BOTULINUM-E-TOXIN LIGHT-CHAIN DOES NOT CLEAVE SNAP-23 AND ONLY PARTIALLY IMPAIRS INSULIN STIMULATION OF GLUT4 TRANSLOCATION IN 3T3-L1 CELLS

The stimulation of glucose uptake into fat and muscle by insulin resul ts predominantly from the translocation of the glucose transporter, GL UT4, from an intracellular vesicle pool to the cell surface. Homologue s of several key proteins known to be involved in the process of synap tic vesicle fusion have been identified on GLUT4 vesicles, including V AMPS and cellubrevin. Syntaxin 4, SNAP-23 and/or SNAP-25 are also impl icated in this process. Bacterial toxins that specifically cleave thes e proteins have been utilised to assess their involvement in cell func tion. We aimed to distinguish which of the SNAP isoforms are specifica lly involved in GLUT4 translocation. Here we show that both human (h) and mouse (m) SNAP-23, unlike SNAP-25, are not substrates for Botulinu m E toxin light chain (BoNT/E). Furthermore, we demonstrate that micro injection of differentiated 3T3-L1 cells with BoNT/E inhibited insulin stimulation of GLUT4 translocation only slightly, 27%, whereas tetanu s toxin light chain, that cleaves VAMPS, inhibited insulin stimulation of GLUT4 translocation by 80%. These studies therefore do not support a major role for SNAP-25 in insulin stimulation of GLUT4 translocatio n and place SNAP-23 as a prime candidate for a role in this process. ( C) 1997 Academic Press.