title: SKIP negatively regulates insulin-induced GLUT4 translocation and membrane ruffle formation.
abstract: Skeletal muscle and kidney enriched inositol phosphatase (SKIP) is an inositol polyphosphate 5-phosphatase that hydrolyzes phosphatidylinositol 3,4,5-trisphosphate [PI(3,4,5)P3] to downregulate intracellular levels. In this study, we show that SKIP inhibits phosphoinositide 3-kinase signaling in insulin-stimulated CHO cells. Ectopic expression of SKIP did not inhibit insulin-induced PI(3,4,5)P3 generation but did rapidly decrease insulin-induced intracellular PI(3,4,5)P3 levels compared with those in control cells. Further, insulin-induced phosphorylation of some downstream targets such as Akt and p70 S6 kinase was markedly inhibited by the ectopic expression of SKIP, whereas phosphorylation of mitogen-activated protein kinase was not. In contrast, downregulation of intracellular SKIP levels by antisense oligonucleotides dramatically enhanced Akt (protein kinase B) phosphorylation in response to insulin, suggesting that endogenous SKIP downregulates insulin signaling. SKIP also markedly inhibited GLUT4 translocation and membrane ruffle formation. We conclude that SKIP preferentially regulates glucose transport and actin cytoskeletal rearrangement among a variety of PI(3,4,5)P3 downstream events.
authors.affiliation: Department of Biochemistry, Institute of Medical Science, University of Tokyo, Minato-ku, Tokyo 108-8639, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Ijuin
authors.forename: Tadaomi
authors.initials: T
authors.lastname: Takenawa
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology*; D006224:Cricetinae; D005947:Glucose / Q000493:pharmacokinetics; D051275:Glucose Transporter Type 4; D006003:Glycogen / Q000096:biosynthesis; D006056:Golgi Apparatus / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000378:metabolism* / Q000494:pharmacology; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects / Q000378:metabolism; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D018485:Muscle Fibers, Skeletal / Q000378:metabolism; D009124:Muscle Proteins; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D021381:Protein Transport / Q000187:drug effects; D011518:Proto-Oncogene Proteins / Q000187:drug effects / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D002118:Calcium; D005947:Glucose; D051275:Glucose Transporter Type 4; D006003:Glycogen; D007328:Insulin; D020928:Mitogen-Activated Protein Kinases; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D019869:Phosphatidylinositol 3-Kinases; D010744:Phosphoric Monoester Hydrolases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D038762:Ribosomal Protein S6 Kinases, 70-kDa; C495692:SLC2A4 protein, human; C494918:AKT1 protein, human; C471548:SKIP enzyme, human