Nongenomic actions of estrogens and xenoestrogens by binding at a plasma membrane receptor unrelated to estrogen receptor alpha and estrogen receptor beta

Extra-nuclear signaling of estrogen receptors

Estrogen controls multiple biological functions through binding to estrogen receptors (ERs). Traditionally, ERs have been regarded as transcription factors regulating the expression of target genes. However, growing evidence of rapid estrogen's actions in a number of tissues has been accumulating and alternative mechanisms of signal transduction have been proposed. These so called "extra-nuclear actions" do not require gene expression or protein synthesis and are independent of the nuclear localization of ERs. Indeed, some of these actions are elicited by ERs residing at or near the plasma membrane. Membrane-associated molecules such as ion channels, G proteins, the tyrosine kinase c-Src as well as growth factor receptors are modulated by liganded ERs within the membrane, leading to the activation of downstream cascades such as mitogen-activated protein kinase, phosphatidylinositol 3-OH kinase, protein kinase A, and protein kinase C. These cascades mediate some important rapid actions of estrogen, such as the activation of nitric oxide synthesis or the remodeling of actin cytoskeleton. In addition, these pathways are critical for the regulation of the expression of a number of target proteins implicated in cell proliferation, apoptosis, differentiation, movement, and homeostasis. In this manner, the extra-nuclear pathways are tightly integrated with the genomic pathways to orchestrate the full spectrum of estrogen's biological functions. The recent advancements in the characterization of the molecular basis of the extra-nuclear signaling of estrogen helps to understand the role of estrogen on human cells, and may in future turn out to be of relevance for clinical purposes.

Epigenetic and phenotypic changes result from a continuous pre and post natal dietary exposure to phytoestrogens in an experimental population of mice

BACKGROUND

Developmental effects of exposure to endocrine disruptors can influence adult characters in mammals, but could also have evolutionary consequences. The aim of this study was to simulate an environmental exposure of an experimental population of mice to high amounts of nutritional phytoestrogens and to evaluate parameters of relevance for evolutionary change in the offspring. The effect of a continuous pre- and post-natal exposure to high levels of dietary isoflavones was evaluated on sexual maturity, morphometric parameters and DNA methylation status in mice. Adult mice male/female couples were fed ad libitum either with control diet (standard laboratory chow) or ISF diet (control diet plus a soy isoflavone extract at 2% (w/w) that contained the phytoestrogens genistein and daidzein). In the offspring we measured: i) the onset of vaginal opening (sexual maturation) in females, ii) weight and size in all pups at 7, 14, 21 and 42 days post-natal (dpn) and iii) DNA methylation patterns in skeletal alpha-actin (Acta1), estrogen receptor-alpha and c-fos in adults (42 dpn).

RESULTS

Vaginal opening was advanced in female pups in the ISF group, from 31.6 +/- 0.75 dpn to 25.7 +/- 0.48. No differences in size or weight at ages 7, 14 or 21 dpn were detected between experimental groups. Nevertheless, at age 42 dpn reduced size and weight were observed in ISF pups, in addition to suppression of normal gender differences in weight seen in the control group (males heavier that females). Also, natural differences seen in DNA methylation at Acta1 promoter in the offspring originated in the control group were suppressed in the ISF group. Acta1 is known to be developmentally regulated and related to morphomotric features.

CONCLUSION

This study demonstrates in mammals that individuals from a population subjected to a high consumption of isoflavones can show alterations in characters that may be of importance from an evolutionary perspective, such as epigenetic and morphometric characters or sexual maturation, a life history character.

Inhibition of rat aortic smooth muscle contraction by 2-methoxyestradiol

Recent studies suggest that 2-methoxyestradiol (2-ME), an estrogen metabolite, has a similar inhibitory effect as 17beta-estradiol (E2) on vascular tone. However, it is not known whether 2-ME mediates the effects of E2 or by what mechanism 2-ME regulates smooth muscle contraction. Therefore, we compared the effects of 2-ME and E2 on rat aortic smooth muscle contraction. A preincubation with 2-ME (10 microM) for 1 h inhibited phenylephrine (PE)-induced tension in endothelium-intact, but not -denuded, tissues, whereas E2 inhibited PE-induced contraction in both preparations. The effects of 2-ME and E2 on endothelium-intact preparations were prevented by L-NAME hydrochloride (a nitric oxide synthase inhibitor). The 2-ME treatment reduced PE-induced phosphorylation of the 20-kDa myosin regulatory light chain. The inhibitory effects of 2-ME and E2 were not affected by ICI-182780 (an estrogen receptor antagonist) or actinomycin D (a gene transcription inhibitor); however, the effect of 2-ME, but not E2, was prevented by cycloheximide (a protein synthesis inhibitor). Furthermore, the effect of E2 was not blocked by 1-aminobenzotriazole (a cytochrome P-450 inhibitor) or Ro 41-0960 (a catechol-O-methyltransferase inhibitor). The effect of 2-ME was not mimicked by microtubule-interfering agents (nocodazole or Taxol). We conclude that 2-ME inhibits smooth muscle contractility through an endothelium- and nitric oxide-dependent mechanism, which does not involve estrogen receptors or microtubule disruption. The effect of 2-ME, but not E2, involves de novo protein synthesis. 2-ME does not mediate the inhibitory effect of E2 on smooth muscle contraction. These results support a potentially important role of 2-ME in the regulation of smooth muscle tone in the vasculature.

Interference by atrazine and bisphenol-A with progestin binding to the ovarian progestin membrane receptor and induction of oocyte maturation in Atlantic croaker

Recent studies have shown that several environmental chemicals which disrupt classical genomic steroid actions can also interfere with nongenomic steroid actions initiated at the cell surface. The effects of bisphenol-A and atrazine on the nongenomic actions of a progestin, 17,20 beta,21-trihydroxy-4-pregnen-3-one (20 beta-S), on oocyte maturation (OM) were investigated an in vitro Atlantic croaker (Micropogonias undulatus) oocyte bioassay. Treatment of croaker follicle-enclosed oocytes with either bisphenol-A or atrazine blocked OM in response to 20 beta-S in a concentration-dependent manner at 10-25 microM (2.2-5.7 ppm) and higher concentrations. These compounds were also effective competitors at concentrations of 10(-6)-10(-5)M of [3H]-20 beta-S binding to the ovarian progestin membrane receptor that mediates the OM response to 20 beta-S. The results suggest that diverse classes of environmental chemicals can disrupt nongenomic progestin actions via receptor-mediated mechanisms.

Estrogen signaling characteristics of Atlantic croaker G protein-coupled receptor 30 (GPR30) and evidence it is involved in maintenance of oocyte meiotic arrest

Human G protein-coupled receptor 30 (GPR30) mediates estradiol-17beta (E2) activation of adenylyl cyclase in breast cancer cells and displays E2 binding typical of membrane estrogen receptors (mERs). We identified a mER in Atlantic croaker ovaries with characteristics similar to those of human GPR30. To confirm the proposed role of GPR30 as a mER in this distantly related vertebrate group, we cloned GPR30 from croaker ovaries and examined its distribution, steroid binding, and signaling characteristics. Western blot analysis showed the GPR30 protein (approximately 40 kDa) is expressed on the plasma membranes of croaker oocytes and HEK293 cells stably transfected with GPR30 cDNA. Plasma membranes prepared from croaker GPR30-transfected cells displayed high-affinity, limited-capacity, and displaceable binding specific for estrogens, characteristic of mERs. Consistent with previous findings with human GPR30, estrogen treatment of plasma membranes from both croaker ovaries and GPR30-transfected cells caused activation of a stimulatory G protein (Gs) resulting in increased cAMP production. Treatment with E2 as well as G-1, a specific GPR30 ligand, significantly reduced both spontaneous and progestin-induced maturation of both croaker and zebrafish oocytes in vitro, suggesting a possible involvement of GPR30 in maintaining oocyte meiotic arrest in these species. Injection of antisense oligonucleotides to GPR30 into zebrafish oocytes blocked the inhibitory effects of estrogen on oocyte maturation, confirming a role for GPR30 in the control of meiotic arrest. These findings further support our previous suggestion that GPR30 is a vertebrate mER. In addition, the results suggest GRP30 may play a critical role in regulating reentry into the meiotic cell cycle in fish oocytes.

Characteristics of membrane progestin receptor alpha (mPRalpha) and progesterone membrane receptor component 1 (PGMRC1) and their roles in mediating rapid progestin actions

Rapid, progestin actions initiated at the cell surface that are often nongenomic have been described in a variety of reproductive tissues, but until recently the identities of the membrane receptors mediating these nonclassical progestins actions remained unclear. Evidence has been obtained in the last 4-5 years for the involvement of two types of novel membrane proteins unrelated to nuclear steroid receptors, progesterone membrane receptors (mPRs) and progesterone receptor membrane component 1 (PGMRC1), in progestin signaling in several vertebrate reproductive tissues and in the brain. The mPRs, (M(W) approximately 40 kDa) initially discovered in fish ovaries, comprise at least three subtypes, alpha, beta and gamma and belong to the seven-transmembrane progesterone adiponectin Q receptor (PAQR) family. Both recombinant and wildtype mPRs display high affinity (K(d) approximately 5 nM), limited capacity, displaceable and specific progesterone binding. The mPRs are directly coupled to G proteins and typically activate pertussis-sensitive inhibitory G proteins (G(i)), to down-regulate adenylyl cyclase activity. Recent studies suggest the alpha subtype (mPRalpha) has important physiological functions in variety of reproductive tissues. The mPRalpha is an intermediary in progestin induction of oocyte maturation and stimulation of sperm hypermotility in fish. In mammals, the mPRalphas have been implicated in progesterone regulation of uterine function in humans and GnRH secretion in rodents. The single-transmembrane protein PGMRC1 (M(W) 26-28 kDa) was first purified from porcine livers and its cDNA was subsequently cloned from porcine smooth muscle cells and a variety of other tissues by different investigators. PGMRC1 and the closely-related PGMRC2 belong to the membrane-associated progesterone receptor (MAPR) family. The PGMRC1 protein displays moderately high binding affinity for progesterone which is 2- to 10-fold greater than that for testosterone and glucocorticoids, and also can bind to other molecules such as heme, cholesterol metabolites and proteins. The signal transduction pathways induced by binding of progesterone to PGMRC1 have not been described to date, although motifs for tyrosine kinase, kinase binding, SH2 and SH3 have been predicted from the amino acid sequence. Evidence has been obtained that PGMRC1 mediates the antiapoptotic affects of progesterone in rat granulosa cells. The PGMRC1 protein may also be an intermediary in the progesterone induction of the acrosome reaction in mammalian sperm. Despite these recent advances, many aspects of progestin signaling through these two families of novel membrane proteins remain unresolved. Biochemical characterization of the receptors has been hampered by rapid degradation of the partially purified proteins. A major technical challenge has been to express sufficient amounts of the recombinant receptors on the plasma membranes in eukaryotic systems to permit investigations of their progestin binding and signal transduction characteristics. Additional basic information on the molecular and cellular mechanisms by which mPRs and PGMRC1 interact with progestins, signal transductions pathways and other proteins will be required to establish a comprehensive model of nontraditional progestin actions mediated through these novel proteins.

Non-genomic actions of estrogens and their interaction with genomic actions in the brain

Ligands for the nuclear receptor superfamily have at least two mechanisms of action: (a) classical transcriptional regulation of target genes (genomic mechanisms); and (b) non-genomic actions, which are initiated at the cell membrane, which could also impact transcription. Though transcriptional mechanisms are increasingly well understood, membrane-initiated actions of these ligands are incompletely understood. This has led to considerable debate over the physiological relevance of membrane-initiated actions of hormones versus genomic actions of hormones, with genomic actions predominating in the endocrine field. There is good evidence that the membrane-limited actions of hormones, particularly estrogens, involve the rapid activation of kinases and the release of calcium and that these are linked to physiologically relevant scenarios in the brain. We show evidence in this review, that membrane actions of estrogens, which activate these rapid signaling cascades, can also potentiate nuclear transcription in both the central nervous system and in non-neuronal cell lines. We present a theoretical scenario which can be used to understand this phenomenon. These signaling cascades may occur in parallel or in series but subsequently, converge at the modification of transcriptionally relevant molecules such as nuclear receptors and/or coactivators. In addition, other non-cognate hormones or neurotransmitters may also activate cascades to crosstalk with estrogen receptor-mediated transcription, though the relevance of this is less clear. The idea that coupling between membrane-initiated and genomic actions of hormones is a novel idea in neuroendocrinology and provides us with a unified view of hormone action in the central nervous system.

Sex hormones' regulation of rodent physical activity: a review

There is a large body of emerging literature suggesting that physical activity is regulated to a varying extent by biological factors. Available animal data strongly suggests that there is a differential regulation of physical activity by sex and that the majority of this differential regulation is mediated by estrogen/testosterone pathways with females in many animal species having higher daily activity levels than males. The purpose of this manuscript is to review the mechanisms by which estrogen, progesterone, and testosterone affect the regulation of physical daily activity. This review lays the foundation for future investigations in humans as well as discussions about relative disease risk mediated by differential biological regulation of physical activity by sex.

Axogenic effect of estrogen in male rat hypothalamic neurons involves Ca(2+), protein kinase C, and extracellular signal-regulated kinase signaling

17-beta-Estradiol (E2) stimulates the growth of axons in male-derived hypothalamic neurons in vitro. This effect is not exerted through the classical intracellular estrogen receptor (ER) but depends on a membrane mechanism involving TrkB. In the present study, we investigate the intracellular signaling cascade that mediates the axogenic effect of E2. Treatment with an intracellular Ca(2+) chelator, a Ca(2+)-dependent protein kinase C (PKC) inhibitor, or two specific inhibitors of extracellular signal-regulated kinases (ERK) mitogen-activated protein kinases (MAPK) completely inhibited the E2-induced axogenesis. E2 and the membrane-impermeant construct E2BSA rapidly induced phosphorylation of ERK, which was blocked by the specific inhibitor of the ERK pathway UO126 but not by the ER antagonist ICI 182,780. Decrease of intracellular free Ca(2+) or disruption of PKC activation by Ro 32-0432 attenuated ERK activation, indicating the confluence of signals in the MAPK pathway. Subcellular analysis of ERK demonstrated that the phospho-ERK signal is augmented in the nucleus after 15 min of E2 stimulation. We have also shown that E2 increased phosphorylation of CREB via ERK signaling. In summary, this study demonstrates that E2, probably via a membrane-associated receptor, induces axonal growth by activating CREB phosphorylation through ERK signaling by a mechanism involving Ca(2+) and PKC activation.

Key developments in endocrine disrupter research and human health

Environmental etiologies involving exposures to chemicals that mimic endogenous hormones are proposed for a number of adverse human health effects, including infertility, abnormal prenatal and childhood development, and reproductive cancers (National Research Council, 1999; World Health Organization, 2002). Endocrine disrupters represent a significant area of environmental research with important implications for human health. This article provides an overview of some of the key developments in this field that may enhance our ability to assess the human health risks posed by exposure to endocrine disrupters. Advances in methodologies of hazard identification (toxicogenomics, transcriptomics, proteomics, metabolomics, bioinformatics) are discussed, as well as epigenetics and emerging biological endpoints.

Estrogens promote human testicular germ cell cancer through a membrane-mediated activation of extracellular regulated kinase and protein kinase A

Clinical and experimental studies have suggested that estrogens, the archetype of female hormones, participate in the control of male germ cell proliferation and that fetal exposure to environmental estrogens may contribute to hypofertility and/or to testicular germ cell cancer. However, the underlying mechanisms remain to be elucidated. 17beta-Estradiol (E2) conjugated to BSA was able to stimulate human testicular seminoma cell proliferation by triggering a rapid, nongenomic, membrane-mediated activation of ERK1/2 and cAMP-dependent protein kinase A (PKA). Both ERK1/2 and PKA participated in this promoting effect. This activation was associated with phosphorylation of the transcription factor cAMP response element-binding protein and the nuclear factor retinoblastoma protein. Enhanced proliferation together with ERK activation could be reversed by pertussis toxin, a G protein inhibitor. Estrogen receptors (ERs) in JKT-1 were characterized by immunofluorescence, subcellular fractioning, and Western blot. JKT-1 cells did not express ERalpha but ERbeta, which localized to the mitochondria and the nucleus but not to the membrane. Moreover, neither ICI-182,780, a classical ER antagonist, nor tamoxifen, a selective ER modulator, could reverse the 17beta-estradiol-BSA-induced promoting effect. Estrogens contribute to human testicular germ cell cancer proliferation by rapid activation of ERK1/2 and PKA through a membrane nonclassical ER. This nongenomic effect represents a new basis for understanding the estrogenic control of spermatogenesis and evaluating the role of fetal exposure to xenoestrogens during malignant transformation of testicular germ stem cells.

Derivation of a bisphenol A oral reference dose (RfD) and drinking-water equivalent concentration

Human exposure to bisphenol A (BPA) is due to that found in the diet, and BPA and its metabolites were detected at parts per billion (or less) concentrations in human urine, milk, saliva, serum, plasma, ovarian follicular fluid, and amniotic fluid. Adverse health effects in mice and rats may be induced after parenteral injection or after massive oral doses. Controlled ingestion trials in healthy adult volunteers with 5 mg d16-BPA were unable to detect parent BPA in plasma despite exquisitely sensitive (limit of detection = 6 nM) methods, but by 96 h 100% of the administered dose was recovered in urine as the glucuronide. The extensive BPA glucuronidation following ingestion is not seen after parenteral injection; only the parent BPA binds plasma proteins and estrogen receptors (ER). The hypothesis that BPA dose-response may be described by a J- or U-shape curve was not supported by toxicogenomic data collected in fetal rat testes and epididymes (after repeated parenteral exposure at 2-400,000 microg/kg-d), where a clear monotonic dose-response both in the numbers of genes and magnitude of individual gene expression was evident. There is no clear indication from available data that the BPA doses normally consumed by humans pose an increased risk for immunologic or neurologic disease. There is no evidence that BPA poses a genotoxic or carcinogenic risk and clinical evaluations of 205 men and women with high-performance liquid chromatography (HPLC)-verified serum or urinary BPA conjugates showed (1) no objective signs, (2) no changes in reproductive hormones or clinical chemistry parameters, and (3) no alterations in the number of children or sons:daughters ratio. Results of benchmark dose (BMD10 and BMDL10) calculations and no-observed-adverse-effect level (NOAEL) inspections of all available and reproducible rodent studies with oral BPA found BMD and NOAEL values all greater than the 5 mg/kg-d NOAELs from mouse and rat multigeneration reproduction toxicity studies. While allometric and physiologically based pharmacokinetic (PBPK) models were constructed for interspecies scaling of BPA and its interaction with ER, multigeneration feeding studies with BPA at doses spanning 5 orders of magnitude failed to identify signs of developmental toxicity or adverse changes in reproductive tract tissues; the 5-mg/kg-d NOAELs identified for systemic toxicity in rats and mice were less than the oral NOAELs for reproductive toxicity. Thus, it is the generalized systemic toxicity of ingested BPA rather than reproductive, immunologic, neurobehavioral, or genotoxic hazard that represents the point of departure. Using U.S. Environmental Protection Agency (EPA) uncertainty factor guidance and application of a threefold database uncertainty factor (to account for the fact that the carcinogenic potential of transplacental BPA exposure has yet to be fully defined and comprehensive neurobehavioral and immunotoxicologic evaluations of BPA by relevant routes and at relevant doses have yet to be completed) to the administered dose NOAEL results in an oral RfD of 0.016 mg/kg-d. Assuming the 70-kg adult consumes 2 L of water each day and adopting the default 20% U.S. EPA drinking water relative source contribution yields a 100 microg/L BPA total allowable concentration (TAC).

Expression of progesterone and oestrogen receptors by early intrauterine equine conceptuses

Progesterone and oestrogen play essential roles in the maintenance of pregnancy in eutherian mammals and are thought to exert their effects on the developing conceptus indirectly, via the endometrium. In some species, early embryos have themselves been shown to express steroid receptors, thereby suggesting that reproductive steroids may also influence embryonic development directly. The aim of this study was to determine whether early intrauterine equine conceptuses express either the classical intracellular progesterone (PR) and oestrogen receptors (ERalpha and ERbeta) or the more recently characterised membrane-bound progesterone receptors (PGRMC1 and mPR). Horse conceptuses recovered on days 7, 10 and 14 after ovulation (n=8 at each stage) were examined for steroid receptor mRNA expression using quantitative rtPCR. Where commercial antibodies were available (PR, ERbeta), receptor localisation was examined immunohistochemically in day 10, 12, 14, 15 and 16 conceptuses (n=2 at each stage). mRNA for PR, PGRMC1 and mPR was detected at all stages examined, but while PGRMC1 and mPR expression increased during the day 7-14 period, PR expression decreased. ERalpha mRNA was not detected at any stage examined, whereas ERbeta mRNA was detected in all day 14, some day 10 and no day 7 conceptuses. Immunoreactive ERbeta receptors were localised to the trophectoderm of day 14-16 conceptuses; PR were not detected immunohistochemically in conceptus tissue. In summary, this study demonstrates that equine conceptuses express mRNA and, in the case of ERbeta, protein for steroid hormone receptors during the period encompassing rapid conceptus growth, differentiation and maternal pregnancy recognition.

Bisphenol-A disruption of the endocrine pancreas and blood glucose homeostasis

The link between endocrine disruptors and altered blood glucose homeostasis has been recently suggested. Epidemiological studies have correlated levels of phthalates, dioxins and persistent organic pollutants with alterations of blood glucose homeostasis in humans. Environmentally relevant doses of the ubiquitous endocrine disruptor bisphenol-A (BPA) have profound effects on mice endocrine pancreas--an essential tissue involved in glucose metabolism. BPA exerts rapid non-genomic effects on insulin releasing beta-cells and glucagon releasing alpha-cells within freshly isolated islets of Langerhans. In vivo, a single BPA injection of 10 microg/kg rapidly increases plasma insulin and concomitantly decreases glycaemia. When mice were treated with BPA 100 microg/kg/day for 4 days, the environmental oestrogen produced an increase in beta-cell insulin content along with a post-prandial hyperinsulinaemia and insulin resistance. The results reviewed here demonstrate that doses well below the current lowest observed adverse effect level considered by the US-EPA, disrupt pancreatic beta-cell function producing insulin resistance in male mice. Therefore, this altered blood glucose homeostasis by BPA exposure may enhance the risk of developing type II diabetes.

Expression of G protein-coupled receptor 30 in the hamster ovary: differential regulation by gonadotropins and steroid hormones

The nongenomic actions of estradiol-17beta are mediated by transmembrane estrogen receptors. Recently, G protein-coupled receptor 30 (GPR30) has been suggested to be a transmembrane estrogen receptor that can mediate rapid and transcription-independent estradiol-17beta signaling in different cell types. However, the expression, regulation, or biological relevance of GPR30 in the ovary remains unknown. We examined the expression and hormonal regulation of GPR30 mRNA and protein in hamster ovarian cells during the estrous cycle and after hypophysectomy and hormone replacement. GPR30 protein expression was high in the theca, appreciable in the granulosa, but low in luteal cells. GPR30 protein levels in granulosa and theca cells increased steadily with the development of preantral and antral follicles, respectively. GPR30 mRNA and protein levels increased significantly on diestrous (d 3 of the estrous cycle), but decreased on d 4 at 1600 h after the LH surge. GPR30 mRNA levels increased significantly after hypophysectomy. Although steroid treatment failed to alter ovarian GPR30 mRNA levels, either FSH or LH effectively reduced the levels. Interestingly, the decrease in GPR30 mRNA corresponded to a marked increase in the receptor protein levels. FSH treatment, either alone or together with LH, resulted in a marked increase in GPR30 immunostaining in granulosa cells. LH alone significantly increased immunostaining in theca cells. These results suggest that GPR30 is expressed in the membrane of hamster granulosa and theca cells, and the expression is regulated by gonadotropins. The unique pattern of GPR30 expression suggests that gonadotropin-regulated follicular cell functions may involve GPR30 activity.

Influence of mycotoxins on spontaneous contraction in myometrial strips of prepubertal lamb

The effects of mycotoxin zearalenone and their major metabolites alpha- and beta-zearalenol on spontaneous contractions in isolated lamb uterine smooth muscle were examined. The study was carried out on 20 female prepubertal lambs aged between 45 and 50 days. Myometrial strips were set up in two isolated organ baths (10ml) at 37 degrees C and were exposed to increasing concentrations (10(-11)M-10(-6)M) of these mycoestrogens and results were compared with the effect, at the same concentrations, of natural estrogen 17beta-estradiol. Our findings suggest that mycotoxins and 17beta-estradiol, at nanomolar concentrations, rapidly enhance phasic spontaneous smooth muscle contraction. In particular, zearalenone increases the uterine activity similarly to 17beta-estradiol. On the contrary, its metabolite alpha-zearalenol significantly inhibits myometrial contractility.

Nongenomic actions of low concentration estrogens and xenoestrogens on multiple tissues

Nongenomic estrogenic mechanisms offer an opportunity to explain the conundrum of environmental estrogen and plant estrogen effects on cells and animals at the very low concentrations which are prevalent in our environments and diets. Heretofore the actions of these compounds have not been adequately accounted for by laboratory tests utilizing assays for actions only via the genomic pathway of steroid action and the nuclear forms of estrogen receptor alpha and beta. Membrane versions of these receptors, and the newly described GPR30 (7TMER) receptor protein provide explanations for the more potent actions of xenoestrogens. The effects of estrogens on many tissues demand a comprehensive assessment of the receptors, receptor levels, and mechanisms that might be involved, to determine which of these estrogen mimetic compounds are harmful and which might even be used therapeutically, depending upon the life stage at which we are exposed to them.

In vitro molecular mechanisms of bisphenol A action

Bisphenol A (BPA, 2,2-bis (4-hydroxyphenyl) propane; CAS# 80-05-7) is a chemical used primarily in the manufacture of polycarbonate plastic, epoxy resins and as a non-polymer additive to other plastics. Recent evidence has demonstrated that human and wildlife populations are exposed to levels of BPA which cause adverse reproductive and developmental effects in a number of different wildlife species and laboratory animal models. However, there are major uncertainties surrounding the spectrum of BPA's mechanisms of action, the tissue-specific impacts of exposures, and the critical windows of susceptibility during which target tissues are sensitive to BPA exposures. As a foundation to address some of those uncertainties, this review was prepared by the "In vitro" expert sub-panel assembled during the "Bisphenol A: An Examination of the Relevance of Ecological, In vitro and Laboratory Animal Studies for Assessing Risks to Human Health" workshop held in Chapel Hill, NC, Nov 28-29, 2006. The specific charge of this expert panel was to review and assess the strength of the published literature pertaining to the mechanisms of BPA action. The resulting document is a detailed review of published studies that have focused on the mechanistic basis of BPA action in diverse experimental models and an assessment of the strength of the evidence regarding the published BPA research.

Differential effects of 17beta-estradiol on function and expression of estrogen receptor alpha, estrogen receptor beta, and GPR30 in arteries and veins of patients with atherosclerosis

Venous complications have been implicated in the adverse effects of hormone replacement therapy. This study investigated acute effects of the natural estrogen, 17beta-estradiol, on function, estrogen receptors/GPR30 expression, and kinase activation in vascular rings and cultured smooth muscle cells from arteries and veins of patients with coronary artery disease. Changes in vascular tone of internal mammary arteries and saphenous veins exposed to the steroid were recorded. 17Beta-estradiol caused concentration-dependent, endothelium-independent relaxation in arteries (P<0.05 versus solvent control) but not in veins (P not significant). 17Beta-estradiol enhanced contractions to endothelin-1 in veins but not in arteries. The novel membrane estrogen receptor GPR30 was detected in both vessels. Moreover, gene expression of estrogen receptor beta was 10-fold higher than that of estrogen receptor alpha or GPR30 (P<0.05). Expression of all 3 of the receptors was reduced after exposure to 17beta-estradiol in arteries but not in veins (P<0.05). Basal phosphorylation levels of extracellular signal-regulated kinase were higher in venous than in arterial smooth muscle cells and were increased by 17beta-estradiol in arterial cells only. In summary, this is the first study to report that, in human arteries but not in veins, 17beta-estradiol acutely affects vascular tone, estrogen receptor expression, including GPR30, and extracellular signal-regulated kinase phosphorylation. These data indicate that effects of natural estrogens in humans differ between arterial and venous vascular beds, which may contribute to the vascular risks associated with menopause or hormone therapy.

Estrogens and epilepsy: why are we so excited?

Estrogens are essential for normal brain function throughout life. The source of estrogens is not only from the periphery, but local production has also been demonstrated in the CNS. Actions of estrogens involve a variety of effects, which include modulation of gene expression, regulation of neurotransmitter release, or direct inter-actions with neurotransmitter receptors. By these effects, estrogens affect neuronal excitability and thus may play an important role in seizure disorders. Although the original clinical as well as animal studies suggest that estrogens have exclusively proconvulsant properties, it has now become clear that estrogens also produce anticonvulsant effects. These opposite effects of estrogens on seizures may depend on treatment duration, latency prior to seizure testing, mode of administration, estrogen dose and hormonal status, estrogenic species, the region/neurotransmitter system involved, seizure type/model used, and sex. Animal data also suggest that estrogens, specifically beta-estradiol, have neuroprotective effects on seizure-induced hippocampal damage. Further studies are necessary to understand the role of estrogens in seizure disorders. Such under-standing is important, especially for women with epilepsy, to make qualified decisions regarding administration of contraceptives and hormonal replacement therapy as well as for the design of new therapeutic strategies for better seizure control and prevention of seizure-induced neuronal damage.

Membrane-initiated actions of estrogens in neuroendocrinology: emerging principles

Hormonal ligands for the nuclear receptor superfamily have at least two interacting mechanisms of action: 1) classical transcriptional regulation of target genes (genomic mechanisms); and 2) nongenomic actions that are initiated at the cell membrane, which could impact transcription. Although transcriptional mechanisms are increasingly well understood, membrane-initiated actions of these ligands are incompletely understood. Historically, this has led to a considerable divergence of thought in the molecular endocrine field. We have attempted to uncover principles of hormone action that are relevant to membrane-initiated actions of estrogens. There is evidence that the membrane-limited actions of hormones, particularly estrogens, involve the rapid activation of kinases and the release of calcium. Membrane actions of estrogens, which activate these rapid signaling cascades, can also potentiate nuclear transcription. These signaling cascades may occur in parallel or in series but subsequently converge at the level of modification of transcriptionally relevant molecules such as nuclear receptors and/or coactivators. In addition, other hormones or neurotransmitters may also activate cascades to crosstalk with estrogen receptor-mediated transcription. The idea of synergistic coupling between membrane-initiated and genomic actions of hormones fundamentally revises the paradigms of cell signaling in neuroendocrinology.

EXPRESSION OF THE ESTROGEN RECEPTOR ALPHA GENE IN THE ANAL FIN OF JAPANESE MEDAKA, ORYZIAS LATIPES, BY ENVIRONMENTAL CONCENTRATIONS OF BISPHENOL A

The anal fin in Japanese medaka, Oryzias latipes, is a typical sexual secondary character. In the present study, we focused on this organ and examined the effects of low doses of a natural estrogen, 17beta-estradiol (E(2)), and an environmental xenoestrogen, bisphenol A (BPA), in vivo by monitoring estrogen receptor (ER) alpha gene expression. Groups of adult male and female medaka were immersed in 10(-9) M E(2) or 10(-10) to 10(-8) M BPA and the levels of ERalpha gene transcripts in the anal fins were measured by semi-quantitative reverse transcription polymerase chain reaction (RT-PCR). One day of treatment with each concentration of BPA examined and 10(-9) M E(2) increased the levels of ERalpha mRNA in female anal fins by 3-fold as compared with controls. In the male specimens, neither 10(-9) M E(2) nor 10(-10) M BPA showed remarkable effects on the anal fins as compared with the results in females, but 10(-9) and 10(-8) M BPA increased the levels of ERalpha mRNA by 2.3- and 3.3-fold with 1 day of exposure, respectively. The present results showed that medaka anal fins may be a sensitive bio-indicator for screening of environmental estrogenic chemicals.

Xenoestrogens are potent activators of nongenomic estrogenic responses

Studies of the nuclear transcriptional regulatory activities of non-physiological estrogens have not explained their actions in mediating endocrine disruption in animals and humans at the low concentrations widespread in the environment. However, xenoestrogens have rarely been tested for their ability to participate in the plethora of nongenomic steroid signaling pathways elucidated over the last several years. Here we review what is known about such responses in comparison to our recent evidence that xenoestrogens can rapidly and potently elicit signaling through nongenomic pathways culminating in functional endpoints. Both estradiol (E(2)) and compounds representing various classes of xenoestrogens (diethylstilbestrol, coumestrol, bisphenol A, DDE, nonylphenol, endosulfan, and dieldrin) act via a membrane version of the estrogen receptor-alpha on pituitary cells, and can provoke Ca(2+) influx via L-type channels, leading to prolactin (PRL) secretion. These hormones and mimetics can also cause the oscillating activation of extracellular regulated kinases (ERKs). However, individual estrogen mimetics differ in their potency and temporal phasing of these activations compared to each other and to E(2). It is perhaps in these ways that they disrupt some endocrine functions when acting in combination with physiological estrogens. Our quantitative assays allow comparison of these outcomes for each mimetic, and let us build a detailed picture of alternative signaling pathway usage. Such an understanding should allow us to determine the estrogenic or antiestrogenic potential of different types of xenoestrogens, and help us to develop strategies for preventing xenoestrogenic disruption of estrogen action in many tissues.

Rapid endocrine disruption: environmental estrogen actions triggered outside the nucleus

An exogenous substance is defined as an endocrine disrupter chemical (EDC) if it alters the function of the endocrine system provoking adverse health effects. Environmental estrogens are the most studied EDCs. They follow the same mechanisms of action as the gonadal hormone 17beta-estradiol. Up to now, the estrogenicity of environmental estrogenic pollutants has been based on the property of these compounds to bind to estrogen receptors (ERs), either ERalpha or ERbeta, and to act subsequently as transcription factors when binding to the estrogen response element (ERE) in the DNA. All the estrogenic bioassays currently used are based on this mechanism of action. New evidence indicates that the definition of estrogenicity for a chemical should take into account other estrogen receptors as well as new signaling pathways. These include the activation of additional transcription factors as well as the action of xenoestrogens through estrogen receptors located outside the nucleus: in the plasma membrane, mitochondria and probably the cytosol. Therefore, new estrogenic bioassays should be developed to include the novel concept of rapid endocrine disruption.

Binding and activation of the seven-transmembrane estrogen receptor GPR30 by environmental estrogens: a potential novel mechanism of endocrine disruption

A wide variety of environmental contaminants have been shown to exert estrogenic actions in wildlife and laboratory animals through binding to nuclear estrogen receptors (ERs) and subsequent transcription of estrogen responsive genes. We show here that several of these environmental estrogens also bind to the novel seven-transmembrane estrogen receptor, GPR30, to activate alternative estrogen signaling pathways in an ER-negative cell line (HEK293) stably transfected with the receptor. Genestein was the most effective competitor for the receptor (IC(50) 133 nM), with a relative binding affinity (RBA) 13% that of estradiol-17beta (E2). Bisphenol A, zearalonone, and nonylphenol also had relatively high binding affinities for GPR30 with RBAs of 2-3%. Kepone, p,p'-DDT, 2,2',5',-PCB-4-OH and o,p'-DDE had lower affinities with RBAs of 0.25-1.3%, whereas o,p'-DDT, p,p'-DDE, methoxychlor and atrazine caused less than 50% displacement of [(3)H]-E2 at concentrations up to 10 microM. Overall, the binding affinities of these compounds for GPR30 are broadly similar to their affinities to the ERs. Environmental estrogens with relatively high binding affinities for GPR30 (genestein, bisphenol A, nonylphenol and Kepone) also displayed estrogen agonist activities in an in vitro assay of membrane-bound adenylyl cyclase activity, a GPR30-dependent signaling pathway activated by estrogens. The results indicate that nontraditional estrogen actions mediated through GPR30 are potentially susceptible to disruption by a variety of environmental estrogens.

Non-genomic steroid hormone effects: membrane or intracellular receptors?

A controversy regarding the identity of receptors that mediate nongenomic, transcription-independent cellular responses to steroids is presently attracting considerable scientific interest. While there is strong evidence for classic receptors belonging to the nuclear receptor superfamily to mediate nongenomic steroid effects in some cases, it does not exist for others. Nongenomic estrogen effects seem to predominantly involve classical estrogen receptors, both residing in cytoplasm and at the cell membrane. On the other hand, there is increasing evidence for the existence of nonrelated membrane receptors for estrogens, mediating CNS effects. Novel membrane receptors for other steroids have been recently cloned, with the demonstration of their biological relevance still largely pending. Recent findings on new and unexpected properties of classic receptors have partially deflected the interest from novel, nonclassic membrane receptors, which are being progressively identified at present. In addition, new findings pose challenges to some of the conclusions drawn from earlier experiments, and potential involvement of receptors and mechanisms of action need to be reconsidered. To know the nature of receptors involved will be key to beneficial medical translation of specific and targeted steroid responses. Differential pharmacological exploitation of different steroid receptors seems to become a tangible option.

Estradiol activates mast cells via a non-genomic estrogen receptor-alpha and calcium influx

BACKGROUND

Allergic airway diseases are more common in females than in males during early adulthood. A relationship between female hormones and asthma prevalence and severity has been suggested, but the cellular and molecular mechanisms are not understood.

OBJECTIVE

To elucidate the mechanism(s) by which estrogens enhance the synthesis and release of mediators of acute hypersensitivity.

METHODS

Two mast cell/basophil cell lines (RBL-2H3 and HMC-1) and primary cultures of bone marrow derived mast cells, all of which naturally express estrogen receptor-alpha, were examined. Cells were incubated with physiological concentrations of 17-beta-estradiol with and without IgE and allergens. Intracellular Ca(2+) concentrations and the release of beta-hexosaminidase and leukotriene C(4) were quantified.

RESULTS

Estradiol alone induced partial release of the preformed, granular protein beta-hexosaminidase from RBL-2H3, BMMC and HMC-1, but not from BMMC derived from estrogen receptor-alpha knock-out mice. The newly synthesized LTC(4) was also released from RBL-2H3. Estradiol also enhanced IgE-induced degranulation and potentiated LTC(4) production. Intracellular Ca(2+) concentration increased prior to and in parallel with mediator release. Estrogen receptor antagonists or Ca(2+) chelation inhibited these estrogenic effects.

CONCLUSION

Binding of physiological concentrations of estradiol to a membrane estrogen receptor-alpha initiates a rapid onset and progressive influx of extracellular Ca(2+), which supports the synthesis and release of allergic mediators. Estradiol also enhances IgE-dependent mast cell activation, resulting in a shift of the allergen dose response.

Estrogen Action in Neuroprotection and Brain Inflammation

The fertile period of women's life compared to menopause is associated with a lower incidence of degenerative inflammatory diseases. In brain, estrogens ameliorate brain performance and have positive effects on selected neural pathologies characterized by a strong inflammatory component. We thus hypothesized that the inflammatory response is a target of estrogen action; several studies including ours provided strong evidence to support this prediction. Microglia, the brain's inflammatory cells, and circulating monocytes express the estrogen receptors ER-alpha and ER-beta and their responsiveness in vivo and in vitro to pro-inflammatory agents, such as lipopolysaccharide (LPS), is controlled by 17beta-estradiol (E(2)). Susceptibility of central nervous system (CNS) macrophage cells to E(2) is also preserved in animal models of neuroinflammatory diseases, in which ER-alpha seems to be specifically involved. At the molecular level, induction of inflammatory gene expression is blocked by E(2). We recently observed that, differently from conventional anti-inflammatory drugs, E(2) stimulates a nongenomic event that interferes with the LPS signal transduction from the plasma membrane to cytoskeleton and intracellular effectors, which results in the inhibition of the nuclear translocation of NF-kappaB, a transcription factor of inflammatory genes. Interference with NF-kappaB intracellular trafficking is selectively mediated by ER-alpha. In summary, evidence from basic research strongly indicates that the use of estrogenic drugs that can mimic the anti-inflammatory activity of E(2) might trigger beneficial effects against neurodegeneration in addition to carrying out their specific therapeutic function.

Greater antiarrhythmic activity of acute 17beta-estradiol in female than male anaesthetized rats: correlation with Ca2+ channel blockade

BACKGROUND AND PURPOSE

Female sex hormones may protect pre-menopausal women from sudden cardiac death. We therefore investigated the effects of the main female sex hormone, 17beta-estradiol, on ischaemia-induced cardiac arrhythmias and on the L-type Ca2+ current (ICaL).

EXPERIMENTAL APPROACH

In vivo experiments were performed in pentobarbital-anaesthetized rats subjected to acute coronary artery occlusion. ICaL was measured by the whole-cell patch-clamp technique, in rat isolated ventricular myocytes.

KEY RESULTS

Acute intravenous administration of 17beta-estradiol as a bolus dose followed by a continuous infusion, commencing 10 min before coronary artery occlusion, had dose-dependent antiarrhythmic activity. In female rats 300 ng kg(-1) + 30 ng kg(-1) min(-1) 17beta-estradiol significantly reduced the number of ventricular premature beats (VPBs) and the incidence of ventricular fibrillation (VF). A ten fold higher dose of 17beta-estradiol was required to cause similar effects in male rats. In vitro 17beta-estradiol reduced peak ICaL in a concentration-dependent manner. The EC50 was ten-fold higher in male myocytes (0.66 microM) than in females (0.06 microM).

CONCLUSIONS AND IMPLICATIONS

These results indicate that 17beta-estradiol has marked dose-dependent antiarrhythmic activity that is greater in female rats than in males. A similar differential potency in blocking ICaL in myocytes from female and male rats can account for this effect. This provides an explanation for the antiarrhythmic activity of 17beta-estradiol and gender-selective protection against sudden cardiac death.

Rapid effects of pesticides on human granulosa-lutein cells

Following our previous demonstration that p,p'-DDE (dichlorodiphenylchloroethylene), at environmentally relevant concentrations, can rapidly increase intracellular calcium [Ca2+]i concentrations in human granulosa-lutein cells, we examined whether other pesticides, such as Kepone, o,p-DDE and methoxychlor, have similar effects. Cultured human granulosa-lutein cells were loaded with Fura-2 AM, and changes in [Ca2+]i concentrations within small areas of single cells were studied with a dynamic digital Ca2+ imaging system. Kepone, at concentrations of 0.2-2 nmol/ml, consistently increased [Ca2+]i concentrations 2-6 times higher than baseline values within minutes of exposure. Methoxychlor at concentrations of 2.8-280 nmol/ml failed to alter [Ca2+]i levels consistently in cells from 10 patients. However, at 0.28 and 1.4 nmol/ml, increases in [Ca2+]i concentrations could be elicited by methoxychlor. The isomer o,p-DDE at 3 nmol/ml increased [Ca2+]i in granulosa cells of 11/20 patients. Pertussis toxin treatment inhibited the [Ca2+]i increases induced by estradiol, p,p'-DDE, o,p-DDE and methoxychlor, but not by Kepone or progesterone, indicating that Kepone and progesterone may act through an insensitive G protein-coupled receptor. The [Ca2+]i increases induced by Kepone also occurred in Ca2+-free medium, suggesting that [Ca2+]i mobilization occurred from the smooth endoplasmic reticulum. Thapsigargin and cyclopiazonic acid, two inhibitors of the endoplasmic reticulum Ca2+ pump, also stimulated [Ca2+]i increases but did not inhibit the Ca2+ response to all the pesticides. These results demonstrate that pesticides can have a rapid effect on human granulosa-lutein cells, and a nongenomic mechanism of action is suggested.

17beta-estradiol potentiates the cardiac cystic fibrosis transmembrane conductance regulator chloride current in guinea-pig ventricular myocytes

There is a well-characterized membrane chloride current (ICl,cAMP) in the heart that can be activated by beta-adrenergic agonists and is due to expression of the cardiac isoform of the epithelial cystic fibrosis transmembrane conductance regulator (CFTR). We have investigated whether 17beta-estradiol (E2) modulates ICl,cAMP in single ventricular myocytes. Under whole-cell tight-seal voltage-clamp conditions, ICl,cAMP was evoked by exposing cells to 20 nM isoprenaline. On the addition of 30 microM E2, membrane slope conductance, measured at potentials near 0 mV, increased over that induced by isoprenaline alone by 2.46 +/- 0.16 (p < 0.001). The effects of E2 were concentration-dependent and described by a Hill Plot with an EC50 of 8.2 microM and a Hill coefficient of 1.63. The application of membrane-impermeant E2 conjugated to bovine serum albumin (E2-BSA) potentiated isoprenaline-evoked ICl,cAMP by approximately the same degree as that for the equivalent level of free E2. Cell surface binding was observed with confocal microscopy by using BSA-FITC tagged E2. This binding was inhibited by nonlabeled, nonconjugate E2, the specific E2 antagonist ICl 182,780, and incubation of E2coBSA with a specific anti-E2 antibody (E2885). ICl 182,780 (100 microM) significantly reduced the increase in ICl,cAMP evoked by 10 microM E2 to 1.46 +/- 0.10 (p < 0.02). The preincubation of myocytes with the NOS inhibitor N-omega-nitro-arginine (L-NNA, 1 mM) reduced the potentiation of ICl,cAMP by 30 microM E2, to 1.93 +/- 0.06 (p < 0.02), and for 10 microM E2, to 1.32 +/- 0.05 (p < 0.002). E2 also increased ICl,cAMP evoked by bath application of 0.5 microM Forskolin. These experiments demonstrate that, under our experimental conditions, E2 dramatically increases ICl,cAMP in ventricular myocytes by mechanisms involving a contribution by NOS, but that can be only partially accounted for through binding to classical plasma membrane estrogen receptor sites. This potentiation of ICl,cAMP by E2 may play a significant role in the observed clinical actions of E2 on the incidence of cardiac arrhythmias and hypertrophy.

Endocrine disruptors in marine organisms: approaches and perspectives

Organic pollutants exhibiting endocrine disrupting activity (Endocrine Disruptors--EDs) are prevalent over a wide range in the aquatic ecosystems; most EDs are resistant to environmental degradation and are considered ubiquitous contaminants. The actual potency of EDs is low compared to that of natural hormones, but environmental concentrations may still be sufficiently high to produce detrimental biological effects. Most information on the biological effects and mechanisms of action of EDs has been focused on vertebrates. Here we summarize recent progress in studies on selected aspects of endocrine disruption in marine organisms that are still poorly understood and that certainly deserve further research in the near future. This review, divided in four sections, focuses mainly on invertebrates (effects of EDs and mechanisms of action) and presents data on top predators (large pelagic fish and cetaceans), a group of vertebrates that are particularly at risk due to their position in the food chain. The first section deals with basic pathways of steroid biosynthesis and metabolism as a target for endocrine disruption in invertebrates. In the second section, data on the effects and alternative mechanisms of action of estrogenic compounds in mussel immunocytes are presented, addressing to the importance of investigating full range responses to estrogenic chemicals in ecologically relevant invertebrate species. In the third section we review the potential use of vitellogenin (Vtg)-like proteins as a biomarker of endocrine disruption in marine bivalve molluscs, used worldwide as sentinels in marine biomonitoring programmes. Finally, we summarize the results of a recent survey on ED accumulation and effects on marine fish and mammals, utilizing both classical biomarkers of endocrine disruption in vertebrates and non-lethal techniques, such as non-destructive biomarkers, indicating the toxicological risk for top predator species in the Mediterranean. Overall, the reviewed data underline the potential to identify specific types of responses to specific groups of chemicals such as EDs in order to develop suitable biomarkers that could be useful as diagnostic tools for endocrine disruption in marine invertebrates and vertebrates.

Nongenomic actions of estrogens: exciting opportunities for pharmacology

Estrogens, like other steroids, elicit a variety of rapid effects in many tissues in addition to their delayed action on gene expression in the cell nucleus. The rapid responses occur without participation of the genome, and are therefore termed nongenomic. Some of the estrogen induced effects acutely modulate vascular function and may contribute to the gender difference in cardiovascular susceptibility. While some actions may be mediated by novel, nonclassic receptors, the classic estrogen receptor has been shown to also act on signalling cascades. There are sparse examples for compounds structurally related to the endogenous hormone estradiol that bind to the estrogen receptor but may selectively elicit nongenomic responses. The further development of such selectively acting drugs holds much promise for better therapies with fewer side effects, e.g. for vascular malfunction, but also for estrogen-dependent cancer.

Nature of functional estrogen receptors at the plasma membrane

Although rapid signaling by estrogen at the plasma membrane is established, it is controversial as to the nature of the receptor protein. Estrogen may bind membrane proteins comparable to classical nuclear estrogen receptors (ERs), but some studies identify nonclassical receptors, such as G protein-coupled receptor (GPR)30. We took several approaches to define membrane-localized estrogen-binding proteins. In endothelial cells (ECs) from ERalpha/ERbeta combined-deleted mice, estradiol (E2) failed to specifically bind, and did not activate cAMP, ERK, or phosphatidyinositol 3-kinase or stimulate DNA synthesis. This is in contrast to wild-type ECs, indicating the lack of any functional estrogen-binding proteins in ERalpha/ERbeta combined-deleted ECs. To directly determine the identity of membrane and nuclear-localized ER, we isolated subcellular receptor pools from MCF7 cells. Putative ER proteins were trypsin digested and subjected to tandem array mass spectrometry. The output analysis identified membrane and nuclear E2-binding proteins as classical human ERalpha. We also determined whether GPR30 plays any role in E2 rapid actions. MCF7 (ER and GPR30 positive) and SKBR-3 (ER negative, GPR30 positive) cells were incubated with E2. Only MCF7 responded with significantly increased signaling. In MCF7, the response to E2 was not different in cells transfected with small interfering RNA to green fluorescent protein or GPR30. In contrast, interfering RNA to ERalpha or ER inhibition prevented rapid signaling and resulting biology in MCF7. In breast cancer and ECs, nuclear and membrane ERs are the same proteins. Furthermore, classical ERs mediate rapid signals induced by E2 in these cells.

Multiple pathways transmit neuroprotective effects of gonadal steroids

Numerous preclinical studies suggest that gonadal steroids, particularly estrogen, may be neuroprotective against insult or disease progression. This paper reviews the mechanisms contributing to estrogen-mediated neuroprotection. Rapid signaling pathways, such as MAPK, PI3K, Akt, and PKC, are required for estrogen's ability to provide neuroprotection. These rapid signaling pathways converge on genomic pathways to modulate transcription of E2-responsive genes via ERE-dependent and ERE-independent mechanisms. It is clear that both rapid signaling and transcription are important for estrogen's neuroprotective effects. A mechanistic understanding of estrogen-mediated neuroprotection is crucial for the development of therapeutic interventions that enhance quality of life without deleterious side effects.

Progestin, estrogen and androgen G-protein coupled receptors in fish gonads

The identities of the membrane receptors mediating the majority of rapid, cell surface-initiated, nongenomic (i.e. nonclassical) steroid actions described to date are unclear. Two novel 7-transmembrane spanning proteins, representing two distinct classes of steroid membrane receptors, membrane progestin receptor alpha (mPRalpha) and a membrane estrogen receptor (mER), GPR30, have recently been identified in several vertebrate species. Evidence that both receptors activate G-proteins and function as G-protein coupled receptors (GPCRs) is briefly reviewed. New data on progestin actions on fish gametes suggest a widespread involvement of mPRalpha in oocyte maturation and sperm hyperactivity in this vertebrate group. Information on the second messenger pathways activated upon estrogen binding to a membrane estrogen receptor in croaker gonads and preliminary evidence for the presence of a GPR30-like protein in fish gonads are discussed. Finally, initial characterization of the ligand binding, G-protein activation and molecular size of a membrane androgen receptor (mAR) in croaker ovaries suggests the presence of a third unique steroid receptor in fish gonads that also may function as a GPCR.

Integration of membrane and nuclear estrogen receptor signaling

The classical mechanism of estradiol (E2) action is mediated by the nuclear estrogen receptors ERalpha and ERbeta, which function as ligand-dependent transcription factors that regulate transcription of target genes containing the consensus estrogen response element (ERE) in their promoter regions. However, accumulating evidence indicates that E2 can also exert its actions through a unique membrane estrogen receptor (mER). Upon activation of the mER, various signaling pathways (i.e. Ca(2+), cAMP, protein kinase cascades) are rapidly activated and ultimately influence downstream transcription factors. Some target genes of the mER pathway may be activated independently of the nuclear estrogen receptor (nER). Additionally, it has been shown that classical nER action can be modulated by mER-initiated signaling through phosphorylation of nER and its coactivators, and by induction of third messengers (i.e. cyclin D1 and c-fos). Based on current evidence, we propose a model for E2 action integrating distinct membrane receptor and nuclear receptor signaling. This membrane receptor-nuclear receptor interaction is likely to exist for other hormones. Steroid hormones and other hormones acting through hormone receptors in the steroid receptor superfamily (i.e. thyroid hormones) also activate many of the same intracellular signaling cascades, which provides the basis for extensive crosstalk networks between hormones. The model proposed serves as a framework to investigate the diverse actions of hormones and endocrine disrupting chemicals (EDCs).

Rapid, nongenomic responses to ecdysteroids and catecholamines mediated by a novel Drosophila G-protein-coupled receptor

Nongenomic response pathways mediate many of the rapid actions of steroid hormones, but the mechanisms underlying such responses remain controversial. In some cases, cell-surface expression of classical nuclear steroid receptors has been suggested to mediate these effects, but, in a few instances, specific G-protein-coupled receptors (GPCRs) have been reported to be responsible. Here, we describe the activation of a novel, neuronally expressed Drosophila GPCR by the insect ecdysteroids ecdysone (E) and 20-hydroxyecdysone (20E). This is the first report of an identified insect GPCR interacting with steroids. The Drosophila melanogaster dopamine/ecdysteroid receptor (DmDopEcR) shows sequence homology with vertebrate beta-adrenergic receptors and is activated by dopamine (DA) to increase cAMP levels and to activate the phosphoinositide 3-kinase pathway. Conversely, E and 20E show high affinity for the receptor in binding studies and can inhibit the effects of DA, as well as coupling the receptor to a rapid activation of the mitogen-activated protein kinase pathway. The receptor may thus represent the Drosophila homolog of the vertebrate "gamma-adrenergic receptors," which are responsible for the modulation of various activities in brain, blood vessels, and pancreas. Thus, DmDopEcR can function as a cell-surface GPCR that may be responsible for some of the rapid, nongenomic actions of ecdysteroids, during both development and signaling in the mature adult nervous system.

Modulation of mitochondrial Ca(2+) uptake by estrogen receptor agonists and antagonists

Ca(2+) uptake by mitochondria is a key element in the control of cellular Ca(2+) homeostasis and Ca(2+)-dependent phenomena. It has been known for many years that this Ca(2+) uptake is mediated by the mitochondrial Ca(2+) uniporter, a specific Ca(2+) channel of the inner mitochondrial membrane. We have shown previously that this channel is strongly activated by a series of natural phytoestrogenic flavonoids. We show here that several agonists and antagonists of estrogen receptors (ERs) also modulate the activity of the uniporter. The specific alpha-ER agonist 4,4',4''-(4-propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol (PPT) was the strongest activator, increasing the rate of mitochondrial Ca(2+) uptake in permeabilized HeLa cells by 10-fold at 2 microM. Consistently, PPT largely increased the histamine-induced mitochondrial [Ca(2+)] peak and reduced the cytosolic one. Diethylstilbestrol and 17-beta-estradiol (but not 17-alpha-estradiol) were active at pharmacological concentrations while the beta-estrogen-receptor agonist 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN) was little effective. The ER modulators tamoxifen and 4-hydroxy-tamoxifen inhibited mitochondrial Ca(2+) uptake (IC(50) 2.5+/-1.5 and 2.5+/-1.4 microM, mean+/-s.d., respectively) both in the presence and in the absence of PPT, but raloxifene and the pure estrogen antagonist ICI 182,780 produced no effect. Activation by PPT was immediate and inhibition by tamoxifen or 4-hydroxy-tamoxifen required only 5 min to reach maximum. Tamoxifen did not modify mitochondrial membrane potential and PPT induced a slow mitochondrial depolarization at higher concentrations than those required to activate mitochondrial Ca(2+) uptake. These results suggest that some kind of ER or related protein located in mitochondria controls the activity of the Ca(2+) uniporter by a nongenomic mechanism. This novel mechanism of action of estrogen agonists and antagonists can provide a new interpretation for several previously reported effects of these compounds.

Signaling networks from Gβ1 subunit to transcription factors and actin remodeling via a membrane-located ERβ-related protein in the rapid action of daidzein in osteoblasts

Although estrogen replacement has been the main therapy to prevent and treat osteoporosis, there are concerns about its safety. Phytoestrogens have attracted attention to their potential impacts in osteoporosis prevention and treatment. Among phytoestrogens, the isoflavone daidzein (Dz) acts on transcription via the intracellular estrogen receptors (ER), mainly ERbeta, in osteoblasts, but mimics only part of the estrogen effects. Since estradiol also exerts rapid effects in osteoblasts, we investigated the multistep processes involved in the rapid actions of low (1-100 pM) doses of daidzein. Dz bound to a membrane moiety, related to ERbeta since the calcium response to Dz was blocked by an anti-ERbeta antibody directed against the C-terminus, but not by a double-stranded siRNA specific for ERbeta. This protein was coupled to a pertussis toxin (PTX)-sensitive Gbeta1 subunit whose transducer was PLC-beta2, which triggered a rapid (5 sec) mobilization of calcium from the endoplasmic reticulum. Dz phosphorylated within 15 sec ERK1/2 whose phosphorylation involved two routes: Gbeta1/PLC-beta2/PKC/c-Raf-1/MEK1/2 and Gbeta1/PI3K/cSrc/c-Raf-1/MEK1/2 as shown using several inhibitors. Dz induced rapid (1 min) changes in the actin cytoskeleton via the two routes. The rapid (20 sec) phosphorylation of Elk-1 and CREB by Dz involved Gbeta1 and ERK1/2. All the processes were insensitive to the estradiol antagonist ICI 182,780. In conclusion, the rapid effects of Dz seem to be biologically relevant for the function of osteoblast in bone since the isoflavone activates transcription factors linked to early genes controlling cellular proliferation and differentiation, and modulates actin cytoskeleton which controls cell adhesion, division, or secretion.

The estrogenic effect of bisphenol A disrupts pancreatic beta-cell function in vivo and induces insulin resistance

The function of the pancreatic beta-cell is the storage and release of insulin, the main hormone involved in blood glucose homeostasis. The results in this article show that the widespread environmental contaminant bisphenol-A (BPA) imitates 17beta-estradiol (E2) effects in vivo on blood glucose homeostasis through genomic and nongenomic pathways. The exposure of adult mice to a single low dose (10 microg/kg) of either E2 or BPA induces a rapid decrease in glycemia that correlates with a rise of plasma insulin. Longer exposures to E2 and BPA induce an increase in pancreatic beta-cell insulin content in an estrogen-receptor-dependent manner. This effect is visible after 2 days of treatment and starting at doses as low as 10 microg/kg/day. After 4 days of treatment with either E2 or BPA, these mice developed chronic hyperinsulinemia, and their glucose and insulin tolerance tests were altered. These experiments unveil the link between environmental estrogens and insulin resistance. Therefore, either abnormal levels of endogenous estrogens or environmental estrogen exposure enhances the risk of developing type 2 diabetes mellitus, hypertension, and dyslipidemia.

Steering estrogen signals from the plasma membrane to the nucleus: Two sides of the coin

Estrogen mediate its biological effects through its association with estrogen receptors (ERs). They also regulate the expression of a variety of genes involved in distinct physiological processes, including development, metabolism, and reproduction. In addition, emerging data suggest that the estrogen-estrogen receptor complex can also function as a cytoplasmic signaling molecule and may influence processes such as cardiovascular protection, bone preservation, neuroprotection, and proliferation of various cell types. Such extranuclear or nongenomic signaling pathways are rapid and supposedly independent of transcription. A recent exciting finding was that G-coupled membrane protein receptor, GPR30, an alternative to the classical ERs, is also involved in the rapid signaling of estrogen through its direct association with estrogen. These new findings combined with the recent advances in the cytoplasmic functions of proline, glutamic acid, luecine rich protein 1 (PELP1), and metastatic tumor antigen 1 short form (MTA1s) have opened a new spectrum and raised several new concerns in the field of estrogen biology and put the attention to unveil many unknown mechanistic actions of estrogen in cellular physiology. In this review, we briefly summarize what is currently known of the cellular mechanisms and physiology of estrogen's nongenomic actions in various cellular systems used by ERs.

Endocrine Disrupting Chemical Atrazine Causes Degranulation through Gq/11 Protein-Coupled Neurosteroid Receptor in Mast Cells

We studied the effects of representative endocrine-disrupting chemicals on beta-hexosaminidase release from mast cells and their putative neurosteroid receptor involvement. Some endocrine-disrupting chemicals, such as amitrol, benzophenon, bisphenol A, pentachlorophenol, and tetrabromophenol A did not cause hexosaminidase release from RBL-2H3 cells, but they blocked the release by dehydroepiandrosterone sulfate, a representative neurosteroid agonist. On the contrary, atrazine, which is a widely used herbicide, caused a rapid and concentration-dependent degranulation in the range between 10 nM and 1 microM in RBL-2H3 and peritoneal mast cells. Atrazine-induced degranulation was also evaluated by Alexa 488-annexin V binding to the phosphatidylserine, which is externalized during degranulation, and these actions were blocked by BSA-conjugated (membrane-impermeable) progesterone (PROG-BSA). The atrazine-induced beta-hexosaminidase release was characterized by various inhibitors including antisense-oligodeoxynucleotide for Galpha(q/11), pertussis toxin, phospholipase C inhibitor U-73122, inositol 1,4,5-triphosphate receptor inhibitor xestospongin C and Ca(2+) channel blocker lanthanum chloride. These analyses revealed that the degranulation is mediated by putative metabotropic neurosteroid receptor, G(q/11), phospholipase C and Ca(2+) mobilization from intracellular stores. Having documented progesterone receptor-modulation of atrazine-induced mast cell degranulation in vitro, this response was evaluated in mice. Atrazine caused pain responses when injected in the foot pads of mice, and they were antagonized by local administration of PROG-BSA or diphenhydramine. Atrazine also caused PROG-BSA-reversible plasma extravasation. All these findings strongly suggest that herbicide atrazine exerts inflammatory activity through activation of putative G(q/11)-coupled neurosteroid receptor and phospholipase C.

Calcium transport and signaling in the mammary gland: targets for breast cancer

The mammary gland is subjected to extensive calcium loads during lactation to support the requirements of milk calcium enrichment. Despite the indispensable nature of calcium homeostasis and signaling in regulating numerous biological functions, the mechanisms by which systemic calcium is transported into milk by the mammary gland are far from completely understood. Furthermore, the implications of calcium signaling in terms of regulating proliferation, differentiation and apoptosis in the breast are currently uncertain. Deregulation of calcium homeostasis and signaling is associated with mammary gland pathophysiology and as such, calcium transporters, channels and binding proteins represent potential drug targets for the treatment of breast cancer.

Stimulation of catecholamine synthesis through unique estrogen receptors in the bovine adrenomedullary plasma membrane by 17beta-estradiol

Incubation of cultured bovine adrenal medullary cells with 17beta-estradiol (E(2)) (0.3-100nM) or membrane-impermeable E(2)-bovine serum albumin (100nM) acutely increased (14)C-catecholamine synthesis from [(14)C]tyrosine. The stimulatory effect of E(2) was not inhibited by ICI182,780, a nuclear estrogen receptor inhibitor. E(2) also increased tyrosine hydroxylase activity and p44/42MAPK phosphorylation, the former of which was attenuated by U0126, an inhibitor of p44/42MAPK kinase. The plasma membrane isolated from the gland showed two classes of specific binding sites of [(3)H]E(2) with apparent K(d)s of 3.2 and 106nM, and B(max)s of 0.44 and 8.5pmol/mg protein, respectively. The high-affinity binding of [(3)H]E(2) was most strongly inhibited by E(2) and phytoestrogens, and to lesser extents by other steroid hormones, while it was enhanced by ICI182,780 and environmental estrogenic pollutants. These findings suggest that E(2) acutely stimulates catecholamine synthesis via activation of p44/42MAPK through unique estrogen receptors in the plasma membrane of bovine adrenal medulla.

Rapid action of pesticides on cytosolic calcium concentrations in cultures of human umbilical vein endothelial cells

Persistent metabolites of pesticides such as p,p'-DDE, at environmentally relevant concentrations, have been shown to have a rapid effect on intracellular calcium [Ca2+]i concentrations in human granulosa-lutein cells. Since endocrine disrupting substances can be transferred from the maternal circulation to the fetus the present study examined whether the pesticides, kepone, o,p-DDE, p,p'-DDE and methoxychlor, could alter cytoplasmic calcium [Ca2+]cyt concentrations in human umbilical vein endothelial (HUVE) cells. Cultured HUVE cells were loaded with Fura-2 AM and changes in [Ca2+]cyt of single cells were studied using a dynamic digital Ca2+ imaging system. Kepone and methoxychlor consistently increased [Ca2+]cyt concentrations, similar to the effects of estradiol and progesterone. p,p'-DDE increased [Ca2+]cyt concentrations in 80% of experiments whereas o,p-DDE stimulated its increases in 42%. Estrone, estriol, pregnenolone and cortisol were not effective. These results demonstrate that pesticides can have a rapid effect on HUVE cells probably through a nongenomic mechanism of action.