Gapex-5, a Rab31 Guanine Nucleotide Exchange Factor that Regulates Glut4 Trafficking in Adipocytes

Abstract

Insulin stimulates glucose uptake by promoting translocation of the Glut4 glucose transporter from intracellular storage compartments to the plasma membrane. In the absence of insulin, Glut4 is retained intracellularly; the mechanism underlying this process remains uncertain. Using the TC10-interacting protein CIP4 as bait in a yeast two-hybrid screen, we cloned a RasGAP and VPS9 domain-containing protein, Gapex-5/RME-6. The VPS9 domain is a guanine nucleotide exchange factor for Rab31, a Rab5 subfamily GTPase implicated in trans-Golgi network (TGN)-to-endosome trafficking. Overexpression of Rab31 blocks insulin-stimulated Glut4 translocation, whereas knockdown of Rab31 potentiates insulin-stimulated Glut4 translocation and glucose uptake. Gapex-5 is predominantly cytosolic in untreated cells; its overexpression promotes intracellular retention of Glut4 in adipocytes. Insulin recruits the CIP4/Gapex-5 complex to the plasma membrane, thus reducing Rab31 activity and permitting Glut4 vesicles to translocate to the cell surface, where Glut4 docks and fuses to transport glucose into the cell.

Ins (endocytosis) and outs (exocytosis) of GLUT4 trafficking

“…The docking of GLUT4 vesicles with the plasma membrane appears to require the Exocyst complex that is formed from the assembly of 8 distinct proteins [29][30][31][32]. In the case of GLUT4, the Exo70, Sec6 and Sec8 protein component of this complex redistribute to the plasma membrane in response to insulin [29] These events are triggered by the insulin activation of a small GTP binding protein TC10 that recruits Exo70 with Sec6 and Sec8 to lipid raft microdomains in the plasma membrane [33,34]. Moreover, Sec8 associates with the PDZ domain of SAP97 a MAGUK (membrane-associated guanylate kinase) family member that is recruited along with Sec8 [33].…”

“…Expression of a dominant-interfering CIP4/2 mutant inhibited insulin-stimulated GLUT4 translocation. Further studies using CIP4 as bait, identified Gapex-5, a RasGAP and VPS9 domain-containing protein that functions as a guanine nucleotide exchange factor (GEF) for Rab31, a Rab5 subfamily GTPase that involved in trans-Golgi network (TGN)-to-endosome trafficking [34]. Insulin recruited the CIP4/Gapex-5 complex to the plasma membrane, thereby decreasing Rab31 activity.…”

VAV2 regulates epidermal growth factor receptor endocytosis and degradation

“…Gapvd1, is an activator of the early endosome regulator protein Rab. It regulates vesicular trafficking processes such as endocytosis of activated transmembrane proteins and exocytosis of GLUT4 vesicles (Hunker et al, 2006;Lodhi et al, 2007). Recent studies have shown that it can regulate EGFR endocytosis and degradation independently of Rab5 function (Su et al, 2007).…”

cAMP antagonizes ERK-dependent antiapoptotic action of insulin

“…A number of observations have accumulated that describe the possible linkages between insulin receptor tyrosine kinase-derived signaling components and heterotrimetic G-proteins (19). G-proteins participate in insulin-stimulated translocation of glucose transporter GLUT4 in 3T3-L1 adipocytes (20,21). In addition, Ptx can alter the action of insulin (22).…”