MicroRNA-regulated gene networks during mammary cell differentiation are associated with breast cancer.

MicroRNAs (miRNAs) play pivotal roles in stem cell biology, differentiation and oncogenesis and are of high interest as potential breast cancer therapeutics. However, their expression and function during normal mammary differentiation and in breast cancer remain to be elucidated. In order to identify which miRNAs are involved in mammary differentiation, we thoroughly investigated miRNA expression during functional differentiation of undifferentiated, stem cell-like, murine mammary cells using two different large-scale approaches followed by qPCR. Significant changes in expression of 21 miRNAs were observed in repeated rounds of mammary cell differentiation. The majority, including the miR-200 family and known tumor suppressor miRNAs, was upregulated during differentiation. Only four miRNAs, including oncomiR miR-17, were downregulated. Pathway analysis indicated complex interactions between regulated miRNA clusters and major pathways involved in differentiation, proliferation and stem cell maintenance. Comparisons with human breast cancer tumors showed the gene profile from the undifferentiated, stem-like stage clustered with that of poor-prognosis breast cancer. A common nominator in these groups was the E2F pathway, which was overrepresented among genes targeted by the differentiation-induced miRNAs. A subset of miRNAs could further discriminate between human non-cancer and breast cancer cell lines, and miR-200a/miR-200b, miR-146b and miR-148a were specifically downregulated in triple-negative breast cancer cells. We show that miR-200a/miR-200b can inhibit epithelial-mesenchymal transition (EMT)-characteristic morphological changes in undifferentiated, non-tumorigenic mammary cells. Our studies propose EphA2 as a novel and important target gene for miR-200a. In conclusion, we present evidentiary data on how miRNAs are involved in mammary cell differentiation and indicate their related roles in breast cancer.

ERbeta1 represses basal breast cancer epithelial to mesenchymal transition by destabilizing EGFR.

INTRODUCTION: Epithelial to mesenchymal transition (EMT) is associated with the basal-like breast cancer phenotypes. 60% of basal-like cancers have been shown to express wild-type estrogen receptor beta (ERbeta1). However, it is still unclear whether the ERbeta expression is related to EMT, invasion and metastasis in breast cancer. In the present study, we examined whether ERbeta1 through regulating EMT can influence invasion and metastasis in basal-like cancers. METHODS: Basal-like breast cancer cells (MDA-MB-231 and Hs578T) in which ERbeta1 was either overexpressed or downregulated were analyzed for their ability to migrate and invade (wound-healing assay, matrigel-coated Transwell assay) as well as for the expression of EMT markers and components of the EGFR pathway (immunoblotting, RT-PCR). Coimmunoprecipitation and ubiquitylation assays were employed to examine whether ERbeta1 alters EGFR protein degradation and the interaction between EGFR and the ubiquitin ligase c-Cbl. The metastatic potential of the ERbeta1-expressing MDA-MB-231 cells was evaluated in vivo in a zebrafish xenotransplantation model and the correlation between ERbeta1 and E-cadherin expression was examined in 208 clinical breast cancer specimens by immunohistochemistry. RESULTS: Here we show that ERbeta1 inhibits EMT and invasion in basal-like breast cancer cells when they grow either in vitro or in vivo in zebrafish. The inhibition of EMT correlates with an ERbeta1-mediated upregulation of miR-200a/b/429 and the subsequent repression of ZEB1 and SIP1, which results in increased expression of E-cadherin. The positive correlation of ERbeta1 and E-cadherin expression was additionally observed in breast tumor samples. Downregulation of the basal marker EGFR through stabilization of the ubiquitin ligase c-Cbl complexes and subsequent ubiquitylation and degradation of the activated receptor is involved in the ERbeta1-mediated repression of EMT and induction of EGFR signaling abolished the ability of ERbeta1 to sustain the epithelial phenotype. CONCLUSIONS: Taken together, the results of our study strengthen the association of ERbeta1 with the regulation of EMT and propose the receptor as a potential crucial marker in predicting metastasis in breast cancer.

Estrogen Receptor ß as a Therapeutic Target in Breast Cancer Stem Cells.

Background: Breast cancer cells with tumor-initiating capabilities (BSCs) are considered to maintain tumor growth and govern metastasis. Hence, targeting BSCs will be crucial to achieve successful treatment of breast cancer. Methods: We characterized mammospheres derived from more than 40 cancer patients and two breast cancer cell lines for the expression of estrogen receptors (ERs) and stem cell markers. Mammosphere formation and proliferation assays were performed on cells from 19 cancer patients and five healthy individuals after incubation with ER-subtype selective ligands. Transcriptional analysis was performed to identify pathways activated in ERß-stimulated mammospheres and verified using in vitro experiments. Xenograft models (n = 4 or 5 per group) were used to study the role of ERs during tumorigenesis. Results: We identified an absence of ERα but upregulation of ERß in BSCs associated with phenotypic stem cell markers and responsible for the proliferative role of estrogens. Knockdown of ERß caused a reduction of mammosphere formation in cell lines and in patient-derived cancer cells (40.7%, 26.8%, and 39.1%, respectively). Gene set enrichment analysis identified glycolysis-related pathways (false discovery rate < 0.001) upregulated in ERß-activated mammospheres. We observed that tamoxifen or fulvestrant alone was insufficient to block proliferation of patient-derived BSCs while this could be accomplished by a selective inhibitor of ERß (PHTPP; 53.7% in luminal and 45.5% in triple-negative breast cancers). Furthermore, PHTPP reduced tumor initiation in two patient-derived xenografts (75.9% and 59.1% reduction in tumor volume, respectively) and potentiated tamoxifen-mediated inhibition of tumor growth in MCF7 xenografts. Conclusion: We identify ERß as a mediator of estrogen action in BSCs and a novel target for endocrine therapy.

Expression Profiles of Estrogen-Regulated MicroRNAs in Breast Cancer Cells.

Molecular signaling through both estrogen and microRNAs are critical for breast cancer development and growth. The activity of estrogen is mediated by transcription factors, the estrogen receptors. Here we describe a method for robust characterization of estrogen-regulated microRNA profiles. The method details how to prepare cells for optimal estrogen response, directions for estrogen treatment, RNA extraction, microRNA large-scale profiling, and subsequent confirmations.

Profiling of estrogen-regulated microRNAs in breast cancer cells.

Estrogen plays vital roles in mammary gland development and breast cancer progression. It mediates its function by binding to and activating the estrogen receptors (ERs), ERα, and ERß. ERα is frequently upregulated in breast cancer and drives the proliferation of breast cancer cells. The ERs function as transcription factors and regulate gene expression. Whereas ERα's regulation of protein-coding genes is well established, its regulation of noncoding microRNA (miRNA) is less explored. miRNAs play a major role in the post-transcriptional regulation of genes, inhibiting their translation or degrading their mRNA. miRNAs can function as oncogenes or tumor suppressors and are also promising biomarkers. Among the miRNA assays available, microarray and quantitative real-time polymerase chain reaction (qPCR) have been extensively used to detect and quantify miRNA levels. To identify miRNAs regulated by estrogen signaling in breast cancer, their expression in ERα-positive breast cancer cell lines were compared before and after estrogen-activation using both the µParaflo-microfluidic microarrays and Dual Labeled Probes-low density arrays. Results were validated using specific qPCR assays, applying both Cyanine dye-based and Dual Labeled Probes-based chemistry. Furthermore, a time-point assay was used to identify regulations over time. Advantages of the miRNA assay approach used in this study is that it enables a fast screening of mature miRNA regulations in numerous samples, even with limited sample amounts. The layout, including the specific conditions for cell culture and estrogen treatment, biological and technical replicates, and large-scale screening followed by in-depth confirmations using separate techniques, ensures a robust detection of miRNA regulations, and eliminates false positives and other artifacts. However, mutated or unknown miRNAs, or regulations at the primary and precursor transcript level, will not be detected. The method presented here represents a thorough investigation of estrogen-mediated miRNA regulation.

Support of a bi-faceted role of estrogen receptor ß (ERß) in ERα-positive breast cancer cells.

The expression of estrogen receptor α (ERα) in breast cancer identifies patients most likely to respond to endocrine treatment. The second ER, ERß, is also expressed in breast tumors, but its function and therapeutic potential need further study. Although in vitro studies have established that ERß opposes transcriptional and proliferative functions of ERα, several clinical studies report its correlation with proliferative markers and poorer prognosis. The data demonstrate that ERß opposes ERα are primarily based on transient expression of ERß. Here, we explored the functions of constitutively expressed ERß in ERα-positive breast cancer lines MCF7 and T47D. We found that ERß, under these conditions heterodimerized with ERα in the presence and absence of 17ß-estradiol, and induced genome-wide transcriptional changes. Widespread anti-ERα signaling was, however, not observed and ERß was not antiproliferative. Tamoxifen antagonized proliferation and ER-mediated gene regulation both in the presence and absence of ERß. In conclusion, ERß's role in cells adapted to its expression appears to differ from its role in cells with transient expression. Our study is important because it provides a deeper understanding of ERß's role in breast tumors that coexpress both receptors and supports an emerging bi-faceted role of ERß.

Coexposure to phytoestrogens and bisphenol a mimics estrogenic effects in an additive manner.

Endocrine-disrupting chemicals (EDC) are abundant in our environment. A number of EDCs, including bisphenol A (BPA) can bind to the estrogen receptors (ER), ERα and ERß, and may contribute to estrogen-linked diseases such as breast cancer. Early exposure is of particular concern; many EDCs cross the placenta and infants have measurable levels of, eg, BPA. In addition, infants are frequently fed soy-based formula (SF) that contains phytoestrogens. Effects of combined exposure to xeno- and phytoestrogens are poorly studied. Here, we extensively compared to what extent BPA, genistein, and an extract of infant SF mimic estrogen-induced gene transcription and cell proliferation. We investigated ligand-specific effects on ER activation in HeLa-ERα and ERß reporter cells; on proliferation, genome-wide gene regulation and non-ER-mediated effects in MCF7 breast cancer cells; and how coexposure influenced these effects. The biological relevance was explored using enrichment analyses of differentially regulated genes and clustering with clinical breast cancer profiles. We demonstrate that coexposure to BPA and genistein, or SF, results in increased functional and transcriptional estrogenic effects. Using statistical modeling, we determine that BPA and phytoestrogens act in an additive manner. The proliferative and transcriptional effects of the tested compounds mimic those of 17ß-estradiol, and are abolished by cotreatment with an ER antagonist. Gene expression profiles induced by each compound clustered with poor prognosis breast cancer, indicating that exposure may adversely affect breast cancer prognosis. This study accentuates that coexposure to BPA and soy-based phytoestrogens results in additive estrogenic effects, and may contribute to estrogen-linked diseases, including breast cancer.

Studies in experimental autoimmune encephalomyelitis do not support developmental bisphenol a exposure as an environmental factor in increasing multiple sclerosis risk.

Multiple sclerosis (MS), a demyelinating immune-mediated central nervous system disease characterized by increasing female penetrance, is the leading cause of disability in young adults in the developed world. Epidemiological data strongly implicate an environmental factor, acting at the population level during gestation, in the increasing incidence of female MS observed over the last 50 years, yet the identity of this factor remains unknown. Gestational exposure to bisphenol A (BPA), an endocrine disruptor used in the manufacture of polycarbonate plastics since the 1950s, has been reported to alter a variety of physiological processes in adulthood. BPA has estrogenic activity, and we hypothesized that increased gestational exposure to environmental BPA may therefore contribute to the increasing female MS risk. To test this hypothesis, we utilized two different mouse models of MS, experimental autoimmune encephalomyelitis (EAE) in C57BL/6J mice (chronic progressive) and in SJL/J mice (relapsing-remitting). Dams were exposed to physiologically relevant levels of BPA in drinking water starting 2 weeks prior to mating and continuing until weaning of offspring. EAE was induced in adult offspring. No significant changes in EAE incidence, progression, or severity were observed with BPA exposure, despite changes in cytokine production by autoreactive T cells. However, endocrine disruption was evidenced by changes in testes development, and transcriptomic profiling revealed that BPA exposure altered the expression of several genes important for testes development, including Pdgfa, which was downregulated. Overall, our results do not support gestational BPA exposure as a significant contributor to the increasing female MS risk.

Estradiol-activated estrogen receptor α does not regulate mature microRNAs in T47D breast cancer cells.

Breast cancers are sensitive to hormones such as estrogen, which binds to and activates estrogen receptors (ER) leading to significant changes in gene expression. microRNAs (miRNA) have emerged as a major player in gene regulation, thus identification of miRNAs associated with normal or disrupted estrogen signaling is critical to enhancing our understanding of the diagnosis and prognosis of breast cancer. We have previously shown that 17ß-estradiol (E2) induced activation of ERα in T47D cells results in significant changes in the expression of protein-coding genes involved in cell cycle, proliferation, and apoptosis. To identify miRNAs regulated by E2-activated ERα, we analysed their expression in T47D cells following E2-activation using both dual-color microarrays and TaqMan Low Density Arrays, and validations were carried out by real-time PCR. Although estrogen treatment results in altered expression of up to 900 protein-coding transcripts, no significant changes in mature miRNA expression levels could be confirmed. Whereas previous studies aiming to elucidate the role of miRNA in ER-positive breast cancers cell lines have yielded conflicting results, the work presented here represents a thorough investigation of and significant step forward in our understanding of ERα mediated miRNA regulation.