MicroRNA biomarkers in glioblastoma

Tumor Suppressor MicroRNAs in Clinical and Preclinical Trials for Neurological Disorders

Cancers and neurological disorders are two major types of diseases in humans. We developed the concept called the "Aberrant Cell Cycle Disease (ACCD)" due to the accumulating evidence that shows that two different diseases share the common mechanism of aberrant cell cycle re-entry. The aberrant cell cycle re-entry is manifested as kinase/oncoprotein activation and tumor suppressor (TS) inactivation, which are associated with both tumor growth in cancers and neuronal death in neurological disorders. Therefore, some cancer therapies (e.g., kinase/oncogene inhibition and TS elevation) can be leveraged for neurological treatments. MicroRNA (miR/miRNA) provides a new style of drug-target binding. For example, a single tumor suppressor miRNA (TS-miR/miRNA) can bind to and decrease tens of target kinases/oncogenes, producing much more robust efficacy to block cell cycle re-entry than inhibiting a single kinase/oncogene. In this review, we summarize the miRNAs that are altered in both cancers and neurological disorders, with an emphasis on miRNA drugs that have entered into clinical trials for neurological treatment.

Exosome‑delivered miR‑486‑3p inhibits the progression of osteosarcoma via sponging CircKEAP1/MARCH1 axis components

Accumulating evidence shows that the disruption of competing endogenous RNA (ceRNA) networks plays a significant role in osteosarcoma (OS) initiation and progression. However, the specific roles and functions of the ceRNAs in OS remain unclear. First, differentially expressed microRNAs (DEMs) were identified by mining the E-MTAB-1136 and GSE28423 datasets. MiRWalk website was used to predict the target gene of miRNA. OS-associated circular RNA (circRNA) expression profiles were downloaded from the published microarray databases. Gene expression levels were assessed through reverse transcription-quantitative PCR and western blotting. The biological effects of circKEAP1, microRNA (miR)-486-3p and membrane-associated RINGCH finger protein 1 (MARCH1) in OS cells were investigated using Cell Counting Kit-8, Transwell, colony formation and wound healing assays. miR-486-3p was aberrantly downregulated in OS tissues and cell lines and was packed with exosomes. miR-486-3p overexpression was shown to inhibit OS cell progression and promoted cell cycle arrest in vitro. In addition, MARCH1 was identified as a direct downstream molecule of miR-486-3p in OS cells. circKEAP1 was found to be upregulated in OS tissues and cells. circKEAP1 was found to have binding sites with miR-486-3p. Mechanistically, circKEAP1 positively regulated MARCH1 expression by sponging miR-486-3p. Exosomal miR-486-3p inhibited the progression of OS by sponging the circKEAP1/MARCH1 axis. These findings may provide a promising treatment approach for OS.

The Role of Long Noncoding Ribonucleic Acids in Glioblastoma: What the Neurosurgeon Should Know

A significant proportion of the human transcriptome, long noncoding RNAs (lncRNAs) play pivotal roles in several aspects of glioblastoma (GBM) pathophysiology including proliferation, invasion, radiation and temozolomide resistance, and immune modulation. The majority of lncRNAs exhibit tissue- and tumor-specific expression, lending them to be attractive targets for therapeutic translation. In recent years, unprecedented progress has been made toward our understanding of lncRNA in GBM. In this review, we discuss the function of lncRNAs, including specific lncRNAs that have critical roles in key aspects of GBM pathophysiology, and potential clinical relevance of lncRNAs for patients with GBM.

Nucleic acid nanoassembly-enhanced RNA therapeutics and diagnosis

RNAs are involved in the crucial processes of disease progression and have emerged as powerful therapeutic targets and diagnostic biomarkers. However, efficient delivery of therapeutic RNA to the targeted location and precise detection of RNA markers remains challenging. Recently, more and more attention has been paid to applying nucleic acid nanoassemblies in diagnosing and treating. Due to the flexibility and deformability of nucleic acids, the nanoassemblies could be fabricated with different shapes and structures. With hybridization, nucleic acid nanoassemblies, including DNA and RNA nanostructures, can be applied to enhance RNA therapeutics and diagnosis. This review briefly introduces the construction and properties of different nucleic acid nanoassemblies and their applications for RNA therapy and diagnosis and makes further prospects for their development.

Exosomal miRNA-21 from Toxoplasma gondii-infected microglial cells induces the growth of U87 glioma cells by inhibiting tumor suppressor genes

Toxoplasma gondii is an intracellular protozoan parasite that can modulate the microenvironment of infected hosts and is known to be associated with the incidence of brain tumor growth. In this study, we suggested that the exosomal microRNA-21 derived from Toxoplasma infection would contribute to the growth of brain tumors. Exosomes of BV2 microglial cells infected with Toxoplasma were characterized and confirmed internalization to U87 glioma cells. Exosomal miRNA expression profiles were analyzed using microRNA array and miR-21A-5p associated with Toxoplasma and tumor sorted. We also examined the mRNA level of tumor-associated genes in U87 glioma cells by changing the level of miR-21 within exosomes and the effects of exosomes on the proliferation of human U87 glioma cells. Expression of miRNA-21 was increased and anti-tumorigenic genes (FoxO1, PTEN, and PDCD4) were decreased in exosomes within T. gondii-infected U87 glioma cells. Toxoplasma-infected BV2-derived exosomes induced proliferation of U87 glioma cells. The exosomes induced the growth of U87 cells in a mouse tumor model. We suggest that the increased exosomal miR-21 from Toxoplasma-infected BV2 microglial cells may play an important role as a cell growth promotor of U87 glioma cells through a down-regulation of anti-tumorigenic genes.

Targeting non-coding RNA family members with artificial endonuclease XNAzymes

Non-coding RNAs (ncRNAs) offer a wealth of therapeutic targets for a range of diseases. However, secondary structures and high similarity within sequence families make specific knockdown challenging. Here, we engineer a series of artificial oligonucleotide enzymes (XNAzymes) composed of 2'-deoxy-2'-fluoro-β-D-arabino nucleic acid (FANA) that specifically or preferentially cleave individual ncRNA family members under quasi-physiological conditions, including members of the classic microRNA cluster miR-17~92 (oncomiR-1) and the Y RNA hY5. We demonstrate self-assembly of three anti-miR XNAzymes into a biostable catalytic XNA nanostructure, which targets the cancer-associated microRNAs miR-17, miR-20a and miR-21. Our results provide a starting point for the development of XNAzymes as a platform technology for precision knockdown of specific non-coding RNAs, with the potential to reduce off-target effects compared with other nucleic acid technologies.

Immune Modulatory Short Noncoding RNAs Targeting the Glioblastoma Microenvironment

Glioblastomas are heterogeneous and have a poor prognosis. Glioblastoma cells interact with their neighbors to form a tumor-permissive and immunosuppressive microenvironment. Short noncoding RNAs are relevant mediators of the dynamic crosstalk among cancer, stromal, and immune cells in establishing the glioblastoma microenvironment. In addition to the ease of combinatorial strategies that are capable of multimodal modulation for both reversing immune suppression and enhancing antitumor immunity, their small size provides an opportunity to overcome the limitations of blood-brain-barrier (BBB) permeability. To enhance glioblastoma delivery, these RNAs have been conjugated with various molecules or packed within delivery vehicles for enhanced tissue-specific delivery and increased payload. Here, we focus on the role of RNA therapeutics by appraising which types of nucleotides are most effective in immune modulation, lead therapeutic candidates, and clarify how to optimize delivery of the therapeutic RNAs and their conjugates specifically to the glioblastoma microenvironment.

miR-106b-5p Inhibits IRF1/IFN-β Signaling to Promote M2 Macrophage Polarization of Glioblastoma

Purpose

The microRNA (miRNA) profile changes in the tumor-associated macrophages. However, the role of miR-106b-5p in the glioblastoma-associated macrophages is poorly understood.

Materials and Methods

In our study, miR-106b-5p and M2 macrophage markers were detected by qRT-PCR and Western blotting in THP1 cells, with the conditioned medium from U251 cells or M2 macrophages in response to IL-4 stimulation and M1 macrophages stimulated by LPS and IFN-γ. IFN regulatory factor (IRF1) was identified as a target of miR-106b-5p in the glioma infiltrating macrophages by luciferase reporter assay. The molecular mechanisms involved in the miR-106b-5p-mediated regulation of M2 polarization were clarified by shRNA knockdown assay.

Results

Our results showed miR-106b-5p expression was upregulated in glioma-infiltrating macrophages. miR-106b-5p regulated M2 polarization of glioma infiltrating macrophages and enhanced the growth of glioma-infiltrating macrophages. IRF1 was identified as a target of miR-106b-5p. Furthermore, miR-106b-5p inhibited IRF1 expression by targeting IRF1/IFN-β pathway to promote M2 polarization of macrophages.

Conclusion

miR-106b-5p may inhibit IRF1/IFN-β signaling to promote M2 macrophage polarization of glioblastoma, and it may become a novel target for the treatment of glioblastoma.

Long noncoding RNA DANCR knockdown inhibits proliferation, migration and invasion of glioma by regulating miR-135a-5p/BMI1

Background

Glioma is the most common and aggressive primary brain tumor with high mortality rate around the world. LncRNAs have been identified to play key roles in tumorigenesis in various cancers, including glioma. However, the precise mechanism of DANCR in progression of glioma remains poorly defined.

Methods

The expression levels of DANCR, miR-135a-5p and BMI1 were measured by qRT-PCR in glioma tissues and cells. Cell proliferation, migration and invasion were detected by CCK-8 assay and transwell assay, respectively. The possible binding sites of miR-135a-5p and DANCR or BMI1 were predicted by online software and verified using luciferase report assay and RNA immunoprecipitation (RIP) assay. Western blot analysis was carried out to detect the protein of BMI1 expression. A xenograft tumor model was established to investigate the functions of DANCR in glioma progression in vivo.

Results

DANCR was upregulated and miR-135a-5p was downregulated in glioma tissues and cells. Knockdown of DANCR inhibited cell proliferation, migration and invasion in glioma cells. In addition, miR-135a-5p was a direct target of DANCR, and its elevated expression could reverse miR-135a-5p inhibition-mediated progression of glioma. Moreover, miR-135a-5p could specially bind to BMI1, and the expression of BMI1 was obviously elevated in glioma tissues and cells. Furthermore, DANCR acted as a ceRNA to regulate BMI1 expression and BMI1-mediated effects on progression of glioma by sponging miR-135a-5p. Besides, inhibition of DANCR limited tumor growth by regulating miR-135a-5p and BMI1 expression in vivo.

Conclusion

DANCR knockdown inhibited cell proliferation, migration and invasion in glioma cells through regulating miR-135a-5p/BMI1 axis, providing viable therapeutic avenues for treatment of glioma.

PTB-AS, a Novel Natural Antisense Transcript, Promotes Glioma Progression by Improving PTBP1 mRNA Stability with SND1

Glioma, the most common primary malignancy in the brain, has high recurrence and lethality rates, and thus, elucidation of the molecular mechanisms of this incurable disease is urgently needed. Poly-pyrimidine tract binding protein (PTBP1, also known as hnRNP I), an RNA-binding protein, has various mechanisms to promote gliomagenesis. However, the mechanisms regulating PTBP1 expression are unclear. Herein, we report a novel natural antisense noncoding RNA, PTB-AS, whose expression correlated positively with PTBP1 mRNA. We found that PTB-AS significantly promoted the proliferation and migration in vivo and in vitro of glioma cells. PTB-AS substantially increased the PTBP1 level by directly binding to its 3' UTR and stabilizing the mRNA. Furthermore, staphylococcal nuclease domain-containing 1 (SND1) dramatically increased the binding capacity between PTB-AS and PTBP1 mRNA. Mechanistically, PTB-AS could mask the binding site of miR-9 in the PTBP1-3' UTR; miR-9 negatively regulates PTBP1. To summarize, we revealed that PTB-AS, which maintains the PTBP1 level through extended base pairing to the PTBP1 3' UTR with the assistance of SND1, could significantly promote gliomagenesis.

Targeting miR‑155‑5p and miR‑221‑3p by peptide nucleic acids induces caspase‑3 activation and apoptosis in temozolomide‑resistant T98G glioma cells

The present study investigated the effects of the combined treatment of two peptide nucleic acids (PNAs), directed against microRNAs involved in caspase‑3 mRNA regulation (miR‑155‑5p and miR‑221‑3p) in the temozolomide (TMZ)‑resistant T98G glioma cell line. These PNAs were conjugated with an octaarginine tail in order to obtain an efficient delivery to treated cells. The effects of singularly administered PNAs or a combined treatment with both PNAs were examined on apoptosis, with the aim to determine whether reversion of the drug‑resistance phenotype was obtained. Specificity of the PNA‑mediated effects was analyzed by reverse transcription‑quantitative polymerase‑chain reaction, which demonstrated that the effects of R8‑PNA‑a155 and R8-PNA-a221 anti‑miR PNAs were specific. Furthermore, the results obtained confirmed that both PNAs induced apoptosis when used on the temozolomide‑resistant T98G glioma cell line. Notably, co‑administration of both anti‑miR‑155 and anti‑miR‑221 PNAs was associated with an increased proapoptotic activity. In addition, TMZ further increased the induction of apoptosis in T98G cells co‑treated with anti‑miR‑155 and anti‑miR‑221 PNAs.

LncRNA LINC00152 promoted glioblastoma progression through targeting the miR-107 expression

Long non-coding RNAs (lncRNAs) LINC00152 plays important roles in the progression of some tumors. However, the role of LINC00152 in human l glioblastoma is still unknown. In this study, we indicated that LINC00152 expression level was upregulated in glioblastoma tissues and cell lines. Overexpression of LINC00152 promoted the U87 and LN229 cell proliferation and invasion. Moreover, overexpression of LINC00152 suppressed the E-cadherin expression, where ectopic expression of LINC00152 promoted the N-cadherin, Vimentin, and Snail expression. These results suggested that LINC00152 enhanced epithelial-to-mesenchymal transition (EMT) program in the glioblastoma cell. Overexpression of LINC00152 suppressed the miR-107 expression in the U87 cell and enhanced the HMGA2 expression, which is a direct target gene of miR-107. In addition, we showed that the miR-107 expression was downregulated in the glioblastoma tissues and cell lines. Interesting, the expression of LINC00152 was negatively related with miR-107 expression in the glioblastoma tissues. Furthermore, LINC00152 promoted the glioblastoma cell proliferation and invasion through inhibiting miR-107 expression. These data suggested that LINC00152 acted as oncogene roles in the glioblastoma cell partly through targeting the miR-107 expression.

Downregulation of microRNA-216b contributes to glioma cell growth and migration by promoting AEG-1-mediated signaling

Accumulating evidence indicates microRNA-216b (miR-216b) plays an important role in the development and progression of various cancers. However, little is known about the function of miR-216b in gliomas. In this study, we aimed to investigate the expression level and functional significance of miR-216b in gliomas. We found that miR-216b was significantly downregulated in glioma specimens and cell lines. Overexpression of miR-216b suppressed the growth and migration of glioma cells, while miR-216b inhibition showed the opposite effects. Astrocyte elevated gene-1 (AEG-1) was predicted as a potential target gene of miR-216b by bioinformatics analysis. A dual-luciferase reporter assay showed that miR-216b could directly target the 3'-untranslated region of AEG-1. RT-qPCR and western blot analysis showed that miR-216 negatively regulated AEG-1 expression in glioma cells. Correlation analysis revealed an inverse correlation between miR-216b and AEG-1 in clinical glioma specimens. miR-216b also regulated the activation of nuclear factor-κB and Wnt signaling in glioma cells. Moreover, restoration of AEG-1 expression partially reversed the inhibitory effect of miR-216b overexpression on glioma cell growth and migration. Overall, these results revealed a tumor suppressive role of miR-216b in glioma tumorigenesis, and identified AEG-1 as a target gene of miR-216b action. Our study suggests that miR-216b can be potentially targeted for the development of novel therapies for gliomas.

miR-340 predicts glioblastoma survival and modulates key cancer hallmarks through down-regulation of NRAS

Glioblastoma is the most common primary brain tumor in adults; with a survival rate of 12 months from diagnosis. However, a small subgroup of patients, termed long-term survivors (LTS), has a survival rate longer then 12–14 months. There is thus increasing interest in the identification of molecular signatures predicting glioblastoma prognosis and in how to improve the therapeutic approach. Here, we report miR-340 as prognostic tumor-suppressor microRNA for glioblastoma. We analyzed microRNA expression in > 500 glioblastoma patients and found that although miR-340 is strongly down-regulated in glioblastoma overall, it is up-regulated in LTS patients compared to short-term survivors (STS). Indeed, miR-340 expression predicted better prognosis in glioblastoma patients. Coherently, overexpression of miR-340 in glioblastoma cells was found to produce a tumor-suppressive activity. We identified NRAS mRNA as a critical, direct target of miR-340: in fact, miR-340 negatively influenced multiple aspects of glioblastoma tumorigenesis by down-regulating NRAS and downstream AKT and ERK pathways. Thus, we demonstrate that expression of miR-340 in glioblastoma is responsible for a strong tumor-suppressive effect in LTS patients by down-regulating NRAS. miR-340 may thus represent a novel marker for glioblastoma diagnosis and prognosis, and may be developed into a tool to improve treatment of glioblastoma.

A 4-miRNA signature to predict survival in glioblastomas

Glioblastomas are among the most lethal cancers; however, recent advances in survival have increased the need for better prognostic markers. microRNAs (miRNAs) hold great prognostic potential being deregulated in glioblastomas and highly stable in stored tissue specimens. Moreover, miRNAs control multiple genes representing an additional level of gene regulation possibly more prognostically powerful than a single gene. The aim of the study was to identify a novel miRNA signature with the ability to separate patients into prognostic subgroups. Samples from 40 glioblastoma patients were included retrospectively; patients were comparable on all clinical aspects except overall survival enabling patients to be categorized as short-term or long-term survivors based on median survival. A miRNome screening was employed, and a prognostic profile was developed using leave-one-out cross-validation. We found that expression patterns of miRNAs; particularly the four miRNAs: hsa-miR-107_st, hsa-miR-548x_st, hsa-miR-3125_st and hsa-miR-331-3p_st could determine short- and long-term survival with a predicted accuracy of 78%. Heatmap dendrograms dichotomized glioblastomas into prognostic subgroups with a significant association to survival in univariate (HR 8.50; 95% CI 3.06–23.62; p<0.001) and multivariate analysis (HR 9.84; 95% CI 2.93–33.06; p<0.001). Similar tendency was seen in The Cancer Genome Atlas (TCGA) using a 2-miRNA signature of miR-107 and miR-331 (miR sum score), which were the only miRNAs available in TCGA. In TCGA, patients with O6-methylguanine-DNA-methyltransferase (MGMT) unmethylated tumors and low miR sum score had the shortest survival. Adjusting for age and MGMT status, low miR sum score was associated with a poorer prognosis (HR 0.66; 95% CI 0.45–0.97; p = 0.033). A Kyoto Encyclopedia of Genes and Genomes analysis predicted the identified miRNAs to regulate genes involved in cell cycle regulation and survival. In conclusion, the biology of miRNAs is complex, but the identified 4-miRNA expression pattern could comprise promising biomarkers in glioblastoma stratifying patients into short- and long-term survivors.

MiR-15a/16 deficiency enhances anti-tumor immunity of glioma-infiltrating CD8+ T cells through targeting mTOR

MiR-15a/16, a miRNA cluster located at chromosome 13q14, has been reported to act as an immune regulator in inflammatory disorders besides its aberrant expression in cancers. However, little is known about its regulation in tumor-infiltrating immune cells. In our study, using an orthotropic GL261 mouse glioma model, we found that miR-15a/16 deficiency in host inhibited tumor growth and prolonged mice survival, which might be associated with the accumulation of tumor-infiltrating CD8+ T cells. More importantly, tumor-infiltrating CD8+ T cells without miR-15a/16 showed lower expression of PD-1, Tim-3 and LAG-3, and stronger secretion of IFN-γ, IL-2 and TNF-α than WT tumor-infiltrating CD8+ T cells. Also, our in vitro experiments further confirmed that miR-15a/16^-/- CD8+ T displayed higher active phenotypes, more cytokines secretion and faster expansion, compared to WT CD8+ T cells. Mechanismly, mTOR was identified as a target gene of miR-15a/16 to negatively regulate the activation of CD8+ T cells. Taken together, these data suggest that miR-15a/16 deficiency resists the exhaustion and maintains the activation of glioma-infiltrating CD8+ T cells to alleviate glioma progression via targeting mTOR. Our findings provide evidence for the potential immunotherapy through targeting miR-15a/16 in tumor-infiltrating immune cells.

MicroRNA Regulation of Glycolytic Metabolism in Glioblastoma

Glioblastoma (GBM) is the most aggressive and common malignant brain tumour in adults. A well-known hallmark of GMB and many other tumours is aerobic glycolysis. MicroRNAs (miRNAs) are a class of short nonprotein coding sequences that exert posttranscriptional controls on gene expression and represent critical regulators of aerobic glycolysis in GBM. In GBM, miRNAs regulate the expression of glycolytic genes directly and via the regulation of metabolism-associated tumour suppressors and oncogenic signalling pathways. This review aims to establish links between miRNAs expression levels, the expression of GBM glycolytic regulatory genes, and the malignant progression and prognosis of GBM. In this review, the involvement of 25 miRNAs in the regulation of glycolytic metabolism of GBM is discussed. Seven of these miRNAs have been shown to regulate glycolytic metabolism in other tumour types. Further eight miRNAs, which are differentially expressed in GBM, have also been reported to regulate glycolytic metabolism in other cancer types. Thus, these miRNAs could serve as potential glycolytic regulators in GBM but will require functional validation. As such, the characterisation of these molecular and metabolic signatures in GBM can facilitate a better understanding of the molecular pathogenesis of this disease.

A Comprehensive Review of Genomics and Noncoding RNA in Gliomas

Glioblastoma (GBM) is the most malignant primary adult brain tumor. In spite of our greater understanding of the biology of GBMs, clinical outcome of GBM patients remains poor, as their median survival with best available treatment is 12 to 18 months. Recent efforts of The Cancer Genome Atlas (TCGA) have subgrouped patients into 4 molecular/transcriptional subgroups: proneural, neural, classical, and mesenchymal. Continuing efforts are underway to provide a comprehensive map of the heterogeneous makeup of GBM to include noncoding transcripts, genetic mutations, and their associations to clinical outcome. In this review, we introduce key molecular events (genetic and epigenetic) that have been deemed most relevant as per studies such as TCGA, with a specific focus on noncoding RNAs such as microRNAs (miRNA) and long noncoding RNAs (lncRNA). One of our main objectives is to illustrate how miRNAs and lncRNAs play a pivotal role in brain tumor biology to define tumor heterogeneity at molecular and cellular levels. Ultimately, we elaborate how radiogenomics-based predictive models can describe miRNA/lncRNA-driven networks to better define heterogeneity of GBM with clinical relevance.

Shift of microRNA profile upon glioma cell migration using patient-derived spheroids and serum-free conditions

Glioblastoma multiforme (GBM) is the most frequent malignant primary brain tumor. A major reason for the overall median survival being only 14.6 months is migrating tumor cells left behind after surgery. Another major reason is tumor cells having a so-called cancer stem cell phenotype being therefore resistant towards traditional chemo- and radiotherapy. A group of novel molecular targets are microRNAs (miRNAs). MiRNAs are small non-coding RNAs exerting post-transcriptional regulation of gene expression. The aim of this study was to identify differentially expressed miRNAs in migrating GBM cells using serum-free stem cell conditions. We used patient-derived GBM spheroid cultures for a novel serum-free migration assay. MiRNA expression of migrating tumor cells isolated at maximum migration speed was compared with corresponding spheroids using an OpenArray Real-Time PCR System. The miRNA profiling revealed 30 miRNAs to be differentially expressed. In total 13 miRNAs were upregulated and 17 downregulated in migrating cells compared to corresponding spheroids. The three most deregulated miRNAs, miR-1227 (up-regulated), miR-32 (down-regulated) and miR-222 (down-regulated), were experimentally overexpressed. A non-significantly increased migration rate was observed after miR-1227 overexpression. A significantly reduced migration rate was observed after miR-32 and miR-222 overexpression. In conclusion a shift in microRNA profile upon glioma cell migration was identified using an assay avoiding serum-induced migration. Both the miRNA profiling and the functional validation suggested that miR-1227 may be associated with increased migration and miR-32 and miR-222 with decreased migration. These miRNAs may represent potential novel targets in migrating glioma cells.

Role of miR-223/paired box 6 signaling in temozolomide chemoresistance in glioblastoma multiforme cells

Glioblastoma (GBM) is the predominant and most fatal type of brain tumor in adults. The prognosis of GBM remains poor despite advances in surgery, chemotherapy and radiotherapy. It is common that patients with GBM exhibit innate or acquired resistance to temozolomide (TMZ), a standard chemotherapeutic agent for GBM, and a previous report demonstrated that miRNA‑233 (miR‑223) promotes the growth and invasion of GBM cells by targeting tumor suppressor paired box 6 (PAX6). The present study explored the effect of TMZ on miR‑223/PAX6 signaling in addition to the effect of miR‑223/PAX6 signaling on TMZ chemoresistance in human GBM cells. Luciferase reporter assays confirmed that miR‑223 directly targets PAX6 through binding to its 3'‑untranslated region. TMZ reduced the expression level of miR‑223 in a concentration‑dependent manner in U251 and U118 GBM cells, which led to increased expression of PAX6. miR‑223 and/or PAX6 were overexpressed and knocked down in U251 and U118 cells, and the half maximal inhibitory concentration (IC50) of TMZ and cell proliferation under TMZ treatment were used as measures of TMZ chemoresistance. The results demonstrated that overexpression of miR-223 in GBM cells markedly decreased TMZ-induced inhibition of cell proliferation and increased TMZ IC50, which could be abolished by overexpression of PAX6. On the other hand, knocking down miR‑223 in GBM cells with antagomir significantly enhanced the inhibitory effect of TMZ on GBM cell proliferation and decreased the TMZ IC50, which could be abolished by knockdown of PAX6. In conclusion, the present study demonstrated that TMZ inhibits GBM cell proliferation by inhibiting the expression of miR‑223, which leads to increased expression of tumor suppressor PAX6. Overexpression of miR‑223 increases TMZ chemoresistance, while inhibition of miR‑223 with antagomir markedly decreases TMZ chemoresistance in GBM cells. The present study provided novel insight into the molecular mechanisms underlying the pharmacological effects, in addition to the chemoresistance, of TMZ for GBM.

Estimating survival time of patients with glioblastoma multiforme and characterization of the identified microRNA signatures

BACKGROUND

Though glioblastoma multiforme (GBM) is the most frequently occurring brain malignancy in adults, clinical treatment still faces challenges due to poor prognoses and tumor relapses. Recently, microRNAs (miRNAs) have been extensively used with the aim of developing accurate molecular therapies, because of their emerging role in the regulation of cancer-related genes. This work aims to identify the miRNA signatures related to survival of GBM patients for developing molecular therapies.

RESULTS

This work proposes a support vector regression (SVR)-based estimator, called SVR-GBM, to estimate the survival time in patients with GBM using their miRNA expression profiles. SVR-GBM identified 24 out of 470 miRNAs that were significantly associated with survival of GBM patients. SVR-GBM had a mean absolute error of 0.63 years and a correlation coefficient of 0.76 between the real and predicted survival time. The 10 top-ranked miRNAs according to prediction contribution are as follows: hsa-miR-222, hsa-miR-345, hsa-miR-587, hsa-miR-526a, hsa-miR-335, hsa-miR-122, hsa-miR-24, hsa-miR-433, hsa-miR-574 and hsa-miR-320. Biological analysis using the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway on the identified miRNAs revealed their influence in GBM cancer.

CONCLUSION

The proposed SVR-GBM using an optimal feature selection algorithm and an optimized SVR to identify the 24 miRNA signatures associated with survival of GBM patients. These miRNA signatures are helpful to uncover the individual role of miRNAs in GBM prognosis and develop miRNA-based therapies.

Dysregulated miR-671-5p / CDR1-AS / CDR1 / VSNL1 axis is involved in glioblastoma multiforme

MiR-671-5p is encoded by a gene localized at 7q36.1, a region amplified in human glioblastoma multiforme (GBM), the most malignant brain cancer. To investigate whether expression of miR-671-5p were altered in GBM, we analyzed biopsies from a cohort of forty-five GBM patients and from five GBM cell lines. Our data show significant overexpression of miR-671-5p in both biopsies and cell lines. By exploiting specific miRNA mimics and inhibitors, we demonstrated that miR-671-5p overexpression significantly increases migration and to a less extent proliferation rates of GBM cells. Through a combined in silico and in vitro approach, we identified CDR1-AS, CDR1, VSNL1 as downstream miR-671-5p targets in GBM. Expression of these genes significantly decreased both in GBM biopsies and cell lines and negatively correlated with that of miR-671-5p. Based on our data, we propose that the axis miR-671-5p / CDR1-AS / CDR1 / VSNL1 is functionally altered in GBM cells and is involved in the modification of their biopathological profile.

miR-133b inhibits glioma cell proliferation and invasion by targeting Sirt1

MicroRNAs (miRs) are a class of small non-coding RNAs that function as mediators of gene expression. Dysregulations of miRs have been implicated in the development and progression of glioma. In the present study, we investigated the role of miR-133b in mediating the proliferation and invasion of glioma cells, and the potential mechanism. Real-time RT-PCR results showed that miR-133b expression was significantly decreased in glioma tissues compared with normal brain tissues. Luciferase reporter assay further identified silent information regulator 1 (Sirt1) as a novel direct target of miR-133b in glioma U87 cells. Overexpression of miR-133b suppressed Sirt1 expression and reduced the proliferation and invasion of U87 cells, which could be partly rescued by forced expression of Sirt1. In addition, the Sirt1 mRNA level was significantly higher in glioma tissues than in normal brain tissues, and was inversely correlated with miR-133b level in glioma tissues. In summary, our study sheds light on the regulatory mechanism of miR-133b in glioma growth and metastasis via direct mediation of Sirt1 expression, and suggests that Sirt1 may serve as a potential therapeutic target for glioma.

Functional genomics analyses of RNA-binding proteins reveal the splicing regulator SNRPB as an oncogenic candidate in glioblastoma

BACKGROUND

Glioblastoma (GBM) is the most common and aggressive type of brain tumor. Currently, GBM has an extremely poor outcome and there is no effective treatment. In this context, genomic and transcriptomic analyses have become important tools to identify new avenues for therapies. RNA-binding proteins (RBPs) are master regulators of co- and post-transcriptional events; however, their role in GBM remains poorly understood. To further our knowledge of novel regulatory pathways that could contribute to gliomagenesis, we have conducted a systematic study of RBPs in GBM.

RESULTS

By measuring expression levels of 1542 human RBPs in GBM samples and glioma stem cell samples, we identified 58 consistently upregulated RBPs. Survival analysis revealed that increased expression of 21 RBPs was also associated with a poor prognosis. To assess the functional impact of those RBPs, we modulated their expression in GBM cell lines and performed viability, proliferation, and apoptosis assays. Combined results revealed a prominent oncogenic candidate, SNRPB, which encodes core spliceosome machinery components. To reveal the impact of SNRPB on splicing and gene expression, we performed its knockdown in a GBM cell line followed by RNA sequencing. We found that the affected genes were involved in RNA processing, DNA repair, and chromatin remodeling. Additionally, genes and pathways already associated with gliomagenesis, as well as a set of general cancer genes, also presented with splicing and expression alterations.

CONCLUSIONS

Our study provides new insights into how RBPs, and specifically SNRPB, regulate gene expression and directly impact GBM development.

Glioma Cells in the Tumor Periphery Have a Stem Cell Phenotype

Gliomas are highly infiltrative tumors incurable with surgery. Although surgery removes the bulk tumor, tumor cells in the periphery are left behind resulting in tumor relapses. The aim of the present study was to characterize the phenotype of tumor cells in the periphery focusing on tumor stemness, proliferation and chemo-resistance. This was investigated in situ in patient glioma tissue as well as in orthotopic glioblastoma xenografts. We identified 26 gliomas having the R132 mutation in Isocitrate DeHydrogenase 1 (mIDH1). A double immunofluorescence approach identifying mIDH1 positive tumor cells and a panel of markers was used. The panel comprised of six stem cell-related markers (CD133, Musashi-1, Bmi-1, Sox-2, Nestin and Glut-3), a proliferation marker (Ki-67) as well as a chemo-resistance marker (MGMT). Computer-based automated classifiers were designed to measure the mIDH1 positive nucleus area-fraction of the chosen markers. Moreover, orthotopic glioblastoma xenografts from five different patient-derived spheroid cultures were obtained and the tumor cells identified by human specific immunohistochemical markers. The results showed that tumor cells in the periphery of patient gliomas expressed stem cell markers, however for most markers at a significantly lower level than in the tumor core. The Ki-67 level was slightly reduced in the periphery, whereas the MGMT level was similar. In orthotopic glioblastoma xenografts all markers showed similar levels in the core and periphery. In conclusion tumor cells in the periphery of patient gliomas have a stem cell phenotype, although it is less pronounced than in the tumor core. Novel therapies aiming at preventing recurrence should therefore take tumor stemness into account. Migrating cells in orthotopic glioblastoma xenografts preserve expression and stem cell markers. The orthotopic model therefore has a promising translational potential.

miR-373 Inhibits Glioma Cell U251 Migration and Invasion by Down-Regulating CD44 and TGFBR2

Glioblastoma multiforme (GBM) is the most malignant glioma, unveiling the underlying mechanisms of its aggressiveness could promote the discovery of potential targets for effective treatment. MicroRNAs (miRNAs) are important participants in both development and disease, its involvement in cancers has long been recognized. In this study, we investigated the role of miRNA-373 (miR-373) in GBM cell line U251, demonstrated that although miR-373 does not affect cell growth of U251, it inhibits migration and invasion of U251. Forced expression of miR-373 down-regulates the expressions CD44 and TGFBR2, while knockdown of CD44 and TGFBR2 presents the similar phenotype as miR-373 overexpression, suggesting that CD44 and TGFBR2 are functional targets of miR-373, down-regulation of CD44 and TGFBR2 by miR-373 are partly responsible for the migration, and invasion suppressive role of miR-373 in U251.

miR-21 Is Linked to Glioma Angiogenesis: A Co-Localization Study

MicroRNA-21 (miR-21) is the most consistently over-expressed microRNA (miRNA) in malignant gliomas. We have previously reported that miR-21 is upregulated in glioma vessels and subsets of glioma cells. To better understand the role of miR-21 in glioma angiogenesis and to characterize miR-21-positive tumor cells, we systematically stained consecutive serial sections from ten astrocytomas for miR-21, hypoxia-inducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF), phosphatase and tensin homolog (PTEN), octamer-binding transcription factor 4 (Oct4), sex-determining region Y box 2 (Sox2) and CD133. We developed an image analysis-based co-localization approach allowing global alignment and quantitation of the individual markers, and measured the miR-21 in situ hybridization signal against the immunohistochemical staining of the six different markers. miR-21 significantly co-localized with the hypoxia- and angiogenesis-associated markers HIF-1α (p=0.0020) and VEGF (p=0.0096), whereas the putative miR-21 target, PTEN, was expressed independently of miR-21. Expression of stem cell markers Oct4, Sox2 and CD133 was not associated with miR-21. In six glioblastoma cultures, miR-21 did not correlate with the six markers. These findings suggest that miR-21 is linked to glioma angiogenesis, that miR-21 is unlikely to regulate PTEN, and that miR-21-positive tumor cells do not possess stem cell characteristics.

High levels of apoptosis are induced in human glioma cell lines by co-administration of peptide nucleic acids targeting miR-221 and miR-222

The biological activity of a combined treatment of U251, U373 and T98G glioma cell lines with two anti-miR PNAs, directed against miR‑221 and miR‑222 and conjugated with an ocataarginine tail (R8-PNA-a221 and R8-PNA-a222) for efficient cellular delivery, was determined. Apoptosis was analyzed, and the effect of the combined treatment of glioma cells with either or both PNAs on the reversion of drug-resistance phenotype was assessed in the temozolomide-resistant T98G glioma cell line. Selectivity of PNA/miRNA interactions was studied by surface plasmon resonance (SPR)-based Biacore analysis. Specificity of the PNA effects at the cellular level was analyzed by RT-qPCR. These experiments support the concept that the effects of R8-PNA-a221 and R8-PNA-a222 are specific. The studies on apoptosis confirmed that the R8-PNA-a221 induces apoptosis and demonstrated the pro-apoptotic effects of R8-PNA-a222. Remarkably, increased pro-apoptotic effects were obtained with the co-administration of both anti-miR‑221 and anti-miR‑222 PNAs. In addition, co-administration of R8-PNA-a221 and R8-PNA-a222 induced apoptosis of TMZ-treated T98G cells at a level higher than that obtained following singular administration of R8-PNA-a221 or R8-PNA-a222.

MicroRNA-663 inhibits the proliferation, migration and invasion of glioblastoma cells via targeting TGF-β1

Cell migration and invasion are key processes involved during tumor metastasis. Recently, microRNAs (miRs) have been demonstrated to play important roles in the regulation of cancer metastasis. However, the underlying mechanisms remain unknown. Here, we aimed to investigate the exact role of miR-663 in the metastasis of glioblastoma as well as the underlying mechanisms. By performing quantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis, we demonstrated that miR-663 was significantly downregulated in glioblastoma tissues (n=25), when compared to that in normal brain tissues (n=15). In addition, its expression levels were also reduced in human glioblastoma cell lines, A172 and U87. Furthermore, restoration of miR-663 expression led to a significant decrease in the cell proliferation, migration and invasion of human glioblastoma A172 and U87 cells. We further identified TGF-β1 as a direct target of miR-663, and found that the expression of TGF-β1 was negatively mediated by miR-663 at the post-transcriptional level in glioblastoma cells. Moreover, overexpression of TGF-β1 significantly reversed the inhibitory effects of miR-663 upregulation on the proliferation, migration and invasion in A172 and U87 cells. In addition, our data suggest that MMP2 and E-cadherin, a key factor in epithelial-mesenchymal transition (EMT), are involved in the miR-633/TGF-β1-mediated metastasis of glioblastoma. In summary, miR-663 plays an inhibitory role in the regulation of proliferation, migration and invasion of glioblastoma cells, partly at least, via direct mediation of TGF-β1 as well as downstream MMP2 and E-cadherin. Therefore, we suggest that miR-663 is a potential candidate for the prevention of glioblastoma metastasis.

MicroRNA as potential biomarkers in Glioblastoma

Glioblastoma is the most aggressive and lethal tumour of the central nervous system and as such the identification of reliable prognostic and predictive biomarkers for patient survival and tumour recurrence is paramount. MicroRNA detection has rapidly emerged as potential biomarkers, in patients with glioblastoma. Over the last decade, analysis of miRNA in laboratory based studies have yielded several candidates as potential biomarkers however, the accepted use of these candidates in the clinic is yet to be validated. Here we will examine the use of miRNA signatures to improve glioblastoma stratification into subgroups and summarise recent advances made in miRNA examination as potential biomarkers for glioblastoma progression and recurrence.

Circulating biomarkers for gliomas

Currently, gliomas are diagnosed by neuroimaging, and refined diagnosis requires resection or biopsy to obtain tumour tissue for histopathological classification and grading. Blood-derived biomarkers, therefore, would be useful as minimally invasive markers that could support diagnosis and enable monitoring of tumour growth and response to treatment. Such circulating biomarkers could distinguish true progression from therapy-associated changes such as radiation necrosis, and help evaluate the persistence or disappearance of a therapeutic target, such as an oncoprotein or a targetable gene mutation, after targeted therapy. Unlike for other tumours, circulating biomarkers for gliomas are still being defined and are not yet in use in clinical practice. Circulating tumour DNA (ctDNA) isolated from plasma has been shown to reflect the mutational status of glioblastoma, and extracellular vesicles (EVs) containing ctDNA, microRNA and proteins function as rapidly adapting reservoirs for glioma biomarkers such as typical DNA mutations, regulatory microRNAs and oncoproteins. Ideally, circulating tumour cells could enable profiling of the whole-tumour genome, but they are difficult to detect and can reflect only a single cell type of the heterogeneous tumour composition, whereas EVs reflect the complex heterogeneity of the whole tumour, as well as its adaptations to therapy. Although all categories of potential blood-derived biomarkers need to be developed further, findings from other tumour types suggest that EVs are the most promising biomarkers.

Development of targeted therapies in treatment of glioblastoma

Glioblastoma (GBM) is a type of tumor that is highly lethal despite maximal therapy. Standard therapeutic approaches provide modest improvement in progression-free and overall survival, necessitating the investigation of novel therapies. Oncologic therapy has recently experienced a rapid evolution toward "targeted therapy", with drugs directed against specific targets which play essential roles in the proliferation, survival, and invasiveness of GBM cells, including numerous molecules involved in signal transduction pathways. Inhibitors of these molecules have already entered or are undergoing clinical trials. However, significant challenges in their development remain because several preclinical and clinical studies present conflicting results. In this article, we will provide an up-to-date review of the current targeted therapies in GBM.

Clinical significance of serum miR-155 expression level in acute pancreatitis patients

AIM: To determine the serum expression level of miR-155 in acute pancreatitis (AP) patients and to analyze its clinical significance.

METHODS: Twenty-eight patients with moderately severe AP (MSAP) or severe AP (SAP) were included in group A, 32 patients with mild AP (MAP) were included in group B, and 20 healthy people were included as normal controls (NCs). Serum miR-155 expression levels were detected by real-time quantitative PCR. The differences in miR-155 expression level in different groups, and the correlation between miR-155 expression level and clinical characteristics of AP patients were analyzed. A receiver operating characteristic curve (ROC curve) was plotted to explore the diagnostic value of serum miR-155.

RESULTS: The mean relative expression level of serum miR-155 was 8.09 ± 2.28 in group A, 4.94 ± 1.41 in group B, and 1.58 ± 0.81 in the NC group, and there were significant differences between groups A and B, group A and the NC group, and group B and the NC group (P < 0.05). The relative expression levels of miR-155 were correlated with patients' BISAP score, Ranson score, APACHE II score and MCTSI score (P < 0.05), but not with patients' gender and age. The area under the ROC curve of miR-155 for prediction of AP severity was 0.882, with a sensitivity of 92.5% and specificity of 85.7%, and the best cutoff value was 3.55.

CONCLUSION: Serum miR-155 may be a potential biomarker for the diagnosis of AP, and it is clinically useful for the prediction of the severity of AP.

Genome-wide hydroxymethylcytosine pattern changes in response to oxidative stress

The TET enzymes convert methylcytosine to the newly discovered base hydroxymethylcytosine. While recent reports suggest that TETs may play a role in response to oxidative stress, this role remains uncertain, and results lackin vivomodels. Here we show a global decrease of hydroxymethylcytosine in cells treated with buthionine sulfoximine, and in mice depleted for the major antioxidant enzymesGPx1 and 2. Furthermore, genome-wide profiling revealed differentially hydroxymethylated regions in coding genes, and intriguingly in microRNA genes, both involved in response to oxidative stress. These results thus suggest a profound effect ofin vivooxidative stress on the global hydroxymethylome.

Suppression of miR-221 inhibits glioma cells proliferation and invasion via targeting SEMA3B

Background

Gliomas are the most common primary tumors in the central nervous system. Due to complicated signaling pathways involved in glioma progression, effective targets for treatment and biomarkers for prognosis prediction are still scant.

Results

In this study we revealed that a new microRNA (miR), the miR-221, was highly expressed in the glioma cells, and suppression of miR-221 resulted in decreased cellular proliferation, migration, and invasion in glioma cells. Mechanistic experiments validated that miR-221 participates in regulating glioma cells proliferation and invasion via suppression of a direct target gene, the Semaphorin 3B (SEMA3B). The rescue experiment with miR-221 and SEMA3B both knockdown results in significant reversion of miR-221 induced phenotypes.

Conclusion

Taken together, our findings highlight an unappreciated role for miR-221 and SEMA3B in glioma.

MicroRNAs and cell cycle of malignant glioma

The control of malignant glioma cell cycle by microRNAs (miRNAs) is well established. The deregulation of miRNAs in glioma may contribute to tumor proliferation by directly targeting the critical cell-cycle regulators. Tumor suppressive miRNAs inhibit cell cycle through repressing the expression of positive cell-cycle regulators. However, oncogenic miRNAs promote the cell-cycle progression by targeting cell-cycle negative regulators. Recent studies have identified that transcription factors had involved in the expression of miRNAs. Transcription factors and miRNAs are implicated in regulatory network of glioma cell cycle, the deregulation of these transcription factors might be a cause of the deregulation of miRNAs. Abnormal versions of miRNAs have been implicated in the cell cycle of glioma. Based on those, miRNAs are excellent biomarker candidates and potential targets for therapeutic intervention in glioma.

Neurotensin signaling stimulates glioblastoma cell proliferation by upregulating c-Myc and inhibiting miR-29b-1 and miR-129-3p

BACKGROUND

Neurotensin (NTS) and its primary receptor NTSR1 are implicated in cancer progression. Aberrant expression of NTS/NTSR1 contributes to the proliferation of glioblastoma cells; however, the mechanism is not fully understood.

METHODS

Microarray and real-time PCR were performed to identify the NTS-regulated micro (mi)RNAs. The targets of the miRNAs were identified by luciferase assays and immunoblot analysis. The c-Myc binding sites in the miR-29b-1 and cyclin-dependent kinase (CDK)4 promoters were identified through chromatin immunoprecipitation assay. Cell proliferation was evaluated by Cell Counting Kit-8 assay and flow cytometry analysis. An orthotopic xenograft model demonstrated the role of NTS/NTSR1 and miRNAs in glioblastoma growth in vivo.

RESULTS

Pharmacological inhibition or small interfering NTSR1 treatment blocked glioblastoma cell cycle progression in the G1 phase with a concomitantly decreased expression of CDK6, CDK4, and c-Myc. Knockdown of NTSR1 increased the expression of miR-29b-1 and miR-129-3p, which were responsible for the decreased CDK6 expression. NTS/NTSR1 signaling activated the transcription factor c-Myc in U87 cells, leading to increased CDK4 expression and repressed miR-29b-1 expression. Knockdown of NTSR1 decreased the glioblastoma growth in vivo and significantly prolonged the survival time of the tumor-bearing mice, an effect that can be largely reversed by antagomir.

CONCLUSIONS

Our study showed a novel regulatory mechanism of NTS/NTSR1, an upstream signaling of miRNAs and c-Myc, in glioblastoma progression. The inhibition of the NTSR1 function or the upregulation of miR-29b-1 and miR-129-3p expression impaired glioma cell proliferation. These results suggested that the NTS/NTSR1/c-Myc/miRNA axis may be a potential therapeutic target for glioblastoma therapy.

Chemoresistance and chemotherapy targeting stem-like cells in malignant glioma

Glioblastoma remains a tumor with a dismal prognosis because of failure of current treatment. Glioblastoma cells with stem cell (GSC) properties survive chemotherapy and give rise to tumor recurrences that invariably result in the death of the patients. Here we summarize the current knowledge on chemoresistance of malignant glioma with a strong focus on GSC. Chemoresistant GSC are the most likely cause of tumor recurrence, but it remains controversial if GSC and under which conditions GSC are more chemoresistant than non-GSC within the tumor. Regardless of this uncertainty, the chemoresistance varies and it is mainly mediated by intrinsic factors. O6-methyl-guanidine methyltransferase (MGMT) remains the most potent mediator of chemoresistance, but disturbed mismatch repair system and multidrug resistance proteins contribute substantially. However, the intrinsic resistance by MGMT expression is regulated by extrinsic factors like hypoxia increasing MGMT expression and thereby resistance to alkylating chemotherapy. The search of new biomarkers helping to predict the tumor response to chemotherapy is ongoing and will complement the already known markers like MGMT.

Role of WW domain proteins WWOX in development, prognosis, and treatment response of glioma

Glioblastoma multiforme (GBM) is the most aggressive and malignant brain tumor. Delicate microenvironment and lineage heterogeneity of GBM cells including infiltration, hypoxia, angiogenesis, and stemness make them highly resistant to current conventional therapies, with an average life expectancy for GBM patients of less than 15 months. Poor response to cytotoxic agents of GBM cells remains the major challenge of GBM treatment. Resistance of GBM to clinical treatment is a result of genomic alternation and deregulated signaling pathways, such as p53 mutation and apoptosis signaling blockage, providing cancer cells more opportunities for survival rather than cell death. WW domain-containing oxidoreductase (WWOX) is a tumor suppressor gene, commonly downregulated in various types of tumors, including GBM. It has been found that the reintroduction of WWOX induced p53-mutant GBM cells to undergo apoptosis, but not in p53 wild-type GBM cells, indicating WWOX is likely to reopen apoptosis pathways in a p53-independent manner in GBM. Identifying the crucial target modulated by WWOX deficiency provides a potential therapeutic target for GBM treatment. Here, we have reviewed the literatures about the role of WWOX in development, signaling pathway, prognosis, and treatment response in malignant glioma.

Belonging to a network--microRNAs, extracellular vesicles, and the glioblastoma microenvironment

The complexity of glioblastoma multiforme (GBM) and its distinct pathophysiology belong to a unique brain microenvironment and its cellular interactions. Despite extensive evidence of a role for microRNAs in GBM cells, little is known about microRNA-dependent communication between different cellular compartments of the microenvironment that may contribute to the tumor phenotype. While the majority of microRNAs are found intracellularly, a significant number of microRNAs have been observed outside of cells, often encapsulated in secreted extracellular vesicles (EVs). The function of these circulating/secreted microRNAs has not been explored in the context of the brain tumor microenvironment. Establishing how microRNAs are involved in the regulation of oncogenic signaling networks between tumor cells and stroma is likely to add a needed additional layer of complexity to the tumor network, consisting of intercellular communication. More importantly, microRNA/EV signaling may provide an additional therapeutic target for this deadly disease.

Molecular heterogeneity of glioblastoma and its clinical relevance

Glioblastoma is the most common intracranial malignancy and constitutes about 50 % of all gliomas. Both inter-tumor and intra-tumor histological heterogeneity had been recognized by the early 1980-ies. Recent works using novel molecular platforms provided molecular definitions of these tumors. Based on comprehensive genomic sequence analyses, The Cancer Genome Atlas Research Network (TCGA) cataloged somatic mutations and recurrent copy number alterations in glioblastoma. Robust transcriptome and epigenome studies also revealed inter-tumor heterogeneity. Integration and cluster analyses of multi-dimensional genomic data lead to a new classification of glioblastoma tumors into subtypes with distinct biological features and clinical correlates. However, multiple observations also revealed tumor area-specific patterns of genomic imbalance. In addition, genetic alterations have been identified that were common to all areas analyzed and other alterations that were area specific. Analyses of intra-tumor transcriptome variations revealed that in more than half of the examined cases, fragments from the same tumor mass could be classified into at least two different glioblastoma molecular subgroups. Intra-tumor heterogeneity of molecular genetic profiles in glioblastoma may explain the difficulties encountered in the validation of oncologic biomarkers, and contribute to a biased selection of patients for single target therapies, treatment failure or drug resistance. In this paper, we summarize the currently available literature concerning inter- and intra-tumor molecular heterogeneity of glioblastomas, and call attention to the importance of this topic in relation to the growing efforts in routine molecular diagnostics and personalized therapy.

Epigenetic regulation of the miR142-3p/interleukin-6 circuit in glioblastoma

Epigenetic regulation plays a critical role in glioblastoma (GBM) tumorigenesis. However, how microRNAs (miRNAs) and cytokines cooperate to regulate GBM tumor progression is still unclear. Here, we show that interleukin-6 (IL-6) inhibits miR142-3p expression and promotes GBM propagation by inducing DNA methyltransferase 1-mediated hypermethylation of the miR142-3p promoter. Interestingly, miR142-3p also suppresses IL-6 secretion by targeting the 3' UTR of IL-6. In addition, miR142-3p also targets the 3' UTR and suppresses the expression of high-mobility group AT-hook 2 (HMGA2), leading to inhibition of Sox2-related stemness. We further show that HMGA2 enhances Sox2 expression by directly binding to the Sox2 promoter. Clinically, GBM patients whose tumors present upregulated IL-6, HMGA2, and Sox2 protein expressions and hypermethylated miR142-3p promoter also demonstrate poor survival outcome. Orthotopic delivery of miR142-3p blocks IL-6/HMGA2/Sox2 expression and suppresses stem-like properties in GBM-xenotransplanted mice. Collectively, we discovered an IL-6/miR142-3p feedback-loop-dependent regulation of GBM malignancy that could be a potential therapeutic target.

Uptake by human glioma cell lines and biological effects of a peptide-nucleic acids targeting miR-221

MicroRNAs are a family of small noncoding RNAs regulating gene expression by sequence-selective mRNA targeting, leading to a translational repression or mRNA degradation. The oncomiR miR-221 is highly expressed in human gliomas, as confirmed in this study in samples of low and high grade gliomas, as well in the cell lines U251, U373 and T98G. In order to alter the biological functions of miR-221, a peptide nucleic acid targeting miR-221 (R8-PNA-a221) was produced, bearing a oligoarginine peptide (R8) to facilitate uptake by glioma cells. The effects of R8-PNA-a221 were analyzed in U251, U373 and T98G glioma cells and found to strongly inhibit miR-221. In addition, the effects of R8-PNA-a221 on p27(Kip1) (a target of miR-221) were analyzed in U251 and T98G cells by RT-qPCR and by Western blotting. No change of p27(Kip1) mRNA content occurs in U251 cells in the presence of PNA-a221 (lacking the R8 peptide), whereas significant increase of p27(Kip1) mRNA was observed with the R8-PNA-a221. These data were confirmed by Western blot assay. A clear increment of p27(Kip1) protein expression in the samples treated with R8-PNA-a221 was detected. In addition, R8-PNA-a221 was found able to increase TIMP3 expression (another target of miR-221) in T98G cells. These results suggest that PNAs against oncomiRNA miR-221 might be proposed for experimental treatment of human gliomas.

Analysis of expression of microRNAs and genes involved in the control of key signaling mechanisms that support or inhibit development of brain tumors of different grades

BACKGROUND

MicroRNAs (miRNAs) are a class of small non-coding RNA molecules involved in the regulation of key biological processes. Different miRNAs with pro-oncogenic and anti-oncogenic properties have been identified in glioblastomas. We decided to analyze expression profiles of 10 mature miRNAs (miR-7-1, miR-10а, miR-17, miR-20а, miR-21, miR-23а, miR-26а, miR-137, and miR-222) in post-surgery glioma specimens of different grades in order to find whether the expression level correlates with tumor grades. We also measured expression of six key genes such as PTEN, p21/CDKN1A, MDR1, ABCG2, BAX, and BCL-2 involved in the regulation of critical glioma signaling pathways to establish the effect of miRNAs on these signaling mechanisms.

METHODS

Using RT-PCR, we performed expression analysis of 25 tumor fresh samples (grades II-IV).

RESULTS

We found gradual increase in miR-21 and miR-23a levels in all tumor grades whereas miR-7 and miR-137 were significantly down-regulated depending on the glioma grade. MDR, ABCG2, and p21/CDKN1A levels were significantly up-regulated while expression of PTEN was down-regulated in tumor samples compared to the normal brain tissue.

CONCLUSIONS

These observations provide new insights into molecular pathogenic mechanisms of glioma progression and suggest about a potential value of miRNAs as a putative diagnostic marker of brain tumors.