Comparison of GLUT4 and GLUT1 subcellular trafficking in basal and insulin-stimulated 3T3-L1 cells.
The two glucose transporter isoforms GLUT4 and GLUT1 present in 3T3-L1 cells were labeled in the insulin-stimulated and basal states with the impermeant bis-mannose photolabel, 2-N-4-(1-azi-2,2,2-trifluoroethyl)benzoyl-1,3-bis-(D-mannos- 4-yloxy)-2-propylamine. The redistributions of these labeled transporters from the plasma membrane to the low density microsome membrane fraction were followed while cells were maintained at either insulin-stimulated or basal steady states. In both these steady states GLUT4 and GLUT1 were continuously recycled. Analysis of the time courses for tracer-tagged GLUT4 and GLUT1 redistribution showed that the endocytosis rate constants were only approximately 30% slower in the insulin-stimulated (0.08 and 0.093 min-1) compared with the basal (0.116 and 0.121 min-1) state. In the insulin-stimulated state, the rate constants for GLUT4 and GLUT1 exocytosis (0.086 and 0.096 min-1) were similar to those of endocytosis. In contrast, the exocytosis rate constants of GLUT4 and GLUT1 in the basal state were 0.01 and 0.035 min-1. We therefore conclude that the main effect of insulin is to increase GLUT4 and GLUT1 exocytosis rate constants by approximately 9- and 3-fold, respectively, and that the unique feature of the GLUT4 isoform is the very slow rate of exocytosis in the basal state.
Yang
J
J
Department of Biochemistry, University of Bath, United Kingdom.
Holman
G D
GD
D016475:3T3 Cells; D000818:Animals; D001692:Biological Transport; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D005089:Exocytosis; D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D007328:Insulin / Q000494:pharmacology*; D051379:Mice; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D009124:Muscle Proteins
D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C495678:Slc2a1 protein, mouse; C495693:Slc2a4 protein, mouse