title: Glucocorticoid receptor (GR)-associated SMRT binding to C/EBPbeta TAD and Nrf2 Neh4/5: role of SMRT recruited to GR in GSTA2 gene repression.
abstract: The expression of the glutathione S-transferase gene (GST), whose induction accounts for cancer chemoprevention, is regulated by activation of CCAAT/enhancer binding protein beta (C/EBPbeta) and NF-E2-related factor 2 (Nrf2). The present study investigated the repressing effects of activating glucocorticoid receptor (GR) on C/EBPbeta- and Nrf2-mediated GSTA2 gene induction and the mechanism. Dexamethasone that activates GR inhibited constitutive and oltipraz- or tert-butylhydroquinone (t-BHQ)-inducible GSTA2 expression in H4IIE cells. Also, dexamethasone repressed GSTA2 promoter-luciferase gene activity. Dexamethasone-GR activation did not inhibit nuclear translocation of C/EBPbeta or Nrf2 nor their DNA binding activities induced by oltipraz or t-BHQ. Deletion of the glucocorticoid response element (GRE) in the GSTA2 promoter abolished dexamethasone inhibition of the gene induction. Immunoprecipitation-immunoblotting, chromatin immunoprecipitation, and GST pull-down assays revealed that silencing mediator for retinoid and thyroid hormone receptors (SMRT), a corepressor recruited to steroid-GR complex for histone deacetylation, bound to TAD domain of C/EBPbeta and Neh4/5 domain of Nrf2. The GSTA2 promoter-luciferase activities were decreased by SMRT but not by truncated SMRTs. The small interference RNA (siRNA) against SMRT abolished SMRT repression of the gene induction by C/EBPbeta or Nrf2. The plasmid transfection and siRNA experiments directly evidenced the functional role of SMRT in GSTA2 repression. In conclusion, dexamethasone antagonizes C/EBPbeta- and Nrf2-mediated GSTA2 gene induction via ligand-GR binding to the GRE, and steroid-mediated GSTA2 repression involves inactivation of C/EBPbeta and Nrf2 by SMRT recruited to steroid-GR complex.
authors.affiliation: College of Pharmacy, Seoul National University, Sillim-dong, Kwanak-gu, Seoul 151-742, South Korea.
authors.forename: Sung Hwan
authors.initials: SH
authors.lastname: Ki
authors.forename: Il Je
authors.initials: IJ
authors.lastname: Cho
authors.forename: Dal Woong
authors.initials: DW
authors.lastname: Choi
authors.forename: Sang Geon
authors.initials: SG
authors.lastname: Kim
mesh_terms: D000107:Acetylation / Q000187:drug effects; D000818:Animals; D001665:Binding Sites; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D003907:Dexamethasone / Q000494:pharmacology; D015536:Down-Regulation; D005982:Glutathione Transferase / Q000235:genetics*; D006657:Histones / Q000378:metabolism; D007527:Isoenzymes / Q000235:genetics*; D051379:Mice; D051267:NF-E2-Related Factor 2; D056985:Nuclear Receptor Co-Repressor 2; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D051381:Rats; D011965:Receptors, Glucocorticoid / Q000378:metabolism*; D012097:Repressor Proteins / Q000378:metabolism*; D020218:Response Elements / Q000235:genetics; D015534:Trans-Activators / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D022782:CCAAT-Enhancer-Binding Protein-beta; D004268:DNA-Binding Proteins; D006657:Histones; D007527:Isoenzymes; D051267:NF-E2-Related Factor 2; C539131:Ncor2 protein, mouse; C539132:Ncor2 protein, rat; C495636:Nfe2l2 protein, mouse; C495637:Nfe2l2 protein, rat; D056985:Nuclear Receptor Co-Repressor 2; D011965:Receptors, Glucocorticoid; D012097:Repressor Proteins; D015534:Trans-Activators; D003907:Dexamethasone; D005982:Glutathione Transferase; C119995:glutathione S-transferase alpha