Induction of microRNAome deregulation in rat liver by long-term tamoxifen exposure. Mutat Res. 2007;619:30-37. [PMID: 17343880 DOI: 10.1016/j.mrfmmm.2006.12.006]

Highly Sensitive Detection of Elevated Exosomal miR-122 Levels in Radiation Injury and Hepatic Inflammation Using an Aptamer-Functionalized SERS-Sandwich Assay

Radiation-induced organ injury is one of the major fallouts noticed during radiotherapy treatment of malignancies and other detrimental radiation exposures. MicroRNA (miRNA), which is involved in multiple critical cellular processes, is released from the cells of damaged organs in cellular vesicles, commonly known as exosomes. Specifically, exosomal miR-122 is reported to be actively involved in radiation-actuated rectal and hepatic injuries or inflammation. In this work, we developed a surface-enhanced Raman spectroscopy (SERS) assay for the quantitative and targeted detection of exosomal miR-122 in mice after drug/radiation treatments. In particular, an aptamer-functionalized magnetic capturing element and Au shell nanoparticle (NP)-based SERS tags were utilized, which upon recognition of the target miRNA constituted a "sandwich" formation, with which an 8 fM limit of detection (LOD) could be achieved. Using this SERS assay, we further found that radiation injury led to the elevated expression of exosomal miR-122 in mice at 4 h postirradiation, confirmed by the quantitative real-time PCR method. It was demonstrated that the drug-induced hepatic inflammation could also be assessed via detecting miR-122 using this SERS method. As such, this work has demonstrated the achievement of a highly selective and sensitive probe of exosomal miRNA, which may thus open a gateway for promising usage in drug/radiation-induced inflammation.

Overview of biological mechanisms of human carcinogens

This review summarizes the carcinogenic mechanisms for 109 Group 1 human carcinogens identified as causes of human cancer through Volume 106 of the IARC Monographs. The International Agency for Research on Cancer (IARC) evaluates human, experimental and mechanistic evidence on agents suspected of inducing cancer in humans, using a well-established weight of evidence approach. The monographs provide detailed mechanistic information about all carcinogens. Carcinogens with closely similar mechanisms of action (e.g. agents emitting alpha particles) were combined into groups for the review. A narrative synopsis of the mechanistic profiles for the 86 carcinogens or carcinogen groups is presented, based primarily on information in the IARC monographs, supplemented with a non-systematic review. Most carcinogens included a genotoxic mechanism.

Evaluation of the diagnostic and therapeutic roles of non-coding RNA and cell proliferation related gene association in hepatocellular carcinoma

Micro RNA-34a-5p (miR-34a-5p) is an important molecule that can act as a modulator of tumor growth. It controls expression of a plenty of proteins controlling cell cycle, differentiation and apoptosis and opposing processes that favor viability of cancer cells, their metastasis and resistance to chemotherapy. Bioinformatics analysis indicated that minichromosome maintenance protein 2 (MCM2) is a target gene of miR-34a-p. In this study, RT-qPCR was employed to detect the expression of miR-34a-5p and MCM2 in 10 hepatocellular carcinoma (HCC) tissues. The functional role of miR-34a-5p in HCC was investigated and the interaction between miR-34a-5p and MCM2 was explored. Results showed miR-34a-5p expression in HCC tissues was significantly lower than in non HCC liver tissues (P < 0.05), but MCM2 expression in HCC tissues was markedly higher than in non HCC liver tissues (P < 0.05). In addition, miR-34a-5p expression was negatively related to MCM2 expression. To confirm effect of miR-34a-5p on tumor growth and its possible effect on MCM2, miR-34a-5p mimic and inhibitor was transfected into HCC cell lines (HepG2). MTS assay, showed miR-34a-5p over-expression could inhibit the proliferation of HCC cells. RT-qPCR was done to detect the expression of miR-34a-5p and MCM2 in HepG2 cells before and after transfection. Results showed that MCM2 expression in HCC tissues was markedly lower in mimic transfected group than in inhibitor transfected group and control group (P < 0.05) while miR-34a-5p expression in HepG2 cells was significantly higher in mimic transfected group than in inhibitor transfected group and control group (P < 0.05). Thus, miR-34a-5p may inhibit the proliferation of HCC cells via regulating MCM2 expression. These findings provide an evidence for the emerging role of microRNAs as diagnostic markers and therapeutic targets in HCC.

Short-term tamoxifen treatment has long-term effects on metabolism in high-fat diet-fed mice with involvement of Nmnat2 in POMC neurons

Short-term tamoxifen treatment has effects on lipid and glucose metabolism in mice fed chow. However, its effects on metabolism in mice fed high-fat diet (HFD) and the underlying mechanisms are unclear. Here, we show that tamoxifen treatment for 5 days decreases fat mass for as long as 18 weeks in mice fed HFD. Tamoxifen alters mRNA levels of some genes involved in lipid metabolism in white adipose tissue and improves glucose and insulin tolerance as well as hepatic insulin signaling for 12-20 weeks. Proopiomelanocortin (POMC) neuron-specific deletion of nicotinamide mononucleotide adenylyltransferase 2 (Nmnat2) attenuates the effects of tamoxifen on glucose and insulin tolerance. These data demonstrate that short-term injection of tamoxifen has long-term effects on lipid and glucose metabolism in HFD mice with involvement of Nmnat2 in POMC neurons.

Evaluation of Bioinformatics Approaches for Next-Generation Sequencing Analysis of microRNAs with a Toxicogenomics Study Design

MicroRNAs (miRNAs) are key post-transcriptional regulators that affect protein translation by targeting mRNAs. Their role in disease etiology and toxicity are well recognized. Given the rapid advancement of next-generation sequencing techniques, miRNA profiling has been increasingly conducted with RNA-seq, namely miRNA-seq. Analysis of miRNA-seq data requires several steps: (1) mapping the reads to miRBase, (2) considering mismatches during the hairpin alignment (windowing), and (3) counting the reads (quantification). The choice made in each step with respect to the parameter settings could affect miRNA quantification, differentially expressed miRNAs (DEMs) detection and novel miRNA identification. Furthermore, these parameters do not act in isolation and their joint effects impact miRNA-seq results and interpretation. In toxicogenomics, the variation associated with parameter setting should not overpower the treatment effect (such as the dose/time-dependent effect). In this study, four commonly used miRNA-seq analysis tools (i.e., miRDeep2, miRExpress, miRNAkey, sRNAbench) were comparatively evaluated with a standard toxicogenomics study design. We tested 30 different parameter settings on miRNA-seq data generated from thioacetamide-treated rat liver samples for three dose levels across four time points, followed by four normalization options. Because both miRExpress and miRNAkey yielded larger variation than that of the treatment effects across multiple parameter settings, our analyses mainly focused on the side-by-side comparison between miRDeep2 and sRNAbench. While the number of miRNAs detected by miRDeep2 was almost the subset of those detected by sRNAbench, the number of DEMs identified by both tools was comparable under the same parameter settings and normalization method. Change in the number of nucleotides out of the mature sequence in the hairpin alignment (window option) yielded the largest variation for miRNA quantification and DEMs detection. However, such a variation is relatively small compared to the treatment effect when the study focused on DEMs that are more critical to interpret the toxicological effect. While the normalization methods introduced a large variation in DEMs, toxic behavior of thioacetamide showed consistency in the trend of time-dose responses. Overall, miRDeep2 was found to be preferable over other choices when the window option allowed up to three nucleotides from both ends.

MicroRNA‑34a inhibits liver cancer cell growth by reprogramming glucose metabolism

MicroRNAs (miRs) have been proposed as minimally invasive prognostic markers for various types of cancer, including liver cancer, which is one of the most common cancers worldwide. In the present study, the expression of miR-34a in human liver cancer tissues and cell lines was evaluated and the effects of miR-34a on cell proliferation, invasion and glycolysis in hepatocellular carcinoma (HCC) cells were determined. The results indicated that miR-34a was downregulated in human liver cancer tissues. Overexpression of miR-34a significantly inhibited liver cancer cell proliferation and clone formation. In terms of the underlying mechanism, miR-34a was indicated to negatively regulate the expression of lactate dehydrogenase A (LDHA), which consequently inhibited LDHA-dependent glucose uptake in the cancer cells, as well as cell proliferation and invasion. Collectively, these data suggest that miR-34a functions as a negative regulator of glucose metabolism and may serve as a novel marker for liver cancer prognosis.

MicroRNAs as biomarkers for liver injury: Current knowledge, challenges and future prospects

MicroRNAs (miRNAs) are short regulatory RNAs that are involved in various biological processes that regulate gene expression posttranscriptionally. Changes in miRNA expression can be detected in many physiological and pathological events, such as liver injury. Drug induced liver injury is a life threatening condition that frequently requires organ transplantation. Hepatotoxicity is also one of the major causes of drug failure in clinical trials and of drug withdrawal from the market. The profiling of miRNA expression shows great promise in monitoring liver injury, in the prediction of outcome in patients, and in the identification of liver-reactive compounds in toxicological assessment. Recent studies have demonstrated organ-specificity of some miRNAs (i.e., miR-122), which are released into biological fluids as a result of hepatocyte damage. This attests to the potential of miRNAs as noninvasive biomarkers to detect liver toxicity. This review presents information on miRNA signatures of hepatotoxicity and on the application of promising miRNA biomarkers in preclinical safety assessment. We further discuss the technical challenges associated with these emerging biomarkers for early diagnosis and detection of hepatotoxicity.

The roles of microRNA families in hepatic fibrosis

When hepatocytes are damaged severely, a variety of signaling pathways will be triggered by inflammatory factors and cytokines involving in the process of hepatic fibrosis. The microRNA (miRNA) family consists of several miRNAs which have the potential for synergistic regulation of these signaling pathways. However, it is poor to understand the roles of miRNA family as a whole in hepatic fibrosis. Increasing studies have suggested several miRNA families are related with activation of hepatic stellate cells and hepatic fibrosis through cooperatively regulating certain signaling pathways. During the process of hepatic fibrosis, miR-29 family primarily induces cell apoptosis by modulating phosphatidylinositol 3-kinase/AKT signaling pathway and regulates extracellular matrix accumulation. miR-34 family promotes the progression of hepatic fibrosis by inducing activation of hepatic stellate cells, while miR-378 family suppresses the process in Glis dependent manner. miR-15 family mainly promotes cell proliferation and induces apoptosis. The miR-199 family and miR-200 family are responsible for extracellular matrix deposition and the release of pro-fibrotic cytokines. These miRNA family members play pro-fibrotic or anti-fibrotic roles by targeting genes collectively or respectively which involve in hepatic fibrosis related signaling pathways and hepatic stellate cell activation. Thus, good understandings of molecular mechanisms which are based on miRNA families may provide new ideas for the molecular targeted therapy of hepatic fibrosis in the future.

High throughput sequencing of small RNAs transcriptomes in two Crassostrea oysters identifies microRNAs involved in osmotic stress response

Increasing evidence suggests that microRNAs post-transcriptionally regulate gene expression and are involved in responses to biotic and abiotic stress. However, the role of miRNAs involved in osmotic plasticity remains largely unknown in marine bivalves. In the present study, we performed low salinity challenge with two Crassostrea species (C. gigas and C. hongkongensis), and conducted high-throughput sequencing of four small RNA libraries constructed from the gill tissues. A total of 202 and 87 miRNAs were identified from C. gigas and C. hongkongensis, respectively. Six miRNAs in C. gigas and two in C. hongkongensis were differentially expressed in response to osmotic stress. The expression profiles of these eight miRNAs were validated by qRT-PCR. Based on GO enrichment and KEGG pathway analysis, genes associated with microtubule-based process and cellular component movement were enriched in both species. In addition, five miRNA-mRNA interaction pairs that showed opposite expression patterns were identified in the C. hongkongensis, Differential expression analysis identified the miRNAs that play important regulatory roles in response to low salinity stress, providing insights into molecular mechanisms that are essential for salinity tolerance in marine bivalves.

microRNAs as pharmacogenomic biomarkers for drug efficacy and drug safety assessment

Much evidence has documented that microRNAs (miRNAs) play an important role in the modulation of interindividual variability in the production of drug metabolizing enzymes and transporters (DMETs) and nuclear receptors (NRs) through multidirectional interactions involving environmental stimuli/stressors, the expression of miRNA molecules and genetic polymorphisms. MiRNA expression has been reported to be affected by drugs and miRNAs themselves may affect drug metabolism and toxicity. In cancer research, miRNA biomarkers have been identified to mediate intrinsic and acquired resistance to cancer therapies. In drug safety assessment, miRNAs have been found associated with cardiotoxicity, hepatotoxicity and nephrotoxicity. This review article summarizes published studies to show that miRNAs can serve as early biomarkers for the evaluation of drug efficacy and drug safety.

Blood miRNAs as sensitive and specific biological indicators of environmental and occupational exposure to volatile organic compound (VOC)

To date, there is still shortage of highly sensitive and specific minimally invasive biomarkers for assessment of environmental toxicants exposure. Because of the significance of microRNA (miRNA) in various diseases, circulating miRNAs in blood may be unique biomarkers for minimally invasive prediction of toxicants exposure. We identified and validated characteristic miRNA expression profiles of human whole blood in workers exposed to volatile organic compounds (VOCs) and compared the usefulness of miRNA indicator of VOCs with the effectiveness of the already used urinary biomarkers of occupational exposure. Using a microarray based approach we screened and detected deregulated miRNAs in their expression in workers exposed to VOCs (toluene [TOL], xylene [XYL] and ethylbenzene [EBZ]). Total 169 workers from four dockyards were enrolled in current study, and 50 subjects of them were used for miRNA microarray analysis. We identified 467 miRNAs for TOL, 211 miRNAs for XYL, and 695 miRNAs for XYL as characteristic discernible exposure indicator, which could discerned each VOC from the control group with higher accuracy, sensitivity, and specificity than urinary biomarkers. Current observations from this study point out that the altered levels of circulating miRNAs can be a reliable novel, minimally invasive biological indicator of occupational exposure to VOCs.

Integrated microRNA, mRNA, and protein expression profiling reveals microRNA regulatory networks in rat kidney treated with a carcinogenic dose of aristolochic acid

Background

Aristolochic Acid (AA), a natural component of Aristolochia plants that is found in a variety of herbal remedies and health supplements, is classified as a Group 1 carcinogen by the International Agency for Research on Cancer. Given that microRNAs (miRNAs) are involved in cancer initiation and progression and their role remains unknown in AA-induced carcinogenesis, we examined genome-wide AA-induced dysregulation of miRNAs as well as the regulation of miRNAs on their target gene expression in rat kidney.

Results

We treated rats with 10 mg/kg AA and vehicle control for 12 weeks and eight kidney samples (4 for the treatment and 4 for the control) were used for examining miRNA and mRNA expression by deep sequencing, and protein expression by proteomics. AA treatment resulted in significant differential expression of miRNAs, mRNAs and proteins as measured by both principal component analysis (PCA) and hierarchical clustering analysis (HCA). Specially, 63 miRNAs (adjusted p value < 0.05 and fold change > 1.5), 6,794 mRNAs (adjusted p value < 0.05 and fold change > 2.0), and 800 proteins (fold change > 2.0) were significantly altered by AA treatment. The expression of 6 selected miRNAs was validated by quantitative real-time PCR analysis. Ingenuity Pathways Analysis (IPA) showed that cancer is the top network and disease associated with those dysregulated miRNAs. To further investigate the influence of miRNAs on kidney mRNA and protein expression, we combined proteomic and transcriptomic data in conjunction with miRNA target selection as confirmed and reported in miRTarBase. In addition to translational repression and transcriptional destabilization, we also found that miRNAs and their target genes were expressed in the same direction at levels of transcription (169) or translation (227). Furthermore, we identified that up-regulation of 13 oncogenic miRNAs was associated with translational activation of 45 out of 54 cancer-related targets.

Conclusions

Our findings suggest that dysregulated miRNA expression plays an important role in AA-induced carcinogenesis in rat kidney, and that the integrated approach of multiple profiling provides a new insight into a post-transcriptional regulation of miRNAs on their target repression and activation in a genome-wide scale.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1516-2) contains supplementary material, which is available to authorized users.

Back to the future: transgenerational transmission of xenobiotic-induced epigenetic remodeling

Epigenetics, or regulation of gene expression independent of DNA sequence, is the missing link between genotype and phenotype. Epigenetic memory, mediated by histone and DNA modifications, is controlled by a set of specialized enzymes, metabolite availability, and signaling pathways. A mostly unstudied subject is how sub-toxic exposure to several xenobiotics during specific developmental stages can alter the epigenome and contribute to the development of disease phenotypes later in life. Furthermore, it has been shown that exposure to low-dose xenobiotics can also result in further epigenetic remodeling in the germ line and contribute to increase disease risk in the next generation (multigenerational and transgenerational effects). We here offer a perspective on current but still incomplete knowledge of xenobiotic-induced epigenetic alterations, and their possible transgenerational transmission. We also propose several molecular mechanisms by which the epigenetic landscape may be altered by environmental xenobiotics and hypothesize how diet and physical activity may counteract epigenetic alterations.

The role for microRNAs in drug toxicity and in safety assessment

INTRODUCTION

Adverse drug reactions present significant challenges that impact pharmaceutical development and are major burdens to public health services worldwide. In response to this need, the field of toxicology is rapidly expanding to identify key pathways involved in drug toxicity.

AREAS COVERED

MicroRNAs (miRNAs) are a class of small evolutionary conserved endogenous non-coding RNAs that regulate the translation of protein-coding genes. A wide range of toxicants alter miRNA levels in target organs and these altered miRNAs can also be detected in easily accessible biological fluids. This, combined with an early miRNA response to toxic insults and miRNA stability, substantiates the potential for these small molecules to be useful biomarkers for drug safety assessment.

EXPERT OPINION

miRNAs are early indicators and useful tools to detect drug-induced toxicity. Incorporation of miRNA profiling into the drug safety testing process will complement currently used techniques and may substantially enhance drug safety. With the increasing interests in translational research, the field of miRNA biomarker research will continue to expand and become an important part of the investigation of human drug toxicity.

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.

MicroRNAs in Drug-induced Liver Injury

Drug-induced liver injury (DILI) is a leading cause of acute liver failure, and a major reason for the recall of marketed drugs. Detection of potential liver injury is a challenge for clinical management and preclinical drug safety studies, as well as a great obstacle to the development of new, effective and safe drugs. Currently, serum levels of alanine and aspartate aminotransferases are the gold standard for evaluating liver injury. However, these levels are assessed by nonspecific, insensitive, and non-predictive tests, and often result in false-positive results. Therefore, there is an urgent need for better DILI biomarkers to guide risk assessment and patient management. The discovery of microRNAs (miRNAs) as a new class of gene expression regulators has triggered an explosion of research, particularly on the measurement of miRNAs in various body fluids as biomarkers for many human diseases. The properties of miRNA-based biomarkers, such as tissue specificity and high stability and sensitivity, suggest they could be used as novel, minimally invasive and stable DILI biomarkers. In the current review, we summarize recent progress concerning the role of miRNAs in diagnosing and monitoring both clinical and preclinical DILI, and discuss the main advantages and challenges of miRNAs as novel DILI biomarkers.

Tissue-specific microRNA responses in rats treated with mutagenic and carcinogenic doses of aristolochic acid

Aristolochic acid (AA) is an active component in herbal drugs derived from the Aristolochia species. Although these drugs have been used since antiquity, AA is both genotoxic and carcinogenic in animals and humans, resulting in kidney tumours in rats and upper urinary tract tumours in humans. In the present study, we conducted microarray analysis of microRNA (miRNA) expression in tissues from transgenic Big Blue rats that were treated for 12 weeks with 0.1-10mg/kg AA, using a protocol that previous studies indicate eventually results in kidney tumours and mutations in kidney and liver. Global analysis of miRNA expression of rats treated with 10 mg/kg AA indicated that 19 miRNAs were significantly dysregulated in the kidney, with most of the miRNAs related to carcinogenesis. Only one miRNA, miR-34a (a tumour suppressor), was differentially expressed in the liver. The expression of the two most responsive kidney miRNAs (miR-21, an oncomiR and miR-34a) was further examined in the kidney, liver and testis of rats exposed to 0, 0.1, 1.0 and 10mg/kg AA. Expression of miR-21 was up-regulated in the kidney only, while miR-34a was dose-dependently up-regulated in both the kidney and liver; the expression of miR-21 and miR-34a was unaltered by the AA treatment in the testis. Analysis of cII mutations in the testis of treated rats also was negative. Our results indicate that AA treatment of rats produced dysregulation of a large number of miRNAs in the tumour target tissue and that the up-regulation of miR-21 correlated with the carcinogenicity of AA while the up-regulation of miR-34a correlated with its mutagenicity.

MicroRNAs as key regulators of xenobiotic biotransformation and drug response

In the last decade, microRNAs have emerged as key factors that negatively regulate mRNA expression. It has been estimated that more than 50% of protein-coding genes are under microRNA control and each microRNA is predicted to repress several mRNA targets. In this respect, it is recognized that microRNAs play a vital role in various cellular and molecular processes and that, depending on the biological pathways in which they intervene, distorted expression of microRNAs can have serious consequences. It has recently been shown that specific microRNA species are also correlated with toxic responses induced by xenobiotics. Since the latter are primarily linked to the extent of detoxification in the liver by phase I and phase II biotransformation enzymes and influx and efflux drug transporters, the regulation of the mRNA levels of this particular set of genes through microRNAs is of great importance for the overall toxicological outcome. Consequently, in this paper, an overview of the current knowledge with respect to the complex interplay between microRNAs and the expression of biotransformation enzymes and drug transporters in the liver is provided. Nuclear receptors and transcription factors, known to be involved in the transcriptional regulation of these genes, are also discussed.

MicroRNA regulation of DNA repair gene expression in 4-aminobiphenyl-treated HepG2 cells

We examined the role of miRNAs in DNA damage response in HepG2 cells following exposure to 4-aminobiphenyl (4-ABP). The arylamine 4-ABP is a human carcinogen. Using the Comet assay, we showed that 4-ABP (18.75-300μM) induces DNA damage in HepG2 cells after 24h. DNA damage signaling pathway-based PCR arrays were used to investigate expression changes in genes involved in DNA damage response. Results showed down-regulation of 16 DNA repair-related genes in 4-ABP-treated cells. Among them, the expression of selected six genes (UNG, LIG1, EXO1, XRCC2, PCNA, and FANCG) from different DNA repair pathways was decreased with quantitative real-time PCR (qRT-PCR). In parallel, using the miRNA array, we reported that the expression of 27 miRNAs in 4-ABP-treated cells was at least 3-fold higher than that in the control group. Of these differential 27 miRNAs, the most significant expression of miRNA-513a-5p and miRNA-630 was further validated by qRT-PCR, and was predicted to be implicated in the deregulation of FANCG and RAD18 genes, respectively, via bioinformatic analysis. Both FANCG and RAD18 proteins were found to be down-regulated in 4-ABP-treated cells. In addition, overexpression and knockdown of miRNA-513a-5p and miRNA-630 reduced and increased the expression of FANCG and RAD18 proteins, respectively. Based on the above results, we indicated that miRNA-513a-5p and miRNA-630 could play a role in the suppression of DNA repair genes, and eventually lead to DNA damage.

miR-21 regulates N-methyl-N-nitro-N'-nitrosoguanidine-induced gastric tumorigenesis by targeting FASLG and BTG2

MicroRNAs (miRNAs) are recently discovered regulators of gene expression and are important in the regulation of many cellular events. Evidence collected to date shows that miRNAs are altered after exposure to environmental toxicants. However, the role that miR-21 plays in the gastric tumorigenesis induced by environmental carcinogens remains largely unknown. The aim of this study was to characterize the regulatory role of miR-21 in the carcinogenic processes following exposure to the N-nitroso carcinogen N-methyl-N-nitro-N'-nitrosoguanidine (MNNG). We found a progressive dose- and time-dependent increase in miR-21 expression following treatment with MNNG. Dysregulated miR-21 affected both cell growth in GES-1 cells and the gastric tumorigenesis induced with MNNG. These data demonstrate the involvement of miR-21 in the malignant transformation and tumorigenesis activated by MNNG. We also established that the Fas ligand (FASLG) and B-cell translocation gene 2 (BTG2), regulated by miR-21, contribute to the transformation induced by MNNG in GES-1 cells. This is the first study to show that miR-21 is involved in chemical carcinogenesis in vivo and in vitro. The regulation by miR-21 of the gastric carcinogenesis induced by MNNG highlights the functional roles of miRNAs in chemical carcinogenesis, and offers a new explanation of the mechanisms underlying chemical carcinogenesis.

The microRNAs as potential biomarkers for predicting the onset of aflatoxin exposure in human beings: a review

The identification of aflatoxins as human carcinogens has stimulated extensive research efforts, which continue to the present, to assess potential health hazards resulting from contamination of the human food supply and to minimize exposure. The use of biomarkers that are mechanistically supported by toxicological studies will be important tools for identifying stages in the progression of development of the health effects of environmental agents. miRNAs are small non-coding mRNAs that regulate post-transcriptional gene expression. Also, they are molecular markers of cellular responses to various chemical agents. Growing evidence has demonstrated that environmental chemicals can induce changes in miRNA expression. miRNAs are good biomarkers because they are well defined, chemically uniform, restricted to a manageable number of species, and stable in cells and in the circulation. miRNAs have been used as serological markers of HCC and other tumors. The expression patterns of different miRNAs can distinguish among HCC-hepatitis viruses related, HCC cirrhosis-derivate, and HCC unrelated to either of them. The main objective of this review is to find unreported miRNAs in HCC related to other causes, so that they can be used as specific molecular biomarkers in populations exposed to aflatoxins and as early markers of exposure, damage/presence of HCC. Until today specific miRNAs as markers for aflatoxins-exposure and their reliability are currently lacking. Based on their elucidated mechanisms of action, potential miRNAs that could serve as possible markers of HCC by exposure to aflatoxins are miR-27a, miR-27b, miR-122, miR-148, miR-155, miR-192, miR-214, miR-221, miR-429, and miR-500. Future validation for all of these miRNAs will be needed to assess their prognostic significance and confirm their relationship with the induction of HCC due to aflatoxin exposure.

Involvement of miRNAs in the early phase of halothane-induced liver injury

MicroRNAs (miRNA) form a class of small non-coding RNA molecules that negatively regulate gene expression. Most cellular pathways are modulated by miRNAs. However, the pathophysiological role of miRNAs during drug-induced liver injury (DILI) remains largely unknown. In this study, the possible involvement of miRNAs in DILI caused by the hepatotoxic drug halothane (HAL) was investigated. Toward this purpose, miRNA microarray studies of HAL-induced liver injury were performed in mice at five different time points up to 24h after dosing. To exclude any pharmacological effects on miRNA expression, isoflurane was used as a low hepatotoxic drug because it is structurally similar to HAL. Approximately 30-50% of the miRNA expression levels changed more than two-fold at every time point. In silico biological pathway analysis was performed to predict the targeted genes. Consequently, the miRNA gene down-regulation that occurred 1h after HAL administration was primarily related to inflammation, immune systems and liver injury. Based on additional in silico analyses, we identified miR-106b. Subsequently target of miR-106b was investigated using liver samples from mice with HAL-induced liver injury. Among the predicted targets, we discovered that a signal transducer and activator of transcription 3 (STAT3) was particularly up-regulated beginning during the early phase of HAL-induced liver injury. Collectively, the suppressed miR-106b expression, as well as the subsequent up-regulation of STAT3, was critical for the pathogenesis of HAL-induced liver injury.

MicroRNAs as potential biomarkers in diseases and toxicology

MiRNAs (microRNAs) are single-stranded non-coding RNAs of approximately 21-23 nucleotides in length whose main function is to inhibit gene expression by interfering with mRNA processes. MicroRNAs suppress gene expression by affecting mRNA (messenger RNAs) stability, targeting the mRNA for degradation, or both. In this review, we have examined how microRNA expression could be altered following exposure to chemicals and how they could represent appropriate tissue and more interestingly circulating biomarkers. Among the key questions before using the microRNA for evaluation of risk toxicity, it remains still to clarify how they could be causally involved in the adverse effects and how stable their changes are.

Absence of mature microRNAs inactivates the response of gene expression to carcinogenesis induced by N-ethyl-N-nitrosourea in mouse liver

This study aims to evaluate the role of microRNAs (miRNAs) in chemical tumorigenesis by evaluating genomic gene expression in miRNA knockout mice. Previous studies showed that mice without mature miRNAs due to hepatocyte-specific Dicer1 knockout (KO) had a much higher liver tumor incidence than wild-type mice. In this study, Dicer1 KO or the wild-type mice were treated intraperitoneally with genotoxic carcinogen N-ethyl-N-nitrosourea (ENU) at a single dose (150 mg kg(-1) that resulted in liver tumorigenesis) or the vehicle at 3 weeks of age. The animals were killed 2 weeks after treatment and the liver samples were collected for the gene expression study. Principal components analysis and hierarchical cluster analysis showed that gene expression was globally altered by the Dicer1 KO and ENU exposure. There were 5621, 3286 and 2565 differentially expressed genes for Dicer1 disruption, ENU treatment in wild-type mice and ENU treatment in Dicer1 KO mice, respectively. Functional analysis of the differentially expressed genes suggests that the Dicer1 KO mouse liver lost their capability to suppress the carcinogenesis induced by ENU exposure in genomic level. In addition, the miRNA-mediated BRCA1 and P53 signaling pathways were identified as the main pathways responsible for the tumorigenesis. We conclude that the mouse livers in the absence of mature miRNAs could not appropriately respond to carcinogenic insults from ENU treatment, indicating that miRNAs play a critical role in chemical carcinogenesis.

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.

Molecular basis of cancer-therapy-induced cardiotoxicity: introducing microRNA biomarkers for early assessment of subclinical myocardial injury

Development of reliable biomarkers for early clinical assessment of drug-induced cardiotoxicity could allow the detection of subclinical cardiac injury risk in vulnerable patients before irreversible damage occurs. Currently, it is difficult to predict who will develop drug-induced cardiotoxicity owing to lack of sensitivity and/or specificity of currently used diagnostics. miRNAs are mRNA regulators and they are currently being extensively profiled for use as biomarkers due to their specific tissue and disease expression signature profiles. Identification of cardiotoxicity-specific miRNA biomarkers could provide clinicians with a valuable tool to allow prognosis of patients at risk of cardiovascular injury, alteration of a treatment regime or the introduction of an adjunct therapy in order to increase the long-term survival rate of patients treated with cardiotoxic drugs.

New insights on the role of epigenetic alterations in hepatocellular carcinoma

Emerging evidence assigns to epigenetic mechanisms heritable differences in gene function that come into being during cell development or via the effect of environmental factors. Epigenetic deregulation is strongly involved in the development of hepatocellular carcinoma (HCC). It includes changes in methionine metabolism, promoter hypermethylation, or increased proteasomal degradation of oncosuppressors, as well as posttranscriptional deregulation by microRNA or messenger RNA (mRNA) binding proteins. Alterations in the methylation of the promoter of methyl adenosyltransferase MAT1A and MAT2A genes in HCC result in decreased S-adenosylmethionine levels, global DNA hypomethylation, and deregulation of signal transduction pathways linked to methionine metabolism and methyl adenosyltransferases activity. Changes in S-adenosylmethionine levels may also depend on MAT1A mRNA destabilization associated with MAT2A mRNA stabilization by specific proteins. Decrease in MAT1A expression has also been attributed to miRNA upregulation in HCC. A complex deregulation of miRNAs is also strongly involved in hepatocarcinogenesis, with up-regulation of different miRNAs targeting oncosuppressor genes and down-regulation of miRNAs targeting genes involved in cell-cycle and signal transduction control. Oncosuppressor gene down-regulation in HCC is also induced by promoter hypermethylation or posttranslational deregulation, leading to proteasomal degradation. The role of epigenetic changes in hepatocarcinogenesis has recently suggested new promising therapeutic approaches for HCC on the basis of the administration of methylating agents, inhibition of methyl adenosyltransferases, and restoration of the expression of tumor-suppressor miRNAs.

Analysis of microRNA and mRNA expression profiles highlights alterations in modulation of the MAPK pathway under octanal exposure

Previous environmental microRNA (miRNA) studies have investigated a limited number of candidate miRNAs and have not evaluated functional effects on gene expression. In this study, we aimed to identify octanal (OC)-sensitive miRNAs and to characterize the relationships between miRNAs and expression of candidate genes involved in OC-induced toxicity. Microarray analysis identified 15 miRNAs that were differentially expressed in OC-exposed A549 human alveolar cells. Integrated analyses of miRNA and mRNA expression profiles identified significant miRNA-mRNA anti-correlations. GO analysis of 101 putative target genes showed that the biological category 'MAPK signaling pathway' was prominently annotated. Moreover, we detected increased phosphorylation of p38 MAPK in the OC-exposed group. By integrating the transcriptome and microRNAome, we provide evidence that OC can affect MAPK-induced toxicity signaling. Therefore, this study demonstrates the added value of an integrated miRNA-mRNA approach for identifying molecular events induced by environmental pollutants in an in vitro human model.

Alteration of the microRNA-122 regulatory network in rat models of hepatotoxicity

MicroRNAs are small RNA molecules that post-transcriptionally regulate gene expression. MicroRNA-122 is the most abundant and specific liver microRNA. Hepatotoxicity involves a significant alteration of liver gene expression. The aim of this work was to evaluate the microRNA-122 regulatory network in models of hepatotoxicity induced by thioacetamide or carbon tetrachloride. We report that the toxins decreased the expression of microRNA-122, which corresponded with an increase in two target genes: Cyclin G1 and the cationic amino acid transporter CAT-1. We found a decreased expression of its precursor, pri-microRNA-122, and of the transcription factors that specifically bind its promoter: CCAAT/enhancer-binding protein alpha, and members of the hepatocyte nuclear factor family. Therefore, microRNA-122 expression levels are under transcriptional control during hepatotoxicity. We propose that the changes observed are associated with the liver response to cope with the injury caused by the hepatotoxins, likely through a cell proliferation process to repair the damaged tissue.

The expression of miR-25 is increased in colorectal cancer and is associated with patient prognosis

MicroRNA-25 (miR-25) has recently been found to be involved in many critical processes in human malignancies. We aimed to investigate the expression pattern and prognostic role of miR-25 in colorectal cancer. Colorectal cancer and adjacent normal specimens from 186 patients who had not received neoadjuvant chemotherapy were collected. The expression of miR-25 was detected with a quantitative real-time PCR assay, and the association of miR-25 with overall patient survival was analyzed via statistical analysis. The results indicated that the level of miR-25 expression was significantly elevated in colorectal cancer compared with the level observed in the adjacent normal tissue. It was also demonstrated that miR-25 expression is associated with tumor invasion, lymph node metastasis, distant metastasis and the TNM stage of colorectal cancer. In addition, a Kaplan-Meier analysis revealed that an increased level of miR-25 expression is associated with a poor overall survival of patients. A multivariate survival analysis also indicated that miR-25 is an independent prognostic marker after adjusting for known prognostic factors. These results prove that miR-25 expression is increased in colorectal cancer and is associated with tumor progression. This study also provides the first evidence that miR-25 is an independent prognostic factor for patients with colorectal cancer, indicating the potential role of miR-25 as a highly specific and sensitive biomarker.

MicroRNA-145 function as a cell growth repressor by directly targeting c-Myc in human ovarian cancer

MiR-145 is reported to be significantly down-regulated in ovarian cancer. This study was aimed at elucidating the roles of miR-145 in regulating the biological behavior of epithelial ovarian cancer (EOC) cells. In this report, we find out that up-regulation of miR-145 in OVCAR-3 and SKOV-3 cells inhibit cell proliferation and promote cell apoptosis. We show that miR-145 directly target the c-Myc 3'-UTR. Moreover, ectopic expression of c-Myc reduces the inhibition of cell proliferation caused by miR-145 transfection. Cell cycle assay showed that up-regulation of miR-145 reduces S phase population, and restoration of c-Myc can rescue this reduction. These findings indicate that miR-145 inhibits cell proliferation and promotes cell apoptosis by targeting c-Myc 3'-UTR. Therefore, the result indicated that miR- 145 could be used as a potential therapeutic target in ovarian cancer.

MicroRNA-34a targets Bcl-2 and sensitizes human hepatocellular carcinoma cells to sorafenib treatment

MiR-34a, a direct target of p53, has been shown to target several molecules associated with the cell cycle and cell survival pathways, and its dysregulation is implicated in cancer drug resistance or sensitivity in several human cancers. However, the correlation between miR-34a expression and chemoresistance has not been explored in HCC. In this study, we confirmed that miR-34a was significantly down-regulated in HCC tissues and HCC cell lines by qRT-PCR. HCC tissues with lower miR-34a expression displayed higher expression of Bcl-2 protein than those with high expression of miR-34a; therefore, an inverse correlation is evident between the miR-34a level and Bcl-2 expression. Moreover, patients with lower miR-34a expression had significantly poorer overall survival. Bioinformatics and luciferase reporter assays revealed that miR-34a binds the 3'-UTR of the Bcl-2 mRNA and represses its translation. Western blotting analysis and qRT-PCR confirmed that Bcl-2 is inhibited by miR-34a overexpression. Functional analyses indicated that the restoration of miR-34a reduced cell viability, promoted cell apoptosis and potentiated sorafenib-induced apoptosis and toxicity in HCC cell lines by inhibiting Bcl-2 expression. This study is the first to demonstrate that miR-34a induces sensitivity to the anti-tumor effect of sorafenib in human HCC cells, suggesting a potential role of miR-34a in the treatment of HCC.

Towards incorporating epigenetic mechanisms into carcinogen identification and evaluation

Remarkable progress in the field of epigenetics has turned academic, medical and public attention to the potential applications of these new advances in medicine and various fields of biomedical research. The result is a broader appreciation of epigenetic phenomena in the a etiology of common human diseases, most notably cancer. These advances also represent an exciting opportunity to incorporate epigenetics and epigenomics into carcinogen identification and safety assessment. Current epigenetic studies, including major international sequencing projects, are expected to generate information for establishing the 'normal' epigenome of tissues and cell types as well as the physiological variability of the epigenome against which carcinogen exposure can be assessed. Recently, epigenetic events have emerged as key mechanisms in cancer development, and while our search of the Monograph Volume 100 revealed that epigenetics have played a modest role in evaluating human carcinogens by the International Agency for Research on Cancer (IARC) Monographs so far, epigenetic data might play a pivotal role in the future. Here, we review (i) the current status of incorporation of epigenetics in carcinogen evaluation in the IARC Monographs Programme, (ii) potential modes of action for epigenetic carcinogens, (iii) current in vivo and in vitro technologies to detect epigenetic carcinogens, (iv) genomic regions and epigenetic modifications and their biological consequences and (v) critical technological and biological issues in assessment of epigenetic carcinogens. We also discuss the issues related to opportunities and challenges in the application of epigenetic testing in carcinogen identification and evaluation. Although the application of epigenetic assays in carcinogen evaluation is still in its infancy, important data are being generated and valuable scientific resources are being established that should catalyse future applications of epigenetic testing.

MiR-590-5P inhibits growth of HepG2 cells via decrease of S100A10 expression and Inhibition of the Wnt pathway

Hepatocellular carcinoma is one of the most common and lethal cancers worldwide, especially in developing countries. In the present study, we found that the expression of a microRNA, miR-590-5P, was down-regulated and S100A10 was up-regulated in six hepatocellular carcinoma cell lines. The reporter gene assay showed that overexpression of miR-590-5P effectively reduced the activity of luciferase expressed by a vector bearing the 3′ untranslated region of S100A10 mRNA. Ectopic miR-590-5P overexpression mediated by lentiviral infection decreased expression of S100A10. Infection of Lv-miR-590-5P inhibited cell growth and induced cell cycle G1 arrest in HepG2 cells. In addition, miR-590-5P expression suppressed the expression of Wnt5a, cMyc and cyclin D1, and increased the phosphorylation of β-catenin and expression of Caspase 3, which may contribute to the inhibitory effect of miR-590-5P on cell growth. Taken together, our data suggest that down-regulation of miR-590-5P is involved in hepatocellular carcinoma and the restoration of miR-590-5P can impair the growth of cancer cells, suggesting that miR-590-5P may be a potential target molecule for the therapy of hepatocellular carcinoma.

Deregulation of signalling pathways in prognostic subtypes of hepatocellular carcinoma: novel insights from interspecies comparison

Hepatocellular carcinoma is a frequent and fatal disease. Recent researches on rodent models and human hepatocarcinogenesis contributed to unravel the molecular mechanisms of hepatocellular carcinoma dedifferentiation and progression, and allowed the discovery of several alterations underlying the deregulation of cell cycle and signalling pathways. This review provides an interpretive analysis of the results of these studies. Mounting evidence emphasises the role of up-regulation of RAS/ERK, P13K/AKT, IKK/NF-kB, WNT, TGF-ß, NOTCH, Hedgehog, and Hippo signalling pathways as well as of aberrant proteasomal activity in hepatocarcinogenesis. Signalling deregulation often occurs in preneoplastic stages of rodent and human hepatocarcinogenesis and progressively increases in carcinomas, being most pronounced in more aggressive tumours. Numerous changes in signalling cascades are involved in the deregulation of carbohydrate, lipid, and methionine metabolism, which play a role in the maintenance of the transformed phenotype. Recent studies on the role of microRNAs in signalling deregulation, and on the interplay between signalling pathways led to crucial achievements in the knowledge of the network of signalling cascades, essential for the development of adjuvant therapies of liver cancer. Furthermore, the analysis of the mechanisms involved in signalling deregulation allowed the identification of numerous putative prognostic markers and novel therapeutic targets of specific hepatocellular carcinoma subtypes associated with different biologic and clinical features. This is of prime importance for the selection of patient subgroups that are most likely to obtain clinical benefit and, hence, for successful development of targeted therapies for liver cancer.

Maternal stress induces epigenetic signatures of psychiatric and neurological diseases in the offspring

The gestational state is a period of particular vulnerability to diseases that affect maternal and fetal health. Stress during gestation may represent a powerful influence on maternal mental health and offspring brain plasticity and development. Here we show that the fetal transcriptome, through microRNA (miRNA) regulation, responds to prenatal stress in association with epigenetic signatures of psychiatric and neurological diseases. Pregnant Long-Evans rats were assigned to stress from gestational days 12 to 18 while others served as handled controls. Gestational stress in the dam disrupted parturient maternal behaviour and was accompanied by characteristic brain miRNA profiles in the mother and her offspring, and altered transcriptomic brain profiles in the offspring. In the offspring brains, prenatal stress upregulated miR-103, which is involved in brain pathologies, and downregulated its potential gene target Ptplb. Prenatal stress downregulated miR-145, a marker of multiple sclerosis in humans. Prenatal stress also upregulated miR-323 and miR-98, which may alter inflammatory responses in the brain. Furthermore, prenatal stress upregulated miR-219, which targets the gene Dazap1. Both miR-219 and Dazap1 are putative markers of schizophrenia and bipolar affective disorder in humans. Offspring transcriptomic changes included genes related to development, axonal guidance and neuropathology. These findings indicate that prenatal stress modifies epigenetic signatures linked to disease during critical periods of fetal brain development. These observations provide a new mechanistic association between environmental and genetic risk factors in psychiatric and neurological disease.

Heart structure-specific transcriptomic atlas reveals conserved microRNA-mRNA interactions

MicroRNAs are short non-coding RNAs that regulate gene expression at the post-transcriptional level and play key roles in heart development and cardiovascular diseases. Here, we have characterized the expression and distribution of microRNAs across eight cardiac structures (left and right ventricles, apex, papillary muscle, septum, left and right atrium and valves) in rat, Beagle dog and cynomolgus monkey using microRNA sequencing. Conserved microRNA signatures enriched in specific heart structures across these species were identified for cardiac valve (miR-let-7c, miR-125b, miR-127, miR-199a-3p, miR-204, miR-320, miR-99b, miR-328 and miR-744) and myocardium (miR-1, miR-133b, miR-133a, miR-208b, miR-30e, miR-499-5p, miR-30e*). The relative abundance of myocardium-enriched (miR-1) and valve-enriched (miR-125b-5p and miR-204) microRNAs was confirmed using in situ hybridization. MicroRNA-mRNA interactions potentially relevant for cardiac functions were explored using anti-correlation expression analysis and microRNA target prediction algorithms. Interactions between miR-1/Timp3, miR-125b/Rbm24, miR-204/Tgfbr2 and miR-208b/Csnk2a2 were identified and experimentally investigated in human pulmonary smooth muscle cells and luciferase reporter assays. In conclusion, we have generated a high-resolution heart structure-specific mRNA/microRNA expression atlas for three mammalian species that provides a novel resource for investigating novel microRNA regulatory circuits involved in cardiac molecular physiopathology.

Environmental toxicants, epigenetics, and cancer

Tumorigenesis, a complex and multifactorial progressive process of transformation of normal cells into malignant cells, is characterized by the accumulation of multiple cancer-specific heritable phenotypes triggered by the mutational and/or non-mutational (i.e., epigenetic) events. Accumulating evidence suggests that environmental and occupational exposures to natural substances, as well as man-made chemical and physical agents, play a causative role in human cancer. In a broad sense, carcinogenesis may be induced through either genotoxic or non-genotoxic mechanisms; however, both genotoxic and non-genotoxic carcinogens also cause prominent epigenetic changes. This review presents current evidence of the epigenetic alterations induced by various chemical carcinogens, including arsenic, 1,3-butadine, and pharmaceutical and biological agents, and highlights the potential for epigenetic changes to serve as markers for carcinogen exposure and cancer risk assessment.

microRNAs as mediators of drug toxicity

microRNAs (miRNAs) represent the most abundant class of gene expression regulators that bind complementarily to transcripts to repress their translation or mRNA degradation. These small ( 21-23 nucleotides in length) noncoding RNAs are derived through a multistep process by miRNA genes located in genomic DNA. Because miRNAs regulate fundamental cellular functions, their dysregulation affects a large range of physiological processes, such as development, immune responses, metabolism, and diseases as well as toxicological outcomes. Cancer-related miRNAs have been extensively studied; however, the roles of miRNAs in xenobiotic metabolism and in toxicology have only recently been explored. This review focuses on the current knowledge of miRNA-dependent regulation of drug-metabolizing enzymes and nuclear receptors and the associated potential toxicological implications. The potential modulation of toxicology-related changes in miRNA expression, the role of miRNA in immune-mediated drug-induced liver injuries, the use of circulating miRNAs in body fluids as potential toxicological biomarkers, and the link between miRNA-related pharmacogenomics and adverse drug reactions are highlighted.

Targeting microRNAs to modulate TRAIL-induced apoptosis of cancer cells

MicroRNAs (miRNAs) are endogenously expressed small non-coding RNAs, which are evolutionarily conserved and function as regulators of gene expression. These molecules are involved in numerous biological processes including differentiation, development, proliferation and apoptosis. Further investigation identifies that miRNAs may act as either potent oncogenes or tumor-suppressor genes, linking to cancer initiation and progression. Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), as a member of the TNF family, is an attractive therapeutic target in cancer because it directly induces tumor cell apoptosis and has no cytotoxicity to normal cell types in vitro or in vivo. However, the resistance to TRAIL-induced apoptosis limits its clinical effectiveness. Interestingly, several studies convincingly demonstrate a role of miRNAs in modulating sensitive/resistant phenotypes to TRAIL. Here, we review the current findings about miRNAs involved in TRAIL-induced apoptosis in different cancers.