title: Ku proteins function as corepressors to regulate farnesoid X receptor-mediated gene expression.
abstract: The farnesoid X receptor (FXR; NR1H4) is a member of the nuclear receptor superfamily and regulates the expression of genes involved in enterohepatic circulation and the metabolism of bile acids. Based on functional analyses, nuclear receptors are divided into regions A-F. To explore the cofactors interacting with FXR, we performed a pull-down assay using GST-fused to the N-terminal A/B region and the C region, which are required for the ligand-independent transactivation and DNA-binding, respectively, of FXR, and nuclear extracts from HeLa cells. We identified DNA-dependent protein kinase catalytic subunit (DNA-PKcs), Ku80, and Ku70 as FXR associated factors. These proteins are known to have an important role in DNA repair, recombination, and transcription. DNA-PKcs mainly interacted with the A/B region of FXR, whereas the Ku proteins interacted with the C region and with the D region (hinge region). Chromatin immunoprecipitation assays revealed that the Ku proteins associated with FXR on the bile salt export pump (BSEP) promoter. Furthermore, we demonstrated that ectopic expression of the Ku proteins decreased the promoter activity and expression of BSEP gene mediated by FXR. These results suggest that the Ku proteins function as corepressors for FXR.
authors.affiliation: Department of Molecular Biology, Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Aichi 467-8603, Japan.
authors.forename: Masae
authors.initials: M
authors.lastname: Ohno
authors.forename: Masaaki
authors.initials: M
authors.lastname: Kunimoto
authors.forename: Makoto
authors.initials: M
authors.lastname: Nishizuka
authors.forename: Shigehiro
authors.initials: S
authors.lastname: Osada
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Imagawa
mesh_terms: D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters / Q000235:genetics*; D034961:Antigens, Nuclear / Q000235:genetics / Q000378:metabolism*; D047369:Chromatin Immunoprecipitation; D051747:DNA-Activated Protein Kinase / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D000072200:Ku Autoantigen; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism*; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D000099150:Receptor, Farnesoid X-Activated
chemical_list: D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters; D034961:Antigens, Nuclear; D051747:DNA-Activated Protein Kinase; D004268:DNA-Binding Proteins; D000072200:Ku Autoantigen; D018160:Receptors, Cytoplasmic and Nuclear; D012097:Repressor Proteins; D000099150:Receptor, Farnesoid X-Activated; C093491:ABCB11 protein, human; C000606509:Xrcc6 protein, human