Thyroid Hormone Receptor Family Members

The thyroid hormone receptor (TR) is a member of the nuclear hormone receptor (NHR) superfamily. These receptors are hormone-dependent transcription factors that regulate gene transcription by binding to regulatory regions of DNA termed hormone response elements (HREs) (1) . TR binds to DNA in the presence or absence of its ligand, triiodothyronine (T 3 ), and is capable of upregulating or downregulating gene transcription depending on the nature of the underlying response element. Genes that are stimulated by T 3 are regulated by positive thyroid hormone response elements (pTREs); genes that are repressed by T 3 are regulated by negative thyroid hormone response elements (nTREs). nTREs are particularly important in feedback inhibition in the hypothalamic-pituitary-thyroid axis, and are present in the promoter regions of the TRH, thyroid stimulating hormone β (TSHβ), and common pituitary glycoprotein α-subunit genes. TR binds to TREs as monomer, homodimer, or heterodimer with thyroid hormone receptor accessory proteins (TRAPs). In addition, TR is capable of binding to other nuclear proteins, including corepressors and coactivators, which enable it to modulate the transcription of T 3 -dependent genes. Thus, the presence of associated nuclear factors, as well as the nature of the underlying DNA response element, enables TR to regulate gene expression differentially. These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.