Circular RNAs: Functions and Prospects in Glioma

Glioma-Derived Exosomes and Their Application as Drug Nanoparticles

Glioblastoma Multiforme (GBM) is the most aggressive primary tumor of the Central Nervous System (CNS) with a low survival rate. The malignancy of GBM is sustained by a bidirectional crosstalk between tumor cells and the Tumor Microenvironment (TME). This mechanism of intercellular communication is mediated, at least in part, by the release of exosomes. Glioma-Derived Exosomes (GDEs) work, indeed, as potent signaling particles promoting the progression of brain tumors by inducing tumor proliferation, invasion, migration, angiogenesis and resistance to chemotherapy or radiation. Given their nanoscale size, exosomes can cross the blood-brain barrier (BBB), thus becoming not only a promising biomarker to predict diagnosis and prognosis but also a therapeutic target to treat GBM. In this review, we describe the structural and functional characteristics of exosomes and their involvement in GBM development, diagnosis, prognosis and treatment. In addition, we discuss how exosomes can be modified to be used as a therapeutic target/drug delivery system for clinical applications.

A novel nanoplatform-based circCSNK1G3 affects CBX7 protein and promotes glioma cell growth

Bioenvironmental and biological factors have the potential to contribute to the development of glioma, a type of brain tumor. Recent studies have suggested that a unique circular RNA called circCSNK1G3 could play a role in promoting the growth of glioma cells. It does this by stabilizing a specific microRNA called miR-181 and reducing the expression of a tumor-suppressor gene known as chromobox protein homolog 7 (CBX7). To further investigate circCSNK1G3 and its effects on glioma, we utilized a nanoplatform called adeno-associated virus (AAV)-RNAi.To explore the functional implications of circCSNK1G3, we employed siRNA to silence its expression. Along with these effects, the silencing of circCSNK1G3 led to a depletion of miR-181d and an upregulation of CBX7. When we introduced miR-181d mimics, which artificially increase the levels of miR-181d, the anti-glioma cell activity induced by circCSNK1G3 siRNA was almost completely reversed. Conversely, inhibiting miR-181d mimicked the effects of circCSNK1G3 silencing. Moreover, when we overexpressed circCSNK1G3 in glioma cells, we observed an elevation of miR-181d and a depletion of CBX7. We found that the growth of A172 xenografts (tumors) carrying circCSNK1G3 shRNA was significantly inhibited. In these xenograft tissues, we detected a depletion of circCSNK1G3 and miR-181d, as well as an upregulation of CBX7.

Y-box protein-1 modulates circSPECC1 to promote glioma tumorigenesis via miR-615-5p/HIP1/AKT axis

Y-box binding protein-1 (YB-1) is upregulated in glioma and plays an important role in its occurrence and drug resistance. However, the involved regulatory processes and downstream pathways are still unclear. Since various circular RNAs (circRNAs) and microRNAs (miRNAs) also play roles in the pathogenesis of glioma, we hypothesize that YB-1 may exert its function through a circRNA-miRNA-protein interaction network. In this study, we use the RNA binding protein immunoprecipitation assay and quantitative reverse transcription polymerase chain reaction to determine the circRNAs involved in the regulation of YB-1 and further elucidate their biological functions. The level of circSPECC1 (hsa_circ_0000745) modulated by YB-1 is significantly upregulated in the U251 and U87 glioma cell lines. Downregulation of circSPECC1 markedly inhibits the proliferation and invasiveness of U251 and U87 cells by inducing apoptosis. Bioinformatics analysis reveals that miR-615-5p could interact with circSPECC1 and huntingtin-interacting protein-1 (HIP-1). Then we determine the interactions between miR-615-5p, circSPECC1, and HIP1 using dual luciferase reporter system and pull-down assays. Mechanistic analysis indicates that the downregulation of circSPECC1 results in a decreased HIP1 expression. This study demonstrates that circSPECC1 modulated by YB-1 is increased in glioma cell lines. In addition, circSPECC1 promotes glioma growth through the upregulation of HIP1 by sponging miR-615-5p and targeting the HIP1/AKT pathway. This indicates that YB-1 and circSPECC1 may both be promising targets for glioma treatment.

Circular RNA XRCC5 aggravates glioma progression by activating CLC3/SGK1 axis via recruiting IGF2BP2

BACKGROUND

Increasing evidences have reported the critical roles of circular RNA (circRNA) in gliomas. Whereas, the role of circXRCC5 in glioma and its underlying molecular mechanism has not been reported.

METHODS

The RNA transcripts and protein levels were detected using qRT-PCR, immunohistochemistry (IHC) and in situ hybridization (ISH) assays. Cell proliferation was characterized by CCK-8 and clone formation assays. The formation of NLRP3-inflammasomes was identified using immunofluorescence (IF) and Western blot assays. The cytokines were determined using immunosorbent assay (ELISA) and Western blot assays. The molecular interactions were validated using RIP and pull-down assays.

RESULTS

circXRCC5 was over-expressed in glioma and positively related to the shorter survival rate, advanced TNM stage and larger tumor volume. circXRCC5 knockdown inhibited cell proliferation and NLRP3-mediated inflammasome activation of glioma cells. Subsequently, we found that circXRCC5 maintained mRNA stability of CLC3 by binding to IGF2BP2. Furthermore, CLC3 accelerated SGK1 expression via PI3K/PDK1/AKT pathway. The rescue experiments showed that both overexpression of CLC3 or SGK1 dramatically alleviated circXRCC5 knockdown-induced inhibition of cell proliferation and NLRP3-mediated inflammasome activation of glioma cells. In vivo, our study proved that circXRCC5 accelerated glioma growth by regulating CLC3/SGK1 axis.

CONCLUSION

Our data concluded that circXRCC5 formed a complex with IGF2BP2 to regulate inflammasome activation and tumor growth via CLC3/SGK1 axis.

Down-regulation of CX43 expression by miR-1 inhibits the proliferation and invasion of glioma cells

BACKGROUND

Connexin (CX) 43 makes glioblastoma resistant to temozolomide, the first-line chemotherapy drug. However, targeting CX43 is very difficult because the mechanisms underlying CX43-mediated resistance remain unclear. CX43 is highly expressed in glioblastoma, which is closely associated with poor prognosis and chemotherapy resistance. The present study was to analyze the mechanism of microRNA (miR)-1 in regulating the proliferation and invasion of glioma cells.

METHODS

The effects of knockdown of miR-1 on the growth of glioma cell lines were observed by establishing blank, miR-1 inhibitor, and miR-1 mimic groups. Cell proliferation was detected using a Cell Counting Kit-8 (CCK-8) assay, cell apoptosis was detected by flow cytometry, and protein expression was detected by western blot. We used the Student's t-test to assess continuous data between the two groups and the Kruskal-Wallis test was adopted for multiple group comparisons.

RESULTS

Compared with the mimics normal control (NC) group, the apoptosis rate of the miR-1-3p mimics group was decreased, while that of the miR-1-3p inhibitor group was increased compared to the inhibitor NC group. In addition, the miR-1-3p mimics model of U251 cells exerted an inhibitory effect on the invasion ability of cells, whereas the miR-1-3p inhibitor model of U251 cells showed an invasion-promoting effect. The dual-luciferase assay showed that miR-1-3p had a targeted relationship with the CX43 gene.

CONCLUSIONS

Down-regulation of CX43 expression by miR-1 inhibited the infiltration and growth of glioma cells and further promoted the apoptosis of glioma cells by regulating CX43 expression.

Circular RNA circ_0079593 facilitates glioma development via modulating miR-324-5p/XBP1 axis

Glioma is a common brain tumor with high mortality. Circular RNAs (circRNAs) play crucial roles in tumor occurrence and development. However, the function and molecular basis of circ_0079593 in glioma remain unknown. Quantitative real-time PCR (qPCR) and Western blot were used for expression determination of circ_0079593, microRNA-324-5p (miR-324-5p) and X-box binding protein 1 (XBP1). Cell Counting Kit-8 (CCK-8), colony formation, flow cytometry, transwell assays, and tube formation assay were employed to evaluate cell functions. Glycolysis was determined via detecting glucose consumption, lactate production and ATP level. The binding relationship between miR-324-5p and circ_0079593 or XBP1 was validated by dual-luciferase reporter assay and RNA Immunoprecipitation (RIP) assay. Besides, xenograft assay was applied to test tumor growth in vivo. Circ_0079593 and XBP1 levels were elevated, while miR-324-5p level was declined in glioma. Silencing of circ_0079593 restrained proliferation, mobility, angiogenesis and glycolysis and induced apoptosis in glioma cells. Circ_0079593 accelerated glioma progression via sequestering miR-324-5p, one of the targets of circ_0079593. XBP1 was a target gene of miR-324-5p, and miR-324-5p alleviated the malignant growth of glioma by repressing XBP1. Furthermore, silence of circ_0079593 hindered tumor growth in vivo. Circ_0079593 contributed to the malignant evolution of glioma via modulating miR-324-5p and downstream XBP1 gene, suggesting that circ_0079593 might be a promising therapeutic target for glioma. Circ_0079593 was boosted in glioma. Circ_0079593 depletion restrained glioma progression. Circ_0079593 triggered glioma development via miR-324-5p/XBP1 axis. Circ_0079593 silence suppressed glioma tumorigenesis in vivo.

CircRNA.0007127 triggers apoptosis through the miR-513a-5p/CASP8 axis in K-562 cells

BACKGROUND: Circular RNAs (circRNAs) are covalently closed single-stranded RNAs with multiple biological functions. CircRNA.0007127 is derived from the carbon catabolite repression 4-negative on TATA-less (CCR4-NOT) complex subunit 2 (CNOT2), which was found to regulate tumor cell apoptosis through caspase pathway. METHODS: Potential circRNA.0007127 target microRNAs (miRNAs) were analyzed by miRanda, TargetScan, and RNAhybrid software, and the miRNAs with binding sites for apoptosis-related genes were screened. The roles of circRNA.0007127 and its downstream target, microRNA (miR)‍-513a-5p, were validated by quantitative real-time polymerase chain reaction (qPCR), flow cytometry, mitochondrial membrane potential, immunofluorescence, western blot, and caspase-8 (CASP8) protein activity in vitro in H₂O₂-induced K-562 cells. The circRNA.‍0007127‍‒‍miR-513a-5p and CASP8‍‒‍miR-513a-5p interactions were verified by luciferase reporter assays. RESULTS: Silencing circRNA.0007127 decreased cell apoptosis by inhibiting CASP8 pathway activation in K-562 cells. Compared with the control group, the expression of CASP8 was reduced by 50% and the 43-kD fragment of CASP8 protein was significantly reduced (P≤0.05). The luciferase reporting assay showed that circRNA.0007127 combined with miR-513a-5p or CASP8, with extremely significant differences (P≤0.001). The overexpression of miR-513a-5p inhibited the gene expression level of CASP8 in a human myeloid leukemia cell model (75% change) and the level of a 43-kD fragment of CASP8 protein (P≤0.01). The rescue experiment showed that cotransfection with circRNA.0007127 small-interfering RNA (siRNA) and the miR-513a-5p inhibitor increased CASP8 gene expression and the apoptosis rate, suggesting that the miR-513a-5p inhibitor is a circRNA.0007127 siRNA antagonist. CONCLUSIONS: CircRNA.0007127 regulates K-562 cell apoptosis through the miR-513a-5p/CASP8 axis, which can serve as a novel powerful molecular target for K-562 cells.

Circular RNA VPS18 Promotes Glioblastoma Progression by Regulating miR-1229-3p/BCAT1 Axis

Circular RNAs (circRNAs) have been verified to play important roles in malignant tumors, including glioblastoma. The aim of this study is to explore the biological roles and underlying mechanisms of circRNA vacuolar protein sorting 18 homolog (circVPS18) in glioblastoma. A quantitative real-time polymerase chain reaction (qRT-PCR) was performed to measure the expression of circVPS18, microRNA (miR)-1299-3p, and branched-chain amino acid transaminase 1 (BCAT1). In vitro experiments were conducted using 5-ethynyl-2'-deoxyuridine (EdU), flow cytometry, transwell, and tube formation assays, respectively. Western blot was conducted to examine all protein levels. Dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay were employed to confirm the interaction between miR-1229-3p and circVPS18 or BCAT1. The murine xenograft model was established to conduct in vivo assay. CircVPS18 and BCAT1 were highly expressed while miR-1229-3p was lowly expressed in glioblastoma tissues and cells. CircVPS18 knockdown inhibited glioblastoma progression by inhibiting cell proliferation, migration, invasion, and angiogenesis, and promoting cell apoptosis. Moreover, miR-1229-3p could be targeted by circVPS18; inhibition of miR-1229-3p could invert the suppressive effect of circVPS18 knockdown on glioblastoma tumorigenesis. Furthermore, BCAT1 was a target of miR-1229-3p; functionally, BCAT1 overexpression could reverse the inhibitory effects of miR-1229-3p upregulation on glioblastoma cell malignant phenotypes. Moreover, we also verified that circVPS18A could regulate BCAT1 expression by sponging miR-1229-3p. Additionally, circVPS18 silencing also restrained tumor growth and metastasis in vivo. CircVPS18 accelerated glioblastoma progression by miR-1229-3p/BCAT1 axis, providing a potential therapeutic target for glioblastoma.

Molecular mechanism of m6A methylation of circDLC1 mediated by RNA methyltransferase METTL3 in the malignant proliferation of glioma cells

Glioma is an intracranial malignant tumor and remains largely incurable. Circular RNAs are prominent modulators in glioma progression. This study investigated the function of circular RNA DLC1 (circDLC1) in the malignant proliferation of glioma cells. circDLC1 expression in glioma tissues and cells was determined using RT-qPCR. The effect of circDLC1 on the malignant proliferation of glioma cells was analyzed using CCK-8, colony formation, and EdU staining assays. METTL3, miR-671-5p, and CTNNBIP1 expressions were determined. N⁶ methyladenosine (m⁶A) level of circDLC1 was analyzed using MeRIP. The binding relationship between miR-671-5p and circDLC1 or CTNNBIP1 was verified using RNA pull-down and dual-luciferase assays. A xenograft tumor model was established in nude mice to verify the effect of METTL3-mediated circDLC1 on glioma in vivo. circDLC1 was poorly expressed in glioma. circDLC1 overexpression suppressed glioma cell proliferation. Mechanically, METTL3-mediated m⁶A modification enhanced circDLC1 stability and upregulated circDLC1 expression in glioma. circDLC1 upregulated CTNNBIP1 transcription by competitively binding to miR-671-5p. METTL3 overexpression repressed the malignant proliferation of glioma via circDLC1/miR-671-5p/CTNNBIP1 in vivo. Collectively, METTL3-mediated m⁶A modification upregulated circDLC1 expression, and circDLC1 promoted CTNNBIP1 transcription by sponging miR-671-5p, thus repressing the malignant proliferation of glioma.

Circular RNA circ_UBAP2 facilitates the progression of osteosarcoma by regulating microRNA miR-637/high-mobility group box (HMGB) 2 axis

Circular RNA circ_UBAP2 has been reported to be closely associated with various tumors. The present work focused on exploring the roles of circ_UBAP2 and its molecular mechanism in osteosarcoma (OS). Circ_UBAP2, miR-637, and high-mobility group box (HMGB) 2 levels in OS cells and tissues were detected by quantitative real-time polymerase chain reaction. The relationship between miR-637 and circ_UBAP2, as well as between miR-637 and HMGB2, was predicted and examined through bioinformatics analysis and luciferase reporter gene experiments. Moreover, OS cell growth, invasion, migration, and apoptosis were detected using the cell counting kit-8 (CCK-8), Transwell and flow cytometry assays, respectively. HMGB2 protein levels were measured using Western blotting. Xenograft tumor formation assay was also performed. Circ_UBAP2 showed high expression levels in OS tissues and cells, which was directly proportional to metastasis and clinical stage of OS. The overexpression of circ_UBAP2 enhanced the growth, invasion, and migration of OS cells, but suppressed their apoptosis. In contrast, circ_UBAP2 silencing had opposite effects. Furthermore, miR-637 served as a downstream target of circ_UBAP2, which played opposite roles to circ_UBAP2 in OS. More importantly, HMGB2 served as miR-637's downstream target. The xenograft experiments in nude mice also proved that knockdown of circ_UBAP2 could increase miR-637 expression, but decrease HMGB2 expression, thus alleviating OS progression. Mechanistically, circ_UBAP2 exerts a cancer-promoting effect on OS by downregulating miR-637 and upregulating the expression of HMGB2. Circ_UBAP2 plays a promoting role in OS, and the circ_UBAP2/miR-637/HMGB2 axis is involved in OS progression.

Circular RNA hsa_circ_0000285 regulates the microRNA‐599/G‐protein subunit gamma 12 (miR‐599/GNG12) axis to promote glioma progression

Objective

Glioma is the most common, rapidly progressing, lethal brain tumor. However, underlying mechanisms behind its abnormal progression remain largely unknown. This study aimed to investigate mechanism of action and effects of the hsa_circ_0000285 on glioma progression.

Methods

RT‐qPCR was utilized to study RNA expression in glioma tissues and cell lines. The effects of hsa_circ_0000285 on glioma progression were studied by measuring cell proliferation and migration, apoptosis, tumor volume and weight in both glioma cells and xenograft glioma mice. The features of hsa_circ_0000285 were identified using chromatin fractionation and RNase digestion. Its mechanism of action was analyzed using bioinformatics, RNA‐binding protein immunoprecipitation, and luciferase reporter assay.

Results

We found glioma tissues and cell lines were overexpressing hsa_circ_0000285. While hsa_circ_0000285 promoted cell proliferation and migration, it inhibited apoptosis in vitro. It also increased tumor volume and weight in vivo. Using bioinformatic analysis and verification experiments for studying its mechanisms, we confirmed that hsa_circ_0000285 sponged miR‐599, which negatively regulated GNG12 by binding to its mRNA.

Conclusion

Hsa_circ_0000285 is overexpressed in the glioma and promotes its progression by directly regulating the miR‐599/GNG12 axis. This novel mechanism, therefore, shows that the hsa_circ_0000285/miR‐599/GNG12 axis may be a promising therapeutic target for glioma treatment.

circFLNA promotes glioblastoma proliferation and invasion by negatively regulating miR‑199‑3p expression

Glioblastoma (GBM) is one of the most common and malignant types of primary cancer in the central nervous system; however, the clinical outcomes of patients with GBM remain poor. Circular RNAs (circRNAs) have been revealed to serve important roles in diverse biological processes, such as regulating cell proliferation, epithelial-mesenchymal transition and tumor development. However, the underlying biological function of circRNA filamin A (circFLNA) and its potential role in GBM remain to be determined. The present study aimed to identify differentially expressed circRNAs in GBM. Reverse transcription-quantitative PCR was used to analyze the expression levels of circFLNA. The results demonstrated that the expression levels of circFLNA were significantly upregulated in clinical GBM samples and GBM cells compared with adjacent healthy brain tissues and normal human astrocytes, respectively. The results of the Cell Counting Kit-8 and Transwell assays revealed that circFLNA knockdown significantly inhibited the proliferative and invasive abilities of GBM cell lines. Moreover, high circFLNA expression levels were associated with a worse prognosis in GBM. MicroRNA (miR)-199-3p was subsequently predicted to be target of circFLNA. The inhibitory effect of miR-199-3p on cell proliferation and invasion was partially reversed following circFLNA knockdown. In conclusion, the findings of the present study identified novel roles for circFLNA in GBM and indicated that the circFLNA/miR-199-3p signaling axis may serve an important role in GBM progression. Therefore, circFLNA may represent a novel target for the diagnosis and treatment of GBM.

Serum Extracellular Vesicle-Derived circHIPK3 and circSMARCA5 Are Two Novel Diagnostic Biomarkers for Glioblastoma Multiforme

Glioblastoma multiforme (GBM) is the most frequent and deadly human brain cancer. Early diagnosis through non-invasive biomarkers may render GBM more easily treatable, improving the prognosis of this currently incurable disease. We suggest the use of serum extracellular vesicle (sEV)-derived circular RNAs (circRNAs) as highly stable minimally invasive diagnostic biomarkers for GBM diagnosis. EVs were isolated by size exclusion chromatography from sera of 23 GBM and 5 grade 3 glioma (GIII) patients, and 10 unaffected controls (UC). The expression of two candidate circRNAs (circSMARCA5 and circHIPK3) was assayed by droplet digital PCR. CircSMARCA5 and circHIPK3 were significantly less abundant in sEVs from GBM patients with respect to UC (fold-change (FC) of -2.15 and -1.92, respectively) and GIII (FC of -1.75 and -1.4, respectively). Receiver operating characteristic curve (ROC) analysis, based on the expression of sEV-derived circSMARCA5 and circHIPK3, allowed us to distinguish GBM from UC (area under the curve (AUC) 0.823 (0.667-0.979) and 0.855 (0.704 to 1.000), with a 95% confidence interval (CI), respectively). Multivariable ROC analysis, performed by combining the expression of sEV-derived circSMARCA5 and circHIPK3 with preoperative neutrophil to lymphocyte (NLR), platelet to lymphocyte (PLR) and lymphocyte to monocyte (LMR) ratios, three known diagnostic and prognostic GBM markers, allowed an improvement in the GBM diagnostic accuracy (AUC 0.901 (0.7912 to 1.000), 95% CI). Our data suggest sEV-derived circSMARCA5 and circHIPK3 as good diagnostic biomarkers for GBM, especially when associated with preoperative NLR, PLR and LMR.

circ_0030018 promotes glioma proliferation and metastasis

Background

Circular RNA (circRNA) plays an essential role in tumor progression, including glioma. circ_0030018 is a newly discovered circRNA that is highly expressed in glioma. However, its role and mechanism in glioma need to be further elucidated.

Methods

The expression of circ_0030018, microRNA (miR)-194-5p, and tripartite motif containing 44 (TRIM44) was examined using quantitative real-time PCR. Cell proliferation, migration, invasion, and apoptosis were determined using MTT assay, colony formation assay, transwell assay, and flow cytometry. Moreover, dual-luciferase reporter assay and RNA pull-down assay were used to verify the interactions among circ_0030018, miR-194-5p, and TRIM44. The protein expression of TRIM44 was assessed by western blot analysis. Animal experiments were conducted to explore the role of circ_0030018 in glioma tumor growth in vivo.

Results

circ_0030018 was overexpressed in glioma tissues and cells, and its silencing could inhibit glioma cell proliferation, migration, invasion, and accelerate apoptosis. miR-194-5p could be sponged by circ_0030018, and its overexpression could hinder the progression of glioma cells. Further experiments revealed that miR-194-5p inhibitor reversed the negative regulation of circ_0030018 knockdown on glioma cell progression. In addition, TRIM44 was a target of miR-194-5p, and its downregulation could repress glioma cell progression. Overexpressed TRIM44 reversed the inhibition effect of miR-194-5p on glioma cell progression. Animal experiments suggested that circ_0030018 knockdown could reduce glioma tumor growth through regulating miR-194-5p and TRIM44.

Conclusion

Our 8data showed that circ_0030018 enhanced glioma progression by sponging miR-194-5p to regulate TRIM44, indicating that circ_0030018 might be a potential treatment target for glioma.

Blocking hsa_circ_0006168 suppresses cell proliferation and motility of human glioblastoma cells by regulating hsa_circ_0006168/miR-628-5p/IGF1R ceRNA axis

BACKGROUND

hsa_circ_0006168 is an oncogenic circular RNA in esophageal cancer. However, its role remains unclarified in tumor progression of gliomas, especially in glioblastoma (GBM).

METHODS

Cell counting kit-8 assay, transwell assays, western blotting, and xenograft experiment, as well as colony formation assay and flow cytometry were performed to measure cell proliferation and motility. Expression of hsa_circ_0006168, microRNA (miR)-628-3p, insulin‑like growth factor 1 receptor (IGF1R), and Ras/extracellular signal regulated kinases (Erk)-related proteins were determined by quantitative real-time polymerase chain reaction and western blotting. The physical interaction was confirmed by dual-luciferase reporter assay and RNA pull-down assay.

RESULTS

hsa_circ_0006168 and IGF1R were upregulated, and miR-628-5p was downregulated in human GBM tissues and cells. Functionally, blocking hsa_circ_0006168 and overexpressing miR-628-5p suppressed cell proliferation, migration, invasion, and expression of Vimentin and Snail (mesenchymal markers) in A172 and LN229 cells, accompanied with increased E-cadherin (epithelial marker), decreased colony formation, and promoted apoptosis rate. Silencing miR-628-5p counteracted the suppression of hsa_circ_0006168 deficiency on these behaviors, and restoring IGF1R blocked miR-628-5p-mediated inhibition as well. More importantly, hsa_circ_0006168 knockdown could delay xenograft tumor growth in vivo and lower Ras and phosphorylated Erk1/2 expression in vitro and in vivo. Mechanically, hsa_circ_0006168 targeted and sponged miR-628-5p, and IFG1R was a novel target for miR-628-5p. Inhibiting miR-628-5p could abrogate in vitro role of hsa_circ_0006168 knockdown, and similarly IGF1R upregulation counteracted miR-628-5p role.

CONCLUSION

Silencing hsa_circ_0006168 might suppress GBM proliferation and motility via serving as competitive endogenous RNA for miR-628-5p and regulating IGF1R/Ras/Erk pathway.

Circular RNA circ_0001162 promotes cell proliferation and invasion of glioma via the miR-936/ERBB4 axis

The biological modulatory roles of many circular RNAs (circRNAs) have been validated in glioma. The current study was designed to research the functional mechanism of circ_0001162 in glioma progression. The quantitative real-time polymerase chain reaction (qRT-PCR) was used for assaying the levels of circ_0001162 and microRNA-936 (miR-936). Cell proliferation and colony formation abilities were evaluated via 3-(4, 5-dimethylthiazol-2-y1)-2, 5-diphenyl tetrazolium bromide (MTT) and colony formation assay, respectively. Transwell assay was applied to assess cell migration and invasion. The impact of circ_0001162 on glioma growth in vivo was performed using xenograft tumor assay. The target binding was affirmed via the dual-luciferase reporter and RNA pull-down assays. All protein expression levels were examined via Western blot. Circ_0001162 was an overexpressed circRNA in glioma. Circ_0001162 promoted glioma cell proliferation, colony formation, migration and invasion in vitro. Tumorigenesis of glioma in vivo was also enhanced by circ_0001162. Circ_0001162 could directly target miR-936 and the biological function of circ_0001162 in glioma was related to the inhibition of miR-936. ErbB2 receptor tyrosine kinase 4 (ERBB4) was a direct target of miR-936. Additionally, miR-936 inhibited the glioma development via targeting ERBB4. The miR-936/ERBB4 axis was responsible for the oncogenic role of circ_0001162 in glioma. The effects of circ_0001162 on glioma cells were also associated with the positive regulation of ERBB4. These results indicated that circ_0001162 contributed to the glioma progression via regulating the miR-936/ERBB4 axis, which laid a foundation for the pathomechanism and molecular treatment of glioma.

Downregulation of circ_0037655 impedes glioma formation and metastasis via the regulation of miR-1229-3p/ITGB8 axis

Background

Glioma is the most frequent, highly aggressive primary intracranial malignant tumor. Circular RNA (circRNA) circ_0037655 has been reported to be a vital regulator in glioma. The different functional mechanism behind circ_0037655 was investigated in the current study.

Methods

The expression of circ_0037655, microRNA-1229-3p (miR-1229-3p) and integrin beta-8 (ITGB8) was detected via the quantitative reverse transcription-polymerase chain reaction (qRT-PCR). Cellular research was performed via colony formation assay for cell proliferation, flow cytometry for cell cycle and cell apoptosis, scratch assay for cell migration, as well as transwell assay for cell migration and invasion. Western blot was used for detection of ITGB8 protein and epithelial–mesenchymal transition (EMT) process. Dual-luciferase reporter assay was implemented for the binding analysis of potential targets. In vivo assay was administered via xenograft in mice.

Results

Upregulation of circ_0037655 was affirmed in glioma samples and cells. Tumor formation and metastasis of glioma were inhibited after circ_0037655 was downregulated. miR-1229-3p acted as a target of circ_0037655, and its upregulation was responsible for the function of si-circ_0037655 in glioma cells. miR-1229-3p functioned as a tumor inhibitor in glioma progression by targeting ITGB8. circ_0037655 modulated the ITGB8 expression by targeting miR-1229-3p. In vivo knockdown of circ_0037655 also suppressed glioma tumorigenesis by acting on the miR-1229-3p/ITGB8 axis.

Conclusion

This study showed that downregulation of the expression of circ_0037655 could inhibit glioma progression by acting on the miR-1229-3p/ITGB8 axis. The specific circ_0037655/miR-1229-3p/ITGB8 axis was disclosed in glioma research.

Gain of circBRAF Represses Glioma Progression by Regulating miR-1290/FBXW7 Axis

Dysregulated circular RNAs (circRNAs) have been confirmed to partake in the modulation of the glioma progression. Here, we intended to explore the role of circBRAF in glioma and the possible action mechanism. The expression levels of circBRAF, microRNA (miR)-1290 and F-box and WD repeat domain containing 7 (FBXW7) were analyzed by quantitative reverse transcription polymerase chain reaction (qRT-PCR) or western blot. Cell viability was assessed by 3-(4, 5)-dimethylthiazole-2-y1)-2, 5-biphenyl tetrazolium bromide (MTT) assay. Cell cycle distribution was determined by flow cytometry. Cell migration and invasion were evaluated through Trans-well assay. Related protein levels were detected by western blot. Targeted relation among circBRAF, miR-1290 and FBXW7 was validated by dual-luciferase reporter, RNA immunoprecipitation (RIP) and pull-down assays. Xenograft model was constructed to explore the function of circBRAF in vivo. Expression of circBRAF and FBXW7 was decreased in glioma tissues and cells. Upregulation of circBRAF inhibited glioma cell proliferation and metastasis in vitro. MiR-1290 was upregulated in glioma, which was sponged by circBRAF. Besides, circBRAF elevated FBXW7 expression by targeting miR-1290. Introduction of miR-1290 or FBXW7 knockdown could counteract the inhibitory effects of circBRAF upregulation on the malignant phenotypes of glioma cells. Overexpression of circBRAF repressed the tumor growth in vivo. Upregulation of circBRAF suppressed glioma evolvement in vitro and in vivo by regulating miR-1290/FBXW7 axis, broadening the cognition of glioma progression.

MYC/NBS1-Mediated DNA Damage Response is Involved in the Inhibitory Effect of Hydroxysafflor Yellow A on Glioma Cells

Background

The role of Hydroxysafflor Yellow A (HSYA) in glioma is less studied, this research determined the effect of HSYA on glioma cells.

Methods

The expressions of MYC and NBS1 in glioma tissues were detected by bioinformatics analysis and verified by RT-qPCR. The target relationship between MYC and NBS1 was predicted by bioinformatics. After treating the cells with HSYA, silenced MYC, or overexpressed NBS1, the viability, apoptosis, proliferation, invasion, migration, and DNA damage of the glioma cells were detected by MTT, flow cytometry, colony formation, transwell, wound healing, and γH2AX immunofluorescence assays, respectively. IC₅₀ of HSYA in glioma cells was analyzed by Probit regression analysis. The expressions of MYC, NBS1, factors related to migration, invasion, apoptosis, and DNA damage of the glioma cells were determined by Western blot or RT-qPCR.

Results

MYC and NBS1 were high-expressed in glioma, and NBS1 was targeted by MYC. HSYA and siRNA targeting MYC inhibited the cell viability, proliferation, invasion, migration, and induced the cell apoptosis of glioma cells. HSYA upregulated the expressions of MYC, γH2AX, E-Cadherin, Bax, and Cleaved-PARP1, stimulated the activation of NBS1, MRE11, RAD50, and ATM, and downregulated the expressions of N-Cadherin and Bcl2 in glioma cells. SiMYC decreased the IC₅₀ of HSYA in the glioma cells, enhanced the sensitivity of glioma cells to HSYA, and inhibited the activation of NBS1 and ATM. NBS1 overexpression reversed the effect of siRNA targeting MYC on glioma cells.

Conclusion

MYC silencing inhibited the DNA damage response via regulation of NBS1, leading to DNA repair deficiency, and subsequently enhanced the sensitivity of glioma cells to HSYA.

Noncoding RNAs in Glioblastoma: Emerging Biological Concepts and Potential Therapeutic Implications

Simple Summary

Since the completion of the Human Genome Project, noncoding RNAs (ncRNAs) have emerged as an important class of genetic regulators. Several classes of ncRNAs, which include microRNAs (miRNAs), long noncoding RNAs (lncRNAs), circular RNAs (circRNAs), and piwi-interacting RNAs (piRNAs), have been shown to play important roles in controlling developmental and disease processes. In this article, we discuss the potential roles of ncRNAs in regulating glioblastoma (GBM) formation and progression as well as potential strategies to exploit the diagnostic and therapeutic potential of ncRNAs in GBM.

Abstract

Noncoding RNAs (ncRNAs) have emerged as a novel class of genomic regulators, ushering in a new era in molecular biology. With the advent of advanced genetic sequencing technology, several different classes of ncRNAs have been uncovered, including microRNAs (miRNAs), long noncoding RNAs (lncRNAs), circular RNAs (circRNAs), and piwi-interacting RNAs (piRNAs), which have been linked to many important developmental and disease processes and are being pursued as clinical and therapeutic targets. Molecular phenotyping studies of glioblastoma (GBM), the most common and lethal cancer of the adult brain, revealed that several ncRNAs are frequently dysregulated in its pathogenesis. Additionally, ncRNAs regulate many important aspects of glioma biology including tumour cell proliferation, migration, invasion, apoptosis, angiogenesis, and self-renewal. Here, we present an overview of the biogenesis of the different classes of ncRNAs, discuss their biological roles, as well as their relevance to gliomagenesis. We conclude by discussing potential approaches to therapeutically target the ncRNAs in clinic.

circ_0082375 promotes the progression of glioma by regulating Wnt7B

Circular RNAs contribute to the progression of glioma. However, the biological role and underlying mechanism of circ_0082375 in glioma remain unclear. Quantitative real-time PCR and Western blot assay were used to evaluate the expression levels of circ_0082375, microRNA-485-5p, and Wnt family member 7B (Wnt7B). The overall survival of glioma patients was estimated by the Kaplan-Meier curve. Cell proliferation, apoptosis, invasion, and migration were detected by cell counting kit-8, 5-ethynyl-2 -deoxyuridine (EdU) staining, flow cytometry, and transwell assays, respectively. Glucose level and lactate production were determined using glucose and lactate assay kits. In vitro angiogenesis assay was used to evaluate the angiogenesis of glioma cells. The interaction between microRNA (miR)-485-5p and circ_0082375 or Wnt family member 7B (Wnt7B) was verified by dual-luciferase reporter and RNA immunoprecipitation assays. A xenograft model was used to verify the function of circ_0082375 in vivo. circ_0082375 was upregulated in glioma tissues, and it was closely related to the prognosis of glioma patients. circ_0082375 knockdown suppressed cell proliferation, migration, invasion, angiogenesis, glycolysis, and epithelial-mesenchymal transition (EMT), and promoted cell apoptosis in glioma cells. irc_0082375 was a sponge of miR-485-5p, which directly targeted Wnt7B. Knockdown of circ_0082375 inhibited the malignancy, angiogenesis, and glycolysis of glioma cells in vitro by sponging miR-485-5p. Besides, circ_0082375 knockdown hampered the growth of glioma growth by regulating the miR-485-5p/Wnt7B axis in vivo. Altogether, circ_0082375 regulated miR-485-5p/Wnt7B axis to promote the malignancy, angiogenesis, and glycolysis of glioma cells, thereby contributing to the progression of glioma.

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.

Knockdown of circ0082374 inhibits cell viability, migration, invasion and glycolysis in glioma cells by miR-326/SIRT1

Circular RNAs (circRNAs) play important roles in the development and treatment of glioma. However, the role and mechanism of circRNA carboxypeptidase A4 (circ0082374) in glioma are largely unknown. Forty-two glioma patients and 28 normal patients were recruited. Glioma cell lines A172 and U251 were used for functional assays. The expression levels of circ0082374, microRNA-326 (miR-326) and sirtuin 1 (SIRT1) were examined via quantitative real-time polymerase chain reaction or western blot. Cell viability, migration, invasion and glycolysis were measured via cell counting kit-8, trans-well, oxygen consumption rate and western blot, respectively. The target correlation of circ0082374/miR-326 or miR-326/SIRT1 was explored via dual-luciferase reporter, RNA immunoprecipitation and pull-down assays. The role of circ0082374 in vivo was investigated via xenograft model. We found circ0082374 expression was elevated in glioma tissues and cells. Knockdown of circ0082374 suppressed the viability, migration, invasion and glycolysis in glioma cells. miR-326 was a target of circ0082374 and miR-326 knockdown attenuated the inhibitive role of circ0082374 silence in glioma progression. SIRT1 was a target of miR-326 and circ0082374 could promote SIRT1 expression by sponging miR-326. Silence of SIRT1 reversed the promoting effect of circ0082374 on glioma progression. Knockdown of circ0082374 reduced xenograft tumor growth by miR-326/SIRT1 in vivo. Collectively, silence of circ0082374 repressed the viability, migration, invasion and glycolysis in glioma cells by regulating miR-326 and SIRT1 in a ceRNA mechanism, providing a new mechanism for the pathogenesis of glioma.

Circular RNA CircHIPK3 Elevates CCND2 Expression and Promotes Cell Proliferation and Invasion Through miR-124 in Glioma

As a malignant tumor of the central nervous system, glioma exhibits high incidence and poor prognosis. Circular RNA HIPK3 (circHIPK3) is a circular RNA (circRNA) related to cancer progression. However, the role of circHIPK3 in gliomas remains unclear. The purpose of this study was to investigate the role of circHIPK3 in gliomas and its mechanism. The qRT-PCR method was used to determine the expression pattern of circHIPK3 in glioma cell lines. CCK-8 assay was used to detect cell proliferation. Cell migration and invasion were evaluated using the Transwell assay. Our results showed that circHIPK3 expression was significantly up-regulated in glioma tissues and cell lines. In vitro, the down-regulation of circHIPK3 significantly inhibited the proliferation, migration and invasion of glioma cells. Besides, we demonstrated that circHIPK3 acted as a sponge to absorb miR-124 and promoted CCND2 expression. In summary, our results indicated that circHIPK3 had carcinogenic effects by regulating the expression of CCND2 in glioma by sponging miR-124. These findings provided favorable evidence to reveal the role of circHIPK3 in the development of gliomas.

Up-regulation of circular RNA hsa_circ_01844 induces apoptosis and suppresses proliferation and migration of glioblastoma cells

BACKGROUND

Previous studies have demonstrated that various circular RNAs are involved in the malignant proliferation of cancers, such as liver cancer, lung cancer, breast cancer, and others. The potential role of circular RNAs in glioblastoma, however, is still uncertain. In this study, we aimed to study the potential role of hsa_circ_01844 in glioblastoma.

METHODS

Using reverse transcription-polymerase chain reaction (RT-PCR) method, hsa_circ_01844 expression was measured in five glioblastoma samples and five normal brain samples. To evaluate the potential function of hsa_circ_01844 in glioblastoma, hsa_circ_01844 was overexpressed in glioblastoma cell lines (U251 and U87 cells). Using these two cell lines, in vitro experiments including the flow cytometry assay, 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay, Transwell assay, and cell apoptosis assay were performed to investigate the role of hsa_circ_01844 in glioblastoma. Student t test and one-way analysis of variance were used for statistical analysis.

RESULTS

The expression of circular RNA hsa_circ_01844 was lower in glioblastoma tissues when compared with the normal brain tissues by RT-PCR method (0.034 ± 0.036 vs. 1.630 ± 0.891, P < 0.001). Using two glioblastoma cell lines, we found that overexpression of hsa_circ_01844 in glioblastoma cells suppressed their proliferation, colony formation, migration, and increased the apoptotic rate compared with empty vector group and blank control group (all P < 0.05).

CONCLUSION

Hsa_circ_01844 shows decreased expression in glioblastoma and its overexpression induces apoptosis and inhibits proliferation, migration, and invasion of glioblastoma cells.

Knockdown of circular RNA CEP128 suppresses proliferation and improves cytotoxic efficacy of temozolomide in glioma cells by regulating miR-145-5p

BACKGROUND

Circular RNAs serve as key players in the development of tumorigenesis and chemoresistance. Circular RNA CEP128 has been reported to be involved in the development of chemoresistance. However, the role of circular RNA CEP128 in the resistance of glioma cells to temozolomide has not yet been characterized.

METHODS

The expression of circular RNA CEP128, miR-145-5p, and ATP-binding cassette super-family G member 2 was evaluated using quantitative real-time PCR and western blot. The effects of circular RNA CEP128 on glioma cell proliferation and chemoresistance were evaluated by cell count kit-8 assay and colony formation assay. Luciferase reporter assay was performed for target validation.

RESULTS

Circular RNA CEP128 was upregulated in glioma tissues and cell lines. Moreover, circular RNA CEP128 expression was higher in temozolomide-resistant glioma cells compared with that in their parental cells. Knockdown of circular RNA CEP128 inhibited cell proliferation, reduced the expression of ATP-binding cassette super-family G member 2, as well as reduced resistance to temozolomide in glioma cells. Additionally, miR-145-5p was underexpressed in glioma cells as well as temozolomide-resistant glioma cells. Also, miR-145-5p was identified as a target of circular RNA CEP128. Overexpression of miR-145-5p inhibited the proliferation of U251/temozolomide cells and reduced the expression of ATP-binding cassette super-family G member 2, however, these changes induced by miR-145-5p overexpression were blocked by circular RNA CEP128 overexpression.

CONCLUSION

Knockdown of circular RNA CEP128 suppresses cell proliferation and improves the cytotoxic efficacy of temozolomide in glioma cells by regulating miR-145-5p, suggesting that circular RNA CEP128 might be a promising target for overcoming the resistance of glioma cells to temozolomide.

Down-regulation of circ-PTN suppresses cell proliferation, invasion and glycolysis in glioma by regulating miR-432-5p/RAB10 axis

BACKGROUND

Circular RNAs (circRNAs) are related to the carcinogenesis of cancers, including glioma. However, the role and mechanism of circRNA pleiotrophin (circ-PTN) remain largely unknown.

METHODS

Glioma tissues (n = 30) and normal tissues were obtained. Glioma cell lines LN229 and A172 were cultured for experiments in vitro. circ-PTN, microRNA-432-5p (miR-432-5p) and Ras-related protein Rab-10 (RAB10) levels were examined via quantitative reverse transcription polymerase chain reaction or western blot. Cell proliferation, invasion and glycolysis were examined via 3-(4, 5-Dimethyl-2-thiazolyl)-2, 5-diphenyl-2-H-tetrazolium bromide, colony formation analysis, transwell invasion analysis, specific glucose, lactate or adenosine triphosphate assay kit and western blot. The relationship of miR-432-5p and circ-PTN or RAB10 was analyzed via dual-luciferase reporter analysis. The effect of circ-PTN on glioma development in vivo was explored by a murine xenograft model.

RESULTS

circ-PTN expression was enhanced and miR-432-5p abundance was reduced in glioma tissues and cells. circ-PTN silence suppressed cell proliferation, invasion and glycolysis. circ-PTN regulated glioma development by directly sponging miR-432-5p. RAB10 was a target of miR-432-5p and miR-432-5p inhibited cell proliferation, invasion and glycolysis by targeting RAB10. circ-PTN could modulate RAB10 expression via miR-432-5p. circ-PTN knockdown reduced glioma cell xenograft tumor growth in vivo.

CONCLUSION

circ-PTN knockdown repressed cell proliferation, invasion and glycolysis in glioma via modulating miR-432-5p and RAB10.

Recent advances in understanding circular RNAs

Exonic circular RNAs (circRNAs) have been discovered in all kingdoms of life. In many cases, the details of circRNA function and their involvement in cellular processes and diseases are not yet fully understood. However, the past few years have seen significant developments in bioinformatics and in experimental protocols that advance the ongoing research in this still-emerging field. Sophisticated methods for circRNA generation in vitro and in vivo have been developed, allowing model studies into circRNA function and application. We here review the ongoing circRNA research, giving special attention to recent progress in the field.

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.

Exosomal noncoding RNAs in Glioma: biological functions and potential clinical applications

Gliomas are complex and heterogeneous brain tumors with poor prognosis. Glioma cells can communicate with their surroundings to create a tumor-permissive microenvironment. Exosomes represent a new means of intercellular communication by delivering various bioactive molecules, including proteins, lipids and nucleic acids, and participate in tumor initiation and progression. Noncoding RNAs (ncRNAs) including microRNA, long-noncoding RNA, and circular RNA, account for a large portion of human transcriptome and play important roles in various pathophysiological processes, especially in cancers. In addition, ncRNAs can be selectively packaged, secreted and transferred between cells in exosomes and modulate numerous hallmarks of glioma, such as proliferation, invasion, angiogenesis, immune-escape, and treatment resistance. Hence, the strategies of specifically targeting exosomal ncRNAs could be attractive therapeutic options. Exosomes are able to cross the blood brain barrier (BBB), and are readily accessible in nearly all types of human biofluids, which make them the promising biomarkers for gliomas. Additionally, given the biocompatibility of exosomes, they can be engineered to deliver therapeutic factors, such as RNA, proteins and drugs, to target cells for therapeutic applications. Here, we reviewed current research on the roles of exosomal ncRNAs in glioma progression. We also discussed their potential clinical applications as novel biomarkers and therapeutics.

Circ_101064 regulates the proliferation, invasion and migration of glioma cells through miR-154-5p/ PIWIL1 axis

This study aimed to investigate the effects of Circ_101064 on glioma cell proliferation, invasion, migration and explore the underlying mechanisms. The expression levels of Circ_101064 in glioma/para-carcinoma tissues and glioma cells were analyzed using RT-qPCR. Moreover, U251 and U87 cells were transfected with si-Circ_101064 or miR-154-5p mimics. Cell proliferation rate was determined by CCK-8 assay; the invasion and migration activities were examined using Transwell assay; the expression levels of PIWIL1 were evaluated by RT-qPCR and western blotting. The expression level of Circ_101064 was significantly upregulated in glioma tissues compared with control, and was closely associated with tumor grading and diameter. Furthermore, increased Circ_101064 expression was detected in human glioma cell lines. In addition, knockdown of Circ_101064 remarkably suppressed cell proliferation, invasion and migration in glioma cells in vitro. Moreover, microRNA-154-5p (miR-154-5p) could be a target of Circ_101064. Additionally, PIWIL1 is a putative downstream molecule of miR-154-5p, and its expression was downregulated by knockdown of Circ_101064. The effects on cell growth and metastasis caused by si-Circ_101064 were notably enhanced by miR-154-5p mimics. However, the influences of miR-154-5p-suppressed proliferation, migration and invasion of glioma cells could be abolished by overexpressed PIWIL1. In summary, our findings provided novel insight into the regulatory functions of Circ_101064 during tumor development in glioma. More importantly, Circ_101064/miR-154-5p/PIWIL1 axis could be a promising therapeutic target for the treatment of this disease.

CircNFIX promotes progression of glioma through regulating miR-378e/RPN2 axis

Background

Circular RNA nuclear factor I X (circNFIX) has been reported to play an important role in glioma progression. However, the mechanism by which circNFIX participates in glioma progression remains poorly understood.

Methods

GERIA online were used to analyze the abnormally expressed genes in glioma tissues. The expression levels of circNFIX, microRNA (miR)-378e and Ribophorin-II (RPN2) were measured by quantitative real-time polymerase chain reaction or western blot. Cell cycle distribution, apoptosis, glycolysis, migration and invasion were determined by flow cytometry, special kit and trans-well assays, respectively. The target association between miR-378e and circNFIX or RPN2 was confirmed by luciferase reporter assay, RNA immunoprecipitation and pull-down. Xenograft model was established to investigate the role of circNFIX in vivo.

Results

The expression of circNFIX was enhanced in glioma tissues and cells compared with matched controls and high expression of circNFIX indicated poor outcomes of patients. Knockdown of circNFIX led to arrest of cell cycle, inhibition of glycolysis, migration and invasion and promotion of apoptosis in glioma cells. circNFIX was a sponge of miR-378e. miR-378e overexpression suppressed cell cycle process, glycolysis, migration and invasion but promoted apoptosis. miR-378e silence abated the suppressive role of circNFIX knockdown in glioma progression. RPN2 as a target of miR-378e was positively regulated via circNFIX by competitively sponging miR-378e. Silencing circNFIX decreased glioma xenograft tumor growth by regulating miR-378e/RPN2 axis.

Conclusion

Knockdown of circNFIX inhibits progression of glioma in vitro and in vivo by increasing miR-378e and decreasing RPN2, providing a novel mechanism for understanding the pathogenesis of glioma.

Upregulated Expression of CUX1 Correlates with Poor Prognosis in Glioma Patients: a Bioinformatic Analysis

Cut-like homeobox-1 (CUX1) is expressed in the upper layer of the cortex and participates in DNA replication, cell cycle control, and DNA repair. It has been shown to be involved in the proliferation of various types of solid tumors. The aims of this study were to explore the relationship between CUX1 expression and the prognosis of glioma by performing a series of functional experiments and bioinformatic analyses. Firstly, we found that CUX1 expression levels differed among patients with different grades of gliomas, and they were significantly correlated with the prognosis of glioma patients according to an analysis of data from a public database. qRT-PCR, western blotting, and immunohistochemical analysis of CUX1 were performed to demonstrate that the expression of CUX1 was positively correlated with the glioma WHO grade (P < 0.05) and several malignant clinical pathological parameters, including Ki67 and P53mut. In addition, the multivariate Cox regression and Kaplan-Meier curves showed that CUX1 expression exerted predictive value for overall survival. Finally, to further investigate the functions of CUX1, we identified CUX1-associated genes and, though GO/KEGG analysis, their associated biological functions and signaling pathways; the results suggested that the activity of CUX1 might be exerted via the JAK-STAT pathway or other key regulators of the cell cycle to promote proliferation, inflammation, and chemotherapy resistance in glioma. Taken together, these results indicate that CUX1 is a potential biomarker of malignancy and prognosis and may serve as a potential therapeutic target for glioma patients.

Current status and potential role of circular RNAs in neurological disorders

Given the importance of non-coding RNAs in modulating normal brain functions and their implications in the treatment of neurological disorders, non-coding RNA-based diagnostic and therapeutic strategies have shown great clinical potential. Circular RNAs (circRNAs) have emerged as potentially important players in this field. Recent studies have indicated that circRNAs might play vital roles in Alzheimer's disease, Parkinson's disease, ischemic brain injury, and neurotoxicity. However, the mechanisms of action of circRNAs have not been fully characterized. We aimed to review recent advances in circRNA research in the brain to provide new insights on the roles of circRNAs in neurological disorders.

MicroRNA based theranostics for brain cancer: basic principles

BACKGROUND

Because of the complexity of the blood-brain barrier (BBB), brain tumors, especially the most common and aggressive primary malignant tumor type arising from the central nervous system (CNS), glioblastoma, remain an essential challenge regarding diagnostic and treatment. There are no approved circulating diagnostic or prognostic biomarkers, nor novel therapies like immune checkpoint inhibitors for glioblastoma, and chemotherapy brings only minimal survival benefits. The development of molecular biology led to the discovery of new potential diagnostic tools and therapeutic targets, offering the premise to detect patients at earlier stages and overcome the current poor prognosis.

MAIN BODY

One potential diagnostic and therapeutic breakthrough might come from microRNAs (miRNAs). It is well-known that miRNAs play a role in the initiation and development of various types of cancer, including glioblastoma. The review aims to answer the following questions concerning the role of RNA theranostics for brain tumors: (1) which miRNAs are the best candidates to become early diagnostic and prognostic circulating biomarkers?; (2) how to deliver the therapeutic agents in the CNS to overcome the BBB?; (3) which are the best methods to restore/inhibit miRNAs?

CONCLUSIONS

Because of the proven roles played by miRNAs in gliomagenesis and of their capacity to pass from the CNS tissue into the blood or cerebrospinal fluid (CSF), we propose miRNAs as ideal diagnostic and prognostic biomarkers. Moreover, recent advances in direct miRNA restoration (miRNA mimics) and miRNA inhibition therapy (antisense oligonucleotides, antagomirs, locked nucleic acid anti-miRNA, small molecule miRNA inhibitors) make miRNAs perfect candidates for entering clinical trials for glioblastoma treatment.