Up-regulated circular RNA VANGL1 contributes to progression of non-small cell lung cancer through inhibition of miR-195 and activation of Bcl-2

Role of circRNAs in regulating cell death in cancer: a comprehensive review

Despite multiple diagnostic and therapeutic advances, including surgery, radiation therapy, and chemotherapy, cancer preserved its spot as a global health concern. Prompt cancer diagnosis, treatment, and prognosis depend on the discovery of new biomarkers and therapeutic strategies. Circular RNAs (circRNAs) are considered as a stable, conserved, abundant, and varied group of RNA molecules that perform multiple roles such as gene regulation. There is evidence that circRNAs interact with RNA-binding proteins, especially capturing miRNAs. An extensive amount of research has presented the substantial contribution of circRNAs in various types of cancer. To fully understand the linkage between circRNAs and cancer growth as a consequence of various cell death processes, including autophagy, ferroptosis, and apoptosis, more research is necessary. The expression of circRNAs could be controlled to limit the occurrence and growth of cancer, providing a more encouraging method of cancer treatment. Consequently, it is critical to understand how circRNAs affect various forms of cancer cell death and evaluate whether circRNAs could be used as targets to induce tumor death and increase the efficacy of chemotherapy. The current study aims to review and comprehend the effects that circular RNAs exert on cell apoptosis, autophagy, and ferroptosis in cancer to investigate potential cancer treatment targets.

Advanced approaches of the use of circRNAs as a replacement for cancer therapy

Cancer is a broad name for a group of diseases in which abnormal cells grow out of control and are characterized by their complexity and recurrence. Although there has been progress in cancer therapy with the entry of precision medicine and immunotherapy, cancer incidence rates have increased globally. Non-coding RNAs in the form of circular RNAs (circRNAs) play crucial roles in the pathogenesis, clinical diagnosis, and therapy of different diseases, including cancer. According to recent studies, circRNAs appear to serve as accurate indicators and therapeutic targets for cancer treatment. However, circRNAs are promising candidates for cutting-edge cancer therapy because of their distinctive circular structure, stability, and wide range of capabilities; many challenges persist that decrease the applications of circRNA-based cancer therapeutics. Here, we explore the roles of circRNAs as a replacement for cancer therapy, highlight the main challenges facing circRNA-based cancer therapies, and discuss the key strategies to overcome these challenges to improve advanced innovative therapies based on circRNAs with long-term health effects.

The role of circular RNAs (circRNAs) as a prognostic factor in lung cancer: a meta-analysis

BACKGROUND

Lung cancer is a leading cause of cancer-related death worldwide. Among various histological types of lung cancer, majority are non-small cell lung cancer (NSCLC) which account for > 80%. Circular RNAs (circRNAs) are widely expressed in various cancers including lung cancer and implicated in tumourigenesis and cancer progression. This study aimed to systematically evaluate the prognostic values of circRNAs in lung cancer.

METHODS

A systematic literature search was done in PubMed, Embase, and MEDLINE databases to select the eligible studies which reported the association between the expression of circRNAs and overall survival (OS) or disease-free survival (DFS) in histopathologically diagnosed lung cancer patients. The pooled hazard ratio (HR) and 95% confidence interval (CI) were assessed to determine the prognostic significance of circRNAs.

RESULTS

A total of 43 studies were eligible for this meta-analysis (MA). 39 different types of circRNAs were reported: 28 showing upregulating and 11 showing downregulating action in lung cancer. High expression of circRNAs with upregulating action in lung cancer was associated with worse prognosis and poor OS (HR 1.93, 95% CI [1.61-2.33], p < 0.00001). High expression of circRNAs with downregulating action in lung cancer was associated with favorable OS and prognosis (HR 0.73, 95% CI [0.58-0.94], p = 0.01). However, there was no statistically significant association between high and low expression of both upregulating and downregulating circRNAs and DFS (HR 1.44, 95% CI [0.92-2.24], p = 0.11).

CONCLUSIONS

This MA confirmed the pivotal role of circRNAs as important prognostic biomarkers for lung cancer, especially NSCLC. High expression of upregulating circRNAs is associated with poor prognosis; however, high expression of downregulating circRNAs is associated with favorable prognosis. Therefore, downregulatory action of circRNAs should be considered a promising treatment in the management of lung cancer, especially NSCLC.

Highlighting functions of apoptosis and circular RNAs in colorectal cancer

Colorectal cancer (CRC) is known as one of the global problems that endangers the lives of thousands of people every year. Various treatments have been used to deal with this disease, but in some cases, they are not effective. Circular RNAs, as a novel class of noncoding RNAs, have different expression levels and various functions in cancer cells, such as gene regulation through microRNA sponging. They play an important role in various cellular processes, including differentiation, proliferation, invasion, and apoptosis. Changes in the process of apoptosis are closely related to the progression or inhibition of various malignancies. Induction of apoptosis in cancer cells is a promising target for tumor therapy. In this study, circRNAs were investigated as being central to the induction or inhibition of apoptosis in CRC. It is hoped that through targeted changes in the function of these biomolecules, better outcomes will be achieved in cancer treatment. Perhaps better outcomes for cancer treatment can be achieved by using new methods and modifying the expression of these nucleic acids. However, using this method may come with challenges and limitations.

Circular RNAs: implications of signaling pathways and bioinformatics in human cancer

Circular RNAs (circRNAs) form a class of endogenous single-stranded RNA transcripts that are widely expressed in eukaryotic cells. These RNAs mediate post-transcriptional control of gene expression and have multiple functions in biological processes, such as transcriptional regulation and splicing. They serve predominantly as microRNA sponges, RNA-binding proteins, and templates for translation. More importantly, circRNAs are involved in cancer progression, and may serve as promising biomarkers for tumor diagnosis and therapy. Although traditional experimental methods are usually time-consuming and laborious, substantial progress has been made in exploring potential circRNA-disease associations by using computational models, summarized signaling pathway data, and other databases. Here, we review the biological characteristics and functions of circRNAs, including their roles in cancer. Specifically, we focus on the signaling pathways associated with carcinogenesis, and the status of circRNA-associated bioinformatics databases. Finally, we explore the potential roles of circRNAs as prognostic biomarkers in cancer.

Exosomal circular RNA: a signature for lung cancer progression

Membrane vesicles having a diameter of 30-150 nm are known as exosomes. Several cancer types secrete exosomes, which may contain proteins, circular RNAs (circRNAs), microRNAs, or DNA. CircRNAs are endogenous RNAs that do not code for proteins and can create continuous and covalently closed loops. In cancer pathogenesis, especially metastasis, exosomal circRNAs (exo-circRNAs) have a crucial role mainly due to the frequently aberrant expression levels within tumors. However, neither the activities nor the regulatory mechanisms of exo-circRNAs in advancing lung cancer (LC) are obvious. A better understanding of the regulation and network connections of exo-circRNAs will lead to better treatment for LCs. The main objective of the current review is to highlight the functions and mechanisms of exo-circRNAs in LC and assess the relationships between exo-circRNA dysregulation and LC progression. In addition, underline the possible therapeutic targets based on exo-circRNA modulating.

hsa_circ_0000518 Facilitates Non-Small-Cell Lung Cancer Progression via Moderating miR-330-3p and Positively Regulating SLC1A5

Background/Aim

Non-small-cell lung cancer (NSCLC) is the principal agent of cancer deaths globally. The goal of this study was to determine how circular RNA_0000518 (circ_0000518) regulates tumor progression. Materials/Methods. circ_0000518 was selected as a study target involved in NSCLC from GEO (Gene Expression Omnibus) database. circ_0000518 level was gauged by qRT-PCR. It was confirmed as circRNA by actinomycin D inhibition and RNase R assay. Subcellular localization of circ_0000518 was identified by FISH. Cell function was determined by CCK-8, Transwell, and western blot. Glutamine metabolic factors were detected by ELISA. The target regulation relationship between genes was clarified by dual-luciferase reporter assay. In vivo models were established to evaluate the impact of circ_0000518 on tumor growth. Immunohistochemical staining for Ki67, vimentin, and E-cadherin was used to detect cell proliferation and metastasis, respectively.

Results

circ_0000518 expression was enhanced in NSCLC. si-circ_0000518 inhibited cell proliferation, invasion, and glutamine metabolism. circ_0000518 functioned as a molecular sponge for miR-330-3p, and inhibition of miR-330-3p in cells markedly reversed circ_0000518 interference-mediated antitumor effects. miR-330-3p interacted with 3′-UTR of SLC1A5. miR-330-3p inhibitor-mediated protumor effect was remarkably reversed in cells after the knockdown of SLC1A5. circ_0000518 knockdown reduced glutamine, glutamate, and α-KG by targeting miR-330-3p. Intertumoral injection of circ_0000518 shRNA adeno-associated virus effectively halted xenograft tumor growth.

Conclusion

The current study revealed that circ_0000518 may have a prooncogenic function in the formation and progression of NSCLC, which might be achieved through moderating the miR-330-3p/SLC1A5 axis.

Diagnostic and prognostic value of circRNAs expression in head and neck squamous cell carcinoma: A meta-analysis

Background

Circular RNAs (circRNAs) have been found to have potential biological applications against tumors in humans. This study aimed to evaluate the diagnostic, prognostic, and clinicopathological value of circRNAs in head and neck squamous cell carcinoma (HNSCC).

Methods

The PubMed, Web of Science, EMBASE, and the Cochrane Library were comprehensively searched for the relevant studies before October 20, 2021. Statistical analysis was performed based on STATA 15.0, Meta‐DiSc 1.4, and RevMan 5.3 software.

Results

A total of 55 reports regarding 56 kinds of circRNA were studied in this meta‐analysis, including 23, 38, and 26 articles on diagnosis, prognosis, and clinicopathological features, respectively. The pooled sensitivity, specificity, and area under the curve (AUC) of the summary receiver‐operating characteristic curve (SROC) were 0.78, 0.84, and 0.87, respectively. Besides, the upregulation of oncogenic circRNAs was significantly associated with poorer overall survival (OS) (HR=2.25, p < 0.05) and disease‐free interval (DFS) (HR=1.92, p < 0.05). In contrast, the elevated expression of tumor suppressor circRNAs was associated with a favorable prognosis (HR=0.50, p < 0.05). In addition, the high expression of oncogenic circRNAs was associated with the tumor size (OR=3.59, p < 0.05), degree of differentiation (OR=1.89, p < 0.05), TNM stage (OR=2.35, p < 0.05), lymph node metastasis (OR=1.85, p < 0.05), and distant metastasis (OR=3.42, p < 0.05). Moreover, the expression of tumor suppressor circRNAs was associated with improved clinicopathological features (lymph node metastasis: OR=0.25, p < 0.05).

Conclusions

CircRNAs could serve as potential predictive indicators and be useful for the diagnosis, prognosis, and identification of clinicopathological features in HNSCC.

A Novel Hypoxia-Related Gene Signature with Strong Predicting Ability in Non-Small-Cell Lung Cancer Identified by Comprehensive Profiling

Background

Non-small-cell lung cancer (NSCLC) is the most common malignant tumor among males and females worldwide. Hypoxia is a typical feature of the tumor microenvironment, and it affects cancer development. Circular RNAs (circRNAs) have been reported to sponge miRNAs to regulate target gene expression and play an essential role in tumorigenesis and progression. This study is aimed at identifying whether circRNAs could be used as the diagnostic biomarkers for NSCLC.

Methods

The heterogeneity of samples in this study was assessed by principal component analysis (PCA). Furthermore, the Gene Expression Omnibus (GEO) database was normalized by the affy R package. We further screened the differentially expressed genes (DEGs) and differentially expressed circular RNAs (DEcircRNAs) using the DEseq2 R package. Moreover, we analyzed the Gene Ontology (GO) annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment of DEGs using the cluster profile R package. Besides, the Gene Set Enrichment Analysis (GSEA) was used to identify the biological function of DEGs. The interaction between DEGs and the competing endogenous RNAs (ceRNA) network was detected using STRING and visualized using Cytoscape. Starbase predicted the miRNAs of target hub genes, and miRanda predicted the target miRNAs of circRNAs. The RNA-seq profiler and clinical information were downloaded from The Cancer Genome Atlas (TCGA) database. Then, the variables were assessed by the univariate and multivariate Cox proportional hazard regression models. Significant variables in the univariate Cox proportional hazard regression model were included in the multivariate Cox proportional hazard regression model to analyze the association between the variables of clinical features. Furthermore, the overall survival of variables was determined by the Kaplan-Meier survival curve, and the time-dependent receiver operating characteristic (ROC) curve analysis was used to calculate and validate the risk score in NSCLC patients. Moreover, predictive nomograms were constructed and used to predict the prognostic features between the high-risk and low-risk score groups.

Results

We screened a total of 2039 DEGs, including 1293 upregulated DEGs and 746 downregulated DEGs in hypoxia-treated A549 cells. A549 cells treated with hypoxia had a total of 70 DEcircRNAs, including 21 upregulated and 49 downregulated DEcircRNAs, compared to A549 cells treated with normoxia. The upregulated genes were significantly enriched in 284 GO terms and 42 KEGG pathways, while the downregulated genes were significantly enriched in 184 GO terms and 25 KEGG pathways. Moreover, the function analysis by GSEA showed enrichment in the enzyme-linked receptor protein signaling pathway, hypoxia-inducible factor- (HIF-) 1 signaling pathway, and G protein-coupled receptor (GPCR) downstream signaling. Furthermore, six hub modules and 10 hub genes, CDC45, EXO1, PLK1, RFC4, CCNB1, CDC6, MCM10, DLGAP5, AURKA, and POLE2, were identified. The ceRNA network was constructed, and it consisted of 4 circRNAs, 14 miRNAs, and 38 mRNAs. The ROC curve was constructed and calculated. The area under the curve (AUC) value was 0.62, and the optimal threshold was 0.28. Based on the optimal threshold, the patients were divided into the high-risk score and low-risk score groups. The survival rate in the high-risk score group was lower than that in the low-risk score group. The expression of SERPINE1, STC2, and LPCAT1; clinical stage; and age of the patient were significantly correlated with the high-risk score. Moreover, nomograms were established based on the risk factors in multivariate analysis, and the median survival time, 3-year survival probability, and 5-year survival were possibly predicted according to nomograms.

Conclusion

The ceRNA network associated with NSCLC was identified, and the hub genes, circRNAs, might act as the potential biomarkers for NSCLC.

CircRNA protein tyrosine phosphatase receptor type a suppresses proliferation and induces apoptosis of lung adenocarcinoma cells via regulation of microRNA-582-3p

Circular RNAs (circRNAs) are associated with cancer progression. The present study aimed to examine the function of circRNA protein tyrosine phosphatase receptor type A (circRNA_PTPRA) in lung cancer cells and elucidate the underlying molecular mechanisms. The levels of circRNA_PTPRA and microRNA (miRNA/miR)-582-3p were measured in lung cancer tissue and cells using reverse transcription-quantitative polymerase chain reaction (RT-qPCR). Cell proliferation and apoptosis were evaluated using an 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and flow cytometry, respectively. The expression of cyclin D1, caspase-3, and cleaved caspase-3 was assessed via western blotting. The sites of circRNA_PTPRA/miR-582-3p interaction were identified using StarBase, and validated using a dual-luciferase reporter assay. We observed that circRNA_PTPRA levels were remarkably decreased, and miR-582-3p expression was up-regulated in lung cancer tissues and cells. circRNA_PTPRA directly interacts with miR-582-3p and downregulates miR-582-3p expression in lung cancer cells. Moreover, an miR-582-3p inhibitor decreased lung cancer cell proliferation and promoted apoptosis. The overexpression of circRNA_PTPRA decreased cell proliferation and increased apoptotic cell numbers, whereas miR-582-3p overexpression reversed these effects. These findings demonstrate that the up-regulation of circRNA_PTPRA significantly reduces lung cancer cell proliferation and induces apoptosis by regulating miR-582-3p expression.

Circ_VANGL1 affects proliferation, migration, and invasion of colorectal cancer cells by regulating miR-493-5p/FXR1 axis

BACKGROUND

CircRNAs are abnormally expressed in colorectal cancer (CRC) tissues, cell lines, and plasma, and are closely related to the clinical malignant characteristics of CRC. However, the expression and functional mechanism of circ_VANGL1 in CRC are still unclear. We hypothesized that circ_VANGL1 affects the proliferation, migration, and invasion of CRC cells by regulating the miR-493-5p/fragile X-related gene 1 (FXR1) axis.

AIM

To investigate the effect of circ_VANGL1 on the prolife-ration, migration, and invasion of CRC cells and the possible mechanism involved.

METHODS

Western blot was used to detect the expression of FXR1 in CRC tissues and adjacent tissues. RT-qPCR was performed to detect the expression of circ_VANGL1 and miR-493-5p. CRC cells Caco-2 were cultured in vitro and divided into si-circ_VANGL1 group, si-NC group, miR-NC group, miR-493-5p mimic group, and si-circ_VANGL1 + miR-493-5p inhibitor group. CCK-8 and clone formation assays were performed to evaluate the proliferation ability of Caco-2 cells. Transwell assay was employed to evaluate the migration and invasion ability of Caco-2 cells. Dual luciferase reporter assay was used to detect the interaction between RNAs (circ_VANGL1 and miR-493-5p, miR-493-5p, and FXR1).

RESULTS

Compared with tumor adjacent tissues, the relative expression levels of circ_VANGL1 and FXR1 protein in CRC tissue were significantly increased (P < 0.05), but the relative level of miR-493-5p was significantly decreased (P < 0.05). Compared with the si-NC group, the inhibition rate of Caco-2 cells and the relative level of miR-493-5p in the si-circ_VANGL1 group were significantly increased (P < 0.05), but the expression of FXR1 protein, the number of colonies formed, and the migration and invasion ability were significantly reduced (P < 0.05). Compared with the miR-NC group, the inhibition rate of Caco-2 cells in the miR-493-5p mimic group was significantly increased (P < 0.05), but the expression of FXR1 protein, the number of colonies formed, and the migration and invasion ability were significantly reduced (P < 0.05). Circ_VANGL1 directly bound to miR-493-5p. Compared with the si-circ_VANGL1 group, the inhibition rate of Caco-2 cells in the si-circ_VANGL1 + miR-493-5p inhibitor group was significantly reduced (P < 0.05), but the expression of FXR1 protein, the number of colonies formed, and the migration and invasion ability were significantly increased (P < 0.05).

CONCLUSION

Silencing circ_VANGL1 inhibits the proliferation, migration, and invasion of CRC cells by regulating the miR-493-5p/FXR1 axis.

Circular RNA VANGL1 Facilitates Migration and Invasion of Papillary Thyroid Cancer by Modulating the miR-194/ZEB1/EMT Axis

Circular RNAs (circRNAs) are often aberrantly expressed in human tumors and also serve a critical regulatory role in papillary thyroid cancer (PTC). The aim of this study is to investigate the expression pattern and biological role of circVANGL1 in PTC. The results revealed that circVANGL1 was significantly upregulated in human PTC samples. In addition, high circVANGL1 expression was closely associated with adverse clinical parameters of PTC patients. Our in vitro experiments further indicated that the knockdown of circVANGL1 using siRNA obviously repressed migration, proliferation, EMT, and invasion of PTC cells, while opposite effects were induced by its overexpression. We further noted that circVANGL1 could interact with miR-194 directly in PTC, and serve as a ceRNA to regulate ZEB1 function. Moreover, miR-194 inhibition markedly abrogated the effects of circVANGL1 knockdown in PTC cells. Therefore, our results provide convincing evidence that circVANGL1 may exert oncogenic effects in PTC, partly via regulating the miR-194/ZEB1 axis.

Circ_0002623 promotes bladder cancer progression by regulating the miR-1276/SMAD2 axis

Circular RNAs (circRNAs) are key regulatory factors in the development of multiple cancers. This study is targeted at exploring the effect of circ_0002623 on bladder cancer (BCa) progression and its mechanism. Circ_0002623 was screened out by analyzing the expression profile of circRNAs in BCa tissues. Circ_0002623, miR-1276 and SMAD2 mRNA expression levels in clinical sample tissues and cell lines were detected through quantitative real-time polymerase chain reaction (qRT-PCR). After circ_0002623 was overexpressed or silenced in BCa cells, the cell proliferation, migration and cell cycle were evaluated by CCK-8, BrdU, Transwell assay and flow cytometry. Tumor xenograft model was used to validate the biological function of circ_0002623 in vivo. Bioinformatics analysis and dual-luciferase reporter gene assay were conducted for analyzing and confirming, respectively, the targeted relationship between circ_0002623 and miR-1276, as well as between miR-1276 and SMAD2. The regulatory effects of circ_0002623 and miR-1276 on the expression levels of TGF-β, WNT1 and SMAD2 in BCa cells were detected by Western blot. We reported that, in BCa tissues and cell lines, circ_0002623 was up-regulated, whereas miR-1276 was down-regulated. Circ_0002623 positively regulated BCa cell proliferation, migration and cell cycle progression. Additionally, circ_0002623 could competitively bind with miR-1276 to increase the expression of SMAD2, the target gene of miR-1276. Furthermore, circ_0002623 could regulate the expression of TGF-β and WNT1 via modulating miR-1276 and SMAD2. This study helps to better understand the molecular mechanism underlying BCa progression.

[Research Progress in CircRNA and Radiotherapy Resistance of Non-small Cell Lung Cancer]

As the main type of lung cancer, non-small cell lung cancer (NSCLC) is a common cancer which is characterized by low 5-year survival rate and worse prognosis. Nowadays, some studies show that the low survival rate and worse prognosis are due to the resistance to radiotherapy caused by circRNA. Therefore, to find out the relationship between circRNA and radiotherapy resistance of NSCLC was imoprtant. According to research the relevant literatures, the relationship between circRNA and radiotherapy resistance of NSCLC was explored. CircRNA plays an important role in the invasion, metastasis, proliferation and treatment resistance of NSCLC. The radiation resistance of tumor cells induced by circRNA has become a crucial problem in radiotherapy. CircRNA plays an important role in the radiotherapy resistance of NSCLC.
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Knockdown of circular RNA VANGL1 inhibits TGF-β-induced epithelial-mesenchymal transition in melanoma cells by sponging miR-150-5p

Melanoma is one of the most aggressive and life-threatening skin cancers, and in this research, we aimed to explore the functional role of circular RNA VANGL1 (circVANGL1) in melanoma progression. The expression levels of circVANGL1 were observed to be significantly increased in clinical melanoma tissues and cell lines. Moreover, circVANGL1 knockdown suppressed, while circVANGL1 overexpression promoted the proliferation, migration and invasion abilities of melanoma cells. Further investigations confirmed the direct binding relation between circVANGL1 and miR-150-5p in melanoma, and restoration of miR-150-5p blocked the effects of circVANGL1 overexpression in melanoma cells. We further found that circVANGL1 was up-regulated by TGF-β treatment, and the enhanced EMT of TGF-β-treated melanoma cells was blocked by circVANGL1 knockdown. In conclusion, these results indicated that circVANGL1 might serve as a promising therapeutic target for melanoma.

Circular RNA circSLC8A1 inhibits the proliferation and invasion of non-small cell lung cancer cells through targeting the miR-106b-5p /FOXJ3 axis

Circular RNA derived from the SLC8A1 gene (circSLC8A1) has been implicated in the pathogenesis of several types of cancers. However, the role of circSLC8A1 in non-small cell lung cancer (NSCLC) remains unclear. In the present study, the expression levels of circSLC8A1 in NSCLC tissues and cell lines were determined by qRT-PCR analysis. Function-gain-assays were then carried out to further validate the role of circSLC8A1 in NSCLC in vitro. Online prediction software and the subsequent luciferase reporter assay were used to identify the target genes of circSLC8A1 and microRNA (miR)-106b-5p. CircSLC8A1 was found to be downregulated in NSCLC tissues and cell lines. Overexpression of circSLC8A1 significantly inhibited the proliferation and invasion of NSCLC cells. Further investigations shown that circSLC8A1 was able to bind to miR-106b-5p as well as inhibit the expression of miR-106b-5p in NSCLC cells. MiR-106b-5p mimics reversed the inhibitory effects of circSLC8A1 overexpression on cell proliferation and invasion. Furthermore, we found that forkhead box J3 (FOXJ3) to be a target gene of miR-106b-5p in NSCLC cells. Knockdown of FOXJ3 reversed the inhibitory effects of miR-106b-5p inhibitor on cell proliferation and invasion. Collectively, these findings indicate that circSLC8A1 exhibits anti-tumor activity in NSCLC, which might be mediated by the miR-106b-5p/FOXJ3 axis. The circSLC8A1/miR-106b-5p/FOXJ3 axis may thus represent a promising therapeutic target for the management of NSCLC.

Biogenesis, Functions, and Role of CircRNAs in Lung Cancer

CircRNAs, a class of endogenous non-coding RNAs with closed-loop structures, have attracted increasing attention because of their good stability, high specificity of tissue expression, long half-life, and highly conserved sequence. CircRNAs have multiple biological functions, including miRNA sponge, transcription regulator, protein translation, interaction with protein, RNA maturation, and so on. These functions indicate the important role of circRNAs in tumorigenesis and malignant progression and their potential as potent diagnostic biomarkers and therapeutic molecules. In recent years, an increasing body of evidence suggests that circRNAs play a crucial role in proliferation, migration, invasion, and apoptosis of lung cancer cells. Therefore, circRNAs have gradually become a research focus in the diagnosis and treatment of lung cancer patients. This review summarizes the classification, biogenesis, and function of circRNAs, and discusses the role of circRNAs in the diagnosis, prognosis, and treatment of lung cancer patients.

Circular RNA VANGL1 knockdown suppressed viability, promoted apoptosis, and increased doxorubicin sensitivity through targeting miR-145-5p to regulate SOX4 in bladder cancer cells

Background

Bladder cancer is a common malignancy in the world. It is reported that circular RNA VANGL1 (circ_VANGL1) was involved in bladder cancer progression. However, the functional role and molecular mechanism of circ_VANGL1 in bladder cancer were still unclear.

Methods

The levels of circ_VANGL1, microRNA-145-5p (miR-145-5p), and Sex-determining region Y-related high-mobility group box 4 (SOX4) in bladder cancer tissues and cells were determined by quantitative real-time polymerase chain (RT-qPCR). The relative protein expression was detected by western blot. Cell counting kit-8 (CCK8) and flow cytometry analysis were used to measure cell viability, IC₅₀ value, and apoptosis rate. The interaction between miR-145-5p and circ_VANGL1 or SOX4 was predicted by online software starBase v2.0 or Targetscan and verified by the dual-luciferase reporter assay. Besides, xenograft mice model was used to detect the effects of circ_VANGL1 in vivo.

Results

The level of circ_VANGL1 and SOX4 was increased, while miR-145-5p was decreased in bladder cancer tissues and cells. Knockdown of circ_VANGL1 suppressed viability, while promoted apoptosis and increased doxorubicin sensitivity in bladder cancer cells. Moreover, circ_VANGL1 acted as a sponge for miR-145-5p. In addition, miR-145-5p partially reversed the effects of miR-145-5p knockdown in T24 and J82 cells. SOX4 was a target of miR-145-5p and negatively regulated by miR-145-5p. Furthermore, miR-145-5p regulated SOX4 to affect cell progression in bladder cancer cells, including viability, apoptosis, and doxorubicin sensitivity. Besides, circ_VANGL1 suppressed tumor growth and enhanced the doxorubicin sensitivity in bladder cancer in vivo.

Conclusion

circ_VANGL1 mediated cell viability, apoptosis, and doxorubicin sensitivity by regulating miR-145-5p/SOX4 axis in bladder cancer, providing a potential therapeutic target for bladder cancer therapy.

Circular RNAs in Lung Cancer: Recent Advances and Future Perspectives

Globally, lung cancer is the most commonly diagnosed cancer and carries with it the greatest mortality rate, with 5-year survival rates varying from 4–17% depending on stage and geographical differences. For decades, researchers have studied disease mechanisms, occurrence rates and disease development, however, the mechanisms underlying disease progression are not yet fully elucidated, thus an increased understanding of disease pathogenesis is key to developing new strategies towards specific disease diagnoses and targeted treatments. Circular RNAs (circRNAs) are a class of non-coding RNA widely expressed in eukaryotic cells, and participate in various biological processes implicated in human disease. Recent studies have indicated that circRNAs both positively and negatively regulate lung cancer cell proliferation, migration, invasion and apoptosis. Additionally, circRNAs could be promising biomarkers and targets for lung cancer therapies. This review systematically highlights recent advances in circRNA regulatory roles in lung cancer, and sheds light on their use as potential biomarkers and treatment targets for this disease.

Serum long non‑coding RNA NNT‑AS1 protected by exosome is a potential biomarker and functions as an oncogene via the miR‑496/RAP2C axis in colorectal cancer

Increasing evidence has indicated that long non-coding RNAs (lncRNAs) serve an essential role in carcinogenesis and cancer development. It has been reported that lncRNA nicotinamide nucleotide transhydrogenase antisense RNA 1 (NNT-AS1) serves a crucial role in several types of cancer. However, the clinical significance of circulating NNT-AS1 expression in colorectal cancer (CRC) remains to be elucidated. The current study aimed to investigate the potential role of NNT-AS1 and the clinical significance of its serum expression levels in patients with CRC. The expression of NNT-AS1 was measured in 40 pairs of tumor and adjacent normal tissues from patients with CRC via reverse transcription-quantitative PCR. The serum expression levels of NNT-AS1 were assayed in an independent cohort of healthy controls and patients with CRC. The levels of NNT-AS1 were also compared between paired preoperative and postoperative serum samples. In addition, the presence of exosomal NNT-AS1 in serum was explored. Furthermore, the biological roles of NNT-AS1 were investigated in CRC cells in vitro. The expression of NNT-AS1 was significantly upregulated in tumor tissues compared with adjacent normal tissues (P<0.05). A higher level of NNT-AS1 was associated with an advanced CRC stage. The serum levels of NNT-AS1 were significantly upregulated in patients with CRC compared with healthy subjects (P<0.05). Furthermore, the NNT-AS1 levels were significantly decreased in postoperative samples compared with preoperative samples (P<0.01). In addition, it was also identified that NNT-AS1 was upregulated in CRC exosomes (P<0.01), whereas no significant difference was observed in NNT-AS1 levels between serum and exosomes. Silencing of NNT-AS1 inhibited the proliferation, migration and invasion of CRC cells. It was also identified that NNT-AS1 exerted its effects via regulation of the microRNA-496/Ras-related protein Rap-2c axis. The present study demonstrated that circulating NNT-AS1, which may be protected by exosomes, could be a novel potential biomarker and therapeutic target in CRC.

Emerging role of circular RNAs in the pathobiology of lung cancer

Lung cancer is among the leading causes of cancer mortality and incidence in both sexes. Different classes of transcripts have been proposed as molecular markers in this type of cancer. Circular RNAs (circRNAs) are a group of transcripts with circular enclosed and stable configuration. These transcripts are stable in the blood, thus can be used as markers for detection of disorders. Moreover, dysregulation of circRNAs in the affected tissues of patients with different cancers shows their possible roles in the carcinogenesis. Several circRNAs including circPRKC1, circFGFR1, hsa-circ-0020123 and circTP63 have been found to be up-regulated in lung cancer samples. Meanwhile, cir-ITCH, hsa_circ_100395, hsa_circ_0033155, circRNF13, circNOL10, circ-UBR5, circPTK2 and circCRIM1 have been shown to be down-regulated in lung cancer tissues compared with noncancerous counterparts. Finally, prognostic values of circPRKC1, circFGFR1, has-circ-00120123, circTP63, circ_0067934, CDR1as, hsa_circRN_103809 and some other circRNAs have been appraised in lung cancer. In the current manuscript, we describe the impact and utility of circRNAs in the pathology of lung cancer.

Emerging roles of circular RNAs in non‑small cell lung cancer (Review)

Circular RNAs (circRNAs) are a class of novel endogenous transcripts with limited protein‑coding abilities. CircRNAs have been demonstrated to function as critical regulators of tumor development and distant metastasis through binding to microRNAs (miRNAs) and interacting with RNA‑binding proteins, thereby regulating transcription and translation. Emerging evidence has illustrated that certain circRNAs can serve as biomarkers for diagnosis and prognosis of cancer, and/or serve as potential therapeutic targets. Expression of functional circRNAs is commonly dysregulated in cancer and this is correlated with advanced Tumor‑Node‑Metastasis stage, lymph node status, distant metastasis, poor differentiation and shorter overall survival of cancer patients. Recently, an increasing number of studies have shown that circRNAs are closely associated with NSCLC. Functional experiments have revealed that circRNAs are intricately associated with the pathological progression of NSCLC. The present review provides an overview of the regulatory effect of circRNAs in the development and progression of NSCLC, taking into consideration various physiological and pathological processes, such as proliferation, apoptosis, invasion and migration, and their potential value as biomarkers and therapeutic targets.

Insights Into circRNAs: Functional Roles in Lung Cancer Management and the Potential Mechanisms

Lung cancer is the most prevalent cancer globally. It is also the leading cause of cancer-related death because of the late diagnosis and the frequent resistance to therapeutics. Therefore, it is impending to identify novel biomarkers and effective therapeutic targets to improve the clinical outcomes. Identified as a new class of RNAs, circular RNAs (circRNAs) derive from pre-mRNA back splicing with considerable stability and conservation. Accumulating research reveal that circRNAs can function as microRNA (miRNA) sponges, regulators of gene transcription and alternative splicing, as well as interact with RNA-binding proteins (RBPs), or even be translated into proteins directly. Currently, a large body of circRNAs have been demonstrated differentially expressed in physiological and pathological processes including cancer. In lung cancer, circRNAs play multiple roles in carcinogenesis, development, and response to different therapies, indicating their potential as diagnostic and prognostic biomarkers as well as novel therapeutics. In this review, we summarize the multi-faceted functions of circRNAs in lung cancer and the underlying mechanisms, together with the possible future of these discoveries in clinical application.

Circular RNAs in Human Cancer

Circular RNAs (circRNAs) are a class of endogenous single-stranded covalently closed RNAs, primarily produced from pre-mRNAs via non-canonical back-splicing. circRNAs are highly conserved, stable, and expressed in tissue- and development-specific pattern. circRNAs play essential roles in physiological process as well as cancer biology. By the advances of deep sequencing and bioinformatics, the number of circRNAs have increased explosively. circRNAs function as miRNA/protein sponge, protein scaffold, protein recruitment, enhancer of protein function, as well as templates for translation involved in the regulation of transcription/splicing, translation, protein degradation, and pri-miRNA processing in human cancers and contributed to the pathogenesis of cancer. Numerous circRNAs may function in diverse manners. In this review, we survey the current understanding of circRNA functions in human cancer including miRNA sponge, circRNA-protein interaction, and circRNA-encoded protein, and summarize available databases for circRNA annotation and functional prediction.

Competing endogenous RNAs in lung cancer

Competing endogenous RNAs (ceRNAs) containing microRNA response elements can competitively interact with microRNA via miRNA response elements, which can combine non-coding RNAs with protein-coding RNAs through complex ceRNA networks. CeRNAs include non-coding RNAs (long non-coding RNAs, circular RNAs, and transcribed pseudogenes) and protein-coding RNAs (mRNAs). Molecular interactions in ceRNA networks can coordinate many biological processes; however, they may also lead to ceRNA network imbalance and thus contribute to cancer occurrence when disturbed. Recent studies indicate that many dysregulated RNAs derived from lung cancer may function as ceRNAs to regulate multitudinous biological functions for lung cancer, including tumor cell proliferation, apoptosis, growth, invasion, migration, and metastasis. This study therefore reviewed the research progress in the field of non-coding and protein-coding RNAs as ceRNAs in lung cancer, and highlighted validated ceRNAs involved in biological lung cancer functions. Furthermore, the roles of ceRNAs as novel prognostic and diagnostic biomarkers were also discussed. Interpreting the involvement of ceRNAs networks in lung cancer will provide new insight into cancer pathogenesis and treatment strategies.

CircHIPK3/miR-381-3p axis modulates proliferation, migration, and glycolysis of lung cancer cells by regulating the AKT/mTOR signaling pathway

Lung cancer is a lethal malignancy. Plenty of circular RNAs (circRNAs) have been identified to be the vital regulators in lung cancer development. Here, we intended to clarify the functional role of circRNA HIPK3 (circHIPK3, also called hsa_circ_0021593) and its underlying mechanism of action. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) was employed to evaluate the levels of circHIPK3 and miR-381-3p. Cell viability and apoptosis rate were monitored by Cell Counting Kit-8 assay and flow cytometry, respectively. Cell migration was estimated through the Transwell assay. To assess glycolysis, commercial kits were utilized to measure the levels of glucose and lactate and the enzyme activity of hexokinase-2 (HK2). Expression of related proteins was detected via western blot analysis. The target connection between circHIPK3 and miR-381-3p was validated by dual-luciferase reporter, RIP, and pull-down assays. The role of circHIPK3 in vivo was determined via the xenograft assay. CircHIPK3 was upregulated, while miR-381-3p was downregulated in lung cancer tissues and cells. And circHIPK3 deficiency inhibited lung cancer progression by lowering cell proliferation, migration, glycolysis, and promoting apoptosis of lung cancer cells in vitro. MiR-381-3p was a target of circHIPK3, and miR-381-3p interference alleviated circHIPK3 knockdown-induced lung cancer progression inhibition. CircHIPK3 could activate the protein kinase B/mammalian target of rapamycin (AKT/mTOR) signaling pathway. Moreover, circHIPK3 knockdown suppressed tumor growth in vivo by inactivating the AKT/mTOR signaling pathway. In conclusion, the silencing of circHIPK3 inhibited lung cancer progression, at least in part, by sponging miR-381-3p and inactivating the AKT/mTOR signaling pathway.

Diagnostic and prognostic values of circular RNAs for lung cancer: a meta-analysis

Circular RNAs (circRNAs) may serve as potential biomarkers for patients with lung cancer. The aim of this meta-analysis was to analyse the diagnostic, prognostic and clinicopathological values of circRNAs in lung cancer patients. A systematic search of PubMed, Embase, Web of Science, Scopus and the Cochrane Library databases was performed for relevant articles from inception to 29 January 2020. Pooled parameters including sensitivity, specificity and area under the curve (AUC) were used to assess the diagnostic performance, HRs and 95% CIs were used to evaluate overall survival (OS) and ORs were used to estimate clinicopathological parameters. 52 studies from 45 articles were enrolled in this study, including 17 on diagnosis and 35 on prognosis. For diagnostic values, circRNAs could discriminate lung cancer patients from the controls, with AUC of 0.83 (95% CI: 0.79 to 0.86), a relatively high sensitivity of 0.77 (95% CI: 0.73 to 0.81) and specificity of 0.75 (95% CI: 0.71 to 0.79). For prognostic significances, overexpression of 23 upregulated circRNAs was relevant to a poor prognosis (OS: HR=2.21, 95% CI: 1.96 to 2.49, p<0.001), and overexpression of 9 downregulated circRNAs was correlated with a favourable prognosis (OS: HR=0.62, 95% CI: 0.53 to 0.73, p<0.001). As for clinicopathological parameters, high expression of 23 upregulated circRNAs was associated with unfavourable clinicopathological features while 9 downregulated circRNAs proved the contrary. In conclusion, this study confirmed that circRNAs might serve as important biomarkers for diagnostic and prognostic values of lung cancer.

CircLARP4 Suppresses Cell Proliferation, Invasion and Glycolysis and Promotes Apoptosis in Non-Small Cell Lung Cancer by Targeting miR-135b

Background

CircLARP4 is reported to act as a tumor suppressor in some cancers. However, the detailed roles and molecular basis of circLARP4 in non-small cell lung cancer (NSCLC) tumorigenesis are still unclear. The aim of the study is to explore the potential roles and molecular basis of circLARP4 in NSCLC tumorigenesis.

Materials and Methods

qRT-PCR was taken to detect circLARP4 and miR-135b expressions. MTT assay, transwell invasion assay and flow cytometry analysis were applied to evaluate cell proliferation, invasion and apoptosis, respectively. Glycolysis was assessed by measuring hexokinase2 (HK2) expression, glucose consumption and lactate production. Association between circLARP4 and miR-135a was examined by luciferase reporter and RIP assays. The changes of the phosphatase and tension homolog (PTEN)/protein kinase B (AKT)/hypoxia-inducible factor-1α (HIF-1α) pathway were evaluated by Western blot. The nude mouse xenograft models were applied to verify the regulation of circLARP4 in vivo.

Results

CircLARP4 was decreased in NSCLC tissues and cells. CircLARP4 overexpression blocked cell proliferation and invasion, and facilitated apoptosis in NSCLC cells. Meanwhile, circLARP4 overexpression suppressed glycolysis in NSCLC cells, as evidenced by the reduced HK2, glucose consumption and lactate production levels. Further analyses proved a downregulation of miR-135b by circLARP4 in a ceRNA-dependent manner in NSCLC cells. CircLARP4-mediated tumor suppression on NSCLC progression was partially overturned by overexpressing miR-135b. Moreover, we confirmed that circLARP4 had antitumor effect on xenograft tumors and downregulated miR-135b. Furthermore, circLARP4 overexpression inhibited the PTEN/AKT/HIF-1α pathway in NSCLC cells and xenograft tumors by downregulating miR-135b.

Conclusion

Our findings suggested that circLARP4 suppressed NSCLC progression by sponging miR-135b through inactivation of the PTEN/AKT/HIF-1α pathway, which broadens our understanding concerning the roles of circLARP4 in NSCLC tumorigenesis.

Biological Roles and Mechanisms of Circular RNA in Human Cancers

Circular RNA (circRNA) is an intriguing class of RNA with covalently closed-loop structure and is highly stable and conservative. As new members of the ncRNAs, the function, mechanism, potential diagnostic biomarker, and therapeutic target have raised increased attention. Most circRNAs are presented with characteristics of abundance, stability, conservatism, and often exhibiting tissue/developmental-stage-specific manner. Over 30,000 circRNAs have been identified with their unique structures to maintain stability more easily than linear RNAs. An increased numbers of circRNAs are dysregulated and involved in several biological processes of malignance, such as tumorigenesis, growth, invasion, metastasis, apoptosis, and vascularization. Emerging evidence suggests that circRNAs play important roles by acting as miRNA sponge or protein scaffolding, autophagy regulators, and interacting with RNA-binding protein (RBP), which may potentially serve as a novel promising biomarker for prevention, diagnosis and therapeutic target for treatment of human cancer with great significance either in scientific research or clinic arena. This review introduces concept, major features of circRNAs, and mainly describes the major biological functions and clinical relevance of circRNAs, as well as expressions and regulatory mechanisms in various types of human cancer, including pathogenesis, mode of action, potential target, signaling regulatory pathways, drug resistance, and therapeutic biomarkers. All of which provide evidence for the potential utilities of circRNAs in the diagnosis and treatment of cancer.