SNAP23 promotes insulin-dependent glucose uptake in 3T3-L1 adipocytes: possible interaction with cytoskeleton.
The acute stimulation of glucose uptake by insulin in fat and muscle cells is primarily the result of translocation of facilitative glucose transporter 4 (GLUT-4) from an internal compartment to the plasma membrane. Here, we investigate the role of SNAP23 (a 23-kDa molecule resembling the 25-kDa synaptosome associated protein) in GLUT-4 translocation and glucose uptake in 3T3-L1 adipocytes. Microinjection of a polyclonal antibody directed to the carboxy terminus of SNAP23 inhibited GLUT-4 incorporation into the membrane in response to insulin, whereas microinjection of full-length recombinant SNAP23 enhanced the insulin effect. Introduction of recombinant SNAP23 into chemically permeabilized cells also enhanced insulin-stimulated glucose transport. These results indicate that SNAP23 is required for insulin-dependent, functional incorporation of GLUT-4 into the plasma membrane and that the carboxy terminus of the protein is essential for this process. SNAP23 is therefore likely to be a fusion catalyst along with syntaxin-4 and vesicle-associated membrane protein (VAMP)-2. Furthermore, the endogenous content of SNAP23 appears to be limiting for insulin-dependent GLUT-4 exposure at the cell surface. A measurable fraction of SNAP23 was sedimented with cytoskeletal elements when extracted with Triton X-100, unlike VAMP-2 and syntaxin-4, which were exclusively soluble in detergent. We hypothesize that SNAP23 and its interaction with the cytoskeleton may be targets for regulation of GLUT-4 traffic.
D016475:3T3 Cells; D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D000906:Antibodies / Q000008:administration & dosage / Q000494:pharmacology; D002352:Carrier Proteins / Q000276:immunology / Q000378:metabolism / Q000494:pharmacology*; D002462:Cell Membrane / Q000378:metabolism; D003599:Cytoskeleton / Q000187:drug effects / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D051275:Glucose Transporter Type 4; D005982:Glutathione Transferase / Q000235:genetics; D007328:Insulin / Q000494:pharmacology*; D007700:Kinetics; D051379:Mice; D008845:Microinjections; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009124:Muscle Proteins; D010446:Peptide Fragments / Q000276:immunology; D050766:Qb-SNARE Proteins; D050767:Qc-SNARE Proteins; D011993:Recombinant Fusion Proteins / Q000008:administration & dosage / Q000494:pharmacology