Hormonal regulation of metastasis-associated protein 3 transcription in breast cancer cells

MicroRNA-495: a therapeutic and diagnostic tumor marker

Therapeutic and diagnostic progresses have significantly reduced the mortality rate among cancer patients during the last decade. However, there is still a high rate of mortality among cancer patients. One of the important reasons involved in the high mortality rate is the late diagnosis in advanced tumor stages that causes the failure of therapeutic strategies in these patients. Therefore, investigating the molecular mechanisms involved in tumor progression has an important role in introducing the efficient early detection markers. MicroRNAs (miRNAs) as stable factors in body fluids are always considered as non-invasive diagnostic and prognostic markers. In the present review, we investigated the role of miR-495 in tumor progression. It has been reported that miR-495 has mainly a tumor suppressor function through the regulation of transcription factors and tyrosine kinases as well as cellular processes such as multidrug resistance, chromatin remodeling, and signaling pathways. This review can be an effective step towards introducing the miR-495 as a non-invasive diagnostic/prognostic marker as well as a suitable target in tumor therapy.

Sphingosine kinase 1 promotes tumor immune evasion by regulating the MTA3-PD-L1 axis

Immune checkpoint blockade (ICB) exhibits considerable benefits in malignancies, but its overall response rate is limited. Previous studies have shown that sphingosine kinases (SPHKs) are critical in the tumor microenvironment (TME), but their role in immunotherapy is unclear. We performed integrative analyses including bioinformatics analysis, functional study, and clinical validation to investigate the role of SPHK1 in tumor immunity. Functionally, we demonstrated that the inhibition of SPHK1 significantly suppressed tumor growth by promoting antitumor immunity in immunocompetent melanoma mouse models and tumor T-cell cocultures. A mechanistic analysis revealed that MTA3 functions as the downstream target of SPHK1 in transcriptionally regulating tumor PD-L1. Preclinically, we found that anti-PD-1 monoclonal antibody (mAb) treatment significantly rescued tumor SPHK1 overexpression or tumor MTA3 overexpression-mediated immune evasion. Significantly, we identified SPHK1 and MTA3 as biological markers for predicting the efficacy of anti-PD-1 mAb therapy in melanoma patients. Our findings revealed a novel role for SPHK1 in tumor evasion mediated by regulating the MTA3-PD-L1 axis, identified SPHK1 and MTA3 as predictors for assessing the efficacy of PD-1 mAb treatment, and provided a therapeutic possibility for the treatment of melanoma patients.

A Functional Network Model of the Metastasis Suppressor PEBP1/RKIP and Its Regulators in Breast Cancer Cells

Drug screening strategies focus on quantifying the phenotypic effects of different compounds on biological systems. High-throughput technologies have the potential to understand further the mechanisms by which these drugs produce the desired outcome. Reverse causal reasoning integrates existing biological knowledge and measurements of gene and protein abundances to infer their function. This approach can be employed to appraise the existing biological knowledge and data to prioritize targets for cancer therapies. We applied text mining and a manual literature search to extract known interactions between several metastasis suppressors and their regulators. We then identified the relevant interactions in the breast cancer cell line MCF7 using a knockdown dataset. We finally adopted a reverse causal reasoning approach to evaluate and prioritize pathways that are most consistent and responsive to drugs that inhibit cell growth. We evaluated this model in terms of agreement with the observations under treatment of several drugs that produced growth inhibition of cancer cell lines. In particular, we suggested that the metastasis suppressor PEBP1/RKIP is on the receiving end of two significant regulatory mechanisms. One involves RELA (transcription factor p65) and SNAI1, which were previously reported to inhibit PEBP1. The other involves the estrogen receptor (ESR1), which induces PEBP1 through the kinase NME1. Our model was derived in the specific context of breast cancer, but the observed responses to drug treatments were consistent in other cell lines. We further validated some of the predicted regulatory links in the breast cancer cell line MCF7 experimentally and highlighted the points of uncertainty in our model. To summarize, our model was consistent with the observed changes in activity with drug perturbations. In particular, two pathways, including PEBP1, were highly responsive and would be likely targets for intervention.

Overexpression of MTA1 inhibits the metastatic ability of ZR-75-30 cells in vitro by promoting MTA2 degradation

BACKGROUND

As the first member of the metastasis-associated protein (MTA) family, MTA1 and another MTA family member, MTA2, have both been reported to promote breast cancer progression and metastasis. However, the difference and relationship between MTA1 and MTA2 have not been fully elucidated.

METHODS

Transwell assays were used to assess the roles of MTA1 and MTA2 in the metastasis of ZR-75-30 luminal B breast cancer cells in vitro. Immunoblotting and qRT-PCR were used to evaluate the effect of MTA1 overexpression on MTA2. Proteases that cleave MTA2 were predicted using an online web server. The role of neutrophil elastase (NE) in MTA1 overexpression-induced MTA2 downregulation was confirmed by specific inhibitor treatment, knockdown, overexpression and immunocytochemistry, and NE cleavage sites in MTA2 were confirmed by MTA2 truncation and mutation. The effect of MTA1 overexpression on the intrinsic inhibitor of NE, elafin, was detected by qRT-PCR, immunoblotting and treatment with inhibitors.

RESULTS

MTA1 overexpression inhibited, while MTA2 promoted the metastasis of ZR-75-30 cells in vitro. MTA1 overexpression downregulated MTA2 expression at the protein level rather than the mRNA level. NE was predicted to cleave MTA2 and was responsible for MTA1 overexpression-induced MTA2 degradation. NE was found to cleave MTA2 in the C-terminus at the 486, 497, 542, 583 and 621 sites. MTA1 overexpression activated NE by downregulating elafin in a histone deacetylase- and DNA methyltransferase-dependent manner.

CONCLUSIONS

MTA1 and MTA2 play opposing roles in the metastasis of ZR-75-30 luminal B breast cancer cells in vitro. MTA1 downregulates MTA2 at the protein level by epigenetically repressing the expression of elafin and releasing the inhibition of neutrophil elastase, which cleaves MTA2 in the C-terminus at multiple specific sites.

The Homeotic Protein SIX3 Suppresses Carcinogenesis and Metastasis through Recruiting the LSD1/NuRD(MTA3) Complex

The homeodomain transcription factor SIX3 was recently reported to be a negative regulator of the Wnt pathway and has an emerging role in cancer. However, how SIX3 contributes to tumorigenesis and metastasis is poorly understood.

METHODS

We employed affinity purification and mass spectrometry (MS) to identify the proteins physically associated with SIX3. Genome-wide analysis of the SIX3/LSD1/NuRD(MTA3) complex using a chromatin immunoprecipitation-on-chip approach identified a cohort of target genes including WNT1 and FOXC2, which are critically involved in cell proliferation and epithelial-to-mesenchymal transition. Also, we used flow cytometry, growth curve analysis, EdU incorporation assay, colony formation assays, trans-well invasion assays, immunohistochemical staining and in vivo bioluminescence assay to investigate the function of SIX3 in tumorigenesis.

RESULTS

We demonstrate that the SIX3/LSD1/NuRD(MTA3) complex inhibits carcinogenesis in breast cancer cells and suppresses metastasis in breast cancer. SIX3 expression is downregulated in various human cancers and high SIX3 is correlated with improved prognosis.

CONCLUSION

Our study revealed an important mechanistic link between the loss of function of SIX3 and tumor progression, identified a molecular basis for the opposing actions of MTA1 and MTA3, and may provide new potential prognostic indicators and targets for cancer therapy.

Corepressor metastasis-associated protein 3 modulates epithelial-to-mesenchymal transition and metastasis

Worldwide, metastasis is the leading cause of more than 90% of cancer-related deaths. Currently, no specific therapies effectively impede metastasis. Metastatic processes are controlled by complex regulatory networks and transcriptional hierarchy. Corepressor metastasis-associated protein 3 (MTA3) has been confirmed as a novel component of nucleosome remodeling and histone deacetylation (NuRD). Increasing evidence supports the theory that, in the recruitment of transcription factors, coregulators function as master regulators rather than passive passengers. As a master regulator, MTA3 governs the target selection for NuRD and functions as a transcriptional repressor. MTA3 dysregulation is associated with tumor progression, invasion, and metastasis in various cancers. MTA3 is also a key regulator of E-cadherin expression and epithelial-to-mesenchymal transition. Elucidating the functions of MTA3 might help to find additional therapeutic approaches for targeting components of NuRD.

Structure, expression and functions of MTA genes

Metastatic associated proteins (MTA) are integrators of upstream regulatory signals with the ability to act as master coregulators for modifying gene transcriptional activity. The MTA family includes three genes and multiple alternatively spliced variants. The MTA proteins neither have their own enzymatic activity nor have been shown to directly interact with DNA. However, MTA proteins interact with a variety of chromatin remodeling factors and complexes with enzymatic activities for modulating the plasticity of nucleosomes, leading to the repression or derepression of target genes or other extra-nuclear and nucleosome remodeling and histone deacetylase (NuRD)-complex independent activities. The functions of MTA family members are driven by the steady state levels and subcellular localization of MTA proteins, the dynamic nature of modifying signals and enzymes, the structural features and post-translational modification of protein domains, interactions with binding proteins, and the nature of the engaged and resulting features of nucleosomes in the proximity of target genes. In general, MTA1 and MTA2 are the most upregulated genes in human cancer and correlate well with aggressive phenotypes, therapeutic resistance, poor prognosis and ultimately, unfavorable survival of cancer patients. Here we will discuss the structure, expression and functions of the MTA family of genes in the context of cancer cells.

Role of MTA2 in human cancer

Metastasis is the ultimate cause of death for most cancer patients. While many mechanisms have been delineated for regulation of growth and tumor initiation of the primary tumor, very little is known about the process of metastasis. Metastasis requires dynamic alteration of cellular processes in order for cells to disseminate from the primary tumor to distant sites. These alterations often involve dramatic changes in the regulation of cytoskeletal and cell-environment interactions. Furthermore, controlled refinement of these interactions requires feedback to regulatory networks in the nucleus. MTA2 is a member of the metastasis tumor-associated family of transcriptional regulators and is a central component of the nucleosome remodeling and histone deacetylation complex. MTA2 acts as a central hub for cytoskeletal organization and transcription and provides a link between nuclear and cytoskeletal organization. We will focus on MTA2 in this chapter, especially its role in breast cancer metastasis.

Unravelling the Complexity and Functions of MTA Coregulators in Human Cancer

Since the initial recognition of the metastasis-associated protein 1 (MTA1) as a metastasis-relevant gene approximately 20 years ago, our appreciation for the complex role of the MTA family of coregulatory proteins in human cancer has profoundly grown. MTA proteins consist of six family members with similar structural units and act as central signaling nodes for integrating upstream signals into regulatory chromatin-remodeling networks, leading to regulation of gene expression in cancer cells. Substantial experimental and clinical evidence demonstrates that MTA proteins, particularly MTA1, are frequently deregulated in a wide range of human cancers. The MTA family governs cell survival, the invasive and metastatic phenotypes of cancer cells, and the aggressiveness of cancer and the prognosis of patients with MTA1 overexpressing cancers. Our discussion here highlights our current understanding of the regulatory mechanisms and functional roles of MTA proteins in cancer progression and expands upon the potential implications of MTA proteins in cancer biology and cancer therapeutics.

BCL-2 family protein, BAD is down-regulated in breast cancer and inhibits cell invasion

We have previously demonstrated that the anti-apoptotic protein BAD is expressed in normal human breast tissue and shown that BAD inhibits expression of cyclin D1 to delay cell-cycle progression in breast cancer cells. Herein, expression of proteins in breast tissues was studied by immunohistochemistry and results were analyzed statistically to obtain semi-quantitative data. Biochemical and functional changes in BAD-overexpressing MCF7 breast cancer cells were evaluated using PCR, reporter assays, western blotting, ELISA and extracellular matrix invasion assays. Compared to normal tissues, Grade II breast cancers expressed low total/phosphorylated forms of BAD in both cytoplasmic and nuclear compartments. BAD overexpression decreased the expression of β-catenin, Sp1, and phosphorylation of STATs. BAD inhibited Ras/MEK/ERK and JNK signaling pathways, without affecting the p38 signaling pathway. Expression of the metastasis-related proteins, MMP10, VEGF, SNAIL, CXCR4, E-cadherin and TlMP2 was regulated by BAD with concomitant inhibition of extracellular matrix invasion. Inhibition of BAD by siRNA increased invasion and Akt/p-Akt levels. Clinical data and the results herein suggest that in addition to the effect on apoptosis, BAD conveys anti-metastatic effects and is a valuable prognostic marker in breast cancer.

Molecular functions and significance of the MTA family in hormone-independent cancer

The members of the metastasis-associated protein (MTA) family play pivotal roles in both physiological and pathophysiological processes, especially in cancer development and metastasis, and their role as master regulators has come to light. Due to the fact that they were first identified as crucial factors in estrogen receptor-mediated breast cancer metastasis, most of the early studies focused on their hormone-dependent functions. However, the accumulating evidence shows that the members of MTA family are deregulated in most, if not all, the cancers studied so far. Therefore, the levels as well as the activities of the MTA family members are widely accepted as potential biomarkers for diagnosis, prognosis, and predictors of overall survival. They function differently in different cancers with specific mechanisms. p53 and HIF-1α appear to be the respectively common upstream and downstream regulator of the MTA family in both development and metastasis of a wide spectrum of cancers. Here, we review the expression and clinical significance of the MTA family, focusing on hormone-independent cancers. To illustrate the molecular mechanisms, we analyze the MTA family-related signaling pathways in different cancers. Finally, targeting the MTA family directly or the pathways involved in the MTA family indirectly could be invaluable strategies in the development of cancer therapeutics.

Subcellular localization of MTA proteins in normal and cancer cells

The subcellular localization of a protein is closely linked to and indicates its function. The metastatic tumor antigen (MTA) family has been under continuous investigation since its identification two decades ago. MTA1, MTA2, and MTA3 are the main members of the MTA family. MTA1, as the representative member of this family, has been shown to be widely expressed in both embryonic and adult tissues, as well as in normal and cancerous conditions, indicating that MTA1 has functions both in physiological and pathological contexts. MTA1 is expressed at a higher level in most cancers than in their normal tissue counterparts. Even in normal cells, MTA1 levels vary a great deal from tissue to tissue. Importantly, MTA1 shows a multiple localization pattern in the cell, as do MTA2 and MTA3. Different MTA components in different subcellular compartments may exert different molecular functions in the cell. Previous studies revealed that MTA1 and MTA2 are predominately localized to the nucleus, while MTA3 is observed in both the nucleus and cytoplasm. Recent studies have reported that MTA1 is located in the nucleus, cytoplasm, and the nuclear envelope. In the nucleus, MTA1 dynamically interacts with chromatin in a MTA1-K532 methylation-dependent manner, whereas cytoplasmic MTA1 binds to the microtubule skeleton. MTA1 also shows a dynamic distribution during the cell cycle. Further investigations are needed to identify the exact subcellular localizations of MTA proteins. We review the sub-cellular localization patterns of the MTA family members and give a comprehensive overview of their respective molecular activities in multiple contexts.

Mechanisms of transcriptional activation of the mouse claudin-5 promoter by estrogen receptor alpha and beta

Claudin-5 is an integral membrane protein and a critical component of endothelial tight junctions that control paracellular permeability. Claudin-5 is expressed at high levels in the brain vascular endothelium. Estrogens have multiple effects on vascular physiology and function. The biological actions of estrogens are mediated by two different estrogen receptor (ER) subtypes, ER alpha and ER beta. Estrogens have beneficial effects in several vascular disorders. Recently we have cloned and characterized a murine claudin-5 promoter and demonstrated 17beta-estradiol (E2)-mediated regulation of claudin-5 in brain and heart microvascular endothelium on promoter, mRNA and protein level. Sequence analysis revealed a putative estrogen response element (ERE) and a putative Sp1 transcription factor binding site in the claudin-5 promoter. The aim of the present study was to further characterize the estrogen-responsive elements of claudin-5 promoter. First, we introduced point mutations in ERE or Sp1 site in -500/+111 or in Sp1 site of -268/+111 claudin-5 promoter construct, respectively. Basal and E2-mediated transcriptional activation of mutated constructs was abrogated in the luciferase reporter gene assay. Next, we examined whether estrogen receptor subtypes bind to the claudin-5 promoter region. For this purpose we performed chromatin immunoprecipitation assays using anti-estrogen receptor antibodies and cellular lysates of E2-treated endothelial cells followed by quantitative PCR analysis. We show enrichment of claudin-5 promoter fragments containing the ERE- and Sp1-binding site in immunoprecipitates after E2 treatment. Finally, in a gel mobility shift assay, we demonstrated DNA-protein interaction of both ER subtypes at ERE. In summary, this study provides evidence that both a non-consensus ERE and a Sp1 site in the claudin-5 promoter are functional and necessary for the basal and E2-mediated activation of the promoter.

Induction of the CLOCK gene by E2-ERα signaling promotes the proliferation of breast cancer cells

Growing genetic and epidemiological evidence suggests a direct connection between the disruption of circadian rhythm and breast cancer. Moreover, the expression of several molecular components constituting the circadian clock machinery has been found to be modulated by estrogen-estrogen receptor α (E2-ERα) signaling in ERα-positive breast cancer cells. In this study, we investigated the regulation of CLOCK expression by ERα and its roles in cell proliferation. Immunohistochemical analysis of human breast tumor samples revealed high expression of CLOCK in ERα-positive breast tumor samples. Subsequent experiments using ERα-positive human breast cancer cell lines showed that both protein and mRNA levels of CLOCK were up-regulated by E2 and ERα. In these cells, E2 promoted the binding of ERα to the EREs (estrogen-response elements) of CLOCK promoter, thereby up-regulating the transcription of CLOCK. Knockdown of CLOCK attenuated cell proliferation in ERα-positive breast cancer cells. Taken together, these results demonstrated that CLOCK could be an important gene that mediates cell proliferation in breast cancer cells.

MiR-495 regulates proliferation and migration in NSCLC by targeting MTA3

Our previous studies have showed that metastasis-associated protein 3 (MTA 3) is overexpressed in non-small cell lung cancer (NSCLC) tissue, and increased MTA3 mRNA levels is a risk factor of lymph node metastasis. Using bioinformatics analyses, we found that MTA3 was a potential target of miR-495. However, the pathophysiological role of miR-495 and its relevance to the growth and development of NSCLC have yet to be investigated. The purpose of this study was to elucidate the molecular mechanisms by which miR-495 acts as a tumor suppressor in NSCLC. qRT-PCR data showed significant downregulation of miR-495 in 56 NSCLC tissue samples and 5 lung cancer cell lines, compared with their adjacent normal tissue; furthermore, western blotting analysis revealed MTA3 protein was overexpressed in the tumor samples compared with the matched adjacent normal tissue. MiR-495 was shown to not only inhibit the proliferation of lung cancer cells (A549 and Calu-3) but also to inhibit cell migration in vitro. Using western blotting and luciferase assays, MTA3 was identified as a target of miR-495. These findings suggest the importance of miR-495 targeting of MTA3 in the regulation of lung cancer growth and migration.

Analysis of MAT3 gene expression in NSCLC

Background

Many studies have suggested different roles of Metastasis-associated protein 3 (MAT3) in different types of human cancers. However, expression of MAT3 in primary lung cancer and its relationship with clinicopathological factors have not been examined and the biological roles of MTA3 in lung cancer cells are still unclear.

Methods

The expression of MAT3 mRNA and protein were detected with quantitative real-time RT-PCR and immunohistochemical methods in 118 NSCLC samples and corresponding non-neoplastic samples. Survival curves were made with follow-up data. The relations of the prognosis with clinical and pathological characteristics were analyzed.

Results

The expression level of MAT3 mRNA and the positive rate of MAT3 protein were significantly higher in NSCLC samples than that in non-neoplastic samples, and in NSCLC samples with lymph node metastasis than that in NSCLC samples without lymph node metastasis (P < 0.01). MAT3 mRNA expression level was a risk factor of lymph node metastasis in patients with NSCLC (P = 0.006). There were significant differences in survival curves between lymph node metastatic group and non-metastatic group (P = 0.000), among groups of MAT3 positive and negative (P = 0.000), among groups of TNM stage I, II and III (P = 0.000) and among groups of tumor status T1, T2 and T3T4 (P = 0.000); but no statistical significance between male patients and female patients (P = 0.516), between ≥60 years old patients and <60 years old patients (P = 0.133), between histology types adenocarcinoma and squamous cell carcinoma (P = 0.865) and between well differentiation and moderate-poor differentiation (P = 0.134). The level of MAT3 mRNA (P = 0.000) and protein (P = 0.000) were risk factors of survival.

Conclusion

Our study showed that MAT3 over-expression in NSCLC tissue, and MAT3 mRNA level is a risk factor of lymph node metastasis. The level of MAT3 mRNA and protein were risk factors of survival in patients with NSCLC. It suggested that this antigen could be used as a simple and efficient parameter with which to identify high-risk patients.

Virtual slides

The virtual slides for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/5585901065503943.

Nuclear expression of snail is an independent negative prognostic factor in human breast cancer

Background. Snail is a key regulator of epithelial-mesenchymal transition of tumor cells. Several studies have shown nuclear Snail expression to be a negative prognostic factor in human cancer, where it is generally associated with more aggressive tumor behavior and worse survival. Objectives and Methods. To further explore the role of Snail expression in breast cancer, we conducted a study on a tissue microarray, encompassing 1043 breast cancer cases. Results. A total of 265 (25.4%) breast cancers were positive for Snail. Snail expression was significantly associated with greater tumor size, higher tumor stage and grade, positive lymph node status, and hormone receptor negative status and was differently expressed in the intrinsic subtypes of breast cancer, being the highest in the basal-like subtype and the lowest in the luminal A subtype. In multivariate analysis, Snail proved to be an independent negative prognostic factor for OS. In the intrinsic subtypes, Snail expression was a negative prognostic factor for OS in the luminal B HER2⁻, the luminal B HER2⁺, and the basal-like subtype. Conclusions. This is the first study demonstrating that nuclear Snail expression is an independent negative predictor of prognosis in breast cancer, thus suggesting that it may represent a potential therapeutic target.

Snail/beta-catenin signaling protects breast cancer cells from hypoxia attack

The tolerance of cancer cells to hypoxia depends on the combination of different factors--from increase of glycolysis (Warburg Effect) to activation of intracellular growth/apoptotic pathways. Less is known about the influence of epithelial-mesenchymal transition (EMT) and EMT-associated pathways on the cell sensitivity to hypoxia. The aim of this study was to explore the role of Snail signaling, one of the key EMT pathways, in the mediating of hypoxia response and regulation of cell sensitivity to hypoxia, using as a model in vitro cultured breast cancer cells. Earlier we have shown that estrogen-independent HBL-100 breast cancer cells differ from estrogen-dependent MCF-7 cells with increased expression of Snail1, and demonstrated Snail1 involvement into formation of hormone-resistant phenotype. Because Snail1 belongs to hypoxia-activated proteins, here we studied the influence of Snail1 signaling on the cell tolerance to hypoxia. We found that Snail1-enriched HBL-100 cells were less sensitive to hypoxia-induced growth suppression if compared with MCF-7 line (31% MCF-7 vs. 71% HBL-100 cell viability after 1% O2 atmosphere for 3 days). Snail1 knock-down enhanced the hypoxia-induced inhibition of cell proliferation giving the direct evidence of Snail1 involvement into cell protection from hypoxia attack. The protective effect of Snail1 was shown to be mediated, at least in a part, via beta-catenin which positively regulated expression of HIF-1-dependent genes. Finally, we found that cell tolerance to hypoxia was accompanied with the failure in the phosphorylation of AMPK - the key energy sensor, and demonstrated an inverse relationship between AMPK and Snail/beta-catenin signaling. Totally, our data show that Snail1 and beta-catenin, besides association with loss of hormone dependence, protect cancer cells from hypoxia and may serve as an important target in the treatment of breast cancer. Moreover, we suggest that the level of these proteins as well the level of AMPK phosphorylation may be considered as predictors of the tumor sensitivity to anti-angiogenic drugs.

β-elemene decreases cell invasion by upregulating E-cadherin expression in MCF-7 human breast cancer cells

Inactivation of E-cadherin results in cell migration and invasion, hence leading to cancer aggressiveness and metastasis. Downregulation of E-cadherin is closely correlated with a poor prognosis in invasive breast cancer. Thus, re-introducing E-cadherin is a novel strategy for cancer therapy. The aim of the present study was to determine the effects of the traditional Chinese medicine, β-elemene (ELE), on E-cadherin expression, cell migration and invasion in the breast cancer cell line MCF-7. MCF-7 cells were treated with 50 and 100 µg/ml ELE. E-cadherin mRNA was analyzed by reverse transcription‑polymerase chain reaction. E-cadherin protein levels were determined by immunofluorescence and western blot assays. Cell motility was measured by a Transwell assay. ELE increased both the protein and mRNA levels of E-cadherin, accompanied by decreased cell migration and invasion. Further analysis demonstrated that ELE upregulated estrogen receptor‑α (ERα) and metastasis-associated protein 3 (MTA3), and decreased the nuclear transcription factor Snail. In conclusion, our results demonstrate that ELE decreases cell migration and invasion by upregulating E-cadherin expression via controlling the ERα/MTA3/Snail signaling pathway.

MTA2 expression is a novel prognostic marker for pancreatic ductal adenocarcinoma

The aim of this study was to detect MTA2 expression in pancreatic ductal adenocarcinoma (PDA) and to analyze its association with prognosis of PDA patients. MTA2 mRNA and protein expression were determined by real-time quantitative reverse transcriptase-polymerase chain reaction and immunohistochemistry in specimens of primary cancer and their adjacent noncancerous tissues in PDA patients. We found that MTA2 mRNA and protein expression levels were both significantly upregulated in PDA lesions compared with adjacent noncancerous tissues. Immunohistochemistry showed that high MTA2 expression was correlated with poor tumor differentiation, TNM stage, and lymph node metastasis. Kaplan-Meier survival analysis showed that patients with high expression levels of MTA2 showed lower overall survival rate than those with low expression levels. Multivariate analysis showed that high MTA2 protein expression was an independent prognostic factor for PDA patients. Our study suggests that overexpression of MTA2 may play an important role in the progression of PDA and MTA2 expression may serve as a biomarker for poor prognosis for PDA.

Occurrence and significance of epithelial-mesenchymal transition in breast cancer

By contrast with developmental epithelial-mesenchymal transition (EMT), where epithelial characteristics undergo transformation to a mesenchymal-like phenotype in a coordinated fashion, oncogenic EMT occurs in the context of unpredictable genetic changes present in the tumour cells, as well as an abnormal tumour microenvironment. Therefore, a partial form of EMT has been proposed as variably participating in the establishment of invasive phenotype in different types of breast carcinoma, in keeping with their morphological and phenotypical diversity. A complex network of signalling pathways and transcription factors appears responding to various growth factors and cytokines released by stromal and neoplastic elements, endowing the system with abundant regulatory opportunities. The process of EMT is largely elusive in histopathological preparations, prompting doubts regarding its significance in tumour progression. This might be related to the presumed focal occurrence of EMT in the majority of tumours. Detailed topological studies might facilitate understanding of the orchestration of events taking place in vivo. Even more importantly, clinical correlations can be endeavoured and, in parallel with advancement in molecular pathology, a contribution to taxonomy refinement can be envisaged.

The relationships between snail1 and estrogen receptor signaling in breast cancer cells

The loss of hormonal dependency of breast tumor cells is often accompanied with the appearance of epithelial-mesenchymal transition (EMT) features and increase in cell metastasis and invasiveness. The central role in the EMT belongs to transcription factors Snail responded for the decrease in E-cadherin expression and cell contacts, stimulation of cell mobility and invasiveness. Aim was to study the relationships between estrogen receptor machinery and Snail1 signaling, and mechanism of Snail1 regulation in hormone-resistant breast cancer cells. The experiments were performed on the estrogen-dependent MCF-7 breast cancer cells, estrogen-hyposensitive MCF-7/LS subline generated through long-term cultivation of the parental cells in steroid-free medium, and ER-negative estrogen-resistant HBL-100 cells. Snail1, estrogen receptor, p65 NF-κB, E-cadherin levels were analyzed by Western blot. We found that decrease in the estrogen dependency is correlated with increase in Snail1 expression and activity, we demonstrated the Snail1 involvement in the negative regulation of ER, and showed that Snail1 inhibition partially restores the sensitivity of the estrogen-hyposensitive cells to antiestrogen tamoxifen. Furthermore, NF-κB was found to serve as a positive regulator of Snail1 in breast cancer cells, and simultaneous inhibition of NF-κB and Snail1 resulted in additional increase in cell response to tamoxifen. In general, the results obtained demonstrate the phenomenon of Snail1 activation in the hormone-resistant breast cancer cells, and show that Snail1 and NF-κB may serve as an important targets in the treatment of breast cancer, both estrogen-dependent and estrogen-independent tumors.

Cell polarity, epithelial-mesenchymal transition, and cell-fate decision gene expression in ductal carcinoma in situ

Loss of epithelial cell identity and acquisition of mesenchymal features are early events in the neoplastic transformation of mammary cells. We investigated the pattern of expression of a selected panel of genes associated with cell polarity and apical junction complex or involved in TGF-β-mediated epithelial-mesenchymal transition and cell-fate decision in a series of DCIS and corresponding patient-matched normal tissue. Additionally, we compared DCIS gene profile with that of atypical ductal hyperplasia (ADH) from the same patient. Statistical analysis identified a “core” of genes differentially expressed in both precursors with respect to the corresponding normal tissue mainly associated with a terminally differentiated luminal estrogen-dependent phenotype, in agreement with the model according to which ER-positive invasive breast cancer derives from ER-positive progenitor cells, and with an autocrine production of estrogens through androgens conversion. Although preliminary, present findings provide transcriptomic confirmation that, at least for the panel of genes considered in present study, ADH and DCIS are part of a tumorigenic multistep process and strongly arise the necessity for the regulation, maybe using aromatase inhibitors, of the intratumoral and/or circulating concentration of biologically active androgens in DCIS patients to timely hamper abnormal estrogens production and block estrogen-induced cell proliferation.

Metastasis-associated protein 3 (MTA3) regulates G2/M progression in proliferating mouse granulosa cells

Metastasis-associated protein 3 (MTA3) is a constituent of the Mi-2/nucleosome remodeling and deacetylase (NuRD) protein complex that regulates gene expression by altering chromatin structure and can facilitate cohesin loading onto DNA. The biological function of MTA3 within the NuRD complex is unknown. Herein, we show that MTA3 was expressed highly in granulosa cell nuclei of all ovarian follicle stages and at lower levels in corpora lutea. We tested the hypothesis that MTA3-NuRD complex function is required for granulosa cell proliferation. In the ovary, MTA3 interacted with NuRD proteins CHD4 and HDAC1 and the core cohesin complex protein RAD21. In cultured mouse primary granulosa cells, depletion of endogenous MTA3 using RNA interference slowed cell proliferation; this effect was rescued by coexpression of exogenous MTA3. Slowing of cell proliferation correlated with a significant decrease in cyclin B1 and cyclin B2 expression. Granulosa cell populations lacking MTA3 contained a significantly higher percentage of cells in G2/M phase and a lower percentage in S phase compared with control cells. Furthermore, MTA3 depletion slowed entry into M phase as indicated by reduced phosphorylation of histone H3 at serine 10. These findings provide the first evidence to date that MTA3 interacts with NuRD and cohesin complex proteins in the ovary in vivo and regulates G2/M progression in proliferating granulosa cells.

Correlation between MTA2 overexpression and tumour progression in esophageal squamous cell carcinoma

The aim of this study was to clarify the clinicopathological outcome and prognostic significance of metastasis-associated gene 2 (MTA2) in esophageal squamous cell carcinoma (ESCC). Immunohistochemical staining for MTA2 was performed on surgical specimens obtained from 162 patients with ESCC. Relationships between MTA2 expression and clinicopathological factors, including prognosis, were analyzed. Significant correlations were noted among MTA2 overexpression and TNM clinical classification staging, depth of invasion, presence of regional lymph node metastasis, presence of distant metastasis, lymphatic invasion, blood-vessel invasion and the 5-year survival rates. The expression of MTA2 protein was correlated with tumour progression. Patients with MTA2 overexpression tended to have poor prognosis compared to patients with MTA2 underexpression.

The Expanding Mi-2/NuRD Complexes: A Schematic Glance

This mini-review will schematically update the progress of the expanding Mi-2/Nucleosome Remodeling Deacetylase (NuRD) complexes in cancer and in normal development such as stemness, with a focus on mammals and the increasingly popular and powerful model organism Caenorhabditis elegans. The Mi-2/NuRD complexes control gene activity during the development of complex organisms. Every Mi-2/NuRD complex contains many different core polypeptides, which form distinct multifunctional complexes with specific context-dependent regulators. The Mi-2/NuRD complexes have unique ATP-dependent chromatin remodeling, histone deacetylase, demethylase activities and higher order chromatin organization. They can regulate the accessibility of transcription factors or repair proteins to DNA. In this review, we summarize our current knowleges in the composition, interaction and function of the subunits within the Mi-2/NuRD complex, the methodology used for the identification of Mi-2/NuRD complexes, as well as the clinical and therapeutic implications targeting the Mi-2/NuRD subunits.

Metastasis tumor antigen 2 (MTA2) is involved in proper imprinted expression of H19 and Peg3 during mouse preimplantation development

The epigenetic mechanisms involved in establishing and maintaining genomic imprinting are steadily being unmasked. The nucleosome remodeling and histone deacetylation (NuRD) complex is implicated in regulating DNA methylation and expression of the maternally expressed H19 gene in preimplantation mouse embryos. To dissect further the function of the NuRD complex in genomic imprinting, we employed an RNA interference (RNAi) strategy to deplete the NuRD complex component Metastasis Tumor Antigen 2 (MTA2). We found that Mta2 is the only zygotically expressed Mta gene prior to the blastocyst stage, and that RNAi-mediated knockdown of Mta2 transcript leads to biallelic H19 expression and loss of DNA methylation in the differentially methylated region in blastocysts. In addition, biallelic expression of the paternally expressed Peg3 gene, but not Snrpn, is also observed in blastocysts following Mta2 knockdown. Loss of MTA2 protein does not result in a decrease in abundance of other NuRD components, including methyl-binding-CpG-binding domain protein 3 (MBD3), histone deacetylases 1 and 2 (HDACs 1 and 2), and chromodomain helicase DNA-binding protein 4 (CHD4). Taken together, our results support a role for MTA2 within the NuRD complex in genomic imprinting.

The TWIST/Mi2/NuRD protein complex and its essential role in cancer metastasis

The epithelial-mesenchymal transition (EMT) converts epithelial tumor cells into invasive and metastatic cancer cells, leading to mortality in cancer patients. Although TWIST is a master regulator of EMT and metastasis for breast and other cancers, the mechanisms responsible for TWIST-mediated gene transcription remain unknown. In this study, purification and characterization of the TWIST protein complex revealed that TWIST interacts with several components of the Mi2/nucleosome remodeling and deacetylase (Mi2/NuRD) complex, MTA2, RbAp46, Mi2 and HDAC2, and recruits them to the proximal regions of the E-cadherin promoter for transcriptional repression. Depletion of these TWIST complex components from cancer cell lines that depend on TWIST for metastasis efficiently suppresses cell migration and invasion in culture and lung metastasis in mice. These findings not only provide novel mechanistic and functional links between TWIST and the Mi2/NuRD complex but also establish new essential roles for the components of Mi2/NuRD complex in cancer metastasis.

Requirement of MTA1 in ATR-mediated DNA damage checkpoint function

MTA1 (metastasis-associated protein 1), an integral component of the nucleosome remodeling and deacetylase complex, has recently been implicated in the ionizing radiation-induced DNA damage response. However, whether MTA1 also participates in the UV-induced DNA damage checkpoint pathway remains unknown. In response to UV radiation, ATR (ataxia teleangiectasia- and Rad3-related) is the major kinase activated that orchestrates cell cycle progression with DNA repair machinery by phosphorylating and activating a number of downstream substrates, such as Chk1 (checkpoint kinase 1) and H2AX (histone 2A variant X). Here, we report that UV radiation stabilizes MTA1 in an ATR-dependent manner and increases MTA1 binding to ATR. On the other hand, depletion of MTA1 compromises the ATR-mediated Chk1 activation following UV treatment, accompanied by a marked down-regulation of Chk1 and its interacting partner Claspin, an adaptor protein that is required for the phosphorylation and activation of Chk1 by ATR. Furthermore, MTA1 deficiency decreases the induction of phosphorylated H2AX (referred to as gamma-H2AX) and gamma-H2AX focus formation after UV treatment. Consequently, depletion of MTA1 results in a defect in the G(2)-M checkpoint and increases cellular sensitivity to UV-induced DNA damage. Thus, MTA1 is required for the activation of the ATR-Claspin-Chk1 and ATR-H2AX pathways following UV treatment, and the noted abrogation of the DNA damage checkpoint in the MTA1-depleted cells may be, at least in part, a consequence of dysregulation of the expression of these two pathways. These findings suggest that, in addition to its role in the repair of double strand breaks caused by ionizing radiation, MTA1 also participates in the UV-induced ATR-mediated DNA damage checkpoint pathway.

Wnt inhibitors Dkk1 and Sost are downstream targets of BMP signaling through the type IA receptor (BMPRIA) in osteoblasts

The bone morphogenetic protein (BMP) and Wnt signaling pathways both contribute essential roles in regulating bone mass. However, the molecular interactions between these pathways in osteoblasts are poorly understood. We recently reported that osteoblast-targeted conditional knockout (cKO) of BMP receptor type IA (BMPRIA) resulted in increased bone mass during embryonic development, where diminished expression of Sost as a downstream effector of BMPRIA resulted in increased Wnt/beta-catenin signaling. Here, we report that Bmpr1a cKO mice exhibit increased bone mass during weanling stages, again with evidence of enhanced Wnt/beta-catenin signaling as assessed by Wnt reporter TOPGAL mice and TOPFLASH luciferase. Consistent with negative regulation of the Wnt pathway by BMPRIA signaling, treatment of osteoblasts with dorsomorphin, an inhibitor of Smad-dependent BMP signaling, enhanced Wnt signaling. In addition to Sost, Wnt inhibitor Dkk1 also was downregulated in cKO bone. Expression levels of Dkk1and Sost were upregulated by BMP2 treatment and downregulated by Noggin. Moreover, expression of a constitutively active Bmpr1a transgene in mice resulted in the upregulation of both Dkk1 and Sost and partially rescued the Bmpr1a cKO bone phenotype. These effectors are differentially regulated by mitogen-activated protein kinase (MAPK) p38 because pretreatment of osteoblasts with SB202190 blocked BMP2-induced Dkk1 expression but not Sost. These results demonstrate that BMPRIA in osteoblasts negatively regulates endogenous bone mass and Wnt/beta-catenin signaling and that this regulation may be mediated by the activities of Sost and Dkk1. This study highlights several interactions between BMP and Wnt signaling cascades in osteoblasts that may be amenable to therapeutic intervention for the modification of bone mass density.

The role of the MTA family and their encoded proteins in human cancers: molecular functions and clinical implications

MTA (metastasis-associated gene) is a newly discovered family of cancer progression-related genes and their encoded products. MTA1, the first gene found in this family, has been repeatedly reported to be overexpressed along with its protein product MTA1 in a wide range of human cancers. In addition, the expression of MTA1/MTA1 correlates with the clinicopathological properties (malignant properties) of human cancers. MTA proteins are transcriptional co-repressors that function in histone deacetylation and are involved in the NuRD complex, which contains nucleosome remodeling and histone deacetylating molecules. MTA1 expression correlates with tumor formation in the mammary gland. In addition, MTA1 converts breast cancer cells to a more aggressive phenotype by repression of the estrogen receptor (ER) alpha trans-activation function through deacetylation of the chromatin in the ER-responsive element of ER-responsive genes. Furthermore, MTA1 plays an essential role in c-MYC-mediated cell transformation. Another member of this family, MTA3, is induced by estrogen and represses the expression of the transcriptional repressor Snail, a master regulator of "epithelial to mesenchymal transitions", resulting in the expression of the cell adhesion molecule E-cadherin and maintenance of a differentiated, normal epithelial phenotype in breast cells. In addition, tumor suppressor p53 protein is deacetylated and inactivated by both MTA1 and MTA2, leading to inhibition of growth arrest and apoptosis. Moreover, a hypoxia-inducible factor-1alpha (HIF-1alpha) is also deacetylated and stabilized by MTA1, resulting in angiogenesis. Thus, MTA proteins, especially MTA1, represent a possible set of master co-regulatory molecules involved in the carcinogenesis and progression of various malignant tumors. MTA proteins are proposed to be important new tools for clinical application in cancer diagnosis and treatment.

Non-classical genomic estrogen receptor (ER)/specificity protein and ER/activating protein-1 signaling pathways

17beta-estradiol binds to the estrogen receptor (ER) to activate gene expression or repression and this involves both genomic (nuclear) and non-genomic (extranuclear) pathways. Genomic pathways include the classical interactions of ligand-bound ER dimers with estrogen-responsive elements in target gene promoters. ER-dependent activation of gene expression also involves DNA-bound ER that subsequently interacts with other DNA-bound transcriptions factors and direct ER-transcription factor (protein-protein) interactions where ER does not bind promoter DNA. Ligand-induced activation of ER/specificity protein (Sp) and ER/activating protein-1 [(AP-1); consisting of jun/fos] complexes are important pathways for modulating expression of a large number of genes. This review summarizes some of the characteristics of ER/Sp- and ER/AP-1-mediated transactivation, which are dependent on ligand structure, cell context, ER-subtype (ERalpha and ERbeta), and Sp protein (SP1, SP3, and SP4) and demonstrates that this non-classical genomic pathway is also functional in vivo.

In vivo profiling of estrogen receptor/specificity protein-dependent transactivation

17beta-Estradiol (E2) activates the estrogen receptor (ER) through multiple genomic and nongenomic pathways in various tissues/organs. ERalpha/specificity protein-dependent activation of E2-responsive genes containing GC-rich promoters has been identified in breast and other cancer cell lines, and in this study, we describe transgenic animals overexpressing a transgene containing three tandem GC-rich sites linked to a minimal TATA or thymidine kinase promoter and a luciferase gene. Several mouse lines expressing the transgenes were characterized and, in line 15, E2 induced a 9-fold increase in luciferase activity in the female mouse uterus, and the synthetic estrogens bisphenol A and nonylphenol also induced uterine luciferase activity. The pure antiestrogen ICI 182,780 induced luciferase activity in the mouse uterus, and similar results were observed for ICI 182,780 in breast cancer cells transfected with this construct. Differences in the ER agonist and antagonist activities of E2, nonylphenol, bisphenol A, and ICI 182,780 were investigated in the male testis and penis and the male and female stomach in line 15 transgenic mice. All of these tissues were hormone responsive; however, the patterns of induced or repressed luciferase activity were ligand structure, tissue, and sex dependent. These results demonstrate for the first time hormonal activation or repression of a GC-rich promoter in vivo, and the results suggest that the ERalpha/specificity protein pathway may contribute to E2-dependent induction and repression of genes.

UV radiation regulates Mi-2 through protein translation and stability

Dermatomyositis (DM) is an autoimmune disease, which is often accompanied by the development of disease-specific autoantibodies directed against the SNF2-superfamily helicase, Mi-2. Recent evidence suggests that ultraviolet radiation exposure may be an important risk factor for the development of not only the disease but also specific autoimmunity against Mi-2. Consequently, we investigated the effects of ultraviolet radiation on Mi-2 protein expression. We observed an increase in protein levels upon ultraviolet radiation exposure in cell culture systems. These changes in expression occur quite rapidly, are maximized just 1 h following exposure, and are unique to Mi-2 when compared with other members of the NuRD complex. Changes in protein levels are not mediated through transcriptional mechanisms. Treatment results in a more efficiently translated message through regulatory elements in the 5'-UTR region of the transcript. Investigation into protein half-life further demonstrated increased stability of Mi-2 following UV exposure. Taken together, we describe a system by which Mi-2 protein expression can be quickly increased following UV exposure and then maintained up to 16 h later. These data provide a novel regulation of an important transcriptional regulator and provide insight into the possible mechanisms of the development of DM and associated autoantibodies.

GC-rich promoter elements maximally confers estrogen-induced transactivation of LRP16 gene through ERalpha/Sp1 interaction in MCF-7 cells

LRP16 gene has been characterized as an estrogen-responsive gene. One 1/2ERE/GC-rich site was previously identified to be indispensable for -676/-214 (region A) fragment within LRP16 regulatory region to confer E2 action. Here, we report that -213/-24 fragment (region B) has higher E2-responsiveness than that of region A in MCF-7 cells, but not in HeLa cells. Deletion and mutation analyses of region B showed that multiple GC-sites are involved in the E2-stimulated response and one 30-bp fragment (-213 to -184 bp) is essential for conferring maximum E2-responsiveness. Results from the cotransfection assays containing Sp1-siRNA revealed that Sp1 is required for the basal transcription activity and E2-responsiveness of both regions A and B. Northern blot analysis demonstrated that inhibition of Sp1 in MCF-7 cells not only decreased the basal expression of LRP16, but markedly impaired its upregulation by E2. Results from gel mobility shift assays exhibited the direct binding of Sp1 protein to the 28-bp fragment (-211 to -184 bp), which was enhanced by the ERalpha titer. Moreover, the functional interaction of ERalpha and Sp1 proteins in the presence of E2 at the GC-rich sites in region B was confirmed by chromatin immunoprecipitation (ChIP) assays. In general, these results demonstrate that GC-rich sites in the proximal promoter of LRP16 gene are sufficient for E2 activation of LRP16 and the -213/-184 fragment containing only one GC site is essential for the maximal induction in MCF-7 cells. We also provide a model for Sp1-dependent regulation of genes by E2 through GC-rich motifs.

MTA family of coregulators in nuclear receptor biology and pathology

Nuclear receptors (NRs) rely on coregulators (coactivators and corepressors) to modulate the transcription of target genes. By interacting with nucleosome remodeling complexes, NR coactivators potentiate transcription, whereas corepressors inhibit transcription of the target genes. Metastasis-associated proteins (MTA) represent an emerging family of novel NR coregulators. In general, MTA family members form independent nucleosome remodeling and deacetylation (NuRD) complexes and repress the transcription of different genes by recruiting histone deacetylases onto their target genes. However, MTA1 also acts as a coactivator in a promoter-context dependent manner. Recent findings that repression of estrogen receptor transactivation functions by MTA1, MTA1s, and MTA2 and regulation of MTA3 by estrogen signaling have indicated the significance of these proteins in NR signaling. Here, we highlight the action of MTA proteins on NR signaling and their roles in pathophysiological conditions.

The human Mi-2/NuRD complex and gene regulation

The Mi-2/nucleosome remodeling and deacetylase (NuRD) complex is an abundant deacetylase complex with a broad cellular and tissue distribution. It is unique in that it couples histone deacetylation and chromatin remodeling ATPase activities in the same complex. A decade of research has uncovered a number of interesting connections between Mi-2/NuRD and gene regulation. The subunit composition of the enzyme appears to vary with cell type and in response to physiologic signals within a tissue. Here, we review the known subunits of the complex, their connections to signaling networks, and their association with cancer. In addition, we propose a working model that integrates the known biochemical properties of the enzyme with emerging models on how chromatin structure and modification relate to gene activity.

MTA family of transcriptional metaregulators in mammary gland morphogenesis and breast cancer

Since breast cancer and its associated metastasis are a global health problem and a major cause of mortality among women, research efforts to understand the development, morphogenesis, and functioning of the mammary gland are a high priority. Myriad signaling pathways, transcription factors, and associated transcriptional coregulators have been identified in both normal functioning and neoplastic transformation of the mammary gland. The discovery of the metastasis tumor antigen 1 (MTA1) gene, its overexpression in cancer and metastasis and its subsequent identification as an integral part of the chromatin remodeling complex heralded extensive research on its physiological role. Subsequent identification of additional gene family members, namely MTA1s, MTA2, and MTA3, and their functions in the cell has resulted in the establishment of the significance of the MTA family. The role of these proteins in modulating hormonal responses in normal mammary glands and in breast cancer has resulted in their identification as important molecular markers and potential therapeutic targets.

The transcription factor snail mediates epithelial to mesenchymal transitions by repression of estrogen receptor-alpha

The estrogen receptor (ER)-alpha (ESR1) is a key regulatory molecule in mammary epithelial cell development. Loss of ER-alpha in breast cancer is correlated with poor prognosis, increased recurrence after treatment, and an elevated incidence of metastasis. A proposed molecular pathway by which ER-alpha acts to constrain invasive growth in breast cancer cells involves direct, ER-alpha-dependent expression of metastasis-associated protein 3, a cell-type-specific component of the Mi-2/NuRD chromatin remodeling complex. MTA3 in turn represses expression of Snail, a transcription factor linked to epithelial to mesenchymal transition and cancer metastasis. To elucidate its role(s) in epithelial to mesenchymal transition (EMT), we expressed Snail in the noninvasive, ER-alpha-positive MCF-7 cell line. Snail expression led to decreased cell-cell adhesion and increased cell invasiveness. Furthermore, we observed loss of ER-alpha expression at both the RNA and protein level that was accompanied by direct interaction of Snail with regulatory DNA sequences at the ESR1 locus. A consequence of loss of ER-alpha function in this system was the increased abundance of key components of the TGF-beta signaling pathway. Thus, cross-talk among ER-alpha, Snail, and the TGF-beta pathway appears to control critical phenotypic properties of breast cancer cells.

Cross-talk between nuclear receptors and nuclear factor kappaB

A variety of studies have shown that some activated nuclear receptors (NRs), especially the glucorticoid receptor, the estrogen receptor and peroxisome proliferator-activated receptor, can inhibit the activity of the transcription factor nuclear factor kappaB (NF-kappaB), which plays a key role in the control of genes involved in inflammation, cell proliferation and apoptosis. This review describes the molecular mechanisms of cross-talk between NRs and NF-kappaB and the biological relevance of this cross-talk. The importance and mechanistic aspects of selective NR modulation are discussed. Also included are future research prospects, which will lead to a new era in the field of NR research with the aim of specifically inhibiting NF-kappaB-driven gene expression for anti-inflammatory, anti-tumor and immune-modulatory purposes.

Metastasis tumor antigens, an emerging family of multifaceted master coregulators

Regulation of fundamental genetic processes demands dynamic participation of transcription factors, their coregulators, and multiprotein chromatin remodeling activities at target genes. One family of chromatin modifiers that is ubiquitously expressed is the metastasis tumor antigens (MTA), which are integral parts of nucleosome remodeling and histone deacetylation (NuRD) complexes. MTA family members exist in distinct NuRD complexes, and functional redundancy is lacking among MTA family members. MTA proteins regulate divergent cellular pathways, including hormonal action, epithelial-to-mesenchymal transitions, differentiation, protein stability and development, and cell fate programs by modifying the acetylation status of crucial target genes. Intriguingly, at least one member of this family, MTA1, itself undergoes acetylation and acts as a coactivator in certain contexts. We discuss the roles of the MTA family of chromatin modifiers, with an emphasis on their physiologic functions.

Breast cancer risk associated with genotypic polymorphism of the genes involved in the estrogen-receptor-signaling pathway: a multigenic study on cancer susceptibility

The reproductive hormone, estrogen, contributes to the development of breast cancer by binding to the estrogen receptor (ER) in the nucleus, triggering cell growth and tumor promotion. In addition to its role in regulating target genes and signaling pathways involved in cell cycle progression, the ER-signaling pathway may regulate the expression of chromatin-remodeling gene, Metastasis-associated 3 (MTA3), or interact with chromatin-remodeling protein, Metastasis-associated 1 (MTA1). The invasion-suppressor gene, E-Cadherin (E-Cad), has recently been identified as a downstream target gene regulated by the ER-MTA3 pathway via the transcriptional repressor, Snail, and the ER-MTA3-Snail-E-Cad pathway has therefore been evoked to explain the clinical observation that ER expression in breast cancer is generally associated with a better clinical outcome. Since E-Cad may play an initiating role during breast tumorigenesis, we hypothesized that this ER-signaling pathway may also determine susceptibility to breast cancer, and examined this in a multigenic case-control study of 468 incident breast cancer patients and 470 healthy controls by genotyping the single nucleotide polymorphisms (SNPs) in five genes (ER, MTA3, Snail, E-Cad, and MTA1) in the ER-signaling pathways. Support for this hypothesis came from the observations that (a) with the exception of Snail, which interacted differently with reproductive risk factors in relation to breast cancer risk, there was a joint effect of the SNPs of these genes and estrogen-related risk factors (age at first full-term pregnancy and obesity, measured by the body mass index) on breast cancer risk (p < 0.05); (b) a trend toward increased risk of developing breast cancer was seen in women harboring a greater number of putative high-risk genotypes of these genes in ER-signaling pathways; (c) this association between risk and the number of putative high-risk genotypes was stronger and more significant in women thought to have experienced higher estrogen level, i.e., obese women; and (d) the risk effect conferred by obesity was only significant in women with a higher number of putative high-risk genotypes of the ER-signaling genes. These epidemiological findings highlight the role of newly identified novel ER-related pathways in breast cancer development and provide a more comprehensive picture of the tumorigenic effect of estrogen in breast cancer development.

Metastasis-associated protein 2 is a repressor of estrogen receptor alpha whose overexpression leads to estrogen-independent growth of human breast cancer cells

Estrogen receptor (ER)alpha activity is controlled by the balance of coactivators and corepressors contained within cells that are recruited into transcriptional complexes. The metastasis-associated protein (MTA) family has been demonstrated to be associated with breast tumor cell progression and ERalpha activity. We demonstrate that MTA2 expression is correlated with ERalpha protein expression in invasive breast tumors. We show that the MTA2 family member can bind to ERalpha and repress its activity in human breast cancer cells. Furthermore, it can inhibit ERalpha-mediated colony formation and render breast cancer cells resistant to estradiol and the growth-inhibitory effects of the antiestrogen tamoxifen. MTA2 participates in the deacetylation of ERalpha protein, potentially through its associated histone deacetylase complex 1 activity. We hypothesize that MTA2 is a repressor of ERalpha activity and that it could represent a new therapeutic target of ERalpha action in human breast tumors.

Changes in attitude, changes in latitude: nuclear receptors remodeling chromatin to regulate transcription

Nuclear receptors (NRs) are a large family of ligand-dependent transcription factors that regulate important physiological processes. To activate or repress genes assembled naturally as chromatin, NRs recruit two distinct enzymatic activities, namely histone-modifying enzymes and ATP-dependent chromatin remodeling complexes, to alter local chromatin structure at target gene promoters. In this review, we examine the functional relationship between ATP-dependent chromatin remodeling complexes and NRs in the context of transcriptional regulation. Using the steroid-responsive mouse mammary tumor virus promoter as a model system, we discuss in detail the molecular mechanisms underlying the recruitment of these complexes and subsequent chromatin structure changes catalyzed by this group of enzymes. In addition, we extend the discussion to other NR-regulated promoters including the pS2 promoter. Finally, we summarize specific principles governing this critical relationship, identify unanswered questions and discuss the potential application of these principles in rational drug design.