Silencing mediator for retinoid and thyroid hormone receptors interacts with octamer transcription factor-1 and acts as a transcriptional repressor

J Biol Chem. 2001 Mar 30;276(13):9720-5. doi: 10.1074/jbc.M008531200. Epub 2000 Dec 27.

Abstract

Octamer transcription factor-1 (Oct-1) is a member of the POU (Pit-1, Oct-1, unc-86) family of transcription factors and is involved in the transcriptional regulation of a variety of gene expressions related to cell cycle regulation, development, and hormonal signals. It has been shown that Oct-1 acts not only as a transcriptional activator but also as a transcriptional repressor for certain genes. The mechanism of the repressive function of Oct-1 has not been well understood. Here we demonstrate by using the glutathione S-transferase pull-down assays and coimmunoprecipitation assays that the POU domain of Oct-1 directly interacts with a silencing mediator for retinoid and thyroid hormone receptors (SMRT). The interaction surfaces are located in the C-terminal region of SMRT, which are different from previously described silencing domains I and II or receptor interacting domains I and II. In transient transfection assays in COS1 cells, overexpression of SMRT attenuated the augmentation of Oct-1 transcriptional activity by OBF-1/OCA-B, activator for Oct-1. In pull-down assays, increasing amounts of SMRT could compete the binding of OCA-B to Oct-1 POU domain. The activity of Oct-1 could be determined by a regulated balance between SMRT and OCA-B. Furthermore, cotransfected unliganded thyroid hormone receptor enhanced the transactivation by Oct-1, and addition of 3,3',5-tri-iodo-l-thyronine obliterated the stimulatory effects. Consequently, in the presence of cotransfected thyroid hormone receptor, the octamer response element acts as an element negatively regulated by 3,3',5-tri-iodo-l-thyronine. The results suggest that the transcriptional activity of Oct-1 can be modulated by interaction through its POU domain by a silencing mediator SMRT resulting in the cross-talk between Oct-1 and nuclear receptors.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Binding, Competitive
  • Blotting, Western
  • COS Cells
  • Cell Nucleus / metabolism
  • DNA-Binding Proteins / metabolism*
  • Down-Regulation
  • Electrophoresis, Polyacrylamide Gel
  • Gene Expression Regulation*
  • Glutathione Transferase / metabolism
  • Host Cell Factor C1
  • Nuclear Receptor Co-Repressor 2
  • Octamer Transcription Factor-1
  • Plasmids / metabolism
  • Precipitin Tests
  • Protein Binding
  • Protein Biosynthesis
  • Protein Structure, Tertiary
  • Recombinant Proteins / metabolism
  • Repressor Proteins / metabolism*
  • Response Elements
  • Trans-Activators / metabolism
  • Transcription Factors / metabolism*
  • Transcription, Genetic
  • Transcriptional Activation
  • Transfection
  • Triiodothyronine, Reverse / pharmacology
  • Up-Regulation

Substances

  • DNA-Binding Proteins
  • Host Cell Factor C1
  • Nuclear Receptor Co-Repressor 2
  • Octamer Transcription Factor-1
  • Recombinant Proteins
  • Repressor Proteins
  • Trans-Activators
  • Transcription Factors
  • Triiodothyronine, Reverse
  • Glutathione Transferase