title: Alternative routes to the cell surface underpin insulin-regulated membrane trafficking of GLUT4.
abstract: Insulin-stimulated delivery of glucose transporters (GLUT4, also known as SLC2A4) from specialized intracellular GLUT4 storage vesicles (GSVs) to the surface of fat and muscle cells is central to whole-body glucose regulation. This translocation and subsequent internalization of GLUT4 back into intracellular stores transits through numerous small membrane-bound compartments (internal GLUT4-containing vesicles; IGVs) including GSVs, but the function of these different compartments is not clear. Cellugyrin (also known as synaptogyrin-2) and sortilin define distinct populations of IGV; sortilin-positive IGVs represent GSVs, but the function of cellugyrin-containing IGVs is unknown. Here, we demonstrate a role for cellugyrin in intracellular sequestration of GLUT4 in HeLa cells and have used a proximity ligation assay to follow changes in pairwise associations between cellugyrin, sortilin, GLUT4 and membrane trafficking machinery following insulin-stimulation of 3T3-L1 adipoctyes. Our data suggest that insulin stimulates traffic from cellugyrin-containing to sortilin-containing membranes, and that cellugyrin-containing IGVs provide an insulin-sensitive reservoir to replenish GSVs following insulin-stimulated exocytosis of GLUT4. Furthermore, our data support the existence of a pathway from cellugyrin-containing membranes to the surface of 3T3-L1 adipocytes that bypasses GSVs under basal conditions, and that insulin diverts traffic away from this into GSVs.
authors.affiliation: Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, G12 8QQ, UK Department of Biology, University of York, York YO10 5DD, UK.
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Kioumourtzoglou
authors.affiliation: Department of Biology, University of York, York YO10 5DD, UK Centre for Immunology and Infection, Hull York Medical School, University of York, York YO10 5DD, UK.
authors.forename: Paul R
authors.initials: PR
authors.lastname: Pryor
authors.affiliation: Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, G12 8QQ, UK.
authors.forename: Gwyn W
authors.initials: GW
authors.lastname: Gould
authors.affiliation: Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, G12 8QQ, UK Department of Biology, University of York, York YO10 5DD, UK gwyn.gould@glasgow.ac.uk nia.bryant@york.ac.uk.
authors.forename: Nia J
authors.initials: NJ
authors.lastname: Bryant
mesh_terms: D041721:3T3-L1 Cells; D033942:Adaptor Proteins, Vesicular Transport / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism*; D005089:Exocytosis / Q000187:drug effects* / Q000235:genetics; D051275:Glucose Transporter Type 4 / Q000235:genetics / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology*; D051379:Mice; D021381:Protein Transport / Q000187:drug effects / Q000235:genetics; D022142:Secretory Vesicles / Q000235:genetics / Q000378:metabolism*; D062805:Synaptogyrins / Q000235:genetics / Q000378:metabolism; D000099183:Sortilin
chemical_list: D033942:Adaptor Proteins, Vesicular Transport; D051275:Glucose Transporter Type 4; D007328:Insulin; D062805:Synaptogyrins; D000099183:Sortilin; C495693:Slc2a4 protein, mouse
keywords: Endosome; Gyrin; Membrane traffic