InterPro

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 Drosophila melanogaster, the steroid hormone ecdysone triggers larval-to- adult metamorphosis, a process in which the hormone induces imaginal tissues to generate adult structures, and larval tissues to degenerate [PMID: 8324824]. The ecdysone receptor (EcR) binds DNA with high specificity at ecdysone response elements. EcR is nuclear and is found in larval wing discs, pupal wings and in prothoracic glands.

In the mosquito Aedes aegypti, 20-hydroxyecdysone plays an important role in the regulation of egg maturation [PMID: 7711747]. There are three EcR transcripts(of 4.2kb, 6kb and 11kb) in adult mosquitoes; 4.2kb mRNA is predominantly expressed in female mosquitoes during vitellogenesis. In both the fat body and ovaries of the female mosquito, the level of EcR mRNA is high at the previtellogenic period and after the onset of vitellogenesis [PMID: 7711747].

Synonym(s): 1H nuclear receptor