Alternate routes to the cell surface underpin insulin-regulated membrane trafficking of GLUT4

Dimitrios Kioumourtzoglou,Nia J Bryant,Gwyn W Gould,Paul R Pryor

doi:10.1242/jcs.166561

Dimitrios Kioumourtzoglou, Nia J Bryant + Show 2 more

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https://doi.org/10.1242/jcs.166561

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Abstract

ABSTRACTInsulin-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.

Highlights

Insulin reduces elevated plasma glucose levels by increasing glucose transport into fat and muscle through the facilitative glucose transporter GLUT4
Concluding remarks The data presented here are consistent with a model in which, in addition to increasing delivery of GLUT4 to the plasma membrane, insulin stimulates traffic between distinct populations of internal GLUT4-containing vesicular structures (IGVs): from cellugyrin-positive to sortilin-positive vesicles
Consistent with this are reports that, unlike sortilin, cellugyrin does not translocate to the plasma membrane in response to insulin, and insulin triggers a reduction in the amount of GLUT4 in cellugyrinpositive membranes (Jedrychowski et al, 2010; Shi and Kandror, 2005)

Summary

Introduction

Insulin reduces elevated plasma glucose levels by increasing glucose transport into fat and muscle through the facilitative glucose transporter GLUT4 ( known as SLC2A4). In the absence of insulin, ∼95% of GLUT4 localises to intracellular compartments, with insulin causing redistribution to the plasma membrane (Bryant and Gould, 2011; Bryant et al, 2002). This is disrupted during the insulin-resistance underlying type-2 diabetes. GLUT4 cycles through the surface of insulin-sensitive cells in both the presence and absence of insulin (Bryant et al, 2002; Kandror and Pilch, 2011).

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