Nongenomic activity and subsequent c-fos induction by estrogen receptor ligands are not sufficient to promote deoxyribonucleic acid synthesis in human endometrial adenocarcinoma cells

The role of sex hormones and steroid receptors on female reproductive cancers

Sex steroids have been widely described to be associated with a number of human diseases, including hormone-dependent tumors. Several studies have been concerned about the factors regulating the availability of sex steroids and its importance in the pathophysiological aspects of the reproductive cancers in women. In premenopausal women, large fluctuations in the concentration of circulating estradiol (E2) and progesterone (P4) orchestrate many events across the menstrual cycle. After menopause, the levels of circulating E2 and P4 decline but remain at high concentration in the peripheral tissues. Notably, there is a strong relationship between circulating sex hormones and female reproductive cancers (e.g. ovarian, breast, and endometrial cancers). These hormones activate a number of specific signaling pathways after binding either to estrogen receptors (ERs), especially ERα, ERα36, and ERβ or progesterone receptors (PRs). Importantly, the course of the disease will depend on particular transactivation pathway. Identifying ER- or PR-positive tumors will benefit patients in terms of proper endocrine therapy. Based on hormonal responsiveness, effective prevention methods for ovarian, breast, and endometrial cancers represent a special opportunity for women at risk of malignancies. Hormone replacement therapy (HRT) might significantly increase the risk of these cancer types, and endocrine treatments targeting ER signaling may be helpful against E2-dependent tumors. This review will present the role of sex steroids and their receptors associated with the risk of developing female reproductive cancers, with emphasis on E2 levels in pre and postmenopausal women. In addition, new therapeutic strategies for improving the survival rate outcomes in women will be addressed.

Roles of ERβ and GPR30 in Proliferative Response of Human Bladder Cancer Cell to Estrogen

Bladder cancer belongs to one of the most common cancers and is a leading cause of deaths in our society. Urothelial carcinoma of the bladder (UCB) is the main type of this cancer, and the estrogen receptors in UCB remain to be studied. Our experiment aimed to investigate the possible biological effect of 17β-estradiol on human bladder-derived T24 carcinoma cells and to indicate its related mechanisms. T24 cells were treated with various doses of 17β-estradiol, and cell proliferation was detected using MTT assays. 17β-estradiol promoted T24 cell proliferation independent of ERβ/GPR30-regulated EGFR-MAPK pathway, while it inhibited cell growth via GPR30. Furthermore, the expression levels of downstream genes (c-FOS, BCL-2, and CYCLIN D1) were increased by 17β-estradiol and this effect was independently associated with activity of the EGFR-MAPK pathway. The two estrogen receptors might be potential therapeutic targets for the treatment of bladder cancer.

DNA homologous recombination factor SFR1 physically and functionally interacts with estrogen receptor alpha

Estrogen receptor alpha (ERα), a ligand-dependent transcription factor, mediates the expression of its target genes by interacting with corepressors and coactivators. Since the first cloning of SRC1, more than 280 nuclear receptor cofactors have been identified, which orchestrate target gene transcription. Aberrant activity of ER or its accessory proteins results in a number of diseases including breast cancer. Here we identified SFR1, a protein involved in DNA homologous recombination, as a novel binding partner of ERα. Initially isolated in a yeast two-hybrid screen, the interaction of SFR1 and ERα was confirmed in vivo by immunoprecipitation and mammalian one-hybrid assays. SFR1 co-localized with ERα in the nucleus, potentiated ER’s ligand-dependent and ligand-independent transcriptional activity, and occupied the ER binding sites of its target gene promoters. Knockdown of SFR1 diminished ER’s transcriptional activity. Manipulating SFR1 expression by knockdown and overexpression revealed a role for SFR1 in ER-dependent and -independent cancer cell proliferation. SFR1 differs from SRC1 by the lack of an intrinsic activation function. Taken together, we propose that SFR1 is a novel transcriptional modulator for ERα and a potential target in breast cancer therapy.

Regulation of the transcriptional activity of nuclear receptors by the MEK/ERK1/2 pathway

Cells undergo continuous and simultaneous external influences regulating their behavior. As an example, during differentiation, they go through different stages of maturation and gene expression is regulated by several simultaneous signaling pathways. We often tend at separating the nuclear pathways from the signaling ones initiated at membrane receptors. However, it is essential to keep in mind that all these pathways are interconnected to achieve a fine regulation of cell functions. The regulation of transcription by nuclear receptors has been thoroughly studied, but it now appears that a critical level of this regulation involves the action of several kinases that target the nuclear receptors themselves as well as their partners. The purpose of this review is to highlight the importance of one family of the mitogen-activated protein kinase (MAPK) superfamily, the MEK/ERK1/2 pathway, in the transcriptional activity of nuclear receptors.

Bisphenol A induces a rapid activation of Erk1/2 through GPR30 in human breast cancer cells

Bisphenol A (BPA) has been considered as an endocrine disruptor due to its ability to interact with estrogen receptors (ERs). While G protein-coupled receptor 30 (GPR30) is a novel estrogen receptor, its role in BPA-induced activation of Erk1/2 remains unknown. Human breast cancer cell lines, MCF-7, MDA-MB-231 and SKBR3, were used as experimental models to discriminate between ERs-dependent, putative ERs-independent and/or GPR30-associated effects. BPA induced a rapid activation of Erk1/2 in both ERα/β-positive and negative breast cancer cells, and this effect was not blocked with an ER antagonist, ICI 182,780. A small interfering RNA assay revealed that the expression of GPR30 was necessary for BPA-induced activation of Erk1/2 and transcriptional regulation of c-fos. In addition, BPA regulates the expression of c-fos likely through an AP1-mediated pathway. As a conclusion, GPR30 plays an important role in the BPA-induced activation of Erk1/2 in a manner distinguishable from that in ERα-mediated signaling.

ER-α36, a novel variant of ER-α, mediates estrogen-stimulated proliferation of endometrial carcinoma cells via the PKCδ/ERK pathway

BACKGROUND

Recently, a variant of ER-α, ER-α36 was identified and cloned. ER-α36 lacks intrinsic transcription activity and mainly mediates non-genomic estrogen signaling. The purpose of this study was to investigate the function and the underlying mechanisms of ER-α36 in growth regulation of endometrial Ishikawa cancer cells.

METHODS

The cellular localization of ER-α36 and ER-α66 were determined by immunofluorescence in the Ishikawa cells. Ishikawa endometrial cancer control cells transfected with an empty expression vector, Ishikawa cells with shRNA knockdown of ER-α36 (Ishikawa/RNAiER36) and Ishikawa cells with shRNA knockdown of ER-α66 (Ishikawa/RNAiER66) were treated with E2 and E2-conjugated to bovine serum albumin (E2-BSA, membrane impermeable) in the absence and presence of different kinase inhibitors HBDDE, bisindolylmaleimide, rottlerin, H89 and U0126. The phosphorylation levels of signaling molecules and cyclin D1/cdk4 expression were examined with Western blot analysis and cell growth was monitored with the MTT assay.

RESULTS

Immunofluorescence staining of Ishikawa cells demonstrated that ER-α36 was expressed mainly on the plasma membrane and in the cytoplasm, while ER-α66 was predominantly localized in the cell nucleus. Both E2 and E2-BSA rapidly activated PKCδ not PKCα in Ishikawa cells, which could be abrogated by ER-α36 shRNA expression. E2-and E2-BSA-induced ERK phosphorylation required ER-α36 and PKCδ. However, only E2 was able to induce Camp-dependent protein kinase A (PKA) phosphorylation. Furthermore, E2 enhances cyclin D1/cdk4 expression via ER-α36.

CONCLUSION

E2 activates the PKCδ/ERK pathway and enhances cyclin D1/cdk4 expression via the membrane-initiated signaling pathways mediated by ER-α36, suggesting a possible involvement of ER-α36 in E2-dependent growth-promoting effects in endometrial cancer cells.

Nongenomic effect of estrogen on the MAPK signaling pathway and calcium influx in endometrial carcinoma cells

17beta-Estradiol (E2) is well known to interact with intracellular receptors that act as nuclear transcription factors. However, abundant evidence now indicates that E2 can also rapidly induce several nongenomic effects through signaling pathways related to cell growth, preservation, and differentiation. We studied the nongenomic effects of E2 in two human endometrial carcinoma cell lines, Ishikawa (estrogen receptor (ER) positive) and Hec-1A (ER negative or low) by cultivating them with either E2 or its membrane-impermeable conjugate, E2-BSA. We found that phosphorylation of Erk1/2 could be induced by either E2 or E2-BSA in Ishikawa cells. In Hec-1A cells, only E2 was able to induce Erk1/2 phosphorylation. Although the existence of a nongenomic component to the response was indicated by the finding that it could not be completely inhibited by the ER antagonist ICI182780,and it can also be inhibited by calcium inhibitor Nifedipine partly. Phosphorylation of Akt could not be induced, either by E2 or E2-BSA, in either cell line. Both E2 and E2-BSA elicited calcium influx in Ishikawa cells. In contrast to these nongenomic effects, only E2 was able to stimulate expression of the anti-apoptotic-protein Bcl-2. Taken together, these data indicate that nongenomic effects such as Erk1/2 phosphorylation and calcium influx can be initiated from the membrane in Ishikawa cell, and calcium can activate Erk1/2 phosphorylation. Except for ER, there must be other binding location of estrogen in endometrial cancer cells, and the nongenomic effects of estrogen initiated from plasma membrane by E2-BSA cannot lead to transcriptional effect of Bcl-2 expression.

G-protein-coupled receptor 30 and estrogen receptor-alpha are involved in the proliferative effects induced by atrazine in ovarian cancer cells

BACKGROUND

Atrazine, one of the most common pesticide contaminants, has been shown to up-regulate aromatase activity in certain estrogen-sensitive tumors without binding or activating the estrogen receptor (ER). Recent investigations have demonstrated that the orphan G-protein-coupled receptor 30 (GPR30), which is structurally unrelated to the ER, mediates rapid actions of 17beta-estradiol and environmental estrogens.

OBJECTIVES

Given the ability of atrazine to exert estrogen-like activity in cancer cells, we evaluated the potential of atrazine to signal through GPR30 in stimulating biological responses in cancer cells.

METHODS AND RESULTS

Atrazine did not transactivate the endogenous ERalpha in different cancer cell contexts or chimeric proteins encoding the ERalpha and ERbeta hormone-binding domain in gene reporter assays. Moreover, atrazine neither regulated the expression of ERalpha nor stimulated aromatase activity. Interestingly, atrazine induced extracellular signal-regulated kinase (ERK) phosphorylation and the expression of estrogen target genes. Using specific signaling inhibitors and gene silencing, we demonstrated that atrazine stimulated the proliferation of ovarian cancer cells through the GPR30-epidermal growth factor receptor transduction pathway and the involvement of ERalpha.

CONCLUSIONS

Our results indicate a novel mechanism through which atrazine may exert relevant biological effects in cancer cells. On the basis of the present data, atrazine should be included among the environmental contaminants potentially able to signal via GPR30 in eliciting estrogenic action.

Role of human pregnane X receptor in tamoxifen- and 4-hydroxytamoxifen-mediated CYP3A4 induction in primary human hepatocytes and LS174T cells

Previously we observed that the antiestrogens tamoxifen and 4-hydroxytamoxifen (4OHT) induce CYP3A4 in primary human hepatocytes and activate human pregnane X receptor (PXR) in cell-based reporter assays. Given the complex cross-talk between nuclear receptors, tissue-specific expression of CYP3A4, and the potential for tamoxifen and 4OHT to interact with a myriad of receptors, this study was undertaken to gain mechanistic insights into the inductive effects of tamoxifen and 4OHT. First, we observed that transfection of the primary cultures of human hepatocytes with PXR-specific small interfering RNA reduced the PXR mRNA expression and the extent of CYP3A4 induction by tamoxifen and 4OHT by 50%. Second, in LS174T colon carcinoma cells, which were observed to have significantly lower PXR expression relative to human hepatocytes, neither tamoxifen nor 4OHT induced CYP3A4. Third, N-desmethyltamoxifen, which did not induce CYP3A4 in human hepatocytes, also did not activate PXR in LS174T cells. We then used cell-based reporter assay to evaluate the effects of other receptors such as glucocorticoid receptor GR alpha and estrogen receptor ER alpha on the transcriptional activation of PXR. The cotransfection of GR alpha in LS174T cells augmented PXR activation by tamoxifen and 4OHT. On the other hand, the presence of ER alpha inhibited PXR-mediated basal activation of CYP3A4 promoter, possibly via competing for common cofactors such as steroid receptor coactivator 1 and glucocorticoid receptor interacting protein 1. Collectively, our findings suggest that the CYP3A4 induction by tamoxifen and 4OHT is primarily mediated by PXR but the overall stoichiometry of other nuclear receptors and transcription cofactors also contributes to the extent of the inductive effect.

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.

Modulation of AP-1 mediated estrogenic response by ormeloxifene in rat uterus

Ormeloxifene is a selective estrogen receptor modulator that exerts antiestrogenic effects and thereby inhibits growth in uterus. The present study was undertaken to examine the AP-1 protein interaction with AP-1 enhancer DNA elements in rat uterus in vivo and in vitro with a view to explore the modulation of estrogen action mediated via alternative pathway under the influence of ormeloxifene (Orm). In addition, the changes in expression of c-fos and c-jun transcription factors and mRNA expression of growth factor (IGF-1) were investigated with a view to assess the AP-1 mediated transcription. Ovariectomizedoung adult rats were administered with estradiol-17beta (5 microg/100 g body weight) or Orm (200 microg/100 g body weight) or vehicle for 3 days and sacrificed on fourth day. Electrophoretic mobility shift assay using uterine nuclear fraction from various treatment groups demonstrated that Orm caused a significant reduction in E2 induced AP-1 DNA binding. In vitro study revealed that Orm promotes AP-1 complex formation whereas its 7-hydroxy derivative inhibits it significantly. Uterine expression of c-fos and c-jun was increased significantly in Orm treated rats as compared to vehicle treated rats. However, the expression of c-fos and c-jun was decreased in rats receiving Orm plus E2. Semi-quantitative RT-PCR analysis revealed that mRNA expression of IGF-1 was increased in E2 treated group as compared to control group whereas reduced expression was observed in Orm treated rats as compared to E2 treated rats. The uterine weight and IGF-1 mRNA showed similar pattern, indicating that IGF-1 is involved in regulation of uterine weight. These results indicate that 7-hydroxy ormeloxifene (an active metabolite of Orm) is a potent antagonist at AP-1 sites. It inhibits the function of AP-1 transcription factors rather than their expression as evident by downregulation of mRNA expression of AP-1 regulated gene IGF-1, thereby inhibits proliferation in rat uterus. Study suggested a non-classicalregulation of estrogen action on uterus by ormeloxifene.

G protein-coupled receptor 30 (GPR30) mediates gene expression changes and growth response to 17beta-estradiol and selective GPR30 ligand G-1 in ovarian cancer cells

Estrogens play a crucial role in the development of ovarian tumors; however, the signal transduction pathways involved in hormone action are still poorly defined. The orphan G protein-coupled receptor 30 (GPR30) mediates the nongenomic signaling of 17beta-estradiol (E2) in a variety of estrogen-sensitive cancer cells through activation of the epidermal growth factor receptor (EGFR) pathway. Whether estrogen receptor alpha (ERalpha) also contributes to GPR30/EGFR signaling is less understood. Here, we show that, in ERalpha-positive BG-1 ovarian cancer cells, both E2 and the GPR30-selective ligand G-1 induced c-fos expression and estrogen-responsive element (ERE)-independent activity of a c-fos reporter gene, whereas only E2 stimulated an ERE-responsive reporter gene, indicating that GPR30 signaling does not activate ERalpha-mediated transcription. Similarly, both ligands up-regulated cyclin D1, cyclin E, and cyclin A, whereas only E2 enhanced progesterone receptor expression. Moreover, both GPR30 and ERalpha expression are required for c-fos stimulation and extracellular signal-regulated kinase (ERK) activation in response to either E2 or G-1. Inhibition of the EGFR transduction pathway inhibited c-fos stimulation and ERK activation by either ligand, suggesting that in ovarian cancer cells GPR30/EGFR signaling relays on ERalpha expression. Interestingly, we show that both GPR30 and ERalpha expression along with active EGFR signaling are required for E2-stimulated and G-1-stimulated proliferation of ovarian cancer cells. Because G-1 was able to induce both c-fos expression and proliferation in the ERalpha-negative/GPR30-positive SKBR3 breast cancer cells, the requirement for ERalpha expression in GPR30/EGFR signaling may depend on the specific cellular context of different tumor types.

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.

Structure-function relationship of estrogen receptor alpha and beta: impact on human health

17Beta-estradiol (E2) controls many aspects of human physiology, including development, reproduction and homeostasis, through regulation of the transcriptional activity of its cognate receptors (ERs). The crystal structures of ERs with agonists and antagonists and the use of transgenic animals have revealed much about how hormone binding influences ER conformation(s) and how this conformation(s), in turn, influences the interaction of ERs with co-activators or co-repressors and hence determines ER binding to DNA and cellular outcomes. This information has helped to shed light on the connection between E2 and the development or progression of numerous diseases. Current therapeutic strategy in the treatment of E2-related pathologies relies on the modulation of ER trancriptional activity by anti-estrogens; however, data accumulated during the last five years reveal that ER activities are not only restricted to the nucleus. ERs are very mobile proteins continuously shuttling between protein targets located within various cellular compartments (e.g., membrane, nucleus). This allows E2 to generate different and synergic signal transduction pathways (i.e., non-genomic and genomic) which provide plasticity for cell response to E2. Understanding the structural basis and the molecular mechanisms by which ER transduce E2 signals in target cells will allow to create new pharmacologic therapies aimed at the treatment of a variety of human diseases affecting the cardiovascular system, the reproductive system, the skeletal system, the nervous system, the mammary gland, and many others.

Oral contraceptives and skin cancer: is there a link?

The skin expresses estrogen, progesterone, and androgen receptors. In the presence of steroid hormones, such as those contained in oral contraceptives, the skin likely responds to hormonal signals that control the cell cycle, apoptosis, DNA replication, and other cellular functions. Some estrogen-responsive pathways have the potential to promote tumor development, including the augmentation of epidermal growth factor signaling, the expression of proto-oncogenes, and inhibition of apoptosis. The question of whether oral contraceptives increase the risk for the development of skin cancer, particularly melanoma, is still an area of concern. This paper reviews the available evidence, the bulk of which suggests that while the skin responds to estrogens, progestins, and androgens, these responses do not significantly increase the risk of developing skin cancer when estrogen exposure is not excessive.

The G protein-coupled receptor GPR30 mediates the proliferative effects induced by 17beta-estradiol and hydroxytamoxifen in endometrial cancer cells

The growth of both normal and transformed epithelial cells of the female reproductive system is stimulated by estrogens, mainly through the activation of estrogen receptor alpha (ERalpha), which is a ligand-regulated transcription factor. The selective ER modulator tamoxifen (TAM) has been widely used as an ER antagonist in breast tumor; however, long-term treatment is associated with an increased risk of endometrial cancer. To provide new insights into the potential mechanisms involved in the agonistic activity exerted by TAM in the uterus, we evaluated the potential of 4-hydroxytamoxifen (OHT), the active metabolite of TAM, to transactivate wild-type ERalpha and its splice variant expressed in Ishikawa and HEC1A endometrial tumor cells, respectively. OHT was able to antagonize only the activation of ERalpha by 17beta-estradiol (E2) in Ishikawa cells, whereas it up-regulated c-fos expression in a rapid manner similar to E2 and independently of ERalpha in both cell lines. This stimulation occurred through the G protein-coupled receptor named GPR30 and required Src-related and epidermal growth factor receptor tyrosine kinase activities, along with the activation of both ERK1/2 and phosphatidylinositol 3-kinase/AKT pathways. Most importantly, OHT, like E2, stimulated the proliferation of Ishikawa as well as HEC1A cells. Transfecting a GPR30 antisense expression vector in both endometrial cancer cell lines, OHT was no longer able to induce growth effects, whereas the proliferative response to E2 was completely abrogated only in HEC1A cells. Furthermore, in the presence of the inhibitors of MAPK and phosphatidylinositol 3-kinase pathways, PD 98059 and wortmannin, respectively, E2 and OHT did not elicit growth stimulation. Our data demonstrate a new mode of action of E2 and OHT in endometrial cancer cells, contributing to a better understanding of the molecular mechanisms involved in their uterine agonistic activity.

Mechanisms of estrogen receptor signaling: convergence of genomic and nongenomic actions on target genes

Estrogen receptors (ERs) act by regulating transcriptional processes. The classical mechanism of ER action involves estrogen binding to receptors in the nucleus, after which the receptors dimerize and bind to specific response elements known as estrogen response elements (EREs) located in the promoters of target genes. However, ERs can also regulate gene expression without directly binding to DNA. This occurs through protein-protein interactions with other DNA-binding transcription factors in the nucleus. In addition, membrane-associated ERs mediate nongenomic actions of estrogens, which can lead both to altered functions of proteins in the cytoplasm and to regulation of gene expression. The latter two mechanisms of ER action enable a broader range of genes to be regulated than the range that can be regulated by the classical mechanism of ER action alone. This review surveys our knowledge about the molecular mechanism by which ERs regulate the expression of genes that do not contain EREs, and it gives examples of the ways in which the genomic and nongenomic actions of ERs on target genes converge. Genomic and nongenomic actions of ERs that do not depend on EREs influence the physiology of many target tissues, and thus, increasing our understanding of the molecular mechanisms behind these actions is highly relevant for the development of novel drugs that target specific receptor actions.

17beta-Estradiol rapidly stimulates c-fos expression via the MAPK pathway in T84 cells

In this study, we show that 17beta-Estradiol (E2) induced the proliferation of T84 colonic carcinoma cells. We, further, investigated the mechanisms underlying this proliferation and show that E2 induced c-fos protooncogene expression in T84 cells in a timescale consistent with a rapid non-genomic action of the hormone. Furthermore, E2 rapidly phosphorylated both CREB and ELK1, transcription factors that bind to the c-fos promoter and stimulate transcription. Pretreatment with PD98059 and H89, mitogen-activated protein kinase (MAPK) pathway and protein kinase A (PKA) inhibitors, respectively showed that phosphorylation of CREB and ELK1 and subsequent c-fos induction was mediated by the MAPK pathway only. Finally, the estrogen receptor (ER) antagonist, ICI 182,780, blocked the activation of MAPK pathway, subsequent CREB and ELK1 phosphorylation and c-fos induction in T84 cells suggesting an ER dependent mechanism. Consistent with this finding, ICI 182,780 caused a substantial reduction in the proliferative effects of E2 on T84 cells.

Crosstalk between steroid receptors and the c-Src-receptor tyrosine kinase pathways: implications for cell proliferation

Both steroids and growth factors stimulate proliferation of steroid-dependent tumor cells, and interaction between these signaling pathways may occur at several levels. Steroid receptors are typically classified as ligand-activated transcription factors, and steps by which they bind ligand, dimerize, recruit coregulatory molecules, and activate target gene transcription are well understood. Several steroid responses are functionally linked to c-Src or tyrosine kinase receptors, and the physiological impact and the precise molecular pathways involved in these responses are under intensive investigation. Ligand-independent stimulation of steroid receptor-mediated transcription by growth factors is now believed to occur through activated protein kinases that phosphorylate the receptors and receptor coregulators. Recently, steroid hormones themselves have been shown to rapidly activate intracellular signaling cascades, via binding to cognate cytoplasmic or membrane-associated receptors. In some contexts, steroid receptors interact directly with c-Src and other cytoplasmic signaling molecules, such as Shc, PI3K, and p130 Cas. Crosstalk between growth factors and steroids in both the cytoplasm and nucleus could have profound impact on complex biological processes such as cell growth, and play a significant role in the treatment of steroid-dependent cancers. The potential roles of progesterone and estrogen receptors in this crosstalk are discussed in this review.

Estrogen, heat shock proteins, and NFkappaB in human vascular endothelium

BACKGROUND

We hypothesized that estrogen would increase HSP72 in human coronary artery endothelial cells (HCAEC), and that these would be more sensitive to estrogen than our previous observations in myocytes.

METHODS AND RESULTS

HCAEC were treated with 17beta-estradiol or tamoxifen, ranging from physiological to pharmacological(1 nM to 10 micromol/L) for either 24 hours (early) or 7 days (chronic). HSP expression was assessed by Western blots. Both early and chronic 17beta-estradiol and tamoxifen increased HSP72. Electromobility shift assays (EMSA) showed activation of HSF-1 with early, but not chronic, 17beta-estradiol. 17beta-Estradiol activated NFkappaB within 10 minutes, and the ER-alpha selective inhibitor, ICI 182 780, abolished this effect. Transcription factor decoys containing the heat shock element blocked HSP72 induction. Estrogen pretreatment decreased lactate dehydrogenase release with hypoxia. This protective effect persisted despite blockade of HSF-1 by decoys. However, an NF-kappaB decoy prevented the increase in HSP72 and abolished the estrogen-associated protection during hypoxia.

CONCLUSIONS

17beta-Estradiol upregulates HSP72 early and chronically via different mechanisms in HCAEC, and provides cytoprotection during hypoxia, independent of HSP72 induction. NF-kappaB mediates the early increase in HSP72, suggesting that estrogen activates NF-kappaB via a nongenomic, receptor-dependent mechanism, and this leads to activation of HSF-1. Activation of NF-kappaB was critical for estrogen-associated protection. Further studies are needed to elucidate the involved signaling pathways. We hypothesized that estrogen would increase HSP72 in human coronary artery endothelial cells (HCAEC). Both early and chronic treatment increased HSP72. EMSA showed activation of HSF-1 with early, but not chronic, 17beta-estradiol. Transcription factor decoys blocked estrogen-related HSP72 induction. Estrogen decreased LDH release with hypoxia. An NF-kappaB decoy blocked the HSP72 increase and estrogen-associated protection.

Bisphenol-A and estradiol exert novel gene regulation in human MCF-7 derived breast cancer cells

Xenoestrogens such as bisphenol-A (BPA) can mimic endogenous 17beta-estradiol (E2) in vitro and in vivo through binding the estrogen receptor (ER), and modulating target gene expression. In the present study, we compared global gene regulation by BPA and E2 in estrogen responsive (ERalpha-HA) human breast cancer cells derived from the MCF-7 cell line. The ERalpha-HA cells (stably over-expressing ERalpha) were exposed to E2 (10(-8)M) or BPA (10(-6)M), for 3h followed by analysis of global gene expression. More than 40 transcripts were significantly changed in ERalpha-HA cells, with many being unique to BPA. At least 15 genes were modulated by BPA in the ER-null C4-12 cell line, indicating ER independent activity. Utilizing quantitative reverse transcription-polymerase chain reaction (RT-PCR), we confirmed BPA and E2 mediated regulation of four selected genes. A consensus Alu-type estrogen responsive element (ERE) was found in the Wiskott-Aldrich syndrome protein (WASP) gene, which conferred responsiveness to BPA and E2 in a reporter gene assay. Significant stimulation was seen only in ERalpha expressing cells, thus indicating a functional ERE. Taken together these data illustrate novel gene regulation by BPA and E2, which has implications for in vivo actions and previous reports of additive and synergistic effects on breast cancer cell growth.

Estradiol induces proliferation of keratinocytes via a receptor mediated mechanism

In this study, we investigated the effects of estradiol on the proliferation of neonatal keratinocytes, the expression of estrogen receptor isoforms, and the signaling mechanisms by which estradiol mediates cell growth. We demonstrate that estradiol binds neonatal keratinocytes with high affinity (Kd=5.2nM) and limited capacity (Bmax of 14.2fmol/mg of protein), confirming the presence of estrogen binding sites. Using specific antibodies, we demonstrate that keratinocytes express both estrogen receptor (ER)-alpha and ER-beta. At physiological concentrations, estradiol up-regulates the level of ER-alpha receptors in keratinocytes and induces keratinocyte proliferation. The proliferative effect of estradiol requires the availability of functional estrogen receptors, as it is abrogated by anti-estrogen administration. Estradiol effect on keratinocyte proliferation is most likely mediated in part by activation of a nongenomic, membrane-associated, signaling pathway involving activation of the extracellular signal regulated kinases 1 and 2 and in part by the genomic signaling pathway through activation of nuclear receptors.

Uterine response to estradiol under action of chorionic gonadotropin in mice

This work examined the effect of chorionic gonadotropin on proliferative and morphogenetic reactions in the uterus under short- and long-term estrogen treatments. Ovariectomized mice received a single injection with estradiol dipropionate (2 micro g per 100 g; subcutaneously, sc) or vehicle and injections with human chorionic gonadotropin (10 IU per 100 g; sc) or vehicle twice a day for 2 days. Other groups of animals received injections with estradiol once a week or vehicle and injections with chorionic gonadotropin or vehicle once a day for 30 days. The uteri were removed 48 h after the last estradiol or vehicle injection. In animals treated with estradiol and chorionic gonadotropin for a month, the incidence of atypical endometrial hyperplasia was significantly higher. In animals treated with estradiol and chorionic gonadotropin for 2 days or for a month, uterine mass was slightly increased, the number of mitotic cells and BrdU-labeled cells was greater in luminal epithelium, glandular epithelium, stromal and myometrial cells, whereas the expression of estrogen receptors-alpha was lower in all uterine compartments, than in control. In mice who received estradiol and chorionic gonadotropin for 2 days, levels of beta-catenin and glycogen synthase kinase-3beta in luminal and glandular epithelia were lower. In animals treated with estradiol and chorionic gonadotropin for a month, the level of beta-catenin was slightly higher, and the expression of glycogen synthase kinase-3beta was lower in luminal and glandular epithelia. Thus, chorionic gonadotropin exerts estradiol-induced proliferative and morphogenetic changes in the uterus. This action of chorionic gonadotropin is associated with decreased expression of estrogen receptors-alpha and with changes in expression of beta-catenin and glycogen synthase kinase-3beta in the uterus.