SYNTAXIN-4, VAMP2, AND OR VAMP3/CELLUBREVIN ARE FUNCTIONAL TARGET MEMBRANE AND VESICLE SNAP RECEPTORS FOR INSULIN-STIMULATED GLUT4 TRANSLOCATION IN ADIPOCYTES/

Introduction of the cytoplasmic domain of syntaxin 4, using either rec ombinant vaccinia virus or single-cell microinjection, resulted in an inhibition of insulin-stimulated GLUT4 but not GLUT1 translocation to the plasma membrane. This was specific for syntaxin 1, since neither t he expression of syntaxin 3 nor the expression of a syntaxin 4 mutant in which the vesicle-associated membrane protein (VAMP) binding site w as deleted had any significant effect. Consistent with the requirement for a functional VAMP binding site, expression of the cytoplasmic dom ains of VAMP2 or VAMP3/cellubrevin also resulted in an inhibition of i nsulin-stimulated GLUT4 translocation. In addition, immunoprecipitatio n of the expressed syntaxin 3 cytoplasmic domain resulted in an insuli n-stimulated increase in the coimmunoprecipitation of GLUT4-containing vesicles. Together, these data demonstrate that syntaxin 4, VAMP2, an d/or VAMP3/cellubrevin can function as target membrane and vesicle SNA P receptors, respectively, for insulin-responsive GLUT4 translocation to the plasma membrane.