Comprehensive circular RNA profiling reveals the regulatory role of the circRNA-100338/miR-141-3p pathway in hepatitis B-related hepatocellular carcinoma

circZFR promotes cell proliferation and migration by regulating miR-511/AKT1 axis in hepatocellular carcinoma

BACKGROUND

Emerging data suggest the crucial regulatory roles of circular RNAs (circRNAs) in hepatocellular carcinoma (HCC). However, the pathophysiology role of circZFR in HCC remains largely unknown.

AIMS

This study aims to disclose the functions of circZFR in HCC progression and its potential molecular mechanism.

METHODS

circZFR and miR-511 were identified by qRT-PCR. Colony formation assay, wound-healing assay, transwell assay, and flow cytometry assay were performed to determine the cell proliferation, migration, invasion and apoptosis. Western blotting and immunohistochemistry (IHC) were utilized to evaluate the expression level of AKT1, GSK3β, β-catenin and cascades of proliferation-related proteins both in vitro and in vivo. Dual luciferase reporter assay was conducted to evaluate the interactions among circZFR, miR-511 and AKT1.

RESULTS

The expression of circZFR was enhanced and the expression of miR-511 was down-regulated in HCC tissues and cells. Functionally, circZFR silencing or miR-511 overexpression suppressed cell proliferation, migration and invasion, and induced apoptosis of HCC cells. Mechanistically, circZFR acted as a miR-511 sponge to up-regulate its target gene AKT1, which activated cascades of proliferation-related proteins (c-Myc, cyclin D1, Survivin and Bcl-2). Furthermore, depletion of circZFR inhibited tumorigenesis and decreased the expression level of AKT1 in xenograft models.

CONCLUSION

circZFR promotes HCC progression by directly down-regulating miR-511 to activate AKT1 signaling, suggesting that circZFR is a potential target in HCC treatment. Targeting circZFR may provide therapeutic benefits for HCC.

The biogenesis and biological functions of circular RNAs and their molecular diagnostic values in cancers

BACKGROUND

In addition to non-coding RNAs (lncRNAs) and microRNAs (miRNAs), circular RNAs (circRNAs) are endogenous RNAs with various functions, which have recently become a research hotspot. CircRNAs are a kind of closed circular RNA molecule widely existing in transcriptomes. Due to lack of free ends, they are not easily cleaved by RNase R, thus avoiding degradation. They are more stable than linear RNAs.

METHODS

Data were collected through PubMed. The following search terms were used: "circular RNA," "circRNA," "cancer," "mechanism," "biogenesis," "biomarker," "diagnosis." Only articles published in English were included.

RESULTS

Most circRNAs express tissue/developmental stage specificity. Moreover, circRNAs are involved in the regulation of a variety of biological activities. In this review, we discuss the formation, classification, and biological functions of circRNAs, especially their molecular diagnostic values in common cancers, including gastric cancer (hsa_circ_002059, circ_LARP4, hsa_circ_0000190, hsa_circ_0000096, circ-SFMBT2, and circ_PVT1), hepatocellular carcinoma (circ_104075, circRNA_100338, circ_MTO1, and circZKSCAN1), colorectal cancer (hsa_circ_0136666 and hsa_circ_0000523), lung cancer (hsa_circ_0006427, circ_100876, and circ_ABCB10), breast cancer (hsa_circ_0089105, circAGFG1, and circEPSTI1), bladder cancer (circFNDC3B and circTFRC), and esophageal squamous cell carcinoma (circ_100876 and circ-DLG1).

CONCLUSION

CircRNAs not only play important roles in tumorigenesis, but also may become new diagnostic biomarkers.

Circ_0015756 promotes proliferation, invasion and migration by microRNA-7-dependent inhibition of FAK in hepatocellular carcinoma

Background: Hepatocellular carcinoma (HCC) afflicts more than half a million people each year worldwide. It was reported that circ_0015756 was up-regulated in HCC, but the mechanism did not extensively studied. Methods: we collected 24 paired cancerous and noncancerous liver tissues surgically resected from HCC patients. HCC cell proliferation, invasion, migration and apoptosis in vitro were evaluated using MTT assay, Transwell assay, scratch test and Annexin-V/PI staining respectively. Interactions between circ_0015756 and miR-7, miR-7 and FAK were further validated by the luciferase reporter assay. Tumor xenografts of HCC cells with circ_0015756 knockdown were established in nude mice. Results: The expression level of circ_0015756 was increased and the expression level of miR-7 was diminished in cancerous liver tissues relative to noncancerous liver tissues. Circ_0015756 knockdown was shown to increase the expression of miR-7, reduce the proliferation, invasion, migration and resistance to apoptosis, and down-regulate the expression of FAK in HCC. We found miR-7 impaired expression of FAK to inhibit HCC cells, suggesting that miR-7 is responsible for the dysfunction of FAK. Importantly, we showed circ_0015756 could up-regulate FAK via targeting miR-7. These in vitro findings were reproduced in vivo that circ_0015756 knockdown decreased HCC xenograft growth. Conclusion: Our present study reveals a model of HCC development that is composed of circ_0015756, miR-7 and FAK. Modulation of their levels exhibits a promise in the treatment of HCC. Abbreviations: HCC: hepatocellular carcinoma; circRNAs: circular RNAs; miRNA/miR: microRNA; miR-7: microRNA-7; FAK: focal adhesion kinase; KLF-4: kruppel like factor 4; DKK1: dickkopf WNT signaling pathway inhibitor 1; ccRCC: clear cell renal cell carcinoma; PI3K: phosphoinositide 3-kinase; Ct: comparative threshold cycle; RPMI: Roswell Park Memorial Institute; FBS: fetal bovine serum; RT: reverse transcription; qPCR: quantitative polymerase chain reaction; RIPA: radioimmunoprecipitation assay; SDS-PAGE: sodium dodecyl sulfate-polyacrylamide gel electrophoresis; PVDF: polyvinylidene difluoride; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; MTT: 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; DMSO: dimethyl sulfoxide; DMEM: Dulbecco's modified Eagle's medium; PI: propidium iodide; SPF: specific pathogen-free; SD: standard deviation; p-Akt: phosphorylated-Akt; shRNAs: small hairpin RNAs; 3'UTR: 3'-untranslated regions.

Molecular mechanisms of circular RNAs, transforming growth factor-β, and long noncoding RNAs in hepatocellular carcinoma

At the heart of hepatocellular carcinoma (HCC) lies disruption of signaling pathways at the level of molecules, genes, and cells. Non‐coding RNAs (ncRNAs) have been implicated in the disease progression of HCC. For instance, dysregulated expression of circular RNAs (circRNAs) has been observed in patients with HCC. As such, these RNAs are potential therapeutic targets and diagnostic markers for HCC. Long non‐coding RNAs (lncRNAs), a type of ncRNA, have also been recognized to participate in the initiation and progression of HCC. Transforming growth factor‐beta (TGF‐β) is another element which is now recognized to play crucial roles in HCC. It has been implicated in many biological processes such as survival, immune surveillance, and cell proliferation. In HCC, TGF‐β promotes disease progression by two mechanisms: an intrinsic signaling pathway and the extrinsic pathway. Through these pathways, it modulates various microenvironment factors such as inflammatory mediators and fibroblasts. An interesting yet‐to‐be resolved concept is whether the HCC‐promoting role of TGF‐β pathways is limited to a subset of HCC patients or it is involved in the whole process of HCC development. This review summarizes recent advancements to highlight the roles of circRNAs, lncRNAs, and TGF‐β in HCC.

Circular RNAs: a new class of biomarkers as a rising interest in laboratory medicine

Circular RNAs (circRNAs) are a distinct family of RNAs derived from the non-regular process of alternative splicing. CircRNAs have recently gained interest in transcriptome research due to their potential regulatory functions during gene expression. CircRNAs can act as microRNA sponges and affect transcription through their complex involvement in regular transcriptional processes. Some early studies also suggested significant roles for circRNAs in human diseases, especially cancer, as biomarkers and potential clinical targets. Therefore, there is a great need for laboratory scientists to translate these findings into clinical tools to advance testing for human diseases. To facilitate a better understanding of the promise of circRNAs, we focus this review on selected basic aspects of circRNA research, specifically biogenesis, function, analytical issues regarding identification and validation and examples of expression data in relation to human diseases. We further emphasize the unique challenges facing laboratory medicine with regard to circRNA research, particularly in the development of robust assays for circRNA detection in different body fluids and the need to collaborate with clinicians in the design of clinical studies.

Circular RNAs: epigenetic regulators in cancerous and noncancerous skin diseases

The most frequent kind of malignancy in the universe is skin cancer, which has been categorized into non-melanoma and melanoma skin cancer. There are no complete information of the skin carcinogenesis process. A variety of external and internal agents contribute to the non-melanoma and melanoma skin cancer pathogenesis. These factors are epigenetic changes, X-rays, genetic, arsenic compounds, UV rays, and additional chemical products. It was found that there could be a relationship between the appearing novel and more suitable therapies for participants in this class of diseases and detection of basic molecular paths. A covalently closed loop structure bond connecting the 5' and 3' ends characterizes a new group of extensively expressed endogenous regulatory RNAs, which are called circular RNAs (circRNAs). Mammals commonly express circRNAs. They are of high importance in tumorigenesis. Multiple lines evidence indicated that a variety of circular RNAs are associated with initiation and development of skin-related diseases such as skin cancers. Given that different circular RNAs (hsa_circ_0025039, hsa_circRNA006612, circRNA005537, and circANRIL) via targeting various cellular and molecular targets (e.g., CDK4, DAB2IP, ZEB1, miR-889, and let-7c-3p) exert their effects on skin cancers progression. Herein, for first time, we summarized different circular RNAs in skin cancers and noncancerous diseases. Moreover, we highlighted crosstalk between circular RNAs and ceRNAs in cancerous conditions.

Circular RNAs in cancer: new insights into functions and implications in ovarian cancer

Circular RNAs (circRNAs) are a class of long non-coding RNAs (lncRNAs) which have a circular and closed loop structure. They are ubiquitous, stable, conserved and diverse RNA molecules with a range of activities such as translation and splicing regulation, which are able to interacting with RNA-binding proteins and specially miRNA sponge. The expression patterns of the circRNAs exhibited tissue specificity and also, step and stage specificity. Accumulating evidences approved the critical role of circular RNAs in many cancers such as ovarian cancer. Given that these molecules exert their effects through multiple cellular and molecular mechanisms (i.e., angiogenesis, apoptosis, growth, and metastasis) which are involved in cancer pathogenesis, circular RNAs, in particular, act by controlling cell proliferation in ovarian cancer, so that, it has been shown that the deregulation of these molecules is associated with initiation and progression of ovarian cancer. Therefore, they are attractive molecules which have introduced them as cancer biomarkers. Moreover, they could be used as new therapeutic candidates for developing novel treatment strategies. Here, for first time, we have provided a comprehensive review on the recent knowledge of circular RNAs and their pathological roles in the ovarian cancer.

Emerging roles of circRNA in formation and progression of cancer

Circular RNAs (circRNAs) are recently discovered as a special novel type of endogenous noncoding RNAs (ncRNAs), which form a covalently closed continuous loop and are highly represented in the eukaryotic transcriptome. Recent research revealed that circRNAs can function as microRNA (miRNA) sponges, regulators of splicing and transcription, as well as interact with RNA-binding proteins (RBPs). In this review, not only the function and mechanism, but also the experimental methods of circRNA are summarized. The summary of the current state of circRNA will help us in the discovery of novel biomarkers, the therapeutic targets and their potential significance in diagnosis and treatment of diseases. CircRNAs might play important roles in cancers especially in hepatocellular carcinoma, gastric carcinoma and colorectal cancer as well as serving as diagnostic or predictive biomarkers of some diseases and providing new treatments of diseases.

Circular RNA circRHOT1 promotes hepatocellular carcinoma progression by initiation of NR2F6 expression

Background

Increasing evidence has revealed a close relationship between non-coding RNAs and cancer progression. Circular RNAs (circRNAs), a recently identified new member of non-coding RNAs, are demonstrated to participate in diverse biological processes, such as development, homeostatic maintenance and pathological responses. The functions of circRNAs in cancer have drawn wide attention recently. Until now, the expression patterns and roles of circRNAs in hepatocellular carcinoma (HCC) have remained largely unknown.

Methods

Bioinformatics method was used to screen differentially expressed novel circRNAs in HCC. Northern blotting, qRT-PCR, in situ hybridization (ISH) and RNA-FISH were utilized to analyzed the expression of circRHOT1 in HCC tisues.CCK8, colony formation, EdU assays were used to analyze proliferation of HCC cells. Transwell assay was utilized to analyze HCC cell migration and invasion. FACS was used for apoptosis analysis. Xenograft experiments were used to analyze tumor growth in vivo. Mass spectrum, RNA pulldown, RIP and EMSA was utilized to test the interaction between circRHOT1 and TIP60. RNA-sequencing method was used to analyze the downstream target gene of circRHOT1.

Results

We identified circRHOT1 (hsa_circRNA_102034) as a conserved and dramatically upregulated circRNA in HCC tissues. HCC patients displaying high circRHOT1 level possessed poor prognosis. Through in vitro and in vivo experiments, we demonstrated circRHOT1 significantly promoted HCC growth and metastasis. Regarding the mechanism, we conducted a RNA pulldown with a biotin-labeled circRHOT1-specific probe and found that circRHOT1 recruited TIP60 to the NR2F6 promoter and initiated NR2F6 transcription. Moreover, NR2F6 knockout inhibited growth, migration and invasion, whereas rescuing NR2F6 in circRHOT1-knockout HCC cells rescued the proliferation and metastasis abilities of HCC cells.

Conclusion

Taken together, circRHOT1 inhibits HCC development and progression via recruiting TIP60 to initiate NR2F6 expression, indicating that circRHOT1 and NR2F6 may be potential biomarkers for HCC prognosis.

Electronic supplementary material

The online version of this article (10.1186/s12943-019-1046-7) contains supplementary material, which is available to authorized users.

Circular RNAs in hepatocellular carcinoma: Biomarkers, functions and mechanisms

Hepatocellular carcinoma (HCC), a leading cause of cancer-related death with high invasive and metastatic potential, has a low survival rate. To improve the survival and quality of life in HCC patients, it is urgently needed to explore novel biomarkers for early diagnosis and prognosis of HCC, as well as therapeutic strategies. Circular RNAs (circRNAs) are a class of highly conserved, stable and abundant non-coding RNAs (ncRNAs) that can regulate gene expression at transcriptional or post-transcriptional levels. Recently, some circRNAs are identified to be potential biomarkers for HCC diagnosis and prognosis. Furthermore, some circRNAs are found to play oncogenic or suppressive roles in HCC progression by regulating various biological processes, including cell proliferation, migration, invasion and metastasis, epithelial-mesenchymal transition (EMT), as well as apoptosis. In this review, we summarize recent findings of deregulated circRNAs, their functions and molecular mechanisms in HCC, and discuss their potential roles as diagnostic biomarkers, prognostic biomarkers, as well as therapeutic targets for HCC.

CircRNA-104718 acts as competing endogenous RNA and promotes hepatocellular carcinoma progression through microRNA-218-5p/TXNDC5 signaling pathway

Accumulating evidences indicate that circular RNAs (circRNAs) play a vital role in diverse cancer biology. However, the contributions of circRNAs to hepatocellular carcinoma (HCC) and their underlying mechanism remain largely unknown. The present study aims at investigating the role of circRNA-104718 in HCC progression, which has been observed to be significantly up-regulated in HCC tissues. We found that, higher expression of circRNA-104718 also leds to a poor prognosis in HCC patients. Using luciferase binding assays and RNA immunoprecipitation studies, we identified circRNA-104718 is physically associated and co-expressed with microRNA (miR)-218-5p in HCC. Mechanistically, we demonstrated that circRNA-104718 functions as a competing endogenous RNAs (ceRNAs) and competes with thioredoxin domain-containing protein 5 (TXNDC5) mRNA and directly binds to miR-218-5p. Functionally, we found that ectopically expressed circRNA-104718 accelerated cell proliferation, migration, invasion, and inhibited apoptosis. In vivo studies on a nude mice model showed that circRNA-104718 overexpression could increase the tumor size and the rate of metastasis. Silencing of circRNA-104718 could decrease both the tumor size and metastasis significantly. Conversely, we also observed overexpression of miR-218-5p could in turn decrease the proliferation, migration, invasion, and increase apoptosis. Furthermore, circRNA-104718 could relieve the suppression of miR-218-5p target TXNDC5 and thereby cause an inhibition of miR’s functions. In summary, our results indicate that circRNA-104718 acts as a ceRNA and promotes HCC progression through the targeting of miR-218-5p/TXNDC5 signaling pathway. Thus, we propose that circRNA-104718 would be a promising target for HCC diagnosis and therapy.

Hsa_circ_0101432 promotes the development of hepatocellular carcinoma (HCC) by adsorbing miR-1258 and miR-622

The present research was major in investigating the regulation association among hsa_circ_0101432 (has_circ_RPPH1), miR-1258, miR-622 and MAPK1 in hepatocellular carcinoma (HCC), and we explored the mechanism underlying pathogenesis of HCC. Microarray analysis was employed to detect hsa_circ_0101432 expression in HCC. Hsa_circ_0101432 was verified as a circRNA by testing divergent primers and RNase R. And qRT-PCR was performed to determine the expression of hsa_circ_0101432, miR-1258, miR-622 and MAPK1 mRNA. Furthermore, miRanda predicted that mRNAs targeted miR-1258 and miR-622. CCK-8 assay, colony formation assay, flow cytometry as well as transwell assay were performed to detect cell viability, proliferation, apoptosis and invasive ability, respectively. Xenograft in nude mice was applied to observe tumor growth in vivo. Up-regulated hsa_circ_0101432 and down-regulated miR-1258 and miR-622 were detected in HCC while Hsa_circ_0101432 enhanced expression of MAPK1 mRNA by targeting miR-1258 and miR-622. Knocking down hsa_circ_0101432 or overexpressing miR-1258 and miR-622 inhibited proliferation and invasive ability of HCC cell and promoted cell apoptosis. Hsa_circ_0101432 was confirmed to promote tumor growth via inhibiting miR-1258 and miR-622 expression and promoting MAPK1 mRNA expression by in vivo experiment. Hsa_circ_0101432 inhibited HCC cell apoptosis, promoted cell proliferation, invasive ability and HCC tumor growth by targeting miR-1258 and miR-622 and upregulating MAPK1 mRNA expression.

Circular RNA hsa_circ_0007142 Is Upregulated and Targets miR-103a-2-5p in Colorectal Cancer

Circular RNAs (circRNAs) are a large class of endogenous noncoding RNAs that regulate gene expression and mainly function as microRNA sponges. This study aimed to explore the aberrant expression of circRNAs in colorectal cancer (CRC). Using a circRNA microarray, we identified 892 differentially expressed circRNAs between six pairs of CRC and adjacent paracancerous tissues. Among them, hsa_circ_0007142 was significantly upregulated. Further analysis in 50 CRC clinical samples revealed that hsa_circ_0007142 upregulation was associated with poor differentiation and lymphatic metastasis of CRC. Bioinformatic analysis and luciferase reporter assay showed that hsa_circ_0007142 targeted miR-103a-2-5p in CRC cells. Moreover, the silencing of hsa_circ_0007142 by siRNAs decreased the proliferation, migration, and invasion of HT-29 and HCT-116 cells. Taken together, these findings suggest that hsa_circ_0007142 is upregulated in CRC and targets miR-103a-2-5p to promote CRC.

Circular RNA Signature in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most common cancers in the world. Circular RNAs (circRNAs) are a new class of endogenous functional non-coding RNAs (ncRNAs), and have been demonstrated to play important roles in the development of HCC. This study aimed to explore the significance of circRNAs in HCC progression. HCC-associated circRNA expression profiles GSE94508 and GSE97332 were downloaded from the Gene Expression Omnibus database (GEO), and 87 differentially expressed circRNAs (DECs) between HCC tissues and paired non-cancer tissues were identified, including 76 up-regulated and 11 down-regulated circRNAs. Gene ontolog (GO) and pathway analyses of the host genes of these DECs suggested that these host genes were enriched in cell adhesion, cytosol, and protein binding, and were associated with tight junction and Wnt signaling pathways. CircRNA-miRNA interaction prediction identified 20 miRNAs that predispose to interact with DECs. Among these, four essential miRNAs, hsa-miR-7-5p, hsa-miR-145-5p, hsa-miR-203a-3p, and hsa-miR-192-5p, were reported to play pivotal roles in HCC progression by targeting multiple genes. Pathway analysis suggested that putative target genes of these essential miRNAs were involved in HCC-associated signaling pathways, such as Wnt, TGF-β, and Ras; whereas protein-protein network (PPI) analysis demonstrated that some validated target genes of these miRNAs, such as PIK3CA, AKT1, MYC, JUN, SMAD4, and SRC, were hub target genes as they have more counts of interacting protein. In the meantime, the deregulation of some DECs was validated in HCC cell line HepG2 compared with normal liver cell line L02 by quantitative real-time polymerase chain reaction (qRT-PCR) and the Sanger sequencing. This study identified a set of DECs in HCC, and provided a comprehensive understanding of the roles of these DECs in HCC progression.

MicroRNA-141 ameliorates alcoholic hepatitis‑induced intestinal injury and intestinal endotoxemia partially via a TLR4-dependent mechanism

Alcoholic hepatitis (AH) is a fatal inflammatory syndrome with no effective treatments. Intestinal injury and intestinal endotoxemia (IETM) contribute greatly in the development of AH. MicroRNAs (miRNAs/miRs) have been reported to affect intestinal injury. The present study aims to investigate the role of miR-141 in intestinal injury and IETM of AH. An AH model was successfully established in mice and they were the injected with a series of miR-141 mimic, miR-141 inhibitor or toll like receptor 4 monoclonal antibody (TLR4mAb; an inhibitor of the Toll-like receptor TLR pathway). After that, the intestinal tissues and intestinal epithelial cells were isolated from differently treated AH mice. The expression of miR-141 and TLR pathway-associated genes and the levels of inflammatory factors were determined. Furthermore, a target prediction program and a luciferase reporter assay were employed to examine whether miR-141 targets TLR4. Finally, MTT and transwell assays were carried out to detect cell viability and cell permeability. Intestinal tissues from AH mice treated with miR-141 mimic or TLR4mAb exhibited lower levels of inflammatory factors and reduced expression of the TLR pathway-associated genes, suggesting a decreased inflammatory response as well as inactivation of the TLR pathway by miR-141. The luciferase reporter assay suggested that miR-141 negatively regulated TLR4. Intestinal epithelial cells treated with miR-141 mimic or TLR4mAb demonstrated enhanced viability and reduced permeability. Opposite results were observed in AH mice treated with a miR-141 inhibitor. Collectively, the results of the present study demonstrated that miR-141 could ameliorate intestinal injury and repress the progression of IETM through targeting TLR4 and inhibiting the TLR pathway.

Circular RNAs in Cancer

Circular RNAs (circRNAs) are a class of single-stranded closed RNA molecules that are formed by precursor mRNA back-splicing or skipping events of thousands of genes in eukaryotes as covalently closed continuous loops. High-throughput sequencing and bioinformatics approaches have uncovered the broad expression of circRNAs across species. Their high stability, abundance, and evolutionary conservation among species points to their distinct properties and diverse cellular functions as efficient microRNAs and protein sponges; they also play important roles in modulating transcription and splicing. Additionally, most circRNAs are aberrantly expressed in pathological conditions and in a tissue-specific manner such as development and progression of cancer. Herein, we highlight the characteristics, functions, and mechanisms of action of circRNAs in cancer; we also provide an overview of recent progress in the circRNA field and future application of circRNAs as cancer biomarkers and novel therapeutic targets.

Regulatory mechanisms and clinical perspectives of circRNA in digestive system neoplasms

A new star, circular RNA (circRNA), is a class of noncoding RNA with a stable cyclic structure. Exonic circRNA mainly exists in the eukaryotic cytoplasm. Intronic circRNAs (ciRNA) and exonic circRNAs with introns (EIciRNA) are found in the nucleus. Recent evidences showed the functional diversity of circRNAs, which could be microRNA (miRNA) sponges, interact with protein or translate into small peptide. Due to the change of human eating habits, digestive cancer remains one of the most common cancers worldwide and it is prone to metastasis. Increasing studies have found a number of circRNAs using RNA sequencing technology and displayed double roles of circRNA in digestive cancer. In this review, we surveyed the biogenesis and regulation of circRNAs, discussed circRNA functions and clinical applications (especially circRNAs in exosome) in digestive cancers, which implied that circRNAs could be as potential biomarkers in diagnosis and treatment of digestive cancers in the future.

Targeting the circBMPR2/miR-553/USP4 Axis as a Potent Therapeutic Approach for Breast Cancer

Emerging evidence suggests that circular RNAs (circRNAs) have crucial roles in various processes, including cancer development and progression. However, the functional roles of circRNAs in breast cancer remain to be elucidated. In this study, we identified a novel circRNA (named circBMPR2) whose expression was lower in breast cancer tissues with metastasis. Moreover, circBMPR2 expression was negatively associated with the motility of breast cancer cells and significantly downregulated in human breast cancer tissues. Functionally, we found that circBMPR2 knockdown effectively enhanced cell proliferation, migration, and invasion. Moreover, circBMPR2 knockdown promoted tamoxifen resistance of breast cancer cells through inhibiting tamoxifen-induced apoptosis, whereas circBMPR2 overexpression led to decreased tamoxifen resistance. Mechanistically, we demonstrated that circBMPR2 could abundantly sponge miR-553 and that miR-553 overexpression could attenuate the inhibitory effects caused by circBMPR2 overexpression. We also found that ubiquitin-specific protease 4 (USP4) was a direct target of miR-553, which functions as a tumor suppressor in breast cancer. Our findings demonstrated that circBMPR2 might function as a miR-553 sponge and then relieve the suppression of USP4 to inhibit the progression and tamoxifen resistance of breast cancer. Targeting this newly identified circRNA may help us to develop potential novel therapies for breast cancer patients.

CircRNA-100338 Is Associated With mTOR Signaling Pathway and Poor Prognosis in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the leading cause of cancer-related deaths worldwide. Despite advances in the diagnosis and treatment of HCC, incidence, and mortality continue to rise. For accurate diagnosis and treatment of HCC, there is an urgent need to precisely understand the molecular mechanisms underlying HCC tumorigenesis and progression. Accumulating evidence showed that circRNAs, which are normally produced by scrambling of exons at the splicing process, are recognized as a novel class of endogenous noncoding RNA, which have microRNA sponging properties. In this study, we aim to investigate the circRNA-100338 mediated downstream pathway, and evaluate its association with clinicopathological parameters. Integrated analysis of circRNA-100338, miR-141-3p, and target genes revealed that RHEB, a key regulator in mTOR signaling pathway, was the target of miR-141-3p in hepatitis B-related HCC. CircRNA-100338 regulates the activity of mTOR signaling pathway in vitro. IHC analysis revealed that mTOR signaling pathway was more active in HCC tissues with elevated circRNA-100338 expression. These results indicated that circRNA-100338 could regulate mTOR signaling pathway through circRNA-100338/miR-141-3p/RHEB axis. Finally, correlation analysis of RHEB and EIF5 expression with clinicopathological parameters of HCC patients revealed that the circRNA-100338, RHEB, and EIF5 were indicators of poor prognosis in hepatitis B-related HCC. In conclusion, elevated circRNA-100338 activates mTOR signaling pathway in HCC via circRNA-100338/miR-141-3p/RHEB axis and associates with poor prognosis of hepatitis B-related HCC patients.

Systematic Review and Meta-Analysis of the Utility of Circular RNAs as Biomarkers of Hepatocellular Carcinoma

Emerging studies have reported circRNAs were dysregulated in HCC. However, the clinical value of these circRNAs remains to be clarified. Herein, we aimed to comprehensively explore their association with the diagnosis, prognosis, and clinicopathological characteristics of HCC. PubMed, EMBASE, Web of Science, and Cochrane Library databases were comprehensively searched for eligible studies up to October 30, 2018. The diagnostic effect was evaluated by the pooled sensitivity, specificity, and other indexes. The pooled hazard ratio (HR) for overall survival (OS) and recurrence free survival (RFS) was calculated to assess the prognostic value. Ten studies on diagnosis, 12 on prognosis, and 23 on clinicopathology were identified from the databases. A total of 11 upregulated and 11 downregulated circRNAs showed an association with clinicopathological features of HCC. For the diagnosis analyses, the pooled sensitivity, specificity, positive likelihood ratio (PLR), negative likelihood ratio (NLR), and diagnostic odds ratio (DOR) of circRNAs for HCC were 0.74 (95%CI: 0.65-0.82) and 0.76 (95%CI: 0.70-0.81), 3.1 (95%CI: 2.5-3.8), 0.34 (95%CI: 0.25-0.47), and 9 (95%CI: 6-14), respectively. The area under SROC curve (AUC) was 0.81 (95% CI: 0.78-0.84), indicating moderate diagnostic accuracy. In stratified analyses, the diagnostic performance of circRNAs varied based on the source of control and specimen type. For the prognosis analyses, increased expression of upregulated circRNAs was associated with worse OS (HR: 3.67, 95%: 2.07-6.48), while high expression of downregulated circRNAs was associated with better OS (HR: 0.38, 95%: 0.30-0.48). In conclusion, this study reveals that circRNAs may serve as promising diagnostic and prognostic biomarkers for HCC. However, further investigations are still required to explore the clinical value of circRNAs.

circRNAs (hsa_circ_00156, hsa_circ _000224, and hsa_circ _000520) are novel potential biomarkers in hepatocellular carcinoma

Circular RNAs (circRNAs) are a newly validated type of noncoding RNAs recently found to be deregulated in several human cancers. More accurate and specific noninvasive biomarkers are strongly needed for better diagnosis and prognosis of hepatocellular carcinoma (HCC). We performed a bioinformatics analysis to retrieve a novel panel of circRNAs potentially relevant to HCC. We examined their expression in the sera of 68 patients with HCC, 60 patients with chronic hepatitis C, and 36 healthy controls using quantitative polymerase chain reaction. We examined the performance characteristics of the selected circRNA biomarker panel in comparison with alpha-fetoprotein (AFP). In addition, we performed a survival analysis to correlate between their expression levels and patient survival. The circRNAs hsa_circ _00224 and hsa_circ _00520 showed a strong biomarker potential with relatively high sensitivities and specificities compared with AFP. The combined panel including the three circRNAs showed superior performance characteristics relative to those of AFP. The median follow-up period was 26 months. hsa_circ_00520 expression has been shown to be associated with relapse-free survival (P < 0.005). circRNAs hsa_circ_00156, hsa_circ_000224, and hsa_circ_000520 are novel potential biomarkers of high sensitivity and specificity, which could potentially be used in the diagnosis of HCC.

Emerging Epigenetic Regulation of Circular RNAs in Human Cancer

Circular RNAs (circRNAs) are novel members of the noncoding RNA family. Their characteristic covalent closed-loop structure endows circRNAs that are much more stable than the corresponding linear transcript. circRNAs are ubiquitous in eukaryotic cells, and their functions are diverse and include adsorbing microRNAs (miRNAs; acting as miRNA sponges), regulating transcription, interacting with RNA-binding proteins, and translating and deriving pseudogenes. Moreover, circRNAs are associated with the occurrence and progression of a variety of cancers, acting as new biomarkers for early diagnosis to evaluate curative effects and patient prognosis. Here, this paper briefly describes the characteristics and functions of circRNAs, and it further concludes the relationship between circRNAs and human cancer.

Reconstruction and analysis of circRNA‑miRNA‑mRNA network in the pathology of cervical cancer

The present study was performed with the aim of understanding the mechanisms of pathogenesis and providing novel biomarkers for cervical cancer by constructing a regulatory circular (circ)RNA‑micro (mi)RNA‑mRNA network. Using an adjusted P-value of <0.05 and an absolute log value of fold-change >1, 16 and 156 miRNAs from GSE30656 and The Cancer Genome Atlas (TCGA), 5,321 mRNAs from GSE63514, 4,076 mRNAs from cervical squamous cell carcinoma and endocervical adenocarcinoma (from TCGA) and 75 circRNAs from GSE102686 were obtained. Using RNAhybrid, Venn and UpSetR plot, 12 circRNA‑miRNA pairs and 266 miRNA‑mRNA pairs were obtained. Once these pairs were combined, a circRNA‑miRNA‑mRNA network with 11 circRNA nodes, 4 miRNA nodes, 153 mRNA nodes and 203 edges was constructed. By constructing the protein‑protein interaction network using Molecular Complex Detection scores >5 and >5 nodes, 7 hubgenes (RRM2, CEP55, CHEK1, KIF23, RACGAP1, ATAD2 and KIF11) were identified. By mapping the 7 hubgenes into the preliminary circRNA‑miRNA‑mRNA network, a circRNA‑miRNA‑hubgenes network consisting of 5 circRNAs (hsa_circRNA_000596, hsa_circRNA_104315, hsa_circRNA_400068, hsa_circRNA_101958 and hsa_circRNA_103519), 2 mRNAs (hsa‑miR‑15b and hsa‑miR‑106b) and 7 mRNAs (RRM2, CEP55, CHEK1, KIF23, RACGAP1, ATAD2 and KIF11) was constructed. There were 22 circRNA‑miRNA‑mRNA regulatory axes identified in the subnetwork. By analyzing the overall survival for the 7 hubgenes using the Gene Expression Profiling Interactive Analysis tool, higher expression of RRM2 was demonstrated to be associated with a significantly poorer overall survival. PharmGkb analysis identified single nucleotide polymorphisms (SNPs) of rs5030743 and rs1130609 of RRM2, which can be treated with cladribine and cytarabine. RRM2 was also indicated to be involved in the gemcitabine pathway. The 5 circRNAs (hsa_circRNA_000596, hsa_circRNA_104315, hsa_circRNA_400068, hsa_circRNA_101958 and hsa_circRNA_103519) may function as competing endogenous RNAs and serve critical roles in cervical cancer. In addition, cytarabine may produce similar effects to gemcitabine and may be an optional chemotherapeutic drug for treating cervical cancer by targeting rs5030743 and rs1130609 or other similar SNPs. However, the specific mechanism of action should be confirmed by further study.

circTADA2As suppress breast cancer progression and metastasis via targeting miR-203a-3p/SOCS3 axis

More and more evidence indicates that circular RNAs (circRNAs) have important roles in several diseases, especially in cancers. However, their involvement remains to be investigated in breast cancer. Through screening circRNA profile, we identified 235 differentially expressed circRNAs in breast cancer. Subsequently, we explored the clinical significance of two circTADA2As in a large cohort of triple-negative breast cancer (TNBC), and performed functional analysis of circTADA2A-E6 in vitro and in vivo to support clinical findings. Finally, we evaluated the effect of circTADA2A-E6 on miR-203a-3p and its target gene SOCS3. We detected two circRNAs, circTADA2A-E6 and circTADA2A-E5/E6, which were among the top five differentially expressed circRNAs in breast cancer. They were consistently and significantly decreased in a large cohort of breast cancer patients, and their downregulation was associated with poor patient survival for TNBC. Especially, circTADA2A-E6 suppressed in vitro cell proliferation, migration, invasion, and clonogenicity and possessed tumor-suppressor capability. circTADA2A-E6 preferentially acted as a miR-203a-3p sponge to restore the expression of miRNA target gene SOCS3, resulting in a less aggressive oncogenic phenotype. circTADA2As as promising prognostic biomarkers in TNBC patients, and therapeutic targeting of circTADA2As/miRNA/mRNA network may be a potential strategy for the treatment of breast cancer.

Prognostic and diagnostic significance of circRNAs expression in hepatocellular carcinoma patients: A meta-analysis

Circular RNAs (circRNAs) as novel biomarkers are widely investigated in various cancers. The aim of our study was to reveal the clinicopathological, prognostic, and diagnostic features of circRNAs in human hepatocellular carcinoma (HCC). A systematical search was conducted on PubMed, Scopus, Web of Science (WOS), EMBASE, and the Cochrane Library databases. Eligible studies reporting on the association among circRNAs and clinicopathological, prognostic, diagnostic values of HCC patients were included. Pooled odds ratios (ORs) and 95% confidence intervals (CIs) were utilized to assess clinicopathological parameters, sensitivity, and specificity, and hazard ratios (HRs) were to evaluate overall survival (OS). 17 eligible studies which included 7 for clinicopathological features, 10 for prognosis, and 8 for diagnosis were in our study. As for clinicopathological parameters, high expression of oncogenic circRNAs had a significant association with poor clinicopathological features and tumor-suppressor circRNAs proved the contrary. In terms of the prognostic values, oncogenic circRNAs had a negative influence on overall survival (OS: HR = 3.39, 95%Cl: 2.59-4.19), and high expression of tumor-suppressor circRNAs was relevant to improved survival outcomes (OS: HR = 0.46, 95%Cl: 0.37-0.56). The pooled diagnostic outcomes indicated an area under the curve (AUC) of 0.84, with sensitivity of 82% and specificity of 72% in discriminating HCC from controls. Our study indicates that circRNAs may be important biomarkers for prognostic and diagnostic values of HCC.

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 RNAs in immune responses and immune diseases

Circular RNAs (circRNAs) are novel clusters of endogenous noncoding RNAs (ncRNAs) that are widely expressed in eukaryotic cells. In contrast to the generation of linear RNA transcripts, circRNAs undergo a "back-splicing" process to form a continuous, covalently closed, stable loop structure without 5' or 3' polarities and poly (A) tails during posttranscriptional modification. Due to the widespread availability of several technologies, especially high-throughput RNA sequencing, numerous circRNAs have been discovered not only in mammals but also in plants and insects. Notably, due to their abilities to serve as microRNA (miRNA) "sponges", miRNA "reservoirs", regulate gene expression and encode proteins, circRNAs participate in the development and progression of different immune responses and immune diseases by enriching various forms of epigenetic modification. CircRNAs have been demonstrated to be expressed in a tissue-specific and pathogenesis-related manner during the occurrence of multiple immune diseases. Additionally, because of their circular configurations, expression in blood and peripheral tissues and coexistence with exosomes, circRNAs show inherent conservation along with environmental resistance stability and may be regarded as potential biomarkers or therapeutic targets for some immune diseases. In this review, we summarize the characteristics, functions and mechanisms of circRNAs and their involvement in immune responses and diseases. Although our knowledge of circRNAs remains preliminary, this field is worthy of deeper exploration and greater research efforts.

Circular RNA hsa_circ_0014243 may serve as a diagnostic biomarker for essential hypertension

Circular RNAs (circRNAs) have a great potential as clinical biomarkers; however, specific circRNAs with a diagnostic value for essential hypertension (EH) largely remain to be identified. In the present study, the potential application of Homo sapiens (hsa)_circ_0014243, which was identified to be significantly upregulated in whole blood samples of EH patients in a previous microarray profiling study by our group, in the diagnosis of EH was evaluated. Reverse transcription-quantitative polymerase chain reaction analysis was performed to determine the expression levels of hsa_circ_0014243 and hsa-microRNA (miR)-10a-5p in a total of 178 blood samples collected from 89 healthy controls and 89 patients diagnosed with EH. Divergent primers were designed for circRNAs, while conventional primers were used for miRs. Independent-samples t-tests and bivariate correlation analyses were performed to analyze the association between clinical factors influencing EH and hsa_circ_0014243 expression levels. A receiver operating characteristics (ROC) curve was generated to estimate the diagnostic value of hsa_circ_0014243 for EH. Finally, the expression levels of circRNAs and miRNAs were combined to propose a possible prediction model for EH. The results indicated that hsa_circ_0014243 was upregulated in whole blood samples of EH patients compared with that in the controls (P<0.001). Furthermore, the relative expression levels of hsa_circ_0014243 (Δ quantification cycle) were identified to be significantly correlated with age (r=-0.259, P<0.001), high-density lipoprotein levels (r=0.196, P=0.009) and glucose levels (r=-0.204, P=0.006). The area under the ROC curve (AUC) of the model using hsa_circ_0014243 as a predictor was 0.732. Of note, the AUC increased to 0.781 when hsa_circ_0014243 levels were combined with hsa-miR-10a-5p levels as predictors. The present results suggest that hsa_circ_0014243 has a crucial role in the genesis and development of EH, and presents a certain diagnostic capability for EH.

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.

Hsa_circ_101280 promotes hepatocellular carcinoma by regulating miR-375/JAK2

In this study, we sought to predict the effects of a certain circular RNA (circRNA), hsa_circ_101280 (also known as hsa_circ_0100929 and hsa_circ_SLAIN1), on hepatocellular carcinoma (HCC) cells and to determine the potential mechanism. After screening differentially expressed circRNAs in HCC tissues through Gene Expression Omnibus data analysis, hsa_circ_101280 was found to be highly expressed, and its high expression was verified in HCC cell lines with qRT-PCR along with the low expression of its downstream miRNA miR-375. Colony formation and flow cytometry assays showed that both hsa_circ_101280 silencing and miR-375 overexpression restrained proliferation and promoted apoptosis in HCC cells. JAK2 was identified as a downstream mRNA target of miR-375 by RNA pull-down and dual-luciferase reporter gene assays, its expression in HCC cell lines were positively regulated by hsa_circ_101280 and negatively by miR-375 expression. Furthermore, the silencing of hsa_circ_101280 significantly inhibited the growth of HCC xenografts in nude mice, with the downregulated expression of JAK2. Overall, both the in vitro and in vivo studies revealed that hsa_circ_101280 largely facilitated the tumorigenesis of HCC, characterized by the promoted proliferation and suppressed apoptosis of HCC cells, by sponging miR-375 and upregulating JAK2.

CircSLC3A2 functions as an oncogenic factor in hepatocellular carcinoma by sponging miR-490-3p and regulating PPM1F expression

Background

Non-coding RNAs (ncRNAs) have been reported to participate in tumor progression by regulating gene expression. Previous studies showed that protein phosphatase Mg2⁺/Mn2⁺ dependent 1F (PPM1F) acts a dual role in cancer growth and metastasis. But, the underlying mechanisms by which ncRNAs regulate PPM1F expression in hepatocellular carcinoma (HCC) are poorly understood.

Methods

The association between PPM1F or miR-490-3p expression and clinicopathological features and prognosis in patients with HCC was analyzed by TCGA RNA-sequencing data. CircSLC3A2 was identified to bind with miR-490-3p by bioinformatic analysis, and the binding sites between miR-490-3p and PPM1F or circSLC3A2 were confirmed by dual luciferase report and RNA immunoprecipitation (RIP) assays. The localization and clinical significance of miR-490-3p and circSLC3A2 in patients with HCC were investigated by fluorescence in situ hybridization (FISH). MTT, Agar, and Transwell assays were conducted to evaluate the effects of miR-490-3p or circSLC3A2 on cell proliferation and invasive potential.

Results

The expression of PPM1F or miR-490-3p was associated with poor survival and tumor recurrence, and acted as an independent prognostic factor in patients with HCC. Re-expression of miR-490-3p inhibited HCC cell proliferation and invasion by targeting PPM1F, but its inhibitor reversed these effects. Moreover, circSLC3A2, predominantly localized in the cytoplasm, exhibited an oncogenic role by sponging miR-490-3p and regulating PPM1F expression, and harbored a positive correlation with poor survival in patients with HCC.

Conclusion

CircSLC3A2 acts as an oncogenic factor in HCC by sponging miR-490-3p and regulating PPM1F expression.

Electronic supplementary material

The online version of this article (10.1186/s12943-018-0909-7) contains supplementary material, which is available to authorized users.

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.

Circular RNA Transcriptomic Analysis of Primary Human Brain Microvascular Endothelial Cells Infected with Meningitic Escherichia coli

With their essential regulatory roles in gene expression and high abundance in the brain, circular RNAs (circRNAs) have recently attracted considerable attention. Many studies have shown that circRNAs play important roles in the pathology of CNS diseases, but whether circRNAs participate in E. coli-induced bacterial meningitis is unclear. We used high-throughput sequencing to analyze the transcriptional profiles of host circRNAs in primary brain microvascular endothelial cells in response to meningitic E. coli. A total of 308 circRNAs were significantly altered, including 140 upregulated and 168 downregulated ones (p < 0.05). Kyoto Encyclopedia of Genes and Genomes (KEGG) and gene ontology enrichment of the parental genes of these altered circRNAs indicated that they are likely to be involved in diverse biological processes via influencing the expression of their parental genes. Coupled with our previous mRNA and microRNA sequencing data, a competing endogenous RNA analysis was performed, and the potential regulatory network was preliminarily constructed and validated. By revealing the transcriptional profiles of the host circRNAs involved in E. coli meningitis, it is envisaged that the novel insight gained into the regulatory mechanisms of circRNAs in the development of bacterial meningitis will lead to better understanding of how to prevent and treat bacterial CNS infections.

circRNA_104075 stimulates YAP-dependent tumorigenesis through the regulation of HNF4a and may serve as a diagnostic marker in hepatocellular carcinoma

Some types of circular RNA (circRNA) are aberrantly expressed in human diseases including hepatocellular carcinoma (HCC). However, its regulation mechanism and diagnostic roles are largely unknown. Here, we identified that circRNA_104075 (circ_104075) was highly expressed in HCC tissues, cell lines and serum. Mechanistically, HNF4a bound to the -1409 to -1401 region of the circ_104075 promoter to stimulate the expression of circ_104075. Moreover, circ_104075 acted as a ceRNA to upregulate YAP expression by absorbing miR-582-3p. Interestingly, an N6-methyladenosine (m6A) motif was identified in the 353-357 region of YAP 3'UTR, and this m6A modification was essential for the interaction between miR-582-3p and YAP 3'UTR. Further, the diagnostic performance of circ_104075 was evaluated. The area under the receiver operating characteristic (AUC-ROC) for circ_104075 was 0.973 with a sensitivity of 96.0% and a specificity of 98.3%. Collectively, we determined that circ_104075 was highly expressed in HCC and elucidated its upstream and downstream regulatory mechanisms. circ_104075 additionally has the potential to serve as a new diagnostic biomarker in HCC. Targeting circ_104075 may provide new strategies in HCC diagnosis and therapy.

Circular RNA circAGO2 drives cancer progression through facilitating HuR-repressed functions of AGO2-miRNA complexes

Argonaute 2 (AGO2), the core component of microRNA (miRNA)-induced silencing complex, plays a compelling role in tumorigenesis and aggressiveness. However, the mechanisms regulating the functions of AGO2 in cancer still remain elusive. Herein, we indentify one intronic circular RNA (circRNA) generated from AGO2 gene (circAGO2) as a novel regulator of AGO2-miRNA complexes and cancer progression. CircAGO2 is up-regulated in gastric cancer, colon cancer, prostate cancer, and neuroblastoma, and is associated with poor prognosis of patients. CircAGO2 promotes the growth, invasion, and metastasis of cancer cells in vitro and in vivo. Mechanistic studies reveal that circAGO2 physically interacts with human antigen R (HuR) protein to facilitate its activation and enrichment on the 3'-untranslated region of target genes, resulting in reduction of AGO2 binding and repression of AGO2/miRNA-mediated gene silencing associated with cancer progression. Pre-clinically, administration of lentivirus-mediated short hairpin RNA targeting circAGO2 inhibits the expression of downstream target genes, and suppresses the tumorigenesis and aggressiveness of xenografts in nude mice. In addition, blocking the interaction between circAGO2 and HuR by cell-penetrating inhibitory peptide represses the tumorigenesis and aggressiveness of cancer cells. Taken together, these results indicate that oncogenic circAGO2 drives cancer progression through facilitating HuR-repressed functions of AGO2-miRNA complexes.

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.

Novel circular RNA, hsa_circ_0025039 promotes cell growth, invasion and glucose metabolism in malignant melanoma via the miR-198/CDK4 axis

Malignant melanoma, a tumor derived from melanocytes, shows severe drug resistance and prompt metastasis, causing a serious threat to human health. Circular RNAs (circRNAs) are widely expressed in mammals and have been indicated to play important roles in tumorigenesis. In the present study, we analyzed the variability of circRNAs in malignant melanoma by microarray and identified six differentially expressed circRNAs. In particular, we found that hsa_circ_0025039, which is formed by FOXM1 exons, is significantly upregulated in melanoma. In vitro, the knockdown of circ_0025039 inhibited cell proliferation, colony formation ability, invasion and glucose metabolism in melanoma cells. Additionally, we identified miR-198 as a direct target of hsa_circ_0025039. Furthermore, we demonstrated that hsa_circ_0025039 regulates CDK4 expression by sponging miR-198. In vivo study indicated that the silencing of hsa_circ_0025039 inhibits melanoma tumor formation and downregulates miR-198 and CDK4 expression. Taken together, our data showed that circ_0025039 promotes cell growth, invasion and glucose metabolism in malignant melanoma by sponging miR-198 and regulating CDK4.

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.

Circular RNA expression profile and potential function of hsa_circ_0045272 in systemic lupus erythematosus

Circular RNAs (circRNAs) represent a class of non-coding RNAs that form covalently closed RNA circles with extensive expression and conservation in mammals. Circular RNAs regulate gene expression through acting as competitive endogenous RNAs (ceRNAs) and modulating gene transcription. Accumulating evidence supports the implication of circRNAs in a variety of human diseases, but studies of circRNA role in systemic lupus erythematosus (SLE) are lacking. The present study measured the circRNA expression profiles in T cells from patients with SLE and healthy controls with human circRNA microarray and identified 127 differentially expressed circRNAs in SLE patients. Down-regulation of hsa_circ_0045272 in SLE T cells was verified with quantitative PCR. Jurkat cells with stable hsa_circ_0045272 knockdown were generated using specific lentiviral short hairpin RNA for functional studies. Flow cytometric analysis indicated that hsa_circ_0045272 knockdown significantly up-regulated the early apoptosis of Jurkat cells. Meanwhile, ELISA showed that hsa_circ_0045272 knockdown significantly enhanced interleukin-2 production of activated Jurkat cells. Then, ceRNAs were predicted for hsa_circ_0045272 and the significant down-regulation of two mRNAs predicted as ceRNAs, NM_003466 (PAX8) and NM_015177 (DTX4), but not their corresponding proteins, was validated. Furthermore, dual luciferase reporter assay indicated binding of hsa_circ_0045272 with hsa-miR-6127. Circular RNA-mRNA co-expression networks showed the correlation of circRNAs with mRNAs and provided additional clues to circRNA functions. Our study demonstrated dysregulated circRNAs in SLE and revealed the function of hsa_circ_0045272 in negatively regulating apoptosis and interleukin-2 secretion and its potential mechanism. The implication of hsa_circ_0045272 and other abnormal circRNAs in SLE merits further investigation.

Overexpression of circ-0067934 is associated with increased cellular proliferation and the prognosis of non-small cell lung cancer

Previous studies have suggested that circular RNAs (circRNAs) serve crucial functions in various human diseases, including cancer. The results of the present study demonstrated that the expression levels of circ-0067934 were significantly increased in non-small cell lung cancer (NSCLC) tissues and NSCLC cells compared with that in adjacent normal tissues and a normal human bronchial epithelium cell line, as assessed using reverse transcription-quantitative polymerase chain reaction. Increased expression levels of circ-0067934 were associated with lymph node metastasis and advanced tumor stage in patients with NSCLC. Increased levels of circ-0067934 were significantly associated with the poor overall survival (OS) time of patients with NSCLC compared with low circ-0067934 expression levels, as assessed using Kaplan-Meier estimator survival curves and log-rank tests. Additionally, circ-0067934 was identified as an independent risk factor for OS time in patients with NSCLC, as assessed using univariate and multivariate Cox proportional hazards regression models. Additionally, cell proliferation and colony formation assays were employed to assess cell proliferation. The results demonstrated that the proliferative ability was significantly inhibited when circ-0067934 was knocked down in NSCLC cells. Therefore, these results indicated that circ-0067934 may be a predictive marker for the prognosis of NSCLC and a target for the treatment of the disease.

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.

Emerging function and potential diagnostic value of circular RNAs in cancer

As a novel class of endogenous RNAs, circRNAs, have a covalently closed continuous loop, with neither a 5'to 3'polarity, nor a polyadenylated tail. Numerous circRNAs have been characterized by abundance, stabilization, conservation, and exhibit tissue/developmental stage-specific expression. Furthermore, circRNAs play vital roles in tumorigenesis and metastasis, such as functioning as a ceRNA or miRNA sponge, interacting with protein and encoding protein. Increasing evidence has revealed that it potentially serves as a required novel biomarker for cancer diagnosis. This review summarized the latest research on circRNAs, including its classification and biogenesis, mechanism and functions, as well as circRNAs in different cancers, as a potential biomarker.

[Circular RNA in Lung Cancer Research: Biogenesis, Functions and Roles]

肺癌（lung cancer）的发病率及死亡率在我国双居首位，近年来针对肿瘤驱动基因和免疫检查点的靶点治疗取得了振奋人心的成果。环状RNA（circular RNA, circRNA）是一类具有环形结构的RNA分子，研究发现其与肿瘤的分期、淋巴结转移等关系密切，在生理过程和疾病中具有特殊的生物学功能。其高度稳定性和特异性使之有望成为肿瘤潜在的预测和治疗靶点。目前环状RNA在肺癌中的生物学功能和调控机制仅有少量研究报道。本文对环状RNA的研究历史、生源机制、生物学功能以及其在肿瘤，尤其是肺癌研究中的进展作一综述，以期为环状RNA在肺癌中的研究提供理论依据和新的思路。

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.