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

From the Programme in Cell Biology, The Hospital for Sick Children, Toronto, Ontario, Canada

Address correspondence and reprint requests to Amira Klip,PhD, Programme in Cell Biology, The Hospital for Sick Children, 555 University Ave., Toronto, Ontario, Canada M5G 1X8. E-mail: amira{at}sickkids.ca

Abbreviations: AICAR, 5-aminoimidazole-4-carboxamide-1-ß-D-ribofuranoside; AMPK, AMP-activated protein kinase; BIM, bisindolylmaleimide; CaMK, Ca²⁺/calmodulin kinase; c/n, conventional/novel; DNP, 2,4-dinitrophenol; GAP, GTPase-activating protein; HA, hemagglutinin; PDGF, platelet-derived growth factor; PI3K, phosphatidylinositol-3-kinase; PKC, protein kinase C; PMA, 4-phorbol-12-myristate-13-acetate

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-ß-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 2-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.

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				H. F. Kramer, E. B. Taylor, C. A. Witczak, N. Fujii, M. F. Hirshman, and L. J. Goodyear Calmodulin-Binding Domain of AS160 Regulates Contraction- but Not Insulin-Stimulated Glucose Uptake in Skeletal Muscle Diabetes, December 1, 2007; 56(12): 2854 - 2862. [Abstract] [Full Text] [PDF]