GLUT-4myc ectopic expression in L6 myoblasts generates a GLUT-4-specific pool conferring insulin sensitivity

• Published in: American journal of physiology: endocrinology and metabolism 1999-09, Vol.277 (3), p.E572-E578
• Main Authors: Ueyama, Atsunori, Yaworsky, Karen L, Wang, Qinghua, Ebina, Yousuke, Klip, Amira
• Format: Article
• Language: English
• ISSN: 0193-1849; 1522-1555
• DOI: 10.1152/ajpendo.1999.277.3.e572

1  Programme in Cell Biology, The Hospital for Sick Children, Toronto M5G 1X8; 2  Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada; 3  Division of Molecular Genetics, Institute for Enzyme Research, University of Tokushima, Tokushima 770-8503, Japan 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- 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. GLUT-4 translocation; GLUT-4 vesicles; insulin action; muscle cells