title: Farnesoid X receptor suppresses constitutive androstane receptor activity at the multidrug resistance protein-4 promoter.
abstract: Multidrug resistance protein-4 (MRP4) is a member of the multidrug resistance associated gene family that is expressed on the basolateral membrane of hepatocytes and undergoes adaptive up-regulation in response to cholestatic injury or bile acid feeding. In this study we demonstrate that farnesoid X receptor (FXR) regulates MRP4 in vivo and in vitro. In vivo deletion of FXR induces MRP4 gene expression. In vitro treatment of HepG2 cells with FXR ligands, chenodeoxycholic acid (CDCA), cholic acid (CA) and the synthetic ligand GW-4064 suppresses basal mRNA level of the MRP4 gene as well as the co-treatment with CDCA and 6-(4-Chlorophenyl)imidazo[2,1-b][1,3]thiazole-5-carbaldehyde-O-(3,4-dichlorobenzyl)oxime (CITCO), an activator of constitutive androstane receptor (CAR). We found in the human MRP4 promoter a CAR responsive element (CARE) embedded within an FXR responsive element (FXRE). We cloned this region and found that FXR suppresses CAR activity in luciferase assay. Finally, we demonstrated that FXR competes with CAR for binding to this overlapping binding site. Our results support the view that FXR activation in obstructive cholestasis might worsen liver injury by hijacking a protective mechanism regulated by CAR and provides a new molecular explanation to the pathophysiology of cholestasis.
authors.affiliation: Dipartimento di Medicina Clinica e Sperimentale, University of Perugia, Via E dal Pozzo, 06122 Perugia, Italy. barbara.renga@unipg.it
authors.forename: Barbara
authors.initials: B
authors.lastname: Renga
authors.forename: Marco
authors.initials: M
authors.lastname: Migliorati
authors.forename: Andrea
authors.initials: A
authors.lastname: Mencarelli
authors.forename: Sabrina
authors.initials: S
authors.lastname: Cipriani
authors.forename: Claudio
authors.initials: C
authors.lastname: D'Amore
authors.forename: Eleonora
authors.initials: E
authors.lastname: Distrutti
authors.forename: Stefano
authors.initials: S
authors.lastname: Fiorucci
mesh_terms: D000818:Animals; D001483:Base Sequence; D001647:Bile Acids and Salts / Q000494:pharmacology; D001665:Binding Sites; D002478:Cells, Cultured; D000090702:Constitutive Androstane Receptor; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics; D017353:Gene Deletion; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D051379:Mice; D008810:Mice, Inbred C57BL; D008954:Models, Biological; D008969:Molecular Sequence Data; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics*; D016296:Mutagenesis / Q000187:drug effects; D056971:Nuclear Receptor Co-Repressor 1 / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects; D000099150:Receptor, Farnesoid X-Activated
chemical_list: D001647:Bile Acids and Salts; D000090702:Constitutive Androstane Receptor; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D056971:Nuclear Receptor Co-Repressor 1; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D000099150:Receptor, Farnesoid X-Activated; C073492:ABCC4 protein, human; C489540:Abcc4 protein, mouse