title: Maturation of the regulation of GLUT4 activity by p38 MAPK during L6 cell myogenesis.
abstract: Insulin stimulates glucose uptake in skeletal muscle cells and fat cells by promoting the rapid translocation of GLUT4 glucose transporters to the plasma membrane. Recent work from our laboratory supports the concept that insulin also stimulates the intrinsic activity of GLUT4 through a signaling pathway that includes p38 MAPK. Here we show that regulation of GLUT4 activity by insulin develops during maturation of skeletal muscle cells into myotubes in concert with the ability of insulin to stimulate p38 MAPK. In L6 myotubes expressing GLUT4 that carries an exofacial myc-epitope (L6-GLUT4myc), insulin-stimulated GLUT4myc translocation equals in magnitude the glucose uptake response. Inhibition of p38 MAPK with SB203580 reduces insulin-stimulated glucose uptake without affecting GLUT4myc translocation. In contrast, in myoblasts, the magnitude of insulin-stimulated glucose uptake is significantly lower than that of GLUT4myc translocation and is insensitive to SB203580. Activation of p38 MAPK by insulin is considerably higher in myotubes than in myoblasts, as is the activation of upstream kinases MKK3/MKK6. In contrast, the activation of all three Akt isoforms and GLUT4 translocation are similar in myoblasts and myotubes. Furthermore, GLUT4myc translocation and phosphorylation of regulatory sites on Akt in L6-GLUT4myc myotubes are equally sensitive to insulin, whereas glucose uptake and phosphorylation of regulatory sites on p38 MAPK show lower sensitivity to the hormone. These observations draw additional parallels between Akt and GLUT4 translocation and between p38 MAPK and GLUT4 activation. Regulation of GLUT4 activity by insulin develops upon muscle cell differentiation and correlates with p38 MAPK activation by insulin.
authors.affiliation: Programme in Cell Biology, The Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada.
authors.forename: Wenyan
authors.initials: W
authors.lastname: Niu
authors.forename: Carol
authors.initials: C
authors.lastname: Huang
authors.forename: Zafar
authors.initials: Z
authors.lastname: Nawaz
authors.forename: Michelle
authors.initials: M
authors.lastname: Levy
authors.forename: Romel
authors.initials: R
authors.lastname: Somwar
authors.forename: Dailin
authors.initials: D
authors.lastname: Li
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Bilan
authors.forename: Amira
authors.initials: A
authors.lastname: Klip
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D002455:Cell Division; D002460:Cell Line; D003847:Deoxyglucose / Q000493:pharmacokinetics; D015536:Down-Regulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005089:Exocytosis; D005786:Gene Expression Regulation; D051275:Glucose Transporter Type 4; D015151:Immunoblotting; D007328:Insulin / Q000378:metabolism / Q000494:pharmacology; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins / Q000096:biosynthesis* / Q000235:genetics*; D009124:Muscle Proteins; D018482:Muscle, Skeletal / Q000378:metabolism; D032390:Myoblasts, Smooth Muscle / Q000378:metabolism; D032389:Myocytes, Smooth Muscle / Q000378:metabolism; D010766:Phosphorylation; D011233:Precipitin Tests; D017346:Protein Serine-Threonine Kinases; D021381:Protein Transport; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D013997:Time Factors; D048051:p38 Mitogen-Activated Protein Kinases
chemical_list: D004791:Enzyme Inhibitors; D051275:Glucose Transporter Type 4; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D011518:Proto-Oncogene Proteins; C495694:Slc2a4 protein, rat; D003847:Deoxyglucose; C494920:Akt1 protein, rat; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases