title: GLUT-4myc ectopic expression in L6 myoblasts generates a GLUT-4-specific pool conferring insulin sensitivity.
abstract: Insulin stimulates glucose uptake into muscle and fat cells via recruitment of the glucose transporter 4 (GLUT-4) from intracellular store(s) to the cell surface. Robust stimulation of glucose uptake by insulin coincides with the expression of GLUT-4 during differentiation of muscle and fat cells, but it is not known if GLUT-4 expression suffices to confer insulin sensitivity to glucose uptake. We have therefore examined the effect of expression of a myc epitope-tagged GLUT-4 (GLUT-4myc) into L6 myoblasts, which do not express endogenous GLUT-4 until differentiated into myotubes. Ectopic expression of GLUT-4myc markedly improved insulin sensitivity of glucose uptake in L6 myoblasts. The GLUT-4myc protein distributed equally to the cell surface and intracellular compartments in myoblasts, and the intracellular fraction of GLUT-4myc further increased in myotubes. In myoblasts, the intracellular GLUT-4myc compartment contained the majority of the insulin-regulatable amino peptidase (IRAP) but less than half of the GLUT-1, suggesting segregation of GLUT-4myc and IRAP to a specific cellular locus. Insulin stimulation of phosphatidylinositol 3-kinase and protein kinase B-alpha activities was similar for L6-GLUT-4myc myoblasts and myotubes. At both stages, GLUT-4myc responded to insulin by translocating to the cell surface. These results suggest that GLUT-4myc segregates into a specific compartment in L6 myoblasts and confers insulin sensitivity to these cells. L6-GLUT-4myc myoblasts, which are easily transfectable with various constructs, are a useful resource to study insulin action.
authors.affiliation: Programme in Cell Biology, The Hospital for Sick Children, Toronto M5G 1X8, Canada.
authors.forename: A
authors.initials: A
authors.lastname: Ueyama
authors.forename: K L
authors.initials: KL
authors.lastname: Yaworsky
authors.forename: Q
authors.initials: Q
authors.lastname: Wang
authors.forename: Y
authors.initials: Y
authors.lastname: Ebina
authors.forename: A
authors.initials: A
authors.lastname: Klip
mesh_terms: D000626:Aminopeptidases / Q000378:metabolism; D001692:Biological Transport; D002454:Cell Differentiation / Q000502:physiology; D002460:Cell Line; D010122:Cystinyl Aminopeptidase; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism*; D016259:Genes, myc; D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D007328:Insulin / Q000502:physiology*; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000378:metabolism*; D009124:Muscle Proteins; D009130:Muscle, Smooth / Q000166:cytology / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D016324:Sequence Tagged Sites; D014018:Tissue Distribution
chemical_list: D000626:Aminopeptidases; D010122:Cystinyl Aminopeptidase; D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; C105964:leucyl-cystinyl aminopeptidase