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Ligand-independent repression by the thyroid hormone receptor mediated by a nuclear receptor co-repressor
A J Hörlein1, A M Näär, T Heinzel
1Howard Hughes Medical Institute, University of California, San Diego, La Jolla 92093-0648, USA.
Abstract:
Thyroid-hormone and retinoic-acid receptors exert their regulatory functions by acting as both activators and repressors of gene expression. A nuclear receptor co-repressor (N-CoR) of relative molecular mass 270K has been identified which mediates ligand-independent inhibition of gene transcription by these receptors, suggesting that the molecular mechanisms of repression by thyroid-hormone and retinoic-acid receptors are analogous to the co-repressor-dependent transcriptional inhibitory mechanisms of yeast and Drosophila.
Insights
A newly identified nuclear receptor co-repressor (N-CoR) inhibits gene transcription by thyroid-hormone and retinoic-acid receptors. This finding suggests analogous repression mechanisms across species for these crucial hormone receptors.
Area of Science:
- Molecular Biology
- Genetics
- Endocrinology
Background:
- Thyroid-hormone and retinoic-acid receptors regulate gene expression as activators and repressors.
- Understanding the mechanisms of gene repression is critical for cellular regulation.
Purpose of the Study:
- To identify and characterize co-repressors involved in nuclear receptor-mediated gene silencing.
- To elucidate the molecular mechanisms underlying ligand-independent repression by thyroid-hormone and retinoic-acid receptors.
Main Methods:
- Biochemical isolation and characterization of a novel nuclear receptor co-repressor.
- Assays to determine the role of the identified co-repressor in gene transcription inhibition.
- Comparative analysis of repression mechanisms across different organisms.
Main Results:
- Identification of a 270K nuclear receptor co-repressor (N-CoR).
- Demonstration that N-CoR mediates ligand-independent inhibition of gene transcription.
- Evidence suggesting conserved co-repressor-dependent repression mechanisms between mammalian receptors and those in yeast and Drosophila.
Conclusions:
- A novel co-repressor, N-CoR, plays a significant role in regulating gene expression by thyroid-hormone and retinoic-acid receptors.
- The mechanisms of repression by these nuclear receptors are conserved across evolution.
- This discovery provides insights into the fundamental processes of gene regulation and potential therapeutic targets.