Role of SNAP23 in Insulin-induced Translocation of GLUT4 in 3T3-L1 Adipocytes

Abstract

Both syntaxin4 and VAMP2 are implicated in insulin regulation of glucose transporter-4 (GLUT4) trafficking in adipocytes as target (t) soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNARE) and vesicle (v)-SNARE proteins, respectively, which mediate fusion of GLUT4-containing vesicles with the plasma membrane. Synaptosome-associated 23-kDa protein (SNAP23) is a widely expressed isoform of SNAP25, the principal t-SNARE of neuronal cells, and colocalizes with syntaxin4 in the plasma membrane of 3T3-L1 adipocytes. In the present study, two SNAP23 mutants, SNAP23-⌬C8 (amino acids 1 to 202) and SNAP23-⌬C49 (amino acids 1 to 161), were generated to determine whether SNAP23 is required for insulin-induced translocation of GLUT4 to the plasma membrane in 3T3-L1 adipocytes. Wild-type SNAP23 (SNAP23-WT) promoted the interaction between syntaxin4 and VAMP2 both in vitro and in vivo. Although SNAP23-⌬C49 bound to neither syntaxin4 nor VAMP2, the SNAP23-⌬C8 mutant bound to syntaxin4 but not to VAMP2. In addition, although SNAP23-⌬C8 bound to syntaxin4, it did not mediate the interaction between syntaxin4 and VAMP2. Moreover, overexpression of SNAP23-⌬C8 in 3T3-L1 adipocytes by adenovirus-mediated gene transfer inhibited insulin-induced translocation of GLUT4 but not that of GLUT1. In contrast, overexpression of neither SNAP23-WT nor SNAP23-⌬C49 in 3T3-L1 adipocytes affected the translocation of GLUT4 or GLUT1. Together, these results demonstrate that SNAP23 contributes to insulin-dependent trafficking of GLUT4 to the plasma membrane in 3T3-L1 adipocytes by mediating the interaction between t-SNARE (syntaxin4) and v-SNARE (VAMP2).A primary function of insulin is to stimulate the transport of glucose into target tissues, prominent among which are skeletal muscle, cardiac muscle, and adipose tissue. Insulin achieves this effect by inducing the translocation of GLUT4 glucose transporters from an intracellular vesicular compartment to the plasma membrane. Under basal conditions, GLUT4 cycles slowly between this intracellular compartment and the plasma membrane (1, 2). However, activation of insulin receptors triggers a large increase in the rate of exocytosis of GLUT4-containing vesicles and a smaller decrease in the rate of GLUT4 internalization by endocytosis (3-5), with the former action likely contributing most to the insulin-induced increase in the amount of GLUT4 in the plasma membrane (6).Intracellular membrane fusion is mediated by evolutionarily conserved membrane proteins known as soluble N-ethylmaleimide-sensitive factor (NSF) 1 attachment protein receptors (SNAREs) (7,8). SNARE proteins that contribute to neuronal exocytosis include the synaptic vesicle protein synaptobrevin (also referred to as VAMP) and the plasma membrane proteins synaptosome-associated 25-kDa protein and syntaxin1A. These proteins readily assemble into a stable ternary complex; however, disassembly of this complex can be reversibly induced by the ATPase NSF in conjunction with soluble cofactors termed SNAPs (soluble NSF-att...

Tomosyn Interacts with the t-SNAREs Syntaxin4 and SNAP23 and Plays a Role in Insulin-stimulated GLUT4 Translocation

“…2B). This indicates that these proteins form a high affinity ternary complex similar to that reported previously for Syntaxin4/SNAP23/VAMP-2 (22,23).…”

“…We have demonstrated previously (22) that VAMP-2 forms a high affinity SNARE complex with Syntaxin4 and SNAP23. This complex regulates a variety of exocytic transport events including the translocation of GLUT4 to the plasma membrane of adipocytes and the translocation of water channels to the cell surface of kidney cells (23,(37)(38)(39). Tomosyn binds to Syntaxin1A via a helical domain that is homologous to the VAMP-2 SNARE motif, and a recently described molecule, Amisyn, contains a Tomosyn-like SNARE motif and has further been shown to interact with both Syntaxin1A and Syntaxin4 from rat brain (18,20,40).…”

“…Further, Syntaxin4 has been shown to form an SDS-resistant SNARE complex with SNAP23 and VAMP-2 (22). This complex plays a role in a number of regulated exocytic processes including the insulin-regulated trafficking of the facilitative glucose transporter GLUT4 in fat and muscle cells (21)(22)(23)(24)(25). Furthermore, this SNARE complex resembles the synaptic ternary complex and is subject to regulation by the ubiquitously expressed SM protein Munc18c (21,26,27).…”

Supramaximal cholecystokinin displaces Munc18c from the pancreatic acinar basal surface, redirecting apical exocytosis to the basal membrane

“…The only v-SNARE present on the ZG membrane shown to be involved in Ca 2+ -evoked enzyme secretion is VAMP-2 (18,19). In fact, the basal membrane-restricted forms, syntaxin-4 and SNAP-23, have been shown to form SNARE complexes with VAMP-2 in vitro (21,22) and function in mediating GLUT4 translocation in adipocytes (42)(43)(44).…”

Triagem funcional de genes envolvidos no processo de manutenção da inativação do cromossomo X em humanos

“…Quando super-expresso antagoniza a atividade das proteínas SR SF2/ASF e SC35. Shin et al, 2004;Fushimi et al, 2005;Shin et al, 2005;Shi & Manley, 2007;Biamonti & Caceres, 2009;Feng et al, 2009;Xiao et al, 2011. Hao et al, 1997;Kawanishi et al, 2000;Schoch et al, 2001;Bonanomi et al, 2007;Prescott et al, 2009;Lin & Sun, 2011;Bogan, 2012. Cisternas et al, 2003;Sadakata et al, 2007;Corpet et al, 2011; 2012. Também expresso no feto sendo importante para seu crescimento e desenvolvimento e para crescimento pós-natal normal.…”