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 h uman muscle and shown to have increased expression in some individuals with Type II diabetes, To ascertain the potential role of Rad in insu lin-mediated signaling, we have overexpressed Rad in myocyte and adipo cyte cell lines, Expression of Rad resulted in a 50-90% reduction in i nsulin-stimulated 2-deoxyglucose glucose uptake in C2C12 murine myotub es, L6 rat myotubes, and 3T3-L1 adipocytes and a 25% reduction in 3-O- methylglucose uptake in 3T3-L1 adipocytes, This occurred despite unalt ered levels of glucose transporter expression, with no detectable chan ge in Glut4 translocation and with no alteration in insulin receptor o r substrate phosphorylation or phosphatidylinositol 3-kinase activity, These data indicate that Rad is a negative regulator of glucose uptak e and that this effect may be due to a decrease in the intrinsic activ ity of the transporter molecules, rather than an effect on the translo cation of Glut4.