Inhibition of Contraction-stimulated AMPK Inhibits Contraction-stimulated Increases in PAS-TBC1D1 and Glucose Transport without Altering PAS-AS160 in Rat Skeletal Muscle

  1. Katsuhiko Funai1 and
  2. Gregory D. Cartee (gcartee{at}umich.edu)1,2
  1. 1 Muscle Biology Laboratory, School of Kinesiology, University of Michigan, Ann Arbor, Michigan
  2. 2 Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan

    Abstract

    Objective. Phosphorylation of two members of the TBC1 domain family of proteins, Akt substrate of 160kD (AS160, also known as TBC1D4) and TBC1D1, has been implicated in the regulation of glucose transport in skeletal muscle. Insulin-stimulated phosphorylation (measured using the phospho-Akt substrate, PAS, antibody) of AS160 and TBC1D1 appears to occur in an Akt-dependent manner, but the kinases responsible for contraction-stimulated PAS-AS160 and PAS-TBC1D1 remain unclear. AMP-activated protein kinase (AMPK) and Akt, both activated by contraction, can each phosphorylate AS160 and TBC1D1 in cell-free assays.

    Research Design and Methods. To evaluate the roles of AMPK and Akt on insulin- or contraction-stimulated PAS-AS160, PAS-TBC1D1 and glucose transport, rat epitrochlearis were incubated ± Compound C (inhibitor of AMPK) or wortmannin (inhibitor of phosphatidylinositol 3-kinase, PI3K, which is upstream of Akt) prior to and during insulin-stimulation or contraction.

    Results. Insulin-stimulated glucose transport and phosphorylation of both AS160 and TBC1D1 were completely inhibited by wortmannin. Wortmannin eliminated contraction stimulation of pGSK3 (Akt substrate) and PAS-AS160, but did not significantly alter pAMPK, pACC (AMPK substrate), PAS-TBC1D1 or glucose transport in contraction-stimulated muscle. Compound C completely inhibited contraction-stimulated pACC and PAS-TBC1D1 and partially blocked glucose transport, but did not significantly alter pAkt, pGSK3 or PAS-AS160.

    Conclusions. These data suggest that: 1) insulin stimulates glucose transport and phosphorylation of AS160 and TBC1D1 in a PI3K/Akt-dependent manner; 2) contraction stimulates PAS-AS160 (but not PAS-TBC1D1 or glucose transport) in a PI3K/Akt-dependent manner; and 3) contraction-stimulates PAS-TBC1D1 and glucose transport (but not PAS-AS160) in an AMPK-dependent manner.

    Footnotes

      • Received October 24, 2008.
      • Accepted February 2, 2009.

    This Article

    1. Diabetes
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