Activation of the silent progesterone receptor gene by ectopic expression of estrogen receptors in a rat fibroblast cell line

Zearalenone affects the growth of endometriosis via estrogen signaling and inflammatory pathways

Endometriosis is a chronic, inflammatory, estrogen-dependent gynecological disease characterized by the growth of endometrial stromal cells and glands outside the uterine cavity in response to hormones, which commonly occurs in reproductive-age women. Zearalenone (ZEA) is a toxic metabolite produced by Fusarium, which acts as estrogen activity because of the similarity of its structure to estrogen. In this study, we used an endometriosis mouse model: 15 days after ovariectomy, endometrial fragments were sutured on the pelvic wall, and exogenous estrogen was supplied using an estrogen-releasing silicone tube embedded subcutaneously. Mice were treated with different doses of ZEA by gavage for 21 days. The results show that ZEA significantly inhibited the growth of ectopic endometrium in a dose-dependent manner. The proliferation of cells decreased while apoptosis increased in the ectopic tissues of ZEA-treated mice compared to the vehicle group. The expression of estrogen receptor-α and its downstream targets MUC1 and p-AKT decreased, indicating an impaired estrogen signaling activity by ZEA treatment. In addition, the decreased expression of pro-inflammatory cytokine Tnf-α, Il-1β, and Il-6, the lower number of macrophages and neutrophils cells, and the inhibited NF-κB signaling pathway suggest the inflammatory response in the ectopic endometrium was also suppressed by ZEA treatment. However, when the exogenous estrogen supply is removed, ZEA, in turn, plays an estrogen-like role that promotes cell proliferation in the ectopic endometrium. In summary, our data suggest ZEA acts as an antagonist in endometriotic tissue when estrogen is sufficient but turns to estrogenic activity in the absence of estrogen in the development of endometriosis. ZEA also inhibits ectopic tissue growth by inhibiting inflammatory response in the endometriosis model.

ER-/PR+ breast cancer: A distinct entity, which is morphologically and molecularly close to triple-negative breast cancer

Determining the status of steroid hormone receptors [oestrogen (ER) and progesterone receptors (PR)] is a crucial part of the breast cancer workup. Thereby, breast cancers can be classified into four subtypes. However, the existence of ER-/PR+ tumours, often reported to be ill-classified due to technical errors, remains controversial. In order to address this controversy, we reviewed the hormone receptor status of 49 breast tumours previously classified as ER-/PR+ by immunohistochemistry, and compared clinical, pathological and molecular characteristics of confirmed ER-/PR+ tumours with those of ER+ and triple-negative tumours. We unequivocally confirmed the ER-/PR+ status in 27 of 49 tumours (0.3% of all breast cancers diagnosed in our institution between 2000 and 2014). We found that ER-/PR+ were morphologically and histologically similar to triple-negative tumours, but very distinct from ER+ tumours, with more aggressive phenotypes and more frequent basal marker expression than the latter. On the molecular level, RNA sequencing revealed different gene expression profiles between the three groups. Of particular interest, several genes controlled by the suppressor of zest 12 (SUZ12) were upregulated in ER-/PR+ tumours. Overall, our results confirm that ER-/PR+ breast cancers are an extremely rare but 'real' tumour subtype that requires careful diagnosis and has distinct features warranting different responsiveness to therapies and different clinical outcomes. Studies on larger cohorts are needed to further characterise these tumours. The likely involvement of SUZ12 in their biology is an interesting finding which may - in a long run - give rise to the development of new therapeutic alternatives.

Transcriptional activation of breast cancer-associated gene 2 by estrogen receptor

RNF115, or Breast Cancer-Associated Gene 2 (BCA2), encodes a RING-finger ubiquitin E3 ligase, expression of which was associated with estrogen receptor (ER)-positive status in human breast tumors. Although the BCA2 promoter contains several estrogen response element (ERE) half-sites, the role of ER in the regulation of BCA2 transcription has not been reported. The aim of this study is to investigate the molecular mechanism by which estrogen regulates BCA2 transcription. BCA2 mRNA and protein levels were examined by RT-PCR and Western blot analysis, respectively, and localization was assessed by immunofluorescence. BCA2 promoter activity in response to E(2) was tested by a dual luciferase reporter assay and ER binding to the BCA2 promoter was examined by chromatin immunoprecipitation assay. We found that BCA2 mRNA and protein levels are regulated by estrogen in ER-positive MCF7 breast cancer cells and MDA MB 231 cells stably transfected with ER. Estrogen treatment in hormonal depleted MCF7 and MDA MB 231/ER stably transfected cells resulted in increased nuclear ER and cytoplasmic and nuclear BCA2 staining. Cycloheximide is not able to inhibit BCA2 mRNA levels, suggesting potential BCA2 regulation at the transcriptional level. Anti-estrogens like tamoxifen and ICI 182 178 counteracted E(2)-induced BCA2 protein and knockdown of ER by ER siRNA resulted in a significant decrease in BCA2 protein and a lower nuclear expression pattern. Estrogen treatment lead to a significant increase in BCA2 promoter response, associated with increased binding of ER to the ERE region of the BCA2 promoter. BCA2 is therefore a newly identified transcriptional target of estrogen receptor.

Female rats are relatively more sensitive to reduced lipid versus reduced carbohydrate availability

Objectives:

Because females have blunted counterregulatory responses to hypoglycemia relative to males, we hypothesized that females would have greater sensitivity to changes in lipid availability.

Design and subjects:

To assess this, we examined the feeding response to glucoprivation (2-deoxyglucose; 2DG) and lipoprivation (mercaptoacetate; MA) in age-matched male and female Long-Evans rats.

Results:

Males versus females had significantly greater food intake after 250 mg kg⁻¹ of 2DG, but there were no sex differences with the 750 mg kg⁻¹ dose of 2DG. Glucose responses to 250 mg kg⁻¹ of 2DG were also significantly greater in males versus females. In contrast, females had a significant increase in food intake with all doses of MA versus saline, and had significantly greater food intake compared with males at the lowest and highest doses of MA with a trend towards significance with the intermediate dose. To determine whether estradiol (E2) is the mechanism underlying this sexual dimorphism, ovariectomized females were injected with vehicle or 2 μg of E2 every fourth day to mimic the variations in across the estrous cycle. Ovariectomized females significantly increased feeding and glucose after 250 mg kg⁻¹ of 2DG over intact females and E2 had no effect on these responses. Although the feeding response to 2DG was not different, the glucose response to 2DG was still significantly greater in males versus ovariectomies females. However, ovariectomized females also did not increase food intake after MA, regardless of E2 treatment.

Conclusions:

These data collectively suggest that males are relatively more sensitive to glucose deprivation and females are relatively more sensitive to lipid deprivation. Further, these data rule out a role for cyclic changes in E2 in these sex differences.

Estrogen regulation of gene expression in GnRH neurons

Estrogen plays an essential role in the regulation of the female reproductive hormone axis, and specifically is a major regulator of GnRH neuronal function in the female brain. GnRH neuronal cell lines were used to explore the direct effects of estradiol on gene expression in GnRH neurons. The presence of estrogen receptor (ER) binding sites was established by a receptor-binding assay, and estrogen receptor alpha and beta mRNA were identified in GN11 cells and ERbeta in GT1-7 cells using RT-PCR analysis of mRNA. ERalpha was more abundantly expressed in GN11 cells than ERbeta as assessed by real-time PCR. Additionally, GN11 cells expressed significantly more of both ERalpha and beta than GT1-7 cells. Functional studies in GN11 and GT1-7 demonstrated estrogen down regulation of endogenous mouse GnRH mRNA levels using quantitative real-time PCR (qRT-PCR). Correspondingly, estradiol also reduced secretion of GnRH from both the GN11 and GT1-7 cell lines. Since estradiol has been shown to regulate progesterone receptor (PR) expression; similar studies were performed demonstrating an estradiol mediated increase in PR in both cell lines. Estradiol regulation of ER expression was also explored and these studies indicated that estradiol decreased ERalpha and ERbeta mRNA levels in a dose-dependent manner in GN11 and GT1-7 cells. These effects were blocked by the addition of the estrogen receptor antagonist ICI 182,780. Both PPT, a specific ERalpha agonist, and DPN, a specific ERbeta agonist, inhibited GnRH gene expression in GN11 cells, but only DPN inhibited GnRH gene expression in GT1-7 cells, consistent with their undetectable levels of ERalpha expression. These studies characterize a direct inhibitory effect of estradiol on GnRH in GnRH neurons, and a direct stimulatory effect of estradiol on PR gene expression. In addition, the agonist studies indicate that there is a functional overlap of ERalpha and ERbeta regulation in GnRH neurons. These studies may give insight into the molecular regulation of estrogen negative feedback in the central reproductive axis.

Differentiation of murine embryonic stem cells induces progesterone receptor gene expression

The role of steroid hormone receptors in very early embryonic development remains unknown. Clearly, expression during organogenesis is important for tissue-specific development. However, progesterone receptor (PR) and estrogen receptors (ERalpha, ERbeta) are expressed during early development through the blastocyst stage in mice and other species, and yet are not essential for embryonic viability. We have utilized the mouse embryonic stem (mES) cell model to investigate the regulated expression of these receptors during differentiation. Surprisingly, one of the earliest changes in gene expression in response to a differentiation signal observed is PR gene induction. It parallels the time course of expression for the patterning genes Hoxb1 and Hoxa5. Unexpectedly, PR gene expression is not regulated in an estrogen-dependent manner by endogenous ERs or by transiently overexpressed ERalpha. Our results suggest a potentially novel mechanism of PR gene regulation within mES cells compared to adult tissues and the possibility of unique targets of PR action during early mES cell differentiation.

Effects of the dietary phytoestrogen biochanin A on cell growth in the mammary carcinoma cell line MCF-7

Studies of the dietary phytoestrogen biochanin A on cell proliferation of the cultured estrogen responsive cells human breast carcinoma MCF-7 showed that biochanin A exhibits biphasic regulation on MCF-7 cells. At concentrations of less than 10 microg/mL, cells respond to biochanin A by increasing cell growth and de novo DNA synthesis. The addition of biochanin A at concentrations of greater than 30 microg/mL significantly inhibited cell growth and DNA synthesis in a dose-dependent fashion, resulting in an IC(50) value of 40 microg/mL. The reversibility of these inhibitory effects by biochanin A appears also to be concentration dependent. Cells previously treated with high concentrations (>60 microg/mL) of biochanin A did not regain normal growth after treatment ceased. Biochanin A was cytostatic at low concentrations (<40 microg/mL) and cytotoxic at higher concentrations. Upon exposure to 100 microg/mL of biochanin A, cell morphology was severely altered, cell volume decreased, and condensation of cell components was clearly noticeable. In addition, biochanin A damaged cell membranes by increasing membrane permeability. These results suggest possible molecular and cellular mechanisms of the action of dietary phytoestrogens on estrogen target cells.

Independent Downstream Gene Expression Profiles in the Presence of Estrogen Receptor α or β1

The two known forms of estrogen receptor (ER), alpha and beta, exhibit differences in structure, affinity for certain ligands, and tissue distribution, suggesting differential roles. It is of interest from several perspectives to determine whether the two receptors elicit similar or differing responses within the same cell type in the presence of the same ligand. To evaluate roles of ER, we have examined responses to estrogen in a rat embryonic fibroblast cell line model, normally naive to ER, engineered to stably express ERalpha or ERbeta. Rat1+ERalpha, Rat1+ERbeta, and precursor Rat1 cell lines were treated with estradiol-17beta (E(2); 1 nM) or an ethanol vehicle for 24 h. Total RNA was extracted, and cDNA generated and subjected to suppression subtractive hybridization (SSH), followed by differential screening using dot blot hybridization. In the presence of ERalpha, products were identified that represent classic responses to E(2), including markers for cell proliferation. In the presence of ERbeta, an alternate transcription profile was observed, including upregulation of pro-alpha-2(I) collagen. These data support a model in which ERalpha and ERbeta regulate unique subsets of downstream genes within a given cell type.

Transcription factor accessibility and histone acetylation of the progesterone receptor gene differs between parental MCF-7 cells and a subline that has lost progesterone receptor expression

The human progesterone receptor (PgR) gene has a complex promoter that produces alternate mRNAs encoding the PgRA (94 kDa) and PgRB (120 kDa) protein isoforms. Expression of PgR is induced by estradiol (E(2)) in the breast, reproductive tract and many cell lines despite the lack of a classical estrogen responsive element (ERE) in the promoter regions. We employed chromatin immunoprecipitation (ChIP) to analyze the sites of estrogen receptor alpha (ERalpha) and Sp1 occupancy of the PgR promoters in vivo. We also assessed the functional relevance of histone acetylation levels on the accessibility of transcription factors to the promoter and subsequent hormone-induced transcription. We utilized MCF-7 human breast cancer cells that express PgR in response to E(2) and the MCF-7 derived C4 cell strain that has lost PgR expression as a model system. We found that promoter-wide levels of histone acetylation were not decreased in C4 cells, but that access was partially blocked for Sp1 and completely blocked for ERalpha. The basal level of histone acetylation at six localized regions of the promoter did show some differences between cell lines, but it did not correlate with transcription factor binding. Furthermore, we found only a modest and highly localized change in histone acetylation levels in response to E(2) at only one of three sites of ERalpha binding in MCF-7 cells. This was at the B1 site at the distal 5' end of the promoter. This site also showed a significant decrease in basal histone acetylation in C4 compared to MCF-7 cells. We speculate that the histone acetylation level at this site may be a marker for chromatin structure that affects the access of transcription factors to the whole promoter.

Insulin-like growth factor-I inhibits progesterone receptor expression in breast cancer cells via the phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin pathway: progesterone receptor as a potential indicator of growth factor activity in breast cancer

Although interactions between estrogen and growth factor signaling pathways have been studied extensively, how growth factors and progesterone regulate each other is less clear. In this study, we found that IGF-I sharply lowers progesterone receptor (PR) mRNA and protein levels in breast cancer cells. Other growth factors, such as epidermal growth factor, also showed the same effect. The decrease of PR levels was associated with reduced PR activity. Unlike progestins, IGF-I does not utilize the proteasome for down-regulating PR. Instead, the IGF-I-mediated decrease in PR levels is via an inhibition of PR gene transcription. In addition, the phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway was found to be specifically involved in this IGF-I effect. Our data also suggest that the IGF-I down-regulation of PR is not mediated via a reduction of estrogen receptor (ER) levels or activity. First, IGF-I induced ligand-independent ER activity while reducing ER-dependent PR levels. Second, whereas PR and cyclin D1 are both ER up-regulated, IGF-I increased cyclin D1 levels while decreasing PR levels. Third, constitutively active PI3K or Akt induced ER activity but reduced PR levels and activity. Taken together, our data indicate that IGF-I inhibits PR expression in breast cancer cells via the PI3K/Akt/mTOR pathway. Because low or absent PR in primary breast cancer is associated with poor prognosis and response to hormone therapy, our results suggest that low PR status may serve as an indicator of activated growth factor signaling in breast tumor cells, and therefore of an aggressive tumor phenotype and resistance against hormonal therapy.

Estrogen receptor isoform-specific induction of progesterone receptors in human osteoblasts

Estrogen induction of progesterone receptor (PR) expression may be important to bone physiology because progesterone has been implicated in the control of bone formation and resorption. Although PR gene expression can be induced in osteoblasts by estrogen signaling through the estrogen receptor (ER) a isoform, it is unknown whether the ER-beta isoform is involved in this regulation. The effect of estrogen on PR expression was examined in human fetal osteoblast (hFOB) cell lines stably transfected with either ER-alpha or ER-beta. Estrogen treatment of hFOB/ER-a cells induced PR messenger RNA (mRNA) steady-state levels after 24 h and protein levels after 48 h, as established by competitive reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blotting. Interestingly, no induction of PR expression was observed in the hFOB/ER-beta cells during this period. However, PR mRNA was induced progressively after 48 h of treatment with estrogen with maximum levels achieved at 12 days posttreatment. ER protein also was increased after 12 days of treatment. Both A and B isoforms of PR (PRA and PRB) were induced by estrogen in the hFOB/ER-a cells as well as much later in hFOB/ER-beta cells. The pure antiestrogen ICI 182,780 prevented PR induction by estrogen in both cell lines. An ER-beta-selective antagonist R, R-tetrahydrochrysene (THC) abolished the induction of PR mRNA in hFOB/ER-beta but not in hFOB/ER-a cells, verifying that the response in the former cell line was ER-beta-mediated. Transient cotransfection of hFOB cells with ER-a or ER-beta together with either a human PRA or PRB promoter linked to a reporter plasmid revealed that although the PRB promoter was stimulated equally by estrogen activation of either ER isoform, PRA was activated preferentially by ER-alpha. Together, these results show that although estrogen can up-regulate endogenous PR gene expression in osteoblasts via both ER isoforms, ER-alpha is the predominant inducer.

Estrogen receptor interaction with estrogen response elements

The estrogen receptor (ER) is a ligand-activated enhancer protein that is a member of the steroid/nuclear receptor superfamily. Two genes encode mammalian ER: ERalpha and ERbeta. ER binds to specific DNA sequences called estrogen response elements (EREs) with high affinity and transactivates gene expression in response to estradiol (E(2)). The purpose of this review is to summarize how natural and synthetic variations in the ERE sequence impact the affinity of ER-ERE binding and E(2)-induced transcriptional activity. Surprisingly, although the consensus ERE sequence was delineated in 1989, there are only seven natural EREs for which both ERalpha binding affinity and transcriptional activation have been examined. Even less information is available regarding how variations in ERE sequence impact ERbeta binding and transcriptional activity. Review of data from our own laboratory and those in the literature indicate that ERalpha binding affinity does not relate linearly with E(2)-induced transcriptional activation. We suggest that the reasons for this discord include cellular amounts of coactivators and adaptor proteins that play roles both in ER binding and transcriptional activation; phosphorylation of ER and other proteins involved in transcriptional activation; and sequence-specific and protein-induced alterations in chromatin architecture.

Estrogen-modulated estrogen receptor x Pit-1 protein complex formation and prolactin gene activation require novel protein synthesis

Both estrogen receptor (ER) and Pit-1 proteins are essential for the estrogen-activated expression of the rat prolactin gene. Our results show that ER.Pit-1 protein complex formation is reduced by estrogen in GH3 and PR1 rat pituitary tumor cells. In the latter, this decrease was blocked by cycloheximide, a protein synthesis inhibitor. On the other hand, the direct addition of estrogen to PR1 cell lysates had no effect on the formation of ER.Pit-1 complexes. Estrogen-activated prolactin gene expression was also inhibited by cycloheximide, suggesting that some form of protein synthesis is involved in ER.Pit-1 complex formation and subsequent prolactin gene activation. In support of this notion, we showed that estrogen-induced regulation of ER.Pit-1 complex formation could be transferred from cell lysates prepared from estrogen-treated PR1 cells to control cell lysates. This is not true for GH3 cells; instead, direct administration of estrogen to GH3 cell lysates readily abolished ER.Pit-1 protein complex formation in a dose-dependent manner, and such estrogen-induced regulation was blocked by the antiestrogen ICI 182,780. These findings thus indicate that 1) interaction between ER and Pit-1 proteins is estrogen-regulated in ways specific to different cell types, and 2) auxiliary protein factor synthesis may be involved in this process.

Progesterone induces focal adhesion in breast cancer cells MDA-MB-231 transfected with progesterone receptor complementary DNA

Since the effects of progesterone are mediated mainly via estrogen-dependent progesterone receptor (PR), the expression of the effects of progesterone may be masked or overridden by the influence of estrogen under conditions in which priming with estrogens is required. We have established a PR-positive but estrogen receptor-alpha (ER-alpha) negative breast cancer cell model by transfecting PR cDNA into ER-alpha- and PR-negative MDA-MB-231 cells in order that the functions of progesterone can be studied independently of estrogens. We have demonstrated using this model that progesterone markedly inhibited cell growth. We have also discovered that progesterone induced remarkable changes in cell morphology and specific adhesion structures. Progesterone-treated cells became considerably more flattened and well spread than vehicle-treated control cells. This was associated with a striking increase of stress fibers, both in number and diameter, and increased focal contacts as shown by the staining of focal adhesion proteins paxillin and talin. There were also distinct increases in tyrosine phosphorylation of focal adhesion protein paxillin and focal adhesion kinase in association with increased focal adhesion. The staining of tyrosine-phosphorylated proteins was concentrated at focal adhesions in progesterone-treated cells. More interestingly, monoclonal antibody (Ab) to beta1 integrin was able to inhibit progesterone-induced cell spreading and formation of actin cytoskeleton. To our knowledge, this is the first report describing a direct effect of progesterone in inducing spreading and adhesion of breast cancer cells, and beta1-integrin appeared to play an essential role in the effect. It is known that the initial step of tumor metastasis is the breakaway of tumor cells from primary tumor mass when they lose the ability to attach. Hence, progesterone-induced cell spreading and adhesion may have significant implications in tumor metastasis.

Mechanisms controlling the function and life span of the corpus luteum

The primary function of the corpus luteum is secretion of the hormone progesterone, which is required for maintenance of normal pregnancy in mammals. The corpus luteum develops from residual follicular granulosal and thecal cells after ovulation. Luteinizing hormone (LH) from the anterior pituitary is important for normal development and function of the corpus luteum in most mammals, although growth hormone, prolactin, and estradiol also play a role in several species. The mature corpus luteum is composed of at least two steroidogenic cell types based on morphological and biochemical criteria and on the follicular source of origin. Small luteal cells appear to be of thecal cell origin and respond to LH with increased secretion of progesterone. LH directly stimulates the secretion of progesterone from small luteal cells via activation of the protein kinase A second messenger pathway. Large luteal cells are of granulosal cell origin and contain receptors for PGF(2alpha) and appear to mediate the luteolytic actions of this hormone. If pregnancy does not occur, the corpus luteum must regress to allow follicular growth and ovulation and the reproductive cycle begins again. Luteal regression is initiated by PGF(2alpha) of uterine origin in most subprimate species. The role played by PGF(2alpha) in primates remains controversial. In primates, if PGF(2alpha) plays a role in luteolysis, it appears to be of ovarian origin. The antisteroidogenic effects of PGF(2alpha) appear to be mediated by the protein kinase C second messenger pathway, whereas loss of luteal cells appears to follow an influx of calcium, activation of endonucleases, and an apoptotic form of cell death. If the female becomes pregnant, continued secretion of progesterone from the corpus luteum is required to provide an appropriate uterine environment for maintenance of pregnancy. The mechanisms whereby the pregnant uterus signals the corpus luteum that a conceptus is present varies from secretion of a chorionic gonadotropin (primates and equids), to secretion of an antiluteolytic factor (domestic ruminants), and to a neuroendocrine reflex arc that modifies the secretory patterns of hormones from the anterior pituitary (most rodents).

Responses to stable ectopic estrogen receptor-beta expression in a rat fibroblast cell line

To examine activity of estrogen receptor-beta (ERbeta) independently of estrogen receptor-alpha (ERalpha), retrovirus-mediated gene transfer was used to insert rat ERbeta into a rat fibroblast cell line (rat-1) that does not ordinarily express ER. Stable expression of ERbeta in rat-1 cells was validated and then characterized by reverse-transcription polymerase chain-reaction (RT-PCR) analysis to examine the effects of estradiol (E2) treatment on expression of specific target mRNAs. Results were compared with rat-1 cells and a previously constructed rat-1 + ERalpha cell line. Progesterone receptor mRNA was not detected in rat-1 cells and was induced by E2 in both rat-1 + ERalpha and rat-1 + ERbeta cells. Treatment with E2 resulted in an increased rate of cell proliferation (P < 0.05) in rat-1 + ERalpha cells, but not in rat-1 or rat-1 + ERbeta cells. Data confirm studies using transient ER expression demonstrating that ERalpha and ERbeta have both discrete and overlapping activity within the same cell type in the presence of the same ligand.

Potentiation of human estrogen receptor alpha transcriptional activation through phosphorylation of serines 104 and 106 by the cyclin A-CDK2 complex

Both estradiol binding and phosphorylation regulate transcriptional activation by the human estrogen receptor alpha (ER). We have previously shown that activation of the cyclin A-CDK2 complex by overexpression of cyclin A leads to enhanced ER-dependent transcriptional activation and that the cyclin A-CDK2 complex phosphorylates the ER N-terminal activation function-1 (AF-1) between residues 82 and 121. Within ER AF-1, serines 104, 106, and 118 represent potential CDK phosphorylation sites, and in this current study, we ascertain their importance in mediating cyclin A-CDK2-dependent enhancement of ER transcriptional activity. Cyclin A overexpression does not enhance transcriptional activation by an ER derivative bearing serine-to-alanine changes at residues 104, 106, and 118. Likewise, the cyclin A-CDK2 complex does not phosphorylate this triple-mutated derivative in vitro. Individual serine-to-alanine mutations at residues 104 and 106, but not 118, decrease ER-dependent transcriptional enhancement in response to cyclin A. The same relationship holds for ER phosphorylation by cyclin A-CDK2 in vitro. Finally, enhancement of ER transcriptional activation by cyclin A is evident in the absence and presence of estradiol, as well as in the presence of tamoxifen, suggesting that the effect of the cyclin A-CDK2 on ER transcriptional activation is AF-2-independent. These results indicate that the enhancement of ER transcriptional activation by the cyclin A-CDK2 complex is mediated via the AF-1 domain by phosphorylation of serines 104 and 106. We propose that these residues control ER AF-1 activity in response to signals that affect cyclin A-CDK2 function.

Estrogen responses in bovine fetal uterine cells involve pathways directed by both estrogen response element and activator protein-1

Objectives were to examine possible roles of estrogen receptor (ER) in development of the bovine uterine endometrium in the context of ER type, enhancer type, and ligand-independent activation. Expression vectors producing either ERalpha or ERbeta were introduced into fetal uterine cells from Day 110 to 120 of gestation (UBF120 cells) and into rat embryo fibroblasts (Rat-1 cells), neither of which express endogenous ER. Reporter constructs containing either an estrogen response element (ERE) or activator protein-1 (AP-1) response element were cotransfected. These reporters were also transfected into fetal uterine cells from Day 180 to 200 of gestation (UBF180 cells), which express ER. In UBF120 and Rat-1 cells transfected with either ERalpha or ERbeta, treatment with estradiol-17beta (E2) resulted in increased activity of an ERE reporter construct, but not an AP-1 element reporter construct. The antiestrogen ICI 182,780 (ICI) exhibited E2 antagonist activity with both ERalpha and ERbeta. Thus, all components were present for E2-dependent transcription from an ERE except ER; however, cells were not competent for E2-dependent transcription mediated through AP-1. In UBF180 cells, E2 treatment increased both ERE and AP-1 reporter activity. ICI exhibited E2 antagonist activity. Treatment with epidermal growth factor resulted in increased ERE reporter activity that was inhibited by ICI, indicative of ligand-independent activation of ER. These data suggest that multiple pathways for ER-mediated gene regulation occur in the developing fetal uterus and that nuclear components necessary for action of both ERalpha and ERbeta are present prior to expression of the receptor.

Expression of human estrogen receptor using an efficient adenoviral gene delivery system is able to restore hormone-dependent features to estrogen receptor-negative breast carcinoma cells

Estrogen receptor (ER)-negative breast carcinomas are often difficult to treat as they do not respond to hormone therapy. In an attempt to determine if expressing the human estrogen receptor in an ectopic manner could restore the hormone responsiveness of these cells, we have expressed the human ER in ER-negative MDA-MB 231 breast cancer cells using a recombinant adenovirus gene delivery system that allows high level expression of ER in essentially all cells. In these cells, the ER was correctly translated, had a wild type hormone binding affinity (Kd = 0.6 nM), bound well to estrogen response element-containing DNA, and showed an activation pattern of estrogen response element-reporter gene activity by estrogen and antiestrogens very similar to that observed in MCF-7 breast cancer cells containing endogenous ER (stimulation by estrogen, no stimulation by the antiestrogens trans-hydroxytamoxifen or ICI 164384, and blockade of estradiol stimulation by trans-hydroxytamoxifen or ICI 164384). Intriguingly, estradiol stimulation of these cells was also able to induce expression of pS2, an estrogen regulated gene considered to be a favorable prognostic marker for endocrine therapy in ER-positive breast cancer cells. Expression of the ER had no effect by itself on the proliferation rate of MDA-MB 231 cells. However, treatment of the ER-containing cells with estradiol or with the pure antiestrogen ICI 164 384 suppressed proliferation of the cells while the antiestrogen trans-hydroxytamoxifen had little effect on proliferation; and cotreatment with trans-hydroxytamoxifen reversed the estradiol- or ICI 164 384-evoked suppression of proliferation. To understand the mechanism underlying the inhibition of proliferation by estradiol, we examined the expression of several growth related endogenous genes. c-Myc protooncogene expression was strongly inhibited by treatment with estradiol as was expression of BRCA1 and BRCA2 genes, which is in agreement with their mitogenic-dependent expression, while expression of beta-actin, a housekeeping gene, was not affected by hormone treatment. Together, these data suggest that reexpressing the human ER in breast cancer cells that no longer express this protein renders them sensitive to hormone treatment. The ability of the antiestrogen ICI 164 384 to suppress the proliferation of ER-negative breast cancer cells that reexpress ER might be useful ultimately as an endocrine gene therapy approach for controlling the growth of ER-negative breast cancer cells. The application of recombinant adenoviruses expressing the human ER presents interesting features which might be used as a basis for designing more powerful and effective treatments for ER-negative breast cancers.

Differential display screening for specific gene expression induced by dietary nonsteroidal estrogen

The dietary phytoestrogen, daidzein, produced a biphasic response in cell proliferation of cultured, estrogen-responsive human breast carcinoma MCF-7 cells. Cell growth was stimulated at a daidzein concentration of 0.25 microg/ml whereas the addition of daidzein at concentrations >25 microg/ml significantly inhibited cell growth in a dose-dependent fashion, resulting in an IC50 value of 50 microg/ml. Upon exposure to 50 microg/ml of daidzein, cell morphology was severely altered, cell volume decreased, and condensation of the chromosomes was clearly noticeable. To identify genes whose expression were inhibited by daidzein, a differential display reverse transcriptase polymerase chain reaction assay (DD-RT-PCR) was performed and the cDNA fragments of several daidzein-regulated genes were visualized. The sequence of one of the cloned cDNA fragments that showed differential mRNA expression level in response to daidzein at a concentration of 50 microg/ml had a high homology with a cDNA expressed in fetal human brain, EST 06411.

Estrogen causes cell death of estrogen receptor stably transfected cells via apoptosis

We examined the effect of estrogen on the growth of estrogen receptor (ER) stably transfected cells (Rat1 + ER). 17-Beta-estradiol (E2, 10 nM) inhibited approximately 35-50% of Rat1 + ER growth after 3 d of treatment. The half-maximal growth inhibition occurred at 0.5-0.75 nM of E2 concentration and was saturated above 10 nM. This E2-induced antiproliferative effect was mediated through the ER since E2 did not cause any change in ER-negative parental Rat1 cells. Cells started to detach from plates and the adherent cells exhibited nuclear condensation. Apoptotic cell populations showed a 25% increase at 2 d of E2 treatment over controls that were quantified by fluorescence-activated cell sorter analysis. This indicates that E2 induced apoptosis in Rat1 + ER cells.

Expression of estrogen receptor and maintenance of hormone-responsive phenotype in bovine fetal uterine cells

Objectives were to establish conditions for preparation, growth, and maintenance of a primary culture cell model of fetal uterine cells, and to determine whether cells maintained under those conditions would maintain their capacity to respond to estrogen stimulation in vitro. Fetal uteri (n = 19) were enzymatically dispersed and grown on Type 1 collagen in Dulbecco's modified Eagle's medium (DMEM) with 10% fetal bovine serum. Fetal-uterine cells appeared fibroblast-like and exhibited positive immunostaining for both vimentin and cytokeratin. Effects of gestational age (GA), passage number (p), and hormonal treatment on appearance of specific mRNAs were determined by RT-PCR; relative concentrations of products determined by densitometry were analyzed as the ratio of target cDNA to the GAPDH loading control. Cells expressed mRNAs for estrogen receptor (ER), TGF-beta, EGF-R, PRL-R, IL-1 alpha, and IL-6. ER mRNA was greater at 185-200 than at 100-110 d GA (P < 0.01). All specific mRNAs examined were greater in p5 cells than p2 at both 100-110 (P < 0.01) and 185-200 d GA (P < 0.02). There was no effect of estradiol on these specific mRNAs in cells from 100-110 d GA; at 185-200 d GA, there was an estradiol (1.0 nM) effect both at 6 hr (P < 0.001) and 24 hr (P < 0.02). Overall, there was an effect of 8-br-cAMP (1 mM; 6 h) on specific mRNAs in cells at both 100-110 (P < 0.001) and 185-200 d GA (P < 0.001). In p5 cells from Day 185-200 GA, there was increased cell proliferation (P < 0.001) in response to estradiol (1 nM; 24 hr). These data suggest that primary fetal uterine cells retain their age-specific and hormone-responsive phenotype under these in vitro conditions.

Estrogen-induced transcription of the progesterone receptor gene does not parallel estrogen receptor occupancy

The activation of the silent endogenous progesterone receptor (PR) gene by 17-beta-estradiol (E2) in cells stably transfected with estrogen receptor (ER) was used as a model system to study the mechanism of E2-induced transcription. The time course of E2-induced PR transcription rate was determined by nuclear run-on assays. No marked effect on specific PR gene transcription rates was detected at 0 and 1 h of E2 treatment. After 3 h of E2 treatment, the PR mRNA synthesis rate increased 2.0- +/- 0.2-fold and continued to increase to 3.5- +/- 0.4-fold by 24 h as compared with 0 h. The transcription rate increase was followed by PR mRNA accumulation. No PR mRNA was detectable at 0, 1, and 3 h of E2 treatment. PR mRNA accumulation was detected at 6 h of E2 treatment and continued to accumulate until 18 h, the longest time point examined. Interestingly, this slow and gradual transcription rate increase of the endogenous PR gene did not parallel binding of E2 to ER, which was maximized within 30 min. Furthermore, the E2-ER level was down-regulated to 15% at 3 h as compared with 30 min of E2 treatment and remained low at 24 h of E2 exposure. These paradoxical observations indicate that E2-induced transcription activation is more complicated than just an association of the occupied ER with the transcription machinery.

Characterization of a nontumorigenic human breast epithelial cell line stably transfected with the human estrogen receptor (ER) cDNA

Estrogens play an important role in breast cancer and the effect of estrogen on growth of breast cancer cells has been extensively studied. However, only little information is available about the response of normal breast epithelial cells to estrogen, mainly due to the difficulties in establishing estrogen receptor (ER)-positive human breast epithelial cells in culture. We have stably transfected the human estrogen receptor (hER) wt cDNA into the ER-negative, spontaneously immortalized human breast epithelial cell line, HMT-3522S1, in order to develop a model for studying the effect of estrogen on nonmalignant human breast epithelial cells. Characterization of the transfected clone F9 confirmed incorporation of the estrogen receptor gene in the genome, expression of hER mRNA and hER protein. However, proliferation of F9 cells was inhibited by both estradiol (E2) and tamoxifen, whereas the pure antiestrogen ICI 182,780 had no effect on cell proliferation. This seems paradoxical since E2 stimulated the expression of the endogenous genes, TGF-alpha, cathepsin D, and alpha1-antitrypsin. In breast cancer cell lines, high expression of these genes is correlated to estrogen-stimulated cell proliferation. The spontaneously immortalized HMT-3522S1 cells transfected with wt ER cDNA behave similarly to cell lines from nonmalignant breast tissue immortalized by carcinogens and transfected with mutated ER cDNA as described by others. The discrepancy between growth inhibition and induction of positive growth factors by E2 indicates that either ER-positive nonmalignant breast epithelial cells are growth-inhibited by E2 in contrast to malignant cells or that introduction of the ER into ER-negative cells is not sufficient for restoring "normal' estrogen responsiveness.

Immunolocalization of estrogen receptor protein in the mouse blastocyst during normal and delayed implantation

We previously showed that estrogen receptor (ER) mRNA is present in preimplantation mouse embryos. The apparent synthesis of ER mRNA by the blastocyst at the time of implantation when estrogen is required was of special interest. A demonstration of the presence of ER protein would support the idea that estrogen can act directly on the embryo. The mouse embryo at the blastocyst stage is differentiated into two cell types, the trophectoderm and the inner cell mass. To determine whether ER mRNA is translated into ER protein and its cell-specific distribution, immunocytochemical analyses were performed in mouse blastocysts. ER protein was detected in all cell types of the normal, dormant, or activated blastocyst. To trace the fate of ER in these cell types, immunocytochemistry was performed in implanting blastocysts and early egg cylinder stage embryos developed in culture. Again, ER was detected in all cells of the implanting blastocyst. At the early egg cylinder stage, continued expression of ER was observed in cells derived from the inner cell mass or the trophoblast. In trophoblast giant cells, ER was concentrated in small regions of the nucleus, possibly the nucleoli, which was similar to that observed in dormant and activated blastocysts. The embryonic expression of ER at such early stages in a broad array of cells suggests that ER may have a general role during early development.

Pituitary-specific chromatin structure of the rat prolactin distal enhancer element

The location of target DNA sequences within chromatin may affect the ability of trans-acting factors to bind cis-elements and regulate gene transcription. To examine the effect of chromatin structure on the ability of the estrogen-estrogen receptor complex (E2R) to bind its respective DNA binding element within the rat prolactin (rPRL) gene and modulate rPRL gene expression, we have developed cell lines derived from the rPRL-expressing (rPRL+) rat pituitary cell line GH3 and the rPRL-non- expressing (rPRL-) rat embryo fibroblast cell line Rat1. These cell lines contain mini-chromosomes composed of the 5' upstream regulatory region of the rPRL gene driving expression of a reporter gene, Tn5, within a bovine papillomavirus (BPV) vector. The rPRL-Tn5 gene retains the characteristics of cell-specific expression and estrogen inducibility of transcription displayed by the endogenous rPRL gene. The distal enhancer region, which contains an estrogen response element, was found to exist in a nucleosome-free region in pituitary-derived cells even in the absence of estrogen. In contrast, the rPRL distal enhancer in fibroblast cells was found to be randomly packaged into nucleosomes. These results indicate that DNA sequence is not sufficient to position nucleosomes in the rPRL gene. Rather, it suggests that cell-specific factors are present in pituitary cells that modify the chromatin structure of the distal enhancer which allow E2R to bind to its response element.

Ectopic expression of thyrotropin releasing hormone (TRH) receptors in liver modulates organ function to regulate blood glucose by TRH

Maintenance of blood glucose by the liver is normally initiated by extracellular regulatory molecules such as glucagon and vasopressin triggering specific hepatocyte receptors to activate the cAMP or phosphoinositide signal transduction pathways, respectively. We now show that the normal ligand-receptor regulators of blood glucose in the liver can be bypassed using an adenovirus vector expressing the mouse pituitary thyrotropin releasing hormone receptor (TRHR) cDNA ectopically in rat liver in vivo. The ectopically expressed TRHR links to the phosphoinositide pathway, providing a means to regulate liver function with TRH, an extracellular ligand that does not normally affect hepatic function. Administration of TRH to these animals activates the phosphoinositide pathway, resulting in a sustained rise in blood glucose. It should be possible to use this general strategy to modulate the differentiated functions of target organs in a wide variety of pathologic states.

Estrogen response in the hFOB 1.19 human fetal osteoblastic cell line stably transfected with the human estrogen receptor gene

The gene coding for the human wild-type estrogen receptor (ER) was stably transfected into the human fetal osteoblastic cell line hFOB 1.19, a clonal cell line which is conditionally immortilized with a temperature sensitive mutant of SV40 large T antigen (tsA58). Five subclones were obtained which express various levels of ER mRNA and protein. The subclone with the highest level of functional (nuclear bound) ER, hFOB/ER9, contained 3,931 (+/- 1,341) 17beta-estradiol molecules bound/nucleus as determined by the nuclear binding (NB) assay. Using the dextran coated charcoal (DCC) method, the level of total cytosolic ER measured was 204 (+/- 2) fmol/mg protein. This subclone was examined further for estradiol (E2) responsiveness. The ER expressed in hFOB/ER9 cells was shown to be functional using a transiently transfected ERE-TK-luciferase construct. Expression of luciferase from this construct increased approximately 25-fold in hFOB/ER9 cells following 10(-9)M E2 treatment. This effect on ERE-TK-luciferase expression was both dose and steroid dependant. Further, treatment of hFOB/ER9 cells with 10(-9)M E2 resulted in a 2.5-4.0-fold increase in endogenous progesterone receptor (PR) levels detected by steroid binding assays, and a noticeable increase in both the A and B forms of PR by western blot assay. The establishment of this estrogen responsive human osteoblastic cell line should provide an excellent model system for the study of estrogen action on osteoblast function.

The role of estrogen receptor in modulation of chromatin conformation in the 5' flanking region of the rat prolactin gene

To determine whether the estrogen receptor (ER) has a role in the modification of chromatin structure, we developed cell lines to model discrete stages in the estrogen response. Each cell line carries a population of stably expressed papillomavirus-based minichromosomes containing the 5' flanking region of the rat prolactin gene. We examined ER effects at the distal enhancer domain of the rat prolactin promoter, using DNaseI to probe for alterations of the nucleoprotein complex. Within 1 h after the start of estrogen treatment, modifications in the chromatin state of the distal enhancer region were detected in a pituitary-derived, permissive cell line (GH3G1J). In rat-1 fibroblast cell lines that maintain the same stably expressed papillomavirus-based minichromosomes in the absence of ER or pituitary-specific transcription factors (Rat-1.2A2; non-permissive), no estrogen-induced modifications in the chromatin state were detected at 1 or 24 h. In rat-1 fibroblast cell lines that also contained ectopically expressed, functional ER (Rat-1 + ER.8A1), no estrogen-induced modifications in the chromatin state were detected at 1 h, but a 24 h a specific modification in the local structure was induced. These data support a model in which the ER interacts with chromatin to modify local structure in such a way as to induce a permissive state for interactions of transcription factors necessary for hormone-induced activation of gene transcription.

Estrogen action in target cells: selective requirements for activation of different hormone response elements

RENE1 cells, an estrogen receptor positive rat uterine endometrial cell line immortalized with the E1A oncogene, were analyzed for the presence of estrogen-dependent signal transduction pathways using the induction of transfected as well as endogenous genes. RENE1 cells express the estrogen receptor as analyzed by Northern blots and ligand binding assays (40 fmoles/mg protein). The receptor system appears functional, based on the induction of reporter constructs containing the consensus estrogen response element (ERE) in transient transfection assays and alterations in endogenous transcripts visualized by utilizing differential display methodology. However, neither transfected repoter constructs containing the c-fos ERE, nor the endogenous c-fos, c-jun, or c-myc genes are induced by estrogens in these cells despite being induced by estrogens in the uterus in vivo. In addition, estradiol did not induce endogenous c-fos expression or the activity of CAT reporters containing the c-fos ERE in a stable transfectant of RENE1 cells with a 3-fold elevation in estrogen receptor content. Under identical conditions, TPA and serum rapidly induce c-fos transcription in RENE1 cells, indicating that the lack of inducibility by estradiol is not due to a general inhibitor of transcription of these genes. These results suggest that RENE1 cells lack factors present in normal uterine cells which are required for the estrogenic induction of a specific subset(s) of EREs. These observations support the generally evolving hypothesis that steroid hormones may act through composite response elements via interactions with other transcription factors, in addition to functioning as homodimers at classical palindromic response elements.

Transfection of human estrogen receptor (ER) cDNA into ER-negative mammalian cell lines

Estrogen responsiveness of breast tumors can be correlated with the presence or absence of the estrogen receptor (ER). Breast cancer cells that contain ER are, in general, responsive to stimulation by estrogen both in vivo and in vitro; therefore hormonal control is possible. Breast tumors that lose the ER, and become hormone-independent are refractory to the direct effect of estrogens and antiestrogens. It is therefore of interest to determine whether the re-expression of the ER will be sufficient to make ER-negative cells sensitive to the growth effect of estrogen. Transfection experiments with wild type and mutant ER cDNAs into different mammalian cell lines have been performed to re-establish hormonal control over hormone-independent cells. Paradoxically, introduction of exogenous ER into ER-negative cells and treatment with estrogen leads to growth inhibition rather than growth promotion. The activation of a number of estrogen-regulated genes has been examined in ER-transfectants but gene regulation is often variable. It is clear that the transfection of the ER gene into cells lacking this protein does not simply re-create the native ER-positive phenotype. Studies need to be extended to identify either the transcription factors that interact with ER to cause the negative effects of estrogen indirectly ("squelching") or the precise target genes that cause growth inhibition directly.