Circular RNA hsa-circ-0012129 Promotes Cell Proliferation and Invasion in 30 Cases of Human Glioma and Human Glioma Cell Lines U373, A172, and SHG44, by Targeting MicroRNA-661 (miR-661)

A comprehensive review of lncRNA CRNDE in cancer progression and pathology, with a specific glance at the epithelial-mesenchymal transition (EMT) process

It has been suggested that the long non-coding RNAs (lncRNAs), such as colorectal neoplasia differentially expressed (CRNDE), may contribute to the formation of human cancer. It is yet unknown, though, what therapeutic significance CRNDE expression has for different forms of cancer. CRNDE has recently been proposed as a possible diagnostic biomarker and prognostic pred for excellent specificity and sensitivity in cancer tissues and plasma. To provide the groundwork for potential future therapeutic uses of CRNDE, we briefly overview its biological action and related cancer-related pathways. Next, we mainly address the impact of CRNDE on the epithelial-mesenchymal transition (EMT). The epithelial-mesenchymal transition, or EMT, is an essential biological mechanism involved in the spread of cancer.

Roles of circular RNAs in regulating the development of glioma

BACKGROUND

Glioma is the most common malignant tumor in the central nervous system. In patients with glioma, the prognosis is poor and median survival is only 12-15 months. With the recent development of sequencing technology, important roles of noncoding RNAs are being discovered in cells, especially those of circular RNAs (circRNAs). Because circRNAs are stable, abundant, and highly conserved, they are regarded as novel biomarkers in the early diagnosis and prognosis of diseases.

PURPOSE

In this review, roles and mechanisms of circRNAs in the development of glioma are summarized.

METHODS

This paper collects and reviews relevant PubMed literature.

CONCLUSION

Several classes of circRNAs are highly expressed in glioma and are associated with malignant biological behaviors of gliomas, including proliferation, migration, invasion, apoptosis, angiogenesis, and drug resistance. Further studies are needed to clarify the roles of circRNAs in glioma and to determine whether it is possible to increase therapeutic effects on tumors through circRNA intervention.

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.

CircWEE1/miR-138 axis promotes the malignant progression of glioma by regulating SIRT1

Background

This study aims to reveal the potential impact of circWEE1 on the malignant progression of gliomas and its mechanism.

Methods

Real-time quantitative polymerase chain reaction (qRT-PCR) were used to detect circWEE1 levels in glioma tissues and cell lines. The relationship between circWEE1 expression and glioma metastasis was analyzed.

Results

After knocking out or over-expressing circWEE1, the effects on glioma cells were examined separately. Subsequently, the regulatory relationship of circWEE1 to miR-138 was detected by a dual luciferase reporter gene. In addition, we evaluated the role of silent information regulator 1 (SIRT1) in the progression of gliomas affected by circWEE1 through a rescue experiment. CircWEE1 was significantly up-regulated in glioma tissues and cell lines. At the same time, its expression level was significantly higher in glioma patients with lymphatic or distant metastasis than in glioma patients with non-metastasis. The down-regulation of circWEE1 reduced the viability, migration, and invasion ability of T98-G cells. The expression of miR-138 is negatively regulated by WEE1, while miR-138 directly targets and regulates the expression of SIRT1.

Conclusions

The rescue experiment confirmed that SIRT1 is a regulator of circWEE1 in the malignant progression of glioma. In summary, the CircWEE1/miR-138 axis may regulate SIRT1 to promote malignant progression in glioma.

CircRFX3 contributes to glioma progression through the circRFX3-miR-1179/miR-1229-VASP axis

Background

Circular RNAs (circRNAs) are implicated in the carcinogenesis of human cancers. However, the functional roles of circRFX3 in glioma are not elucidated.

Methods

Quantitative real-time polymerase chain reaction (qRT-PCR) assay was performed for the levels of circRFX3, RFX3, miR-1179, miR-1229 and vasodilator stimulated phosphoprotein (VASP). Actinomycin D assay and RNase R assay were employed to analyze the characteristics of circRFX3. Cell Counting Kit-8 (CCK-8) assay and colony formation assay were conducted for cell proliferation. Transwell assay was used for cell migration and invasion. Flow cytometry analysis was adopted for cell apoptosis. RNA pull-down assay, dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay were employed to analyze the interaction between miR-1179/miR-1229 and circRFX3 or VASP. Western blot assay was conducted for VASP protein level. Murine xenograft model assay was used to investigate the role of circRFX3 in vivo.

Results

CircRFX3 level was increased in glioma tissues and cells. Knockdown of circRFX3 suppressed glioma cell proliferation, migration and invasion and promoted apoptosis in vitro and repressed tumorigenesis of glioma in vivo. MiR-1179 and miR-1229 were identified to be the targets of circRFX3. MiR-1179 or miR-1229 inhibition reversed the impacts of circRFX3 knockdown on glioma cell malignant behaviors. Additionally, VASP was demonstrated to be the target gene of miR-1179 and miR-1229, and VASP overexpression abolished the effect of circRFX3 knockdown on glioma cell progression.

Conclusion

CircRFX3 served as a tumor promoter in glioma via modulating miR-1179/miR-1229-VASP axis, which might provide a novel target for glioma therapy.

Circular RNA circ_0001588 sponges miR-211-5p to facilitate the progression of glioblastoma via up-regulating YY1 expression

BACKGROUND

As the most common and detrimental brain tumor with high invasiveness and poor prognosis, glioblastoma (GBM) has severely threatened people's health globally. Therefore, it is of great importance and necessary to identify the molecular mechanisms involved in tumorigenesis and development, thus contributing to potential therapeutic targets and strategies.

METHODS

The level of circ_0001588 was detected in 68 pairs of GBM tissues and adjacent normal tissues and human glioma cell lines via a real-time quantitative reverse transcriptase polymerase chain reaction (qRT-PCR). Then, the effect of circ_0001588 on the proliferation, migration and invasion of glioma cells was evaluated. In addition, potential downstream targets of circ_0001588 were forecasted by circBANK and Starbase. Their interaction was confirmed by introducing luciferase reporter assays. Moreover, sh-circ_0001588 transfected U251 cells were used to form tumors in vivo. Finally, the functional mechanism of circ_0001588 was identified by qRT-PCR, western blotting, xenograft and immunohistochemistry (IHC) assays.

RESULTS

The expression of circ_0001588 is markedly up-regulated in GBM tissues and human gliomas cells. Additionally, increased expression of circ_0001588 is positively relevant with poor survival in GBM patients. The down-regulation of circ_0001588 distinctly inhibits the proliferation, migration and invasion of GBM in vitro, as well as tumor growth in vivo. Moreover, knockdown of circ_0001588 reduces the tumor volume and weight, enhances the relative IHC staining index of E-cadherin and decreases the relative IHC staining index of Ki-67, Yin Yang 1 (YY1) and vinmentin in vivo. Mechanistically, circ_0001588 locates in the cytoplasm, which is directly bound with miR-211-5p. Furthermore, circ_0001588 can positively regulate YY1 via sponging miR-211-5p. Moreover, circ_0001588 accelerates the proliferation, migration and invasion of GBM by modulating miR-211-5p/YY1 signaling.

CONCLUSIONS

These results illustrate a new circ_0001588/miR-211-5p/YY1 regulatory signaling axis in GBM.

hsa_circ_0058357 acts as a ceRNA to promote non‑small cell lung cancer progression via the hsa‑miR‑24‑3p/AVL9 axis

Abnormal circular RNAs (circRNAs) are associated with biological processes in cancer; however, the function of circRNAs remains largely unknown in non-small cell lung cancer (NSCLC). The present study aimed to investigate the role of hsa_circ_0058357 on the progression of NSCLC. Cell proliferation, migration and apoptosis were determined using Cell Counting Kit-8, Transwell and flow cytometry assays, respectively. Gene [circRNA and microRNA (miR)] and protein expression levels were determined via reverse transcription-quantitative PCR and immunoblotting. A luciferase assay was employed to detect the binding of miR-24-3p with AVL9 cell migration associated (AVL9), while a cancer xenograft model was established to evaluate cancer growth in vivo. The results demonstrated that hsa_circ_0058357 was highly expressed in human NSCLC tissues and NSCLC cells compared with para-cancerous tissues and human bronchial epithelial (HBE) cells, respectively. Knockdown of hsa_circ_0058357 significantly suppressed cell viability, migration and tumor growth, while it promoted apoptosis in NSCLC cells. As a competing endogenous RNA, hsa_circ_0058357 knockdown contributed to the increase of miR-24-3p expression in NSCLC cells. Of note, overexpression of miR-24-3p markedly abolished the exogenous hsa_circ_0058357-induced excessive proliferation, migration and apoptosis resistance of NSCLC cells. Mechanistically, as a signaling molecule in late secretory pathway, AVL9 was also expressed at a high level in NSCLC tissues and cells, which could be directly suppressed by miR-24-3p. In the tumor tissues, along with growth inhibition, hsa_circ_0058357 knockdown also mediated the elevation of miR-24-3p and the reduction of AVL9. Thus, it was suggested that hsa_circ_0058357 may be a crucial regulation factor in NSCLC by sponging hsa-miR-24-3p, leading to a decrease in miR-24-3p expression, and subsequent increase in AVL9 expression. Therefore, hsa_circ_0058357 may serve as a potential target for diagnosis and gene therapy for NSCLC.

Review on circular RNAs and new insights into their roles in cancer

Circular RNAs (circRNAs) are a very interesting class of conserved single-stranded RNA molecules derived from exonic or intronic sequences by precursor mRNA back-splicing. Unlike canonical linear RNAs, circRNAs form covalently closed, continuous stable loops without a 5'end cap and 3'end poly(A) tail, and therefore are resistant to exonuclease digestion. The majority of circRNAs are highly abundant, and conserved across different species with a tissue or developmental-stage-specific expression. circRNAs have been shown to play important roles as microRNA sponges, regulators of gene splicing and transcription, RNA-binding protein sponges and protein/peptide translators. Emerging evidence reveals that circRNAs function in various human diseases, particularly cancers, and may function as better predictive biomarkers and therapeutic targets for cancer treatment. In consideration of their potential clinical relevance, circRNAs have become a new research hotspot in the field of tumor pathology. In the present study, the current understanding of the biogenesis, characteristics, databases, research methods, biological functions subcellular distribution, epigenetic regulation, extracellular transport and degradation of circRNAs was discussed. In particular, the multiple databases and methods involved in circRNA research were first summarized, and the recent advances in determining the potential roles of circRNAs in tumor growth, migration and invasion, which render circRNAs better predictive biomarkers, were described. Furthermore, future perspectives for the clinical application of circRNAs in the management of patients with cancer were proposed, which could provide new insights into circRNAs in the future.

Lidocaine inhibits glioma cell proliferation, migration and invasion by modulating the circEZH2/miR-181b-5p pathway

BACKGROUND

Lidocaine is well known as a local anesthetic that has been reported to play an antitumor role in numerous cancers, including glioma. Circular RNAs (circRNAs) play multiple biological roles in cancers. The aim of this study was to determine the effects of lidocaine in glioma in vitro and in vivo and explore functional mechanisms.

METHODS

The effects of lidocaine on glioma progression were investigated by cell proliferation, migration and invasion using 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay, colony formation assay and transwell assay. The expression of CD133 and glial fibrillary acidic protein (GFAP) was quantified by western blot to assess cell differentiation. The expression of circEZH2 and miR-181b-5p was detected by a quantitative real-time PCR (qRT-PCR). The target relationship between circEZH2 and miR-181b-5p was verified by dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay. The effect of lidocaine on tumor growth in vivo was investigated by establishing Xenograft models.

RESULTS

Lidocaine inhibited proliferation, migration, invasion and induced differentiation of glioma cells in vitro. Lidocaine suppressed the expression of circEZH2, and circEZH2 was highly expressed in glioma tissues and cells. CircEZH2 overexpression partly inhibited the function of lidocaine. CircEZH2 was a sponge of miR-181b-5p, and miR-181b-5p was downregulated in glioma tissues and cells. Besides, miR-181b-5p restoration reversed the effects of circEZH2 overexpression to repress the malignant behaviors of glioma cells. In addition, lidocaine mediated the circEZH2/miR-181b-5p axis to inhibit tumor growth in vivo.

CONCLUSION

Lidocaine suppressed glioma progression by modulating the circEZH2/miR-181b-5p pathway.

CircRNAs as potential biomarkers for the clinicopathology and prognosis of glioma patients: a meta-analysis

BACKGROUND

An increasing number of studies have reported circular RNAs (circRNAs) as new potential biomarkers for the prognosis of gliomas. However, the overall prognostic value of circRNAs for glioma remains unclear. Therefore, this study is the first comprehensive evaluation of the clinicopathological and prognostic value of dysregulated circRNAs in the treatment of glioma patients.

METHODS

We systematically reviewed the online databases of PubMed, Web of Science, EMBASE, and Cochrane Library to identify studies that explored the relationship between circRNA expression and clinicopathological and prognostic factors in glioma through April 11, 2020. The quality of the included studies was evaluated by the Newcastle-Ottawa Scale (NOS) checklists. Clinicopathological features were assessed by pooled odds ratios (ORs) and 95% confidence intervals (CIs), and overall survival (OS) was assessed by hazard ratios (HRs) and 95% CIs.

RESULTS

Twenty-four eligible studies, including 22 studies of clinicopathological features, 1 diagnostic study, and 18 studies of prognosis, that included a total of 1390 patients were ultimately included in this study. Meta-analysis showed that highly expressed oncogenic circRNAs were significantly related to poor clinicopathological features (age: P = 0.026; tumor size: P ≤ 0.001; tumor grade: P ≤ 0.001; KPS: P = 0.012) and worse overall survival (OS) (HR = 2.01, 95% CI: 1.61-2.50, P ≤ 0.001). Moreover, we found that highly expressed tumor-suppressor circRNAs were related to better clinicopathological features (gender: P = 0.042; age: P = 0.014; tumor size: P = 0.022; tumor grade: P ≤ 0.001) and longer OS (HR = 2.70, 95% CI: 1.82-3.99, P ≤ 0.001).

CONCLUSIONS

In conclusion, there is a significant correlation between the dysregulated expression of circRNAs and the clinicopathology and prognosis of glioma patients.

Expression of circular RNAs in the vascular dementia rats

PURPOSE

Circular RNAs (circRNAs) are a class of endogenous noncoding RNA molecules that lack free 5' and a 3' end poly(A) tail. CircRNAs are enriched in neural tissues, and have been found to be associated with various diseases of the central nervous system. This study aimed to examine key circRNAs involved in vascular dementia(VD) model rats.

METHODS

Total RNA-seq profiles of hippocampus samples from normal and vascular dementia rats were extracted and high throughput sequencing was performed. Quantitative real-time polymerase chain reaction (qPCR) was used to confirm the circRNA expression profiles. Differential expression of circRNA has been used for analysis via the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. The circRNA-miRNA-mRNA network was then constructed.

RESULTS

The data of high-throughput sequencing showed that there were 425 circRNAs differentially expressed between VD and normal rats (fold change (FC)≥2.0 and p-value< 0.05). In the VD group, a total of 237 were significantly upwardly revised, while the other 188 were downwardly revised. Eleven of these expressed more than 10 times in the VD model rats. The Expression levels of 10 circRNAs (circ_Map2k5, circ_Ulk2, circ_Plekha5, circ_Plcl1, circ_Sntg1, circ_Morc3, circ_Rims1, circ_ Stxbp5l, circ_ Agtpbp1, circ_Lrrc28) were verified by qPCR, which were persistent with RNA-seq data(P < 0.05). GO analysis indicated that majority of predicted target genes were involved in biological processes, such as cellular processes, nervous system development, etc. Cellular component, such as cellular parts, intracellular parts, cytoplasm and molecular function, such as binding, catalytic activity, etc. Moreover, KEGG analysis showed that many genes were enriched in cholinergic synapses, the MAPK signaling pathways, GABAergic synapses, metabolic pathways, the mTOR signaling pathways, and so on.

CONCLUSIONS

Our results suggest the involvement of different ncRNA expression patterns in the pathogenesis (are associated with the pathogenesis of VD. Our findings provide a novel perspective for further research into potential mechanisms of VD and might facilitate the development of novel therapeutics targeting ncRNAs.

Knockdown of circHIPK3 Facilitates Temozolomide Sensitivity in Glioma by Regulating Cellular Behaviors Through miR-524-5p/KIF2A-Mediated PI3K/AKT Pathway

Background: Temozolomide (TMZ) resistance is a serious hindrance in clinical chemotherapy for glioma. Circular RNA homeodomain interacting protein kinase 3 (circHIPK3) can be involved in regulating the progression of glioma, but the molecular mechanism of circHIPK3 in TMZ-resistant-glioma is completely unclear. Materials and Methods: The levels of circRNA, miRNA, and mRNA were examined using quantitative real-time polymerase chain reaction. 3-(4,5-dimethylthiazol-2-y1)-2, 5-diphenyl tetrazolium bromide assay was used for assessing the half inhibitory concentration (IC₅₀) of TMZ and cell proliferation. Cell apoptosis and metastasis (migration and invasion) were detected by flow cytometry and transwell assay, respectively. Western blot and dual-luciferase reporter assay were performed several times to analyze the expression levels of associated proteins and the targeted relation. Results: The upregulation of circHIPK3 was found in TMZ-resistant glioma tissues and cells. Both circHIPK3 knockdown and kinesin family member 2A (KIF2A) inhibition could facilitate TMZ sensitivity and apoptosis but repress proliferation and metastasis in TMZ-resistant glioma cells. CircHIPK3 targeted microRNA-524-5p (miR-524-5p) and KIF2A functioned as a downstream target of miR-524-5p. Decrease of miR-524-5p relieved the effects of si-circHIPK3 on TMZ-resistant glioma cells by upregulating KIF2A. Downregulation of circHIPK3 refrained the phosphatidylinositol-3-kinase (PI3K)/protein kinase B (AKT) signal pathway partly through miR-524-5p/KIF2A axis. Conclusions: Knockdown of circHIPK3 promoted TMZ sensitivity in glioma by modulating proliferation, metastasis, and apoptosis through miR-524-5p/KIF2A-mediated PI3K/AKT pathway. CircHIPK3 may be the potential target for the diagnosis and therapy of TMZ-resistant glioma.

Advances in circular RNAs and their role in glioma (Review)

Glioma is the most common primary tumour of the central nervous system, and is associated with a high postoperative recurrence rate and resistance to chemotherapy. High‑grade glioblastoma in particular has a very poor prognosis and poses a serious threat to human health. Related studies have confirmed that the occurrence and development of gliomas are closely associated with the abnormal expression and regulation of genes. Moreover, the number of studies on the association of the expression of non‑coding RNAs [linear RNAs, microRNAs and circular RNAs (circRNAs)] in human cells with glioma has been gradually increasing in recent years. Among those, circRNAs, previously considered to be 'splicing errors', have been shown to be highly expressed in eukaryotic cells and regulate the biological behaviour of gliomas. circRNAs are highly abundant and stable, and have become a research hotspot in the field of glioma molecular biology. The aim of the present review was to focus on the research progress regarding the association between circRNA expression and gliomas, and to provide a theoretical basis according to the currently available literature for further exploring this association. The present study may be of value for the early diagnosis, pathological grading, targeted therapy and prognostic evaluation of gliomas.

circKIF4A promotes tumorogenesis of glioma by targeting miR-139-3p to activate Wnt5a signaling

Background

Glioma has the characteristics of high incidence and mortality, and is a common malignant tumor of the central nervous system. Circular RNAs (circRNAs) have been reported to play vital roles in progression of cancer including glioma, and circKIF4A is up-regulated in glioma tissues. However, its role and mechanisms in gliomas are unclear.

Methods

circKIF4A and miR-139-3p were determined by qRT-PCR. Transwell assay, wound-healing assay, cell colony formation and flow cytometry were performed to measure cell invasion, migration, proliferation and apoptosis. Western blotting was used to evaluate Wnt/β-catenin pathway-related protein. Luciferase reporter assays confirmed the relationship among circKIF4A, miR-139-3p and Wnt5a. Sphere formation was performed to measure the ability of glioma-initiating cells (GICs) spheroid formation. A nude mouse xenograft model was established and immunohistochemical staining was used to detect Ki-67 and Wnt5a levels.

Results

circKIF4A and Wnt5a were up-regulated and miR-139-3p was down-regulated in both glioma cells and tissues. circKIF4A promoted Wnt5a expression by sponging miR-139-3p. Knockdown of circKIF4A inhibited the colony formation ability, migration and invasion, and promoted the apoptosis of glioma cells by regulating miR-139-3p. Knockdown of circKIF4A inhibited Wnt/β-catenin signaling pathway and proliferation-related signal via miR-139-3p. Furthermore, knockdown of circKIF4A or overexpression of miR-139 suppressed the ability of sphere formation of GICs and inhibitd Wnt/β-catenin signaling pathway and proliferation-related signal in GICs. Additionally, depletion of circKIF4A decreased the expression level of Wnt5a and Ki-67, inhibited tumorigenesis in xenograft modes.

Conclusion

circKIF4A was overexpressed in glioma, and knockdown of circKIF4A suppressed glioma progression via miR-139-3p/Wnt5a axis. The results indicated that circKIF4A may be a potential target for clinical treatment of glioma.

Role of circular RNAs in brain development and CNS diseases

In mammals, many classes of noncoding RNAs (ncRNAs) are expressed at a much higher level in the brain than in other organs. Recent studies have identified a new class of ncRNAs called circular RNAs (circRNAs), which are produced by back-splicing and fusion of either exons, introns, or both exon-intron into covalently closed loops. The circRNAs are also highly enriched in the brain and increase continuously from the embryonic to the adult stage. Although the functional significance and mechanism of action of circRNAs are still being actively explored, they are thought to regulate the transcription of their host genes and sequestration of miRNAs and RNA binding proteins. Some circRNAs are also shown to have translation potential to form peptides. The expression and abundance of circRNAs seem to be spatiotemporally maintained in a normal brain. Altered expression of circRNAs is also thought to mediate several disorders, including brain-tumor growth, and acute and chronic neurodegenerative disorders by affecting mechanisms such as angiogenesis, neuronal plasticity, autophagy, apoptosis, and inflammation. This review discusses the involvement of various circRNAs in brain development and CNS diseases. A better understanding of the circRNA function will help to develop novel therapeutic strategies to treat CNS complications.

Lcn2-derived Circular RNA (hsa_circ_0088732) Inhibits Cell Apoptosis and Promotes EMT in Glioma via the miR-661/RAB3D Axis

Background: Glioma is the most common malignant tumor of the central nervous system, and often displays invasive growth. Recently, circular RNA (circRNA), which is a novel non-coding type of RNA, has been shown to play a vital role in glioma tumorigenesis. However, the functions and mechanism of lipocalin-2 (Lcn2)-derived circular RNA (hsa_circ_0088732) in glioma progression remain unclear.

Methods: We evaluated hsa_circ_0088732 expression by fluorescence in situ hybridization (FISH), Sanger sequencing, and PCR assays. Cell apoptosis was evaluated by flow cytometry and Hoechst 33258 staining. Transwell migration and invasion assays were performed to measure cell metastasis and viability. In addition, the target miRNA of hsa_circ_0088732 and the target gene of miR-661 were predicted by a bioinformatics analysis, and the interactions were verified by dual-luciferase reporter assays. RAB3D expression was analyzed by an immunochemistry assay, and E-cadherin, N-cadherin, and vimentin protein expression were examined by western blot assays. A mouse xenograft model was developed and used to analyze the effects of hsa_circ_0088732 on glioma growth in vivo.

Results: We verified that hsa_circ_0088732 is circular and highly expressed in glioma tissues. Knockdown of hsa_circ_0088732 induced glioma cell apoptosis and inhibited glioma cell migration, invasion, and epithelial-mesenchymal transition (EMT). We found that hsa_circ_0088732 negatively regulated miR-661 by targeting miR-661, and RAB3D was a target gene of miR-661. In addition, inhibition of miR-661 promoted glioma cell metastasis and suppressed cell apoptosis. Knockdown of RAB3D induced cell apoptosis and suppressed cell metastasis. Moreover, hsa_circ_0088732 accelerated glioma progression through its effects on the miR-661/RAB3D axis. Finally, results from a mouse xenograft model confirmed that knockdown of hsa_circ_0088732 induced miR-661 expression, resulting in suppression of RAB3D expression and inhibition of tumor growth in vivo.

Conclusion: We demonstrated that hsa_circ_0088732 facilitated glioma progression by sponging miR-661 to increase RAB3D expression. This study provides a theoretical basis for understanding the development and occurrence of glioma, as well as for the development of targeted drugs.

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.

Ectopic expression of CYP24A1 circular RNA hsa_circ_0060927 in uterine leiomyomas

Background

As a novel class of non‐coding RNAs, the role of circular RNAs (circRNAs) in tumor biogenesis and progression has been proved in a number of human tumors; however, up to now, the relation between circRNAs and uterine leiomyomas (ULM) remains unclear.

Methods

In this study, we have estimated the expression level of CYP24A1 hsa_circ_0060927 in uterine leiomyoma and adjacent tissues considering the mediator complex subunit 12 gene (MED12) mutation profile by quantitative real‐time polymerase chain reaction (qRT‐PCRs).

Results

Using Sanger sequencing method, somatic mutations in the MED12 exon 2 were detected in 14 (35.90%) ULM samples, including 10 (71.43%) missense mutations and 4 (28.57%) in‐frame deletions. Our results revealed that hsa_circ_0060927 was ectopically expressed in 33.33% of ULM tissues; although, this expression was independent of the MED12 mutation profile in the ULM samples.

Conclusions

Present results provide primary evidence for the role of circular RNAs in the leiomyoma development; however, further studies are essential to confirm the importance of these molecules as potential biomarkers for diagnosis and/or prognosis in ULM.

Functional Roles of Long Non-Coding RNAs (LncRNAs) in Glioma Stem Cells

Glioma, the most common and aggressive type of brain tumor, has a poor prognosis. Glioma stem cells (GSCs) are thought to be responsible for glioma genesis, proliferation, resistance to chemoradiotherapy, and recurrence. Long non-coding RNAs (lncRNAs) have been viewed as a prospective novel target in glioma therapy in recent years due to their functional roles in GSC biological processes. However, how lncRNAs interact with GSCs and the underlining mechanisms associated with these interactions are not yet clear. In this review, we briefly illustrate recent advancements in the functional roles of lncRNA and their potential mechanisms in GSCs.

Circular RNA circMAN2B2 facilitates glioma progression by regulating the miR-1205/S100A8 axis

The aim of this study was to research the mechanism of circMAN2B2 in the development of glioma. In our study, we found that circMAN2B2 has a higher expression in glioma tissues and cells, which was negatively related to the overall survival of glioma patients. The cell counting kit-8 assay, 5-ethynyl-2'-deoxyuridine labeling assay, transwell assay, and the nude mice assay indicated that knockdown of circMAN2B2 inhibited the cell proliferation, invasion, migration and decreased tumor size. In terms of mechanism, knockdown of circMAN2B2 increased the expression of miR-1205. Moreover, circMAN2B2 regulated S100A8 expression by inhibiting miR-1205. We also showed that knockdown of S100A8 inhibited cell proliferation, invasion, and migration. Increasing S100A8 expression rescued the effect of si-circMAN2B2. In conclusion, circMAN2B2 could improve cell proliferation, invasion, and migration of the glioma by inhibiting miR-1205 and promoting the expression of S100A8.

Circ-ZNF264 Promotes the Growth of Glioma Cells by Upregulating the Expression of miR-4493 Target Gene Apelin

Glioma is the most common malignant tumor in the brain and nervous system, with high recurrence and high mortality rate. Recent researches have shown that circular RNAs (circRNAs) play key roles in the genesis and progress of glioma. Detection of circRNAs in glioma cells revealed that the expression of circ-ZNF264 was upregulated. At the same time, the expression of miR-4493 was downregulated in glioma cells and had multiple binding sites on the circ-ZNF264 sequence. Dual luciferase reporter gene assay confirmed that miR-4493 could bind to circ-ZNF264 and apelin specifically. MiR-4493 expression was not changed, but its target gene apelin expression could be significantly upregulated by circ-ZNF264. MiR-4493 could inhibit the expression of circ-ZNF264 and apelin. Biological behaviors of glioma cells were detected; circ-ZNF264 promoted cell proliferation and invasion and inhibited apoptosis. MiR-4493 had the opposite effects and could terminate the above effects of circ-ZNF264. When the expression of apelin was downregulated and that of circ-ZNF264 was upregulated, the changes of the above biological behaviors were not obvious. Therefore, in glioma cells, circ-ZNF264 can inhibit the function of miR-4493 and then upregulate its target gene apelin expression, thus regulating glioma cell proliferation, apoptosis, and invasion. This finding provides more evidence for the role of circRNAs in glioma.

Matrine induces apoptosis and autophagy of glioma cell line U251 by regulation of circRNA-104075/BCL-9

BACKGROUND

Matrine, a traditional Chinese medicine, has been reported to exert anti-tumor effects in several types of cancers. Here, we explored the anti-tumor effects of matrine on the glioma cells.

METHODS

Glioma cell line U251 cells were treated with matrine to assess viability and proliferation using CCK8 and EdU assays. PI/FITC staining was performed for apoptosis assay. Transfections were performed for circRNA-104075 or Bcl-9 overexpression. Western blot analysis was performed to evaluate changes of protein levels and changes of gene level were detected by qRT-PCR in U251 cells.

RESULTS

Matrine suppressed cell viability while induced apoptosis and autophagy in U251 cells. Matrine also decreased circRNA-104075 expression significantly. Overexpression of circRNA-104075 was found to counteract the inhibitory effects of matrine on cell proliferation and promoting effects on apoptosis and autophagy in U251 cells. Moreover, the suppressed Wnt/β-catenin and PI3K/AKT signaling pathways by matrine were activated by circRNA-104075 overexpression. Furthermore, Bcl-9 expression was also down-regulated by matrine treatment. Bcl-9 overexpression elevated the decreased cell proliferation while suppressed the increased apoptosis and autophagy induced by matrine in U251 cells.

CONCLUSION

Taken together, the present findings suggested that matrine induced apoptosis and autophagy through down-regulating circ-104075 and Bcl-9 expression via inhibition of PI3K/AKT and Wnt-β-catenin pathways in glioma cells. The present study provides a foundation for further preclinical and clinical evaluations of matrine as a glioma therapy.

Putative biomarkers of malignant transformation of sinonasal inverted papilloma into squamous cell carcinoma

OBJECTIVE

To compare genome-wide DNA methylation between samples of sinonasal inverted papilloma (SNIP) and squamous cell carcinoma (SCC) samples in order to identify aberrantly methylated genes that might be involved in malignant transformation.

METHODS

Tissue samples were collected from patients. DNA methylation in C-phosphate-G islands and gene promoters was analysed using a DNA methylation microarray kit. The levels of mRNA or protein from aberrantly methylated genes were measured using real-time polymerase chain reaction or Western blot analysis.

RESULTS

A total of 27 tissue samples were included in this study; 15 SNIP samples and 12 SCCs arising in SNIPs. A total of 11 201 nominally differentially methylated sites were observed between SNIP and SCC arising in SNIPs. Six sites were significantly different at P < 0.01 and contained three genes ( MIR661, PLEC and OPA3). These three genes were hypermethylated. In addition, the levels of mature miR-661 mRNA and PLEC protein were significantly upregulated in SCC tissues compared with SNIP samples. The levels of OPA3 protein were downregulated in SCC tissues compared with SNIP samples.

CONCLUSIONS

This study demonstrated hypermethylation and abnormal expression of the MIR661, PLEC and OPA3 genes, suggesting a role for their involvement in the malignant transformation of SNIP.

Circular RNAs and human glioma

As a newly discovered type of RNA, circular RNAs (circRNAs) are widespread throughout the eukaryotic genome. The expression of circRNAs is regulated by both cis-elements and trans-factors, and the expression pattern of circRNAs is cell type- and disease-specific. Similar to other types of non-coding RNAs, functions of circRNAs are also versatile. CircRNAs have been reported previously to function as microRNA (miRNA) sponges, protein sponges, coding RNAs or scaffolds for protein complexes. Recently, several circRNAs have been reported to play important roles in human malignancies, including glioma. Here, we reviewed several reports related to circRNAs and glioma, as well as the potential diagnostic and therapeutic applications of circRNAs in brain cancer. In general, some circRNAs, such as circSMARCA5 and circCFH, are found to be expressed in a glioma-specific pattern, these circRNAs may be used as tumor biomarkers. In addition, some circRNAs have been found to play oncogenic roles in glioma (e.g., circNFIX and circNT5E), whereas others have been reported to function as tumor suppressors (e.g., circFBXW7 and circSHPRH). Furthermore, circRNA is a good tool for protein expression because of its higher stability compared to linear RNAs. Thus, circRNAs may also be an ideal choice for gene/protein delivery in future brain cancer therapies. There are some challenges in circRNA research in glioma and other diseases. Research related to circRNAs in glioma is comparatively new and many mysteries remain to be solved.

Signature of circular RNAs in peripheral blood mononuclear cells from patients with active tuberculosis

The study was to characterize the expression profiles of circular RNAs (circRNAs) in peripheral blood mononuclear cells (PBMCs) from active tuberculosis (TB) patients and to investigate their function. Microarray was applied to detect circRNA expression and reverse transcription‐quantitative polymerase chain reaction was conducted to validate the microarray results. Meanwhile, receiver operating characteristic curve (ROC) curve was calculated to evaluate the predictive power of the selected circRNAs for TB diagnosis. Additionally, circRNA/miRNA interaction was predicted based on miRNA target prediction software, and gene ontology as well as Kyoto Encyclopedia of Genes and Genomes pathway analysis were used to predict their biological function. In total, 171 circRNAs were found to be dysregulated in TB samples. Specifically, circRNA_103017, circRNA_059914 and circRNA_101128 were confirmed to be increased, while circRNA_062400 was decreased in TB samples. ROC analysis revealed that circRNA_103017 had potential value for TB diagnosis, followed by circRNA_059914 and circRNA_101128. Moreover, circRNA_101128 expression in TB samples was negatively correlated with the level of its possible target let‐7a and bioinformatics analysis showed that circRNA_101128 was potentially involved in MAPK and P13K‐Akt pathway possibly via modulation of let‐7a. Taken together, our results indicated that some dysregulated circRNAs were potential biomarkers for the diagnosis of TB and circRNA_101128‐let‐7a interplay may play considerable role in PBMCs response to Mtb infection.

Circular RNAs: Functions and Prospects in Glioma

Improving the survival rate of patients with glioma, a malignant tumor of the human brain has become increasingly important. In recent years, the function of circular RNAs (circRNAs) in different diseases and the pathophysiological mechanisms involved have been elucidated. In the pathophysiological mechanism, the primary function of circRNAs is to act as microRNA sponges. An increasing number of studies have found that circRNAs are differentially expressed in gliomas and regulate the occurrence, proliferation, and invasion of glioma and thus may be potential markers for the diagnosis of gliomas. Additionally, some circRNAs have been associated with glioma staging and may be useful in determining prognosis. Based on the stability and high conservation of circRNAs, we believe that circRNAs may have molecular targets that are useful for the treatment of glioma. In this review, we summarize the current research regarding the role of circRNAs in gliomas, discuss the potential value and role of circRNAs in gliomas, and provide new perspectives for future research.

hsa_circ_0000177-miR-638-FZD7-Wnt Signaling Cascade Contributes to the Malignant Behaviors in Glioma

As a new member of the noncoding RNA family, circular RNAs (circRNAs) have been demonstrated as critical regulators in various physiological and pathological processes, such as tumorigenesis. However, the role of circRNAs has not been well understood until now. In our study, we found that circRNA hsa_circ_0000177 was upregulated in glioma tissues and cell lines. Also, hsa_circ_0000177 overexpression was associated with poor prognosis in glioma patients. Through functional experiments, we found that hsa_circ_0000177 knockdown dramatically inhibited glioma cell proliferation and invasion in vitro. Consistently, hsa_circ_0000177 knockdown significantly repressed glioma growth in vivo. In terms of mechanism, we used bioinformatics analysis and identified hsa_circ_0000177 as a miR-638 sponge. We showed that miR-638 inhibition could restore the proliferation and invasion of glioma cells transfected with hsa_circ_0000177 small interfering RNA. Furthermore, we demonstrated that frizzled class receptor 7 (FZD7) was targeted by miR-638 and upregulated by hsa_circ_0000177. Through upregulating FZD7 expression, hsa_circ_0000177 activated Wnt signaling and facilitated glioma growth. Taken together, our study revealed a novel signaling pathway involved in glioma progression.