Loss of tumourigenicity of stably ERbeta-transfected MCF-7 breast cancer cells

Steviol glycosides affect functional properties and macromolecular expression of breast cancer cells

Steviol glycosides, the active sweet components of stevia plant, have been recently found to possess a number of therapeutic properties, including some recorded anticancer ones against various cancer cell types (breast, ovarian, cervical, pancreatic, and colon cancer). Our aim was to investigate this anticancer potential on the two most commonly used breast cancer cell lines which differ in the phenotype and estrogen receptor (ER) status: the low metastatic, ERα+ MCF-7 and the highly metastatic, ERα-/ERβ+ MDA-MB-231. Specifically, glycosides' effect was studied on cancer cells': (a) viability, (b) functionality (proliferation, migration, and adhesion), and (c) gene expression (mRNA level) of crucial molecules implicated in cancer's pathophysiology. Results showed that steviol glycosides induced cell death in both cell lines, in the first 24 hr, which was in line with the antiapoptotic BCL2 decrease. However, cells that managed to survive showcased diametrically opposite behavior. The low metastatic ERα+ MCF-7 cells acquired an aggressive phenotype, depicted by the upregulation of all receptors and co-receptors (ESR, PGR, AR, GPER1, EGFR, IGF1R, CD44, SDC2, and SDC4), as well as VIM and MMP14. On the contrary, the highly metastatic ERα-/ERβ+ MDA-MB-231 cells became less aggressive as pointed out by the respective downregulation of EGFR, IGF1R, CD44, and SDC2. Changes observed in gene expression were compatible with altered cell functions. Glycosides increased MCF-7 cells migration and adhesion, but reduced MDA-MB-231 cells migratory and metastatic potential. In conclusion, the above data clearly demonstrate that steviol glycosides have different effects on breast cancer cells according to their ER status, suggesting that steviol glycosides might be examined for their potential anticancer activity against breast cancer, especially triple negative breast cancer (TNBC).

Insights into the Role of Estrogen Receptor β in Triple-Negative Breast Cancer

Estrogen receptors (ERα and ERβ) are ligand-activated transcription factors that play different roles in gene regulation and show both overlapping and specific tissue distribution patterns. ERβ, contrary to the oncogenic ERα, has been shown to act as an oncosuppressor in several instances. However, while the tumor-promoting actions of ERα are well-known, the exact role of ERβ in carcinogenesis and tumor progression is not yet fully understood. Indeed, to date, highly variable and even opposite effects have been ascribed to ERβ in cancer, including for example both proliferative and growth-inhibitory actions. Recently ERβ has been proposed as a potential target for cancer therapy, since it is expressed in a variety of breast cancers (BCs), including triple-negative ones (TNBCs). Because of the dependence of TNBCs on active cellular signaling, numerous studies have attempted to unravel the mechanism(s) behind ERβ-regulated gene expression programs but the scenario has not been fully revealed. We comprehensively reviewed the current state of knowledge concerning ERβ role in TNBC biology, focusing on the different signaling pathways and cellular processes regulated by this transcription factor, as they could be useful in identifying new diagnostic and therapeutic approaches for TNBC.

miR-142-3p is a tumor suppressor that inhibits estrogen receptor expression in ER-positive breast cancer

Estrogen receptors (ERs) are involved in the development of many types of malignant tumors, in particular, breast cancer. Among others, ERs affect cell growth, proliferation, and differentiation. The microRNA (miRNA) miR-142-3p has been shown to inhibit carcinogenesis by regulating various cellular processes, including cell cycle progression, cell migration, apoptosis, and invasion. It does so via targeting molecules involved in a range of signaling pathways. We surgically collected 20 ER-positive breast cancer samples, each with matched adjacent normal breast tissue, and measured the expression of miR-142-3p via quantitative real-time polymerase chain reaction (qRT-PCR). Bioinformatics methods, luciferase reporter assay, qRT-PCR, and western blot analysis were used to assess whether miR-142-3p could target ESR1, which encodes the estrogen receptor, in ER-positive breast cancer cells and patient samples. We also restored miRNA expression and performed cell viability, cytotoxicity, and colony formation assays. Western blot analysis and qRT-PCR were used to study the expression of apoptosis and stemness markers. We found that miR-142-3p is downregulated in ER-positive breast cancers. Restoration of miR-142-3p expression in ER-positive breast cancer cells reduced cell viability, induced apoptosis via the intrinsic pathway and decreased both colony formation and the expression of stem cell markers. Bioinformatic analysis predicted miR-142-3p could bind to 3'-untranslated region ESR1 messenger RNA (mRNA). Consistently, we demonstrated that miR-142-3p reduced luciferase activity in ER-positive breast cancer cells, and decreased ESR1 expression in both mRNA and protein levels. The results revealed miR-142-3p and ESR1 expression correlated negatively in ER-positive breast cancer samples. The results suggest miR-142-3p acts as a tumor suppressor via multiple mechanisms. Thus, restoration of miR-142-3p expression, for example, via miRNA replacement therapy, may represent an effective strategy for the treatment of ER-positive breast cancer patients.

Beyond the Antioxidant Activity of Dietary Polyphenols in Cancer: the Modulation of Estrogen Receptors (ERs) Signaling

The potential "health benefits" of dietary polyphenols have been ascribed to their direct antioxidant activity and their impact on the regulation of cell and tissue redox balance. However, because of the relative poor bioavailability of many of these compounds, their effects could not be easily explained by the antioxidant action, which may occur only at high circulating and tissue concentrations. Therefore, many efforts have been put forward to clarify the molecular mechanisms underlining the biological effect of polyphenols in physiological and pathological conditions. Polyphenols' bioavailability, metabolism, and their effects on enzyme, membrane, and/or nuclear receptors and intracellular transduction mechanisms may define the overall impact of these compounds on cancer risk and progression, which is still debated and not yet clarified. Polyphenols are able to bind to estrogen receptor α (ERα) and β (ERβ), and therefore induce biological effects in human cells through mimicking or inhibiting the action of endogenous estrogens, even at low concentrations. In this work, the role and effects of food-contained polyphenols in hormone-related cancers will be reviewed, mainly focusing on the different polyphenols' mechanisms of action with particular attention on their estrogen receptor-based effects, and on the consequences of such processes on tumor progression and development.

Estrogen receptor subtypes dictate the proliferative nature of the mammary gland

Estrogen induces proliferation of breast epithelial cells and is responsible for breast development at puberty. This tightly regulated control is lost in estrogen-receptor-positive (ER+) breast cancers, which comprise over 70% of all breast cancers. Currently, breast cancer diagnosis and treatment considers only the α isoform of ER; however, there is a second ER, ERβ. Whilst ERα mediates estrogen-driven proliferation of the normal breast in puberty and breast cancers, ERβ has been shown to exert an anti-proliferative effect on the normal breast. It is not known how the expression of each ER (alone or in combination) correlates with the ability of estrogen to induce proliferation in the breast. We assessed the levels of each ER in normal mouse mammary glands subdivided into proliferative and non-proliferative regions. ERα was most abundant in the proliferative regions of younger mice, with ERβ expressed most abundantly in old mice. We correlated this expression profile with function by showing that the ability of estrogen to induce proliferation was reduced in older mice. To show that the ER profile associated with breast cancer risk, we assessed ER expression in parous mice which are known to have a reduced risk of developing ERα breast cancer. ERα expression was significantly decreased yet co-localization analysis revealed ERβ expression increased with parity. Parous mice had less unopposed nuclear ERα expression and increased levels of ERβ. These changes suggest that the nuclear expression of ERs dictates the proliferative nature of the breast and may explain the decreased breast cancer risk with parity.

Oxybenzone Alters Mammary Gland Morphology in Mice Exposed During Pregnancy and Lactation

Hormones and endocrine-disrupting chemicals are generally thought to have permanent “organizational” effects when exposures occur during development but not adulthood. Yet, an increasing number of studies have shown that pregnant females are disrupted by endocrine-disrupting chemical exposures, with some effects that are permanent. Here, we examined the long-term effects of exposure to oxybenzone, an estrogenic chemical found in sunscreen and personal care products, on the morphology of the mammary gland in mice exposed during pregnancy and lactation. Female mice were exposed to vehicle or 30, 212, or 3000 µg oxybenzone/kg/d, from pregnancy day 0 until weaning. A nulliparous group, receiving vehicle treatment, was also evaluated. Mammary glands were collected 5 weeks after involution for whole-mount, histological, immunohistochemical, and molecular analyses. Exposure to 3000 µg oxybenzone/kg/d induced permanent changes to ductal density that was significantly different from both the nulliparous and vehicle groups. The two highest doses of oxybenzone similarly induced an intermediate phenotype for expression of progesterone receptor. A monotonic, dose-dependent increase in cell proliferation was also observed in the oxybenzone-treated females, becoming statistically significant at the highest dose. Finally, oxybenzone exposure induced an intermediate phenotype for Esr1 expression in all oxybenzone-treated groups. These data suggest that oxybenzone, at doses relevant to human exposures, produces long-lasting alterations to mammary gland morphology and function. Further studies are needed to determine if exposure to this chemical during pregnancy and lactation will interfere with the known protection that pregnancy provides against breast cancer.

E2/ERβ Inhibits PPARα to Regulate Cell-Proliferation and Enhance Apoptosis in Hep3B-Hepatocellular Carcinoma

Peroxisome proliferator-activated receptor-α (PPARα) is a member of the nuclear receptor superfamily involved in hepatocarcinogenesis in rodents. In previous studies on liver tumor tissues, PPARα mRNA expression was found to be significantly higher and overexpression of ERα inhibited the PPARα expression, cell-proliferation and also induced apoptosis in Hep3B cell. However, the role of ERβ is not known yet. Therefore, the aim of this study is to define the role of ERβ on PPARα in Hep3B cells. The effect of PPARα signaling cascade were monitored by inducing Hep3B cells by fenofibrate. Further the cells were transfected with pCMV-ERβ and the consequences of ERβ-overexpression on the PPARα induced changes such as enhanced cell-proliferation and suppressed apoptosis were determined using western blot analysis and TUNEL assay. The EMSA was used to identify whether ERβ modulates PPARα expression by binding to PPARα promoter region to repress PPARα promoter activity. In addition, the direct interaction between ERβ and PPARα proteins was verified by co-immunoprecipitation assay. Our results show that the overexpressed ERβ not only attenuated the effects of fenofibrate to induce the levels of apoptosis protein such as Cyt.c, Caspase 9 and Caspase 3 but also inhibited the levels of survival protein such Bcl-xL, p-Bad, cyclin A and cyclin E. All these effects of E₂/ERβ resulted in the enhancement of mitochondria dependent apoptotic pathway and the attenuation of cell proliferation. Moreover, the overexpressed ERβ reduced the mRNA and protein levels of PPARα and its downstream Acyl-CoA oxidase (ACO). EMSA results show that ERβ directly binds to PPRE and inhibit PPARα gene expression and according to immunoprecipitation assay ERβ also binds strongly with PPARα. The E₂/ERβ further inhibited the fenofibrate-induced nuclear translocation of PPARα. Taken together, ERβ might directly downregulate PPARα gene expression and inhibit the nuclear translocation to suppress the proliferation and induce the apoptosis of Hep3B cells.

Methyltransferase-like 17 physically and functionally interacts with estrogen receptors

Estrogen exerts its physiological and pathological functions through two estrogen receptors (ERs), ERα and ERβ, which act as transcription factors. Coregulators, including coactivators and corepressors, have been shown to be crucial for regulation of ER transcriptional activity. Although many coregulators have been identified to regulate activities of ERs, novel coregulators are still needed to be investigated. Here, we show that human methyltransferase-like 17 (METTL17), whose function is unknown, physically interacts with ERα and ERβ, and functionally acts as a coactivator for ERs. METTL17 interacts with ER in vitro and in yeast and mammalian cells. Activation function-1 (AF1) and AF2 domains of ERs are responsible for the interaction between METTL17 and ERs. Knockdown of METTL17 reduces transcriptional activities of ERα and ERβ in breast cancer cells, whereas METTL17 overexpression increases ERα and ERβ transcriptional activities. Inhibition of METTL17 expression decreases mRNA and protein levels of ER target genes, including PR, cathepsin D, and pS2. Moreover, METTL17 knockdown reduces breast cancer cell growth. These results indicate that METTL17 is a novel coactivator of ERs and may play a role in breast tumorigenesis.

ERβ-dependent neuroglobin up-regulation impairs 17β-estradiol-induced apoptosis in DLD-1 colon cancer cells upon oxidative stress injury

Besides other mechanism(s) 17β-estradiol (E2) facilitates neuronal survival by increasing, via estrogen receptor β (ERβ), the levels of neuroglobin (NGB) an anti-apoptotic protein. In contrast, E2 could exert protective effects in cancer cells by activating apoptosis when the ERβ level prevails on that of ERα as in colon cancer cell lines. These apparently contrasting results raise the possibility that E2-induced NGB up-regulation could regulate the ERβ activities shunning this receptor subtype to trigger an apoptotic cascade in neurons but not in non-neuronal cells. Here, human colorectal adenocarcinoma cell line (DLD-1) that only expresses ERβ and HeLa cells transiently transfected with ERβ encoding vector has been used to verify this hypothesis. In addition, neuroblastoma SK-N-BE cells were used as positive control. Surprisingly, E2 also induced NGB up-regulation, in a dose- and time-dependent manner, in DLD-1 cells. The ERβ-mediated activation of p38/MAPK was necessary for this E2 effect. E2 induced NGB re-allocation in mitochondria where, subsequently to an oxidative stress injury (i.e., 100μM H2O2), NGB interacted with cytochrome c preventing its release into the cytosol and the activation of an apoptotic cascade. As a whole, these results demonstrate that E2-induced NGB up-regulation could act as an oxidative stress sensor, which does not oppose to the pro-apoptotic E2 effect in ERβ-containing colon cancer cells unless a rise of oxidative stress occurs. These results support the concept that oxidative stress plays a critical role in E2-induced carcinogenesis and further open an important scenario to develop novel therapeutic strategies that target NGB against E2-related cancers.

Clinical significance of estrogen receptor β in breast and prostate cancer from biological aspects

Breast and prostate cancers are among the most common of all cancers. They are referred to as hormone-dependent cancers, because estrogen and androgen are involved in their development and growth. The effects of these hormones are mediated by their respective receptors, estrogen receptor (ER) α and androgen receptor. Around 18 years ago, a second ER, ERβ, which has a very similar structure to ERα, was discovered. Its function has been investigated using a variety of methods and biological systems, leading to our present understanding that ERβ can interact with or inhibit ERα and androgen receptor function directly and/or indirectly, suppress cell growth, and influence responsiveness to endocrine therapy. In order to apply the “inhibition of cell growth” function to cancer treatment, several specific ERβ agonists have been synthesized and are being tested for effectiveness in cancer treatment. We need to keep our eyes on ERβ.

Estrogen receptor α/β-cofactor motif interactions; interplay of tyrosine 537/488 phosphorylation and LXXLL motifs

The Estrogen Receptors ERα and ERβ bind cofactor proteins via short LXXLL motifs. The exact regulation and selectivity of these interactions remains an open question and the role of post-translational modifications (PTMs) is virtually unexplored. Here, we designed an X(7)-LXXLL-X(7) T7 phage display library and screened this against four ER protein constructs: the 'naked' ERα and ERβ Ligand Binding Domains (LBDs) and the tyrosine phosphorylated ERα (pY537) and ERβ (pY488) LBDs. The site-selective tyrosine phosphorylated protein constructs were obtained via a protein semi-synthesis approach. Phage display screening yielded preferential sets of peptides. LXXLL peptides with a low pI/acidic C-terminus prefer binding to the naked ERβ over the phosphorylated ERβ analogue and ERα constructs. Peptides with a high pI/basic C-terminus show the opposite behaviour. These findings not only show regulation of the ERβ-cofactor interaction via tyrosine phosphorylation, but also suggest that ERβ and its tyrosine 488 phosphorylation play crucial roles in modulating interactions of coactivators to ERα since the natural Steroid Receptor Coactivators (SRCs) feature LXXLL motifs with acidic C-termini, while the repressor protein RIP140 features LXXLL motifs with basic C-termini. This insight provides explanation for ER transcriptional activity and can lead to more focussed targeting of the ER-coactivator interaction.

Inhibitory effects of ERβ on proliferation, invasion, and tumor formation of MCF-7 breast cancer cells--prognostication for the use of ERβ-selective therapy

CONTEXT

Estrogen is well-known as an important factor in the physiological functions and pathological processes of breast. Estrogen receptor β (ERβ) is expressed in the majority of breast cancers at lower levels compared with the normal breast tissue.

OBJECTIVE

The effect of ERβ on the characteristics of breast tumor cells and its prognostication for the use of ERβ-selective therapy were investigated here for the first time.

MATERIALS AND METHODS

ERβ was overexpressed in ERα positive MCF-7 breast cancer cells by gene transfection. The proliferation, motility, and xenografts growth of MCF-7 cells were investigated by MTT assays, wound-healing assay and animal study.

RESULTS

Results demonstrated that ERβ-GFP localized in both the cytoplasm and the nucleus in the presence of 17β-estradiol (E2), with stronger fluorescence-signal intensity in the nucleus, 2.8-times higher than that in the cytoplasm. The ERβ overexpressed MCF-7 cells resulted in a 38.7% decreased growth rate and motility in vitro. Furthermore, ERβ overexpression enhanced the antiproliferative effects of phytoestrogen, antiestrogen, and histone deacetylase inhibitor. Exogenous ERβ expression reduced tumor volume by 99% at 27 days postadministration, indicated that overexpression of ERβ led to retardation of tumor formation and growth in immunodeficient mice.

DISCUSSION AND CONCLUSION

This study provided a relatively new evidence to support that ERβ is an important modulator of proliferation and motility of breast cancer cells, and implied for the first time a possibility for the use of novel ERβ-selective therapies in breast cancer treatment.

Estrogen receptor beta binds Sp1 and recruits a corepressor complex to the estrogen receptor alpha gene promoter

Human estrogen receptors alpha and beta are crucially involved in the regulation of mammary growth and development. Normal breast tissues display a relative higher expression of ER beta than ER alpha, which drastically changes during breast tumorogenesis. Thus, it is reasonable to suggest that a dysregulation of the two estrogen receptor subtypes may induce breast cancer development. However, the molecular mechanisms underlying the potential opposing roles played by the two estrogen receptors on tumor cell growth remain to be elucidated. In the present study, we have demonstrated that ER beta overexpression in breast cancer cells decreases cell proliferation and down-regulates ER alpha mRNA and protein content, along with a concomitant repression of estrogen-regulated genes. Transient transfection experiments, using a vector containing the human ER alpha promoter region, showed that elevated levels of ER beta down-regulated basal ER alpha promoter activity. Furthermore, site-directed mutagenesis and deletion analysis revealed that the proximal GC-rich motifs at -223 and -214 are critical for the ER beta-induced ER alpha down-regulation in breast cancer cells. This occurred through ER beta-Sp1 protein-protein interactions within the ER alpha promoter region and the recruitment of a corepressor complex containing the nuclear receptor corepressor NCoR, accompanied by hypoacetylation of histone H4 and displacement of RNA-polymerase II. Silencing of NCoR gene expression by RNA interference reversed the down-regulatory effects of ER beta on ER alpha gene expression and cell proliferation. Our results provide evidence for a novel mechanism by which overexpression of ER beta through NCoR is able to down regulate ER alpha gene expression, thus blocking ER alpha's driving role on breast cancer cell growth.

The DHEA metabolite 7β-hydroxy-epiandrosterone exerts anti-estrogenic effects on breast cancer cell lines

7β-Hydroxy-epiandrosterone (7β-OH-EpiA), an endogenous androgenic derivative of dehydroepiandrosterone, has previously been shown to exert anti-inflammatory action in vitro and in vivo via a shift from prostaglandin E2 (PGE2) to 15-deoxy-Δ(12,14)-PGJ2 production. This modulation in prostaglandin production was obtained with low concentrations of 7β-OH-EpiA (1-100nM) and suggested that it might act through a specific receptor. Inflammation and prostaglandin synthesis is important in the development and survival of estrogen-dependent mammary cancers. Estrogen induced PGE2 production and cell proliferation via its binding to estrogen receptors (ERs) in these tumors. Our objective was to test the effects of 7β-OH-EpiA on the proliferation (by counting with trypan blue exclusion), cell cycle and cell apoptosis (by flow cytometry) of breast cancer cell lines MCF-7 (ERα+, ERβ+, G-protein coupled receptor 30: GPR30+) and MDA-MB-231 (ERα-, ERβ+, GPR30+) and to identify a potential target of this steroid in these cell lineages (by transactivations) and in the nuclear ER-negative SKBr3 cells (GPR30+) (by proliferation assays). 7β-OH-EpiA exerted anti-estrogenic effects in MCF-7 and MDA-MB-231 cells associated with cell proliferation inhibition and cell cycle arrest. Moreover, transactivation and proliferation with ER agonists assays indicated that 7β-OH-EpiA interacted with ERβ. Data from proliferation assays on the MCF-7, MDA-MB-231 and SKBr3 cell lines suggested that 7β-OH-EpiA may also act through the membrane GPR30 receptor. These results support that this androgenic steroid acts as an anti-estrogenic compound. Moreover, this is the first evidence that low doses of androgenic steroid exert antiproliferative effects in these mammary cancer cells. Further investigations are needed to improve understanding of the observed actions of endogenous 7β-OH-EpiA.

Cracking the estrogen receptor's posttranslational code in breast tumors

Estrogen signaling pathways, because of their central role in regulating the growth and survival of breast tumor cells, have been identified as suitable and efficient targets for cancer therapies. Agents blocking estrogen activity are already widely used clinically, and many new molecules have entered clinical trials, but intrinsic or acquired resistance to treatment limits their efficacy. The basic molecular studies underlying estrogen signaling have defined the critical role of estrogen receptors (ER) in many aspects of breast tumorigenesis. However, important knowledge gaps remain about the role of posttranslational modifications (PTM) of ER in initiation and progression of breast carcinogenesis. Whereas major attention has been focused on the phosphorylation of ER, many other PTM (such as acetylation, ubiquitination, sumoylation, methylation, and palmitoylation) have been identified as events modifying ER expression and stability, subcellular localization, and sensitivity to hormonal response. This article will provide an overview of the current and emerging knowledge on ER PTM, with a particular focus on their deregulation in breast cancer. We also discuss their clinical relevance and the functional relationship between PTM. A thorough understanding of the complete picture of these modifications in ER carcinogenesis might not only open new avenues for identifying new markers for prognosis or prediction of response to endocrine therapy but also could promote the development of novel therapeutic strategies.

P2Y2 receptor-mediated modulation of estrogen-induced proliferation of breast cancer cells

It is known that estrogen promotes the proliferation of breast cancer cells. Agonists to P2Y(2) receptors promote or suppress proliferation in different cancers. In the present study, the methods of methylthiazoltetrazolium (MTT) assay, real-time RT-PCR, Western blot and fluorescent calcium imaging analysis were used to investigate whether P2Y(2) receptors play a role in the effects of estrogen on the breast cancer cell lines, MCF-7 and MDA-MB-231. We found that P2Y(2) receptors were expressed in both the estrogen receptor alpha (ER(α))-positive breast cancer cell line MCF-7 and the ER(α)-negative breast cancer cell line MDA-MB-231. 17β-Estradiol (17β-E(2)) (1 pM to 1000 nM) promoted proliferation of MCF-7 cells, which was blocked by the ER antagonist ICI 182,780 (1 μM) and the ER(α) antagonist methyl-piperidino-pyrazole (MPP, 50 μM), but not by the ER(β) antagonist 4-[2-phenyl-5,7-bis(trifluoromethyl)pyrazolo[1,5-a]pyrimidin-3-yl]phenol (PHTPP, 50 μM) or ER(β) small interfering RNA. The P2Y(2) and P2Y(4) receptor agonist UTP (10-100 μM) suppressed the viability of breast cancer cells in both MCF-7 and MDA-MB-231 cells. The effect was blocked by suramin (10-100 μM), known to be an effective antagonist against P2Y(2), but not P2Y(4), receptor-mediated responses. 17β-E(2) played a more positive role in promoting proliferation in MCF-7 cells when suramin blocked the functional P2Y(2) receptors. 17β-E(2) (0.1-1000 nM) downregulated the expression of P2Y(2) receptors in terms of both mRNA and protein levels in MCF-7 cells. The effect was blocked by ICI 182,780 and MPP, but not PHTPP or ER(β) small interfering RNA. 17β-E(2) did not affect the expression of P2Y(2) receptors in MDA-MB-231. UTP (10-100 μM) led to a sharp increase in intracellular Ca(2+) in MCF-7 cells. Pre-incubation with 17β-E(2) (0.1 μM) attenuated UTP-induced [Ca(2+)](i), which was blocked by ICI182,780 and MPP, but not PHTPP. It is suggested that estrogen, via ER(α) receptors, promotes proliferation of breast cancer cells by down-regulating P2Y(2) receptor expression and attenuating P2Y(2)-induced increase of [Ca(2+)](i).

Global analysis of estrogen receptor beta binding to breast cancer cell genome reveals an extensive interplay with estrogen receptor alpha for target gene regulation

Background

Estrogen receptors alpha (ERα) and beta (ERβ) are transcription factors (TFs) that mediate estrogen signaling and define the hormone-responsive phenotype of breast cancer (BC). The two receptors can be found co-expressed and play specific, often opposite, roles, with ERβ being able to modulate the effects of ERα on gene transcription and cell proliferation. ERβ is frequently lost in BC, where its presence generally correlates with a better prognosis of the disease. The identification of the genomic targets of ERβ in hormone-responsive BC cells is thus a critical step to elucidate the roles of this receptor in estrogen signaling and tumor cell biology.

Results

Expression of full-length ERβ in hormone-responsive, ERα-positive MCF-7 cells resulted in a marked reduction in cell proliferation in response to estrogen and marked effects on the cell transcriptome. By ChIP-Seq we identified 9702 ERβ and 6024 ERα binding sites in estrogen-stimulated cells, comprising sites occupied by either ERβ, ERα or both ER subtypes. A search for TF binding matrices revealed that the majority of the binding sites identified comprise one or more Estrogen Response Element and the remaining show binding matrixes for other TFs known to mediate ER interaction with chromatin by tethering, including AP2, E2F and SP1. Of 921 genes differentially regulated by estrogen in ERβ+ vs ERβ- cells, 424 showed one or more ERβ site within 10 kb. These putative primary ERβ target genes control cell proliferation, death, differentiation, motility and adhesion, signal transduction and transcription, key cellular processes that might explain the biological and clinical phenotype of tumors expressing this ER subtype. ERβ binding in close proximity of several miRNA genes and in the mitochondrial genome, suggests the possible involvement of this receptor in small non-coding RNA biogenesis and mitochondrial genome functions.

Conclusions

Results indicate that the vast majority of the genomic targets of ERβ can bind also ERα, suggesting that the overall action of ERβ on the genome of hormone-responsive BC cells depends mainly on the relative concentration of both ERs in the cell.

A positive feedback loop of ER-α36/EGFR promotes malignant growth of ER-negative breast cancer cells

It is prevailingly thought that estrogen signaling is not involved in development of estrogen receptor (ER)-negative breast cancer. However, there is evidence indicating that ovariectomy prevents the development of both ER-positive and -negative breast cancer, suggesting that estrogen signaling is involved in the development of ER-negative breast cancer. Previously, our laboratory cloned a variant of ER-α, ER-α36, and found that ER-α36 mediated non-genomic estrogen signaling and is highly expressed in ER-negative breast cancer cells. In this study, we found that ER-α36 was highly expressed in 10/12 cases of triple-negative breast cancer. We investigated the role of mitogenic estrogen signaling mediated by ER-α36 in malignant growth of triple-negative breast cancer MDA-MB-231 and MDA-MB-436 cells that express high levels of ER-α36 and found these cells were strongly responded to mitogenic estrogen signaling both in vitro and in vivo. Knock-down of ER-α36 expression in these cells using the shRNA method diminished their responsiveness to estrogen. ER-α36 physically interacted with the EGFR/Src/Shc complex and mediated estrogen-induced phosphorylation of EGFR and Src. EGFR signaling activated ER-α36 transcription through an AP1 site in the ER-α36 promoter and ER-α36 expression was able to stabilize EGFR protein. Our results thus demonstrated that ER-α36 mediates non-genomic estrogen signaling through the EGFR/Src/ERK signaling pathway in ER-negative breast cancer cells and suggested that a subset of ER-negative breast tumors that express ER-α36 retain responsiveness to mitogenic estrogen signaling.

Estrogen receptor alpha 46 is reduced in tamoxifen resistant breast cancer cells and re-expression inhibits cell proliferation and estrogen receptor alpha 66-regulated target gene transcription

Resistance to endocrine therapy is a major clinical problem in breast cancer. The role of ERalpha splice variants in endocrine resistance is largely unknown. We observed reduced protein expression of an N-terminally truncated ERalpha46 in endocrine-resistant LCC2, LCC9, and LY2 compared to MCF-7 breast cancer cells. Transfection of LCC9 and LY2 cells with hERalpha46 partially restored growth inhibition by TAM. Overexpression of hERalpha46 in MCF-7 cells reduced estradiol (E(2))-stimulated endogenous pS2, cyclin D1, nuclear respiratory factor-1 (NRF-1), and progesterone receptor transcription. Expression of oncomiR miR-21 was lower in TAM-resistant LCC9 and LY2 cells compared to MCF-7 cells. Transfection with ERalpha46 altered the pharmacology of E(2) regulation of miR-21 expression from inhibition to stimulation, consistent with the hypothesis that hERalpha46 inhibits ERalpha activity. Established miR-21 targets PTEN and PDCD4 were reduced in ERalpha46-transfected, E(2)-treated MCF-7 cells. In conclusion, ERalpha46 appears to enhance endocrine responses by inhibiting selected ERalpha66 responses.

Estrogens, regulation of p53 and breast cancer risk: a balancing act

The paradoxical effects of ovarian hormones in both the promotion and prevention of breast cancer have been debated for over 30 years. Genetic studies have demonstrated that ovarian hormones act through NF-kappaB to stimulate proliferation and ductal elongation, whereas the p53 tumor suppressor protein plays a central role in rendering the mammary epithelium resistant to tumorigenesis. Transcriptional profiles now suggest that ovarian hormones stimulate a constellation of genes that interact with NF-kappaB and p53 to arbitrate the competing demands for proliferation and surveillance. Genes that participate in chromatin remodeling are among the acute transcriptional responses to estrogens and progestins. These genes are proposed to initiate epigenetic programs that influence the balance between proliferation and surveillance, and render the breast epithelium resistant to tumors.

Anacardic acid inhibits estrogen receptor alpha-DNA binding and reduces target gene transcription and breast cancer cell proliferation

Anacardic acid (AnAc; 2-hydroxy-6-alkylbenzoic acid) is a dietary and medicinal phytochemical with established anticancer activity in cell and animal models. The mechanisms by which AnAc inhibits cancer cell proliferation remain undefined. AnAc 24:1(omega5) was purified from geranium (Pelargonium x hortorum) and shown to inhibit the proliferation of estrogen receptor alpha (ERalpha)-positive MCF-7 and endocrine-resistant LCC9 and LY2 breast cancer cells with greater efficacy than ERalpha-negative primary human breast epithelial cells, MCF-10A normal breast epithelial cells, and MDA-MB-231 basal-like breast cancer cells. AnAc 24:1(omega5) inhibited cell cycle progression and induced apoptosis in a cell-specific manner. AnAc 24:1(omega5) inhibited estradiol (E(2))-induced estrogen response element (ERE) reporter activity and transcription of the endogenous E(2) target genes pS2, cyclin D1, and cathepsin D in MCF-7 cells. AnAc 24:1(omega5) did not compete with E(2) for ERalpha or ERbeta binding, nor did AnAc 24:1(omega5) reduce ERalpha or ERbeta steady-state protein levels in MCF-7 cells; rather, AnAc 24:1(omega5) inhibited ER-ERE binding in vitro. Virtual screening with the molecular docking software Surflex evaluated AnAc 24:1(omega5) interaction with ERalpha ligand binding (LBD) and DNA binding (DBD) domains in conjunction with experimental validation. Molecular modeling revealed AnAc 24:1(omega5) interaction with the ERalpha DBD but not the LBD. Chromatin immunoprecipitation experiments revealed that AnAc 24:1(omega5) inhibited E(2)-ERalpha interaction with the endogenous pS2 gene promoter region containing an ERE. These data indicate that AnAc 24:1(omega5) inhibits cell proliferation, cell cycle progression, and apoptosis in an ER-dependent manner by reducing ER-DNA interaction and inhibiting ER-mediated transcriptional responses.

Differential effects of overexpression of ERα and ERβ in MCF10A immortalised, non-transformed human breast epithelial cells

: Cellular effects of oestrogen are mediated by two intracellular receptors ERα and ERβ. However, to compare responses mediated through these two receptors, experimental models are needed where ERα and ERβ are individually stably overexpressed in the same cell type.

: We compared the effects of stable overexpression of ERα and ERβ in the MCF10A cell line, which is an immortalised but non-transformed breast epithelial cell line without high endogenous ER expression.

: Clones of MCF10A cells were characterised which stably overexpressed ERα (10A-ERα2, 10A-ERα13) or which stably overexpressed ERβ (10A-ERβ12, 10A-ERβ15). Overexpression of either ERα or ERβ allowed induction of an oestrogen-regulated ERE-LUC reporter gene by oestradiol which was not found in the untransfected cells. Oestradiol also increased proliferation of 10A-ERα13 and 10A-ERβ12 cells, but not untransfected cells, by 1.3-fold over 7 days. The phytoestrogen, genistein, which is reported to bind more strongly to ERβ than to ERα, could induce luciferase gene expression from an ERE-LUC reporter gene at concentrations of 10

: This provides a model system to compare effects of oestradiol with other oestrogenic ligands in cells stably overexpressing individually ERα or ERβ.

Microarray analysis of altered gene expression in ERbeta-overexpressing HEK293 cells

Estrogen receptors (ERs), ERalpha and ERbeta, mediate estrogen actions in a broad range of target tissues. With the introduction of microarray techniques, a significant understanding has been gained regarding the interplay between the ERalpha and ERbeta in breast cancer cell lines. To gain a more comprehensive understanding of ERbeta-dependent gene regulation independent of ERalpha, we performed microarray analysis on HEK293/mock and HEK293/ERbeta cells. A total of 332 genes was identified as ERbeta-upregulated genes and 210 identified as ERbeta-downregulated genes. ERbeta-induced and ERbeta-repressed genes were involved in cell-cell signaling, morphogenesis, and cell proliferation. The ERbeta repressive effect on genes related to proliferation was further studied by proliferation assays, where ERbeta expression resulted in a significant decrease in cell proliferation. To identify primary ERbeta target genes, we examined a number of ERbeta-regulated genes using chromatin immunoprecipitation assays for regions bound by ERbeta. Our results showed that ERbeta recruitment was significant to regions associated with 12 genes (IL1RAP, TMSB4X, COLEC12, ENPP2, KLRC1, RERG, RGS16, TNNT2, CYR61, FER1L3, FAM108A1, and CYP4X1), suggesting that these genes are likely to be ERbeta primary target genes. This study has provided novel information on the gene regulatory function of ERbeta independent of ERalpha and identified a number of ERbeta primary target genes. The results of Gene Ontology analysis and proliferation assays are consistent with an antiproliferative role of ERbeta independent of ERalpha.

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

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

Estradiol downregulates miR-21 expression and increases miR-21 target gene expression in MCF-7 breast cancer cells

Select changes in microRNA (miRNA) expression correlate with estrogen receptor α (ERα) expression in breast tumors. miR-21 is higher in ERα positive than negative tumors, but no one has examined how estradiol (E₂) regulates miR-21 in breast cancer cells. Here we report that E₂ inhibits miR-21 expression in MCF-7 human breast cancer cells. The E₂-induced reduction in miR-21 was inhibited by 4-hydroxytamoxifen (4-OHT), ICI 182 780 (Faslodex), and siRNA ERα indicating that the suppression is ERα-mediated. ERα and ERβ agonists PPT and DPN inhibited and 4-OHT increased miR-21 expression. E₂ increased luciferase activity from reporters containing the miR-21 recognition elements from the 3′-UTRs of miR-21 target genes, corroborating that E₂ represses miR-21 expression resulting in a loss of target gene suppression. The E₂-mediated decrease in miR-21 correlated with increased protein expression of endogenous miR-21-targets Pdcd4, PTEN and Bcl-2. siRNA knockdown of ERα blocked the E₂-induced increase in Pdcd4, PTEN and Bcl-2. Transfection of MCF-7 cells with antisense (AS) to miR-21 mimicked the E₂-induced increase in Pdcd4, PTEN and Bcl-2. These results are the first to demonstrate that E₂ represses the expression of an oncogenic miRNA, miR-21, by activating estrogen receptor in MCF-7 cells.

Estrogen and its receptors in cancer

The involvement of estrogen and its receptors in the development of cancer has been known for years. However, the exact mechanism responsible is far from clear. The estrogen-mediated carcinogenic process is complicated by recent findings, which reveal that estrogens have multiple functions in cells, which can be either adverse or beneficial, and that the effects of estrogen may be cell-type or organ dependent. The estrogenic effect may be also greatly influenced by the state of two estrogen receptors, ERalpha and ERbeta. This review will discuss the role and function of estrogens and its receptors in cancers of three categories: (1) Breast cancer and gynecologic cancers, (2) Cancers of endocrine organs, (3) Lung cancer and cancers of digestive system. We will also review some novel treatments aiming to interfere with relevant pathways mediated by estrogens and its receptors.

ERbeta in breast cancer--onlooker, passive player, or active protector?

The role of estrogen exposure in breast cancer risk is well-documented, and both estrogen synthesis and actions through the estrogen receptor (ER) have been targeted by therapies to control hormone-dependent breast cancer. The discovery of a second ER form and its therapeutic implications sparked great interest. Both the original ERalpha and the more recently identified ERbeta subtypes bind and respond similarly to many physiological and pharmacological ligands. However, differences in phytoestrogen binding have been noted, and subtype-specific ligands have been developed. Cell-based assays show that ERbeta and its variants are generally less active on gene transcription than ERalpha, and may influence ERalpha activity; however, both gene- and cell-specific responses occur, and nongenomic activities are less well explored. Specific ligands, and methods to disrupt or eliminate receptor subtype expression in animal and cell models, demonstrate that the ERs have both overlapping and distinct biological functions. Overall, in cell-based studies, ERalpha appears to play a predominant role in cell proliferation, and ERbeta is suggested to be antiproliferative. The potential for distinct populations of breast tumors to be identified based on ER subtype expression, and to exhibit distinct clinical behaviors, is of greatest interest. Several studies suggest that the majority of ER-positive tumors contain both subtypes, but that some tumors contain only ERbeta and may have distinct clinical behaviors and responses. Expression of ERbeta together with ERalpha favors positive responses to endocrine therapy in most studies, and additional studies to determine if the addition of ERbeta to ERalpha as a tumor marker is of clinical benefit are warranted. In contrast, the positive association between ERbeta and HER2 expression in high-grade ERalpha-negative breast cancer does not favor positive responses to endocrine therapy. Expression of ERbeta in specific clinical subpopulations, and the potential for therapies targeting ERbeta specifically, is discussed.

Dietary lariciresinol attenuates mammary tumor growth and reduces blood vessel density in human MCF-7 breast cancer xenografts and carcinogen-induced mammary tumors in rats

Lariciresinol is a dietary lignan that accounts for a significant portion of the total phytoestrogen intake from Western foods. Recent epidemiological studies suggest that high dietary intake of lignans and lariciresinol is associated with reduced breast cancer risk. However, no causal relationship between lariciresinol intake and breast cancer development has been established. In this study, we investigated for the first time the effects and possible mechanisms of action of lariciresinol on hormone responsive mammary cancer in vivo in dimethylbenz[a]anthracene induced mammary cancer in rats, and in human MCF-7 breast cancer xenografts in athymic mice. For tumor bearing rats, lariciresinol (3 or 15 mg/kg of body weight) or vehicle was administered p.o. daily for 9 weeks. For E2-maintained ovariectomized athymic mice bearing orthotopic MCF-7 tumors, control diet (AIN-93G) or lariciresinol containing diet (AIN-93G supplemented with 20 or 100 mg of lariciresinol/kg of diet) was administered for 5 weeks. In both models, lariciresinol administration inhibited the tumor growth and tumor angiogenesis. In MCF-7 cells, enterolactone significantly inhibited the E2-stimulated VEGF secretion. Moreover, in MCF-7 xenografts, lariciresinol administration enhanced tumor cell apoptosis and increased estrogen receptor beta expression. Lariciresinol and its further metabolites secoisolariciresinol, enterodiol and enterolactone were found in serum of both rats and athymic mice confirming a similar lignan metabolism pattern as in humans. These findings indicate conceivable importance of dietary lignan lariciresinol in inhibition of breast cancer development.