New advances of microRNAs in glioma stem cells, with special emphasis on aberrant methylation of microRNAs

Molecular mechanisms of microRNAs in glioblastoma pathogenesis

Glioblastoma (GBM) is human's most prevalent and severe brain cancer. Epigenetic regulators, micro(mi)RNAs, significantly impact cellular health and disease because of their wide range of targets and functions. The "epigenetic symphony" in which miRNAs perform is responsible for orchestrating the transcription of genetic information. The discovery of regulatory miRNA activities in GBM biology has shown that various miRNAs play a vital role in disease onset and development. Here, we summarize our current understanding of the current state-of-the-art and latest findings regarding the interactions between miRNAs and molecular mechanisms commonly associated with GBM pathogenesis. Moreover, by literature review and reconstruction of the GBM gene regulatory network, we uncovered the connection between miRNAs and critical signaling pathways such as cell proliferation, invasion, and cell death, which provides promising hints for identifying potential therapeutic targets for the treatment of GBM. In addition, the role of miRNAs in GBM patient survival was investigated. The present review, which contains new analyses of the previous literature, may lead to new avenues to explore in the future for the development of multitargeted miRNA-based therapies for GBM.

microRNAs (miRNAs) in Glioblastoma Multiforme (GBM)-Recent Literature Review

Glioblastoma multiforme (GBM) is the most common, malignant, poorly promising primary brain tumor. GBM is characterized by an infiltrating growth nature, abundant vascularization, and a rapid and aggressive clinical course. For many years, the standard treatment of gliomas has invariably been surgical treatment supported by radio- and chemotherapy. Due to the location and significant resistance of gliomas to conventional therapies, the prognosis of glioblastoma patients is very poor and the cure rate is low. The search for new therapy targets and effective therapeutic tools for cancer treatment is a current challenge for medicine and science. microRNAs (miRNAs) play a key role in many cellular processes, such as growth, differentiation, cell division, apoptosis, and cell signaling. Their discovery was a breakthrough in the diagnosis and prognosis of many diseases. Understanding the structure of miRNAs may contribute to the understanding of the mechanisms of cellular regulation dependent on miRNA and the pathogenesis of diseases underlying these short non-coding RNAs, including glial brain tumors. This paper provides a detailed review of the latest reports on the relationship between changes in the expression of individual microRNAs and the formation and development of gliomas. The use of miRNAs in the treatment of this cancer is also discussed.

A Signature of Three microRNAs Is a Potential Diagnostic Biomarker for Glioblastoma

Background:

Glioblastoma is the most common primary malignant neoplasm of the central nervous system. Despite progress in diagnosis and treatment, glioblastoma still has a poor prognosis. This study aimed to examine whether a signature of three candidate miRNAs (i.e. hsa-let-7c-5p, hsa-miR-206-5p, and hsa-miR-1909-5p) can be used as a diagnostic biomarker for distinguishing glioblastoma from healthy brain tissues.

Methods:

In this study, 50 FFPE glioblastoma tissue samples and 50 healthy tissue samples adjacent to tumor were included. The expression of each candidate miRNA (i.e. hsa-let-7c-5p, hsa-miR-206-5p, and hsa-miR-1909-5p) was measured using RT-qPCR. To show the roles of each miRNA and their biological effects on glioblastoma development and clinicopathological characteristics, in silico tools were used. ROC curves were performed to assess the diagnostic accuracy of each miRNA.

Results:

Based on the results, hsa-let-7c-5p and hsa-miR-206-5p were downregulated, while hsa-miR-1909-5p was upregulated in glioblastoma tumors compared to healthy samples. No association was detected between the expression of each candidate miRNA and sex. Except for hsa-let-7c-5p, other miRNAs did not correlate with age status. ROC curve analysis indicated that the signature of candidate miRNAs is a potential biomarker distinguishing between glioblastoma and healthy samples. Only hsa-miR-206-5p suggested the association with poor prognosis in glioblastoma patients.

Conclusion:

Our findings revealed that the signature of three miRNAs is capable of distinguishing glioblastoma tumor and healthy tissues. These results are beneficial for the clinical management of glioblastoma patients.

MicroRNAs at the Crossroad of the Dichotomic Pathway Cell Death vs. Stemness in Neural Somatic and Cancer Stem Cells: Implications and Therapeutic Strategies

Stemness and apoptosis may highlight the dichotomy between regeneration and demise in the complex pathway proceeding from ontogenesis to the end of life. In the last few years, the concept has emerged that the same microRNAs (miRNAs) can be concurrently implicated in both apoptosis-related mechanisms and cell differentiation. Whether the differentiation process gives rise to the architecture of brain areas, any long-lasting perturbation of miRNA expression can be related to the occurrence of neurodevelopmental/neuropathological conditions. Moreover, as a consequence of neural stem cell (NSC) transformation to cancer stem cells (CSCs), the fine modulation of distinct miRNAs becomes necessary. This event implies controlling the expression of pro/anti-apoptotic target genes, which is crucial for the management of neural/neural crest-derived CSCs in brain tumors, neuroblastoma, and melanoma. From a translational point of view, the current progress on the emerging miRNA-based neuropathology therapeutic applications and antitumor strategies will be disclosed and their advantages and shortcomings discussed.

The Chinese Medicine, Shezhi Huangling Decoction, Inhibits the Growth and Metastasis of Glioma Cells via the Regulation of miR-1298-5p/TGIF1 Axis

Purpose

In recent years, traditional Chinese medicine has achieved good results in treating gliomas. This research aimed to reveal the effect of Shezhi Huangling decoction (SD) on glioma cell process.

Methods

U87 and U251 cells were treated with different concentrations (10, 30 and 50 μg/mL) of SD or transfected with miR-1298-5p mimic, inhibitor and siRNA targeting TGIF1. Cell proliferation, migration, invasion and apoptosis were detected. The expression of miR-1298-5p was measured by qRT-PCR, while TGIF1 expression was examined by immunohistochemical analysis and Western blot.

Results

SD treatment inhibited the proliferation, migration and invasion of glioma cells and induced the apoptosis. In addition, SD treatment induced the expression of miR-1298-5p in glioma cells. The low expression of miR-1298-5p was examined in glioma tissues and was significantly related to the high histological grade of glioma patients and predicted a poor prognosis. MiR-1298-5p directly targeted the 3'-UTR of transforming growth factor β induced factor 1 (TGIF1) and reduced TGIF1 protein expression. MiR-1298-5p restricted the proliferation, migration and invasion of glioma cells and induced cell apoptosis by targeting TGIF1.

Conclusion

Our data reveal that SD acts as a cancer-inhibiting agent in glioma via miR-1298-5p/TGIF1 axis, suggesting a potential therapeutic application of SD in glioma.

MicroRNA-30a suppresses self-renewal and tumorigenicity of glioma stem cells by blocking the NT5E-dependent Akt signaling pathway

Over the past decade, increasing researches have demonstrated the implication of microRNAs (miRNAs or miRs) in tumorigenicity of glioma stem cells (GSCs). The regulatory functions of miRNAs in GSCs have emerged as potential therapeutic candidates for glioma treatment. Herein, we aim to investigate the role of miR-30a in the proliferation and self-renewal of GSCs and the possible mechanism in relation to ecto-5'-nucleotidase (NT5E)-dependent Akt signaling pathway. RT-qPCR and Western blot analysis were performed to determine the expression of miR-30a and NT5E in glioma tissues and cell lines. GSCs were isolated from glioma cells and identified using flow cytometry. The relationship between miR-30a and NT5E was determined by dual-luciferase reporter gene assay. Gain- and loss-of-function experiments were performed to examine the effects of miR-30a and NT5E on sphere formation, colony formation, and proliferation of GSCs in vitro, as well as orthotopic tumor growth of GSCs in nude mice. Additionally, the Akt signaling pathway was blocked with an Akt inhibitor, LY294002, to investigate its involvement in the regulatory effect of miR30a. miR-30a was poorly expressed in glioma tissues and cell lines as well as GSCs. NT5E, highly expressed in GSCs, was identified as a target of miR-30a. In addition, miR-30a upregulation or NT5E silencing could reduce GSC sphere formation, clone formation, proliferation, and orthotopic tumor growth in nude mice. Moreover, miR-30a inhibited the activation of the Akt signaling pathway by targeting NT5E, and ultimately suppressing the self-renewal and orthotopic tumor growth of GSCs. Our results demonstrate that miR-30a targets NT5E to inhibit the Akt signaling pathway, by which could suppress the self-renewal and orthotopic tumor growth of GSCs. Those findings may provide theoretical basis of miR-30a as a therapeutic target to suppress the glioma progression.

MiR-330-3p functions as a tumor suppressor that regulates glioma cell proliferation and migration by targeting CELF1

INTRODUCTION

Glioma is a common type of neoplasm that occurs in the central nervous system. miRNAs have been demonstrated to act as critical regulators of carcinogenesis and tumor progression in multiple cancers, but the molecular mechanism of miR-330-3p in glioma remained unclear. The purpose of the study was to explore the role of miR-330-3p in glioma cell reproduction and migration.

MATERIAL AND METHODS

The expression levels of miR-330-3p and CELF1 in 27 glioma tissue specimens and human glioma cell lines were examined by qRT-PCR and western blot. The TargetScan database was used to predict the relationship between miR-330-3p and CELF1. Then the target relationship was verified using dual-luciferase reporter assay. The effects of miR-330-3p/CELF1 on glioma cell proliferation were evaluated by MTT and colony formation assay. Wound healing assay was employed to measure the migration ability of glioma cells.

RESULTS

MiR-330-3p was found lowly expressed in glioma tissues and cells compared with adjacent tissues and normal astrocytes, while CELF1 expression was relatively high in the glioma tissues and cells. Dual-luciferase reporter assay confirmed that miR-330-3p could directly target CELF1. Furthermore, miR-330-3p could down-regulate the expression of CELF1, therefore suppressing glioma cell reproduction and migration.

CONCLUSIONS

MiR-330-3p inhibited the propagation and migration of glioma cells by repressing CELF1 expression.

MicroRNA Signature in Human Normal and Tumoral Neural Stem Cells

MicroRNAs, also called miRNAs or simply miR-, represent a unique class of non-coding RNAs that have gained exponential interest during recent years because of their determinant involvement in regulating the expression of several genes. Despite the increasing number of mature miRNAs recognized in the human species, only a limited proportion is engaged in the ontogeny of the central nervous system (CNS). miRNAs also play a pivotal role during the transition of normal neural stem cells (NSCs) into tumor-forming NSCs. More specifically, extensive studies have identified some shared miRNAs between NSCs and neural cancer stem cells (CSCs), namely miR-7, -124, -125, -181 and miR-9, -10, -130. In the context of NSCs, miRNAs are intercalated from embryonic stages throughout the differentiation pathway in order to achieve mature neuronal lineages. Within CSCs, under a different cellular context, miRNAs perform tumor suppressive or oncogenic functions that govern the homeostasis of brain tumors. This review will draw attention to the most characterizing studies dealing with miRNAs engaged in neurogenesis and in the tumoral neural stem cell context, offering the reader insight into the power of next generation miRNA-targeted therapies against brain malignances.

TFAP2E methylation promotes 5‑fluorouracil resistance via exosomal miR‑106a‑5p and miR‑421 in gastric cancer MGC‑803 cells

Hypermethylation of transcription factor activating enhancer-binding protein 2e (TFAP2E) has been reported to be associated with chemoresistance to 5-fluorouracil (5-FU) in gastric cancer (GC). In the present study, the molecular mechanism governing this chemoresistance was investigated. Drug-resistant human GC MGC-803/5-FU cells were established and TFAP2E expression and methylation levels were assessed. Autocrine exosomes from GC culture medium were isolated and characterized. MicroRNA (miRNA) microarray analysis was used to determine the miRNA expression profile of GC cell-derived exosomes. Exosomes collected from MGC-803/5-FU cells were co-cultured with control cells, and 5-Aza-2′-deoxycytidine (5Aza) was added into MGC-803/5-FU cells to investigate the relationship between TFAP2E, exosomes and chemosensitivity. In the present study, it was demonstrated that hypermethylation of TFAP2E resulted in its reduced expression and 5-FU chemoresistance in GC cells. miRNAs miR-106a-5p and miR-421 were highly expressed and regulated the chemoresistance induced by TFAP2E methylation. Target gene prediction using miRBase, TargetScan and PicTar revealed that E2F1, MTOR and STAT3 may be TFAP2E target genes in GC. Collectively, our data support an important role of exosomes and exosomal miRNAs in TFAP2E methylation-induced chemoresistance to 5-FU in GC. These results highlight their potential for miRNA-based therapeutics.

MicroRNAs, Hypoxia and the Stem-Like State as Contributors to Cancer Aggressiveness

MicroRNAs (miRNAs) are small non-coding RNA molecules that play key regulatory roles in cancer acting as both oncogenes and tumor suppressors. Due to their potential roles in improving cancer prognostic, predictive, diagnostic and therapeutic approaches, they have become an area of intense research focus in recent years. Several studies have demonstrated an altered expression of several miRNAs under hypoxic condition and even shown that the hypoxic microenvironment drives the selection of a more aggressive cancer cell population through cellular adaptations referred as the cancer stem-like cell. These minor fractions of cells are characterized by their self-renewal abilities and their ability to maintain the tumor mass, suggesting their crucial roles in cancer development. This review aims to highlight the interconnected role between miRNAs, hypoxia and the stem-like state in contributing to the cancer aggressiveness as opposed to their independent contributions, and it is based in four aggressive tumors, namely glioblastoma, cervical, prostate, and breast cancers.

Lauryl Gallate Induces Apoptotic Cell Death through Caspase-dependent Pathway in U87 Human Glioblastoma Cells In Vitro

BACKGROUND/AIM

The treatment of human glioma tumor is still an unmet medical need. Natural products are always promising resources for discovery of anticancer drugs. Lauryl gallate (LG) is one of the derivatives of gallic acid, widely present in plants, that has been shown to induce anticancer activities in many human cancer cell lines; however, it has not been studied in human glioma cell lines. Thus, the effects of LG on human glioblastoma U87 cells were investigated in the present in vitro study.

MATERIALS AND METHODS

Cell morphology and viability were examined by phase-contrast microscopy. Annexin V/Propidium iodide (PI) double staining were performed and assayed by flow cytometry to confirm that viable cell number reduction was due to the induction of apoptosis. Furthermore, U87 cells were exposed to LG in various concentrations and were analyzed by caspase activity assay. To further confirm that LG induced apoptotic cell death, the expression of apoptosis-associated proteins in LG-treated U87 cells was tested by western blot.

RESULTS

LG induced morphological changes and decreased viability in U87 cells. Annexin V/PI double staining revealed that LG induced apoptotic cell death in U87 cells in a dose-dependent manner. The increased activities of caspase-2, -3, -8 and -9 demonstrated that LG induced U87 cell apoptosis through a caspase-dependent pathway. In terms of molecular level, LG increased pro-apoptotic proteins Bax and Bak and decreased anti-apoptotic protein Bcl-2 in U87 cells. Furthermore, LG also suppressed the expression of p-Akt, Pak1, Hif-1α and Hif-2α, β-catenin and Tcf-1 in U87 cells.

CONCLUSION

These results suggest that LG induced apoptotic cell death via the caspase-dependent pathway in U87 cells.

MicroRNAs in glioblastoma pathogenesis and therapy: A comprehensive review

Glioblastoma (GBM), also known as grade IV astrocytoma, is the most aggressive primary intracranial tumor of the adult brain. MicroRNAs (miRNAs), a class of small non-coding RNA species, have critical functions across various biological processes. A great deal of progress has been made recently in dissecting miRNA pathways associated with the pathogenesis of GBM. miRNA expression signatures called gene signatures also characterize and contribute to the phenotypic diversity of GBM subclasses through their ability to regulate developmental growth and differentiation. miRNA molecules have been identified as diagnostic and prognostic biomarkers for patient stratification and may also serve as therapeutic targets and agents. This review summarizes: (i) the current understanding of the roles of miRNAs in the pathogenesis of GBM, (ii) the potential use of miRNAs in GBM diagnosis and glioma grading, (iii) further prospects of developing miRNAs as novel biomarkers and therapeutic targets for GBM, and (iv) important practical considerations when considering miRNA therapy for GBM patients.

MicroRNA-203 As a Stemness Inhibitor of Glioblastoma Stem Cells

Glioblastoma stem cells (GBM-SCs) are believed to be a subpopulation within all glioblastoma (GBM) cells that are in large part responsible for tumor growth and the high grade of therapeutic resistance that is so characteristic of GBM. MicroRNAs (miR) have been implicated in regulating the expression of oncogenes and tumor suppressor genes in cancer stem cells, including GBM-SCs, and they are a potential target for cancer therapy. In the current study, miR-203 expression was reduced in CD133(+) GBM-SCs derived from six human GBM biopsies. MicroRNA-203 transfected GBM-SCs had reduced capacity for self-renewal in the cell sphere assay and increased expression of glial and neuronal differentiation markers. In addition, a reduced proliferation rate and an increased rate of apoptosis were observed. Therefore, miR-203 has the potential to reduce features of stemness, specifically in GBM-SCs, and is a logical target for GBM gene therapy.

Exosomal levels of miRNA-21 from cerebrospinal fluids associated with poor prognosis and tumor recurrence of glioma patients

Glioma is a most common type of primary brain tumors. Extracellular vesicles, in the form of exosomes, are known to mediate cell–cell communication by transporting cell-derived proteins and nucleic acids, including various microRNAs (miRNAs). Here we examined the cerebrospinal fluid (CSF) from patients with recurrent glioma for the levels of cancer-related miRNAs, and evaluated the values for prognosis by comparing the measures of CSF-, serum-, and exosome-contained miR-21 levels. Samples from seventy glioma patients following surgery were compared with those from brain trauma patients as a non-tumor control group. Exosomal miR-21 levels in the CSF of glioma patients were found significantly higher than in the controls; whereas no difference was detected in serum-derived exosomal miR-21 expression. The CSF-derived exosomal miR-21 levels correlated with tumor spinal/ventricle metastasis and the recurrence with anatomical site preference. From additional 198 glioma tissue samples, we verified that miR-21 levels associated with tumor grade of diagnosis and negatively correlated with the median values of patient overall survival time. We further used a lentiviral inhibitor to suppress miR-21 expression in U251 cells. The results showed that the levels of miR-21 target genes of PTEN, RECK and PDCD4 were up-regulated at protein levels. Therefore, we concluded that the exosomal miR-21 levels could be demonstrated as a promising indicator for glioma diagnosis and prognosis, particularly with values to predict tumor recurrence or metastasis.

Epigenetic silencing of miR-181c by DNA methylation in glioblastoma cell lines

Background

Post-transcriptional regulation by microRNAs is recognized as one of the major pathways for the control of cellular homeostasis. Less well understood is the transcriptional and epigenetic regulation of genes encoding microRNAs. In the present study we addressed the epigenetic regulation of the miR-181c in normal and malignant brain cells.

Methods

To explore the epigenetic regulation of the miR-181c we evaluated its expression using RT-qPCR and the in vivo binding of the CCCTC-binding factor (CTCF) to its regulatory region in different glioblastoma cell lines. DNA methylation survey, chromatin immunoprecipitation and RNA interference assays were used to assess the role of CTCF in the miR-181c epigenetic silencing.

Results

We found that miR-181c is downregulated in glioblastoma cell lines, as compared to normal brain tissues. Loss of expression correlated with a notorious gain of DNA methylation at the miR-181c promoter region and the dissociation of the multifunctional nuclear factor CTCF. Taking advantage of the genomic distribution of CTCF in different cell types we propose that CTCF has a local and cell type specific regulatory role over the miR-181c and not an architectural one through chromatin loop formation. This is supported by the depletion of CTCF in glioblastoma cells affecting the expression levels of NOTCH2 as a target of miR-181c.

Conclusion

Together, our results point to the epigenetic role of CTCF in the regulation of microRNAs implicated in tumorigenesis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2273-6) contains supplementary material, which is available to authorized users.

MicroRNAs Enhance Keratinocyte Proliferative Capacity in a Stem Cell-Enriched Epithelium

MicroRNAs are critical regulators of stem cell behavior. The miR-103/107 family is preferentially expressed in the stem cell-enriched corneal limbal epithelium and plays an important role in coordinating several intrinsic characteristics of limbal epithelial stem cells. To elucidate further the mechanisms by which miRs-103/107 function in regulating limbal epithelial stem cells, we investigate the global effects of miRs-103/107 on gene expression in an unbiased manner. Using antagomirs-103/107, we knocked down endogenous miRs-103/107 in keratinocytes and conducted an mRNA profiling study. We show that miRs-103/107 target mitogen-activated protein kinase kinase kinase 7 (MAP3K7) and thereby negatively regulate the p38/AP-1 pathway, which directs epithelial cells towards a differentiated state. Pharmacological inhibition of p38 increases holoclone colony formation, a measure of proliferative capacity. This suggests that the negative regulation of p38 by miRs-103/107 contributes to enhanced proliferative capacity, which is a hallmark of stem cells. Since miRs-103/107 also promote increased holoclone colony formation by regulating JNK activation through non-canonical Wnt signaling, we believe that this microRNA family preserves “stemness” by mediating the crosstalk between the Wnt/JNK and MAP3K7/p38/AP-1 pathways.

MicroRNA Regulation of Brain Tumour Initiating Cells in Central Nervous System Tumours

CNS tumours occur in both pediatric and adult patients and many of these tumours are associated with poor clinical outcome. Due to a paradigm shift in thinking for the last several years, these tumours are now considered to originate from a small population of stem-like cells within the bulk tumour tissue. These cells, termed as brain tumour initiating cells (BTICs), are perceived to be regulated by microRNAs at the posttranscriptional/translational levels. Proliferation, stemness, differentiation, invasion, angiogenesis, metastasis, apoptosis, and cell cycle constitute some of the significant processes modulated by microRNAs in cancer initiation and progression. Characterization and functional studies on oncogenic or tumour suppressive microRNAs are made possible because of developments in sequencing and microarray techniques. In the current review, we bring recent knowledge of the role of microRNAs in BTIC formation and therapy. Special attention is paid to two highly aggressive and well-characterized brain tumours: gliomas and medulloblastoma. As microRNA seems to be altered in the pathogenesis of many human diseases, “microRNA therapy” may now have potential to improve outcomes for brain tumour patients. In this rapidly evolving field, further understanding of miRNA biology and its contribution towards cancer can be mined for new therapeutic tools.