The Rab GTPase-activating protein AS160 integrates Akt, protein kinase C, and AMP-activated protein kinase signals regulating GLUT4 traffic.
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.
Thong
Farah S L
FS
Programme in Cell Biology, The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario, Canada M5G 1X8.
Bilan
Philip J
PJ
Klip
Amira
A
D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D020690:GTPase-Activating Proteins / Q000378:metabolism*; D051275:Glucose Transporter Type 4 / Q000187:drug effects / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology; D018482:Muscle, Skeletal; D032446:Myoblasts / Q000502:physiology; D010766:Phosphorylation / Q000187:drug effects; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D011493:Protein Kinase C / Q000187:drug effects / Q000378:metabolism*; D021381:Protein Transport; D051057:Proto-Oncogene Proteins c-akt / Q000187:drug effects / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*
D020690:GTPase-Activating Proteins; D051275:Glucose Transporter Type 4; D007328:Insulin; D010982:Platelet-Derived Growth Factor; D051057:Proto-Oncogene Proteins c-akt; D011493:Protein Kinase C