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The role of thyroid hormone receptor DNA binding in negative thyroid hormone-mediated gene transcription

Anne Wulf1, Marianne G Wetzel, Maxim Kebenko

  • 1Zentrum für Experimentelle Medizin, Institut für Biochemie und Molekularbiologie I, Universitätsklinikum Hamburg-Eppendorf, 20246 Hamburg, Germany.

Journal of Molecular Endocrinology
|June 20, 2008
PubMed

Insights

Thyroid hormone receptor (TR) plays distinct roles in gene regulation. Its DNA-binding domain is crucial for activating positively regulated genes but not essential for negatively regulated genes.

Area of Science:

  • Molecular Biology
  • Endocrinology
  • Genetics

Background:

  • Thyroid hormone (T3) is a key regulator of gene expression.
  • Thyroid hormone receptor (TR) mediates T3's effects.
  • TR can activate or repress gene transcription.

Purpose of the Study:

  • To investigate the role of TR's DNA-binding domain (DBD) in gene regulation.
  • To differentiate TR's function in positive versus negative T3-regulated genes.
  • To explore TR's DNA-binding independent functions.

Main Methods:

  • Mammalian one-hybrid assay to study TR's interaction with promoter fragments.
  • Chimeric protein approach (Gal4-DBD-TR) to target TR to DNA.
  • Site-directed mutagenesis to analyze TR domain functions.
  • Analysis of T3-regulated genes: mitochondrial glycerol-3-phosphate dehydrogenase (mGPDH) and TSHalpha.

Main Results:

  • TR activates mGPDH promoter but not TSHalpha promoter directly.
  • A chimeric protein with Gal4-DBD and TR activates transcription in a T3-dependent manner.
  • Mutations in TR's DBD enhance T3-mediated activation by the chimeric protein.
  • TR can negatively regulate transcription independently of direct DNA binding.
  • TR's DBD is critical for positive gene regulation via DNA binding, but not for negative regulation.

Conclusions:

  • TR's DBD is essential for direct DNA binding and activation of positively regulated genes.
  • TR can mediate negative gene regulation through mechanisms independent of its DNA-binding capacity.
  • TR's DBD plays a dual role, being involved in both DNA-binding dependent and independent regulatory functions.

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