MicroRNA-20a Regulates Glioma Cell Proliferation, Invasion, and Apoptosis by Targeting CUGBP Elav-Like Family Member 2

CELF2 Sustains a Proliferating/OLIG2+ Glioblastoma Cell Phenotype via the Epigenetic Repression of SOX3

Glioblastomas (GBs) are incurable brain tumors. The persistence of aggressive stem-like tumor cells after cytotoxic treatments compromises therapeutic efficacy, leading to GBM recurrence. Forcing the GBM cells to irreversibly abandon their aggressive stem-like phenotype may offer an alternative to conventional cytotoxic treatments. Here, we show that the RNA binding protein CELF2 is strongly expressed in mitotic and OLIG2-positive GBM cells, while it is downregulated in differentiated and non-mitotic cells by miR-199a-3p, exemplifying GBM intra-tumor heterogeneity. Using patient-derived cells and human GBM samples, we demonstrate that CELF2 plays a key role in maintaining the proliferative/OLIG2 cell phenotype with clonal and tumorigenic properties. Indeed, we show that CELF2 deficiency in patient-derived GSCs drastically reduced tumor growth in the brains of nude mice. We further show that CELF2 promotes TRIM28 and G9a expression, which drive a H3K9me3 epigenetic profile responsible for the silencing of the SOX3 gene. Thus, CELF2, which is positively correlated with OLIG2 and Ki67 expression in human GBM samples, is inversely correlated with SOX3 and miR-199a-3p. Accordingly, the invalidation of SOX3 in CELF2-deficient patient-derived cells rescued proliferation and OLIG2 expression. Finally, patients expressing SOX3 above the median level of expression tend to have a longer life expectancy. CELF2 is therefore a crucial target for the malignant potential of GBM and warrants attention when developing novel anticancer strategies.

Comparison of Oncogenes, Tumor Suppressors, and MicroRNAs Between Schizophrenia and Glioma: The Balance of Power

The risk of cancer in schizophrenia has been controversial. Confounders of the issue are cigarette smoking in schizophrenia, and antiproliferative effects of antipsychotic medications. The author has previously suggested comparison of a specific cancer like glioma to schizophrenia might help determine a more accurate relationship between cancer and schizophrenia. To accomplish this goal, the author performed three comparisons of data; the first a comparison of conventional tumor suppressors and oncogenes between schizophrenia and cancer including glioma. This comparison determined schizophrenia has both tumor-suppressive and tumor-promoting characteristics. A second, larger comparison between brain-expressed microRNAs in schizophrenia with their expression in glioma was then performed. This identified a core carcinogenic group of miRNAs in schizophrenia offset by a larger group of tumor-suppressive miRNAs. This proposed "balance of power" between oncogenes and tumor suppressors could cause neuroinflammation. This was assessed by a third comparison between schizophrenia, glioma and inflammation in asbestos-related lung cancer and mesothelioma (ALRCM). This revealed that schizophrenia shares more oncogenic similarity to ALRCM than glioma.

Non-coding RNAs and glioma: Focus on cancer stem cells

Glioblastoma and gliomas can have a wide range of histopathologic subtypes. These heterogeneous histologic phenotypes originate from tumor cells with the distinct functions of tumorigenesis and self-renewal, called glioma stem cells (GSCs). GSCs are characterized based on multi-layered epigenetic mechanisms, which control the expression of many genes. This epigenetic regulatory mechanism is often based on functional non-coding RNAs (ncRNAs). ncRNAs have become increasingly important in the pathogenesis of human cancer and work as oncogenes or tumor suppressors to regulate carcinogenesis and progression. These RNAs by being involved in chromatin remodeling and modification, transcriptional regulation, and alternative splicing of pre-mRNA, as well as mRNA stability and protein translation, play a key role in tumor development and progression. Numerous studies have been performed to try to understand the dysregulation pattern of these ncRNAs in tumors and cancer stem cells (CSCs), which show robust differentiation and self-regeneration capacity. This review provides recent findings on the role of ncRNAs in glioma development and progression, particularly their effects on CSCs, thus accelerating the clinical implementation of ncRNAs as promising tumor biomarkers and therapeutic targets.

Long Non-coding RNA Peg13 Alleviates Hypoxic-Ischemic Brain Damage in Neonatal Mice via miR-20a-5p/XIAP Axis

Long noncoding RNA (LncRNA) Peg13 has been demonstrated to protect against neurological diseases. However, its underlying mechanism in the progression of hypoxic-ischemic brain damage (HIBD) has not been well investigated. The expression of target genes was determined in neonatal mice with HIBD and in mouse hippocampal neurons during oxygen-glucose deprivation (OGD) using quantitative real-time PCR (qRT-PCR) and immunoblotting. Functional assays, including CCK-8 cell viability and apoptotic cell detection using TdT mediated dUTP nick ending labeling (TUNEL) assay were used to examine the neuroprotective role of Peg13 in mouse hippocampal neurons. Luciferase assays were performed to determine the regulatory mechanism of Peg13 in OGD-induced neuronal apoptosis. Peg13 was reduced in HIBD mice and OGD-treated mouse hippocampal neurons. Altered Peg13 expression relieved OGD-induced neuronal apoptosis. Mechanistically, Peg13 may serve as a sponge for miR-20a-5p to increase the expression of X chromosome-linked inhibitor of apoptosis (XIAP), a downstream target of miR-20a-5p. Our study showed that Peg13 fulfilled its anti-apoptotic function in neurons through suppressing XIAP expression by sponging miR-20a-5p. Together, Peg13 binds to miR-20a-5p to upregulate XIAP and alleviate HIBD in neonatal mice. The Peg13/miR-20a-5p/XIAP competing endogenous RNA (ceRNA) axis could be a potential therapeutic target for HIBD.

miRNA-Based Regulation of Alternative RNA Splicing in Metazoans

Alternative RNA splicing is an important regulatory process used by genes to increase their diversity. This process is mainly executed by specific classes of RNA binding proteins that act in a dosage-dependent manner to include or exclude selected exons in the final transcripts. While these processes are tightly regulated in cells and tissues, little is known on how the dosage of these factors is achieved and maintained. Several recent studies have suggested that alternative RNA splicing may be in part modulated by microRNAs (miRNAs), which are short, non-coding RNAs (~22 nt in length) that inhibit translation of specific mRNA transcripts. As evidenced in tissues and in diseases, such as cancer and neurological disorders, the dysregulation of miRNA pathways disrupts downstream alternative RNA splicing events by altering the dosage of splicing factors involved in RNA splicing. This attractive model suggests that miRNAs can not only influence the dosage of gene expression at the post-transcriptional level but also indirectly interfere in pre-mRNA splicing at the co-transcriptional level. The purpose of this review is to compile and analyze recent studies on miRNAs modulating alternative RNA splicing factors, and how these events contribute to transcript rearrangements in tissue development and disease.

CELF Family Proteins in Cancer: Highlights on the RNA-Binding Protein/Noncoding RNA Regulatory Axis

Post-transcriptional modifications to coding and non-coding RNAs are unquestionably a pivotal way in which human mRNA and protein diversity can influence the different phases of a transcript's life cycle. CELF (CUGBP Elav-like family) proteins are RBPs (RNA-binding proteins) with pleiotropic capabilities in RNA processing. Their responsibilities extend from alternative splicing and transcript editing in the nucleus to mRNA stability, and translation into the cytoplasm. In this way, CELF family members have been connected to global alterations in cancer proliferation and invasion, leading to their identification as potential tumor suppressors or even oncogenes. Notably, genetic variants, alternative splicing, phosphorylation, acetylation, subcellular distribution, competition with other RBPs, and ultimately lncRNAs, miRNAs, and circRNAs all impact CELF regulation. Discoveries have emerged about the control of CELF functions, particularly via noncoding RNAs, and CELF proteins have been identified as competing, antagonizing, and regulating agents of noncoding RNA biogenesis. On the other hand, CELFs are an intriguing example through which to broaden our understanding of the RBP/noncoding RNA regulatory axis. Balancing these complex pathways in cancer is undeniably pivotal and deserves further research. This review outlines some mechanisms of CELF protein regulation and their functional consequences in cancer physiology.

Hypoxic colorectal cancer-secreted exosomes deliver miR-210-3p to normoxic tumor cells to elicit a protumoral effect

Hypoxia, the most common feature in the tumor microenvironment, is closely related to tumor malignant progression and poor patient's prognosis. Exosomes, initially recognized as cellular "garbage dumpsters", are now known to be important mediums for mediating cellular communication in tumor microenvironment. However, the mechanisms of hypoxic tumor cell-derived exosomes facilitate colorectal cancer progression still need further exploration. In the present study, we found that exosomes from hypoxic colorectal cancer cells (H-Exos) promoted G1-S cycle transition and proliferation while preventing the apoptosis of colorectal cancer cells by transmitting miR-210-3p to normoxic tumor cells. Mechanistic investigation indicated that miR-210-3p from H-Exos elicited its protumoral effect via suppressing CELF2 expression. A preclinical study further confirmed that H-Exos could promote tumorigenesis in vivo. Clinically, the expression of miR-210-3p in circulating plasma exosomes was markedly upregulated in colorectal cancer patients, which were closely associated with multiple unfavorable clinicopathological features. Taken together, these results suggest that hypoxia may stimulate colorectal cancer cells to secrete miR-210-3p-enriched exosomes in tumor microenvironment, which elicit protumoral effects by inhibiting CELF2 expression. These findings provide new insights on the mechanism of colorectal cancer progression and potential therapeutic targets for colorectal cancer.

mRNA and miRNA Expression Analyses of the MYC/E2F/miR-17-92 Network in the Most Common Pediatric Brain Tumors

Numerous molecular factors disrupt the correctness of the cell cycle process leading to the development of cancer due to increased cell proliferation. Among known causative factors of such process is abnormal gene expression. Nowadays in the light of current knowledge such alterations are frequently considered in the context of mRNA–miRNA correlation. One of the molecular factors with potential value in tumorigenesis is the feedback loop between MYC and E2F genes in which miR-17-5p and miR-20a from the miR-17-92 cluster are involved. The current literature shows that overexpression of the members of the OncomiR-1 are involved in the development of many solid tumors. In the present work, we investigated the expression of components of the MYC/E2F/miR-17-92 network and their closely related elements including members of MYC and E2F families and miRNAs from two paralogs of miR-17-92: miR-106b-25 and miR-106a-363, in the most common brain tumors of childhood, pilocytic astrocytoma (PA), WHO grade 1; ependymoma (EP), WHO grade 2; and medulloblastoma (MB), WHO grade 4. We showed that the highest gene expression was observed in the MYC family for MYCN and in the E2F family for E2F2. Positive correlation was observed between the gene expression and tumor grade and type, with the highest expression being noted for medulloblastomas, followed by ependymomas, and the lowest for pilocytic astrocytomas. Most members of miR-17-92, miR-106a-363 and miR-106b-25 clusters were upregulated and the highest expression was noted for miR-18a and miR-18b. The rest of the miRNAs, including miR-19a, miR-92a, miR-106a, miR-93, or miR-25 also showed high values. miR-17-5p, miR-20a obtained a high level of expression in medulloblastomas and ependymomas, while close to the control in the pilocytic astrocytoma samples. miRNA expression also depended on tumor grade and histology.

Brain Perfusion Mediates the Relationship Between miRNA Levels and Postural Control

Transcriptomics, regional cerebral blood flow (rCBF), and a virtual reality-based spatial motor task were integrated using mediation analysis in a novel demonstration of “imaging omics.” Data collected in National Collegiate Athletic Association (NCAA) Division I football athletes cleared for play before in-season training showed significant relationships in 1) elevated levels of miR-30d and miR-92a to elevated putamen rCBF, 2) elevated putamen rCBF to compromised Balance scores, and 3) compromised Balance scores to elevated microRNA (miRNA) levels. rCBF acted as a consistent mediator variable (Sobel’s test P < 0.05) between abnormal miRNA levels and compromised Balance scores. Given the involvement of these miRNAs in inflammation and immune function and that vascular perfusion is a component of the inflammatory response, these findings support a chronic inflammatory model in these athletes with 11 years of average football exposure. rCBF, a systems biology measure, was necessary for miRNA to affect behavior.

Emerging Roles and Potential Applications of Non-Coding RNAs in Glioblastoma

Non-coding RNAs (ncRNAs) comprise a diversity of RNA species, which do not have the potential to encode proteins. Non-coding RNAs include two classes of RNAs, namely: short regulatory ncRNAs and long non-coding RNAs (lncRNAs). The short regulatory RNAs, containing up to 200 nucleotides, include small RNAs, such as microRNAs (miRNA), short interfering RNAs (siRNAs), piwi-interacting RNAs (piRNAs), and small nucleolar RNAs (snoRNAs). The lncRNAs include long antisense RNAs and long intergenic RNAs (lincRNAs). Non-coding RNAs have been implicated as master regulators of several biological processes, their expression being strictly regulated under physiological conditions. In recent years, particularly in the last decade, substantial effort has been made to investigate the function of ncRNAs in several human diseases, including cancer. Glioblastoma is the most common and aggressive type of brain cancer in adults, with deregulated expression of small and long ncRNAs having been implicated in onset, progression, invasiveness, and recurrence of this tumor. The aim of this review is to guide the reader through important aspects of miRNA and lncRNA biology, focusing on the molecular mechanism associated with the progression of this highly malignant cancer type.

miR-92 Regulates the Proliferation, Migration, Invasion and Apoptosis of Glioma Cells by Targeting Neogenin

This study aimed to explore the pathological mechanism in regulating glioma progression. The expression of miR-92 and neogenin was evaluated by qRT-PCR and western blot. Cell viability and apoptosis were measured by MTT and flow cytometry assays, respectively. The migration and invasion abilities were examined by transwell assays. The interaction between miR-92 and neogenin was conducted by dual-luciferase reporter system. As a result, we found that the expression of miR-92 was up-regulated in glioma tissues and cell lines. Down-regulation of miR-92 inhibited glioma cell proliferation, migration, invasion and promoted cell apoptosis rate of U251 and U87 cells. Notably, miR-92 was identified to directly target to 3’-UTR of neogenin. Furthermore, neogenin was down-regulated in glioma tissues and cells in a miR-92-correlated manner. Overexpression of neigenin could cause similar results to miR-92 knockdown in U251 and U87 cells. However, the silencing of neogenin partially reversed the effects of miR-92 knockdown on cell proliferation, migration, invasion and apoptosis of glioma cells in vitro. In conclusion, we clarified that miR-92 knockdown could suppress the malignant progression of glioma cells in vitro by targeting neogenin. Therefore, miR-92 could serve as a potential diagnostic and prognostic marker in glioma patients

Function and mechanisms of microRNA-20a in colorectal cancer

Colorectal cancer (CRC) is the third most common malignancy and the second leading cause of cancer-associated mortality worldwide. CRC currently has no specific biomarkers to promote its diagnosis and treatment and the underlying mechanisms regulating its pathogenesis have not yet been determined. MicroRNAs (miRs) are small, non-coding RNAs that exhibit regulatory functions and have been demonstrated to serve a crucial role in the post-transcriptional regulatory processes of gene expression that is associated with cell physiology and disease progression. Recently, abnormal miR-20a expression has been identified in a number of cancers types and this has become a novel focus within cancer research. High levels of miR-20a expression have been identified in CRC tissues, serum and plasma. In a recent study, miR-20a was indicated to be present in feces and to exhibit a high sensitivity to CRC. Therefore, miR-20a may be used as a marker for CRC and an indicator that can prevent the invasive examination of patients with this disease. Changes in the expression of miR-20a during chemotherapy can be used as a biomarker for monitoring resistance to treatment. In conclusion, miR-20a exhibits the potential for clinical application as a novel diagnostic biomarker and therapeutic target for use in patients with CRC. The present study focused on the role and mechanisms of miR-20a in CRC.

MicroRNA Dysregulation in Cutaneous Squamous Cell Carcinoma

Cutaneous squamous cell carcinoma (CSCC) is the second most frequent cancer in humans and it can be locally invasive and metastatic to distant sites. MicroRNAs (miRNAs or miRs) are endogenous, small, non-coding RNAs of 19–25 nucleotides in length, that are involved in regulating gene expression at a post-transcriptional level. MicroRNAs have been implicated in diverse biological functions and diseases. In cancer, miRNAs can proceed either as oncogenic miRNAs (onco-miRs) or as tumor suppressor miRNAs (oncosuppressor-miRs), depending on the pathway in which they are involved. Dysregulation of miRNA expression has been shown in most of the tumors evaluated. MiRNA dysregulation is known to be involved in the development of cutaneous squamous cell carcinoma (CSCC). In this review, we focus on the recent evidence about the role of miRNAs in the development of CSCC and in the prognosis of this form of skin cancer.