Per-Arnt-Sim kinase regulates pancreatic duodenal homeobox-1 protein stability via phosphorylation of glycogen synthase kinase 3β in pancreatic β-cells

J Biol Chem. 2013 Aug 23;288(34):24825-33. doi: 10.1074/jbc.M113.495945. Epub 2013 Jul 12.

Abstract

In pancreatic β-cells, glucose induces the binding of the transcription factor pancreatic duodenal homeobox-1 (PDX-1) to the insulin gene promoter to activate insulin gene transcription. At low glucose levels, glycogen synthase kinase 3β (GSK3β) is known to phosphorylate PDX-1 on C-terminal serine residues, which triggers PDX-1 proteasomal degradation. We previously showed that the serine/threonine Per-Arnt-Sim domain-containing kinase (PASK) regulates insulin gene transcription via PDX-1. However, the mechanisms underlying this regulation are unknown. In this study, we aimed to identify the role of PASK in the regulation of PDX-1 phosphorylation, protein expression, and stability in insulin-secreting cells and isolated rodent islets of Langerhans. We observed that glucose induces a decrease in overall PDX-1 serine phosphorylation and that overexpression of WT PASK mimics this effect. In vitro, PASK directly phosphorylates GSK3β on its inactivating phosphorylation site Ser(9). Overexpression of a kinase-dead (KD), dominant negative version of PASK blocks glucose-induced Ser(9) phosphorylation of GSK3β. Accordingly, GSK3β Ser(9) phosphorylation is reduced in islets from pask-null mice. Overexpression of WT PASK or KD GSK3β protects PDX-1 from degradation and results in increased PDX-1 protein abundance. Conversely, overexpression of KD PASK blocks glucose-induction of PDX-1 protein. We conclude that PASK phosphorylates and inactivates GSK3β, thereby preventing PDX-1 serine phosphorylation and alleviating GSK3β-mediated PDX-1 protein degradation in pancreatic β-cells.

Keywords: Diabetes; Glycogen Synthase Kinase 3; Insulin; Pancreatic Duodenal Homeobox-1; Pancreatic Islets; β-Cell.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Glucose / pharmacology
  • Glycogen Synthase Kinase 3 / genetics
  • Glycogen Synthase Kinase 3 / metabolism*
  • Glycogen Synthase Kinase 3 beta
  • Hep G2 Cells
  • Homeodomain Proteins / genetics
  • Homeodomain Proteins / metabolism*
  • Humans
  • Insulin-Secreting Cells / cytology
  • Insulin-Secreting Cells / metabolism*
  • Male
  • Mice
  • Mutation
  • Phosphorylation / drug effects
  • Phosphorylation / physiology
  • Protein Stability / drug effects
  • Protein-Serine-Threonine Kinases / genetics
  • Protein-Serine-Threonine Kinases / metabolism*
  • Rats
  • Rats, Wistar
  • Sweetening Agents / pharmacology
  • Trans-Activators / genetics
  • Trans-Activators / metabolism*
  • Transcription, Genetic / drug effects
  • Transcription, Genetic / physiology

Substances

  • Homeodomain Proteins
  • Sweetening Agents
  • Trans-Activators
  • pancreatic and duodenal homeobox 1 protein
  • PAS domain kinases
  • GSK3B protein, human
  • Glycogen Synthase Kinase 3 beta
  • Gsk3b protein, mouse
  • Gsk3b protein, rat
  • Protein-Serine-Threonine Kinases
  • Glycogen Synthase Kinase 3
  • Glucose