The silencing mediator of retinoic acid and thyroid hormone receptors can interact with the aryl hydrocarbon (Ah) receptor but fails to repress Ah receptor-dependent gene expression

S. Renée Rushing, Michael S. Denison

Research output: Contribution to journalArticle

42 Scopus citations


Exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related chemicals causes a variety of tissue- and species-specific biological and toxicological effects, most of which are mediated by the aryl hydrocarbon receptor (AhR). The AhR complex is a ligand-dependent transcription factor that binds to its specific DNA recognition site as a dimer with the AhR nuclear translocator (ARNT) and activates gene transcription. Here, we have examined the ability of a nuclear corepressor, the silencing mediator of retinoic acid and thyroid hormone receptors (SMRT), to interact with and modulate AhR-dependent gene expression. Using glutathione S-transferase (GST) "pull-down" binding assays, we have mapped a major interaction between these factors to the silencing domain of SMRT and the PAS B ligand binding domain of AhR, and this interaction is unaffected by the addition of an AhR ligand. Association of SMRT with the AhR:ARNT:DNA complex was not detected by GST pull-down or gel retardation assays. Transient cotransfections of mammalian cells (Hepalclc7, MCF-7, and BG-1) with SMRT and a TCDD-inducible luciferase reporter containing the dioxin-responsive domain from the mouse CYP1A1 regulatory region revealed that SMRT does not repress, but enhances, AhR signaling. However, when a reporter containing a human CYP1A1 upstream region was cotransfected with SMRT into human MCF-7 cells, AhR-driven reporter activity was decreased by half, suggesting that SMRT acts on the human CYP1A1 promoter via a factor other than the AhR in MCF-7 cells. Furthermore, the interaction between SMRT and the AhR may have implications in pathways other than the AhR signaling pathway.

Original languageEnglish (US)
Pages (from-to)189-201
Number of pages13
JournalArchives of Biochemistry and Biophysics
Issue number2
StatePublished - Jul 15 2002



  • ARNT
  • Aryl hydrocarbon receptor
  • Dioxin
  • SMRT
  • TCDD
  • Transcriptional regulation

ASJC Scopus subject areas

  • Biochemistry
  • Biophysics
  • Molecular Biology

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