SUMOylation of Pancreatic Glucokinase Regulates Its Cellular Stability and Activity[S]

• Published in: The Journal of biological chemistry 2013-02, Vol.288 (8), p.5951-5962
• Main Authors: Aukrust, Ingvild, Bjørkhaug, Lise, Negahdar, Maria, Molnes, Janne, Johansson, Bente B., MÜller, Yvonne, Haas, Wilhelm, Gygi, Steven P., Søvik, Oddmund, Flatmark, Torgeir, Kulkarni, Rohit N., Njølstad, Pål R.
• Format: Article
• Language: English
• Subjects: Animals; Carbohydrates - chemistry; Catalysis; Cell Biology; Electrophoresis, Gel, Two-Dimensional - methods; Enzyme Activity; Enzyme Kinetics; Gene Expression Regulation, Enzymologic; Glucokinase; Glucokinase - chemistry; Insulin-Secreting Cells - cytology; Kinetics; Liver - enzymology; Mass Spectrometry (MS); Mass Spectrometry - methods; Mice; Mutation; Pancreas - enzymology; Protein Isoforms; Protein Processing, Post-Translational; Protein Stability; Recombinant Proteins - chemistry; Sumoylation
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M112.393769

Glucokinase is the predominant hexokinase expressed in hepatocytes and pancreatic β-cells, with a pivotal role in regulating glucose-stimulated insulin secretion, illustrated by glucokinase gene mutations causing monogenic diabetes and congenital hyperinsulinemic hypoglycemia. A complex tissue-specific network of mechanisms regulates this enzyme, and a major unanswered question in glucokinase biology is how post-translational modifications control the function of the enzyme. Here, we show that the pancreatic isoform of human glucokinase is SUMOylated in vitro, using recombinant enzymes, and in insulin-secreting model cells. Three N-terminal lysines unique for the pancreatic isoform (Lys-12/Lys-13 and/or Lys-15) may represent one SUMOylation site, with an additional site (Lys-346) common for the pancreatic and the liver isoform. SUMO-1 and E2 overexpression stabilized preferentially the wild-type human pancreatic enzyme in MIN6 β-cells, and SUMOylation increased the catalytic activity of recombinant human glucokinase in vitro and also of glucokinase in target cells. Small ubiquitin-like modifier conjugation represents a novel form of post-translational modification of the enzyme, and it may have an important regulatory function in pancreatic β-cells. Background: Glucokinase is a key player in carbohydrate metabolism, but how this enzyme is regulated by post-translational modifications is largely unknown. Results: Glucokinase is SUMO-modified in vitro and in pancreatic β-cells, increasing its activity and stability. Conclusion: SUMOylation of glucokinase is a novel form of modification, regulating its cellular stability and activity. Significance: SUMO conjugation of glucokinase may have an important regulatory function in pancreatic β-cells.