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Silencing subdomains of v-ErbA interact cooperatively with corepressors: involvement of helices 5/6

K Busch1, B Martin, A Baniahmad

  • 1Laboratoire de Biologie Moléculaire et de Génie Génétique, Institut de Chimie, Université de Liège, Belgium.

Molecular Endocrinology (Baltimore, Md.)
|February 16, 2000
PubMed

Insights

Thyroid hormone receptor (TR) silencing requires three subdomains (SSD1-3) to cooperate. The SSD2 subdomain is crucial for binding corepressors like N-CoR and SMRT, enabling gene repression.

Area of Science:

  • Molecular Endocrinology
  • Gene Regulation
  • Oncogene Biology

Background:

  • Thyroid hormone receptors (TRs) regulate vertebrate development and homeostasis through ligand-dependent gene transcription.
  • TRs can actively repress gene transcription in the absence of ligand.
  • The oncogenic v-ErbA protein is a TR variant that constitutively represses gene expression.

Purpose of the Study:

  • To investigate the mechanism of transcriptional repression mediated by the TR/v-ErbA silencing domain.
  • To identify the specific roles of the three silencing subdomains (SSD1-3) in corepressor interaction and silencing function.

Main Methods:

  • Protein interaction assays (in vitro and in vivo) to assess binding between v-ErbA mutants and corepressors.
  • Functional studies and mutation analysis of the v-ErbA silencing domain.
  • Mammalian two-hybrid assays to evaluate cooperative binding to corepressors.

Main Results:

  • A specific v-ErbA point mutant (L489R) in SSD2 failed to interact with corepressors N-CoR and SMRT.
  • Mutants in SSD1 and SSD3 showed reduced corepressor binding, correlating with diminished silencing activity.
  • Cooperative binding of all three subdomains (SSD1-3) was necessary for robust corepressor recruitment, mimicking full-length v-ErbA.

Conclusions:

  • Transcriptional repression by v-ErbA requires the synergistic interaction of all three silencing subdomains (SSD1-3).
  • SSD2 is identified as a novel and essential interaction site for N-CoR and SMRT corepressors.
  • Effective gene silencing by TRs/v-ErbA depends on the cooperative engagement of multiple silencing subdomains with corepressor complexes.

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