Overexpression of Rad inhibits glucose uptake in cultured muscle and fat cells.
Rad is a Ras-like GTPase that was isolated by subtraction cloning of human muscle and shown to have increased expression in some individuals with Type II diabetes. To ascertain the potential role of Rad in insulin-mediated signaling, we have overexpressed Rad in myocyte and adipocyte cell lines. Expression of Rad resulted in a 50-90% reduction in insulin-stimulated 2-deoxyglucose glucose uptake in C2C12 murine myotubes, L6 rat myotubes, and 3T3-L1 adipocytes and a 25% reduction in 3-O-methylglucose uptake in 3T3-L1 adipocytes. This occurred despite unaltered levels of glucose transporter expression, with no detectable change in Glut4 translocation and with no alteration in insulin receptor or substrate phosphorylation or phosphatidylinositol 3-kinase activity. These data indicate that Rad is a negative regulator of glucose uptake and that this effect may be due to a decrease in the intrinsic activity of the transporter molecules, rather than an effect on the translocation of Glut4.
Moyers
J S
JS
Research Division, Joslin Diabetes Center, and Department of Medicine, Harvard Medical School, Boston, Massachusetts 02215, USA.
Bilan
P J
PJ
Reynet
C
C
Kahn
C R
CR
D017667:Adipocytes / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002451:Cell Compartmentation; D002454:Cell Differentiation; D002460:Cell Line; D004247:DNA / Q000096:biosynthesis; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology*; D051379:Mice; D009004:Monosaccharide Transport Proteins / Q000302:isolation & purification / Q000378:metabolism; D009132:Muscles / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction; D018631:ras Proteins
D007328:Insulin; D009004:Monosaccharide Transport Proteins; D011994:Recombinant Proteins; C490030:Rrad protein, mouse; C490031:Rrad protein, rat; D004247:DNA; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019204:GTP-Binding Proteins; D018631:ras Proteins; D005947:Glucose