Inhibition of Estradiol Receptor/Src Association and Cell Growth by an Estradiol Receptor α Tyrosine-Phosphorylated Peptide

Regulation of mRNA translation by estrogen receptor in breast cancer

Breast cancer is one of the leading causes of cancer-related fatalities and the most often diagnosed malignancy in women globally. Dysregulation of sex hormone signaling pathways mediated by the estrogen receptor (ER) in breast cancer is well characterized. Although ER is known to promote cell growth and survival by altering gene transcription, recent research suggests that its effects in cancers are also mediated through dysregulation of protein synthesis. This implies that ER can coordinately affect gene expression through both translational and transcriptional pathways, leading to the development of malignancy. In this review, we will cover the current understanding of how the ER controls mRNA translation in breast cancer and discuss any potential clinical implications of this phenomenon.

Mechanisms of breast cancer progression induced by environment-polluting aryl hydrocarbon receptor agonists

Breast cancer is the most common invasive malignancy among women worldwide and constitutes a complex and heterogeneous disease. Interest has recently grown in the role of the aryl hydrocarbon receptor (AhR) in breast cancer and the contribution of environment-polluting AhR agonists. Here, we present a literature review addressing AhR ligands, including pesticides hexachlorobenzene and chlorpyrifos, polycyclic aromatic hydrocarbons, polychlorinated dibenzo-p-dioxins and dibenzofurans, polychlorinated biphenyls, parabens, and phthalates. The objectives of this review are a) to summarize recent original experimental, preclinical, and clinical studies on the biological mechanisms of AhR agonists which interfere with the regulation of breast endocrine functions, and b) to examine the biological effects of AhR ligands and their impact on breast cancer development and progression. We discuss biological mechanisms of action in cell viability, cell cycle, proliferation, epigenetic changes, epithelial to mesenchymal transition, and cell migration and invasion. In addition, we examine the effects of AhR ligands on angiogenic processes, metastasis, chemoresistance, and stem cell renewal. We conclude that exposure to AhR agonists stimulates pathways that promote breast cancer development and may contribute to tumor progression. Given the massive use of industrial and agricultural chemicals, ongoing evaluation of their effects in laboratory assays and preclinical studies in breast cancer at environmentally relevant doses is deemed essential. Likewise, awareness should be raised in the population regarding the most harmful toxicants to eradicate or minimize their use.

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.

A Basic Review on Estrogen Receptor Signaling Pathways in Breast Cancer

Breast cancer is the most common cancer and the deadliest among women worldwide. Estrogen signaling is closely associated with hormone-dependent breast cancer (estrogen and progesterone receptor positive), which accounts for two-thirds of tumors. Hormone therapy using antiestrogens is the gold standard, but resistance to these treatments invariably occurs through various biological mechanisms, such as changes in estrogen receptor activity, mutations in the ESR1 gene, aberrant activation of the PI3K pathway or cell cycle dysregulations. All these factors have led to the development of new therapies, such as selective estrogen receptor degraders (SERDs), or combination therapies with cyclin-dependent kinases (CDK) 4/6 or PI3K inhibitors. Therefore, understanding the estrogen pathway is essential for the treatment and new drug development of hormone-dependent cancers. This mini-review summarizes current literature on the signalization, mechanisms of action and clinical implications of estrogen receptors in breast cancer.

Activation of estrogen receptor ESR1 and ESR2 induces proliferation of the human testicular embryonal carcinoma NT2/D1 cells

The aims of the present study were to investigate the expression of the classic estrogen receptors ESR1 and ESR2, the splicing variant ESR1-36 and GPER in human testicular embryonal carcinoma NT2/D1 cells, and the effects of the activation of the ESR1 and ESR2 on cell proliferation. Immunostaining of ESR1, ESR2, and GPER were predominantly found in the nuclei, and less abundant in the cytoplasm. ESR1-36 isoform was predominantly expressed in the perinuclear region and cytoplasm, and some weakly immunostained in the nuclei. In nonstimulated NT2/D1 cells (control), proteins of the cell cycle CCND1, CCND2, CCNE1 and CDKN1B are present. Activation of ESR1 and ESR2 increases, respectively, CCND2 and CCNE1 expression, but not CCND1. Activation of ESR2 also mediates upregulation of the cell cycle inhibitor CDKN1B. This protein co-immunoprecipitated with CCND2. Also, E2 induces an increase in the number and viability of the NT2/D1 cells. These effects are blocked by simultaneous pretreatment with ESR1-and ESR2-selective antagonists, confirming that both estrogen receptors regulate NT2/D1 cell proliferation. In addition, E2 increases SRC phosphorylation, and SRC mediates cell proliferation. Our study provides novel insights into the signatures and molecular mechanisms of estrogen receptor in NT2/D1 cells.

Endocrine disruptor hexachlorobenzene induces cell migration and invasion, and enhances aromatase expression levels in human endometrial stromal cells

Endometriosis is the presence and growth of endometrial tissue outside of the uterus. Previous studies have suggested that endocrine disrupting chemicals such as organochlorine pesticides could be a risk factor for endometriosis. Hexachlorobenzene (HCB) is a weak ligand of the aryl hydrocarbon receptor (AhR) and promotes metalloproteinase and cyclooxygenase-2 (COX-2) expression, as well as, c-Src activation in human endometrial stromal cells (T-HESC) and in rat endometriosis model. Our aim was to evaluate the effect of HCB exposure on oestrogen receptor (ER) ɑ and β, progesterone receptor (PR) and aromatase expression, as well as, on cell migration and invasion in T-HESC and primary cultures of endometrial stromal cells from eutopic endometria of control subjects (ESC). Results show that HCB increases ERɑ and aromatase protein levels and reduces PR content in both T-HESC and ESC. However, the pesticide only increases ERβ expression in ESC, without changes in T-HESC. Moreover, cell migration and invasion are promoted by pesticide exposure involving the AhR, c-Src, COX-2 and ER pathways in T-HESC. HCB also triggers ERɑ activation via phosphorylation in Y537 through AhR/c-Src pathway. Our results provide experimental evidence that HCB induces alterations associated with endometriosis, suggesting that these mechanisms could contribute to pesticide exposure-induced endometriosis development.

New Insights and Emerging Therapeutic Approaches in Prostate Cancer

Prostate cancer is the second most frequently diagnosed cancer in men and several therapeutic approaches are currently available for patient's care. Although the androgen receptor status represents a good predictor of response to androgen deprivation therapy, prostate cancer frequently becomes resistant to this approach and spreads. The molecular mechanisms that contribute to progression and drug-resistance of this cancer remain still debated. However, few therapeutic options are available for patient's management, at this stage. Recent years have seen a great expansion of the studies concerning the role of stromal-epithelial interactions and tumor microenvironment in prostate cancer progression. The findings so far collected have provided new insights into diagnostic and clinical management of prostate cancer patients. Further, new fascinating aspects concerning the intersection of the androgen receptor with survival factors as well as calcium channels have been reported in cultured prostate cancer cells and mouse models. The results of these researches have opened the way for a better understanding of the basic mechanisms involved in prostate cancer invasion and drug-resistance. They have also significantly expanded the list of new biomarkers and druggable targets in prostate cancer. The primary aim of this manuscript is to provide an update of these issues, together with their translational aspects. Exploiting the power of novel promising therapeutics would increase the success rate in the diagnostic path and clinical management of patients with advanced disease.

Segregation of nuclear and membrane-initiated actions of estrogen receptor using genetically modified animals and pharmacological tools

Estrogen receptor alpha (ERα) and beta (ERβ) are members of the nuclear receptor superfamily, playing widespread functions in reproductive and non-reproductive tissues. Beside the canonical function of ERs as nuclear receptors, in this review, we summarize our current understanding of extra-nuclear, membrane-initiated functions of ERs with a specific focus on ERα. Over the last decade, in vivo evidence has accumulated to demonstrate the physiological relevance of this ERα membrane-initiated-signaling from mouse models to selective pharmacological tools. Finally, we discuss the perspectives and future challenges opened by the integration of extra-nuclear ERα signaling in physiology and pathology of estrogens.

Non-genomic signaling of steroid receptors in cancer

Steroid receptors (SRs) are members of the nuclear receptor family, which are ligand-activated transcription factors. SRs regulate many physiological functions including development and reproduction, though they can also be involved in several pathologies, especially cancer. Highly controlled cellular responses to steroids involve transcriptional regulation (genomic activity) combined with direct activation of signaling cascades (non-genomic activity). Non-genomic signaling has been extensively studied in cancer, mainly in breast cancer for ER and PR, and prostate cancer for AR. Even though most of the studies have been conducted in cells, some of them have been confirmed in vivo, highlighting the relevance of this pathway in cancer. This review provides an overview of the current and emerging knowledge on non-genomic signaling with a focus on breast and prostate cancers and its clinical relevance. A thorough understanding of ER, PR, AR and GR non-genomic pathways may open new perspectives for the development of therapeutic strategies.

Mechanisms of endocrine therapy resistance in breast cancer

The most commonly diagnosed breast cancer (BC) subtype is characterized by estrogen receptor (ER) expression. Treatment of this BC subtype typically involves modalities that either suppress the production of estrogen or impede the binding of estrgen to its receptors, constituting the basis for endocrine therapy. While many patients have benefitted from endocrine therapy with clear reduction in mortality and cancer recurrence, one of the clinical hurdles that remain involves overcoming intrinsic (de novo) or acquired resistance to endocrine therapy driven by diverse and complex changes occurring in the tumor microenvironment. Moreover, such resistance may persist even after progression through additional antiestrogen therapies thus demonstrating the importance of further investigation of mechanisms of ER modulation. Here, we discuss a number of advances that provide a better understanding of the complex mechanistic basis for resistance to endocrine therapy as well as future therapeutic maneuvers that may break this resistance.

Analysis of genomic and non-genomic signaling of estrogen receptor in PDX models of breast cancer treated with a combination of the PI3K inhibitor alpelisib (BYL719) and fulvestrant

BACKGROUND

Endocrine therapies targeting estrogen signaling have significantly improved breast cancer (BC) patient survival, although 40% of ERα-positive BCs do not respond to those therapies. Aside from genomic signaling, estrogen triggers non-genomic pathways by forming a complex containing methylERα/Src/PI3K, a hallmark of aggressiveness and resistance to tamoxifen. We aimed to confirm the prognostic value of this complex and investigated whether its targeting could improve tumor response in vivo.

METHODS

The interaction of ERα/Src and ERα/PI3K was studied by proximity ligation assay (PLA) in a cohort of 440 BC patients. We then treated patient-derived BC xenografts (PDXs) with fulvestrant or the PI3K inhibitor alpelisib (BYL719) alone or in combination. We analyzed their anti-proliferative effects on 6 ERα+ and 3 ERα- PDX models. Genomic and non-genomic estrogen signaling were assessed by measuring ERα/PI3K interaction by PLA and the expression of estrogen target genes by RT-QPCR, respectively.

RESULTS

We confirmed that ERα/Src and ERα/PI3K interactions were associated with a trend to poorer survival, the latter displaying the most significant effects. In ERα+ tumors, the combination of BYL719 and fulvestrant was more effective than fulvestrant alone in 3 models, irrespective of PI3K, PTEN status, or ERα/PI3K targeting. Remarkably, resistance to fulvestrant was associated with non-genomic ERα signaling, since genomic degradation of ERα was unaltered in these tumors, whereas the treatment did not diminish the level of ERα/PI3K interaction. Interestingly, in 2 ERα- models, fulvestrant alone impacted tumor growth, and this was associated with a decrease in ERα/PI3K interaction.

CONCLUSIONS

Our results demonstrate that ERα/PI3K may constitute a new prognostic marker, as well as a new target in BC. Indeed, resistance to fulvestrant in ERα+ tumors was associated with a lack of impairment of ERα/PI3K interaction in the cytoplasm. In addition, an efficient targeting of ERα/PI3K in ERα- tumors could constitute a promising therapeutic option.

Carcinogenic effects of bisphenol A in breast and ovarian cancers

Endocrine-disrupting chemicals (EDCs) are exogenous chemical compounds ubiquitously found in everyday life of the modern world. EDCs enter the human body where they act similarly to endogenous hormones, altering the functions of the endocrine system and causing adverse effects on human health. Bisphenol A (BPA), the principal representative of this class, is a carbon-based synthetic plastic, and a key element in manufacturing cans, reusable water bottles and medical equipment. BPA mimics the actions of estrogen on multiple levels by activating estrogen receptors α and β. BPA regulates various processes, such as cell proliferation, migration and apoptosis, leading to neoplastic changes. Considering genetic mechanisms, BPA exerts its functions via multiple oncogenic signaling pathways, including the STAT3, PI3K/AKT and MAPK pathways. Furthermore, BPA is associated with various modifications of the reproductive system in both males and females. These alterations include benign lesions, such as endometrial hyperplasia, the development of ovarian cysts, an increase in the ductal density of mammary gland cells and other preneoplastic lesions. These benign lesions may continue to develop to breast or ovarian cancer; the effects of BPA depend on various molecular and epigenetic mechanisms that dictate whether the endocrine or reproductive system is impacted, wherein preexisting benign lesions can become cancerous. The present review supports the need for continuous research on BPA, considering its widespread use and most available data suggesting a carcinogenic effect of BPA on the female reproductive system. Although most studies on BPA have been conducted in vitro with human cells or in vivo with animal models, it can be argued that more studies should be conducted in vivo with humans to further promote understanding of the impact of BPA.

Sex Hormones and Inflammation Role in Oral Cancer Progression: A Molecular and Biological Point of View

Oral cancers have been proven to arise from precursors lesions and to be related to risk behaviour such as alcohol consumption and smoke. However, the present paper focuses on the role of chronic inflammation, related to chronical oral infections and/or altered immune responses occurring during dysimmune and autoimmune diseases, in the oral cancerogenesis. Particularly, oral candidiasis and periodontal diseases introduce a vicious circle of nonhealing and perpetuation of the inflammatory processes, thus leading toward cancer occurrence via local and systemic inflammatory modulators and via genetic and epigenetic factors.

Expression of estrogen receptor α variants and c-Fos in rat mammary gland and tumors

Breast cancer is currently the leading cause of cancer death among women worldwide. AP-1 (c-Fos/c-Jun) is associated with proliferation and survival, while cytoplasmic c-Fos activates phospholipid synthesis in cells induced to differentiate or grow. Estrogen receptor α 46 (ERα46) is a splice variant of full-length ERα66 and it is known that it has an inhibitory role in cancer cell growth. We investigated c-Fos localization, its relationship to AP-1, the non genomic pathway of phospho-Tyr537-ERα66, as well as ERα46 and ERα66 isoforms in rat mammary gland development and carcinogenic transformation, and in mammary tumors. Female rats were injected: a) saline solution (Control mammary gland, CMG) or b) N-Nitroso-N-methyl urea (NMU), and samples were taken at 60, 90, 120 and 150 days of life. In addition, we analyzed hormone-dependent (HD) and independent (HI) tumors in ovariectomized rats, and intact tumors (IT) in non-ovariectomized ones. Our results show that, in CMG, nuclear c-Fos and proliferation decreased with age, AP-1 content was low, and nuclear ERα46/ERα66 ratio was higher than 1. In NMU, nuclear c-Fos and proliferation increased with carcinogenic transformation, AP-1 content was high, and nuclear ERα46/ERα66 was below 1. As tumor grade increased, proliferation, nuclear c-Fos and AP-1 expression were negatively associated to nuclear ERα46/ERα66 in IT. In HD, nuclear ERα46/ERα66, nuclear c-Fos expression, AP-1 levels and proliferation were lower than in HI, whose growth is estrogen-independent. Phospho-Tyr537-ERα66 content and ERK1/2 activation were associated with AP-1 levels and cell proliferation. Collectively, our findings support the notion that variant detection and ERα46/ERα66 ratio could shed light on the role of ERα isoforms in mammary gland transformation and the behavior of ERα positive mammary tumors.

Estrogen receptor-positive (ER+) breast cancer treatment: Are multi-target compounds the next promising approach?

Endocrine therapy is currently the main therapeutic approach for estrogen receptor-positive (ER⁺) breast cancer, the most frequent subtype of breast cancer in women worldwide. For this subtype of tumors, the current clinical treatment includes aromatase inhibitors (AIs) and anti-estrogenic compounds, such as Tamoxifen and Fulvestrant, being AIs the first-line treatment option for post-menopausal women. Moreover, the recent guidelines also suggest the use of these compounds by pre-menopausal women after suppressing ovaries function. However, besides its therapeutic efficacy, the prolonged use of this type of therapies may lead to the development of several adverse effects, as well as, endocrine resistance, limiting the effectiveness of such treatments. In order to surpass this issues and clinical concerns, during the last years, several studies have been suggesting alternative therapeutic approaches, considering the function of aromatase, ERα and ERβ. Here, we review the structural and functional features of these three targets and their importance in ER⁺ breast cancer treatment, as well as, the current treatment strategies used in clinic, emphasizing the importance of the development of multi-target compounds able to simultaneously modulate these key targets, as a novel and promising therapeutic strategy for this type of cancer.

Liposomes and drug-in-cyclodextrin-in-liposomes formulations encapsulating 17β-estradiol: An innovative drug delivery system that prevents the activation of the membrane-initiated steroid signaling (MISS) of estrogen receptor α

The encapsulation into liposomes of several types of molecules presents the advantages to protect the activity of these molecules and to target specific tissues. Nevertheless, a major obstacle remains the incomplete understanding of nano-bio interactions. Specifically, the impact that inclusion of drug into liposomes or of drug-in-cyclodextrin-in liposomes (DCL) could have on the molecular and cellular mechanism of drug action is largely unknown. As a proof of concept, we evaluated the impact of 17β-estradiol (E2) included into liposomes or DCL on estrogen receptor (ER)α signaling pathways. Indeed, ERα relays the pleiotropic actions of E2 in physiology and pathophysiology through two major pathways: (1) the genomic/nuclear effects associated to the transcriptional activity of the ERα and (2) the rapid/nongenomic/membrane-initiated steroid signaling (MISS) effects related to the induction of fast signaling pathways occurring when ERα is anchored to the plasma membrane. We evidenced that the inclusion of E2 into liposomes (Lipo-E2) or into DCL (DCL-E2) prevented the activation of the rapid/nongenomic/extranuclear/MISS pathway of ERα, while the activation of the genomic/nuclear pathway was maintained. These results support that Lipo-E2 and DCL-E2 could be a useful tool to delineate the complex molecular mechanisms associated to ERα. In conclusion, this study supports the notion that inclusion of drugs into liposomes or DCL could modify some specific pathways of their molecular and cellular mechanisms of action. These results emphasized that attention should be paid to nano-bio interactions induced by the use of nanovectors in medicine.

Randomized phase-II evaluation of letrozole plus dasatinib in hormone receptor positive metastatic breast cancer patients

The non-receptor tyrosine kinase Src activation plays a role in the malignant progression of breast cancer, including development of endocrine therapy resistance and survival of bone metastases. This study investigated whether adding Src kinase inhibitor dasatinib to aromatase inhibitor (AI) therapy improved outcomes in estrogen receptor (ER)-positive, HER2-negative metastatic breast cancer (MBC). Postmenopausal patients with ER-positive, HER2-negative MBC (0-1 prior chemotherapies and no prior AI for MBC) were eligible for this non-comparative, parallel group, phase-II study. Patients were randomized to letrozole (2.5 mg/day PO) alone or with dasatinib (100 mg/day PO). Patients with disease progression on letrozole alone could crossover to dasatinib plus continued letrozole. The primary endpoint was clinical-benefit-rate (CBR; complete response + partial response + stable disease ≥6 months). A total of 120 patients were randomized. The CBR of 71% (95% CI 58-83%) was observed with letrozole + dasatinib versus the projected CBR of the combination of 56%. The CBR of 66% (95% CI 52-77%) with letrozole alone also exceeded the projected CBR of 39% with letrozole alone. The CBR was 23% in the crossover arm of letrozole plus dasatinib in patients progressing on letrozole alone. Median progression-free survival with the combination was 20.1 months and 9.9 months with letrozole alone. Letrozole plus dasatinib was well tolerated, although 26% of patients required dasatinib dose reductions. In this non-comparative phase-II trial, the CBR of 71% and the median PFS of 20.1 months with letrozole + dasatinib are encouraging and suggest that dasatinib may inhibit the emergence of acquired resistance to AI therapy.

Oestrogen Non-Genomic Signalling is Activated in Tamoxifen-Resistant Breast Cancer

Endocrine therapies targeting oestrogen signalling have significantly improved breast cancer management. However, their efficacy is limited by intrinsic and acquired resistance to treatment, which remains a major challenge for oestrogen receptor α (ERα)-positive tumours. Though many studies using in vitro models of endocrine resistance have identified putative actors of resistance, no consensus has been reached. We demonstrated previously that oestrogen non-genomic signalling, characterized by the formation of the ERα/Src/PI3K complex, is activated in aggressive breast cancers (BC). We wondered herein whether the activation of this pathway is also involved in resistance to endocrine therapies. We studied the interactions between ERα and Src or PI3K by proximity ligation assay (PLA) in in-vitro and in-vivo endocrine therapy-resistant breast cancer models. We reveal an increase in ERα/Src and ERα/PI3K interactions in patient-derived xenografts (PDXs) with acquired resistance to tamoxifen, as well as in tamoxifen-resistant MCF-7 cells compared to parental counterparts. Moreover, no interactions were observed in breast cancer cells resistant to other endocrine therapies. Finally, the use of a peptide inhibiting the ERα–Src interaction partially restored tamoxifen sensitivity in resistant cells, suggesting that such components could constitute promising targets to circumvent resistance to tamoxifen in BC.

Impact of endocrine disruptor hexachlorobenzene on the mammary gland and breast cancer: The story thus far

Breast cancer incidence is increasing globally and exposure to endocrine disruptors has gained importance as a potential risk factor. Hexachlorobenzene (HCB) was once used as a fungicide and, despite being banned, considerable amounts are still released into the environment. HCB acts as an endocrine disruptor in thyroid, uterus and mammary gland and was classified as possibly carcinogenic to human. This review provides a thorough analysis of results obtained in the last 15 years of research and evaluates data from assays in mammary gland and breast cancer in diverse animal models. We discuss the effects of environmentally relevant HCB concentrations on the normal mammary gland and different stages of carcinogenesis, and attempt to elucidate its mechanisms of action at molecular level. HCB weakly binds to the aryl hydrocarbon receptor (AhR), activating both membrane (c-Src) and nuclear pathways. Through c-Src stimulation, AhR signaling interacts with other membrane receptors including estrogen receptor-α, insulin-like growth factor-1 receptor, epidermal growth factor receptor and transforming growth factor beta 1 receptors. In this way, several pathways involved in mammary morphogenesis and breast cancer development are modified, inducing tumor progression. HCB thus stimulates epithelial cell proliferation, preneoplastic lesions and alterations in mammary gland development as well as neoplastic cell migration and invasion, metastasis and angiogenesis in breast cancer. In conclusion, our findings support the hypothesis that the presence and bioaccumulation of HCB in high-fat tissues and during highly sensitive time windows such as pregnancy, childhood and adolescence make exposure a risk factor for breast tumor development.

Aberrant FGFR signaling mediates resistance to CDK4/6 inhibitors in ER+ breast cancer

Using an ORF kinome screen in MCF-7 cells treated with the CDK4/6 inhibitor ribociclib plus fulvestrant, we identified FGFR1 as a mechanism of drug resistance. FGFR1-amplified/ER+ breast cancer cells and MCF-7 cells transduced with FGFR1 were resistant to fulvestrant ± ribociclib or palbociclib. This resistance was abrogated by treatment with the FGFR tyrosine kinase inhibitor (TKI) lucitanib. Addition of the FGFR TKI erdafitinib to palbociclib/fulvestrant induced complete responses of FGFR1-amplified/ER+ patient-derived-xenografts. Next generation sequencing of circulating tumor DNA (ctDNA) in 34 patients after progression on CDK4/6 inhibitors identified FGFR1/2 amplification or activating mutations in 14/34 (41%) post-progression specimens. Finally, ctDNA from patients enrolled in MONALEESA-2, the registration trial of ribociclib, showed that patients with FGFR1 amplification exhibited a shorter progression-free survival compared to patients with wild type FGFR1. Thus, we propose breast cancers with FGFR pathway alterations should be considered for trials using combinations of ER, CDK4/6 and FGFR antagonists.

Era+ breast cancer patients often develop resistance to endocrine therapy. Here, the authors show that FGFR1 amplification is a resistance mechanism to CDK4/6 inhibitor and endocrine therapy and that combined treatment with FGFR, CDK4/6, and anti-estrogens is a potential therapeutic strategy in Era+ breast cancer tumors.

Estrogens and Their Receptors in Prostate Cancer: Therapeutic Implications

A major challenge in clinical management of prostate cancer (PC) is to limit tumor growth and prevent metastatic spreading. Considerable efforts have been made to discover new compounds for PC therapy and recent years have seen promising progress in this field. Pharmacological approaches have been designed to achieve benefits in PC treatment and avoid the negative side effects resulting from administration of antagonists or agonists or new drugs. Nonetheless, the currently available therapies frequently induce resistance and PC progresses toward castration-resistant forms that can be caused by the androgen receptor reactivation and/or mutations, or derangement of signaling pathways. Preclinical and clinical findings have also shown that other nuclear receptors are frequently altered in PC. In this review, we focus on the role of estradiol/estradiol receptor (ER) axis, which controls PC growth and progression. Selective targeting of ER subtypes (α or β) may be an attractive way to limit the growth and spreading of prostatic cancer cells.

Bisphenol A induces cell cycle arrest in primary and prostate cancer cells through EGFR/ERK/p53 signaling pathway activation

Bisphenol A (BPA) belongs to the class of chemicals known as endocrine disruptors and has been also involved in the pathogenesis and progression of endocrine related cancer such as breast and prostate cancers. Here, we have investigated the effect of BPA in human prostate cancer LNCaP cells and in human non-transformed epithelial prostate EPN cells. Our data showed that BPA induces the down regulation of cyclin D1 expression and the upregulation of the cell cycle inhibitors p21 and p27, leading to cell cycle arrest. Interestingly, we found that the BPA anti-proliferative response depends on a strong and rapid activation of epidermal growth factor receptor (EGFR), which stimulates ERK-dependent pathway. This, in turn, induces expression of p53 and its phosphorylation on residue Ser15, which is responsible for cell cycle arrest. EGFR activation occurs upon a cross talk with androgen (AR) and estradiol receptor-β (ERβ) which are known to bind BPA.

Altogether, these findings show a novel signaling pathway in which EGFR activation plays a key role on BPA-induced cell cycle inhibition through a pathway involving AR and ERβ/EGFR complexes, ERK and p53. Our results provide new insights for understanding the molecular mechanisms in human prostate cancer. On the other, they could allow the development of new compounds that may be used to overcome human prostate cancer resistance to endocrine therapy in promising target therapeutic approaches.

Recent advances on bisphenol-A and endocrine disruptor effects on human prostate cancer

Endocrine disrupting chemicals (EDCs) are man-made substances widespread in the environment that include, among many others, bisphenol A (BPA), organochlorinated pesticides and hormone derivatives detectable in meat from animals raised in concentrated animal feeding operations. Increasing evidence indicates that EDCs have a negative impact on human health as well as on male and female fertility. They may also be associated with some endocrine diseases and increased incidence of breast and prostate cancer. This review aims to summarize available data on the (potential) impact of some common EDCs, focusing particularly on BPA, prostate cancer and their mechanisms of action. These compounds interfere with normal hormone signal pathway transduction, resulting in prolonged exposure of receptors to stimuli or interference with cellular hormone signaling in target cells. Understanding the effects of BPA and other EDCs as well as their molecular mechanism(s) may be useful in sensitizing the scientific community and the manufacturing industry to the importance of finding alternatives to their indiscriminate use.

Membrane and Nuclear Estrogen Receptor Alpha Actions: From Tissue Specificity to Medical Implications

Estrogen receptor alpha (ERα) has been recognized now for several decades as playing a key role in reproduction and exerting functions in numerous nonreproductive tissues. In this review, we attempt to summarize the in vitro studies that are the basis of our current understanding of the mechanisms of action of ERα as a nuclear receptor and the key roles played by its two activation functions (AFs) in its transcriptional activities. We then depict the consequences of the selective inactivation of these AFs in mouse models, focusing on the prominent roles played by ERα in the reproductive tract and in the vascular system. Evidence has accumulated over the two last decades that ERα is also associated with the plasma membrane and activates non-nuclear signaling from this site. These rapid/nongenomic/membrane-initiated steroid signals (MISS) have been characterized in a variety of cell lines, and in particular in endothelial cells. The development of selective pharmacological tools that specifically activate MISS and the generation of mice expressing an ERα protein impeded for membrane localization have begun to unravel the physiological role of MISS in vivo. Finally, we discuss novel perspectives for the design of tissue-selective ER modulators based on the integration of the physiological and pathophysiological roles of MISS actions of estrogens.

The molecular mechanisms underlying the ERα-36-mediated signaling in breast cancer

Alterations in estrogen-mediated cellular signaling have largely been implicated in the pathogenesis of breast cancer. Here, we investigated the signaling regulation of a splice variant of the estrogen receptor, namely estrogen receptor (ERα-36), associated with a poor prognosis in breast cancers. Coupling in vitro and in vivo approaches we determined the precise sequential molecular events of a new estrogen signaling network in an ERα-negative cell line and in an original patient-derived xenograft. After estrogen treatment, ERα-36 rapidly associates with Src at the level of the plasma membrane, initiating downstream cascades, including MEK1/ERK activation and paxillin phosphorylation on S126, which in turn triggers a higher expression of cyclin D1. Of note, the direct binding of ERα-36 to ERK2 prevents its dephosphorylation by MKP3 and enhances the downstream signaling. These findings improve our understanding of the regulation of non-genomic estrogen signaling and open new avenues for personalized therapeutic approaches targeting Src or MEK in ERα-36-positive patients.

Hyaluronan-conjugated liposomes encapsulating gemcitabine for breast cancer stem cells

Investigation of potential therapeutics for targeting breast cancer stem cells (BCSCs) is important because these cells are regarded as culprit of breast cancer relapse. Accomplishing this kind of strategy requires a specific drug-delivery system using the distinct features of liposomes. Studies on targeted liposomal delivery systems have indicated the conjugation of hyaluronan (HA), a primary ligand for CD44 surface markers, as an appropriate method for targeting BCSCs. For this study, enriched BCSCs were obtained by culturing MCF-7 breast cancer cells in nonadherent conditions. The enriched BCSCs were challenged with HA-conjugated liposomes encapsulating gemcitabine (2, 2-difluoro-2-deoxycytidine, GEM). In vitro study showed that the HA-conjugated liposomes significantly enhanced the cytotoxicity, anti-migration, and anti-colony formation abilities of GEM through targeting of CD44 expressed on BCSCs. In pharmacokinetic study, area under the drug concentration vs time curve (AUC) of the immunoliposomal GEM was 3.5 times higher than that of free GEM, indicating that the HA-conjugated liposomes enhanced the stability of GEM in the bloodstream and therefore prolonged its half-life time. The antitumor effect of the immunoliposomal GEM was 3.3 times higher than that of free GEM in a xenograft mouse model, probably reflecting the unique targeting of the CD44 receptor by HA and the increased cytotoxicity and stability through the liposomal formulation. Furthermore, marginal change in body weight demonstrated that the use of liposomes considerably reduced the systemic toxicity of GEM on normal healthy cells. Taken together, this study demonstrates that HA-conjugated liposomes encapsulating GEM show promise for the therapy of breast cancer in vitro and in a xenograft model by targeting the BCSCs.

Estrogen Receptor Folding Modulates cSrc Kinase SH2 Interaction via a Helical Binding Mode

The estrogen receptors (ERs) feature, next to their transcriptional role, important nongenomic signaling actions, with emerging clinical relevance. The Src Homology 2 (SH2) domain mediated interaction between cSrc kinase and ER plays a key role in this; however the molecular determinants of this interaction have not been elucidated. Here, we used phosphorylated ER peptide and semisynthetic protein constructs in a combined biochemical and structural study to, for the first time, provide a quantitative and structural characterization of the cSrc SH2-ER interaction. Fluorescence polarization experiments delineated the SH2 binding motif in the ER sequence. Chemical shift perturbation analysis by nuclear magnetic resonance (NMR) together with molecular dynamics (MD) simulations allowed us to put forward a 3D model of the ER-SH2 interaction. The structural basis of this protein-protein interaction has been compared with that of the high affinity SH2 binding sequence GpYEEI. The ER features a different binding mode from that of the "two-pronged plug two-hole socket" model in the so-called specificity determining region. This alternative binding mode is modulated via the folding of ER helix 12, a structural element directly C-terminal of the key phosphorylated tyrosine. The present findings provide novel molecular entries for understanding nongenomic ER signaling and targeting the corresponding disease states.

Src-dependent phosphorylation at Y406 on the thyroid hormone receptor β confers the tumor suppressor activity

Association studies suggest that the thyroid hormone receptor β1 (TRβ1) could function as a tumor suppressor in cancer cells. However, the underlying molecular mechanisms remain to be elucidated. We explored how TRβ1 acted as a tumor suppressor in breast cancer MDA cells. Proliferation and invasiveness were markedly inhibited in cells stably expressing TRβ1 (MDA-TRβ1 cells). cSrc-phosphorylated TRβ1 at Y406 signaled T3-induced degradation. Mutation of Y406 to Phe (TRβ1Y406F) did not affect T3 binding affinity, but blocked T3-induced degradation in cells. Importantly, cell-based studies showed that TRβ1Y406F lost the inhibitory effects by TRβ1 on cell proliferation and invasion. Consistently, in xenograft models, MDA-TRβ1 cells exhibited significantly slower tumor growth rates than those of Neo control cells. In contrast, the tumor growth rates of MDA-TRβ1Y406F cells were indistinguishable from those of Neo control cells. We further showed that markedly more TRβ1Y406F than TRβ1 was physically associated with cSrc in cells, leading to constitutive activation of cSrc-FAK-ERK signaling. In contrast, degradation of T3-bound TRβ1 complexed with cSrc attenuated signaling to decrease cell proliferation and invasiveness, thus confirming TRβ1 as a tumor suppressor. Thus, the present studies suggested that TRβ1 could be tested as a novel potential therapeutic target.

Cross-talk between androgen receptor/filamin A and TrkA regulates neurite outgrowth in PC12 cells

Steroids and growth factors control neuronal development through their receptors under physiological and pathological conditions. We show that PC12 cells harbor endogenous androgen receptor (AR), whose inhibition or silencing strongly interferes with neuritogenesis stimulated by the nonaromatizable synthetic androgen R1881 or NGF. This implies a role for AR not only in androgen signaling, but also in NGF signaling. In turn, a pharmacological TrkA inhibitor interferes with NGF- or androgen-induced neuritogenesis. In addition, androgen or NGF triggers AR association with TrkA, TrkA interaction with PI3-K δ, and downstream activation of PI3-K δ and Rac in PC12 cells. Once associated with AR, filamin A (FlnA) contributes to androgen or NGF neuritogenesis, likely through its interaction with signaling effectors, such as Rac. This study thus identifies a previously unrecognized reciprocal cross-talk between AR and TrkA, which is controlled by β1 integrin. The contribution of FlnA/AR complex and PI3-K δ to neuronal differentiation by androgens and NGF is also novel. This is the first description of AR function in PC12 cells.

Subtype-specific modulation of estrogen receptor-coactivator interaction by phosphorylation

The estrogen receptor (ER) is the number one target for the treatment of endocrine responsive breast cancer and remains a highly attractive target for new drug development. Despite considerable efforts to understand the role of ER post-translational modifications (PTMs), the complexity of these modifications and their impact, at the molecular level, are poorly understood. Using a chemical biology approach, fundamentally rooted in an efficient protein semisynthesis of tyrosine phosphorylated ER constructs, the complex role of the ER tyrosine phosphorylation is addressed here for the first time on a molecular level. The semisynthetic approach allows for the site-specific introduction of PTMs as well as biophysical probes. A combination of biophysical techniques, including NMR, with molecular dynamics studies reveals the role of the phosphorylation of the clinically relevant tyrosine 537 (Y537) in ERα and the analogous tyrosine (Y488) in ERβ. Phosphorylation has important effects on the dynamics of the ER Helix 12, which is centrally involved in receptor activity regulation, and on its interplay with ligand and cofactor binding, but with differential regulatory effects of the analogous PTMs on the two ER subtypes. Combined, the results bring forward a novel molecular model of a phosphorylation-induced subtype specific ER modulatory mechanism, alternative to the widely accepted ligand-induced activation mechanism.

Role of non-genomic androgen signalling in suppressing proliferation of fibroblasts and fibrosarcoma cells

The functions of androgen receptor (AR) in stromal cells are still debated in spite of the demonstrated importance of these cells in organ development and diseases. Here, we show that physiological androgen concentration (10 nM R1881 or DHT) fails to induce DNA synthesis, while it consistently stimulates cell migration in mesenchymal and transformed mesenchymal cells. Ten nanomolar R1881 triggers p27 Ser10 phosphorylation and its stabilization in NIH3T3 fibroblasts. Activation of Rac and its downstream effector DYRK 1B is responsible for p27 Ser10 phosphorylation and cell quiescence. Ten nanomolar androgen also inhibits transformation induced by oncogenic Ras in NIH3T3 fibroblasts. Overexpression of an AR mutant unable to interact with filamin A, use of a small peptide displacing AR/filamin A interaction, and filamin A knockdown indicate that the androgen-triggered AR/filamin A complex regulates the pathway leading to p27 Ser10 phosphorylation and cell cycle arrest. As the AR/filamin A complex is also responsible for migration stimulated by 10 nM androgen, our report shows that the androgen-triggered AR/filamin A complex controls, through Rac 1, the decision of cells to halt cell cycle and migration. This study reveals a new and unexpected role of androgen/AR signalling in coordinating stromal cell functions.

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.

LKB1 when associated with methylatedERα is a marker of bad prognosis in breast cancer

Although the presence of nuclear estrogen receptor is widely used to guide breast cancer therapy, less attention has been paid to the receptor cytoplasmic signaling. Recently, we have shown that this pathway is operative in vivo and is activated in aggressive tumors representing a new potential target for breast cancer therapy. Here, we identified LKB1 as a partner of ERα and we explored its potential role in estrogen nongenomic signaling. The associations between LKB1 expression and the actors of this pathway, namely the methylated form of ERα (metERα), Src and PI3K, have been analyzed both in cultured cells and in 154 primary breast tumor samples. We found that LKB1 is a component of the cytoplasmic signaling complex in breast cell lines as well as in primary breast tumors. Moreover, an inverse correlation between the localization of LKB1 in nuclear and cytoplasmic compartments is observed. Importantly, high expression of cytoplasmic LKB1 is an independent marker of poor prognosis, associated with reduced overall survival (OS) and disease free survival (DFS). Conversely, the presence of nuclear LKB1 associates with increased OS and DFS. In conclusion, our results highlight that LKB1 expression in breast cancer appears to have opposite effects depending on its subcellular localization and may be used as a new prognostic biomarker.

Targeting androgen receptor/Src complex impairs the aggressive phenotype of human fibrosarcoma cells

Background

Hormones and growth factors influence the proliferation and invasiveness of human mesenchymal tumors. The highly aggressive human fibrosarcoma HT1080 cell line harbors classical androgen receptor (AR) that responds to androgens triggering cell migration in the absence of significant mitogenesis. As occurs in many human cancer cells, HT1080 cells also express epidermal growth factor receptor (EGFR).

Experimental

Findings: We report that the pure anti-androgen Casodex inhibits the growth of HT1080 cell xenografts in immune-depressed mice, revealing a novel role of AR in fibrosarcoma progression. In HT1080 cultured cells EGF, but not androgens, robustly increases DNA synthesis. Casodex abolishes the EGF mitogenic effect, implying a crosstalk between EGFR and AR. The mechanism underlying this crosstalk has been analyzed using an AR-derived small peptide, S1, which prevents AR/Src tyrosine kinase association and androgen-dependent Src activation. Present findings show that in HT1080 cells EGF induces AR/Src Association, and the S1 peptide abolishes both the assembly of this complex and Src activation. The S1 peptide inhibits EGF-stimulated DNA synthesis, cell matrix metalloproteinase-9 (MMP-9) secretion and invasiveness of HT1080 cells. Both Casodex and S1 peptide also prevent DNA synthesis and migration triggered by EGF in various human cancer-derived cells (prostate, breast, colon and pancreas) that express AR.

Conclusion

This study shows that targeting the AR domain involved in AR/Src association impairs EGF signaling in human fibrosarcoma HT1080 cells. The EGF-elicited processes inhibited by the peptide (DNA synthesis, MMP-9 secretion and invasiveness) cooperate in increasing the aggressive phenotype of HT1080 cells. Therefore, AR represents a new potential therapeutic target in human fibrosarcoma, as supported by Casodex inhibition of HT1080 cell xenografts. The extension of these findings in various human cancer-derived cell lines highlights the conservation of this process across divergent cancer cells and identifies new potential targets in the therapeutic approach to human cancers.

Unliganded estrogen receptor alpha promotes PC12 survival during serum starvation

Many studies have reported proliferative, differentiating or protective effects of estradiol, notably through estrogen receptor alpha (ERα). On the contrary, the ligand-independent action of ERα is currently poorly documented notably in cell protection. The stable transfection of wild type, substituted or truncated form of ERα in PC12 cells (ERα negative cell line) lead the specific study of its ligand-independent action. Hence, we demonstrate here that, in the absence of E2, the expression of ERα prevents cells from apoptosis induced by serum deprivation. This protection is not due to an ERE-mediated transcription and does not require either AF-1 or AF-2 transactivation functions. It is afforded to the Y537 residue of ERα and activation of c-Src/Stat3 signaling pathway.

Estrogen receptor α/β-cofactor motif interactions; interplay of tyrosine 537/488 phosphorylation and LXXLL motifs

The Estrogen Receptors ERα and ERβ bind cofactor proteins via short LXXLL motifs. The exact regulation and selectivity of these interactions remains an open question and the role of post-translational modifications (PTMs) is virtually unexplored. Here, we designed an X(7)-LXXLL-X(7) T7 phage display library and screened this against four ER protein constructs: the 'naked' ERα and ERβ Ligand Binding Domains (LBDs) and the tyrosine phosphorylated ERα (pY537) and ERβ (pY488) LBDs. The site-selective tyrosine phosphorylated protein constructs were obtained via a protein semi-synthesis approach. Phage display screening yielded preferential sets of peptides. LXXLL peptides with a low pI/acidic C-terminus prefer binding to the naked ERβ over the phosphorylated ERβ analogue and ERα constructs. Peptides with a high pI/basic C-terminus show the opposite behaviour. These findings not only show regulation of the ERβ-cofactor interaction via tyrosine phosphorylation, but also suggest that ERβ and its tyrosine 488 phosphorylation play crucial roles in modulating interactions of coactivators to ERα since the natural Steroid Receptor Coactivators (SRCs) feature LXXLL motifs with acidic C-termini, while the repressor protein RIP140 features LXXLL motifs with basic C-termini. This insight provides explanation for ER transcriptional activity and can lead to more focussed targeting of the ER-coactivator interaction.

Dasatinib : a novel therapy for breast cancer?

INTRODUCTION

Dasatinib is a novel tyrosine kinase inhibitor with activity against the Src family kinases. The Src pathway is active in breast cancer and has been shown to promote cell proliferation, invasiveness, and metastases. Preclinical data support the use of dasatinib to inhibit breast cancer cell growth, modulate hormone and EGFR signaling, and alter cell migration.

AREAS COVERED

This article details the preclinical data supporting dasatinib's use in breast cancer treatment. Additionally, Phase I/II studies that have tested dasatinib as a single agent and in combination with chemotherapy and antihormonal agents are discussed.

EXPERT OPINION

Phase I/II studies to date have shown only limited responses to dasatinib among breast cancer patients. Dasatinib has no current role in the treatment of breast cancer, and its future is uncertain. No specific subset of patients has been identified which preferentially responds to treatment. Studies are under way to identify specific molecular markers that might predict response to dasatinib.

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.

Derailed estrogen signaling and breast cancer: an authentic couple

Estrogen or 17β-estradiol, a steroid hormone, plays a critical role in the development of mammary gland via acting through specific receptors. In particular, estrogen receptor-α (ERα) acts as a transcription factor and/or a signal transducer while participating in the development of mammary gland and breast cancer. Accumulating evidence suggests that the transcriptional activity of ERα is altered by the action of nuclear receptor coregulators and might be responsible, at least in part, for the development of breast cancer. In addition, this process is driven by various posttranslational modifications of ERα, implicating active participation of the upstream receptor modifying enzymes in breast cancer progression. Emerging studies suggest that the biological outcome of breast cancer cells is also influenced by the cross talk between microRNA and ERα signaling, as well as by breast cancer stem cells. Thus, multiple regulatory controls of ERα render mammary epithelium at risk for transformation upon deregulation of normal homeostasis. Given the importance that ERα signaling has in breast cancer development, here we will highlight how the activity of ERα is controlled by various regulators in a spatial and temporal manner, impacting the progression of the disease. We will also discuss the possible therapeutic value of ERα modulators as alternative drug targets to retard the progression of breast cancer.

Tyrosine phosphorylation of estradiol receptor by Src regulates its hormone-dependent nuclear export and cell cycle progression in breast cancer cells

We report that in breast cancer cells, tyrosine phosphorylation of the estradiol receptor alpha (ERalpha) by Src regulates cytoplasmic localization of the receptor and DNA synthesis. Inhibition of Src or use of a peptide mimicking the ERalpha p-Tyr537 sequence abolishes ERalpha tyrosine phosphorylation and traps the receptor in nuclei of estradiol-treated MCF-7 cells. An ERalpha mutant carrying a mutation of Tyr537 to phenylalanine (ER537F) persistently localizes in nuclei of various cell types. In contrast with ERalpha wt, ER537F does not associate with Ran and its interaction with Crm1 is insensitive to estradiol. Thus, independently of estradiol, ER537F is retained in nuclei, where it entangles FKHR-driving cell cycle arrest. Chromatin immunoprecipitation analysis reveals that overexpression of ER537F in breast cancer cells enhances FKHR interaction with cyclin D1 promoter. This mutant also counteracts cell transformation by the activated forms of Src or PI3-K. In conclusion, in addition to regulating receptor localization, ERalpha phosphorylation by Src is required for hormone responsiveness of DNA synthesis in breast cancer cells.

Activation of rapid oestrogen signalling in aggressive human breast cancers

Oestrogen receptors can mediate rapid activation of cytoplasmic signalling cascades by recruiting Src and PI3K. However, the involvement of this pathway in breast cancer remains poorly defined. We have previously shown that methylation of ERα is required for the formation of the ERα/Src/PI3K complex and that ERα is hypermethylated in a subset of breast cancers. Here, we used Proximity Ligation Assay to demonstrate that this complex is present in the cytoplasm of breast cancer cell lines as well as formalin-fixed, paraffin-embedded tumours. Of particular interest, the analysis of 175 breast tumours showed that overexpression of this complex in a subset of breast tumours correlates to the activation of the downstream effector Akt. Survival analysis revealed that high expression of this complex is an independent marker of poor prognosis and associated with reduced disease-free survival. Our data introduces the new concept that the rapid oestrogen pathway is operative in vivo. It also provides a rationale for patient stratification defined by the activation of this pathway and the identification of target therapies.

Estradiol receptors in breast cancer cells: associated co-factors as targets for new therapeutic approaches

Estrogen receptors α (ERα) and β (ERβ) are nuclear receptors which transduce estradiol (E2) response in many tissues including the mammary gland and breast cancers (BC). They activate or inhibit specific genes involved in cell cycle progression and cell survival through multiple enzyme activities leading to malignant transformation. Hormone therapy (antiestrogens (AEs) and aromatase inhibitors (AIs) have been widely used to block the mitogenic action of E2 in patients with ER-positive BC. ERs act in concert with numerous other proteins outside and inside the nucleus where co-activators such as histone modifying enzymes help reaching optimum gene activation. Moreover, E2-mediated gene regulation can occur through ERs located at the plasma membrane or G protein-coupled estrogen receptor (GPER), triggering protein kinase signaling cascades. Classical AEs as well as AIs are inefficient to block the cascades of events emanating from the membrane and from E2 binding to GPER, leading patients to escape anti-hormone treatments and hormone therapy resistance. Many pathways are involved in resistance, mostly resulting from over-expression of growth factor membrane receptors, in particular the HER2/ErbB2 which can be inhibited by specific antibodies or tyrosine kinases inhibitors. Together with the Hsp90 molecular chaperone machinery, a complex interplay between ERs, co-activators, co-repressors and growth factor-activated membrane pathways represents potent targets which warrant to be manipulated alone and in combination to designing novel therapies. The discovery of new potential targets arising from micro array studies gives the opportunity to activate or inhibit different new ER-modulating effectors for innovative therapeutic interventions.

Polyproline and Tat transduction peptides in the study of the rapid actions of steroid receptors

Cellular responses to signals require the action of a myriad of protein networks, which are regulated by protein/protein associations. Rapid actions of steroid hormones are also subject to this regulation. They induce direct association of steroid receptors with different proteins (e.g., growth factor receptors, signaling effectors, scaffold proteins, transcription factors). These multi-molecular complexes drive signaling activation and finally trigger basic hormonal effects. Receptor/protein associations are attracting increased interest concerning their role in hormone action as well as their potential use as therapeutic targets in hormonal diseases.

Cracking the estrogen receptor's posttranslational code in breast tumors

Estrogen signaling pathways, because of their central role in regulating the growth and survival of breast tumor cells, have been identified as suitable and efficient targets for cancer therapies. Agents blocking estrogen activity are already widely used clinically, and many new molecules have entered clinical trials, but intrinsic or acquired resistance to treatment limits their efficacy. The basic molecular studies underlying estrogen signaling have defined the critical role of estrogen receptors (ER) in many aspects of breast tumorigenesis. However, important knowledge gaps remain about the role of posttranslational modifications (PTM) of ER in initiation and progression of breast carcinogenesis. Whereas major attention has been focused on the phosphorylation of ER, many other PTM (such as acetylation, ubiquitination, sumoylation, methylation, and palmitoylation) have been identified as events modifying ER expression and stability, subcellular localization, and sensitivity to hormonal response. This article will provide an overview of the current and emerging knowledge on ER PTM, with a particular focus on their deregulation in breast cancer. We also discuss their clinical relevance and the functional relationship between PTM. A thorough understanding of the complete picture of these modifications in ER carcinogenesis might not only open new avenues for identifying new markers for prognosis or prediction of response to endocrine therapy but also could promote the development of novel therapeutic strategies.

Inhibition of SRC family kinases and receptor tyrosine kinases by dasatinib: possible combinations in solid tumors

Dasatinib is a small molecule tyrosine kinase inhibitor that targets a wide variety of tyrosine kinases implicated in the pathophysiology of several neoplasias. Among the most sensitive dasatinib targets are ABL, the SRC family kinases (SRC, LCK, HCK, FYN, YES, FGR, BLK, LYN, and FRK), and the receptor tyrosine kinases c-KIT, platelet-derived growth factor receptor (PDGFR) α and β, discoidin domain receptor 1 (DDR1), c-FMS, and ephrin receptors. Dasatinib inhibits cell duplication, migration, and invasion, and it triggers apoptosis of tumoral cells. As a consequence, dasatinib reduces tumoral mass and decreases the metastatic dissemination of tumoral cells. Dasatinib also acts on the tumoral microenvironment, which is particularly important in the bone, where dasatinib inhibits osteoclastic activity and favors osteogenesis, exerting a bone-protecting effect. Several preclinical studies have shown that dasatinib potentiates the antitumoral action of various drugs used in the oncology clinic, paving the way for the initiation of clinical trials of dasatinib in combination with standard-of-care treatments for the therapy of various neoplasias. Trials using combinations of dasatinib with ErbB/HER receptor antagonists are being explored in breast, head and neck, and colorectal cancers. In hormone receptor-positive breast cancer, trials using combinations of dasatinib with antihormonal therapies are ongoing. Dasatinib combinations with chemotherapeutic agents are also under development in prostate cancer (dasatinib plus docetaxel), melanoma (dasatinib plus dacarbazine), and colorectal cancer (dasatinib plus oxaliplatin plus capecitabine). Here, we review the preclinical evidence that supports the use of dasatinib in combination for the treatment of solid tumors and describe various clinical trials developed following a preclinical rationale.