Role of SNAP23 in insulin-induced translocation of GLUT4 in 3T3-L1 adipocytes - Mediation of complex formation between syntaxin4 and VAMP2

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-Delta C8 (amino acids 1 to 202) and SNAP23-Delta 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-Delta C49 bound to neither syntaxin4 nor VAMP2, the SNAP23-Delta C8 mutant bound to syntaxin4 but not to VAMP2, In addition, although SNAP23-Delta C8 bound to syntaxin4, it did not mediate the interaction between syntaxin4 and VAMP2;. Moreover, overexpression of SNAP23-Delta 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-Delta 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).