N-glycan remodeling on glucagon receptor is an effector of nutrient sensing by the hexosamine biosynthesis pathway

J Biol Chem. 2014 Jun 6;289(23):15927-41. doi: 10.1074/jbc.M114.563734. Epub 2014 Apr 17.

Abstract

Glucose homeostasis in mammals is dependent on the opposing actions of insulin and glucagon. The Golgi N-acetylglucosaminyltransferases encoded by Mgat1, Mgat2, Mgat4a/b/c, and Mgat5 modify the N-glycans on receptors and solute transporter, possibly adapting activities in response to the metabolic environment. Herein we report that Mgat5(-/-) mice display diminished glycemic response to exogenous glucagon, together with increased insulin sensitivity. Glucagon receptor signaling and gluconeogenesis in Mgat5(-/-) cultured hepatocytes was impaired. In HEK293 cells, signaling by ectopically expressed glucagon receptor was increased by Mgat5 expression and GlcNAc supplementation to UDP-GlcNAc, the donor substrate shared by Mgat branching enzymes. The mobility of glucagon receptor in primary hepatocytes was reduced by galectin-9 binding, and the strength of the interaction was dependent on Mgat5 and UDP-GlcNAc levels. Finally, oral GlcNAc supplementation rescued the glucagon response in Mgat5(-/-) hepatocytes and mice, as well as glycolytic metabolites and UDP-GlcNAc levels in liver. Our results reveal that the hexosamine biosynthesis pathway and GlcNAc salvage contribute to glucose homeostasis through N-glycan branching on glucagon receptor.

Keywords: Glucagon Receptor; Gluconeogenesis; Glycosylation; Glycosyltransferase; Golgi N-Acetylglucosaminyltransferases; Metabolism; Receptor Regulation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Chromatography, Liquid
  • Glucagon / pharmacology
  • HEK293 Cells
  • Hexosamines / biosynthesis*
  • Humans
  • Hypoglycemia / metabolism
  • Hypoglycemia / physiopathology
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • N-Acetylglucosaminyltransferases / genetics
  • N-Acetylglucosaminyltransferases / metabolism
  • Polysaccharides / metabolism*
  • Receptors, Glucagon / metabolism*
  • Tandem Mass Spectrometry

Substances

  • Hexosamines
  • Polysaccharides
  • Receptors, Glucagon
  • Glucagon
  • N-Acetylglucosaminyltransferases
  • alpha-1,6-mannosylglycoprotein beta 1,6-N-acetylglucosaminyltransferase