Steroid hormone receptor
Steroid hormone receptors are found in the
A steroid hormone receptor is a protein molecule located either within the cell cytoplasm or nucleus that specifically binds to steroid hormones, such as estrogen, progesterone, and testosterone, leading to the activation or suppression of gene expression and subsequent cellular responses. This interaction is crucial for mediating the physiological effects of steroid hormones in various tissues and organs of the body.[3]
Types
Steroid hormone receptors can be categorized into several types based on their specific ligands and functions:
1.Estrogen Receptors (ER): There are two subtypes, ERα and ERβ, which bind to the hormone estrogen. They regulate gene expression in response to estrogen, playing essential roles in reproductive tissues, bone metabolism, and cardiovascular health.
2. Progesterone Receptors (PR): PRs bind to the hormone progesterone and regulate gene expression in response to its signaling. They are critical for various reproductive processes, including menstruation, pregnancy, and mammary gland development.
3. Androgen Receptors (AR): These receptors bind to androgens such as testosterone and dihydrotestosterone (DHT). They play key roles in the development and function of male reproductive organs, as well as in secondary sexual characteristics and muscle growth.
4. Glucocorticoid Receptors (GR): GRs bind to glucocorticoids like cortisol and regulate gene expression in response to stress and metabolic signals. They are involved in processes such as immune response, metabolism, and stress adaptation.
5. Mineralocorticoid Receptors (MR): MRs primarily bind to mineralocorticoids such as aldosterone and regulate electrolyte balance and blood pressure by controlling ion transport in epithelial cells of the kidney and other tissues.[4]
Nuclear receptors
Steroid receptors of the nuclear receptor family are all
- Nuclear receptors
- Subfamily 3: Estrogen Receptor-like
- Group A: Estrogen receptor (Sex hormones: Estrogen)
- Group C: 3-Ketosteroid receptors
- 1: Glucocorticoid receptor (GR; NR3C1) (Cortisol)
- 2: Mineralocorticoid receptor (MR; NR3C2) (Aldosterone)
- 3: Progesterone receptor (PR; NR3C3, PGR) (Sex hormones: Progesterone)
- 4: Androgen receptor (AR; NR3C4, AR) (Sex hormones: Testosterone)
- Subfamily 3: Estrogen Receptor-like
Structure
Intracellular steroid hormone receptors share a common structure of four units that are functionally homologous, so-called "domains":
- Variable domain: It begins at the N-terminal and is the most variable domain between the different receptors.
- DNA binding domain: This centrally located highly conserved DNA binding domain (DBD) consists of two non-repetitive globular motifshormone response element(HRE).
- Hinge region: This area controls the movement of the receptor to the nucleus.
- Hormone binding domain: The moderately conserved nuclear localization signal, amino-acid sequences capable of binding chaperones and parts of dimerization interfaces. Such receptors are closely related to chaperones (namely heat shock proteins hsp90 and hsp56), which are required to maintain their inactive (but receptive) cytoplasmic conformation. At the end of this domain is the C-terminal. The terminal connects the molecule to its pair in the homodimer or heterodimer. It may affect the magnitude of the response.
Mechanism of action
Genomic
Depending on their mechanism of action and subcellular distribution, nuclear receptors may be classified into at least two classes.
Free (that is, unbound) steroids enter the cell cytoplasm and interact with their receptor. In this process heat shock protein is dissociated, and the activated receptor-ligand complex is translocated into the nucleus. It is also related to EAATs.
After binding to the
Type II receptors are located in the nucleus. Thus, their ligands pass through the cell membrane and cytoplasm and enter the nucleus where they activate the receptor without release of HSP. The activated receptor interacts with the hormone response element and the transcription process is initiated as with type I receptors.
Non-genomic
The cell membrane
There is some evidence that certain steroid hormone receptors can extend through lipid bilayer membranes at the surface of cells and might be able to interact with hormones that remain outside cells.[9]
Steroid hormone receptors can also function outside the nucleus and couple to cytoplasmic signal transduction proteins such as
Other
Steroid hormone receptors exert their effects through several mechanisms, including:
1.
2. Transcriptional Coactivators and Corepressors: Steroid hormone receptors recruit coactivator or corepressor proteins to the gene promoter regions, which modulate the activity of RNA polymerase and other transcriptional machinery, thereby influencing gene expression.
3. Chromatin Remodeling: Steroid hormone receptors can also induce changes in chromatin structure through the recruitment of chromatin remodeling complexes. This allows for accessibility of the transcriptional machinery to specific gene regulatory regions, facilitating or inhibiting gene transcription.
4. Non-Genomic Signaling: In addition to classical genomic actions, steroid hormone receptors can initiate rapid, non-genomic signaling pathways in the cytoplasm or at the cell membrane. These pathways involve activation of various protein kinases and other signaling molecules, leading to rapid cellular responses such as ion fluxes, cytoskeletal rearrangements, and activation of second messenger systems.
5. Cross-Talk with Other Signaling Pathways: Steroid hormone receptors can also interact with and modulate the activity of other signaling pathways, such as growth factor signaling pathways, thereby integrating hormonal and growth factor signals to regulate cellular processes.[11]
A new class of steroid hormone receptors has recently been elucidated and these new receptors are found on the cell membrane. New studies suggest that along with the well documented intracellular receptors that cell membrane receptors are present for several steroid hormones and that their cellular responses are much quicker than the intracellular receptors.[12]
G protein-coupled receptors
GPCR linked proteins most likely interact with steroid hormones through an amino acid consensus sequence traditionally thought of as a cholesterol recognition and interaction site. About a third of Class A GPCRs contain this sequence. The steroid hormones themselves are different enough from one another that they do not all affect all of the GPCR linked proteins; however, the similarities between the steroid hormones and between the receptors make plausible the argument that each receptor may respond to multiple steroid hormones or that each hormone could affect multiple receptors. This is contrary to the traditional model of having a unique receptor for each unique ligand.[13]
At least four different GPCR-linked proteins are known to respond to steroid hormones. G Protein-Coupled Receptor 30 (GPR30) binds estrogen, Membrane Progestin Receptor (mPR) binds progesterone, G Protein-Coupled Receptor Family C Group 6 Member A (GPRC6A) binds androgens, and Thyroid Hormone and Trace Amine Associated Receptor 1 (TAAR1) binds Thyroid hormone (though not technically steroid hormones, thyroid hormones can be grouped here because their receptors belong to the nuclear receptor superfamily). As an example of the effects of these GPCR-linked proteins consider GPR30. GPR30 binds estrogen, and upon binding estrogen this pathway activates adenylyl cyclase and epidermal growth factor receptor. It results in vasodilation, renoprotection, mammary gland development, etc.[13]
Sulfated steroids and
Ion channels
The steroid progesterone has been found to modulate the activity of CatSper (cation channels of sperm) voltage-gated Ca2+ channels. Since eggs release progesterone, sperm may use progesterone as a homing signal to swim toward eggs (chemotaxis).[23][24]
SHBG/SHBG-R complex
See also
References
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- ^ Thornton JW, Need E, Crews D. Resurrecting the ancestral steroid receptor: ancient origin of estrogen signaling. Science. 2003 Jul 4;301(5637):1714-7. doi: 10.1126/science.1086185. PMID 12805548.
- ^ Evans RM. The steroid and thyroid hormone receptor superfamily. Science. 1988 Nov 18;240(4859):889-95. doi: 10.1126/science.3283939. PMID 3283939.
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- ^ Mangelsdorf DJ, Thummel C, Beato M, Herrlich P, Schütz G, Umesono K, Blumberg B, Kastner P, Mark M, Chambon P, Evans RM. The nuclear receptor superfamily: the second decade. Cell. 1995 Dec 15;83(6):835-9. doi: 10.1016/0092-8674(95)90199-x. PMID 8521507.
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External links
- Steroid+Receptors at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
- Messer WS (3 April 2000). "MBC 3320 Steroid hormones and receptors". The University of Toledo. Archived from the original on 17 April 2008.