A novel RARα/CAR-mediated mechanism for regulation of human organic solute transporter-β gene expression.
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.
['Xu|Shuhua|S|', 'Sun|An-Qiang|AQ|', 'Suchy|Frederick J|FJ|']
D001483:Base Sequence D015153:Blotting, Western D045744:Cell Line, Tumor D002779:Cholestasis D002784:Cholesterol D047369:Chromatin Immunoprecipitation D024202:Electrophoretic Mobility Shift Assay D017930:Genes, Reporter D006801:Humans D026901:Membrane Transport Proteins D008969:Molecular Sequence Data D016297:Mutagenesis, Site-Directed D012313:RNA D034741:RNA, Small Interfering D060888:Real-Time Polymerase Chain Reaction D018160:Receptors, Cytoplasmic and Nuclear D018168:Receptors, Retinoic Acid D020218:Response Elements D000072482:Retinoic Acid Receptor alpha D047490:Retinoid X Receptor alpha D014162:Transfection D014212:Tretinoin D015262:Xenobiotics
organic solute transporter-β DR5 constitutive androstane receptor retinoic acid receptor-α