Implication of phosphorylation of the myosin II regulatory light chain in insulin-stimulated GLUT4 translocation in 3T3-F442A adipocytes.

In adipocytes, insulin stimulates glucose transport primarily by promoting the translocation of GLUT4 to the plasma membrane. Requirements for Ca 2+ /calmodulin during insulin-stimulated GLUT4 trans - location have been demonstrated; however, the mechanism of action of Ca 2+ in this process is unknown. Recently, myosin Ⅱ, whose function in non-muscle cells is primarily regulated by phosphorylation of its regulatory light chain by the Ca 2+ /calmodulin-dependent myosin light chain kinase (MLCK), was implicated in insulin-stimulated GLUT4 translocation. The present studies in 3T3-F442A adipocytes demonstrate the novel finding that insulin significantly increases phosphorylation of the myosin Ⅱ RLC in a Ca 2+ -dependent manner. In addition, 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. Our studies suggest that MLCK may be a regulatory target of Ca 2+ /calmodulin and may play an important role in insulin-stimulated glucose trans - port in adipocytes.