Circular RNA CircMTO1 Inhibits Proliferation of Glioblastoma Cells via miR-92/WWOX Signaling Pathway

The importance of the circRNA/Wnt axis in gliomas: Biological functions and clinical opportunities

Gliomas are among the most common cancers in the central nervous system, arising through various signaling pathways. One significant pathway is Wnt signaling, a tightly regulated process that plays a crucial role in gliomagenesis and development. The current study aims to explore the relationship between circular RNAs (circRNAs) and the Wnt/β-catenin signaling pathway in gliomas, considering the growing recognition of circRNAs in disease pathogenesis. A comprehensive review of recent research was conducted to investigate the roles of circRNAs in gliomas, focusing on their expression patterns and interactions with the Wnt signaling pathway. The analysis included studies examining circRNAs' function as microRNA sponges and their impact on glioma biology. The findings reveal that circRNAs are differentially expressed in gliomas and significantly influence the occurrence, growth, and metastasis of these tumors. Specifically, circRNAs interact with the Wnt signaling pathway, affecting glioma development and progression. This interaction highlights the importance of circRNAs in glioma pathophysiology. Understanding the regulatory network involving circRNAs and Wnt signaling offers valuable insights into glioma pathophysiology. CircRNAs hold promise as diagnostic and prognostic biomarkers and may serve as targets for novel therapeutic strategies in glioma treatment.

A spotlight on the interplay between Wnt/β-catenin signaling and circular RNAs in hepatocellular carcinoma progression

Hepatocellular carcinoma (HCC) is one of the deadliest cancers due to multifocal development and distant metastasis resulting from late diagnosis. Consequently, new approaches to HCC diagnosis and treatment are required to reduce mortality rates. A large body of evidence suggests that non-coding RNAs (ncRNAs) are important in cancer initiation and progression. Cancer cells release many of these ncRNAs into the blood or urine, enabling their use as a diagnostic tool. Circular RNAs (CircRNAs) are as a members of the ncRNAs that regulate cancer cell expansion, migration, metastasis, and chemoresistance through different mechanisms such as the Wnt/β-catenin Signaling pathway. The Wnt/β-catenin pathway plays prominent roles in several biological processes including organogenesis, stem cell regeneration, and cell survival. Aberrant signaling of both pathways mentioned above could affect the progression and metastasis of many cancers, including HCC. Based on several studies investigated in the current review, circRNAs have an effect on HCC formation and progression by sponging miRNAs and RNA-binding proteins (RBPs) and regulating the Wnt/β-catenin signaling pathway. Therefore, circRNAs/miRNAs or RBPs/Wnt/β-catenin signaling pathway could be considered promising prognostic and therapeutic targets in HCC.

LINC01137/miR-186-5p/WWOX: a novel axis identified from WWOX-related RNA interactome in bladder cancer

Introduction: The discovery of non-coding RNA (ncRNA) dates back to the pre-genomics era, but the progress in this field is still dynamic and leverages current post-genomics solutions. WWOX is a global gene expression modulator that is scarcely investigated for its role in regulating cancer-related ncRNAs. In bladder cancer (BLCA), the link between WWOX and ncRNA remains unexplored. The description of AP-2α and AP-2γ transcription factors, known as WWOX-interacting proteins, is more commonplace regarding ncRNA but still merits investigation. Therefore, this in vitro and in silico study aimed to construct an ncRNA-containing network with WWOX/AP-2 and to investigate the most relevant observation in the context of BLCA cell lines and patients. Methods: RT-112, HT-1376, and CAL-29 cell lines were subjected to two stable lentiviral transductions. High-throughput sequencing of cellular variants (deposited in the Gene Expression Omnibus database under the GSE193659 record) enabled the investigation of WWOX/AP-2-dependent differences using various bioinformatics tools (e.g., limma-voom, FactoMineR, multiple Support Vector Machine Recursive Feature Elimination (mSVM-RFE), miRDB, Arena-Idb, ncFANs, RNAhybrid, TargetScan, Protein Annotation Through Evolutionary Relationships (PANTHER), Gene Transcription Regulation Database (GTRD), or Evaluate Cutpoints) and repositories such as The Cancer Genome Atlas (TCGA) and Cancer Cell Line Encyclopedia. The most relevant observations from cap analysis gene expression sequencing (CAGE-seq) were confirmed using real-time PCR, whereas TCGA data were validated using the GSE31684 cohort. Results: The first stage of the whole study justified focusing solely on WWOX rather than on WWOX combined with AP-2α/γ. The most relevant observation of the developed ncRNA-containing network was LINC01137, i.e., long non-coding RNAs (lncRNAs) that unraveled the core network containing UPF1, ZC3H12A, LINC01137, WWOX, and miR-186-5p, the last three being a novel lncRNA/miRNA/mRNA axis. Patients' data confirmed the LINC01137/miR-186-5p/WWOX relationship and provided a set of dependent genes (i.e., KRT18, HES1, VCP, FTH1, IFITM3, RAB34, and CLU). Together with the core network, the gene set was subjected to survival analysis for both TCGA-BLCA and GSE31684 patients, which indicated that the increased expression of WWOX or LINC01137 is favorable, similar to their combination with each other (WWOX↑ and LINC01137↑) or with MIR186 (WWOX↑/LINC01137↑ but MIR186↓). Conclusion: WWOX is implicated in the positive feedback loop with LINC01137 that sponges WWOX-targeting miR-186-5p. This novel WWOX-containing lncRNA/miRNA/mRNA axis should be further investigated to depict its relationships in a broader context, which could contribute to BLCA research and treatment.

Circ_0067934 as a novel therapeutic target in cancer: From mechanistic to clinical perspectives

Circular RNAs, as a type of non-coding RNAs, are identified in a various cell. Circular RNAs have stable structures, conserved sequence, and tissue and cell-specific level. High throughput technologies have proposed that circular RNAs act via various mechanisms like sponging microRNAs and proteins, regulating transcription factors, and scaffolding mediators. Cancer is one of the major threat for human health. Emerging data have proposed that circular RNAs are dysregulated in cancers as well as are associated with aggressive behaviors of cancer -related behaviors like cell cycle, proliferation, apoptosis, invasion, migration, and epithelial-mesenchymal transition (EMT). Among them, circ_0067934 was shown to act as an oncogene in cancers to enhance migration, invasion, proliferation, cell cycle, EMT, and inhibit cell apoptosis. In addition, these studies have proposed that it could be a promising diagnostic and prognostic biomarker in cancer. This study aimed to review the expression and molecular mechanism of circ_0067934 in modulating the malignant behaviors of cancers as well as to explore its potential as a target in cancer chemotherapy, diagnosis, prognosis and treatment.

Investigation of the clinicopathological and prognostic role of circMTO1 in multiple cancers

OBJECTIVE

To observe the prognostic value of circular RNA mitochondrial tRNA translation optimization 1 (circMTO1) in human tumors.

METHODS

We searched multiple databases for related reports published before November 01, 2021. The OR/HR and 95% CI were extracted to explore the correlation between circMTO1 expression and clinicopathological features in various cancers. The stability of the results from meta-analysis was estimated via sensitivity analysis. We adopted Begg's funnel plots and Egger's test to appraise the potential bias of publication. Subgroup analysis for overall survival (OS) were also performed.

RESULTS

11 studies containing 1383 patients and 4 articles including 536 patients were enrolled. We found that low expression status of circMTO1 was significantly related to big tumor size (OR=2.11, 95% CI: 1.26-3.56, P<0.05), poor differentiation tumors (OR=2.09, 95% CI: 1.46-2.98, P<0.05), OS (HR=2.02, 95% CI: 1.63-2.50, P<0.05), disease-free survival (DFS) (HR=1.83, 95% CI: 1.27-2.56, P<0.05) of cancers. Subgroup analysis indicated that low expression status of circMTO1 was correlated with OS, regardless of analysis method, cut-off value, case number and NOS score.

CONCLUSIONS

The low expression of circMTO1 may predict big tumor size, poor differentiation and worse outcome of cancer, presenting that circMTO1 may be a useful biomarker for prognosis of tumors.

CircRNA and Ageing

Circular RNAs (circRNAs) are closed-loop RNA transcripts formed by a noncanonical back splicing mechanism. circRNAs are expressed in various tissues and cell types in a temporospatially regulated manner and have diverse molecular functions including their ability to act as miRNA sponges, transcriptional and splicing regulators, protein traps, and even templates for polypeptide synthesis. Emerging evidence suggests that circRNAs are themselves dynamically regulated throughout development in various organisms, with a substantial accumulation during ageing. Their regulatory roles in cellular pathways associated with ageing and senescence, as well as their implications in ageing-related diseases, such as neurological disease, cancer, and cardiovascular disease, suggest that circRNAs are key molecular determinants of the ageing process. Their unique structure, expression specificity, and biological functions highlight a potential capacity for use as novel biomarkers for diagnosis, prognosis, and treatment outcomes in a variety of conditions including pathological ageing. CircRNA may also have potential as target for interventions that manipulate ageing and longevity. In this chapter, we discuss the most recent advances in circRNA changes in ageing and ageing-associated disease.

Systematic characterization and biological functions of non-coding RNAs in glioblastoma

Glioblastoma multiforme (GBM) is the most malignant and aggressive type of glioma. Non-coding RNAs (ncRNAs) are RNAs that do not encode proteins but widely exist in eukaryotic cells. The common characteristics of these RNAs are that they can all be transcribed from the genome without being translated into proteins, thus performing biological functions, particularly microRNAs (miRNAs), long non-coding RNAs (lncRNAs) and circular RNAs. Studies have found that ncRNAs are associated with the occurrence and development of GBM, and there is a complex regulatory network among ncRNAs, which can regulate cell proliferation, migration, apoptosis and differentiation, thus provide a basis for the development of highly specific diagnostic tools and therapeutic strategies in the future. The present review aimed to comprehensively describe the biogenesis, general features and functions of regulatory ncRNAs in GBM, and to interpret the potential biological functions of these ncRNAs in GBM as well as their impact on clinical diagnosis, treatment and prognosis and discusses the potential mechanisms of these RNA subtypes leading to cancer in order to contribute to the better design of personalized GBM therapies in the future.

Circular RNA 0010117 promotes aggressive glioblastoma behavior by regulating the miRNA-6779-5p/SPEN axis

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Circ-0010117 is down-regulated in glioblastoma.

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Circ-0010117 regulates aggressiveness via miRNA-6779-5p in glioblastoma.

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SPEN contributed to regulate miRNA-6779-5p in glioblastoma.

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Upregulated Circ-0010117 inhibited in vivo tumor growth of human glioblastoma xenograft.

Noncoding RNAs (ncRNAs) play important roles in cancer biology, providing potential targets for cancer intervention. As a new class of endogenous noncoding RNAs, circular RNAs (circRNAs) have been recently identified in cell development and function, and certain types of pathological responses contribute to cancer progression, including glioblastoma. However, the potential mechanisms underlying the relationship between circRNAs and glioblastoma progression are still largely unknown. Methods: The expression and roles of circular RNA 0010117 (circ-0010117) were examined in vitro and in vivo. Quantitative RT‒PCR and western blotting were used to measure the expression of circRNA, miRNA, each gene, or related proteins. Cell biology experiments were performed to detect the biological function of circ-0010117 in glioblastoma cell lines. Moreover, bioinformatics analysis, luciferase reporter assays, and functional complementation analysis were carried out to investigate the target genes. Tumorigenesis was also evaluated by xenografting cells into nude mice. In this study, we found that circ-0010117 is downregulated in glioblastoma compared with corresponding paratumoural tissues. Subsequently, we observed that circ-0010117 can regulate aggressiveness in glioblastoma cells through miR-6779-5p. Furthermore, SPEN was verified as a direct target of miR-6779-5p and contributes to the circ-0010117 regulatory network. In addition, we identified that overexpression of circ-0010117 can suppress tumorigenesis in nude mice. Our findings indicate that circular RNA 0010117 promotes the aggressive behavior of glioblastoma by regulating the miRNA-6779-5p/SPEN axis. Our results provide a rationale for the use of circ-0010117 as a novel potential therapeutic target in glioblastoma.

Role of Circular RNA in Brain Tumor Development

Central nervous system tumors are a leading cause of cancer-related death in children and adults, with medulloblastoma (MB) and glioblastoma (GBM) being the most prevalent malignant brain tumors, respectively. Despite tremendous breakthroughs in neurosurgery, radiation, and chemotherapeutic techniques, cell heterogeneity and various genetic mutations impacting cell cycle control, cell proliferation, apoptosis, and cell invasion result in unwanted resistance to treatment approaches, with a 5-year survival rate of 70–80% for medulloblastoma, and the median survival time for patients with glioblastoma is only 15 months. Developing new medicines and utilizing combination medications may be viewed as excellent techniques for battling MB and GBM. Circular RNAs (circRNAs) can affect cancer-developing processes such as cell proliferation, cell apoptosis, invasion, and chemoresistance in this regard. As a result, several compounds have been introduced as prospective therapeutic targets in the fight against MB and GBM. The current study aims to elucidate the fundamental molecular and cellular mechanisms underlying the pathogenesis of GBM in conjunction with circRNAs. Several mechanisms were examined in detail, including PI3K/Akt/mTOR signaling, Wnt/-catenin signaling, angiogenic processes, and metastatic pathways, in order to provide a comprehensive knowledge of the involvement of circRNAs in the pathophysiology of MB and GBM.

High Expression of Circular RNA-Mitochondrial tRNA Translation Optimization 1 Assists the Diagnosis of High-Risk Human Papillomavirus Infection in Cervical Cancer

OBJECTIVE

Persistence of high-risk human papillomavirus (HR-HPV) infection is a paramount determinant in cervical cancer (CC) development. Circular RNAs have the potential to be promising biomarkers for various cancers. This study explored circular RNA-mitochondrial tRNA translation optimization 1 (circMTO1) expression in the serum of CC patients and its clinical value in diagnosing CC and predicting HR-HPV infection.

MATERIALS AND METHODS

In total, 125 CC patients (including 78 cases with HR-HPV) were enrolled, with another 76 healthy people as controls. Serum circMTO1 and miR-199a expressions were detected by reverse transcription-quantitative polymerase chain reaction, and the diagnostic efficacy of circMTO1 for CC and HR-HPV infection was analyzed by the receiver operating characteristic curve. According to the median of serum circMTO1 expression, CC patients were assigned into circMTO1 low/high expression groups to analyze the correlation between circMTO1 and clinical parameters using the Fisher and χ 2 tests. Independent association of circMTO1 with HR-HPV infection in CC was evaluated via logistics multivariate regression analysis. Targeted relationship between miR-199a and circMTO1 was predicted by Starbase Web site and validated via dual-luciferase assay, with their correlation further assessed by Pearson analysis.

RESULTS

Serum circMTO1 was increased in CC patients and prominently elevated in HR-HPV-positive CC patients, with a level greater than 1.485 assisting CC diagnosis and a level greater than 2.480 assisting HR-HPV-positive diagnosis. The circMTO1 was interrelated to clinical stage, tumor differentiation, lymph node metastasis, invasion depth, and independently linked with HR-HPV infection in CC. Serum miR-199a was downregulated in HR-HPV-positive CC patients and inversely correlated with circMTO1.

CONCLUSIONS

Serum circMTO1 is upregulated in HR-HPV-positive CC patients and has a diagnostic value for HR-HPV infection in CC.

Circular RNAs and glioblastoma multiforme: focus on molecular mechanisms

Glioblastoma multiforme (GBM), as a deadly and almost incurable brain cancer, is the most invasive form of CNS tumors that affects both children and adult population. It accounts for approximately half of all primary brain tumors. Despite the remarkable advances in neurosurgery, radiotherapy, and chemotherapeutic approaches, cell heterogeneity and numerous genetic alterations in cell cycle control, cell growth, apoptosis, and cell invasion, result in an undesirable resistance to therapeutic strategies; thereby, the median survival duration for GBM patients is unfortunately still less than two years. Identifying new therapeutics and employing the combination therapies may be considered as wonderful strategies against the GBM. In this regard, circular RNAs (circRNAs), as tumor inhibiting and/or stimulating RNA molecules, can regulate the cancer-developing processes, including cell proliferation, cell apoptosis, invasion, and chemoresistance. Hereupon, these molecules have been introduced as potentially effective therapeutic targets to defeat GBM. The current study aims to investigate the fundamental molecular and cellular mechanisms in association with circRNAs involved in GBM pathogenesis. Among multiple mechanisms, the PI3K/Akt/mTOR, Wnt/β-catenin, and MAPK signaling, angiogenic processes, and metastatic pathways will be thoroughly discussed to provide a comprehensive understanding of the role of circRNAs in pathophysiology of GBM. Video Abstract.

CircMTO1 suppresses hepatocellular carcinoma progression via the miR-541-5p/ZIC1 axis by regulating Wnt/β-catenin signaling pathway and epithelial-to-mesenchymal transition

CircRNA mitochondrial tRNA translation optimization 1 (circMTO1) functions as a tumor suppressor usually and is related to the progression of many tumors, including hepatocellular carcinoma (HCC). CircMTO1 is downregulated in HCC as compared to adjacent nontumor tissue, which may suppress the HCC progression by certain signal pathways. However, the underlying signal pathway remains largely unknown. The interactions between circMTO1 and miR-541-5p were predicted through bioinformatics analysis and verified using pull-down and dual-luciferase reporter assays. CCK-8, transwell, and apoptosis assays were performed to determine the effect of miR-541-5p on HCC progression. Using bioinformatic analysis, dual-luciferase reporter assay, RT-qPCR, and western blot, ZIC1 was found to be the downstream target gene of miR-541-5p. The regulatory mechanisms of circMTO1, miR-541-5p, and ZIC1 were investigated using in vitro and in vivo rescue experiments. The results depicted that silencing circMTO1 or upregulating miR-541-5p expression facilitated HCC cell proliferation, migration, and invasion and inhibited apoptosis. CircMTO1 silencing upregulated the expression of downstream ZIC1 regulators of the Wnt/β-catenin pathway markers, β-catenin, cyclin D1, c-myc, and the mesenchymal markers N-cadherin, Vimentin, and MMP2, while the epithelial marker E-cadherin was downregulated. MiR-541-5p knockdown had the opposite effect and reversed the effect of circMTO1 silencing on the regulation of downstream ZIC1 regulators. Intratumoral injection of miR-541-5p inhibitor suppressed tumor growth and reversed the effect of circMTO1 silencing on the promotion of tumor growth in HCC. These findings indicated that circMTO1 suppressed HCC progression via the circMTO1/ miR-541-5p/ZIC1 axis by regulating Wnt/β-catenin signaling and epithelial-to-mesenchymal transition, making it a novel therapeutic target.

Research Progress of circRNAs in Glioblastoma

Circular RNAs (circRNAs) are a class of single-stranded covalently closed non-coding RNAs without a 5' cap structure or 3' terminal poly (A) tail, which are expressed in a variety of tissues and cells with conserved, stable and specific characteristics. Glioblastoma (GBM) is the most aggressive and lethal tumor in the central nervous system, characterized by high recurrence and mortality rates. The specific expression of circRNAs in GBM has demonstrated their potential to become new biomarkers for the development of GBM. The specific expression of circRNAs in GBM has shown their potential as new biomarkers for GBM cell proliferation, apoptosis, migration and invasion, which provides new ideas for GBM treatment. In this paper, we will review the biological properties and functions of circRNAs and their biological roles and clinical applications in GBM.

Noncoding RNAs in pediatric brain tumors: Molecular functions and pathological implications

Brain tumors are common solid pediatric malignancies and the main reason for cancer-related death in the pediatric setting. Recently, evidence has revealed that noncoding RNAs (ncRNAs), including microRNAs (miRNAs), long ncRNAs (lncRNAs), and circular RNAs (circRNAs), play a critical role in brain tumor development and progression. Therefore, in this review article, we describe the functions and molecular mechanisms of ncRNAs in multiple types of cancer, including medulloblastoma, pilocytic astrocytoma, ependymoma, atypical teratoid/rhabdoid tumor, glioblastoma, diffuse intrinsic pontine glioma, and craniopharyngioma. We also mention the limitations of using ncRNAs as therapeutic targets because of the nonspecificity of ncRNA targets and the delivery methods of ncRNAs. Due to the critical role of ncRNAs in brain oncogenesis, targeting aberrantly expressed ncRNAs might be an effective strategy to improve the outcomes of pediatric patients with brain tumors.

LRRC4 mediates the formation of circular RNA CD44 to inhibitGBM cell proliferation

Mounting evidence reveals that dysregulation of circular RNAs (circRNAs) is involved in the development of glioblastoma. Leucine-rich repeat-containing 4 (LRRC4) has been shown to suppress tumors in glioblastoma. However, whether LRRC4 can regulate the formation of circRNA is not yet understood. In this study, LRRC4 was found to interact with SAM68. LRRC4 promoted the generation of circCD44 by inhibiting the binding between SAM68 and CD44 pre-mRNA. Moreover, downregulated expression of circCD44 was found in glioblastoma multiforme (GBM) tissues and GBM primary cells. Re-expression of circCD44 significantly suppressed the proliferation, colony formation, and invasion of GBM cells and inhibited tumor growth in vivo. Mechanistically, circCD44 could regulate the expression of SMAD6 via sponging miR-326 and miR-330-5p involved in the progression of GBM. Thus, the LRRC4/SAM68/circCD44/miR-326/miR-330-5p/SMAD6 signaling axis could be a potential target for GBM treatment.

Circular RNA MTO1 intercorrelates with microRNA-630, both associate with Enneking stage and/or pathological fracture as well as prognosis in osteosarcoma patients

Objective

Circular RNA‐mitochondrial tRNA translation optimization 1 (circ‐MTO1) not only involves in bioprocess of various cancers, but also regulates osteosarcoma progression by regulating microRNA‐630 (miR‐630). However, the clinical role of circ‐MTO1 and miR‐630 in osteosarcoma is still obscure. This study aimed to assess the correlation of circ‐MTO1 and miR‐630 with disease features and prognosis and to explore their association with each other in osteosarcoma patients.

Methods

Forty‐four osteosarcoma patients who received neoadjuvant chemotherapy to surgical resection were analyzed in this retrospective study. Then, circ‐MTO1 and miR‐630 expressions were evaluated in tumor and adjacent non‐tumor specimens by reverse transcription quantitative polymerase chain reaction.

Results

Circ‐MTO1 was lower in tumor than in non‐tumor tissues (p<0.001); meanwhile, its elevated tumor expression was correlated with less advanced Enneking stage (p=0.049), good neoadjuvant chemotherapy response (p=0.029), and longer disease‐free survival (DFS) (p=0.047). However, no association was found between circ‐MTO1 and overall survival (OS) (p=0.122). Additionally, miR‐630 in tumor was higher than in non‐tumor tissues (p<0.001), while its raised tumor expression was associated with pathological fracture occurrence (p=0.003), advanced Enneking stage (p=0.036), poor neoadjuvant chemotherapy response (p=0.035), and shorter DFS (p=0.011). However, no association was found between miR‐630 and OS (p=0.066). In addition, tumor circ‐MTO1 was negatively associated with miR‐630 (r=−0.323, p=0.032).

Conclusion

Circ‐MTO1 and miR‐630 expressions are inter‐correlated and dysregulated in osteosarcoma patients. Besides, they associate with Enneking stage and/or pathological fracture, as well as neoadjuvant treatment response and accumulating DFS in these patients.

SNAI2-Induced CircMTO1 Promotes Cell Proliferation and Inhibits Apoptosis Through the miR-320b/MCL1 Axis in Human Granulosa-Like Tumor Cells

Polycystic ovary syndrome (PCOS), one of the most common types of endocrine diseases, is characterized by a high prevalence among women of reproductive-age. However, its pathogenesis and molecular mechanisms remain unclear. CircMTO1 has been reported to participate in numerous biological processes, but, its role in PCOS progression remains unknown. In the current study, we elucidated the expression and circRNA characterization of circMTO1 in human granulosa-like tumor cells. We found that circMTO1 knockdown promoted human granulosa-like tumor cell proliferation and inhibited its apoptosis rate. Next, we explored the underlying molecular mechanisms by using a series of experiments. Our results revealed the effect of the novel circMTO1/miR-320b/MCL1 axis in human granulosa-like tumor cells. Furthermore, we found that the expression of circMTO1 was induced by Snail family transcriptional repressor 2 (SNAI2) in human granulosa-like tumor cells. Our results may provide potential targets for PCOS research and a novel direction for the diagnosis and treatment of PCOS.

CircMTO1: A circular RNA with roles in the carcinogenesis

Circular RNAs (circRNAs) have a closed loop structure which endows them high stability. These transcripts are made through back splicing instead of classical splicing and are abundant in the human transcriptome. Recent advances in the development and implementation of high-throughput sequencing methods in cooperation with novel bioinformatics tools have shown contribution of circRNAs in the developmental processes, physiological settings and pathoetiology of cancers. CircMTO1 is a circRNA which was firstly identified as a down-regulated circRNA in hepatocellular carcinoma through circRNA profiling using microarray technique. Subsequent independent studies in lung adenocarcinoma, colorectal cancer, bladder cancer, glioblastoma, prostate cancer, osteosarcoma, gastric cancer and ovarian cancer have verified down-regulation of circMTO1 in neoplastic tissues compared with non-neoplastic ones. However, expression of circMTO1 has been found to be up-regulated in cervical and gallbladder cancers. miR-17, miR-9, miR-221, miR-6893, miR-92, miR-219a-5p, miR-337, miR-630, miR-3200-5p and miR-199a-3p have been shown to be sequestered by circMTO1. This circRNA can regulate activity of Notch, Wnt/β-Catenin, TGF-β/Smad, JAK1/STAT3 and AMPK signaling pathways. In the current study, we review the literature on the role of circMTO1 in the tumorigenesis.

Dysregulation of circRNA expression in the peripheral blood of individuals with schizophrenia and bipolar disorder

Circular RNAs (circRNAs) are head-to-tail back-spliced RNA transcripts that have been linked to several biological processes and their perturbation is evident in human disease, including neurological disorders. There is also emerging research suggesting circRNA expression may also be altered in psychiatric and behavioural syndromes. Here, we provide a comprehensive analysis of circRNA expression in peripheral blood mononuclear cells (PBMCs) from 39 patients with schizophrenia and bipolar disorder as well as 20 healthy individuals using deep RNA-seq. We observed systematic alternative splicing leading to a complex and diverse profile of RNA transcripts including 8762 high confidence circRNAs. More specific scrutiny of the circular transcriptome in schizophrenia and bipolar disorder, compared to a non-psychiatric control group, revealed significant dysregulation of 55 circRNAs with a bias towards downregulation. These molecules were predicted to interact with a large number of miRNAs that target genes enriched in psychiatric disorders. Further replication and cross-validation to determine the specificity of these circRNAs across broader diagnostic groups and subgroups in psychiatry will enable their potential utility as biomarkers to be established. KEY MESSAGES: • We identified 8762 high confidence circRNAs with systematic alternative splicing in human PBMCs. • CircRNAs were dysregulated in schizophrenia and bipolar disorder, compared to a non-psychiatric control group. • The DE circRNAs were predicted to interact with miRNAs with target genes enriched in psychiatric disorders. • Some circRNAs have the potential to serve as biomarkers in psychiatry.

The Roles of circMTO1 in Cancer

Circular RNAs (circRNAs) are a recently discovered type of covalently-closed circular non-coding RNAs, mainly formed by non-sequential back-splicing of precursor mRNAs (pre-mRNAs). Recent studies have demonstrated that circRNAs can have either oncogenic or tumor-suppressor roles depending on the cellular context. CircRNA mitochondrial tRNA translation optimization 1 (circMTO1), a recently reported circular RNA originating from exons of MTO1 located on chromosome 6q13, was proved to be abnormally expressed in many malignant tumors, such as hepatocellular carcinoma, gastric carcinoma and colorectal cancer, resulting in tumor initiation and progression. However, there are no reviews focusing on the roles of circMTO1 in cancer. Here, we first summarize the main biological characteristics of circMTO1, and then focus on its biological functions and the possible underlying molecular mechanisms. Finally, we summarize the roles of circMTO1 in cancer and discuss future prospects in this area of research.

circMTO1 sponges microRNA-219a-5p to enhance gallbladder cancer progression via the TGF-β/Smad and EGFR pathways

Circular mitochondrial translation optimization 1 homologue (circMTO1) has been reported to regulate the tumorigenesis of different types of cancer; however, the role of circMTO1 in gallbladder cancer (GBC) remains unknown. The present study aimed to identify the potential miRNAs and target genes of circMTO1 during GBC progression, and clarify the regulatory mechanism between circMTO1 and miRNAs or target genes. The present study performed MTT and Transwell assays, and Annexin V staining to assess cell viability, migration and apoptosis, respectively. In addition, a lymphatic vessel formation assay was performed to assess tube formation of human dermal lymphatic endothelial cells (HDLECs), and GBC-SD and NOZ cells. The results demonstrated that circMTO1 knockdown significantly attenuated the viability and migration of GBC cells and tube formation of HDLECs, and promoted apoptosis, indicating a tumor-promoting role of circMTO1. In addition, transfection with microRNA (miRNA/miR)-219a-5p inhibitor rescued short hairpin RNA-circMTO1-inhibited tumorigenesis of GBC cells, suggesting that miR-219a-5p acts as a downstream effector for circMTO1. Mechanistically, transfection with miR-219a-5p mimic suppressed the expression levels of Smad2/4 and epidermal growth factor receptor. Analysis of The Cancer Genome Atlas datasets revealed that circMTO1 expression was associated with overall survival and the stage of patients with GBC. Taken together, the results of the present study provide novel insight for the role of circMTO1-induced GBC tumorigenesis via regulation of miR-219a-5p expression.

Circ-EGFR Functions as an Inhibitory Factor in the Malignant Progression of Glioma by Regulating the miR-183-5p/TUSC2 Axis

Circular RNAs (circRNAs) have pivotal functions in regulating diverse biological processes of human tumors, including glioma. Herein, a novel circRNA epidermal growth factor receptor (circ-EGFR, hsa_circ_0080223) was researched in glioma. The molecular expression levels were analyzed via quantitative real-time polymerase chain reaction (qRT-PCR). Cell Counting Kit-8 (CCK-8) and colony formation assays were conducted to assess cell proliferation. Apoptosis was analyzed using flow cytometry. Cell migration and invasion were examined via transwell assay. Interaction relations between targets were verified using dual-luciferase reporter assay. Tumor Suppressor Candidate 2 (TUSC2) protein expression was examined by Western blot. In vivo experiment was performed by establishing xenograft model in mice. The qRT-PCR showed the downregulation of circ-EGFR and TUSC2 but the upregulation of microRNA-183-5p (miR-183-5p) in glioma samples. In vitro assays revealed that circ-EGFR overexpression induced the repression of cell proliferation, migration, and invasion but the promotion of apoptosis. Circ-EGFR was identified as a sponge of miR-183-5p and circ-EGFR-mediated glioma progression inhibition was abolished by miR-183-5p downregulation. Additionally, miR-183-5p targeted TUSC2 and miR-183-5p inhibitor impeded the development of glioma by upregulating the expression of TUSC2. Furthermore, circ-EGFR could regulate the TUSC2 level by sponging miR-183-5p. Glioma growth in vivo was also reduced by circ-EGFR via targeting the miR-183-5p/TUSC2 axis. Altogether, our results suggested that circ-EGFR inhibited the malignant progression of glioma by regulating the levels of miR-183-5p and TUSC2. Circ-EGFR may be a useful therapeutic target to antagonize the glioma progression.

Hsa_circ_0072309 inhibits proliferation and invasion of glioblastoma

Increasing literature reported that circRNAs play vital roles in the occurrence and progression of GBM and regulate GBM cell proliferation, metastases, and chemosensitivity. However, the expression pattern and function of circRNAs in GBM still need further studies. In our work, hsa_circ_0072309 was remarkably downregulated in GBM. Hsa_circ_0072309 inhibits proliferation and invasion of glioblastoma and affects cytoskeletal of GBM cells. Moreover, we found that the function of hsa_circ_0,072,309 in GBM was associated with HSP27, which was reported to be an important regulator of cell proliferation, invasion and cytoskeletal. Our study provides a novel view of hsa_circ_0072309 in GBM cell proliferation and invasion, indicating that hsa_circ_0072309 may act as a potential therapeutic target for GBM comprehensive treatment.

Glioblastoma and MiRNAs

Glioblastoma (GB) is one of the most common types of lethal brain tumors. Although several treatment options are available including surgery, along with adjuvant chemo and radiotherapy, the disease has a poor prognosis and patients generally die within 14 months of diagnosis. GB is chemo and radio resistant. Thus, there is a critical need for new insights into GB treatment to increase the chance of therapeutic success. This is why microRNA (miRNA) is being potentially considered in the diagnosis and treatment of glioblastoma. The objective of our review is to provide a holistic picture of GB up-regulated and down-regulated miRNA, in relationship with the expression of other genes, cell signaling pathways, and their role in GB diagnosis and treatment. MiRNA treatment is being considered to be used against GB together with radiotherapy and chemotherapy. Moreover, the use of miRNA as a diagnostic tool has also begun. Knowing that miRNAs are isolated in almost all human body fluids and that there are more than 3000 miRNAs in the human genome, plus the fact that each miRNA controls hundreds of different mRNAs, there is still much study needed to explore how miRNAs relate to GB for its proliferation, progression, and inhibition.

Emerging Role of Long Non-Coding RNAs in the Pathobiology of Glioblastoma

Glioblastoma is the utmost aggressive diffuse kind of glioma which is originated from astrocytes, neural stem cells or progenitors. This malignant tumor has a poor survival rate. A number of genetic aberrations and somatic mutations have been associated with this kind of cancer. In recent times, the impact of long non-coding RNAs (lncRNAs) in glioblastoma has been underscored by several investigations. Up-regulation of a number of oncogenic lncRNAs such as H19, MALAT1, SNHGs, MIAT, UCA, HIF1A-AS2 and XIST in addition to down-regulation of other tumor suppressor lncRNAs namely GAS5, RNCR3 and NBAT1 indicate the role of these lncRNAs in the pathogenesis of glioblastoma. Several in vitro and a number of in vivo studies have demonstrated the contribution of these transcripts in the regulation of cell proliferation and apoptosis, cell survival, invasion and metastasis of glioblastoma cells. Moreover, some lncRNAs such as SBF2-AS1 are involved in conferring resistance to temozolomide. Finally, few circularRNAs have been identified that influence the evolution of glioblastoma. In this paper, we discuss the impacts of lncRNAs in the pathogenesis of glioblastoma, their applications as markers and their implications in the therapeutic responses in this kind of cancer.

Variability in Cerebrospinal Fluid MicroRNAs Through Life

The development of the human brain starts in the first weeks of embryo differentiation. However, there are many relevant neurodevelopmental processes that take place after birth and during lifespan. Such a fine and changing scenario requires the coordinated expression of thousands of genes to achieve the proper specialization and inter-connectivity. In this context, microRNAs (miRNAs), which can modulate mRNA stability and translation, are gaining recognition for their involvement in both brain development and neurodevelopmental disorders. Therefore, cerebrospinal fluid (CSF) miRNAs should be perfectly differentiated in relevant age periods. In this study, we aimed to highlight the biological variability of miRNA expression in the CSF throughout life, which is also crucial for biomarker discovery in CNS pathologies, especially in children, where they are desperately needed. We analyzed the CSF microRNAome of 14 healthy children (aged 0-7.4 years) by smallRNA-Seq and compared it with previously published data in adults (N = 7) and elders (N = 11). miR-423-5p and miR-22-3p were overexpressed in the < 1 and > 3 years groups, respectively. Additionally, we detected 18 miRNAs that reached their highest peak of expression at different time-points during the lifespan and sets of miRNAs that were exclusively expressed in a specific age group. On the contrary, miR-191-5p showed stable expression in CSF from the first year of life. Our results remark the complex differential miRNA expression profile that can be observed through life, which underlines the need for including appropriate age-matched controls when the expression of CSF miRNAs is analyzed in different pathological contexts. Graphical abstract.

The WWOX gene in brain development and pathology

Shortly after its discovery in 2000, WWOX was hailed as a tumor suppressor gene. In subsequent years of research, this function was confirmed indisputably. Majority of tumors show high rate of loss of heterozygosity and decreased expression of WWOX. Nevertheless, over the years, the range of its known functions, at the cellular, organ and system levels, has expanded to include metabolism and endocrine system control and CNS differentiation and functioning. Despite of its function as a tumor suppressor gene, WWOX genetic alternations were found in a number of metabolic and neural diseases. A lack of WWOX protein as a consequence of germline mutations results in brain development disturbances and malfunctions.

Functions and clinical significance of circular RNAs in glioma

CircRNAs are a class of single-stranded RNA molecules with a covalently closed loop structure and have been characterized by high stability, abundance, conservation, and display tissue/developmental stage-specific expression, furthermore, based on the abundance in distinct body fluids or exosomes, circRNAs present novel biomarkers and targets for the diagnosis and prognosis of cancers. Recently, the regulatory mechanisms of biogenesis and molecular functions, including miRNAs and RBPs sponge, translation as well as transcriptional and splicing regulation, have been gradually uncovered, although various aspects remained to be elucidated in combination with deep-sequence and bioinformatics. Accumulating studies have indicated that circRNAs are more enriched in neuronal tissues partly due to the abundance of specific genes promoting circularization, suggesting dysregulation of circRNAs is closely related to diseases of the nervous system, including glioma. In this review, we elaborate on the biogenesis, functions, databases as well as novel advances especially involved in the molecular pathways, highlight its great value as diagnostic or therapeutic targets in glioma.