Thyroid hormone receptor (IPR001728)
Short name: ThyrH_rcpt
Overlapping homologous superfamilies
- Nuclear hormone receptor (IPR001723)
- Thyroid hormone receptor (IPR001728)
Steroid or nuclear hormone receptors (4A nuclear receptor, NRs) constitute an important superfamily of transcription regulators that are involved in widely diverse physiological functions, including control of embryonic development, cell differentiation and homeostasis. Members of the superfamily include the steroid hormone receptors and receptors for thyroid hormone, retinoids, 1,25-dihydroxy-vitamin D3 and a variety of other ligands [PMID: 14747695]. The proteins function as dimeric molecules in nuclei to regulate the transcription of target genes in a ligand-responsive manner [PMID: 7899080, PMID: 8165128]. In addition to C-terminal ligand-binding domains, these nuclear receptors contain a highly-conserved, N-terminal zinc-finger that mediates specific binding to target DNA sequences, termed ligand-responsive elements. In the absence of ligand, steroid hormone receptors are thought to be weakly associated with nuclear components; hormone binding greatly increases receptor affinity.
NRs are extremely important in medical research, a large number of them being implicated in diseases such as cancer, diabetes, hormone resistance syndromes, etc. While several NRs act as ligand-inducible transcription factors, many do not yet have a defined ligand and are accordingly termed 'orphan' receptors. During the last decade, more than 300 NRs have been described, many of which are orphans, which cannot easily be named due to current nomenclature confusions in the literature. However, a new system has recently been introduced in an attempt to rationalise the increasingly complex set of names used to describe superfamily members.
In common with other members of the steroid hormone receptor family, thyroid hormone receptors (TRs) contain 2 major highly-conserved domains, involved in DNA- and ligand-binding respectively. Except for a conserved 12 residue motif adjacent to the DNA-binding domain, the N-terminal domains are divergent between alpha- and beta-TR isoforms (but are conserved within isoforms). The DNA-binding domain is the most highly conserved feature of the family; it contains 2 zinc-binding modules, which are sometimes referred to as zinc fingers (see IPR001628). The ligand-binding domain [PMID: 7501015] includes a number of conserved motifs, parts of which are thought to be involved in dimerisation. The hinge region between these 2 domains [PMID: 7566127] is thought to contain the binding site for transcriptional co-repressor proteins that mediate the transcriptional repression function of unliganded receptors.
- PR00546 (THYROIDHORMR)