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

ERBB3 targeting: A promising approach to overcoming cancer therapeutic resistance

Human epidermal growth factor receptor-3 (ERBB3) is a member of the ERBB receptor tyrosine kinases (RTKs) and is expressed in many malignancies. Along with other ERBB receptors, ERBB3 is associated with regulating normal cell proliferation, apoptosis, differentiation, and survival, and has received increased research attention for its involvement in cancer therapies. ERBB3 expression or co-expression levels have been investigated as predictive factors for cancer prognosis and drug sensitivity. Additionally, the association between the elevated expression of ERBB3 and treatment failure in cancer therapy further established ERBB3-targeting therapy as a crucial therapeutic approach. This review delves into the molecular mechanisms of ERBB3-driven resistance to targeted therapeutics against ERBB2 and EGFR and other signal transduction inhibitors, endocrine therapy, chemotherapy, and radiotherapy. Using preclinical and clinical evidence, we synthesise and explicate how various aspects of aberrant ERBB3 activities-such as compensatory activation, signal crosstalk interactions, dysregulation in the endocytic pathway, mutations, ligand-independent activation, intrinsic kinase activity, and homodimerisation-can lead to resistance development and/or treatment failures. Several ERBB3-directed monoclonal antibodies, bispecific antibodies, and the emerging antibody-drug conjugate demonstrate encouraging clinical outcomes for improving therapeutic efficacy and overcoming resistance, especially when combined with other anti-cancer approaches. More research efforts are needed to identify appropriate biomarkers tailored for ERBB3-targeted therapies.

Innovative Thiosemicarbazones that Induce Multi-Modal Mechanisms to Down-Regulate Estrogen-, Progesterone-, Androgen- and Prolactin-Receptors in Breast Cancer

The estrogen receptor-α (ER-α) is a key driver of breast cancer (BC) and the ER-antagonist, tamoxifen, is a central pillar of BC treatment. However, cross-talk between ER-α, other hormone and growth factor receptors enables development of de novo resistance to tamoxifen. Herein, we mechanistically dissect the activity of a new class of anti-cancer agents that inhibit multiple growth factor receptors and down-stream signaling for the treatment of ER-positive BC. Using RNA sequencing and comprehensive protein expression analysis, we examined the activity of di-2-pyridylketone-4,4-dimethyl-3-thiosemicarbazone (Dp44mT) and di-2-pyridylketone-4-cyclohexyl-4-methyl-3-thiosemicarbazone (DpC), on the expression and activation of hormone and growth factor receptors, co-factors, and key resistance pathways in ER-α-positive BC. DpC differentially regulated 106 estrogen-response genes, and this was linked to decreased mRNA levels of 4 central hormone receptors involved in BC pathogenesis, namely ER, progesterone receptor (PR), androgen receptor (AR), and prolactin receptor (PRL-R). Mechanistic investigation demonstrated that due to DpC and Dp44mT binding metal ions, these agents caused a pronounced decrease in ER-α, AR, PR, and PRL-R protein expression. DpC and Dp44mT also inhibited activation and down-stream signaling of the epidermal growth factor (EGF) family receptors, and expression of co-factors that promote ER-α transcriptional activity, including SRC3, NF-κB p65, and SP1. In vivo, DpC was highly tolerable and effectively inhibited ER-α-positive BC growth. Through bespoke, non-hormonal, multi-modal mechanisms, Dp44mT and DpC decrease the expression of PR, AR, PRL-R, and tyrosine kinases that act with ER-α to promote BC, constituting an innovative therapeutic approach.

ERβ1 Sensitizes and ERβ2 Desensitizes ERα-Positive Breast Cancer Cells to the Inhibitory Effects of Tamoxifen, Fulvestrant and Their Combination with All-Trans Retinoic Acid

Adjuvant endocrine therapy (AET) is the treatment of choice for early-stage estrogen receptor alpha (ERα)-positive breast cancer (BC). However, almost 40% of tamoxifen-treated cases display no response or a partial response to AET, thus increasing the need for new treatment options and strong predictors of the therapeutic response of patients at high risk of relapse. In addition to ERα, BC research has focused on ERβ1 and ERβ2 (isoforms of ERβ), the second ER isotype. At present, the impact of ERβ isoforms on ERα-positive BC prognosis and treatment remains elusive. In the present study, we established clones of MCF7 cells constitutively expressing human ERβ1 or ERβ2 and investigated their role in the response of MCF7 cells to antiestrogens [4-hydroxytamoxifen (OHΤ) and fulvestrant (ICI182,780)] and retinoids [all-trans retinoic acid (ATRA)]. We show that, compared to MCF7 cells, MCF7-ERβ1 and MCF7-ERβ2 cells were sensitized and desensitized, respectively, to the antiproliferative effect of the antiestrogens, ATRA and their combination and to the cytocidal effect of the combination of OHT and ATRA. Analysis of the global transcriptional changes upon OHT-ATRA combinatorial treatment revealed uniquely regulated genes associated with anticancer effects in MCF7-ERβ1 cells and cancer-promoting effects in MCF7-ERβ2 cells. Our data are favorable to ERβ1 being a marker of responsiveness and ERβ2 being a marker of resistance of MCF7 cells to antiestrogens alone and in combination with ATRA.

Anticancer or carcinogenic? The role of estrogen receptor β in breast cancer progression

Estrogen receptor β (ERβ) is closely related to breast cancer (BC) progression. Traditional concepts regard ERβ as a tumor suppressor. As studies show the carcinogenic effect of ERβ, some people have come to a new conclusion that ERβ serves as a tumor suppressor in estrogen receptor α (ERα)-positive breast cancer, while it is a carcinogen in ERα-negative breast cancer. However, we re-examine the role of ERβ and find this conclusion to be misleading based on the last decade's research. A large number of studies have shown that ERβ plays an anticancer role in both ERα-positive and ERα-negative breast cancers, and its carcinogenicity does not depend solely on the presence of ERα. Herein, we review the anticancer and oncogenic effects of ERβ on breast cancer progression in the past ten years, discuss the mechanism respectively, analyze the main reasons for the inconsistency and update ERβ selective ligand library. We believe a detailed and continuously updated review will help correct the one-sided understanding of ERβ, promoting ERβ-targeted breast cancer therapy.

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

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

Polyamine Oxidase Expression Is Downregulated by 17β-Estradiol via Estrogen Receptor 2 in Human MCF-7 Breast Cancer Cells

Polyamine levels decrease with menopause; however, little is known about the mechanisms regulated by menopause. In this study, we found that among the genes involved in the polyamine pathway, polyamine oxidase (PAOX) mRNA levels were the most significantly reduced by treatment with 17β-estradiol in estrogen receptor (ESR)-positive MCF-7 breast cancer cells. Treatment with 17β-estradiol also reduced the PAOX protein levels. Treatment with selective ESR antagonists and knockdown of ESR members revealed that estrogen receptor 2 (ESR2; also known as ERβ) was responsible for the repression of PAOX by 17β-estradiol. A luciferase reporter assay showed that 17β-estradiol downregulates PAOX promoter activity and that 17β-estradiol-dependent PAOX repression disappeared after deletions (−3126/−2730 and −1271/−1099 regions) or mutations of activator protein 1 (AP-1) binding sites in the PAOX promoter. Chromatin immunoprecipitation analysis showed that ESR2 interacts with AP-1 bound to each of the two AP-1 binding sites. These results demonstrate that 17β-estradiol represses PAOX transcription by the interaction of ESR2 with AP-1 bound to the PAOX promoter. This suggests that estrogen deficiency may upregulate PAOX expression and decrease polyamine levels.

Hormonal and Genetic Regulatory Events in Breast Cancer and Its Therapeutics: Importance of the Steroidogenic Acute Regulatory Protein

Estrogen promotes the development and survival of the majority of breast cancers (BCs). Aromatase is the rate-limiting enzyme in estrogen biosynthesis, and it is immensely expressed in both cancerous and non-cancerous breast tissues. Endocrine therapy based on estrogen blockade, by aromatase inhibitors, has been the mainstay of BC treatment in post-menopausal women; however, resistance to hormone therapy is the leading cause of cancer death. An improved understanding of the molecular underpinnings is the key to develop therapeutic strategies for countering the most prevalent hormone receptor positive BCs. Of note, cholesterol is the precursor of all steroid hormones that are synthesized in a variety of tissues and play crucial roles in diverse processes, ranging from organogenesis to homeostasis to carcinogenesis. The rate-limiting step in steroid biosynthesis is the transport of cholesterol from the outer to the inner mitochondrial membrane, a process that is primarily mediated by the steroidogenic acute regulatory (StAR) protein. Advances in genomic and proteomic technologies have revealed a dynamic link between histone deacetylases (HDACs) and StAR, aromatase, and estrogen regulation. We were the first to report that StAR is abundantly expressed, along with large amounts of 17β-estradiol (E2), in hormone-dependent, but not hormone-independent, BCs, in which StAR was also identified as a novel acetylated protein. Our in-silico analyses of The Cancer Genome Atlas (TCGA) datasets, for StAR and steroidogenic enzyme genes, revealed an inverse correlation between the amplification of the StAR gene and the poor survival of BC patients. Additionally, we reported that a number of HDAC inhibitors, by altering StAR acetylation patterns, repress E2 synthesis in hormone-sensitive BC cells. This review highlights the current understanding of molecular pathogenesis of BCs, especially for luminal subtypes, and their therapeutics, underlining that StAR could serve not only as a prognostic marker, but also as a therapeutic candidate, in the prevention and treatment of this life-threatening disease.

Therapeutic Strategies and Potential Actions of Female Sex Steroid Hormones and Their Receptors in Colon Cancer Based on Preclinical Studies

Several epidemiological studies have reported that the use of female sex steroid hormones could reduce the risk of colon cancer (CRC). This review summarizes the available data related to estradiol (E2) and progesterone (P4) single and dual treatments in CRC male and female in vitro and in vivo models, mainly from preclinical studies, alongside their potential molecular mechanisms. Most of the studies showed that E2 exogenous treatment and/or reactivation of its beta receptor (ERβ) significantly inhibited cell proliferation, induced cell cycle arrest, and promoted apoptosis by modulating several molecular pathways. Likewise, the inhibition of ERα receptors produced similar antitumorigenic actions, both in vivo and in vitro, suggesting that E2 could have dual opposing roles in CRC that are dependent on the expression profile of its nuclear receptors. The available studies on P4 are scarce, and the results revealed that in vitro and in vivo treatments with natural and synthetic progesterone were also associated with promising tumoricidal actions. Nevertheless, the combination of E2 with P4 showed enhanced anticancer activities compared with their monotherapy protocols in male–female cell lines and animals. Collectively, the studies suggested that the female sex steroid hormones could provide a novel and effective therapeutic strategy against CRC.

Cure and Long-Term Remission Strategies

The majority of virally suppressed individuals will experience rapid viral rebound upon antiretroviral therapy (ART) interruption, providing a strong rationale for the development of cure strategies. Moreover, despite ART virological control, HIV infection is still associated with chronic immune activation, inflammation, comorbidities, and accelerated aging. These effects are believed to be due, in part, to low-grade persistent transcription and trickling production of viral proteins from the pool of latent proviruses constituting the viral reservoir. In recent years there has been an increasing interest in developing what has been termed a functional cure for HIV. This approach entails the long-term, durable control of viral expression in the absence of therapy, preventing disease progression and transmission, despite the presence of detectable integrated proviruses. One such strategy, the block-and-lock approach for a functional cure, proposes the epigenetic silencing of proviral expression, locking the virus in a profound latent state, from which reactivation is very unlikely. The proof-of-concept for this approach was demonstrated with the use of a specific small molecule targeting HIV transcription. Here we review the principles behind the block-and-lock approach and some of the additional strategies proposed to silence HIV expression.

Expression and regulation of estrogen receptor 2 and its coregulators in mouse granulosa cells

The cooperative effects of estrogen and oocyte-derived paracrine factors (ODPFs) play critical roles in the normal development of ovarian follicles; however, the mechanism underlying this cooperation has not been well studied. The present study aimed to determine whether ODPFs affect estrogen signaling by regulating the expression of estrogen receptor (ESR) and its coregulators in mouse granulosa cells. Some transcripts encoding ESR coregulators were differentially expressed between cumulus and mural granulosa cells (MGCs). The transcript levels of ESR coregulators, including nuclear receptor corepressor 1 and activator 2, in cumulus cells were significantly suppressed by ODPFs; however, they increased when cumulus cell-oocyte complexes were treated with the transforming growth factor beta receptor I inhibitor, SB431542. Moreover, MGCs exhibited significantly higher ESR2 protein and transcript levels than those in cumulus cells. ODPFs promoted Esr2 expression in cumulus cells but had no effect on that in MGCs. Overall, regulation of the expression of ESR2 and its coregulators in cumulus cells by oocytes seems to be one of the mechanisms underlying estrogen-oocyte cooperation in well-developed antral follicles in mice.

Estrogen Receptor Bio-Activities Determine Clinical Endocrine Treatment Options in Estrogen Receptor-Positive Breast Cancer

In estrogen receptor positive (ER+) breast cancer therapy, estrogen receptors (ERs) are the major targeting molecules. ER-targeted therapy has provided clinical benefits for approximately 70% of all breast cancer patients through targeting the ERα subtype. In recent years, mechanisms underlying breast cancer occurrence and progression have been extensively studied and largely clarified. The PI3K/AKT/mTOR pathway, microRNA regulation, and other ER downstream signaling pathways are found to be the effective therapeutic targets in ER+ BC therapy. A number of the ER+ (ER+) breast cancer biomarkers have been established for diagnosis and prognosis. The ESR1 gene mutations that lead to endocrine therapy resistance in ER+ breast cancer had been identified. Mutations in the ligand-binding domain of ERα which encoded by ESR1 gene occur in most cases. The targeted drugs combined with endocrine therapy have been developed to improve the therapeutic efficacy of ER+ breast cancer, particularly the endocrine therapy resistance ER+ breast cancer. The combination therapy has been demonstrated to be superior to monotherapy in overall clinical evaluation. In this review, we focus on recent progress in studies on ERs and related clinical applications for targeted therapy and provide a perspective view for therapy of ER+ breast cancer.

Enhanced anti-cancer effects of oestrogen and progesterone co-therapy against colorectal cancer in males

Although ovarian sex steroids could have protective roles against colorectal cancer (CRC) in women, little is currently known about their potential anti-tumorigenic effects in men. Hence, this study measured the therapeutic effects of 17β-oestradiol (E2) and/or progesterone (P4) against azoxymethane-induced CRC in male mice that were divided into (n = 10 mice/group): negative (NC) and positive (PC) controls, E2 (580 µg/Kg/day; five times/week) and P4 (2.9 mg/Kg/day; five times/week) monotherapies, and concurrent (EP) and sequential (E/P) co-therapy groups. Both hormones were injected intraperitoneally to the designated groups for four consecutive weeks. Similar treatment protocols with E2 (10 nM) and/or P4 (20 nM) were also used in the SW480 and SW620 human male CRC cell lines. The PC group showed abundant colonic tumours alongside increased colonic tissue testosterone levels and androgen (AR) and oestrogen (ERα) receptors, whereas E2 and P4 levels with ERβ and progesterone receptor (PGR) decreased significantly compared with the NC group. E2 and P4 monotherapies equally increased ERβ/PGR with p21/Cytochrome-C/Caspase-3, reduced testosterone levels, inhibited ERα/AR and CCND1/survivin and promoted apoptosis relative to the PC group. Both co-therapy protocols also revealed better anti-cancer effects with enhanced modulation of colonic sex steroid hormones and their receptors, with E/P the most prominent protocol. In vitro, E/P regimen showed the highest increases in the numbers of SW480 (2.1-fold) and SW620 (3.5-fold) cells in Sub-G1 phase of cell cycle. The E/P co-therapy also disclosed the lowest percentages of viable SW480 cells (2.8-fold), whilst both co-therapy protocols equally showed the greatest SW620 apoptotic cell numbers (5.2-fold) relative to untreated cells. Moreover, both co-therapy regimens revealed maximal inhibitions of cell cycle inducers, cell survival markers, and AR/ERα alongside the highest expression of cell cycle suppressors, pro-apoptotic molecules, and ERβ/PGR in both cell lines. In conclusion, CRC was associated with abnormal levels of colonic sex steroid hormones alongside aberrant protein expression of their receptors. While the anti-cancer effects of E2 and P4 monotherapies were equal, their combination protocols showed boosted tumoricidal actions against CRC in males, possibly by promoting ERβ and PGR-mediated androgen deprivation together with inhibition of ERα-regulated oncogenic pathways.

Lipedema and the Potential Role of Estrogen in Excessive Adipose Tissue Accumulation

Lipedema is a painful fat disorder that affects ~11% of the female population. It is characterized by bilateral, disproportionate accumulation of subcutaneous adipose tissue predominantly in the lower body. The onset of lipedema pathophysiology is thought to occur during periods of hormonal fluctuation, such as puberty, pregnancy, or menopause. Although the identification and characterization of lipedema have improved, the underlying disease etiology remains to be elucidated. Estrogen, a key regulator of adipocyte lipid and glucose metabolism, and female-associated body fat distribution are postulated to play a contributory role in the pathophysiology of lipedema. Dysregulation of adipose tissue accumulation via estrogen signaling likely occurs by two mechanisms: (1). altered adipocyte estrogen receptor distribution (ERα/ERß ratio) and subsequent metabolic signaling and/or (2). increased release of adipocyte-produced steroidogenic enzymes leading to increased paracrine estrogen release. These alterations could result in increased activation of peroxisome proliferator-activated receptor γ (PPARγ), free fatty acid entry into adipocytes, glucose uptake, and angiogenesis while decreasing lipolysis, mitochondriogenesis, and mitochondrial function. Together, these metabolic alterations would lead to increased adipogenesis and adipocyte lipid deposition, resulting in increased adipose depot mass. This review summarizes research characterizing estrogen-mediated adipose tissue metabolism and its possible relation to excessive adipose tissue accumulation associated with lipedema.

Estrogen-Driven Changes in Immunoglobulin G Fc Glycosylation

Glycosylation within the immunoglobulin G (IgG) Fc region modulates its ability to engage complement and Fc receptors, affording the opportunity to fine-tune effector functions. Mechanisms regulating IgG Fc glycans remain poorly understood. Changes accompanying menarche, menopause, and pregnancy have long implicated hormonal factors. Intervention studies now confirm that estrogens enhance IgG Fc galactosylation, in females and also in males, defining the first pathway modulating Fc glycans and thereby a new link between sex and immunity. This mechanism may participate in fetal-maternal immunity, antibody-mediated inflammation, and other aspects of age- and sex-specific immune function. Here we review the changes affecting the IgG Fc glycome from childhood through old age, the evidence establishing a role for estrogens, and research directions to uncover associated mechanisms that may inform therapeutic intervention.

Methylation of ERβ 5'-untranslated region attenuates its inhibitory effect on ERα gene transcription and promotes the initiation and progression of papillary thyroid cancer

Normal thyroid tissue displays a prevalent expression of ERβ than ERα, which drastically turns upside down in the initiation and progression of papillary thyroid cancer (PTC). The underlying molecular mechanism of this phenomenon remains unclear. Here, we demonstrated that ERα and ERβ were coexpressed in human thyroid tissues and cells. ERα mRNA (A-1) and ERβ mRNA (0N-1), transcribed from Promoter A of ERα gene and Promoter 0N of ERβ gene, respectively, were the major mRNA isoforms which mainly contributed to total ERα mRNA and total ERβ mRNA in human thyroid-derived cell lines and tissues. The expression levels of ERα mRNA (A-1) and total ERα mRNA were gradually increased, and those of ERβ mRNA (0N-1) and total ERβ mRNA were decreased by degree in the initiation and progression of PTC. No aberrant DNA methylation of ERα 5'-untranslated region was involved in its up-regulation; however, aberrant DNA methylation in Promoter 0N and Exon 0N of ERβ gene was found to be involved in its down-regulation in the initiation and progression of PTC. ERβ can repress ERα gene transcription via recruitment of NCoR and displacement of RNA polymerase II at the Sp1 site in ERα Promoter A-specific region in thyroid-derived cells. It is suggested that DNA methylation of CpG islands in Promoter 0N and Exon 0N of ERβ gene leads to a decreased ERβ gene expression, which attenuates its inhibitory effect on ERα gene transcription and results in an increased ERα gene expression, cell proliferation, initiation, and progression of PTC.

Abnormal Long Non-Coding RNAs Expression Patterns Have the Potential Ability for Predicting Survival and Treatment Response in Breast Cancer

Abnormal long non-coding RNAs (lncRNAs) expression has been documented to have oncogene or tumor suppressor functions in the development and progression of cancer, emerging as promising independent biomarkers for molecular cancer stratification and patients’ prognosis. Examining the relationship between lncRNAs and the survival rates in malignancies creates new scenarios for precision medicine and targeted therapy. Breast cancer (BRCA) is a heterogeneous malignancy. Despite advances in its molecular classification, there are still gaps to explain in its multifaceted presentations and a substantial lack of biomarkers that can better predict patients’ prognosis in response to different therapeutic strategies. Here, we performed a re-analysis of gene expression data generated using cDNA microarrays in a previous study of our group, aiming to identify differentially expressed lncRNAs (DELncRNAs) with a potential predictive value for response to treatment with taxanes in breast cancer patients. Results revealed 157 DELncRNAs (90 up- and 67 down-regulated). We validated these new biomarkers as having prognostic and predictive value for breast cancer using in silico analysis in public databases. Data from TCGA showed that compared to normal tissue, MIAT was up-regulated, while KCNQ1OT1, LOC100270804, and FLJ10038 were down-regulated in breast tumor tissues. KCNQ1OT1, LOC100270804, and FLJ10038 median levels were found to be significantly higher in the luminal subtype. The ROC plotter platform results showed that reduced expression of these three DElncRNAs was associated with breast cancer patients who did not respond to taxane treatment. Kaplan–Meier survival analysis revealed that a lower expression of the selected lncRNAs was significantly associated with worse relapse-free survival (RFS) in breast cancer patients. Further validation of the expression of these DELncRNAs might be helpful to better tailor breast cancer prognosis and treatment.

[Estradiol activates ERK phosphorylation by binding to ERβ to inhibit proliferation and promote apoptosis of human chondrocytes]

OBJECTIVE

To explore the effect of estradiol (E2) binding to its receptor ERβ on the proliferation and apoptosis of C28I2 cells.

OBJECTIVE

We cloned the sequence of ESR2 into a recombinant adenovirus plasmid (pAd-ESR2) and packaged the plasmid in HEK293 cells. Normal human chondrocyte C28I2 cells were transfected with Ad-ESR2 or small interfering RNA targeting ESR2-siRNA (ESR2-siRNA), and the effects of treatment with DMSO or E2 on the expression of the proteins associated with endoplasmic reticulum (ER) stress and cell apoptosis were determined using Western blotting. qRT-PCR was used to detect the expressions of proliferation-related marker genes, and an EdU kit and flow cytometry were used to assess cell proliferation and apoptosis. We also tested the effects of U0126 (an ERK pathway inhibitor) and E2, alone or in combination, on ER stress, apoptosis and the ERK signaling pathway in C28I2 cells infected with Ad-ESR2 using Western blotting.

OBJECTIVE

Overexpression of Ad-ESR2 in C28I2 cells significantly promoted the expressions of IRE1α, PERK, XBP1s, and cleaved caspase-12, inhibited proliferation related marker genes PCNA, cyclin B1, cyclin D1, and decreased the level of ERK phosphorylation following E2 treatment (all P < 0.05). Interference of ESR2 caused significant reduction in the expressions of ER stress-related proteins and apoptosis-related proteins, up-regulated the genes related to cell proliferation, and increased intracellular pERK/ERK ratio in C28I2 cells. The effect of E2 binding to ERβ, which promoted the expressions of ER stress associated proteins and apoptosis related proteins, was obviously antagonized by treatment of the cells with U0126.

OBJECTIVE

The binding of E2 to ERβ promotes ER stress and apoptosis in human chondrocytes by activating ERK pathway phosphorylation inhibit cell proliferation.

Balance between Retroviral Latency and Transcription: Based on HIV Model

The representative of the Lentivirus genus is the human immunodeficiency virus type 1 (HIV-1), the causative agent of acquired immunodeficiency syndrome (AIDS). To date, there is no cure for AIDS because of the existence of the HIV-1 reservoir. HIV-1 infection can persist for decades despite effective antiretroviral therapy (ART), due to the persistence of infectious latent viruses in long-lived resting memory CD4+ T cells, macrophages, monocytes, microglial cells, and other cell types. However, the biology of HIV-1 latency remains incompletely understood. Retroviral long terminal repeat region (LTR) plays an indispensable role in controlling viral gene expression. Regulation of the transcription initiation plays a crucial role in establishing and maintaining a retrovirus latency. Whether and how retroviruses establish latency and reactivate remains unclear. In this article, we describe what is known about the regulation of LTR-driven transcription in HIV-1, that is, the cis-elements present in the LTR, the role of LTR transcription factor binding sites in LTR-driven transcription, the role of HIV-1-encoded transactivator protein, hormonal effects on virus transcription, impact of LTR variability on transcription, and epigenetic control of retrovirus LTR. Finally, we focus on a novel clustered regularly interspaced short palindromic repeats-associated protein 9 (CRISPR/dCas9)-based strategy for HIV-1 reservoir purging.

Estrogen Receptor Beta (ERβ): A Ligand Activated Tumor Suppressor

Estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ) belong to a superfamily of nuclear receptors called steroid hormone receptors, which, upon binding ligand, dimerize and translocate to the nucleus where they activate or repress the transcription of a large number of genes, thus modulating critical physiologic processes. ERβ has multiple isoforms that show differing association with prognosis. Expression levels of the full length ERβ1 isoform are often lower in aggressive cancers as compared to normal tissue. High ERβ1 expression is associated with improved overall survival in women with breast cancer. The promise of ERβ activation, as a potential targeted therapy, is based on concurrent activation of multiple tumor suppressor pathways with few side effects compared to chemotherapy. Thus, ERβ is a nuclear receptor with broad-spectrum tumor suppressor activity, which could serve as a potential treatment target in a variety of human cancers including breast cancer. Further development of highly selective agonists that lack ERα agonist activity, will be necessary to fully harness the potential of ERβ.

Regulation of Expression and Latency in BLV and HTLV

Human T-lymphotrophic virus type 1 (HTLV-1) and Bovine leukemia virus (BLV) belong to the Deltaretrovirus genus. HTLV-1 is the etiologic agent of the highly aggressive and currently incurable cancer adult T-cell leukemia (ATL) and a neurological disease HTLV-1-associated myelopathy (HAM)/tropical spastic paraparesis (TSP). BLV causes neoplastic proliferation of B cells in cattle: enzootic bovine leucosis (EBL). Despite the severity of these conditions, infection by HTLV-1 and BLV appear in most cases clinically asymptomatic. These viruses can undergo latency in their hosts. The silencing of proviral gene expression and maintenance of latency are central for the establishment of persistent infection, as well as for pathogenesis in vivo. In this review, we will present the mechanisms that control proviral activation and retroviral latency in deltaretroviruses, in comparison with other exogenous retroviruses. The 5′ long terminal repeats (5′-LTRs) play a main role in controlling viral gene expression. While the regulation of transcription initiation is a major mechanism of silencing, we discuss topics that include (i) the epigenetic control of the provirus, (ii) the cis-elements present in the LTR, (iii) enhancers with cell-type specific regulatory functions, (iv) the role of virally-encoded transactivator proteins, (v) the role of repressors in transcription and silencing, (vi) the effect of hormonal signaling, (vii) implications of LTR variability on transcription and latency, and (viii) the regulatory role of non-coding RNAs. Finally, we discuss how a better understanding of these mechanisms may allow for the development of more effective treatments against Deltaretroviruses.

The role of estrogen receptor beta in breast cancer

Breast cancer, a malignant tumor originating from mammary epithelial tissue, is the most common cancer among women worldwide. Challenges facing the diagnosis and treatment of breast cancer necessitate the search for new mechanisms and drugs to improve outcomes. Estrogen receptor (ER) is considered to be important for determining the diagnosis and treatment strategy. The discovery of the second estrogen receptor, ERβ, provides an opportunity to understand estrogen action. The emergence of ERβ can be traced back to 1996. Over the past 20 years, an increasing body of evidence has implicated the vital effect of ERβ in breast cancer. Although there is controversy among scholars, ERβ is generally thought to have antiproliferative effects in disease progression. This review summarizes available evidence regarding the involvement of ERβ in the clinical treatment and prognosis of breast cancer and describes signaling pathways associated with ERβ. We hope to highlight the potential of ERβ as a therapeutic target.

Leptin Signaling Contributes to Aromatase Inhibitor Resistant Breast Cancer Cell Growth and Activation of Macrophages

Obesity represents a risk factor for breast cancer development and therapy resistance, but the molecular players underling these links are unclear. Here, we identify a role for the obesity-cytokine leptin in sustaining aromatase inhibitor (AI) resistant growth and progression in breast cancer. Using as experimental models MCF-7 breast cancer cells surviving long-term treatment with the AI anastrozole (AnaR) and Ana-sensitive counterparts, we found that AnaR cells expressed higher levels of leptin and its receptors (ObR) along with a constitutive activation of downstream effectors. Accordingly, leptin signaling inhibition reduced only AnaR cell growth and motility, highlighting the existence of an autocrine loop in mechanisms governing drug-resistant phenotypes. In agreement with ObR overexpression, increasing doses of leptin were able to stimulate to a greater extent growth and migration in AnaR than sensitive cells. Moreover, leptin contributed to enhanced crosstalk between AnaR cells and macrophages within the tumor microenvironment. Indeed, AnaR, through leptin secretion, modulated macrophage profiles and increased macrophage motility through CXCR4 signaling, as evidenced by RNA-sequencing, real-time PCR, and immunoblotting. Reciprocally, activated macrophages increased AnaR cell growth and motility in coculture systems. In conclusion, acquired AI resistance is accompanied by the development of a leptin-driven phenotype, highlighting the potential clinical benefit of targeting this cytokine network in hormone-resistant breast cancers, especially in obese women.

Phosphodiesterase 5 (PDE5) Is Highly Expressed in Cancer-Associated Fibroblasts and Enhances Breast Tumor Progression

The overexpression of phosphodiesterase (PDE) 5 is frequently found in various human cancers, such as those of the breast. However, PDE5’s role in the tumor microenvironment is still unknown. As PDE5 represents a high-value therapeutic target, we investigated whether the expression and function of PDE5 in breast cancer-associated fibroblasts (CAFs) may be clinically relevant to malignant progression. PDE5 expression was increased in human breast cancer stroma compared with normal stroma and was correlated to a shorter overall survival. Treatment of CAFs, isolated from breast tumor biopsies, with selective PDE5 inhibitors inhibited their proliferation, motility, and invasiveness, and negatively controlled tumor–stroma interactions in both ‘in vitro’ and ‘in vivo’ models. PDE5 stable overexpression transformed immortalized mouse embryonic fibroblasts (MEFs) towards an activated fibroblast phenotype, impacting their intrinsic characteristics and paracrine effects on breast cancer cell growth and migration through an enhanced production of the C-X-C motif chemokine 16 (CXCL16). On the other hand, CAF exposure to PDE5 inhibitors was associated with reduced CXCL16 expression and secretion. Importantly, CXCL16 levels in breast cancer stroma showed a strong correlation with PDE5 levels and poor patient outcomes. In conclusion, PDE5 is overexpressed in breast cancer stroma, enhances the tumor-stimulatory activities of fibroblasts, and impacts clinical outcomes; thus, we propose this enzyme as an attractive candidate for prognosis and a potential target for treatments in breast cancer patients.

Estrogen receptor-1 is a key regulator of HIV-1 latency that imparts gender-specific restrictions on the latent reservoir

The molecular mechanisms leading to the creation and maintenance of the latent HIV reservoir remain incompletely understood. Unbiased shRNA screens showed that the estrogen receptor acts as a potent repressor of proviral reactivation in T cells. Antagonists of ESR-1 activate latent HIV-1 proviruses while agonists, including β-estradiol, potently block HIV reactivation. Using a well-matched set of male and female donors, we found that ESR-1 plays an important role in regulating HIV transcription in both sexes. However, women are much more responsive to estrogen and appear to harbor smaller inducible RNA reservoirs. Accounting for the impact of estrogen on HIV viral reservoirs will therefore be critical for devising curative therapies for women, a group representing 51% of global HIV infections.

Unbiased shRNA library screens revealed that the estrogen receptor-1 (ESR-1) is a key factor regulating HIV-1 latency. In both Jurkat T cells and a Th17 primary cell model for HIV-1 latency, selective estrogen receptor modulators (SERMs, i.e., fulvestrant, raloxifene, and tamoxifen) are weak proviral activators and sensitize cells to latency-reversing agents (LRAs) including low doses of TNF-α (an NF-κB inducer), the histone deacetylase inhibitor vorinostat (soruberoylanilide hydroxamic acid, SAHA), and IL-15. To probe the physiologic relevance of these observations, leukapheresis samples from a cohort of 12 well-matched reproductive-age women and men on fully suppressive antiretroviral therapy were evaluated by an assay measuring the production of spliced envelope (env) mRNA (the EDITS assay) by next-generation sequencing. The cells were activated by T cell receptor (TCR) stimulation, IL-15, or SAHA in the presence of either β-estradiol or an SERM. β-Estradiol potently inhibited TCR activation of HIV-1 transcription, while SERMs enhanced the activity of most LRAs. Although both sexes responded to SERMs and β-estradiol, females showed much higher levels of inhibition in response to the hormone and higher reactivity in response to ESR-1 modulators than males. Importantly, the total inducible RNA reservoir, as measured by the EDITS assay, was significantly smaller in the women than in the men. We conclude that concurrent exposure to estrogen is likely to limit the efficacy of viral emergence from latency and that ESR-1 is a pharmacologically attractive target that can be exploited in the design of therapeutic strategies for latency reversal.

Tissue control of androgen action: The ups and downs of androgen receptor expression

The hormone testosterone plays crucial roles during male development and puberty and throughout life, as an anabolic regulator of muscle and bone structure and function. The actions of testosterone are mediated, primarily, through the androgen receptor, a member of the nuclear receptor superfamily. The androgen receptor gene is located on the X-chromosome and receptor levels are tightly controlled both at the level of transcription of the gene and post-translationally at the protein level. Sp1 has emerged as the major driver of expression of the androgen receptor gene, while auto-regulation by androgens is associated with both positive and negative regulation in a possible cell-selective manner. Research into the networks of positive and negative regulators of the androgen receptor gene are vital in order to understand the temporal and spatial control of receptor levels and the consequences for healthy aging and disease. A clear understanding of the multiple transcription factors participating in regulation of the androgen receptor gene will likely aid in the development and application of hormone therapies to boast or curb receptor activity.

Probing the origin of estrogen receptor alpha inhibition via large-scale QSAR study

Estrogen is an important component for the sustenance of normal physiological functions of the mammary glands, particularly for growth and differentiation. Approximately, two-thirds of breast cancers are positive for estrogen receptor (ERs), which is a predisposing factor for the growth of breast cancer cells. As such, ERα represents a lucrative therapeutic target for breast cancer that has attracted wide interest in the search for inhibitory agents. However, the conventional laboratory processes are cost- and time-consuming. Thus, it is highly desirable to develop alternative methods such as quantitative structure-activity relationship (QSAR) models for predicting ER-mediated endocrine agitation as to simplify their prioritization for future screening. In this study, we compiled and curated a large, non-redundant data set of 1231 compounds with ERα inhibitory activity (pIC50). Using comprehensive validation tests, it was clearly observed that the model utilizing the substructure count as descriptors, performed well considering two objectives: using less descriptors for model development and achieving high predictive performance (R Tr 2 = 0.94, Q CV 2 = 0.73, and Q Ext 2 = 0.73). It is anticipated that our proposed QSAR model may become a useful high-throughput tool for identifying novel inhibitors against ERα.

Estrogen Signaling in ERα-Negative Breast Cancer: ERβ and GPER

Estrogen receptors are important regulators of the growth of breast tumors. Three different receptors for estrogens have been identified in breast tumors, two nuclear receptors, ERα and ERβ, and a G-protein coupled estrogen receptor 1 (GPER) that initiates non-genomic effects of estrogens in the cytosol. Recent findings show that the stimulation of cytoplasmic ERα and ERβ also triggers non-genomic signaling pathways. The treatment of breast cancer with anti-estrogens depends on the presence of ERα. About 40% of all breast cancers, however, do not express ERα. One subgroup of these tumors overexpress Her-2, another important group is designated as triple-negative breast cancer, as they neither express ERα, nor progesterone receptors, nor do they overexpress Her-2. This review addresses the signaling of ERβ and GPER in ERα-negative breast tumors. In addition to the well-established EGF-receptor transactivation pathways of GPER, more recent findings of GPER-dependent activation of FOXO3a, the Hippo-pathway, and HOTAIR-activation are summarized.

The Interaction of PPARα and CYP7B1 with ERα, β Impacted the Occurrence and Development of Intrahepatic Cholestasis in Pregnant Rats

Intrahepatic cholestasis of pregnancy (ICP) is a disorder of bile acid (BA) synthesis, excretion, and metabolism, with systemic accumulation of BAs, which can lead to prematurity, fetal distress, and intrauterine death. Here, we investigate the expression of peroxisome proliferator-activated receptor alpha and cytochrome P450 oxysterol 7alpha-hydroxylase by exposing to 17α-ethynylestradiol with or without the estrogen receptor signaling pathway in pregnant rats with intrahepatic cholestasis. In vivo and in vitro evidences showed that estrogen receptor alpha (ERα) may be the key point of occurrence and development of intrahepatic cholestasis in pregnant rats. Besides, the abnormalities in genes could be reversed by ERα small interfering RNA. Our findings provide the ERα-centered hypothesis on the mechanisms of ICP. New perspectives are emerging for the treatment of estrogen-induced hepatic complication.

Oxytocin receptor DNA methylation in postpartum depression

The oxytocin receptor (OXTR) is a key regulator of stress and anxiety and may be regulated by both psychosocial risk factors and gonadal hormones, making it an attractive candidate for study in postpartum depression (PPD). The objective of this study was to investigate both serum hormone and PPD specific DNA methylation variation in the OXTR. Illumina HM450 microarray data generated in a prospective PPD cohort identified significant associations (P=0.014) with PPD in an intronic region in the OXTR located 4bp proximal to an estrogen receptor (ER) binding region. Pyrosequencing confirmed moderate evidence for an interaction of CpGs in the region with childhood abuse status to mediate PPD. These CpGs located on chr3 at positions 8810078 and 8810069 exhibited significant associations with postpartum depression scores from an independent cohort of 240 women with no prior psychiatric history. Hormone analysis suggested a PPD specific negative correlation of DNA methylation in the region with serum estradiol levels. Estradiol levels and OXTR DNA methylation exhibited a significant interaction to associate with the ratio of allopregnanolone to progesterone. Cumulatively, the data corroborate our previous hypotheses of a PPD specific increased sensitivity of epigenetic reprogramming at estrogen target genes and suggests that OXTR epigenetic variation may be an important mediator of mood relevant neuroactive steroid production.

3-(Dipropylamino)-5-hydroxybenzofuro[2,3-f]quinazolin-1(2H)-one (DPA-HBFQ-1) plays an inhibitory role on breast cancer cell growth and progression

A series of unknown 3-(alkyl(dialkyl)amino)benzofuro[2,3-f]quinazolin-1(2H)-ones 4-17 has been synthesized as new ellipticine analogs, in which the carbazole moiety and the pyridine ring were replaced by a dibenzofuran residue and a pyrimidine ring, respectively. The synthesis of these benzofuroquinazolinones 4-17 was performed in a simple one-pot reaction using 3-aminodibenzofuran or its 2-methoxy derivative, as starting materials. From 3-(dipropylamino)-5-methoxybenzofuro[2,3-f] quinazolin-1(2H)-one (13), we prepared 3-(dipropylamino)-5-hydroxybenzofuro[2,3-f]quinazolin-1(2H)-one (18), referred to as DPA-HBFQ-1. The cytotoxic activities of all the synthesized compounds, tested in different human breast cancer cell lines, revealed that DPA-HBFQ-1 was the most active compound. In particular, the latter was able to inhibit anchorage-dependent and -independent cell growth and to induce apoptosis in estrogen receptor alpha (ERα)-positive and -negative breast cancer cells. It did not affect proliferation and apoptotic responses in MCF-10A normal breast epithelial cells. The observed effects have been ascribed to an enhanced p21(Cip1/WAF1) expression in a p53-dependent manner of tumor suppressor and to a selective inhibition of human topoisomerase II. In addition, DPA-HBFQ-1 exerted growth inhibitory effects also in other cancer cell lines, even though with a lower cytotoxic activity. Our results indicate DPA-HBFQ-1 as a good candidate to be useful as cancer therapeutic agent, particularly for breast cancer.

Impacts of Alternative Splicing Events on the Differentiation of Adipocytes

Alternative splicing was found to be a common phenomenon after the advent of whole transcriptome analyses or next generation sequencing. Over 90% of human genes were demonstrated to undergo at least one alternative splicing event. Alternative splicing is an effective mechanism to spatiotemporally expand protein diversity, which influences the cell fate and tissue development. The first focus of this review is to highlight recent studies, which demonstrated effects of alternative splicing on the differentiation of adipocytes. Moreover, use of evolving high-throughput approaches, such as transcriptome analyses (RNA sequencing), to profile adipogenic transcriptomes, is also addressed.

Estrogen receptor signal in regulation of B cell activation during diverse immune responses

The role of signalling through oestrogen receptors (ERs) in the regulation of B cell activation is an area of growing importance not only in terms protective immunity but also in the determination of the mechanisms of the onset of autoimmune disorders and cancers. The mode of signalling action of this single chain nuclear receptor protein molecule depends on its ability to bind to the promoters of Pax5, HOXC4 and apolipoprotein B RNA-editing enzyme activation-induced cytidine deaminase (AID) genes. ER-mediated transcriptional regulation induces class switch recombination of the immunoglobulin heavy chain variable (VH) to DH-JH genes and somatic hypermutation in developing B cells. The mode of action of ER is associated with BCR-signal pathways that involve the regulator proteins BAFF and APRIL. Additionally, the plasma membrane-bound G protein-coupled oestrogen receptor-1 (GEPR1) directs diverse cell signalling events in B cells that involve the MAPK pathways. These signals are immensely important during progenitor and precursor B cell activation. We have focused our goals on the medicinal aspects of ER-signalling mechanisms and their effects on polyclonal B cell activation.

Nuclear receptor corepressor complexes in cancer: mechanism, function and regulation

Nuclear receptor corepressor (NCoR) and silencing mediator for retinoid and thyroid hormone receptors (SMRT) function as corepressors for diverse transcription factors including nuclear receptors such as estrogen receptors and androgen receptors. Deregulated functions of NCoR and SMRT have been observed in many types of cancers and leukemias. NCoR and SMRT directly bind to transcription factors and nucleate the formation of stable complexes that include histone deacetylase 3, transducin b-like protein 1/TBL1-related protein 1, and G-protein pathway suppressor 2. These NCoR/SMRT-interacting proteins also show deregulated functions in cancers. In this review, we summarize the literature on the mechanism, regulation, and function of the core components of NCoR/SMRT complexes in the context of their involvement in cancers and leukemias. While the current studies support the view that the corepressors are promising targets for cancer treatment, elucidation of the mechanisms of corepressors involved in individual types of cancers is likely required for effective therapy.

Differential regulation of estrogen receptors α and β by 4-(E)-{(4-hydroxyphenylimino)-methylbenzene,1,2-diol}, a novel resveratrol analog

Breast cancer is the second leading cause of death among women in the United States. Estrogens have been implicated as major risk factors in the development of breast neoplasms. Recent epidemiologic studies have suggested a protective role of phytoestrogens in prevention of breast and other cancers. Resveratrol, a naturally occurring phytoestrogen found notably in red grapes, berries and peanuts, has been shown to possess potent anti-cancer properties. However, the poor efficacy of resveratrol has prevented its use in a clinical setting. In order to improve the efficacy of resveratrol, we have synthesized a small combinatorial library of azaresveratrol analogs and tested them for their ability to inhibit the growth of breast cancer cell lines. We have recently shown that one of the synthesized analogs, 4-(E)-{(4-hydroxyphenylimino)-methylbenzene,1,2-diol} (HPIMBD), has better anti-cancer properties than resveratrol. The objective of this study was to investigate the differential regulation of estrogen receptors (ERs) α and β as a potential mechanism of inhibition of breast cancer by HPIMBD. Estrogen receptors α and β have been shown to have opposing roles in cellular proliferation. Estrogen receptor α mediates the proliferative responses of estrogens while ERβ plays an anti-proliferative and pro-apoptotic role. We demonstrate that HPIMBD significantly induces the expression of ERβ and inhibits the expression of ERα. HPIMBD also inhibits the protein expression levels of oncogene c-Myc and cell cycle protein cyclin D1, genes downstream to ERα and important regulators of cell cycle, and cellular proliferation. HPIMBD significantly induces protein expression levels of tumor suppressors p53 and p21 in MCF-7 cells. Additionally, HPIMBD inhibits c-Myc in an ERβ-dependent fashion in MCF-10A and ERβ1-transfected MDA-MB-231 cells, suggesting regulation of ERs as an important upstream mechanism of this novel compound. Molecular docking studies confirm higher affinity for binding of HPIMBD in the ERβ cavity. Thus, HPIMBD, a novel azaresveratrol analog may inhibit the proliferation of breast cancer cells by differentially modulating the expressions of ERs α and β.

Antenatal prediction of postpartum depression with blood DNA methylation biomarkers

Postpartum depression (PPD) affects ∼10-18% of women in the general population and results in serious consequences to both the mother and offspring. We hypothesized that predisposition to PPD risk is due to an altered sensitivity to estrogen-mediated epigenetic changes that act in a cell autonomous manner detectable in the blood. We investigated estrogen-mediated epigenetic reprogramming events in the hippocampus and risk to PPD using a cross-species translational design. DNA methylation profiles were generated using methylation microarrays in a prospective sample of the blood from the antenatal period of pregnant mood disorder patients who would and would not develop depression postpartum. These profiles were cross-referenced with syntenic locations exhibiting hippocampal DNA methylation changes in the mouse responsive to long-term treatment with 17β-estradiol (E2). DNA methylation associated with PPD risk correlated significantly with E2-induced DNA methylation change, suggesting an enhanced sensitivity to estrogen-based DNA methylation reprogramming exists in those at risk for PPD. Using the combined mouse and human data, we identified two biomarker loci at the HP1BP3 and TTC9B genes that predicted PPD with an area under the receiver operator characteristic (ROC) curve (area under the curve (AUC)) of 0.87 in antenatally euthymic women and 0.12 in a replication sample of antenatally depressed women. Incorporation of blood count data into the model accounted for the discrepancy and produced an AUC of 0.96 across both prepartum depressed and euthymic women. Pathway analyses demonstrated that DNA methylation patterns related to hippocampal synaptic plasticity may be of etiological importance to PPD.

Estrogen receptor beta as a novel target of androgen receptor action in breast cancer cell lines

INTRODUCTION

The two isoforms of estrogen receptor (ER) alpha and beta play opposite roles in regulating proliferation and differentiation of breast cancers, with ER-alpha mediating mitogenic effects and ER-beta acting as a tumor suppressor. Emerging data have reported that androgen receptor (AR) activation inhibits ER-positive breast cancer progression mainly by antagonizing ER-alpha signaling. However, to date no studies have specifically evaluated a potential involvement of ER-beta in the inhibitory effects of androgens.

METHODS

ER-beta expression was examined in human breast cancer cell lines using real-time PCR, Western blotting and small interfering RNA (siRNA) assays. Mutagenesis studies, electromobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP) analysis were performed to assess the effects of mibolerone/AR on ER-beta promoter activity and binding.

RESULTS

In this study, we demonstrate that mibolerone, a synthetic androgen ligand, up-regulates ER-beta mRNA and protein levels in ER-positive breast cancer cells. Transient transfection experiments, using a vector containing the human ER-beta promoter region, show that mibolerone increases basal ER-beta promoter activity. Site-directed mutagenesis and deletion analysis reveal that an androgen response element (ARE), TGTTCT motif located at positions -383 and -377, is critical for mibolerone-induced ER-beta up-regulation in breast cancer cells. This occurs through an increased recruitment of AR to the ARE site within the ER-beta promoter region, along with an enhanced occupancy of RNA polymerase II. Finally, silencing of ER-beta gene expression by RNA interference is able to partially reverse the effects of mibolerone on cell proliferation, p21 and cyclin D1 expression.

CONCLUSIONS

Collectively, these data provide evidence for a novel mechanism by which activated AR, through an up-regulation of ER-beta gene expression, inhibits breast cancer cell growth.

Feeding soy protein isolate and treatment with estradiol have different effects on mammary gland morphology and gene expression in weanling male and female rats

Isoflavones are phytochemical components of soy diets that bind weakly to estrogen receptors (ERs). To study potential estrogen-like actions of soy in the mammary gland during early development, we fed weanling male and female Sprague-Dawley rats a semipurified diet with casein as the sole protein source from postnatal day 21 to 33, the same diet substituting soy protein isolate (SPI) for casein, or the casein diet supplemented with estradiol (E2) at 10 μg/kg/day. In contrast to E2, the SPI diet induced no significant change in mammary morphology. In males, there were 34 genes for which expression was changed ≥2-fold in the SPI group vs. 509 changed significantly by E2, and 8 vs. 174 genes in females. Nearly half of SPI-responsive genes in males were also E2 responsive, including adipogenic genes. Serum insulin was found to be decreased by the SPI diet in males. SPI and E2 both downregulated the expression of ERα ( Esr1) in males and females, and ERβ ( Esr2) only in males. Chromatin immunoprecipitation revealed an increased binding of ERα to the promoter of the progesterone receptor ( Pgr) and Esr1 in both SPI- and E2-treated males compared with the casein group but differential recruitment of ERβ. ER promoter binding did not correlate with differences in Pgr mRNA expression. This suggests that SPI fails to recruit appropriate co-activators at E2-inducible genes. Our results indicate that SPI behaves like a selective estrogen receptor modulator rather than a weak estrogen in the developing mammary gland.

Estrogen signaling and the aging brain: context-dependent considerations for postmenopausal hormone therapy

Recent clinical studies have spurred rigorous debate about the benefits of hormone therapy (HT) for postmenopausal women. Controversy first emerged based on a sharp increase in the risk of cardiovascular disease in participants of the Women's Health Initiative (WHI) studies, suggesting that decades of empirical research in animal models was not necessarily applicable to humans. However, a reexamination of the data from the WHI studies suggests that the timing of HT might be a critical factor and that advanced age and/or length of estrogen deprivation might alter the body's ability to respond to estrogens. Dichotomous estrogenic effects are mediated primarily by the actions of two high-affinity estrogen receptors alpha and beta (ER α & ER β ). The expression of the ERs can be overlapping or distinct, dependent upon brain region, sex, age, and exposure to hormone, and, during the time of menopause, there may be changes in receptor expression profiles, post-translational modifications, and protein:protein interactions that could lead to a completely different environment for E2 to exert its effects. In this review, factors affecting estrogen-signaling processes will be discussed with particular attention paid to the expression and transcriptional actions of ER β in brain regions that regulate cognition and affect.

Interaction of 14-3-3 proteins with the estrogen receptor alpha F domain provides a drug target interface

Estrogen receptor alpha (ERα) is involved in numerous physiological and pathological processes, including breast cancer. Breast cancer therapy is therefore currently directed at inhibiting the transcriptional potency of ERα, either by blocking estrogen production through aromatase inhibitors or antiestrogens that compete for hormone binding. Due to resistance, new treatment modalities are needed and as ERα dimerization is essential for its activity, interference with receptor dimerization offers a new opportunity to exploit in drug design. Here we describe a unique mechanism of how ERα dimerization is negatively controlled by interaction with 14-3-3 proteins at the extreme C terminus of the receptor. Moreover, the small-molecule fusicoccin (FC) stabilizes this ERα/14-3-3 interaction. Cocrystallization of the trimeric ERα/14-3-3/FC complex provides the structural basis for this stabilization and shows the importance of phosphorylation of the penultimate Threonine (ERα-T(594)) for high-affinity interaction. We confirm that T(594) is a distinct ERα phosphorylation site in the breast cancer cell line MCF-7 using a phospho-T(594)-specific antibody and by mass spectrometry. In line with its ERα/14-3-3 interaction stabilizing effect, fusicoccin reduces the estradiol-stimulated ERα dimerization, inhibits ERα/chromatin interactions and downstream gene expression, resulting in decreased cell proliferation. Herewith, a unique functional phosphosite and an alternative regulation mechanism of ERα are provided, together with a small molecule that selectively targets this ERα/14-3-3 interface.

MicroRNA-191, an estrogen-responsive microRNA, functions as an oncogenic regulator in human breast cancer

Estrogen- and microRNA-mediated gene regulation play a crucial role in breast cancer biology. However, a functional link between the two major players remains unclear. This study reveals miR-191 as an estrogen-inducible onco-miR in breast cancer, which promotes several hallmarks of cancer including enhanced cell proliferation, migration, chemoresistance and survival in tumor microenvironment. miR-191 is a direct estrogen receptor (ER) target and our results suggest existence of a positive regulatory feedback loop. We show miR-191 as critical mediator of estrogen-mediated cell proliferation. Investigations of mechanistic details of miR-191 functions identify several cancer-related genes like BDNF, CDK6 and SATB1 as miR-191 targets. miR-191 and SATB1 show inverse correlation of expression. miR-191-mediated enhanced cell proliferation and migration are partly dependent on targeted downregulation of SATB1. Further, functional validation of estrogen:miR-191:SATB1 link suggests a cascade initiated by estrogen that induces miR-191 in ER-dependent manner to target SATB1, a global chromatin remodeler, thereby contributing to estrogen-specific gene signature to regulate genes like ANXA1, PIWIL2, CASP4, ESR1/ESR2, PLAC1 and SOCS2 involved in breast cancer progression and migration. Overall, the identification of estrogen/ER/miR-191/SATB1 cascade seems to be a significant pathway in estrogen signaling in breast cancer with miR-191 as oncogenic player.

Estrogen receptor α mediates proliferation of osteoblastic cells stimulated by estrogen and mechanical strain, but their acute down-regulation of the Wnt antagonist Sost is mediated by estrogen receptor β

Mechanical strain and estrogens both stimulate osteoblast proliferation through estrogen receptor (ER)-mediated effects, and both down-regulate the Wnt antagonist Sost/sclerostin. Here, we investigate the differential effects of ERα and -β in these processes in mouse long bone-derived osteoblastic cells and human Saos-2 cells. Recruitment to the cell cycle following strain or 17β-estradiol occurs within 30 min, as determined by Ki-67 staining, and is prevented by the ERα antagonist 1,3-bis(4-hydroxyphenyl)-4-methyl-5-[4-(2-piperidinylethoxy)phenol]-1H-pyrazole dihydrochloride. ERβ inhibition with 4-[2-phenyl-5,7-bis(trifluoromethyl)pyrazolo[1,5-β]pyrimidin-3-yl] phenol (PTHPP) increases basal proliferation similarly to strain or estradiol. Both strain and estradiol down-regulate Sost expression, as does in vitro inhibition or in vivo deletion of ERα. The ERβ agonists 2,3-bis(4-hydroxyphenyl)-propionitrile and ERB041 also down-regulated Sost expression in vitro, whereas the ERα agonist 4,4′,4″-[4-propyl-(1H)-pyrazol-1,3,5-triyl]tris-phenol or the ERβ antagonist PTHPP has no effect. Tamoxifen, a nongenomic ERβ agonist, down-regulates Sost expression in vitro and in bones in vivo. Inhibition of both ERs with fulvestrant or selective antagonism of ERβ, but not ERα, prevents Sost down-regulation by strain or estradiol. Sost down-regulation by strain or ERβ activation is prevented by MEK/ERK blockade. Exogenous sclerostin has no effect on estradiol-induced proliferation but prevents that following strain. Thus, in osteoblastic cells the acute proliferative effects of both estradiol and strain are ERα-mediated. Basal Sost down-regulation follows decreased activity of ERα and increased activity of ERβ. Sost down-regulation by strain or increased estrogens is mediated by ERβ, not ERα. ER-targeting therapy may facilitate structurally appropriate bone formation by enhancing the distinct ligand-independent, strain-related contributions to proliferation of both ERα and ERβ.

Bergapten induces ER depletion in breast cancer cells through SMAD4-mediated ubiquitination

ERα function is crucial for the development of normal mammary gland as well as in the process of progression of breast cancer cells. Signals that target receptor levels contribute to regulate estrogens effects in the cells. An intricate cross-regulation has been documented between ERα and TGF-β down-stream molecules: SMAD2, SMAD3, and SMAD4, that can bind ERα and regulate their signaling. Thus, identification of natural anticancer drugs able to influence the latter molecule might provide alternative choices for breast cancer treatment. Taking into account our previous published data we wanted to study the effect of 5-Methoxypsoralen (bergapten) on ERα and on TGF-β pathway. We reported that bergapten, a coumarin containing compound, effectively depletes ERα in MCF-7 breast cancer sensitive cells and in tamoxifen-resistant clone. The decrease of ERα protein after bergapten treatment results from the ubiquitine-proteasome pathway as demonstrated by the use of MG-132. IP experiments with ER antibody, demonstrated that the protein has physical interaction with SMAD4 and poly-ubiquitine and the amount of ubiquitinated receptor, linked to SMAD4, is greater under bergapten. The crucial role played by SMAD4, in this process, emerges from the observation that in breast cancer cells, silencing of SMAD4, resulted in increased expression of endogenous ERα in both control and bergapten-treated cells, compared to wild- type cells. The same results were confirmed in siRNA TGF-β RII cells. The results suggest a novel negative regulation of ERα by TGF-β/SMAD4 in breast cancer cells and indicate that the SMAD4 protein is involved in the degradation of ERα induced by bergapten. We propose that bergapten may efficiently act as a natural antitumoral agent, able to deplete ERα from breast cancer tamoxifen-sensitive and resistant cells, thereby retraining the effect of membrane signals targeting ERα and in such way its mitogenic potentiality.