The Rab GTPase-Activating Protein AS160 Integrates Akt, Protein Kinase C, and AMP-Activated Protein Kinase Signals Regulating GLUT4 Traffic

Abstract

Insulin-dependent phosphorylation of Akt target AS160 is required for GLUT4 translocation. Insulin and platelet-derived growth factor (PDGF) (Akt activators) or activation of conventional/novel (c/n) protein kinase C (PKC) and 5' AMP-activated protein kinase (AMPK) all promote a rise in membrane GLUT4 in skeletal muscle and cultured cells. However, the downstream effectors linking these pathways to GLUT4 traffic are unknown. Here we explore the hypothesis that AS160 is a molecular link among diverse signaling cascades converging on GLUT4 translocation. PDGF and insulin increased AS160 phosphorylation in CHO-IR cells. Stimuli that activate c/n PKC or AMPK also elevated AS160 phosphorylation. We therefore examined if these signaling pathways engage AS160 to regulate GLUT4 traffic in muscle cells. Nonphosphorylatable AS160 (4P-AS160) virtually abolished the net surface GLUT4myc gains elicited by insulin, PDGF, K(+) depolarization, or 5-aminoimidazole-4-carboxamide-1-beta-d-ribofuranoside but partly, yet significantly, inhibited the effects of 4-phorbol-12-myristate-13-acetate. However, the hypertonicity or 2,4-dinitrophenol-dependent gains in surface GLUT4myc were unaffected by 4P-AS160. RK-AS160 (GTPase-activating protein [GAP] inactive) or 4PRK-AS160 (GAP inactive, nonphosphorylatable) had no effect on surface GLUT4myc elicited by all stimuli. Collectively, these results indicate that activation of Akt, c/n PKC, or alpha2-AMPK intersect at AS160 to regulate GLUT4 traffic, as well as highlight the potential of AS160 as a therapy target to increase muscle glucose uptake.