Distinct Signals Regulate AS160 Phosphorylation in Response to Insulin, AICAR, and Contraction in Mouse Skeletal Muscle

H. F. Kramer, C. A. Witczak, N. Fujii, N. Jessen, E. B. Taylor, D. E. Arnolds, K. Sakamoto, M. F. Hirshman, L. J. Goodyear
2006 Diabetes  
Insulin and contraction increase GLUT4 translocation in skeletal muscle via distinct signaling mechanisms. Akt substrate of 160 kDa (AS160) mediates insulin-stimulated GLUT4 translocation in L6 myotubes, presumably through activation of Akt. Using in vivo, in vitro, and in situ methods, insulin, contraction, and the AMP-activated protein kinase (AMPK) activator AICAR all increased AS160 phosphorylation in mouse skeletal muscle. Insulin-stimulated AS160 phosphorylation was fully blunted by
more » ... nnin in vitro and in Akt2 knockout (KO) mice in vivo. In contrast, contraction-stimulated AS160 phosphorylation was only partially decreased by wortmannin and unaffected in Akt2 KO mice, suggesting additional regulatory mechanisms. To determine if AMPK mediates AS160 signaling, we used AMPK ␣2-inactive (␣2i) transgenic mice. AICARstimulated AS160 phosphorylation was fully inhibited, whereas contraction-stimulated AS160 phosphorylation was partially reduced in the AMPK ␣2i transgenic mice. Combined AMPK ␣2 and Akt inhibition by wortmannin treatment of AMPK ␣2 transgenic mice did not fully ablate contraction-stimulated AS160 phosphorylation. Maximal insulin, together with either AICAR or contraction, increased AS160 phosphorylation in an additive manner. In conclusion, AS160 may be a point of convergence linking insulin, contraction, and AICAR signaling. While Akt and AMPK ␣2 activities are essential for AS160 phosphorylation by insulin and AICAR, respectively, neither kinase is indispensable for the entire effects of contraction on AS160 phosphorylation.
doi:10.2337/db06-0150 pmid:16804077 fatcat:rcrbdy7aonghbpljbwx6w5ge7q