title: Insulin recruits GLUT4 from distinct compartments via distinct traffic pathways with differential microtubule dependence in rat adipocytes.
abstract: In the present study, we investigated the physiological significance of the microtubules in the subcellular localization and trafficking of GLUT4 in rat primary adipocytes. Morphological and biochemical analyses revealed a dose- and time-dependent disruption of the microtubules by treatment with nocodazole. With nearly complete disruption of the microtubules, the insulin-stimulated glucose transport activity was inhibited by 55%. This inhibition was concomitant with a comparable inhibition of GLUT4 translocation measured by the subcellular fractionation and the cell-surface GLUT4 labeling by trypsin cleavage. In addition, the time-course of insulin stimulation of the glucose transport activity was significantly delayed by microtubule disruption (t(1/2) were 7 and 2.3 min in nocodazole-treated and control cells, respectively), while the rate of GLUT4 endocytosis was little affected. The impaired insulin-stimulated glucose transport activity was not fully restored to the level in control cells by blocking GLUT4 endocytosis, suggesting that the inhibition was due to the existence of a microtubule-dependent subpopulation in the insulin-responsive GLUT4 pool. On the other hand, nocodazole partially inhibited insulin-induced translocation of the insulin-regulated aminopeptidase and the vesicle-associated membrane protein (VAMP)-2 without affecting GLUT1 and VAMP-3. In electrically permeabilized adipocytes, the insulin-stimulated glucose transport was inhibited by 40% by disruption of the microtubules whereas that stimulated with GTP gamma S was not affected. Intriguingly, the two reagents stimulated glucose transport to the comparable level by disruption of the microtubules. These data suggest that insulin recruits GLUT4 to the plasma membrane from at least two distinct intracellular compartments via distinct traffic routes with differential microtubule dependence in rat primary adipocytes.
authors.affiliation: Department of Cell Biology, Institute for Molecular and Cellular Regulation, Gunma University, 3-39-15 Showa-machi, Maebashi 371-8512, Japan.
authors.forename: Li-Bin
authors.initials: LB
authors.lastname: Liu
authors.forename: Waka
authors.initials: W
authors.lastname: Omata
authors.forename: Itaru
authors.initials: I
authors.lastname: Kojima
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Shibata
mesh_terms: D019325:3-O-Methylglucose / Q000493:pharmacokinetics; D017667:Adipocytes / Q000378:metabolism*; D000626:Aminopeptidases / Q000737:chemistry; D000818:Animals; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004705:Endocytosis; D005947:Glucose / Q000378:metabolism; D051275:Glucose Transporter Type 4; D015151:Immunoblotting; D007328:Insulin / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D008870:Microtubules / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins / Q000737:chemistry / Q000378:metabolism*; D009124:Muscle Proteins; D015739:Nocodazole / Q000494:pharmacology; D010766:Phosphorylation; D021381:Protein Transport; D051381:Rats; D017207:Rats, Sprague-Dawley; D013347:Subcellular Fractions; D013997:Time Factors; D014357:Trypsin / Q000494:pharmacology; D014404:Tubulin / Q000378:metabolism; D014746:Vimentin / Q000378:metabolism
chemical_list: D051275:Glucose Transporter Type 4; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C495694:Slc2a4 protein, rat; D014404:Tubulin; D014746:Vimentin; D019325:3-O-Methylglucose; D000626:Aminopeptidases; D014357:Trypsin; D005947:Glucose; D015739:Nocodazole