Loss of miR-200 inhibition of Suz12 leads to polycomb-mediated repression required for the formation and maintenance of cancer stem cells

miR-135b Stimulates Osteosarcoma Recurrence and Lung Metastasis via Notch and Wnt/β-Catenin Signaling

Cancer stem cells (CSCs) play an important role in osteosarcoma (OS) metastasis and recurrence, and both Wnt/β-catenin and Notch signaling are essential for the development of the biological traits of CSCs. However, the mechanism that underlies the simultaneous hyperactivation of both Wnt/β-catenin and Notch signaling in OS remains unclear. Here, we report that expression of miR-135b correlates with the overall and recurrence-free survival of OS patients, and that miR-135b has an activating effect on both Wnt/β-catenin and Notch signaling. The overexpression of miR-135b simultaneously targets multiple negative regulators of the Wnt/β-catenin and Notch signaling pathways, including glycogen synthase kinase-3 beta (GSK3β), casein kinase 1a (CK1α), and ten-eleven translocation 3 (TET3). Therefore, upregulated miR-135b promotes CSC traits, lung metastasis, and tumor recurrence in OS. Notably, antagonizing miR-135b potently inhibits OS lung metastasis, cancer cell stemness, CSC-induced tumor formation, and recurrence in xenograft animal models. These findings suggest that miR-135b mediates the constitutive activation of Wnt/β-catenin and Notch signaling, and that the inhibition of miR-135b is a novel strategy to inhibit tumor metastasis and prevent CSC-induced recurrence in OS.

c-Myc is Required for BRAFV600E-Induced Epigenetic Silencing by H3K27me3 in Tumorigenesis

BRAF^V600E mutation is frequently found in human cancers particularly thyroid cancer and melanoma, and is involved in the regulation of gene expression through activating MAPK/Erk signaling. Trimethylation of histone 3 lysine 27 (H3K27me3) is a critical epigenetic mark for the maintenance of gene silencing in tumorigenesis. However, molecular mechanism underlying the complex interplay between these two molecular events remains to be explored. In the present study, we conducted chromatin immunoprecipitation combined with next-generation sequencing (ChIP-Seq) and expression microarray analysis in NIH3T3 cells to explore the relationship between H3K27me3 and transcriptional regulation by BRAF^V600E mutation. Our results showed that activated MAPK/Erk signaling by BRAF^V600E mutation was a trigger of this epigenetic processing at many downstream target genes in cancer cell lines and Braf^V600E-induced thyroid cancer of transgenetic mice. By integrating ChIP-Seq and gene expression microarray data, we identified 150 down-regulated loci with increased levels of H3K27me3 in BRAF-mutant cells relative to BRAF wild-type cells. Our data also demonstrated that c-Myc, a downstream key effector of BRAF^V600E signaling, was required for BRAF^V600E-induced changes in H3K27me3 through regulating the components of the polycomb repressive complex 2 (PRC2) genes Ezh2, Suz12 and Jarid2 at both transcriptional levels via direct binding to their regulatory elements and post-transcriptional levels via repressing the miR-26a, miR-200b and miR-155. In addition, BRAF^V600E also caused gene silencing through Erk1/2-induced RNA polymerase II (RNAPII) poising and chromatin architecture. Collectively, our data uncover a previously unknown epigenetic mechanism in the tumorigenesis of BRAF^V600E-driven cancers.

Metabolic reprogramming and epithelial-to-mesenchymal transition in cancer

Several lines of evidence indicate that during transformation epithelial cancer cells can acquire mesenchymal features via a process called epithelial-to-mesenchymal transition (EMT). This process endows cancer cells with increased invasive and migratory capacity, enabling tumour dissemination and metastasis. EMT is associated with a complex metabolic reprogramming, orchestrated by EMT transcription factors, which support the energy requirements of increased motility and growth in harsh environmental conditions. The discovery that mutations in metabolic genes such as FH, SDH and IDH activate EMT provided further evidence that EMT and metabolism are intertwined. In this review, we discuss the role of EMT in cancer and the underpinning metabolic reprogramming. We also put forward the hypothesis that, by altering chromatin structure and function, metabolic pathways engaged by EMT are necessary for its full activation.

tRF/miR-1280 Suppresses Stem Cell-like Cells and Metastasis in Colorectal Cancer

Several studies have shown that tRNAs can be enzymatically cleaved to generate distinct classes of tRNA-derived fragments (tRF). Here, we report that tRF/miR-1280, a 17-bp fragment derived from tRNA^Leu and pre-miRNA, influences Notch signaling pathways that support the function of cancer stem-like cells (CSC) in colorectal cancer progression. tRF/miR-1280 expression was decreased in human specimens of colorectal cancer. Ectopic expression of tRF/miR-1280 reduced cell proliferation and colony formation, whereas its suppression reversed these effects. Mechanistic investigations implicated the Notch ligand JAG2 as a direct target of tRF/miR-1280 binding through which it reduced tumor formation and metastasis. Notably, tRF/miR-1280-mediated inactivation of Notch signaling suppressed CSC phenotypes, including by direct transcriptional repression of the Gata1/3 and miR-200b genes. These results were consistent with findings of decreased levels of miR-200b and elevated levels of JAG2, Gata1, Gata3, Zeb1, and Suz12 in colorectal cancer tissue specimens. Taken together, our results established that tRF/miR-1280 suppresses colorectal cancer growth and metastasis by repressing Notch signaling pathways that support CSC phenotypes. Furthermore, they provide evidence that functionally active miRNA can be derived from tRNA, offering potential biomarker and therapeutic uses. Cancer Res; 77(12); 3194-206. ©2017 AACR.

The miR-200b-ZEB1 circuit regulates diverse stemness of human hepatocellular carcinoma

Accumulating evidence suggests that human hepatocellular carcinoma (HCC) can be derived from cancer stem cells (CSCs), which contribute to tumor initiation, metastasis, chemoresistance, and recurrence. A great variety of HCC CSCs resulting in diverse clinical manifestations have been reported. However, how CSC diversity is regulated and generated remains unclear. Here we report that the miR-200b-ZEB1 circuit is closely involved with the induction and maintenance of a diverse group of CSCs. We found that miR-200b downregulation occurred in early HCC and associated with poor prognosis. The downregulation was attributable to genome deletion and promoter methylation of the miR-200a/b/429 gene. Ectopic expression of miR-200b or silencing of ZEB1 led to a decrease in CD13⁺ and CD24⁺ HCC CSCs and an increase in EpCAM⁺ HCC CSCs. Mechanistically, miR-200b directly suppressed BMI1 and ZEB1 expressions. ZEB1 recognized promoters of CD13, CD24, and EpCAM genes resulting in CD13 and CD24 upregulation and EpCAM downregulation. Neither miR-200b nor ZEB1 had obvious effects on CD133 or CD90 expression. Silencing CD13 or CD24 expression suppressed tumorigenicity of HCC cells. Ectopic expression of CD24 reversed the suppression of tumorigenicity by ectopic expression of miR-200b. Clinically, miR-200b downregulation was coupled with ZEB1 upregulation in approximately two-thirds of HCC patients. ZEB1 expression was positively correlated with CD13 and CD24 expressions in HCCs, while miR-200b expression was positively correlated with EpCAM. Our findings suggest that the miR-200b-ZEB1 circuit is a master regulator of diverse stemness of HCC, which differentiates HCCs into those containing CD13⁺ /CD24⁺ CSCs from those containing EpCAM⁺ CSCs.

Cancer stem cell heterogeneity: origin and new perspectives on CSC targeting

Most of the cancers are still incurable human diseases. According to recent findings, especially targeting cancer stem cells (CSCs) is the most promising therapeutic strategy. CSCs take charge of a cancer hierarchy, harboring stem cell-like properties involving self-renewal and aberrant differentiation potential. Most of all, the presence of CSCs is closely associated with tumorigenesis and therapeutic resistance. Despite the numerous efforts to target CSCs, current anti-cancer therapies are still impeded by CSC-derived cancer malignancies; increased metastases, tumor recurrence, and even acquired resistance against the anti-CSC therapies developed in experimental models. One of the most forceful underlying reasons is a “cancer heterogeneity” due to “CSC plasticity” A comprehensive understanding of CSC-derived heterogeneity will provide novel insights into the establishment of efficient targeting strategies to eliminate CSCs. Here, we introduce findings on mechanisms of CSC reprogramming and CSC plasticity, which give rise to phenotypically varied CSCs. Also, we suggest concepts to improve CSC-targeted therapy in order to overcome therapeutic resistance caused by CSC plasticity and heterogeneity.

Overexpression of suppressor of zest 12 is associated with cervical node metastasis and unfavorable prognosis in tongue squamous cell carcinoma

OBJECTIVE

Increased expression of suppressor of zest 12 (SUZ12), a core component of the polycomb repressive complex 2, contributes to human tumorigenesis and associates with patient prognosis. In the present study, we sought to investigate the expression of SUZ12 and its clinicopathological significance in primary tongue squamous cell carcinoma (TSCC).

METHODS

The expression of SUZ12 protein was determined by immunohistochemistry in clinical samples from a retrospective cohort of 72 patients with primary TSCC who were treated at our institution from Jan. 2007 to Dec. 2013. The potential associations between SUZ12 abundance and multiple clinicopathological parameters were assessed by Chi square test. Moreover, the effect of SUZ12 expression on patients' survival was further estimated by Kaplan-Meier and Cox regression analyses.

RESULTS

Our immunohistochemical staining data revealed aberrant overexpression of SUZ12 in a large subset of TSCC as compared to normal tongue mucosa. Elevated SUZ12 was found to be significantly associated with cervical nodes metastasis (P = 0.0325) and reduced overall as well as disease-free survival (Log-rank test, P = 0.0225, 0.0179, respectively). Both univariate and multivariate Cox regression analysis identified the expression status of SUZ12 (low/high) as an important independent prognostic factor for patients' survival.

CONCLUSIONS

Our data reveal that aberrant SUZ12 overexpression is associated with cervical nodes metastasis and reduced survival in TSCC. These findings suggest that SUZ12 might play critical roles during tongue tumorigenesis and serve as a novel biomarker with diagnostic and prognostic significance.

MicroRNA-218 inhibits tumor growth and increases chemosensitivity to CDDP treatment by targeting BCAT1 in prostate cancer

MicroRNAs have been reported to be associated with chemosensitivity of several types of cancers. However, the underlying molecular mechanisms are poorly understood. In this study, we explored miR-218 increased the chemosensitivity to cis-diaminedichloroplatinum treatment of prostate cancer. We found that the expression level of miR-218 was down-regulated in the human prostate cancer specimens. Moreover, overexpression of miR-218 inhibited cell viability, migration, and invasion in PC3 and DU145 cells. Furthermore, we demonstrated that the tumor suppressive role of miR-218 was mediated by negatively regulating branched-chain amino acid transaminase 1 (BCAT1) protein expression. Importantly, overexpression of BCAT1 decreased the chemosensitivity to CDDP treatment of PC3 and DU145 cells. Our study is the first to identify the positive role of miR-218 in chemosensitivity, which will facilitate the development of novel therapeutic strategies for prostate cancer in the future.

EMT: 2016

The significant parallels between cell plasticity during embryonic development and carcinoma progression have helped us understand the importance of the epithelial-mesenchymal transition (EMT) in human disease. Our expanding knowledge of EMT has led to a clarification of the EMT program as a set of multiple and dynamic transitional states between the epithelial and mesenchymal phenotypes, as opposed to a process involving a single binary decision. EMT and its intermediate states have recently been identified as crucial drivers of organ fibrosis and tumor progression, although there is some need for caution when interpreting its contribution to metastatic colonization. Here, we discuss the current state-of-the-art and latest findings regarding the concept of cellular plasticity and heterogeneity in EMT. We raise some of the questions pending and identify the challenges faced in this fast-moving field.

Maintaining cell identity: PRC2-mediated regulation of transcription and cancer

Enhancer of zeste homologue 2 (EZH2), the catalytic subunit of Polycomb repressive complex 2 (PRC2), has attracted broad research attention in the past few years because of its involvement in the development and maintenance of many types of cancer and the use of specific EZH2 inhibitors in clinical trials. Several observations show that PRC2 can have both oncogenic and tumour-suppressive functions. We propose that these apparently opposing roles of PRC2 in cancer are a consequence of the molecular function of the complex in maintaining, rather than specifying, the transcriptional repression state of its several thousand target genes.

Epigenetic regulation of epithelial-mesenchymal transition

Epithelial-mesenchymal transition (EMT) is an essential process for morphogenesis and organ development which reversibly enables polarized epithelial cells to lose their epithelial characteristics and to acquire mesenchymal properties. It is now evident that the aberrant activation of EMT is also a critical mechanism to endow epithelial cancer cells with migratory and invasive capabilities associated with metastatic competence. This dedifferentiation program is mediated by a small cohort of pleiotropic transcription factors which orchestrate a complex array of epigenetic mechanisms for the wide-spread changes in gene expression. Here, we review major epigenetic mechanisms with an emphasis on histone modifications and discuss their implications in EMT and tumor progression. We also highlight mechanisms underlying transcription regulation concerted by various chromatin-modifying proteins and EMT-inducing transcription factors at different molecular layers. Owing to the reversible nature of epigenetic modifications, a thorough understanding of their functions in EMT will not only provide new insights into our knowledge of cancer progression and metastasis, but also facilitate the development of diagnostic and therapeutic strategies for human malignancy.

microRNA-214 promotes epithelial-mesenchymal transition and metastasis in lung adenocarcinoma by targeting the suppressor-of-fused protein (Sufu)

Distant metastasis is the major cause of cancer-related deaths in patients with lung adenocarcinoma (LAD). Emerging evidence reveals that miRNA is critical for tumor metastasis. miR-214 expression has been associated with LAD progression. However, whether and how miR-214 is involved in the development and metastasis of LAD remain unaddressed. Here, we found that the expression of miR-214 was elevated in LAD and correlated positively with LAD metastasis and epithelial-mesenchymal transition (EMT). In addition, we found that miR-214 enhanced the molecular program controlling the EMT of LAD cells and promoted LAD cell metastasis both in vitro and in vivo. This study thus provides the first evidence to show that the miR-214 expression by LAD cells contributes to the EMT and metastasis of LAD. Mechanistically, Sufu was identified as an important miR-214 functional target for the EMT and metastasis of LAD, ectopic expression of Sufu alleviated miR-214 promoted EMT and metastasis. Importantly, the expression of Sufu inversely correlated with the expression of miR-214 and vimentin and positively associated with the expression of E-cadherin in the tumor cells from human LAD patients. Collectively, this study uncovers a previously unappreciated miR-214-Sufu pathway in controlling EMT and metastasis of LAD and suggests that interfering with miR-214 and Sufu could be a viable approach to treat late stage metastatic LAD patients.

Regulatory mechanisms of microRNAs in lung cancer stem cells

Increasing evidence suggests that cancer stem cells (CSCs) are a key occurrence in the process of many human cancers. Lung cancer is the most common aggressive malignancy and cause of cancer death worldwide. The research on lung cancer stem cells has been highlighted for many years. Lung CSCs seem to play a major role in lung cancer metastasis, drug resistance and tumour-self-renewal. MicroRNAs (miRNAs), a class of newly emerging small noncoding RNAs that act as post-transcriptional regulators of gene expression, have been demonstrated to serve as a vital player in fine-tuning a number of biological activities ranging from embryogenesis to programmed cell death as well as tumourigenesis. In recent years, several miRNAs have been highlighted to be specifically expressed in CSCs. The miRNA profile of CSCs is remarkably different from non-stem cancer cells. As such, many miRNAs have been shown to regulate self-renewal and differentiation properties of CSCs. In this review, we present the latest findings on miRNAs that regulate the tumour microenvironment of lung CSCs with the goal to prompt the development of novel therapeutic strategies for patients with lung cancer.

A Polycomb-mir200 loop regulates clinical outcome in bladder cancer

Bladder cancer (BC) is a highly prevalent disease, ranking fifth in the most common cancers worldwide. Various miRNAs have recently emerged as potential prognostic biomarkers in cancer. The miR-200 family, which repressed the epithelial-to-mesenchymal transition (EMT), is repressed in multiple advanced cancers. However, its expression and function in BC is still poorly understood. Here we show that miR-200 family displays increased expression, probably due to the activation of specific oncogenic signaling pathways, and reduced promoter methylation, in BC compared to normal bladder samples. Furthermore, we show that the expression of these miRNAs is decreased in high grade and stage tumors, and the down-regulation is associated with patient's poor clinical outcome. Our data indicate that the miR-200 family plays distinct roles in Non-Muscle (NMIBC) and Muscle-Invasive BC (MIBC). In MIBC, miR-200 expression post transcriptionally regulates EMT-promoting transcription factors ZEB1 and ZEB2, whereas suppresses BMI1 expression in NMIBC. Interestingly, we show that increased EZH2 and/or BMI1 expression repress the expression of miR-200 family members. Collectively, these findings support a model of BC progression through a coordinated action between the Polycomb Repression Complex (PRC) members repressing the miR-200 expression, which ultimately favors invasive BC development. Since pharmacological inhibition of EZH2 in BC cell lines lead to increased miR-200 expression, our findings may support new therapeutic strategies for BC clinical management.

miR-200b induces cell cycle arrest and represses cell growth in esophageal squamous cell carcinoma

miR-200b is a pleiotropically acting microRNA in cancer progression, representing an attractive therapeutic target. We previously identified miR-200b as an invasiveness repressor in esophageal squamous cell carcinoma (ESCC), whereas further understanding is warranted to establish it as a therapeutic target. Here, we show that miR-200b mitigates ESCC cell growth by inducing G2-phase cell cycle arrest and apoptosis. The expression/activation of multiple key cell cycle regulators such as CDK1, CDK2, CDK4 and Cyclin B, and the Wnt/β-Catenin signaling are modulated by miR-200b. We identified CDK2 and PAF (PCNA-associated factor), two important tumor-promoting factors, as direct miR-200b targets in ESCC. Correlating with the frequent loss of miR-200b in ESCC, both CDK2 and PAF levels are significantly increased in ESCC tumors compared to case-matched normal tissues (n = 119, both P < 0.0001), and correlate with markedly reduced survival (P = 0.007 and P = 0.041, respectively). Furthermore, CDK2 and PAF are also associated with poor prognosis in certain subtypes of breast cancer (n = 1802) and gastric cancer (n = 233). Although CDK2 could not significantly mediate the biological function of miR-200b, PAF siRNA knockdown phenocopied while restored expression of PAF abrogated the biological effects of miR-200b on ESCC cells. Moreover, PAF was revealed to mediate the inhibitory effects of miR-200b on Wnt/β-Catenin signaling. Collectively, the pleiotropic effects of miR-200b in ESCC highlight its potential for therapeutic intervention in this aggressive disease.

Cross Talk between Cancer and Mesenchymal Stem Cells through Extracellular Vesicles Carrying Nucleic Acids

Extracellular vesicles (EVs) are considered to be a novel complex mechanism of cell communication within the tumor microenvironment. EVs may act as vehicles for transcription factors and nucleic acids inducing epigenetic changes in recipient cells. Since tumor EVs may be present in patient biological fluids, it is important to investigate their function and molecular mechanisms of action. It has been shown that tumor cells release EVs, which are capable of regulating cell apoptosis, proliferation, invasion, and epithelial-mesenchymal transition, as well as to suppress activity of immune cells, to enhance angiogenesis, and to prepare a favorable microenvironment for metastasis. On the other hand, EVs derived from stromal cells, such as mesenchymal stem cells (MSCs), may influence the phenotype of tumor cells through reciprocal cross talk greatly influenced by the transcription factors and nucleic acids they carry. In particular, non-coding RNAs (ncRNAs), including microRNAs and long ncRNAs, have recently been identified as the main candidates for the phenotypic changes induced in the recipient cells by EVs. ncRNAs, which are important regulators of mRNA and protein expression, can function either as tumor suppressors or as oncogenes, depending on their targets. Herein, we have attempted to revise actual evidence reported in the literature on the role of EVs in tumor biology with particular regard to the cross talk of ncRNAs between cancer cells and MSCs.

miR-29s: a family of epi-miRNAs with therapeutic implications in hematologic malignancies

A wealth of studies has highlighted the biological complexity of hematologic malignancies and the role of dysregulated signal transduction pathways. Along with the crucial role of genetic abnormalities, epigenetic aberrations are nowadays emerging as relevant players in cancer development, and significant research efforts are currently focusing on mechanisms by which histone post-translational modifications, DNA methylation and noncoding RNAs contribute to the pathobiology of cancer. As a consequence, these studies have provided the rationale for the development of epigenetic drugs, such as histone deacetylase inhibitors and demethylating compounds, some of which are currently in advanced phase of pre-clinical investigation or in clinical trials. In addition, a more recent body of evidence indicates that microRNAs (miRNAs) might target effectors of the epigenetic machinery, which are aberrantly expressed or active in cancers, thus reverting those epigenetic abnormalities driving tumor initiation and progression. This review will focus on the broad epigenetic activity triggered by members of the miR-29 family, which underlines the potential of miR-29s as candidate epi-therapeutics for the treatment of hematologic malignancies.

Epigenetic regulators: Polycomb-miRNA circuits in cancer

Polycomb group (PcG) proteins belong to a family of epigenetic modifiers and play a key role in dynamic control of their target genes. Several reports have found that aberrations in PcG-microRNA (miRNA) interplay in various cancer types often associated with poor clinical prognosis. This review discusses important PcG-miRNA molecular networks which act as critical interfaces between chromatin remodeling, and transcriptional and post-transcriptional regulation of their target genes in cancer. Moreover, here are discussed several compounds influencing the activity of PcG proteins entered in clinical arena for the treatment of solid tumors, multiple myeloma and B lymphomas, thus highlighting the therapeutic potential of targeting this protein family.

Breast cancer stem cells programs: enter the (non)-code

Breast tumors exhibit a hierarchical cellular organization driven by several subpopulations of cancer stem cells (CSCs). These breast CSC subpopulations are able to infinitely self-renew and to differentiate, giving rise to tumor heterogeneity. Accumulating evidence show that breast CSCs resist conventional therapies and i`nitiate tumor relapse. The development of anti-CSCs therapies may therefore greatly improve patient survival. A better elucidation of molecular circuitries involved in stemness would offer new relevant targets. Noncoding RNAs, especially microRNAs and long noncoding RNAs, are regulators of cell identity and are notably found deregulated in breast CSCs. This review will focus on noncoding RNAs involved in CSCs biology during breast cancer initiation, maintenance, therapeutic resistance and metastatic progression. Potential clinical applications using noncoding RNAs as biomarkers or therapies will be discussed.

Dysregulated miRNA in progression of hepatocellular carcinoma: A systematic review

Hepatocellular carcinoma (HCC) is the fifth most frequent cancer and the third cause of cancer-related mortality worldwide. The primary risk factor for HCC is liver cirrhosis secondary to persistent infection with hepatitis B virus or hepatitis C virus. Although a number of cellular phenomena and molecular events have been reported to facilitate tumor initiation, progression and metastasis, the exact etiology of HCC has not yet been fully uncovered. miRNA, a class of non-coding RNA, negatively regulate post-transcriptional processes that participate in crucial biological processes, including development, differentiation, apoptosis and proliferation. In the liver, specific miRNA can be negative regulators of gene expression. Recent studies have uncovered the contribution of miRNA to cancer pathogenesis as they can function as oncogenes or tumor suppressor genes. In addition, other studies have demonstrated their potential value in the clinical management of patients with HCC as some miRNA may be used as prognostic or diagnostic markers. In this review, we summarize the current knowledge about the roles of miRNA in the carcinogenesis and progression of HCC.

MicroRNA-200b suppresses cell invasion and metastasis by inhibiting the epithelial-mesenchymal transition in cervical carcinoma

The expression of microRNA (miR)-200b is suppressed in numerous tumor types, leading to epithelial-mesenchymal transition, which enables solid tissue epithelial cancers to invade and metastasize. The present study assessed the role of miR-200b in cervical cancer with the aim of clarifying the underlying pathophysiological mechanisms and to identify potential strategies for its prevention and treatment of cervical cancer. Reverse‑transcription quantitative PCR revealed that miR‑200b was downregulated in invasive cervical carcinoma tissues compared with that in normal adjacent tissues. A Transwell migration assay indicated that transfection of cervical cancer cells with miR‑200b mimics significantly inhibited their migratory potential, while migration was enhanced in cells transfected with miR‑200b inhibitor. Furthermore, western blot analysis indicated a negative correlation between miR‑200b and mesenchymal marker vimentin as well as matrix metalloproteinase‑9, which has a key role in tumor invasion and metastasis. In addition, a positive correlation between miR‑200b and the epithelial marker E‑cadherin was revealed by western blot and immunofluorescence. The results of the present study suggested that miR‑200b suppressed the migratory potential of cervical carcinoma cells and therefore their ability to metastasize by inhibiting the epithelial-mesenchymal transition, which may be utilized for the treatment of cervical cancer.

The microRNA-200 family: small molecules with novel roles in cancer development, progression and therapy

MicroRNAs (miRNAs) are a large family of small non-coding RNAs that negatively regulate protein-coding gene expression post-transcriptionally via base pairing between the 5′ seed region of a miRNA and the 3′ untranslated region (3′UTR) of a messenger RNA (mRNA). Recent evidence has supported the critical role that miRNAs play in many diseases including cancer. The miR-200 family consisting of 5 members (miR-200a, -200b, -200c, -141, -429) is an emerging miRNA family that has been shown to play crucial roles in cancer initiation and metastasis, and potentially be important for the diagnosis and treatment of cancer. While miR-200s were found to be critically involved in the metastatic colonization to the lungs in mouse mammary xenograft tumor models, a large number of studies demonstrated their strong suppressive effects on cell transformation, cancer cell proliferation, migration, invasion, tumor growth and metastasis. This review aims to discuss research findings about the role of the miR-200 family in cancer initiation, each step of cancer metastatic cascade, cancer diagnosis and treatment. A comprehensive summary of currently validated miR-200 targets is also presented. It is concluded that miR-200 family may serve as novel targets for the therapy of multiple types of cancer.

Androgen receptor expands the population of cancer stem cells in upper urinary tract urothelial cell carcinoma cells

Androgen receptor (AR) affects the development and progression of upper urinary tract urothelial cell carcinoma (UUTUC). However, the regulatory mechanism exerted by AR to affect UUTUC cells remains unclear. Here we investigated whether AR promotes UUTUC development and progression, possibly by expanding the population of cancer stem cells (CSCs), which are a particular population of cells within cancer cells responsible for tumor initiation, drug resistance and metastasis. We compared UUTUC cells with or without the addition of AR on their CSC population with flow cytometry, colony formation and sphere formation assay to determine the effect of AR on CSC activity, and real-time PCR was used to detect the expression stemness genes and miRNAs. In vivo tumor formation was evaluated with the implantation of cancer cells in nude mice. We found that the addition of AR in UUTUC cells, significantly increased the population of CSC, clonogenicity, sphere formation and the expression of stemness genes (Oct4, Bmi1 and Nanog), altered CSC-related miRNA profile, as well as promoted epithelial mesenchymal transition (EMT). And AR inhibitor, enzalutamide was shown to suppress AR's effect on tumorsphere formation. Furthermore, in an immune-deficient mouse model, the addition of AR in UUTUC cells also increased the tumor formation capacity. This study will help us better understand the extent to which AR contributes to UUTUC progression by expanding their CSC population and capacity. Our findings could explain high incidence of UUTUC observed in males. And targeting AR may lead to novel therapeutic approaches for genetically diversified urothelial carcinomas in precision medicine era.

Analysis of EZH2: micro-RNA network in low and high grade astrocytic tumors

Enhancer of Zeste homologue2 (EZH2) is an epigenetic regulator that functions as oncogene in astrocytic tumors, however, EZH2 regulation remains little studied. In this study, we measured EZH2 levels in low (Gr-II,DA) and high grade (Gr-IV,GBM) astrocytic tumors and found significant increased EZH2 transcript level with grade(median DA-8.5, GBM-28.9).However, a different trend was reflected in protein levels, with GBMs showing high EZH2 LI(median-26.5) compared to DA (median 0.3). This difference in correlation of EZH2 protein and RNA levels suggested post-transcriptional regulation of EZH2, likely mediated by miRNAs. We selected eleven miRNAs that strongly predicted to target EZH2 and measured their expression. Three miRNAs (miR-26a-5p,miR27a-3p and miR-498) showed significant correlation with EZH2 protein, suggesting them as regulators of EZH2, however miR-26a-5p levels decreased with grade. ChIP analyses revealed H3K27me3 modifications in miR-26a promoter suggesting feedback loop between EZH2 and miR26a. We further measured six downstream miRNA targets of EZH2 and found significant downregulation of four (miR-181a/b and 200b/c) in GBM. Interestingly, EZH2 associated miRNAs were predicted to target 25 genes in glioma-pathway, suggesting their role in tumor formation or progression. Collectively, our work suggests EZH2 and its miRNA interactors may serve as promising biomarkers for progression of astrocytic tumors and may offer novel therapeutic strategies.

Regulation of miR-200c/141 expression by intergenic DNA-looping and transcriptional read-through

The miR-200 family members have been implicated in stress responses and ovarian tumorigenesis. Here, we find that miR-200c/141 transcription is intimately linked to the transcription of the proximal upstream gene PTPN6 (SHP1) in all physiological conditions tested. PTPN6 and miR-200c/141 are transcriptionally co-regulated by two complementary mechanisms. First, a bypass of the regular PTPN6 polyadenylation signal allows the transcription of the downstream miR-200c/141. Second, the promoters of the PTPN6 and miR-200c/141 transcription units physically interact through a 3-dimensional DNA loop and exhibit similar epigenetic regulation. Our findings highlight that transcription of intergenic miRNAs is a novel outcome of transcriptional read-through and reveal a yet unexplored type of DNA loop associating two closely located promoters. These mechanisms have significant relevance in ovarian cancers and stress response, pathophysiological conditions in which miR-200c/141 exert key functions.

The miR-141/200 familly of micro RNAs control oxidative stress and impact on ovarian tumorigenesis. Here the authors show that the transcription of miR-200c/141 is regulated through transcriptional read-through of the upstream gene PTPN6, and DNA looping linking the PTPN6 and miR-200c/141 promoters.

Non-coding RNAs in Mammary Gland Development and Disease

Non-coding RNAs (ncRNAs) are untranslated RNA molecules that function to regulate the expression of numerous genes and associated biochemical pathways and cellular functions. NcRNAs include small interfering RNAs (siRNAs), microRNAs (miRNAs), PIWI-interacting RNAs (piRNAs), small nucleolar RNAs (snoRNAs) and long non-coding RNAs (lncRNAs). They participate in the regulation of all developmental processes and are frequently aberrantly expressed or functionally defective in disease. This Chapter will focus on the role of ncRNAs, in particular miRNAs and lncRNAs, in mammary gland development and disease.

lnflammation-induced epigenetic switches in cancer

The link between inflammation and cancer is well established. Chronic inflammation promotes cancer initiation and progression. Various studies showed that the underlying mechanisms involve epigenetic alterations. These epigenetic alterations might culminate into an epigenetic switch that transforms premalignant cells into tumor cells or non-invasive into invasive tumor cells, thereby promoting metastasis. Epigenetic switches require an initiating event, which can be inflammation, whereas the resulting phenotype is inherited without the initiating signal. Epigenetic switches are induced and maintained by DNA methylation, histone modifications, polycomb group (PcG)/trithorax group (TrxG) proteins, and feedback loops consisting of transcription factors and microRNAs. Since epigenetic switches are reversible, they might represent an important basis for the design of novel anticancer therapeutics. This review summarizes published evidence of epigenetic switches in cancer development that are induced by inflammation.

Common stemness regulators of embryonic and cancer stem cells

Pluripotency of embryonic stem cells (ESCs) and induced pluripotent stem cells is regulated by a well characterized gene transcription circuitry. The circuitry is assembled by ESC specific transcription factors, signal transducing molecules and epigenetic regulators. Growing understanding of stem-like cells, albeit of more complex phenotypes, present in tumors (cancer stem cells), provides a common conceptual and research framework for basic and applied stem cell biology. In this review, we highlight current results on biomarkers, gene signatures, signaling pathways and epigenetic regulators that are common in embryonic and cancer stem cells. We discuss their role in determining the cell phenotype and finally, their potential use to design next generation biological and pharmaceutical approaches for regenerative medicine and cancer therapies.

Epithelial-mesenchymal plasticity of breast cancer stem cells: implications for metastasis and therapeutic resistance

Over the past several decades the traditional view of cancer being a homogeneous mass of rapid proliferating malignant cells is being replaced by a model of ever increasing complexity, which points out that cancers are complex tissues composed of multiple cell types. A large variety of immune and other host cells constitute the tumor microenvironment, which supports the growth and progression of the tumor where individual cancer cells evolve with increasing phenotypic and genetic heterogeneity. Furthermore, it has also become clear that, in addition to this cellular and genetic heterogeneity, most tumors exhibit a hierarchical organization composed of tumor cells displaying divergent lineage markers and at the apex of this hierarchy are cells capable of self-renewal. These "cancer stem cells" not only drive tumor growth, but also mediate metastasis and contribute to treatment resistance. Besides displaying remarkable genetic and phenotypic heterogeneity, cancer stem cells maintain plasticity to transition between mesenchymal-like (EMT) and epithelial-like (MET) states in a process regulated by the tumor microenvironment. These stem cell state transitions may play a fundamental role in the process of tumor metastasis. In this review, we will discuss emerging knowledge regarding the plasticity of cancer stem cells and the role that this plasticity plays in tumor metastasis. We also discuss the implications of these findings for the development of cancer stem cell targeted therapeutics.

Molecular mechanisms controlling asymmetric and symmetric self-renewal of cancer stem cells

Cancer stem cells (CSCs), or alternatively called tumor initiating cells (TICs), are a subpopulation of tumor cells, which possesses the ability to self-renew and differentiate into bulk tumor mass. An accumulating body of evidence suggests that CSCs contribute to the growth and recurrence of tumors and the resistance to chemo- and radiotherapy. CSCs achieve self-renewal through asymmetric division, in which one daughter cell retains the self-renewal ability, and the other is destined to differentiation. Recent studies revealed the mechanisms of asymmetric division in normal stem cells (NSCs) and, to a limited degree, CSCs as well. Asymmetric division initiates when a set of polarity-determining proteins mark the apical side of mother stem cells, which arranges the unequal alignment of mitotic spindle and centrosomes along the apical-basal polarity axis. This subsequently guides the recruitment of fate-determining proteins to the basal side of mother cells. Following cytokinesis, two daughter cells unequally inherit centrosomes, differentiation-promoting fate determinants, and other proteins involved in the maintenance of stemness. Modulation of asymmetric and symmetric division of CSCs may provide new strategies for dual targeting of CSCs and the bulk tumor mass. In this review, we discuss the current understanding of the mechanisms by which NSCs and CSCs achieve asymmetric division, including the functions of polarity- and fate-determining factors.

The roles of ncRNAs and histone-modifiers in regulating breast cancer stem cells

Cancer stem cells (CSCs), a subpopulation of cancer cells with ability of initiating tumorigenesis, exist in many kinds of tumors including breast cancer. Cancer stem cells contribute to treatment resistance and relapse. Conventional treatments only kill differentiated cancer cells, but spare CSCs. Combining conventional treatments with therapeutic drugs targeting to CSCs will eradicate cancer cells more efficiently. Studying the molecular mechanisms of CSCs regulation is essential for developing new therapeutic strategies. Growing evidences showed CSCs are regulated by non-coding RNA (ncRNA) including microRNAs and long non-coding RNAs (lncRNAs), and histone-modifiers, such as let-7, miR-93, miR-100, HOTAIR, Bmi-1 and EZH2. Herein we review the roles of microRNAs, lncRNAs and histone-modifiers especially Polycomb family proteins in regulating breast cancer stem cells (BCSCs).

Cancer stem cells: The potential of carbon ion beam radiation and new radiosensitizers (Review)

Cancer stem cells (CSCs) are a small population of cells in cancer with stem-like properties such as cell proliferation, multiple differentiation and tumor initiation capacities. CSCs are therapy-resistant and cause cancer metastasis and recurrence. One key issue in cancer therapy is how to target and eliminate CSCs, in order to cure cancer completely without relapse and metastasis. To target CSCs, many cell surface markers, DNAs and microRNAs are considered as CSC markers. To date, the majority of the reported markers are not very specific to CSCs and are also present in non-CSCs. However, the combination of several markers is quite valuable for identifying and targeting CSCs, although more specific identification methods are needed. While CSCs are considered as critical therapeutic targets, useful treatment methods remain to be established. Epigenetic gene regulators, microRNAs, are associated with tumor initiation and progression. MicroRNAs have been recently considered as promising therapeutic targets, which can alter the therapeutic resistance of CSCs through epigenetic modification. Moreover, carbon ion beam radiotherapy is a promising treatment for CSCs. Evidence indicates that the carbon ion beam is more effective against CSCs than the conventional X-ray beam. Combination therapies of radiosensitizing microRNAs and carbon ion beam radiotherapy may be a promising cancer strategy. This review focuses on the identification and treatment resistance of CSCs and the potential of microRNAs as new radiosensitizers and carbon ion beam radiotherapy as a promising therapeutic strategy against CSCs.

MiR-449a suppresses cell invasion by inhibiting MAP2K1 in non-small cell lung cancer

Increasing evidence reveals that deregulation of miRNAs contributes to carcinogenesis of the human non-small cell lung cancer (NSCLC). Our study discovered that the expression of miR-449a was markedly decreased in NSCLC cells with high metastatic capacity and tissues of positive lymph node metastasis. Moreover, our results showed that miR-449a could act as a tumor suppressor by inhibiting the invasion of NSCLC cells in vitro and in vivo. Mechanistically, miR-449a inhibited the expression of MAP2K1 by direct targeting its 3'UTR, and regulated the activity of MEK1/ERK1/2/c-Jun pathway through an auto-regulatory feedback loop. Furthermore, the histone methylation mediated the decreased expression of miR-449a through SUZ12. Taken together, the novel connection between miR-449a and MAP2K1 demonstrated here provided a new, potential therapeutic target for the treatment of non-small cell lung cancer.

Activation of EZH2 and SUZ12 Regulated by E2F1 Predicts the Disease Progression and Aggressive Characteristics of Bladder Cancer

PURPOSE

Previous study identified E2F1 as a key mediator of non-muscle-invasive bladder cancer (NMIBC) progression. The aim of this study was to identify the E2F1-related genes associated with poor prognosis and aggressive characteristics of bladder cancer.

EXPERIMENTAL DESIGN

Microarray analysis was performed to find E2F1-related genes associated with tumor progression and aggressiveness in the gene expression data from 165 primary patients with bladder cancer. The biologic activity of E2F1-related genes in tumor progression and aggressiveness was confirmed with experimental assays using bladder cancer cells and tumor xenograft assay.

RESULTS

The expression of E2F1 was significantly associated with EZH2 and SUZ12. The overexpression of E2F1, EZH2, and SUZ12 enhanced cancer progression including cell colony formation, migration, and invasiveness. Knockdown of these genes reduced motility, blocked invasion, and decreased tumor size in vivo. E2F1 bound the proximal EZH2 and SUZ12 promoter to activate transcription, suggesting that E2F1 and its downstream effectors, EZH2 and SUZ12, could be important mediators for the cancer progression. In addition, we confirmed an association between these genes and aggressive characteristics. Interestingly, the treatment of anticancer drugs to the cells overexpressing E2F1, EZH2, and SUZ12 induced the expression of CD44, KLF4, OCT4, and ABCG2 known as cancer stem cell (CSC)-related genes.

CONCLUSIONS

The link between E2F1, EZH2, and/or SUZ12 revealed that E2f1 directly regulates transcription of the EZH2 and SUZ12 genes. The signature of E2F1-EZH2-SUZ12 shows a predictive value for prognosis in bladder tumors and the E2F1-EZH2-SUZ12-driven transcriptional events may regulate the cancer aggressiveness and chemo-resistance, which may provide opportunity for development of new treatment modalities.

MicroRNA-494 is a master epigenetic regulator of multiple invasion-suppressor microRNAs by targeting ten eleven translocation 1 in invasive human hepatocellular carcinoma tumors

Vascular invasion provides a direct route for tumor metastasis. The degree to which microRNA (miRNA) expression plays a role in tumor vascular invasion is unclear. Here, we report that miR-494 is up-regulated in human hepatocellular carcinoma (HCC) tumors with vascular invasion and can promote HCC cell invasiveness by gene inactivation of multiple invasion-suppressor miRNAs. Our results show that ten eleven translocation (TET) methylcytosine dioxygenase, predominantly TET1 in HCC cells, is a direct target of miR-494. The reduced 5'-hydroxymethylcytosine levels observed in the proximal cytosine-phosphate-guanine (CpG) regions of multiple invasion-suppressor miRNA genes are strongly associated with their transcriptional repression upon miR-494 overexpression, whereas enforced DNA demethylation can abolish the repression. Furthermore, TET1 knockdown shows a similar effect as miR-494 overexpression. Conversely, miR-494 inhibition or enforced TET1 expression is able to restore invasion-suppressor miRNAs and inhibit miR-494-mediated HCC cell invasion.

CONCLUSIONS

miR-494 can trigger gene silencing of multiple invasion-suppressor miRNAs by inhibiting genomic DNA demethylation by direct targeting of TET1, thereby leading to tumor vascular invasion.

MicroRNAs: New Biomarkers for Diagnosis, Prognosis, Therapy Prediction and Therapeutic Tools for Breast Cancer

Dysregulation of microRNAs (miRNAs) is involved in the initiation and progression of several human cancers, including breast cancer (BC), as strong evidence has been found that miRNAs can act as oncogenes or tumor suppressor genes. This review presents the state of the art on the role of miRNAs in the diagnosis, prognosis, and therapy of BC. Based on the results obtained in the last decade, some miRNAs are emerging as biomarkers of BC for diagnosis (i.e., miR-9, miR-10b, and miR-17-5p), prognosis (i.e., miR-148a and miR-335), and prediction of therapeutic outcomes (i.e., miR-30c, miR-187, and miR-339-5p) and have important roles in the control of BC hallmark functions such as invasion, metastasis, proliferation, resting death, apoptosis, and genomic instability. Other miRNAs are of interest as new, easily accessible, affordable, non-invasive tools for the personalized management of patients with BC because they are circulating in body fluids (e.g., miR-155 and miR-210). In particular, circulating multiple miRNA profiles are showing better diagnostic and prognostic performance as well as better sensitivity than individual miRNAs in BC. New miRNA-based drugs are also promising therapy for BC (e.g., miR-9, miR-21, miR34a, miR145, and miR150), and other miRNAs are showing a fundamental role in modulation of the response to other non-miRNA treatments, being able to increase their efficacy (e.g., miR-21, miR34a, miR195, miR200c, and miR203 in combination with chemotherapy).

MicroRNAs: biogenesis, roles for carcinogenesis and as potential biomarkers for cancer diagnosis and prognosis

MicroRNAs (miRNAs) are short non-coding RNAs of 20-24 nucleotides that play important roles in carcinogenesis. Accordingly, miRNAs control numerous cancer-relevant biological events such as cell proliferation, cell cycle control, metabolism and apoptosis. In this review, we summarize the current knowledge and concepts concerning the biogenesis of miRNAs, miRNA roles in cancer and their potential as biomarkers for cancer diagnosis and prognosis including the regulation of key cancer-related pathways, such as cell cycle control and miRNA dysregulation. Moreover, microRNA molecules are already receiving the attention of world researchers as therapeutic targets and agents. Therefore, in-depth knowledge of microRNAs has the potential not only to identify their roles in cancer, but also to exploit them as potential biomarkers for cancer diagnosis and identify therapeutic targets for new drug discovery.

miR-200a inhibits migration of triple-negative breast cancer cells through direct repression of the EPHA2 oncogene

Triple-negative breast cancer (TNBC) is characterized by aggressiveness and affects 10-20% of breast cancer patients. Since TNBC lacks expression of ERα, PR and HER2, existing targeted treatments are not effective and the survival is poor. In this study, we demonstrate that the tumor suppressor microRNA miR-200a directly regulates the oncogene EPH receptor A2 (EPHA2) and modulates TNBC migration. We show that EPHA2 expression is correlated with poor survival specifically in basal-like breast cancer and that its expression is repressed by miR-200a through direct interaction with the 3'UTR of EPHA2. This regulation subsequently affects the downstream activation of AMP-activated protein kinase (AMPK) and results in decreased cell migration of TNBC. We establish that miR-200a directs cell migration in a dual manner; in addition to regulating the well-characterized E-cadherin pathway it also regulates a EPHA2 pathway. The miR-200a-EPHA2 axis is a novel mechanism highlighting the possibility of utilizing miR-200a delivery to target TNBC metastases.

Tamoxifen induces a pluripotency signature in breast cancer cells and human tumors

Tamoxifen is the treatment of choice in estrogen receptor alpha breast cancer patients that are eligible for adjuvant endocrine therapy. However, ∼50% of ERα-positive tumors exhibit intrinsic or rapidly acquire resistance to endocrine treatment. Unfortunately, prediction of de novo resistance to endocrine therapy and/or assessment of relapse likelihood remain difficult. While several mechanisms regulating the acquisition and the maintenance of endocrine resistance have been reported, there are several aspects of this phenomenon that need to be further elucidated. Altered metabolic fate of tamoxifen within patients and emergence of tamoxifen-resistant clones, driven by evolution of the disease phenotype during treatment, appear as the most compelling hypotheses so far. In addition, tamoxifen was reported to induce pluripotency in breast cancer cell lines, in vitro. In this context, we have performed a whole transcriptome analysis of an ERα-positive (T47D) and a triple-negative breast cancer cell line (MDA-MB-231), exposed to tamoxifen for a short time frame (hours), in order to identify how early pluripotency-related effects of tamoxifen may occur. Our ultimate goal was to identify whether the transcriptional actions of tamoxifen related to induction of pluripotency are mediated through specific ER-dependent or independent mechanisms. We report that even as early as 3 hours after the exposure of breast cancer cells to tamoxifen, a subset of ERα-dependent genes associated with developmental processes and pluripotency are induced and this is accompanied by specific phenotypic changes (expression of pluripotency-related proteins). Furthermore we report an association between the increased expression of pluripotency-related genes in ERα-positive breast cancer tissues samples and disease relapse after tamoxifen therapy. Finally we describe that in a small group of ERα-positive breast cancer patients, with disease relapse after surgery and tamoxifen treatment, ALDH1A1 (a marker of pluripotency in epithelial cancers which is absent in normal breast tissue) is increased in relapsing tumors, with a concurrent modification of its intra-cellular localization. Our data could be of value in the discrimination of patients susceptible to develop tamoxifen resistance and in the selection of optimized patient-tailored therapies.

Targeting CD133 in the enhancement of chemosensitivity in oral squamous cell carcinoma-derived side population cancer stem cells

BACKGROUND

Oral squamous cell carcinoma (OSCC) is one of the most common cancers in the world. Previously, we enriched a subpopulation of OSCC-derived cancer stem cells (OSCC-CSCs), and identified CD133 as an OSCC-CSC marker.

METHOD

We determined the function of CD133 on chemosensitivity of oral cancer CSCs by silencing CD133.

RESULTS

Initially, we observed that the expression profile of CD133 in OSCC-side population (OSCC-SPs) cells, which exerted properties of CSCs, was significantly upregulated than that of major population (MPs) cells of OSCCs. The cell viability experiments showed that SPs were more chemoresistant compared with major populations. Importantly, targeting CD133 ameliorated the drug resistance of OSCC-SPs to cisplatin treatment. Targeting CD133 and cisplatin co-treatment led to the maximal inhibition on tumor initiating properties in OSCC-SPs.

CONCLUSION

Side population cells with CSCs properties existed in OSCCs, and silencing CD133 exhibited a prominent therapeutic effect in enhancing the sensitivity of chemotherapy in OSCC through elimination of CSCs. © 2015 Wiley Periodicals, Inc. Head Neck 38: E231-E238, 2016.

Reciprocal regulation of amino acid import and epigenetic state through Lat1 and EZH2

Lat1 (SLC7A5) is an amino acid transporter often required for tumor cell import of essential amino acids (AA) including Methionine (Met). Met is the obligate precursor of S-adenosylmethionine (SAM), the methyl donor utilized by all methyltransferases including the polycomb repressor complex (PRC2)-specific EZH2. Cell populations sorted for surface Lat1 exhibit activated EZH2, enrichment for Met-cycle intermediates, and aggressive tumor growth in mice. In agreement, EZH2 and Lat1 expression are co-regulated in models of cancer cell differentiation and co-expression is observed at the invasive front of human lung tumors. EZH2 knockdown or small-molecule inhibition leads to de-repression of RXRα resulting in reduced Lat1 expression. Our results describe a Lat1-EZH2 positive feedback loop illustrated by AA depletion or Lat1 knockdown resulting in SAM reduction and concomitant reduction in EZH2 activity. shRNA-mediated knockdown of Lat1 results in tumor growth inhibition and points to Lat1 as a potential therapeutic target.

Antioxidant Mechanisms and ROS-Related MicroRNAs in Cancer Stem Cells

Increasing evidence indicates that most of the tumors are sustained by a distinct population of cancer stem cells (CSCs), which are responsible for growth, metastasis, invasion, and recurrence. CSCs are typically characterized by self-renewal, the key biological process allowing continuous tumor proliferation, as well as by differentiation potential, which leads to the formation of the bulk of the tumor mass. CSCs have several advantages over the differentiated cancer cell populations, including the resistance to radio- and chemotherapy, and their gene-expression programs have been shown to correlate with poor clinical outcome, further supporting the relevance of stemness properties in cancer. The observation that CSCs possess enhanced mechanisms of protection from reactive oxygen species (ROS) induced stress and a different metabolism from the differentiated part of the tumor has paved the way to develop drugs targeting CSC specific signaling. In this review, we describe the role of ROS and of ROS-related microRNAs in the establishment and maintenance of self-renewal and differentiation capacities of CSCs.