Insulin induces translocation of glucose transporter GLUT4 to plasma membrane caveolae in adipocytes.
Insulin-stimulated glucose uptake in muscle and adipose tissue is the result of translocation of insulin-regulated glucose transporters (GLUT4) from intracellular vesicles to the plasma membrane. Here we report that GLUT4 in the plasma membrane of 3T3-L1 adipocytes were located predominantly in caveolae invaginations: by immunogold electron microscopy of plasma membranes, 88% of GLUT4 were localized to caveolae structures and this distribution within the plasma membrane was not affected by insulin. By immunofluorescence microscopy, a major part of GLUT 4 was colocalized with caveolin. The total amount of GLUT4 in the plasma membrane increased 2.2-fold in response to insulin as determined by immunogold electron or immunofluorescence microscopy. GLUT4 were enriched in caveolae fractions isolated without detergents from plasma membranes of rat adipocytes. In these fractions, GLUT4 were largely confined to caveolin-containing membranes of the caveolae preparation isolated from insulin-stimulated cells, determined by electron microscopy. Insulin increased the amount of GLUT4 2.7-fold in this caveolae fraction. Caveolae were purified further by immunoisolation with antibodies against caveolin. The amount of GLUT4 increased to the same extent in the immunopurified caveolae as in the cruder caveolae fractions from insulin-stimulated cells. We conclude that insulin induces translocation of GLUT4 to caveolae.
Karlsson
Margareta
M
Department of Cell Biology, Faculty of Health Sciences, University of Linköping, S-58185 Linköping, Sweden.
Thorn
Hans
H
Parpal
Santiago
S
Strålfors
Peter
P
Gustavsson
Johanna
J
D016475:3T3 Cells; D017667:Adipocytes / Q000187:drug effects* / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D021941:Caveolae / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D051242:Caveolin 1; D022461:Caveolins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D051275:Glucose Transporter Type 4; D007328:Insulin / Q000494:pharmacology*; D051379:Mice; D008854:Microscopy, Electron; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D009124:Muscle Proteins
C495541:Cav1 protein, mouse; D051242:Caveolin 1; D022461:Caveolins; D051275:Glucose Transporter Type 4; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C495693:Slc2a4 protein, mouse