Hormonal regulation of estrogen receptor messenger ribonucleic acid in T47Dco and MCF-7 breast cancer cells

High estrogen receptor alpha activation confers resistance to estrogen deprivation and is required for therapeutic response to estrogen in breast cancer

Estrogen receptor alpha (ER)-positive breast cancer is commonly treated with endocrine therapies, including antiestrogens that bind and inhibit ER activity, and aromatase inhibitors that suppress estrogen biosynthesis to inhibit estrogen-dependent ER activity. Paradoxically, treatment with estrogens such as 17b-estradiol can also be effective against ER+ breast cancer. Despite the known efficacy of estrogen therapy, the lack of a predictive biomarker of response and understanding of the mechanism of action have contributed to its limited clinical use. Herein, we demonstrate that ER overexpression confers resistance to estrogen deprivation through ER activation in human ER+ breast cancer cells and xenografts grown in mice. However, ER overexpression and the associated high levels of ER transcriptional activation converted 17b-estradiol from a growth-promoter to a growth-suppressor, offering a targetable therapeutic vulnerability and a potential means of identifying patients likely to benefit from estrogen therapy. Since ER+ breast cancer cells and tumors ultimately developed resistance to continuous estrogen deprivation or continuous 17b-estradiol treatment, we tested schedules of alternating treatments. Oscillation of ER activity through cycling of 17b-estradiol and estrogen deprivation provided long-term control of patient-derived xenografts, offering a novel endocrine-only strategy to manage ER+ breast cancer.

Intrinsic and Extrinsic Factors Governing the Transcriptional Regulation of ESR1

Transcriptional regulation of ESR1, the gene that encodes for estrogen receptor α (ER), is critical for regulating the downstream effects of the estrogen signaling pathway in breast cancer such as cell growth. ESR1 is a large and complex gene that is regulated by multiple regulatory elements, which has complicated our understanding of how ESR1 expression is controlled in the context of breast cancer. Early studies characterized the genomic structure of ESR1 with subsequent studies focused on identifying intrinsic (chromatin environment, transcription factors, signaling pathways) and extrinsic (tumor microenvironment, secreted factors) mechanisms that impact ESR1 gene expression. Currently, the introduction of genomic sequencing platforms and additional genome-wide technologies has provided additional insight on how chromatin structures may coordinate with these intrinsic and extrinsic mechanisms to regulate ESR1 expression. Understanding these interactions will allow us to have a clearer understanding of how ESR1 expression is regulated and eventually provide clues on how to influence its regulation with potential treatments. In this review, we highlight key studies concerning the genomic structure of ESR1, mechanisms that affect the dynamics of ESR1 expression, and considerations towards affecting ESR1 expression and hormone responsiveness in breast cancer.

Inter-Individual Variation in Response to Estrogen in Human Breast Explants

Exposure to estrogen is strongly associated with increased breast cancer risk. While all women are exposed to estrogen, only 12% are expected to develop breast cancer during their lifetime. These women may be more sensitive to estrogen, as rodent models have demonstrated variability in estrogen sensitivity. Our objective was to determine individual variation in expression of estrogen receptor (ER) and estrogen-induced responses in the normal human breast. Human breast tissue from female donors undergoing reduction mammoplasty surgery were collected for microarray analysis of ER expression. To examine estrogen-induced responses, breast tissue from 23 female donors were cultured ex- vivo in basal or 10 nM 17β-estradiol (E2) media for 4 days. Expression of ER genes (ESR1 and ESR2) increased significantly with age. E2 induced consistent increases in global gene transcription, but expression of target genes AREG, PGR, and TGFβ2 increased significantly only in explants from nulliparous women. E2-treatment did not induce consistent changes in proliferation or radiation induced apoptosis. Responses to estrogen are highly variable among women and not associated with levels of ER expression, suggesting differences in intracellular signaling among individuals. The differences in sensitivity to E2-stimulated responses may contribute to variation in risk of breast cancer.

Intratumoral Estrogen Receptor Heterogeneity of Expression in Human Epidermal Growth Factor Receptor 2-Positive Breast Cancer as Evaluated by a Brightfield Multiplex Assay

Breast cancer (BC) is a heterogeneous disease with evolving genetic alterations and expressions of receptor proteins. Intratumoral heterogeneity (ITH) is considered to be a resistance factor in response to targeted therapies. The current single-slide, single-marker immunohistochemistry techniques cannot accurately assess ITH at the individual cancer cell level. In this study, we develop a novel brightfield multiplex assay to simultaneously assess estrogen receptor (ER) and human epidermal growth factor receptor 2 (HER2) protein markers, together with the HER2 gene and the centromere of chromosome 17 (CEP17) copy numbers, using a single tissue section. The data presented herein demonstrate heterogeneous cancer cell subpopulations in 11 HER2-positive/ER-positive (HER2+/ER+) tumors among 33 BCs analyzed immunohistochemically (HER2 score of 2+ or 3+). The predominant cancer cell subpopulation was HER2+/ER- (50.18%), followed by HER2+/ER+ (39.05%), HER2-/ER+ (4.26%), ER- with HER2 microheterogeneity cancer cells (3.58%), and ER+ with HER2 microheterogeneity cancer cells (2.93%). The three other tumor subtypes, namely, HER2-/ER+, HER2+/ER-, and HER2-/ER-, were more homogeneous, representing 82.59%, 99.22%, and 100% of cancer cells, respectively. This novel assay revealed that HER2+ cancer cells were more predominant than ER+ cancer cells in HER2+/ER+ tumors and provided new insights toward our understanding of BC carcinogenesis.

Delineating the regulation of estrogen and androgen receptor expression by sex steroids during rat spermatogenesis

Estrogen receptors (ERα and β) and androgen receptor (AR) regulate various critical processes during spermatogenesis. Since spermatogenesis is very sensitive to hormonal stimuli and perturbations, it is important to understand the regulation of expression of these receptors by sex steroid hormones. Although many studies have reported deregulation of steroid receptors on endocrine disruption, there is no consensus on the regulation of their expression by steroid hormones during spermatogenesis, and a lack of clear understanding of the mechanism of regulation. Here, we evaluated the receptor expressions in a well-established exogenous estradiol administration model. We then investigated the mechanisms by which the individual receptors regulate their expression by binding to the respective hormone response elements upstream of these receptor genes. By further employing in vitro and in vivo models of ER and AR stimulation or antagonism, we delineated their regulation in a receptor subtype-specific manner. Our results indicate that ERα positively regulates expression of both the ERs; whereas, ERβ and AR negatively regulate expression of both ERβ and AR by direct binding to upstream regulatory regions. The perturbations in the levels of steroid receptors could be an important factor contributing to spermatogenic defects and male sub-fertility after estradiol and ER agonist treatment. Our study delineates the direct contribution of the individual steroid receptors in the regulation of their own expression.

Progesterone agonists and antagonists induce down– and up–regulation of estrogen receptors and estrogen inducible genes in human breast cancer cell lines

The effects of the synthetic progestin R5020 and the antiprogestin RU486 on the cellular content of estrogen receptors (ER) and on cell responsiveness to estrogens, have been investigated in the sex hormone-sensitive human breast cancer cell lines MCF-7 and T47D. When T47D cells were treated with R5020 (Promegestone) (10–8 M), ER was down-regulated to about 50% of the control level in a time-dependent manner. Maximum down-regulation was observed after 24 hours and remained at this level for the next 24 hours. Dihydrotestosterone (DHT) or dexamethasone (DEX) had no effect on ER sites. R5020 also down-regulated, although to a lesser extent, ER in the MCF-7 cells which contain fewer progesterone receptor (PR) sites.

When MCF-7 cells were transfected with a progesterone receptor expression vector (tMCF-7) to increase the number of PR sites, R5020 down-regulated the ER to a level similar to that reached in T47D cells. In both cell lines ER down-regulation was completely inhibited by a 10-fold molar excess of the antiprogestin RU486 (Mifepristone) (10–7 M). Surprisingly, when incubated with RU486 alone, T47D cells responded by up-regulating ER 2-4 fold.

The functional relevance of inhibition and up-regulation of ER for the estrogen responsiveness of hormone-sensitive human breast cancer cells was tested by assaying the synthesis of an estrogen-regulated product, the PS2 protein. Estrogen induction of this protein was inhibited by at least 70% in T47D cells exposed to R5020 for 24 hours before estrogen administration and by about 25% in MCF-7 cells under the same conditions. A 55% inhibition was observed in tMCF-7 cells. Up-regulation of ER by RU486 in T47D cells led to an increase in the estrogen induction of PS2 by about 18-20% compared to RU486 untreated cells.

These results indicate that the progestin and antiprogestin regulation of ER is functionally important for the estrogen responsiveness of breast cancer cells.

Deciphering the divergent roles of progestogens in breast cancer

Most breast cancers are driven by oestrogen receptor-α. Anti-oestrogenic drugs are the standard treatment for these breast cancers; however, treatment resistance is common, necessitating new therapeutic strategies. Recent preclinical and historical clinical studies support the use of progestogens to activate the progesterone receptor (PR) in breast cancers. However, widespread controversy exists regarding the role of progestogens in this disease, hindering the clinical implementation of PR-targeted therapies. Herein, we present and discuss data at the root of this controversy and clarify the confusion and misinterpretations that have consequently arisen. We then present our view on how progestogens may be safely and effectively used in treating breast cancer.

Krüppel-like factors are effectors of nuclear receptor signaling

Binding of steroid and thyroid hormones to their cognate nuclear receptors (NRs) impacts virtually every aspect of postembryonic development, physiology and behavior, and inappropriate signaling by NRs may contribute to disease. While NRs regulate genes by direct binding to hormone response elements in the genome, their actions may depend on the activity of other transcription factors (TFs) that may or may not bind DNA. The Krüppel-like family of transcription factors (KLF) is an evolutionarily conserved class of DNA-binding proteins that influence many aspects of development and physiology. Several members of this family have been shown to play diverse roles in NR signaling. For example, KLFs (1) act as accessory transcription factors for NR actions, (2) regulate expression of NR genes, and (3) as gene products of primary NR response genes function as key players in NR-dependent transcriptional networks. In mouse models, deletion of different KLFs leads to aberrant transcriptional and physiological responses to hormones, underscoring the importance of these proteins in the regulation of hormonal signaling. Understanding the functional relationships between NRs and KLFs will yield important insights into mechanisms of NR signaling. In this review we present a conceptual framework for understanding how KLFs participate in NR signaling, and we provide examples of how these proteins function to effect hormone action.

The proteasome inhibitor bortezomib induces an inhibitory chromatin environment at a distal enhancer of the estrogen receptor-α gene

Expression of the estrogen receptor-α (ERα) gene, ESR1, is a clinical biomarker used to predict therapeutic outcome of breast cancer. Hence, there is significant interest in understanding the mechanisms regulating ESR1 gene expression. Proteasome activity is increased in cancer and we previously showed that proteasome inhibition leads to loss of ESR1 gene expression in breast cancer cells. Expression of ESR1 mRNA in breast cancer cells is controlled predominantly through a proximal promoter within ∼400 base pair (bp) of the transcription start site (TSS). Here, we show that loss of ESR1 gene expression induced by the proteasome inhibitor bortezomib is associated with inactivation of a distal enhancer located 150 kilobases (kb) from the TSS. Chromatin immunoprecipitation assays reveal several bortezomib-induced changes at the distal site including decreased occupancy of three critical transcription factors, GATA3, FOXA1, and AP2γ. Bortezomib treatment also resulted in decreased histone H3 and H4 acetylation and decreased occupancy of histone acetyltransferase, p300. These data suggest a mechanism to explain proteasome inhibitor-induced loss of ESR1 mRNA expression that highlights the importance of the chromatin environment at the −150 kb distal enhancer in regulation of basal expression of ESR1 in breast cancer cells.

Thyroid hormone and estradiol have overlapping effects on kidney glutathione S-transferase-α gene expression

α-Class GST (Gsta) represents an essential component of cellular antioxidant defense mechanisms in both the liver and the kidney. Estrogens and thyroid hormones (TH) play central roles in animal development, physiology, and behavior. Evidence of the overlapping functions of thyroid hormones and estrogens has been shown, although the molecular mechanisms are not always clear. We evaluated an interaction between TH and estradiol in regulating kidney Gsta expression and function. First, we observed that female mice expressed greater amounts of Gsta compared with males and showed an opposite pattern of expression in TRβ knock-in mice. To further investigate these sex differences, hypothyroidism was induced by a 5-propyl-2-thiouracil diet, and hyperthyroidism was induced by daily T₃ injections. Hypothyroidism increased kidney Gsta expression in male mice but not in female mice, indicating that sex hormones could be influencing the regulation of Gsta by thyroid hormones. To analyze this hypothesis, ovariectomized females were subjected to hypo- and hyperthyroidism, which led to a male profile of Gsta expression. When hypo- or hyperthyroid ovariectomized mice were treated with 17β-estradiol benzoate, we were able to confirm that estradiol was interfering with TH modulation; Gsta expression is increased by T₃ when estradiol is present and decreased by T₃ when estradiol is absent. Using proximal tubule cells, we also showed that estradiol and T₃ worked together to modulate Gsta expression in an overlapping fashion. In summary, 1) the sex difference in the basal expression of Gsta impacts the detoxification process, 2) kidney Gsta expression is regulated by TH in males and females but in opposite directions, and 3) T₃ and estradiol interact directly in renal proximal cells to regulate Gsta expression in females.

Mechanisms and significance of nuclear receptor auto- and cross-regulation

The number of functional hormone receptors expressed by a cell in large part determines its responsiveness to the hormonal signal. The regulation of hormone receptor gene expression is therefore a central component of hormone action. Vertebrate steroid and thyroid hormones act by binding to nuclear receptors (NR) that function as ligand-activated transcription factors. Nuclear receptor genes are regulated by diverse and interacting intracellular signaling pathways. Nuclear receptor ligands can regulate the expression of the gene for the NR that mediates the hormone's action (autoregulation), thus influencing how a cell responds to the hormone. Autoregulation can be either positive or negative, the hormone increasing or decreasing, respectively, the expression of its own NR. Positive autoregulation (autoinduction) is often observed during postembryonic development, and during the ovarian cycle, where it enhances cellular sensitivity to the hormonal signal to drive the developmental process. By contrast, negative autoregulation (autorepression) may become important in the juvenile and adult for homeostatic negative feedback responses. In addition to autoregulation, a NR can influence the expression other types of NRs (cross-regulation), thus modifying how a cell responds to a different hormone. Cross-regulation by NRs is an important means to temporally coordinate cell responses to a subsequent (different) hormonal signal, or to allow for crosstalk between hormone signaling pathways.

Sex Hormone-Binding Globulin (SHBG), estradiol and breast cancer

The human serum Sex Hormone-Binding Globulin (SHBG) plays an important role in breast cancer pathophysiology and risk definition, since it regulates the bioavailable fraction of circulating estradiol. We here summarize data reported over the years concerning the involvement of SHBG and SHBG polymorphisms in the definition of breast cancer risk. We also report what is known about the direct action of SHBG in breast cancer cells, illustrating its interaction with these cells and the subsequent initiation of a specific intracellular pathway leading to cross-talk with the estradiol-activated pathway and, finally, to the inhibition of several effects of estradiol in breast cancer cells. In conclusion, as a result of its unique property of regulating the estrogen free fraction and cross-talking with the estradiol pathways, by inhibiting estradiol-induced breast cancer cell growth and proliferation, SHBG is associated with a reduced risk of developing the neoplasm after estrogen exposure.

Repression of ESR1 through actions of estrogen receptor alpha and Sin3A at the proximal promoter

Gene expression results from the coordinated actions of transcription factor proteins and coregulators. Estrogen receptor alpha (ERalpha) is a ligand-activated transcription factor that can both activate and repress the expression of genes. Activation of transcription by estrogen-bound ERalpha has been studied in detail, as has antagonist-induced repression, such as that which occurs by tamoxifen. How estrogen-bound ERalpha represses gene transcription remains unclear. In this report, we identify a new mechanism of estrogen-induced transcriptional repression by using the ERalpha gene, ESR1. Upon estrogen treatment, ERalpha is recruited to two sites on ESR1, one distal (ENH1) and the other at the proximal (A) promoter. Coactivator proteins, namely, p300 and AIB1, are found at both ERalpha-binding sites. However, recruitment of the Sin3A repressor, loss of RNA polymerase II, and changes in histone modifications occur only at the A promoter. Reduction of Sin3A expression by RNA interference specifically inhibits estrogen-induced repression of ESR1. Furthermore, an estrogen-responsive interaction between Sin3A and ERalpha is identified. These data support a model of repression wherein actions of ERalpha and Sin3A at the proximal promoter can overcome activating signals at distal or proximal sites and ultimately decrease gene expression.

ER re-expression and re-sensitization to endocrine therapies in ER-negative breast cancers

Breast cancer is the leading cause of cancer amongst women in the westernized world. The presence or absence of ERalpha in breast cancers is an important prognostic indicator. About 30-40% of breast cancers lack detectable ERalpha protein. ERalpha- breast cancers are resistant to endocrine therapies and have a worse prognosis than ERalpha+ breast cancers. Since expression of ERalpha is necessary for response to endocrine therapies, investigational studies are ongoing in order to understand the generation of the ERalpha- phenotype and develop interventions to restore ERalpha expression in ERalpha- breast cancers. DNA methylation and chromatin remodeling are two epigenetic mechanisms that have been linked with the lack of ERalpha expression and in these cases; demethylation of the ERalpha promoter or treatment with HDAC inhibitors shows promise in restoring ERalpha expression in ERalpha- breast cancers. Two additional potential mechanisms underlying generation of the ERalpha- phenotype involve E6-AP and Src, both of which have been shown to be elevated in ERalpha- breast cancer and can drive the proteasomal degradation of ERalpha. Recently, studies have demonstrated that upregulated growth factor signaling due to hyperactive MAPK activity significantly contributes to generation of the ERalpha- phenotype and that inhibition of MAPK activity can cause re-expression of the ERalpha and restore sensitivity to endocrine therapies. Given the challenges in treating ERalpha- breast cancer, understanding and manipulating the cellular mechanisms that effect expression of ERalpha are imperative in order to restore sensitivity to endocrine therapies and to design novel therapeutics for the treatment of ERalpha- breast cancers.

Activation of estrogen response elements is mediated both via estrogen and muscle contractions in rat skeletal muscle myotubes

The aim of the present study was to investigate the activation of estrogen response elements (EREs) by estrogen and muscle contractions in rat myotubes in culture and to assess whether the activation is dependent on the estrogen receptors (ERs). In addition, the effect of estrogen and contraction on the mRNA levels of ERalpha and ERbeta was studied to determine the functional consequence of the transactivation. Myoblasts were isolated from rat skeletal muscle and transfected with a vector consisting of sequences of EREs coupled to the gene for luciferase. The transfected myoblasts were then differentiated into myotubes and subjected to either estrogen or electrical stimulation. Activation of the ERE sequence was determined by measurement of luciferase activity. The results show that both ERalpha and ERbeta are expressed in myotubes from rats. Both estrogen stimulation and muscle contraction increased (P < 0.05) transactivation of the ERE sequence and enhanced ERbeta mRNA, whereas ERalpha was unaffected by estrogen and attenuated (P < 0.05) by muscle contraction. Use of ER antagonists showed that, whereas the estrogen-induced transactivation is mediated via ERs, the effect of muscle contraction is ER independent. The muscle contraction-induced transactivation of ERE and increase in ERbeta mRNA were instead found to be MAP kinase (MAPK) dependent. This study demonstrates for the first time that muscle contractions have a similar functional effect as estrogen in skeletal muscle myotubes, causing ERE activation and an enhancement in ERbeta mRNA. However, in contrast to estrogen, the effect is independent of ERs and dependent on MAPK, suggesting activation via the estrogen related receptor (ERR).

Estrogen receptor α-negative and progesterone receptor-positive breast cancer: Lab error or real entity?

Aretrospective study comparing the estrogen receptor (ER) alpha subtype and progesterone receptor (PR) profile of breast carcinomas amongst 1625 cases over 2.5 years was carried out. Strictly speaking it is generally believed that breast carcinomas can biochemically express PR only if they are ER-positive. However, a few ERalpha-PR+ cases do exist paradoxically. This class of tumors was the focus of our study in which we looked at the possible reasons for such an immunophenotype and compared it with a group of ERalpha+PR+ breast carcinomas. An internationally recognized immunohistochemical method employing monoclonal antibodies against estrogen and progesterone receptors was used. Correlations with established risk factors i.e. menopausal status, grade, tumor size and lymph node status were analyzed for our study group (ERalpha-PR+) and compared with a control (ERalpha+PR+). Out of the total 1625 cases, 29.91% (486) were ERalpha+PR+, 5.11% (83) were ERalpha+PR-, 56.86% (924) were ERalpha-PR- and 8.12% (132) were ERalpha-PR+. Patients' age was significantly lower in the ERalpha-PR+ group (P=0.002). Statistical analysis of the grading between the two study groups revealed no significant difference (P=0.091), although the ERalpha-PR+ group contained significantly more poorly differentiated tumors than the ERalpha+PR+ one (P=0.032). Tumor size was also significantly larger in the ERalpha-PR+ than in the ERalpha+PR+ group (P=0.046). The frequency of lymph node metastases was independent of receptor profile. In conclusion, our study group does exhibit characteristics which are suggestive of a distinct breast cancer phenotype (ERalpha-PR+) with a different etiology and prognosis.

Standardized on-slide control for quality assurance in the immunohistochemical assessment of therapeutic target molecules in breast cancer

Individualization and optimization of risk-adapted therapy in breast cancer requires molecular profiling of individual cancer specimens. In tissues of heterogeneous cellular composition, such as mammary tissue, cancer prognostic markers and potential therapeutic target molecules are preferentially detected by in situ techniques such as immunohistochemistry. The more therapy decisions are based on immunohistochemical findings, the more histopathologists are confronted with the demand to establish standardized procedures that enable reproducible evaluation independent from the investigating laboratory. Disappointing results of recent national and international immunohistochemistry trials for steroid receptor and HER-2 analysis in breast cancer underline the need to act now beyond recommendations and well-formulated guidelines for standardization. In order to ensure staining quality in every individual immunohistochemical analysis, we have developed an on-slide control with standardized samples which are placed on every slide of a therapy-decisive stain together with the tissue of interest. Novel mini tissue microarrays were constructed comprising cell lines as standardized controls, indicating the sensitivity and reliability of the staining procedure. Standardized control material on the same slide as the patient's specimen require neither additional reagents nor time and are automatically archived on the diagnostic slide to prove the quality of staining even after years.

Regulation of estrogen receptor-beta expression in the female rat hypothalamus: differential effects of dexamethasone and estradiol

Estrogen and glucocorticoids interact in multiple aspects of endocrine regulation by exerting opposing influences on the expression of selective genes. In rats, estrogen receptor (ER)-beta is the predominant form of ER present in the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei, suggesting its involvement in neuroendocrine regulation. To date, the hormonal regulatory profile of the ERbeta gene in the rat central nervous system has not been closely elucidated. In the present study, we first examined the effects of dexamethasone (DEX) and estradiol benzoate (EB) on the ERbeta protein expression in the PVN and SON of ovariectomized female rats. In the SON and parvocellular and magnocellular parts of the PVN, the number of ERbeta immunoreactive nuclei significantly increased after DEX treatment, compared with the control group, whereas EB treatment caused a significant decrease. The effect of EB was consistent across other brain nuclei such as the anteroventral periventricular nucleus and medial preoptic nucleus. To determine the molecular level at which DEX and EB control ERbeta expression, we examined the effects of these steroids on ERbeta mRNA levels using real-time RT-PCR. EB significantly decreased the expression of ERbeta mRNA in the PVN (P = 0.0006) and SON (P < 0.01). In contrast, DEX did not change ERbeta mRNA levels. These results indicate that glucocorticoids and estrogen exert opposing regulatory influences on the ERbeta gene expression. This may represent a mechanism by which these steroids can alter the cellular sensitivity of ERbeta-expressing neurons to subsequent steroidal activation.

Serotonergic neurones in the dorsal raphe nucleus that project into the medial preoptic area contain oestrogen receptor beta

Serotonin is involved in female sexual behaviour in which the medial preoptic area (MPA) has a pivotal role. The present study used immunohistochemistry, in situ hybridization and retrograde transport analysis to investigate whether serotonin neurones in the dorsal raphe nucleus (DRN) of females projecting into the MPA contained oestrogen receptor alpha or beta. The projection of serotonin neurones from the DRN to the MPA was confirmed using the microinjection of Fluoro-Gold (FG), a fluorescent retrograde tracer, into the MPA of ovariectomized (OVX-group) and OVX-rats treated with oestradiol benzoate (E2-group). A number of serotonin neurones in the DRN were labelled with FG, indicating that these serotonin neurones in DRN project their terminals into the MPA. FG-labelled serotonin neurones expressed ERbeta mRNA in the DRN, and the number of the serotonin neurones containing ERbeta mRNA between the OVX-group and the E2-treated group was not significantly different. Serotonin neurones in the DRN did not express ERalpha-immunoreactivity. Since previous findings showed that the density of serotonin-immunoreactive fibres and the concentration of serotonin within the MPA was significantly lower in the E2-group than the OVX-group, our present observations suggested that the regulatory effects of E2 on the serotonergic neurone system in the MPA may be via ERbeta within the serotonin-containing cells in the DRN of female rats.

The control of progesterone receptor expression in MCF-7 breast cancer cells: effects of estradiol and sex hormone-binding globulin (SHBG)

Estradiol controls the gene transcription and expression of many proteins in breast cancer cells, like the progesterone receptor, PR, that is up-regulated by the hormone. Moreover, estradiol is one of the crucial factors inducing the proliferation of breast cancer cells. Sex Hormone-Binding Globulin (SHBG), the plasma carrier for both estradiol and androgens, inhibits the estradiol-induced growth of MCF-7 cells (estrogen-dependent breast cancer cells), through its membrane receptor (SHBG-R), cAMP and PKA. The anti-estrogenic effect of SHBG, which has been described only as far as cell proliferation is concerned, could also play a meaningful role in the estradiol control of other factors in breast cancer cells. In the present study, the effect of SHBG on the estradiol control of PR expression (both mRNA and protein) and function (receptor binding capacity) in MCF-7 cells was examined. SHBG inhibited the estradiol-induced up-regulation of PR mRNA as well as protein level and function. Moreover, the effect of SHBG on estradiol control of PR expression and function was showed to be specific and mediated by PKA. The intermediacy of PKA in the PR expression control, together with the observation that it is effective in the condition in which the SHBG receptor is activated, supports the hypothesis that the anti-estrogenic effect of SHBG could be receptor-mediated. The ability of SHBG to inhibit estradiol action in a specific way in estrogen-dependent breast cancer cells has, therefore, to be taken into account for the development of future therapeutic strategies.

Tissue-specific expression of multiple mRNA variants of the mouse estrogen receptor alpha gene

The isolation of five new mouse estrogen receptor alpha mRNA variants (mERalpha A, B, F1, F2 and H) is described. All of these transcripts are generated by alternative splicing and all encode the 66 kDa ERalpha protein that the previously identified mRNA C variant generates. However, these transcripts differ in their 5' untranslated regions. RT-PCR and S1 nuclease protection assays revealed a tissue- and sex-specific expression pattern of all variants. The C and F mRNA variants are the predominantly expressed mERalpha variants in mouse. The expression of mERalpha H mRNA is restricted to liver, although female mice produce around a five fold higher level of this transcript than males. Our results show that the mERalpha gene is a complex genomic unit in mice that exhibits alternative splicing which is regulated in a tissue-specific manner.

Effect of ovarian steroid deficiency on oestrogen receptor alpha expression in bone

The mechanism by which oestrogen and hormone replacement therapy (HRT) maintain bone mass in women is still unclear. It has previously been shown that cells of osteoblast lineage in vivo, particularly osteocytes, express oestrogen receptor alpha (ERalpha). Nevertheless, it is still debatable whether oestrogen and the ovarian steroids have a direct affect on osteocytes. If they could regulate osteocyte ERalpha expression, this would be strong evidence for the involvement of these cells in the hormonal regulation of bone mass. This study therefore aimed to compare bone biopsies from women who were replete with ovarian steroids (pre-ovariectomy or post-HRT) with those from the same women when hormone-deficient (post-ovariectomy or pre-HRT) for cellular localization of ERalpha protein or mRNA expression by indirect immunofluorescence, or by in situ hybridization combined with reverse transcriptase-polymerase chain reaction (IS-RT-PCR) respectively. Image analysis showed that proportions of osteocytes positive for immunodetectable ERalpha were higher in hormone-replete than in hormone-deficient women (25+/-SEM 3 per cent, 12+/-SEM 4 per cent, respectively; n=5), with similar but non-statistically significant changes in osteoblasts. This was observed even when HRT was commenced 18 years after menopause. In contrast, grain volume/unit cell area of osteoblast mRNA signal was markedly higher when hormone-deficient (0.055+/-0.01) than when hormone-replete (0.016+/-0.004), with similar but non-significant differences in osteocytes. This preliminary study indicates up-regulation of osteocyte ERalpha protein by ovarian steroids in these patients, which is accompanied by decreased osteoblast ERalpha mRNA expression, providing further evidence for the involvement of osteocytes in the regulation of skeletal structure by ovarian steroids.

Suppression of parathyroid hormone-related protein messenger RNA expression by medroxyprogesterone acetate in breast cancer tissues

The level of parathyroid hormone-related protein (PTHrP) expressed in breast cancer tissue is closely related to the incidence of bone metastasis. We examined the PTHrP mRNA expression in breast cancer tissues by coamplification polymerase chain reaction (PCR) in mole ratio to internal standard beta-actin mRNA. The PTHrP expression was higher in premenopausal patients than in postmenopausal patients (P < 0.05). More pronounced difference by menopause found in estrogen receptor (ER) positive groups (P < 0.001) indicated that the PTHrP expression in breast cancer tissue is hormonally regulated and might be altered by endocrine agents. To clarify the changes of PTHrP expression by endocrine therapy of breast cancer, we measured PTHrP expression in the breast cancer tissue incubated for 24 h with 1 x 10(-8) M of estradiol (E2), 1 x 10(-6) M of tamoxifen (TAM) and 1 x 10(-5) M of medroxyprogesterone acetate (MPA). The PTHrP expression was decreased significantly by MPA (P < 0.005), while E2 and TAM did not change the PTHrP expression. Progesterone receptor (PgR) mRNA expression was also examined to confirm that the breast cancer tissue responds to E2 and TAM. The results were well compatible with the better therapeutic effect of MPA reported for the treatment of breast cancer with bone metastases. As a potential candidate for the receptor that mediates the suppressive effect of MPA, androgen receptor (AR) is suggested most probable. Present results also demonstrated that the clinical response of individual tumors is closely associated with the early in vitro changes of gene expression detected in the cancer specimen.

Estrogenicity of bisphenol A in a human endometrial carcinoma cell line

The ability of bisphenol A (BPA) to affect human estrogen receptor (ER) binding, expression of progesterone receptor (PR) mRNA and protein, and cell proliferation has been measured in the human endometrial cell line, ECC-1. Although less potent than 17beta-estradiol, BPA was able to bind to the human uterine ER. BPA also induced both mRNA and protein to levels similar to E2. BPA-mediated PR mRNA induction was antagonized by ICI, suggesting an ER-mediated pathway. Finally, E2 produced a 2-fold increase in cell number, while BPA showed no difference compared with vehicle control. The increase by E2 was inhibited by treatment with the either ICI 182,780 (ICI) or BPA, suggesting similar binding sites. Although ER binding is similar, E2 affected both proliferation and PR expression, while BPA only affected PR gene expression. The results of this study provide evidence that two ER agonists can act differentially in vitro to affect the expression of genes involved in regulating cellular growth and development, though the human risk potential remains to be determined.

Acetaminophen-induced proliferation of breast cancer cells involves estrogen receptors

Previous studies have shown that acetaminophen, a common analgesic/antipyretic, induces proliferation of cultured breast cancer cells containing both estrogen and progesterone receptors (ER+/PR+). The main objective of this study was to evaluate the involvement of ERs in this effect. First, the effects of therapeutic acetaminophen concentrations were compared in breast cancer cells with high ERs and in T47Dco cells with lower ERs, to determine if acetaminophen-induced proliferation depends on ER levels. Second, the effects of two antiestrogens (ICI 182,780 and 4'-hydroxytamoxifen) on acetaminophen-induced proliferation were determined in three human breast cancer cell lines: two ER+/PR+ (MCF7, T47D) and one ER-/PR- (MDA-MB-231). Third, ER binding assays were performed in MCF7 cells to determine if acetaminophen competed with estradiol for binding to ERs. Proliferation endpoints monitored included percent cells in the DNA synthesis phase of the cell cycle, 3H-thymidine incorporation into DNA, and cell number. Acetaminophen did not induce DNA synthesis in T47Dco cells, but did in cells with higher ER levels, suggesting high ER levels are necessary for acetaminophen to induce proliferation. Antiestrogens inhibited acetaminophen-induced proliferation in ER+/PR+ cells while no effects were observed in ER-/PR- cells, further supporting ER involvement. However, acetaminophen did not compete with estradiol for binding to ERs in ER+/PR+ cells. Collectively, these data suggest that acetaminophen induces breast cancer cell proliferation via ERs without binding to ERs like estradiol. The second purpose of this study was to determine if acetaminophen is estrogenic/antiestrogenic in vivo (uterotrophic assays). Acetaminophen has no antiestrogenic/estrogenic activity in mice or rats uteri.

Differential regulation of specific genes in MCF-7 and the ICI 182780-resistant cell line MCF-7/182R-6

To elucidate the mechanisms involved in anti-oestrogen resistance, two human breast cancer cell lines MCF-7 and the ICI 182780-resistant cell line, MCF-7/182R-6, have been compared with regard to oestrogen receptor (ER) expression, ER function, ER regulation, growth requirements and differentially expressed gene products. MCF-7/182R-6 cells express a reduced level of ER protein. The ER protein is functional with respect to binding of oestradiol and the anti-oestrogens tamoxifen, 4-hydroxy-tamoxifen and ICI 182780, whereas expression and oestrogen induction of the progesterone receptor is lost in MCF-7/182R-6 cells. The ER protein and the ER mRNA are regulated similarly in the two cell lines when subjected to treatment with oestradiol or ICI 182780. Oestradiol down-regulates ER mRNA and ER protein expression. ICI 182780 has no initial effect on ER mRNA expression whereas the ER protein level decreases rapidly in cells treated with ICI 182780, indicating a severely decreased stability of the ER protein when bound to ICI 182780. In vitro growth experiments revealed that the ICI 182780-resistant cell line had evolved to an oestradiol-independent phenotype, able to grow with close to maximal growth rate both in the absence of oestradiol and in the presence of ICI 182780. Comparison of gene expression between the two cell lines revealed relatively few differences, indicating that a limited number of changes is involved in the development of anti-oestrogen resistance. Identification of the differentially expressed gene products are currently in progress.

Synergism between a half-site and an imperfect estrogen-responsive element, and cooperation with COUP-TFI are required for estrogen receptor (ER) to achieve a maximal estrogen-stimulation of rainbow trout ER gene

In all oviparous, liver represents one of the main E2-target tissues where estrogen receptor (ER) constitutes the key mediator of estrogen action. The rainbow trout estrogen receptor (rtER) gene expression is markedly up-regulated by estrogens and the sequences responsible for this autoregulation have been located in a 0.2 kb upstream transcription start site within - 40/- 248 enhancer region. Absence of interference with steroid hormone receptors and tissue-specific factors and a conserved basal transcriptional machinery between yeast and higher eukaryotes, make yeast a simple assay system that will enable determination of important cis-acting regulatory sequences within rtER gene promoter and identification of transcription factors implicated in the regulation of this gene. Deletion analysis allowed to show a synergistic effect between an imperfect estrogen-responsive element (ERE) and a consensus half-ERE to achieve a high hormone-dependent transcriptional activation of the rtER gene promoter in the presence of stably expressed rtER. As in mammalian cells, here we observed a positive regulation of the rtER gene promoter by the chicken ovalbumin upstream promoter-transcription factor I (COUP-TFI) through enhancing autoregulation. Using a point mutation COUP-TFI mutant unable to bind DNA demonstrates that enhancement of rtER gene autoregulation requires the interaction of COUP-TFI to the DNA. Moreover, this enhancement of transcriptional activation by COUP-TFI requires specifically the AF-1 transactivation function of ER and can be observed in the presence of E2 or 4-hydroxytamoxifen but not ICI 164384. Thus, this paper describes the reconstitution of a hormone-responsive transcription unit in yeast in which the regulation of rtER gene promoter could be enhanced by the participation of cis-elements and/or trans-acting factors, such as ER itself or COUP-TF.

Estradiol regulates estrogen receptor mRNA stability

Previous studies suggest that post-transcriptional events play an important role in estrogen-induced loss of estrogen receptor expression. The present study shows that treatment of MCF-7 cells with estradiol resulted in a six-fold decrease in estrogen receptor mRNA half-life from 4 h in control cells to 40 min in estradiol treated cells. To determine the role of protein synthesis in the regulation of estrogen receptor mRNA stability, several translational inhibitors were utilized. Pactamycin and puromycin, which prevent ribosome association with mRNA, inhibited the effect of estradiol on receptor mRNA stability, whereas cycloheximide, which has no effect on ribosome association with mRNA, had no effect on estradiol regulation of estrogen receptor mRNA stability. In control cells, the total cellular content of estrogen receptor mRNA was associated with high molecular weight polyribosomes. Treatment with estradiol resulted in a 70% decrease in estrogen receptor mRNA associated with polyribosomes but had no effect on the polyribosome distribution of estrogen receptor mRNA. In an in vitro degradation assay, polyribosomes isolated from estradiol-treated cells degraded ER mRNA faster than polyribosomes isolated from control cells. The nuclease activity associated with the polysome fraction appeared to be Mg2+ independent and inhibited by RNasin. Freeze-thawing and heating at 90 degrees C for 10 min resulted in the loss of nuclease activity. These studies suggest that an estrogen-regulated nuclease activity associated with ribosomes alters the stability of estrogen receptor mRNA.

Mammary gland growth and development from the postnatal period to postmenopause: ovarian steroid receptor ontogeny and regulation in the mouse

Ovarian steroid hormones play a critical role in regulating mammary gland growth and development. The mammary gland sequentially acquires and cyclically exhibits proliferative responses to estrogen and/or progesterone from birth to postmenopause. The focus of this review is to present our current understanding of estrogen and progesterone receptor distribution in epithelial and stromal cells and their functions in relation to mammary gland development. Insights gained from the study of the normal mammary gland are relevant to our understanding of the conditions which may predispose women to the development of breast cancer as well as to alterations in hormonal regulation that occur in breast cancer.

The estrogen receptor gene: promoter organization and expression

The estrogen receptor (ER) is a ligand-activated transcription factor and a member of a large family of nuclear hormone receptors. As a mediator of estrogen hormone action, the ER is involved in many important physiological processes. ER gene expression has been demonstrated to be restricted to certain tissues and under complex hormonal control. However, the molecular mechanisms involved have remained largely unknown. Due to this lack of knowledge an investigation was undertaken to characterize the promoter organization of ER gene and investigate its expression. Approximately 3 kb of the 5' flanking region of the human ER (hER) gene was isolated and sequenced. By performing RT-PCR and RACE experiments it was shown that the hER gene is transcribed from three different promoters. Transcription of the hER gene from these promoters yields three different mRNA isoforms with unique 5' untranslated regions (5'UTRs), but identical coding regions. The expression pattern of the hER mRNA isoforms was investigated by RT-PCR. Both the A- and B-mRNA isoforms were found to be expressed in breast and uterus, whereas expression of the C-transcript was predominantly detected in liver. In bone cells only expression of the B-mRNA could be detected. The steady-state levels of the A- and B-transcripts in normal breast and uterus were quantified and compared with the hER mRNA levels in established cancer cell lines derived from the same tissues. This demonstrated approximately equal levels of the two transcripts in normal tissues whereas the A-mRNA was the most abundant isoform in the cancer cell lines investigated. Approximately 4.5 kb of the 5' flanking region of the rat ER (rER) gene were sequenced. Sequence analysis and PCR experiments suggested that the promoter organization of the rat and human ER genes is only partially conserved which might indicate species-specific differences in the regulation of ER expression. In conclusion, this work suggests tissue-specific alternative promoter usage as a mechanism in the regulation of human and rat ER gene expression.

The nuclear orphan receptors COUP-TF and ARP-1 positively regulate the trout estrogen receptor gene through enhancing autoregulation

The rainbow trout estrogen receptor (rtER) is a positively autoregulated gene in liver cells. In a previous report, we showed that upregulation is mediated by an estrogen response element (ERE) located in the proximal promoter of the gene and that a half binding site for nuclear receptors (5'-TGACCT-3') located 15 bp upstream of the ERE is involved in the magnitude of the estrogen response. We now report that the human orphan receptor COUP-TF and a COUP-TF-like protein from trout liver are able to bind to the consensus half-site. When cotransfected with the rtER gene proximal promoter, COUP-TF had no regulatory functions on its own. Interestingly, COUP-TF enhanced rtER transactivation properties in the presence of estradiol in a dose-dependent manner when cotransfected with the rtER gene promoter. Unliganded retinoid receptor heterodimers had the same helper function as COUP-TF in the presence of estradiol but were switched to repressors when the ligand all-trans-retinoic acid was added. Mutation of the consensus half-site only slightly reduced COUP-TF helper function, suggesting that it actually results from a complex mechanism that probably involves both DNA binding of COUP-TF to the promoter and protein-protein interaction with another transcription factor bound to the promoter. Nevertheless, a DNA-binding-defective mutant of COUP-TF was also defective in ER helper function. Competition footprinting analysis suggested that COUP-TF actually establishes contacts with the consensus upstream half-site and the downstream ERE half-site that would form a DR-24-like response element. Interaction of COUP-TF with the DR-24 element was confirmed in footprinting assays by using nuclear extracts from Saccharomyces cerevisiae expressing COUP-TF. Finally, interaction of COUP-TF with mutants of the rtER gene promoter showed that COUP-TF recognizes the ERE when the upstream half-site is mutated. These data show that COUP-TF may activate transcription through interaction with other nuclear receptors. This cross-talk between liganded nuclear receptors and orphan receptors is likely to modulate the spectrum of action of a particular ligand-receptor complex and may participate in the cell-type specificity of the ligand effect.

Protein synthesis is not implicated in the ligand-dependent activation of the estrogen receptor in MCF-7 cells

In MCF-7 cells, estrogen receptor (ER) elimination occurs rapidly under stimulation with estradiol (E2) at 1 nM ('ER processing'); cycloheximide (CHX) at 50 microM impedes this phenomenon. ER processing is also observed when E2 is removed after the first hour of incubation, indicating that the role of the hormone would be limited to the initiation of this process. When CHX is removed at the same time, receptor processing and, later, the induction of progesterone receptor (PgR) both proceed. The initial estrogenic signal which activates ER is therefore not influenced by CHX. In support of this conclusion, no effect of the drug on E2 binding affinity of residual ER was detected. A similar result was recorded for a series of estrogens and antiestrogens, indicating that CHX exerts no influence on the potential agonistic/antagonistic potency of any ligand. Size-exclusion chromatography (FPLC) revealed that [3H]E2-induced ER activation leads to the cleavage of the native receptor (67 kDa) into low molecular weight isoforms which subsequently become less detectable over time (proteolysis). In the presence of CHX, such ER isoforms persist, confirming the absence of interference of the drug with the activation step. When the cells were prelabelled with [3H]tamoxifen aziridine ([3H]TAZ) before their exposure to E2, ER cleavage could not be detected due to the lack of activation potency of the antiestrogenic ligand. However, the [3H]TAZ-ER complexes were subjected to E2-induced processing; CHX blocked this phenomenon, which is associated with the maintenance of ER synthesis and activation.

Insulin-like growth factors control the regulation of oestrogen and progesterone receptor expression by oestrogens

Ligands for the type I insulin-like growth factor (IGF) receptor interact with oestrogens to control the proliferation of oestrogen responsive breast cancer cells. The aim of this study was to determine the involvement of ligands for the type I IGF receptor in the regulation of oestrogen receptor (OR) expression by oestrogens and antioestrogens in these cells. Oestrogen decreased OR mRNA levels in MCF-7 cells whereas it increased them in T47D, EFM-19 and ZR-75 cells. In MCF-7 cells, IGF-I and insulin lowered further OR expression in the presence of oestrogen. In the presence of IGF-I or insulin, the induction of progesterone receptor mRNA by oestradiol was considerably attenuated in MCF-7 cells, showing that the enhanced down-regulation of OR mRNA levels influenced the expression of oestrogen-regulated genes. The oestrogen agonist activity of the antioestrogens tamoxifen and ICI 182 780 for the down-regulation of OR expression in MCF-7 cells was modulated by type I IGF receptor ligands. Overall these experiments show that OR expression is differentially regulated by oestrogen in individual oestrogen-responsive breast cancer cell lines. Ligands for the type I IGF receptor can modulate regulation of OR expression by oestrogens and antioestrogens principally in cells in which oestrogens down-regulate OR expression.

Transcriptional and post-transcriptional regulation of rainbow trout estrogen receptor and vitellogenin gene expression

Estrogen receptor (ER) and vitellogenin (Vg) gene expression are strongly up-regulated by estrogens in rainbow trout liver. In this paper, we have used primary cultured hepatocytes to examine the mechanisms implicated in estrogen regulation of ER and Vg gene expression. Treatment of hepatocytes with 1 microM estradiol (E2) led to a rapid increase in ER and mRNA level (15 fold) followed by Vg and mRNA induction. Transcription rate and mRNA half-life determination carried out in the presence or absence of E2, demonstrated that E2 increases both the ER and Vg gene transcriptional activity and mRNA stability (ca. 3 fold). The effect of E2 was inhibited by an excess of antiestrogen, showing that E2-stimulation of ER and mRNA level is mediated by the estrogen receptor. Our data show that ER and Vg genes have different hormonal sensitivity. In fact, the Vg gene required a higher concentration of E2 to be stimulated compared to the ER gene. Examination of the mechanisms involved in post-transcriptional regulation of ER mRNA showed that the setting up and maintenance of this regulation process implies that estrogen receptor and the general translational activity within the cells, suggesting that ER mRNA depends on the synthesis of an estrogen-dependent protein. However, the cis and trans elements involved in E2-stabilization process remain to be identified.

Up-regulation of estrogen receptor mRNA and estrogen receptor activity by estradiol in liver of rainbow trout and other teleostean fish

Injection of estradiol (E2) into immature rainbow trout resulted in the induction of the hepatic vitellogenin gene mediated by the nuclear estrogen receptor (ER). Liver ER mRNA rose markedly on E2 treatment in three groups of trout kept at different temperatures. Only in the group kept at 4 degrees C did the total cellular ER, as measured by [3H]estradiol-binding activity in nuclear and cytosol fractions, parallel the ER mRNA level. In fish kept at 9 degrees C and 15 degrees C, the ratio of total ER activity to ER mRNA fell during chronic E2 treatment, probably reflecting translational of post-translational control mechanisms. Upregulation of ER mRNA also occurred in sea raven, sculpin, winter flounder, and Atlantic salmon after E2 treatment. Intrahepatic ER activity rose proportionately in Atlantic salmon kept at 6-9 degrees C but not in sea raven, sculpin, or flounder. We conclude that the regulation of ER expression in teleosts is complex and includes transcriptional, translational, and post-translational elements and is influenced by environmental temperature.

Exogenous estrogen acts differently on production of estrogen receptor in the preoptic area and the mediobasal hypothalamic nuclei in the newborn rat

Expression of the estrogen receptor (ER) in the preoptic area (POA) and the mediobasal hypothalamus (MBH) in newborn female rats was studied by immunohistochemistry (IHC) and in situ hybridization histochemistry (ISHH). The number of ER immunoreactive (ER-IR) cells decreased and expression of ER mRNA was suppressed in the arcuate (ARH) and the ventromedial (VMH) hypothalamic nuclei by daily injections of estradiol benzoate (EB) for ten consecutive days. In contrast, in the POA, expression of ER mRNA was not suppressed by EB treatment, while the ER immunoreactivity and the number of ER-IR cells was decreased by EB treatment. Results of quantification of ER mRNA by reverse transcription-polymerase chain reaction correlated well with results from ISHH: that is, ER mRNA expression decreased in the MBH but not in the POA. Thus, estrogen affects ER gene expression differently in these two brain regions.

Functional analysis of the human androgen receptor promoter

Although androgen receptor levels vary widely during development, our previous studies have suggested that a single promoter is active in a number of human and rat tissues and cell lines. To examine the elements controlling androgen receptor expression, we performed deletion mapping and site-directed mutagenesis of the human androgen receptor promoter and assayed these promoter fusions in human cell lines that produce the androgen receptor as well as those deficient in the androgen receptor, both in the presence and absence of androgen. Our studies identify a region (-74 to +87) surrounding the site of transcription initiation that constitutes the core of the androgen receptor promoter. When assayed in T47D cells (an AR-expressing cell line), this segment was sufficient to direct the expression of reporter genes at levels similar to that observed for larger promoter fragments, and further deletions led to an appreciable loss of promoter activity. DNA sequences surrounding this region appear to modulate the activity of this minimal promoter in a cooperative fashion. Site-directed mutagenesis and mobility shift assays demonstrated the importance of regulatory regions upstream of the transcription initiation site including an SP1 binding site and two segments with similarities to consensus HLH protein binding sites (E-boxes). Androgen treatment did not cause a decrease in activity of any of the transiently transfected promoter fusions tested, suggesting that the promoter does not contain the information necessary for autoregulation or that a posttranscriptional or posttranslational mechanism is responsible for the regulation of AR mRNA by ligand. Furthermore, the androgen receptor promoter fusions displayed differing transcriptional activities when transfected into two cell lines deficient in androgen receptor expression suggesting heterogeneity in the mechanisms responsible for this deficiency.

Estrogenic and antiestrogenic regulation of the half-life of covalently labeled estrogen receptor in MCF-7 breast cancer cells

Effect of estrogens and antiestrogens (AEs) on estrogen receptor (ER) half-life was analyzed in MCF-7 cells by assessing its progressive disappearance after covalent labeling in situ with [3H]tamoxifen aziridine ([3H]TAZ). Cells were incubated for 1 h with 20 nM [3H]TAZ either in the absence or presence of a 500-fold excess of unlabeled estradiol (E2) (non-specific binding). The entire ER population was labeled by this method as established by subsequent incubation of the cells with [125I]E2. [3H]TAZ labeled cells were maintained in culture for additional 5 h in the absence (control) or presence of increasing amounts (0.1 nM - 1 microM) of either a given estrogen (E2, estrone, diethylstilbestrol, bisphenol), a pure AE (RU 58 668, ICI 164 384) or an AE with residual estrogenic activity (RU 39 411, 4-hydroxytamoxifen, keoxifene). The progressive disappearance of nuclear and cytosolic [3H]TAZ-ER complex during 5 h incubation were assessed by their immunoprecipitation with anti-ER monoclonal antibody (H 222) followed by scintillation counting or SDS-PAGE and fluorography. Fading of labeled receptors was extremely slow (approximately 10% loss after 6 h) in absence of any hormone/antihormone indicating a long half-life of the [3H]TAZ-ER complex. Addition of estrogens as well as pure AEs led to a dramatic reduction of the half-life while AEs with residual estrogenic activity were extremely less efficient in this regard providing an explanation for the ability of latter compounds to up-regulate the receptor since they do not affect ER mRNA synthesis and stability. Receptor disappearance induced by estrogens was closely related to their binding affinity for ER. Newly synthesized ER emerged during the treatment with hormones or antihormones seems to be implicated in the phenomenon since [3H]TAZ was covalently bound and could, therefore, not be displaced by these compounds. Induction of synthesis of a short half-life peptide(s) with degradative activity was demonstrated by addition of cycloheximide or puromycine (both at 50 microM) which completely blocked ER disappearance. The fact that no cleavage products of ER were detected by SDS-PAGE suggested a lysosomial hydrolysis. Hence, hormonal modulation of only a part of ERs may down-regulate their total population until it reaches the steady-state level.

Estrogen regulated messenger RNAs in human breast cancer cells

A large number of estrogen-regulated mRNAs have been identified in human breast cancer cells. Some of these encode proteins whose regulation by estrogen had been established previously. Others have been identified by differential screening of cDNA libraries established from estrogen-stimulated breast cancer cells. The regulation of these RNAs by estrogens in different cell lines is reviewed. The possible role of their gene products where known is discussed as is the possibility that the proteins mediate the proliferative effects of estrogens on breast cancer cells. The possibility that measurement of one or more of these estrogen-regulated gene products in breast tumours might allow prediction of the likely benefit of patients from endocrine therapies is evaluated. Finally the impact that they have had on current understanding of how estrogens and antiestrogens regulate transcription of endogenous genes in human breast cancer cells is considered.

The androgen receptor mRNA is up-regulated by testosterone in both the Harderian gland and thumb pad of the frog, Rana esculenta

Alpha 32P-labelled cDNA probe from plasmid containing rat androgen receptor (rAR) has been tested in hybridization experiments using RNAs from the Harderian gland and thumb pad of the edible frog, Rana esculenta. Northern blot analysis has shown a high degree of homology between the rAR cDNA and the frog androgen receptor mRNA (fAR mRNA); this has been supported by both the hybridization conditions (high stringency) and the molecular size of fAR mRNA which is quite similar to those described in mammals (9.4 kb). The role of androgens has been further investigated with respect to the kinetics of expression of fAR mRNA in in vivo experiments. In both the Harderian gland and thumb pad, testosterone has increased the levels of fAR mRNA as compared with the untreated groups. The use of cyproterone acetate (CPA) in combination with testosterone has resulted in a loss of the increase in fAR mRNA as compared to testosterone-treated groups, while CPA alone has resembled the control group. In primary cultures of frog Harderian gland and thumb pad cells, the steady-state levels of fAR mRNA have been increased in the cells exposed to testosterone as compared to those not exposed. These findings confirm that, in these androgen target tissues, testosterone exerts an up-regulation on its own receptors, increasing the accumulation of fAR mRNA in the same way as oestrogens up-regulate the expression of their own receptors in Xenopus liver and oviduct cells.

Equilibrium hormone binding to human estrogen receptors in highly diluted cell extracts is non-cooperative and has a Kd of approximately 10 pM

It is generally accepted that the Kd for hormone binding to estrogen receptors in extracts ranges between 0.1-1 nM and that binding displays positive cooperativity due to formation of homodimers. After carefully optimizing assay procedures, to diminish ligand depletion phenomena and to fully control recoveries, we find a single class of non-interacting high affinity hormone binding sites with a Kd of approx. 10 pM. Ligand depletion was avoided by decreasing receptor concentrations to 5-8 pM. We were therefore obliged to employ radioiodinated estradiol as a probe as the specific radioactivity of tritiated estradiol was too low to maintain the accuracy of the binding assay. Human estrogen receptor extracted from the MCF7 cell line and recombinantly produced (in yeast) wild-type human receptor have identical equilibrium hormone binding characteristics.

Estrogen regulation of the estrogen receptor and insulinlike growth factor-I in the rat uterus: a potential coupling between effects of estrogen and IGF-I

The interrelationship between estrogen and insulin-like growth factor-I (IGF-I) in the regulation of uterine growth was studied in the rat. The levels of the estrogen receptor (ER), ER mRNA, and IGF-I mRNA in rat uterus and liver were monitored. Uterine ER in normal cycling rats was highest in proestrus and diestrus, as was IGF-I mRNA. ER mRNA and plasma estradiol peaked in proestrus. Hepatic ER mRNA and IGF-I mRNA were highest in diestrus, whereas ER was not significantly changed during the estrous cycle. The temporal effects of multiple injections or continuous infusion of 17 beta-estradiol in ovariectomized rats were examined. In the uterus of animals subjected to multiple injections, a 10-fold increase in IGF-I mRNA was seen 24 h after the start of the treatment, whereas rats given continuous infusion of estradiol showed a more than 16-fold increase. In both groups, the increase of IGF-I mRNA was transient although estrogen treatment was continued. To study local hormonal effects, ovariectomized rats were given estradiol in vaginal implants. The uterine IGF-I mRNA level increased two-fold in 3 days. The ER mRNA level increased 1.5-fold and the uterine weights were doubled. The plasma estradiol concentration did not change during the treatment. A separate experiment was carried out to establish whether IGF-I itself exercises estrogen-like effects. Ovariectomized rats were given hrIGF-I in osmotic minipumps for 3 days. The uteri of the treated animals weighted significantly more than did the controls. Quantitation of the level of uterine estrogen receptors revealed a significant decrease.(ABSTRACT TRUNCATED AT 250 WORDS)

Estradiol-induced down-regulation of estrogen receptor. Effect of various modulators of protein synthesis and expression

Incubation of MCF-7 cells with estradiol (E2) down-regulates estrogen receptor (ER) resulting in a progressive reduction of the capacity of cells to concentrate selectively [3H]E2. Scatchard plot analysis failed to detect any transformation of residual receptors into peptides of lower binding affinity. [3H]Estrone gave an identical ER disappearance pattern with an ER half-life comprised between 2 and 3 h. A similar value was established by incubating the cells with [3H]tamoxifenaziridine ([3H]TAZ) for 1 h before the addition of excessive unlabeled E2 which induced ER-down regulation and impeded any further labeling of the residual receptors. Submission of the [3H]TAZ labeled cell extracts to SDS-PAGE revealed no progressive emergence of low molecular weight cleavage products of the receptor (< 67 kDa). Two inhibitors of protein kinases, H-7 at 40 microM and H-89 at 20 microM, failed to block the E2-induced ER down-regulation. On the contrary, the protein phosphatases 1 and 2A inhibitor, okadaic acid, was effective with concentrations higher than 0.1 microM indicating that a dephosphorylation mechanism was involved in this phenomenon. Cycloheximide (CHX) also significantly reduced the receptor decrease at concentrations higher than 1 microM. G-C specific intercalating agents [actinomycin D (AMD) and chromomycin A3 at 1 microM] also prevented ER disappearance; ethidium bromide (EB) and quinacrine were ineffective. AMD and CHX operated immediately after their addition to the medium indicating an inhibitory action on the synthesis of an RNA and/or a peptide with high turnover rate involved in ER decline. Moreover, AMD produced its suppressive effects under conditions impeding any labeling of newly synthetized receptors (i.e. [3H]TAZ with an excess of unlabeled E2) rejecting the possibility of an increasing ER production which may partially hamper its disappearance. Finally, E2-induced ER mRNA down-regulation was similarly abolished by AMD while EB and CHX were devoid of effect.

Regulation of the levels of three transforming growth factor beta mRNAs by estrogen and their effects on the proliferation of human breast cancer cells

Transforming growth factor (TGF) beta is a potent regulator of cell proliferation and may play a role in breast cancer cell growth. We have evaluated the regulation of TGF beta 1, TGF beta 2, and TGF beta 3 mRNAs by 17 beta-estradiol (E2) and 4-hydroxytamoxifen (MOH) in estrogen receptor-positive (ER(+)) MCF-7 and estrogen receptor-negative (ER(-)) MDA-MB-231 human breast cancer cells. We also determined the effect of TGF beta 1, TGF beta 2, and TGF beta 3 on the proliferation of these cells. Cells were deprived of estrogen before the addition of hormones, and mRNA was measured by Northern blot analysis. We found that MCF-7 cells expressed mRNAs of all three TGF beta species. Treatment of MCF-7 cells with 10(-10) M E2 for 7 days resulted in a dramatic decrease in the TGF beta 2 and TGF beta 3 mRNA levels, but not in the TGF beta 1 mRNA level. MOH was found to block these effects. In addition, the regulation of TGF beta 2 and beta 3 gene expression occurs at both transcriptional and post-transcriptional levels. There is an inverse correlation between E2-induced growth and levels of TGF beta 2 and TGF beta 3 mRNA. In contrast to MCF-7 cells, MDA-MB-231 cells expressed TGF beta 1 and TGF beta 2 mRNAs but TGF beta 3 mRNA was not detected, and the TGF beta 1 and TGF beta 2 mRNAs were not regulated by estrogens or antiestrogens.(ABSTRACT TRUNCATED AT 250 WORDS)