Susceptibility of Glucokinase-MODY Mutants to Inactivation by Oxidative Stress in Pancreatic β-Cells

  1. Catherine Arden1
  1. 1Institute of Cellular Medicine, Newcastle University, Newcastle Upon Tyne, U.K.
  2. 2Department of Biochemistry and Biophysics and Institute for Diabetes, Obesity and Metabolism, School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
  1. Corresponding author: Catherine Arden, catherine.arden{at}ncl.ac.uk.
  1. L.A. and C.A. share joint senior authorship.

Abstract

OBJECTIVE The posttranslational regulation of glucokinase (GK) differs in hepatocytes and pancreatic β-cells. We tested the hypothesis that GK mutants that cause maturity-onset diabetes of the young (GK-MODY) show compromised activity and posttranslational regulation in β-cells.

RESEARCH DESIGN AND METHODS Activity and protein expression of GK-MODY and persistent hyperinsulinemic hypoglycemia of infancy (PHHI) mutants were studied in β-cell (MIN6) and non–β-cell (H4IIE) models. Binding of GK to phosphofructo-2-kinase, fructose-2,6-bisphosphatase (PFK2/FBPase2) was studied by bimolecular fluorescence complementation in cell-based models.

RESULTS Nine of 11 GK-MODY mutants that have minimal effect on enzyme kinetics in vitro showed decreased specific activity relative to wild type when expressed in β-cells. A subset of these were stable in non–β-cells but showed increased inactivation in conditions of oxidative stress and partial reversal of inactivation by dithiothreitol. Unlike the GK-MODY mutants, four of five GK-PHHI mutants had similar specific activity to wild type and Y214C had higher activity than wild type. The GK-binding protein PFK2/FBPase2 protected wild-type GK from oxidative inactivation and the decreased stability of GK-MODY mutants correlated with decreased interaction with PFK2/FBPase2.

CONCLUSIONS Several GK-MODY mutants show posttranslational defects in β-cells characterized by increased susceptibility to oxidative stress and/or protein instability. Regulation of GK activity through modulation of thiol status may be a physiological regulatory mechanism for the control of GK activity in β-cells.

Footnotes

  • Received March 29, 2011.
  • Accepted August 31, 2011.

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  1. Diabetes vol. 60 no. 12 3175-3185
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