Molecular basis for the subtype discrimination of the estrogen receptor-beta-selective ligand, diarylpropionitrile

A novel ERβ high throughput microscopy platform for testing endocrine disrupting chemicals

In this study we present an inducible biosensor model for the Estrogen Receptor Beta (ERβ), GFP-ERβ:PRL-HeLa, a single-cell-based high throughput (HT) in vitro assay that allows direct visualization and measurement of GFP-tagged ERβ binding to ER-specific DNA response elements (EREs), ERβ-induced chromatin remodeling, and monitor transcriptional alterations via mRNA fluorescence in situ hybridization for a prolactin (PRL)-dsRED2 reporter gene. The model was used to accurately (Z' = 0.58-0.8) differentiate ERβ-selective ligands from ERα ligands when treated with a panel of selective agonists and antagonists. Next, we tested an Environmental Protection Agency (EPA)-provided set of 45 estrogenic reference chemicals with known ERα in vivo activity and identified several that activated ERβ as well, with varying sensitivity, including a subset that is completely novel. We then used an orthogonal ERE-containing transgenic zebrafish (ZF) model to cross validate ERβ and ERα selective activities at the organism level. Using this environmentally relevant ZF assay, some compounds were confirmed to have ERβ activity, validating the GFP-ERβ:PRL-HeLa assay as a screening tool for potential ERβ active endocrine disruptors (EDCs). These data demonstrate the value of sensitive multiplex mechanistic data gathered by the GFP-ERβ:PRL-HeLa assay coupled with an orthogonal zebrafish model to rapidly identify environmentally relevant ERβ EDCs and improve upon currently available screening tools for this understudied nuclear receptor.

Evaluating the correlation of binding affinities between isothermal titration calorimetry and fragment molecular orbital method of estrogen receptor beta with diarylpropionitrile (DPN) or DPN derivatives

Estrogen receptors (ERs) are ligand-activated transcription factors, with two subtypes ERα and ERβ. The endogenous ligand of ERs is the common 17β-estradiol, and the ligand-binding pocket of ERα and ERβ is very similar. Nevertheless, some ERβ-selective agonist ligands have been reported. DPN (diarylpropionitrile) is a widely used ERβ-selective agonist; however, the structure of the ERβ-DPN complex has not been solved. Therefore, the bound-state conformation of DPN and its enantioselectivity remain unresolved. In this report, we present the structures of the complexes of ERβ with DPN or its derivatives that include a chlorine atom by the X-ray crystallography. Additionally, we measured the binding affinity between ERβ and DPN or derivatives by isothermal titration calorimetry (ITC) and estimated the binding affinity by fragment molecular orbital (FMO) calculations. We also examined the correlation between the ITC data and results from the FMO calculations. FMO calculations showed that S-DPN interacts strongly with three amino acids (Glu305, Phe356, and His475) of ERβ, and ITC measurements confirmed that the chlorine atom of the DPN derivatives enhances binding affinity. The enthalpy change by ITC correlated strongly with the interaction energy (total IFIEs; inter-fragment interaction energies) calculated by FMO (R = 0.870). We propose that FMO calculations are a valuable approach for enhancing enthalpy contributions in drug design, and its scope of applications includes halogen atoms such as chlorine. This study is the first quantitative comparison of thermodynamic parameters obtained from ITC measurements and FMO calculations, providing new insights for future precise drug design.

The peri-menopause in a woman's life: a systemic inflammatory phase that enables later neurodegenerative disease

The peri-menopause or menopausal transition—the time period that surrounds the final years of a woman’s reproductive life—is associated with profound reproductive and hormonal changes in a woman’s body and exponentially increases a woman’s risk of cerebral ischemia and Alzheimer’s disease. Although our understanding of the exact timeline or definition of peri-menopause is limited, it is clear that there are two stages to the peri-menopause. These are the early menopausal transition, where menstrual cycles are mostly regular, with relatively few interruptions, and the late transition, where amenorrhea becomes more prolonged and lasts for at least 60 days, up to the final menstrual period. Emerging evidence is showing that peri-menopause is pro-inflammatory and disrupts estrogen-regulated neurological systems. Estrogen is a master regulator that functions through a network of estrogen receptors subtypes alpha (ER-α) and beta (ER-β). Estrogen receptor-beta has been shown to regulate a key component of the innate immune response known as the inflammasome, and it also is involved in regulation of neuronal mitochondrial function. This review will present an overview of the menopausal transition as an inflammatory event, with associated systemic and central nervous system inflammation, plus regulation of the innate immune response by ER-β-mediated mechanisms.

Optimisation of estrogen receptor subtype-selectivity of a 4-Aryl-4H-chromene scaffold previously identified by virtual screening

4-Aryl-4H-Chromene derivatives have been previously shown to exhibit anti-proliferative, apoptotic and anti-angiogenic activity in a variety of tumor models in vitro and in vivo generally via activation of caspases through inhibition of tubulin polymerisation. We have previously identified by Virtual Screening (VS) a 4-aryl-4H-chromene scaffold, of which two examples were shown to bind Estrogen Receptor α and β with low nanomolar affinity and <20-fold selectivity for α over β and low micromolar anti-proliferative activity in the MCF-7 cell line. Thus, using the 4-aryl-4H-chromene scaffold as a starting point, a series of compounds with a range of basic arylethers at C-4 and modifications at the C3-ester substituent of the benzopyran ring were synthesised, producing some potent ER antagonists in the MCF-7 cell line which were highly selective for ERα (compound 35; 350-fold selectivity) or ERβ (compound 42; 170-fold selectivity).

LARMD: integration of bioinformatic resources to profile ligand-driven protein dynamics with a case on the activation of estrogen receptor

Protein dynamics is central to all biological processes, including signal transduction, cellular regulation and biological catalysis. Among them, in-depth exploration of ligand-driven protein dynamics contributes to an optimal understanding of protein function, which is particularly relevant to drug discovery. Hence, a wide range of computational tools have been designed to investigate the important dynamic information in proteins. However, performing and analyzing protein dynamics is still challenging due to the complicated operation steps, giving rise to great difficulty, especially for nonexperts. Moreover, there is a lack of web protocol to provide online facility to investigate and visualize ligand-driven protein dynamics. To this end, in this study, we integrated several bioinformatic tools to develop a protocol, named Ligand and Receptor Molecular Dynamics (LARMD, http://chemyang.ccnu.edu.cn/ccb/server/LARMD/ and http://agroda.gzu.edu.cn:9999/ccb/server/LARMD/), for profiling ligand-driven protein dynamics. To be specific, estrogen receptor (ER) was used as a case to reveal ERβ-selective mechanism, which plays a vital role in the treatment of inflammatory diseases and many types of cancers in clinical practice. Two different residues (Ile373/Met421 and Met336/Leu384) in the pocket of ERβ/ERα were the significant determinants for selectivity, especially Met336 of ERβ. The helix H8, helix H11 and H7-H8 loop influenced the migration of selective agonist (WAY-244). These computational results were consistent with the experimental results. Therefore, LARMD provides a user-friendly online protocol to study the dynamic property of protein and to design new ligand or site-directed mutagenesis.

Computational Study of the Binding Modes of Diverse DPN Analogues on Estrogen Receptors (ER) and the Biological Evaluation of a New Potential Antiestrogenic Ligand

Estrogen (17β-estradiol) is essential for normal growth and differentiation in the mammary gland. In the last three decades, previous investigations have revealed that Estrogen Receptor Alpha (ERα) plays a critical role in breast cancer. More recently, observations regarding the widespread expression of ERβ-like proteins in normal and neoplastic mammary tissues have suggested that ERβ is also involved in the mentioned pathology. Design of new drugs both steroidal and nonsteroidal that target any of these receptors represents a promise to treat breast cancer although it remains a challenge due to the sequence similarity between their catalytic domains. In this work, we propose a new set of compounds that could effectively target the estrogen receptors ERα and ERβ. These ligands were designed based on the chemical structure of the ERβ-selective agonist Diarylpropionitrile (DPN). The designed ligands were submitted to in silico ADMET studies, yielding in a filtered list of ligands that showed better drug-like properties. Molecular dynamics simulations of both estrogen receptors and docking analysis were carried-out employing the designed compounds, from which two were chosen due to their promising characteristics retrieved from theoretical results (docking analysis or targeting receptor predictions). They were chemically synthetized and during the process, two precursor ligands were also obtained. These four ligands were subjected to biological studies from which it could be detected that compound mol60b dislplayed inhibitory activity and its ability to activate the transcription via an estrogenic mechanism of action was also determined. Interestinly, this observation can be related to theoretical binding free energy calculations, where the complex: ERβ-mol60b showed the highest energy ΔGbind value in comparison to others.

Estrogen receptor beta expression and prognosis of diffuse large B cell lymphoma

OBJECTIVES

Estrogen receptor beta (ERβ)-selective agonists inhibited B cell lymphoma growth in animal models. However, a recent study found that higher ERβ expression in tissue from diffuse large B cell lymphoma (DLBCL) patients indicated a poorer survival. This study aimed to determine the ERβ expression in DLBCL tissue using immunohistochemistry and correlate with clinical outcomes.

METHODS

Diagnostic tissues from newly diagnosed adult DLBCL patients treated with Rituximab-Cyclophosphamide/Doxorubicin/Vincristine/Prednisolone were counted for ERβ1-expressing cells. Nodal lymphoma (N = 41) was analyzed separately from extra-nodal DLBCL (N = 31).

RESULTS

On immunohistochemistry, ERβ1 was expressed in 73.6% of cases with the median expressing cells of 20%. For nodal lymphoma, high ERβ expression (≥25%) was associated with poorer event free survival (EFS) independent of the international prognostic index with the adjusted hazard ratio (HR) of 2.49 (95% Confidence interval (CI) 1.03-6.00, P = 0.042). On the contrary, high ERβ expression (≥25%) was associated with superior outcomes in extra-nodal DLBCL with the adjusted HR of 0.25 (95% CI 0.09-0.75, P = 0.013) for EFS and adjusted HR of 0.29 (95% CI 0.10-0.85, P = 0.024) for overall survival in multivariate analyses.

CONCLUSION

ERβ1 protein expression represented opposite prognostic factors in nodal vs. extra-nodal DLBCL.

Synthesis and structure-activity relationships of 1-benzylindane derivatives as selective agonists for estrogen receptor beta

The estrogen receptor beta (ERβ) selective agonist is considered a promising candidate for the treatment of estrogen deficiency symptoms in ERβ-expressing tissues, without the risk of breast cancer, and multiple classes of compounds have been reported as ERβ selective agonists. Among them, 6-6 bicyclic ring-containing structures (e.g., isoflavone phytoestrogens) are regarded as one of the cyclized analogues of isobutestrol 5b, and suggest that other cyclized scaffolds comprising 5-6 bicyclic rings could also act as selective ERβ ligands. In this study, we evaluated the selective ERβ agonistic activity of 1-(4-hydroxybenzyl)indan-5-ol 7a and studied structure-activity relationship (SAR) of its derivatives. Some functional groups improved the properties of 7a; introduction of a nitrile group on the indane-1-position resulted in higher selectivity for ERβ (12a), and further substitution with a fluoro or a methyl group to the pendant phenyl ring was also preferable (12b, d, and e). Subsequent chiral resolution of 12a identified that R-12a has a superior profile over S-12a. This is comparable to diarylpropionitrile (DPN) 5c, one of the promising selective ERβ agonists and indicates that this indane-based scaffold has the potential to provide better ERβ agonistic probes.

Long-Term Estrogen Receptor Beta Agonist Treatment Modifies the Hippocampal Transcriptome in Middle-Aged Ovariectomized Rats

Estradiol (E2) robustly activates transcription of a broad array of genes in the hippocampal formation of middle-aged ovariectomized rats via estrogen receptors (ERα, ERβ, and G protein-coupled ER). Selective ERβ agonists also influence hippocampal functions, although their downstream molecular targets and mechanisms are not known. In this study, we explored the effects of long-term treatment with ERβ agonist diarylpropionitrile (DPN, 0.05 mg/kg/day, sc.) on the hippocampal transcriptome in ovariectomized, middle-aged (13 month) rats. Isolated hippocampal formations were analyzed by Affymetrix oligonucleotide microarray and quantitative real-time PCR. Four hundred ninety-seven genes fulfilled the absolute fold change higher than 2 (FC > 2) selection criterion. Among them 370 genes were activated. Pathway analysis identified terms including glutamatergic and cholinergic synapse, RNA transport, endocytosis, thyroid hormone signaling, RNA degradation, retrograde endocannabinoid signaling, and mRNA surveillance. PCR studies showed transcriptional regulation of 58 genes encoding growth factors (Igf2, Igfb2, Igf1r, Fgf1, Mdk, Ntf3, Bdnf), transcription factors (Otx2, Msx1), potassium channels (Kcne2), neuropeptides (Cck, Pdyn), peptide receptors (Crhr2, Oprm1, Gnrhr, Galr2, Sstr1, Sstr3), neurotransmitter receptors (Htr1a, Htr2c, Htr2a, Gria2, Gria3, Grm5, Gabra1, Chrm5, Adrb1), and vesicular neurotransmitter transporters (Slc32a1, Slc17a7). Protein-protein interaction analysis revealed networking of clusters associated with the regulation of growth/troph factor signaling, transcription, translation, neurotransmitter and neurohormone signaling mechanisms and potassium channels. Collectively, the results reveal the contribution of ERβ-mediated processes to the regulation of transcription, translation, neurogenesis, neuromodulation, and neuroprotection in the hippocampal formation of ovariectomized, middle-aged rats and elucidate regulatory channels responsible for DPN-altered functional patterns. These findings support the notion that selective activation of ERβ may be a viable approach for treating the neural symptoms of E2 deficiency in menopause.

Effects of selective estrogen receptor alpha and beta modulators on prepulse inhibition in male mice

RATIONALE

Multiple lines of evidence suggest that the sex steroid hormone 17-β estradiol (E2) plays a protective role in schizophrenia. Systemic E2 enhances prepulse inhibition (PPI) of the acoustic startle reflex, an operational measure of sensorimotor gating known to be impaired in schizophrenia and related disorders. However, the relative contribution of different estrogen-receptor (ER) isoforms in these associations still awaits examination.

OBJECTIVES

The present study explored the effects of ER-α and ER-β stimulation or blockade on PPI and their functional relevance in an amphetamine-induced PPI deficiency model in male mice.

METHODS

Prior to the assessment of PPI, C57BL/6N male mice were injected with the ER-α agonist 4,4',4″-(4-propyl-[1H]-pyrazole-1,3,5-triyl) trisphenol (PPT), the ER-α antagonist 1,3-bis (4-hydroxyphenyl)-4-methyl-5-[4-(2-piperidinylethoxy) phenol]-1N-pyrozole dihydrochloride (MPP), the ER-β agonist 2,3-bis (4-hydroxyphenyl)-propionitrile (DPN), or the ER-β antagonist 4-[2-phenyl-5,7-bis (trifluoromethyl) pyrazolo [1,5-a] pyrimidin-3-yl] phenol (PHTPP), with or without concomitant amphetamine treatment.

RESULTS

Acute pharmacological stimulation and blockade of ER-α, respectively, led to a dose-dependent increase and decrease in basal PPI. In contrast, acute treatment with preferential ER-β modulators spared PPI under basal conditions. Pretreatment with either ER-α or ER-β agonist was, however, effective in blocking amphetamine-induced PPI disruption.

CONCLUSIONS

Our study demonstrates that activation of either ER isoform is capable of modulating dopamine-dependent PPI levels. At the same time, our results suggest that endogenous ER-α signaling may be more relevant than ER-β in the regulation of sensorimotor gating under basal conditions.

Estrogen receptor β and oxytocin interact to modulate anxiety-like behavior and neuroendocrine stress reactivity in adult male and female rats

The hypothalamic-pituitary-adrenal (HPA) axis is activated in response to stressors and is controlled by neurons residing in the paraventricular nucleus of the hypothalamus (PVN). Although gonadal steroid hormones can influence HPA reactivity to stressors, the exact mechanism of action is not fully understood. It is known, however, that estrogen receptor β (ERβ) inhibits HPA reactivity and decreases anxiety-like behavior in rodents. Since ERβ is co-expressed with oxytocin (OT) in neurons of the PVN, an ERβ-selective agonist was utilized to test the whether ERβ decreases stress-induced HPA reactivity and anxiety-like behaviors via an OTergic pathway. Adult gonadectomized male and female rats were administered diarylpropionitrile, or vehicle, peripherally for 5days. When tested for anxiety-like behavior on the elevated plus maze (EPM), diarylpropionitrile-treated males and females significantly increased time on the open arm of the EPM compared to vehicle controls indicating that ERβ reduces anxiety-like behaviors. One week after behavioral evaluation, rats were subjected to a 20minute restraint stress. Treatment with diarylpropionitrile reduced CORT and ACTH responses in both males and females. Subsequently, another group of animals was implanted with cannulae directed at the lateral ventricle. One week later, rats underwent the same protocol as above but with the additional treatment of intracerebroventricular infusion with an OT antagonist (des Gly-NH2 d(CH2)5 [Tyr(Me)(2), Thr(4)] OVT) or VEH, 20min prior to behavioral evaluation. OT antagonist treatment blocked the effects of diarylpropionitrile on the display of anxiety-like behaviors and plasma CORT levels. These data indicate that ERβ and OT interact to modulate the HPA reactivity and the display of anxiety-like behaviors.

Ovariectomy and subsequent treatment with estrogen receptor agonists tune the innate immune system of the hippocampus in middle-aged female rats

The innate immune system including microglia has a major contribution to maintenance of the physiological functions of the hippocampus by permanent monitoring of the neural milieu and elimination of tissue-damaging threats. The hippocampus is vulnerable to age-related changes ranging from gene expression to network connectivity. The risk of hippocampal deterioration increases with the decline of gonadal hormone supply. To explore the impact of hormone milieu on the function of the innate immune system in middle-aged female rats, we compared mRNA expression in the hippocampus after gonadal hormone withdrawal, with or without subsequent estrogen replacement using estradiol and isotype-selective estrogen receptor (ER) agonists. Targeted profiling assessed the status of the innate immune system (macrophage-associated receptors, complement, inhibitory neuronal ligands), local estradiol synthesis (P450 aromatase) and estrogen reception (ER). Results established upregulation of macrophage-associated (Cd45, Iba1, Cd68, Cd11b, Cd18, Fcgr1a, Fcgr2b) and complement (C3, factor B, properdin) genes in response to ovariectomy. Ovariectomy upregulated Cd22 and downregulated semaphorin3A (Sema3a) expression, indicating altered neuronal regulation of microglia. Ovariectomy also led to downregulation of aromatase and upregulation of ERα gene. Of note, analogous changes were observed in the hippocampus of postmenopausal women. In ovariectomized rats, estradiol replacement attenuated Iba1, Cd11b, Fcgr1a, C3, increased mannose receptor Mrc1, Cd163 and reversed Sema3a expression. In contrast, reduced expression of aromatase was not reversed by estradiol. While the effects of ERα agonist closely resembled those of estradiol, ERβ agonist was also capable of attenuating the expression of several macrophage-associated and complement genes. These data together indicate that the innate immune system of the aging hippocampus is highly responsive to the gonadal hormone milieu. In ovariectomized female rats, estradiol replacement exerts potent immunomodulatory effects including attenuation of microglia sensitization, initiation of M2-like activation and modulation of complement expression by targeting hippocampal neurons and glial cells through ERα and ERβ.

Understanding nuclear receptor form and function using structural biology

Nuclear receptors (NRs) are a major transcription factor family whose members selectively bind small-molecule lipophilic ligands and transduce those signals into specific changes in gene programs. For over two decades, structural biology efforts were focused exclusively on the individual ligand-binding domains (LBDs) or DNA-binding domains of NRs. These analyses revealed the basis for both ligand and DNA binding and also revealed receptor conformations representing both the activated and repressed states. Additionally, crystallographic studies explained how NR LBD surfaces recognize discrete portions of transcriptional coregulators. The many structural snapshots of LBDs have also guided the development of synthetic ligands with therapeutic potential. Yet, the exclusive structural focus on isolated NR domains has made it difficult to conceptualize how all the NR polypeptide segments are coordinated physically and functionally in the context of receptor quaternary architectures. Newly emerged crystal structures of the peroxisome proliferator-activated receptor-γ-retinoid X receptor α (PPARγ-RXRα) heterodimer and hepatocyte nuclear factor (HNF)-4α homodimer have recently revealed the higher order organizations of these receptor complexes on DNA, as well as the complexity and uniqueness of their domain-domain interfaces. These emerging structural advances promise to better explain how signals in one domain can be allosterically transmitted to distal receptor domains, also providing much better frameworks for guiding future drug discovery efforts.

G protein-coupled estrogen receptor-selective ligands modulate endometrial tumor growth

Endometrial carcinoma is the most common cancer of the female reproductive tract. GPER/GPR30 is a 7-transmembrane spanning G protein-coupled receptor that has been identified as the third estrogen receptor, in addition to ERα and ERβ. High GPER expression is predictive of poor survival in endometrial and ovarian cancer, but despite this, the estrogen-mediated signaling pathways and specific estrogen receptors involved in endometrial cancer remain unclear. Here, employing ERα-negative Hec50 endometrial cancer cells, we demonstrate that GPER mediates estrogen-stimulated activation of ERK and PI3K via matrix metalloproteinase activation and subsequent transactivation of the EGFR and that ER-targeted therapeutic agents (4-hydroxytamoxifen, ICI182,780/fulvestrant, and Raloxifene), the phytoestrogen genistein, and the “ERα-selective” agonist propylpyrazole triol also function as GPER agonists. Furthermore, xenograft tumors of Hec50 cells yield enhanced growth with G-1 and estrogen, the latter being inhibited by GPER-selective pharmacologic antagonism with G36. These results have important implications with respect to the use of putatively ER-selective ligands and particularly for the widespread long-term use of “ER-targeted” therapeutics. Moreover, our findings shed light on the potential mechanisms of SERM/SERD side effects reported in many clinical studies. Finally, our results provide the first demonstration that pharmacological inhibition of GPER activity in vivo prevents estrogen-mediated tumor growth.

A cell-biased effect of estrogen in prion infection

Prion disorders are associated with the accumulation of a misfolded form (PrP(Sc)) of the normal prion protein, PrP(C). Here, we show that estrogen acts as a regulator of the processes of both prion infection and prion maintenance. Estrogen was found to be cell biased in its effect; it protected cells against prion infection in a prevention mode and enabled prion maintenance in a treatment mode. These processes were regulated by the estrogen receptor subtypes Erα and Erβ. By using specific receptor agonists, Erα was found to be the main receptor active in slowing prion infection, whereas in chronically infected cells, although Erα allowed partial maintenance of PrP(Sc) levels, Erβ was the main receptor involved in maintaining PrP(Sc) in a treatment paradigm. A cell-biased effect of estrogen has been reported for other neurodegenerative disorders, including Alzheimer's disease. Estrogen's effect is dependent on the cell's health status, which impacts the use of estrogen. This work also identified that by targeting the estrogen receptors with the selective estrogen receptor modulators tamoxifen (Tam) and 4-hydroxy-tamoxifen (OHT), PrP(Sc) could be cleared from prion-infected cell culture. Tam and OHT had half-maximal inhibitory concentrations for clearance of PrP(Sc) of 0.47 μM and 0.14 nM, respectively. This work identifies further factors involved in the prion disease process, and through antagonism of the estrogen system, we demonstrate that the estrogen system is a target for controlling PrP(Sc) levels.

Estrogen receptor-β regulates human tryptophan hydroxylase-2 through an estrogen response element in the 5' untranslated region

In the dorsal raphe nucleus, 17β-estradiol (E2) increases the expression of the brain-specific, rate-limiting enzyme for serotonin biosynthesis, tryptophan hydroxylase-2 (Tph2). Although estrogen receptor beta (ERβ) has been localized to Tph2 neurons, little is known about the transcriptional regulation of the Tph2 gene by estrogen. Since the ERβ agonist, diarylpropionitrile (DPN) also increases Tph2 expression, we tested the hypothesis that E2 regulates the Tph2 promoter through direct interactions with ERβ. A serotonergic cell line, B14, which endogenously expresses ERβ was transiently transfected with a fragment of the human TPH2 5'-untranslated region (5'-UTR) cloned into a luciferase reporter vector (TPH2-luc). Treatment with E2 or DPN caused a dose-dependent increase of TPH2-luc activity. In contrast, E2 conjugated to bovine serum albumin, which is cell membrane impermeable, had no effect on TPH2-luc activity. An estrogen receptor (ER) antagonist blocked E2 or DPN-induced TPH2-luc activity suggesting a classical ER mechanism. In silico analysis revealed an estrogen-response element (ERE) half-site located within the TPH2 5'-UTR. Deletion and site-directed mutation of this site abolished ligand-induced TPH2-luc activity. These results support the concept that there is a direct and functional interaction between E2:ERβ and the ERE half-site of the TPH2 promoter to regulate Tph2 expression. We illustrate a direct regulation of the TPH2 transcription by estradiol and ERβ via a newly identified ERE half-site within the TPH2 promoter: (i) Estradiol- or an ERβ agonist-induced TPH2 transcription was blocked by an ER antagonist, while (ii) membrane impermeable form of estradiol did not induce transcription. (iii) Deletion or mutation of the ERE half-site abolished ligand-induced TPH2 transcription.

ERβ-dependent effects on uterine endothelial cells are cell specific and mediated via Sp1

STUDY QUESTION

What are the in vitro effects of estrogen receptor β (ERβ) activation on the function of endothelial cells (ECs) from different vascular beds: human endometrial ECs (HEECs; endometrium), uterine myometrial microvascular ECs (UtMVECs; myometrium) and human umbilical vein ECs (HUVECs)?

SUMMARY ANSWER

Studies conducted in vitro demonstrate that the ERβ agonist 2,3-bis(4-hydroxy-phenyl)-propionitrile (DPN) has EC type-specific effects on patterns of gene expression and network formation. Identification of a key role for the transcription factor Sp1 in ERβ-dependent signaling in uterine ECs offers new insights into cell-specific molecular mechanisms of estrogen action in the human uterus.

WHAT IS KNOWN ALREADY

Estrogens, acting via ERs (ERα and ERβ), have important, body-wide impacts on the vasculature. The human uterus is an estrogen target organ, the endometrial lining of which exhibits physiological, cyclical angiogenesis. In fixed tissue sections, human endometrial ECs are immunopositive for ERβ.

STUDY DESIGN, SIZE, DURATION

Cells were treated with a vehicle control or the ERβ agonist, DPN, for 2 h or 24 h (n = 5) followed by gene expression analysis. Functional assays were analyzed after a 16 h incubation with ligand (n = 5).

PARTICIPANT/MATERIALS, SETTING, METHODS

Analysis of DPN-treated ECs using Taqman gene array cards focused on genes involved in angiogenesis and inflammation identified cell type-specific ERβ-dependent changes in gene expression, with validation using qPCR and immunohistochemistry. Molecular mechanisms involved in ERβ signaling were investigated using bioinformatics, reporter assays, immunoprecipitation, siRNA and a specific inhibitor blocking Sp1-binding sites. The endometrium and myometrium from women with regular menses were used to validate the protein expression of candidate genes.

MAIN RESULTS AND THE ROLE OF CHANCE

HEECs and UtMVECs were ERβ+/ERα−. Treatment of ECs with DPN had opposite effects on network formation: a decrease in network formation in HEECs (P ≤ 0.001) but an increase in UtMVECs (P ≤ 0.05). Genomic analysis identified opposite changes in ERβ target gene expression with only three common transcripts (HEY1, ICAM1, CASP1) in all three ECs; a unique profile was observed for each. An important role for Sp1 was identified, consistent with the regulation of ERβ target genes via association with the transcription factor (‘tethered’ mechanism).

LIMITATIONS, REASONS FOR CAUTION

The study was mainly carried out in vitro using ECs of which one type was immortalized. Although the analysis of the protein expression of candidate genes was carried out using intact tissue samples from patients, investigations into in vivo angiogenesis were not carried out.

WIDER IMPLICATIONS OF THE FINDINGS

These results have implications for our understanding of the mechanisms responsible for ERβ-dependent changes in EC gene expression in hormone-dependent disorders.

STUDY FUNDING/COMPETEING INTEREST(S)

The study was funded by a Medical Research Council Programme Grant. E.G. is the recipient of an MRC Career Development Fellowship. The authors have nothing to disclose.

Computational study of estrogen receptor-alpha antagonist with three-dimensional quantitative structure-activity relationship, support vector regression, and linear regression methods

Human estrogen receptor (ER) isoforms, ERα and ERβ, have long been an important focus in the field of biology. To better understand the structural features associated with the binding of ERα ligands to ERα and modulate their function, several QSAR models, including CoMFA, CoMSIA, SVR, and LR methods, have been employed to predict the inhibitory activity of 68 raloxifene derivatives. In the SVR and LR modeling, 11 descriptors were selected through feature ranking and sequential feature addition/deletion to generate equations to predict the inhibitory activity toward ERα. Among four descriptors that constantly appear in various generated equations, two agree with CoMFA and CoMSIA steric fields and another two can be correlated to a calculated electrostatic potential of ERα.

Ligand selectivity of estrogen receptors by a molecular dynamics study

Estrogen receptors α (ERα) and β (ERβ) have different physiological functions and expression levels in different tissues. ERα and ERβ are highly homologous and have only two residue substitutions in the binding pocket. This high similarity at the active site stimulates the interests for discovering subtype selective ligands. In this study, molecular dynamics (MD) simulations combined with molecular mechanics generalized Born surface area (MM-GBSA) method have been carried out to analyze the basis of selectivity of three ligands (659, 818 and 041). The calculated binding free energies show that all the ligands bind more tightly to ERβ than to ERα. The dominant free energy components of selectivity for 659 are similar to that for 041, but different from that for 818. The decompositions of free energy contributions and structural analysis imply that there are eight residues primarily contributing to the selectivity for 659, five residues for 041, as well as two residues for 818. The structural analysis implies that two residue substitutions in binding packet cause the position of 659 in ERβ-659 complex to shift relative to that in ERα-659 complex and also cause the conformational changes of other residues in the binding pocket. The higher selectivity for 041 is mainly caused by three residues, Ile373 (Met421), His475 (His524) and Leu476 (Leu525).

Estrogenic effect of three substituted deoxybenzoins

Deoxybenzoins (1-(2,4-dihydroxyphenyl)-2-(4-hydroxyphenyl)ethanone) are possible precursors or metabolites of isoflavanones which may have xenoestrogenic potential on estrogen receptor (ER). In this study we evaluated three 2'-substituted deoxybenzoin derivatives for their estrogenic effect based upon their ability to affect the proliferation of ERα(+) MCF7 cells, ERβ(+) PC3 cells and Hep2 cells stably transfected and expressing either ERα or ERβ. These compounds designated as CMPD3, CMPD6 and CMPD9 had -COOH, -(CH(2))(4)-CH(3) and -CH(3) substitutions, respectively on the 2'-position of the 2,4-dihydroxyphenyl ring of deoxybenzoin. We found that all three compounds increased the proliferation of ERα(+) MCF7 cells (EC(50)~1-12 μM) and ERα(+) Hep2 cells, while causing apoptosis in ERβ(+) PC3 cells (IC(50)~1-5 μM) and ERβ(+) Hep2 cells. The compounds also up-regulated the expression of estrogen sensitive genes, trefoil factor 1 (TFF1, previously known as pS2) and cathepsin-D (CTSD), in these cells. We performed in vitro ER transcription activation assays using Hep2 cells transiently co-transfected with estrogen response element driven luciferase and either ERα or ERβ vectors to ascertain the mechanism of action of these compounds through the 'classical' genomic pathway of estrogenic activity and to determine their ER subtype selectivity. Molecular docking of the compounds with the Ligand Binding Domain of ERα and ERβ showed similar docking scores (Glidescores of -6.5 to -8.5 kcal/mol) indicating that these compounds were ligands of both ERα and ERβ with similar affinity.

Anxiolytic effects and neuroanatomical targets of estrogen receptor-β (ERβ) activation by a selective ERβ agonist in female mice

The dichotomous anxiogenic and anxiolytic properties of estrogens have been reported to be mediated by two distinct neural estrogen receptors (ER), ERα and ERβ, respectively. Using a combination of pharmacological and genetic approaches, we confirmed that the anxiolytic actions of estradiol are mediated by ERβ and extended and these observations to demonstrate the neuroanatomical targets involved in ERβ activation in these behavioral responses. We examined the effects of the biologically active S-enantiomer of diarylpropionitrile (S-DPN) on anxiety-related behavioral measures, the corresponding stress hormonal response to hypothalamo-pituitary-adrenal axis reactivity, and potential sites of neuronal activation in mutant female mice carrying a null mutation for ERβ gene (βERKO). S-DPN administration significantly reduced anxiety-like behaviors in the open field, light-dark exploration, and the elevated plus maze (EPM) in ovariectomized wild-type (WT) mice, but not in their βERKO littermates. Stress-induced corticosterone (CORT) and ACTH were also attenuated by S-DPN in the WT mice but not in the βERKO mice. Using c-fos induction after elevated plus maze, as a marker of stress-induced neuronal activation, we identified the anterodorsal medial amygdala and bed nucleus of the stria terminalis as the neuronal targets of S-DPN action. Both areas showed elevated c-fos mRNA expression with S-DPN treatment in the WT but not βERKO females. These studies provide compelling evidence for anxiolytic effects mediated by ERβ, and its neuroanatomical targets, that send or receive projections to/from the paraventricular nucleus, providing potential indirect mode of action for the control of hypothalamo-pituitary-adrenal axis function and behaviors.

Diarylpropionitrile (DPN) enantiomers: synthesis and evaluation of estrogen receptor β-selective ligands

Two estrogen receptor (ER) subtypes, ERα and ERβ, mediate the actions of estrogens in diverse reproductive and nonreproductive target tissues. ER subtype-selective ligands, which bind to and activate these subtypes differentially, have proved to be useful in elucidating which actions of estrogens proceed through ERα vs ERβ. Some of these ligands show potential as novel therapeutic agents. Diarylpropionitrile (DPN), an ERβ selective ligand that we developed, is a chiral molecule, but it has been studied almost exclusively as the racemic mixture (rac-DPN, 1). Herein we report the development of an efficient enantioselective synthesis of the two isomers, R-DPN (3) and S-DPN (2), and we have compared the in vitro ligand binding affinities, coactivator binding affinities, recruitment potencies, and cellular transcriptional potencies of these isomers. Both enantiomers show a very high affinity and potency preference for ERβ over ERα, typically in the range of 80-300-fold. Although the enantioselectivity is only modest (3-4-fold), the R-enantiomer is the higher affinity and more potent isomer. While ERβ can be effectively and selectively stimulated by rac-DPN or by either R-DPN or S-DPN, R-DPN might be the preferred member of this isomeric series for biological studies of ERβ function.

Estrogens regulate neuroinflammatory genes via estrogen receptors α and β in the frontal cortex of middle-aged female rats

Background

Estrogens exert anti-inflammatory and neuroprotective effects in the brain mainly via estrogen receptors α (ERα) and β (ERβ). These receptors are members of the nuclear receptor superfamily of ligand-dependent transcription factors. This study was aimed at the elucidation of the effects of ERα and ERβ agonists on the expression of neuroinflammatory genes in the frontal cortex of aging female rats.

Methods

To identify estrogen-responsive immunity/inflammation genes, we treated middle-aged, ovariectomized rats with 17β-estradiol (E2), ERα agonist 16α-lactone-estradiol (16α-LE2) and ERβ agonist diarylpropionitrile (DPN), or vehicle by Alzet minipump delivery for 29 days. Then we compared the transcriptomes of the frontal cortex of estrogen-deprived versus ER agonist-treated animals using Affymetrix Rat230 2.0 expression arrays and TaqMan-based quantitative real-time PCR. Microarray and PCR data were evaluated by using Bioconductor packages and the RealTime StatMiner software, respectively.

Results

Microarray analysis revealed the transcriptional regulation of 21 immunity/inflammation genes by 16α-LE2. The subsequent comparative real-time PCR study analyzed the isotype specific effects of ER agonists on neuroinflammatory genes of primarily glial origin. E2 regulated the expression of sixteen genes, including down-regulation of complement C3 and C4b, Ccl2, Tgfb1, macrophage expressed gene Mpeg1, RT1-Aw2, Cx3cr1, Fcgr2b, Cd11b, Tlr4 and Tlr9, and up-regulation of defensin Np4 and RatNP-3b, IgG-2a, Il6 and ER gene Esr1. Similar to E2, both 16α-LE2 and DPN evoked up-regulation of defensins, IgG-2a and Il6, and down-regulation of C3 and its receptor Cd11b, Ccl2, RT1-Aw2 and Fcgr2b.

Conclusions

These findings provide evidence that E2, 16α-LE2 and DPN modulate the expression of neuroinflammatory genes in the frontal cortex of middle-aged female rats via both ERα and ERβ. We propose that ERβ is a promising target to suppress regulatory functions of glial cells in the E2-deprived female brain and in various neuroinflammatory diseases.

Activation of estrogen receptor alpha disrupts differentiation of the reproductive organs in chicken embryos

Gonadal estrogen plays an important role in the differentiation of a female phenotype in birds. Exogenous compounds that interfere with estrogen signaling, for instance by binding to the estrogen receptors alpha and beta (ERα and ERβ), are therefore potential disruptors of sexual differentiation in birds. The ERα agonist propyl-pyrazole-triol (PPT), the ERα antagonist methyl piperidino pyrazole (MPP) and the ERβ agonist diarylproprionitrile (DPN) were used in the present study to explore the roles of the ERs in normal and disrupted sex differentiation in the chicken embryo. Activation of ERα by PPT caused disturbed differentiation of the reproductive organs in both sexes. In male embryos, PPT caused left-side ovotestis formation and retention of the Müllerian ducts. In female embryos, PPT caused retention of the right Müllerian duct (which normally regresses) and malformation of both Müllerian ducts. PPT also induced hepatic expression of mRNA for the estrogen-regulated egg yolk protein apoVLDL II. Notably, none of these effects were observed following treatment with DPN. ERα-inactivation by MPP counteracted the action of PPT but had little effect by its own. Our results indicate that ERα plays an important role in sex differentiation of the reproductive tract in female chicken embryos and show that ERα can mediate xenoestrogen-induced disturbances of sex differentiation.

Selectively targeting estrogen receptors for cancer treatment

Estrogens regulate growth and development through the action of two distinct estrogen receptors (ERs), ERα and ERβ, which mediate proliferation and differentiation of cells. For decades, ERα mediated estrogen signaling has been therapeutically targeted to treat breast cancer, most notably with the selective estrogen receptor modulator (SERM) tamoxifen. Selectively targeting ERs occurs at two levels: tissue selectivity and receptor subtype selectivity. SERMs have been developed with emphasis on tissue selectivity to target ER signaling for breast cancer treatment. Additionally, new approaches to selectively target the action of ERα going beyond ligand-dependent activity are under current investigation. As evidence of the anti-proliferative role of ERβ accumulates, selectively targeting ERβ is an attractive approach for designing new cancer therapies with the emphasis shifted to designing ligands with subtype selectivity. This review will present the mechanistic and structural features of ERs that determine tissue and subtype selectivity with an emphasis on current approaches to selectively target ERα and ERβ for cancer treatment.

Oestrogen prevents cardiomyocyte apoptosis by suppressing p38α-mediated activation of p53 and by down-regulating p53 inhibition on p38β

AIMS

we have previously shown that 17-β-estradiol (E2) protects cardiomyocytes exposed to simulated ischaemia-reperfusion (I/R) by differentially regulating pro-apoptotic p38α mitogen-activated protein kinase (p38α MAPK) and pro-survival p38β. However, little is known about how E2 modulation of these kinases alters apoptotic signalling. An attractive downstream target is p53, a well-known mediator of apoptosis and a substrate of p38α MAPK. The aim of this study was to determine whether the cytoprotective actions of oestrogen involve regulation of p53 via cardiac p38 MAPKs.

METHODS AND RESULTS

cultured rat cardiomyocytes underwent hypoxia followed by reoxygenation (H/R) to simulate I/R. We found that inhibiting p53 significantly reduced apoptosis. Phosphorylation of p53 at serine 15 [p-p53(S15)] increased after H/R in a p38α MAPK- and reactive oxygen species (ROS)-dependent manner. E2 at 10 nM effectively inhibited p-p53(S15) and mitochondrial translocation of p53. Blocking p53 led to augmented p38β activity and attenuated ROS, suggesting suppression of this antioxidant kinase by p53. The use of a specific agonist for each oestrogen receptor (ER) isoform, ERα and ERβ, demonstrated that both isoforms participate in preventing cell death by inhibiting p53 in the mitochondria-centred apoptotic processes.

CONCLUSION

our results demonstrate that during H/R stress, cardiomyocytes undergo p53-dependent apoptosis following phosphorylation of p53 by p38α MAPK, leading to p38β suppression. E2 protects cardiomyocytes by inhibiting p38α-p53 signalling in apoptosis.

Phosphorylation of estrogen receptor beta at serine 105 is associated with good prognosis in breast cancer

Estrogen receptor (ER) action is modulated by posttranslational modifications. Although ERalpha phosphorylation correlates with patient outcome, ERbeta is similarly phosphorylated but its significance in breast cancer has not been addressed. We investigated whether ERbeta that is phosphorylated at serine 105 (S105-ERbeta) is expressed in breast cancer and assessed potential clinical implications of this phosphorylation. Following antibody validation, S105-ERbeta expression was studied in tissue microarrays comprising 108 tamoxifen-resistant and 351 tamoxifen-sensitive cases and analyzed against clinical data. S105-ERbeta regulation in vitro was assessed by Western blot, flow cytometry, and immunofluorescence. Nuclear S105-ERbeta was observed in breast carcinoma and was associated with better survival (Allred score > or =3), even in tamoxifen-resistant cases, and additionally correlated with ERbeta1 and ERbeta2 expression. Distinct S105-ERbeta nuclear speckles were seen in some higher grade tumors. S105-ERbeta levels increased in MCF-7 cells in response to 17beta-estradiol, the ERbeta-specific agonist diarylpropionitrile, and the partial ERbeta-agonist genistein. S105-ERbeta nuclear speckles were also seen in MCF-7 cells and markedly increased in size and number at 24 hours following 17beta-estradiol and, in particular diarylpropionitrile, treatment. These speckles were coexpressed with ERbeta1 and ERbeta2. Presence of S105-ERbeta in breast cancer and association with improved survival, even in endocrine resistant breast tumors suggest S105-ERbeta might be a useful additional prognostic marker in this disease.

Computational insights into the mechanism of ligand unbinding and selectivity of estrogen receptors

Estrogen receptors (ER) belong to the nuclear receptor superfamily, and two subtypes, ERalpha and ERbeta, have been identified to date. The differentiated functions and receptor expressions of ERalpha and ERbeta made it attracted to discover subtype-specified ligands with high selectivity. However, these two subtypes are highly homologous and only two residues differ in the ligand binding pocket. Therefore, the mechanism of ligand selectivity has become an important issue in searching selective ligands of ER subtypes. In this study, steered molecular dynamics simulations were carried out to investigate the unbinding pathways of two selective ERbeta ligands from the binding pocket of both ERalpha and ERbeta, which demonstrated that the pathway between the H11 helix and the H7 approximately H8 loop was the most probable for ligand escaping. Then potentials of mean force for ligands unbinding along this pathway were calculated in order to gain insights into the molecular basis for energetics of ligand unbinding and find clues of ligand selectivity. The results indicated that His524/475 in ERalpha/ERbeta acted as a "gatekeeper" during the ligand unbinding. Especially, the H7 approximately H8 loop of ERbeta acted as a polar "transmitter" that controlled the ligand unbinding from the binding site and contributed to the ligand selectivity. Finally, the mechanism of ligand selectivity of ER subtypes was discussed from a kinetic perspective and suggestions for improving the ligand selectivity of ERbeta were also presented. These findings could be helpful for rational design of highly selective ERbeta ligands.

Differential regulation of gonadotropin-releasing hormone neuron activity and membrane properties by acutely applied estradiol: dependence on dose and estrogen receptor subtype

Gonadotropin-releasing hormone (GnRH) neurons are critical to controlling fertility. In vivo, estradiol can inhibit or stimulate GnRH release depending on concentration and physiological state. We examined rapid, nongenomic effects of estradiol. Whole-cell recordings were made of GnRH neurons in brain slices from ovariectomized mice with ionotropic GABA and glutamate receptors blocked. Estradiol was bath applied and measurements completed within 15 min. Estradiol from high physiological (preovulatory) concentrations (100 pm) to 100 nm enhanced action potential firing, reduced afterhyperpolarizing potential (AHP) and increased slow afterdepolarization amplitudes (ADP), and reduced I(AHP) and enhanced I(ADP). The reduction of I(AHP) was occluded by previous blockade of calcium-activated potassium channels. These effects were mimicked by an estrogen receptor (ER) beta-specific agonist and were blocked by the classical receptor antagonist ICI182780. ERalpha or GPR30 agonists had no effect. The acute stimulatory effect of high physiological estradiol on firing rate was dependent on signaling via protein kinase A. In contrast, low physiological levels of estradiol (10 pm) did not affect intrinsic properties. Without blockade of ionotropic GABA and glutamate receptors, however, 10 pm estradiol reduced firing of GnRH neurons; this was mimicked by an ERalpha agonist. ERalpha agonists reduced the frequency of GABA transmission to GnRH neurons; GABA can excite to these cells. In contrast, ERbeta agonists increased GABA transmission and postsynaptic response. These data suggest rapid intrinsic and network modulation of GnRH neurons by estradiol is dependent on both dose and receptor subtype. In cooperation with genomic actions, nongenomic effects may play a role in feedback regulation of GnRH secretion.

Estrogen receptor-beta agonist diarylpropionitrile: biological activities of R- and S-enantiomers on behavior and hormonal response to stress

Estrogens have been shown to have positive and negative effects on anxiety and depressive-like behaviors, perhaps explained by the existence of two distinct estrogen receptor (ER) systems, ERalpha and ERbeta. The ERbeta agonist, diarylpropionitrile (DPN) has been shown to have anxiolytic properties in rats. DPN exists as a racemic mixture of two enantiomers, R-DPN and S-DPN. In this study, we compared R-DPN and S-DPN for their in vitro binding affinity, ability to activate transcription in vitro at an estrogen response element, and in vivo endocrine and behavioral responses. In vitro binding studies using recombinant rat ERbeta revealed that S-DPN has a severalfold greater relative binding affinity for ERbeta than does R-DPN. Furthermore, cotransfection of N-38 immortalized hypothalamic cells with an estrogen response element-luc reporter and ERbeta revealed that S-DPN is a potent activator of transcription in vitro, whereas R-DPN is not. Subsequently, we examined anxiety-like behaviors using the open-field test and elevated plus maze or depressive-like behaviors, using the forced swim test. Ovariectomized young adult female Sprague Dawley rats treated with racemic DPN, S-DPN, and the ERbeta agonist, WAY-200070, showed significantly decreased anxiety-like behaviors in both the open-field and elevated plus maze and significantly less depressive-like behaviors in the forced swim test compared with vehicle-, R-DPN-, or propylpyrazoletriol (ERalpha agonist)-treated animals. In concordance with the relative binding affinity and transcriptional potency, these results demonstrate that the S-enantiomer is the biologically active form of DPN. These studies also indicate that estrogen's positive effects on mood, including its anxiolytic and antidepressive actions, are due to its actions at ERbeta.

Biphenyl C-cyclopropylalkylamides: New scaffolds for targeting estrogen receptor beta

The C-cyclopropylalkylamide scaffold was previously identified as a new structural framework for antiestrogens. A second generation library provided three compounds that bind estrogen receptor (ER)alpha. Further screening of this library identified an ERbeta hit and inspired another round of SAR. A new focused library was tested for binding to the ERs, and for effects on the growth of breast cancer cell lines and protein levels of common cell cycle regulators.

Structure-based approach for the study of estrogen receptor binding affinity and subtype selectivity

Estrogens exert important physiological effects through the modulation of two human estrogen receptor (hER) subtypes, alpha (hERalpha) and beta (hERbeta). Because the levels and relative proportion of hERalpha and hERbeta differ significantly in different target cells, selective hER ligands could target specific tissues or pathways regulated by one receptor subtype without affecting the other. To understand the structural and chemical basis by which small molecule modulators are able to discriminate between the two subtypes, we have applied three-dimensional target-based approaches employing a series of potent hER-ligands. Comparative molecular field analysis (CoMFA) studies were applied to a data set of 81 hER modulators, for which binding affinity values were collected for both hERalpha and hERbeta. Significant statistical coefficients were obtained (hERalpha, q(2) = 0.76; hERbeta, q(2) = 0.70), indicating the internal consistency of the models. The generated models were validated using external test sets, and the predicted values were in good agreement with the experimental results. Five hER crystal structures were used in GRID/PCA investigations to generate molecular interaction fields (MIF) maps. hERalpha and hERbeta were separated using one factor. The resulting 3D information was integrated with the aim of revealing the most relevant structural features involved in hER subtype selectivity. The final QSAR and GRID/PCA models and the information gathered from 3D contour maps should be useful for the design of novel hER modulators with improved selectivity.

Synthesis and evaluation of aryl-substituted diarylpropionitriles, selective ligands for estrogen receptor beta, as positron-emission tomographic imaging agents

We have investigated halogen-substituted non-steroidal estrogens with selective binding affinity for the estrogen receptor beta (ERbeta that might be used for imaging the levels of this ER-subtype in breast tumors by positron emission tomography (PET). Based on diarylpropionitrile (DPN, 1a), a compound previously reported that has a 72-fold binding selectivity for ERbeta, we developed a series of DPN analogs having methyl-, hydroxyl-, and halogen substituents, including fluoroethyl and fluoropropyl groups. In competitive radiometric binding assays with [(3)H]estradiol, all of these DPN analogs showed high ERbeta/ERalpha selectivity; while the selectivity varied, in some cases it reached nearly 300-fold (RBA: ERalpha, 0.023%; ERbeta, 6.25%). The absolute ERbeta binding affinities, however, were not sufficient to merit further consideration for developing these ligands as PET imaging agents.

The novel estrogen receptor, G protein-coupled receptor 30, mediates the proliferative effects induced by 17beta-estradiol on mouse spermatogonial GC-1 cell line

Many studies have indicated that estrogens could have a role in the regulation of testicular function. However, it remains uncertain whether estrogens are able to directly activate signaling pathways in male germ cells. Estrogens are synthesized by the enzyme aromatase and classically act by binding to estrogen receptors (ERs)-alpha and ERbeta. Knockout mice for both receptor isoforms exhibit a testicular phenotype that is less severe than aromatase knockout mice, suggesting the existence of an estrogen-binding receptor that may compensate for the lack of ERs. Recently studies using estrogen-sensitive tumor cell lines have demonstrated that the G-protein-coupled receptor (GPR)-30 binds and mediates estrogen action through the activation of the epidermal growth factor receptor (EGFR)/ERK/fos transduction pathway. The present study investigated the ability of 17beta-estradiol (E2) to activate this pathway in the mouse spermatogonial cell line (GC-1). Using the GC-1 cell line as a model system, we demonstrated that GC-1 cells express GPR30 and ERalpha but not ERbeta. E2, the selective GPR30 agonist G1, and the selective ERalpha agonist 4,4',4''-(4-propyl-[1H]pyrazole-1,3,5-triyl) trisphenol activated the rapid ERK1/2-fos signaling cascade. This response was abrogated by the EGFR inhibitor AG1478, ERK inhibitor PD98059 and ER inhibitor ICI 182780, or by silencing GPR30 expression. Moreover, E2 and G1 up-regulated cyclin D1 expression and GC-1 cell proliferation. Our results indicate for the first time that estrogens, through a cross talk between GPR30 and ERalpha, activate the rapid EGFR/ERK/fos pathway, which in turn stimulate mouse GC-1 cell proliferation. Further studies to elucidate the involvement of rapid estrogen signaling pathways in the regulation of male fertility are warranted.

Differential mass spectrometry of rat plasma reveals proteins that are responsive to 17beta-estradiol and a selective estrogen receptor modulator PPT

Estrogens are a class of steroid hormones that interact with two related but distinct nuclear receptors, estrogen receptor (ER) alpha and beta. To identify potential ER biomarkers, we profiled the rat plasma glycoproteome after treatment with vehicle or 17beta-estradiol (E2) or an ERalpha-selective agonist PPT by differential mass spectrometry. Our comparative proteomic experiment identifies novel E2- and PPT-responsive proteins, such as serine protease inhibitor family members.

Selective estrogen receptor α activation disrupts sex organ differentiation and induces expression of vitellogenin II and very low-density apolipoprotein II in Japanese quail embryos

The Japanese quail (Coturnix japonica) is a widely used model species for studying the roles of steroid hormones in avian sex differentiation. The aim of the present study was to elucidate the significance of estrogen receptors α and β (ERα and ERβ) in normal sex differentiation of the reproductive organs in the Japanese quail and in xenoestrogen-induced disruption of reproductive organ differentiation. Real-time PCR indicated that ERα (ESR1) mRNA is expressed in both right and left gonads and Müllerian ducts (MDs) in both sexes during early morphological differentiation. ERβ (ESR2) transcripts were also detected in gonads and MDs, but at very low levels. Both receptor subtypes were expressed in the liver and may therefore mediate the expression of estrogen-regulated egg-yolk proteins. Aromatase mRNA was expressed at much higher levels in female than male gonads as early as embryonic day 5, indicating early sex differences in estrogen synthesis. Treatment with the ERα-selective agonist propyl pyrazole triol showed that frequently reported xenoestrogen effects, such as ovotestis formation, abnormal MD development, and hepatic expression of egg-yolk proteins, were induced by selective activation of ERα. Taken together, our results suggest that activation of ERα is crucial for estrogen-dependent sex differentiation of the reproductive organs and that ERα mediates xenoestrogen-induced toxicity during reproductive development in birds.

Influence of cellular ERalpha/ERbeta ratio on the ERalpha-agonist induced proliferation of human T47D breast cancer cells

Breast cancer cells show overexpression of estrogen receptor (ER) alpha relative to ERbeta compared to normal breast tissues. This observation has lead to the hypothesis that ERbeta may modulate the proliferative effect of ERalpha. This study investigated how variable cellular expression ratios of the ERalpha and ERbeta modulate the effects on cell proliferation induced by ERalpha or ERbeta agonists, respectively. Using human osteosarcoma (U2OS) ERalpha or ERbeta reporter cells, propyl-pyrazole-triol (PPT) was shown to be a selective ERalpha and diarylpropionitrile (DPN) a preferential ERbeta modulator. The effects of these selective estrogen receptor modulators (SERMs) and of the model compound E2 on the proliferation of T47D human breast cancer cells with tetracycline-dependent expression of ERbeta (T47D-ERbeta) were characterized. E2-induced cell proliferation of cells in which ERbeta expression was inhibited was similar to that of the T47D wild-type cells, whereas this E2-induced cell proliferation was no longer observed when ERbeta expression in the T47D-ERbeta cells was increased. In the T47D-ERbeta cell line, DPN also appeared to be able to suppress cell proliferation when levels of ERbeta expression were high. In the T47D-ERbeta cell line, PPT was unable to suppress cell proliferation at all ratios of ERalpha/ERbeta expression, reflecting its ability to activate only ERalpha and not ERbeta. It is concluded that effects of estrogen-like compounds on cell proliferation are dependent on the actual ERalpha/ERbeta expression levels in these cells or tissues and the potential of the estrogen agonists to activate ERalpha and/or ERbeta.

Oestrogen and the colon: potential mechanisms for cancer prevention

The role of oestrogen in oncogenesis has been examined extensively, especially in the context of breast cancer, and receptor modulators are an integral part of targeted treatment in this disease. The role of oestrogen signalling in colonic carcinoma is poorly understood. Men are more susceptible than women to colon cancer. Furthermore, hormone-replacement therapy affords an additive protective effect for postmenopausal women, and when these women do develop cancer, they typically have less aggressive disease. The discovery of a second oestrogen receptor (ERbeta) and its over expression in healthy human colon coupled with reduced expression in colon cancer suggests that this receptor might be involved. The underlying mechanism, however, remains largely unknown. In this Review, we discuss the various hypotheses presented in the published literature. We examine the cellular and molecular mechanisms through which oestrogen is purported to exert its protective influence, and we review the evidence available to support these claims.

Functional effects and molecular mechanisms of subtype-selective ERalpha and ERbeta agonists in the cardiovascular system

Gender differences in the development of cardiovascular disease suggested for a protective function of estrogens in heart disease. The negative or neutral outcome of clinical trials on hormone replacement therapy provides clear evidence that the role of female sex hormones in the cardiovascular system is more complex than previously thought. In particular, the function of estrogens can not be understood without detailed knowledge on the specific function of both estrogen receptor subtypes in the heart and in the vasculature. In here, we review recent studies on subtype selective ERalpha and ERbeta agonists in different animal models of hypertension, cardiac hypertrophy and vascular inflammation. The results indicate that the activation of specific ER subtypes confers specific as well as redundant protective effects in hypertensive heart disease that might ultimately translate into novel treatment options for hypertensive heart disease.

Androgen receptor or estrogen receptor-beta blockade alters DHEA-, DHT-, and E(2)-induced proliferation and PSA production in human prostate cancer cells

BACKGROUND

Dehydroepiandrosterone (DHEA) is an endogenous steroid that is metabolized to androgens and/or estrogens in the human prostate. DHEA levels decline with age, and use of DHEA supplements to retard the aging process is of unproved effectiveness and safety. LNCaP and LAPC-4 prostate cancer cells were used to determine whether DHEA-modulated proliferation and prostate specific antigen (PSA) production were mediated via the androgen receptor (AR) and/or ERbeta.

METHODS

Cells were treated with DHEA, DHT, or E(2) and antagonists to AR (Casodex-bicalutamide) or ER (ICI 182,780) or siRNA to the respective receptors. Proliferation was assessed by MTT assay and PSA mRNA and protein secretion were measured by quantitative real-time PCR and ELISA. Associations of AR and ERbeta were analyzed by co-immunoprecipitation studies and fluorescent confocal microscopy.

RESULTS

DHEA-, T-, and E(2)-induced proliferation of LNCaP cells was blunted by Casodex but not by ICI treatment. In LNCaP cells, Casodex and ICI suppressed hormone-induced PSA production. In LAPC-4 cells, DHT-stimulated PSA mRNA was inhibited by Casodex and ICI, and the minimal stimulation by DHEA was inhibited by ICI. Use of siRNAs confirmed involvement of AR and ERbeta in hormone-induced PSA production while AR-ERbeta co-association was suggested by immunoprecipitation and nuclear co-localization.

CONCLUSIONS

These findings support involvement of both AR and ERbeta in mediating DHEA-, DHT-, and E(2)-induced PSA expression in prostate cancer cells.

Benzopyrans as selective estrogen receptor beta agonists (SERBAs). Part 4: functionalization of the benzopyran A-ring

Benzopyrans are selective estrogen receptor (ER) beta agonists (SERBAs), which bind the ER receptor subtypes alpha and beta in opposite orientations. We have used structure based drug design to show that this unique phenomena can be exploited via substitution at the 8-position of the benzopyran A-ring to disrupt binding to ERalpha, thus improving ERbeta subtype selectivity. X-ray cocrystal structures with ERalpha and ERbeta are supportive of this approach to improve selectivity in this structural class.

Estrogen receptor beta in the brain: from form to function

Estrogens have numerous effects on the brain, both in adulthood and during development. These actions of estrogen are mediated by two distinct estrogen receptor (ER) systems, ER alpha (ERalpha) and ER beta (ERbeta). In brain, ERalpha plays a critical role in regulating reproductive neuroendocrine function and behavior, however, a definitive role for ERbeta in any neurobiological function has been slow in forthcoming. Clues to the function of ERbeta in the central nervous system can be gleaned from the neuroanatomical distribution of ERbeta and the phenotypes of neurons that express ERbeta. ERbeta immunoreactivity has been found in populations of GnRH, CRH, vasopressin, oxytocin and prolactin containing neurons in the hypothalamus. Utilizing subtype-selective estrogen receptor agonists can help determine the roles for ERbeta in non-reproductive behaviors in rat models. ERbeta-selective agonists exert potent anxiolytic activity when animals were tested in a number of behavioral paradigms. Consistent with this, ERbeta-selective agonists also inhibited the ACTH and corticosterone response to stress. In contrast, ERalpha selective agonists were found to be anxiogenic and correspondingly increased the hormonal stress response. Taken together, our studies implicate ERbeta as an important modulator of some non-reproductive neurobiological systems. The molecular and neuroanatomical targets of estrogen that are mediated by ERbeta remain to be determined. A number of splice variants of ERbeta mRNA have been reported in brain tissue. Imaging of eGFP labeled chimeric receptor proteins transfected into cell lines shows that ERbeta splice variation can alter trafficking patterns and function. The originally described ERbeta (herein termed ERbeta1) is characterized by possessing a high affinity for estradiol. Similar to ERalpha, it is localized in the nucleus and is trafficked to nuclear sites termed "hyperspeckles" following ligand binding. In contrast, ERbeta2 contains an 18 amino acid insert within the ligand-binding domain and as a result can be best described as a low affinity form of ERbeta. A delta3 (delta3) variant of ERbeta has a deletion of the 3rd exon (coding for the second half of the DNA-binding domain) and as a result does not bind an estrogen response element in DNA. delta3 variants are trafficked to a unique low abundance and larger nuclear site following ligand binding. A delta4 (delta4) variant lacks exon 4 and as a result is localized to the cytoplasm. The amount of individual splice variant mRNAs varies depending upon brain region. Examination of neuropeptide promoter regulation by ERbeta splice variants demonstrates that ERbeta functions as a constitutively active transcription factor. Moreover, it appears that splice variation of ERbeta alters its ability to regulate transcription in a promoter-dependent and ligand-dependent fashion.