miR-124 and miR-137 inhibit proliferation of glioblastoma multiforme cells and induce differentiation of brain tumor stem cells

MicroRNA-200a inhibits CD133/1+ ovarian cancer stem cells migration and invasion by targeting E-cadherin repressor ZEB2

OBJECTIVES

MicroRNA-200a (miR-200a) has been reported to be a prognostic marker and to play an important role in ovarian cancer progression. The aim of the study was to elucidate the mechanism of miR-200a involved in migration and invasion in CD133/1+ ovarian cancer stem cells (OCSCs).

METHODS

The expression of miR-200a between CD133/1+ and CD133/1- cells was performed using real-time PCR, and wound healing assay and matrigel invasion assay were used to detect migration and invasion of CD133/1+ cells, respectively, target gene regulated by miR-200a was detected using Dual Luciferase Reporter system, The expression levels of target gene were confirmed using real-time PCR and western blot.

RESULTS

miR-200a was downregulated in CD133/1+ cells compared with CD133/1- cells, and overexpression of miR-200a significantly reduced CD133/1+ cells migration and invasion compare with negative control (NC) (p<0.05). The 3'-UTR of ZEB2 mRNA, a transcriptional repressor of E-cadherin, was found to be regulated directly by miR-200a. In addition, when miR-200a was overexpressed in CD133/1+ cells, the mRNA and protein levels of ZEB2 were both suppressed, which resulted in an increase in the E-cadherin expression level, suggesting that ZEB2 was a functionally important target of miR-200a in CD133/1+ cells.

CONCLUSIONS

Our results suggest that loss of expression of miR-200a may play a critical role in the repression of E-cadherin by ZEB2, thereby enhancing migration and invasion in CD133/1+ cells.

A ten-microRNA expression signature predicts survival in glioblastoma

Glioblastoma (GBM) is the most common and aggressive primary brain tumor with very poor patient median survival. To identify a microRNA (miRNA) expression signature that can predict GBM patient survival, we analyzed the miRNA expression data of GBM patients (n = 222) derived from The Cancer Genome Atlas (TCGA) dataset. We divided the patients randomly into training and testing sets with equal number in each group. We identified 10 significant miRNAs using Cox regression analysis on the training set and formulated a risk score based on the expression signature of these miRNAs that segregated the patients into high and low risk groups with significantly different survival times (hazard ratio [HR] = 2.4; 95% CI = 1.4–3.8; p<0.0001). Of these 10 miRNAs, 7 were found to be risky miRNAs and 3 were found to be protective. This signature was independently validated in the testing set (HR = 1.7; 95% CI = 1.1–2.8; p = 0.002). GBM patients with high risk scores had overall poor survival compared to the patients with low risk scores. Overall survival among the entire patient set was 35.0% at 2 years, 21.5% at 3 years, 18.5% at 4 years and 11.8% at 5 years in the low risk group, versus 11.0%, 5.5%, 0.0 and 0.0% respectively in the high risk group (HR = 2.0; 95% CI = 1.4–2.8; p<0.0001). Cox multivariate analysis with patient age as a covariate on the entire patient set identified risk score based on the 10 miRNA expression signature to be an independent predictor of patient survival (HR = 1.120; 95% CI = 1.04–1.20; p = 0.003). Thus we have identified a miRNA expression signature that can predict GBM patient survival. These findings may have implications in the understanding of gliomagenesis, development of targeted therapy and selection of high risk cancer patients for adjuvant therapy.

MicroRNA gene dosage alterations and drug response in lung cancer

Chemotherapy resistance is a key contributor to the dismal prognoses for lung cancer patients. While the majority of studies have focused on sequence mutations and expression changes in protein-coding genes, recent reports have suggested that microRNA (miRNA) expression changes also play an influential role in chemotherapy response. However, the role of genetic alterations at miRNA loci in the context of chemotherapy response has yet to be investigated. In this study, we demonstrate the application of an integrative, multidimensional approach in order to identify miRNAs that are associated with chemotherapeutic resistance and sensitivity utilizing publicly available drug response, miRNA loci copy number, miRNA expression, and mRNA expression data from independent resources. By instigating a logical stepwise strategy, we have identified specific miRNAs that are associated with resistance to several chemotherapeutic agents and provide a proof of principle demonstration of how these various databases may be exploited to derive relevant pharmacogenomic results.

MicroRNAs and epigenetics

MicroRNAs (miRNAs) comprise species of short noncoding RNA that regulate gene expression post-transcriptionally. Recent studies have demonstrated that epigenetic mechanisms, including DNA methylation and histone modification, not only regulate the expression of protein-encoding genes, but also miRNAs, such as let-7a, miR-9, miR-34a, miR-124, miR-137, miR-148 and miR-203. Conversely, another subset of miRNAs controls the expression of important epigenetic regulators, including DNA methyltransferases, histone deacetylases and polycomb group genes. This complicated network of feedback between miRNAs and epigenetic pathways appears to form an epigenetics-miRNA regulatory circuit, and to organize the whole gene expression profile. When this regulatory circuit is disrupted, normal physiological functions are interfered with, contributing to various disease processes. The present minireview details recent discoveries involving the epigenetics-miRNA regulatory circuit, suggesting possible biological insights into gene-regulatory mechanisms that may underlie a variety of diseases.

A developmental taxonomy of glioblastoma defined and maintained by MicroRNAs

mRNA expression profiling has suggested the existence of multiple glioblastoma subclasses, but their number and characteristics vary among studies and the etiology underlying their development is unclear. In this study, we analyzed 261 microRNA expression profiles from The Cancer Genome Atlas (TCGA), identifying five clinically and genetically distinct subclasses of glioblastoma that each related to a different neural precursor cell type. These microRNA-based glioblastoma subclasses displayed microRNA and mRNA expression signatures resembling those of radial glia, oligoneuronal precursors, neuronal precursors, neuroepithelial/neural crest precursors, or astrocyte precursors. Each subclass was determined to be genetically distinct, based on the significant differences they displayed in terms of patient race, age, treatment response, and survival. We also identified several microRNAs as potent regulators of subclass-specific gene expression networks in glioblastoma. Foremost among these is miR-9, which suppresses mesenchymal differentiation in glioblastoma by downregulating expression of JAK kinases and inhibiting activation of STAT3. Our findings suggest that microRNAs are important determinants of glioblastoma subclasses through their ability to regulate developmental growth and differentiation programs in several transformed neural precursor cell types. Taken together, our results define developmental microRNA expression signatures that both characterize and contribute to the phenotypic diversity of glioblastoma subclasses, thereby providing an expanded framework for understanding the pathogenesis of glioblastoma in a human neurodevelopmental context.

Potential role of miRNAs and their inhibitors in glioma treatment

Recent years have seen an intense period of research on the functions of miRNAs, recently discovered key regulators of gene expression that act through suppression of translation of target mRNAs. Several hundred miRNAs have been identified in humans, and these show characteristic expression patterns, depending on tissue type, cell type or environmental stimuli. Like other types of cancer, the brain tumor glioblastoma shows a distinct miRNA expression signature, and a number of recent studies have linked these miRNA alterations to key hallmarks of glioblastoma including proliferation, survival, invasion, angiogenesis and stem cell-like behavior. These studies have opened the door to the possibility of utilizing miRNAs or miRNA antagonists as therapeutic agents for the treatment of brain tumors.

Temporal differences in microRNA expression patterns in astrocytes and neurons after ischemic injury

MicroRNAs (miRNAs) are small, non-protein-coding RNA molecules that modulate gene translation. Their expression is altered in many central nervous system (CNS) injuries suggesting a role in the cellular response to stress. Current studies in brain tissue have not yet described the cell-specific temporal miRNA expression patterns following ischemic injury. In this study, we analyzed the expression alterations of a set of miRNAs in neurons and astrocytes subjected to 60 minutes of ischemia and collected at different time-points following this injury. To mimic ischemic conditions and reperfusion in vitro, cortical primary neuronal and astrocytic cultures prepared from fetal rats were first placed in oxygen and glucose deprived (OGD) medium for 60 minutes, followed by their transfer into normoxic pre-conditioned medium. Total RNA was extracted at different time-points after the termination of the ischemic insult and the expression levels of miRNAs were measured. In neurons exposed to OGD, expression of miR-29b was upregulated 2-fold within 6 h and up to 4-fold at 24 h post-OGD, whereas induction of miR-21 was upregulated 2-fold after 24 h when compared to expression in neurons under normoxic conditions. In contrast, in astrocytes, miR-29b and miR-21 were upregulated only after 12 h. MiR-30b, 107, and 137 showed expression alteration in astrocytes, but not in neurons. Furthermore, we show that expression of miR-29b was significantly decreased in neurons exposed to Insulin-Like Growth Factor I (IGF-I), a well documented neuroprotectant in ischemic models. Our study indicates that miRNAs expression is altered in neurons and astrocytes after ischemic injury. Furthermore, we found that following OGD, specific miRNAs have unique cell-specific temporal expression patterns in CNS. Therefore the specific role of each miRNA in different intracellular processes in ischemic brain and the relevance of their temporal and spatial expression patterns warrant further investigation that may lead to novel strategies for therapeutic interventions.

Age-dependent expression of MeCP2 in a heterozygous mosaic mouse model

Functional deficiency of the X-linked methyl-CPG binding protein 2 (MeCP2) leads to the neurodevelopmental disorder Rett syndrome (RTT). Due to random X-chromosome inactivation (XCI), most RTT patients are females who are heterozygous for the MECP2 mutation and therefore mosaic in MeCP2 deficiency. Some MECP2 heterozygote females are found to have unbalanced XCI, which may affect the severity of neurological symptoms seen in these patients; however, whether MeCP2 deficiency affects XCI in the postnatal and adult brain is unclear. Here we developed a novel MeCP2 mosaic mouse model in which the X chromosome containing the wild-type Mecp2 expresses a green fluorescent protein (GFP) transgene, while the X chromosome harboring the mutant Mecp2 does not. Due to random XCI, the neurons in the female MeCP2 mosaic mice express either wild-type MeCP2 (GFP+) or mutant MeCP2 (GFP-), and the two can be distinguished by GFP fluorescence. Using this mouse model, we evaluated XCI in female heterozygote mice from 3 to 9 months after birth. We found that MeCP2 deficiency does not affect XCI at 3 months of age, but does alter the proportion of wild-type MeCP2-expressing neurons at later ages, suggesting that MeCP2 impacts XCI patterns in an age-dependent manner. Given the important function of MeCP2 in neuronal development, our data could shed light on how MeCP2 deficiency affects postnatal brain functions and the dynamic changes in the neurological symptoms of RTT.

Prediction of Associations between microRNAs and Gene Expression in Glioma Biology

Despite progress in the determination of miR interactions, their regulatory role in cancer is only beginning to be unraveled. Utilizing gene expression data from 27 glioblastoma samples we found that the mere knowledge of physical interactions between specific mRNAs and miRs can be used to determine associated regulatory interactions, allowing us to identify 626 associated interactions, involving 128 miRs that putatively modulate the expression of 246 mRNAs. Experimentally determining the expression of miRs, we found an over-representation of over(under)-expressed miRs with various predicted mRNA target sequences. Such significantly associated miRs that putatively bind over-expressed genes strongly tend to have binding sites nearby the 3′UTR of the corresponding mRNAs, suggesting that the presence of the miRs near the translation stop site may be a factor in their regulatory ability. Our analysis predicted a significant association between miR-128 and the protein kinase WEE1, which we subsequently validated experimentally by showing that the over-expression of the naturally under-expressed miR-128 in glioma cells resulted in the inhibition of WEE1 in glioblastoma cells.

MicroRNA as a Novel Modulator in Head and Neck Squamous Carcinoma

MicroRNAs have emerged as important regulators of cell proliferation, development, cancer formation, stress responses, cell death, and other physiological conditions in the past decade. On the other hand, head and neck cancer is one of the top ten most common cancers worldwide. Recent advances in microRNAs have revealed their prominent role in regulating gene expression and provided new aspects of applications in diagnosis, prognosis, and therapeutic strategies in head and neck squamous carcinoma. In the present paper, we focus on microRNAs showing significant differences between normal and tumor cells or between cells with differential ability of metastasis. We also emphasize specific microRNAs that could modulate tumor cell properties, such as apoptosis, metastasis, and proliferation. These microRNAs possess the potential to be applied on clinical therapy in the future.

The Role of Cancer Stem Cells (CD133+) in Malignant Gliomas

Malignant gliomas, particularly glioblastoma multiforme (GBM) tumors, are very difficult to treat by conventional approaches. Although most of the tumor mass can be removed by surgical resection, radiotherapy, and chemotherapy, it eventually recurs. There is growing evidence that cancer stem cells (CSCs) play an important role in tumor recurrence. These stem cells are radioresistant and chemoresistant. The most commonly used tumor marker for CSCs is CD133. The amount of CSC component is closely correlated with tumor malignancy grading. Isolating, identifying, and treating CSCs as the target is crucial for treating malignant gliomas. CSC-associated vascular endothelial growth factor (VEGF) promotes tumor angiogenesis, tumor hemorrhage, and tumor infiltration. Micro-RNA (miRNA) plays a role in CSC gene expression, which may regulate oncogenesis or suppression to influence tumor development or progression. The antigenesis of CSCs and normal stem cells may be different. The CSCs may escape the T-cell immune response. Identifying a new specific antigen from CSCs for vaccine treatment is a key point for immunotherapy. On the other hand, augmented treatment with radiosensitizer or chemosensitizer may lead to reduction of CSCs and lead to CSCs being vulnerable to radiotherapy and chemotherapy. The control of signaling pathway and cell differentiation to CSC growth is another new hope for treatment of malignant gliomas. Although the many physiological behavioral differences between CSCs and normal stem cells are unclear, the more we know about these differences the better we will be able to treat CSCs effectively.

Survey of MicroRNA expression in pediatric brain tumors

BACKGROUND

A better understanding of pediatric brain tumor biology is needed to assist in the development of less toxic therapies and to provide better markers for disease stratification. MicroRNAs (miRNA) may play a significant role in brain tumor biology. The present study provides an initial survey of miRNA expression in pediatric central nervous system (CNS) malignancies including atypical teratoid/rhabdoid tumor, ependymoma, glioblastoma, medulloblastoma, and pilocytic astrocytoma.

PROCEDURE

MicroRNA expression in pediatric brain tumors and normal tissue controls was examined by microarray. Three aberrantly expressed miRNAs were further studied in a larger cohort by quantitative real-time PCR (qRT-PCR).

RESULTS

MicroRNA-129, miR-142-5p, and miR-25 were differentially expressed in every pediatric brain tumor type compared to normal tissue controls as measured by microarray. When further examined by qRT-PCR, these miRNAs demonstrated differential expression that significantly correlated with the microarray findings. Distinctive miRNA expression profiles were also observed in the different pediatric brain tumor types.

CONCLUSIONS

MicroRNAs are differentially expressed between pediatric CNS neoplasms and normal tissue suggesting that they may play a significant role in oncogenesis. A greater understanding of aberrant miRNA expression in pediatric brain tumors may aid in the development of novel therapies. The characterization of tumor-specific miRNA signatures may aid in the discovery of biomarkers with diagnostic or prognostic utility.

MicroRNA-137 targets carboxyl-terminal binding protein 1 in melanoma cell lines

Carboxyl-terminal binding protein 1 (CtBP1) is a transcriptional co-repressor that represses expression of various tumor suppressor genes. In the present study, we identified miR-137 as a potential regulator of CtBP1 expression in melanoma cells. Expression of miR-137 in melanoma cell lines was found to inversely correlate with CtBP1 levels. Target Scan predicted a putative site for miR-137 within the CtBP1 3′ untranslated region (3′UTR) at nt 710-716, which is highly conserved across species. To explore the mechanism of miR-137 targeting CtBP1, we performed an Argonaute 2 (Ago2)-pull down assay, and miR-137 was identified in complex with CtBP1 mRNA. miR-137 suppressed CtBP1 3' UTR luciferase-reporter activity, and this effect was lost with deletion of the putative 3' UTR target-site. Consistent with the results of the reporter assay, ectopic expression of miR-137 reduced expression levels of CtBP1. Furthermore, expression of miR-137 increased the immediate downstream effectors of CtBP1, such as E-cadherin and Bax. The human miR-137 gene is located at chromosome 1p22, which has previously been determined to be a susceptive region for melanoma. This study suggests miR-137 may act as a tumor suppressor by directly targeting CtBP1 to inhibit epithelial-mesenchymal transition (EMT) and inducing apoptosis of melanoma cells, thus illustrating a functional link between miR-137 and CtBP1 in melanoma development.

miR-29b and miR-125a regulate podoplanin and suppress invasion in glioblastoma

Glioblastoma is the most frequent and malignant brain tumor, characterized by an elevated capacity for cellular proliferation and invasion. Recently, it was demonstrated that podoplanin membrane sialo-glycoprotein encoded by PDPN gene is over-expressed and related to cellular invasion in astrocytic tumors; however the mechanisms of regulation are still unknown. MicroRNAs are noncoding RNAs that regulate gene expression and several biological processes and diseases, including cancer. Nevertheless, their roles in invasion, proliferation, and apoptosis of glioblastoma are not completely understood. In this study, we focused on miR-29b and miR-125a, which were predicted to regulate PDPN, and demonstrated that these microRNAs directly target the 3' untranslated region of PDPN and inhibit invasion, apoptosis, and proliferation of glioblastomas. Furthermore, we report that miR-29b and miR-125a are downregulated in glioblastomas and also in CD133-positive cells. Taken together, these results suggest that miR-29b and miR-125a represent potential therapeutic targets in glioblastoma.

miR-124a is frequently down-regulated in glioblastoma and is involved in migration and invasion

Glioblastoma (GBM) represents a formidable clinical challenge for both patients and treating physicians. Due to better local treatments and prolonged patient survival, remote recurrences are increasingly observed, underpinning the importance of targeting tumour migration and attachment. Aberrant expression of microRNA (miRNA) is commonly associated with cancer and loss of miR-124a has previously been implicated to function as a tumour suppressor. The assessment of miR-124a in clinical specimens has been limited and a potential role in migration and invasion has been unexplored until now. We measured the expression levels of mature miR-124a in a retrospective series of 119 cases of histologically confirmed GBM and found its expression was markedly lower in over 80% of the GBM clinical specimens compared to normal brain tissue. The level of reduction in the clinical cohort varied significantly and patients with lower than the average miR-124a expression levels displayed shorter survival times. Endogenous miR-124a expression and the protein expression of three of its targets; IQ motif containing GTPase activating protein 1 (IQGAP1), laminin γ1 (LAMC1) and integrin β1 (ITGB1) were significantly reciprocally associated in the majority of the clinical cases. We confirmed this association in our in vitro model. Functionally, the ectopic expression of mature miR-124a in a GBM cell line resulted in significant inhibition of migration and invasion, demonstrating a role for miR-124a in promoting tumour invasiveness. Our results suggest that miR-124a may play a role in GBM migration, and that targeted delivery of miR-124a may be a novel inhibitor of GBM invasion.

Aberrant epigenetic landscape in cancer: how cellular identity goes awry

Appropriate patterns of DNA methylation and histone modifications are required to assure cell identity, and their deregulation can contribute to human diseases, such as cancer. Our aim here is to provide an overview of how epigenetic factors, including genomic DNA methylation, histone modifications, and microRNA regulation, contribute to normal development, paying special attention to their role in regulating tissue-specific genes. In addition, we summarize how these epigenetic patterns go awry during human cancer development. The possibility of "resetting" the abnormal cancer epigenome by applying pharmacological or genetic strategies is also discussed.

MicroRNA-124 promotes microglia quiescence and suppresses EAE by deactivating macrophages via the C/EBP-α-PU.1 pathway

MicroRNAs are a family of regulatory molecules involved in many physiological processes, including differentiation and activation of cells of the immune system. We found that brain-specific miR-124 is expressed in microglia but not in peripheral monocytes or macrophages. When overexpressed in macrophages, miR-124 directly inhibited the transcription factor CCAAT/enhancer-binding protein-α (C/EBP-α) and its downstream target PU.1, resulting in transformation of these cells from an activated phenotype into a quiescent CD45(low), major histocompatibility complex (MHC) class II(low) phenotype resembling resting microglia. During experimental autoimmune encephalomyelitis (EAE), miR-124 was downregulated in activated microglia. Peripheral administration of miR-124 in EAE caused systemic deactivation of macrophages, reduced activation of myelin-specific T cells and marked suppression of disease. Conversely, knockdown of miR-124 in microglia and macrophages resulted in activation of these cells in vitro and in vivo. These findings identify miR-124 both as a key regulator of microglia quiescence in the central nervous system and as a previously unknown modulator of monocyte and macrophage activation.

Investigation gene and microRNA expression in glioblastoma

Background

Glioblastoma is the most common primary brain tumor in adults. Though a lot of research has been focused on this disease, the causes and pathogenesis of glioblastoma have not been indentified clearly.

Results

We indentified 1,236 significantly differentially expressed genes, and 30 pathways enriched in the set of differentially expressed genes among 243 tumor and 11 normal samples. We also indentified 97 differentially expressed microRNAs among 240 tumor and 10 normal samples. 22 of which have been reported to affect glioblastoma and 50 of which were implicated in other cancers and brain diseases. We regressed gene expression on microRNA expression in 237 tumor tissues and 10 normal tissues comprehensively. We found two experimentally validated microRNA targets and 1,094 miRNA-target gene pairs in our datasets which were predicted by miRanda algorithm, 8 of the target genes were tumor suppressor genes and 3 were oncogenes. Further function analysis of target genes suggested that microRNAs most frequently targeted genes associated with Cell Signalling and Nervous System.

Conclusion

We investigated gene and microRNA Expression in Glioblastoma and gave a comprehensive function study of differential expressed gene and microRNA in glioblastoma patients. These findings gave important clues to study of the carcinogenic process in glioblastomas.

Role of microRNAs in cardiac preconditioning

Preconditioning (PC) of the heart by sublethal ischemia, mild heat shock, or hypoxia has evolved as a powerful experimental tool to discover novel signaling mechanisms in cardioprotection. The ultimate goal is to determine novel therapeutic targets for potential application in humans to protect the heart against ischemia-related injuries. In recent years, there has been a tremendous interest in understanding the role of small noncoding RNAs, microRNAs (miRs), in cardiovascular diseases. miRs have been recognized as regulators of gene expression by destabilization and translational inhibition of target messenger RNAs. Studies have shown that several miRs, including miR-1, miR-133, miR-21, miR-126, miR-320, miR-92a, and miR-199a, are regulated after preconditioning and play an active role in protecting the heart against ischemia/reperfusion injury. These miRs also drive the synthesis of important cardioprotective proteins including heat shock protein (HSP)-70, endothelial nitric oxide synthase, inducible nitric oxide synthase, HSP-20, Sirt1, and hypoxia-inducible factor 1a. We believe that identification and targeted delivery of miR(s) in the heart could have an immense therapeutic potential in reducing myocardial infarction in patients suffering from heart disease.

Stem cells in cancer: instigators and propagators?

There is growing realization that many - if not all - cancer-cell populations contain a subpopulation of self-renewing stem cells known as cancer stem cells (CSCs). Unlike normal adult stem cells that remain constant in number, CSCs can increase in number as tumours grow, and give rise to progeny that can be both locally invasive and colonise distant sites - the two hallmarks of malignancy. Immunodeficient mouse models in which human tumours can be xenografted provide persuasive evidence that CSCs are present in human leukaemias and many types of solid tumour. In addition, many studies have found similar subpopulations in mouse tumours that show enhanced tumorigenic properties when they are transplanted into histocompatible mice. In this Commentary, we refer to CSCs as tumour-propagating cells (TPCs), a term that reflects the assays that are currently employed to identify them. We first discuss evidence that cancer can originate from normal stem cells or closely related descendants. We then outline the attributes of TPCs and review studies in which they have been identified in various cancers. Finally, we discuss the implications of these findings for successful cancer therapies.

MicroRNA-137 promoter methylation is associated with poorer overall survival in patients with squamous cell carcinoma of the head and neck

BACKGROUND

The overall 5-year survival rate of approximately 60% for head and neck cancer patients has remained essentially unchanged over the past 30 years. MicroRNA-137 (miR-137) plays an essential role in cell-cycle control at the G1/S-phase checkpoint. However, the aberrant miR-137 promoter methylation observed in squamous cell carcinoma of the head and neck (SCCHN) suggests a tumor-specific molecular defect that may contribute to disease progression.

METHODS

The goal of this study was to assess, in formalin-fixed, paraffin-embedded tumor tissue, the association between miR-137 promoter methylation and survival (both overall and disease free) and with prognostic factors including stage, tumor size, lymph node positivity, tumor grade, and surgical tumor margin positivity.

RESULTS

The promoter methylation status of miR-137 was ascertained by methylation-specific polymerase chain reaction and detected in 11 of 67 SCCHN patients (16.4%), with no significant differences according to site (oral cavity, pharynx, larynx). Methylation of the miR-137 promoter was significantly associated with overall survival (hazard ratio, 3.68; 95% confidence interval, 1.01-13.38) but not with disease-free survival or any of the prognostic factors evaluated.

CONCLUSIONS

The results of this study indicate that miR-137 is methylated in tumor tissue from pharyngeal and laryngeal squamous cancers, in addition to oral squamous cell carcinoma, and that miR-137 promoter methylation has potential utility as a prognostic marker for SCCHN.

Cancer stem cells: problems for therapy?

Many, if not all, tumours contain a sub-population of self-renewing and expanding stem cells known as cancer stem cells (CSCs). The symmetric division of CSCs is one mechanism enabling expansion in their numbers as tumours grow, while epithelial-mesenchymal transition (EMT) is an increasingly recognized mechanism to generate further CSCs endowed with a more invasive and metastatic phenotype. Putative CSCs are prospectively isolated using methods based on either a surface marker or an intracellular enzyme activity and then assessed by a 'sphere-forming' assay in non-adherent culture and/or by their ability to initiate new tumour growth when xenotransplanted into immunocompromised mice-hence, these cells are often referred to as tumour-propagating cells (TPCs). Cell sub-populations enriched for tumour-initiating ability have also been found in murine tumours, countering the argument that xenografting human cells merely select human cells with an ability to grow in mice. Cancer progression can be viewed as an evolutionary process that generates new/multiple clones with a fresh identity; this may be a major obstacle to successful cancer stem cell eradication if treatment targets only a single type of stem cell. In this review, we first briefly discuss evidence that cancer can originate from normal stem cells or closely related descendants. We then outline the attributes of CSCs and review studies in which they have been identified in various cancers. Finally, we discuss the implications of these findings for successful cancer therapies, concentrating on the self-renewal pathways (Wnt, Notch, and Hedgehog), aldehyde dehydrogenase activity, EMT, miRNAs, and other epigenetic modifiers as potential targets for therapeutic manipulation.

Inhibition of mir-21, which is up-regulated during MYCN knockdown-mediated differentiation, does not prevent differentiation of neuroblastoma cells

BACKGROUND

Neuroblastoma is a malignant childhood tumour arising from precursor cells of the sympathetic nervous system. Genomic amplification of the MYCN oncogene is associated with dismal prognosis. For this group of high-risk tumours, the induction of tumour cell differentiation is part of current treatment protocols. MicroRNAs (miRNAs) are small non-coding RNA molecules that effectively reduce the translation of target mRNAs. MiRNAs play an important role in cell proliferation, apoptosis, differentiation and cancer. In this study, we investigated the role of N-myc on miRNA expression in MYCN-amplified neuroblastoma. We performed a miRNA profiling study on SK-N-BE (2) cells, and determined differentially expressed miRNAs during differentiation initiated by MYCN knockdown, using anti-MYCN short-hairpin RNA (shRNA) technology.

RESULTS

Microarray analyses revealed 23 miRNAs differentially expressed during the MYCN knockdown-mediated neuronal differentiation of MNA neuroblastoma cells. The expression changes were bidirectional, with 11 and 12 miRNAs being up- and down-regulated, respectively. Among the down-regulated miRNAs, we found several members of the mir-17 family of miRNAs. Mir-21, an established oncomir in a variety of cancer types, became strongly up-regulated upon MYCN knockdown and the subsequent differentiation. Neither overexpression of mir-21 in the high-MYCN neuroblastoma cells, nor repression of increased mir-21 levels during MYCN knockdown-mediated differentiation had any significant effects on cell differentiation or proliferation.

CONCLUSIONS

We describe a subset of miRNAs that were altered during the N-myc deprived differentiation of MYCN-amplified neuroblastoma cells. In this context, N-myc acts as both an activator and suppressor of miRNA expression. Mir-21 was up-regulated during cell differentiation, but inhibition of mir-21 did not prevent this process. We were unable to establish a role for this miRNA during differentiation and proliferation of the two neuroblastoma cell lines used in this study.

A LIF/Nanog axis is revealed in T lymphocytes that lack MARCH-7, a RINGv E3 ligase that regulates the LIF-receptor

Nanog is a stem cell transcription factor required for self-renewal and for maintaining pluripotency, and Nanog itself is regulated at least in part by leukaemia inhibitory factor (LIF)--a pluripotent cytokine of the IL6 family. MARCH-7 is an E-3 ligase linked to regulation of the LIF-receptor in T lymphocytes and T cells from mice that lack expression of MARCH-7 are hyper-responsive to activation signals and show a five-fold increase in LIF activity. Here we ask, does MARCH-7 influence the expression profile of Nanog during the synchronized entry of T cells into the cell cycle? We discovered that lack of MARCH-7 was permissive for Nanog expression at both transcript and protein levels during G₁/S: moreover, addition of exogenous LIF to the MARCH-7 null cells caused a further 13-fold induction of Nanog; other measured transcripts including TGFβ, p53 and STAT3 were relatively unchanged. Since lack of MARCH-7 altered responsiveness to activation signals we sought evidence for pre-existing regulatory miR's that might correlate with MARCH-7 gene dose using head-to-head comparisons between MARCH-7 null, heterozygous and wt spleen cells. 34 miRs were found including miR-346 that is known to target LIF transcripts and miR-346 is one of 16 miRs differentially expressed between hESCs and induced hiPSCs. Of the 34 miRs, 12 were known to be temporally regulated in embryonic nerve cells. In summary, in the absence of MARCH-7 a new signaling pathway is unmasked that involves Nanog expression in the T cell lineage. This is the first demonstration that T cells retain responsiveness to a LIF/Nanog axis and that this axis is linked to MARCH-7.

Genome-wide expression profiling identifies deregulated miRNAs in malignant astrocytoma

Malignant astrocytoma includes anaplastic astrocytoma (grade III) and glioblastoma (grade IV). Among them, glioblastoma is the most common primary brain tumor with dismal responses to all therapeutic modalities. We performed a large-scale, genome-wide microRNA (miRNA) (n=756) expression profiling of 26 glioblastoma, 13 anaplastic astrocytoma and 7 normal brain samples with an aim to find deregulated miRNA in malignant astrocytoma. We identified several differentially regulated miRNAs between these groups, which could differentiate glioma grades and normal brain as recognized by PCA. More importantly, we identified a most discriminatory 23-miRNA expression signature, by using PAM, which precisely distinguished glioblastoma from anaplastic astrocytoma with an accuracy of 95%. The differential expression pattern of nine miRNAs was further validated by real-time RT-PCR on an independent set of malignant astrocytomas (n=72) and normal samples (n=7). Inhibition of two glioblastoma-upregulated miRNAs (miR-21 and miR-23a) and exogenous overexpression of two glioblastoma-downregulated miRNAs (miR-218 and miR-219-5p) resulted in reduced soft agar colony formation but showed varying effects on cell proliferation and chemosensitivity. Thus we have identified the miRNA expression signature for malignant astrocytoma, in particular glioblastoma, and showed the miRNA involvement and their importance in astrocytoma development.

MicroRNA and endometrial cancer: Roles of small RNAs in human tumors and clinical applications (Review)

MicroRNAs (miRNAs) are small non-coding RNAs of approximately 22 base pairs that regulate the expression of genes by targeting messenger RNA with complementarity with the miRNA base sequence. Regulation of gene expression by miRNAs is crucial in cellular development and differentiation, and recent studies suggest a relationship between human diseases and the breakdown of gene silencing mechanisms induced by miRNA abnormalities. In particular, abnormal miRNA expression has been detected in various types of cancer and the target genes have been identified. These results indicate that miRNAs act in a manner equivalent to oncogenes or tumor suppressors. miRNAs may also serve as diagnostic biomarkers and therapeutic targets. In this review, we introduce the latest findings on miRNAs in human endometrial cancer, a common malignancy, and discuss the potential of miRNAs as biomarkers and targets for molecular therapy.

MicroRNA miR-137 regulates neuronal maturation by targeting ubiquitin ligase mind bomb-1

The maturation of young neurons is regulated by complex mechanisms and dysregulation of this process is frequently found in neurodevepmental disorders. MicroRNAs have been implicated in several steps of neuronal maturation including dendritic and axonal growth, spine development, and synaptogenesis. We demonstrate that one brain-enriched microRNA, miR-137, has a significant role in regulating neuronal maturation. Overexpression of miR-137 inhibits dendritic morphogenesis, phenotypic maturation, and spine development both in brain and cultured primary neurons. On the other hand, a reduction in miR-137 had opposite effects. We further show that miR-137 targets the Mind bomb one (Mib1) protein through the conserved target site located in the 3' untranslated region of Mib1 messenger RNA. Mib1 is an ubiquitin ligase known to be important for neurodevelopment. We show that exogenously expressed Mib1 could partially rescue the phenotypes associated with miR-137 overexpression. These results demonstrate a novel miRNA-mediated mechanism involving miR-137 and Mib1 that function to regulate neuronal maturation and dendritic morphogenesis during development.

miRNAs as molecular biomarkers of cancer

miRNAs are noncoding RNAs that regulate gene expression. The advent of high-throughput techniques has revealed that miRNA expression is deregulated in almost all human tumors (both solid and hematologic) with respect to the normal tissue counterpart. These differences frequently recur in tumor-specific miRNA signatures, which are very helpful to diagnose the tissue of origin of the neoplasia, and sometimes also specific tumor subtypes. Increasing evidence also supports a role for miRNAs as prognostic biomarkers of human cancers. Finally, miRNAs are differentially expressed in the blood of cancer patients versus healthy donors, providing a rationale for the detection of miRNAs and diagnostic and prognostic circulating biomarkers.

Epigenetic silencing of miR-137 is an early event in colorectal carcinogenesis

Global downregulation of microRNAs (miRNA) is a common feature in colorectal cancer (CRC). Whereas CpG island hypermethylation constitutes a mechanism for miRNA silencing, this field largely remains unexplored. Herein, we describe the epigenetic regulation of miR-137 and its contribution to colorectal carcinogenesis. We determined the methylation status of miR-137 CpG island in a panel of six CRC cell lines and 409 colorectal tissues [21 normal colonic mucosa from healthy individuals (N-N), 160 primary CRC tissues and their corresponding normal mucosa (N-C), and 68 adenomas]. TaqMan reverse transcription-PCR and in situ hybridization were used to analyze miR-137 expression. In vitro functional analysis of miR-137 was performed. Gene targets of miR-137 were identified using a combination of bioinformatic and transcriptomic approaches. We experimentally validated the miRNA:mRNA interactions. Methylation of the miR-137 CpG island was a cancer-specific event and was frequently observed in CRC cell lines (100%), adenomas (82.3%), and CRC (81.4%), but not in N-C (14.4%; P < 0.0001 for CRC) and N-N (4.7%; P < 0.0001 for CRC). Expression of miR-137 was restricted to the colonocytes in normal mucosa and inversely correlated with the level of methylation. Transfection of miR-137 precursor in CRC cells significantly inhibited cell proliferation. Gene expression profiling after miR-137 transfection discovered novel potential mRNA targets. We validated the interaction between miR-137 and LSD-1. Our data indicate that miR-137 acts as a tumor suppressor in the colon and is frequently silenced by promoter hypermethylation. Methylation silencing of miR-137 in colorectal adenomas suggests it to be an early event, which has prognostic and therapeutic implications.

Cancer stem cells in glioblastoma--molecular signaling and therapeutic targeting

Glioblastomas (GBMs) are highly lethal primary brain tumors. Despite current therapeutic advances in other solid cancers, the treatment of these malignant gliomas remains essentially palliative. GBMs are extremely resistant to conventional radiation and chemotherapies. We and others have demonstrated that a highly tumorigenic subpopulation of cancer cells called GBM stem cells (GSCs) promotes therapeutic resistance. We also found that GSCs stimulate tumor angiogenesis by expressing elevated levels of VEGF and contribute to tumor growth, which has been translated into a useful therapeutic strategy in the treatment of recurrent or progressive GBMs. Furthermore, stem cell-like cancer cells (cancer stem cells) have been shown to promote metastasis. Although GBMs rarely metastasize beyond the central nervous system, these highly infiltrative cancers often invade into normal brain tissues preventing surgical resection, and GSCs display an aggressive invasive phenotype. These studies suggest that targeting GSCs may effectively reduce tumor recurrence and significantly improve GBM treatment. Recent studies indicate that cancer stem cells share core signaling pathways with normal somatic or embryonic stem cells, but also display critical distinctions that provide important clues into useful therapeutic targets. In this review, we summarize the current understanding and advances in glioma stem cell research, and discuss potential targeting strategies for future development of anti-GSC therapies.

miR-148 regulates Mitf in melanoma cells

The Microphthalmia associated transcription factor (Mitf) is an important regulator in melanocyte development and has been shown to be involved in melanoma progression. The current model for the role of Mitf in melanoma assumes that the total activity of the protein is tightly regulated in order to secure cell proliferation. Previous research has shown that regulation of Mitf is complex and involves regulation of expression, splicing, protein stability and post-translational modifications. Here we show that microRNAs (miRNAs) are also involved in regulating Mitf in melanoma cells. Sequence analysis revealed conserved binding sites for several miRNAs in the Mitf 3′UTR sequence. Furthermore, miR-148 was shown to affect Mitf mRNA expression in melanoma cells through a conserved binding site in the 3′UTR sequence of mouse and human Mitf. In addition we confirm the previously reported effects of miR-137 on Mitf. Other miRNAs, miR-27a, miR-32 and miR-124 which all have conserved binding sites in the Mitf 3′UTR sequence did not have effects on Mitf. Our data show that miR-148 and miR-137 present an additional level of regulating Mitf expression in melanocytes and melanoma cells. Loss of this regulation, either by mutations or by shortening of the 3′UTR sequence, is therefore a likely factor in melanoma formation and/or progression.

Let-7 microRNA inhibits the proliferation of human glioblastoma cells

MicroRNAs (miRNAs) are small noncoding RNAs comprising 21-23 nucleotides that regulate gene expression by transcriptionally repressing their complementary mRNAs. In particular, let-7 miRNA has been postulated to function as a tumor suppressor in various cancer cells, but not yet in glioblastoma. In this study, we investigated the anti-tumorigenic effect of let-7 miRNA in glioblastoma cells. Human glioblastoma cells (U251 or U87 cells) were transfected with let-7 miRNA and assayed for in-vitro proliferation, migration, and in-vivo tumor formation. Transfection of let-7 miRNA reduced expression of pan-RAS, N-RAS, and K-RAS in the glioblastoma cells. Let-7 miRNA also reduced the in-vitro proliferation and migration of the cells, and reduced the sizes of the tumors produced after transplantation into nude mice. However, let-7 miRNA exerted no effect on the proliferation of normal human astrocytes. These results indicate that let-7 miRNA has an anti-tumorigenic effect on glioblastoma cells, and suggest possible use of let-7 miRNA for treating glioblastoma.

miR-182 as a prognostic marker for glioma progression and patient survival

Accumulating evidence indicates that miRNA expression can be used as a diagnostic and prognostic marker for human cancers. We report that the expression level of miR-182 was markedly up-regulated in glioma cell lines and in human primary glioma specimens. Quantitative PCR analysis showed that miR-182 was significantly increased by up to 32-fold in glioma tumors compared with the adjacent nontumor brain tissues obtained from the same patient. Elevated expression of miR-182 was further identified by in situ hybridization in 248 of 253 (98%) archived human glioma biopsies tested. Statistical analysis revealed a significant correlation between miR-182 expression and World Health Organization glioma grading (P < 0.001). The cumulative 5-year survival rate of glioma patients was 51.54% (95% confidence interval, 0.435 to 0.596) in the low miR-182-expression group, whereas it was only 7.23% (95% confidence interval, 0.027 to 0.118) in the high miR-182-expression group (P = 0.001), and multivariate Cox regression analysis indicated that miR-182 expression was an independent prognostic indicator for the survival of glioma patients. Moreover, the correlations of miR-182 level with the clinical features of glioma suggested in the in situ hybridization analysis were further verified by the real-time RT-PCR analysis. Taken together, our results suggest that miR-182 could be a valuable marker of glioma progression and that high miR-182 expression is associated with poor overall survival in patients with malignant glioma.

Cross talk between microRNA and epigenetic regulation in adult neurogenesis

The microRNA miR-137 represses expression of Ezh2, a histone methyltransferase, which in turn alters the epigenetic architecture of chromatin that is important for regulation of miR-137 levels.

Both microRNAs (miRNAs) and epigenetic regulation have important functions in stem cell biology, although the interactions between these two pathways are not well understood. Here, we show that MeCP2, a DNA methyl-CpG–binding protein, can epigenetically regulate specific miRNAs in adult neural stem cells (aNSCs). MeCP2-mediated epigenetic regulation of one such miRNA, miR-137, involves coregulation by Sox2, a core transcription factor in stem cells. miR-137 modulates the proliferation and differentiation of aNSCs in vitro and in vivo. Overexpression of miR-137 promotes the proliferation of aNSCs, whereas a reduction of miR-137 enhances aNSC differentiation. We further show that miR-137 post-transcriptionally represses the expression of Ezh2, a histone methyltransferase and Polycomb group (PcG) protein. The miR-137–mediated repression of Ezh2 feeds back to chromatin, resulting in a global decrease in histone H3 trimethyl lysine 27. Coexpression of Ezh2 can rescue phenotypes associated with miR-137 overexpression. These results demonstrate that cross talk between miRNA and epigenetic regulation contributes to the modulation of adult neurogenesis.

MicroRNA 128a increases intracellular ROS level by targeting Bmi-1 and inhibits medulloblastoma cancer cell growth by promoting senescence

Background

MicroRNAs (miRNAs) are a class of short non-coding RNAs that regulate cell homeostasis by inhibiting translation or degrading mRNA of target genes, and thereby can act as tumor suppressor genes or oncogenes. The role of microRNAs in medulloblastoma has only recently been addressed. We hypothesized that microRNAs differentially expressed during normal CNS development might be abnormally regulated in medulloblastoma and are functionally important for medulloblastoma cell growth.

Methodology and Principal Findings

We examined the expression of microRNAs in medulloblastoma and then investigated the functional role of one specific one, miR-128a, in regulating medulloblastoma cell growth. We found that many microRNAs associated with normal neuronal differentiation are significantly down regulated in medulloblastoma. One of these, miR-128a, inhibits growth of medulloblastoma cells by targeting the Bmi-1 oncogene. In addition, miR-128a alters the intracellular redox state of the tumor cells and promotes cellular senescence.

Conclusions and Significance

Here we report the novel regulation of reactive oxygen species (ROS) by microRNA 128a via the specific inhibition of the Bmi-1 oncogene. We demonstrate that miR-128a has growth suppressive activity in medulloblastoma and that this activity is partially mediated by targeting Bmi-1. This data has implications for the modulation of redox states in cancer stem cells, which are thought to be resistant to therapy due to their low ROS states.

HSV Recombinant Vectors for Gene Therapy

The very deep knowledge acquired on the genetics and molecular biology of herpes simplex virus (HSV), has allowed the development of potential replication-competent and replication-defective vectors for several applications in human healthcare. These include delivery and expression of human genes to cells of the nervous systems, selective destruction of cancer cells, prophylaxis against infection with HSV or other infectious diseases, and targeted infection to specific tissues or organs. Replication-defective recombinant vectors are non-toxic gene transfer tools that preserve most of the neurotropic features of wild type HSV-1, particularly the ability to express genes after having established latent infections, and are thus proficient candidates for therapeutic gene transfer settings in neurons. A replication-defective HSV vector for the treatment of pain has recently entered in phase 1 clinical trial. Replication-competent (oncolytic) vectors are becoming a suitable and powerful tool to eradicate brain tumours due to their ability to replicate and spread only within the tumour mass, and have reached phase II/III clinical trials in some cases. The progress in understanding the host immune response induced by the vector is also improving the use of HSV as a vaccine vector against both HSV infection and other pathogens. This review briefly summarizes the obstacle encountered in the delivery of HSV vectors and examines the various strategies developed or proposed to overcome such challenges.

HSV Recombinant Vectors for Gene Therapy

The very deep knowledge acquired on the genetics and molecular biology of herpes simplex virus (HSV), has allowed the development of potential replication-competent and replication-defective vectors for several applications in human healthcare. These include delivery and expression of human genes to cells of the nervous systems, selective destruction of cancer cells, prophylaxis against infection with HSV or other infectious diseases, and targeted infection to specific tissues or organs. Replication-defective recombinant vectors are non-toxic gene transfer tools that preserve most of the neurotropic features of wild type HSV-1, particularly the ability to express genes after having established latent infections, and are thus proficient candidates for therapeutic gene transfer settings in neurons. A replication-defective HSV vector for the treatment of pain has recently entered in phase 1 clinical trial. Replication-competent (oncolytic) vectors are becoming a suitable and powerful tool to eradicate brain tumours due to their ability to replicate and spread only within the tumour mass, and have reached phase II/III clinical trials in some cases. The progress in understanding the host immune response induced by the vector is also improving the use of HSV as a vaccine vector against both HSV infection and other pathogens. This review briefly summarizes the obstacle encountered in the delivery of HSV vectors and examines the various strategies developed or proposed to overcome such challenges.

Non-coding RNAs: identification of cancer-associated microRNAs by gene profiling

MicroRNAs (miRNAs) belong to the heterogeneous class of non-coding RNAs (ncRNAs), which are by definition RNA molecules that do not encode for proteins, but have instead important structural, catalytic or regulatory functions. In this review we first provide an overview of the different ncRNA families, focusing in particular on miRNAs and their relevance in tumour development and progression. Second we shortly describe the available ncRNA expression profiling methods, which comprise microarray, bead-based hybridization methods, in situ hybridization, quantitative real-time polymerase chain reaction, cloning and deep sequencing methods. Finally, we used the PubMed database to perform an extensive literature search for miRNA expression profiling research articles in cancer and identified 58 studies that were published between 2004 and 2009; we identified 70 miRNAs that were reported in at least five studies as being either up- or downregulated, depending on the type of cancer, and 192 miRNAs that were reported to be up- or downregulated in at least two reports. MiRNA expression profiling of human tumours has identified signatures associated with diagnosis, staging, progression, prognosis, and response to treatment. Based on the most important findings we discuss the possible use of miRNAs as clinical biomarkers in the management of cancer patients for diagnosis, prognosis, and response to therapy.

Modulation of miR-122 on persistently Borna disease virus infected human oligodendroglial cells

Using RNAhybrid software we found the predicted binding of complementary sequences between miR-122 and viral mRNAs, may be important for the antiviral effect of miR-122 on Borna disease virus (BDV). A moderate expression of miR-122 was identified in human oligodendroglial cells (OL), but with a much lower level of miR-122 in BDV persistent infection (OL/BDV) and cells transfected with BDV gene expression vectors. Over-expression of miR-122 and specific blocking experiments demonstrated that miR-122 was able to specifically inhibit BDV protein synthesis, viral gene replication and transcription, and induce the secretion/synthesis of interferon (IFN) in OL and OL/BDV cells. The abolishment of miR-122 by AMO-122 inhibited endogenous IFN induction by IFN-beta. These results indicate that miR-122 can exert direct antiviral function by inhibiting BDV translation and replication on one hand, while acting indirectly through IFN to increase the host innate immunity to modulate the virus-host interactions on the other hand.

Small molecules with big effects: the role of the microRNAome in cancer and carcinogenesis

Small non-coding RNAs-microRNAs, are potent negative regulators of gene expression. MicroRNAs are involved in multiple biological processes, metabolic regulation, including cell proliferation, differentiation, and programmed cell death. Since the dysregulation of these processes is a hallmark of cancer, microRNAs can be viewed as major contributors to the pathogenesis of cancer, including initiation and progression of cancer. This review focuses on microRNA biogenesis and function, and their role in cancer, metastasis, drug resistance, and tumorigenesis.

Potential therapeutic implications of cancer stem cells in glioblastoma

Glioblastoma is the most common and lethal type of primary brain tumor. Despite recent therapeutic advances in other cancers, the treatment of glioblastomas remains ineffective and essentially palliative. The treatment failure is a result of a number of causes, but we and others have demonstrated that a highly tumorigenic subpopulation of cancer cells called glioblastoma stem cells (GSCs) display relative resistance to radiation and chemotherapy. GSCs also contribute to tumor growth through the stimulation of angiogenesis, which has been shown to be a useful therapeutic target in the treatment of recurrent or progressive malignant gliomas. Cancer stem cells also have been hypothesized as a contributor to systemic metastases. While glioblastomas rarely metastasize beyond the central nervous system, glioblastomas invade into brain structures to prevent surgical cure and GSCs have an extremely invasive phenotype. Collectively, these studies and others suggest that GSCs may be important therapeutic targets not only to achieve cure but even reduce tumor relapse and improve overall survival. Many recent studies suggest that GSCs share core regulatory pathways with normal embryonic and somatic stem cells, but display important distinctions that provide clues into useful treatment targets. The cancer stem cell hypothesis may also modify our approaches in tumor imaging and biomarker development, but clinical validation waits. In this review, we summarize the current understanding of GSC biology with a focus on potential anti-GSC therapies.

Methylation and silencing of miRNA-124 by EVI1 and self-renewal exhaustion of hematopoietic stem cells in murine myelodysplastic syndrome

By expressing EVI1 in murine bone marrow (BM), we previously described a myelodysplastic syndrome (MDS) model characterized by pancytopenia, dysmegakaryopoiesis, dyserythropoiesis, and BM failure. The mice invariably died 11-14 months after BM transplantation (BMT). Here, we show that a double point mutant EVI1-(1+6Mut), unable to bind Gata1, abrogates the onset of MDS in the mouse and re-establishes normal megakaryopoiesis, erythropoiesis, BM function, and peripheral blood profiles. These normal features were maintained in the reconstituted mice until the study was ended at 21 months after BMT. We also report that EVI1 deregulates several genes that control cell division and cell self-renewal. In striking contrast, these genes are normalized in the presence of the EVI1 mutant. Moreover, EVI1, but not the EVI1 mutant, seemingly deregulates these cellular processes by altering miRNA expression. In particular, the silencing of miRNA-124 by DNA methylation is associated with EVI1 expression, but not that of the EVI1 mutant, and appears to play a key role in the up-regulation of cell division in murine BM cells and in the hematopoietic cell line 32Dcl3. The results presented here demonstrate that EVI1 induces MDS in the mouse through two major pathways, both of which require the interaction of EVI1 with other factors: one, results from EVI1-Gata1 interaction, which deregulates erythropoiesis and leads to fatal anemia, whereas the other occurs by interaction of EVI1 with unidentified factors causing perturbation of the cell cycle and self-renewal, as a consequence of silencing miRNA-124 by EVI1 and, ultimately, ensues in BM failure.