title: Insulin accelerates inter-endosomal GLUT4 traffic via phosphatidylinositol 3-kinase and protein kinase B.
abstract: Insulin enhances plasmalemmal-directed traffic of glucose transporter-4 (GLUT4), but it is unknown whether insulin regulates GLUT4 traffic through endosomal compartments. In L6 myoblasts expressing Myc-tagged GLUT4, insulin markedly stimulated the rate of GLUT4myc recycling. In myoblasts stimulated with insulin to maximize surface GLUT4myc levels, we followed the rates of surface-labeled GLUT4myc endocytosis and chased its intracellular distribution in space and time using confocal immunofluorescence microscopy. Surface-labeled GLUT4myc internalized rapidly (t(12) 3 min), reaching the early endosome by 2 min and the transferrin receptor-rich, perinuclear recycling endosome by 20 min. Upon re-addition of insulin, the t(12) of GLUT4 disappearance from the plasma membrane was unchanged (3 min), but strikingly, GLUT4myc reached the recycling endosome by 10 and left by 20 min. This effect of insulin was blocked by the phosphatidylinositol 3-kinase inhibitor LY294002 or by transiently transfected dominant-negative phosphatidylinositol 3-kinase and protein kinase B mutants. In contrast, insulin did not alter the rate of arrival of rhodamine-labeled transferrin at the recycling endosome. These results reveal a heretofore unknown effect of insulin to accelerate inter-endosomal travel rates of GLUT4 and identify the recycling endosome as an obligatory stage in insulin-dependent GLUT4 recycling.
authors.affiliation: Programme in Cell Biology, The Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada.
authors.forename: L J
authors.initials: LJ
authors.lastname: Foster
authors.forename: D
authors.initials: D
authors.lastname: Li
authors.forename: V K
authors.initials: VK
authors.lastname: Randhawa
authors.forename: A
authors.initials: A
authors.lastname: Klip
mesh_terms: D000818:Animals; D002460:Cell Line; D011992:Endosomes / Q000187:drug effects* / Q000378:metabolism; D051275:Glucose Transporter Type 4; D007328:Insulin / Q000378:metabolism / Q000494:pharmacology*; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D009124:Muscle Proteins; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D021381:Protein Transport; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D015398:Signal Transduction
chemical_list: D051275:Glucose Transporter Type 4; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; C495694:Slc2a4 protein, rat