Comprehensive Circular RNA Profiling Reveals That hsa_circ_0005075, a New Circular RNA Biomarker, Is Involved in Hepatocellular Crcinoma Development

Microarray expression profile of circular RNAs and mRNAs in children with systemic lupus erythematosus

BACKGROUND

Recently, it was reported that circular RNAs (circRNAs) play the crucial role in many physiological and biological processes and can be used as biomarkers. However, the information about circRNAs in children with systemic lupus erythematosus (SLE) is limited. The aim of this study is to determine the expression of circRNAs in children with SLE and investigate the significance of circRNA for diagnosing SLE.

METHODS

Microarray profile of circRNAs and mRNAs was performed for identifying the changes in expression of circRNAs and mRNAs between children with SLE and healthy children. Quantitative polymerase chain reaction (qPCR) was used to confirm the results. Spearman correlation test was performed to assess the correlation between circRNAs and clinical variables. The receiver operating characteristic (ROC) curve was calculated for evaluating the diagnostic value.

RESULTS

A comparison between the children with SLE and healthy children revealed that 348 circRNAs and 1162 mRNAs were expressed differentially. The authors constructed a complex circRNA target network consisting of 307 matched circRNA-mRNA pairs for 124 differentially expressed circRNAs (74 circRNAs were upregulated, and 50 circRNAs were downregulated) and 142 differentially expressed mRNAs (83 mRNAs were upregulated, and 59 mRNAs were downregulated) by using gene co-expression network analysis. The competing for endogenous RNA (ceRNA) network includes 42 differentially expressed circRNAs, 41 differentially expressed mRNAs, and 71 predicted miRNAs. Among these SLE patients, we detected that the hsa_circ_0021372 and hsa_circ_0075699 levels are associated with C3 and C4 levels in children with SLE. The hsa_circ_0057762 level is positively associated with the SLEDAI-2K score. The ROC curves of circRNAs showed that the levels of hsa_circ_0057762 (AUC 0.804, 95% CI 0.607-1.0, P = 0.02) and hsa_circ_0003090 (AUC 0.848, 95% CI 0.688-1.0, P = 0.008) could differentiate the patients with SLE from the healthy controls.

CONCLUSIONS

We firstly characterized the expression profiles of circRNA and mRNA in children with SLE and propose herein their possible roles in the pathogenesis of SLE. These results provide novel insight into the mechanisms of SLE pathogenesis, and circRNAs may serve as useful biomarkers for SLE.

Circular RNA profiling identifies circADAMTS13 as a miR-484 sponge which suppresses cell proliferation in hepatocellular carcinoma

Circular RNA (circRNA) can participate in various biological processes, including tumorigenesis, through their microRNA response elements. Alterations in circRNA profiles during hepatocellular carcinoma (HCC) progression and their clinical significance remain unclear. Here, we present extensive analysis of circRNA profiles in tumor and matched peritumor tissues collected from 10 HCC patients, conducted to identify circRNA related to HCC progression. A total of 42 dysregulated circRNA (38 down‐regulated and 4 up‐regulated) were identified in HCC tumor tissues compared with matched peritumor tissues, revealing the heterogeneity of circRNA profiles in HCC. CircADAMTS13, derived from Exon 13–14 of the ADAMTS13 gene, was significantly downregulated in HCC tumor tissues. Furthermore, clinicopathological analysis revealed that up‐regulation of circADAMTS13 was negatively associated with tumor size but positively associated with prognosis. In addition, overexpression of circADAMTS13 could markedly inhibit HCC cell proliferation in vitro. Bioinformatic analysis and luciferase reporter assays further revealed that circADAMTS13 directly interacts with microRNA (miR)‐484. Rescue experiments showed that miR‐484 mimics can reverse the tumor‐suppressing roles of circADAMTS13 in HCC. Therefore, our results demonstrated that circADAMTS13 can serve as a tumor suppressor during HCC progression via the functional pathway of sponging miR‐484.

Epigenetic dysregulation in hepatocellular carcinoma: an up-to-date review

Due to the advances made in research based on next generation sequencers, it is now possible to detect and analyze epigenetic abnormalities associated with cancer. DNA methylation, various histone modifications, chromatin remodeling, and non-coding RNA-associated gene silencing are considered to be transcriptional regulatory mechanisms associated with gene expression changes. The breakdown of this precise regulatory system is involved in the transition to cancer. The important role of epigenetic regulation can be observed from the high rate of genetic mutations and abnormal gene expression leading to a breakdown in epigenetic gene expression regulation seen in hepatocellular carcinoma (HCC). Based on an understanding of epigenomic abnormalities associated with pathological conditions, these findings will lead the way to diagnosis and treatment. In particular, in addition to the fact that there are few choices in terms of extant drug therapies aimed at HCC, there are limits to their antitumor effects. The clinical application of epigenetic therapeutic agents for HCC has only just begun, and future developments are expected.

Circular RNA: a novel biomarker and therapeutic target for human cancers

Circular (circ)RNAs, a newly recognized class of noncoding RNA, have been implicated in the occurrence and development of several diseases, including neurological and cardiovascular diseases. Studies of human tumors, including those of liver cancer, gastric cancer, lung cancer and colorectal cancer, have shown differential expression profiles of circRNAs, suggesting regulatory roles in cancer pathogenesis and metastasis. In this review, we discuss the most recent research into tumor-related circRNAs, providing a comprehensive summary of the expression or/and function of these circRNAs and proposing rational perspectives on the potential clinical application of circRNAs as helpful biomarkers or therapeutic targets in human tumors.

A Role for Circular Non-Coding RNAs in the Pathogenesis of Sporadic Parathyroid Adenomas and the Impact of Gender-Specific Epigenetic Regulation

Epigenetic changes, including altered small non-coding RNAs, appear to be implicated in the pathogenesis of sporadic parathyroid adenomas (PAs). In this study, we investigated the circular RNAs (circRNAs) expression profile in sporadic PAs. Sixteen tissue samples of sporadic PAs, and four samples of normal parathyroid tissue (NPT) were investigated. Sample preparation and microarray hybridization were performed based on the Arraystar’s standard protocols, and circRNAs sequences were predicted by bioinformatics tools. We identified 35 circRNAs that were differentially expressed in sporadic PAs compared to NPT; 22 were upregulated, and 13 were downregulated, according to the pre-defined thresholds of fold-change > 2.0 and p< 0.05. In the subgroup analysis of PAs from male patients (n = 7) compared to PAs from female patients (n = 9), we also find a different expression profile. In particular, 19 circRNAs were significantly upregulated, and four circRNAs were significantly downregulated in male patients, compared to female counterparts. We show here for the first time a differential circRNA expression pattern in sporadic PAs compared to NPT, and a different expression profile in PA samples from male compared to female patients, suggesting an epigenetic role in the PA pathogenesis, and also an effect of gender in the epigenetic regulation of PAs.

hsa_circRNA_0006528 as a competing endogenous RNA promotes human breast cancer progression by sponging miR-7-5p and activating the MAPK/ERK signaling pathway

Emerging research has indicated that circular RNAs (circRNAs), a novel class of non-coding RNAs, play a vital role in human tumorigenesis and progression. Our previous results suggested that hsa_circ_0006528 (circ_0006528), a circRNA with an unknown function, mediates adriamycin resistance in human breast cancer cells. However, the role of circ_0006528 in breast cancer progression remains unknown. Here, we investigated the probable involvement of circ_0006528 in breast cancer. We analyzed a cohort of 97 patients and found that circ_0006528 expression was significantly upregulated in human breast cancer tissues compared with that in adjacent non-tumorous tissues and was significantly associated with advanced tumor-node-metastasis (TNM) stage and poor prognosis. In addition, we found that in breast cancer cells, circ_0006528 could promote DNA synthesis and cell proliferation, invasion, and migration. Downregulating circ_0006528 induced G2 phase arrest and cell apoptosis. Further mechanistic studies revealed that circ_0006528 could sponge endogenous miR-7-5p and inhibit its activity. We also identified Raf1, which activates the MAPK/ERK signaling pathway, as a target of miR-7-5p and determined that circ_0006528 promotes breast cancer growth, invasion, and migration by promoting the expression of Raf1 and activates the MAPK/ERK pathway. Thus, this study provides the first evidence of the circ_0006528/miR-7-5p/Raf1/MEK/ERK regulatory network in the development of breast cancer and suggests that circ_0006528 is a potential therapeutic target and prognostic predictor for breast cancer.

CircRNAs and cancer: Biomarkers and master regulators

Circular RNAs (circRNAs) are a novel class of regulatory RNAs that despite being relatively abundant have only recently begun to be explored. There are many thousands of genes that appear capable of producing circRNAs, however the function of all but a handful remain to be determined. What is emerging about these highly conserved molecules is that they play important roles in biology and cancer biology in particular. The most explored function of circRNAs is as master regulators of gene expression that act to sequester or ´sponge´ other gene expression regulators, in particular miRNAs. They have also been demonstrated to function via direct modulation of transcription, and by interfering with splicing mechanisms. Although generally expressed in low abundance when compared to their linear counterparts, they are often expressed in a tissue- and developmental stage- specific manner. Coupled with their remarkable resistance to RNAse activity due to a covalent closed cyclic structure, circRNAs show great promise as novel biomarkers of cancer and other diseases. In this review we consider the current state of knowledge regarding these molecules, their synthesis, function, and association with cancer. We will also review some of the challenges that remain to be resolved if this emerging class of RNAs are really to become useful in the clinic.

Cell Type-Selective Expression of Circular RNAs in Human Pancreatic Islets

Understanding distinct cell-type specific gene expression in human pancreatic islets is important for developing islet regeneration strategies and therapies to improve β-cell function in type 1 diabetes (T1D). While numerous transcriptome-wide studies on human islet cell-types have focused on protein-coding genes, the non-coding repertoire, such as long non-coding RNA, including circular RNAs, remains mostly unexplored. Here, we explored transcriptional landscape of human α-, β-, and exocrine cells from published total RNA sequencing (RNA-seq) datasets to identify circular RNAs (circRNAs). Our analysis revealed that circRNAs are highly abundant in both α- and β-cells. We identified 10,830 high-confidence circRNAs expressed in human α-, β-, and exocrine cells. The most highly expressed candidates were MAN1A2, RMST, and HIPK3 across the three cell-types. Alternate circular isoforms were observed for circRNAs in the three cell-types, indicative of potential distinct functions. Highly selective α- and β-cell circRNAs were identified, which is suggestive of their potential role in regulating β-cell function.

Circ5379-6, a circular form of tumor suppressor PPARα, participates in the inhibition of hepatocellular carcinoma tumorigenesis and metastasis

This study aimed to investigate the role of circRNAs encoded by PPARα in regulating the pathogenesis processes of hepatocellular carcinoma (HCC). Comprehensive analysis of 3 circular RNA databases revealed multiple circular RNAs within the PPARα gene. The candidate circRNAs were first structurally validated via specific convergent and divergent primer amplification, RNase R treatment, and Sanger sequencing. According to a further validation of the cell viability assay, cell cycle and apoptosis, and transwell assays, the circRNAs correlated to PPARα were obtained. Their functions in tumorigenesis were further validated via the subcutaneous tumor model and the migration model in nude mice. We showed that the overexpression of circ5379-6 decreased cell proliferation, inhibited cell migration and invasion, and induced cell apoptosis in the HCC cell lines. Consistently, in vivo studies in nude mice confirmed that the overexpression of circ5379-6 effectively inhibited the tumorigenesis and metastasis of HCC. We conclude that circ5379-6 plays a role similar to its linear counterpart PPARα to inhibit HCC tumorigenesis and progression.

Screening and bioinformatics analysis of circular RNA expression profiles in hepatitis B-related hepatocellular carcinoma

BACKGROUND

Circular RNAs (circRNAs) play an important role in pathogenesis and development of hepatocellular carcinoma (HCC). However, circRNA expression profiles in hepatitis B Virus (HBV)-related HCC remain to be studied.

METHODS

Total 13 HBV-related HCC patients were enrolled for study. Three HCC and 3 paired adjacent non-tumorous (NT) tissues from 3 patients were performed for microarray. Ten pairs of HCC tissues were used to verify the identified up-regulated and down-regulated circRNAs obtained from the microarray data by quantitative real-time reverse transcription PCR (qRT-PCR). Total RNA was isolated and treated with Rnase R to remove linear RNA, then hybridized to the array to screen for circRNAs. Bioinformatics analyses including clustering, differential expression, annotation of circRNA/microRNA (miRNA) interactions, Go analysis and KEGG pathway analysis, were performed.

RESULTS

Based on the microarray data, we found significantly up-regulation of 24 circRNAs and down-regulation of 23 circRNAs in the HCC samples compared to NT samples (fold change ⩾ 2.0 and P< 0.05). Of them, 6 candidate circRNAs (hsa_circRNA_102814, 100381, 103489, 101764, 100327, and 103361) were verified by qRT-PCR. Of them, hsa_circRNA 100381, 103489 up-regulation and 101764 down-regulation were found to be significantly different in the 10 validation HCC tissue. Clusters of circRNAs were aberrantly expressed in HCC compared with NT samples. CircRNA_101764 was the largest nodes in circRNA/microRNA co-expression network, especially co-expression with hsa-miR-181 family, which plays an important role in cell network. Annotation of circRNA/miRNA interactions indicated that the biological effects of circRNA may be achieved by binding of miRNAs. GO analysis revealed that numerous target genes were involved in the biological processes, cellular component and molecular function. There was nearly 30 target genes enrichment on KEGG pathways analysis, PI3K-Akt signaling pathway which the most number of genes involved.

CONCLUSION

In this study, we comprehensively explored the expression of differentially expressed circRNAs in HBV-related HCC, and our results indicate that circRNA_101764 may play an important role in the development of HCC.

Novel biomarkers in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the second leading cause of cancer-related deaths and the fifth most common cancer worldwide. Most of these patients are seen with advanced disease at the time of presentation. In spite of its high prevalence, there are not many therapeutic options available for patients with advanced-stage HCC. There is an urgent need for improving early detection and prognostication of patients with HCC. In addition, the development of new therapies targeting specific pathways involved in the pathogenesis of HCC should be a major goal for future research, with the objective of improving outcomes of patients with HCC. Biomarkers represent a relatively easy and noninvasive way to detect and estimate disease prognosis. In spite of the numerous efforts to find molecules as possible biomarkers, there is not a single ideal marker in HCC. Many new findings have shown promising results both in diagnosing and treating HCC. In this review, we summarized the most recent and relevant biomarkers in HCC.

The competing endogenous circular RNA ADAMTS14 suppressed hepatocellular carcinoma progression through regulating microRNA-572/regulator of calcineurin 1

Emerging evidence have discovered that circular RNAs (circRNAs) may serve as diagnostic or tumor promising biomarkers. This study aimed to investigate how circular RNA ADAMTS14 (circADAMTS14) regulates microRNA-572/ regulator of calcineurin 1(miR-572/ RCAN1) in hepatocellular carcinoma (HCC). The expression profiles of circRNA/microRNA (mRNA) between HCC tissues and paired adjacent tissues were analyzed via microarray analysis. The expressions of circADAMTS14, miR-572, and RCAN1 were measured by real-time polymerase chain reaction (PCR). The protein expression level of RCAN1 in HCC cells was detected by western blot. The viability and apoptosis levels of HCC cell lines were measured by the cell counting Kit-8 (CCK-8) assay and fluorescence-activated cell sorter. The invasiveness and migration of cells were detected based on the transwell and wound-healing assay, respectively. The dual-luciferase reporter assays were used to reveal circADAMTS14 and RCAN1 as a potential target of miR-572, which was predicted by TargetScan and miRBase. The effect of circADAMTS14 on HCC cells was demonstrated by tumor formation in nude mice in vivo. CircADAMTS14 and RCAN1 were lowly expressed in HCC clinical specimens and cell lines using microarrays and qRT-PCR, but miR-572 inversely. Our study further verified the direct interaction between circADAMTS14 and RCAN1 with miR-572 via the dual-luciferase reporter gene assay. Overexpressed circADAMTS14 and RCAN1 induced apoptosis of HCC cells and inhibited cell proliferation and invasion. But overexpressed miR-572 could decrease apoptosis of HCC cells and promote proliferation and invasion. In vivo, circADAMTS14 inhibited the tumor growth, correlated positively with the protein expression levels of RCAN1. Our results demonstrated that circADAMTS14 might suppress HCC progression through regulating miR-572/ RCAN1 as the competing endogenous RNA.

CircR2Disease: a manually curated database for experimentally supported circular RNAs associated with various diseases

CircR2Disease is a manually curated database, which provides a comprehensive resource for circRNA deregulation in various diseases. Increasing evidences have shown that circRNAs play critical roles in transcriptional, post-transcriptional and translational regulation. Therefore, the aberrant expression of circRNAs has been associated with a group of diseases. It is significant to develop a high-quality database to deposit the deregulated circRNAs in diseases. The current version of CircR2Disease contains 725 associations between 661 circRNAs and 100 diseases by reviewing existing literatures. Each entry in the CircR2Disease contains detailed information for the circRNA–disease relationship, including circRNA name, coordinates and gene symbol, disease name, expression patterns of circRNA, experimental techniques, a brief description of the circRNA–disease relationship, year of publication and the PubMed ID. CircR2Disease provides a user-friendly interface to browse, search and download as well as to submit novel disease-related circRNAs. CircR2Disease could be very beneficial for researches to investigate the mechanism of disease-related circRNAs and explore the appropriate algorithms for predicting novel associations.

Database URL: http://bioinfo.snnu.edu.cn/CircR2Disease/

Down-regulation of hsa_circ_0001649 in hepatocellular carcinoma predicts a poor prognosis

BACKGROUND

Circular RNAs (circRNA)are involved in the progression of cancers, and previous study showed that hsa_circ_0001649 expression is down-regulated in hepatocellular carcinoma (HCC).

OBJECTIVE

To explore whether hsa_circ_0001649 is a prognostic biomarker for HCC and to investigate the biological functions of hsa_circ_0001649 in HCC.

METHODS

Hsa_circ_0001649 expression was measured in 77 pairs of HCC and adjacent no-tumor tissues by quantitative Real-Time polymerase chain reaction. Kaplan-Meier curve and Cox regression were used to analyze its prognostic significance for HCC patients. In addition, the hsa_circ_0001649 was over-expressed using a circRNA-forming plasmid in HCC cells, and the biological function of hsa_circ_0001649 was investigated in vitro.

RESULTS

We verified that hsa_circ_0001649 was down-regulated in HCC tissues compared with adjacent non-tumor tissues. In addition, low hsa_circ_0001649 expression was associated with the poor overall survival of HCC patients, and Cox multivariate analysis showed that hsa_circ_0001649 is a novel independent prognostic factor for HCC patients. Furthermore, the in vitro experiments demonstrated that over-expressed hsa_circ_0001649 inhibits the proliferation, migration, and invasion and promotes the apoptosis of HCC cells.

CONCLUSIONS

Hsa_circ_0001649 could act as a novel prognostic biomarker for HCC patients. In addition, hsa_circ_ 0001649 might be a potential therapeutic target for HCC.

Circular RNAs: Crucial regulators in the human body (Review)

Circular RNAs (circRNAs) belong to a new type of endogenous non‑coding RNAs (ncRNAs) that are derived from exons and/or introns, and are widely distributed in mammals. The majority of circRNAs have a specific expression profile in cells or tissues, as well as during different stages of development. CircRNAs were originally thought to be the products of mis‑splicing. However, with the assistance of bioinformatics tools and the rapid development of high‑throughput sequencing, an increasing body of evidence has suggested that circRNAs bind micro(mi)RNAs, and have a role as miRNA sponges, thereby regulating target mRNA splicing and transcription. Human diseases are closely associated with circRNAs, especially in cancer as their expression is typically altered during the progression of cancer; this may provide a novel type of biomarker for cancer diagnosis and prognosis. CircRNAs are becoming a key area of interest within the field of cancer research. In the present review, we summarize the known molecular mechanisms and biological origin of circRNAs, as well as their functions, especially those related to human tumors.

Circular RNA profiling reveals circEXOC6B and circN4BP2L2 as novel prognostic biomarkers in epithelial ovarian cancer

Circular RNAs (circRNAs) are regarded as a novel class of widespread endogenous non-coding RNAs, which may play important roles in tumorigenesis by regulating gene expression. Nevertheless, the characterization of circRNAs in epithelial ovarian cancer (EOC) remains largely unknown. This study aimed to investigate circRNA expression profiles in EOC. A total of 54 EOC specimens and 54 normal ovarian tissues (controls) were collected. circRNA-sequencing based circRNA expression profiles were identified in 4 EOC specimens and compared with 4 normal ovarian tissues. circRNA-sequencing data were validated by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) in the 54 EOC specimens and 54 normal ovarian tissues. The association between differentially expressed circRNAs and various clinicopathological features of EOC was determined using a non-parametric test. Univariate analysis was performed using the log-rank test. A total of 4,388 circRNAs (2,556 up- and 1,832 downregulated; fold change of ≥2 and P<0.05) were identified to be differentially expressed in the EOC specimens compared with the normal ovarian tissues. Of these, the levels of 6 circRNAs (circBNC2, circEXOC6B, circFAM13B, circN4BP2L2, circRHOBTB3 and circCELSR1) were confirmed by RT-qPCR. Our data further indicated that these 6 circRNAs were associated with various clinicopathological features of EOC. More importantly, we found that circEXOC6B and circN4BP2L2 may act as novel prognostic biomarkers in patients with EOC. On the whole, the results of this study indicate that differentially expressed circRNAs may participate in the pathogenesis of EOC and may thus have potential for use as novel diagnostic and prognostic biomarkers for EOC. Future experiments with larger sample sizes are required to verify the current findings and illuminate the regulatory mechanisms of action of circRNAs in the tumorigenesis of EOC.

Differentially expressed circular RNAs in systemic lupus erythematosus and their clinical significance

It has been reported that circRNAs are diff ;erentially expressed in many diseases and can be used as new biomarker to facilitate disease diagnosis. Circular RNAs (circRNAs) microarray were used to identify dysregulated circRNAs in plasma of systemic lupus erythematosus (SLE) patients. Then, we confirmed the microarray data by quantitative reverse transcription polymerase chain reaction (qRT-PCR) in both plasma and peripheral blood mononuclear cells (PBMCs) of SLE. One hundred and twelve circRNAs were identified to dysregulated expressed in plasma of SLE as compared to healthy controls. The results of qRT-PCR showed that the levels of hsa_circRNA_407176 and hsa_circRNA_001308 were decreased in both plasma and PBMCs of SLE when compared with healthy controls. The receiver operating characteristic (ROC) curve area of hsa_circRNA_407176 and hsa_circRNA_001308 in plasma were 0.599 and 0.662, respectively. The area under the ROC curves of hsa_circRNA_407176, hsa_circRNA_406567 and hsa_circRNA_001308 in PBMCs were 0.806, 0.744, and 0.722, respectively. Our study illustrated that hsa_circRNA_407176 and hsa_circRNA_001308 in plasma and PBMCs could be potential biomarkers for SLE.

Circulating microRNAs associated with prolonged overall survival in lung cancer patients treated with nivolumab

BACKGROUND

The introduction of immune check-point inhibition in non-small cell lung cancer (NSCLC) therapy represents improved prospects for the patients. The response rates to check-point inhibitors are approximately 20% in unselected NSCLC patients. Increasing levels of tumor PD-L1 expression are associated with higher response rates. However, patients with low PD-L1 levels may also have durable responses, and improved strategies for patient stratification are needed.

MATERIAL AND METHODS

In this study, we investigated circulating microRNAs aiming to identify circulating predictive biomarkers associated with increased overall survival after immune check-point treatment. Using next generation sequencing, we performed microRNA profiling in serum from NSCLC patients (n = 20) treated with nivolumab. Serum samples from 31 patients were used for validation using qPCR assays. Serum samples were collected prior to immune therapy initiation.

RESULTS

Based on multivariate regression analysis, we identified a signature of seven microRNAs (miR-215-5p, miR-411-3p, miR-493-5p, miR-494-3p, miR-495-3p, miR-548j-5p and miR-93-3p) significantly associated with overall survival (OS) > 6 months in discovery cohort (p = .0003). We further validated this in another similar set of samples (n = 31) and the model was significantly associated with overall survival (OS) > 6 months (p = .001) with sensitivity and specificity of 71% and 90%, respectively.

CONCLUSIONS

In this study of circulating microRNAs, we have identified a 7-miR signature associated with survival in nivolumab-treated NSCLC patients. This signature may lead to better treatment options for patients with NSCLC, but a validation in an independent cohort is needed to confirm the predicted potential.

Tandem DNAzyme for double digestion: a new tool for circRNA suppression

Circular RNA (circRNA) play a crucial role in many biological processes and have been proved as potential biomarkers and therapeutic targets in many diseases. Manipulation of their expression is a critical task. In this study, we developed a new strategy for circRNA suppression with DNAzyme. Data showed single-digestion DNAzymes cleaved circRNA efficiently in vitro but not in cell culture. However, tandem DNAzymes for double digestion showed higher cleavage efficacy both in vitro and in cell culture. Functional study demonstrated that double-digestion DNAzymes suppressed the miRNA sponge function of circRNA and changed the proliferation and migration rates of HCC cells.

Circular RNA hsa_circ_0052112 promotes cell migration and invasion by acting as sponge for miR-125a-5p in breast cancer

OBJECTIVES

Accumulating evidence has been reported that circular RNAs (circRNAs) are a class of relatively stable, non-coding RNAs, which are involved in the progression of many types of diseases. However, the mechanism of hsa_circ_0052112 in breast cancer cells is not entirely clear. Hsa_circ_0052112, generated from the ZNF83 gene, is selected by analyzing circRNA expression profiles of breast cancer cell by using microarray assay. In this study, we will show the role of hsa_circ_0052112 in regulating cell invasion and migration in breast cancer.

METHODS

The expression level of hsa_circ_0052112 in MCF-7 and MDA-MB-231 cells was detected by RT-qPCR; we performed transwell assay to evaluate breast cancer cells' migration and invasion; predicated circRNA/miRNAs interaction using the miRanda and RNAhybrid software; identified the relationship between hsa_circ_0052112 and miR-125a-5p by luciferase activity assay and show the localization of hsa_circ_0052112 by FISH assay and show the significance of ZNF83 in clinical prognosis by Kaplan-Meier survival analysis.

RESULTS

Hsa_circ_0052112 expression was significantly higher in MDA-MB-231 cells than that in MCF-7 cells. Overexpression of hsa_circ_0052112 promoted cell migration and invasion in breast cancer. Inversely, down-regulation of hsa_circ_0052112 suppressed breast cancer cells migration and invasion. Hsa_circ_0052112 was mostly located in cytoplasm. Hsa_circ_0052112 could directly sponge to miR-125a-5p; overexpression of miR-125a-5p significantly inhibited breast cancer cells migration and invasion. However, high or low expression of miR-125a-5p was not correlated with relapse free survival (RFS) by TCGA database validation, but high expression of ZNF83 was closely correlated with poor RFS by Kaplan-Meier plotter.

CONCLUSIONS

These data suggest that hsa_circ_0052112 may be a potent biomarker for breast cancer, and may provide a new perspective on treatment of breast cancer.

A comprehensive review of circRNA: from purification and identification to disease marker potential

Circular RNA (circRNA) is an endogenous noncoding RNA with a covalently closed cyclic structure. Based on their components, circRNAs are divided into exonic circRNAs, intronic circRNAs, and exon-intron circRNAs. CircRNAs have well-conserved sequences and often have high stability due to their resistance to exonucleases. Depending on their sequence, circRNAs are involved in different biological functions, including microRNA sponge activity, modulation of alternative splicing or transcription, interaction with RNA-binding proteins, and rolling translation, and are a derivative of pseudogenes. CircRNAs are involved in the development of a variety of pathological conditions, such as cardiovascular diseases, diabetes, neurological diseases, and cancer. Emerging evidence has shown that circRNAs are likely to be new potential clinical diagnostic markers or treatments for many diseases. Here we describe circRNA research methods and biological functions, and discuss the potential relationship between circRNAs and disease progression.

Prospect of Circular RNA in Hepatocellular Carcinoma: A Novel Potential Biomarker and Therapeutic Target

CircRNA, a kind of tissue specific and covalently closed circular non-coding RNA is very abundant in eukaryocyte. Generally, circRNA is generated by back-splicing of protein-coding genes' pre-mRNA. Hepatocellular carcinoma (HCC) is one of the most common malignant tumors in the world. Due to the characteristics of poor prognosis and high recurrence, the pathogenesis of HCC is highly concerned by researchers worldwide. Recent studies demonstrated that numerous circRNAs were differentially expressed in HCC tissues and normal liver tissues, which is closely related with the development and prognosis of HCC. However, the mechanism of circRNA in HCC remains unclear. In this review, we summarized the abnormal expressions of circRNAs in HCC, discussed its role, and potential mechanisms, and tried to explore the prospective values of circRNA in the diagnosis, therapy, and prognosis of HCC.

Hsa_circ_0000520, a potential new circular RNA biomarker, is involved in gastric carcinoma

BACKGROUND

Circular RNAs (circRNAs) have been found playing important roles in regulating cancer progression. Human circRNA microarray was performed to screen for abnormally expressed circRNA in gastric cancer tissues. In this study, we are aimed to investigate the relationship between a new circular RNA named hsa_circ_0000520 and gastric cancer development.

METHODS

The hsa_circ_0000520 levels were detected by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) in gastric tissue, cell and plasma levels, respectively. Then, the association between the expression level of hsa_circ_0000520 and the clinicopathological features of patients with gastric cancer was further analyzed. Finally, a network of hsa_circ_0000520-miRNA-mRNA interactions was predicated.

RESULTS

In this study, hsa_circ_0000520 was first found to be significantly down-regulated in gastric cancer tissues, plasma and gastric cancer cell lines compared with control cases. Clinicopathological features showed that hsa_circ_0000520 level in GC tissues was negatively associated with TNM stage and in GC plasma linked with CEA expression. Finally, a total of 9 miRNAs and 9 candidate mRNA were predicted to have an interaction with hsa_circ_0000520.

CONCLUSIONS

We first identified that hsa_circ_0000520 was significantly down-regulated in gastric cancer. Our study indicated hsa_circ_0000520 might serve as a novel biomarker for gastric cancer and is involved in gastric carcinoma development.

MiR-145 affected the circular RNA expression in prostate cancer LNCaP cells

Recent evidence has demonstrated that circular RNAs (circRNAs) played crucial roles in fine‐tuning the levels of gene expression by sequestering the corresponding microRNA (miRNAs). Their interaction with disease‐associated miRNAs indicates that circRNAs are important for the development of disease, and miR‐145 has been previously shown to have antitumor effect in prostate cancer. In the current study, we successfully established the miR‐145‐overexpressed prostate cancer LNCaP cells (LNCaP‐miR‐145) using lentiviral vectors. LNCaP cells expressing the empty vector (LNCaP‐NC) were used as the negative control. The circRNA expression in LNCaP‐miR‐145 cells was detected by microarray analysis, and the miRNA targets of circRNAs were predicted using the bioinformatics software TargetScan and miRanda. Quantitative reverse transcription polymerase chain reaction was used to detect the expression levels of circRNAs in the prostate cancer tissue, nonmalignant tissue, LNCaP‐miR‐145 cells, and LNCaP‐NC cells. The interaction of miRNA and circRNA was further confirmed by the dual‐luciferase reporter assay. A total of 267 and 149 circRNAs were significantly up‐ and downregulated in LNCaP‐miR‐145 cells, respectively. hsa_circRNA_101981, hsa_circRNA_101996 and hsa_circRNA_09142 were the 3 circRNAs that interacted with hsa‐miR‐145‐5p; hsa_circRNA_008068 and hsa_circRNA_406557 were the 2 circRNAs that interacted with hsa‐miR‐145‐3p. Most of the circRNAs corresponded to the protein‐coding exons. The expression levels of hsa_circRNA_101981, hsa_circRNA_00806, and hsa_circRNA_406557 were upregulated in the LNCaP‐miR‐145 cells, but downregulated in the prostate cancer tissue. In contrast, the expression levels of hsa_circRNA_101996 and hsa_circRNA_091420 were downregulated in the LNCaP‐miR‐145 cells, but upregulated in the prostate cancer tissue. Moreover, miR‐145‐5P might regulate the expression of hsa_circRNA_101981, hsa_circRNA_101996, and hsa_circRNA_09142, while miR‐145‐3P might regulate the expression of hsa_circRNA_008068 and hsa_circRNA_406557. Overexpression of miR‐145 promoted the expression of hsa_circRNA_101981, hsa_circRNA_008068, and hsa_circRNA_406557 but suppressed the expressions of hsa_circRNA_101996 and hsa_circRNA_091420 in LNCaP cells. The results from the current study should give us a clue to clarify the tumor suppressive effect of miR‐145.

Circular RNA: new star, new hope in cancer

BACKGROUND

Circular RNAs are a new class of endogenous non-coding RNA that can function as crucial regulators of diverse cellular processes. The diverse types of circular RNAs with varying cytogenetics in cancer have also been reported. Circular RNAs can act as a microRNA sponge or through other mechanisms to regulate gene expression as either tumor inhibitors or accelerators, suggesting that circular RNAs can serve as newly developed biomarkers with clinic implications. Here, we summerized recent advances on circular RNAs in cancer and described a circular RNA network associated with tumorigenesis. The clinical implications of circular RNAs in cancer were also discussed in this paper.

SHORT CONCLUSION

Growing evidence has revealed the crucial regulatory roles of circular RNAs in cancer and the elucidation of functional mechanisms involving circular RNAs would be helpful to construct a circRNA-miRNA-mRNA regulatory network. Moreover, circular RNAs can be easily detected due to their relative stability, widespread expression, and abundance in exosomes, blood and saliva; thus, circular RNAs have potential as new and ideal clinical biomarkers in cancer.

Global microarray profiling identified hsa_circ_0064428 as a potential immune-associated prognosis biomarker for hepatocellular carcinoma

BACKGROUND

Increasing evidence has shown that circular RNAs (circRNAs) are involved tumourigenesis and metastasis of hepatocellular carcinoma (HCC); however, progression about its function in HCC is relatively slow. Here, we aimed to investigate whether plasma circRNAs could reflect the tumour-infiltrating lymphocytes (TILs) in HCC tumour tissues and serve as prognosis biomarker for HCC.

METHODS

Tissue samples of patients with HCC were subjected to immunohistochemistry staining against CD8 to examine the TILs. Then, we investigated the expression profile of circRNAs by microarray between plasma of patients with HCC with high TILs and low TILs, and the differentially expressed circRNAs were validated with qRT-PCR. Statistical analysis was performed with SPSS software and GraphPad Prism.

RESULTS

We have demonstrated that patients with HCC with high TILs exhibit a significant better overall survival, suggesting clinical outcome could be predicted by TILs. Global circRNA microarray between plasma of patients with HCC with high TILs and low TILs successfully identified six differentially expressed novel circRNAs. Among them, the expression of hsa_circ_0064428 was significantly reduced in patients with HCC with high TILs but increased in patients with low TILs. Moreover, hsa_circ_0064428 was negatively correlated with patient's survival, tumour size and metastasis.

CONCLUSION

These findings together imply that hsa_circ_0064428 could be considered as a potential HCC prognosis biomarker. Future in-depth research is required to further illustrate the involvement of hsa_circ_0064428 in HCC tumourigenesis and metastasis.

Profile and clinical implication of circular RNAs in human papillary thyroid carcinoma

Background

Differently expressed circular RNAs (circRNAs) have been reported to play a considerable role in tumor behavior; however, the expression profile and biological function of circRNAs in papillary thyroid carcinoma (PTC) remains unknown. Thus, the study was aimed to characterize the circRNA expression profile to comprehensively understand the biological behavior of PTC.

Methods

We investigated the expression profile of circRNAs using circRNA microarray in three pairs of PTC and adjacent normal tissues. Quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) was used to validate eight candidate circRNAs in 40 paired PTC tumors and adjacent normal samples. Next, we employed a bioinformatics tool to identify putative miRNA and circRNA-associated downstream genes, followed by constructing a network map of circRNA-miRNA-mRNA interactions and exploring the potential role of the candidate circRNAs.

Results

In total, 206 up- and 177 downregulated circRNAs were identified in PTC tissues (fold change >1.5; P < 0.05). The expression levels of eight candidate circRNAs confirmed by qRT-PCR were significantly different between the PTC and normal samples. The downstream genes of candidate circRNAs participated in various biological processes and signaling pathways. The most up and downregulated circRNAs were hsa_circRNA_007148 and hsa_circRNA_047771. The lower expression level of hsa_circRNA_047771 was associated BRAFV600 mutation, lymph node metastasis (LNM), as well as with advanced TNM stage (all P < 0.05). The higher expression level of hsa_circRNA_007148 was significantly correlated with LNM (P < 0.05). The areas under receiver operating curve were 0.876 (95% CI [0.78-0.94]) for hsa_circRNA_047771 and 0.846 (95% CI [0.75-0.96]) for hsa_circRNA_007148.

Discussion

The study suggests that dysregulated circRNAs play a critical role in PTC pathogenesis. PTC-related hsa_circRNA_047771 and hsa_circRNA_007148 may serve as potential diagnostic biomarkers and prognostic predictors for PTC patients.

Functional role of circular RNAs in cancer development and progression

Circular RNAs (circRNAs) are a large class of endogenously expressed non-coding RNAs formed by covalently closed loops through back-splicing. High throughput sequencing technologies have identified thousands of circRNAs with high sequence conservation and cell type specific expression in eukaryotes. CircRNAs play multiple important roles in cellular physiology functioning as miRNA sponges, transcriptional regulators, RBP binding molecules, templates for protein translation, and immune regulators. In a clinical context, circRNAs expression is correlated with patient's clinicopathological features in cancers including breast, liver, gastric, colorectal, and lung cancer. Additionally, distinct properties of circRNAs, such as high stability, exonuclease resistance, and existence in body fluids, show promising role for circRNAs as molecular biomarkers for tumor diagnosis, non-invasive monitoring, prognosis, and therapeutic intervention. Therefore, it is critical to further understand the molecular mechanism underlying circRNAs interaction in tumors and the recent progress of this RNA species in cancer development. In this review, we provide a detailed description of biological functions, molecular role of circRNAs in different cancers, and its potential role as biomarkers in a clinical context.

Circular RNAs: Characteristics, Function and Clinical Significance in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related deaths worldwide. HCC patients are commonly diagnosed at an advanced stage, for which highly effective therapies are limited. Moreover, the five-year survival rate of HCC patients remains poor due to high frequency of tumor metastasis and recurrence. These challenges give rise to the emergent need to discover promising biomarkers for HCC diagnosis and identify novel targets for HCC therapy. Circular RNAs (circRNAs), a class of long-overlook non-coding RNA, have been revealed as multi-functional RNAs in recent years. Growing evidence indicates that circRNA expression alterations have a broad impact in biological characteristics of HCC. Most of these circRNAs regulate HCC progression by acting as miRNA sponges, suggesting that circRNAs may function as promising diagnostic biomarkers and ideal therapeutic targets for HCC. In this review, we summarize the current progress in studying the functional role of circRNAs in HCC pathogenesis and present their potential values as diagnostic biomarkers and therapeutic targets. In-depth investigations on the function and mechanism of circRNAs in HCC will enrich our knowledge of HCC pathogenesis and contribute to the development of effective diagnostic biomarkers and therapeutic targets for HCC.

Systematic investigation of circular RNAs in Ascosphaera apis, a fungal pathogen of honeybee larvae

Ascosphaera apis is a widespread fungal pathogen of honeybee larvae, which causes heavy losses in apiculture. To date, knowledge about non-coding RNA (ncRNA) including circular RNA (circRNA) in A. apis is lacking. In this study, A. apis mycelia and spores were sequenced using RNA-seq technology. A total of 551 circRNAs were predicted on the basis of bioinformatic analyses, and most of the circRNAs were 200-600 bp in length, which were different from animal and plant circRNAs. In addition, the expression of six circRNAs in A. apis were confirmed using divergent and convergent PCR. Moreover, circRNA-microRNA regulation networks in A. apis were constructed, and further investigation showed that A. apis circRNAs could regulate gene expression by competitively binding miRNAs. GO and KEGG pathway enrichment analyses of the miRNAs target genes of circRNAs demonstrated that these A. apis circRNAs are likely to play key roles in metabolism, environmental response and gene expression.

Advances of circular RNAs in carcinoma

Circular RNAs (circRNAs) are a type of non-coding RNAs with single-stranded closed structure. The rapid development of high-throughput sequencing technology has allowed for the widespread presence of circRNAs in transcriptomes. Moreover, increasing studies have identified a correlation between circRNAs and different cancers. In addition, most circRNAs are dysregulated in various cancers, and some of them have been reported be vital in the occurrence and development of tumors. For example, ciRS-7 plays a role in tumor promotion and circ-ITCH acts as a tumor suppressor. This review summarizes the latest progressions in the field regarding the functions of circRNAs in relation with cancers, and anticipates the emerging roles of circRNAs and future challenges in cancer research.

CircRNA circFNDC3B promotes esophageal cancer progression via cell proliferation, apoptosis, and migration regulation

BACKGROUND

Esophageal cancer is one of the most common malignant tumors threatening human health worldwide. Circular RNAs (circRNAs) are a large group of covalently closed continuous loops that are prevalently expressed in human cells and might be applied as novel esophageal cancer biomarkers.

PURPOSE

To investigate the expression of a novel circular RNA, circFNDC3B, in esophageal cancer, as well as determine its function in the regulation of esophageal cell proliferation, apoptosis, migration, and invasion.

METHODS

Quantitative RT-PCR using circular RNA-specific primers was performed to analyze the existence and expressional change of circFNDC3B in esophageal cancer tissues. The esophageal cancer cell lines ECA109 and KYSE150 with inhibited circFNDC3B expression by gene silencing were subjected to proliferation analysis with the MTS method, FITC Annexin V apoptosis detection, and a proliferation and invasion evaluation using a transwell system.

RESULTS

circFNDC3B was specifically up-regulated in esophageal cancer tissues. Esophageal cancer cell lines ECA109 and KYSE150 with decreased circFNDC3B expression by gene silencing showed inhibited proliferation, increased apoptosis, and weakened migration and invasion abilities.

CONCLUSION

The circFNDC3B encoded by two FNDC3B gene exons is an important regulator of esophageal cancer progression.

Function and clinical significance of circRNAs in solid tumors

Circular RNA (circRNA) is a new type of endogenous non-coding RNAs (ncRNAs). circRNA regulates gene expression in many biological processes, and it also participates in the initiation and development of various diseases, including tumors, which are the focus of present research. With the development of high-throughput sequencing technique, an increasing number of circRNAs closely related to tumors have been discovered. According to numerous studies, there is a significant difference in the expressions of circRNAs among a variety of tumor tissues and para-carcinoma normal tissues. Some specifically expressed circRNAs may potentially serve as new biomarkers for tumor diagnosis and prognosis. This systemic review briefly introduces the characteristics, biogenesis, and functions of circRNAs, as well as discusses their relationship with cancer in detail. In addition, this article also describes several research strategies for circRNAs.

Circular RNA CEP128 acts as a sponge of miR-145-5p in promoting the bladder cancer progression via regulating SOX11

Background

This study aimed to investigate the effect of over-expressing circular RNA CEP128 (circCEP128) on cell functions and explore the molecular mechanism of which in bladder carcinoma.

Methods

The differentially expressed circRNAs and mRNAs in bladder carcinoma cells and cells in adjacent tissues were screened out using microarray analysis. Expression levels of circRNAs and mRNAs in tissues and cells were determined by qRT-PCR. Expression of SOX11 was detected by western blot. Luciferase reporter assay and RNA pull-down assay were used to investigate the interactions between the specific circRNA, miRNA and mRNA. Cell cycle and apoptosis were measured using flow cytometry after transfection. MTT assay was also performed to detect the cell proliferation.

Results

In present study, circCEP128 and SOX11 were observed significantly up-regulated in bladder cancer tissues, while the expression of miR-145-5p was decreased in cancer samples compared to normal samples. Cytoscape was used to visualize circCEP128-miRNA-target gene interactions based on the TargetScan and circular RNA interactome, which revealed that circCEP128 served as a sponge of miR-145-5p and indirectly regulated SOX11. Knockdown of circCEP128 induced the inhibition of cell proliferation and the increased bladder cancer cell apoptosis rate.

Conclusions

CircCEP128 functions as a ceRNA for miR-145-5p, which could up regulates SOX11 and further promotes cell proliferation and inhibits cell apoptosis of bladder cancer.

Circular RNA, a novel marker for cancer determination (Review)

Circular RNAs are abundant and conserved endogenous RNAs that are formed by exon skipping or back‑splicing events and occur in all forms of life. They have been proven to exhibit tissue‑ or cell‑type specificity and to be able to regulate cell behavior through multiple pathways. In cancer research, numerous studies have indicated that circular RNAs serve as potential biomarkers and therapeutic targets. Furthermore, differential expression of certain circular RNAs clearly predicts the clinical outcomes of cancer patients. Circular RNAs regulate carcinogenesis and cancer progression by acting as a microRNA sponge, coding for proteins and interacting with proteins. The present review mainly focuses on the recent literature regarding the role of circular RNAs in cancer, which may suggest novel strategies for cancer prognosis, diagnosis and clinical treatment.

Prospects of Noncoding RNAs in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a global health problem and one of the most common malignant tumors. Recent studies have shown that noncoding RNAs (ncRNAs) contribute to the pathogenesis of hepatocellular carcinoma (HCC). These RNAs may be involved in a variety of pathological processes such as cell proliferation, apoptosis, angiogenesis, invasion, and metastasis. In addition, abnormal expression of ncRNAs in HCC may provide potential prognostic or diagnostic biomarkers. This review provides an overview of the role and potential applications of ncRNAs, miRNAs, lncRNAs, circRNAs, and snoRNAs in liver cancer.

Circular RNA as a biomarker for cancer: A systematic meta-analysis

Circular RNAs (circRNAs) may serve as biomarkers for a potentially non-invasive diagnosis of cancer. To understand their diagnostic performance, a systematic meta-analysis of the published literature was conducted to review the diagnostic efficiency of circRNAs in patients with cancer. Eligible studies published up to November 30, 2017, on PubMed and EMBASE, were selected for the meta-analysis. All studies were carefully and independently reviewed by two researchers based on their titles and abstracts, following which full texts were perused for potential eligibility. All statistical analyses were performed by STATA 13.0 statistical software and Meta-DiSc 1.4. A total of 10 eligible studies were included. The pooled diagnostic odds ratio was 7.265. The pooled sensitivity was 0.708 and the pooled specificity was 0.722. The positive likelihood and negative likelihood ratios were 2.483 and 0.372, respectively. The area under the curve was 0.793. circRNA was determined to be a notably effective assistant diagnostic biomarker for cancer.

Overexpressed CDR1as functions as an oncogene to promote the tumor progression via miR-7 in non-small-cell lung cancer

Background

Circular RNA (circRNA) is a novel member of the noncoding RNA and function as efficient microRNA sponges with gene-regulatory potential, especially the circular RNA ciRS-7 (CDR1as)/tumor suppressor miRNA-7 (miR-7) signals. However, the function of CDR1as/miR-7 in non-small cell lung cancer (NSCLC) is unknown.

Methods

Normal lung tissues (n=20), adjacent non-tumor tissues (n=60), and NSCLC tissues (n=60) were collected to determine the expression and significance of CDR1as/miR-7. Lung cancer cell lines A549 and H460 were overexpressed or knocked down of CDR1as, miR-7 to determine the tumor growth etc. The CDR1as/miR-7-related pathway were analyzed.

Results

CDR1as levels was robustly increased with the development of NSCLC (P<0.001) and the NSCLC tissues harbored highest expression of CDR1as, which negatively correlated to the expression of miR-7. Patients with high expression of CDR1as had high TNM stage (P=0.004), more lymph nodes metastasis (LNM) (P=0.021) and shorted overall survival time (OS) (P=0.0135). The CDR1as level was an independent prognostic factor for the patients with NSCLC. Overexpression of CDR1as induced increased cell vitalities and growth, which could be abrogated by knockdown of CDR1as or overexpressed miR-7 to induce apoptosis and G1/S arrest. Mechanistically, CDR1as functioned as miR-7 sponges to up-regulate the key target genes of miR-7 including EGFR, CCNE1 and PIK3CD. The results in vivo further confirmed that CDR1as functioned as oncogene to inhibit the anti-tumor effects of tumor suppressor miR-7 by up-regulation of proliferation index Ki-67, EGFR, CCNE1 and PIK3CD levels.

Conclusion

Overexpressed CDR1as in NSCLC functions promotes the tumor progression via miR-7 signals.

The emerging role of circRNAs and their clinical significance in human cancers

Circular RNA (circRNA), a recently discovered subclass of non-coding RNAs (ncRNAs), forms a covalently closed loop with neither a 5' cap structure nor a 3' polyadenylated tail. Generated from precursor mRNA (pre-mRNA) through "backsplicing" (a type of alternative RNA splicing), the majority of circRNAs are located in the cytoplasm and are widespread among living organisms. They are stable and conserved and exhibit spatiotemporal-specific expression. CircRNAs are known to be involved in the development and progression of multiple diseases, including cancer, by acting as microRNA (miRNA) sponges and by regulating processes such as transcription and translation. The extensively aberrant expression profiles of circRNAs in multiple cancerous tissues make these molecules promising diagnostic biomarkers and therapeutic targets for cancer. Here, we briefly review the characteristics, biogenesis, classification, and functions of circRNAs, with a particular focus on the role of circRNAs in various cancers.

The progress of circular RNAs in various tumors

Circular RNAs (circRNAs), a novel type of non-coding RNAs, presented as covalently closed continuous loops. Recent researches had found that circRNAs could function as microRNA sponges, regulators of gene transcription and encoding proteins. They were relatively stable and expressed widely in cytoplasm, which played important roles in carcinogenesis of cancers, such as esophageal cancer, gastric cancer, colorectal cancer, hepatocarcinoma, bladder cancer, glioma, breast cancer, osteosarcoma and so on. Furthermore, they were involved in many biological functions, like cell proliferation, drug resistance, cell cycle, invasion and metastasis. Therefore, the further studies were meaningful on the mechanism of cancers and circRNAs. In the review, we will summarize the current biogenesis of circRNAs and the roles of them in various cancers, which might be a novel biomarker and therapeutic avenue.

Hsa_circ_0103809 promotes cell proliferation and inhibits apoptosis in hepatocellular carcinoma by targeting miR-490-5p/SOX2 signaling pathway

BACKGROUND

Circular RNAs (circRNAs) represent a class of non-coding RNAs that are emerging as important regulators during tumorigenesis and provide potential targets for cancer intervention. However, the expression profiles and functions of circRNAs in hepatocellular carcinoma (HCC) have not been completely clarified. Herein, the role of hsa_circ_0103809 was investigated in HCC tissues and cell lines.

METHODS

High-throughput circRNA sequencing was performed to detect the expression profiles of circRNA in HCC tissues. The CCK-8, wound healing and flow cytometry were performed to measure the cell viability, migration and apoptosis in HCC cells. The expression levels of gene and protein in HCC tissues and cell lines were assayed by RT-qPCR and western blotting, respectively. Immunohistochemical staining was used to assess the protein expression of SOX2 in HCC tissues.

RESULTS

We discovered that hsa_circ_0103809 was significantly increased in HCC tissues and cell lines. Knockdown of hsa_circ_0103809 inhibited proliferation and migration and induced apoptosis in HCC cell lines. Investigation to the molecular mechanisms of hsa_circ_0103809 in HCC cells had revealed that hsa_circ_0103809 directly suppressed miR-490-5p, which targeted to the 3'-UTR of SOX2. Hsa_circ_0103809 loss-of-function could increase the expression of miR-490-5p as well as decreased the expression of SOX2. Furthermore, we found that si-0103809 induced growth and migration inhibition and apoptosis could be reversed by transfected with miR-490-5p inhibitors or SOX2 in HCC cells.

CONCLUSION

Our findings suggested that hsa_circ_0103809 might facilitate HCC malignant progression, at least partially, by regulating miR-490-5p/SOX2 signaling pathway.

Circular RNAs in hepatocellular carcinoma: Functions and implications

At present, as hotspot members of the noncoding RNA network, circular RNAs (circRNAs) with distinct properties and diverse pathophysiological functions are being increasingly delineated. CircRNAs play roles at the epigenetic, transcriptional and posttranscriptional regulatory levels. Major studies have focused on their functions as efficient microRNA sponges. The validated number of endogenous circRNAs involved in hepatocellular carcinoma (HCC) continues to increase. Altered circRNA expression is associated with HCC occurrence, invasion, and metastasis. Moreover, the aberrant expression of circRNAs is also significantly related to HCC tumor stage, size, differentiation and metastasis. Because they are exceptionally stable, highly conserved and have tissue‐specific expression patterns, some circRNAs, including hsa_circ_0004018, hsa_circ_0003570, and hsa_circ_0005075, may be potential markers for the diagnosis of HCC. We herein summarize the current knowledge of HCC‐associated circRNAs and present their implications for carcinogenesis and their potential value as diagnostic and prognostic biomarkers. Finally, we discuss the future directions of studies on HCC‐associated circRNAs.

Circular RNA cSMARCA5 inhibits growth and metastasis in hepatocellular carcinoma

BACKGROUND & AIMS

In recent years, circular RNAs (circRNAs) have been shown to have critical regulatory roles in cancer biology. However, the contributions of circRNAs to hepatocellular carcinoma (HCC) remain largely unknown.

METHODS

cSMARCA5 (a circRNA derived from exons 15 and 16 of the SMARCA5 gene, hsa_circ_0001445) was identified by RNA-sequencing and validated by quantitative reverse transcription PCR. The role of cSMARCA5 in HCC progression was assessed both in vitro and in vivo. circRNAs in vivo precipitation, luciferase reporter assay, biotin-coupled microRNA capture and fluorescence in situ hybridization were conducted to evaluate the interaction between cSMARCA5 and miR-17-3p/miR-181b-5p.

RESULTS

The expression of cSMARCA5 was lower in HCC tissues, because of the regulation of DExH-Box Helicase 9, an abundant nuclear RNA helicase. The downregulation of cSMARCA5 in HCC was significantly correlated with aggressive characteristics and served as an independent risk factor for overall survival and recurrence-free survival in patients with HCC after hepatectomy. Our in vivo and in vitro data indicated that cSMARCA5 inhibits the proliferation and migration of HCC cells. Mechanistically, we found that cSMARCA5 could promote the expression of TIMP3, a well-known tumor suppressor, by sponging miR-17-3p and miR-181b-5p.

CONCLUSION

These results reveal an important role of cSMARCA5 in the growth and metastasis of HCC and provide a fresh perspective on circRNAs in HCC progression.

LAY SUMMARY

Herein, we studied the role of cSMARCA5, a circular RNA, in hepatocellular carcinoma. Our in vitro and in vivo data showed that cSMARCA5 inhibits the growth and migration of hepatocellular carcinoma cells, making it a potential therapeutic target.

Circular RNAs as novel biomarkers with regulatory potency in human diseases

Circular RNAs (circRNAs) are a large class of noncoding RNAs characterized with closed loop structures without 3′ and 5′ polar ends. They can roughly be divided into exonic circRNAs, exon–intron circRNAs and circular intronic RNAs. CircRNAs are characterized with stability, prevalence, specificity and conservation, which arouse great interest in circRNAs as disease biomarkers. Their abilities to sponge to miRNAs, cis-regulate parent genes, bind to proteins and encode proteins endow circRNAs a critical role of regulation in eukaryotic cells. This concise review focuses on circRNAs as functional biomarkers and therapeutic targets in both tumor and nontumorous diseases.

Although they were discovered in 1970s, circular RNAs (circRNAs) have attracted great interest only relatively recently. Instead of genome ‘junk matters’, circRNAs are now considered as promising biomarkers and treatment targets. CircRNAs are involved in numerous cancer-related and noncancer diseases, such as lung cancer, gastric cancer, cardiovascular diseases, diabetes mellitus and so on. This review outlines the classification, characterization and function of circRNAs, with a specific focus on recent studies concerning the role of circRNAs in human diseases.

Circular RNA 0068669 as a new biomarker for hepatocellular carcinoma metastasis

BACKGROUND

Circular RNAs (circRNAs) play important roles in disease occurrence. However, the roles of circRNAs in the diagnosis of hepatocellular carcinoma (HCC) are largely unknown. The aim of this study is to investigate the clinical diagnostic values of hsa_circ_0068669 (Alias: hsa_circ_103561), one of the representative HCC-associated circRNAs.

METHODS

Hsa_circ_0068669 expression levels in HCC tissues, HCC cell lines, and chronic hepatitis tissues were detected by real-time quantitative reverse transcription-polymerase chain reaction. Its expression levels between HCC tissues and adjacent non-tumorous tissues were analyzed using paired t test. Independent t test and one-way analysis of variance (ANOVA) were performed to analyze the relationships between hsa_circ_0068669 expression levels and clinicopathological factors of patients with HCC. A receiver operating characteristic (ROC) curve was established to estimate the value of hsa_circ_0068669 as a biomarker in HCC.

RESULTS

Hsa_circ_0068669 expression was significantly downregulated in HCC tissues and HCC cell lines compared with paired non-tumorous tissues and normal hepatic cell line, respectively. Moreover, hsa_circ_0068669 expression in HCC tissues was decreased comparing with chronic hepatitis tissues. Furthermore, hsa_circ_0068669 expression was correlated with microvascular invasion and TNM stages.

CONCLUSIONS

Our findings indicate that hsa_circ_0068669 might be served as a novel potential biomarker for HCC metastasis.

Circular RNAs are differentially expressed in liver ischemia/reperfusion injury model

Liver ischemia/reperfusion (I/R) injury has high mortality due to the intense inflammatory process occurs in the liver. However, the pathological mechanism underlying I/R injury is still not clear. Recent works showed that circular RNAs play critical roles in many human diseases. In this study, the occurrence of liver I/R injury was validated by an analysis of the blood samples and hematoxylin-eosin (HE) staining of liver tissues. Total RNA was purified and followed by RNA-seq in the purpose of screening the circRNAs in significant differentially expression, which were validated by quantitative PCR. GO and KEGG analysis were performed to determine the function of these differentially expressed circular RNAs. The circular structure of the circRNA was validated with gel electrophoresis and RNase R treatment. We found that some circular RNAs were differentially expressed in Liver I/R mouse models through bioinformatics analysis. These circular RNAs play roles in biological process, cellular component, and molecular function through GO analysis. Meanwhile, Hippo signaling pathway was found to be correlated with circular RNAs function in I/R models by KEGG analysis. To further validate bioinformatics data, two up-regulated and three down-regulated circular RNAs were confirmed in I/R models. The circularity of these differentially expressed circular RNAs was validated through gel electrophoresis and RNase R treatment. In summary, this work provides new insights into the mechanism underlying pathogenesis of liver I/R injury, providing new and potentially efficient targets against I/R injury.