title: Species-specific mechanisms for cholesterol 7alpha-hydroxylase (CYP7A1) regulation by drugs and bile acids.
abstract: The gene encoding cholesterol 7alpha-hydroxylase (CYP7A1) is tightly regulated in order to control intrahepatic cholesterol and bile acid levels. Ligands of the xenobiotic-sensing pregnane X receptor inhibit CYP7A1 expression. To retrace the evolution of the molecular mechanisms underlying CYP7A1 inhibition, we used a chicken hepatoma cell system that retains the ability to be induced by phenobarbital and other drugs. Whereas bile acids regulate CYP7A1 via small heterodimer partner and liver receptor homolog-1, mRNA expression of these nuclear receptors is unchanged by xenobiotics. Instead, drugs repress chicken hepatic nuclear factor 4alpha (HNF4alpha) transcript levels concomitant with a reduction in CYP7A1 expression. Importantly, no reduction of HNF4alpha levels is found in mouse liver in vivo and in human primary hepatocyte cultures, respectively. Thus, besides the importance of HNF4alpha in CYP7A1 regulation in all species, birds and mammals use different signaling pathways to adjust CYP7A1 levels after exposure to xenobiotics.
authors.affiliation: Division of Pharmacology/Neurobiology, Biozentrum of the University of Basel, Klingelbergstrasse 50-70, CH-4056 Basel, Switzerland.
authors.forename: Christoph
authors.initials: C
authors.lastname: Handschin
authors.forename: Carmela
authors.initials: C
authors.lastname: Gnerre
authors.forename: David J
authors.initials: DJ
authors.lastname: Fraser
authors.forename: Celia
authors.initials: C
authors.lastname: Martinez-Jimenez
authors.forename: Ramiro
authors.initials: R
authors.lastname: Jover
authors.forename: Urs A
authors.initials: UA
authors.lastname: Meyer
mesh_terms: D000818:Animals; D001647:Bile Acids and Salts / Q000378:metabolism* / Q000494:pharmacology; D002478:Cells, Cultured; D002645:Chickens; D002790:Cholesterol 7-alpha-Hydroxylase / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D051557:Hepatocyte Nuclear Factor 4; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D051379:Mice; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D010634:Phenobarbital / Q000494:pharmacology; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D000077297:Pregnane X Receptor; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D011987:Receptors, Steroid / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction; D013045:Species Specificity; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D001647:Bile Acids and Salts; D004268:DNA-Binding Proteins; C496592:HNF4A protein, human; D051557:Hepatocyte Nuclear Factor 4; C496593:Hnf4a protein, mouse; D010750:Phosphoproteins; D000077297:Pregnane X Receptor; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D011987:Receptors, Steroid; D011994:Recombinant Proteins; D014157:Transcription Factors; C099713:nuclear receptor subfamily 0, group B, member 2; D002790:Cholesterol 7-alpha-Hydroxylase; D010634:Phenobarbital