title: Interaction of silencing mediator for retinoid and thyroid receptors with steroid and xenobiotic receptor on multidrug resistance 1 promoter.
abstract: OBJECTIVE
  The steroid and xenobiotic receptor (SXR) regulates the transcription of its target genes by interacting with various nuclear receptor cofactors. We have previously shown that silencing mediator for retinoid and thyroid receptors (SMRT) interacts with SXR even in the presence of rifampicin on cytochrome P450 monooxygenase 3A4 (CYP3A4) promoter in HepG2 cells. To examine the specificity of such interaction, the involvement of SMRT on SXR-mediated transcription through multidrug resistance (MDR) 1 gene promoter was examined using LS174T intestine-derived clonal cells.
  
  
  METHODS
  Transient transfection-based reporter gene assay was carried out to examine the effect of SMRT or nuclear receptor corepressor (NCoR) on SXR-mediated transcription in LS174T cells. Semi-quantitative RT-PCR was performed to confirm the expression of MDR1 mRNA in LS174T cells. To examine the interaction of SMRT with SXR, we carried out mammalian one-hybrid assay in CV-1 cells and immunoprecipitation study in HEK-293 cells.
  
  
  RESULTS
  SMRT, but not NCoR suppressed rifampicin-induced SXR-mediated transcription. The SXR-mediated MDR1 mRNA expression was augmented in the presence of rifampicin, whereas it suppressed the expression following the overexpression of SMRT. In mammalian one-hybrid assay, only SMRT but not NCoR interacted with SXR on MDR1 promoter in the presence of rifampicin. In immunoprecipitation study, SMRT bound to SXR regardless of the presence or absence of rifampicin.
  
  
  CONCLUSIONS
  SMRT may be recruited in the SXR-cofactor complex even in the presence of ligand. SMRT may be involved not only in SXR-mediated suppression without ligand, but also in ligand-activated transcription to suppress the overactivation of transcription.
authors.affiliation: Department of Integrative Physiology, Gunma University Graduate School of Medicine, 3-39-22 Showa-machi, Maebashi, Gunma 371-8511, Japan.
authors.forename: Kazumi
authors.initials: K
authors.lastname: Hirooka-Masui
authors.forename: Ronny
authors.initials: R
authors.lastname: Lesmana
authors.forename: Toshiharu
authors.initials: T
authors.lastname: Iwasaki
authors.forename: Ming
authors.initials: M
authors.lastname: Xu
authors.forename: Kaori
authors.initials: K
authors.lastname: Hayasaka
authors.forename: Mizuki
authors.initials: M
authors.lastname: Haraguchi
authors.forename: Akira
authors.initials: A
authors.lastname: Takeshita
authors.forename: Noriaki
authors.initials: N
authors.lastname: Shimokawa
authors.forename: Koujirou
authors.initials: K
authors.lastname: Yamamoto
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Koibuchi
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D045744:Cell Line, Tumor; D002522:Chlorocebus aethiops; D002999:Clone Cells / Q000378:metabolism; D056970:Co-Repressor Proteins / Q000378:metabolism*; D015870:Gene Expression; D057809:HEK293 Cells; D056945:Hep G2 Cells; D006801:Humans; D047468:Immunoprecipitation; D056985:Nuclear Receptor Co-Repressor 2 / Q000378:metabolism*; D000077297:Pregnane X Receptor; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D011987:Receptors, Steroid / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012293:Rifampin / Q000494:pharmacology; D014162:Transfection
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D056970:Co-Repressor Proteins; D056985:Nuclear Receptor Co-Repressor 2; D000077297:Pregnane X Receptor; D012333:RNA, Messenger; D011987:Receptors, Steroid; D012293:Rifampin