REVIEWS Intracellular Signal for Skeletal Muscle Adaptation The role of CaMKII in regulating GLUT4 expression in skeletal muscle

Ojuka EO, Goyaram V, Smith JA. The role of CaMKII in regulating GLUT4 expression in skeletal muscle. Am J Physiol Endocrinol Metab 303: E322–E331, 2012. First published April 10, 2012; doi:10.1152/ajpendo.00091.2012.—Contractile activity during physical exercise induces an increase in GLUT4 expression in skeletal muscle, helping to improve glucose transport capacity and insulin sensitivity. An important mechanism by which exercise upregulates GLUT4 is through the activation of Ca /calmodulin-dependent protein kinase II (CaMKII) in response to elevated levels of cytosolic Ca during muscle contraction. This review discusses the mechanism by which Ca activates CaMKII, explains research techniques currently used to alter CaMK activity in cells, and highlights various exercise models and pharmacological agents that have been used to provide evidence that CaMKII plays an important role in regulating GLUT4 expression. With regard to transcriptional mechanisms, the key research studies that identified myocyte enhancer factor 2 (MEF2) and GLUT4 enhancer factor as the major transcription factors regulating glut4 gene expression, together with their binding domains, are underlined. Experimental evidence showing that CaMK activation induces hyperacetylation of histones in the vicinity of the MEF2 domain and increases MEF2 binding to its cis element to influence MEF2-dependent Glut4 gene expression are also given along with data suggesting that p300 might be involved in acetylating histones on the Glut4 gene. Finally, an appraisal of the roles of other calciumand non-calcium-dependent mechanisms, including the major HDAC kinases in GLUT4 expression, is also given.