Parity and lactation in relation to estrogen receptor negative breast cancer in African American women

BACKGROUND

Estrogen receptor (ER)-negative breast tumors and progesterone receptor (PR)-negative breast tumors occur more commonly in women of African ancestry. Recent research indicates that the effects of reproductive factors may differ by hormone receptor status. We assessed the relation of parity and lactation to incidence of ER(-)/PR(-) and ER(+)/PR(+) breast cancer in a cohort of African American women.

METHODS

From 1995-2009, 457 incident cases of ER(+)/PR(+) and 318 cases of ER(-)/PR(-) breast cancer were confirmed by review of pathology data among 59,000 African American women followed in the Black Women's Health Study through biennial questionnaires. HRs and two-sided 95% CIs for the incidence of breast cancer subtypes were derived from proportional hazards regression models that controlled for age, reproductive variables, and breast cancer risk factors.

RESULTS

Higher parity was associated with an increased risk of ER(-)/PR(-) breast cancer (HR = 1.48, 95% CI: 0.98-1.84 for 3+ versus 0 births, P(trend) = 0.009), and with a reduced risk of ER(+)/PR(+) cancer (HR = 0.53, 95% CI: 0.39-0.73 for 3+ versus 0 births, P(trend) = 0.0002). Among women who had breastfed, high parity was no longer associated with increased incidence of ER(-)/PR(-) breast, but the inverse association with ER(+)/PR(+) cancer persisted.

CONCLUSIONS

The higher incidence of ER(-)/PR(-) breast cancer in African American women may be explained in part by their higher parity and lower prevalence of breastfeeding relative to white women.

IMPACT

Increased breastfeeding may lead to a reduction in the incidence of this breast cancer subtype.

The Effects of 17β-estradiol in Cancer are Mediated by Estrogen Receptor Signaling at the Plasma Membrane

Two different isoforms of the estrogen receptors (i.e., ERα and ERβ) mediate pleiotropic 17β-estradiol (E2)-induced cellular effects. The ERs are principally localized in the nucleus where they act by globally modifying the expression of the E2-target genes. The premise that E2 effects are exclusively mediated through the nuclear localized ERs has been rendered obsolete by research over the last 15 years demonstrating that ERα and ERβ proteins are also localized at the plasma membranes and in other extra-nuclear organelles. The E2 modulation of cancer cell proliferation represents a good example of the impact of membrane-initiated signals on E2 effects. In fact, E2 via ERα elicits rapid signals driving cancer cells to proliferation (e.g., in breast cancer cells), while E2-induced ERβ rapid signaling inhibits proliferation (e.g., in colon cancer cells). In this review we provide with an overview of the complex system of E2-induced signal transduction pathways, their impact on E2-induced cancer cell proliferation, and the participation of E2-induced membrane-initiated signals in tumor environment.

Comparative evaluation of ERα and ERβ significance in breast cancer: state of the art

Over 30 years of clinical data have unequivocally established estrogen receptor (ER)-α as a critical clinical biomarker and valid therapeutic target to fight breast cancer. However, ERα remains imperfect with respect to both of these activities, mainly because the mechanisms by which estrogens mediate their activity are far more complex than originally anticipated. The cloning of a second estrogen receptor, ERβ, has led to a full re-evaluation of our original view of the action of estrogen in breast tissues. Important challenges remain with respect to the design, selection and normalization of the most appropriate methods for assaying the expression and functionality of both receptors. Solving these challenges remains a priority in order to decide upon specific endocrine therapies and save patients who are still dying from a potentially curable disease.

Insulin-like growth factor-2 (IGF-2) activates estrogen receptor-α and -β via the IGF-1 and the insulin receptors in breast cancer cells

The estrogen receptor (ER) is a primary target for breast cancer (BC) treatment. As BC progresses to estrogen-independent growth, the insulin-like growth factor-1 receptor (IGF-1R) and the ER interact in synergistic cross-talk mechanisms, which result in enhanced activation of both receptors' signaling cascades. Insulin-like growth factor-2 (IGF-2) is critical in BC progression and its actions are mediated by the IGF-1R. Our previous studies showed that IGF-2 regulates survival genes that protect the mitochondria and promote chemoresistance. In this study, we analyzed BC cells by subcellular fractionation, Western-Blot, qRT-PCR, and siRNA analysis. Our results demonstrate that IGF-2 activates ER-α and ER-β, and modulates their translocation to the nucleus, membrane organelles, and the mitochondria. IGF-2 actions are mediated by the IGF-1R and the insulin receptor. This novel mechanism of IGF-2 synergistic cross-talk signaling with ER-α and ER-β can promote estrogen-independent BC progression and provide new therapeutic targets for the treatment of BC patients.

Epigenetic organization of brain sex differences and juvenile social play behavior

The study of epigenetic mechanisms is important for elucidating how gene-by-environment interactions can have lasting outcomes on brain function and behavior. In general, studies of epigenetic processes mainly focus on the methylation status of DNA. While methylation of DNA alone can interfere with gene transcription, it is the binding of methyl-CpG binding proteins to methylated DNA, and subsequent recruitment of nuclear corepressors and histone deacetylases, that results in more efficient gene repression. In this review, we will discuss sex differences in DNA methylation patterns, methyl binding proteins, and corepressor proteins that contribute to lasting differences in brain and juvenile behavior. Specifically, we will discuss new data on sex differences in ERα DNA promoter methylation patterns, and the role of MeCP2 and the nuclear corepressor, NCoR, on the organization of juvenile social play behavior.

Estradiol meets notch signaling in developing neurons

The transmembrane receptor Notch, a master developmental regulator, controls gliogenesis, neurogenesis, and neurite development in the nervous system. Estradiol, acting as a hormonal signal or as a neurosteroid, also regulates these developmental processes. Here we review recent evidence indicating that estradiol and Notch signaling interact in developing hippocampal neurons by a mechanism involving the putative membrane receptor G protein-coupled receptor 30. This interaction is relevant for the control of neuronal differentiation, since the downregulation of Notch signaling by estradiol results in the upregulation of neurogenin 3, which in turn promotes dendritogenesis.

Interactions between IGF-I, estrogen receptor-α (ERα), and ERβ in regulating growth/apoptosis of MCF-7 human breast cancer cells

Understanding of the interactions between estradiol (E₂) and IGF-I is still incomplete. Cell lines derived from the MCF-7 breast cancer cells were generated with suppressed expression of the IGF-I receptor (IGF-IR), termed IGF-IR.low cells, by stable transfection using small interfering RNA (siRNA) expression vector. Vector for control cells carried sequence generating noninterfering RNA. Concomitant with reduction in the IGF-IR levels, the IGF-IR.low cells also showed a reduction in estrogen receptor α (ERα) and progesterone receptor expressions, and an elevation in the expression of ERβ. The number of the IGF-IR.low cells was reduced in response to IGF-I and human GH plus epidermal growth factor, but E₂ did not cause an increase in the number of the IGF-IR.low cells compared to controls. The proliferation rate of IGF-IR.low cells was only reduced in response to E₂ compared to controls, whereas their basal and hormone-stimulated apoptosis rate was increased. Phosphorylation of p38 mitogen-activated protein kinase (p38 MAPK) was increased in the IGF-IR.low cells after treatment with E₂, without affecting control cells. Furthermore, phosphorylation of the tumor suppressor protein p53 was elevated in the IGF-IR.low cells compared to the controls. In conclusion, suppressing IGF-IR expression decreased the level of ERα but increased the level of ERβ. Overall growth rate of the IGF-IR.low cells was reduced mostly through an increase in apoptosis without affecting proliferation substantially. We hypothesize that a decreased ERα:ERβ ratio triggered a rapid phosphorylation of p38 MAPK, which in turn phosphorylated the p53 tumor suppressor and accelerated apoptosis rate.

Regulation of endogenous conductances in GnRH neurons by estrogens

17β-estradiol (E2) regulates the activity of the gonadotropin-releasing hormone (GnRH) neurons through both presynaptic and postsynaptic mechanisms, and this ovarian steroid hormone is essential for cyclical GnRH neuronal activity and secretion. E2 has significant actions to modulate the mRNA expression of numerous ion channels in GnRH neurons and/or to enhance (suppress) endogenous conductances (currents) including potassium (K(ATP), A-type) and calcium low voltage T-type and high voltage L-type currents. Also, it is well documented that E2 can alter the excitability of GnRH neurons via direct action, but the intracellular signaling cascades mediating these actions are not well understood. As an example, K(ATP) channels are critical ion channels needed for maintaining GnRH neurons in a hyperpolarized state for recruiting T-type calcium channels that are important for burst firing in GnRH neurons. E2 modulates the activity of K(ATP) channels via a membrane-initiated signaling pathway in GnRH neurons. Obviously there are other channels, including the small conductance activated K(+) (SK) channels, that maybe modulated by this signaling pathway, but the ensemble of mER-, ERα-, and ERβ-mediated effects both pre- and post-synaptic will ultimately dictate the excitability of GnRH neurons.

Estrogen-like effects of cadmium in vivo do not appear to be mediated via the classical estrogen receptor transcriptional pathway

BACKGROUND

Cadmium (Cd), a ubiquitous food contaminant, has been proposed to be an endocrine disruptor by inducing estrogenic responses in vivo. Several in vitro studies suggested that these effects are mediated via estrogen receptors (ERs).

OBJECTIVE

We performed this study to clarify whether Cd-induced effects in vivo are mediated via classical ER signaling through estrogen responsive element (ERE)-regulated genes or if other signaling pathways are involved.

METHODS

We investigated the estrogenic effects of cadmium chloride (CdCl2) exposure in vivo by applying the Organisation for Economic Co-operation and Development (OECD) rodent uterotrophic bioassay to transgenic ERE-luciferase reporter mice. Immature female mice were injected subcutaneously with CdCl2 (5, 50, or 500 µg/kg body weight) or with 17α-ethinylestradiol (EE2) on 3 consecutive days. We examined uterine weight and histology, vaginal opening, body and organ weights, Cd tissue retention, activation of mitogen-activated protein kinase (MAPK) pathways, and ERE-dependent luciferase expression.

RESULTS

CdCl2 increased the height of the uterine luminal epithelium in a dose-dependent manner without increasing the uterine wet weight, altering the timing of vaginal opening, or affecting the luciferase activity in reproductive or nonreproductive organs. However, we observed changes in the phosphorylation of mouse double minute 2 oncoprotein (Mdm2) and extracellular signal-regulated kinase (Erk1/2) in the liver after CdCl2 exposure. As we expected, EE2 advanced vaginal opening and increased uterine epithelial height, uterine wet weight, and luciferase activity in various tissues.

CONCLUSION

Our data suggest that Cd exposure induces a limited spectrum of estrogenic responses in vivo and that, in certain targets, effects of Cd might not be mediated via classical ER signaling through ERE-regulated genes.

Bisphenol AF is a full agonist for the estrogen receptor ERalpha but a highly specific antagonist for ERbeta

BACKGROUND

Bisphenol AF has been acknowledged to be useful for the production of CF3-containing polymers with improved chemical, thermal, and mechanical properties. Because of the lack of adequate toxicity data, bisphenol AF has been nominated for comprehensive toxicological characterization.

OBJECTIVES

We aimed to determine the relative preference of bisphenol AF for the human nuclear estrogenic receptors ERalpha and ERbeta and the bisphenol A-specific estrogen-related receptor ERRgamma, and to clarify structural characteristics of receptors that influence bisphenol AF binding.

METHODS

We examined receptor-binding activities of bisphenol AF relative to [3H]17beta-estradiol (for ERalpha and ERbeta) and [3H]bisphenol A (for ERRgamma). Functional luciferase reporter gene assays were performed to assess receptor activation in HeLa cells.

RESULTS

We found that bisphenol AF strongly and selectively binds to ERs over ERRgamma. Furthermore, bisphenol AF receptor-binding activity was three times stronger for ERbeta [IC50 (median inhibitory concentration) = 18.9 nM] than for ERalpha. When examined using a reporter gene assay, bisphenol AF was a full agonist for ERalpha. In contrast, it was almost completely inactive in stimulating the basal constitutive activity of ERbeta. Surprisingly, bisphenol AF acted as a distinct and strong antagonist against the activity of the endogenous ERbeta agonist 17beta-estradiol.

CONCLUSION

Our results suggest that bisphenol AF could function as an endocrine-disrupting chemical by acting as an agonist or antagonist to perturb physiological processes mediated through ERalpha and/or ERbeta.

Estrogen responses in killifish (Fundulus heteroclitus) from polluted and unpolluted environments are site- and gene-specific

Epidemiological, ecological, and laboratory-based studies support the hypothesis that endocrine disrupting chemicals (EDCs) in the environment are responsible for developmental and reproductive abnormalities. We have previously described a killifish population resident in a highly polluted Superfund site (New Bedford Harbor, NBH) that shows evidence of exposure to an estrogenic environment and endocrine disruption. Here, we compare NBH with a local reference population (Scorton Creek, SC) for developmental patterns and direct effects of exogenous estradiol on the estrogenic markers, brain cytochrome P450 aromatase (CYP19A2 or AroB), hepatic vitellogenin (Vtg), and hepatic estrogen receptor alpha (ER alpha). In contrast to our previous observation of elevated ER alpha in NBH embryos, developmental levels of AroB and Vtg mRNAs did not differ between the two sites, demonstrating that not all estrogen-responsive genes are upregulated in NBH embryos. A dose-response experiment showed that NBH larvae are less responsive (lower maximum induction, as measured by ER alpha) and less sensitive (higher EC(50) for induction, as measured by AroB) to estradiol than SC larvae, changes that would be adaptive in an estrogenic environment. In contrast, induction of Vtg mRNA is similar in the two populations, indicating that the adaptive mechanism is target gene-specific. Based on the lower basal levels of ER alpha mRNA in several tissues from adult NBH fish vs SC fish (Greytak and Callard, 2007), we predicted estrogen hyporesponsiveness; however, induction of ER alpha by estradiol exposure in reproductively inactive males did not differ between the two sites. Moreover, AroB was more responsive and Vtg induction was greater (2d) or similar (5d) in NBH as compared to SC males. Worth noting is the high inter-individual variability in estrogen responses of gene targets, especially in NBH killifish, which may indicate evolving preadaptive or adaptive mechanisms. In conclusion, although multi-generational exposure to a highly polluted environment is associated with changes in basal levels of ER alpha mRNA, this is not a simple predictor of estrogen responsiveness. We hypothesize that adaptation of killifish to the estrogenic and polluted environment may be occurring through diverse mechanisms that are gene-, tissue type- and life-stage-specific.

Estrogen receptor 1 gene (ESR1) is associated with restrictive anorexia nervosa

Anorexia nervosa (AN) is a highly heritable young-onset psychiatric illness the etiology of which remains unknown. Estrogen alpha and beta receptors, encoded by ESR1 and ESR2 genes, are involved in food intake regulation and eating behavior, and may have a potential role in AN. We performed a family-based association study of 17 single-nucleotide polymorphisms (SNPs) encompassing ESR1 and ESR2 genes in a cohort of 321 French AN families. We attempted to replicate this finding in a cohort of 41 restrictive AN (RAN) families and in a population-based study of 693 young women. Using the transmission disequilibrium test, a significant over-transmission was detected between AN and ESR1 rs726281 and rs2295193. These SNPs and another among ESR1 were more specifically associated with the RAN subtype (rs726281, p=0.005, odds ratio (OR)=2.1, 95% confidence interval (95% CI)=1.2-3.6; rs3798577, p=0.021, OR=1.6, 95% CI=1.1-2.3; and rs2295193, p=0.007, OR=1.7, 95% CI=1.2-2.5). A large eight-SNPs haplotype of ESR1 gene was also associated with AN (p<0.0001, OR=3.1, 95% CI=1.8-5.1). Association of ESR1 SNPs and RAN was driven by paternal over-transmissions (p<0.0001, OR=3.7, 95% CI=1.9-7.3). Furthermore, we confirmed the preferential paternal over-transmission of the ESR1 rs726281 on the independent German sample of 41 RAN trios (p=0.025, OR=3, 95% CI=1.1-8.3). Finally, rs3798577 was associated with eating disorders in a population-based sample of 693 women (p<0.01). Our findings are strongly in favor of an association between ESR1 polymorphisms and AN. In particular, ESR1 gene confers a high risk of vulnerability to the restrictive subtype of AN, and suggests that the estrogen pathway has to be further analyzed in AN.

Estrogen augments the T cell-dependent but not the T-independent immune response

Estrogen plays a critical regulatory role in the development and maintenance of immunity. Its role in the regulation of antibody synthesis in vivo is still not completely clear. Here, we have compared the effect of estrogen on T cell-dependent (TD) and T cell-independent type 2 (TI-2) antibody responses. The results provide the first evidence that estrogen enhances the TD but not the TI-2 response. Ovariectomy significantly decreased, while estrogen re-administration increased the number of hapten-specific IgM- and IgG-producing cells in response to TD antigen. In vitro experiments also show that estrogen may have a direct impact on B and T cells by inducing rapid signaling events, such as Erk and AKT phosphorylation, cell-specific Ca(2+) signal, and NFkappaB activation. These non-transcriptional effects are mediated by classical estrogen receptors and partly by an as yet unidentified plasma membrane estrogen receptor. Such receptor- mediated rapid signals may modulate the in vivo T cell-dependent immune response.

Breast tumor developed in a pregnant rat after treatment with the teratogen Cycloheximide

AIM

To describe histochemically and immunohistochemically a breast tumor presented in a pregnant rat given Cycloheximide to examine its teratogenic and embryotoxic effect on the embryos.

METHODS

Cycloheximide was injected in pregnant Wistar rats at a dose of 3 mg/kg.b.w. on both 10th and 11th gestational days. In one of the rats, a large breast tumor developed rapidly. Histochemical staining with Hematoxylin-Eosin and Masson Trichrome and immunohistochemical identification with mouse monoclonal antibodies: a) Estrogen Receptor A and b) Estrogen Receptor B was performed.

RESULTS

Analysis with A-receptor and B-receptor showed that the breast tumor which was developed after treatment with Cycloheximide was malignant. Positive immunohistochemical reaction was evident especially with A-receptor indicating the malignancy of the tumor.

CONCLUSIONS

Cycloheximide is a known toxic and teratogenic agent and potentially a carcinogenic drug. Thus it should be used with extreme caution as a pesticide.

Loss of estrogen receptor beta decreases mitochondrial energetic potential and increases thrombogenicity of platelets in aged female mice

Platelets derived from aged (reproductively senescent) female mice with genetic deletion of estrogen receptor beta (betaER) are more thrombogenic than those from age-matched wild-type (WT) mice. Intracellular processes contributing to this increased thrombogenicity are not known. Experiments were designed to identify subcellular localization of estrogen receptors and evaluate both glycolytic and mitochondrial energetic processes which might affect platelet activation. Platelets and blood from aged (22-24 months) WT and estrogen receptor beta knockout (betaERKO) female mice were used in this study. Body, spleen weight, and serum concentrations of follicle-stimulating hormone and 17beta-estradiol were comparable between WT and betaERKO mice. Number of spontaneous deaths was greater in the betaERKO colony (50% compared to 30% in WT) over the course of 24 months. In resting (nonactivated) platelets, estrogen receptors did not appear to colocalize with mitochondria by immunostaining. Lactate production and mitochondrial membrane potential of intact platelets were similar in both groups of mice. However, activities of NADH dehydrogenase, cytochrome bc ( 1 ) complex, and cytochrome c oxidase of the electron transport chain were reduced in mitochondria isolated from platelets from betaERKO compared to WT mice. There were a significantly higher number of phosphatidylserine-expressing platelet-derived microvesicles in the plasma and a greater thrombin-generating capacity in betaERKO compared to WT mice. These results suggest that deficiencies in betaER affect energy metabolism of platelets resulting in greater production of circulating thrombogenic microvesicles and could potentially explain increased predisposition to thromboembolism in some elderly females.

Neuroprotective actions of selective estrogen receptor modulators

Decreasing levels of sex hormones with aging may have a negative impact on brain function, since this decrease is associated with the progression of neurodegenerative disorders, increased depressive symptoms and other psychological disturbances. Extensive evidence from animal studies indicates that sex steroids, in particular estradiol, are neuroprotective. However, the potential benefits of estradiol therapy for the brain are counterbalanced by negative, life-threatening risks in the periphery. A potential therapeutic alternative to promote neuroprotection is the use of selective estrogen receptor modulators (SERMs), which may be designed to act with tissue selectivity as estrogen receptor agonists in the brain and not in other organs. Currently available SERMs act not only with tissue selectivity, but also with cellular selectivity within the brain and differentially modulate the activation of microglia, astroglia and neurons. Finally, SERMs may promote the interaction of estrogen receptors with the neuroprotective signaling of growth factors, such as the phosphatidylinositol 3-kinase/glycogen synthase kinase 3 pathway.

Seasonal relationship between gonadotropin, growth hormone, and estrogen receptor mRNA expression in the pituitary gland of largemouth bass

The objectives of this study were to investigate the seasonal changes in pituitary gonadotropins, growth hormone (GH), and estrogen receptor (ER) isoform mRNA in wild female and male largemouth bass (LMB) (Micropterus salmoides) from an unpolluted habitat to better understand reproductive physiology in this ecologically important species. Female pituitary luteinizing hormone (LH) beta subunit and follicle stimulating hormone (FSH) beta subunit mRNA showed significant seasonal variation with levels peaking from January to April and were lowest from May to August. Male LMB showed more variation in gonadotropin subunit expression from month to month. Females had approximately 2-3 times higher gonadotropin mRNA levels in the pituitary when compared to males. All three gonadotropin mRNAs in females were positively correlated to gonadosomatic index (GSI), but only LHbeta mRNA was correlated to GSI in males. Gonadotropin mRNA expression also increased with increasing oocyte and sperm maturation. Gonadotropin beta subunit mRNA expression was positively correlated to GH mRNA in both sexes. The expression of all three ER isoforms was significantly correlated to each other in both sexes. The concurrent increase in all three ER mRNA isoforms with increasing gonadotropin mRNA in females and males suggests a prominent role for E2 feedback on pituitary gonadotropin synthesis in both sexes and that each of the three ER isoforms are likely to play a role in the pituitary during teleost reproduction.

[Estrogen receptors in the diagnosis and treatment of hormone-dependent tumors]

The paper presents the current data available on the etiology of tumor diseases, among other things, shows the role of hormones, namely: estrogens and their receptors, in the mechanism responsible for the occurrence of these diseases. Each tumor was shown to have its receptor status and to be unresponsive to this or that therapy differently. The efficiency of treatment and its prognosis may be determined if the receptor composition of an involved organ is estimated correctly. The authors summarize the data available in the literature, as well as the results of their own investigations explaining the selective effect of estradiol receptor agonists and antagonists in various tissues. The mRNA varieties that potentially encoding for the synthesis of different subtypes of estrogen receptors (ER) - ER-α and ERβ, which are also coded by various genes located in different chromosomes. Pituitary adenomas as hormone-dependent masses are described in detail. The authors data on the concentration of nuclear estrogen receptors in different types of adenomas are given.

Androgen- and estrogen-independent regulation of copulatory behavior following castration in male B6D2F1 mice

Male reproductive behavior is highly dependent upon gonadal steroids. However, between individuals and across species, the role of gonadal steroids in male reproductive behavior is highly variable. In male B6D2F1 hybrid mice, a large proportion (about 30%) of animals demonstrate the persistence of the ejaculatory reflex long after castration. This provides a model to investigate the basis of gonadal steroid-independent male sexual behavior. Here we assessed whether non-gonadal steroids promote mating behavior in castrated mice. Castrated B6D2F1 hybrids that persisted in copulating (persistent copulators) were treated with the androgen receptor blocker, flutamide, and the aromatase enzyme inhibitor, letrozole, for 8 weeks. Other animals were treated with the estrogen receptor blocker, ICI 182,780, via continual intraventricular infusion for 2 weeks. None of these treatments eliminated persistent copulation. A motivational aspect of male sexual behavior, the preference for a receptive female over another male, was also assessed. This preference persisted after long-term castration in persistent copulators, and administration of ICI 182,780 did not influence partner preference. To assess the possibility of elevated sensitivity to sex steroids in brains of persistent copulators, we measured mRNA levels for genes that code for the estrogen receptor-alpha, androgen receptor, and aromatase enzyme in the medial preoptic area and bed nucleus of the stria terminalis. No differences in mRNA of these genes were noted in brains of persistent versus non-persistent copulators. Taken together our results suggest that non-gonadal androgens and estrogens do not maintain copulatory behavior in B6D2F1 mice which display copulatory behavior after castration.

Role of protein phosphatases and mitochondria in the neuroprotective effects of estrogens

In the present treatise, we provide evidence that the neuroprotective and mito-protective effects of estrogens are inexorably linked and involve the ability of estrogens to maintain mitochondrial function during neurotoxic stress. This is achieved by the induction of nuclear and mitochondrial gene expression, the maintenance of protein phosphatases levels in a manner that likely involves modulation of the phosphorylation state of signaling kinases and mitochondrial pro- and anti-apoptotic proteins, and the potent redox/antioxidant activity of estrogens. These estrogen actions are mediated through a combination of estrogens receptor (ER)-mediated effects on nuclear and mitochondrial transcription of protein vital to mitochondrial function, ER-mediated, non-genomic signaling and non-ER-mediated effects of estrogens on signaling and oxidative stress. Collectively, these multifaceted, coordinated action of estrogens leads to their potency in protecting neurons from a wide variety of acute insults as well as chronic neurodegenerative processes.

Long-term effects of environmental endocrine disruptors on reproductive physiology and behavior

It is well established that, over the course of development, hormones shape the vertebrate brain such that sex specific physiology and behaviors emerge. Much of this occurs in discrete developmental windows that span gestation through the prenatal period, although it is now becoming clear that at least some of this process continues through puberty. Perturbation of this developmental progression can permanently alter the capacity for reproductive success. Wildlife studies have revealed that exposure to endocrine disrupting compounds (EDCs), either naturally occurring or man made, can profoundly alter reproductive physiology and ultimately impact entire populations. Laboratory studies in rodents and other species have elucidated some of the mechanisms by which this occurs and strongly indicate that humans are also vulnerable to disruption. Use of hormonally active compounds in human medicine has also unfortunately revealed that the developing fetus can be exposed to and affected by endocrine disruptors, and that it might take decades for adverse effects to manifest. Research within the field of environmental endocrine disruption has also contributed to the general understanding of how early life experiences can alter reproductive physiology and behavior through non-genomic, epigenetic mechanisms such as DNA methylation and histone acetylation. These types of effects have the potential to impact future generations if the germ line is affected. This review provides an overview of how exposure to EDCs, particularly those that interfere with estrogen action, impacts reproductive physiology and behaviors in vertebrates.

Female hormone receptors are differentially expressed in mouse fibrocartilages

OBJECTIVE

Despite the female predilection for joint diseases, and the known effects of female hormones in regulating chondrocyte function, the various female hormone receptor subtypes in joints are not well characterized, and comparisons in receptor profiles between joints and genders are lacking. This investigation characterized and compared the relative levels of estrogen receptors (ER)-alpha and -beta, relaxin receptors LGR7 and LGR8, and progesterone receptor (PR) in the temporomandibular joint (TMJ) disc, knee meniscus (KM) and pubic symphysis fibrocartilages.

METHODS

Fibrocartilaginous cells from 12-week-old mice were maintained in serum-containing alpha-modified Eagle's medium (MEM) until confluence. Total RNA and cell lysates were assayed by RT-PCR, qRT-PCR, immunocytochemistry and Western blots, and joint sections subjected to immunohistochemistry.

RESULTS

All hormone receptors assayed were present in the three joints, but showed substantial differences in expression levels between joints. TMJ cells had higher ER-alpha (>2.8-fold), ER-beta (>2.2-fold), LGR7 (>3-fold) and PR (>1.8-fold), and lower LGR8 (0.5-fold) gene expression levels than KM cells. The ratio of ER-alpha:ER-beta and LGR7:LGR8 was 1.8- and 7.5-fold higher, respectively, in TMJ than in KM cells. The profile of hormone receptors in the TMJ disc was similar to those in the pubic symphysis. Immunochemistry confirmed the differential expression patterns of these receptors in the three tissues. The TMJ cells demonstrated sexual dimorphism in the levels of both ER isoforms, but not of LGR7, LGR8 or PR.

CONCLUSIONS

The findings suggest that these fibrocartilages are putative target tissues for actions of female hormones. The differential expression profiles of the hormone receptors in the three joint fibrocartilages and the sexual dimorphism in ERs in TMJ disc cells are likely to result in varied downstream effects in response to hormones within these fibrocartilaginous tissues.

Bisphenol A at low nanomolar doses confers chemoresistance in estrogen receptor-alpha-positive and -negative breast cancer cells

BACKGROUND

Resistance to chemotherapy is a major problem facing breast cancer patients, and identifying potential contributors to chemoresistance is a critical area of research. Bisphenol A (BPA) has long been suspected to promote carcinogenesis, but the high doses of BPA used in many studies generated conflicting results. In addition, the mechanism by which BPA exerts its biological actions is unclear. Although estrogen has been shown to antagonize anticancer drugs, the role of BPA in chemoresistance has not been examined.

OBJECTIVE

The objective of our study was to determine whether BPA at low nanomolar concentrations opposes the action of doxorubicin, cisplatin, and vinblastine in the estrogen receptor-alpha (ERalpha)-positive T47D and the ERalpha-negative MDA-MB-468 breast cancer cells.

METHODS

We determined the responsiveness of cells to anticancer drugs and BPA using the 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl tetrazolium bromide (MTT) cytotoxicity assay. Specific ERalpha and ERbeta inhibitors and real-time polymerase chain reaction were used to identify potential receptor(s) that mediate the actions of BPA. Expression of antiapoptotic proteins was assessed by Western blotting.

RESULTS

BPA antagonizes the cytotoxicity of multiple chemotherapeutic agents in both ERalpha-positive and -negative breast cancer cells independent of the classical ERs. Both cell types express alternative ERs, including G-protein-coupled receptor 30 (GPR30) and members of the estrogen-related receptor family. Increased expression of antiapoptotic proteins is a potential mechanism by which BPA exerts its anticytotoxic effects.

CONCLUSIONS

BPA at environmentally relevant doses reduces the efficacy of chemotherapeutic agents. These data provide considerable support to the accumulating evidence that BPA is hazardous to human health.

Bisphenol A at environmentally relevant doses inhibits adiponectin release from human adipose tissue explants and adipocytes

BACKGROUND

The incidence of obesity has risen dramatically over the last few decades. This epidemic may be affected by exposure to xenobiotic chemicals. Bisphenol A (BPA), an endocrine disruptor, is detectable at nanomolar levels in human serum worldwide. Adiponectin is an adipocyte-specific hormone that increases insulin sensitivity and reduces tissue inflammation. Thus, any factor that suppresses adiponectin release could lead to insulin resistance and increased susceptibility to obesity-associated diseases.

OBJECTIVES

In this study we aimed to compare a) the effects of low doses of BPA and estradiol (E(2)) on adiponectin secretion from human breast, subcutaneous, and visceral adipose explants and mature adipocytes, and b) expression of putative estrogen and estrogen-related receptors (ERRs) in these tissues.

METHODS

We determined adiponectin levels in conditioned media from adipose explants or adipocytes by enzyme-linked immunosorbant assay. We determined expression of estrogen receptors (ERs) alpha and beta, G-protein-coupled receptor 30 (GPR30), and ERRs alpha, beta, and gamma by quantitative real-time polymerase chain reaction.

RESULTS

BPA at 0.1 and 1 nM doses suppressed adiponectin release from all adipose depots examined. Despite substantial variability among patients, BPA was as effective, and often more effective, than equimolar concentrations of E(2). Adipose tissue expresses similar mRNA levels of ERalpha, ERbeta, and ERRgamma, and 20- to 30-fold lower levels of GPR30, ERRalpha, and ERRbeta.

CONCLUSIONS

BPA at environmentally relevant doses inhibits the release of a key adipokine that protects humans from metabolic syndrome. The mechanism by which BPA suppresses adiponectin and the receptors involved remains to be determined.

Dimethandrolone (7alpha,11beta-dimethyl-19-nortestosterone) and 11beta-methyl-19-nortestosterone are not converted to aromatic A-ring products in the presence of recombinant human aromatase

Dimethandrolone undecanoate (DMAU: 7alpha,11beta-dimethyl-19-nortestosterone 17beta-undecanoate) is a potent orally active androgen in development for hormonal therapy in men. Cleavage of the 17beta-ester bond by esterases in vivo leads to liberation of the biologically active androgen, dimethandrolone (DMA), a 19-norandrogen. For hormone replacement in men, administration of C19 androgens such as testosterone (T) may lead to elevations in circulating levels of estrogens due to aromatization. As several reports have suggested that certain 19-norandrogens may serve as substrates for the aromatase enzyme and are converted to the corresponding aromatic A-ring products, it was important to investigate whether DMA, the related compound, 11beta-methyl-19-nortestosterone (11beta-MNT), also being tested for hormonal therapy in men, and other 19-norandrogens can be converted to aromatic A-ring products by human aromatase. The hypothetical aromatic A-ring product corresponding to each substrate was obtained by chemical synthesis. These estrogens bound with high affinity to purified recombinant human estrogen receptors (ER) alpha and beta in competitive binding assays (IC50's: 5-12 x 10(-9) M) and stimulated transcription of 3XERE-luciferase in T47Dco human breast cancer cells with a potency equal to or greater than that of estradiol (E2) (EC50's: 10(-12) to 10(-11) M). C19 androgens (T, 17alpha-methyltestosterone (17alpha-MT), androstenedione (AD), and 16alpha-hydroxyandrostenedione (16alpha-OHAD)), 19-norandrogens (DMA, 11beta-MNT, 19-nortestosterone (19-NT), and 7alpha-methyl-19-nortestosterone (MENT)) or the structurally similar 19-norprogestin, norethindrone (NET) were incubated at 50 microM with recombinant human aromatase for 10-180 min at 37 degrees C. The reactions were terminated by extraction with acetonitrile and centrifugation, and substrate and potential product were separated by HPLC. Retention times were monitored by UV absorption, and UV peaks were quantified using standard curves. Aromatization of the positive controls, T, AD, and 16alpha-OHAD was linear for 40-60 min, and conversion of T or AD was complete by 120 min. The nonsteroidal aromatase inhibitor, letrozole, demonstrated concentration-dependent suppression of T aromatization. Under the same conditions, there was no detectable conversion of DMA, 11beta-MNT, or NET to their respective hypothetical aromatic A-ring products during incubation times up to 180 min. Aromatization of MENT and 19-NT proceeded slowly and was limited. Collectively, these data support the notion that in the absence of the C19-methyl group, which is the site of attack by oxygen, aromatization of androgenic substrates proceeds slowly or not at all and that this reaction is impeded by the presence of a methyl group at the 11beta position.