Protein kinase B stimulates the translocation of GLUT4 but not GLUT1 or transferrin receptors in 3T3-L1 adipocytes by a pathway involving SNAP-23, synaptobrevin-2, and/or cellubrevin

An interaction of SNAP-23 and syntaxin 4 on the plasma membrane with vesicl e-associated synaptobrevin-2 and/or cellubrevin, known as SNAP (soluble N-e thyl-maleimide-sensitive factor attachment protein) receptors or SNAREs, ha s been proposed to provide the targeting and/or fusion apparatus for insuli n-stimulated translocation of the GLUT4 isoform of glucose transporter to t he plasma membrane. By microinjecting 3T3-L1 adipocytes with the Clostridiu m botulinum toxin B or E, which proteolyzed synaptobrevin-2/cellubrevin and SNAP-23, respectively, we investigated the role of these SNAREs in GLUT4, GLUT1, and transferrin receptor trafficking. As expected, insulin stimulate d the translocation of GLUT4, GLUT1, and transferrin receptors to the plasm a membrane, By contrast, a constitutively active protein kinase B (PKB-DD) only stimulated a translocation of GLUT4 and not GLUT1 or the transferrin r eceptor. The GLUT4 response to PKB-DD was abolished by toxins B or E, where as the insulin-evoked translocation of GLUT4 was inhibited by approximately 65%. These toxins had no significant effect on insulin-stimulated transfer rin receptor appearance at the cell surface. Thus, insulin appears to induc e GLUT4 translocation via two distinct routes, only one of which involves S NAP-23 and synaptobrevin-2/cellubrevin, and can be mobilized by PKB-DD, The PKB-, SNAP-23-, and synaptobrevin-2/cellubrevin-independent GLUT4 transloc ation pathway may involve movement through recycling endosomes, together wi th GLUT1 and transferrin receptors.