title: ChREBP mediates glucose repression of peroxisome proliferator-activated receptor alpha expression in pancreatic beta-cells.
abstract: Chronic exposure to elevated levels of glucose and fatty acids leads to dysfunction of pancreatic β-cells by mechanisms that are only partly understood. The transcription factor peroxisome proliferator-activated receptor α (PPARα) is an important regulator of genes involved in fatty acid metabolism and has been shown to protect against lipid-induced β-cell dysfunction. We and others have previously shown that expression of the PPARα gene in β-cells is rapidly repressed by glucose. Here we show that the PPARα gene is transcribed from five alternative transcription start sites, resulting in three alternative first exons that are spliced to exon 2. Expression of all PPARα transcripts is repressed by glucose both in insulinoma cells and in isolated pancreatic islets. The observation that the dynamics of glucose repression of PPARα transcription are very similar to those of glucose activation of target genes by the carbohydrate response element-binding protein (ChREBP) prompted us to investigate the potential role of ChREBP in the regulation of PPARα expression. We show that a constitutively active ChREBP lacking the N-terminal domain efficiently represses PPARα expression in insulinoma cells and in rodent and human islets. In addition, we demonstrate that siRNA-mediated knockdown of ChREBP abrogates glucose repression of PPARα expression as well as induction of well established ChREBP target genes in insulinoma cells. In conclusion, this work shows that ChREBP is a critical and direct mediator of glucose repression of PPARα gene expression in pancreatic β-cells, suggesting that ChREBP may be important for glucose suppression of the fatty acid oxidation capacity of β-cells.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Southern Denmark, 5230 Odense M, Denmark.
authors.forename: Michael
authors.initials: M
authors.lastname: Boergesen
authors.forename: Lars la Cour
authors.initials: Ll
authors.lastname: Poulsen
authors.forename: Søren Fisker
authors.initials: SF
authors.lastname: Schmidt
authors.forename: Francesca
authors.initials: F
authors.lastname: Frigerio
authors.forename: Pierre
authors.initials: P
authors.lastname: Maechler
authors.forename: Susanne
authors.initials: S
authors.lastname: Mandrup
mesh_terms: D000818:Animals; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D005091:Exons / Q000502:physiology; D005227:Fatty Acids / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D055785:Gene Knockdown Techniques; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D057809:HEK293 Cells; D006801:Humans; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010084:Oxidation-Reduction; D047493:PPAR alpha / Q000096:biosynthesis* / Q000235:genetics; D017434:Protein Structure, Tertiary; D051381:Rats; D017208:Rats, Wistar; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D013549:Sweetening Agents / Q000378:metabolism / Q000494:pharmacology; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects / Q000502:physiology
chemical_list: D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D005227:Fatty Acids; C116385:MLXIPL protein, human; C506001:Mlxipl protein, mouse; C442825:Mlxipl protein, rat; D009687:Nuclear Proteins; D047493:PPAR alpha; D012097:Repressor Proteins; D013549:Sweetening Agents; D014157:Transcription Factors; D005947:Glucose