Mechanism of Action
Thyroid hormone receptors regulate gene expression by binding to hormone response elements (HREs) in DNA either as monomers, heterodimers with retinoid X receptor (RXR; which in turn is activated by binding to 9-cis-retinoic acid) or as homodimers. However TR/RXR heterodimers are the most transcriptionally active form of TR.
In the absence of hormone, TR in complex with corepressor proteins bind to HREs in a transcriptionally inactive state. Binding of thyroid hormone results in a conformational change in TR which displaces corepressor from the receptor/DNA complex and recruitment of coactivator proteins. The DNA/TR/coactivator complex then recruits RNA polymerase that transcribes downstream DNA into messenger RNA and eventually protein that results in a change in cell function.
Read more about this topic: Thyroid Hormone Receptor
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