Trichostatin A and 5 Aza-2' deoxycytidine decrease estrogen receptor mRNA stability in ER positive MCF7 cells through modulation of HuR

Readers of RNA Modification in Cancer and Their Anticancer Inhibitors

Cancer treatment has always been a challenge for humanity. The inadequacies of current technologies underscore the limitations of our efforts against this disease. Nevertheless, the advent of targeted therapy has introduced a promising avenue, furnishing us with more efficacious tools. Consequently, researchers have turned their attention toward epigenetics, offering a novel perspective in this realm. The investigation of epigenetics has brought RNA readers to the forefront, as they play pivotal roles in recognizing and regulating RNA functions. Recently, the development of inhibitors targeting these RNA readers has emerged as a focal point in research and holds promise for further strides in targeted therapy. In this review, we comprehensively summarize various types of inhibitors targeting RNA readers, including non-coding RNA (ncRNA) inhibitors, small-molecule inhibitors, and other potential inhibitors. We systematically elucidate their mechanisms in suppressing cancer progression by inhibiting readers, aiming to present inhibitors of readers at the current stage and provide more insights into the development of anticancer drugs.

Inflammation as a driver of hematological malignancies

Hematopoiesis is a tightly regulated process that produces all adult blood cells and immune cells from multipotent hematopoietic stem cells (HSCs). HSCs usually remain quiescent, and in the presence of external stimuli like infection or inflammation, they undergo division and differentiation as a compensatory mechanism. Normal hematopoiesis is impacted by systemic inflammation, which causes HSCs to transition from quiescence to emergency myelopoiesis. At the molecular level, inflammatory cytokine signaling molecules such as tumor necrosis factor (TNF), interferons, interleukins, and toll-like receptors can all cause HSCs to multiply directly. These cytokines actively encourage HSC activation, proliferation, and differentiation during inflammation, which results in the generation and activation of immune cells required to combat acute injury. The bone marrow niche provides numerous soluble and stromal cell signals, which are essential for maintaining normal homeostasis and output of the bone marrow cells. Inflammatory signals also impact this bone marrow microenvironment called the HSC niche to regulate the inflammatory-induced hematopoiesis. Continuous pro-inflammatory cytokine and chemokine activation can have detrimental effects on the hematopoietic system, which can lead to cancer development, HSC depletion, and bone marrow failure. Reactive oxygen species (ROS), which damage DNA and ultimately lead to the transformation of HSCs into cancerous cells, are produced due to chronic inflammation. The biological elements of the HSC niche produce pro-inflammatory cytokines that cause clonal growth and the development of leukemic stem cells (LSCs) in hematological malignancies. The processes underlying how inflammation affects hematological malignancies are still not fully understood. In this review, we emphasize the effects of inflammation on normal hematopoiesis, the part it plays in the development and progression of hematological malignancies, and potential therapeutic applications for targeting these pathways for therapy in hematological malignancies.

RNA-binding proteins in breast cancer: Biological implications and therapeutic opportunities

RNA-binding proteins (RBPs) refer to a class of proteins that participate in alternative splicing, RNA stability, polyadenylation, localization and translation of RNAs, thus regulating gene expression in post-transcriptional manner. Dysregulation of RNA-RBP interaction contributes to various diseases, including cancer. In breast cancer, disorders in RBP expression and function influence the biological characteristics of tumor cells. Targeting RBPs has fostered the development of innovative therapies for breast cancer. However, the RBP-related mechanisms in breast cancer are not completely clear. In this review, we summarize the regulatory mechanisms of RBPs and their signaling crosstalk in breast cancer. Specifically, we emphasize the potential of certain RBPs as prognostic factors due to their effects on proliferation, invasion, apoptosis, and therapy resistance of breast cancer cells. Most importantly, we present a comprehensive overview of the latest RBP-related therapeutic strategies and novel therapeutic targets that have proven to be useful in the treatment of breast cancer.

Expressions of HuR, Methyl-HuR and Phospho-HuR in Endometrial Endometrioid Adenocarcinoma Are Associated with Clinical Features

HuR regulates cytoplasmic mRNA stability and translatability, with its expression correlating with adverse outcomes in various cancers. This study aimed to assess the prognostic value and pro-oncogenic properties of HuR and its post-translational isoforms methyl-HuR and phospho-HuR in endometrial adenocarcinoma. Examining 89 endometrioid adenocarcinomas, we analyzed the relationship between HuR nuclear or cytoplasmic immunostaining, tumor-cell proliferation, and patient survival. HuR cytoplasmic expression was significantly increased in grade 3 vs. grade 1 adenocarcinomas (p < 0.001), correlating with worse overall survival (OS) (p = 0.02). Methyl-HuR cytoplasmic expression significantly decreased in grade 3 vs. grade 1 adenocarcinomas (p < 0.001) and correlated with better OS (p = 0.002). Phospho-HuR nuclear expression significantly decreased in grade 3 vs. grade 1 adenocarcinomas (p < 0.001) and non-significantly correlated with increased OS (p = 0.06). Cytoplasmic HuR expression strongly correlated with proliferation markers MCM6 (rho = 0.59 and p < 0.001) and Ki67 (rho = 0.49 and p < 0.001). Conversely, these latter inversely correlated with cytoplasmic methyl-HuR and nuclear phospho-HuR. Cytoplasmic HuR expression is a poor prognosis marker in endometrioid endometrial adenocarcinoma, while cytoplasmic methyl-HuR and nuclear phosphoHuR expressions are markers of better prognosis. This study highlights HuR as a promising potential therapeutic target, especially in treatment-resistant tumors, though further research is needed to understand the mechanisms regulating HuR subcellular localization and post-translational modifications.

RNA regulation of inflammatory responses in glia and its potential as a therapeutic target in central nervous system disorders

A major hallmark of neuroinflammation is the activation of microglia and astrocytes with the induction of inflammatory mediators such as IL-1β, TNF-α, iNOS, and IL-6. Neuroinflammation contributes to disease progression in a plethora of neurological disorders ranging from acute CNS trauma to chronic neurodegenerative disease. Posttranscriptional pathways of mRNA stability and translational efficiency are major drivers for the expression of these inflammatory mediators. A common element in this level of regulation centers around the adenine- and uridine-rich element (ARE) which is present in the 3' untranslated region (UTR) of the mRNAs encoding these inflammatory mediators. (ARE)-binding proteins (AUBPs) such as Human antigen R (HuR), Tristetraprolin (TTP) and KH- type splicing regulatory protein (KSRP) are key nodes for directing these posttranscriptional pathways and either promote (HuR) or suppress (TTP and KSRP) glial production of inflammatory mediators. This review will discuss basic concepts of ARE-mediated RNA regulation and its impact on glial-driven neuroinflammatory diseases. We will discuss strategies to target this novel level of gene regulation for therapeutic effect and review exciting preliminary studies that underscore its potential for treating neurological disorders.

Sex Lethal Gene Manipulates Gonadal Development of Medaka, Oryzias latipes, through Estrogenic Interventions

Germ cells are pivotal for gonadal sexuality maintenance and reproduction. Sex lethal (sxl), the somatic sex determining gene of Drosophila, is the known regulator and initiator of germ cell femininity in invertebrates. However, the role of the Sxl homologue has rarely been investigated in vertebrates. So, we used medaka to clarify the role of sxl in vertebrate gonadogenesis and sexuality and identified two Sxl homologues, i.e., Sxl1a and Sxl1b. We found that sxl1a specifically expresses in the primordial germ cells (PGC), ovary, (early gonia and oocytes), while sxl1b distributions are ubiquitous. An mRNA overexpression of sxl1a accelerated germ cell numbers in 10 DAH XY fish, and sxl1a knockdown (KD), on the other hand, induced PGC mis-migration, aberrant PGC structuring and ultimately caused significant germ cell reduction in XX fish. Using an in vitro promoter analysis and in vivo steroid treatment, we found a strong link between sxl1a and estrogenic germ cell-population maintenance. Further, using sxl1a-KD and erβ2-knockout fish, we determined that sxl1 acts through erβ2 and controls PGC sexuality. Cumulatively, our study highlights the novel role of sxl1a in germ cell maintenance and sexual identity assignment and thus might become a steppingstone to understanding the commonalities of animal sexual development.

RNA-binding proteins in regulating mRNA stability and translation: roles and mechanisms in cancer

RNA-binding proteins (RBPs) are key players in cellular physiology through posttranscriptional regulation of the expression of target RNA transcripts. By modulating the processing, stability and translation of cancer-related messenger RNA (mRNA) transcripts, a large set of RBPs play essential roles in various types of cancers. Perturbations in RBP activity have been causally associated with cancer development, tumor metabolism, drug resistance, cancer stem cell self-renewal, and tumor immune evasion. Here, we summarize the recent advances in cancer pathological roles and mechanisms of RBPs in regulating mRNA stability and translation with an emphasis on the emerging category of RNA modification-associated RBPs. The functional diversity of RBPs in different types of cancers and the therapeutic potential of targeting dysregulated RBPs for cancer treatment are also discussed.

The E3 Ligase TRIM4 Facilitates SET Ubiquitin-Mediated Degradation to Enhance ER-α Action in Breast Cancer

Estrogen receptor alpha (ER-α) action is critical for hormone-dependent breast cancer, and ER-α dysregulation can lead to the emergence of resistance to endocrine therapy. Here, it is found that TRIM4 is downregulated in tamoxifen (TAM)-resistant breast cancer cells, while the loss of TRIM4 is associated with an unfavorable prognosis. In vitro and in vivo experiments confirm that TRIM4 increased ER-α expression and the sensitivity of breast cancer cells to TAM. Mechanistically, TRIM4 is found to target SET, and TRIM4-SET interactions are mediated by the RING and B-box domains of TRIM4 and the carboxyl terminus of SET. Moreover, it is determined that TRIM4 catalyzed the K48-linked polyubiquitination of SET (K150 and K172), promoting its proteasomal degradation and disassociation from p53 and PP2A. Once released, p53 and PP2A are able to further promote ESR1 gene transcription and enhance mRNA stability. Moreover, univariate and multivariate Cox proportional hazards regression analyses confirm that TRIM4 expression is an independent predictor of overall survival and recurrence-free survival outcomes in patients with ER-α positive breast cancer. Taken together, the data highlights a previously undiscovered mechanism and suggest that TRIM4 is a valuable biomarker that can be analyzed to predict response to endocrine therapy in breast cancer patients.

HuR as a molecular target for cancer therapeutics and immune-related disorders

The control of eukaryotic gene expression occurs at multiple levels, from transcription to messenger RNA processing, transport, localization, turnover, and translation. RNA-binding proteins control gene expression and are involved in different stages of mRNA processing, including splicing, maturation, turnover, and translation. A ubiquitously expressed RBP Human antigen R is engaged in the RNA processes mentioned above but, most importantly, controls mRNA stability and turnover. Dysregulation of HuR is linked to many diseases, including cancer and other immune-related disorders. HuR targets mRNAs containing AU-rich elements at their 3'untranslated region, which encodes proteins involved in cell growth, proliferation, tumor formation, angiogenesis, immune evasion, inflammation, invasion, and metastasis. HuR overexpression has been reported in many tumor types, which led to a poor prognosis for patients. Hence, HuR is considered an appealing drug target for cancer treatment. Therefore, multiple attempts have been made to identify small molecule inhibitors for blocking HuR functions. This article reviews the current prospects of drugs that target HuR in numerous cancer types, their mode of action, and off-target effects. Furthermore, we will summarize drugs that interfered with HuR-RNA interactions and established themselves as novel therapeutics. We will also highlight the significance of HuR overexpression in multiple cancers and discuss its role in immune functions. This review provides evidence of a new era of HuR-targeted small molecules that can be used for cancer therapeutics either as a monotherapy or in combination with other cancer treatment modalities.

HuR as Therapeutic Target in Cancer: What the Future Holds

ELAV-like protein 1, or HuR (human antigen R), is an RNA-binding protein encoded by the ELAVL1 gene in humans. One of its best functions is to stabilize mRNAs in order to regulate gene expression. HuR protein overexpression has undoubtedly been linked to an increased risk of tumor growth, progression, and metastasis, rendering it a potential therapeutic target candidate in cancer. Novel agents interfering with HuR expression have been tested, both in vitro and in vivo, with promising results. The aim of this paper is to review the existing literature regarding the potential agents that could actively act on and inhibit HuR expression. HuR molecule controls the expression of various proto-oncogenes, cytokines and growth factors, representing a major player in tumor progression, invasion, and metastasis and constituting an emerging target for cancer therapy. PubMed database was thoroughly searched, and all published articles providing scientific data on molecules that can exhibit antitumorigenic effects via HuR inhibition were included. According to these data, HuR inhibition should be a promising target in cancer therapeutics.

The regulation of RNA metabolism in hormone signaling and breast cancer

As the most frequent women's cancer, breast cancer causes the second most cancer-related death in women worldwide. Majority of the breast cancers are hormone receptor-positive and commonly treated by hormone therapy. Thus, the expression levels of hormone receptors signaling pathways are pivotal in the development and therapy of breast cancer. The expression of hormone receptors signaling pathways is not only regulated at the transcription level but also at the post-transcription level by both proteins and RNAs. In addition to that, the function of hormone receptors can also be regulated by RNAs. In this review, we summarize the roles of RNAs in hormone receptor-positive breast cancer. We introduce how mRNA stability and protein function of genes in hormone receptors signaling pathways are regulated by RNA-binding proteins, miRNAs, and lncRNAs. We believe these proteins and RNAs can be potential therapeutic targets of breast cancer.

Intrinsic and Extrinsic Factors Governing the Transcriptional Regulation of ESR1

Transcriptional regulation of ESR1, the gene that encodes for estrogen receptor α (ER), is critical for regulating the downstream effects of the estrogen signaling pathway in breast cancer such as cell growth. ESR1 is a large and complex gene that is regulated by multiple regulatory elements, which has complicated our understanding of how ESR1 expression is controlled in the context of breast cancer. Early studies characterized the genomic structure of ESR1 with subsequent studies focused on identifying intrinsic (chromatin environment, transcription factors, signaling pathways) and extrinsic (tumor microenvironment, secreted factors) mechanisms that impact ESR1 gene expression. Currently, the introduction of genomic sequencing platforms and additional genome-wide technologies has provided additional insight on how chromatin structures may coordinate with these intrinsic and extrinsic mechanisms to regulate ESR1 expression. Understanding these interactions will allow us to have a clearer understanding of how ESR1 expression is regulated and eventually provide clues on how to influence its regulation with potential treatments. In this review, we highlight key studies concerning the genomic structure of ESR1, mechanisms that affect the dynamics of ESR1 expression, and considerations towards affecting ESR1 expression and hormone responsiveness in breast cancer.

Interplay of ERα binding and DNA methylation in the intron-2 determines the expression and estrogen regulation of cystatin A in breast cancer cells

Despite advances in early detection and treatment, invasion and metastasis of breast tumors remains a major hurdle. Cystatin A (CSTA, also called stefin A), an estrogen-regulated gene in breast cancer cells, is an inhibitor of cysteine cathepsins, and a purported tumor suppressor. Loss of CSTA expression in breast tumors evidently shifts the balance in favor of cysteine cathepsins, thereby promoting extracellular matrix remodeling, tumor invasion and metastasis. However, the underlying mechanism behind the loss of CSTA expression in breast tumors is not known. Here, we have analyzed CSTA expression, and methylation of upstream and intron-2 CpG sites within the CSTA locus in human breast cancer cell lines and breast tumors of the TCGA cohort. Results showed an inverse relationship between expression and methylation. Sequence analysis revealed a potential estrogen response element (ERE) in the intron-2. Analysis of ChIP-seq data (ERP000380) and our own ChIP experiments showed that 17β-estradiol (E2) enhanced ERα binding to this ERE in MCF-7 cells. This ERE was located amidst the differentially methylated intron-2 CpG sites, which provoked us to examine the possible conflict between estrogen-regulation of CSTA and DNA methylation in the intron-2. We analyzed the expression of CSTA and its regulation by E2 in MDA-MB-231 and T47D cells subjected to global demethylation by 5-azacytidine (5-aza). 5-aza significantly demethylated intron-2 CpGs, and enhanced estrogen-induced ERα occupancy at the intron-2 ERE, leading to restoration of estrogen-regulation. Taken together, our results indicate that DNA methylation-dependent silencing could play a significant role in the loss of CSTA expression in breast tumors. The potential of DNA methylation as an indicator of CSTA expression or as a marker of tumor progression can be explored in future investigations. Furthermore, our results indicate the convergence of ERα-mediated estrogen regulation and DNA methylation in the intron-2, thereby offering a novel context to understand the role of estrogen-ERα signaling axis in breast tumor invasion and metastasis.

Interplay between Epigenetics, Expression of Estrogen Receptor- α, HER2/ERBB2 and Sensitivity of Triple Negative Breast Cancer Cells to Hormonal Therapy

Triple negative breast cancer (TNBC) cells are resistant to hormonal/targeted therapies. This study aims to investigate epigenetic differences between TNBC and other types of breast cancer and the effect of epigenetic modulation on the response of TNBC cells to hormonal therapy. Thus, we investigated (i) the expression of different epigenetic markers, (ii) the effect of epigenetic modifying agents on the expression of ERα and HER2/ERBB2 and (iii) the effect on the response to tamoxifen in four breast cancer cell lines with different hormonal receptor status. Our results revealed a differential expression patterns of epigenetic markers in the four breast cancer cells. In TNBC cells, histone deacetylases (HDAC) 1 and 2 were less expressed, whereas HDACs 4 and 6 were overexpressed. Interestingly, treatment with epigenetic modifiers resulted in (i) a pronounced increase in the expression of ERα and HER2/ERBB2 along with (ii) an increase in the sensitivity of TNBC cells to tamoxifen. Collectively, this study indicates a different epigenetic background for TNBC cells, which represses the expression of ERα and HER2/ERBB2. Furthermore, we provide here the rationale for the use of epigenetic modifiers to enhance the response of TNBC to hormonal therapy through upregulation of ERα.

Mechanisms for estrogen receptor expression in human cancer

Estrogen is a steroid hormone that has critical roles in reproductive development, bone homeostasis, cardiovascular remodeling and brain functions. However, estrogen also promotes mammary, ovarian and endometrial tumorigenesis. Estrogen antagonists and drugs that reduce estrogen biosynthesis have become highly successful therapeutic agents for breast cancer patients. The effects of estrogen are largely mediated by estrogen receptor (ER) α and ERβ, which are members of the nuclear receptor superfamily of transcription factors. The mechanisms underlying the aberrant expression of ER in breast cancer and other types of human tumors are complex, involving considerable alternative splicing of ERα and ERβ, transcription factors, epigenetic and post-transcriptional regulation of ER expression. Elucidation of mechanisms for ER expression may not only help understand cancer progression and evolution, but also shed light on overcoming endocrine therapy resistance. Herein, we review the complex mechanisms for regulating ER expression in human cancer.

Derivative of Stevioside; CPUK02; Restores ESR1 Gene Methylation in MDA-MB 231

Background:

CPUK02 (15-Oxosteviol benzyl ester) is a new ent-kaurenoid derivative of stevioside and exhibits strong anti-cancer activity. Nowadays, the pattern of epigenetic in cancer has been topic of many studies and DNA methylation targeting represents a relevant strategy for cancer treatment. Since, no study conducted to this mechanism, we attempt to evaluate whether CPUK02 induce its anti-cancer effects via alteration the level of mRNA DNMT3B, DNMT3A expression and ESR1 methylation pattern in breast cancer cells line.

Methods:

MCF-7 (ER +) and MDA-MB231 (ER-) cell lines were treated for 24, 48 hours with 1 µM CPUK02 and 5-AZA-CdR (DNA methyltransferase inhibitor). Quantitative expression of DNMT3B and DNMT3A genes and ESR1 promoter methylation was assessed by Real-Time PCR and MS-PCR, respectively.

Results:

CPUK02 restored ESR1 promoter unmethylated allele in MDA-MB 231 cells. Also treatment with CPUK02 decreased the expression of both DNMT3A and DNMT3B genes like 5-AZA. The expression of DNMT genes were diminished by half compared with control cells.

Conclusions:

These results showed that CPUK02 has an anticancer effect on MDA-MB 231 cells which this effect can be done through several pathways.

Post-transcriptional regulation of ERBB2 by miR26a/b and HuR confers resistance to tamoxifen in estrogen receptor-positive breast cancer cells

Tamoxifen-resistant (TAMR) estrogen receptor-positive (ER+) breast cancer is characterized by elevated Erb-B2 receptor tyrosine kinase 2 (ERBB2) expression. However, the underlying mechanisms responsible for the increased ERBB2 expression in the TAMR cells remain poorly understood. Herein, we reported that the ERBB2 expression is regulated at the post-transcriptional level by miR26a/b and the RNA-binding protein human antigen R (HuR), both of which associate with the 3'-UTR of the ERBB2 transcripts. We demonstrated that miR26a/b inhibits the translation of ERBB2 mRNA, whereas HuR enhances the stability of the ERBB2 mRNA. In TAMR ER+ breast cancer cells with elevated ERBB2 expression, we observed a decrease in the level of miR26a/b and an increase in the level of HuR. The forced expression of miR26a/b or the depletion of HuR decreased ERBB2 expression in the TAMR cells, resulting in the reversal of tamoxifen resistance. In contrast, the inactivation of miR26a/b or forced expression of HuR decreased tamoxifen responsiveness of the parental ER+ breast cancer cells. We further showed that the increase in HuR expression in the TAMR ER+ breast cancer cells is attributable to an increase in the HuR mRNA isoform with shortened 3'-UTR, which exhibits increased translational activity. This shortening of the HuR mRNA 3'-UTR via alternative polyadenylation (APA) was observed to be dependent on cleavage stimulation factor subunit 2 (CSTF2/CstF-64), which is up-regulated in the TAMR breast cancer cells. Taken together, we have characterized a model in which the interplay between miR26a/b and HuR post-transcriptionally up-regulates ERBB2 expression in TAMR ER+ breast cancer cells.

The Histone-Deacetylase-Inhibitor Suberoylanilide Hydroxamic Acid Promotes Dental Pulp Repair Mechanisms Through Modulation of Matrix Metalloproteinase-13 Activity

Direct application of histone-deacetylase-inhibitors (HDACis) to dental pulp cells (DPCs) induces chromatin changes, promoting gene expression and cellular-reparative events. We have previously demonstrated that HDACis (valproic acid, trichostatin A) increase mineralization in dental papillae-derived cell-lines and primary DPCs by stimulation of dentinogenic gene expression. Here, we investigated novel genes regulated by the HDACi, suberoylanilide hydroxamic acid (SAHA), to identify new pathways contributing to DPC differentiation. SAHA significantly compromised DPC viability only at relatively high concentrations (5 μM); while low concentrations (1 μM) SAHA did not increase apoptosis. HDACi-exposure for 24 h induced mineralization-per-cell dose-dependently after 2 weeks; however, constant 14d SAHA-exposure inhibited mineralization. Microarray analysis (24 h and 14 days) of SAHA exposed cultures highlighted that 764 transcripts showed a significant >2.0-fold change at 24 h, which reduced to 36 genes at 14 days. 59% of genes were down-regulated at 24 h and 36% at 14 days, respectively. Pathway analysis indicated SAHA increased expression of members of the matrix metalloproteinase (MMP) family. Furthermore, SAHA-supplementation increased MMP-13 protein expression (7 d, 14 days) and enzyme activity (48 h, 14 days). Selective MMP-13-inhibition (MMP-13i) dose-dependently accelerated mineralization in both SAHA-treated and non-treated cultures. MMP-13i-supplementation promoted expression of several mineralization-associated markers, however, HDACi-induced cell migration and wound healing were impaired. Data demonstrate that short-term low-dose SAHA-exposure promotes mineralization in DPCs by modulating gene pathways and tissue proteases. MMP-13i further increased mineralization-associated events, but decreased HDACi cell migration indicating a specific role for MMP-13 in pulpal repair processes. Pharmacological inhibition of HDAC and MMP may provide novel insights into pulpal repair processes with significant translational benefit. J. Cell. Physiol. 231: 798-816, 2016. © 2015 Wiley Periodicals, Inc.

Different epigenetic mechanisms of ERα implicated in the fate of fulvestrant-resistant breast cancer

Approximately 70% of breast cancers express estrogen receptor α (ERα), which plays critical roles in breast cancer development. Fulvestrant has been effectively used to treat ERα-positive breast cancer, although resistance remains a critical problem. To elucidate the mechanism of resistance to fulvestrant, we established fulvestrant-resistant cell-lines named MFR (MCF-7 derived fulvestrant resistance) and TFR (T-47D derived fulvestrant resistance) from the ERα-positive luminal breast cancer cell lines MCF-7 and T-47D, respectively. Both fulvestrant-resistant cell lines lost sensitivity to estrogen and anti-estrogens. We observed diminished ERα expression at both the protein and mRNA levels. To address the mechanism of gene expression regulation, we examined epigenetic alteration, especially the DNA methylation level of ERα gene promoters. MFR cells displayed high methylation levels upstream of the ERα gene, whereas no change in DNA methylation was observed in TFR cells. Hence, we examined the gene expression plasticity of ERα, as there are differences in its reversibility following fulvestrant withdrawal. ERα gene expression was not restored in MFR cells, and alternative intracellular phosphorylation signals were activated. By contrast, TFR cells exhibited plasticity of ERα gene expression and ERα-dependent growth; moreover, these cells were resensitized to estrogen and anti-estrogens. The difference in epigenetic regulation among individual cells might explain the difference in the plasticity of ERα expression. We also identified an MFR cell-activating HER/Src-Akt/MAPK pathway; thus, the specific inhibitors effectively blocked MFR cell growth. This finding implies the presence of multiple fulvestrant resistance mechanisms and suggests that the optimal therapies differ among individual tumors as a result of differing epigenetic mechanisms regulating ERα gene expression.

Current Evidence and Future Perspectives on HuR and Breast Cancer Development, Prognosis, and Treatment

Hu-antigen R (HuR) is an RNA-binding posttranscriptional regulator that belongs to the Hu/ELAV family. HuR expression levels are modulated by a variety of proteins, microRNAs, chemical compounds, or the microenvironment, and in turn, HuR affects mRNA stability and translation of various genes implicated in breast cancer formation, progression, metastasis, and treatment. The aim of the present review is to critically summarize the role of HuR in breast cancer development and its potential as a prognosticator and a therapeutic target. In this aspect, all the existing English literature concerning HuR expression and function in breast cancer cell lines, in vivo animal models, and clinical studies is critically presented and summarized. HuR modulates many genes implicated in biological processes crucial for breast cancer formation, growth, and metastasis, whereas the link between HuR and these processes has been demonstrated directly in vitro and in vivo. Additionally, clinical studies reveal that HuR is associated with more aggressive forms of breast cancer and is a putative prognosticator for patients' survival. All the above indicate HuR as a promising drug target for cancer therapy; nevertheless, additional studies are required to fully understand its potential and determine against which types of breast cancer and at which stage of the disease a therapeutic agent targeting HuR would be more effective.

Trichostatin A enhances estrogen receptor-alpha repression in MCF-7 breast cancer cells under hypoxia

Estrogen receptor (ER) is a crucial determinant of resistance to endocrine therapy, which may change during the progression of breast cancer. We previously showed that hypoxia induces ESR1 gene repression and ERα protein degradation via proteasome-mediated pathway in breast cancer cells. HDAC plays important roles in the regulation of histone and non-histone protein post-translational modification. HDAC inhibitors can induce epigenetic changes and have therapeutic potential for targeting various cancers. Trichostatin A exerts potent antitumor activities against breast cancer cells in vitro and in vivo. In this report, we show that TSA augments ESR1 gene repression at the transcriptional level and downregulates ERα protein expression under hypoxic conditions through a proteasome-mediated pathway. TSA-induced estrogen response element-driven reporter activity in the absence of estrogen was synergistically enhanced under hypoxia; however, TSA inhibited cell proliferation under both normoxia and hypoxia. Our data show that the hypoxia-induced repression of ESR1 and degradation of ERα are enhanced by concomitant treatment with TSA. These findings expand our understanding of hormone responsiveness in the tumor microenvironment; however, additional in-depth studies are required to elucidate the detailed mechanisms of TSA-induced ERα regulation under hypoxia.

Post-transcriptional regulation of programmed cell death 4 (PDCD4) mRNA by the RNA-binding proteins human antigen R (HuR) and T-cell intracellular antigen 1 (TIA1)

Post-transcriptional processing of mRNA transcripts plays a critical role in establishing the gene expression profile of a cell. Such processing events are mediated by a host of factors, including RNA-binding proteins and microRNAs. A number of critical cellular pathways are subject to regulation at multiple levels that allow fine-tuning of key biological responses. Programmed cell death 4 (PDCD4) is a tumor suppressor and an important modulator of mRNA translation that is regulated by a number of mechanisms, most notably as a target of the oncomiR, miR-21. Here, we provide evidence for post-transcriptional regulation of PDCD4 by the RNA-binding proteins, HuR and TIA1. Complementary approaches reveal binding of both HuR and TIA1 to the PDCD4 transcript. Consistent with a model where RNA-binding proteins modulate the PDCD4 transcript, knockdown of HuR and/or TIA1 results in a significant decrease in steady-state PDCD4 mRNA and protein levels. However, fractionation experiments suggest that the mode of regulation of the PDCD4 transcript likely differs in the cytoplasm and the nucleus as the pool of PDCD4 mRNA present in the cytoplasm is more stable than the nuclear pool of PDCD4 transcript. We observe a competitive mode of binding between HuR and TIA1 on the PDCD4 transcript in the cytoplasm, suggesting that these two factors dynamically interact with one another as well as the PDCD4 transcript to maintain tight control of PDCD4 levels. Overall, this study reveals an additional set of regulatory interactions that modulate the expression of PDCD4, a key pro-apoptotic factor, and also reveals new insights into how HuR and TIA1 functions are integrated to achieve such regulation.

Neuroprotection requires the functions of the RNA-binding protein HuR

Alterations in the functions of neuronal RNA-binding proteins (RBPs) can contribute to neurodegenerative diseases. However, neurons also express a set of widely distributed RBPs that may have developed specialized functions. Here, we show that the ubiquitous member of the otherwise neuronal Elavl/Hu family of RNA-binding proteins, Elavl1/HuR, has a neuroprotective role. Mice engineered to lack exclusively HuR in the hippocampal neurons of the central nervous system (CNS), maintain physiologic levels of neuronal Elavls and develop a partially diminished seizure response following strong glutamatergic excitation; however, they display an exacerbated neurodegenerative response subsequent to the initial excitotoxic event. This response was phenocopied in hippocampal cells devoid of ionotropic glutamate receptors in which the loss of HuR results in enhanced mitochondrial dysfunction, oxidative damage and programmed necrosis solely after glutamate challenge. The molecular dissection of HuR and nElavl mRNA targets revealed the existence of a HuR-restricted posttranscriptional regulon that failed in HuR-deficient neurons and is involved in cellular energetics and oxidation defense. Thus, HuR acts as a specialized controller of oxidative metabolism in neurons to confer protection from neurodegeneration.

Pedrosa F, Souza EM, Costa FF, Klassen G. Fibronectin affects transient MMP2 gene expression through DNA demethylation changes in non-invasive breast cancer cell lines

Metastasis accounts for more than 90% of cancer deaths. Cells from primary solid tumors may invade adjacent tissues and migrate to distant sites where they establish new colonies. The tumor microenvironment is now recognized as an important participant in the signaling that induces cancer cell migration. An essential process for metastasis is extracellular matrix (ECM) degradation by metalloproteases (MMPs), which allows tumor cells to invade local tissues and to reach blood vessels. The members of this protein family include gelatinase A, or MMP-2, which is responsible for the degradation of type IV collagen, the most abundant component of the basal membrane, that separates epithelial cells in the stroma. It is known that fibronectin is capable of promoting the expression of MMP-2 in MCF7 breast cancer cells in culture. In addition, it was already shown that the MMP2 gene expression is regulated by epigenetic mechanisms. In this work, we showed that fibronectin was able to induce MMP2 expression by 30% decrease in its promoter methylation. In addition, a histone marker for an open chromatin conformation was significantly increased. These results indicate a new role for fibronectin in the communication between cancer cells and the ECM, promoting epigenetic modifications.

Expression of the ELAV-like protein HuR in the cytoplasm is associated with endometrial carcinoma progression

Human antigen R (HuR) is an mRNA-binding factor that belongs to the embryonic lethal abnormal vision/Hu protein family which may function as a tumor maintenance gene in a variety of carcinomas. However, there is no study to analyze HuR expression in endometrial carcinoma. Here, we investigated the expression of HuR in endometrial carcinoma carcinogenesis and subsequent progression. The expression of HuR and estrogen receptor alpha (ER-α) protein was examined by immunohistochemistry on paraffin embedding specimens containing endometrial carcinoma and adjacent non-cancerous tissues. Short hairpin RNA against HuR was transfected to investigate the role of HuR in regulating the expression of ER-α and progression in endometrial carcinoma. Cell viability and cycle were measured using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and flow cytometry, respectively. Apoptosis was examined by annexin V apoptosis assay. Our study result show that cytoplasmic HuR expression is more frequent in poorly differentiated carcinomas (p = 0.005), advanced stage (p = 0.020), and positive ER-α expression (p = 0.026). Three HuR short hairpin RNAs (shRNAs) were transfected into Ishikawa cells, and we selected the most effective shRNA for the following experiments. After the transfection, the ER-α protein level was decreased. Further, decreased expression of HuR resulted in the inhibition of proliferation and induced apoptosis in Ishikawa cells. Our results showed that HuR could be a causal factor of ER-α regulation in Ishikawa cells and thus may induce the hormone-dependent endometrial carcinoma.

Evaluation of wild yam (Dioscorea villosa) root extract as a potential epigenetic agent in breast cancer cells

The present study was designed to evaluate the efficacy of wild yam root extract (WYRE) as a potential demethylating agent using two breast cancer cell lines, MCF-7 (estrogen receptor positive; ER(+)) and MDA-MB-231 (Estrogen receptor negative; ER(-)), and a methylated gene, GATA3, as a potential marker of breast cancer development. The cells were treated with WYRE (0-50 μg/mL) for 72 h and used for viability, mRNA, and methylation analyses. WYRE significantly reduced viability of both cell lines and enhanced mRNA content of GATA3 in a concentration-dependent manner; however, DNMT mRNAs (DNMT1, 3A, 3B) were found to increase significantly only in MDA-MB-231 cells. Global DNA methylation, analyzed as 5'-methyl-2'-deoxycytidine (5-mC) and 5-hydroxymethylcytosine (5-hmC), showed a concentration-dependent enhancement of 5-mC with no alteration in 5-hmC level in MCF-7 cells; however, in MDA-MB-231 cells, in contrast to MCF-7 cells, 5-mC remained unaltered but 5-hmC reduced significantly in all WYRE concentrations (10-50 μg/mL) used in this study. Since 5-hmC is generated from 5-mC by ten-eleven-translocation (TET) enzymes, analysis of TET mRNAs (TET1, TET2, and TET3) in MDA-MB-231 cells indicated a concentration-dependent reduction in TET1 and induction of TET3; however, TET2 remained unaltered. No alterations in any of the TET mRNAs were found in MCF-7 cells. Methylation analysis of GATA3 promoter at specific locus indicates probable demethylating activity of WYRE in MDA-MB-231 cells. We conclude that activation of GATA3 gene in ER(-) MDA-MB-231 cells may occur by altering DNA methylation pattern on the promoter region which may be different from the mechanisms operated in ER(+) MCF-7 cells.

Clinical significance of HuR expression in human malignancy

Hu-antigen R (HuR) is an RNA-binding protein that regulates the stability, translation, and nucleus-to-cytoplasm translocation of target mRNAs. The aim of the present review was to summarize and present the currently available information in the English literature on HuR expression in various human tumors, verifying its possible clinical significance. HuR function is directly linked to its subcellular localization. In normal cells, HuR is mostly localized in the nucleus, while in malignant cells, an increase in cytoplasmic HuR levels has been noted, in both cell lines and tissue samples. Moreover, in malignancy, elevated HuR expression levels and cytoplasmic immunohistochemical pattern have been correlated with advanced clinicopathological parameters and altered expression levels of proteins implicated in neoplasia. Additionally, elevated HuR expression levels and mainly cytoplasmic immunohistochemical pattern were correlated with decreased patients' survival rate in various human tumors. HuR is a putative drug target for cancer therapy, since it is expressed ubiquitously in malignant clinical samples and has an apparently consistent role in tumor formation and progression.

Epigenetic silencing of the human NOS2 gene: rethinking the role of nitric oxide in human macrophage inflammatory responses

Macrophages, including alveolar macrophages, are primary phagocytic cells of the innate immune system. Many studies of macrophages and inflammation have been done in mouse models, in which inducible NO synthase (NOS2) and NO are important components of the inflammatory response. Human macrophages, in contrast to mouse macrophages, express little detectable NOS2 and generate little NO in response to potent inflammatory stimuli. The human NOS2 gene is highly methylated around the NOS2 transcription start site. In contrast, mouse macrophages contain unmethylated cytosine-phosphate-guanine (CpG) dinucleotides proximal to the NOS2 transcription start site. Further analysis of chromatin accessibility and histone modifications demonstrated a closed conformation at the human NOS2 locus and an open conformation at the murine NOS2 locus. In examining the potential for CpG demethylation at the NOS2 locus, we found that the human NOS2 gene was resistant to the effects of demethylation agents both in vitro and in vivo. Our data demonstrate that epigenetic modifications in human macrophages are associated with CpG methylation, chromatin compaction, and histone modifications that effectively silence the NOS2 gene. Taken together, our findings suggest there are significant and underappreciated differences in how murine and human macrophages respond to inflammatory stimuli.

5-Aza-2-deoxycytidine and trichostatin A increase COUP-TFII expression in antiestrogen-resistant breast cancer cell lines

COUP-TFII is reduced in endocrine-resistant breast cancer cells and is negatively associated with tumor grade. Transient re-expression of COUP-TFII restores antiestrogen sensitivity in resistant LCC2 and LCC9 cells and repression of COUP-TFII results in antiestrogen-resistance in MCF-7 endocrine-sensitive cells. We addressed the hypothesis that reduced COUP-TFII expression in endocrine-resistant breast cancer cells results from epigenetic modification. The NR2F2 gene encoding COUP-TFII includes seven CpG islands, including one in the 5' promoter and one in exon 1. Treatment of LCC2 and LCC9 endocrine-resistant breast cancer cells with 5-aza-2'-deoxycytidine (AZA), a DNA methyltransferase (DNMT) inhibitor, +/- trichostatin A (TSA), a histone deacetylase (HDAC) inhibitor, increased COUP-TFII suggesting that the decrease in COUP-TFII is mediated by epigenetic changes. Methylation-specific PCR (MSP) revealed higher methylation of NR2F2 in the first exon in LCC2 and LCC9 cells compared to MCF-7 cells and AZA reduced this methylation. Translational importance is suggested by Cancer Methylome System (CMS) analysis revealing that breast tumors have increased COUP-TFII (NR2F2) promoter and gene methylation versus normal breast.

Effects of physiological levels of the green tea extract epigallocatechin-3-gallate on breast cancer cells

Physiological concentrations of the green tea extract epigallocatechin-3-gallate (EGCG) caused growth inhibition in estrogen receptor α (ERα)-positive MCF7 cells that was associated with down-regulation of the ERα and reduced insulin-like growth factor binding protein-2 abundance and increased protein abundance of the tumor suppressor genes p53/p21. In contrast to MCF7 cells that have wt p53, EGCG alone did not change cell proliferation or death significantly in another ERα-positive cell line T47D that possesses mutant p53. EGCG increased ERα protein levels and as a consequence, the cells responded significantly better to an ERα antagonist tamoxifen (TAM) in the presence of EGCG. EGCG significantly increased cell death in an ERα-negative cell line, MDA-MB-231 that also possesses mutant p53. EGCG significantly increased the ERα and insulin-like growth factor-I receptor levels and thereby enhanced the sensitivities of the cells to TAM and a blocking antibody targeting the insulin-like growth factor-1 receptor (αIR3). In contrast to MCF7, T47D and MDA-MB-231 breast cancer cells that exhibited significant changes in key molecules involved in breast growth and survival upon treatment with physiological levels of EGCG, the growth, survival, and levels of these proteins in non-malignant breast epithelial cells, MCF10A cells, were not affected.

Post-transcriptional controls by ribonucleoprotein complexes in the acquisition of drug resistance

Acquisition of drug resistance leads to failure of anti-cancer treatments and therapies. Although several successive chemotherapies are available, along with efforts towards clinical applications of new anti-cancer drugs, it is generally realized that there is a long way to go to treat cancers. Resistance to anti-cancer drugs results from various factors, including genetic as well as epigenetic differences in tumors. Determining the molecular and cellular mechanisms responsible for the acquisition of drug resistance may be a helpful approach for the development of new therapeutic strategies to overcome treatment failure. Several studies have shown that the acquisition of drug resistance is tightly regulated by post-transcriptional regulators such as RNA binding proteins (RBPs) and microRNAs (miRNAs), which change the stability and translation of mRNAs encoding factors involved in cell survival, proliferation, epithelial-mesenchymal transition, and drug metabolism. Here, we review our current understanding of ribonucleoprotein complexes, including RBPs and miRNAs, which play critical roles in the acquisition of drug resistance and have potential clinical implications for cancer.

Insulin-like growth factor binding protein-3 (IGFBP-3) plays a role in the anti-tumorigenic effects of 5-Aza-2'-deoxycytidine (AZA) in breast cancer cells

Breast cancer progression is associated with loss of estrogen receptor (ER-α), often due to epigenetic silencing. IGFBP genes have consistently been identified among the most common to be aberrantly methylated in tumours. To understand the impact of losing IGFBP-3 tumour expression via DNA methylation, we treated four breast cancer cell lines (MCF-7, T47D, Hs578T and MDA-MB-231) with a DNA methyltransferase inhibitor, 5-Aza-2'-deoxycytidine (AZA) to determine IGFBP-3's role in the effects of AZA on total cell number and survival relative to changes in the ER. AZA induced cell growth inhibition, death and a reduction in the formation of colonies, despite increasing ER-α expression in ER-negative cells but reducing ER-α in ER-positive cells. Regardless of the differential effects on the ER-α, AZA consistently increased the abundance of IGFBP-3 and negating this increase in IGFBP-3 with siRNA reduced the AZA-induced growth inhibition and induction of cell death and virtually negated the AZA-induced inhibition of colony formation. With ER-α positive cells AZA increased the abundance of the tumour suppressor gene, p53 and induced demethylation of the IGFBP-3 promoter, whereas with ER negative cells, AZA epigenetically increased the transcription factor AP2-α, which when silenced prevented the increase in IGFBP-3. IGFBP-3 plays an important role in the anti-tumorigenic effects of AZA on breast cancer cells.

MPT0B098, a novel microtubule inhibitor that destabilizes the hypoxia-inducible factor-1α mRNA through decreasing nuclear-cytoplasmic translocation of RNA-binding protein HuR

Microtubule inhibitors have been shown to inhibit hypoxia-inducible factor-1α (HIF-1α) expression through inhibition translation or enhancing protein degradation. Little is known of the effect of microtubule inhibitors on the stability of HIF-1α mRNA. We recently discovered a novel indoline-sulfonamide compound, 7-aryl-indoline-1-benzene-sulfonamide (MPT0B098), as a potent microtubule inhibitor through binding to the colchicine-binding site of tubulin. MPT0B098 is active against the growth of various human cancer cells, including chemoresistant cells with IC50 values ranging from 70 to 150 nmol/L. However, normal cells, such as human umbilical vein endothelial cells (HUVEC), exhibit less susceptibility to the inhibitory effect of MPT0B098 with IC50 of 510 nmol/L. Similar to typical microtubule inhibitors, MPT0B098 arrests cells in the G2-M phase and subsequently induces cell apoptosis. In addition, MPT0B098 effectively suppresses VEGF-induced cell migration and capillary-like tube formation of HUVECs. Distinguished from other microtubule inhibitors, MPT0B098 not only inhibited the expression levels of HIF-1α protein but also destabilized HIF-1α mRNA. The mechanism of causing unstable of HIF-1α mRNA by MPT0B098 is through decreasing RNA-binding protein, HuR, translocation from the nucleus to the cytoplasm. Notably, MPT0B098 effectively suppresses tumor growth and microvessel density of tumor specimens in vivo. Taken together, our results provide a novel mechanism of inhibiting HIF-1α of a microtubule inhibitor MPT0B098. MPT0B098 is a promising anticancer drug candidate with potential for the treatment of human malignancies.

Reduced expression of miR-200 family members contributes to antiestrogen resistance in LY2 human breast cancer cells

INTRODUCTION

The role of miRNAs in acquired endocrine-resistant breast cancer is not fully understood. One hallmark of tumor progression is epithelial-to-mesenchymal transition (EMT), characterized by a loss of cell adhesion resulting from reduced E-cadherin and increased cell mobility. miR-200 family members regulate EMT by suppressing expression of transcriptional repressors ZEB1/2. Previously we reported that the expression of miR-200a, miR-200b, and miR-200c was lower in LY2 endocrine-resistant, mesenchymal breast cancer cells compared to parental, endocrine sensitive, epithelial MCF-7 breast cancer cells. Here we investigated the regulation of miR-200 family members and their role in endocrine-sensitivity in breast cancer cells.

RESULTS

miR-200 family expression was progressively reduced in a breast cancer cell line model of advancing endocrine/tamoxifen (TAM) resistance. Concomitant with miR-200 decrease, there was an increase in ZEB1 mRNA expression. Overexpression of miR-200b or miR-200c in LY2 cells altered cell morphology to a more epithelial appearance and inhibited cell migration. Further, miR-200b and miR-200c overexpression sensitized LY2 cells to growth inhibition by estrogen receptor (ER) antagonists TAM and fulvestrant. Knockdown of ZEB1 in LY2 cells recapitulated the effect of miR-200b and miR-200c overexpression resulting in inhibition of LY2 cell proliferation by TAM and fulvestrant, but not the aromatase inhibitor exemestane. Demethylating agent 5-aza-2'-deoxycytidine (5-aza-dC) in combination with histone deacetylase inhibitor trichostatin A (TSA) increased miR-200b and miR-200c in LY2 cells. Concomitant with the increase in miR-200b and miR-200c, ZEB1 expression was decreased and cells appeared more epithelial in morphology and were sensitized to TAM and fulvestrant inhibition. Likewise, knockdown of ZEB1 increased antiestrogen sensitivity of LY2 cells resulting in inhibition of cell proliferation.

CONCLUSIONS

Our data indicate that reduced miRNA-200b and miR-200c expression contributes to endocrine resistance in breast cancer cells and that the reduced expression of these miR-200 family members in endocrine-resistant cells can be reversed by 5-aza-dC+TSA.

HDAC3 regulates stability of estrogen receptor α mRNA

Estrogen receptor alpha (ERα) expression is a risk factor for breast cancer. HDAC inhibitors have been demonstrated to down-regulate ERα expression in ERα-positive breast cancer cell lines, but the molecular mechanisms are poorly understood. Here, we showed that HDAC inhibitors decrease the stability of ERα mRNA, and that knockdown of HDAC3 decreases the stability of ERα mRNA and suppresses estrogen-dependent proliferation of ERα-positive MCF-7 breast cancer cells. In the Oncomine database, expression levels of HDAC3 in ERα-positive tumors are higher than those in ERα-negative tumors, thus suggesting that HDAC3 is necessary for ERα mRNA stability, and is involved in the estrogen-dependent proliferation of ERα-positive tumors.

Transcriptional and translational regulation of cytokine signaling in inflammatory β-cell dysfunction and apoptosis

Disease is conventionally viewed as the chaotic inappropriate outcome of deranged tissue function resulting from aberrancies in cellular processes. Yet the patho-biology of cellular dysfunction and death encompasses a coordinated network no less sophisticated and regulated than maintenance of homeostatic balance. Cellular demise is far from passive subordination to stress but requires controlled coordination of energy-requiring activities including gene transcription and protein translation that determine the graded transition between defensive mechanisms, cell cycle regulation, dedifferentiation and ultimately to the activation of death programmes. In fact, most stressors stimulate both homeostasis and regeneration on one hand and impairment and destruction on the other, depending on the ambient circumstances. Here we illustrate this bimodal ambiguity in cell response by reviewing recent progress in our understanding of how the pancreatic β cell copes with inflammatory stress by changing gene transcription and protein translation by the differential and interconnected action of reactive oxygen and nitric oxide species, microRNAs and posttranslational protein modifications.

5-aza-2'-deoxycytidine leads to reduced embryo implantation and reduced expression of DNA methyltransferases and essential endometrial genes

BACKGROUND

The DNA demethylating agent 5-aza-2'-deoxycytidine (5-aza-CdR) incorporates into DNA and decreases DNA methylation, sparking interest in its use as a potential therapeutic agent. We aimed to determine the effects of maternal 5-aza-CdR treatment on embryo implantation in the mouse and to evaluate whether these effects are associated with decreased levels of DNA methyltransferases (Dnmts) and three genes (estrogen receptor α [Esr1], progesterone receptor [Pgr], and homeobox A10 [Hoxa10]) that are vital for control of endometrial changes during implantation.

METHODS AND PRINCIPAL FINDINGS

Mice treated with 5-aza-CdR had a dose-dependent decrease in number of implantation sites, with defected endometrial decidualization and stromal cell proliferation. Western blot analysis on pseudo-pregnant day 3 (PD3) showed that 0.1 mg/kg 5-aza-CdR significantly repressed Dnmt3a protein level, and 0.5 mg/kg 5-aza-CdR significantly repressed Dnmt1, Dnmt3a, and Dnmt3b protein levels in the endometrium. On PD5, mice showed significantly decreased Dnmt3a protein level with 0.1 mg/kg 5-aza-CdR, and significantly decreased Dnmt1 and Dnmt3a with 0.5 mg/kg 5-aza-CdR. Immunohistochemical staining showed that 5-aza-CdR repressed DNMT expression in a cell type-specific fashion within the uterus, including decreased expression of Dnmt1 in luminal and/or glandular epithelium and of Dnmt3a and Dnmt3b in stroma. Furthermore, the 5' flanking regions of the Esr1, Pgr, and Hoxa10 were hypomethylated on PD5. Interestingly, the higher (0.5 mg/kg) dose of 5-aza-CdR decreased protein expression of Esr1, Pgr, and Hoxa10 in the endometrium on PD5 in both methylation-dependent and methylation-independent manners.

CONCLUSIONS

The effects of 5-aza-CdR on embryo implantation in mice were associated with altered expression of endometrial Dnmts and genes controlling endometrial changes, suggesting that altered gene methylation, and not cytotoxicity alone, contributes to implantation defects induced by 5-aza-CdR.

HuR is necessary for mammary epithelial cell proliferation and polarity at least in part via ΔNp63

HuR, a RNA binding protein, is known to function as a tumor maintenance gene in breast cancer and associated with tumor growth and poor prognosis. However, the cellular function of this protein remains largely unknown in normal mammary epithelial cells. Here, we showed that in immortalized MCF10A mammary epithelial cells, HuR knockdown inhibits cell proliferation and enhances premature senescence. We also showed that in three-dimensional culture, MCF10A cells with HuR knockdown form abnormal acini with filled lumen and an aberrant expression pattern of the extracellular matrix protein laminin V. In addition, we showed that HuR knockdown increases ΔNp63, but decreases wild-type p53, expression in MCF10A cells. Moreover, we showed that ΔNp63 knockdown partially rescues the proliferative defect induced by HuR knockdown in MCF10A cells. Consistent with this, we identified two U-rich elements in the 3'-untranslated region of p63 mRNA, to which HuR specifically binds. Finally, we showed that HuR knockdown enhances ΔNp63 mRNA translation but has no effect on p63 mRNA turnover. Together, our data suggest that HuR maintains cell proliferation and polarity of mammary epithelial cells at least in part via ΔNp63.

Genetic polymorphisms in RNA binding proteins contribute to breast cancer survival

The RNA-binding proteins TTP and HuR control expression of numerous genes associated with breast cancer pathogenesis by regulating mRNA stability. However, the role of genetic variation in TTP (ZFP36) and HuR (ELAVL1) genes is unknown in breast cancer prognosis. A total of 251 breast cancer patients (170 Caucasians and 81 African-Americans) were enrolled and followed up from 2001 to 2011 (or until death). Genotyping was performed for 10 SNPs in ZFP36 and 7 in ELAVL1 genes. On comparing both races with one another, significant differences were found for clinical and genetic variables. The influence of genetic polymorphisms on survival was analyzed by using Cox-regression, Kaplan-Meier analysis and the log-rank test. Univariate (Kaplan-Meier/Cox-regression) and multivariate (Cox-regression) analysis showed that the TTP gene polymorphism ZFP36*2 A > G was significantly associated with poor prognosis of Caucasian patients (HR = 2.03; 95% CI = 1.09-3.76; p = 0.025; log-rank p = 0.022). None of the haplotypes, but presence of more than six risk genotypes in Caucasian patients, was significantly associated with poor prognosis (HR=2.42; 95% CI = 1.17-4.99; p = 0.017; log-rank p = 0.007). The effect of ZFP36*2 A > G on gene expression was evaluated from patients' tissue samples. Both TTP mRNA and protein expression was significantly decreased in ZFP36*2 G allele carriers compared to A allele homozygotes. Conversely, upregulation of the TTP-target gene COX-2 was observed ZFP36*2 G allele carriers. Through its ability to attenuate TTP gene expression, the ZFP36*2 A > G gene polymorphism has appeared as a novel prognostic breast cancer marker in Caucasian patients.

Global identification of genes regulated by estrogen signaling and demethylation in MCF-7 breast cancer cells

Estrogen signaling and epigenetic modifications, in particular DNA methylation, are involved in regulation of gene expression in breast cancers. Here we investigated a potential regulatory cross-talk between these two pathways by identifying their common target genes and exploring underlying molecular mechanisms in human MCF-7 breast cancer cells. Gene expression profiling revealed that the expression of approximately 140 genes was influenced by both 17β-estradiol (E2) and a demethylating agent 5-aza-2'-deoxycytidine (DAC). Gene ontology (GO) analysis suggests that these genes are involved in intracellular signaling cascades, regulation of cell proliferation and apoptosis. Based on previously reported association with breast cancer, estrogen signaling and/or DNA methylation, CpG island prediction and GO analysis, we selected six genes (BTG3, FHL2, PMAIP1, BTG2, CDKN1A and TGFB2) for further analysis. Tamoxifen reverses the effect of E2 on the expression of all selected genes, suggesting that they are direct targets of estrogen receptor. Furthermore, DAC treatment reactivates the expression of all selected genes in a dose-dependent manner. Promoter CpG island methylation status analysis revealed that only the promoters of BTG3 and FHL2 genes are methylated, with DAC inducing demethylation, suggesting DNA methylation directs repression of these genes in MCF-7 cells. In a further analysis of the potential interplay between estrogen signaling and DNA methylation, E2 treatment showed no effect on the methylation status of these promoters. Additionally, we show that the ERα recruitment occurs at the FHL2 promoter in an E2- and DAC-independent fashion. In conclusion, we identified a set of genes regulated by both estrogen signaling and DNA methylation. However, our data does not support a direct molecular interplay of mediators of estrogen and epigenetic signaling at promoters of regulated genes.

HuR function in disease

The cytoplasmic events that control mammalian gene expression, primarily mRNA stability and translation, potently influence the cellular response to internal and external signals. The ubiquitous RNA-binding protein (RBP) HuR is one of the best-studied regulators of cytoplasmic mRNA fate. Through its post-transcriptional influence on specific target mRNAs, HuR can alter the cellular response to proliferative, stress, apoptotic, differentiation, senescence, inflammatory and immune stimuli. In light of its central role in important cellular functions, HuR's role in diseases in which these responses are aberrant is increasingly appreciated. Here, we review the mechanisms that control HuR function, its influence on target mRNAs, and how impairment in HuR-governed gene expression programs impact upon different disease processes. We focus on HuR's well-recognized implication in cancer and chronic inflammation, and discuss emerging studies linking HuR to cardiovascular, neurological, and muscular pathologies. We also discuss the progress, potential, and challenges of targeting HuR therapeutically.

Histone deacetylase inhibitors suppress rheumatoid arthritis fibroblast-like synoviocyte and macrophage IL-6 production by accelerating mRNA decay

Background

Histone deacetylase inhibitors (HDACi) display potent therapeutic efficacy in animal models of arthritis and suppress inflammatory cytokine production in rheumatoid arthritis (RA) synovial macrophages and tissue.

Objectives

To determine the molecular mechanisms contributing to the suppressive effects of HDACi on RA synovial cell activation, using interleukin 6 (IL-6) regulation as a model.

Methods

RA fibroblast-like synoviocytes (FLS) and healthy donor macrophages were treated with IL-1β, tumour necrosis factor (TNF)α, lipopolysaccharide or polyinosinic:polycytidylic acid (poly(I:C)) in the absence or presence of the HDACi trichostatin A (TSA) or ITF2357 (givinostat). IL-6 production and mRNA expression was measured by ELISA and quantitative PCR (qPCR), respectively. Protein acetylation and the activation of intracellular signalling pathways were assessed by immunoblotting. The DNA-binding activity of nuclear factor κB (NFκB) and activator protein 1 (AP-1) components was measured by ELISA-based assays.

Results

HDACi (0.25–1.0 μM) suppressed RA FLS IL-6 production induced by IL-1β, TNFα and Toll-like receptor ligands. Phosphorylation of mitogen-activated protein kinases and inhibitor of κBα (IκBα) following IL-1β stimulation were unaffected by HDACi, as were AP-1 composition and binding activity, and c-Jun induction. TSA induced a significant reduction in nuclear retention of NFκB in FLS 24 h after IL-1β stimulation, but this did not reduce NFκB transcriptional activity or correlate temporally with reductions in IL-6 mRNA accumulation. HDACi significantly reduced the stability of IL-6 mRNA in FLS and macrophages.

Conclusions

Our study identifies a novel, shared molecular mechanism by which HDACi can disrupt inflammatory cytokine production in RA synovial cells, namely the promotion of mRNA decay, and suggests that targeting HDAC activity may be clinically useful in suppressing inflammation in RA.

Manipulating protein acetylation in breast cancer: a promising approach in combination with hormonal therapies?

Estrogens play an essential role in the normal physiology of the breast as well as in mammary tumorigenesis. Their effects are mediated by two nuclear estrogen receptors, ERα and β, which regulate transcription of specific genes by interacting with multiprotein complexes, including histone deacetylases (HDACs). During the past few years, HDACs have raised great interest as therapeutic targets in the field of cancer therapy. In breast cancer, several experimental arguments suggest that HDACs are involved at multiple levels in mammary tumorigenesis: their expression is deregulated in breast tumors; they interfere with ER signaling in intricate ways, restoring hormone sensitivity in models of estrogen resistance, and they clinically represent new potential targets for HDACs inhibitors (HDIs) in combination with hormonal therapies. In this paper, we will describe these different aspects and underline the clinical interest of HDIs in the context of breast cancer resistance to hormone therapies (HTs).

Posttranscriptional regulation of cancer traits by HuR

Cancer-related gene expression programs are strongly influenced by posttranscriptional mechanisms. The RNA-binding protein HuR is highly abundant in many cancers. Numerous HuR-regulated mRNAs encode proteins implicated in carcinogenesis. Here, we review the collections of HuR target mRNAs that encode proteins responsible for implementing five major cancer traits. By interacting with specific mRNA subsets, HuR enhances the levels of proteins that (1) promote cell proliferation, (2) increase cell survival, (3) elevate local angiogenesis, (4) help the cancer cell evade immune recognition, and (5) facilitate cancer cell invasion and metastasis. We propose that HuR exerts a tumorigenic function by enabling these cancer phenotypes. We discuss evidence that links HuR to several specific cancers and suggests its potential usefulness in cancer diagnosis, prognosis, and therapy.

The poly(c)-binding protein-1 regulates expression of the androgen receptor

The androgen receptor (AR) is a ligand-dependent transcription factor, expressed in male and female reproductive organs, and essential for normal reproduction in both sexes. The levels of AR are tightly controlled in androgen-responsive cells in which it plays a central role in the regulation of target gene expression. The AR is abundantly expressed in human endometrial stromal cells (HESCs), but levels decline markedly after differentiation into decidual cells in vivo and in primary cultures. Decidualization profoundly down-regulated AR protein levels with no discernible effect on either AR mRNA or protein stability, suggesting that loss of the receptor was a consequence of translational inhibition. Here we show that HESCs express three RNA-binding proteins, Hu antigen R and the poly(C)-binding proteins PCBP1 and PCBP2, that reportedly target the 3'-untranslated region of AR transcripts. Only PCBP1 expression was enhanced in secretory endometrium in vivo and in decidualizing HESCs. Furthermore, knockdown of PCBP1 in decidualizing cells was sufficient to restore AR protein levels, indicating that loss of the AR protein is primarily the consequence of a translational block. PCBP1 also blocked AR translation in a cell-free system, although this did not require binding to the 3'-untranslated region of the receptor mRNA. Furthermore, knockdown of PCBP1 in the prostate cancer LNCaP cell line also increased AR protein. Therefore, PCBP1 plays a major role in the dynamic expression of AR in both male and female androgen-responsive cells.

Promoter- and cell-specific epigenetic regulation of CD44, Cyclin D2, GLIPR1 and PTEN by methyl-CpG binding proteins and histone modifications

Background

The aim of the current study was to analyze the involvement of methyl-CpG binding proteins (MBDs) and histone modifications on the regulation of CD44, Cyclin D2, GLIPR1 and PTEN in different cellular contexts such as the prostate cancer cells DU145 and LNCaP, and the breast cancer cells MCF-7. Since global chromatin changes have been shown to occur in tumours and regions of tumour-associated genes are affected by epigenetic modifications, these may constitute important regulatory mechanisms for the pathogenesis of malignant transformation.

Methods

In DU145, LNCaP and MCF-7 cells mRNA expression levels of CD44, Cyclin D2, GLIPR1 and PTEN were determined by quantitative RT-PCR at the basal status as well as after treatment with demethylating agent 5-aza-2'-deoxycytidine and/or histone deacetylase inhibitor Trichostatin A. Furthermore, genomic DNA was bisulfite-converted and sequenced. Chromatin immunoprecipitation was performed with the stimulated and unstimulated cells using antibodies for MBD1, MBD2 and MeCP2 as well as 17 different histone antibodies.

Results

Comparison of the different promoters showed that MeCP2 and MBD2a repressed promoter-specifically Cyclin D2 in all cell lines, whereas in MCF-7 cells MeCP2 repressed cell-specifically all methylated promoters. Chromatin immunoprecipitation showed that all methylated promoters associated with at least one MBD. Treatment of the cells by the demethylating agent 5-aza-2'-deoxycytidine (5-aza-CdR) caused dissociation of the MBDs from the promoters. Only MBD1v1 bound and repressed methylation-independently all promoters. Real-time amplification of DNA immunoprecipitated by 17 different antibodies showed a preferential enrichment for methylated lysine of histone H3 (H3K4me1, H3K4me2 and H3K4me3) at the particular promoters. Notably, the silent promoters were associated with unmodified histones which were acetylated following treatment by 5-aza-CdR.

Conclusions

This study is one of the first to reveal the histone code and MBD profile at the promoters of CD44, Cyclin D2, GLIPR1 and PTEN in different tumour cells and associated changes after stimulation with methylation inhibitor 5-aza-CdR.

The RNA binding protein HuR differentially regulates unique subsets of mRNAs in estrogen receptor negative and estrogen receptor positive breast cancer

BACKGROUND

The discordance between steady-state levels of mRNAs and protein has been attributed to posttranscriptional control mechanisms affecting mRNA stability and translation. Traditional methods of genome wide microarray analysis, profiling steady-state levels of mRNA, may miss important mRNA targets owing to significant posttranscriptional gene regulation by RNA binding proteins (RBPs).

METHODS

The ribonomic approach, utilizing RNA immunoprecipitation hybridized to microarray (RIP-Chip), provides global identification of putative endogenous mRNA targets of different RBPs. HuR is an RBP that binds to the AU-rich elements (ARE) of labile mRNAs, such as proto-oncogenes, facilitating their translation into protein. HuR has been shown to play a role in cancer progression and elevated levels of cytoplasmic HuR directly correlate with increased invasiveness and poor prognosis for many cancers, including those of the breast. HuR has been described to control genes in several of the acquired capabilities of cancer and has been hypothesized to be a tumor-maintenance gene, allowing for cancers to proliferate once they are established.

RESULTS

We used HuR RIP-Chip as a comprehensive and systematic method to survey breast cancer target genes in both MCF-7 (estrogen receptor positive, ER+) and MDA-MB-231 (estrogen receptor negative, ER-) breast cancer cell lines. We identified unique subsets of HuR-associated mRNAs found individually or in both cell types. Two novel HuR targets, CD9 and CALM2 mRNAs, were identified and validated by quantitative RT-PCR and biotin pull-down analysis.

CONCLUSION

This is the first report of a side-by-side genome-wide comparison of HuR-associated targets in wild type ER+ and ER- breast cancer. We found distinct, differentially expressed subsets of cancer related genes in ER+ and ER- breast cancer cell lines, and noted that the differential regulation of two cancer-related genes by HuR was contingent upon the cellular environment.

Minireview: global regulation and dynamics of ribonucleic Acid

Gene expression starts with transcription and is followed by multiple posttranscriptional processes that carry out the splicing, capping, polyadenylation, and export of each mRNA. Interest in posttranscriptional regulation has increased recently with explosive discoveries of large numbers of noncoding RNAs such as microRNAs, yet posttranscriptional processes depend largely on the functions of RNA-binding proteins as well. Glucocorticoid nuclear receptors are classical examples of environmentally reactive activators and repressors of transcription, but there has also been a significant increase in studies of the role of posttranscriptional regulation in endocrine responses, including insulin and insulin receptors, and parathyroid hormone as well as other hormonal responses, at the levels of RNA stability and translation. On the global level, the transcriptome is defined as the total RNA complement of the genome, and thereby, represents the accumulated levels of all expressed RNAs, because they are each being produced and eventually degraded in either the nucleus or the cytoplasm. In addition to RNA turnover, the many underlying posttranscriptional layers noted above that follow from the transcriptome function within a dynamic ribonucleoprotein (RNP) environment of global RNA-protein and RNA-RNA interactions. With the exception of the spliceosome and the ribosome, thousands of heterodispersed RNP complexes wherein RNAs are dynamically processed, trafficked, and exchanged are heterogeneous in size and composition, thus providing significant challenges to their investigation. Among the diverse RNPs that show dynamic features in the cytoplasm are processing bodies and stress granules as well as a large number of smaller heterogeneous RNPs distributed throughout the cell. Although the localization of functionally related RNAs within these RNPs are responsive to developmental and environmental signals, recent studies have begun to elucidate the global RNA components of RNPs that are dynamically coordinated in response to these signals. Among the factors that have been found to affect coordinated RNA regulation are developmental signals and treatments with small molecule drugs, hormones, and toxins, but this field is just beginning to understand the role of RNA dynamics in these responses.

HDAC inhibitors regulate claudin-1 expression in colon cancer cells through modulation of mRNA stability

Expression and cellular distribution of claudin-1, a tight junction protein, is dysregulated in colon cancer and its overexpression in colon cancer cells induced dedifferentiation and increased invasion. However, the molecular mechanism(s) underlying dysregulated claudin-1 expression in colon cancer remains poorly understood. Histone deacetylase (HDAC)-dependent histone acetylation is an important mechanism of the regulation of cancer-related genes and inhibition of HDACs induces epithelial differentiation and decreased invasion. Therefore, in this study, we examined the role of HDAC-dependent epigenetic regulation of claudin-1 in colon cancer. In this study, we show that sodium butyrate and Trichostatin A (TSA), two structurally different and widely used HDAC inhibitors, inhibited claudin-1 expression in multiple colon cancer cell lines. Further studies revealed modulation of claudin-1 mRNA stability by its 3'-UTR as the major mechanism underlying HDAC-dependent claudin-1 expression. In addition, overexpression of claudin-1 abrogated the TSA-induced inhibition of invasion in colon cancer cells suggesting functional crosstalk. Analysis of mRNA expression in colon cancer patients, showed a similar pattern of increase in claudin-1 and HDAC-2 mRNA expression throughout all stages of colon cancer. Inhibition of claudin-1 expression by HDAC-2-specific small interfering RNA further supported the role of HDAC-2 in this regulation. Taken together, we report a novel post-transcriptional regulation of claudin-1 expression in colon cancer cells and further show a functional correlation between claudin-1 expression and TSA-mediated regulation of invasion. As HDAC inhibitors are considered to be promising anticancer drugs, these new findings will have implications in both laboratory and clinical settings.