title: Coordinated control of cholesterol catabolism to bile acids and of gluconeogenesis via a novel mechanism of transcription regulation linked to the fasted-to-fed cycle.
abstract: Bile acid metabolism plays an essential role in cholesterol homeostasis and is critical for the initiation of atherosclerotic disease. However, despite the recent advances, the molecular mechanisms whereby bile acids regulate gene transcription and cholesterol homeostasis in mammals still need further investigations. Here, we show that bile acids suppress transcription of the gene (CYP7A1) encoding cholesterol 7alpha-hydroxylase, the rate-limiting enzyme in bile acid biosynthesis, also through an unusual mechanism not involving the bile acid nuclear receptor, farnesoid X receptor. By performing cell-based reporter assays, protein/protein interaction, and chromatin immunoprecipitation assays, we demonstrate that bile acids impair the recruitment of peroxisome proliferator-activated receptor-gamma coactivator-1alpha and cAMP response element-binding protein-binding protein by hepatocyte nuclear factor-4alpha, a master regulator of CYP7A1. We also show for the first time that bile acids inhibit transcription of the gene (PEPCK) encoding phosphoenolpyruvate carboxykinase, the rate-limiting enzyme in gluconeogenesis, through the same farnesoid X receptor-independent mechanism. Chromatin immunoprecipitation assay revealed that bile acid-induced dissociation of coactivators from hepatocyte nuclear factor-4alpha decreased the recruitment of RNA polymerase II to the core promoter and downstream in the 3'-untranslated regions of these two genes, reflecting the reduction of gene transcription. Finally, we found that Cyp7a1 expression was stimulated in fasted mice in parallel to Pepck, whereas the same genes were repressed by bile acids. Collectively, these results reveal a novel regulatory mechanism that controls gene transcription in response to extracellular stimuli and argue that the transcription regulation by bile acids of genes central to cholesterol and glucose metabolism should be viewed dynamically in the context of the fasted-to-fed cycle.
authors.affiliation: Dipartimento di Scienze Farmacologiche, Facoltà di Farmacia, Università degli Studi di Milano, via Balzaretti 9, 20133 Milan, Italy.
authors.forename: Emma
authors.initials: E
authors.lastname: De Fabiani
authors.forename: Nico
authors.initials: N
authors.lastname: Mitro
authors.forename: Federica
authors.initials: F
authors.lastname: Gilardi
authors.forename: Donatella
authors.initials: D
authors.lastname: Caruso
authors.forename: Giovanni
authors.initials: G
authors.lastname: Galli
authors.forename: Maurizio
authors.initials: M
authors.lastname: Crestani
mesh_terms: D020413:3' Untranslated Regions; D000818:Animals; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D001647:Bile Acids and Salts / Q000378:metabolism*; D015153:Blotting, Western; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism*; D002790:Cholesterol 7-alpha-Hydroxylase / Q000235:genetics* / Q000378:metabolism; D002843:Chromatin / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D015536:Down-Regulation; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D005822:Genetic Vectors; D005943:Gluconeogenesis; D005979:Glutathione Peroxidase; D051557:Hepatocyte Nuclear Factor 4; D006801:Humans; D008024:Ligands; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008954:Models, Biological; D010750:Phosphoproteins / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000378:metabolism; D012319:RNA Polymerase II / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D014162:Transfection; D000099150:Receptor, Farnesoid X-Activated
chemical_list: D020413:3' Untranslated Regions; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D001647:Bile Acids and Salts; D002784:Cholesterol; D002790:Cholesterol 7-alpha-Hydroxylase; D002843:Chromatin; D004268:DNA-Binding Proteins; D005979:Glutathione Peroxidase; D051557:Hepatocyte Nuclear Factor 4; D008024:Ligands; D010750:Phosphoproteins; D011506:Proteins; D012319:RNA Polymerase II; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; D000099150:Receptor, Farnesoid X-Activated; C403128:MLX protein, human; C501970:Tcfl4 protein, mouse; C111264:peroxisome-proliferator-activated receptor-gamma coactivator-1; C014149:phosphoenolpyruvate carboxykinase ferroactivator protein, rat