title: FXR induces the UGT2B4 enzyme in hepatocytes: a potential mechanism of negative feedback control of FXR activity.
abstract: OBJECTIVE
  Bile acids are essential for bile formation and intestinal absorption of lipids and fat-soluble vitamins. However, the intrinsic toxicity of hydrophobic bile acids demands a tight control of their intracellular concentrations. Bile acids are ligands for the farnesoid X receptor (FXR) that regulates the expression of genes controlling bile acid synthesis and transport. The human uridine 5'-diphosphate-glucuronosyltransferase 2B4 (UGT2B4) converts hydrophobic bile acids into more hydrophilic glucuronide derivatives. In this study, we identify UGT2B4 as an FXR target gene.
  
  
  METHODS
  Human hepatocytes or hepatoblastoma HepG2 cells were treated with chenodeoxycholic acid or the synthetic FXR agonist GW4064, and the levels of UGT2B4 messenger RNA, protein, and activity were determined by using real-time polymerase chain reaction, Western blot, and glucuronidation assays.
  
  
  RESULTS
  Treatment of hepatocytes and HepG2 cells with FXR agonists resulted in an increase of UGT2B4 messenger RNA, protein, and activity. A bile acid response element in the UGT2B4 promoter (B4-BARE) to which FXR, but not retinoid X receptor, binds, was identified by site-directed mutagenesis, electromobility shift, and chromatin immunoprecipitation assays. Retinoid X receptor activation abolished the induction of UGT2B4 expression and inhibited binding of FXR to the B4-BARE, suggesting that retinoid X receptor modulates FXR target gene activation. Overexpression of UGT2B4 in HepG2 cells resulted in the attenuation of bile acid induction of the FXR target gene small heterodimeric partner.
  
  
  CONCLUSIONS
  These data suggest that UGT2B4 gene induction by bile acids contributes to a feed-forward reduction of bile acid toxicity and a decrease of the activity of these biological FXR activators.
authors.affiliation: U545 INSERM, Department of Atherosclerosis, Faculty of Pharmacy, Lille Pasteur Institute and University of Lille II, 1 Rue du Pr Calmette, BP 245, 59019 Lille, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Barbier
authors.forename: Ines Pineda
authors.initials: IP
authors.lastname: Torra
authors.forename: Audrey
authors.initials: A
authors.lastname: Sirvent
authors.forename: Thierry
authors.initials: T
authors.lastname: Claudel
authors.forename: Christophe
authors.initials: C
authors.lastname: Blanquart
authors.forename: Daniel
authors.initials: D
authors.lastname: Duran-Sandoval
authors.forename: Folkert
authors.initials: F
authors.lastname: Kuipers
authors.forename: Vladimir
authors.initials: V
authors.lastname: Kosykh
authors.forename: Jean-Charles
authors.initials: JC
authors.lastname: Fruchart
authors.forename: Bart
authors.initials: B
authors.lastname: Staels
mesh_terms: D001647:Bile Acids and Salts / Q000494:pharmacology; D002478:Cells, Cultured; D002635:Chenodeoxycholic Acid / Q000494:pharmacology; D004268:DNA-Binding Proteins; D004790:Enzyme Induction; D005246:Feedback; D014453:Glucuronosyltransferase / Q000096:biosynthesis* / Q000235:genetics; D022781:Hepatocytes / Q000201:enzymology*; D006801:Humans; D011401:Promoter Regions, Genetic; D018160:Receptors, Cytoplasmic and Nuclear / Q000502:physiology*; D020218:Response Elements; D014157:Transcription Factors; D000099150:Receptor, Farnesoid X-Activated
chemical_list: D001647:Bile Acids and Salts; D002635:Chenodeoxycholic Acid; D004268:DNA-Binding Proteins; D014453:Glucuronosyltransferase; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; D000099150:Receptor, Farnesoid X-Activated; C486404:UGT2B4 protein, human