Ligand-Induced Regulation of ERα and ERβ is Indicative of Human Breast Cancer Cell Proliferation

Cyclopia extracts act as selective estrogen receptor subtype downregulators in estrogen receptor positive breast cancer cell lines: Comparison to standard of care breast cancer endocrine therapies and a selective estrogen receptor agonist and antagonist

Breast cancer is the most diagnosed type of cancer amongst women in economically developing countries and globally. Most breast cancers express estrogen receptor alpha (ERα) and are categorized as positive (ER+) breast cancer. Endocrine therapies such as, selective estrogen receptor modulators (SERMs), aromatase inhibitors (AIs), and selective estrogen receptor downregulators (SERDs) are used to treat ER+ breast cancer. However, despite their effectiveness, severe side-effects and resistance are associated with these endocrine therapies. Thus, it would be highly beneficial to develop breast cancer drugs that are as effective as current therapies, but less toxic with fewer side effects, and less likely to induce resistance. Extracts of Cyclopia species, an indigenous South African fynbos plant, have been shown to possess phenolic compounds that exhibit phytoestrogenic and chemopreventive activities against breast cancer development and progression. In the current study, three well characterized Cyclopia extracts, SM6Met, cup of tea (CoT) and P104, were examined for their abilities to modulate the levels of the estrogen receptor subtypes, estrogen receptor alpha and estrogen receptor beta (ERβ), which have been recognized as crucial to breast cancer prognosis and treatment. We showed that the Cyclopia subternata Vogel (C. subternata Vogel) extracts, SM6Met and cup of tea, but not the C. genistoides extract, P104, reduced estrogen receptor alpha protein levels while elevating estrogen receptor beta protein levels, thereby reducing the ERα:ERβ ratio in a similar manner as standard of care breast cancer endocrine therapies such as fulvestrant (selective estrogen receptor downregulator) and 4-hydroxytamoxifen (elective estrogen receptor modulator). Estrogen receptor alpha expression enhances the proliferation of breast cancer cells while estrogen receptor beta inhibits the proliferative activities of estrogen receptor alpha. We also showed that in terms of the molecular mechanisms involved all the Cyclopia extracts regulated estrogen receptor alpha and estrogen receptor beta protein levels through both transcriptional and translational, and proteasomal degradation mechanisms. Therefore, from our findings, we proffer that the C. subternata Vogel extracts, SM6Met and cup of tea, but not the C. genistoides extract, P104, selectively modulate estrogen receptor subtypes levels in a manner that generally supports inhibition of breast cancer proliferation, thereby demonstrating attributes that could be explored as potential therapeutic agents for breast cancer.

Repeated Exposure to 4-Methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (MBP), an Active Metabolite of Bisphenol A, Aggressively Stimulates Breast Cancer Cell Growth in an Estrogen Receptor β (ERβ)-Dependent Manner

Bisphenol A (BPA), recognized as an endocrine disruptor, is thought to exert its activity through a mechanism involving the activation of estrogen receptors (ERs) α/β However, a major problem is that very high concentrations of BPA are required (i.e., those in excess of environmental levels) for effective activation of ERα/β-mediated transcriptional activities in vitro, despite the BPA-induced estrogenic effects observed in vivo. To elucidate the causal reasons, we successfully identified a BPA metabolite, 4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (MBP), which exhibits highly potent estrogenic activity both in vivo and in vitro. We have focused on the biologic relationship between breast tumor promotion and MBP/BPA, because BPA is considered to be a human carcinogen owing to its breast tumor-promoting properties. In general, humans are exposed to many endocrine disruptors, including BPA. In the present study, we used the ERα/β-positive human breast cancer cell line MCF-7 as an experimental model to investigate the effects of repeated exposure to BPA/MBP at concentrations found in the environment on the expression of ERα/β and to determine the particular ER subtype involved. We demonstrated that repeated exposure to MBP, but not to BPA, significantly downregulated ERα protein expression and stimulated the proliferation of MCF-7 cells through the activation of ERβ-mediated signaling.

Polyfluorinated iodine alkanes regulated distinct breast cancer cell progression through binding with estrogen receptor alpha or beta isoforms

Polyfluorinated iodine alkanes (PFIs) are a kind of emerging chemicals with endocrine disrupting effects. Based on the different binding preferences of PFIs to estrogen receptor alpha and beta isoforms (ERα and β), two representative PFIs, dodecafluoro-1,6-diiodohexane (PFHxDI) and tridecafluorohexyl iodide (PFHxI), were selected to evaluate their effects on the proliferation of two kinds of breast cancer cells with different ERα/β expression levels, MCF-7 and T47D. The cell viability assay showed PFHxDI could cause higher cellular toxicity than did PFHxI in both MCF-7 and T47D. MCF-7 with relatively higher ERα/β expression ratio was more vulnerable to the cytotoxic treatments of PFHxI and PFHxDI when compared with T47D cells with relatively lower ERα/β expression ratio. EdU incorporation and cell cycle analysis revealed that, similar to 17β-estrodiol (E₂), non-cytotoxic levels of PFHxDI could significantly promote the proliferation of MCF-7 by increasing cell population at S phase (p < 0.01), while T47D proliferation was not influenced by PFHxI exposure due to cell cycle arrest at G2/M phase. The cellular responses caused by estrogenic PFIs were dominantly mediated by their preferential binding affinities for ER isoforms, which would be helpful in the accurate assessment for their potential influences on the breast cancer progression.

7-ketocholesterol and 27-hydroxycholesterol decreased doxorubicin sensitivity in breast cancer cells: estrogenic activity and mTOR pathway

Hypercholesterolemia is one of the risk factors for poor outcome in breast cancer therapy. To elucidate the influence of the main circulating oxysterols, cholesterol oxidation products, on the cell-killing effect of doxorubicin, cells were exposed to oxysterols at a subtoxic concentration. When cells were exposed to oxysterols in fetal bovine serum-supplemented medium, 7-ketocholesterol (7-KC), but not 27-hydroxycholesterol (27-HC), decreased the cytotoxicity of doxorubicin in MCF-7 (high estrogen receptor (ER)α/ERβ ratio) cells and the decreased cytotoxicity was restored by the P-glycoprotein inhibitor verapamil. 7-KC stimulated the efflux function of P-glycoprotein and reduced intracellular doxorubicin accumulation in MCF-7 but not in ERα(-) MDA-MB-231 and the resistant MCF-7/ADR cells. In MCF-7 cells, 7-KC increased the mRNA and protein levels of P-glycoprotein. The 7-KC-suppressed doxorubicin accumulation was restored by the fluvestrant and ERα knockdown. In a yeast reporter assay, the ERα activation by 7-KC was more potent than 27-HC. 7-KC, but not 27-HC, stimulated the expression of an ER target, Trefoil factor 1 in MCF-7 cells. When charcoal-stripped fetal bovine serum was used, both 7-KC and 27-HC induced Trefoil factor 1 expression and reduced doxorubicin accumulation in MCF-7 cells. 7-KC-reduced doxorubicin accumulation could be reversed by inhibitors of phosphatidylinositol 3-kinase, Akt, and mammalian target of rapamycin (mTOR). These findings demonstrate that 7-KC decreases the cytotoxicity of doxorubicin through the up-regulation of P-glycoprotein in an ERα- and mTOR-dependent pathway. The 7-KC- and 27-HC-elicited estrogenic effects are crucial in the P-glycoprotein induction in breast cancer cells.

A novel FOXA1/ESR1 interacting pathway: A study of Oncomine™ breast cancer microarrays

Forkhead box protein A1 (FOXA1) is essential for the growth and differentiation of breast epithelium, and has a favorable outcome in breast cancer (BC). Elevated FOXA1 expression in BC also facilitates hormone responsiveness in estrogen receptor (ESR)-positive BC. However, the interaction between these two pathways is not fully understood. FOXA1 and GATA binding protein 3 (GATA3) along with ESR1 expression are responsible for maintaining a luminal phenotype, thus suggesting the existence of a strong association between them. The present study utilized the Oncomine™ microarray database to identify FOXA1:ESR1 and FOXA1:ESR1:GATA3 co-expression co-regulated genes. Oncomine™ analysis revealed 115 and 79 overlapping genes clusters in FOXA1:ESR1 and FOXA1:ESR1:GATA3 microarrays, respectively. Five ESR1 direct target genes [trefoil factor 1 (TFF1/PS2), B-cell lymphoma 2 (BCL2), seven in absentia homolog 2 (SIAH2), cellular myeloblastosis viral oncogene homolog (CMYB) and progesterone receptor (PGR)] were detected in the co-expression clusters. To further investigate the role of FOXA1 in ESR1-positive cells, MCF7 cells were transfected with a FOXA1 expression plasmid, and it was observed that the direct target genes of ESR1 (PS2, BCL2, SIAH2 and PGR) were significantly regulated upon transfection. Analysis of one of these target genes, PS2, revealed the presence of two FOXA1 binding sites in the vicinity of the estrogen response element (ERE), which was confirmed by binding assays. Under estrogen stimulation, FOXA1 protein was recruited to the FOXA1 site and could also bind to the ERE site (although in minimal amounts) in the PS2 promoter. Co-transfection of FOXA1/ESR1 expression plasmids demonstrated a significantly regulation of the target genes identified in the FOXA1/ESR1 multi-arrays compared with only FOXA1 transfection, which was suggestive of a synergistic effect of ESR1 and FOXA1 on the target genes. In summary, the present study identified novel FOXA1, ESR1 and GATA3 co-expressed genes that may be involved in breast tumorigenesis.

Effect of Enterococcus faecalis EF-2001 on experimentally induced atopic eczema in mice

Here, the effects of heat-killed Enterococcus faecalis EF-2001 (EF-2001) on atopic eczema (AE) were assessed. An AE model was established in vivo by repetitious topical exposure to 1-chloro-2,4-dinitrobenzene (CDNB) and dermatophagoidesfarinae extract (DFE) via application on each ear. Mice were administered EF-2001 orally for 4 weeks, dermal and epidermal ear thickness, mast cell infiltration of the ear tissue, and serum IgE and IgG2a levels were evaluated. Moreover, pathogenic cytokines levels of the ears, splenocytes, and cervical lymph nodes were determined. EF-2001 reduced AE symptoms grounded in the ear thickness, histopathological analysis, and serum IgE levels. Furthermore, EF-2001 attenuated mast cell infiltration in the ears and CDNB/DFE-induced various pathogenic cytokines levels of the ears, splenocytes and cervical lymph nodes. Thus, our data suggested that EF-2001 may have potential medicinal applications in the treatment of AE through its immunomodulatory properties.

Effects of early and late treatment with soy isoflavones in the mammary gland of ovariectomized rats

INTRODUCTION

Soy isoflavones have been shown to be an alternative to hormone therapy at menopause, without causing side-effects such as breast cancer. However, the effects of early and late treatment with isoflavones on the mammary gland remain controversial.

OBJECTIVE

To investigate the effects of early and late treatment with soy isoflavones on the mammary gland of ovariectomized rats.

METHODS

Thirty 3-month-old rats were ovariectomized and divided equally into groups: Control, treated with vehicle solution; or with 150 mg/kg/body weight of isoflavones by gavage; or subcutaneously treated with 10 μg/kg/body weight with 17β-estradiol. Treatments started 3 days (early treatment) or 30 days (late treatment) after ovariectomy and lasted for 30 consecutive days. Thereafter, the animals were euthanized and the mammary glands were removed and processed for paraffin embedding. Sections were stained with hematoxylin and eosin for histomorphometry or subjected to immunohistochemical detection of Ki-67 and VEGF-A.

RESULTS

The ductal, lobular and total epithelial fractions were similar between controls and the early/late isoflavone groups, but they were significantly higher in the groups treated with estradiol. In both epithelial and stromal regions, the immunoreactivity of VEGF-A and the percentage of Ki-67-positive cells were significantly higher in the groups treated with estradiol, while they were similar in the early/late isoflavone groups and control groups.

CONCLUSION

Our results indicate that early and late treatment with soy isoflavones at the dose of 150 mg/kg/body weight does not show proliferative and angiogenic effects on the mammary gland of ovariectomized rats.

The Combinatory Effects of Glabridin and Tamoxifen on Ishikawa and MCF-7 Cell Lines

Estrogen replacement therapy is commonly used to replace the loss of estrogen in post-menopausal women. However, it is not suitable to be used in women taking tamoxifen as both of the drugs increase the risk of endometrial cancer. This project aimed to study the potential of using the natural compound glabridin in combination with tamoxifen as a drug for estrogen replacement therapy. Ishikawa and MCF-7 cells were used to investigate the estrogenic activities stimulated by the combination of tamoxifen and glabridin through ALP and MTT assays. The expressions of the ESR1 and bcl-2 genes have also been determined using RT-PCR. The results indicated that the combination of 1×10−5M tamoxifen and 1×10−6M glabridin exhibited estrogenic activities and suppressed cell growth in both cell lines. The relative expressions of ESR1 and bcl-2 genes indicated that the estrogenicity expressed by the combinatory drug was regulated by estrogen receptor α; however, the reduction in cell proliferation was not modulated by bcl-2 anti-apoptotic proteins. These results suggested that the combination of tamoxifen and glabridin has potential to be used as an estrogen replacement drug with a reduced risk of endometrial cancer that has arisen from the intake of tamoxifen.

Bioenergetic differences between MCF-7 and T47D breast cancer cells and their regulation by oestradiol and tamoxifen

Oestrogen receptor α (ERα+) breast tumours rely on mitochondria (mt) to generate ATP. The goal of the present study was to determine how oestradiol (E2) and 4-hydroxytamoxifen (4-OHT) affect cellular bioenergetic function in MCF-7 and T47D ERα+ breast cancer cells in serum-replete compared with dextran-coated charcoal (DCC)-stripped foetal bovine serum (FBS)-containing medium ('serum-starved'). Serum-starvation reduced oxygen consumption rate (OCR), extracellular acidification rate (ECAR), ATP-linked OCR and maximum mt capacity, reflecting lower ATP demand and mt respiration. Cellular respiratory stateapparent was unchanged by serum deprivation. 4-OHT reduced OCR independent of serum status. Despite having a higher mt DNA/nuclear DNA ratio than MCF-7 cells, T47D cells have a lower OCR and ATP levels and higher proton leak. T47D express higher nuclear respiratory factor-1 (NRF-1) and NRF-1-regulated, nuclear-encoded mitochondrial transcription factor TFAM and cytochrome c, but lower levels of cytochrome c oxidase, subunit IV, isoform 1 (COX4, COX4I1). Mitochondrial reserve capacity, reflecting tolerance to cellular stress, was higher in serum-starved T47D cells and was increased by 4-OHT, but was decreased by 4-OHT in MCF-7 cells. These data demonstrate critical differences in cellular energetics and responses to 4-OHT in these two ERα+ cell lines, likely reflecting cancer cell avoidance of apoptosis.

A precisely substituted benzopyran targets androgen refractory prostate cancer cells through selective modulation of estrogen receptors

Dietary consumption of phytoestrogens like genistein has been linked with lower incidence of prostate cancer. The estradiol-like benzopyran core of genistein confers estrogen receptor-β (ER-β) selectivity that imparts weak anti-proliferative activity against prostate cancer cells. DL-2-[4-(2-piperidinoethoxy)phenyl]-3-phenyl-2H-1-benzopyran (BP), a SERM designed with benzopyran core, targeted androgen independent prostate cancer (PC-3) cells 14-times more potently than genistein, ~25% more efficiently than tamoxifen and 6.5-times more actively than ICI-182780, without forfeiting significant specificity in comparison to genistein. BP increased apoptosis (annexin-V and TUNEL labeling), arrested cell cycle, and significantly increased caspase-3 activity along with mRNA expressions of estrogen receptor (ER)-β and FasL (qPCR) in PC-3 cells. In classical ERE-luc reporter assay BP behaved as a potent ER-α antagonist and ER-β agonist. Accordingly, it decreased expression of ER-α target PS2 (P<0.01) and increased expression of ER-β target TNF-α (P<0.05) genes in PC-3. ER-β deficient PC-3 (siRNA-transfected) was resistant to apoptotic and anti-proliferative actions of SERMs, including stimulation of FasL expression by BP. BP significantly inhibited phosphorylation of Akt and ERK-1/2, JNK and p38 in PC-3 (immunoblotting), and thus adopted a multi-pathway mechanism to exert a more potent anti-proliferative activity against prostate cancer cells than natural and synthetic SERMs. Its precise ER-subtype specific activity presents a unique lead structure for further optimization.

ERα regulates chromosome alignment and spindle dynamics during mitosis

Estrogen receptors are activated by the hormone estrogen and they control cell growth by altering gene expression as a transcription factor. So far two estrogen receptors have been found: ERα and ERβ. Estrogen receptors are also implicated in the development and progression of breast cancer. Here, we found that ERα localized on the spindle and spindle poles at the metaphase during mitosis. Depletion of ERα generated unaligned chromosomes in metaphase cells and lagging chromosomes in anaphase cells in a transcription-independent manner. Furthermore, the levels of β-tubulin and γ-tubulin were reduced in ERα-depleted cells. Consistent with this, polymerization of microtubules in ERα-depleted cells and turnover rate of α/β-tubulin were decreased than in control cells. We suggest that ERα regulates chromosome alignment and spindle dynamics by stabilizing microtubules during mitosis.

The potential role of estrogen receptor β2 in breast cancer

Endocrine therapy is provided to all patients with estrogen receptor (ER)-positive breast cancer, but only a subset of them derives clinical benefit. The discovery of ERβ and its five isoforms added another layer of complexity in the regulation of estrogen activity in breast cancer cells. Two large retrospective studies showed conflicting results with regard to the prognostic value of the different ERβ isoforms in patients treated with tamoxifen in an adjuvant setting. This study tested the hypothesis that ERβ1 and, or ERβ2 are correlated with clinical outcome. We identified patients with breast cancer who had undergone surgery at Bucheon St. Mary's Hospital, the Catholic University of Korea, between January 2004 and March 2006. We evaluated 101 consecutive cases for ERβ1 and ERβ2 expression using immunohistochemical staining and obtained other clinicopathology by reviewing medical records. ERβ1 was expressed in 81.2% (79 of 97) and ERβ2 was expressed in 50.5% (51 of 101) of primary breast cancer tissues. Disease-free survival (DFS) and overall survival (OS) of patients with cancers expressing ERβ2 was significantly worse. Moreover, in subgroup analysis according to the tamoxifen treatment, ERβ2 expression was significantly associated with shorter DFS of tamoxifen-treated patients. This study indicates that breast cancer with ERβ2 expression was associated with worse DFS and OS, especially in tamoxifen treated patients. Our results suggest a role for ERβ2 as an independent prognostic marker and might serve as a new therapeutic target.

Estrogen receptor, progesterone receptor, interleukin-6 and interleukin-8 are variable in breast cancer and benign stem/progenitor cell populations. BMC Cancer. 2014;14:733. [PMID: 25269750 PMCID: PMC4190475 DOI: 10.1186/1471-2407-14-733]

Background

Estrogen receptor positive breast cancers have high recurrence rates despite tamoxifen therapy. Breast cancer stem/progenitor cells (BCSCs) initiate tumors, but expression of estrogen (ER) or progesterone receptors (PR) and response to tamoxifen is unknown. Interleukin-6 (IL-6) and interleukin-8 (IL-8) may influence tumor response to therapy but expression in BCSCs is also unknown.

Methods

BCSCs were isolated from breast cancer and benign surgical specimens based on CD49f/CD24 markers. CD44 was measured. Gene and protein expression of ER alpha, ER beta, PR, IL-6 and IL-8 were measured by proximity ligation assay and qRT-PCR.

Results

Gene expression was highly variable between patients. On average, BCSCs expressed 10-10⁶ fold less ERα mRNA and 10-10³ fold more ERβ than tumors or benign stem/progenitor cells (SC). BCSC lin-CD49f⁻CD24⁻cells were the exception and expressed higher ERα mRNA. PR mRNA in BCSCs averaged 10-10⁴ fold less than in tumors or benign tissue, but was similar to benign SCs. ERα and PR protein detection in BCSCs was lower than ER positive and similar to ER negative tumors. IL-8 mRNA was 10-10⁴ higher than tumor and 10² fold higher than benign tissue. IL-6 mRNA levels were equivalent to benign and only higher than tumor in lin-CD49f⁻CD24⁻cells. IL-6 and IL-8 proteins showed overlapping levels of expressions among various tissues and cell populations.

Conclusions

BCSCs and SCs demonstrate patient-specific variability of gene/protein expression. BCSC gene/protein expression may vary from that of other tumor cells, suggesting a mechanism by which hormone refractory disease may occur.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2407-14-733) contains supplementary material, which is available to authorized users.

Ritonavir binds to and downregulates estrogen receptors: molecular mechanism of promoting early atherosclerosis

Estrogenic actions are closely related to cardiovascular disease. Ritonavir (RTV), a human immunodeficiency virus (HIV) protease inhibitor, induces atherosclerosis in an estrogen-related manner. However, how RTV induce pathological phenotypes through estrogen pathway remains unclear. In this study, we found that RTV increases thickness of coronary artery walls of Sprague Dawley rats and plasma free fatty acids (FFA) levels. In addition, RTV could induce foam cell formation, downregulate both estrogen receptor α (ERα) and ERβ expression, upregulate G protein-coupled estrogen receptor (GPER) expression, and all of them could be partially blocked by 17β-estradiol (E2), suggesting RTV acts as an antagonist for E2. Computational modeling shows a similar interaction with ERα between RTV and 2-aryl indoles, which are highly subtype-selective ligands for ERα. We also found that RTV directly bound to ERα and selectively inhibited the nuclear localization of ERα, and residue Leu536 in the hydrophobic core of ligand binding domain (LBD) was essential for the interaction with RTV. In addition, RTV did not change the secondary structure of ERα-LBD like E2, which explained how ERα lost the capacity of nuclear translocation under the treatment of RTV. All of the evidences suggest that ritonavir acts as an antagonist for 17β-estradiol in regulating α subtype estrogen receptor function and early events of atherosclerosis.

Bridging the gap from screening assays to estrogenic effects in fish: potential roles of multiple estrogen receptor subtypes

This study seeks to delineate the ligand interactions that drive biomarker induction in fish exposed to estrogenic pollutants and provide a case study on the capacity of human (h) estrogen receptor (ER)-based in vitro screening assays to predict estrogenic effects in aquatic species. Adult male Japanese medaka (Oryzias latipes) were exposed to solutions of singular steroidal estrogens or to the estrogenic extract of an anaerobic swine waste lagoon. All exposure concentrations were calibrated to be equipotent based on the yeast estrogen screen (YES), which reports activation of hERα. These exposures elicited significantly different magnitudes of hepatic vitellogenin and choriogenin gene induction in the male medaka. Effects of the same YES-calibrated solutions in the T47D-KBluc assay, which reports activation of hERα and hERβ, generally recapitulated observations in medaka. Using competitive ligand binding assays, it was found that the magnitude of vitellogenin/choriogenin induction by different estrogenic ligands correlated positively with preferential binding affinity for medaka ERβ subtypes, which are highly expressed in male medaka liver prior to estrogen exposure. Results support emerging evidence that ERβ subtypes are critically involved in the teleost estrogenic response, with the ERα:ERβ ratio being of particular importance. Accordingly, incorporation of multiple ER subtypes into estrogen screening protocols may increase predictive value for the risk assessment of aquatic systems, including complex estrogenic mixtures.

The orphan nuclear receptor LRH-1 and ERα activate GREB1 expression to induce breast cancer cell proliferation

Background

Liver Receptor Homolog 1 (LRH-1, NR5A2) is an orphan nuclear receptor that is over-expressed in cancers in tissues such as the breast, colon and pancreas. LRH-1 plays important roles in embryonic development, steroidogenesis and cholesterol homeostasis. In tumor cells, LRH-1 induces proliferation and cell cycle progression. High LRH-1 expression is demonstrated in breast cancers, positively correlating with ERα status and aromatase activity. LRH-1 dependent cellular mechanisms in breast cancer epithelial cells are poorly defined. Hence in the present study we investigated the actions of LRH-1 in estrogen receptor α (ERα) positive breast cancer cells.

Results

The study aimed to investigate LRH-1 dependent mechanisms that promote breast cancer proliferation. We identified that LRH-1 regulated the expression of Growth Regulation by Estrogen in Breast Cancer 1 (GREB1) in MCF-7 and MDA-MB-231 cells. Over-expression of LRH-1 increased GREB1 mRNA levels while knockdown of LRH-1 reduced its expression. GREB1 is a well characterised ERα target gene, with three estrogen response elements (ERE) located on its promoter. Chromatin immunoprecipitation studies provided evidence of the co-localisation of LRH-1 and ERα at all three EREs. With electrophoretic mobility shift assays, we demonstrated direct binding of LRH-1 to EREs located on GREB1 and Trefoil Factor 1 (TFF1, pS2) promoters. LRH-1 and ERα co-operatively activated transcription of ERE luciferase reporter constructs suggesting an overlap in regulation of target genes in breast cancer cells. Over-expression of LRH-1 resulted in an increase in cell proliferation. This effect was more pronounced with estradiol treatment. In the presence of ICI 182,780, an ERα antagonist, LRH-1 still induced proliferation.

Conclusions

We conclude that in ER-positive breast cancer cells, LRH-1 promotes cell proliferation by enhancing ERα mediated transcription of target genes such as GREB-1. Collectively these findings indicate the importance of LRH-1 in the progression of hormone-dependent breast cancer and implicate LRH-1 as a potential avenue for drug development.

Dose-dependent effects of genistein on bone homeostasis in rats' mandibular subchondral bone

AIM

To investigate the effect of genistein on bone homeostasis in mandibular subchondral bone of rats.

METHODS

Female SD rats were administered with genistein (10 and 50 mg/kg) or placebo by oral gavage for 6 weeks. Then the animals were sacrificed, and histomorphology and micro-structure of mandibular condyle were examined using HE staining and micro-CT analysis, respectively. The expression levels of alkaline phosphatase (ALP), osteocalcin (OC), osteoprotegerin (OPG), the receptor activator of nuclear factor κB ligand (RANKL) and estrogen receptors (ERs) in mandibular condyle were detected using real-time PCR. Cultured osteoblasts were prepared from rat mandibular condyle for in in vitro study. The cells were treated with genistein (10(-7) or 10(-4) mol/L) for 48 h. The expression of the bone homeostasis-associated factors and estrogen receptors (ERs) was detected using real-time PCR, and ER silencing was performed.

RESULTS

At both the low- and high-doses, genistein significantly increased the bone mineral density (BMD) and bone volume, and resulted in thicker subchondral trabecular bone in vivo. In both in vivo and in vitro study, the low-dose genistein significantly increased the expression of ALP, OC and OPG, but decreased the expression of RANKL and the RANKL/OPG ratio. The high-dose genistein decreased the expression of all these bone homeostasis-associated factors. Both the low and high doses of genistein significantly increased the expression of ERβ, while ERα expression was increased by the low dose genistein and decreased by the high dose genistein. ERβ silencing abrogated most of the effects of genistein treatment.

CONCLUSION

In rat mandibular condylar subchondral bone, low-dose genistein increases bone formation and inhibit bone resorption, while excess genistein inhibits both bone formation and resorption. The effects of genistein were predominantly mediated through ERβ.

Superinduction of estrogen receptor mediated gene expression in luciferase based reporter gene assays is mediated by a post-transcriptional mechanism

Several estrogenic compounds including the isoflavonoid genistein have been reported to induce a higher maximal response than the natural estrogen 17β-estradiol in in vitro luciferase based reporter gene bioassays for testing estrogenicity. The phenomenon has been referred to as superinduction. The mechanism underlying this effect and thus also its biological relevance remain to be elucidated. In the present study several hypotheses for the possible mechanisms underlying this superinduction were investigated using genistein as the model compound. These hypotheses included (i) a non-estrogen receptor (ER)-mediated mechanism, (ii) a role for an ER activating genistein metabolite with higher ER inducing activity than genistein itself, and (iii) a post-transcriptional mechanism that is not biologically relevant but specific for the luciferase based reporter gene assays. The data presented in this study indicate that induction and also superinduction of the reporter gene is ER-mediated, and that superinduction by genistein could be ascribed to stabilization of the firefly luciferase reporter enzyme increasing the bioluminescent signal during the cell-based assay. This indicates that the phenomenon of superinduction may not be biologically relevant but may rather represent a post-transcriptional effect on enzyme stability.

Quantitative proteomics and transcriptomics addressing the estrogen receptor subtype-mediated effects in T47D breast cancer cells exposed to the phytoestrogen genistein

The present study addresses, by transcriptomics and quantitative stable isotope labeling by amino acids in cell culture (SILAC)-based proteomics, the estrogen receptor α (ERα) and β (ERβ)-mediated effects on gene and protein expression in T47D breast cancer cells exposed to the phytoestrogen genistein. Using the T47D human breast cancer cell line with tetracycline-dependent ERβ expression (T47D-ERβ), the effect of a varying intracellular ERα/ERβ ratio on genistein-induced gene and protein expression was characterized. Results obtained reveal that in ERα-expressing T47D-ERβ cells with inhibited ERβ expression genistein induces transcriptomics and proteomics signatures pointing at rapid cell growth and migration by dynamic activation of cytoskeleton remodeling. The data reveal an interplay between integrins, focal adhesion kinase, CDC42, and actin cytoskeleton signaling cascades, occurring upon genistein treatment, in the T47D-ERβ breast cancer cells with low levels of ERα and no expression of ERβ. In addition, data from our study indicate that ERβ-mediated gene and protein expression counteracts ERα-mediated effects because in T47D-ERβ cells expressing ERβ and exposed to genistein transcriptomics and proteomics signatures pointing at a clear down-regulation of cell growth and induction of cell cycle arrest and apoptosis were demonstrated. These results suggest that ERβ decreases cell motility and metastatic potential as well as cell survival of the breast cancer cell line. It is concluded that the effects of genistein on proteomics and transcriptomics end points in the T47D-ERβ cell model are comparable with those reported previously for estradiol with the ultimate estrogenic effect being dependent on the relative affinity for both receptors and on the receptor phenotype (ERα/ERβ ratio) in the cells or tissue of interest.

Effect of Obesity on Breast Cancer Development

In recent years, obesity has been identified as a risk factor for the development of breast cancer in postmenopausal women, and it has been associated with a poor outcome. Many factors appear to be important in the mechanism of this increased risk, including estrogen, estrogen receptors, and the adipokines leptin and adiponectin. Estrogen, a potent mitogen for mammary cells, has long been implicated in the development of mammary tumors. Because adipose-associated aromatase activity increases the conversion of androgen to estrogen, mammary adipose tissue is thought to be an important source of local estrogen production. Leptin, which increases in the circulation in proportion to body fat stores, has been demonstrated in vitro to promote breast cancer cell growth. Animal models have also identified leptin as an important factor for the development of mammary tumors. In contrast to leptin, serum adiponectin concentrations are inversely related to body fat stores, and the addition of adiponectin to human breast cancer cells reduces cell proliferation and enhances apoptosis. This review explores the relationship between these factors and the development of mammary cancer in humans and mouse models.

The vitamin A family can significantly decrease the expression of ERbeta of ERs positive breast cancer cells in the presence or absence of ER ligands and paclitaxel

Taxanes have high activity against breast cancer cells either as the single agent or in combination with other anticancer compounds. The aim of the study was to determine the effects of vitamin A compounds on the cytotoxic action of paclitaxel and on the expression of ERs in the MCF-7 breast cancer cells. Retinol and beta-carotene, but not retinoids, added to the culture exerted an effect on paclitaxel activity. However, only beta-carotene significantly reduced the percentage of proliferating cells (40.36% +/- 5.64, p < 0.01). We observed that vitamin A and its derivatives combined with paclitaxel and estradiol decreased the percentage of proliferating cells, but only in comparison to estradiol group, whereas retinol and lycopene administered together with paclitaxel and tamoxifen decrease significantly the percentage of proliferatin cells (36.85% +/- 4.71, p < 0.0001 and 37.22% +/- 1.59, p < 0.0001 respectively, compared with paclitaxel group). We have shown that paclitaxel increases the expression of ERalpha and ERbeta mRNA in MCF-7 line. The strongest effect of transcription inhibition ERalpha (2.5 times) and especially ERbeta (10 times) was observed after addition of 9-cis retinoic acid and paclitaxel. This data suggests a synergistic effect of the compounds on ERbeta down-regulation. Our results support the use of retinoid is treatment of ER positive breast cancer patients.

Estrogen receptor-beta as a potential target for colon cancer prevention: chemoprevention of azoxymethane-induced colon carcinogenesis by raloxifene in F344 rats

Raloxifene, selective estrogen receptor (ER) modulator, is not fully explored in colorectal cancer. In the present study we, (a) investigated the effect of raloxifene on ER-positive colon cancer HCT-116 cell growth, (b) assessed the relevance of ER-beta in colon tumorigenesis, and (c) assessed the chemopreventive efficacy of raloxifene against azoxymethane (AOM)-induced colon carcinogenesis using aberrant crypt foci (ACF) as surrogate end point marker. HCT-116 cells treated with raloxifene showed a significant decrease in cell growth associated with a decrease in ER-beta expression levels. AOM-induced colon adenocarcinoma showed significant up-regulation of ER-beta expression at both the protein and mRNA levels compared with normal mucosa, suggesting that ER-beta is positively associated with colon cancer. An assay using five different dietary dose levels (0.31, 0.62, 1.25, 2.5, or 5 ppm) of raloxifene for 6 weeks in male F344 rats found the maximum tolerated dose to be 5 ppm. To evaluate inhibitory properties of raloxifene on colonic ACF, 7-week-old rats were fed experimental diets containing 0, 0.625, 1.25, and 2.5 ppm of raloxifene. After 1 week, rats received s.c. injections of AOM, 15 mg/kg body weight, once weekly for 2 weeks. Rats continued to receive respective experimental diets and sacrificed 8 weeks after the last AOM treatment. Raloxifene given in the diet significantly inhibited AOM-induced total colonic ACF (31-40%; P < 0.001-0.0005) and multicrypt (four or more) aberrant foci (23-50%; P < 0.05-0.005) in F344 rats. Our findings suggest that ER-beta acts as a colon tumor promoter and raloxifene as an antagonist to ER-beta, providing protection against colon carcinogenesis.

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.

Isoflavones and the prevention of breast and prostate cancer: new perspectives opened by nutrigenomics

Epidemiological evidence together with preclinical data from animal and in vitro studies strongly support a correlation between soy isoflavone consumption and protection towards breast and prostate cancers. The biological processes modulated by isoflavones, and especially by genistein, have been extensively studied, yet without leading to a clear understanding of the cellular and molecular mechanisms of action involved. This review discusses the existing gaps in our knowledge and evaluates the potential of the new nutrigenomic approaches to improve the study of the molecular effects of isoflavones. Several issues need to be taken into account for the proper interpretation of the results already published for isoflavones. Too often knowledge on isoflavone bioavailability is not taken into account; supra-physiological doses are frequently used. Characterization of the individual variability as defined by the gut microflora composition and gene polymorphisms may also help to explain the discrepancies observed so far in the clinical studies. Finally, the complex inter-relations existing between tissues and cell types as well as cross-talks between metabolic and signalling pathways have been insufficiently considered. By appraising critically the abundant literature with these considerations in mind, the mechanisms of action that are the more likely to play a role in the preventive effects of isoflavones towards breast and prostate cancers are reviewed. Furthermore, the new perspectives opened by the use of genetic, transcriptomic, proteomic and metabolomic approaches are highlighted.

Phytoestrogen-mediated inhibition of proliferation of the human T47D breast cancer cells depends on the ERalpha/ERbeta ratio

This study investigates the importance of the intracellular ratio of the two estrogen receptors ERalpha and ERbeta for the ultimate potential of the phytoestrogens genistein and quercetin to stimulate or inhibit cancer cell proliferation. This is of importance because (i) ERbeta has been postulated to play a role in modulating ERalpha-mediated cell proliferation, (ii) genistein and quercetin may be agonists for both receptor types and (iii) the ratio of ERalpha to ERbeta is known to vary between tissues. Using human osteosarcoma (U2OS) ERalpha or ERbeta reporter cells it was shown that compared to estradiol (E2), genistein and quercetin have not only a relatively greater preference for ERbeta but also a higher maximal potential for activating ERbeta-mediated gene expression. Using the human T47D breast cancer cell line with tetracycline-dependent ERbeta expression (T47D-ERbeta), the effect of a varying intracellular ERalpha/ERbeta ratio on E2- or pythoestrogen-induced cell proliferation was characterised. E2-induced proliferation of cells in which ERbeta expression was inhibited was similar to that of the T47D wild type cells, whereas this E2-induced cell proliferation was no longer observed when ERbeta expression was increased. With increased expression of ERbeta the phytoestrogen-induced cell proliferation was also reduced. These results point at the importance of the cellular ERalpha/ERbeta ratio for the ultimate effect of (phyto)estrogens on cell proliferation.

Enterodiol and enterolactone, two major diet-derived polyphenol metabolites have different impact on ERalpha transcriptional activation in human breast cancer cells

Lignans are plant compounds metabolized in the mammalian gut to produce the estrogenic enterolignans, enterodiol (ED) and enterolactone (EL). Because estrogens have been linked to breast cancer etiology, enterolignans could affect breast cancer risk, but to our knowledge, the mechanisms by which they exert their estrogenic and/or anti-estrogenic effects in humans are still unclear. To better understand how estrogenic compounds from the food, such as the enterolignans, might influence breast cancer progression and their mechanisms to interfere with human estrogen receptor (ER) signalling in hormone-dependant diseases, we examined and compared the ability of ED, EL and 17beta-estradiol (E2) to induce the transactivation of ERalpha and ERbeta, to modulate ERalpha target genes, to exert either growth stimulatory or anti-proliferative effects and finally to modulate MCF-7 cell migration by acting on matrix metalloproteases (MMP)-2 and -9, at concentrations that are achievable through a lignan-rich diet. This study indicates that enterolignans show distinct properties for transactivation of ERalpha and ERbeta. ED, as E2, induces ERalpha transcriptional activation through transactivation functions AF-1 and AF-2, while EL is less efficient in inducing AF-1, acting predominantly through AF-2. Furthermore, ED and EL modulate ERalpha mRNA and protein contents as well as MCF-7 cell proliferation and secreted MMP activities in a different way. Enterolignans are compounds of wide interest nowadays and our results help to unveil their mechanisms of action on ER, emphasizing the fact that the dietary load in lignans could be of importance in the balance between being risk or chemopreventive factors for breast cancer and women's health.

Mammary tumor development from T47-D human breast cancer cells in obese ovariectomized mice with and without estradiol supplements

Obesity is a risk factor for postmenopausal breast cancer, particularly for development of estrogen-receptor (ER)-positive tumors. Additionally, obesity is implicated in breast cancer progression. However, few studies address mechanisms of action of how obesity mediates these responses. Our goal was to address how obesity and/or elevated serum leptin affects tumor formation from ER-positive T47-D cells. In Study 1 ovariectomized CD-1 nude female mice were injected with goldthioglucose (GTG) at 0.5 mg/g body weight in saline or the vehicle at 6 weeks of age. At 10 weeks of age mice were inoculated with T47-D cells and implanted with estrogen pellets. In Study 2 mice were injected with 0.3 mg/g GTG or the vehicle. At 10 weeks of age cells were inoculated and mice were implanted with estrogen or placebo pellets. Mice were followed until 30 weeks of age. Some GTG mice became obese and others were non-responders. In Study 1 no mice developed tumors. In Study 2 mice with placebo pellets developed more tumors than mice with estrogen pellets, 50% vs. 13%. GTG-obese mice with placebo pellets had a 100% tumor incidence compared to 50% and 20% for GTG-lean and controls without estrogen. Serum leptin was higher in obese compared to lean mice and adiponectin was not affected by body weight. Adiponectin:leptin ratio was significantly reduced in obese compared to lean mice. Leptin, leptin receptor and signaling protein expression were determined in mammary and tumor tissue. Leptin and STAT3 were most abundant in tumors. These findings suggest that in vivo estrogen suppressed proliferation of T47-D cells but without supplemental estrogen obesity enhanced tumor development. The exact reason for this is not presently clear.

Effects of thyroid hormones on human breast cancer cell proliferation

The involvement of estrogens in breast cancer development and growth has been well established. However, the effects of thyroid hormones and their combined effects with estrogens are not well studied. We investigated the response of human breast cancer cells to thyroid hormone, particularly the role of T3 in mediating cell proliferation and gene expression. We demonstrated that 17beta-estradiol (E2) or triiodothyronine (T3) promoted cell proliferation in a dose-dependent manner in both MCF-7 and T47-D cell lines. The E2- or T3-dependent cell proliferation was suppressed by co-administration of the ER antagonist ICI. We also demonstrated that T3 could enhance the effect of E2 on cell proliferation in T47-D cells. Using an estrogen response element (ERE)-mediated luciferase assay, we determined that T3 was able to induce the activation of ERE-mediated gene expression in MCF-7 cells, although the effects were much weaker than that induced by E2. These results suggest that T3 can promote breast cancer cell proliferation and increase the effect of E2 on cell proliferation in some breast cancer cell lines and thus that T3 may play a role in breast cancer development and progression.

Can the combination of flaxseed and its lignans with soy and its isoflavones reduce the growth stimulatory effect of soy and its isoflavones on established breast cancer?

Consumption of phytoestrogen (PE)-rich foods (i. e., soy and flaxseed (FS)) is increasing because of their suggested health benefits. However, recent studies raise concern over the safety of soy and its isoflavones, particularly genistein (GEN), for postmenopausal breast cancer (BC), due to their potential stimulatory effects on human breast tissue and on the growth of existing tumors in rodents. FS, rich in PE lignans, which is metabolized to the mammalian lignans enterolactone (ENL) and enterodiol (END), has consistently been shown to have tumor inhibitory effects in a human clinical trial as well as rodent BC models. Using the preclinical athymic mouse postmenopausal BC model, combining FS with soy protein or GEN with END and ENL, was found to negate the tumor stimulatory effects of soy protein or GEN alone. The mechanism may be related to the modulation of estrogen receptor and MAPK signaling pathways. If these studies can be confirmed in clinical trials, then consumption of combined soy and FS, or their PEs, may reduce the tumor growth stimulatory effect of soy or GEN. This may indicate that if soy is consumed with lignan-rich foods, it may continue to induce its other beneficial health effects, without inducing adverse effect on postmenopausal BC.

Effects of flavonoids genistein and biochanin a on gene expression and their metabolism in human mammary cells

Genistein (GEN) and biochanin A (BCA), dietary isoflavones, possess breast cancer-preventive properties. Our objective was to examine the effect of physiologically relevant concentrations of BCA and GEN on gene expression in normal (HMEC), immortalized but nontumorigenic (MCF12A), and tumorigenic (MCF7) mammary cells and to determine whether the differences in gene expression are related to differences in metabolism in the three types of mammary cells. Using cDNA arrays, we compared the gene expression after a 48-h incubation with 1 microM BCA, GEN, or vehicle. Treatment with GEN or BCA produced the greatest number of significant changes in HMEC compared with MCF12A or MCF7 cells. Unlike GEN, effects of BCA on gene expression were mostly beneficial, involving induction of tumor suppressor genes. Different extents of metabolism were observed in the three mammary cell types; however, GEN concentrations were very low following either GEN or BCA administration in all of the three cell types. Because there were only very low concentrations of GEN, compared with BCA concentrations, in HMEC and MCF12A cells treated with BCA and different gene expression changes were found after BCA and GEN treatment, these findings suggest that BCA has distinct effects compared with GEN. The results suggest that BCA may represent a better breast cancer-preventive agent than GEN.

Identification of novel proteins induced by estradiol, 4-hydroxytamoxifen and acolbifene in T47D breast cancer cells

Tamoxifen is currently used as adjuvant therapy for estrogen receptor (ER) positive breast cancer patients and as a chemopreventative agent. Although ER is a predictive marker for tamoxifen response, ER status fails to predict tamoxifen response in a significant number of patients highlighting the need to identify new pathways for tamoxifen sensitivity/resistance. To identify novel proteins induced by tamoxifen in breast cancer cells sensitive to tamoxifen growth inhibition, two-dimensional (2D) gel electrophoresis was used to profile proteins in T47D breast cancer cells. Six proteins were identified that were differentially regulated by 17beta-estradiol, 4-hydroxytamoxifen and the pure antagonist acolbifene (EM-652); calreticulin, synapse associated protein 1 (SYAP1), CD2 antigen binding protein 2 (CD2BP2), nucleosome assembly protein 1 like 1 (NAP1L1), d-3-phosphoglycerate dehydrogenase (3-PHGDH) and pyridoxine 5' phosphate oxidase (PNPO). At the mRNA level, these ligands differentially regulated expression of mRNAs encoding the identified proteins in T47D and MCF7 cells but had no effect on mRNA in ERalpha-negative MDA-MB-231 breast cancer cells. These novel SERM-regulated proteins may participate in new or existing pathways for sensitivity or resistance to SERMs.

Addressing the soy and breast cancer relationship: review, commentary, and workshop proceedings

The impact of soyfood intake on breast cancer risk has been investigated extensively. Much of this focus can be attributed to the soybean being a dietary source that is uniquely rich in isoflavones. The chemical structure of isoflavones is similar to that of estrogen, and isoflavones bind to both estrogen receptors (ER alpha and ER beta) (although they preferentially bind to and activate ER beta) and exert estrogen-like effects under some experimental conditions. Isoflavones also possess nonhormonal properties that are associated with the inhibition of cancer cell growth. Thus, there are several possible mechanisms by which soy may reduce the risk of breast cancer. However, the role of isoflavones in breast cancer has become controversial because, in contrast to the possible beneficial effects, some data from in vitro and animal studies suggest that isoflavones, especially genistein, the aglycone of the main soybean isoflavone genistin, may stimulate the growth of estrogen-sensitive tumors. Limited human data directly address the tumor-promoting effects of isoflavones and soy. Because the use of soyfoods and isoflavone supplements is increasing, it is important from a public health perspective to understand the impact of these products on breast cancer risk in women at high risk of the disease and on the survival of breast cancer patients. To this end, a workshop was held in November 2005 to review the existing literature and to make research recommendations. This paper summarizes the workshop findings and recommendations. The primary research recommendation is that the impact of isoflavones on breast tissue needs to be evaluated at the cellular level in women at high risk for breast cancer.

Mammalian lignans enterolactone and enterodiol, alone and in combination with the isoflavone genistein, do not promote the growth of MCF-7 xenografts in ovariectomized athymic nude mice

This study determined the effect of the mammalian lignans enterolactone (ENL) and enterodiol (END) alone and in combination with the isoflavone genistein (GEN) on the growth of MCF-7 tumors in ovariectomized nude mice. Ovariectomized athymic nude mice with established MCF-7 tumors were fed a basal diet (AIN-93G) and divided into 5 groups that received daily subcutaneous injections (10 mg/kg body weight (BW)) of ENL, END, GEN, a mixture of these compounds (MIX), or vehicle as a negative control for 22 weeks. A positive control group was implanted with an estradiol pellet in order to establish an estrogenic tumor growth response. In the ENL- and END-treated mice, palpable tumors regressed significantly by 91 and 83%, respectively, resulting in final tumors that were similar to the negative control tumors. However, tumor cell apoptosis was significantly enhanced by the lignans. In the GEN-treated mice, tumors initially regressed significantly by 64% but regression ceased following prolonged treatment, resulting in final tumors that were significantly larger compared to negative control, ENL-, and END-treated mice, in part by increasing tumor cell proliferation. The MIX treatment significantly regressed palpable tumors by 87% similar to negative control group, with no effects on tumor cell apoptosis or proliferation. The isoflavone GEN alone promoted the growth of established MCF-7 human breast cancer xenografts after prolonged treatment while the mammalian lignans ENL and END did not. When these phytoestrogens were given in combination, no tumor growth-promoting effects were observed. (c) 2005 Wiley-Liss, Inc.

Flaxseed attenuates the tumor growth stimulating effect of soy protein in ovariectomized athymic mice with MCF-7 human breast cancer xenografts

In several epidemiological studies, a phytoestrogen-rich diet containing lignans and isoflavones is associated with reduced breast cancer risk, but experimental findings are controversial. In postmenopausal mammary cancer xenograft model, flaxseed (FS), a rich source of plant lignans, reduced breast cancer growth, while soy protein (SP), a rich source of isoflavones, enhanced it. The intake of phytoestrogens is increasing particularly among postmenopausal women, emphasizing the importance of elucidating their interactive effects on breast cancer. Our study determined the effect of FS and SP diets, alone and in combination, on the established human breast cancer MCF-7 tumor growth in ovariectomized athymic nude mice. Tumor bearing mice were divided into 4 groups and fed for 25 weeks either the basal diet (BD), or BD supplemented with 10% FS, 20% SP or 10% FS and 20% SP. After estrogen deprivation, FS regressed the tumor size similar to that of control. SP initially regressed the tumors but starting at week 13, the tumors regressed significantly less than in control and 43% of the tumors were regrowing until the end of the experiment and were significantly larger in size than in control. The combination of SP with FS reduced the tumor growth similar to that of control, as suggested also by the reduced tumor cell proliferation index. In conclusion, dietary FS did not stimulate the growth of estrogen responsive MCF-7 cancers in ovariectomized mice, while long-term consumption of SP did. Furthermore, FS reduced the tumor growth stimulating effect of SP to the same level as control, suggesting tumor growth attenuating effect of FS.

Genistein stimulates hematopoiesis and increases survival in irradiated mice

Radiation protection from death and stimulating hematopoietic recovery by oral administrations of genistein, 160 mg/kg b.w., once daily for seven consecutive days before whole-body gamma-rays irradiation, were confirmed by tests with adult male BALB/c mice. Moreover, the protective action of genistein was compared to that of diethylstilbestrol (DES). Based on the studies of survival, behavior of hematograms, endogenous hematopoietic spleen colony formation (endoCFUs), and numbers of nucleated cell, granulocyte-macrophage colony forming units (CFU-GM) in bone marrow following irradiation, it was demonstrated that genistein was an effective radioprotector. The survival of irradiated mice protected by genistein was significantly increased and statistically higher than that of mice pre-treated with DES. Stimulated recovery of leukocytes, erythrocytes, lymphocytes and thrombocytes were observed in mice pre-treated with genistein or DES, however, the effects of genistein on promoting recovery of bone marrow nucleated cells, leukocytes and lymphocytes were significantly higher than those of DES. Enhanced endoCFUs, numbers of bone marrow nucleated cells and CFU-GM were also found in mice pre-treated with genistein as well as DES. Meanwhile, endoCFU numbers in mice pre-treated with genistein was 3.47-fold higher than that in the irradiated control group, although no significant difference was found between genistein administration and DES administration. It could be deduced that the radioprotective action against death is induced by a possible process of enhanced regeneration of the hematopoietic stem cells due to not only strengthened radioresistance and increased numbers of remained hematopoietic cells, but also enhanced post-irradiation repair or promoted proliferation of the hematopoietic stem cells. These effects of genistein may have some therapeutic implications for radiation-induced injuries.

Aryl hydrocarbon receptor-independent activation of estrogen receptor-dependent transcription by 3-methylcholanthrene

Aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that stimulates transcription directed by xenobiotic response elements upstream of target genes. Recently, AhR ligands were reported to induce formation of an AhR-estrogen receptor (ER) complex, which can bind to estrogen response elements (EREs) and stimulate transcription of ER target genes. Presently, we investigate the effect of the AhR ligands 3-methylcholanthrene (3MC), 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 3,3',4,4',5-pentachlorobiphenyl (BZ126) on ERE-regulated luciferase reporter activity and endogenous ER target gene expression. In MCF-7 human breast cancer cells, 3MC induced transcription of ER reporter genes containing native promoter sequences of the ER-responsive genes complement 3 and pS2 and heterologous promoters regulated by isolated EREs. Dose-response studies revealed that the concentration of 3MC required to half-maximally activate transcription (EC(50)) was >100-fold higher for an ER reporter (27-57 muM) than for an AhR reporter (86-250 nM) in both MCF-7 cells and in human endometrial cancer Ishikawa cells. 3MC also stimulated expression of the endogenous ER target genes amphiregulin, cathepsin D and progesterone receptor, albeit to a much lower extent than was achieved following stimulation with 17beta-estradiol. In Ishikawa cells, 3MC, but not BZ126 or TCDD, stimulated ERalpha-dependent reporter activity but did not induce expression of endogenous ER target genes. Finally, studies carried out in the AhR-positive rat hepatoma cell line 5L and the AhR-deficient variant BP8 demonstrated that ER reporter activity could be induced by 3MC in a manner that was independent of AhR and thus distinct from the AhR-ER 'hijacking' mechanism described recently. 3MC may thus elicit estrogenic activity by multiple mechanisms.

The stimulation of cell proliferation by quercetin is mediated by the estrogen receptor

Quercetin causes biphasic modulation of the proliferation of specific colon and mammary cancer cells. In this study, the possible involvement of the estrogen receptor (ER) in the stimulation of cell proliferation by quercetin was investigated. For this purpose, the effect of quercetin on cell proliferation was tested in ER-positive MCF-7 and T47D cells, and in ER-negative HCC-38 and MDA-MB231 cells. Quercetin stimulated proliferation of ER-positive cells only, suggesting this effect to be ER-dependent. In support of these results, quercetin induced ER-ERE-mediated gene expression in a reporter gene assay using U2-OS cells transfected with either ERalpha or ERbeta, with 10(5)-10(6) times lower affinity than 17beta-estradiol (E2) and 10(2)-10(3 )times lower affinity than genistein. Quercetin activated the ERbeta to a 4.5-fold higher level than E2, whereas the maximum induction level of ERalpha by quercetin was only 1.7 fold that of E2. These results point at the relatively high capacity of quercetin to stimulate supposed 'beneficial' ERbeta responses as compared to the stimulation of ERalpha, the receptor possibly involved in adverse cell proliferative effects. Altogether, the results of this study reveal that physiologically relevant concentrations of quercetin can exert phytoestrogen-like activity similar to that observed for the isoflavonoid genistein.

Regulation of osteoblastic phenotype and gene expression by hop-derived phytoestrogens

Certain plant-derived compounds show selective estrogen receptor modulator (SERM) activity and may therefore be an alternative to the conventional hormone replacement therapy, which prevents osteoporosis but is also associated with an increased risk of breast and endometrial cancers. In the current study, we tested the effects of the hop-derived compounds 8-prenylnaringenin, 6-prenylnaringenin, xanthohumol and isoxanthohumol (1) to modulate markers of differentiation and gene expression in osteoblasts and (2) to regulate proliferation in MCF-7 breast cancer cells. Additionally, we analyzed the ER-binding affinities of these hop compounds as well as the ER-mediation of their effects. Bone-forming activity and ER-subtype specificity were investigated by measuring alkaline phosphatase (AP) activity in hFOB/ERalpha cells and regulation of gene transcription for AP, interleukin-6, pS2 and von Willebrand factor (VWF) in U-2 OS/ERalpha and U-2 OS/ERbeta cells. Our results demonstrate that AP, pS2 and VWF mRNA levels are significantly increased by the compounds in an estrogen-like manner via both ERalpha and ERbeta, while IL-6 is down-regulated in U-2 OS/ERalpha cells. Consistently, AP enzymatic activity is up-regulated by all compounds in hFOB/ERalpha9 cells. Depending on their concentration, all compounds show proliferative effects in MCF-7 cells. Except for 8-PN the hop constituents display an ERbeta-preference. Reversal of estrogen-specific AP-induction in Ishikawa cells indicates an ER-regulated mechanism. Finally, the flavonoids display cytotoxic effects only at high concentrations (> or =10(-4)M). In summary, we have demonstrated for the first time that specific phytoestrogen compounds found in hop extracts exert estrogen-like activities on bone metabolism. Regarding a potential for use in osteoporosis-prevention therapy, the dosage of a phytoestrogen, which is taken, will play an important role concerning a desired in vivo profile.

In vitro and in vivo Effects of Combination of Trastuzumab (Herceptin) and Tamoxifen in Breast Cancer

Extensive interactions between estrogen receptor alpha (ERalpha) and HER2 signaling pathways have been described. Using BT-474 human breast cancer cells, we have previously shown that the combination of tamoxifen (TAM) and Herceptin results in strong synergistic growth inhibition, enhancement of G(0)-G(1) cell cycle accumulation, inhibition of HER2 activity and a cytostatic effect without cell death. To further examine the underlying mechanism of synergy, we investigated the effect of this drug combination on ERalpha function and growth factor downstream signaling. TAM caused a small increase in ERalpha levels while Herceptin had no effect, and both drugs caused an increase in the level of Ser118-phosphorylated ERalpha. However, both TAM and Herceptin individually inhibited ERalpha transcriptional activity, although the combination did not have a greater effect than either single agent. Herceptin inhibited MAPK and Akt activity, while TAM had no effect on these either as a single agent or when added to Herceptin. Using a BALB/c athymic BT-474 in vivo xenograft model, the drug combination (Herceptin 0.3 mg/kg i.p. twice weekly, TAM 1.0 mg/mouse i.p. three times per week) showed a greater inhibition of tumor growth compared to either single agent. Tumor extracts and fixed sections were examined at the end of the treatment period for treatment-specific alterations: we noted a paradoxical proliferation-inducing effect of TAM that was reversed by the addition of Herceptin. Our results indicate that combined targeting of both peptide growth factor receptors and ERalpha represents a promising breast cancer treatment strategy.

Potentiation of genomic actions of estrogen by membrane actions in mcf-7 cells and the involvement of protein kinase C activation

It is now well established that estrogens (E) have at least two kinds of actions: genomic and nongenomic. But the relationship between these actions has hardly been explored. In this study we investigated this relationship in MCF-7 cells, a human breast cancer cell line, and explored the possible involvement of protein kinase C (PKC) signaling pathways. For this purpose a two-pulse paradigm was used: cells were treated with 17beta-estradiol (E), E conjugated with bovine serum albumin (E-BSA or fE'), or other test agents in the first pulse and with E in the second pulse following a 4-h interval. An E-BSA+E paradigm was used to show that replacement of E with the membrane-impermeable E-BSA in the first pulse could potentiate genomic actions of E, in the second pulse. To investigate involvement of signaling pathways, two PKC activators, phorbol 12,13-diacetate (PDAc) or phorbol 12-myristate 13-acetate (PMA), and inhibitors (chelerythrine chloride and H7-dihydrochloride) were used to replace E or E-BSA in the first pulse. PDAc was as effective as E or E-BSA in potentiating the genomic action of E in the second pulse, while PMA was almost without an effect. Conversely, the potentiating effects of E-BSA and PDAc were blocked by chelerythrine chloride but, interestingly, not by H7. The exact reason underlying these differences is not known. In summary, in MCF-7 cells a membrane action of E can potentiate a later genomic action and involves PKC signaling.

Comparative study of oestrogenic properties of eight phytoestrogens in MCF7 human breast cancer cells

Previous studies have compared the oestrogenic properties of phytoestrogens in a wide variety of disparate assays. Since not all phytoestrogens have been tested in each assay, this makes inter-study comparisons and ranking oestrogenic potency difficult. In this report, we have compared the oestrogen agonist and antagonist activity of eight phytoestrogens (genistein, daidzein, equol, miroestrol, deoxymiroestrol, 8-prenylnaringenin, coumestrol and resveratrol) in a range of assays all based within the same receptor and cellular context of the MCF7 human breast cancer cell line. The relative binding of each phytoestrogen to oestrogen receptor (ER) of MCF7 cytosol was calculated from the molar excess needed for 50% inhibition of 3H]oestradiol binding (IC50), and was in the order coumestrol (35x)/8-prenylnaringenin (45x)/deoxymiroestrol (50x)>miroestrol (260x)>genistein (1000x)>equol (4000x)>daidzein (not achieved: 40% inhibition at 10(4)-fold molar excess)>resveratrol (not achieved: 10% inhibition at 10(5)-fold molar excess). For cell-based assays, the rank order of potency (estimated in terms of the concentration needed to achieve a response equivalent to 50% of that found with 17beta-oestradiol (IC50)) remained very similar for all the assays whether measuring ligand ability to induce a stably transfected oestrogen-responsive ERE-CAT reporter gene, cell growth in terms of proliferation rate after 7 days or cell growth in terms of saturation density after 14 days. The IC50 values for these three assays in order were for 17beta-oestradiol (1 x 10(-11)M, 1 x 10(-11)M, 2 x 10(-11)M), and in rank order of potency for the phytoestrogens, deoxymiroestrol (1 x 10(-10)M, 3 x 10(-11)M, 2 x 10(-11)M)>miroestrol (3 x 10(-10)M, 2 x 10(-10)M, 8 x 10(-11)M)>8-prenylnaringenin (1 x 10(-9)M, 3 x 10(-10)M, 3 x 10(-10)M)>coumestrol (3 x 10(-8)M, 2 x 10(-8)M, 3 x 10(-8)M)>genistein (4 x 10(-8)M, 2 x 10(-8)M, 1 x 10(-8)M)/equol (1 x 10(-7)M, 3 x 10(-8)M, 2 x 10(-8)M)>daidzein (3 x 10(-7)M, 2 x 10(-7)M, 4 x 10(-8)M)>resveratrol (4 x 10(-6)M, not achieved, not achieved). Despite using the same receptor context of the MCF7 cells, this rank order differed from that determined from receptor binding. The most marked difference was for coumestrol and 8-prenylnaringenin which both displayed a relatively potent ability to displace [3H]oestradiol from cytosolic ER compared with their much lower activity in the cell-based assays. Albeit at varying concentrations, seven of the eight phytoestrogens (all except resveratrol) gave similar maximal responses to that given by 17beta-oestradiol in cell-based assays which makes them full oestrogen agonists. We found no evidence for any oestrogen antagonist action of any of these phytoestrogens at concentrations of up to 10(-6)M on either reporter gene induction or on stimulation of cell growth.