The Catecholestrogen, 2-Hydroxyestradiol-17beta, Acts as a G Protein-Coupled Estrogen Receptor 1 (GPER/GPR30) Antagonist to Promote the Resumption of Meiosis in Zebrafish Oocytes1

Abstract

Estradiol-17beta (E2) maintains high cAMP levels and meiotic arrest in zebrafish oocytes through activation of G protein-coupled estrogen receptor (GPER). The catecholestrogen 2-hydroxyestradiol-17beta (2-OHE2) has an opposite effect to that of E2 on oocyte maturation (OM) and cAMP levels in Indian catfish oocytes. We tested the hypothesis that 2-OHE2 is produced in zebrafish ovaries and promotes the resumption of oocyte meiosis through its action as a GPER antagonist. Ovarian 2-OHE2 production by estrogen-2-hydroxylase (EH) was up-regulated by gonadotropin treatment at the onset of OM, consistent with a physiological role for 2-OHE2 in regulating OM. The increases in EH activity and OM were blocked by treatment with CYP1A1 and CYP1B1 inhibitors. Expression of cyp1a, cyp1b1, and cyp1c mRNAs was increased by gonadotropin treatment, further implicating these Cyp1s in 2-OHE2 synthesis prior to OM. Conversely, aromatase activity and cyp19a1 mRNA expression declined during gonadotropin induction of OM. 2-OHE2 treatment significantly increased spontaneous OM in defolliculated zebrafish oocytes and reversed the inhibition of OM by E2 and the GPER agonist G-1. 2-OHE2 was an effective competitor of [(3)H]-E2 binding to recombinant zebrafish GPER expressed in HEK-293 cells. 2-OHE2 also antagonized estrogen actions through GPER on cAMP production in zebrafish oocytes, resulting in a reduction in cAMP levels. Stimulation of OM by 2-OHE2 was blocked by pretreatment of defolliculated oocytes with the GPER antibody. Collectively, the results suggest that 2-OHE2 functions as a GPER antagonist and promotes OM in zebrafish through blocking GPER-dependent E2 inhibition of the resumption of OM.

Releasing prophase arrest in zebrafish oocyte: synergism between maturational steroid and Igf1

“…Previously, treatment of Atlantic croaker ovarian membranes by GPER agonist has been shown to increase Ac activity and also reversed the downregulation of Ac activity by 20b-S (Pang et al 2008). While stimulation with catecholestrogen has been shown to down-regulate intra-oocyte cAMP level (Chourasia et al 2015), MIS action, presumably through mPRa, attenuates Ac activity and intra-oocyte cAMP level by activating the inhibitory G protein, Ga i (Zhu et al 2003). Earlier we have reported that PI3K/Akt pathway is indispensable for insulin-induced meiotic maturation in denuded zebrafish oocyte, where PDE3 might act as possible a down-stream target (Das et al 2013).…”

“…In addition to its role in epidermal growth factor receptor (Egfr) transactivation and MAPK activation, studies in Atlantic croaker and zebrafish oocytes have indicated that binding of E 2 to its novel G-protein coupled membrane receptor Gper, promotes intra-oocyte adenylate cyclase activity and ensures prophase-I arrest (Pang et al 2008, Peyton & Thomas 2011. Further, recent evidence demonstrates that catecholestrogen (17b-2-hydroxyestradiol) functions as a Gper antagonist and promotes GVBD response in zebrafish by blocking Gper-dependent E 2 action (Chourasia et al 2015).…”

International Union of Basic and Clinical Pharmacology. XCVII. G Protein–Coupled Estrogen Receptor and Its Pharmacologic Modulators

“…2-MeO-E2 has been investigated clinically under the trade name Panzem (EntreMed, Inc., Rockville, MD) for ovarian cancer and other indications (Verenich and Gerk, 2010). In addition, 2-hydroxyestradiol has recently been shown to act as a GPER antagonist, acting to promote the resumption of meiosis in zebrafish oocytes, with a binding affinity in the range of 0.1-1 mM (Chourasia et al, 2015). The GPER binding of the other oxidized E2 metabolites 4-hydroxy-E2 and 4-methoxy-E2 has not been reported.…”

Emerging roles of GPER in diabetes and atherosclerosis

“…Rather, it has been found recently that E2 - via ERα - inhibits mineralocorticoid receptor (MR) function [29]. Natural estrogen metabolites formed by catchol-O-methyltransferase, have recently been shown to bind to and signal through GPER, either as an agonist (2-methoxyestradiol, 2-ME2) [30], or antagonist (2-hydroxy estradiol (2-OH-E2) – a hydroxylated metabolite of E2) [31] (Figure 1). Furthermore, a large number of synthetic and natural estrogenic compounds have been shown to interact with GPER (Figure 1), including the therapeutic anti-estrogens ICI182,780 (a selective ER downregulator, SERD) and 4-hydroxytamoxifen and raloxifene (selective ER modulators, SERMs), which surprisingly all act as GPER agonists [13, 32, 33], and synthetic compounds such as MIBE (ethyl 3-[5-(2-ethoxycarbonyl-1-methylvinyloxy)-1-methyl-1H-indol-3-yl]but-2-enoate)) [34].…”