AMP-Activated Protein Kinase: A New Beta-Cell Glucose Sensor?

Regulation by Amino Acids and Calcium Ions

  1. Isabelle Leclerc and
  2. Guy A. Rutter
  1. From the Henry Wellcome Laboratories for Integrated Cell Signalling and Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol, U.K
  1. Address correspondence and reprint requests to Professor Guy A. Rutter, Henry Wellcome Laboratories for Integrated Cell Signalling and Department of Biochemistry, School of Medical Sciences, University of Bristol, University Walk, BS8 1TD Bristol, U.K. E-mail: g.a.rutter{at}bristol.ac.uk

Abstract

Stimulation of AMP-activated protein kinase (AMPK) in skeletal muscle and liver is seen as an exciting prospect for the treatment of type 2 diabetes. However, we have recently demonstrated that changes in AMPK activity accompany the exposure of pancreatic islet β-cells to elevated glucose concentrations and may be involved in the activation of insulin secretion. Here, we discuss this hypothesis and explore the potential role of changes in AMPK activity in the actions of other secretagogues. Amino acids decreased AMPK activity in MIN6 β-cells with an order of potency for inhibition: arg = leu < gln = leu + glu < glucose, which was closely correlated with the stimulation of insulin release (r2 = 0.76). By contrast, increases in intracellular Ca2+ concentration provoked by cell depolarization with KCl activated AMPK in the face of increased free intracellular ATP concentrations. Elevation of intracellular cAMP levels with isobutylmethyxanthine or forskolin had no effect on AMPK activity. We conclude that metabolizable amino acids regulate AMPK in the β-cell via increases in the cytosolic ATP/AMP ratio and via phosphorylation by the upstream kinase LKB1. Intracellular Ca2+ ions may activate AMPK by calmodulin kinase 1 kinase-mediated phosphorylation. The latter may act as a novel feedback mechanism to inhibit excessive insulin secretion under some circumstances.

Footnotes

  • This article is based on a presentation at a symposium. The symposium and the publication of this article were made possible by an unrestricted educational grant from Servier.

    • Accepted May 21, 2004.
    • Received March 8, 2004.
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