title: Per-Arnt-Sim kinase regulates pancreatic duodenal homeobox-1 protein stability via phosphorylation of glycogen synthase kinase 3β in pancreatic β-cells.
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.
authors.affiliation: Montreal Diabetes Research Center, CRCHUM, Quebec City H1W4A4, Canada.
authors.forename: Meriem
authors.initials: M
authors.lastname: Semache
authors.forename: Bader
authors.initials: B
authors.lastname: Zarrouki
authors.forename: Ghislaine
authors.initials: G
authors.lastname: Fontés
authors.forename: Sarah
authors.initials: S
authors.lastname: Fogarty
authors.forename: Chintan
authors.initials: C
authors.lastname: Kikani
authors.forename: Mohammad B
authors.initials: MB
authors.lastname: Chawki
authors.forename: Jared
authors.initials: J
authors.lastname: Rutter
authors.forename: Vincent
authors.initials: V
authors.lastname: Poitout
mesh_terms: D000818:Animals; D005947:Glucose / Q000494:pharmacology; D038362:Glycogen Synthase Kinase 3 / Q000235:genetics / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D056945:Hep G2 Cells; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000378:metabolism*; D008297:Male; D051379:Mice; D009154:Mutation; D010766:Phosphorylation / Q000187:drug effects / Q000502:physiology; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D055550:Protein Stability / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D013549:Sweetening Agents / Q000494:pharmacology; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects / Q000502:physiology
chemical_list: D018398:Homeodomain Proteins; D013549:Sweetening Agents; D015534:Trans-Activators; C084010:pancreatic and duodenal homeobox 1 protein; C116037:PAS domain kinases; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; C000605508:Gsk3b protein, rat; D017346:Protein Serine-Threonine Kinases; D038362:Glycogen Synthase Kinase 3; D005947:Glucose
keywords: Diabetes; Glycogen Synthase Kinase 3; Insulin; Pancreatic Duodenal Homeobox-1; Pancreatic Islets; β-Cell