The trimeric GTP-binding protein (Gq/G11) alpha subunit is required for insulin-stimulated GLUT4 translocation in 3T3L1 adipocytes

To investigate the potential role of trimeric GTP-binding proteins regulati ng GLUT4 translocation in adipocytes, wild type and constitutively active G (q) (G(q)/Q209L), G(i) (G(i)/Q205L), and G(s) (G(s)/Q227L) alpha subunit mu tants were expressed in 3T3L1 adipocytes, Although expression of neither th e wild type nor G(i)/Q205L and G(s)/Q227L alpha subunit mutants had any eff ect on the basal or insulin-stimulated translocation of a co-expressed GLUT 4-enhanced green fluorescent protein (EGFP) fusion protein, expression of G (q)/Q209L resulted in GLUT4-EGFP translocation in the absence of insulin. I n contrast, microinjection of an inhibitory G(q)/G(11) alpha subunit-specif ic antibody but not a G(i) or G(s) alpha subunit antibody prevented insulin -stimulated endogenous GLUT4 translocation, Consistent with a required role for GTP-bound G(q)/G(11), expression of the regulators of G protein signal ing (RGS4 and RGS16) also attenuated insulin-stimulated GLUT4-EGFP transloc ation. To assess the relationship between G(q)/G(11) function with the phos phatidylinositol 3-kinase dependent pathway, expression of a dominant-inter fering p85 regulatory subunit, as well as wortmannin treatment inhibited in sulin-stimulated but not G(q)/Q209L-stimulated GLUT4-EGFP translocation, Fu rthermore, G(q)/Q209L did not induce the in vivo accumulation of phosphatid ylinositol-3,4,5-trisphosphate (PIP3), whereas expression of the RGS protei ns did not prevent the insulin-stimulated accumulation of PIP3. Together, t hese data demonstrate that insulin stimulation of GLUT4 translocation requi res at least two independent signal transduction pathways, one mediated thr ough the phosphatidylinositol 3-kinase and another through the trimeric GTP -binding proteins G(q) and/or G(11).