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Inducible and Reversible Dominant-negative (DN) Protein Inhibition
08:35

Inducible and Reversible Dominant-negative (DN) Protein Inhibition

Published on: January 7, 2019

Dominant negative activity of an endogenous thyroid hormone receptor variant (alpha 2) is due to competition for

D Katz1, M A Lazar

  • 1Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia 19104-6149.

The Journal of Biological Chemistry
|October 5, 1993
PubMed

Insights

Thyroid hormone receptor alpha 2 (TR alpha 2) inhibits thyroid hormone (T3) action by competing with TR alpha 1 for binding to T3 response elements (TREs). This TR alpha 2 mechanism impacts gene regulation and cellular metabolism.

Area of Science:

  • Molecular Endocrinology
  • Gene Regulation
  • Nuclear Receptors

Background:

  • Thyroid hormone (T3) regulates critical physiological processes, including development and metabolism.
  • Thyroid hormone receptors (TRs) mediate T3's effects by binding to T3 response elements (TREs) and regulating gene transcription.
  • The TR alpha 2 isoform, which does not bind T3, is known to inhibit the activity of canonical TRs, but its precise mechanism remains debated.

Purpose of the Study:

  • To elucidate the molecular mechanism by which the TR alpha 2 isoform inhibits T3-mediated transcriptional activation.
  • To determine if TR alpha 2 directly interferes with TR alpha 1 binding to TREs.
  • To investigate the role of TR alpha 2's DNA-binding capacity in its inhibitory function.

Main Methods:

  • Transfection assays using various TR alpha 1 and TR alpha 2 constructs with TRE-containing reporter genes.
  • In vitro DNA-binding assays using purified TR proteins and TRE sequences.
  • Analysis of TR alpha 2's interaction with TR alpha 1 monomers, homodimers, and RXR-heterodimers.
  • Characterization of a TR alpha 2 mutant with enhanced TRE-binding affinity.

Main Results:

  • TR alpha 2 inhibited TR alpha 1-mediated transactivation from TREs in a dose-dependent manner.
  • TR alpha 2's inhibitory effect was specific to TRE-containing genes, not affecting chimeric proteins activating transcription from non-TRE sites.
  • TR alpha 2 directly inhibited the binding of TR alpha 1 and its various complexes to DNA in vitro.
  • TR alpha 2 bound to TREs, and a mutant with higher affinity exhibited enhanced inhibitory activity.

Conclusions:

  • TR alpha 2 inhibits T3 action primarily by directly competing with TR alpha 1 for binding to TREs.
  • The DNA-binding capacity of TR alpha 2, rather than just squelching or inactive heterodimer formation, is crucial for its dominant-negative function.
  • These findings clarify a key mechanism by which TR alpha 2 modulates thyroid hormone signaling pathways.

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