Arrest of endosome acidification by bafilomycin A1 mimics insulin action on GLUT4 translocation in 3T3-L1 adipocytes.
In insulin-sensitive fat and muscle cells, the major glucose transporter GLUT4 is constitutively sequestered in endosomal tubulovesicular membranes, and moves to the cell surface in response to insulin. While sequence information within GLUT4 appears to be responsible for its constitutive intracellular sequestration, the regulatory elements and mechanisms that enable this protein to achieve its unique sorting pattern under basal and insulin-stimulated conditions are poorly understood. We show here that arrest of endosome acidification in insulin-sensitive 3T3-L1 adipocytes by bafilomycin A1, a specific inhibitor of the vacuolar proton pump, results in the rapid and dose-dependent translocation of GLUT4 from the cell interior to the membrane surface; the effects of maximally stimulatory concentrations of bafilomycin A1 (400-800 nM) were equivalent to 50-65% of the effects of acute insulin treatment. Like insulin, bafilomycin A1 induced the redistribution of GLUT1 and Rab4, but not that of other proteins whose membrane localization has been shown to be insulin-insensitive. Studies to address the mechanism of this effect demonstrated that neither autophosphorylation nor internalization of the insulin receptor was altered by bafilomycin A1 treatment. Bafilomycin-induced GLUT4 translocation was not blocked by cell pretreatment with wortmannin. Taken together, these data indicate that arrest of endosome acidification mimics insulin action on GLUT4 and GLUT1 translocation by a mechanism distal to insulin receptor and phosphatidylinositol 3-kinase activation, and suggest an important role for endosomal pH in the membrane dynamics of the glucose transporters.
Chinni
S R
SR
Department of Physiology, Wayne State University School of Medicine, 540 East Canfield, Detriot, MI 48201, USA.
Shisheva
A
A
D016475:3T3 Cells; D000165:Acridine Orange; D017667:Adipocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001692:Biological Transport / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D011992:Endosomes / Q000187:drug effects / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism; D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D020730:Guanine Nucleotide Dissociation Inhibitors; D006863:Hydrogen-Ion Concentration; D007328:Insulin / Q000494:pharmacology*; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism; D008247:Lysosomes / Q000187:drug effects / Q000378:metabolism; D018942:Macrolides; D051379:Mice; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D009124:Muscle Proteins; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors; D011972:Receptor, Insulin / Q000502:physiology; D000077191:Wortmannin; D020695:rab4 GTP-Binding Proteins
D000730:Androstadienes; D000900:Anti-Bacterial Agents; C086796:GDP dissociation inhibitor 1; D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D020730:Guanine Nucleotide Dissociation Inhibitors; D007328:Insulin; D018942:Macrolides; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C495678:Slc2a1 protein, mouse; C495693:Slc2a4 protein, mouse; C040929:bafilomycin A1; D019869:Phosphatidylinositol 3-Kinases; D011972:Receptor, Insulin; D019204:GTP-Binding Proteins; D006180:Proton-Translocating ATPases; D020695:rab4 GTP-Binding Proteins; D000165:Acridine Orange; D000077191:Wortmannin