miR-106a-mediated malignant transformation of cells induced by anti-benzo[a]pyrene-trans-7,8-diol-9,10-epoxide

Influences of polycyclic aromatic hydrocarbon on the epigenome toxicity and its applicability in human health risk assessment

The existence of polycyclic aromatic hydrocarbons (PAHs) in ambient air is an escalating concern worldwide because of their ability to cause cancer and induce permanent changes in the genetic material. Growing evidence implies that during early life-sensitive stages, the risk of progression of acute and chronic diseases depends on epigenetic changes initiated by the influence of environmental cues. Several reports deciphered the relationship between exposure to environmental chemicals and epigenetics, and have known toxicants that alter the epigenetic states. Amongst PAHs, benzo[a]pyrene (B[a]P) is accepted as a group 1 cancer-causing agent by the International Agency for the Research on Cancer (IARC). B[a]P is a well-studied pro-carcinogen that is metabolically activated by the aryl hydrocarbon receptor (AhR)/cytochrome P450 pathway. Cytochrome P450 plays a pivotal role in the stimulation step, which is essential for DNA adduct formation. Accruing evidence suggests that epigenetic alterations assume a fundamental part in PAH-promoted carcinogenesis. This interaction between PAHs and epigenetic factors results in an altered profile of these marks, globally and locus-specific. Some of the epigenetic changes due to exposure to PAHs lead to increased disease susceptibility and progression. It is well understood that exposure to environmental carcinogens, such as PAH triggers disease pathways through changes in the genome. Several evidence reported due to the epigenome-wide association studies, that early life adverse environmental events may trigger widespread and persistent variations in transcriptional profiling. Moreover, these variations respond to DNA damage and/or a consequence of epigenetic modifications that need further investigation. Growing evidence has associated PAHs with epigenetic variations involving alterations in DNA methylation, histone modification, and micro RNA (miRNA) regulation. Epigenetic alterations to PAH exposure were related to chronic diseases, such as pulmonary disease, cardiovascular disease, endocrine disruptor, nervous system disorder, and cancer. This hormetic response gives a novel perception concerning the toxicity of PAHs and the biological reaction that may be a distinct reliance on exposure. This review sheds light on understanding the latest evidence about how PAHs can alter epigenetic patterns and human health. In conclusion, as several epigenetic change mechanisms remain unclear yet, further analyses derived from PAHs exposure must be performed to find new targets and disease biomarkers. In spite of the current limitations, numerous evidence supports the perception that epigenetics grips substantial potential for advancing our knowledge about the molecular mechanisms of environmental toxicants, also for predicting health-associated risks due to environmental circumstances exposure and individual susceptibility.

Regulation of Neuroendocrine-like Differentiation in Prostate Cancer by Non-Coding RNAs

Neuroendocrine prostate cancer (NEPC) represents a variant of prostate cancer that occurs in response to treatment resistance or, to a much lesser extent, de novo. Unravelling the molecular mechanisms behind transdifferentiation of cancer cells to neuroendocrine-like cancer cells is essential for development of new treatment opportunities. This review focuses on summarizing the role of small molecules, predominantly microRNAs, in this phenomenon. A published literature search was performed to identify microRNAs, which are reported and experimentally validated to modulate neuroendocrine markers and/or regulators and to affect the complex neuroendocrine phenotype. Next, available patients’ expression datasets were surveyed to identify deregulated microRNAs, and their effect on NEPC and prostate cancer progression is summarized. Finally, possibilities of miRNA detection and quantification in body fluids of prostate cancer patients and their possible use as liquid biopsy in prostate cancer monitoring are discussed. All the addressed clinical and experimental contexts point to an association of NEPC with upregulation of miR-375 and downregulation of miR-34a and miR-19b-3p. Together, this review provides an overview of different roles of non-coding RNAs in the emergence of neuroendocrine prostate cancer.

The Circ_CARM1 controls cell migration by regulating CTNNBIP1 in anti-benzo[a]pyrene-trans-7,8-dihydrodiol-9,10-epoxide-transformed 16HBE cells

BACKGROUND

Circular RNAs (circRNAs) have an important role in the development and progression of human tumors, including lung cancer. Yet, their role in lung cancer induced by benzo(a)pyrene (B[a]P) remains unclear. In this study, circRNA chips and qRT-PCR were used to examine downregulated circRNAs in malignantly transformed 16HBE cells (16HBE-T) induced by B[a]P. Five down-regulated circRNAs were found, among which hsa_circ_0004552 (circ_CARM1) had the most significant downregulation. Consequently, the role of circ_CARM1 on 16HBE-T cells biological behavior was further examined using several in vitro experiments.

MATERIALS AND METHODS

Detecting RNA expression via qRT-PCR. Fluorescence in situ hybridization (FISH) was used to identify the localization of circ_CARM1 in 16HBE-T. The effect of circ_CARM1 on cell behavior (cell migration, proliferation, and apoptosis) was explored by transfecting cells with a vector carrying an overexpression and then using wound healing, transwell migration assay, and flow cytometry. Also, the regulation mechanism for circ_CARM1, miR-1288-3p, and CTNNBIP1 was studied by Dual-Luciferase® Reporter (DLR™) Assay System and western blotting.

RESULTS

Reduced expression of circ_CARM1 is observed in 16HBE-T. The overexpression of circ_CARM1 further inhibited the migration of 16HBE-T cells but did not affect cell proliferation and apoptosis. Furthermore, bioinformatic analysis and Dual-Luciferase® Reporter (DLR™) Assay System showed that the competitive binding of circ_CARM1 and miR-1288-3p enhanced the expression of CTNNBIP1, thereby inhibiting the migration of 16HBE-T cells.

CONCLUSION

Downregulation of circ_CARM1 can stimulate the expression of miR-1288-3p, thereby reducing the expression of CTNNBIP1, spurring cell migration.

Upregulation of long noncoding RNA XIST has anticancer effects on ovarian cancer through sponging miR-106a

Ovarian cancer (OC) is a highly malignant tumor. X inactive specific transcript (XIST) was identified as a cancer-related gene, while its therapeutic effect in OC was poorly defined. The present study was designed to investigate the effectual corollary of the lncRNA XIST in OC. RT-qPCR was used to detect the XIST and miR-106a expression levels of OC tissues and cell lines. OC cell apoptosis and proliferation were detected by flow cytometry, colony formation, and CCK-8 assays. Moreover, bioinformatics analysis was used to predict the targeted miRNA of XIST. The dual-luciferase reporter and RNA pull-down assays were then used to verify the interaction between miR-106a and XIST. OC xenograft nude mice were raised to measure tumor growth. Notably, OC tissues and cells exhibited low XIST levels and high miR-106a levels. The XIST upregulation decreased the OVCAR3 and CAOV3 cell proliferation and inversely promoted cell apoptosis. miR-106a targeted the XIST. Also, the miR-106a overexpression reversed the inhibitory effects of XIST on OC cell proliferation and apoptosis. Our in vivo results suggested that XIST was involved in tumor growth deceleration, while the miR-106a reversed the effect. To conclusion, the present study demonstrated that XIST suppressed OC development via sponging miR-106a both in vitro and in vivo.

Circular RNAs in Toxicology

Circular RNAs (circRNAs) are a type of closed, long, non-coding RNAs, which have attracted significant attention in recent years. CircRNAs exhibit unique functions and are characterized by stable expression in various tissues across different species. Because the identification of circRNA in plant viroids in 1976, numerous studies have been conducted to elucidate its generation as well as expression under normal and disease conditions. The rapid development of research focused on the roles of circRNAs as biomarkers in diseases such as cancers has led to increased interests in evaluating the effects of toxicants on the human genetics from a toxicological perspective. Notably, increasing amounts of chemicals are generated in the environment; however, their toxic features and interactions with the human body, particularly from the epigenetic viewpoint, remain largely unknown. Considering the unique features of circRNAs as potential prognostic biomarkers as well as their roles in evaluating health risks following exposure to toxicants, the aim of this review was to assess the latest progress in the research concerning circRNA, to address the role of the circRNA-miRNA-mRNA axis in diseases and processes occurring after exposure to toxic compounds. Another goal was to identify the gaps in understanding the interactions between toxic compounds and circRNAs as potential biomarkers. The review presents general information about circRNA (ie, biogenesis and functions) and provides insights into newly discovered exosome-contained circRNA. The roles of circRNAs as potential biomarkers are also explored. A comprehensive review of the available literature on the role of circRNA in toxicological research (ie, chemical carcinogenesis, respiratory toxicology, neurotoxicology, and other unclassified toxicological categories) is included.

Mediation of association between polycyclic aromatic hydrocarbon exposure and semen quality by spermatogenesis-related microRNAs: A pilot study in an infertility clinic

Spermatogenesis-related microRNAs (miRNAs) are vulnerable to polycyclic aromatic hydrocarbons (PAHs). Changes in spermatogenesis-related miRNAs may be biological intermedia in mechanisms linking PAHs and semen quality. This study aimed to investigate whether spermatogenesis-related microRNAs mediate the associations between PAHs and semen quality. We measured 10 monohydroxylated PAHs (OH-PAHs) in repeated urine samples and three candidate spermatogenesis-related miRNAs (miRNA106a, miRNA21, and miRNA34c) in seminal plasma from men attending an infertility clinic (n = 111). Mediation analysis was applied to determine the mediating role of spermatogenesis-related miRNAs in the association of PAH exposure with semen quality. Urinary 2-OHFlu and 2-OHPh were related to reduced seminal plasma miRNA34c (p for trend = 0.05 and 0.03, respectively). Urinary 9-OHPh was related to reduced seminal plasma miR106a (p for trend = 0.02), which in turn, was positively associated with sperm concentration, sperm count, sperm total motility, and progressive motility (all p for trends<0.05). Up to 43.8% of the eff ;ect of urinary 9-OHPh on decreased sperm concentration was mediated by seminal plasma miR106a. Our results suggested that certain PAH exposure was associated with reduced spermatogenesis-related miRNAs and such alterations might be an intermediate mechanism by which PAHs exert its adverse effects on semen quality.

MicroRNAs and their role in environmental chemical carcinogenesis

MicroRNAs (miRNAs) are a class of small, noncoding RNA species that play crucial roles across many biological processes and in the pathogenesis of major diseases, including cancer. Recent studies suggest that the expression of miRNA is altered by certain environmental chemicals, including metals, organic pollutants, cigarette smoke, pesticides and carcinogenic drugs. In addition, extensive studies have indicated the existence and importance of miRNA in different cancers, suggesting that cancer-related miRNAs could serve as potential markers for chemically induced cancers. The altered expression of miRNA was considered to be a vital pathogenic role in xenobiotic-induced cancer development. However, the significance of miRNA in the etiology of cancer and the exact mechanisms by which environmental factors alter miRNA expression remain relatively unexplored. Hence, understanding the interaction of miRNAs with environmental chemicals will provide important information on mechanisms underlying the pathogenesis of chemically induced cancers, and effectively diagnose and treat human cancers resulting from chronic or acute carcinogen exposure. This study presents the current evidence that the miRNA deregulation induced by various chemical carcinogens, different cancers caused by environmental carcinogens and the potentially related genes in the onset or progression of cancer. For each carcinogen, the specifically expressed miRNA may be considered as the early biomarkers of the cancer process. In this review, we also summarize various target genes of the altered miRNA, oncogenes or anti-oncogenes, and the existing evidence regarding the gene regulation mechanisms of cancer caused by environmentally induced miRNA alteration. The future perspective of miRNA may become attractive targets for the diagnosis and treatment of carcinogen-induced cancer.

Circular RNA circNOL10 Inhibits Lung Cancer Development by Promoting SCLM1-Mediated Transcriptional Regulation of the Humanin Polypeptide Family

circNOL10 is a circular RNA expressed at low levels in lung cancer, though its functions in lung cancer remain unknown. Here, the function and molecular mechanism of circNOL10 in lung cancer development are investigated using in vitro and in vivo studies, and it is shown that circNOL10 significantly inhibits the development of lung cancer and that circNOL10 expression is co-regulated by methylation of its parental gene Pre-NOL10 and by splicing factor epithelial splicing regulatory protein 1 (ESRP1). circNOL10 promotes the expression of transcription factor sex comb on midleg-like 1 (SCML1) by inhibiting transcription factor ubiquitination and thus also affects regulation of the humanin (HN) polypeptide family by SCML1. circNOL10 also affects mitochondrial function through regulating the humanin polypeptide family and affecting multiple signaling pathways, ultimately inhibiting cell proliferation and cell cycle progression, and promoting the apoptosis of lung cancer cells, thereby inhibiting lung cancer development. This study investigates the functions and molecular mechanisms of circNOL10 in the development of lung cancer and reveals its involvement in the transcriptional regulation of the HN polypeptide family by SCML1. The results also demonstrate the inhibitory effect of HN on lung cancer cells growth. These findings may identify novel targets for the molecular therapy of lung cancer.

Clusterin and neuropilin-2 as potential biomarkers of tumor progression in benzo[a]pyrene-transformed 16HBE cells xenografted nude mouse model

Benzo[a]pyrene (BaP) is a ubiquitous environment contaminant and its exposure could increase incidence of human lung cancer. In order to confirm and compare potential biomarkers of BaP-induce carcinogenesis and tumor progression, time-dependent changes of clusterin (CLU) and neuropilin-2 (NRP2) levels were evaluated in sera of BaP-transformed 16HBE cell line T-16HBE-C1 cells xenografted nude mice. Performance of CLU and NRP2 on tissue classification and tumor progression forecast was also calculated. Levels of CLU and NRP2 were significant elevated in both culture supernatant of T-16HBE-C1 cells and sera of T-16HBE-C1 cells xenografted nude mice compared with control. CLU and NRP2 were both found positively stained in tumor tissue. CLU and NRP2 alone could well predicate tumor progression in nude mice and CLU appeared to be more sensitive than NRP2. When both of them combined, performance of predication would improve. In conclusion, CLU and NRP2 could serve as potential biomarkers of tumor progression in nude mice xenografted with T-16HBE-C1 cells.

MicroRNA-21 activation of ERK signaling via PTEN is involved in arsenite-induced autophagy in human hepatic L-02 cells

Autophagy, an evolutionarily conserved cellular process, has diverse physiological and pathological roles in biological functions. Whether autophagy is induced by arsenite, a well-established human carcinogen, and the molecular mechanisms involved, remain to be established. Further, microRNAs (miRNAs) act as regulators in various cancers, but how miRNAs regulate autophagy remains largely unexplored. We have found that, in human hepatic epithelial (L-02) cells, arsenite increases levels of autophagy-related proteins in a concentration- and time-dependent manner and elevates the number of autophagic vacuoles (AVs). Arsenite also activates the ERK pathway in a dose- and time-dependent manner. In L-02 cells exposed to arsenite, microRNA-21 (miRNA-21) is over-expressed, and its target proteins, PTEN, PDCD4, and Spry1, are decreased. Moreover, inhibition of miR-21 increases levels of PTEN, and reduces levels of Beclin 1 and LC3 II/I, indicating that miR-21 is involved in arsenite-induced autophagy. In addition, ectopic expression of PTEN blocks the effect of miR-21 on the arsenite-induced autophagy and decreases p-ERK levels. Also, ERK promotes the autophagy induced by arsenite. In sum, upon exposure of cells to arsenite, over-expression of miR-21 activates ERK through PTEN, factors that participate in arsenite-induced autophagy. This link, mediated through miRNAs, establishes a mechanism for the development of autophagy that is associated with arsenic toxicity. Such information contributes to an understanding of the liver toxicity caused by arsenite.

Label-free quantitative proteomic analysis of benzo(a)pyrene-transformed 16HBE cells serum-free culture supernatant and xenografted nude mice sera

To screen potential biomarkers of benzo(a)pyrene (BaP)-induced lung cancer, the proteomic profiles of BaP-transformed 16HBE cell line T-16HBE-C1 cells serum-free culture supernatant and xenografted nude mice sera were compared with those of 16HBE group by utilizing label-free quantitative proteomic strategy. By employing nano-LC-MS/MS technology followed by MaxQuant and Perseus processing, 489 differentially expressed proteins were identified between T-16HBE-C1 and 16HBE cells serum-free culture supernatant, and 49 significantly up-regulated proteins were identified in T-16HBE-C1 xenografted nude mice sera. Three proteins neuropilin-2 (NRP2), clusterin (CLU) and A-kinase anchor protein 12 (AKAP12) were up-regulated in the serum-free culture supernatant of T-16HBE-C1 cells. These 3 human proteins were present in the sera of nude mice xenografted with T-16HBE-C1 cells, but were undetectable in mice xenografted with 16HBE cells. The proteomic results of NRP2 and AKAP12 were confirmed by Western blotting and enzyme-linked immunosorbent assays, respectively. Moreover, the serum NRP2 levels were significantly elevated at the 4th day after tumor cell implantation and showed good positive correlation with tumor growth characterized by tumor volume. In conclusion, serum NRP2, CLU and AKAP12 could be potential biomarkers of BaP-induced lung cancer. The proteomic results will gain deeper insights into the mechanisms of BaP-induced carcinogenesis.

Pre- and post-natal muscle microRNA expression profiles of two pig breeds differing in muscularity

miRNAs regulate the expression of target genes in diverse cellular processes and hence play important roles in physiological processes including developmental timing, patterning, embryogenesis, organogenesis, cell lineage, myogenesis and growth control. A comparative expression analysis of miRNAs expressed in the longissimus dorsi muscle at two prenatal stages (63 and 91 days post-conception (dpc)), and one adult stage (180 days post-natum) in both German Landrace (DL) and Pietrain (Pi) pig breeds was performed using a custom-designed array. During the prenatal stages, miR-199 and the miR-17 families were significantly up-regulated at 63 dpc, whereas miR-1 and miR-133a were overexpressed at 91 dpc. The abundance of several miRNAs was increased in the adult stage compared to 91 dpc including miR-1, miR-133, miR-22(a/b) and miR-29a. Some miRNAs were breed-specific, such as miR-199 and the miR-17 families which were all up-regulated in Pi pigs, while miR-133, miR-181 and miR-214 were up-regulated in DL pigs. Several pathways related to muscle development were enriched with predicted targets for the differentially expressed miRNAs. The dynamic expression and breed-associated regulation of porcine muscle miRNAs suggests a functional role for miRNA-mediated gene regulation during muscle development and phenotypic variations of muscle traits.

Molecular fingerprints of environmental carcinogens in human cancer

Identification of specific molecular changes (fingerprints) is important to identify cancer etiology. Exploitable biomarkers are related to DNA, epigenetics, and proteins. DNA adducts are the turning point between environmental exposures and biological damage. DNA mutational fingerprints are induced by carcinogens in tumor suppressor and oncogenes. In an epigenetic domain, methylation changes occurs in specific genes for arsenic, benzene, chromium, and cigarette smoke. Alteration of specific microRNA has been reported for environmental carcinogens. Benzo(a)pyrene, cadmium, coal, and wood dust hits specific heat-shock proteins and metalloproteases. The multiple analysis of these biomarkers provides information on the carcinogenic mechanisms activated by exposure to environmental carcinogens.

miR-CLIP capture of a miRNA targetome uncovers a lincRNA H19-miR-106a interaction

Identifying the interaction partners of noncoding RNAs is essential for elucidating their functions. We have developed an approach, termed microRNA crosslinking and immunoprecipitation (miR-CLIP), using pre-miRNAs modified with psoralen and biotin to capture their targets in cells. Photo-crosslinking and Argonaute 2 immunopurification followed by streptavidin affinity purification of probe-linked RNAs provided selectivity in the capture of targets, which were identified by deep sequencing. miR-CLIP with pre-miR-106a, a miR-17-5p family member, identified hundreds of putative targets in HeLa cells, many carrying conserved sequences complementary to the miRNA seed but also many that were not predicted computationally. miR-106a overexpression experiments confirmed that miR-CLIP captured functional targets, including H19, a long noncoding RNA that is expressed during skeletal muscle cell differentiation. We showed that miR-17-5p family members bind H19 in HeLa cells and myoblasts. During myoblast differentiation, levels of H19, miR-17-5p family members and mRNA targets changed in a manner suggesting that H19 acts as a 'sponge' for these miRNAs.

MicroRNA-191, by promoting the EMT and increasing CSC-like properties, is involved in neoplastic and metastatic properties of transformed human bronchial epithelial cells

Lung cancer is the leading cause of cancer mortality worldwide. A common interest in lung cancer research is the identification of biomarkers for early diagnosis and accurate prognosis. There is increasing evidence that microRNAs (miRNAs) are involved in lung cancer. To explore new biomarkers of chemical exposure in risk assessment of chemical carcinogenesis and lung cancer, we analyzed miRNA expression profiles of human bronchial epithelial (HBE) cells malignantly transformed by arsenite. High-throughput microarray analysis showed that 51 miRNAs were differentially expressed in transformed HBE cells relative to normal HBE cells. In particular, miR-191 was up-regulated in transformed cells. In HBE cells, arsenite induced increases of miR-191 and WT1 levels, decreased BASP1 expression, and activated the Wnt/β-catenin pathway, effects that were blocked by miR-191 knockdown. In addition, a luciferase reporter assay indicated that BASP1 is a direct target of miR-191. By inhibiting the expression of BASP1, miR-191 increased the expression of WT1 to promote activation of Wnt/β-catenin pathway. In transformed cells, inhibition of miR-191 expression blocked the epithelial-mesenchymal transition (EMT) and cancer stem cell (CSC)-like properties of cells and decreased their migratory capacity and neoplastic properties. Thus, these results demonstrate that miR-191 modulates the EMT and the CSC-like properties of transformed cells and indicate that it is an onco-miR involved in the neoplastic and metastatic properties of transformed cells.

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.

Oncogenic role of long noncoding RNA AF118081 in anti-benzo[a]pyrene-trans-7,8-dihydrodiol-9,10-epoxide-transformed 16HBE cells

Lung cancer is the leading cause of cancer deaths and remains an important public health problem worldwide. Long noncoding RNAs (lncRNAs) are newly identified regulators of tumorigenesis and tumor progression. However, the role of lncRNAs in lung cancer induced by environmental carcinogens remains largely unknown. In this study, an lncRNA microarray was used to compare the expression profiles of malignantly transformed 16HBE cells (16HBE-T) induced with anti-benzo[a]pyrene-trans-7,8-diol-9,10-epoxide (anti-BPDE) and normal 16HBE cells (16HBE-N). Using quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR), lncRNA AF118081 was identified as the most significantly overexpressed lncRNA in 16HBE-T cells, lung cancer cells, and patient samples. Cell proliferation, colony formation, apoptosis, migration, and invasion were assayed in 16HBE-T cells following the knockdown of lncRNA AF118081 with small interfering RNA. AF118081 knockdown inhibited cell growth and tumor invasion. An in vivo (nude mouse) model was then used to assay tumor growth, and the downregulation of AF118081 clearly suppressed tumor growth, consistent with the results of the in vitro assays. Together, these findings identify a new oncogenic lncRNA, lncRNA AF118081, in malignantly transformed 16HBE cells. This enhances our understanding of lncRNAs as important regulatory elements in chemical carcinogenesis and potential targets of lung cancer therapies.

Angiotensin II-regulated microRNA 483-3p directly targets multiple components of the renin-angiotensin system

Improper regulation of signaling in vascular smooth muscle cells (VSMCs) by angiotensin II (AngII) can lead to hypertension, vascular hypertrophy and atherosclerosis. The extent to which the homeostatic levels of the components of signaling networks are regulated through microRNAs (miRNA) modulated by AngII type 1 receptor (AT1R) in VSMCs is not fully understood. Whether AT1R blockers used to treat vascular disorders modulate expression of miRNAs is also not known. To report differential miRNA expression following AT1R activation by AngII, we performed microarray analysis in 23 biological and technical replicates derived from humans, rats and mice. Profiling data revealed a robust regulation of miRNA expression by AngII through AT1R, but not the AngII type 2 receptor (AT2R). The AT1R-specific blockers, losartan and candesartan antagonized >90% of AT1R-regulated miRNAs and AngII-activated AT2R did not modulate their expression. We discovered VSMC-specific modulation of 22 miRNAs by AngII, and validated AT1R-mediated regulation of 17 of those miRNAs by real-time polymerase chain reaction analysis. We selected miR-483-3p as a novel representative candidate for further study because mRNAs of multiple components of the renin-angiotensin system (RAS) were predicted to contain the target sequence for this miRNA. MiR-483-3p inhibited the expression of luciferase reporters bearing 3'-UTRs of four different RAS genes and the inhibition was reversed by antagomir-483-3p. The AT1R-regulated expression levels of angiotensinogen and angiotensin converting enzyme 1 (ACE-1) proteins in VSMCs are modulated specifically by miR-483-3p. Our study demonstrates that the AT1R-regulated miRNA expression fingerprint is conserved in VSMCs of humans and rodents. Furthermore, we identify the AT1R-regulated miR-483-3p as a potential negative regulator of steady-state levels of RAS components in VSMCs. Thus, miRNA-regulation by AngII to affect cellular signaling is a novel aspect of RAS biology, which may lead to discovery of potential candidate prognostic markers and therapeutic targets.

The effects of environmental chemical carcinogens on the microRNA machinery

The first evidence that microRNA expression is early altered by exposure to environmental chemical carcinogens in still healthy organisms was obtained for cigarette smoke. To date, the cumulative experimental data indicate that similar effects are caused by a variety of environmental carcinogens, including polycyclic aromatic hydrocarbons, nitropyrenes, endocrine disruptors, airborne mixtures, carcinogens in food and water, and carcinogenic drugs. Accordingly, the alteration of miRNA expression is a general mechanism that plays an important pathogenic role in linking exposure to environmental toxic agents with their pathological consequences, mainly including cancer development. This review summarizes the existing experimental evidence concerning the effects of chemical carcinogens on the microRNA machinery. For each carcinogen, the specific microRNA alteration signature, as detected in experimental studies, is reported. These data are useful for applying microRNA alterations as early biomarkers of biological effects in healthy organisms exposed to environmental carcinogens. However, microRNA alteration results in carcinogenesis only if accompanied by other molecular damages. As an example, microRNAs altered by chemical carcinogens often inhibits the expression of mutated oncogenes. The long-term exposure to chemical carcinogens causes irreversible suppression of microRNA expression thus allowing the transduction into proteins of mutated oncogenes. This review also analyzes the existing knowledge regarding the mechanisms by which environmental carcinogens alter microRNA expression. The underlying molecular mechanism involves p53-microRNA interconnection, microRNA adduct formation, and alterations of Dicer function. On the whole, reported findings provide evidence that microRNA analysis is a molecular toxicology tool that can elucidate the pathogenic mechanisms activated by environmental carcinogens.

Upregulated miR-106a plays an oncogenic role in pancreatic cancer

Carcinogenesis is a complex process during which cells undergo genetic and epigenetic alterations. MicroRNAs control gene expression by negatively regulating protein-coding mRNAs. Several reports demonstrated that miR-106a is up-regulated in gastric and colorectal cancers and promotes tumor progression. In contrast, in glioma miR-106a plays the role of a tumor suppressor gene rather than an oncogene. Here we demonstrate that a high level of miR-106a expression is present in pancreatic cancer. Furthermore, our investigation shows that miR-106a has an oncogenic role in pancreatic tumorigenesis by promoting cancer cell proliferation, epithelial-mesenchymal transition and invasion by targeting tissue inhibitors of metalloproteinase 2 (TIMP-2). MiR-106a could be a critical therapeutic target in pancreatic cancer.

LncRNA-DQ786227-mediated cell malignant transformation induced by benzo(a)pyrene

It has recently been found that the new class of transcripts, long non-coding RNAs (lncRNAs), are pervasively transcribed in the genome. LncRNAs are a large family of non-coding RNAs and regulate many protein-coding genes. Growing evidence indicates that lncRNAs may play an important functional role in cancer biology. Emerging data have shown that lncRNAs are closely related to the occurrence and development of lung cancer. However, the function and mechanism of lncRNAs in lung cancer remain elusive. Here, we investigated the role of a novel lncRNA in transformed human bronchial epithelial cells induced by benzo(a)pyrene. After establishing the transformed cell model using the BEAS-2B cell line in vitro, we found that expression of lncRNA-DQ786227 was high and changed during the transformation of BEAS-2B cells. Silencing of lncRNA-DQ786227 expression in malignant transformed BEAS-2B cells led to inhibition of cell proliferation and colony formation, and increased apoptosis. LncRNA-DQ786227 dramatically promoted the ability of BEAS-2B-T cells to form colonies in vitro and develop tumors in nude mice. These findings revealed that lncRNA-DQ786227 acts as an oncogene in malignantly transformed BEAS-2B cells induced by benzo(a)pyrene. The identification of lncRNA could provide new insight into the molecular mechanisms of chemical carcinogenesis.

Altered miRNA expression profiles and miR-1a associated with urethane-induced pulmonary carcinogenesis

MicroRNAs (miRNAs) are small RNA molecules that regulate posttranscriptional gene expression. Previous research has suggested that aberrant miRNA expression often plays a critical role in many types of cancer, including lung cancer. However, the exact miRNAs that are involved in pulmonary carcinogenesis remain unclear. We investigated the miRNA-based molecular changes that occur in urethane-induced carcinogenicity and identified specific miRNA deregulation in pulmonary carcinogenesis induced by urethane. In this study, we used a lung cancer model in which Balb/c mice were exposed to urethane via ip injection once a week for four consecutive weeks. The mice were then killed in weeks 6, 12, or 24. Two small RNA libraries were constructed with the total RNA from the lung tumor and normal adjacent lung tissues of the urethane-injected mice collected in week 24. Using Solexa sequencing, we identified a plethora of differentially expressed miRNAs and predicted nine novel miRNAs. Further analysis demonstrated the sustainable downregulation of miR-1a in the lung tissues in lung carcinogenesis induced by urethane. The levels of miR-1a were also reduced in the serum. Our findings indicate that urethane exposure alters the expression of a cluster of miRNAs. The simultaneous downregulation of miR-1a in lung tissues and serum in urethane-induced pulmonary carcinogenesis suggests that miR-1a is associated with tumorigenesis.

Growth-promoting role of the miR-106a~363 cluster in Ewing sarcoma

MicroRNAs (miRs) have been identified as potent regulators of both normal development and the hallmarks of cancer. Targeting of microRNAs has been shown to have preclinical promise, and select miR-based therapies are now in clinical trials. Ewing Sarcoma is a biologically aggressive pediatric cancer with little change in clinical outcomes despite improved chemotherapeutic regimens. There is a substantial need for new therapies to improve Ewing Sarcoma outcomes and to prevent chemotherapy-related secondary sequelae. Most Ewing Sarcoma tumors are driven by the EWS/Fli-1 fusion oncoprotein, acting as a gain-of-function transcription factor causing dysregulation of a variety of targets, including microRNAs. Our previous studies, and those of others, have identified upregulation of miRs belonging to the related miR-17∼92a, miR-106b∼25, and miR-106a∼363 clusters in Ewing Sarcoma. However, the functional consequences of this have not been characterized, nor has miR blockade been explored as an anti-cancer strategy in Ewing Sarcoma. To simulate a potential therapeutic approach, we examined the effects of blockade of these clusters, and their component miRs. Using colony formation as a read-out, we find that blockade of selected individual cluster component miRs, using specific inhibitors, has little or no effect. Combinatorial inhibition using miR “sponge” methodology, on the other hand, is inhibitory to colony formation, with blockade of whole clusters generally more effective than blockade of miR families. We show that a miR-blocking sponge directed against the poorly characterized miR-106a∼363 cluster is a particularly potent inhibitor of clonogenic growth in a subset of Ewing Sarcoma cell lines. We further identify upregulation of miR-15a as a downstream mechanism contributing to the miR-106a∼363 sponge growth-inhibitory effect. Taken together, our studies provide support for a pro-oncogenic role of the miR-106a∼363 cluster in Ewing Sarcoma, and identify miR-106a∼363 blockade, as well as miR-15a replacement, as possible strategies for inhibition of Ewing Sarcoma growth.

Feedback regulations of miR-21 and MAPKs via Pdcd4 and Spry1 are involved in arsenite-induced cell malignant transformation

OBJECTIVE

To establish the functions of miR-21 and the roles of two feedback regulation loops, miR-21-Spry1-ERK/NF-κB and miR-21-Pdcd4-JNK/c-Jun, in arsenite-transformed human embryo lung fibroblast (HELF) cells.

METHODS

For arsenite-transformed HELF cells, apoptosis, clonogenicity, and capacity for migration were determined by Hoechst staining, assessment of their capacity for anchorage-independent growth, and wound-healing, respectively, after blockage, with inhibitors or with siRNAs, of signal pathways for JNK/c-Jun or ERK/NF-κB. Decreases of miR-21 levels were determined with anti-miR-21, and the up-regulation of Pdcd4 and Spry1 was assessed in transfected cells; these cells were molecularly characterized by RT-PCR, qRT-PCR, Western blots, and immunofluorescence assays.

RESULTS

MiR-21 was highly expressed in arsenite-transformed HELF cells and normal HELF cells acutely treated with arsenite, an effect that was concomitant with activation of JNK/c-Jun and ERK/NF-κB and down-regulation of Pdcd4 and Spry1 protein levels. However, there were no significant changes in mRNA levels for Pdcd4 and Spry1, which suggested that miR-21 regulates the expressions of Pdcd4 and Spry1 through translational repression. In arsenite-transformed HELF cells, blockages of JNK/c-Jun or ERK/NF-κB with inhibitors or with siRNAs prevented the increases of miR-21and the decreases of the protein levels but not the mRNA levels of Pdcd4 and Spry1. Down-regulation of miR-21 and up-regulations of Pdcd44 or Spry1 blocked the arsenite-induced activations of JNK/c-Jun or ERK/NF-κB, indicating that knockdown of miR-21 inhibits feedback of ERK activation and JNK activation via increases of Pdcd4 and Spry1 protein levels, respectively. Moreover, in arsenite-transformed HELF cells, inhibition of miR-21 promoted cell apoptosis, inhibited clonogenicity, and reduced migration.

CONCLUSION

The results indicate that miR-21 is both a target and a regulator of ERK/NF-κB and JNK/c-Jun and the feedback regulations of miR-21 and MAPKs via Pdcd4 and Spry1, respectively, are involved in arsenite-induced malignant transformation of HELF cells.

Human bronchial epithelial cells exposed in vitro to cigarette smoke at the air-liquid interface resemble bronchial epithelium from human smokers

Organotypic culture of human primary bronchial epithelial cells is a useful in vitro system to study normal biological processes and lung disease mechanisms, to develop new therapies, and to assess the biological perturbations induced by environmental pollutants. Herein, we investigate whether the perturbations induced by cigarette smoke (CS) and observed in the epithelium of smokers' airways are reproducible in this in vitro system (AIR-100 tissue), which has been shown to recapitulate most of the characteristics of the human bronchial epithelium. Human AIR-100 tissues were exposed to mainstream CS for 7, 14, 21, or 28 min at the air-liquid interface, and we investigated various biological endpoints [e.g., gene expression and microRNA profiles, matrix metalloproteinase 1 (MMP-1) release] at multiple postexposure time points (0.5, 2, 4, 24, 48 h). By performing a Gene Set Enrichment Analysis, we observed a significant enrichment of human smokers' bronchial epithelium gene signatures derived from different public transcriptomics datasets in CS-exposed AIR-100 tissue. Comparison of in vitro microRNA profiles with microRNA data from healthy smokers highlighted various highly translatable microRNAs associated with inflammation or with cell cycle processes that are known to be perturbed by CS in lung tissue. We also found a dose-dependent increase of MMP-1 release by AIR-100 tissue 48 h after CS exposure in agreement with the known effect of CS on this collagenase expression in smokers' tissues. In conclusion, a similar biological perturbation than the one observed in vivo in smokers' airway epithelium could be induced after a single CS exposure of a human organotypic bronchial epithelium-like tissue culture.

Alteration of serum miR-206 and miR-133b is associated with lung carcinogenesis induced by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone

The alteration of microRNA (miRNA) expression plays an important role in chemical carcinogenesis. Presently, few reports have been published that concern the significance of circulating miRNAs in lung carcinogenesis induced by environmental carcinogens. The purpose of this study was to identify serum miRNAs that could be associated with lung carcinogenesis induced by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). Male F344 rats were systemically administered with NNK. The rat serum differential expression profiles of miRNAs were analyzed by small RNA solexa sequencing. Using quantitative real-time PCR, the differentially expressed serum miRNAs were identified in each individual rat. Serum miR-206 and miR-133b were selected for further identification in rat serum at different stages of lung carcinogenesis; we detected the levels of serum miR-206 and miR-133b in lung cancer tissues induced by NNK. NNK causes significant alteration of serum miRNA expression. Compared to the control group, serum miR-206 and miR-133b were significantly up-regulated in the early stage of NNK-induced lung carcinogenesis. miR-206 and miR-133b exhibited low-expression in lung cancer tissues. Our results demonstrate that lung carcinogen NNK exposure changes the expression of serum miRNAs. Serum miR-206 and miR-133b could be associated with lung carcinogenesis induced by NNK.

Gastric juice MicroRNAs as potential biomarkers for the screening of gastric cancer

BACKGROUND

MicroRNAs (miRNAs) play a crucial role in carcinogenesis; however, it largely remains unclear whether miRNAs in gastric juice, which is specific for gastric tissues, can be used as biomarkers for gastric cancer. The objective of the current study was to investigate the feasibility of using gastric juice miRNAs as potential biomarkers to assist in screening for gastric cancer.

METHODS

Gastric juice samples were collected from 141 patients who underwent upper gastrointestinal endoscopy examination between September 2010 and December 2011. Gastric cancer and adjacent normal biopsy specimens also were collected. The existence and stability of miRNAs in gastric juices were determined by real-time reverse transcriptase-quantitative polymerase chain reaction (RT-qPCR) and sequencing. miRNA levels in tissues and gastric juices were detected by RT-qPCR. A receiver operating characteristic (ROC) curve was constructed for differentiating gastric cancer from benign gastric diseases.

RESULTS

Levels of miRNA-21 (miR-21) and miR-106a in gastric cancer tissues were significantly higher compared with the levels in adjacent tissues (P = .006 and P = .001, respectively). Patients who had gastric cancer had significantly different levels of gastric juice miR-21 and miR-106a compared with patients who had benign gastric diseases (both P < .001). There were significant correlations between miR-21/miR-106a levels and Borrmann types. miR-21 levels in intestinal type gastric cancer specimens were higher than that in diffuse (P = .003) or mixed (P < .001) gastric cancer types. The area under the ROC curve was up to 0.969 for miR-21 and 0.871 for miR-106a.

CONCLUSIONS

The current results indicated that certain miRNAs in gastric juice are potential biomarkers that can assist in screening for gastric cancer.

miR-106a overexpression and pRB downregulation in sporadic colorectal cancer

Rb1 plays an important role in cell cycle progression and therefore may be involved in malignant transformation of colonic cells. The aim of our research was to define the potential role of Rb1 as a prognostic biomarker in tumorigenesis of sporadic colorectal cancer, and to examine the role of miR-106a in Rb1 regulation as it functionally binds to 3'UTR of transcribed mRNA. We examined LOH and promoter methylation status. Real-time PCR was used for Rb1 mRNA and miR-106a, and immunohistochemistry for protein expression analysis. All the results obtained from patients' samples were correlated with the clinicopathological parameters in order to determine its influence on the sporadic colorectal carcinogenesis. LOH showed no correlation with mRNA and pRb expression. 51.5% of tumor samples were scored negative for pRb staining. Despite this finding, we detected overexpression of Rb1 mRNA in tumor samples in comparison to the adjacent normal tissue (p=0.023). mRNA overexpression was consistent with Rb1 promoter methylation analysis results, which showed no methylation in the investigated samples. Expression analysis of miR-106a in the patients samples showed its overexpression in colorectal cancer (p<10(-4)). Negative pRb score was expected according to the definition of tumor suppressor genes and their proposed role in the malignant transformation of the cells. The observed discrepancy between mRNA and protein expression can be explained by a regulatory mechanism that inhibits translation, such as microRNA silencing. Our results suggest that miR-106a might have a regulatory role for Rb1 in sporadic colorectal cancer.

Antagonism of mmu-mir-106a attenuates asthma features in allergic murine model

MicroRNAs (miRs) regulate immunological pathways in health and disease, and a number of miRs have been shown to be altered in mouse models of asthma. The secretion of interleukin-10 (IL-10), an anti-inflammatory cytokine, has been shown to be defective in many inflammatory diseases including asthma. We recently demonstrated that miR-106a inhibits IL-10 in a post-transcriptional manner. In this study, we investigated the effect of inhibition of mmu-miR106a in asthmatic condition to find its possible role as a therapeutic target. Our in vitro experiments with mouse macrophage, RAW264.7, revealed that mmu-miR-106a potentially decreased IL-10 along with increase in proinflammatory cytokine. Furthermore, administration of mmu-miR-106a to naive mice reduced IL-10 levels in lungs in a dose-dependent manner without altering lung histology. Most interestingly, knockdown of mmu-miR-106a in an established allergic airway inflammation has significantly alleviated most of the features of asthma such as airway hyperresponsiveness, airway inflammation, increased Th2 response, goblet cell metaplasia, and subepithelial fibrosis along with increase in IL-10 levels in lung. This represents the first in vivo proof of a miRNA-mediated regulation of IL-10 with a potential to reverse an established asthmatic condition.

Regulation of miRNA-21 by reactive oxygen species-activated ERK/NF-κB in arsenite-induced cell transformation

After acute exposure of cells to arsenic, reactive oxygen species mediate changes in cell behavior, including activation of proliferative signaling. For chronic exposure to arsenic, however, the function of reactive oxygen species in cell transformation remains poorly understood. Although microRNA-21 (miR-21) has been implicated in various aspects of carcinogenesis, its functions and molecular mechanisms in carcinogen-induced tumorigenesis are unclear. The purpose of this study was to determine if miR-21 is involved in arsenite-induced malignant transformation and to characterize the associated signaling pathways. During arsenite-induced transformation of human embryo lung fibroblast (HELF) cells, miR-21 was upregulated, and the extracellular signal-regulated kinase (ERK)/nuclear factor-κB (NF-κB) signal pathway was activated. Moreover, superoxide radical dismutase (a scavenger of superoxide) and catalase (a scavenger of hydroperoxides) blocked the arsenite-induced effects in HELF cells and mouse embryonic fibroblasts. Blockage of ERK by the inhibitor U0126 or inhibition of NF-κB p65 by siRNA or Bay 11-7082 prevented the increases in miR-21 and the decreases in Spry1, Pten, and Pdcd4, the target proteins of miR-21, induced by arsenite. As determined by a ChIP-qPCR assay, NF-κB p65 regulated miR-21 expression by binding directly to the promoter of miR-21. Further, anti-miR-21 downregulated miR-21 expression and prevented the arsenite-induced activation of ERK via the increase in Spry1, indicating that miR-21 has a feedback effect in regulating ERK activation. Overexpression of miR-21 with an miR-21 mimic and feedback activation of ERK and NF-κB via the decrease in Spry1 promoted the malignancy of HELF cells exposed to arsenite, but knockdown of miR-21 with anti-miR-21 and feedback blockage of ERK and NF-κB activation through an increase in Spry1 decreased anchorage-independent growth of arsenite-transformed cells. Thus, the transformation of HELF cells induced by chronic exposure to arsenite is mediated by increased miR-21 expression, which, in turn, is mediated by reactive oxygen species activation of the ERK/NF-κB pathway.

Mutagens interfere with microRNA maturation by inhibiting DICER. An in silico biology analysis

Exposure to environmental mutagens results in alteration of microRNA expression mainly oriented towards down-regulation, as typically observed in cigarette smoke. However, the molecular mechanism triggering this event is still unknown. To shed light on this issue, we developed an 'in silico' analysis testing 25 established environmental mutagens (polycyclic aromatic hydrocarbons, heterocyclic compounds, nitrosoamines, morpholine, ethylnitrosurea, benzene derivatives, hydroxyl amines, alkenes) for their potential to interfere with the function of DICER, the enzyme involved in the cytoplasmic phase of microRNA maturation. In order to analyse the binding affinity between DICER and each mutagen, the three-dimensional bioinformatic structures of DICER-RNase III domains and of mutagens have been constructed. The binding affinity of mutagens for each DICER's RNase III domain was estimated by calculating the global contact-energy and the number of intermolecular contacts. These two parameters reflect the stability of the DICER-mutagen complexes. All the 25 mutagens tested form stable complexes with DICER, 20 of which form a complex with DICER A domain, that is more stable than those formed by DICER with its natural substrate, i.e. double strand short RNAs. These mutagens are benzo(a)pyrene diol epoxide, nitroimidazoles, fluorenes, naphthalene, morpholine, stilbenes, hydroxylamines, fecapentenes. In the case of exposure to mutagen mixtures (benzo(a)pyrene-diolepoxide and 4-acetylaminostilbene), synergistic or less than addictive effects occur depending on the docking order of the compounds. A group of 8 mutagens with the highest ability to interfere with this DICER function, was identified by hierarchical cluster analysis. This group included 1-ethyl-1-nitrosourea and 4-nitrosomorpholine. Herein, presented data support the view that mutagens interfere with microRNA maturation by binding DICER. This finding sheds light on a new epigenetic mechanism exerted by environmental mutagens in inducing cell damage.

Aberrant expression of miR-638 contributes to benzo(a)pyrene-induced human cell transformation

Identification of aberrant microRNA (miRNA) expression during chemical carcinogen-induced cell transformation will lead to a better understanding of the substantial role of miRNAs in cancer development. To explore whether aberrant miRNAs expression can be used as biomarkers of chemical exposure in risk assessment of chemical carcinogenesis, we analyzed miRNA expression profiles of human bronchial epithelial cells expressing an oncogenic allele of H-Ras (HBER) at different stages of transformation induced by benzo(a)pyrene (BaP) by miRNA array. It revealed 12 miRNAs differentially expressed in HBER cells at both pretransformed and transformed stages. Differentially expressed miRNAs were confirmed in transformed cells and examined in 50 pairs of primary human non-small-cell lung cancer (NSCLC) tissues using real-time PCR. Among these miRNAs, downregulation of miR-638 was found in 68% (34/50) of NSCLC tissues. However, the expression of miR-638 in HBER cells increased upon treatment of BaP in a dose-dependent manner. The expression of miR-638 was also examined in peripheral lymphocytes from 86 polycyclic aromatic hydrocarbons (PAHs)-exposed (PE) workers. We found that the average expression level of miR-638 in peripheral lymphocytes from 86 PE workers increased by 72% compared with control group. The levels of miR-638 were correlated with the concentration of urinary 1-hydroxypyrene (1-OHP) and external levels of PAHs. Overexpression of miR-638 aggravated cell DNA damage induced by BaP, which might be mediated by suppression of breast cancer 1 (BRCA1), one of the target genes of miR-638. In summary, we suggest that miR-638 is involved in the BaP-induced carcinogenesis by targeting BRCA1.

miR-10a overexpression is associated with NPM1 mutations and MDM4 downregulation in intermediate-risk acute myeloid leukemia

OBJECTIVE

The study investigated differential microRNA (miRNA) expression patterns in acute myeloid leukemia (AML) patients with intermediate-risk (IR) characteristics. After characterization and validation of miR-10a, which was specifically upregulated in nucleophosmin 1 (NPM1) mutant AML samples, functional consequences of miR-10a overexpression were further delineated in vitro.

MATERIALS AND METHODS

Microarray analysis of miRNAs in bone marrow samples from AML (IR) patients with NPM1 mutations and healthy donors was performed to detect differential expression patterns. After validation of miRNA expression specific for NPM1 mutation in AML patients by quantitative reverse transcription polymerase chain reaction, a functional target gene search was conducted using complementary DNA microarray data from samples transfected with miR-10a. Potential target gene validation was done using transient transfection of K562 cells followed by Western blotting and luciferase reporter assay.

RESULTS

In comparison with wild-type samples, NPM1 mutant AML samples were shown to markedly overexpress miR-10a. Subsequent in vitro miR-10a overexpression induced differential gene expression as determined by microarray analysis. Here the murine double minute 4 (MDM4) gene turned out as a candidate gene for miR-10a. Validation of MDM4 in leukemic cells revealed a robust negative relationship between miR-10a overexpression and MDM4 downregulation. Furthermore, we determined an inverse association between miR-10a and MDM4 expression in AML (IR) samples with respect to their NPM1 mutational status.

CONCLUSIONS

miR-10a expression is highly characteristic for AML (IR) patients with NPM1 mutations and may influence its biological properties in AML by interfering with the p53 machinery partly regulated by MDM4.

Reversal and prevention of arsenic-induced human bronchial epithelial cell malignant transformation by microRNA-200b

Arsenic is a well-recognized human carcinogen, yet the mechanism by which it causes human cancer has not been elucidated. MicroRNAs (miRNAs) are a big family of small noncoding RNAs and negatively regulate the expression of a large number of protein-coding genes. We investigated the role of miRNAs in arsenic-induced human bronchial epithelial cell malignant transformation and tumor formation. We found that prolonged exposure of immortalized p53-knocked down human bronchial epithelial cells (p53(low)HBECs) to low levels of arsenite (NaAsO₂, 2.5 μM) caused malignant transformation that was accompanied by epithelial to mesenchymal transition (EMT) and reduction in the levels of miR-200 family members. Stably reexpressing miR-200b in arsenite-transformed cells (As-p53(low)HBECs) completely reversed their transformed phenotypes, as evidenced by inhibition of colony formation in soft agar and prevention of xenograft tumor formation in nude mice. Moreover, stably expressing miR-200b alone in parental nontransformed p53(low)HBECs was sufficient to completely prevent arsenite exposure from inducing EMT and malignant transformation. Further mechanistic studies showed that depletion of miR-200 in arsenite-transformed cells involved induction of the EMT-inducing transcription factors zinc-finger E-box-binding homeobox factor 1 (ZEB1) and ZEB2 and increased methylation of miR-200 promoters. Stably expressing ZEB1 alone in parental nontransformed p53(low)HBECs was sufficient to deplete miR-200, induce EMT and cause cell transformation, phenocopying the oncogenic effect of 16-week arsenite exposure. These findings establish for the first time a causal role for depletion of miR-200b expression in human cell malignant transformation and tumor formation resulting from arsenic exposure.