title: Transactivation of ABCG2 through a novel cis-element in the distal promoter by constitutive androstane receptor but not pregnane X receptor in human hepatocytes.
abstract: A previous report demonstrated that treatment of human hepatocytes with phenobarbital, an activator of nuclear receptor constitutive androstane receptor (CAR), increases mRNA levels of an efflux transporter ABCG2, which is involved in the excretion of xenobiotics in liver and intestine. The results suggest that human CAR (hCAR) transactivates human ABCG2 (hABCG2) expression. In this study, we confirmed increase in ABCG2 mRNA levels in human hepatocytes after adenoviral expression of hCAR and treatment with its activator. Reporter assays suggested the existence of an hCAR-responsive element between -8000 and -7485 of hABCG2 promoter. Electrophoretic mobility shift assays and chromatin immunoprecipitation assays identified a DR5 motif (direct repeat separated by five nucleotides) within the region as a binding motif of hCAR/human retinoid X receptor α heterodimer. The introduction of mutations into the DR5 motif resulted in the complete loss of the hCAR-mediated transactivation. Interestingly, human pregnane X receptor, belonging to the same NR1I subfamily as CAR, did not activate any reporter gene containing the DR5 motif. Taken together, our present findings suggest that hCAR transactivates hABCG2 through the DR5 motif located in its distal promoter in human hepatocytes and that the motif prefers hCAR to pregnane X receptor.
authors.affiliation: Division of Drug Metabolism and Molecular Toxicology, Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba-ku, Sendai, Miyagi Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Benoki
authors.forename: Kouichi
authors.initials: K
authors.lastname: Yoshinari
authors.forename: Tsubasa
authors.initials: T
authors.lastname: Chikada
authors.forename: Jun
authors.initials: J
authors.lastname: Imai
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Yamazoe
mesh_terms: D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000235:genetics*; D020816:Amino Acid Motifs; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D000090702:Constitutive Androstane Receptor; D017931:DNA Primers / Q000235:genetics; D005816:Genetic Complementation Test; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000378:metabolism*; D006801:Humans; D016297:Mutagenesis, Site-Directed; D009363:Neoplasm Proteins / Q000235:genetics*; D000077297:Pregnane X Receptor; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011987:Receptors, Steroid / Q000737:chemistry / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015533:Transcriptional Activation
chemical_list: C116614:ABCG2 protein, human; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D000090702:Constitutive Androstane Receptor; D017931:DNA Primers; D009363:Neoplasm Proteins; D000077297:Pregnane X Receptor; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D011987:Receptors, Steroid; D011994:Recombinant Proteins