Implication of Myosin Light Chain Kinase in the Insulin-Stimulated GLUT4 translocation in Adipocytes

Abstract

In adipocytes, insulin stimulates glucose transport principally by promoting translocation of glucose transporter GLUT4 from an intracellular compartment to the plasma membrane. Requirements for Ca²⁺/calmodulin during insulin-stimulated GLUT4 translocation have been demonstrated; however, the mechanism of action of Ca²⁺ in this process is unknown. Recently, myosin II, whose function in non-muscle cells is primarily regulated by phosphorylation of its regulatory light chain (RLC) by the Ca²⁺/calmodulin-dependent myosin light chain kinase (MLCK), was implicated in insulin-stimulated GLUT4 translocation. We have investigated, using 3T3-L1 and 3T3-F442A adipocytes, the possibility that MLCK may be involved in the insulin-stimulated translocation of GLUT4. Insulin significantly increases phosphorylation of the myosin II RLC in a Ca²⁺-dependent manner. ML-7, a selective inhibitor of MLCK, as well as inhibitors of myosin II, such as blebbistatin and 2,3-butanedione monoxime, block insulin-stimulated GLUT4 translocation and subsequent glucose transport. In addition, suppression of MLCK expression via stably expressing antisense-MLCK decreases insulin-stimulated glucose transport. Our studies strongly suggest that MLCK may be a regulatory target of Ca²⁺/calmodulin and may play an important role in insulin-stimulated GLUT4 translocation in adipocytes. [J Physiol Sci. 2006;56 Suppl:S17]