Glucocorticoid receptor (GR)-associated SMRT binding to C/EBPβ TAD and Nrf2 Neh4/5

Role of SMRT recruited to GR in GSTA2 gene repression

Hwan Ki Sung, Je Cho Il, DalWoong Choi, Geon Kim Sang

Research output: Contribution to journalArticle

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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 β (C/EBPβ) and NF-E2-related factor 2 (Nrf2). The present study investigated the repressing effects of activating glucocorticoid receptor (GR) on C/EBPβ- 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/EBPβ 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/EBPβ 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/EBPβ or Nrf2. The plasmid transfection and siRNA experiments directly evidenced the functional role of SMRT in GSTA2 repression. In conclusion, dexamethasone antagonizes C/EBPβ- and Nrf2-mediated GSTA2 gene induction via ligand-GR binding to the GRE, and steroid-mediated GSTA2 repression involves inactivation of C/EBPβ and Nrf2 by SMRT recruited to steroid-GR complex.

Original languageEnglish
Pages (from-to)4150-4165
Number of pages16
JournalMolecular and Cellular Biology
Volume25
Issue number10
DOIs
Publication statusPublished - 2005 May 1
Externally publishedYes

Fingerprint

NF-E2-Related Factor 2
CCAAT-Enhancer-Binding Proteins
Glucocorticoid Receptors
Dexamethasone
Genes
Steroid Receptors
Response Elements
RNA Interference
Glutathione Transferase
Luciferases
Glucocorticoids
Nuclear Receptor Co-Repressor 2
Thyroid Hormone Receptors
Chromatin Immunoprecipitation
Retinoids
Chemoprevention
Immunoprecipitation
Immunoblotting
Histones
Transfection

ASJC Scopus subject areas

  • Molecular Biology
  • Genetics
  • Cell Biology

Cite this

Glucocorticoid receptor (GR)-associated SMRT binding to C/EBPβ TAD and Nrf2 Neh4/5 : Role of SMRT recruited to GR in GSTA2 gene repression. / Sung, Hwan Ki; Il, Je Cho; Choi, DalWoong; Sang, Geon Kim.

In: Molecular and Cellular Biology, Vol. 25, No. 10, 01.05.2005, p. 4150-4165.

Research output: Contribution to journalArticle

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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 β (C/EBPβ) and NF-E2-related factor 2 (Nrf2). The present study investigated the repressing effects of activating glucocorticoid receptor (GR) on C/EBPβ- 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/EBPβ 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/EBPβ 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/EBPβ or Nrf2. The plasmid transfection and siRNA experiments directly evidenced the functional role of SMRT in GSTA2 repression. In conclusion, dexamethasone antagonizes C/EBPβ- and Nrf2-mediated GSTA2 gene induction via ligand-GR binding to the GRE, and steroid-mediated GSTA2 repression involves inactivation of C/EBPβ and Nrf2 by SMRT recruited to steroid-GR complex.",
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