase with an expression cloning method using 32P-labeled insulin receptor substrate-1 (IRS-1). This 50-kDa protein contains two SH2 domains and an inter-SH2 domain of p85alpha, but the SH3 and bcr homology domains of p85alpha were replaced by a unique 6-amino acid sequence. Thus, this protein appears to be generated by alternative splicing of the p85alpha gene product. We suggest that this protein be called p50alpha. Northern blotting using a specific DNA probe corresponding to p50alpha revealed 6.0- and 2.8-kb bands in hepatic, brain, and renal tissues. The expression of p50alpha protein and its associated PI 3-kinase were detected in lysates prepared from the liver, brain, and muscle using a specific antibody against p50alpha. Taken together, these observations indicate that the p85alpha gene actually generates three protein products of 85, 55, and 50 kDa. The distributions of the three proteins (p85alpha, p55alpha, and p50alpha), in various rat tissues and also in various brain compartments, were found to be different. Interestingly, p50alpha forms a heterodimer with p110 that can as well as cannot be labeled with wortmannin, whereas p85alpha and p55alpha associate only with p110 that can be wortmannin-labeled. Furthermore, p50alpha exhibits a markedly higher capacity for activation of associated PI 3-kinase via insulin stimulation and has a higher affinity for tyrosine-phosphorylated IRS-1 than the other isoforms. Considering the high level of p50alpha expression in the liver and its marked responsiveness to insulin, p50alpha appears to play an important role in the activation of hepatic PI 3-kinase. Each of the three alpha isoforms has a different function and may have specific roles in various tissues.
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Affiliation(s)
- K Inukai
- Third Department of Internal Medicine, Faculty of Medicine, University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113, The, Japan
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172
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Laviola L, Giorgino F, Chow JC, Baquero JA, Hansen H, Ooi J, Zhu J, Riedel H, Smith RJ. The adapter protein Grb10 associates preferentially with the insulin receptor as compared with the IGF-I receptor in mouse fibroblasts. J Clin Invest 1997; 99:830-7. [PMID: 9062339 PMCID: PMC507889 DOI: 10.1172/jci119246] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
To identify receptor-associated proteins that may contribute to the specificity of insulin and IGF-I signaling responses, a mouse embryo library was screened using the yeast two-hybrid system. Multiple receptor-interactive clones encoding the SH2 domain of the adapter protein Grb10 were isolated. Subsequent cloning of the full-length Grb10 sequence from a mouse fat cDNA library defined a previously unknown Grb10 variant, that appears to be the predominant isoform in mouse tissues. Receptor-deficient R- cells (fibroblasts from mice with homologous disruption of the IGF-I receptor gene) and transfected R- cells expressing either insulin receptors (R-IR cells) or IGF-I receptors (R+ cells) were used to investigate the specificity of Grb10 interaction with the two related receptors. Hormone-activated insulin receptors in R-IR cells coprecipitated with three species, all recognized as Grb10 isoforms by specific Grb10 antibody. Under the same conditions, Grb10 was essentially undetectable in IGF-I receptor immunoprecipitates from stimulated R+ cells. Grb10 association with insulin receptors was maximal at 10 nM insulin stimulation and sustained from 5-10 min after hormone stimulation in R-IR cells. In conclusion, Grb10 interacts preferentially with insulin vs. IGF-I receptors in intact cells and, thus, may have a role in mediating insulin receptor-specific cellular responses.
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Affiliation(s)
- L Laviola
- Research Division, Joslin Diabetes Center, Harvard Medical School, Boston, Massachusetts 02215, USA
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173
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Katagiri H, Asano T, Inukai K, Ogihara T, Ishihara H, Shibasaki Y, Murata T, Terasaki J, Kikuchi M, Yazaki Y, Oka Y. Roles of PI 3-kinase and Ras on insulin-stimulated glucose transport in 3T3-L1 adipocytes. THE AMERICAN JOURNAL OF PHYSIOLOGY 1997; 272:E326-31. [PMID: 9124342 DOI: 10.1152/ajpendo.1997.272.2.e326] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The dominant negative p85alpha regulatory subunit (delta p85alpha) of phosphatidylinositol (PI) 3-kinase or dominant negative Ras (N17Ras) was overexpressed in 3T3-L1 adipocytes using an adenovirus-mediated gene transduction system. Functional expression of delta p85alpha and N17Ras was confirmed by marked inhibition of insulin-stimulated PI 3-kinase activity and mitogen-activated protein kinase activity, respectively. N17Ras expression did not affect glucose transport activity, whereas delta p85alpha expression inhibited insulin-stimulated glucose transport with impairment of GLUT-4 translocation, although inhibition of glucose transport activity was less remarkable than that of PI 3-kinase activity in delta p85alpha-expressing cells. Thus the Ras signaling pathway does not play a major part in either translocation or intrinsic activity of glucose transporters, but PI 3-kinase activation, via phosphotyrosyl proteins and heterodimeric PI 3-kinase, plays a pivotal role in insulin-stimulated glucose transport. However, a discrepancy was observed between PI 3-kinase activity and glucose transport activity, suggesting a possibility that a different pathway(s) is involved in insulin-stimulated intrinsic activity of glucose transporters.
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Affiliation(s)
- H Katagiri
- Third Department of Internal Medicine, Faculty of Medicine, University of Tokyo, Hongo, Japan
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174
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Linassier C, MacDougall LK, Domin J, Waterfield MD. Molecular cloning and biochemical characterization of a Drosophila phosphatidylinositol-specific phosphoinositide 3-kinase. Biochem J 1997; 321 ( Pt 3):849-56. [PMID: 9032475 PMCID: PMC1218144 DOI: 10.1042/bj3210849] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Molecular, biochemical and genetic characterization of phosphoinositide 3-kinases (PI3Ks) have identified distinct classes of enzymes involved in processes mediated by activation of cell-surface receptors and in constitutive intracellular protein trafficking events. The latter process appears to involve a PtdIns-specific PI3K first described in yeast as a mutant, vps34, defective in the sorting of newly synthesized proteins from the Golgi to the vacuole. We have identified a representative member of each class of PI3Ks in Drosophila using a PCR-based approach. In the present paper we describe the molecular cloning of a PI3K from Drosophila, P13K_59F, that shows sequence similarity to Vps34. PI3K_59F encodes a protein of 108 kDa co-linear with Vps34 homologues, and with three regions of sequence similarity to other PI3Ks. Biochemical characterization of the enzyme, by expression of the complete coding sequence as a glutathione S-transferase fusion protein in Sf9 cells, demonstrates that PI3K_59F is a PtdIns-specific PI3K that can utilize either Mg2+ or Mn2+. This activity is sensitive to inhibition both by non-ionic detergent (Nonidet P40) and by wortmannin (IC50 10 nM). PI3K_59F, therefore, conserves both the structural and biochemical properties of the Vps34 class of enzymes.
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Affiliation(s)
- C Linassier
- Ludwig Institute for Cancer Research, University College London, U.K
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175
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McIlroy J, Chen D, Wjasow C, Michaeli T, Backer JM. Specific activation of p85-p110 phosphatidylinositol 3'-kinase stimulates DNA synthesis by ras- and p70 S6 kinase-dependent pathways. Mol Cell Biol 1997; 17:248-55. [PMID: 8972205 PMCID: PMC231749 DOI: 10.1128/mcb.17.1.248] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
We have developed a polyclonal antibody that activates the heterodimeric p85-p110 phosphatidylinositol (PI) 3'-kinase in vitro and in microinjected cells. Affinity purification revealed that the activating antibody recognized the N-terminal SH2 (NSH2) domain of p85, and the antibody increased the catalytic activity of recombinant p85-p110 dimers threefold in vitro. To study the role of endogenous PI 3'-kinase in intact cells, the activating anti-NSH2 antibody was microinjected into GRC + LR73 cells, a CHO cell derivative selected for tight quiescence during serum withdrawal. Microinjection of anti-NSH2 antibodies increased bromodeoxyuridine (BrdU) incorporation fivefold in quiescent cells and enhanced the response to serum. These data reflect a specific activation of PI 3'-kinase, as the effect was blocked by coinjection of the appropriate antigen (glutathione S-transferase-NSH2 domains from p85 alpha), coinjection of inhibitory anti-p110 antibodies, or treatment of cells with wortmannin. We used the activating antibodies to study signals downstream from PI 3'-kinase. Although treatment of cells with 50 nM rapamycin only partially decreased anti-NSH2-stimulated BrdU incorporation, coinjection with an anti-p70 S6 kinase antibody effectively blocked anti-NSH2-stimulated DNA synthesis. We also found that coinjection of inhibitory anti-ras antibodies blocked both serum- and anti-NSH2-stimulated BrdU incorporation by approximately 60%, and treatment of cells with a specific inhibitor of MEK abolished antibody-stimulated BrdU incorporation. We conclude that selective activation of physiological levels of PI 3'-kinase is sufficient to stimulate DNA synthesis in quiescent cells. PI 3'-kinase-mediated DNA synthesis requires both p70 S6 kinase and the P21ras/MEK pathway.
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Affiliation(s)
- J McIlroy
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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176
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Leevers SJ, Weinkove D, MacDougall LK, Hafen E, Waterfield MD. The Drosophila phosphoinositide 3-kinase Dp110 promotes cell growth. EMBO J 1996; 15:6584-94. [PMID: 8978685 PMCID: PMC452483] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Phosphoinositide 3-kinases (PI3Ks) have been identified in an evolutionarily diverse range of organisms, including mammals, Drosophila, yeast, plants and Dictyostelium. They are activated by a multitude of extracellular signals and implicated in mitogenesis, differentiation and cell survival, as well as in the control of the cytoskeleton and cell shape. Here we describe the molecular and functional analysis of Drosophila p110 (Dp110). A full-length Dp110 cDNA was isolated and found to encode a protein homologous throughout its length to the class I mammalian PI3Ks p110alpha and p110beta. Overexpression of Dp110 in wing or eye imaginal discs resulted in flies with enlarged wings or eyes respectively. In contrast, overexpression of Dp110 containing a mutation predicted to result in the loss of catalytic activity resulted in smaller wings and eyes. The alterations in wing size result from changes in both cell size and cell number, whereas in the eye only differences in cell size were detected. These data imply a role for Dp110 in growth control during Drosophila development and have implications for the function of class I PI3Ks in other organisms.
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Affiliation(s)
- S J Leevers
- Ludwig Institute for Cancer Research, London, UK
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177
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Kanagasundaram V, Jaworowski A, Hamilton JA. Association between phosphatidylinositol-3 kinase, Cbl and other tyrosine phosphorylated proteins in colony-stimulating factor-1-stimulated macrophages. Biochem J 1996; 320 ( Pt 1):69-77. [PMID: 8947469 PMCID: PMC1217899 DOI: 10.1042/bj3200069] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Colony stimulating factor-1 (CSF-1) stimulation of the macrophage cell line BAC1.2F5 and murine bone marrow-derived macrophages resulted in tyrosine phosphorylation of phosphatidylinositol-3 kinase (PI-3 kinase) p85 alpha and its stable association with several tyrosine phosphorylated proteins, including CSF-1 receptor (p165), p120, p95 and p55-p60. p120 co-migrated with the product of the protooncogene c-cb1 in anti-p85 alpha immunoprecipitates, and associated with p85 alpha in a rapid and transient manner. Reciprocal experiments confirmed the presence of p85 alpha in anti-Cb1 immunoprecipitates on CSF-1 stimulation of macrophages. PI-3 kinase immunoprecipitates from the myeloid FDC-P1 cell line expressing mutant CSF-1 receptor (Y721F), which does not associate with PI-3 kinase, still contained Cbl. The identity of the tyrosine phosphorylated protein p95 remains unknown. The interaction between p85 alpha and the tyrosine phosphorylated proteins survived anion-exchange chromatography, suggesting perhaps the presence of a stable complex; furthermore, in CSF-1-treated BAC1.2F5 cell extracts, only one of the two pools of PI-3 kinase separated by chromatography was present in this putative complex. The association did not appear to correlate with proliferation, since a similar interaction between p85 alpha and tyrosine phosphorylated proteins was also observed in poorly proliferating resident peritoneal macrophages stimulated with CSF-1. The possible significance of these findings for CSF-1-regulated macrophage functions is discussed.
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Affiliation(s)
- V Kanagasundaram
- University of Melbourne, Department of Medicine, Royal Melbourne Hospital, Parkville, Victoria, Australia
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178
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Yamamoto-Honda R, Honda Z, Ueki K, Tobe K, Kaburagi Y, Takahashi Y, Tamemoto H, Suzuki T, Itoh K, Akanuma Y, Yazaki Y, Kadowaki T. Mutant of insulin receptor substrate-1 incapable of activating phosphatidylinositol 3-kinase did not mediate insulin-stimulated maturation of Xenopus laevis oocytes. J Biol Chem 1996; 271:28677-81. [PMID: 8910502 DOI: 10.1074/jbc.271.45.28677] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Insulin receptor substrate-1 (IRS-1) is rapidly phosphorylated on multiple tyrosine residues in response to insulin and binds several Src homology 2 domain-containing proteins, thereby initiating downstream signaling. To assess the tyrosine phosphorylation sites that mediate relevant downstream signaling and biological effects, we created site-directed mutants of IRS-1 and overexpressed them in the Xenopus laevis oocyte. In oocytes overexpressing IRS-1 or IRS-1-895F (Tyr-895 replaced with phenylalanine), insulin activated phosphatidylinositol (PI) 3-kinase, p70 S6 kinase, and mitogen-activated protein kinase and induced oocyte maturation. In contrast, in oocytes overexpressing IRS-1-4F (Tyr-460, Tyr-608, Tyr-939, and Tyr-987 of IRS-1 replaced with phenylalanine), insulin did not activate PI 3-kinase, p70 S6 kinase, and mitogen-activated protein kinase and failed to induce oocyte maturation. These observations indicate that in X. laevis oocytes overexpressing IRS-1, the association of PI 3-kinase rather than Grb2 (growth factor-bound protein 2) with IRS-1 plays a major role in insulin-induced oocyte maturation. Activation of PI 3-kinase may lie upstream of mitogen-activated protein kinase activation and p70 S6 kinase activation in response to insulin.
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Affiliation(s)
- R Yamamoto-Honda
- Third Department of Internal Medicine, Faculty of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan
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179
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Joos H, Trouliaris S, Helftenbein G, Niemann H, Tamura T. Tyrosine phosphorylation of the juxtamembrane domain of the v-Fms oncogene product is required for its association with a 55-kDa protein. J Biol Chem 1996; 271:24476-81. [PMID: 8798707 DOI: 10.1074/jbc.271.40.24476] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Tyrosine autophosphorylation of the v-Fms oncogene product results in the formation of high affinity binding sites for cellular proteins with Src homology 2 (SH2) domains that are involved in various signal cascades. Tryptic digestion of the autophosphorylated v-Fms and of its cellular counterpart, the feline c-Fms polypeptide, gave rise to at least six common major phosphopeptides, four of which have been characterized previously. Employing site-directed mutagenesis and phosphopeptide mapping of in vitro phosphorylated glutathione S-transferase v-Fms fusion proteins as well as full-length v-Fms molecules expressed in various cells, we show here that Tyr543 of the juxtamembrane domain and Tyr696 of the kinase insert domain constitute major autophosphorylation sites. Recombinant fusion proteins containing the tyrosine-phosphorylated kinase insert domain bind the growth factor receptor bound protein 2 and the p85 and p110 subunits of phosphatidylinositol 3'-kinase. In contrast, fusion proteins containing the juxtamembrane domain phosphorylated on Tyr543 fail to bind any of the known SH2 domain-containing cellular proteins but associate specifically with an as yet undefined 55-kDa cellular protein that by itself is phosphorylated on tyrosine.
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Affiliation(s)
- H Joos
- Institut für Virologie, Justus-Liebig-Universität Giessen, Frankfurter Strasse 107, D-35392 Giessen, Federal Republic of Germany
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180
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Folli F, Ghidella S, Bonfanti L, Kahn CR, Merighi A. The early intracellular signaling pathway for the insulin/insulin-like growth factor receptor family in the mammalian central nervous system. Mol Neurobiol 1996; 13:155-83. [PMID: 8938649 DOI: 10.1007/bf02740639] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Several studies support the idea that the polypeptides belonging to the family of insulin and insulin-like growth factors (IGFs) play an important role in brain development and continue to be produced in discrete areas of the adult brain. In numerous neuronal populations within the olfactory bulb, the cerebral and cerebellar cortex, the hippocampus, some diencephalic and brainstem nuclei, the spinal cord and the retina, specific insulin and IGF receptors, as well as crucial components of the intracellular receptor signaling pathway have been demonstrated. Thus, mature neurons are endowed with the cellular machinery to respond to insulin and IGF stimulation. Studies in vitro and in vivo, using normal and transgenic animals, have led to the hypothesis that, in the adult brain, IGF-I not only acts as a trophic factor, but also as a neuromodulator of some higher brain functions, such as long-term potentiation and depression. Furthermore, a trophic effect on certain neuronal populations becomes clearly evident in the ischemic brain or neurodegenerative disorders. Thus, the analysis of the early intracellular signaling pathway for the insulin/IGF receptor family in the brain is providing us with new intriguing findings on the way the mammalian brain is sculpted and operates.
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MESH Headings
- Adult
- Animals
- Ataxia Telangiectasia/genetics
- Ataxia Telangiectasia/pathology
- Brain/embryology
- Brain/growth & development
- Brain/physiology
- Brain Ischemia/metabolism
- Brain Ischemia/pathology
- Cells, Cultured
- Encephalomyelitis, Autoimmune, Experimental/genetics
- Encephalomyelitis, Autoimmune, Experimental/pathology
- Gene Expression Regulation
- Humans
- Insulin/physiology
- Mammals/embryology
- Mammals/growth & development
- Mammals/physiology
- Mice
- Mice, Neurologic Mutants
- Mice, Transgenic
- Models, Neurological
- Nerve Tissue Proteins/drug effects
- Nerve Tissue Proteins/physiology
- Phosphorylation
- Protein Processing, Post-Translational
- Protein-Tyrosine Kinases/metabolism
- Rats
- Receptor, Insulin/drug effects
- Receptor, Insulin/physiology
- Receptors, Somatomedin/drug effects
- Receptors, Somatomedin/physiology
- Retina/physiology
- Signal Transduction/physiology
- Somatomedins/physiology
- Spinal Cord/physiology
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Affiliation(s)
- F Folli
- Joslin Diabetes Center, Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115, USA
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181
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Domin J, Dhand R, Waterfield MD. Binding to the platelet-derived growth factor receptor transiently activates the p85alpha-p110alpha phosphoinositide 3-kinase complex in vivo. J Biol Chem 1996; 271:21614-21. [PMID: 8702949 DOI: 10.1074/jbc.271.35.21614] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Ligand stimulation of the platelet-derived growth factor (PDGF) receptor results in its association with phosphoinositide 3-kinase activity and a corresponding synthesis of 3'-phosphorylated lipids. Early studies that examined this interaction in vivo employed anti-phosphotyrosine antiserum or antiserum against the PDGF receptor. The recent identification of multiple isoforms of both the regulatory and the catalytic subunit of the enzyme have led us to utilize antisera against p85alpha and p110alpha to characterize the association of this particular phosphoinositide 3-kinase complex with the PDGF receptor following ligand stimulation of murine fibroblasts. Both the p85alpha and p110alpha subunits rapidly associated with the ligand-activated receptor resulting in a transient, 2-fold increase in the total pool of p110alpha lipid kinase activity. This association was stable for 15 min after initial stimulation. Subsequently, both subunits began to dissociate from the receptor with similar kinetics. By 60 min this process was complete, demonstrating that p85alpha and p110alpha both associate with the receptor and dissociate from the receptor as a dimeric complex. At this time, marked PDGF receptor down-regulation was observed. Immunoprecipitation from metabolically labeled cells revealed that p85alpha is constitutively phosphorylated on serine residues in quiescent cultures. Upon PDGF stimulation, this phosphorylation upon serine residues was maintained in addition to tyrosine phosphorylation of this subunit. No phosphorylation of the p110alpha subunit was detected in either quiescent or PDGF-stimulated cells. Quantitation of Western blot analysis demonstrated that only 5% of the total pool of p85alpha associated with the PDGF receptor upon ligand stimulation. The 2-fold increase in the lipid kinase activity measured in immunoprecipitates using either anti-p85alpha or anti-p110alpha antiserum therefore reflects a far greater increase in the specific activity of the enzyme upon its association with the PDGF receptor.
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Affiliation(s)
- J Domin
- Ludwig Institute for Cancer Research, London, W1P 8BT, United Kingdom
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182
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Navé BT, Haigh RJ, Hayward AC, Siddle K, Shepherd PR. Compartment-specific regulation of phosphoinositide 3-kinase by platelet-derived growth factor and insulin in 3T3-L1 adipocytes. Biochem J 1996; 318 ( Pt 1):55-60. [PMID: 8761452 PMCID: PMC1217588 DOI: 10.1042/bj3180055] [Citation(s) in RCA: 114] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
To understand how the stimulation of phosphoinositide 3-kinase (PI 3-kinase) by different growth factors can activate different subsets of downstream responses, growth-factor regulation of PI 3-kinase activity at different intracellular locations was investigated in 3T3-L1 adipocytes. Insulin caused a large stimulation of glucose transport and stimulated recruitment of transferrin receptors to the plasma membrane (PM) in these cells, whereas platelet-derived growth factor (PDGF)-bb was virtually without effect on these responses. Subcellular fractionation studies after stimulation with PDGF-bb or insulin revealed a differential effect of these growth factors on subcellular localization of PI 3-kinase activity. PDGF was more effective than insulin in stimulating PI 3-kinase activity and recruiting the p85 alpha PI 3-kinase adaptor subunit in the fraction containing the PM. However, in the microsomal fraction insulin significantly increased PI 3-kinase activity and p85 alpha levels, whereas PDGF was almost without effect. In the microsomal membrane fraction the insulin-stimulated recruitment of p85 alpha closely matched the increase PI 3-kinase activity, indicating that insulin stimulation of PI 3-kinase in this fraction is largely due to recruitment of PI 3-kinase enzyme rather than alterations in specific activity. Insulin-stimulated recruitment of p85 alpha to the microsomal membranes was not inhibited by wortmannin, indicating that PI 3-kinase activity was not required for this process. A further level of compartment-specific regulation of PI 3-kinase in response to PDGF was revealed by the finding that tyrosine phosphorylation of the p85 alpha adaptor was restricted to the PM-containing fraction. Insulin had no effect on p85 tyrosine phosphorylation in either fraction. In summary, these results suggest a basis by which insulin and PDGF could both use PI 3-kinase signalling cascades but achieve different signalling outcomes.
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Affiliation(s)
- B T Navé
- Department of Clinical Biochemistry, University of Cambridge, Addenbrooke's Hospital, U.K
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183
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Morris JZ, Tissenbaum HA, Ruvkun G. A phosphatidylinositol-3-OH kinase family member regulating longevity and diapause in Caenorhabditis elegans. Nature 1996; 382:536-9. [PMID: 8700226 DOI: 10.1038/382536a0] [Citation(s) in RCA: 632] [Impact Index Per Article: 22.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
A pheromone-induced neurosecretory pathway in Caenorhabditis elegans triggers developmental arrest and an increase in longevity at the dauer diapause stage. The gene age-1 is required for non-dauer development and normal senescence. age-1 encodes a homologue of mammalian phosphatidylinositol-3-OH kinase (PI(3)K) catalytic subunits. Lack of both maternal and zygotic age-1 activity causes dauer formation, whereas animals with maternal but not zygotic age-1 activity develop as non-dauers that live more than twice as long as normal. These data suggest that phosphatidylinositol signalling mediated by AGE-1 protein controls lifespan and the dauer diapause decision.
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Affiliation(s)
- J Z Morris
- Department of Molecular Biology, Massachusetts General Hospital, Boston 02114, USA
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184
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Carpenter CL, Cantley LC. Phosphoinositide 3-kinase and the regulation of cell growth. BIOCHIMICA ET BIOPHYSICA ACTA 1996; 1288:M11-6. [PMID: 8764841 DOI: 10.1016/0304-419x(96)00018-2] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Affiliation(s)
- C L Carpenter
- Department of Medicine, Beth Israel Hospital, Harvard Medical School, Boston, MA 02115, USA
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185
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Myers MG, Zhang Y, Aldaz GA, Grammer T, Glasheen EM, Yenush L, Wang LM, Sun XJ, Blenis J, Pierce JH, White MF. YMXM motifs and signaling by an insulin receptor substrate 1 molecule without tyrosine phosphorylation sites. Mol Cell Biol 1996; 16:4147-55. [PMID: 8754813 PMCID: PMC231411 DOI: 10.1128/mcb.16.8.4147] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Tyrosine phosphorylation of insulin receptor substrate 1 (IRS-1) by the activated receptors for insulin, IGF-1, and various cytokines creates binding sites for signaling proteins with Src homology 2 domains (SH2 proteins). Determining the role of specific SH2 proteins during insulin signaling has been difficult because IRS-1 possesses as many as 18 potential tyrosine phosphorylation sites, several of which contain redundant motifs. Using 32D cells, which contain no endogenous IRS proteins, we compared the signaling ability of an IRS-1 molecule in which 18 potential tyrosine phosphorylation sites were replaced by phenylalanine (IRS-1(F18)) with two derivative molecules which retained three YMXM motifs (IRS-1(3YMXM)) or the two COOH-terminal SHP2-Fyn binding sites (IRS-1(YCT)). During insulin stimulation, IRS-1(F18) failed to undergo tyrosine phosphorylation or mediate activation of the phosphotidylinositol (PI) 3'-kinase or p70(s6k); IRS-1(YCT) was tyrosine phosphorylated but also failed to mediate these signaling events. Neither IRS-1(3YMXM) nor IRS-1(YCT) mediated activation of mitogen-activated protein kinases. IRS-1(F18) and IRS-1(YCT) partially mediated similar levels of insulin-stimulated mitogenesis at high insulin concentrations, however, suggesting that IRS-1 contains phosphotyrosine-independent elements which effect mitogenic signals, and that the sites in IRS-l(YCT) do not augment this signal. IRS-1(3YMXM) mediated the maximal mitogenic response to insulin, although the response to insulin was more sensitive with wild-type IRS-1. By contrast, the association of IRS-1(3YMXM) with PI 3'-kinase was more sensitive to insulin than the association with IRS-1. Thus, the binding of SH2 proteins (such as PI 3'-kinase) by YMXM motifs in IRS-1 is an important element in the mitogenic response, but other elements are essential for full mitogenic sensitivity.
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Affiliation(s)
- M G Myers
- Research Division, Joslin Diabetes Center and Program in Biological and Biochemical Sciences, Boston, Massachusetts 02115, USA
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186
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Abstract
This review discusses some rules for assessing the completeness of a cDNA sequence and identifying the start site for translation. Features commonly invoked-such as an ATG codon in a favorable context for initiation, or the presence of an upstream in-frame terminator codon, or the prediction of a signal peptide-like sequence at the amino terminus-have some validity; but examples drawn from the literature illustrate limitations to each of these criteria. The best advice is to inspect a cDNA sequence not only for these positive features but also for the absence of certain negative indicators. Three specific warning signs are discussed and documented: (i) The presence of numerous ATG codons upstream from the presumptive start site for translation often indicates an aberration (sometimes a retained intron) at the 5' end of the cDNA. (ii) Even one strong, upstream, out-of-frame ATG codon poses a problem if the reading frame set by the upstream ATG overlaps the presumptive start of the major open reading frame. Many cDNAs that display this arrangement turn out to be incomplete; that is, the out-of-frame ATG codon is within, rather than upstream from, the protein coding domain. (iii) A very weak context at the putative start site for translation often means that the cDNA lacks the authentic initiator codon. In addition to presenting some criteria that may aid in recognizing incomplete cDNA sequences, the review includes some advice for using in vitro translation systems for the expression of cDNAs. Some unresolved questions about translational regulation are discussed by way of illustrating the importance of verifying mRNA structures before making deductions about translation.
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Affiliation(s)
- M Kozak
- Department of Biochemistry, University of Medicine and Dentistry of New Jersey, 675 Hoes Lane, Piscataway, New Jersey 08854, USA
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187
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Katagiri H, Asano T, Ishihara H, Inukai K, Shibasaki Y, Kikuchi M, Yazaki Y, Oka Y. Overexpression of catalytic subunit p110alpha of phosphatidylinositol 3-kinase increases glucose transport activity with translocation of glucose transporters in 3T3-L1 adipocytes. J Biol Chem 1996; 271:16987-90. [PMID: 8663584 DOI: 10.1074/jbc.271.29.16987] [Citation(s) in RCA: 151] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
To elucidate the mechanisms of phosphatidylinositol (PI) 3-kinase involvement in insulin-stimulated glucose transport activity, the epitope-tagged p110alpha subunit of PI 3-kinase was overexpressed in 3T3-L1 adipocytes using an adenovirus-mediated gene transduction system. Overexpression of p110alpha was confirmed by immunoblot using anti-tagged epitope antibody. p110alpha overexpression induced a 2.5-fold increase in PI 3-kinase activity associated with its regulatory subunits in the basal state, an increase exceeding that of the maximally insulin-stimulated control cells, while PI 3-kinase activity associated with phosphotyrosyl protein was only modestly elevated. Overexpression of p110alpha induced an approximately 14-fold increase in the basal glucose transport rate, which was also greater than that observed in the stimulated control. No apparent difference was observed in the cellular expression level of either GLUT1 or GLUT4 proteins between control and p110alpha-overexpressing 3T3-L1 adipocytes. Subcellular fractionation revealed translocation of glucose transporters from intracellular to plasma membranes in basal p110alpha-overexpressing cells. The translocation of GLUT4 protein to the plasma membrane was further confirmed using a membrane sheet assay. These findings indicate that an increment in PI 3-kinase activity induced by overexpression of p110alpha of PI 3-kinase stimulates glucose transport activity with translocation of glucose transporters, i.e., mimics the effect of insulin.
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Affiliation(s)
- H Katagiri
- Third Department of Internal Medicine, Faculty of Medicine, University of Tokyo, Hongo, Tokyo 113, Japan
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188
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Mothe I, Van Obberghen E. Phosphorylation of insulin receptor substrate-1 on multiple serine residues, 612, 632, 662, and 731, modulates insulin action. J Biol Chem 1996; 271:11222-7. [PMID: 8626671 DOI: 10.1074/jbc.271.19.11222] [Citation(s) in RCA: 203] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Okadaic acid has been described previously as being a negative regulator of insulin signaling, as it inhibits insulin stimulation of glucose transport. In addition, this drug induces on insulin receptor substrate-1 (IRS-1) a decrease in tyrosine phosphorylation, concomitantly with an increase in serine/threonine phosphorylation. The present work was aimed at the identification of the serine/threonine residues that, upon phosphorylation, might be involved in modulating insulin signaling. To this end, we studied double-point mutants of IRS-1, in which serines 612/632 and 662/731 were replaced with alanine. These are four plausible sites of phosphorylation by mitogen-activated protein kinases and are in the immediate proximity of tyrosine residues, which are potential sites of interaction with phosphatidylinositol 3-kinase Src homology 2 domains. Using transient expression in 293 EBNA cells, we demonstrate that serines 612, 632, 662, and 731 and mitogen-activated protein kinases are not involved in the okadaic acid effect on IRS-1. Rather, these serines appear to play a role in modulating basal and insulin-stimulated IRS-1 tyrosine phosphorylation, association of IRS-1, with p85, and phosphatidylinositol 3-kinase activity in the IRS-1.p85 immune complex, since mutation of these sites enhances these events. Our findings suggest the existence of an IRS-1 desensitization mechanism resulting from serine/threonine phosphorylation, occurring at least on serines 612, 632, 662, and 731.
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Affiliation(s)
- I Mothe
- INSERM Unité 145, Nice, France
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189
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Sun XJ, Pons S, Asano T, Myers MG, Glasheen E, White MF. The Fyn tyrosine kinase binds Irs-1 and forms a distinct signaling complex during insulin stimulation. J Biol Chem 1996; 271:10583-7. [PMID: 8631859 DOI: 10.1074/jbc.271.18.10583] [Citation(s) in RCA: 106] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Irs-proteins link the receptors for insulin/IGF-1, growth hormones, and several interleukins and interferons to signaling proteins that contain Src homology-2 (SH2). To identify new Irs-1-binding proteins, we screened a mouse embryo expression library with recombinant [32P]Irs-1, which revealed a specific association between p59fyn and Irs-1. The SH2 domain in p59fyn bound to phosphorylated Tyr895 and Tyr1172, which are located in YXX(L/I) motifs. Mutation of p59fyn at the COOH-terminal tyrosine phosphorylation site (Tyr531) enhanced its binding to Irs-1 during insulin stimulation. Binding experiments with various SH2 protein revealed that Grb-2 was largely excluded from Irs-1 complexes containing p59fyn, whereas Grb-2 and p85 occurred in the same Irs-1 complex. By comparison with the insulin receptor, p59fyn kinase phosphorylated a unique cohort of tyrosine residues in Irs-1. These results outline a role for p59fyn or other related Src-kinases during insulin and cytokine signaling.
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Affiliation(s)
- X J Sun
- Research Division, Joslin Diabetes Center, Boston, Massachusetts 02215, USA
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190
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Antonetti DA, Algenstaedt P, Kahn CR. Insulin receptor substrate 1 binds two novel splice variants of the regulatory subunit of phosphatidylinositol 3-kinase in muscle and brain. Mol Cell Biol 1996; 16:2195-203. [PMID: 8628286 PMCID: PMC231207 DOI: 10.1128/mcb.16.5.2195] [Citation(s) in RCA: 108] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
We have identified two novel alternatively spliced forms of the p85alpha regulatory subunit of phosphatidylinositol (PI) 3-kinase by expression screening of a human skeletal muscle library with phosphorylated baculovirus- produced human insulin receptor substrate 1. One form is identical to p85alpha throughout the region which encodes both Src homology 2 (SH2) domains and the inter-SH2 domain/p110 binding region but diverges in sequence from p85alpha on the 5' side of nucleotide 953, where the entire break point cluster gene and SH3 regions are replaced by a unique 34-amino-acid N terminus. This form has an estimated molecular mass of approximately 53 kDa and has been termed p85/AS53. The second form is identical to p85 and p85/AS53 except for a 24-nucleotide insert between the SH2 domains that results in a replacement of aspartic acid 605 with nine amino acids, adding two potential serine phosphorylation sites in the vicinity of the known serine autophosphorylation site (Ser-608). Northern (RNA) analyses reveal a wide tissue distribution of p85alpha, whereas p85/AS53 is dominant in skeletal muscle and brain, and the insert isoforms are restricted to cardiac muscle and skeletal muscle. Western blot (immunoblot) analyses using an anti-p85 polyclonal antibody and a specific anti-p85/AS53 antibody confirmed the tissue distribution of p85/AS53 protein and indicate a approximately 7-fold higher expression of p85/AS53 protein than of p85 in skeletal muscle. Both p85 and p85/AS53 bind to p110 in coprecipitation experiments, but p85alpha itself appears to have preferential binding to insulin receptor substrate 1 following insulin stimulation. These data indicate that the gene for the p85alpha regulatory subunit of PI 3-kinase can undergo tissue-specific alternative splicing. Two novel splice variants of the regulatory subunit of PI 3-kinase are present in skeletal muscle, cardiac muscle, and brain; these variants may have important functional differences in activity and may play a role in tissue-specific signals such as insulin-stimulated glucose transport or control of neurotransmitter secretion or action.
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Affiliation(s)
- D A Antonetti
- Research Division, Joslin Diabetes Center, Harvard Medical School, Boston, Massachusetts 02215, USA
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191
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Ward SG, June CH, Olive D. PI 3-kinase: a pivotal pathway in T-cell activation? IMMUNOLOGY TODAY 1996; 17:187-97. [PMID: 8871351 DOI: 10.1016/0167-5699(96)80618-9] [Citation(s) in RCA: 147] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Affiliation(s)
- S G Ward
- Dept. of Pharmacology, School of Pharmacy and Pharmacology, University of Bath, Claverton Down, UK.
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192
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Sawka-Verhelle D, Tartare-Deckert S, White MF, Van Obberghen E. Insulin receptor substrate-2 binds to the insulin receptor through its phosphotyrosine-binding domain and through a newly identified domain comprising amino acids 591-786. J Biol Chem 1996; 271:5980-3. [PMID: 8626379 DOI: 10.1074/jbc.271.11.5980] [Citation(s) in RCA: 147] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
We compared the interaction between the insulin receptor (IR) and the IR substrate (IRS) proteins IRS-1 and IRS-2) using the yeast two-hybrid system. Both IRS proteins interact specifically with the cytoplasmic portion of the IR and the related insulin-like growth factor-I receptor, and these interactions require receptor tyrosine kinase activity. Alignment of IRS-1 and IRS-2 revealed two conserved domains at the NH2 terminus, called IH1PH and IH2PTB, which resemble a pleckstrin homology (PH) domain and a phosphotyrosine binding (PTB) domain, respectively. The IH2PTB binds to the phosphorylated NPXY motif (Tyr-960) in the activated insulin receptor, providing a specific mechanism for the interaction between the receptor and IRS-1. Although the IH2PTB of IRS-2 also interacts with the NPEY motif of the insulin receptor, it is not essential for the interaction between the insulin receptor and IRS-2 in the yeast two-hybrid system. IRS-2 contains another interaction domain between residues 591 and 786, which is absent in IRS-1. This IRS-2-specific domain is independent of the IH2PTB and does not require the NPEY motif; however, it requires a functional insulin receptor kinase and the presence of three tyrosine phosphorylation sites in the regulatory loop (Tyr-1146, Tyr-1150, and Tyr-1151). Importantly, this novel domain mediates the association between IRS-2 and insulin receptor lacking the NPXY motif and may provide a mechanism by which the stoichiometry of regulatory loop autophosphorylation enhances IRS-2 phosphorylation.
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193
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Inukai K, Anai M, Van Breda E, Hosaka T, Katagiri H, Funaki M, Fukushima Y, Ogihara T, Yazaki Y, Oka Y, Asano T. A novel 55-kDa regulatory subunit for phosphatidylinositol 3-kinase structurally similar to p55PIK Is generated by alternative splicing of the p85alpha gene. J Biol Chem 1996; 271:5317-20. [PMID: 8621382 DOI: 10.1074/jbc.271.10.5317] [Citation(s) in RCA: 96] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Phosphatidylinositol 3-kinase, which is composed of a 110-kDa catalytic subunit and a regulatory subunit, plays important roles in various cellular signaling mechanisms. We screened a rat brain cDNA expression library with 32P-labeled human IRS-1 protein and cloned cDNAs that were very likely to be generated by alternative splicing of p85alpha gene products. These cDNAs were demonstrated to encode a 55-kDa protein (p55alpha) containing two SH2 domains and an inter-SH2 domain of p85alpha but neither a bcr domain nor a SH3 homology domain. Interestingly, p55 alpha contains a unique 34-amino acid sequence at its NH2 terminus, which is not included in the p85alpha amino acid sequence. This 34-amino acid portion was revealed to be comparable with p55PIK (p55gamma) in length, with a high homology between the two, suggesting that these NH2-terminal domains of p55alpha and p5 gamma may have a specific role that p85 does not. The expression of p55alpha mRNA is most abundant in the brain, but expression is ubiquitous in most rat tissues. Furthermore, it should be noted that the expression of p85alpha mRNA in muscle is almost undetectably low by Northern blotting with a cDNA probe coding for the p85alpha SH3 domain, while the expression of p55alpha can be readily detected. These results suggest that p55 alpha may play an unique regulatory role for phosphatidylinositol 3-kinase in brain and muscle.
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Affiliation(s)
- K Inukai
- Third Department of Internal Medicine, Faculty of Medicine, University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113, Japan
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194
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Von Willebrand M, Jascur T, Bonnefoy-Bérard N, Yano H, Altman A, Matsuda Y, Mustelin T. Inhibition of phosphatidylinositol 3-kinase blocks T cell antigen receptor/CD3-induced activation of the mitogen-activated kinase Erk2. EUROPEAN JOURNAL OF BIOCHEMISTRY 1996; 235:828-35. [PMID: 8654435 DOI: 10.1111/j.1432-1033.1996.00828.x] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The production of 3-phosphorylated inositol phospholipids is implicated in regulation of cell growth and transformation. To explore the role of these lipids in T cell antigen receptor (TCR)/CD3-induced signaling, we have examined the effects of a specific phosphatidylinositol 3-kinase (PtdIns3K) inhibitor, wortmannin, and overexpression of two PtdIns3K constructs on the activation of down-stream effectors in anti-CD3 treated T cells. We report that treatment of cells with wortmannin blocked anti-CD3-induced activation of the mitogen-activation kinase Erk2 while not affecting phorbol-ester-induced Erk2 activation. An inactive analog of wortmannin, WM12, did not affect TCR/CD3-induced Erk2 activation, and wortmannin had no effect on the activity of Erk2 when added directly to the in vitro assays. Expression of a disruptive PtdIns3K construct also reduced Erk2 activation, while a construct that stimulates PtdIns3K enhanced the activation of Erk2. Receptor-induced activation of other Ser/Thr kinases, such as c-Raf, B-Raf, Mek1, Mek2, Mekk, was not affected by wortmannin. Our results suggest that the production of 3-phosphorylated inositol phospholipids is involved in the activation of Erk2, but does not regulate the enzymes that are thought to be upstream of Erk2.
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Affiliation(s)
- M Von Willebrand
- Division of Cell Biology, La Jolla Institute for Allergy and Immunology, CA, USA
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195
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MacDougall LK, Domin J, Waterfield MD. A family of phosphoinositide 3-kinases in Drosophila identifies a new mediator of signal transduction. Curr Biol 1995; 5:1404-15. [PMID: 8749393 DOI: 10.1016/s0960-9822(95)00278-8] [Citation(s) in RCA: 112] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
BACKGROUND Mammalian phosphoinositide 3-kinases (PI 3-kinases) are involved in receptor-mediated signal transduction and have been implicated in processes such as transformation and mitogenesis through their role in elevating cellular phosphatidylinositol (3,4,5)-trisphosphate. Additionally, a PI 3-kinase activity which generates phosphatidylinositol 3-phosphate has been shown to be required for protein trafficking in yeast. RESULTS We have identified a family of three distinct PI 3-kinases in Drosophila, using an approach based on the polymerase chain reaction to amplify a region corresponding to the conserved catalytic domain of PI 3-kinases. One of these family members, PI3K_92D, is closely related to the prototypical PI 3-kinase, p110 alpha; PI3K_59F is homologous to Vps34p, whereas the third, PI3K_68D, is a novel PI 3-kinase which is widely expressed throughout the Drosophila life cycle. The PI3K_68D cDNA encodes a protein of 210 kDa, which lacks sequences implicated in linking p110 PI 3-kinases to p85 adaptor proteins, but contains an amino-terminal proline-rich sequence, which could bind to SH3 domains, and a carboxy-terminal C2 domain. Biochemical analyses demonstrate that PI3K_68D has a novel substrate specificity in vitro, restricted to phosphatidylinositol and phosphatidylinositol 4-phosphate, and is unable to phosphorylate phosphatidylinositol (4,5)-bisphosphate, the implied in vivo substrate for p110. CONCLUSIONS A family of PI 3-kinases in Drosophila, including a novel class represented by PI3K_68D, is described. PI3K_68D has the potential to bind to signalling molecules containing SH3 domains, lacks p85-adaptor-binding sequences, has a Ca(2+)-independent phospholipid-binding domain and displays a restricted in vitro substrate specificity, so it could define a novel signal transduction pathway.
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Affiliation(s)
- L K MacDougall
- Ludwig Institute for Cancer Research, University College Branch, London, UK
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196
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Patti ME, Sun XJ, Bruening JC, Araki E, Lipes MA, White MF, Kahn CR. 4PS/insulin receptor substrate (IRS)-2 is the alternative substrate of the insulin receptor in IRS-1-deficient mice. J Biol Chem 1995; 270:24670-3. [PMID: 7559579 DOI: 10.1074/jbc.270.42.24670] [Citation(s) in RCA: 160] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Insulin receptor substrate-1 (IRS-1) is the major cytoplasmic substrate of the insulin and insulin-like growth factor (IGF)-1 receptors. Transgenic mice lacking IRS-1 are resistant to insulin and IGF-1, but exhibit significant residual insulin action which corresponds to the presence of an alternative high molecular weight substrate in liver and muscle. Recently, Sun et al. (Sun, X.-J., Wang, L.-M., Zhang, Y., Yenush, L. P., Myers, M. G., Jr., Glasheen, E., Lane, W.S., Pierce, J. H., and White, M. F. (1995) Nature 377, 173-177) purified and cloned 4PS, the major substrate of the IL-4 receptor-associated tyrosine kinase in myeloid cells, which has significant structural similarity to IRS-1. To determine if 4PS is the alternative substrate of the insulin receptor in IRS-1-deficient mice, we performed immunoprecipitation, immunoblotting, and phosphatidylinositol (PI) 3-kinase assays using specific antibodies to 4PS. Following insulin stimulation, 4PS is rapidly phosphorylated in liver and muscle, binds to the p85 subunit of PI 3-kinase, and activates the enzyme. Insulin stimulation also results in the association of 4PS with Grb 2 in both liver and muscle. In IRS-1-deficient mice, both the phosphorylation of 4PS and associated PI 3-kinase activity are enhanced, without an increase in protein expression. Immunodepletion of 4PS from liver and muscle homogenates removes most of the phosphotyrosine-associated PI 3-kinase activity in IRS-1-deficient mice. Thus, 4PS is the primary alternative substrate, i.e. IRS-2, which plays a major role in physiologic insulin signal transduction via both PI 3-kinase activation and Grb 2/Sos association. In IRS-1-deficient mice, 4PS/IRS-2 provides signal transduction to these two major pathways of insulin signaling.
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Affiliation(s)
- M E Patti
- Research Division, Joslin Diabetes Center, Boston, Massachusetts 02215, USA
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Abstract
Although most tyrosine kinase growth factor receptors directly bind Src homology 2 (SH2) proteins, the insulin receptor, and a select group of other hormone receptors-including an emerging group of cytokine receptors-phosphorylate intracellular insulin receptor substrate (IRS) proteins, which subsequently bind SH2 proteins. There are currently two members of the IRS family (IRS-1 and IRS-2); these IRS proteins contain elements of substantial similarity, but may also play divergent roles in mammalian physiology. The engagement of IRS proteins by other receptors suggests that IRS proteins mediate diverse biological signals.
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Affiliation(s)
- M G Myers
- Research Division, Joslin Diabetes Center and Division of Medical Sciences, Harvard Medical School, Boston, MA 02215, USA
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Chattopadhyay A, James H, Fair D. Molecular recognition sites on factor Xa which participate in the prothrombinase complex. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(19)49842-6] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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