Linkage of rapid estrogen action to MAPK activation by ERalpha-Shc association and Shc pathway activation

The emerging role of estrogen's non-nuclear signaling in the cardiovascular disease

Sexual dimorphism exists in the epidemiology of cardiovascular disease (CVD), which indicates the involvement of sexual hormones in the pathophysiology of CVD. In particular, ample evidence has demonstrated estrogen's protective effect on the cardiovascular system. While estrogen receptors, bound to estrogen, act as a transcription factor which regulates gene expressions by binding to the specific DNA sequence, a subpopulation of estrogen receptors localized at the plasma membrane induces activation of intracellular signaling, called "non-nuclear signaling" or "membrane-initiated steroid signaling of estrogen". Although the precise molecular mechanism of non-nuclear signaling as well as its physiological impact was unclear for a long time, recent development of genetically modified animal models and pathway-selective estrogen receptor stimulant bring new insights into this pathway. We review the published experimental studies on non-nuclear signaling of estrogen, and summarize its role in cardiovascular system, especially focusing on: (1) the molecular mechanism of non-nuclear signaling; (2) the design of genetically modified animals and pathway-selective stimulant of estrogen receptor.

The hormonal environment and estrogen receptor signaling alters Chlamydia muridarum infection in vivo

Genital Chlamydia is the most common bacterial sexually transmitted infection in the United States and worldwide. Previous studies indicate that the progression of chlamydial infection is influenced by various factors, including the female sex hormones estrogen and progesterone. Sex hormone levels naturally fluctuate in women throughout their menstrual cycle. Varying concentrations of estrogen and progesterone may impact the progression of chlamydial infection and the host's immune response to Chlamydia. Estrogen signals through estrogen receptors (ERs), ERα and ERβ. These receptors are similar in structure and function, but are differentially expressed in tissues throughout the body, including the genital tract and on cells of the immune system. In this study, we used ovariectomized (OVT) BALB/c mice to investigate the impact of long-term administration of physiologically relevant concentrations of estrogen (E2), progesterone (P4), or a combination of E2/P4 on the progression of and immune response to C. muridarum infection. Additionally, we used ERα and ERβ knockout C57/BL6 mice to determine the how ERs affect chlamydial infection and the resulting immune response. Estrogen exposure prevented C. muridarum infection in vaginally infected OVT mice exposed to E2 alone or in combination with P4, while OVT or Sham mice exposed to hormone free, P4 or depo-medroxyprogesterone acetate shed similar amounts of chlamydiae. The hormonal environment also altered T cell recruitment and IFNϵ production the genital tracts of infected OVT and Sham mice on day 10 post infection. The absence of ERα, but not ERβ, in ER knockout mouse strains significantly changed the timing of C. muridarum infection. ERαKO mice shed significantly more chlamydiae at day 3 post infection and resolved the infection faster than WT or ERβKO animals. At day 9 post infection, flow cytometry showed that ERαKO mice had more T cells present and targeted RNA sequencing revealed increased expression of CD4 and FOXP3, suggesting that ERαKO mice had increased numbers of regulatory T cells compared to ERβKO and WT mice. Mock and chlamydia-infected ERαKO mice also expressed more IFNϵ early during infection. Overall, the data from these studies indicate that sex hormones and their receptors, particularly ERα and ERβ, differentially affect C. muridarum infection in murine models of infection.

Estrogen Receptor-α Targeting: PROTACs, SNIPERs, Peptide-PROTACs, Antibody Conjugated PROTACs and SNIPERs

Targeting selective estrogen subtype receptors through typical medicinal chemistry approaches is based on occupancy-driven pharmacology. In occupancy-driven pharmacology, molecules are developed in order to inhibit the protein of interest (POI), and their popularity is based on their virtue of faster kinetics. However, such approaches have intrinsic flaws, such as pico-to-nanomolar range binding affinity and continuous dosage after a time interval for sustained inhibition of POI. These shortcomings were addressed by event-driven pharmacology-based approaches, which degrade the POI rather than inhibit it. One such example is PROTACs (Proteolysis targeting chimeras), which has become one of the highly successful strategies of event-driven pharmacology (pharmacology that does the degradation of POI and diminishes its functions). The selective targeting of estrogen receptor subtypes is always challenging for chemical biologists and medicinal chemists. Specifically, estrogen receptor α (ER-α) is expressed in nearly 70% of breast cancer and commonly overexpressed in ovarian, prostate, colon, and endometrial cancer. Therefore, conventional hormonal therapies are most prescribed to patients with ER + cancers. However, on prolonged use, resistance commonly developed against these therapies, which led to selective estrogen receptor degrader (SERD) becoming the first-line drug for metastatic ER + breast cancer. The SERD success shows that removing cellular ER-α is a promising approach to overcoming endocrine resistance. Depending on the mechanism of degradation of ER-α, various types of strategies of developed.

ERα is an RNA-binding protein sustaining tumor cell survival and drug resistance

Estrogen receptor α (ERα) is a hormone receptor and key driver for over 70% of breast cancers that has been studied for decades as a transcription factor. Unexpectedly, we discover that ERα is a potent non-canonical RNA-binding protein. We show that ERα RNA binding function is uncoupled from its activity to bind DNA and critical for breast cancer progression. Employing genome-wide cross-linking immunoprecipitation (CLIP) sequencing and a functional CRISPRi screen, we find that ERα-associated mRNAs sustain cancer cell fitness and elicit cellular responses to stress. Mechanistically, ERα controls different steps of RNA metabolism. In particular, we demonstrate that ERα RNA binding mediates alternative splicing of XBP1 and translation of the eIF4G2 and MCL1 mRNAs, which facilitates survival upon stress conditions and sustains tamoxifen resistance of cancer cells. ERα is therefore a multifaceted RNA-binding protein, and this activity transforms our knowledge of post-transcriptional regulation underlying cancer development and drug response.

PELP-1 regulates adverse responses to endocrine therapy in Estrogen Receptor (ER) positive breast cancer

Introduction: Endocrine therapy has played an important role in the management of ER positive breast cancer over recent decades. Despite this, not all patients respond equally to endocrine intervention, which can lead to resistance, associated disease relapse and progression. Previous reports suggest that endocrine agents themselves may induce an invasive phenotype in ER positive breast cancers with low/aberrant expression of E-cadherin. Here we investigate this phenomenon further and provide data supporting a role for the ER co-receptor, PELP-1, in mediating an adverse response to endocrine agents.

Materials and Methods: The effects of tamoxifen, fulvestrant and estrogen withdrawal (as a model for aromatase inhibitor therapy) on the invasive and migratory capacity of endocrine-sensitive MCF-7 and T47D cells, in the presence or absence of functional E-cadherin and/or PELP-1 (using siRNA knockdown), was assessed via Matrigel invasion and Boyden chamber migration assays. The effects of these endocrine therapies alongside E-cadherin/PELP-1 modulation on cell proliferation were further assessed by MTT assay. Western blotting using phospho-specific antibodies was performed to investigate signalling pathway changes associated with endocrine-induced changes in invasion and migration.

Results: Both tamoxifen and fulvestrant induced a pro-invasive and pro-migratory phenotype in ER positive breast cancer cells displaying a high basal expression of PELP-1, which was augmented in the context of poor cell-cell contact. This process occurred in a Src-dependent manner with Src inhibition reversing endocrine induced invasion/migration. While this adverse response was observed using both tamoxifen and fulvestrant therapy, it was not observed under conditions of estrogen withdrawal.

Conclusions: Our data confirms previous reports that anti-estrogens induce an adverse cell phenotype in ER+ breast cancer, particularly in the absence of homotypic cell contact. These results implicate E-cadherin and PELP-1 as potential biomarkers when deciding upon optimum adjuvant endocrine therapy, whereby tumours with high PELP-1/low E-cadherin expression may benefit from estrogen withdrawal therapy via aromatase inhibition, as opposed to ER modulation/antagonism.

Microenvironmental Determinants of Breast Cancer Metastasis: Focus on the Crucial Interplay Between Estrogen and Insulin/Insulin-Like Growth Factor Signaling

The development and progression of the great majority of breast cancers (BCs) are mainly dependent on the biological action elicited by estrogens through the classical estrogen receptor (ER), as well as the alternate receptor named G-protein–coupled estrogen receptor (GPER). In addition to estrogens, other hormones and growth factors, including the insulin and insulin-like growth factor system (IIGFs), play a role in BC. IIGFs cooperates with estrogen signaling to generate a multilevel cross-communication that ultimately facilitates the transition toward aggressive and life-threatening BC phenotypes. In this regard, the majority of BC deaths are correlated with the formation of metastatic lesions at distant sites. A thorough scrutiny of the biological and biochemical events orchestrating metastasis formation and dissemination has shown that virtually all cell types within the tumor microenvironment work closely with BC cells to seed cancerous units at distant sites. By establishing an intricate scheme of paracrine interactions that lead to the expression of genes involved in metastasis initiation, progression, and virulence, the cross-talk between BC cells and the surrounding microenvironmental components does dictate tumor fate and patients’ prognosis. Following (i) a description of the main microenvironmental events prompting BC metastases and (ii) a concise overview of estrogen and the IIGFs signaling and their major regulatory functions in BC, here we provide a comprehensive analysis of the most recent findings on the role of these transduction pathways toward metastatic dissemination. In particular, we focused our attention on the main microenvironmental targets of the estrogen-IIGFs interplay, and we recapitulated relevant molecular nodes that orientate shared biological responses fostering the metastatic program. On the basis of available studies, we propose that a functional cross-talk between estrogens and IIGFs, by affecting the BC microenvironment, may contribute to the metastatic process and may be regarded as a novel target for combination therapies aimed at preventing the metastatic evolution.

17β-estradiol binding to ERα promotes the progression of prolactinoma through estrogen-response element-induced CaBP-9k up-regulation

17β-estradiol (E2) is considered to be an important instigator of prolactinoma, and can positively regulate the expression of calbindin-D9k (CaBP-9k) which contains an estrogen responsive element (ERE) via estrogen receptors (ERs). However, the detailed mechanism of E2 in promoting CaBP-9k expression and their roles in prolactinoma progression remain unclear. Here, we aimed to characterize it. The luciferase gene reporter assay with luc-ERE transfection showed that E2 treatment significantly enhanced the transcriptional level of CaBP-9k, whereas CaBP-9k activity was reduced when GH3 and MMQ cells were treated with AZD9496, an antagonist of ERα. E2 treatment increased the protein expressions of CaBP-9k and ERα but not ERβ, whereas this effect was also abolished when cells were treated with AZD9496. Besides, immunoprecipitation (IP) and immunofluorescence assays demonstrated that CaBP-9k could directly interact with ERα not ERβ, and Chromatin IP (ChIP) assay showed that ERα could bind to ERE of the CaBP-9k promoter. Moreover, cell counting kit-8 (CCK-8) and flow cytometry assays showed that E2 treatment significantly enhanced cell viability and inhibited cell apoptosis, but these effects were all abolished when ERα was down-regulated by short hairpin RNA (shRNA) or inhibited by AZD9496, as well as CaBP-9K suppression in both GH3 and MMQ cell lines. Taken together, these findings indicated that E2 stimulation promoted prolactin cell proliferation and inhibited cell apoptosis through ERα-induced CaBP-9k up-regulation, which then accelerated the advanced progression of prolactinoma.

Grb2 dimer interacts with Coumarin through SH2 domains: A combined experimental and molecular modeling study

Grb2 is an important regulator of normal vs. oncogenic cell signaling transduction. It plays a pivotal role on kinase-mediated signaling transduction by linking Receptor Tyrosine kinases to Ras/MAPK pathway which is known to bring oncogenic outcome. Coumarins are phenolic molecules found in several plants and seeds widely studied because of the antibiotic, anti-inflammatory, anticoagulant, vasodilator, and anti-tumor properties. Despite several studies about the anti-tumor properties of Coumarin in vivo and the role of Grb2 in signaling pathways related to cell proliferation, a molecular level investigation of the interaction between Grb2 and Coumarin is still missing. In this study, we performed a combined set of biophysical approaches to get insights on the interaction between Grb2 in a dimer state and Coumarin. Our results showed that Coumarin interacts with Grb2 dimer through its SH2 domain. The interaction is entropically driven, 1:1 molecular ratio and presents equilibrium constant of 105 M-1. In fact, SH2 is a well-known domain and a versatile signaling module for drug targeting which has been reported to bind compounds that block Ras activation in vivo. Despite we don't know the biological role coming from interaction between Grb2-SH2 domain and Coumarin, it is clear that this molecule could work in the same way as a SH2 domain inhibitor in order to block the link of Receptor Tyrosine kinases to Ras/MAPK pathway.

The p52 isoform of SHC1 is a key driver of breast cancer initiation

Background

SHC1 proteins (also called SHCA) exist in three functionally distinct isoforms (p46SHC, p52SHC, and p66SHC) that serve as intracellular adaptors for several key signaling pathways in breast cancer. Despite the broad evidence implicating SHC1 gene products as a central mediator of breast cancer, testing the isoform-specific roles of SHC1 proteins have been inaccessible due to the lack of isoform-specific inhibitors or gene knockout models.

Methods

Here, we addressed this issue by generating the first isoform-specific gene knockout models for p52SHC and p66SHC, using germline gene editing in the salt-sensitive rat strain. Compared with the wild-type (WT) rats, we found that genetic ablation of the p52SHC isoform significantly attenuated mammary tumor formation, whereas the p66SHC knockout had no effect. Rats were dosed with 7,12-dimethylbenz(a)anthracene (DMBA) by oral gavage to induce mammary tumors, and progression of tumor development was followed for 15 weeks. At 15 weeks, tumors were excised and analyzed by RNA-seq to determine differences between tumors lacking p66SHC or p52SHC.

Results

Compared with the wild-type (WT) rats, we found that genetic ablation of the p52SHC isoform significantly attenuated mammary tumor formation, whereas the p66SHC knockout had no effect. These data, combined with p52SHC being the predominant isoform that is upregulated in human and rat tumors, provide the first evidence that p52SHC is the oncogenic isoform of Shc1 gene products in breast cancer. Compared with WT tumors, 893 differentially expressed (DE; FDR < 0.05) genes were detected in p52SHC KO tumors compared with only 18 DE genes in the p66SHC KO tumors, further highlighting that p52SHC is the relevant SHC1 isoform in breast cancer. Finally, gene network analysis revealed that p52SHC KO disrupted multiple key pathways that have been previously implicated in breast cancer initiation and progression, including ESR1 and mTORC2/RICTOR.

Conclusion

Collectively, these data demonstrate the p52SHC isoform is the key driver of DMBA-induced breast cancer while the expression of p66SHC and p46SHC are not enough to compensate.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-019-1155-7) contains supplementary material, which is available to authorized users.

Role of phospho-ezrin in differentiating thyroid carcinoma

Comprehensive theory explaining the relationship between estrogen (E2) and ezrin in metastasis of thyroid cancer remains non-elicited. In vitro results revealed that E2 could stimulate the expression and phosphorylation of ezrin in a time and dose dependent manner. Our data clearly showed that E2 enhanced the migration and invasion of cells, which was reversed by the transfection of cells with ezrin specific siRNA. Further, we observed that Phosphoinositide 3-kinase (PI3K) ROCK-2 are among the kinases responsible for E2 induced phosphorylation of ezrin. Clinical validation of ezrin/phospho-ezrin revealed that phospho-ezrin was intensely expressed in follicular thyroid carcinoma (FTC) and follicular variant of papillary thyroid carcinoma (FVPTC), while it was completely absent in follicular adenoma (FA) lesions in which the differentiation of the follicular neoplasms remains subtle. When histology of different carcinomas is correlated with benign FA with respect to phospho-ezrin, we observed that the marker was highly significant (p = 0.0001). 100% sensitivity, specificity and diagnostic accuracy of the above marker in the histological association of FTC, FVPTC with FA, enables us to suggest phospho-ezrin as a diagnostic marker to differentiate the follicular neoplasms. These data are the first to suggest the dynamic regulation of ezrin phosphorylation during metastasis in FTC.

The Role of 17β-Estradiol and Estrogen Receptors in Regulation of Ca2+ Channels and Mitochondrial Function in Cardiomyocytes

Numerous epidemiological, clinical, and animal studies showed that cardiac function and manifestation of cardiovascular diseases (CVDs) are different between males and females. The underlying reasons for these sex differences are definitely multifactorial, but major evidence points to a causal role of the sex steroid hormone 17β-estradiol (E2) and its receptors (ER) in the physiology and pathophysiology of the heart. Interestingly, it has been shown that cardiac calcium (Ca²⁺) ion channels and mitochondrial function are regulated in a sex-specific manner. Accurate mitochondrial function and Ca²⁺ signaling are of utmost importance for adequate heart function and crucial to maintaining the cardiovascular health. Due to the highly sensitive nature of these processes in the heart, this review article highlights the current knowledge regarding sex dimorphisms in the heart implicating the importance of E2 and ERs in the regulation of cardiac mitochondrial function and Ca²⁺ ion channels, thus the contractility. In particular, we provide an overview of in-vitro and in-vivo studies using either E2 deficiency; ER deficiency or selective ER activation, which suggest that E2 and ERs are strongly involved in these processes. In this context, this review also discusses the divergent E2-responses resulting from the activation of different ER subtypes in these processes. Detailed understanding of the E2 and ER-mediated molecular and cellular mechanisms in the heart under physiological and pathological conditions may help to design more specifically targeted drugs for the management of CVDs in men and women.

Role of estrogen and RAS signaling in repeated implantation failure

In humans, hormonal regulation is crucial for the preparation of uterine environment leading to either successful implantation or menstrual cycle. Estrogen is a pivotal female steroid hormone that regulates the uterine dynamics along with progesterone in the estrous and menstrual cycles in humans. Estrogen signals act via nuclear estrogen receptor or membrane-bound receptor. The membrane-bound estrogen receptor plays a crucial role in the rapid response of estrogen in the uterine epithelium. Recently, RASD1 has received attention as a novel signal transducer of estrogen in various systems including female reproductive organs. In this review, we discuss the regulation of estrogen and RASD1 signaling in the uterus and also provide insights into RAS as a novel signaling molecule in repeated implantation failure.

Communication between genomic and non-genomic signaling events coordinate steroid hormone actions

Steroid hormones are lipophilic molecules produced in one cell that can travel great distances within the body to elicit biological effects in another cell. In the canonical pathway, steroid hormone binding to a nuclear receptor (NR), often in the cytoplasm, causes the receptor to undergo a conformational change and translocate to the nucleus, where it interacts with specific sequences of DNA to regulate transcription. In addition to the classical genomic mechanism of action, alternate mechanisms of steroid activity have emerged that involve rapid, non-genomic signaling. The distinction between these two major mechanisms of action lies in the subcellular location of the initiating steroid hormone action. Importantly, the mechanisms of action are not exclusive, in that each can affect the activity of the other. Here, we describe the different types of genomic and non-genomic steroid hormone signaling mechanisms and how they can influence one another to ultimately regulate biology. Further, we discuss the approaches being used to study the non-genomic signaling events and address important caveats to be considered when designing new experiments. Thus, this minireview can serve as an introduction to the diverse signaling mechanisms of steroid hormones and offers initial, experimental guidance to those entering the field.

Dynamic changes in binding interaction networks of sex steroids establish their non-classical effects

Non-classical signaling in the intracellular second messenger system plays a pivotal role in the cytoprotective effect of estradiol. Estrogen receptor is a common target of sex steroids and important in mediating estradiol-induced neuroprotection. Whereas the mechanism of genomic effects of sex steroids is fairly understood, their non-classical effects have not been elucidated completely. We use real time molecular dynamics calculations to uncover the interaction network of estradiol and activator estren. Besides steroid interactions, we also investigate the co-activation of the receptor. We show how steroid binding to the alternative binding site of the non-classical action is facilitated by the presence of a steroid in the classical binding site and the absence of the co-activator peptide. Uncovering such dynamic mechanisms behind steroid action will help the structure-based design of new drugs with non-classical responses and cytoprotective potential.

Inhibitory effects of 17β-estradiol or a resveratrol dimer on hypoxia-inducible factor-1α in genioglossus myoblasts: Involvement of ERα and its downstream p38 MAPK pathways

Deficiency in the functioning of the genioglossus, which is one of the upper airway dilator muscles, is an important cause of obstructive sleep apnea/hypopnea syndrome (OSAHS). Estrogens have been reported to inhibit hypoxia-inducible factor-1α (HIF-1α) expression in hypoxia, regulating its target genes and exerting protective effects on the genioglossus in chronic intermittent hypoxia (CIH). This study aimed to investigate the role of 17β-estradiol (E2) and a resveratrol dimer (RD) on HIF-1α and the underlying mechanism. Mouse genioglossus myoblasts were isolated and cultured, and the estrogen receptor α (ERα) shRNA lentivirus was used for gene knockdown. Then MTT assay was used to determine the effects of E2 and RD on the viability of the cells. Cells in different groups were treated with different agents (E2, or RD, or E2 and SB203580), incubated under normoxia or hypoxia for 24 h, and then expression levels of HIF-1α, ERα, ERβ, total-p38 MAPK and phospho-p38 MAPK were detected. We observed that both E2 and RD inhibited the overexpression of HIF-1α induced by hypoxia at the mRNA and protein levels, and these effects were eliminated by genetic silencing of ERα by RNAi. In addition, we found that E2 activated p38 MAPK pathways to inhibit HIF-1α expression. On the whole, ERα may be responsible for downregulation of HIF-1α by E2 or RD via activation of downstream p38 MAPK pathways.

Extra-nuclear effects of estrogen on cortical bone in males require ERαAF-1

Estradiol (E2) signaling via estrogen receptor alpha (ERα) is important for the male skeleton as demonstrated by ERα inactivation in both mice and man. ERα mediates estrogenic effects not only by translocating to the nucleus and affecting gene transcription but also by extra-nuclear actions e.g., triggering cytoplasmic signaling cascades. ERα contains various domains, and the role of activation function 1 (ERαAF-1) is known to be tissue specific. The aim of this study was to determine the importance of extra-nuclear estrogen effects for the skeleton in males and to determine the role of ERαAF-1 for mediating these effects. Five-month-old male wild-type (WT) and ERαAF-1-inactivated (ERαAF-1⁰) mice were orchidectomized and treated with equimolar doses of 17β-estradiol (E2) or an estrogen dendrimer conjugate (EDC), which is incapable of entering the nucleus and thereby only initiates extra-nuclear ER actions or their corresponding vehicles for 3.5 weeks. As expected, E2 treatment increased cortical thickness and trabecular bone volume per total volume (BV/TV) in WT males. EDC treatment increased cortical thickness in WT males, whereas no effect was detected in trabecular bone. In ERαAF-1⁰ males, E2 treatment increased cortical thickness, but did not affect trabecular bone. Interestingly, the effect of EDC on cortical bone was abolished in ERαAF-1⁰ mice. In conclusion, extra-nuclear estrogen signaling affects cortical bone mass in males, and this effect is dependent on a functional ERαAF-1. Increased knowledge regarding estrogen signaling mechanisms in the regulation of the male skeleton may aid the development of new treatment options for male osteoporosis.

IGF-IR cooperates with ERα to inhibit breast cancer cell aggressiveness by regulating the expression and localisation of ECM molecules

IGF-IR is highly associated with the behaviour of breast cancer cells. In ERα-positive breast cancer, IGF-IR is present at high levels. In clinical practice, prolonged treatment with anti-estrogen agents results in resistance to the therapy with activation of alternative signaling pathways. Receptor Tyrosine Kinases, and especially IGF-IR, have crucial roles in these processes. Here, we report a nodal role of IGF-IR in the regulation of ERα-positive breast cancer cell aggressiveness and the regulation of expression levels of several extracellular matrix molecules. In particular, activation of IGF-IR, but not EGFR, in MCF-7 breast cancer cells results in the reduction of specific matrix metalloproteinases and their inhibitors. In contrast, IGF-IR inhibition leads to the depletion by endocytosis of syndecan-4. Global important changes in cell adhesion receptors, which include integrins and syndecan-4 triggered by IGF-IR inhibition, regulate adhesion and invasion. Cell function assays that were performed in MCF-7 cells as well as their ERα-suppressed counterparts indicate that ER status is a major determinant of IGF-IR regulatory role on cell adhesion and invasion. The strong inhibitory role of IGF-IR on breast cancer cells aggressiveness for which E2-ERα signaling pathway seems to be essential, highlights IGF-IR as a major molecular target for novel therapeutic strategies.

Estrogen receptor alpha is cell cycle-regulated and regulates the cell cycle in a ligand-dependent fashion

Estrogen receptor alpha (ERα) has been implicated in several cell cycle regulatory events and is an important predictive marker of disease outcome in breast cancer patients. Here, we aimed to elucidate the mechanism through which ERα influences proliferation in breast cancer cells. Our results show that ERα protein is cell cycle-regulated in human breast cancer cells and that the presence of 17-β-estradiol (E2) in the culture medium shortened the cell cycle significantly (by 4.5 hours, P < 0.05) compared with unliganded conditions. The alterations in cell cycle duration were observed in the S and G2/M phases, whereas the G1 phase was indistinguishable under liganded and unliganded conditions. In addition, ERα knockdown in MCF-7 cells accelerated mitotic exit, whereas transfection of ERα-negative MDA-MB-231 cells with exogenous ERα significantly shortened the S and G2/M phases (by 9.1 hours, P < 0.05) compared with parental cells. Finally, treatment of MCF-7 cells with antiestrogens revealed that tamoxifen yields a slower cell cycle progression through the S and G2/M phases than fulvestrant does, presumably because of the destabilizing effect of fulvestrant on ERα protein. Together, these results show that ERα modulates breast cancer cell proliferation by regulating events during the S and G2/M phases of the cell cycle in a ligand-dependent fashion. These results provide the rationale for an effective treatment strategy that includes a cell cycle inhibitor in combination with a drug that lowers estrogen levels, such as an aromatase inhibitor, and an antiestrogen that does not result in the degradation of ERα, such as tamoxifen.

Differences in GPR30 Regulation by Chlorotriazine Herbicides in Human Breast Cells

Over 200,000 cases of invasive breast cancer are diagnosed annually; herbicide contaminants in local water sources may contribute to the growth of these cancers. GPR30, a G protein coupled receptor, was identified as a potential orphan receptor that may interact with triazine herbicides such as atrazine, one of the most commonly utilized chlorotriazines in agricultural practices in the United States. Our goal was to identify whether chlorotriazines affected the expression of GPR30. Two breast cancer cell lines, MDA-MB-231 and MCF-7, as well as one normal breast cell line, MCF-10A, were treated with a 100-fold range of atrazine, cyanazine, or simazine, with levels flanking the EPA safe level for each compound. Using real-time PCR, we assessed changes in GPR30 mRNA compared to a GAPDH control. Our results indicate that GPR30 expression increased in breast cancer cells at levels lower than the US EPA drinking water contamination limit. During this treatment, the viability of cells was unaltered. In contrast, treatment with chlorotriazines reduced the expression of GPR30 in noncancerous MCF-10A cells. Thus, our results indicate that cell milieu and potential to metastasize may play a role in the extent of GPR30 response to pesticide exposure.

Androgen receptor-mediated non-genomic regulation of prostate cancer cell proliferation

Androgen receptor (AR)-mediated signaling is necessary for prostate cancer cell proliferation and an important target for therapeutic drug development. Canonically, AR signals through a genomic or transcriptional pathway, involving the translocation of androgen-bound AR to the nucleus, its binding to cognate androgen response elements on promoter, with ensuing modulation of target gene expression, leading to cell proliferation. However, prostate cancer cells can show dose-dependent proliferation responses to androgen within minutes, without the need for genomic AR signaling. This proliferation response known as the non-genomic AR signaling is mediated by cytoplasmic AR, which facilitates the activation of kinase-signaling cascades, including the Ras-Raf-1, phosphatidyl-inositol 3-kinase (PI3K)/Akt and protein kinase C (PKC), which in turn converge on mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) activation, leading to cell proliferation. Further, since activated ERK may also phosphorylate AR and its coactivators, the non-genomic AR signaling may enhance AR genomic activity. Non-genomic AR signaling may occur in an ERK-independent manner, via activation of mammalian target of rapamycin (mTOR) pathway, or modulation of intracellular Ca²⁺ concentration through plasma membrane G protein-coupled receptors (GPCRs). These data suggest that therapeutic strategies aimed at preventing AR nuclear translocation and genomic AR signaling alone may not completely abrogate AR signaling. Thus, elucidation of mechanisms that underlie non-genomic AR signaling may identify potential mechanisms of resistance to current anti-androgens and help developing novel therapies that abolish all AR signaling in prostate cancer.

Nodes-and-connections RNAi knockdown screening: identification of a signaling molecule network involved in fulvestrant action and breast cancer prognosis

Although RNA interference (RNAi) knockdown screening of cancer cell cultures is an effective approach to predict drug targets or therapeutic/prognostic biomarkers, interactions among identified targets often remain obscure. Here, we introduce the nodes-and-connections RNAi knockdown screening that generates a map of target interactions through systematic iterations of in silico prediction of targets and their experimental validation. An initial RNAi knockdown screening of MCF-7 human breast cancer cells targeting 6560 proteins identified four signaling molecules required for their fulvestrant-induced apoptosis. Signaling molecules physically or functionally interacting with these four primary node targets were computationally predicted and experimentally validated, resulting in identification of four second-generation nodes. Three rounds of further iterations of the prediction–validation cycle generated third, fourth and fifth generation of nodes, completing a 19-node interaction map that contained three predicted nodes but without experimental validation because of technical limitations. The interaction map involved all three members of the death-associated protein kinases (DAPKs) as well as their upstream and downstream signaling molecules (calmodulins and myosin light chain kinases), suggesting that DAPKs play critical roles in the cytocidal action of fulvestrant. The in silico Kaplan–Meier analysis of previously reported human breast cancer cohorts demonstrated significant prognostic predictive power for five of the experimentally validated nodes and for three of the prediction-only nodes. Immunohistochemical studies on the expression of 10 nodal proteins in human breast cancer tissues not only supported their prognostic prediction power but also provided statistically significant evidence of their synchronized expression, implying functional interactions among these nodal proteins. Thus, the Nodes-and-Connections approach to RNAi knockdown screening yields biologically meaningful outcomes by taking advantage of the existing knowledge of the physical and functional interactions between the predicted target genes. The resulting interaction maps provide useful information on signaling pathways cooperatively involved in clinically important features of the malignant cells, such as drug resistance.

Genes located in a chromosomal inversion are correlated with territorial song in white-throated sparrows

The genome of the white-throated sparrow (Zonotrichia albicollis) contains an inversion polymorphism on chromosome 2 that is linked to predictable variation in a suite of phenotypic traits including plumage color, aggression and parental behavior. Differences in gene expression between the two color morphs, which represent the two common inversion genotypes (ZAL2/ZAL2 and ZAL2/ZAL2(m) ), may therefore advance our understanding of the molecular underpinnings of these phenotypes. To identify genes that are differentially expressed between the two morphs and correlated with behavior, we quantified gene expression and terrirorial aggression, including song, in a population of free-living white-throated sparrows. We analyzed gene expression in two brain regions, the medial amygdala (MeA) and hypothalamus. Both regions are part of a 'social behavior network', which is rich in steroid hormone receptors and previously linked with territorial behavior. Using weighted gene co-expression network analyses, we identified modules of genes that were correlated with both morph and singing behavior. The majority of these genes were located within the inversion, showing the profound effect of the inversion on the expression of genes captured by the rearrangement. These modules were enriched with genes related to retinoic acid signaling and basic cellular functioning. In the MeA, the most prominent pathways were those related to steroid hormone receptor activity. Within these pathways, the only gene encoding such a receptor was ESR1 (estrogen receptor 1), a gene previously shown to predict song rate in this species. The set of candidate genes we identified may mediate the effects of a chromosomal inversion on territorial behavior.

Liganded ERα Stimulates the E3 Ubiquitin Ligase Activity of UBE3C to Facilitate Cell Proliferation

Estrogen receptor (ER)α is a well-characterized ligand-dependent transcription factor. However, the global picture of its nongenomic functions remains to be illustrated. Here, we demonstrate a novel function of ERα during mitosis that facilitates estrogen-dependent cell proliferation. An E3 ubiquitin ligase, UBE3C, was identified in an ERα complex from estrogen-treated MCF-7 breast cancer cells arrested at mitosis. UBE3C interacts with ERα during mitosis in an estrogen-dependent manner. In vitro, estrogen dramatically stimulates the E3 activity of UBE3C in the presence of ERα. This effect was inhibited by the estrogen antagonist tamoxifen. Importantly, estrogen enhances the ubiquitination of cyclin B1 (CCNB1) and destabilizes CCNB1 during mitosis in a manner dependent on endogenous UBE3C. ERα, UBE3C, and CCNB1 colocalize in prophase nuclei and at metaphase spindles before CCNB1 is degraded in anaphase. Depletion of UBE3C attenuates estrogen-dependent cell proliferation without affecting the transactivation function of ERα. Collectively, these results demonstrate a novel ligand-dependent action of ERα that stimulates the activity of an E3 ligase. The mitotic role of estrogen may contribute to its effects on proliferation in addition to its roles in target gene expression.

Altered radiation responses of breast cancer cells resistant to hormonal therapy

Endocrine therapy agents (the selective estrogen receptor (ER) modulators such as tamoxifen or the selective ER down-regulators such as ICI 182,780) are key treatment regimens for hormone receptor-positive breast cancers. While these drugs are very effective in controlling ER-positive breast cancer, many tumors that initially respond well to treatment often acquire drug resistance, which is a major clinical problem. In clinical practice, hormonal therapy agents are commonly used in combination or sequence with radiation therapy. Tamoxifen treatment and radiotherapy improve both local tumor control and patient survival. However, tamoxifen treatment may render cancer cells less responsive to radiation therapy. Only a handful of data exist on the effects of radiation on cells resistant to hormonal therapy agents. These scarce data show that cells that were resistant to tamoxifen were also resistant to radiation. Yet, the existence and mechanisms of cross-resistance to endocrine therapy and radiation therapy need to be established. Here, we for the first time examined and compared radiation responses of MCF-7 breast adenocarcinoma cells (MCF-7/S0.5) and two antiestrogen resistant cell lines derived from MCF-7/S0.5: the tamoxifen resistant MCF-7/TAMR-1 and ICI 182,780 resistant MCF-7/182R-6 cell lines. Specifically, we analyzed the radiation-induced changes in the expression of genes involved in DNA damage, apoptosis, and cell cycle regulation. We found that the tamoxifen-resistant cell line in contrast to the parental and ICI 182,780-resistant cell lines displayed a significantly less radiation-induced decrease in the expression of genes involved in DNA repair. Furthermore, we show that MCF-7/TAMR-1 and MCF-7/182R-6 cells were less susceptible to radiation-induced apoptosis as compared to the parental line. These data indicate that tamoxifen-resistant breast cancer cells have a reduced sensitivity to radiation treatment. The current study may therefore serve as a roadmap to the future analysis of the mechanisms of cross-resistance between hormonal therapy and radiation.

Estrogen-dependent sushi domain containing 3 regulates cytoskeleton organization and migration in breast cancer cells

Aromatase inhibitors (AIs) are the standard endocrine therapy for postmenopausal breast cancer; however, currently used biomarkers, such as, estrogen receptor-alpha/progesterone receptor (ERα/PR), predict only slightly more than half of the potential responders to AI treatment. To identify novel markers of AI responsiveness, a genome-wide microarray analysis was performed using primary breast tumor samples from 50 postmenopausal women who later developed metastatic breast cancer. Sushi domain containing 3 (SUSD3) is a significantly differentially expressed gene, with 3.38-fold higher mRNA levels in AI-responsive breast tumors vs non-responders (P<0.001). SUSD3 was highly expressed in ERα-positive breast tumors and treatment with estradiol increased SUSD3 expression in ERα-positive breast cancer cells. Treatment with an antiestrogen or ERα knockdown abolished basal and estradiol-dependent SUSD3 expression. Recruitment of ERα upstream of the transcription start site of SUSD3 was demonstrated by chromatin immunoprecipitation-PCR. Flow cytometric analysis of SUSD3-knockdown cells revealed blunted estradiol effects on progression into S and M phases. SUSD3 was localized to the plasma membrane of breast cancer cells. SUSD3 knockdown decreased the appearance of actin-rich protrusions, stress fibers and large basal focal adhesions, while increasing the presence of cortical actin concomitant with a decrease in Rho and focal adhesion kinase activity. SUSD3-deficient cells demonstrated diminished cell spreading, cell-cell adhesion and motility. In conclusion, SUSD3 is a novel promoter of estrogen-dependent cell proliferation and regulator of cell-cell and cell-substrate interactions and migration in breast cancer. It may serve as a novel predictor of response to endocrine therapy and potential therapeutic target.

Obesity enhances nongenomic estrogen receptor crosstalk with the PI3K/Akt and MAPK pathways to promote in vitro measures of breast cancer progression

Introduction

Epidemiological and clinical studies indicate that obesity is associated with a worse postmenopausal breast cancer prognosis and an increased risk of endocrine therapy resistance. However, the mechanisms mediating these effects remain poorly understood. Here we investigate the molecular pathways by which obesity-associated circulating factors in the blood enhance estrogen receptor alpha (ERα) positive breast cancer cell viability and growth.

Methods

Blood serum was collected from postmenopausal breast cancer patients and pooled by body mass index (BMI) category (Control: 18.5 to 24.9 kg/m²; Obese: ≥30.0 kg/m²). The effects of patient sera on MCF-7 and T47D breast cancer cell viability and growth were examined by MTT and colony formation assays, respectively. Insulin-like growth factor receptor 1(IGF-1R), Akt, and ERK1/2 activation and genomic ERα activity were assessed to determine their possible contribution to obese patient sera-induced cell viability and growth. To further define the relative contribution of these signaling pathways, cells grown in patient sera were treated with various combinations of ERα, PI3K/Akt and MAPK targeted therapies. Comparisons between cells exposed to different experimental conditions were made using one-way analysis of variance (ANOVA) and Student's t test.

Results

Cells grown in media supplemented with obese patient sera displayed greater cell viability and growth as well as IGF-1R, Akt and ERK1/2 activation relative to control sera. Despite the lack of a significant difference in genomic ERα activity following growth in obese versus control patient sera, we observed a dramatic reduction in cell viability and growth after concurrent inhibition of the ERα and PI3K/Akt signaling pathways. Further, we demonstrated that ERα inhibition was sufficient to attenuate obese serum-induced Akt and ERK1/2 activation. Together, these data suggest that obesity promotes greater ERα positive breast cancer cell viability and growth through enhanced crosstalk between nongenomic ERα signaling and the PI3K/Akt and MAPK pathways.

Conclusions

Circulating factors in the serum of obese postmenopausal women stimulate ERα positive breast cancer cell viability and growth by facilitating non-genomic ERα crosstalk with the PI3K/Akt and MAPK signaling pathways. These findings provide valuable insight into one mechanism by which obesity may promote ERα positive postmenopausal breast cancer progression and endocrine therapy resistance.

Estrogen signaling crosstalk: Implications for endocrine resistance in ovarian cancer

Resistance to anti-estrogen therapies is a prominent challenge in the treatment of ovarian cancer. Tumors develop endocrine resistance by acquiring adaptations that help them rely on alternative oncogenic signaling cascades, which crosstalk with estrogen signaling pathways. An understanding of estrogen signaling crosstalk with these growth promoting cascades is essential in order to maximize efficacy of anti-estrogen treatments in ovarian cancer. Herein, we provide an overview of estrogen signaling in ovarian cancer and discuss the major challenges associated with anti-estrogen therapies. We also review what is currently known about how genomic and non-genomic estrogen signaling pathways crosstalk with several major oncogenic signaling cascades. The insights provided here illustrate existing strategies for targeting endocrine resistant ovarian tumors and may help identify new strategies to improve the treatment of this disease.

Tyrosine phosphatase Shp2 mediates the estrogen biological action in breast cancer via interaction with the estrogen extranuclear receptor

The extranuclear estrogen receptor pathway opens up novel perspectives in many physiological and pathological processes, especially in breast carcinogenesis. However, its function and mechanisms are not fully understood. Herein we present data identifying Shp2, a SH2-containing tyrosine phosphatase, as a critical component of extranuclear ER pathway in breast cancer. The research checked that the effect of Shp2 on the tumor formation and growth in animal model and investigated the regulation of Shp2 on the bio-effect and signaling transduction of estrogen in breast cancer cell lines. The results showed that Shp2 was highly expressed in more than 60% of total 151 breast cancer cases. The inhibition of Shp2 activity by PHPS1 (a Shp2 inhibitor) delayed the development of dimethylbenz(a)anthracene (DMBA)-induced tumors in the rat mammary gland and also blocked tumor formation in MMTV-pyvt transgenic mice. Estradiol (E2) stimulated protein expression and phosphorylation of Shp2, and induced Shp2 binding to ERα and IGF-1R around the membrane to facilitate the phosphorylation of Erk and Akt in breast cancer cells MCF7. Shp2 was also involved in several biological effects of the extranuclear ER-initiated pathway in breast cancer cells. Specific inhibitors (phps1, phps4 and NSC87877) or small interference RNAs (siRNA) of Shp2 remarkably suppressed E2-induced gene transcription (Cyclin D1 and trefoil factor 1 (TFF1)), rapid DNA synthesis and late effects on cell growth. These results introduced a new mechanism for Shp2 oncogenic action and shed new light on extranuclear ER-initiated action in breast tumorigenesis by identifying a novel associated protein, Shp2, for extranuclear ER pathway, which might benefit the therapy of breast cancer.

Oestrogen receptor-alpha regulates non-canonical Hedgehog-signalling in the mammary gland

Mesenchymal dysplasia (mes) mice harbour a truncation in the C-terminal region of the Hh-ligand receptor, Patched-1 (mPtch1). While the mes variant of mPtch1 binds to Hh-ligands with an affinity similar to that of wild type mPtch1 and appears to normally regulate canonical Hh-signalling via smoothened, the mes mutation causes, among other non-lethal defects, a block to mammary ductal elongation at puberty. We demonstrated previously Hh-signalling induces the activation of Erk1/2 and c-src independently of its control of smo activity. Furthermore, mammary epithelial cell-directed expression of an activated allele of c-src rescued the block to ductal elongation in mes mice, albeit with delayed kinetics. Given that this rescue was accompanied by an induction in estrogen receptor-alpha (ERα) expression and that complex regulatory interactions between ERα and c-src are required for normal mammary gland development, it was hypothesized that expression of ERα would also overcome the block to mammary ductal elongation at puberty in the mes mouse. We demonstrate here that conditional expression of ERα in luminal mammary epithelial cells on the mes background facilitates ductal morphogenesis with kinetics similar to that of the MMTV-c-src(Act) mice. We demonstrate further that Erk1/2 is activated in primary mammary epithelial cells by Shh-ligand and that this activation is blocked by the inhibitor of c-src, PP2, is partially blocked by the ERα inhibitor, ICI 182780 but is not blocked by the smo-inhibitor, SANT-1. These data reveal an apparent Hh-signalling cascade operating through c-src and ERα that is required for mammary gland morphogenesis at puberty.

Sex differences in anxiety and depression: role of testosterone

Compelling evidence exists for pervasive sex differences in pathological conditions, including anxiety and depressive disorders, with females more than twice as likely to be afflicted. Gonadal hormones may be a major factor in this disparity, given that women are more likely to experience mood disturbances during times of hormonal flux, and testosterone may have protective benefits against anxiety and depression. In this review we focus on the effects of testosterone in males and females, revealed in both human and animal studies. We also present possible neurobiological mechanisms underlying testosterone's mostly protective benefits, including the brain regions, neural circuits, and cellular and molecular pathways involved. While the precise underlying mechanisms remain unclear, both activational and organizational effects of testosterone appear to contribute to these effects. Future clinical studies are necessary in order to better understand when and how testosterone therapy may be effective in both sexes.

Links between oestrogen receptor activation and proteolysis: relevance to hormone-regulated cancer therapy

Oestrogen receptor-α (ERα) is a master transcription factor that regulates cell proliferation and homeostasis in many tissues. Despite beneficial ERα functions, sustained oestrogenic exposure increases the risk and/or the progression of various cancers, including those of the breast, endometrium and ovary. Oestrogen–ERα interaction can trigger post-translational ERα modifications through crosstalk with signalling pathways to promote transcriptional activation and ubiquitin-mediated ERα proteolysis, with co-activators that have dual roles as ubiquitin ligases. These processes are reviewed herein. The elucidation of mechanisms whereby oestrogen drives both ERα transactivation and receptor proteolysis might have important therapeutic implications not only for breast cancer but also potentially for other hormone-regulated cancers.

Effects of Estetrol on Migration and Invasion in T47-D Breast Cancer Cells through the Actin Cytoskeleton

Estetrol (E4) is a natural human estrogen present at high concentrations during pregnancy. Due to its high oral bioavailability and long plasma half-life, E4 is particularly suitable for therapeutic applications. E4 acts as a selective estrogen receptor (ER) modulator, exerting estrogenic actions on the endometrium or the central nervous system, while antagonizing the actions of estradiol in the breast. We tested the effects of E4 on its own or in the presence of 17β-estradiol (E2) on T47-D ER+ breast cancer cell migration and invasion of three-dimensional matrices. E4 administration to T47-D cells weakly stimulated migration and invasion. However, E4 decreased the extent of movement and invasion induced by E2. Breast cancer cell movement requires a remodeling of the actin cytoskeleton. During exposure to E4, a weak, concentration-dependent, re-distribution of actin fibers toward the cell membrane was observed. However, when E4 was added to E2, an inhibition of actin remodeling induced by E2 was seen. Estrogens stimulate ER+ breast cancer cell movement through the ezrin-radixin-moesin family of actin regulatory proteins, inducing actin and cell membrane remodeling. E4 was a weak inducer of moesin phosphorylation on Thr(558), which accounts for its functional activation. In co-treatment with E2, E4 blocked the activation of this actin controller in a concentration-related fashion. These effects were obtained through recruitment of estrogen receptor-α. In conclusion, E4 acted as a weak estrogen on breast cancer cell cytoskeleton remodeling and movement. However, when E2 was present, E4 counteracted the stimulatory actions of E2. This contributes to the emerging hypothesis that E4 may be a naturally occurring ER modulator in the breast.

Estrogen receptor alpha is expressed in mesenteric mesothelial cells and is internalized in caveolae upon Freund's adjuvant treatment

Transformation of epithelial cells into connective tissue cells (epithelial-mesenchymal transition, EMT) is a complex mechanism involved in tumor metastasis, and in normal embryogenesis, while type II EMT is mainly associated with inflammatory events and tissue regenaration.

In this study we examined type II EMT at the ultrastructural and molecular level during the inflammatory process induced by Freund's adjuvant treatment in rat mesenteric mesothelial cells. We found that upon the inflammatory stimulus mesothelial cells lost contact with the basal lamina and with each other, and were transformed into spindle-shaped cells. These morphological changes were accompanied by release of interleukins IL-1alpha, -1beta and IL-6 and by secretion of transforming growth factor beta (TGF-β) into the peritoneal cavity. Mesothelial cells also expressed estrogen receptor alpha (ER-α) as shown by immunolabeling at the light and electron microscopical levels, as well as by quantitative RT-PCR. The mRNA level of ER-α showed an inverse correlation with the secretion of TGF-β. At the cellular and subcellular levels ER-α was colocalized with the coat protein caveolin-1 and was found in the plasma membrane of mesothelial cells, in caveolae close to multivesicular bodies (MVBs) or in the membrane of these organelles, suggesting that ER-α is internalized via caveola-mediated endocytosis during inflammation. We found asymmetric, thickened, electron dense areas on the limiting membrane of MVBs (MVB plaques) indicating that these sites may serve as platforms for collecting and organizing regulatory proteins. Our morphological observations and biochemical data can contribute to form a potential model whereby ER-α and its caveola-mediated endocytosis might play role in TGF-β induced type II EMT in vivo.

Conserved steroid hormone homology converges on nuclear factor κB to modulate inflammation in asthma

Asthma is a complex, multifactorial disease comprising multiple different subtypes, rather than a single disease entity, yet it has a consistent clinical phenotype: recurring episodes of chest tightness, wheezing, and difficulty breathing (Pediatr Pulmonol Suppl. 1997;15:9-12). Despite the complex pathogenesis of asthma, steroid hormones (eg, glucocorticoids) are ubiquitous in the short-term and long-term management of all types of asthma. Overall, steroid hormones are a class of widely relevant, biologically active compounds originating from cholesterol and altered in a stepwise fashion, but maintain a basic 17-carbon, 4-ring structure. Steroids are lipophilic molecules that diffuse readily through cell membranes to directly and/or indirectly affect gene transcription. In addition, they use rapid, nongenomic actions to affect cellular products. Steroid hormones comprise several groups (including glucocorticoids, sex steroid hormones, and secosteroids) with critical divergent biological and physiological functions relevant to health and disease. However, the conserved homology of steroid hormone molecules, receptors, and signaling pathways suggests that each of these is part of a dynamic system of hormone interaction, likely involving an overlap of downstream signaling mechanisms. Therefore, we will review the similarities and differences of these 3 groups of steroid hormones (ie, glucocorticoids, sex steroid hormones, and secosteroids), identifying nuclear factor κB as a common inflammatory mediator. Despite our understanding of the impact of individual steroids (eg, glucocorticoids, sex steroids and secosteroids) on asthma, research has yet to explain the interplay of the dynamic system in which these hormones function. To do so, there needs to be a better understanding of the interplay of classic, nonclassic, and nongenomic steroid hormone functions. However, clues from the conserved homology steroid hormone structure and function and signaling pathways offer insight into a possible model of steroid hormone regulation of inflammation in asthma through common nuclear factor κB-mediated downstream events.

Exposure to estrogen and ionizing radiation causes epigenetic dysregulation, activation of mitogen-activated protein kinase pathways, and genome instability in the mammary gland of ACI rats

The impact of environmental mutagens and carcinogens on the mammary gland has recently received a lot of attention. Among the most generally accepted carcinogenic agents identified as factors that may increase breast cancer incidence are ionizing radiation and elevated estrogen levels. However, the molecular mechanisms of mammary gland aberrations associated with radiation and estrogen exposure still need to be further elucidated, especially the interplay between elevated hormone levels and radiation. Therefore, in the present study, we investigated molecular changes induced in rat mammary gland tissue by estrogen, ionizing radiation, and the combined action of these two carcinogens using a well-established ACI rat model. We found that continuous exposure of intact female ACI rats to elevated levels of estrogen or to both estrogen and radiation resulted in significant hyperproliferative changes in rat mammary glands. In contrast, radiation exposure alone did not induce hyperplasia. Interestingly, despite the obvious disparity in mammary gland morphology, we did not detect significant differences in the levels of genomic methylation among animals exposed to estrogen, radiation, or both agents together. Specifically, we observed a significant global genomic hypomethylation at 6 weeks of exposure. However, by 12 and 18 weeks, the levels of global DNA methylation returned to those of age-matched controls. We also found that combined exposure to radiation and estrogen significantly altered the levels of histone H3 and H4 methylation and acetylation. Most importantly, we for the first time demonstrated that estrogen and radiation exposure caused a significant induction of p42/44 MAPK and p38 pathways that was paralleled by elevated levels of H3S10 phosphorylation, a well-established biomarker of genome and chromosome instability. The precise role of MAPK pathways and their inter-relationship with H3S10 phosphorylation and genome instability in mammary gland tissues needs to be explored further.

Extranuclear ERα is associated with regression of T47D PKCα-overexpressing, tamoxifen-resistant breast cancer

Background

Prior to the introduction of tamoxifen, high dose estradiol was used to treat breast cancer patients with similar efficacy as tamoxifen, albeit with some undesirable side effects. There is renewed interest to utilize estradiol to treat endocrine resistant breast cancers, especially since findings from several preclinical models and clinical trials indicate that estradiol may be a rational second-line therapy in patients exhibiting resistance to tamoxifen and/or aromatase inhibitors. We and others reported that breast cancer patients bearing protein kinase C alpha (PKCα)- expressing tumors exhibit endocrine resistance and tumor aggressiveness. Our T47D:A18/PKCα preclinical model is tamoxifen-resistant, hormone-independent, yet is inhibited by 17β-estradiol (E2) in vivo. We previously reported that E2-induced T47D:A18/PKCα tumor regression requires extranuclear ERα and interaction with the extracellular matrix.

Methods

T47D:A18/PKCα cells were grown in vitro using two-dimensional (2D) cell culture, three-dimensional (3D) Matrigel and in vivo by establishing xenografts in athymic mice. Immunofluoresence confocal microscopy and co-localization were applied to determine estrogen receptor alpha (ERα) subcellular localization. Co-immunoprecipitation and western blot were used to examine interaction of ERα with caveolin-1.

Results

We report that although T47D:A18/PKCα cells are cross-resistant to raloxifene in cell culture and in Matrigel, raloxifene induces regression of tamoxifen-resistant tumors. ERα rapidly translocates to extranuclear sites during T47D:A18/PKCα tumor regression in response to both raloxifene and E2, whereas ERα is primarily localized in the nucleus in proliferating tumors. E2 treatment induced complete tumor regression whereas cessation of raloxifene treatment resulted in tumor regrowth accompanied by re-localization of ERα to the nucleus. T47D:A18/neo tumors that do not overexpress PKCα maintain ERα in the nucleus during tamoxifen-mediated regression. An association between ERα and caveolin-1 increases in tumors regressing in response to E2.

Conclusions

Extranuclear ERα plays a role in the regression of PKCα-overexpressing tamoxifen-resistant tumors. These studies underline the unique role of extranuclear ERα in E2- and raloxifene-induced tumor regression that may have implications for treatment of endocrine-resistant PKCα-expressing tumors encountered in the clinic.

Fulvestrant-induced cell death and proteasomal degradation of estrogen receptor α protein in MCF-7 cells require the CSK c-Src tyrosine kinase

Fulvestrant is a representative pure antiestrogen and a Selective Estrogen Receptor Down-regulator (SERD). In contrast to the Selective Estrogen Receptor Modulators (SERMs) such as 4-hydroxytamoxifen that bind to estrogen receptor α (ERα) as antagonists or partial agonists, fulvestrant causes proteasomal degradation of ERα protein, shutting down the estrogen signaling to induce proliferation arrest and apoptosis of estrogen-dependent breast cancer cells. We performed genome-wide RNAi knockdown screenings for protein kinases required for fulvestrant-induced apoptosis of the MCF-7 estrogen-dependent human breast caner cells and identified the c-Src tyrosine kinase (CSK), a negative regulator of the oncoprotein c-Src and related protein tyrosine kinases, as one of the necessary molecules. Whereas RNAi knockdown of CSK in MCF-7 cells by shRNA-expressing lentiviruses strongly suppressed fulvestrant-induced cell death, CSK knockdown did not affect cytocidal actions of 4-hydroxytamoxifen or paclitaxel, a chemotherapeutic agent. In the absence of CSK, fulvestrant-induced proteasomal degradation of ERα protein was suppressed in both MCF-7 and T47D estrogen-dependent breast cancer cells whereas the TP53-mutated T47D cells were resistant to the cytocidal action of fulvestrant in the presence or absence of CSK. MCF-7 cell sensitivities to fulvestrant-induced cell death or ERα protein degradation was not affected by small-molecular-weight inhibitors of the tyrosine kinase activity of c-Src, suggesting possible involvement of other signaling molecules in CSK-dependent MCF-7 cell death induced by fulvestrant. Our observations suggest the importance of CSK in the determination of cellular sensitivity to the cytocidal action of fulvestrant.

Point mutations in the ERα Gαi binding domain segregate nonnuclear from nuclear receptor function

A subpopulation of plasma membrane-associated estrogen receptor (ER)α interact directly with G proteins and mediate nonnuclear receptor signaling. This mechanism underlies numerous processes, including important cardiovascular protective actions of estradiol (E(2)), such as the activation of endothelial NO synthase (eNOS) and endothelial cell growth and migration. In the present work we sought a genetic approach to differentiate nonnuclear from nuclear ERα actions. We generated single alanine substitutions within the Gαi-binding domain of ERα (amino acids 251-260) and tested signaling to eNOS or ERK1,2 and activation of luciferase (Luc) reporters signifying transactivation via direct or indirect ERα-DNA binding in HeLa cells. The point mutants ERα-R256A, ERα-K257A, ERα-D258A, and ERα-R260A were all incapable of activating eNOS in response to E(2), and ERα-R256A and ERα-D258A also showed loss of ERK1,2 activation. In contrast, ERα-R256A, ERα-K257A, ERα-D258A, and ERα-R260A all displayed normal capacity to invoke E(2)-induced transactivation of estrogen response element (ERE)-Luc or Sp1-Luc. However, whereas activator protein 1-Luc activation by ERα-R256A and ERα-D258A was intact, ERα-K257A and ERα-R260A were incapable of activator protein 1-Luc activation. In in vitro pull-down assays with the two mutants that lack all nonnuclear functions tested and retain all nuclear functions tested, ERα-R256A and ERα-D258A, there was normal direct interaction between Gαi and ERα-R256A and an absence of interaction between Gαi and ERα-D258A. When expressed in endothelial cells, these two mutants prevented E(2)-induced migration and eNOS activation mediated by endogenous receptor, indicative of dominant-negative action. Thus, the point mutants ERα-R256A and ERα-D258A in the receptor GαI-binding domain provide genetic segregation of nonnuclear from nuclear ERα function.

p130Cas over-expression impairs mammary branching morphogenesis in response to estrogen and EGF

p130Cas adaptor protein regulates basic processes such as cell cycle control, survival and migration. p130Cas over-expression has been related to mammary gland transformation, however the in vivo consequences of p130Cas over-expression during mammary gland morphogenesis are not known. In ex vivo mammary explants from MMTV-p130Cas transgenic mice, we show that p130Cas impairs the functional interplay between Epidermal Growth Factor Receptor (EGFR) and Estrogen Receptor (ER) during mammary gland development. Indeed, we demonstrate that p130Cas over-expression upon the concomitant stimulation with EGF and estrogen (E2) severely impairs mammary morphogenesis giving rise to enlarged multicellular spherical structures with altered architecture and absence of the central lumen. These filled acinar structures are characterized by increased cell survival and proliferation and by a strong activation of Erk1/2 MAPKs and Akt. Interestingly, antagonizing the ER activity is sufficient to re-establish branching morphogenesis and normal Erk1/2 MAPK activity. Overall, these results indicate that high levels of p130Cas expression profoundly affect mammary morphogenesis by altering epithelial architecture, survival and unbalancing Erk1/2 MAPKs activation in response to growth factors and hormones. These results suggest that alteration of morphogenetic pathways due to p130Cas over-expression might prime mammary epithelium to tumorigenesis.

M-Ras induces Ral and JNK activation to regulate MEK/ERK-independent gene expression in MCF-7 breast cancer cells

Constitutive activation of M-Ras has previously been reported to cause morphologic and growth transformation of murine cells, suggesting that M-Ras plays a role in tumorigenesis. Cell transformation by M-Ras correlated with weak activation of the Raf/MEK/ERK pathway, although contributions from other downstream effectors were suggested. Recent studies indicate that signaling events distinct from the Raf/MEK/ERK cascade are critical for human tumorigenesis. However, it is unknown what signaling events M-Ras triggers in human cells. Using constitutively active M-Ras (Q71L) containing additional mutations within its effector-binding loop, we found that M-Ras induces MEK/ERK-dependent and -independent Elk1 activation as well as phosphatidylinositol 3 kinase (PI3K)/Akt and JNK/cJun activation in human MCF-7 breast cancer cells. Among several human cell lines examined, M-Ras-induced MEK/ERK-independent Elk1 activation was only detected in MCF-7 cells, and correlated with Rlf/M-Ras interaction and Ral/JNK activation. Supporting a role for M-Ras signaling in breast cancer, EGF activated M-Ras and promoted its interaction with endogenous Rlf. In addition, constitutive activation of M-Ras induced estrogen-independent growth of MCF-7 cells that was dependent on PI3K/Akt, MEK/ERK, and JNK activation. Thus, our studies demonstrate that M-Ras signaling activity differs between human cells, highlighting the importance of defining Ras protein signaling within each cell type, especially when designing treatments for Ras-induced cancer. These findings also demonstrate that M-Ras activity may be important for progression of EGFR-dependent tumors.

Extracellular signal-regulated kinase 2 signaling in the hippocampal dentate gyrus mediates the antidepressant effects of testosterone

BACKGROUND

Human and animal studies suggest that testosterone may have antidepressant effects. In this study, we sought to investigate the molecular mechanisms underlying the antidepressant effects of testosterone within the hippocampus, an area that is fundamental in the etiology of depression.

METHODS

The effects of testosterone replacements in gonadectomized adult male rats were investigated using the sucrose preference and forced swim tests. We explored possible effects of testosterone on hippocampal neurogenesis and gene expression of stress-related molecules. Through the use of viral vectors, we pursued the antidepressant molecular mechanism(s) of testosterone in mediating anhedonia and manipulated extracellular signal-regulated kinase 2 (ERK2) expression in the dentate gyrus in gonadectomized rats with testosterone replacements.

RESULTS

Testosterone had antidepressant effects, likely mediated by aromatization to estrogen metabolites, in the sucrose preference and forced swim tests despite having no effects on hippocampal cell proliferation or survival. We found a testosterone-dependent regulation of hippocampal ERK2 expression. Functionally, reducing ERK2 activity within the dentate gyrus induced anhedonia in gonadectomized rats receiving testosterone supplementation, whereas the overexpression of ERK2 rescued this behavior in gonadectomized rats.

CONCLUSIONS

These results implicate a role for ERK2 signaling within the dentate gyrus area of the hippocampus as a key mediator of the antidepressant effects of testosterone.

Breaking the cycle: An insight into the role of ERα in eukaryotic cell cycles

There have been numerous reviews written to date on estrogen receptor (ER), focusing on topics such as its role in the etiology of breast cancer, its mode of regulation, its role as a transcriptional activator and how to target it therapeutically, just to name a few. One reason for so much attention on this nuclear receptor is that it acts not only as a prognostic marker, but also as a target for therapy. However, a relatively undiscovered area in the literature regarding ER is how its activity in the presence and absence of ligand affects its role in proliferation and cell cycle transition. In this review, we provide a brief overview of ER signaling, ligand dependent and independent, genomic and non-genomic, and how these signaling events affect the role of ER in the mammalian cell cycle.

Phosphatidylinositol 3-kinase and antiestrogen resistance in breast cancer

Although antiestrogen therapies targeting estrogen receptor (ER) α signaling prevent disease recurrence in the majority of patients with hormone-dependent breast cancer, a significant fraction of patients exhibit de novo or acquired resistance. Currently, the only accepted mechanism linked with endocrine resistance is amplification or overexpression of the ERBB2 (human epidermal growth factor receptor 2 [HER2]) proto-oncogene. Experimental and clinical evidence suggests that hyperactivation of the phosphatidylinositol 3-kinase (PI3K) pathway, the most frequently mutated pathway in breast cancer, promotes antiestrogen resistance. PI3K is a major signaling hub downstream of HER2 and other receptor tyrosine kinases. PI3K activates several molecules involved in cell-cycle progression and survival, and in ER-positive breast cancer cells, it promotes estrogen-dependent and -independent ER transcriptional activity. Preclinical tumor models of antiestrogen-resistant breast cancer often remain sensitive to estrogens and PI3K inhibition, suggesting that simultaneous targeting of the PI3K and ER pathways may be most effective. Herein, we review alterations in the PI3K pathway associated with resistance to endocrine therapy, the state of clinical development of PI3K inhibitors, and strategies for the clinical investigation of such drugs in hormone receptor-positive breast cancer.

Mutations in the phosphatidylinositol 3-kinase pathway: role in tumor progression and therapeutic implications in breast cancer

Mutations in genes that constitute the phosphatidylinositol 3-kinase (PI3K) pathway occur in >70% of breast cancers. Clinical and experimental evidence suggest that PI3K pathway activation promotes resistance to some of the current breast cancer therapies. PI3K is a major signaling hub downstream of human epidermal growth factor receptor (HER)2 and other receptor tyrosine kinases. PI3K activates AKT, serum/glucocorticoid regulated kinase (SGK), phosphoinositide-dependent kinase 1 (PDK1), mammalian target of rapamycin (mTOR), and several other molecules involved in cell cycle progression and survival. In estrogen receptor (ER)+ breast cancer cells, PI3K activation promotes estrogen-dependent and -independent ER transcriptional activity, which, in turn, may contribute to anti-estrogen resistance. Activation of this pathway also confers resistance to HER2-targeted therapies. In experimental models of resistance to anti-estrogens and HER2 inhibitors, pharmacological inhibition of PI3K/AKT/mTOR has been shown to overcome drug resistance. Early clinical data suggest that combined inhibition of either HER2 or ER plus inhibition of the PI3K pathway might be an effective strategy for treatment of respective HER2+ and ER+ breast cancers resistant to standard therapies. Here, we review alterations in the PI3K pathway in breast cancer, their association with therapeutic resistance, and the state of clinical development of PI3K pathway inhibitors.

Dual targeting of the insulin-like growth factor and collateral pathways in cancer: combating drug resistance

The insulin-like growth factor pathway, regulated by a complex interplay of growth factors, cognate receptors, and binding proteins, is critically important for many of the hallmarks of cancer such as oncogenesis, cell division, growth, and antineoplastic resistance. Naturally, a number of clinical trials have sought to directly abrogate insulin-like growth factor receptor 1 (IGF-1R) function and/or indirectly mitigate its downstream mediators such as mTOR, PI3K, MAPK, and others under the assumption that such therapeutic interventions would provide clinical benefit, demonstrable by impaired tumor growth as well as prolonged progression-free and overall survival for patients. Though a small subset of patients enrolled within phase I or II clinical trials revealed dramatic clinical response to IGF-1R targeted therapies (most using monoclonal antibodies to IGF-1R), in toto, the anticancer effect has been underwhelming and unsustained, as even those with marked clinical responses seem to rapidly acquire resistance to IGF-1R targeted agents when used alone through yet to be identified mechanisms. As the IGF-1R receptor is just one of many that converge upon common intracellular signaling cascades, it is likely that effective IGF-1R targeting must occur in parallel with blockade of redundant signaling paths. Herein, we present the rationale for dual targeting of IGF-1R and other signaling molecules as an effective strategy to combat acquired drug resistance by carcinomas and sarcomas.

The different roles of ER subtypes in cancer biology and therapy

By eliciting distinct transcriptional responses, the oestrogen receptors (ERs) ERα and ERβ exert opposite effects on cellular processes that include proliferation, apoptosis and migration and that differentially influence the development and the progression of cancer. Perturbation of ER subtype-specific expression has been detected in various types of cancer, and the differences in the expression of ERs are correlated with the clinical outcome. The changes in the bioavailability of ERs in tumours, together with their specific biological functions, promote the selective restoration of their activity as one of the major therapeutic approaches for hormone-dependent cancers.

Epigenomic reprogramming of the developing reproductive tract and disease susceptibility in adulthood

During development, epigenetic programs are "installed" on the genome that direct differentiation and normal tissue and organ function in adulthood. Consequently, development is also a period of susceptibility to reprogramming of the epigenome. Developmental reprogramming occurs when an adverse stimulus or insult interrupts the proper "install" of epigenetic programs during development, reprogramming normal physiologic responses in such a way as to promote disease later in life. Some of the best examples of developmental reprogramming involve the reproductive tract, where early life exposures to environmental estrogens can increase susceptibility to benign and malignant tumors in adulthood including leiomyoma (fibroids), endometrial, and prostate cancer. Although specific mechanism(s) by which environmental estrogens reprogram the developing epigenome were unknown, both DNA and histone methylation were considered likely targets for epigenetic reprogramming. We have now identified a mechanism by which developmental exposures to environmental estrogens reprogram the epigenome by inducing inappropriate activation of nongenomic estrogen receptor (ER) signaling. Activation of nongenomic ER signaling via the phosphotidylinositol-3-kinase (PI3K) pathway activates the kinase AKT/PKB in the developing reproductive tract, which phosphorylates the histone lysine methyltransferase (HKMT) EZH2, the key "installer" of epigenetic histone H3 lysine 27 trimethylation (H3K27me3). AKT phosphorylation inactivates EZH2, decreasing levels of H3K27 methylation, a repressive mark that inhibits gene expression, in the developing uterus. As a result of this developmental reprogramming, many estrogen-responsive genes become hypersensitive to estrogen in adulthood, exhibiting elevated expression throughout the estrus cycle, and resulting in a "hyper-estrogenized" phenotype in the adult uterus that promotes development of hormone-dependent tumors.

Non-nuclear estrogen receptor signaling in the endothelium

In addition to the classical function of estrogen receptors (ER) as transcription factors, evidence continues to accumulate that they mediate non-nuclear processes in numerous cell types, including the endothelium, in which they activate endothelial NO synthase. Non-nuclear ER signaling entails unique post-translational modifications and protein-protein interactions of the receptor with adaptor molecules, kinases, and G proteins. Recent in vitro and in vivo studies in mice using an estrogen-dendrimer conjugate that is excluded from the nucleus indicate that non-nuclear ER activation underlies the migration and growth responses of endothelial cells to estrogen but not the growth responses of endometrial or breast cancer cells to the hormone. In this minireview, the features of ERα and protein-protein interactions that enable it to invoke extranuclear signaling in the endothelium and the consequences of that signaling are discussed.

GPR30 activation opposes estrogen-dependent uterine growth via inhibition of stromal ERK1/2 and estrogen receptor alpha (ERα) phosphorylation signals

Although estradiol-17β (E2)-regulated early and late phase uterine responses have been well defined, the molecular mechanisms linking the phases remain poorly understood. We have previously shown that E2-regulated early signals mediate cross talk with estrogen receptor (ER)-α to elicit uterine late growth responses. G protein-coupled receptor (GPR30) has been implicated in early nongenomic signaling mediated by E2, although its role in E2-dependent uterine biology is unclear. Using selective activation of GPR30 by G-1, we show here a new function of GPR30 in regulating early signaling events, including the inhibition of ERK1/2 and ERα (Ser118) phosphorylation signals and perturbation of growth regulation under the direction of E2 in the mouse uterus. We observed that GPR30 primarily localizes in the uterine epithelial cells, and its activation alters gene expression and mediates inhibition of ERK1/2 and ERα (Ser118) phosphorylation signals in the stromal compartment, suggesting a paracrine signaling is involved. Importantly, viral-driven manipulation of GPR30 or pharmacological inhibition of ERK1/2 activation effectively alters E2-dependent uterine growth responses. Overall, GPR30 is a negative regulator of ERα-dependent uterine growth in response to E2. Our work has uncovered a novel GPR30-regulated inhibitory event, which may be physiologically relevant in both normal and pathological situations to negatively balance ERα-dependent uterine growth regulatory functions induced by E2.

Steroid signaling activation and intracellular localization of sex steroid receptors

In addition to stimulating gene transcription, sex steroids trigger rapid, non-genomic responses in the extra-nuclear compartment of target cells. These events take place within seconds or minutes after hormone administration and do not require transcriptional activity of sex steroid receptors. Depending on cell systems, activation of extra-nuclear signaling pathways by sex steroids fosters cell cycle progression, prevents apoptosis, leads to epigenetic modifications and increases cell migration through cytoskeleton changes. These findings have raised the question of intracellular localization of sex steroid receptors mediating these responses. During the past years, increasing evidence has shown that classical sex steroid receptors localized in the extra-nuclear compartment or close to membranes of target cells induce these events. The emerging picture is that a process of bidirectional control between signaling activation and sex steroid receptor localization regulates the outcome of hormonal responses in target cells. This mechanism ensures cell cycle progression in estradiol-treated breast cancer cells, and its derangement might occur in progression of human proliferative diseases. These findings will be reviewed here together with unexpected examples of the relationship between sex steroid receptor localization, signaling activation and biological responses in target cells. We apologize to scientists whose reports are not mentioned or extensively discussed owing to space limitations.