Glucose activates free fatty acid receptor 1 gene transcription via phosphatidylinositol-3-kinase-dependent O-GlcNAcylation of pancreas-duodenum homeobox-1.
The G protein-coupled free fatty acid receptor-1 (FFA1/GPR40) plays a major role in the regulation of insulin secretion by fatty acids. GPR40 is considered a potential therapeutic target to enhance insulin secretion in type 2 diabetes; however, its mode of regulation is essentially unknown. The aims of this study were to test the hypothesis that glucose regulates GPR40 gene expression in pancreatic β-cells and to determine the mechanisms of this regulation. We observed that glucose stimulates GPR40 gene transcription in pancreatic β-cells via increased binding of pancreas-duodenum homeobox-1 (Pdx-1) to the A-box in the HR2 region of the GPR40 promoter. Mutation of the Pdx-1 binding site within the HR2 abolishes glucose activation of GPR40 promoter activity. The stimulation of GPR40 expression and Pdx-1 binding to the HR2 in response to glucose are mimicked by N-acetyl glucosamine, an intermediate of the hexosamine biosynthesis pathway, and involve PI3K-dependent O-GlcNAcylation of Pdx-1 in the nucleus. We demonstrate that O-GlcNAc transferase (OGT) interacts with the product of the PI3K reaction, phosphatidylinositol 3,4,5-trisphosphate (PIP(3)), in the nucleus. This interaction enables OGT to catalyze O-GlcNAcylation of nuclear proteins, including Pdx-1. We conclude that glucose stimulates GPR40 gene expression at the transcriptional level through Pdx-1 binding to the HR2 region and via a signaling cascade that involves an interaction between OGT and PIP(3) at the nuclear membrane. These observations reveal a unique mechanism by which glucose metabolism regulates the function of transcription factors in the nucleus to induce gene expression.
Montreal Diabetes Research Center, Centre de Recherche du Centre Hospitalier de l'Universite de Montreal, and Department of Medicine, University of Montreal, Montreal, QC, Canada H3T 1J4.
Melkam
M
Kebede
Mourad
M
Ferdaoussi
Arturo
A
Mancini
Thierry
T
Alquier
Rohit N
RN
Kulkarni
Michael D
MD
Walker
Vincent
V
Poitout
D000117:Acetylglucosamine / Q000378:metabolism*; D000818:Animals; D004386:Duodenum / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D006595:Hexosamines / Q000096:biosynthesis; D018398:Homeodomain Proteins / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D051379:Mice; D008810:Mice, Inbred C57BL; D010179:Pancreas / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled / Q000235:genetics*; D014158:Transcription, Genetic
C473034:FFAR1 protein, human; D006595:Hexosamines; D018398:Homeodomain Proteins; D007328:Insulin; D043562:Receptors, G-Protein-Coupled; D019869:Phosphatidylinositol 3-Kinases; D005947:Glucose; D000117:Acetylglucosamine