OSMOTIC SHOCK STIMULATES GLUT4 TRANSLOCATION IN 3T3L1 ADIPOCYTES BY ANOVEL TYROSINE KINASE PATHWAYS

Similar to insulin, osmotic shock of 3T3L1 adipocytes stimulated an in crease in glucose transport activity and translocation of GLUT4 protei n from intracellularly localized vesicles to the plasma membrane, The docking/ fusion of GLUT4 vesicles with the plasma membrane appeared to utilize a similar mechanism, since expression of a dominant interferi ng mutant of syntaxin-4 prevented both insulin-and osmotic shock-induc ed GLUT4 translocation, However, although the insulin stimulation of G LUT4 translocation and glucose transport activity was completely inhib ited by wortmannin, activation by osmotic shock was wortmannin-insensi tive, Furthermore, insulin stimulated the phosphorylation and activati on of the Akt kinase, whereas osmotic shock was completely without eff ect, Surprisingly, treatment of cells with the tyrosine kinase inhibit or, genistein, or microinjection of phosphotyrosine antibody prevented both the insulin-and osmotic shock stimulated translocation of GLUT4, In addition, osmotic shock induced the tyrosine phosphorylation of se veral discrete proteins including Cbl, p130(cas), and the recently ide ntified soluble tyrosine kinase, calcium-dependent tyrosine kinase (CA DTK), In contrast, insulin had no effect on CADTK but stimulated the t yrosine phosphorylation of Cbl and the tyrosine dephosphorylation of p p125(FAK) and p130(cas), These data demonstrate that the osmotic shock stimulation of GLUT4 translocation in adipocytes occurs through a nov el tyrosine kinase pathway that is independent of both the phosphatidy linositol S-kinase and the Akt kinase.