title: A novel RARα/CAR-mediated mechanism for regulation of human organic solute transporter-β gene expression.
abstract: The organic solute transporter-α/β (OSTα/β) is a heteromeric transporter that is essential for bile acid and sterol disposition and for the enterohepatic circulation. To better understand the mechanism underlying OST gene regulation, the effects of retinoic acid (RA) on OSTα/β gene expression were investigated. The results show a dose-dependent induction of OSTβ but not OSTα expression in both Huh7 and HepG2 cells by RA treatment. A novel functional RA receptor response element (RARE; so-called DR5) in the promoter of OSTβ gene was identified. The interaction of RARα/RXRα with the RARE was verified by electrophoretic mobility shift and chromatin immunoprecipitation assays and its functional importance by hOSTβ promoter activation in luciferase reporter assays. The studies demonstrated that the RARE is also a constitutive androstane receptor (CAR) binding site for OSTβ gene regulation. These results suggest that OSTβ is a target of both FXR-mediated (by binding to IR-1 element) and RARα- and CAR-mediated (by binding to DR5 element) gene regulation pathways. In summary, this study has uncovered a novel RARE (DR5) element in the promoter of OSTβ that binds RARα or CAR heterodimerized with RXRα and appears to function synergistically with the IR-1 element to provide maximal induction of OSTβ in response to RA. These findings demonstrate a role for RARα and CAR in controlling OSTβ expression levels.
authors.affiliation: Children's Hospital Colorado, Univ. of Colorado School of Medicine, 13123 E. 16th Ave., B065 Aurora, CO 80045. frederick.suchy@childrenscolorado.org.
authors.forename: Shuhua
authors.initials: S
authors.lastname: Xu
authors.forename: An-Qiang
authors.initials: AQ
authors.lastname: Sun
authors.forename: Frederick J
authors.initials: FJ
authors.lastname: Suchy
mesh_terms: D001483:Base Sequence; D015153:Blotting, Western; D045744:Cell Line, Tumor; D002779:Cholestasis / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism; D047369:Chromatin Immunoprecipitation; D024202:Electrophoretic Mobility Shift Assay; D017930:Genes, Reporter; D006801:Humans; D026901:Membrane Transport Proteins / Q000096:biosynthesis* / Q000235:genetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D012313:RNA / Q000096:biosynthesis / Q000235:genetics; D034741:RNA, Small Interfering / Q000494:pharmacology; D060888:Real-Time Polymerase Chain Reaction; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism / Q000502:physiology; D018168:Receptors, Retinoic Acid / Q000502:physiology*; D020218:Response Elements / Q000502:physiology; D000072482:Retinoic Acid Receptor alpha; D047490:Retinoid X Receptor alpha / Q000378:metabolism; D014162:Transfection; D014212:Tretinoin / Q000494:pharmacology; D015262:Xenobiotics / Q000378:metabolism; D000099150:Receptor, Farnesoid X-Activated
chemical_list: D002784:Cholesterol; D026901:Membrane Transport Proteins; D012313:RNA; D034741:RNA, Small Interfering; D018160:Receptors, Cytoplasmic and Nuclear; D018168:Receptors, Retinoic Acid; D000072482:Retinoic Acid Receptor alpha; D047490:Retinoid X Receptor alpha; D014212:Tretinoin; D015262:Xenobiotics; D000099150:Receptor, Farnesoid X-Activated; C000607071:RARA protein, human; C476577:SLC51B protein, human
keywords: DR5; constitutive androstane receptor; organic solute transporter-β; retinoic acid receptor-α