Bisphenol-A and diethylstilbestrol exposure induces the expression of breast cancer associated long noncoding RNA HOTAIR in vitro and in vivo

Minireview: Epigenomic Plasticity and Vulnerability to EDC Exposures

The epigenome undergoes significant remodeling during tissue and organ development, which coincides with a period of exquisite sensitivity to environmental exposures. In the case of endocrine-disrupting compounds (EDCs), exposures can reprogram the epigenome of developing tissues to increase susceptibility to diseases later in life, a process termed "developmental reprogramming." Both DNA methylation and histone modifications have been shown to be vulnerable to disruption by EDC exposures, and several mechanisms have been identified by which EDCs can reprogram the epigenome. These include altered methyl donor availability, loss of imprinting control, changes in dioxygenase activity, altered expression of noncoding RNAs, and activation of cell signaling pathways that can phosphorylate, and alter the activity of, histone methyltransferases. This altered epigenomic programming can persist across the life course, and in some instances generations, to alter gene expression in ways that correlate with increased disease susceptibility. Together, these studies on developmental reprogramming of the epigenome by EDCs are providing new insights into epigenomic plasticity that is vulnerable to disruption by environmental exposures.

Long noncoding RNA are aberrantly expressed in human papillary thyroid carcinoma

Long noncoding RNAs (lncRNAs) have emerged as key regulatory molecules at almost every level of gene expression regulation. The altered expression of lncRNAs is a characteristic of numerous types of cancer, and lncRNAs have been demonstrated to promote the development, invasion and metastasis of tumors through various mechanisms. However, the role of lncRNAs in papillary thyroid carcinoma (PTC) remain unclear. In the present study, differentially expressed lncRNAs and mRNAs were detected by human lncRNA microarray in three pairs of PTC and adjacent noncancerous samples. The microarray results revealed that 675 lncRNAs and 751 mRNAs were abnormally expressed in the three PTC samples compared with adjacent noncancerous samples (fold change ≥2.0; P<0.05). To validate the microarray results, 8 differentially expressed lncRNAs were randomly selected for quantitative polymerase chain reaction (qPCR). The results of qPCR were consistent with the microarray data; the 8 lncRNAs had an aberrant expression in the PTC samples compared with the adjacent noncancerous samples. Gene ontology and pathway analysis indicated that there were 7 downregulated pathways and 29 upregulated pathways in PTC. LncRNA classification and subgroup analysis revealed 7 pairs of enhancer-like lncRNA-mRNA, 9 pairs of antisense lncRNA-mRNA and 45 pairs of lncRNA-mRNA were differentially expressed between PTC and their paired noncancerous samples. In conclusion, the present study identified a series of novel PTC-associated lncRNAs. Further study with these lncRNAs is instrumental for the identification of novel target molecules that could lead to improved diagnosis and treatment for PTC.

Endocrine disrupting chemical, bisphenol-A, induces breast cancer associated gene HOXB9 expression in vitro and in vivo

HOXB9 is a homeobox-containing gene that plays a key role in mammary gland development and is associated with breast and other types of cancer. Here, we demonstrate that HOXB9 expression is transcriptionally regulated by estradiol (E2), in vitro and in vivo. We also demonstrate that the endocrine disrupting chemical bisphenol-A (BPA) induces HOXB9 expression in cultured human breast cancer cells (MCF7) as well as in vivo in the mammary glands of ovariectomized (OVX) rats. Luciferase assay showed that estrogen-response-elements (EREs) in the HOXB9 promoter are required for BPA-induced expression. Estrogen-receptors (ERs) and ER-co-regulators such as MLL-histone methylase (MLL3), histone acetylases, CBP/P300, bind to the HOXB9 promoter EREs in the presence of BPA, modify chromatin (histone methylation and acetylation) and lead to gene activation. In summary, our results demonstrate that BPA exposure, like estradiol, increases HOXB9 expression in breast cells both in vitro and in vivo through a mechanism that involves increased recruitment of transcription and chromatin modification factors.

ChemiRs: a web application for microRNAs and chemicals

Background

MicroRNAs (miRNAs) are about 22 nucleotides, non-coding RNAs that affect various cellular functions, and play a regulatory role in different organisms including human. Until now, more than 2500 mature miRNAs in human have been discovered and registered, but still lack of information or algorithms to reveal the relations among miRNAs, environmental chemicals and human health. Chemicals in environment affect our health and daily life, and some of them can lead to diseases by inferring biological pathways.

Results

We develop a creditable online web server, ChemiRs, for predicting interactions and relations among miRNAs, chemicals and pathways. The database not only compares gene lists affected by chemicals and miRNAs, but also incorporates curated pathways to identify possible interactions.

Conclusions

Here, we manually retrieved associations of miRNAs and chemicals from biomedical literature. We developed an online system, ChemiRs, which contains miRNAs, diseases, Medical Subject Heading (MeSH) terms, chemicals, genes, pathways and PubMed IDs. We connected each miRNA to miRBase, and every current gene symbol to HUGO Gene Nomenclature Committee (HGNC) for genome annotation. Human pathway information is also provided from KEGG and REACTOME databases. Information about Gene Ontology (GO) is queried from GO Online SQL Environment (GOOSE). With a user-friendly interface, the web application is easy to use. Multiple query results can be easily integrated and exported as report documents in PDF format. Association analysis of miRNAs and chemicals can help us understand the pathogenesis of chemical components. ChemiRs is freely available for public use at http://omics.biol.ntnu.edu.tw/ChemiRs.

Role of Non-Coding RNAs in the Transgenerational Epigenetic Transmission of the Effects of Reprotoxicants

Non-coding RNAs (ncRNAs) are regulatory elements of gene expression and chromatin structure. Both long and small ncRNAs can also act as inductors and targets of epigenetic programs. Epigenetic patterns can be transmitted from one cell to the daughter cell, but, importantly, also through generations. Diversity of ncRNAs is emerging with new and surprising roles. Functional interactions among ncRNAs and between specific ncRNAs and structural elements of the chromatin are drawing a complex landscape. In this scenario, epigenetic changes induced by environmental stressors, including reprotoxicants, can explain some transgenerationally-transmitted phenotypes in non-Mendelian ways. In this review, we analyze mechanisms of action of reprotoxicants upon different types of ncRNAs and epigenetic modifications causing transgenerationally transmitted characters through germ cells but affecting germ cells and reproductive systems. A functional model of epigenetic mechanisms of transgenerational transmission ncRNAs-mediated is also proposed.

Identification of a long non-coding RNA NR_026689 associated with lung carcinogenesis induced by NNK

Long non-coding RNAs (lncRNA) are thought to be important epigenetic regulators involved in the development of a variety of cancers. Alterations in lncRNA expression are associated with exposure to chemical carcinogens. However, it is still unclear whether lncRNA expression during lung carcinogenesis is induced by chemical carcinogens. In this study, using NNK-induced rat lung cancer model established by our previous study, we determined the lncRNA expression profiles, and an alteration in lncRNA expression was observed in lung cancer tissues and blood in the NNK treatment group. Using quantitative reverse-transcription PCR (qRT-PCR), five differentially expressed lncRNAs were further detected and validated. We identified a novel lncRNA, NR_026689, which showed increased expression in lung cancer tissues induced by NNK and the alteration of lncRNA NR_026689 was specifically observed in lung tissue. The level of NR_026689 was determined and significantly increased in rat whole blood at the 10th and 20th week after NNK treatment to evaluate it as a potential early marker for lung cancer. Together, these findings suggest that lncRNA NR_026689 may be a potential early biomarker for lung cancer and is associated with lung carcinogenesis induced by NNK.

Exposure of Human Prostaspheres to Bisphenol A Epigenetically Regulates SNORD Family Noncoding RNAs via Histone Modification

Bisphenol A (BPA) is a ubiquitous endocrine disruptor exerting lifelong effects on gene expression in rodent prostate cancer (PCa) models. Here, we aimed to determine whether epigenetic events mediating the action of BPA on human prostaspheres enriched in epithelial stem-like/progenitor cells is linked to PCa. We performed genome-wide transcriptome and methylome analyses to identify changes in prostaspheres treated with BPA (10 nM, 200 nM, and 1000 nM) or estradiol-17β (E2) (0.1 nM) for 7 days and validated changes in expression, methylation, and histone marks in parallel-treated prostaspheres. BPA/E2-treatment altered expression of 91 genes but not the methylation status of 485,000 CpG sites in BPA/E2-treated prostaspheres. A panel of 26 genes was found repressed in all treatment groups. Fifteen of them were small nucleolar RNAs with C/D motif (SNORDs), which are noncoding, small nucleolar RNAs known to regulate ribosomal RNA assembly and function. Ten of the most down-regulated SNORDs were further studied. All 10 were confirmed repressed by BPA, but only 3 ratified as E2-repressed. SNORD suppression showed no correlation with methylation status changes in CpG sites in gene regulatory regions. Instead, BPA-induced gene silencing was found to associate with altered recruitments of H3K9me3, H3K4me3, and H3K27me3 to 5'-regulatory/exonic sequences of 5 SNORDs. Expression of 4 out of these 5 SNORDs (SNORD59A, SNORD82, SNORD116, and SNORD117) was shown to be reduced in PCa compared with adjacent normal tissue. This study reveals a novel and unique action of BPA in disrupting expression of PCa-associated SNORDs and a putative mechanism for reprogramming the prostasphere epigenome via histone modification.

RNAseq by Total RNA Library Identifies Additional RNAs Compared to Poly(A) RNA Library

The most popular RNA library used for RNA sequencing is the poly(A) captured RNA library. This library captures RNA based on the presence of poly(A) tails at the 3' end. Another type of RNA library for RNA sequencing is the total RNA library which differs from the poly(A) library by capture method and price. The total RNA library costs more and its capture of RNA is not dependent on the presence of poly(A) tails. In practice, only ribosomal RNAs and small RNAs are washed out in the total RNA library preparation. To evaluate the ability of detecting RNA for both RNA libraries we designed a study using RNA sequencing data of the same two breast cancer cell lines from both RNA libraries. We found that the RNA expression values captured by both RNA libraries were highly correlated. However, the number of RNAs captured was significantly higher for the total RNA library. Furthermore, we identify several subsets of protein coding RNAs that were not captured efficiently by the poly(A) library. One of the most noticeable is the histone-encode genes, which lack the poly(A) tail.

The regulatory roles of non-coding RNAs in nerve injury and regeneration

Non-coding RNAs (ncRNAs), especially microRNAs (miRNAs) and long non-coding RNAs (lncRNAs), have attracted much attention since their regulatory roles in diverse cell processes were recognized. Emerging studies demonstrate that many ncRNAs are differentially expressed after injury to the nervous system, significantly affecting nerve regeneration. In this review, we compile the miRNAs and lncRNAs that have been reported to be dysregulated following a variety of central and peripheral nerve injuries, including acquired brain injury, spinal cord injury, and peripheral nerve injury. We also list investigations on how these miRNAs and lncRNAs exert the regulatory actions in neurodegenerative and neuroregenerative processes through different mechanisms involving their interaction with target coding genes. We believe that comprehension of the expression profiles and the possible functions of ncRNAs during the processes of nerve injury and regeneration will help understand the molecular mechanisms responsible for post-nerve-injury changes, and may contribute to the potential use of ncRNAs as a diagnostic marker and therapeutic target for nerve injury.

Bisphenol-A and Female Infertility: A Possible Role of Gene-Environment Interactions

Background: Bisphenol-A (BPA) is widely used and ubiquitous in the environment. Animal studies indicate that BPA affects reproduction, however, the gene-environment interaction mechanism(s) involved in this association remains unclear. We performed a literature review to summarize the evidence on this topic. Methods: A comprehensive search was conducted in PubMed using as keywords BPA, gene, infertility and female reproduction. Full-text articles in both human and animals published in English prior to December 2014 were selected. Results: Evidence shows that BPA can interfere with endocrine function of hypothalamic-pituitary axis, such as by changing gonadotropin-releasing hormones (GnRH) secretion in hypothalamus and promoting pituitary proliferation. Such actions affect puberty, ovulation and may even result in infertility. Ovary, uterus and other reproductive organs are also targets of BPA. BPA exposure impairs the structure and functions of female reproductive system in different times of life cycle and may contribute to infertility. Both epidemiological and experimental evidences demonstrate that BPA affects reproduction-related gene expression and epigenetic modification that are closely associated with infertility. The detrimental effects on reproduction may be lifelong and transgenerational. Conclusions: Evidence on gene-environment interactions, especially from human studies, is still limited. Further research on this topic is warranted.

Expression and regulation of long non-coding RNAs in colorectal cancer

Long non-coding RNA (lncRNA) has a messenger RNA-like structure, greater than 200 nucleotides in length, and extensively existing in both the cytoplasm and nucleus. However, almost all lncRNAs cannot be transcribed into proteins. Increasing studies showed that lncRNAs participate in many eukaryotic activities, such as regulating the expression of genes at epigenetic, transcriptional and post-transcriptional levels, and regulating human growth and development, and also, cell apoptosis. Their aberrant expression is involved in many human diseases and tumorigenesis. This article reviews the latest results of lncRNAs in colorectal cancer with regards to their expression and regulation.

Long non-coding RNA HOTAIR: A novel oncogene (Review)

Long non-coding RNAs (lncRNAs) have been found to be pervasively transcribed in the genome and are critical regulators of the epigenome. Increasing evidence suggests that lncRNAs are aberrantly expressed in several types of human cancer and that they are important in the initiation, development and metastasis of human cancer. Previous studies have revealed that HOX transcript antisense intergenic RNA (HOTAIR) was frequently upregulated in various types of cancer, including breast cancer, esophageal cancer, lung cancer and gastric cancer. In addition, patients with high expression levels of HOTAIR have a significantly poorer prognosis, compared with those with low levels of expression. HOTAIR is involved in the control of cell apoptosis, growth, metastasis, angiogenesis, DNA repair and tumor cells metabolism. The present review provides an overview of the current knowledge concerning the role of HOTAIR in tumor development and progression.

LncRNA HOTAIR: A master regulator of chromatin dynamics and cancer

Non-coding RNAs (ncRNAs) are emerging classes of regulatory RNA that play key roles in various cellular and physiological processes such as in gene regulation, chromatin dynamics, cell differentiation, and development. NcRNAs are dysregulated in a variety of human disorders including cancers, neurological disorders, and immunological disorders. The mechanisms through which ncRNAs regulate various biological processes and human diseases still remain elusive. HOX antisense intergenic RNA (HOTAIR) is a recently discovered long non-coding RNA (lncRNA) that plays critical role in gene regulation and chromatin dynamics, appears to be misregulated in a variety of cancers. HOTAIR interacts with key epigenetic regulators such as histone methyltransferase PRC2 and histone demethylase LSD1 and regulates gene silencing. Here, we have reviewed recent advancements in understanding the functions and regulation of HOTAIR and its association with cancer and other diseases.

Impact of diethylhexyl phthalate on gene expression and development of mammary glands of pregnant mouse

The widely used diethylhexyl phthalate (DEHP) is a known endocrine disruptor that causes persistent alterations in the structure and function of female reproductive system, including ovaries, uterus and oviducts. To explore the molecular mechanism of the effect of DEHP on the development of mammary glands, we investigated the cell cycle, growth, proliferation and gene expression of mammary gland cells of pregnant mice exposed to DEHP. It was demonstrated, for the first time, that the mammary gland cells of pregnant mice treated with DEHP for 0.5-3.5 days post-coitum had increased proliferation, growth rate and number of cells in the G2/S phase. The expression of cell proliferation-related genes was significantly altered after short time and low-dose DEHP treatment of mammary gland cells in vivo and in vitro. These findings showed adverse effects of DEHP on mammary gland cells in pregnant mice.

Prognostic role of HOTAIR in four estrogen-dependent malignant tumors: a meta-analysis

Background

HOX transcript antisense intergenic RNA (HOTAIR), a long non-coding RNA transcribed from the antisense strand of the HOXC gene locus, has been shown to be overexpressed in various carcinomas and is thought to be an indicator of poor prognosis. Recently, HOTAIR was found to be an estrogen-responsive gene. We therefore conducted a meta-analysis to systematically summarize and clarify the association between HOTAIR expression and prognosis in the four main estrogen-dependent tumors.

Methods

A systematic search of studies that examined the association and prognostic impact of HOTAIR in four of the main estrogen-dependent tumors was conducted in PubMed and Embase. Hazard ratios (HRs) and 95% confidence intervals (95% CIs) were calculated to pool the effect size.

Results

A total of 1,200 patients from eight eligible studies were included. The current study found an association between HOTAIR expression and overall survival (OS) in four estrogen-dependent tumor types (HR, 1.99; 95% CI: 1.02–3.90; P_{Heterogeneity}=0.001). Subgroup analyses indicated that high HOTAIR expression appeared to be a potential prognostic biomarker in non-breast cancer patients (HR, 2.72; 95% CI: 1.65–4.48). There was also an increased risk in Asian populations (HR, 2.55; 95% CI: 1.62–4.00) compared with Caucasian populations (HR, 1.19; 95% CI: 0.16–8.83) and in patients without preoperative treatment (HR, 2.55; 95% CI: 1.62–4.00) compared with patients with preoperative treatment (HR, 1.19; 95% CI: 0.16–8.83). In addition, the HRs of patients with high HOTAIR expression for metastasis-free survival (MFS), relapse-free survival (RFS), and disease-free survival (DFS) were 2.30 (P=0.120), 1.39 (P=0.000), and 2.53 (P=0.714), respectively, but there were insufficient data to fully confirm these associations.

Conclusion

HOTAIR may be a predictor of poor prognosis in four of the main estrogen-dependent tumors, especially in cervical, ovarian, and endometrial cancer patients without preoperative treatment in Asian populations. It is important to note that the prognostic value of HOTAIR in MFS, RFS, and DFS should be interpreted with caution due to the limited sample size and sample heterogeneity. Well-designed and larger-scale studies are needed to validate our findings.

Endocrine disruptors and female cancer: Informing the patients (Review)

Pollutants altering the endocrine system, known as endocrine disruptors (ED), may modify the risk of female cancers. The carcinogenic effect of ED on humans has been confirmed by experimental studies for various substances including pesticides, DDT, dioxins, phthalates, bisphenol A, diethylstilbestrol, as well as heavy metals, but it is difficult to quantify precisely for several reasons hereby reviewed. Carcinogenesis is a complex and multifactorial mechanism that manifests itself over a long period of time, making difficult the detection of the specific contribution of the pollutants, whose absorbed dose is often unknown. The combined effect of various substances leads to complex interactions whose outcome is difficult to predict. These substances may accumulate and carry out their harmful effect on critical periods of life, probably also at doses considered harmless to an adult. ED can also have epigenetic adverse effects on the health of future generations. In conclusion, the carcinogenic effects of endocrine disruptors on female cancer types is plausible although additional studies are needed to clarify their mechanisms and entities. In the last part of the review we suggest ways to reduce ED exposure as it is mandatory to implement necessary measures to limit exposure, particularly during those periods of life most vulnerable to the impact of oncogenic environmental causes, such as the embryonic period and puberty.

Long non-coding RNA HOTAIR promotes tumor cell invasion and metastasis by recruiting EZH2 and repressing E-cadherin in oral squamous cell carcinoma

HOX transcript antisense RNA (HOTAIR), a long intergenic non-coding RNA (lncRNA), functions as a molecular scaffold to link and target the histone modification complexes PRC2 and LSD1, then reprograms chromatin states by coupling histone H3K27 methylation and H3K4 demethylation for epigenetic gene silencing to promote cancer metastasis. It is associated with poor survival in several solid cancers. In this study, we show that HOTAIR expression increased in oral squamous cell carcinoma (OSCC) compared with non-tumor tissue and is associated with metastasis, the stage and histological differentiation. In addition, overexpression of HOTAIR indicated poor overall survival (OS) and disease-free survival (DFS) in OSCC patients. Knockdown of HOTAIR by siRNA in OSCC cells decreased cell proliferation and colony formation, increased cell invasion and migration, and induced apoptosis in vitro. Furthermore, significant negative correlation between HOTAIR levels and E-cadherin levels was found in OSCC tissues and cell lines, and HOTAIR contributed to the regulation of E-cadherin through binding to EZH2 and H3K27me3 with the E-cadherin promoter. Our findings suggest that HOTAIR expression is associated with OSCC and may be one of critical targets in progression and metastasis, and an indicator of poor survival in OSCC.

Prognostic impact of HOTAIR expression is restricted to ER-negative breast cancers

Expression of HOX transcript antisense intergenic RNA (HOTAIR), a large intergenic noncoding RNA (lincRNA), has been described as a metastases-associated lincRNA in various cancers including breast, liver and colon cancer cancers. We sought to determine if expression of HOTAIR could be used as a surrogate for assessing nodal metastases and evaluated RNA in situ hybridization (RNA-ISH) assay in a tissue microarray constructed from 133 breast cancer patients. The prognostic value of HOTAIR was further validated in large cohorts using The Cancer Genome Atlas (TCGA) breast cancer subjects. RNA-ISH analysis was successful in 94 cases (17% cases scored 0, 32.9% scored 1, 30.8% scored 2, and 19.1% scored 3). The expression of HOTAIR did not correlate with nodal metastasis regardless of the scoring intensity or with other study parameters (age, tumor size and grade, expression status). Further analysis of TCGA dataset showed that HOTAIR expression was lower in ductal carcinomas but higher in ER-negative tumors. Overexpression of HOTAIR was not associated with nodal metastases or prognosis in ER-positive patients. Its function as a poor prognostic indicator in ER-negative patients was restricted to node-positive patients. HOTAIR appears to be a marker for lymphatic metastases rather than hematogenous metastases in ER-negative patients.

HOTAIR: an oncogenic long non-coding RNA in different cancers

Long non-coding RNAs (lncRNAs) refer to a group of RNAs that are usually more than 200 nucleotides and are not involved in protein generation. Instead, lncRNAs are involved in different regulatory processes, such as regulation of gene expression. Different lncRNAs exist throughout the genome. LncRNAs are also known for their roles in different human diseases such as cancer. HOTAIR is an lncRNA that plays a role as an oncogenic molecule in different cancer cells, such as breast, gastric, colorectal, and cervical cancer cells. Therefore, HOTAIR expression level is a potential biomarker for diagnostic and therapeutic purposes in several cancers. This RNA takes part in epigenetic regulation of genes and plays an important role in different cellular pathways by interacting with Polycomb Repressive Complex 2 (PRC2). In this review, we describe the molecular function and regulation of HOTAIR and its role in different types of cancers.

Bisphenol-A induces expression of HOXC6, an estrogen-regulated homeobox-containing gene associated with breast cancer

HOXC6 is a homeobox-containing gene associated with mammary gland development and is overexpressed in variety of cancers including breast and prostate cancers. Here, we have examined the expression of HOXC6 in breast cancer tissue, investigated its transcriptional regulation via estradiol (E2) and bisphenol-A (BPA, an estrogenic endocrine disruptor) in vitro and in vivo. We observed that HOXC6 is differentially over-expressed in breast cancer tissue. E2 induces HOXC6 expression in cultured breast cancer cells and in mammary glands of Sprague Dawley rats. HOXC6 expression is also induced upon exposure to BPA both in vitro and in vivo. Estrogen-receptor-alpha (ERα) and ER-coregulators such as MLL-histone methylases are bound to the HOXC6 promoter upon exposure to E2 or BPA and that resulted in increased histone H3K4-trimethylation, histone acetylation, and recruitment of RNA polymerase II at the HOXC6 promoter. HOXC6 overexpression induces expression of tumor growth factors and facilitates growth 3D-colony formation, indicating its potential roles in tumor growth. Our studies demonstrate that HOXC6, which is a critical player in mammary gland development, is upregulated in multiple cases of breast cancer, and is transcriptionally regulated by E2 and BPA, in vitro and in vivo.

Epigenetic Regulation of Non-Lymphoid Cells by Bisphenol A, a Model Endocrine Disrupter: Potential Implications for Immunoregulation

Endocrine disrupting chemicals (EDC) abound in the environment since many compounds are released from chemical, agricultural, pharmaceutical, and consumer product industries. Many of the EDCs such as Bisphenol A (BPA) have estrogenic activity or interfere with endogenous sex hormones. Experimental studies have reported a positive correlation of BPA with reproductive toxicity, altered growth, and immune dysregulation. Although the precise relevance of these studies to the environmental levels is unclear, nevertheless, their potential health implications remain a concern. One possible mechanism by which BPA can alter genes is by regulating epigenetics, including microRNA, alteration of methylation, and histone acetylation. There is now wealth of information on BPA effects on non-lymphoid cells and by comparison, paucity of data on effects of BPA on the immune system. In this mini review, we will highlight the BPA regulation of estrogen receptor-mediated immune cell functions and in different inflammatory conditions. In addition, BPA-mediated epigenetic regulation of non-lymphoid cells is emphasized. We recognize that most of these studies are on non-lymphoid cells, and given that BPA also affects the immune system, it is plausible that BPA could have similar epigenetic regulation in immune cells. It is hoped that this review will stimulate studies in this area to ascertain whether or not BPA epigenetically regulates the cells of the immune system.

Bisphenol A as epigenetic modulator: setting the stage for carcinogenesis?

BACKGROUND

Bisphenol A (BPA) is one of the most widely produced chemicals worldwide and is often used in the production of food and beverage containers. As a result of BPA contact with food, drink and toiletries, its ingestion and absorption by humans has been growing. The industrialization and modern lifestyles brought a constant exposure to several health-disturbing compounds and ushered a new era of chronic diseases. The endocrine disruptor potential of BPA is well known, but the research around its epigenotoxic effects raised further concerns whether chronic exposure to BPA can contribute to chronic human illness, including cancer in hormone-sensitive organs.

MATERIALS AND METHODS

Focusing on computerized databases, we reviewed original and review articles which elucidate and link some of the information already available about BPA and related epigenetic alterations.

RESULTS

A number of studies indicate that short-term administration of low or high-doses of BPA may be associated with an increased risk of epigenetic modifications, increasing the risk for carcinogenesis. However, it is clear that more studies considering real daily exposures are essential to define a real tolerable daily intake and to tighten up manufactory regulations.

CONCLUSION

In this review, we highlight some evidences suggesting a relationship between BPA exposure, genotoxic activity and epigenetic modifications, which may prime for carcinogenesis.

The molecular mechanism of HOTAIR in tumorigenesis, metastasis, and drug resistance

Long non-coding RNAs have been reported to play an important role in cellular metabolism and development. Homeobox transcript antisense intergenic RNA (HOTAIR), a long non-coding RNA, is pervasively over-expressed in most human cancers compared with non-cancerous adjacent tissues. Although many articles have reported that HOTAIR is closely associated with metastasis, epithelial-mesenchymal transition, advanced pathological stage, drug resistance, and poor prognosis, the role of HOTAIR in gene regulation and tumor development is largely unknown, and the potential molecular mechanisms are not completely clear yet. In this review, we summarized the recent progress in the study of the major functions of HOTAIR. miR-331-3p, miR-130a, miR-7, miR-141, HER2, c-MYC, WIF-1, RBM38, PTEN, and Col-1 are involved in the HOTAIR regulation network. We tried to elucidate the molecular mechanisms of HOTAIR in the aspects of tumorigenesis, metastasis, drug resistance, and regulation.

Noncoding RNA response to xenobiotic exposure: an indicator of toxicity and carcinogenicity

INTRODUCTION

Human exposure to certain environmental and occupational chemicals is one of the major risk factors for noncommunicable diseases, including cancer. Therefore, it is desirable to take advantage of subtle exposure-related adverse cellular events for early disease detection and to identify potential dangers caused by new and currently under-evaluated drugs and chemicals. Nongenotoxic events due to carcinogen/toxicant exposure are a general hallmark of sustained cellular stress leading to tumorigenesis. These processes are globally regulated via noncoding RNAs (ncRNAs). Tumorigenesis-associated genotoxic and nongenotoxic events lead to the altered expression of ncRNAs and may provide a mechanistic link between chemical exposure and tumorigenesis. Current advances in toxicogenomics are beginning to provide valuable insight into gene-chemical interactions at the transcriptome level.

AREAS COVERED

In this review, we summarize recent information about the impact of xenobiotics on ncRNAs. Evidence highlighted in this review suggests a critical role of ncRNAs in response to carcinogen/toxicant exposure.

EXPERT OPINION

Benefits for the use of ncRNAs in carcinogenicity assessment include remarkable tissue specificity, early appearance, low baseline variability, and their presence and stability in biological fluids, which suggests that the incorporation of ncRNAs in the evaluation of cancer risk assessment may enhance substantially the efficiency of toxicity and carcinogenicity testing.