Biology:GPER

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Short description: Protein-coding gene in the species Homo sapiens


A representation of the 3D structure of the protein myoglobin showing turquoise α-helices.
Generic protein structure example


G protein-coupled estrogen receptor 1 (GPER), also known as G protein-coupled receptor 30 (GPR30), is a protein that in humans is encoded by the GPER gene.[1] GPER binds to and is activated by the female sex hormone estradiol and is responsible for some of the rapid effects that estradiol has on cells.[2]

Discovery

The classical estrogen receptors first characterized in 1958[3] are water-soluble proteins located in the interior of cells that are activated by estrogenenic hormones such as estradiol and several of its metabolites such as estrone or estriol. These proteins belong to the nuclear hormone receptor class of transcription factors that regulate gene transcription. Since it takes time for genes to be transcribed into RNA and translated into protein, the effects of estrogens binding to these classical estrogen receptors is delayed. However, estrogens are also known to have effects that are too fast to be caused by regulation of gene transcription.[4] In 2005, it was discovered that a member of the G protein-coupled receptor (GPCR) family, GPR30 also binds with high affinity to estradiol and is responsible in part for the rapid non-genomic actions of estradiol. Based on its ability to bind estradiol, GPR30 was renamed as G protein-coupled estrogen receptor (GPER). GPER is localized in the plasma membrane but is predominantly detected in the endoplasmic reticulum.[5][4]

Ligands

GPER binds estradiol with high affinity though not other endogenous estrogens, such as estrone or estriol, nor other endogenous steroids, including progesterone, testosterone, and cortisol.[2][5][6][7][8] Although potentially involved in signaling by aldosterone, GPER does not show any detectable binding towards aldosterone.[2][9][10] Niacin and nicotinamide bind to the receptor in vitro with very low affinity.[11][12] CCL18 has been identified as an endogenous antagonist of the GPER.[13] GPER-selective ligands (that do not bind the classical estrogen receptors) include the agonist G-1[14] and the antagonists G15[15] and G36.[16][2]

Agonists

Antagonists

Unknown

Non-ligand

Function

This protein is a member of the rhodopsin-like family of G protein-coupled receptors and is a multi-pass membrane protein that localizes to the plasma membrane. The protein binds estradiol, resulting in intracellular calcium mobilization and synthesis of phosphatidylinositol (3,4,5)-trisphosphate in the nucleus.[5] This protein therefore plays a role in the rapid nongenomic signaling events widely observed following stimulation of cells and tissues with estradiol.[17] The distribution of GPER is well established in the rodent, with high expression observed in the hypothalamus, pituitary gland, adrenal medulla, kidney medulla and developing follicles of the ovary.[18]

Animal studies

Reproductive tissue

Estradiol produces cell proliferation in both normal and malignant breast epithelial tissue.[19][20] However, GPER knockout mice show no overt mammary phenotype, unlike ERα knockout mice, but similarly to ERβ knockout mice.[19] This indicates that although GPER and ERβ play a modulatory role in breast development, ERα is the main receptor responsible for estrogen-mediated breast tissue growth.[19] GPER is expressed in germ cells and has been found to be essential for male fertility, specifically, in spermatogenesis.[21][22][23][24] GPER has been found to modulate gonadotropin-releasing hormone (GnRH) secretion in the hypothalamic-pituitary-gonadal (HPG) axis.[24]

Cardiovascular effects

GPER is expressed in the blood vessel endothelium and is responsible for vasodilation and as a result, blood pressure lowering effects of 17β-estradiol.[25] GPER also regulates components of the renin–angiotensin system, which also controls blood pressure,[26][27] and is required for superoxide-mediated cardiovascular function and aging.[28]

Central nervous system activity

GPER and ERα, but not ERβ, have been found to mediate the antidepressant-like effects of estradiol.[29][30][31] Contrarily, activation of GPER has been found to be anxiogenic in mice, while activation of ERβ has been found to be anxiolytic.[32] There is a high expression of GPER, as well as ERβ, in oxytocin neurons in various parts of the hypothalamus, including the paraventricular nucleus and the supraoptic nucleus.[31][33] It is speculated that activation of GPER may be the mechanism by which estradiol mediates rapid effects on the oxytocin system,[31][33] for instance, rapidly increasing oxytocin receptor expression.[34] Estradiol has also been found to increase oxytocin levels and release in the medial preoptic area and medial basal hypothalamus, actions that may be mediated by activation of GPER and/or ERβ.[34] Estradiol, as well as tamoxifen and fulvestrant, have been found to rapidly induce lordosis through activation of GPER in the arcuate nucleus of the hypothalamus of female rats.[35][36]

Metabolic roles

Female GPER knockout mice display hyperglycemia and impaired glucose tolerance, reduced body growth, and increased blood pressure.[37] Male GPER knockout mice are observed to have increased growth, body fat, insulin resistance and glucose intolerance, dyslipidemia, increased osteoblast function (mineralization), resulting in higher bone mineral density and trabecular bone volume, and persistent growth plate activity resulting in longer bones.[38][39] The GPER-selective agonist G-1 shows therapeutic efficacy in mouse models of obesity and diabetes.[40]

Role in cancer

Immunohistochemical and transcriptomic analyses of neoplasms derived from a variety of tissues including but not limited to: breast,[41][42][43][44][45][46] endometrial,[47] ovarian,[48] and testicular [49] directly link GPER to advanced disease and prometastatic growth and survival. Experimental data also strong supports a pro-oncogenic role for GPER. First, GPER is required for the survival of tumor-initiating “stem” cells derived from patient-derived tumor xenografts (PDXs).[50] Secondly, less aggressive disease occurs upon the somatic cell silencing of GPER in a robust model of PyMT-induced breast carcinogenesis.[51] Additionally, GPER-selective ligands show efficacy in nonclinical and clinical settings. For example, the GPER antagonist, G36, delays the estrogen-dependent outgrowth of transplanted endometrial carcinoma in mice,[52] while the GPER agonist, G1, has been shown to attenuate the growth of patient-derived xenografts of pancreatic ductal adenocarcinoma.[53]

A contrary argument that GPER may be tumor suppressive has been hypothesized.[54][55] However, it is important to note that Linnaeus Therapeutics is currently running NCI clinical trial (NCT04130516) using GPER agonist. LNS8801, as monotherapy or in the combination with the checkpoint inhibitor, pembroluzimab, for the treatment of multiple solid tumor malignancies.

Role in neurological disorders

GPER is broadly expressed on the nervous system, and GPER activation promotes beneficial effects in several brain disorders.[56] A study suggests that GPER levels were significantly lower in children with ADHD compared to controls.[47]

See also

References

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  2. 2.0 2.1 2.2 2.3 "International Union of Basic and Clinical Pharmacology. XCVII. G Protein-Coupled Estrogen Receptor and Its Pharmacologic Modulators". Pharmacol. Rev. 67 (3): 505–40. July 2015. doi:10.1124/pr.114.009712. PMID 26023144. 
  3. "A conversation with Elwood Jensen. Interview by David D. Moore". Annual Review of Physiology 74: 1–11. 2012. doi:10.1146/annurev-physiol-020911-153327. PMID 21888507. 
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  9. "Nongenomic actions of aldosterone and progesterone revisited". Steroids 77 (10): 1002–6. August 2012. doi:10.1016/j.steroids.2011.12.023. PMID 22285849. 
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  11. "Niacin activates the G protein estrogen receptor (GPER)-mediated signalling". Cell. Signal. 26 (7): 1466–1475. July 2014. doi:10.1016/j.cellsig.2014.03.011. PMID 24662263. "Nicotinic acid, also known as niacin, is the water soluble vitamin B3 used for decades for the treatment of dyslipidemic diseases. Its action is mainly mediated by the G protein-coupled receptor (GPR) 109A; however, certain regulatory effects on lipid levels occur in a GPR109A-independent manner. The amide form of nicotinic acid, named nicotinamide, acts as a vitamin although neither activates the GPR109A nor exhibits the pharmacological properties of nicotinic acid. In the present study, we demonstrate for the first time that nicotinic acid and nicotinamide bind to and activate the GPER-mediated signalling in breast cancer cells and cancer-associated fibroblasts (CAFs)". 
  12. "Not lost in translation: Emerging clinical importance of the G protein-coupled estrogen receptor GPER". Steroids 111: 37–45. February 2016. doi:10.1016/j.steroids.2016.02.016. PMID 26921679. 
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  25. "Deletion of G protein-coupled estrogen receptor increases endothelial vasoconstriction". Hypertension 59 (2): 507–12. February 2012. doi:10.1161/HYPERTENSIONAHA.111.184606. PMID 22203741. "The development of the GPER-selective agonist G-114 has facilitated studies that demonstrate GPER activation induces acute vasodilation and lowers blood pressure in rodents. We18 and others17,19 have shown that acute GPER-mediated vasodilator effects are at least partly endothelium- and NO-dependent.". 
  26. "Evidence that the G protein-coupled membrane receptor GPR30 contributes to the cardiovascular actions of estrogen". Gender Medicine 8 (6): 343–54. December 2011. doi:10.1016/j.genm.2011.10.004. PMID 22153880. 
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External links

This article incorporates text from the United States National Library of Medicine, which is in the public domain.