The human oestrogen receptor functions in yeast

Nuclear Receptors and the Hidden Language of the Metabolome

Nuclear hormone receptors (NHRs) are a family of ligand-regulated transcription factors that control key aspects of development and physiology. The regulation of NHRs by ligands derived from metabolism or diet makes them excellent pharmacological targets, and the mechanistic understanding of how NHRs interact with their ligands to regulate downstream gene networks, along with the identification of ligands for orphan NHRs, could enable innovative approaches for cellular engineering, disease modeling and regenerative medicine. We review recent discoveries in the identification of physiologic ligands for NHRs. We propose new models of ligand-receptor co-evolution, the emergence of hormonal function and models of regulation of NHR specificity and activity via one-ligand and two-ligand models as well as feedback loops. Lastly, we discuss limitations on the processes for the identification of physiologic NHR ligands and emerging new methodologies that could be used to identify the natural ligands for the remaining 17 orphan NHRs in the human genome.

The use of in silico molecular modelling to screen potential estrogen mimics as part of medicines and agrochemicals development and product license applications

Estrogen mimics are a diverse group of synthetic and naturally occurring compounds that can interact with estrogen receptors (ERs) in animals, including humans. These interactions rely on key structural features of 17b-estradiol (E2) and if these molecular features are in a similar spatial arrangement on other compounds, they are likely to elicit an agonist (i.e., they are E2 mimics) or antagonist response. The structural diversity of some compounds vis-à-vis analogies with E2 makes it difficult to reliably predict E2 mimicry on simple structural grounds alone. We propose a new approach methodology: in silico molecular modelling augmented by an in vitro transactivation reporter gene assay to predict E2 mimicry and thus further reduce regulatory reliance on animal studies. Transactivation reporter gene assay dose response curves and in silico molecular modelling were used to obtain EC50-values and docking parameters (DockScores), respectively of thirty E2 mimics to assess the reliability of in silico receptor interaction parameters to predict E2 mimicry. A linear relationship (R2 = 0.75) was found between DockScores and EC50s, suggesting molecular modelling is a good tool for predicting E2 mimicry in a regulatory setting.

Endocrine disruptors of sex hormone activities

Sex hormones, such as androgens, estrogens and progestins are naturally occurring compounds that tightly regulate endocrine systems in a variety of living organisms. Uncontrolled environmental exposure to these hormones or their biological and synthetic mimetics has been widely documented. Furthermore, water contaminants penetrate soil to affect flora, fauna and ultimately humans. Because endocrine systems evolved to respond to very small changes in hormone levels, the low levels found in the environment cannot be ignored. The combined actions of sex hormones with glucocorticoids and other nuclear receptors disruptors creates additional level of complexity including the newly described "dynamic assisted loading" mechanism. We reviewed the extensive literature pertaining to world-wide detection of these disruptors and created a detailed Table on the development and current status of methods used for their analysis.

Function and Evolution of Nuclear Receptors in Environmental-Dependent Postembryonic Development

Nuclear receptors (NRs) fulfill key roles in the coordination of postembryonal developmental transitions in animal species. They control the metamorphosis and sexual maturation in virtually all animals and by that the two main environmental-dependent developmental decision points. Sexual maturation and metamorphosis are controlled by steroid receptors and thyroid receptors, respectively in vertebrates, while both processes are orchestrated by the ecdysone receptor (EcR) in insects. The regulation of these processes depends on environmental factors like nutrition, temperature, or photoperiods and by that NRs form evolutionary conserved mediators of phenotypic plasticity. While the mechanism of action for metamorphosis and sexual maturation are well studied in model organisms, the evolution of these systems is not entirely understood and requires further investigation. We here review the current knowledge of NR involvement in metamorphosis and sexual maturation across the animal tree of life with special attention to environmental integration and evolution of the signaling mechanism. Furthermore, we compare commonalities and differences of the different signaling systems. Finally, we identify key gaps in our knowledge of NR evolution, which, if sufficiently investigated, would lead to an importantly improved understanding of the evolution of complex signaling systems, the evolution of life history decision points, and, ultimately, speciation events in the metazoan kingdom.

Steroid receptors and vertebrate evolution

Considering that life on earth evolved about 3.7 billion years ago, vertebrates are young, appearing in the fossil record during the Cambrian explosion about 542 to 515 million years ago. Results from sequence analyses of genomes from bacteria, yeast, plants, invertebrates and vertebrates indicate that receptors for adrenal steroids (aldosterone, cortisol), and sex steroids (estrogen, progesterone, testosterone) also are young, with an estrogen receptor and a 3-ketosteroid receptor first appearing in basal chordates (cephalochordates: amphioxus), which are close ancestors of vertebrates. Duplication and divergence of the 3-ketosteroid receptor yielded an ancestral progesterone receptor and an ancestral corticoid receptor, the common ancestor of the glucocorticoid and mineralocorticoid receptors, in jawless vertebrates (cyclostomes: lampreys, hagfish). This was followed by evolution of an androgen receptor, distinct glucocorticoid and mineralocorticoid receptors and estrogen receptor-α and -β in cartilaginous fishes (Chondrichthyes: sharks). Further evolution of mineralocorticoid signaling occurred with the evolution of aldosterone synthase in lungfish, a forerunner of terrestrial vertebrates. Adrenal and sex steroid receptors are not found in echinoderms and hemichordates, which are ancestors in the lineage of cephalochordates and vertebrates. The evolution of steroid receptors at key nodes in the evolution of vertebrates, in which steroid receptors act as master switches to regulate differentiation, development, reproduction, immune responses, electrolyte homeostasis and stress responses, suggests an important role for steroid receptors in the evolutionary success of vertebrates, considering that the human genome contains about 22,000 genes, which is not much larger than genomes of invertebrates, such as Caenorhabditis elegans (~18,000 genes) and Drosophila (~14,000 genes).

Planar yeast estrogen screen with resorufin-β-d-galactopyranoside as substrate

For the planar yeast estrogen screen (pYES), 4-methylumbelliferyl-β-d-galactopyranoside was generally employed as substrate, delivering blue fluorescing 4-methylumbelliferone after enzymatic cleavage by the YES reporter β-d-galactosidase as the positive signal for the presence of estrogen active compounds (EAC). As environmental samples like waste water also contain blue fluorescent components, it is difficult to differentiate them from pYES signals. Therefore, resorufin-β-d-galactopyranoside (RGP), providing the orange fluorescing resorufin after enzymatic cleavage, was introduced as pYES substrate to determine EAC. With 17β-estradiol (E2) and 17α-ethinylestradiol (EE2), mean limits of detection and quantitation of 3.5 and 6.5pg/zone, respectively, were determined. Obtained recoveries for both E2 and EE2 from spiked water samples in a concentration range of 2-20ng/L were close to 100%. The application of the RGP-pYES on waste water influent and effluent samples showed the clear detection of EAC without interferences. Estrone (E1), Estriol, E2, and an unknown EAC were found in the influent sample (E2 with a mean of 16.9 ng/L and a precision of 11% RSD; n=4), while another unknown EAC was observed in the effluent sample. In addition, the presence of conjugated EAC in the influent was demonstrated by hydrolysis with β-glucuronidase, when the signals of E1 and the unknown increased by about 25% and 100%, respectively.

Phytoestrogens in Botanical Dietary Supplements: Implications for Cancer

Phytoestrogens are plant constituents that possess either estrogenic or antiestrogenic activity. Although their activities are weak as compared with human endogenous estrogens, the consumption of phytoestrogens may have clinically significant consequences. A number of botanicals, or the compounds contained therein, have been identified as putative estrogenic agents, but consensus in the biomedical community has been hampered by conflicting data from various in vitro and in vivo models of estrogenic activity. Phytoestrogens may serve as chemopreventive agents while at the same time being capable of promoting growth in estrogen receptor positive cancer cell lines. Furthermore, they may exert their estrogenic influence through receptor-dependent and/or receptor-independent mechanisms. These findings have led to speculation that phytoestrogen intake might be ill advised for patients at an increased risk for hormone-dependent cancers, cancer patients, or cancer survivors. This article will attempt to sort out discrepancies between various experimental models and establish whether certain herbs possess estrogenic activity. The review will focus on 5 popular botanical dietary supplements: Trifolium pratense (red clover), Cimicifuga racemosa (black cohosh), Humulus lupulus (hops), Angelica sinensis (dong quai), and Glycyrrhiza glabra (licorice). It will address their mechanisms of action, clinical evidence bases, and implications for use in cancer.

Oestrogenic and (anti)androgenic activity of zearalenone and its metabolites in two in vitro yeast bioassays

Selected resorcylic acid lactones (RALs) – zearalenone (ZEA), α-zearalanol (α-ZAL), β-zearalanol (β-ZAL), α-zearalenol (α-ZOL) and β-zearalenol (β-ZOL) were investigated for their oestrogenic and (anti)androgenic activity using two in vitro RIKILT yeast Estrogen and Androgen bioAssays. Our results show that all tested compounds are able to induce hERα-dependent transcription and the rank of their potencies, based on EC50 values is as follows: α-ZOL > α-ZAL > ZEA > β-ZAL > β-ZOL. None of the tested compounds appeared to be androgenic when tested individually at concentrations ranging from 0.1 pM to 0.1 mM. However, all RALs inhibited 17β-testosterone-induced transcriptional activity. The highest antiandrogenic potential showed α-ZOL, β-ZAL and β-ZOL with the IC50 of 6.2 μM, 11.5 μM and 15.2 μM, respectively. When compared with flutamide, for which a relative antiandrogenic potency (RAAP) was assumed as 100%, the corresponding RAAPs for α-ZOL, β-ZAL and β-ZOL were 220, 119 and 89.8%, respectively. In summary, our study revealed that RALs possess not only oestrogenic, but also antiandrogenic activity. Further research is warranted to clarify the role of disruption of androgen receptor signalling in humans and animals.

Origin of the response to adrenal and sex steroids: Roles of promiscuity and co-evolution of enzymes and steroid receptors

Many responses to adrenal and sex steroids are mediated by receptors that belong to the nuclear receptor family of transcription factors. We investigated the co-evolution of these vertebrate steroid receptors and the enzymes that synthesize adrenal and sex steroids through data mining of genomes from cephalochordates [amphioxus], cyclostomes [lampreys, hagfish], chondrichthyes [sharks, rays, skates], actinopterygii [ray-finned fish], sarcopterygii [coelacanths, lungfishes and terrestrial vertebrates]. An ancestor of the estrogen receptor and 3-ketosteroid receptors evolved in amphioxus. A corticoid receptor and a progesterone receptor evolved in cyclostomes, and an androgen receptor evolved in gnathostomes. Amphioxus contains CYP11, CYP17, CYP19, 3β/Δ5-4-HSD and 17β-HSD14, which suffice for the synthesis of estradiol and Δ5-androstenediol. Amphioxus also contains CYP27, which catalyzes the synthesis of 27-hydroxy-cholesterol, another estrogen. Lamprey contains, in addition, CYP21, which catalyzes the synthesis of 11-deoxycortisol. Chondrichthyes contain, in addition, CYP11A, CYP11C, CYP17A1, CYP17A2. Coelacanth also contains CYP11C1, the current descendent from a common ancestor with modern land vertebrate CYP11B genes, which catalyze the synthesis of cortisol, corticosterone and aldosterone. Interestingly, CYP11B2, aldosterone synthase, evolved from separate gene duplications in at least old world monkeys and two suborders of rodents. Sciurognathi (including mice and rats) and Hystricomorpha (including guinea pigs). Thus, steroid receptors and steroidogenic enzymes co-evolved at key transitions in the evolution of vertebrates. Together, this suite of receptors and enzymes through their roles in transcriptional regulation of reproduction, development, homeostasis and the response to stress contributed to the evolutionary diversification of vertebrates. This article is part of a Special Issue entitled 'Steroid/Sterol signaling'.

Sex steroids in uterine endometrial cancers

Some uterine endometrial cancers conserve estrogen dependency in advancement. However, the concept of advancement in tumor is complicated, because it involves simple growth in primary tumor and secondary spreading. The expression manner of estrogen receptor alpha exon 5 splicing variant, ER beta, progesterone receptor-A (N-terminus deletion mutant) is associated with metastatic potential in uterine endometrial cancers. Increased estrogen-related receptor alpha expression is related to tumor advancement with the loss of estrogen dependency. Steroid receptor coactivator-3 contributes to tumor progression and can be used as a treatment target for advanced uterine endometrial cancers. Estrogen responsive oncogenes, c-jun and c-Ha-ras, are not modi-fied by progestin in uterine endometrial cancer cells and are considered to be an instinct phenotype as such cancers. By contrast, metastatic potential of estrogen-dependent uterine endometrial cancers can be partially controlled by progestin via metastasis-related genes, E-cadherin/catenins, plasminogen activator inhibitor-1, vascular endothelial growth factor. Thus, sex steroids related phenomena are impress-ive in the advancement of uterine endometrial cancers.

SETD6 controls the expression of estrogen-responsive genes and proliferation of breast carcinoma cells

The lysine methyltransferase SETD6 modifies the histone variant H2AZ, a key component of nuclear receptor-dependent transcription. Herein, we report the identification of several factors that associate with SETD6 and are implicated in nuclear hormone receptor signaling. Specifically, SETD6 associates with the estrogen receptor α (ERα), histone deacetylase HDAC1, metastasis protein MTA2, and the transcriptional co-activator TRRAP. Luciferase reporter assays identify SETD6 as a transcriptional repressor, in agreement with its association with HDAC1 and MTA2. However, SETD6 behaves as a co-activator of several estrogen-responsive genes, such as PGR and TFF1. Consistent with these results, silencing of SETD6 in several breast carcinoma cell lines induced cellular proliferation defects accompanied by enhanced expression of the cell cycle inhibitor CDKN1A and induction of apoptosis. Herein, we have identified several chromatin proteins that associate with SETD6 and described SETD6 as an essential factor for nuclear receptor signaling and cellular proliferation.

Genetically modified whole-cell bioreporters for environmental assessment

Living whole-cell bioreporters serve as environmental biosentinels that survey their ecosystems for harmful pollutants and chemical toxicants, and in the process act as human and other higher animal proxies to pre-alert for unfavorable, damaging, or toxic conditions. Endowed with bioluminescent, fluorescent, or colorimetric signaling elements, bioreporters can provide a fast, easily measured link to chemical contaminant presence, bioavailability, and toxicity relative to a living system. Though well tested in the confines of the laboratory, real-world applications of bioreporters are limited. In this review, we will consider bioreporter technologies that have evolved from the laboratory towards true environmental applications, and discuss their merits as well as crucial advancements that still require adoption for more widespread utilization. Although the vast majority of environmental monitoring strategies rely upon bioreporters constructed from bacteria, we will also examine environmental biosensing through the use of less conventional eukaryotic-based bioreporters, whose chemical signaling capacity facilitates a more human-relevant link to toxicity and health-related consequences.

A versatile transfection assay system to evaluate the biological effects of diverse industrial chemicals

Gene expression processes are now recognized as important targets of the toxic effects exerted by industrial chemicals. The transient transfection assay is a powerful tool to evaluate such effects. Thus, we developed a versatile assay system by constructing a basic reporter plasmid in which the regulatory DNA sequence to be studied can easily be substituted. To verify the performance of this system, reporter plasmids carrying any of the three distinct regulatory sequences, estrogen responsive element (ERE), glucocorticoid responsive element (GRE) and xenobiotic responsive element (XRE) were constructed. After transfection of human cells, these plasmids successfully expressed the relevant reporter genes in response to specific inducers, β-estradiol, dexamethasone and 3-methylcholanthrene, respectively. Several industrial chemicals were assayed using these reporter plasmids, and the ability of p-dimethylaminoazobenzene to elevate GRE- and XRE-mediated transcription was detected. α-Naphthylamine and o-tolidine were also observed to increase the XRE-mediated response. The transfection assay system established here will be useful to evaluate the effects of a wide variety of industrial chemicals.

Yeast one-hybrid assays: a historical and technical perspective

Since its development about two decades ago, the yeast one-hybrid (Y1H) assay has become an important technique for detecting physical interactions between sequence-specific regulatory transcription factor proteins (TFs) and their DNA target sites. Multiple versions of the Y1H methodology have been developed, each with technical differences and unique advantages. We will discuss several of these technical variations in detail, and also provide some ideas for how Y1H assays can be further improved.

Isoflavones are safe compounds for therapeutical applications - evaluation of in vitro data

Isoflavone-rich food and food supplements have gained increasing popularity also in the Western world. Their weak estrogenic effect has been considered as a potential risk, although all epidemiological studies and clinical trials show a significant cancer protection and decreased risk of cardiovascular diseases. In vitro data suggest that the concerted action of the isoflavones and their metabolites show antiproliferative behaviour, reduce angiogenesis, reduce tumor progression and exert antiinflammatory effects. For the evaluation of the biological effects, special emphasis has to be put on the concerted action between the isoflavones and their metabolites. For instance, while isolated genistein shows some growth promoting effect at low concentrations, the metabolite equol or soy extract show growth retardation as well as higher concentrations of genistein do. The isoflavones have multiple affinities to other members of the steroid hormone receptor superfamily. The beneficial effect on metabolic diseases and weight reduction by isoflavone consumption can be partly explained by its affinity for the PPAR family. In light of the in vitro experiments, together with the epidemiological observations and the clinical experience, isoflavones can be considered as safe compounds and their consumption as food and food supplements has to be promoted.

Exogenous and endogenous hormones, mammographic density and breast cancer risk: can mammographic density be considered an intermediate marker of risk?

Elevated mammographic density measures are a well-established, relatively strong risk factor for breast cancer development. A systematic review of prospective cohort studies and cross-sectional studies strikingly establishes parallels between the associations of combined postmenopausal estrogen and progestin replacement therapy with, on the one hand, mammographic densities and, on the other hand, breast cancer risk. Other parallel observations were the inverse associations of both mammographic density and breast cancer risk with the selective estrogen receptor modulator tamoxifen, and direct associations with prolactin. Paradoxically, however, high mammographic density has been found associated with higher risks of both estrogen- and progesterone-receptor positive (ER+/ PR+) and negative (ER-/PR-) breast cancers, while hormone replacement therapy (HRT) use, but also circulating (blood) levels of androgens, estrogens, and prolactin appear to be associated more specifically to the risk of ER+ tumors. The effects of aromatase inhibitors and gonadotropin-releasing hormone agonists on breast density, as well as on breast cancer risk, still require further investigation. Regarding circulating levels of insulin-like growth factor (IGF)-I or IGFBP-3, studies did not show fully consistent relationships with mammographic density measures and breast cancer risk. In view of these various findings, it is impossible, at present, to propose mammographic density measures as an intermediate risk-related phenotype, integrating the effects of exogenous and/or endogenous hormones on the risk of developing breast cancer.

Detecting ligands and dissecting nuclear receptor-signaling pathways using recombinant strains of the yeast Saccharomyces cerevisiae

This is a general protocol for the identification of natural and xenobiotic ligands of metazoan nuclear receptors (NRs) expressed in yeast. Yeast engineered to express an NR and a response element-driven reporter gene provide a system to detect and quantify ligand-dependent transcriptional activity. Such assays allow researchers to measure different types of ligands and determine dose-dependent activation of NRs. This methodology can also be used to examine the components of signal transduction pathways when conducted with mutant or engineered yeast strains expressing additional proteins or having alternate DNA response elements. This assay typically takes 2-3 d to complete, but most of this time entails cell growth rather than 'hands on' time.

Structure-activity relationships of synthetic progestins in a yeast-based in vitro androgen bioassay

The recent identification of tetrahydrogestrinone (THG), a non-marketed designer androgen used for sports doping but previously undetectable by established mass spectrometry-based urine drug screens, and its production by a facile chemical modification of gestrinone has raised concerns about the risks of developing designer androgens from numerous marketed progestins. We therefore have used yeast-based in vitro androgen and progesterone bioassays to conduct a structure-activity study assessing the intrinsic androgenic potential of commercially available progestins and their derivatives, to identify those compounds or structures with the highest risk of forming a basis for such misapplication. Progestins had a wide range of androgenic bioactivity that was not reliably predicted for individual steroids by their progestin bioactivity. 17alpha-Hydroxyprogesterone and 19-norprogesterone derivatives with their bulky 17beta-substituents were strong progestins but generally weak androgens. 17alpha-Ethynylated derivatives of testosterone, 19-nortestosterone and 18-methyl-19-nortestosterone such as gestrinone, ethisterone, norethisterone and norgestrel had the most significant intrinsic androgenicity of all the commercially marketed progestins. Facile chemical modification of the 17alpha-ethynyl group of each of these progestins produces 17alpha-methyl, ethyl and allyl derivatives, including THG and norbolethone, which further enhanced androgenic bioactivity. Thus by using the rapid and sensitive yeast bioassay we have screened a comprehensive set of progestins and associated structures and identified the ethynylated testosterone, 19-nortestosterone and 18-methyl-19-nortestosterone derivatives as possessing the highest risk for abuse and potential for conversion to still more potent androgens. By contrast, modern progestins such as progesterone, 17alpha-hydroxyprogesterone and 19-norprogesterone derivatives had minimal androgenic bioactivity and pose low risk.

Intron 1 and exon 1 alpha estrogen receptor gene polymorphisms in women with endometriosis

OBJECTIVE

To evaluate the association of intron 1 and exon 1 polymorphisms in the estrogen receptor alpha gene (ER-alpha) with endometriosis in women.

DESIGN

Association study.

SETTING

Endometriosis Unit, Federal University of São Paulo.

PATIENT(S)

The control group consisted of volunteers older than 45 years who had no evidence of endometriosis antecedents. Two groups with the disease were evaluated: the first group had stage I or II endometriosis and the second group stage III or IV.

INTERVENTION(S)

Polymerase chain reaction (PCR) followed by digestion with HaeIII and MspI endonucleases (RFLP) were applied to detect intron 1 and exon 1 polymorphisms, respectively, in a total of 125 controls and 105 affected women.

MAIN OUTCOME MEASURE(S)

Frequency and distribution of HaeIII and MspI polymorphisms in ER-alpha.

RESULT(S)

No significant differences in the frequency of polymorphisms either in intron 1 or exon 1 of ER-alpha were found when endometriosis patients were compared with control subjects. Furthermore, the frequency of ER-alpha polymorphisms within the two different groups of patients with disease was statistically similar. The odds ratio between presence of intron 1 single-nucleotide polymorphisms (SNP) and endometriosis was 0.904, and the odds ratio between exon 1 SNP and endometriosis was 0.976.

CONCLUSION(S)

The evaluated polymorphisms were not associated with endometriosis.

Determination of the differential estrogenicity of isoflavonoids by E2-ER-ERE-dependent gene expression in recombinant yeast and MCF-7 human breast cancer cells

The use of phytoestrogens-containing natural sources as alternative hormone replacement therapy (HRT) has been a subject of debate for decades. Development of assays to characterize these phytoestrogens is required. In this study, differential estrogenicities of five isoflavonoids found in red clover and soy, including biochanin A, daidzein, formononetin, genistein and glycitein were examined in a yeast-based screen system with a classical palindromic estrogen response element (ERE)-ADE2 reporter and in a MCF-7 cell culture system with mRNA levels of ER-dependent genes compared. In a yeast-based assay, five isoflavonoids showed various extents of estrogenic potencies. A collection of primary estrogen receptor (ER)-regulated genes by estradiol (E2), including hTERT, c-MYC, BCL2 and Ha-ras (oncogenic) and quinone reductase (QR), human complement 3 (C3) and COX7RP (non-oncogenic) were selected as marker genes for a MCF-7 cell-based endogenous gene expression assay. The results indicated that the mRNA levels of these E2-ER-ERE-dependent marker genes were regulated differentially by five isoflavonoids, leading to distinct expression patterns, which are also significantly different from that of E2. Moreover, the anti-estrogenic effects of biochanin A and formononetin on E2-induced transcriptions of marker genes in MCF-7 cells were also displayed. Taken together, these results are significant for these naturally occurring isoflavonoids regarding the issues of safety and efficacy.

Development of a yeast-based assay to determine the (anti)androgenic contaminants from pulp and paper mill effluents in India

We have constructed an efficient and reliable yeast-based detection system to evaluate the androgenic activity of endocrine disruptors from pulp and paper mill effluents (PPME). This system consists of human androgen receptor and androgen response elements driven β-galactosidase genes transformed in yeast, Saccharomyces cerevisiae. The transcriptional activation by known androgens, correlated with androgenic activities as measured by other assay systems. This assay system when applied to evaluate anti-androgenic activities, the known anti-androgens effectively inhibited reporter gene induction by testosterone. The specificity of the assay was tested by incubating the transformed cells with supraphysiological concentrations of non-androgenic steroids and none of them gave a significant response. The extracted PPME from five different mills demonstrated strong androgenic activities (about five- to eight-folds over control). These results suggest that PPME are rich in androgenic chemicals and the employed detection system could be applicable to primary screening for effectors on androgen receptor functions.

An evolvable oestrogen receptor activity sensor: development of a modular system for integrating multiple genes into the yeast genome

To study a gene interaction network, we developed a gene-targeting strategy that allows efficient and stable genomic integration of multiple genetic constructs at distinct target loci in the yeast genome. This gene-targeting strategy uses a modular plasmid with a recyclable selectable marker and a multiple cloning site into which the gene of interest is cloned, flanked by two long regions of homology to the target genomic locus that are generated using adaptamer primers. We used this strategy to integrate into a single yeast strain components of the oestrogen receptor (ER) signalling network, comprising the human ERalpha and three reporter genes driven by oestrogen response elements (EREs). The engineered strain contains multiple reporters of ligand-dependent receptor signalling, providing sensitive, reproducible, rapid, low-cost quantitative assays of ERalpha activity in order to screen potential receptor agonists. Further, because two of the ERE-driven reporter genes are required for growth in deficient media, the strain's growth rate-and therefore its fitness-depends on ligand-induced ERalpha activity. This evolvable oestrogen receptor activity sensor (EERAS) can therefore provide the foundation of a long-term experimental evolution strategy to elucidate ER structure-function relations and ligand-receptor evolution.

An improved system for estradiol-dependent regulation of gene expression in yeast

Background

Saccharomyces cerevisiae is widely utilized in basic research as a model eukaryotic organism and in biotechnology as a host for heterologous protein production. Both activities demand the use of highly regulated systems, able to provide accurate control of gene expression in functional analysis, and timely recombinant protein synthesis during fermentative production. The tightly regulated GAL1-10 promoter is commonly used. However, induction of the GAL system requires the presence of the rather expensive inducer galactose and the absence of glucose in the culture media. An alternative to regulate transcription driven by GAL promoters, free of general metabolic changes, is the incorporation of the hybrid Gal4-ER-VP16 protein developed by D. Picard. This chimeric protein provides galactose-independent activation of transcription from GAL promoters in response to β-estradiol, even in the presence of glucose. However, constitutive expression of this transactivator results in relatively high basal activity of the GAL promoters, therefore limiting the gene expression capacity that is required for a number of applications.

Results

In order to improve this expression tool, we have introduced additional regulatory elements allowing a simultaneous control of both the abundance and the intrinsic activity of the Gal4-ER-VP16 chimeric transactivator. The most efficient combination was obtained by placing the coding sequence of the hybrid activator under the control of the GAL1 promoter. This configuration results in an amplification feedback loop that is triggered by the hormone, and ultimately leads to the enhanced regulation of recombinant genes when these are also driven by a GAL1 promoter. The basal expression level of this system is as low as that of native GAL-driven genes in glucose-containing media.

Conclusion

The feedback regulatory loop that we have engineered allows a 250-fold induction of the regulated gene, without increasing the basal activity of the target promoter, and achieving a 12-fold higher regulation efficiency than the previous configuration.

Regulation of human estrogen receptor alpha-mediated gene transactivation in Saccharomyces cerevisiae by human coactivator and corepressor proteins

Human estrogen receptor alpha (ERalpha)-mediated transcription activation was evaluated in the yeast Saccharomyces cerevisiae using both the native ERalpha and a G400V variant. A previous study demonstrated that coexpression of human SRC-1, a potent stimulator of ERalpha function in mammalian cells, potentiated ERalpha-mediated gene expression in yeast over five-fold in an E(2)-dependent manner. In the present study, two additional human coactivator proteins were shown to potentiate ERalpha-mediated gene expression in yeast. SRC2 potentiated transactivation two- to three-fold while SRC3 potentiated transactivation five- to eight-fold. Both human coactivators potentiated both the native ERalpha and the G400V variant in an E(2)-dependent manner. The effect of a human corepressor protein was also evaluated in yeast. Repressor of estrogen receptor activity (REA) did not affect E(2)-induced transactivation by ERalpha (either isoform). However, in a strain that coexpressed human SRC1, REA reduced E(2)-induced transactivation to that observed with ERalpha alone. Furthermore, repression of SRC1 potentiation was specific for the native ERalpha since REA had no effect on SRC1 potentiation of the G400V variant. Additionally, REA repression was specific for SRC1 since potentiation of ERalpha (either isoform) transactivation by SRC2 and SRC3 was unaffected by coexpression of REA. These results support previous observations in mammalian cells that REA does not prevent ERalpha from binding to DNA but does inhibit potentiation of ERalpha-mediated transactivation by SRC1. The results in the present study further characterize REA-mediated repression, and demonstrate the utility of this yeast system for dissecting molecular mechanisms involved in regulating gene transactivation by human ERalpha.

Signaling by estrogens

By regulating activities and expression levels of key signaling molecules, estrogens control mechanisms that are responsible for crucial cellular functions. Ligand binding to estrogen receptor (ER) leads to conformational changes that regulate the receptor activity, its interaction with other proteins and DNA. In the cytoplasm, receptor interactions with kinases and scaffolding molecules regulate cell signaling cascades (extranuclear/nongenomic action). In the nucleus, estrogens control a repertoire of coregulators and other auxiliary proteins that are associated with ER, which in turn determines the nature of regulated genes and level of their expression (genomic action). The combination of genomic and nongenomic actions of estrogens ultimately confers the cell-type and tissue-type selectivity. Recent studies have revealed some important new insights into the molecular mechanisms underlying ER action, which may help to explain the functional basis of existing selective ER modulators (SERMs) and provide evidence into how ER might be selectively targeted to achieve specific therapeutic goals. In this review, we will summarize some new molecular details that relate to estrogen signaling. We will also discuss some new strategies that may potentially lead to the development of functionally selective ER modulators that can separate between the beneficial, prodifferentiative effects in bone, the cardiovascular system and the CNS as well as the "detrimental," proliferative effects in reproductive tissues and organs.

GFP-reporter for a high throughput assay to monitor estrogenic compounds

In vitro test systems using yeast cells are a useful tool for the determination of the estrogenic activity of estrogens, phyto- and xeno-estrogens and can be used for monitoring large sample numbers in a routine analysis procedure. Our conventional transactivation assay functions with an expression plasmid expressing estrogen receptor alpha (ERalpha) under the control of a copper-inducible CUP1 promoter and a reporter plasmid expressing beta-galactosidase under the control of the vitellogenin estrogen response element (ERE). In the novel yeast screen system the lacZ gene in the reporter plasmid was substituted by a gene for green fluorescent protein (GFP). Incubation of yeast with various concentrations of estrogenically active substances led to expression of the reporter gene product GFP in a dose dependent manner. The yeast transactivation assay was further down-scaled to be performed in a microplate scale, which is an important step to facilitate handling of large sample numbers. The sensitivity and reproducibility of the novel test system could be confirmed by analysis of the potencies of various estrogenically active substances. Thus, the newly developed yeast estrogen screen using GFP as a reporter can substitute the assay that has been used for a period of several years.

Genome-wide linkage analyses and candidate gene fine mapping for HDL3 cholesterol: the Framingham Study

High density lipoprotein cholesterol (HDL-C) is inversely associated with coronary heart disease and has a genetic component; however, linkage to HDL-C is not conclusive. Subfractions of HDL, such as HDL(3)-C, may be better phenotypes for linkage studies. Using HDL(3)-C levels measured on 907 Framingham Heart Study subjects from 330 families around 1987, we conducted a genome-wide variance components linkage analysis with 401 microsatellite markers spaced approximately 10 centimorgan (cM) apart. Nine candidate genes were identified and annotated using a bioinformatics approach in the region of the highest linkage peak. Twenty-eight single nucleotide polymorphisms (SNPs) were selected from these candidate genes, and linkage and family-based association fine mapping were conducted using these SNPs. The highest multipoint log-of-the-odds (LOD) score from the initial linkage analysis was 3.7 at 133 cM on chromosome 6. Linkage analyses with additional SNPs yielded the highest LOD score of 4.0 at 129 cM on chromosome 6. Family-based association analysis revealed that SNP rs2257104 in PLAGL1 at approximately 143 cM was associated with multivariable adjusted HDL(3) (P = 0.03). Further study of the linkage region and exploration of other variants in PLAGL1 are warranted to define the potential functional variants of HDL-C metabolism.

Metabolically independent and accurately adjustable Aspergillus sp. expression system

Filamentous fungi are well-established expression hosts often used to produce extracellular proteins of use in the food and pharmaceutical industries. The expression systems presently used in Aspergillus species rely on either strong constitutive promoters, e.g., that for glyceraldehyde-3-phosphate dehydrogenase, or inducible systems derived from metabolic pathways, e.g., glaA (glucoamylase) or alc (alcohol dehydrogenase). We describe for Aspergillus nidulans and Aspergillus niger a novel expression system that utilizes the transcriptional activation of the human estrogen receptor by estrogenic substances. The system functions independently from metabolic signals and therefore can be used with low-cost, complex media. A combination of positive and negative regulatory elements in the promoter drives the expression of a reporter gene, yielding a linear dose response to the inducer. The off status is completely tight, yet the system responds within minutes to induction and reaches a level of expression of up to 15% of total cell protein after 8 h. Both Aspergillus species are very sensitive to estrogenic substances, and low-cost inducers function in the picomolar concentration range, at which estrogenic substances also can be found in the environment. Given this high sensitivity to estrogens, Aspergillus cells carrying estrogen-responsive units could be used to detect xenoestrogens in food or in the environment.

Association of estrogen receptor 1 intron 1 C/T polymorphism in Korean vitiligo patients

BACKGROUND

Vitiligo is a common disease characterized by cutaneous white maculae due to loss of melanocytes. It is a polygenic disease, however, the exact pathogenesis of vitiligo is not yet known. The estrogen receptor (ESR) 1 gene was selected as a candidate gene because some researchers treated vitiligo successfully with the steroid-thyroid hormone mixture containing estrogen. Furthermore ESR was expressed in the melanocytes which have an important role in the pigmentation. The polymorphisms of ESR1 gene in vitiligo patients was not reported yet.

OBJECTIVE

To determine whether polymorphisms of ESR1 gene were associated with susceptibility to vitiligo patients in Korean population.

METHODS

We conducted case-control association study of vitiligo patients (120) and healthy controls (254). Genotypes of ESR1 gene (intron 1 C/T, exon 4 C/G, and exon 8 A/G) were determined by polymerase chain reaction followed by restriction enzyme digestion.

RESULTS

Intron 1 T/C allele frequency was significantly different between patients and controls (P = 0.034). Intron 1 T/C genotype distribution (P = 0.021) and allele frequency (P = 0.013) were different between female vitiligo patients and female controls. Intron 1 T/C allele frequency showed significantly difference between generalized type of vitiligo patients and controls (P = 0.044). Genotype distributions and allele frequencies of exon 4 C/G and exon 8 A/G polymorphisms were not different between patients and controls.

CONCLUSION

The present study suggests that ESR1 may be a possible risk factor for female or generalized type of vitiligo patients.

Removal of estrogenicity in Swedish municipal sewage treatment plants

The human estrogen receptor alpha-test, hosted in a yeast strain, was used to quantify estrogenicity in three-week composite samples of untreated and treated effluents from 20 Swedish municipal sewage treatment plants. The treatment plants were selected to represent different treatment processes regarding chemical precipitation and microbial procedures. The discharge from Swedish domestic sewage treatment plants contained estrogenic compounds corresponding to <0.1-15 ng estradiol equivalents/L. Low levels of estrogenic activity were also found in a river receiving municipal effluents, 3.5-35 km downstream the outlet from a sewage treatment works. The range of estrogenicity in untreated, raw sewage effluents was found to be 1-30 ng estradiol equivalents/L. Generally, wastewater treatment reduced the estrogenicity and extended biological treatment was most effective in its removal. Activated sludge treatment tended to be more effective than trickling filters, whereas chemical precipitation using iron or aluminium salts without biological treatment showed little effectivity. The study showed that treatment methods in current use are able to eliminate or largely reduce estrogenicity in domestic wastewater.

Endocrine disruptors: effects on male fertility and screening tools for their assessment

During the recent decades, a lot of research has been performed concerning the so-called "endocrine disruptors", which are widespread in the environment. These compounds of anthropogenic or natural origin mimic the action of sex hormones and can interfere with the endocrine system. The largest body of evidence exists for those compounds that are estrogenic in nature, but the amount of experimental data on other types of interactions, especially anti-androgenic, steadily increases. Because of the growing public and scientific concern, epidemiological studies have been initiated to analyse the short and long-term effects of endocrine disruptors. In addition, a number of assays have been developed and are undergoing validation, aiming at high throughput screening of chemical agents with suspected endocrine disrupting properties. In the present review, we briefly describe the results of epidemiological studies dealing with observed time trends in male fertility disorders. In the second part of the article, an overview is given of the different classes of endocrine disruptors, followed by a description of the most important in vitro and in vivo bioassays, used to screen for the possible endocrine disruptive capacity of chemicals, together with future research needs for in vitro test development.

Ini, a small nuclear protein that enhances the response of the connexin43 gene to estrogen

This article describes the structural and functional characterization of Ini (AF495522), a novel highly conserved zinc-finger protein that had been identified by screening an estrogen-induced rat myometrial expression library. Ini localizes to the nucleus of HeLa cells and binds to the proximal connexin43 (cx43) promoter, as demonstrated by EMSA. In addition, transient transfection experiments performed with estrogen receptor alpha (ERalpha) cDNA show that overexpression of Ini enhances, in a dose-dependent fashion, the up-regulation of the cx43 gene by estrogen. On binding to the cx43 promoter, Ini stimulates the transcriptional activating function (AF)-1, but not the AF-2, of the ERalpha. This makes Ini one of the few known coactivators specific for AF-1. Because estrogen up-regulates Ini mRNA in the myometrium, it is likely that Ini's physiological role in this tissue is to modulate the response of the cx43 gene to estrogen. Transfection studies with an Ini antisense construct seem to indicate that Ini plays an additional role in the cellular response to estrogen affecting both AF-1 and AF-2 activities of the ERalpha. This broader effect may be associated with cell cycle progression that in yeast has been shown to require Ini.

Potentiation of human estrogen receptor alpha-mediated gene expression by steroid receptor coactivator-1 (SRC-1) in Saccharomyces cerevisiae

The yeast Saccharomyces cerevisiae was used to reconstruct a human estrogen receptor alpha (ERalpha)-mediated transcription activation system. The level of reporter gene activation was dependent on both the position of the estrogen response element (ERE) relative to the translation start site and the number of EREs in the hybrid promoter. A G400V amino acid alteration in the ERalpha polypeptide decreased sensitivity to 17beta-estradiol (E(2)), demonstrating the hormone responsiveness of ERalpha to be qualitatively and quantitatively similar in yeast and mammalian cells. Coexpression of SRC-1a, a potent stimulator of ERalpha function in mammalian cells, potentiated ERalpha-mediated gene expression over fivefold in a E(2)-dependent manner. Deletion of 56 amino acids at the C-terminal end of SRC-1a resulted in a protein with enhanced ability to potentiate ERalpha-mediated gene expression, which mimics the activity of the same truncation in human SRC-1a as well as the SRC-1e isoform that has the 56 C-terminal residues replaced with a different 14 amino acid peptide. The selective estrogen receptor modulator tamoxifen acted as a weak agonist of ERalpha-mediated gene expression and this weak activity was potentiated by SRC-1. Tamoxifen had no effect on E(2)-induced gene activation in either the presence or absence of SRC-1. In contrast to previously reported yeast-based ERalpha-transactivation systems, the system reported here in which SRC-1 functions as a bona fide coactivator should permit a more thorough dissection of the factors involved in ERalpha-mediated transcriptional activation.

Current status of estrogen receptors

Increasing knowledge on structure and function of estrogen receptors is providing information on the mechanism of action of estrogen agonists, as well as antagonists, and in understanding their tissue-selective action. However, there are still many factors associated with estrogen response which are poorly understood. Therefore, the task of designing a tissue-selective estrogen for use as a pharmaceutical in estrogen-dependent disorders remains an uncertain game. This review provides information on the current status of estrogen receptors for a better understanding.

Expression of estrogen receptor beta exon-deleted variant mRNAs in ovary and uterine endometrium

Various estrogen receptor beta exon-deleted variant (ER-beta EDV) mRNAs were expressed in human ovary and uterine endometrium. Estrogen receptor beta (ER-beta) completely or partially deleted exon n is expressed as ER-beta EnDV or En'DV, respectively. The mRNAs for ER-beta single exon-deleted variant (EDV), ER-beta E2DV, E4DV, E5DV and E6DV; for ER-beta double exon-deleted variants, ER-beta E1'+2DV, E4+5DV and E5+6DV; and for ER-beta triple exon-deleted variants, ER-beta E2'+3+4DV and E4+5+6DV were detected. In ER-beta E2DV, E4+5DV, E5DV and E6DV mRNAs, the new stop codon is made in the exon following the deleted exon(s), and the new proteins may lack the corresponding domains. In ER-beta E1'+2DV, E2'+3+4DV, E4DV, E4+5+6DV and E5+6DV mRNAs, the original stop codon is still present, and the new proteins may conserve the new short amino acid sequences surrounding the deleted exons. ER-beta E1'+2DV, E2DV, E2'+3+4DV, E4DV, E4+5DV and E4+5+6 are unlikely to work as a transcription factors. On the other hand, ER-beta E5DV, E6DV and E5+6DV lack only the ligand-binding domain, and might work as dominant positive or negative factors. Therefore, ER-beta E5DV, E6DV and E5+6DV, constitutively expressed in human ovary and uterine endometrium might, in part regulate estrogen responsiveness.

High-throughput cell-based assays in yeast

With the sequencing of many genomes now completed, biologists are faced with the challenge of deciphering the function and association of an immense number of predicted proteins. Comprehension of the networks of proteins and chemicals that comprise the cells and tissues of an organism, and the specific roles of proteins in these networks, will be a necessary next step to understanding cellular function in healthy and diseased states. In the past decade, the budding yeast Saccharomyces cerevisiae has emerged as an important tool for large-scale functional genomics analyses. This review describes the use of yeast cell-based assays in the post-genomic era, focusing on high-throughput functional genomics and drug discovery.