Thyroid hormone receptor coactivators and corepressors

The thyroid hormone receptor (TR) acts like a molecular switch. In the absence of ligand, TR binds to specific DNA sequences and actively represses transcription via interactions with other proteins, termed corepressors. The binding of ligand results in a conformational change in the TR that leads to transcriptional activation via the release of corepressors and the recruitment of coactivator proteins. The recent identification of some of the components of TR corepressor and coactivator complexes, and the discovery of respectively associated histone deacetylase and acetylase activity, has led to a greater understanding of how TR might accomplish its dual role. Additionally, several cofactors have been found to interact with TR and modulate transcription via mechanisms unrelated to histone acetylation or deacetylation.