The expression profile and clinical significance of circRNA0003906 in colorectal cancer

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

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

CircRNA as an Achilles heel of cancer: characterization, biomarker and therapeutic modalities

Circular RNAs (circRNAs) are a class of endogenous noncoding RNAs characterized by their lack of 5' caps and 3' poly(A) tails. These molecules have garnered substantial attention from the scientific community. A wide range of circRNA types has been found to be expressed in various tissues of the human body, exhibiting unique characteristics such as high abundance, remarkable stability, and tissue-specific expression patterns. These attributes, along with their detectability in liquid biopsy samples such as plasma, position circRNAs an ideal choice as cancer diagnostic and prognostic biomarkers. Additionally, several studies have reported that the functions of circRNAs are associated with tumor proliferation, metastasis, and drug resistance. They achieve this through various mechanisms, including modulation of parental gene expression, regulation of gene transcription, acting as microRNA (miRNA) sponges, and encoding functional proteins. In recent years, a large number of studies have focused on synthesizing circRNAs in vitro and delivering them to tumor tissue to exert its effects in inhibit tumor progression. Herein, we briefly discuss the biogenesis, characteristics, functions, and detection of circRNAs, emphasizing their clinical potential as biomarkers for cancer diagnosis and prognosis. We also provide an overview the recent techniques for synthesizing circRNAs and delivery strategies, and outline the application of engineered circRNAs in clinical cancer therapy.

Characterization of cell-type specific circular RNAs associated with colorectal cancer metastasis

Colorectal cancer (CRC) is the most common gastrointestinal malignancy and a leading cause of cancer deaths in the United States. More than half of CRC patients develop metastatic disease (mCRC) with an average 5-year survival rate of 13%. Circular RNAs (circRNAs) have recently emerged as important tumorigenesis regulators; however, their role in mCRC progression remains poorly characterized. Further, little is known about their cell-type specificity to elucidate their functions in the tumor microenvironment (TME). To address this, we performed total RNA sequencing (RNA-seq) on 30 matched normal, primary and metastatic samples from 14 mCRC patients. Additionally, five CRC cell lines were sequenced to construct a circRNA catalog in CRC. We detected 47 869 circRNAs, with 51% previously unannotated in CRC and 14% novel candidates when compared to existing circRNA databases. We identified 362 circRNAs differentially expressed in primary and/or metastatic tissues, termed circular RNAs associated with metastasis (CRAMS). We performed cell-type deconvolution using published single-cell RNA-seq datasets and applied a non-negative least squares statistical model to estimate cell-type specific circRNA expression. This predicted 667 circRNAs as exclusively expressed in a single cell type. Collectively, this serves as a valuable resource, TMECircDB (accessible at https://www.maherlab.com/tmecircdb-overview), for functional characterization of circRNAs in mCRC, specifically in the TME.

Colon cancer transcriptome

Over the last four decades, methodological innovations have continuously changed transcriptome profiling. It is now feasible to sequence and quantify the transcriptional outputs of individual cells or thousands of samples using RNA sequencing (RNA-seq). These transcriptomes serve as a connection between cellular behaviors and their underlying molecular mechanisms, such as mutations. This relationship, in the context of cancer, provides a chance to unravel tumor complexity and heterogeneity and uncover novel biomarkers or treatment options. Since colon cancer is one of the most frequent malignancies, its prognosis and diagnosis seem to be critical. The transcriptome technology is developing for an earlier and more accurate diagnosis of cancer which can provide better protectivity and prognostic utility to medical teams and patients. A transcriptome is a whole set of expressed coding and non-coding RNAs in an individual or cell population. The cancer transcriptome includes RNA-based changes. The combined genome and transcriptome of a patient may provide a comprehensive picture of their cancer, and this information is beginning to affect treatment decision-making in real-time. A full assessment of the transcriptome of colon (colorectal) cancer has been assessed in this review paper based on risk factors such as age, obesity, gender, alcohol use, race, and also different stages of cancer, as well as non-coding RNAs like circRNAs, miRNAs, lncRNAs, and siRNAs. Similarly, they have been examined independently in the transcriptome study of colon cancer.

Circulating cell-free circRNA panel predicted tumorigenesis and development of colorectal cancer

Background

Colorectal cancer (CRC) is reported with high morbidity and mortality. Currently, the sensitivity of diagnostic markers for colorectal cancer is low. Therefore, further exploration of new plasma diagnostic markers for early detection of colorectal cancer is of great value. We aimed to explore potential circRNAs in plasma as biomarkers for early diagnosis of CRC.

Methods

We employed the circRNA microarray to investigate dysregulated circRNAs in plasma samples of CRC patients, colorectal adenoma patients (CRA), and healthy controls. Through in‐depth analysis, significantly differentially expressed circRNAs were screened as candidate targets.

Results

Eight circRNAs (hsa_circ_104885, hsa_circ_100185, hsa_circ_103171, hsa_circ_001978, hsa_circ_105039, hsa_circ_103627, hsa_circ_101717, and hsa_circ_104192) were obtained as candidate circRNAs with upregulation in CRC comparing with both CRA and healthy control. Through detecting the plasma expression levels of eight candidate targets, we identified three circRNA (hsa_circ_001978, hsa_circ_105039, and hsa_circ_103627) with increased level which were consistent with the microarray results in training set. Further validation found the circRNA panel was consistent with training set. The ROC curve also revealed a high diagnostic ability of hsa_circ_001978, hsa_circ_105039, and hsa_circ_103627 in predicted the CRC from CRA patients (AUC = 0.966) as well as healthy controls (AUC = 0.969).

Conclusion

Our data suggest that hsa_circ_001978, hsa_circ_105039, and hsa_circ_103627 might be a CRC‐specific biomarker for early diagnosis.

Circular RNAs as Diagnostic and Prognostic Indicators of Colorectal Cancer: A Pooled Analysis of Individual Studies

Background: Circular RNAs (circRNAs) have proven as a special subset of endogenous RNAs that are implicated in the tumorigenesis of various cancers. This study sought to evaluate the role of circRNAs in the diagnosis and prognosis of colorectal cancer (CRC).

Methods: The online databases were searched for collecting relevant studies on circRNAs as diagnostic and prognostic biomarkers of CRC. Two researchers independently screened literature, extracted data, and evaluated the bias and risks of included studies. The diagnostic and prognostic indicators were merged and analyzed using STATA 12.0 software, and sources of heterogeneity were traced by the sensitivity analysis and the meta-regression test.

Results: A total of 29 articles representing 2639 CRC patients were included. The pooled sensitivity, specificity, and area under the curve (AUC) of circRNAs in differentiating CRC from non-tumor control were 0.75 (95% CI: 0.69–0.80) and 0.74 (95% CI: 0.69–0.78) and 0.81, respectively. The survival analysis showed that up-regulations of up-regulated circRNAs were significantly related to dismal survival in CRC patients (HR = 2.38, p < 0.001). A stratified analysis showed that the comprehensive diagnostic value of up-regualted circRNAs in CRC was higher than that of down-regualted circRNAs (AUC: 0.83 vs. 0.77; Z test, p < 0.05). The efficacy of tissue-derived circRNAs in the diagnosis of CRC was equal to that of plasma/serum-derived ones (AUC: 0.81 vs. 0.82; Z test, p > 0.05).

Conclusion: Abnormally expressed circRNAs as auxiliary biomarkers present underlying value in the diagnosis and prognosis prediction of CRC.

The Role of circRNAs in the Diagnosis of Colorectal Cancer: A Meta-Analysis

Background: A novel category of non-coding circular RNAs (circRNAs) has been found to be dysregulated in colorectal cancer (CRC) and significantly contribute to its progression. However, the feasibility of using circRNA as a diagnostic biomarker for CRC remains to be elucidated. Herein, we aimed to comprehensively collect and analyze evidence regarding the potential application of circRNAs as diagnostic indicators for CRC.

Methods: A comprehensive retrieval of relevant studies dating from January, 2015 to December 2020, was carried out in PubMed, Cochrane Library, and Web of Science. Data regarding the diagnostic accuracy of circRNA for CRC, including sensitivity, specificity, positive likelihood ratio (PLR), negative likelihood ratio (NLR), diagnostic odds ratio (DOR), and area under the curve (AUC), were obtained from the included studies. Quality assessment of diagnostic accuracy studies (QUADAS-2) was used to assess the methodological quality of each study. Statistical analysis was performed using STAT and RevMan software.

Results: Eighteen studies, involving a total of 2021 individuals, were included in the present meta-analysis. The specimens examined included tissue, serum, and plasma. The pooled sensitivity, specificity, DOR, PLR, NLR, and AUC, with a 95% confidence interval (CI), of circRNAs in the diagnosis of CRC were 0.78 (0.71–0.83), 0.73 (0.68–0.78), 9.68 (6.76–13.85), 2.92 (2.45–3.50), 0.30 (0.23–0.39), and 0.81 (0.78–0.85), respectively. Subgroup analysis showed that the upregulated circRNAs in the tissue or plasma possessed relatively higher diagnostic values for CRC than the downregulated circRNAs. There was no significant difference between the tissue-derived and non-tissue-derived circRNA subgroups.

Conclusion: circRNA may be used as a diagnostic biomarker for CRC because of its relatively high diagnostic accuracy in distinguishing CRC patients from normal controls. Further prospective studies are needed to identify more representative circRNAs as diagnostic markers for CRC.

Integrative and in-vitro analysis reveal hsa_circ_001787 can act as a diagnostic biomarker for colorectal cancer

Background

Circular RNAs (circRNAs) are a new kind of non-coding RNA(ncRNA). Throughout research, we see an increase in the number of studies demonstrating that circRNAs occupy a pivotal role in the growth and advancement of human tumors. Nevertheless, hsa_circ_001787′s role in the evolution of colorectal cancer (CRC) remains unclear. This current study ascertained the expression level of circRNA001787 in CRC specimens and neighboring healthy tissues, and investigated the miRNAs associate with hsa_circ_001787, as well as the relationship between hsa_circ_001787 and pathological factors.

Method

First, the expression level of hsa_circ_001787 was measured in 43 matched Tissues from CRC and normal tissues through using real-time quantitative reverse transcription PCR (qRT-PCR). Second, based on circular RNA-microRNA and microRNA-mRNA pairs, a circRNA-miRNA-mRNA network was created. The survival rate of mRNAs was investigated through the GEPIA in the network. Regarding the elucidated function analysis of hsa_circ_001787, The biological, molecular, cellular function (GO) and pathway (KEGG) enrichment was obtained.

Result

We detected that hsa_circ_001787 expression level was significantly down expressed in CRC tissue versus paired CRC histological normal tissue. The area under the curve (AUC) was 0.83. The expression level of hsa_circ_001787 was significantly associated with pathological factors such as tumor grade and the primary site of the tumor. Based on the hsa_circ_001787, a novel circRNA/miRNA/mRNA network has been built up, four miRNAs, and 24 mRNA. The pathway of mRNAs analyzed in the pathogenesis of CRC. Four genes distinguished via the GEPIA database were positively linked to the overall survival of CRC patients.

Conclusion

Our study suggested that hsa_circ_001787 was significantly down-regulated in CRC. We might be able to use this as a new biomarker in the screening of CRC. Furthermore, our finding achieves a broader understanding of the regulatory mechanisms by which hsa_circ_001787 acts as ceRNA in colorectal cancer.

The effective function of circular RNA in colorectal cancer

Colorectal cancer (CRC) is the 3rd most common type of cancer worldwide. Late detection plays role in one-third of annual mortality due to CRC. Therefore, it is essential to find a precise and optimal diagnostic and prognostic biomarker for the identification and treatment of colorectal tumorigenesis. Covalently closed, circular RNAs (circRNAs) are a class of non-coding RNAs, which can have the same function as microRNA (miRNA) sponges, as regulators of splicing and transcription, and as interactors with RNA-binding proteins (RBPs). Therefore, circRNAs have been investigated as specific targets for diagnostic and prognostic detection of CRC. These non-coding RNAs are also linked to metastasis, proliferation, differentiation, migration, angiogenesis, apoptosis, and drug resistance, illustrating the importance of understanding their involvement in the molecular mechanisms of development and progression of CRC. In this review, we present a detailed summary of recent findings relating to the dysregulation of circRNAs and their potential role in CRC.

Roles of circular RNAs in colorectal cancer

Colorectal cancer (CRC) is one of the most common types of malignant cancer worldwide and poses a significant burden on both the individual and healthcare systems. Despite advances in treatment options, advanced-stage CRC has a high mortality rate due to its heterogeneity, metastatic potential and/or delay in diagnosis. In recent years, an increasing number of studies have indicated that circular RNAs (circRNAs) serve important roles in several types of cancer, including CRC. Recent studies have revealed that circRNAs are aberrantly expressed in CRC tissues and function as oncogenic or tumor suppressive regulators of CRC carcinogenesis and development. Numerous circRNAs have been associated with the clinicopathological features of patients with CRC and have been considered as potential biomarkers for the diagnosis and prognosis of CRC, as well as targets for treatment. However, a deeper understanding of their potential function is required. In the present review, the current body of knowledge on the biogenesis and functions of CRC-associated circRNAs, and their potential value in clinical applications, such as in CRC diagnosis, prognosis and treatment, is discussed and summarized.

CircFAM120B Blocks the Development of Colorectal Cancer by Activating TGF-Beta Receptor II Expression via Targeting miR-645

Circular RNAs (circRNAs) are implicated in various human cancers, including colorectal cancer (CRC). The objective of this study was to investigate the function and regulatory mechanism of a novel circRNA, circFAM120B, in CRC development. The expression of circFAM120B, miR-645 and TGF-beta receptor II (TGFBR2) mRNA was detected by quantitative real-time polymerase chain reaction. Cellular biological functions, including cell proliferation, migration/invasion, and glycolysis metabolism, were assessed using CCK-8 assay, colony formation assay, transwell assay, and glycolysis stress test, respectively. Glycolysis progression was also monitored by lactate production and glucose consumption. The expression of glycolysis-related markers and TGFBR2 at the protein level was detected by western blot. The interaction between miR-645 and circFAM120B or TGFBR2 was predicted by bioinformatics analysis and verified by pull-down assay, dual-luciferase reporter assay and RIP assay. In vivo animal experiments were performed to further explore the function of circFAM120B. The expression of circFAM120B was decreased in CRC tissues and cells. CircFAM120B overexpression blocked CRC cell proliferation, migration/invasion, and glycolysis metabolism. MiR-645 was a target of circFAM120B, and miR-645 restoration reversed the effects of circFAM120B overexpression. In addition, TGFBR2 was a target of miR-645, and miR-645 inhibition-suppressed CRC cell proliferation, migration/invasion and glycolysis were restored by TGFBR2 knockdown. Moreover, circFAM120B activated the expression of TGFBR2 by targeting miR-645. TGFBR2 also blocked tumor growth in vivo by targeting the miR-645/TGFBR2 axis. CircFAM120B inhibited CRC progression partly by mediating the miR-645/TGFBR2 network, which explained the potential mechanism of circFAM120B function in CRC.

circNSUN2 promotes the malignant biological behavior of colorectal cancer cells via the miR‑181a‑5p/ROCK2 axis

Aberrant expression of circular RNAs (circRNAs) has been demonstrated to be related to the development of colorectal cancer (CRC), the third most common cancer worldwide. However, the mechanism of the effect of circRNA NOP2/Sun domain family, member 2 (circNSUN2) on the malignant biological behavior of CRC remains unclear. In the present study, the expression of circNSUN2 and microRNA (miR)‑181a‑5p was detected by RT‑qPCR. The expression of Rho‑associated coiled‑coil‑containing protein kinase 2 (ROCK2) was measured by western blotting. Cell proliferation was detected by CCK‑8 assay. The cell apoptosis rate was measured by flow cytometry. Cell migration ability was evaluated by Transwell assay. The interactions between circNSUN2, miR‑181a‑5p and ROCK2 were verified by dual‑luciferase reporter assay. The results revealed that circNSUN2 was highly expressed in CRC tissues and cell lines. Knockdown of circNSUN2 inhibited the malignant biological behavior of CRC in vivo and in vitro. Moreover, miR‑181a‑5p was revealed to be a target gene of circNSUN2, and the expression of ROCK2 was negatively regulated by miR‑181a‑5p. Knockdown of circNSUN2 inhibited proliferation and migration, and induced apoptosis of CRC cells and suppressed tumor growth by targeting miR‑181a‑5p to decrease ROCK2 expression. In conclusion, circNSUN2 promoted the progression of CRC by sponging miR‑181a‑5p to increase the expression of ROCK2.

Plasma cell-free circRNAs panel act as fingerprint predicts the occurrence of laryngeal squamous cell carcinoma

Background: Circular RNAs (circRNAs) have recently emerged as a new class of RNAs, highly enriched in the human tissues and very stable within cells, exosomes and body fluids. In this study, we aimed to screen the plasma cell-free derived circRNAs in laryngeal squamous cell carcinoma (LSCC) and investigate whether these circRNAs could predicted LSCC as potential biomarkers.

Methods: The circRNA microarray was employed with three samples in each group to screen the dysregulated circRNAs isolated from plasma samples. The top 20 circRNAs were first selected as candidates with the upregulated level in the plasma of LSCC.

Results: Further validation found that only circ_0019201, circ_0011773 and circ_0122790 was consistent with training set. The ROC curve also revealed a high diagnostic ability an area under ROC curve value (AUC) for single circRNA and combined. The AUC for circ_0019201, circ_0011773 and circ_0122790 and the combined was 0.933, 0.908, 0.965 and 0.990 in training set. For the validation set, the AUC was 0.766, 0.864, 0.908 and 0.951. The three circRNAs were further investigated with stable expression in human plasma samples.

Conclusions: The plasma derived circ_0019201, circ_0011773 and circ_0122790 might be the potential biomarker for predicting the LSCC.

Molecular Mechanism of circRAPGEF5 in Regulating the Molecular Axis of microRNA-4712-5p/Tyrosine 3-Monooxygenase/Tryptophan 5-Monooxygenase Activation Protein Epsilon Affecting Cellular Proliferation and Apoptosis in Mammary Cancer

To understand the molecular mechanism of circRAPGEF5, its effect on the proliferation and apoptosis of mammary cancer cells, and its regulatory effect on the molecular axis of miRNA-4712-5p/YWHAE. qRT-PCR and Western blot were used to test circRAPGEF5, miRNA-4712-5p, and YWHAE expression in mammary cancer and paracancerous tissues. The human mammary cancer cell, MDA-MB-231, was cultured in vitro, and pcDNA-NC, pcDNA-circRAPGEF5, anti-miRNA-NC, anti-miRNA-4712-5p, pcDNA-circRAPGEF5, and miRNA-NC, pcDNA-circRAPGEF5 were transfected into MDA-MB-231 cells with miRNA-4712-5p mimics. qRT-PCR and Western blot were employed to detect circRAPGEF5, miRNA-4712-5p, and YWHAE expression in cells. The CCK-8 methodand plate clone formation experiment were conducted to test cellular proliferation ability. Flow cytometry was performed to detect apoptosis rate. Dual luciferase reporter assays were used to test the targeting association between circRAPGEF5 and miRNA-4712-5p, and the targeting association between miRNA-4712-5p and YWHAE. Western blot was utilized to detect Bcl-2, Bax, and Cleared Caspase-3 protein expression. In comparison with paracancerous tissues, circRAPGEF5 and YWHAE expression levels in mammary cancer tissues were significantly reduced (P < 0.05), and miRNA-4712-5p expression levels were significantly increased (P < 0.05). Transfection of pcDNA-circRAPGEF5 or trans-anti-miRNA-4712-5p could reduce the optical density (OD) value, Bcl-2 protein level and clonal formation number to a significant extent (P < 0.05), and it increases Bax and Cleaved Caspase-3 apoptosis rate and protein levels (P < 0.05). Dual luciferase reporter assays confirmed that there was target binding between circRAPGEF5 and miRNA-4712-5p and between miRNA-4712-5p and YWHAE. Co-transfection of pcDNA-circRAP GEF5 and miRNA-4712-5p could greatly reduce transfection of pcDNA-circRAP GEF5 and its effect on the proliferation and apoptosis of MDA-MB-231 cells. Overexpression of circRAPGEF5 can inhibit the proliferation of mammary cancer cells and induce apoptosis by regulating the molecular axis of miRNA-4712-5p/YWHAE.

Expression profiles of circular RNAs in colon biopsies from Crohn's disease patients by microarray analysis

BACKGROUND

Circular RNAs (circRNAs) are involved in various diseases and serve as biomarkers. The present study aimed to investigate unique expression profiles of circRNAs in colon tissues of Crohn's disease (CD) and search novel biomarkers for the diagnosis.

METHODS

Differentially expressed (DE) circRNAs in biopsies from four CD patients, four ulcerative colitis (UC) patients, and four healthy controls (HC) were screened by microarray. Hsa_circ_0062142 and hsa_circ_0001666 were verified in another expanded validation cohort. Bioinformatics analysis was applied to predict the function of two DE circRNAs. Receiver operating characteristic (ROC) curves were constructed to evaluate the diagnostic value of CD.

RESULTS

The top 10 upregulated circRNAs in CD compared with HC were hsa_circ_0000691, hsa_circ_0001666, hsa_circ_0004183, hsa_circ_0009024, hsa_circ RNA_405324, hsa_circ_0002003, hsa_circ_0085323, hsa_circ_0040994, hsa_circ_0062142, and hsa_circ_0048148; the top 10 downregulated circRNAs were hsa_circ_0049356, hsa_circ RNA_405443, hsa_circ RNA_403556, hsa_circ_0092328, hsa_circ_0003979, hsa_circ_0074491, hsa_circ_0023461, hsa_circ RNA_406237, hsa_circ_0034044, and hsa_circ RNA_400564 (fold change in descending order). The expression levels of hsa_circ_0001666 and hsa_circ_0062142 in CD were significantly higher than those in UC and HC (p < 0.01). ROC curves suggested the favorable diagnostic value of hsa_circ_0062142 and hsa_circ_0001666 (AUC = 0.803 and 0.858, respectively, p < 0.01). In silico analysis indicated that these circRNAs may be involved in the progress of CD.

CONCLUSION

Hsa_circ_0062142 and hsa_circ_0001666 may play critical roles in the pathogenesis and serve as potential biomarkers of CD.

Circular RNA in colorectal cancer

Circular RNA (circRNA) is a highly abundant type of single-stranded non-coding RNA. Novel research has discovered many roles of circRNA in colorectal cancer (CRC) including proliferation, metastasis and apoptosis. Furthermore, circRNAs also play a role in the development of drug resistance and have unique associations with tumour size, staging and overall survival in CRC that lend circRNAs the potential to serve as diagnostic and prognostic biomarkers. Among cancers worldwide, CRC ranks second in mortality and third in incidence. In order to have a better understanding of the influence of circRNA on CRC development and progression, this review summarizes the role of specific circRNAs in CRC and evaluates their potential value as therapeutic targets and biomarkers for CRC. We aim to provide insight in the development of therapy and clinical decision-making.

Circ_ 0115744 acts as miR-144 sponge to promote and predict the metastasis of colorectal cancer

Colorectal cancer (CRC) is one of the most common human malignant tumors in recent years. Although multiple approaches have been developed for the diagnosis and therapy of CRC, the overall survival rates of patients with metastatic and recurrent CRC remain poor. In the present study, we used the high-throughput microarray technology to screen circular RNAs (circRNAs) as a potential fingerprint for CRC. We mainly aimed to screen potential biomarkers for liver metastasis by performing risk score analysis. We detected the upregulated expression of circ_0115744 in patients with CRC with liver metastasis (CRLM). Further investigation using a validation set indicated that circ_0115744 might be considered as a fingerprint for CRLM. Functionally, the overexpression of circ_0115744 significantly promoted the invasion of CRC cell lines, while decreased expression of circ_0115744 suppressed cell invasion in vitro. Mechanistic analysis showed that circ_0115744 acted as a competing endogenous RNA of miR-144 to diminish the repressive effect of miR-144 on its target EZH2. In conclusion, we found that increased expression of circ_0115744 could differentiate CRLM from CRC and that the newly identified circ_0115744/miR-144/EZH2 axis was involved in the progression of CRC, which might be used as a potential diagnostic and therapeutic target for patients with CRC.

Cancer-related circular RNA: diverse biological functions

Noncoding RNAs, including long noncoding RNAs (lncRNAs), microRNAs (miRNAs) and circular RNAs (circRNAs), are involved in regulating biological functions. In recent decades, miRNAs and lncRNAs have both inspired a wave of research, but the study of circRNA functions is still in its infancy. Studies have found that circRNAs actively participate in the occurrence and development of various diseases, which emphasizes the importance of circRNAs. Here, we review the features and classification of circRNAs and summarize their functions. Then, we briefly describe how to analyze circRNAs by bioinformatics procedures. In addition, the relationship between circRNAs and cancers is discussed with an emphasis on proving whether circRNAs can be potential biomarkers for the prognosis and diagnosis of cancer.

Identification of functional circRNA/miRNA/mRNA regulatory network for exploring prospective therapy strategy of colorectal cancer

Circular RNA (circRNA) has been reported to have great scientific significance and clinical value in multiple cancers including colorectal cancer (CRC). However, the biological function of most circRNAs in CRC is still in its infancy. Herein, we discovered the differential expressed circRNAs (DECs) between CRC tissues and matched adjacent using deep RNA sequencing and further confirmed the DECs expression by combining with another Gene Expression Omnibus dataset. Furthermore, we validated the expression of the top four upregulated circRNAs (hsa_circ_0030632, hsa_circ_0004887, hsa_circ_0001550, and hsa_circ_0001681) in both of paired CRC tissues and CRC cell lines. Then, a circRNA/microRNA/messenger RNA regulatory network was established and the Gene Ontology analysis and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis showed these four circRNAs participated in various biological processed including apoptotic process and multiple metabolic processes. Moreover, based on the regulatory network, three bioactive compounds (pergolide, pivampicillin, and methylergometrine) for the treatment of CRC were also found. In conclusion, this study improved our understanding of circRNAs and may also facilitate the finding of promising targets and biomarkers in CRC.

Circular RNAs: Emerging Role in Cancer Diagnostics and Therapeutics

Circular RNAs (circRNAs) are rapidly coming to the fore as major regulators of gene expression and cellular functions. They elicit their influence via a plethora of diverse molecular mechanisms. It is not surprising that aberrant circRNA expression is common in cancers and they have been implicated in multiple aspects of cancer pathophysiology such as apoptosis, invasion, migration, and proliferation. We summarize the emerging role of circRNAs as biomarkers and therapeutic targets in cancer.

Circular RNAs Serve as Novel Biomarkers and Therapeutic Targets in Cancers

Circular RNAs (circRNAs) are a class of non-coding RNAs (ncRNAs) that structurally form closed loops without 5'-end cap and 3'-end poly(A) tail unlike linear RNAs. CircRNAs are widely present in eukaryotic cells with the capabilities of structural stability, high abundance and cell- /tissue-specific expression. A growing body of researches suggest that the dysregulated circRNAs are intimately relevant to the occurrence and development of cancer. In this review, we mainly discuss the differentially expressed circRNAs in cancer tissues, plasma and exosomes, which makes it possible for clinicians to use certain circRNAs as novel biomarkers for cancer diagnosis and prognosis. In particular, we primarily focus on circRNAs as potential therapeutic targets, which will provide promising applications in cancer gene therapy.

Circular RNA is a popular molecule in tumors of the digestive system (Review)

Most tumors of the digestive system, including esophageal, gastric, liver and colorectal cancer, are malignant tumors that are associated with rates of high morbidity and mortality. The lack of effective methods for early diagnosis is an important cause of poor prognosis for these malignancies. Circular RNAs (circRNAs) belong to a family of endogenous, covalently closed non‑coding RNAs that are characterized as having no 5' cap structures or 3' poly‑A tails. Shortly following discovery, circRNAs were considered to be a product of mis‑splicing and have no significant biological function. However, in recent years, accumulating evidence is demonstrating that they serve key roles in tumorigenesis and have the potential to serve as diagnostic markers. The present article summarizes the biogenesis and function of circRNAs and reviews their role in seven common types of tumor of the digestive system whilst exploring their potential as tumor markers and the significant roles they can serve in the digestive system, in addition to providing a referencing point for future studies of digestive system malignancies.

The function and mechanism of circular RNAs in gastrointestinal tumours

Gastrointestinal tumours are tumours that originate in the digestive tract and have extremely high morbidity and mortality. The main categories include: oesophageal, gastric, and colorectal cancers. Circular RNAs are a new class of non‐coding RNAs with a covalent closed‐loop structure without a 5’ cap or a 3’ poly A tail, which can encode a small amount of polypeptide. Recent studies have shown that circRNAs are involved in multiple biological processes during the development of gastrointestinal tumours including proliferation, invasion and metastasis, radio‐ and chemoresistance, and inflammatory responses. Also, the clinical and pathological characteristics of the patient, such as staging and lymph node metastasis, are closely associated with the expression level of circRNAs. Further investigation of the function and the role of circRNAs in the development of gastrointestinal tumours will provide new directions for its clinical diagnosis and treatment.

CircFADS2: A potential prognostic biomarker of colorectal cancer

IMPACT STATEMENT

Colorectal cancer (CRC) is the third most common malignancy worldwide with the second highest mortality rate. Although multidisciplinary cooperative therapies are helpful for improving the survival of CRC patients, the prognosis remains poor. Therefore, it is imperative to seek new biomarkers for the development of individualized treatment for each CRC patient. Circular RNA, an endogenous transcript with specific covalent closed loop, exhibits higher stability, conservation and expression abundance than the corresponding linear component and thus may be utilized as a promised biomarker. Although the majority of studies have focused on circular RNA expression profiling in various types of cancers, evidence supporting their critical role in the diagnosis and prognosis of CRC is limited. This study aimed to screen and identify novel circular RNA biomarkers of CRC by chip analysis and qPCR verification, and to highlight their potential as targets for CRC prognosis, and therapy.

Prognostic and diagnostic value of circRNA expression in colorectal carcinoma: a meta-analysis

BACKGROUND

Circular RNAs (circRNAs) are research hotspots in the network of noncoding RNAs in numerous tumours. The purpose of our study was to evaluate the clinicopathological, prognostic and diagnostic value of circRNAs in colorectal cancer.

METHODS

The PubMed, Cochrane Library, and Web of Science online databases were searched for relevant studies before May 15, 2019. Pooled hazard ratios (HRs) and odds ratios (ORs) with 95% confidence intervals (CIs) were calculated to assess the association between circRNAs expression, and overall survival (OS) and clinical parameters. Pooled sensitivity, specificity, and the area under the curve (AUC) were employed to assess the diagnostic value of circRNAs.

RESULTS

A total of 19 studies were enrolled in this meta-analysis, with 11 on clinicopathological parameters, 8 on prognosis and 7 on diagnosis. For clinicopathological and prognostic value, elevated expression of oncogenic circRNAs was correlated with poor clinical parameters (tumor size: OR = 1.769, 95% CI: 1.097-2.852; differentiation grade: OR = 1.743, 95% CI: 1.032-2.946; TNM stage: OR = 3.320, 95% CI: 1.529-7.207; T classification: OR = 3.410, 95% CI: 2.088-5.567; lymph node metastasis: OR = 3.357, 95% CI: 2.160-5.215; distal metastasis: OR = 4.338, 95% CI: 2.503-7.520) and worse prognosis (HR = 2.29, 95% CI: 1.50-3.52). However, elevated expression of tumor-suppressor circRNAs was correlated with better clinical parameters (differentiation grade: OR = 0.453, 95% CI: 0.261-0.787; T classification: OR = 0.553, 95% CI: 0.328-0.934; distal metastasis: OR = 0.196, 95% CI: 0.077-0.498) and favorable prognosis (HR = 0.37, 95% CI: 0.22-0.64). For diagnostic value, the pooled sensitivity, specificity, and AUC were 0.82 (95% CI, 0.75-0.88), 0.72 (95% CI, 0.66-0.78), and 0.82 (95% CI, 0.78-0.85), respectively.

CONCLUSIONS

These results indicate that circRNAs may be potential biomarkers for the diagnosis and prognosis of colorectal cancer.

The Regulatory Functions of Circular RNAs in Digestive System Cancers

Circular ribonucleic acids (circRNAs), which are a type of covalently closed circular RNA, are receiving increasing attention. An increasing amount of evidence suggests that circRNAs are involved in the biogenesis and development of multiple diseases such as digestive system cancers. Dysregulated circRNAs have been found to act as oncogenes or tumour suppressors in digestive system cancers. Moreover, circRNAs are related to ageing and a wide variety of processes in tumour cells, such as cell apoptosis, invasion, migration, and proliferation. Moreover, circRNAs can perform a remarkable multitude of biological functions, such as regulating splicing or transcription, binding RNA-binding proteins to enable function, acting as microRNA (miRNA) sponges, and undergoing translated into proteins. However, in digestive system cancers, circRNAs function mainly as miRNA sponges. Herein, we summarise the latest research progress on biological functions of circRNAs in digestive system cancers. This review serves as a synopsis of potential therapeutic targets and biological markers for digestive system cancer.

Circ_0000218 plays a carcinogenic role in colorectal cancer progression by regulating miR-139-3p/RAB1A axis

Accumulating researches have confirmed that circRNA abnormal expression plays a prominent role in the progression of colorectal cancer (CRC). The role of circ_0000218 in CRC and its potential mechanism are not clear. In this study, real-time polymerase chain reaction (RT-PCR) was employed to measure the circ_0000218, miR-139-3p and RAB1A mRNA expression in CRC tissues and cells. Immunohistochemistry and western blot were conducted to determine the RAB1A expression in CRC tissues and cells, respectively. Colony formation assay and BrdU method were employed to monitor the effect of circ_0000218 on cell proliferation. Transwell assay was adopted to detect cell migration and invasion. Dual luciferase reporter assay and RNA immunoprecipitation assay were adopted to confirm the targeting relationship between circ_0000218 and miR-139-3p, miR-139-3p and RAB1A. We demonstrated that circ_0000218 was notably upregulated in CRC tissues and cell lines, and its high expression level was markedly linked to the increase of T staging and local lymph node metastasis. Circ_0000218 overexpression enhanced the proliferation and metastasis of CRC cells while knocking down circ_0000218 caused the opposite effects. We also observed that miR-139-3p was negatively regulated by circ_0000218, while RAB1A was positively regulated by it. Collectively, this study suggested that circ_0000218 upregulated RAB1A and promoted CRC proliferation and metastasis via sponging miR-139-3p.

Circular RNAs: The crucial regulatory molecules in colorectal cancer

Colorectal cancer (CRC) is one of the most common malignancies worldwide. Recent studies have shown that circular RNAs (circRNAs) play critical roles in the pathogenesis and progression of CRC. CircRNAs are a special class of endogenous non-coding RNAs (ncRNAs) that harbor covalently closed ring structure with high conservation and stability, which are expressed in a tissue- and developmental-stage-specific manner. A growing body of evidence suggests that circRNAs are abnormally expressed in CRC tissues, cell lines and plasma, and are closely linked with CRC clinical malignant features. CircRNAs participate in various biological processes of CRC cells, including cell proliferation, apoptosis, senescence, migration and invasion and so on, through acting as "microRNA (miRNA) sponges", binding to protein and even translating protein. In the present review, we systematically introduce the CRC-related circRNAs and their functional mechanisms, as well as the potential applications for CRC diagnosis and prognosis.

Circular RNA hsa_circ_0004277 contributes to malignant phenotype of colorectal cancer by sponging miR-512-5p to upregulate the expression of PTMA

In recent years, extensive reports have been published concerning the molecular mechanism underlying the occurrence and progression of colorectal cancer. Circular RNAs (circRNAs) have been identified as important modulators in the biological processes of colorectal cancer. Microarray analysis unveiled that differential circ-0004277 expression was identified in tissue samples of colorectal cancer. High circ-0004277 expression was then verified in tissue samples and cell lines of colorectal cancer via qRT-PCR. Kaplan-Meier analysis was used for identifying the association between circ-0004277 expression and the overall survival rate of colorectal cancer patients. A relationship existed between higher circ-0004277 expression and decreased overall survival rate of colorectal cancer patients. From a functional perspective, circ-0004277 knockdown accelerated cell apoptosis and restrained cell proliferation of colorectal cancer. From mechanistic perspective, circ-0004277 upregulated PTMA by sponging miR-512-5p. Rescue assay was used for verifying the roles of the circ-0004277-miR-512-5p-PTMA axis. Both miR-512-5p and PTMA participated in circ-0004277-mediated colorectal cancer cell proliferation based on experiments. In summary, our study showed that circ-0004277 promoted the proliferation of colorectal cancer cells as a miR-512-5p sponge to upregulate the PTMA expression.

Circular RNAs and gastrointestinal cancers: Epigenetic regulators with a prognostic and therapeutic role

Both environmental and genetic factors are involved in the initiation and development of gastrointestinal cancer. Covalent closed circular RNAs (circRNAs) are produced by a mechanism called "back-splicing" from mRNAs. They are highly stable and show cell and tissue specific expression patterns. Although some functions such as "microRNA sponge" and "RNA binding protein sponge" have been reported for a small number of circRNAs, the function of thousands of other circRNAs is still unknown. Dysregulation of circRNAs has been reported in many GI cancers and are involved in metastasis and invasion. CircRNAs have been reported to be useful as prognostic markers and targets for developing new treatments. We first describe the properties and biogenesis of circRNAs. We then summarize recent reports about circRNA functions, expression status, and their potential to be used as biomarkers in GI cancers including, gastric cancer, colorectal cancer, esophageal cancer, hepatocellular carcinoma, gallbladder cancer and pancreatic cancer.

A pair-wise meta-analysis highlights circular RNAs as potential biomarkers for colorectal cancer

Background

Circular RNAs (circRNAs) have emerged as a special subset of endogenous RNAs that are implicated in tumorigenesis and cancer progression. Herein we aim to carry out a meta-analysis to evaluate the clinicopathologic, diagnostic and prognostic significance of circRNA expression in colorectal cancer (CRC).

Methods

A systematic search of online databases was performed for original articles published in English, which investigated the diagnostic accuracy, prognostic utility, and clinicopathologic association of circRNA(s) in CRC. Data were strictly extracted and study bias was judged using the Quality Assessment for Studies of Diagnostic Accuracy II (QUADAS II) and Newcastle-Ottawa Scale (NOS) checklists.

Results

A total of 13 studies, involving 1430 patients with CRC, were included in the meta-analysis. The clinicopathologic study showed that abnormally expressed circRNAs were correlated with tumor diameter (P = 0.0350), differentiation (P = 0.0038), lymphatic metastasis (P = 0.0119), distant metastasis (P < 0.0001), TNM stage (P = 0.0002), and depth of invasion (P = 0.001) in patients with CRC. The summary area under the curve (AUC) of circRNA for the discriminative efficacy between patients with and without CRC was estimated to be 0.79, corresponding to a weighted sensitivity of 0.77 [95% confidence interval (CI): 0.74–0.79], specificity of 0.67 (95%CI: 0.64–0.70), and diagnostic odds ratio (DOR) of 7.52 (95%CI: 4.66–12.12). Survival analysis showed that highly expressed circRNAs were correlated with significantly worse overall survival (OS) [hazard ratio (HR) = 2.66, 95%CI: 2.03–3.50, P = 0.000; X² = 4.34, P = 0.740, I² = 0.0%], whereas lower expression of circRNAs was associated with prolonged OS (weighted HR = 0.30, 95%CI: 0.17–0.53, P = 0.000; X² = 1.34, P = 0.909, I² = 0.0%). Stratified analysis in circRNA expression status, and test matrix also showed robust results.

Conclusion

Abnormally expressed circRNAs may be auxiliary biomarkers facilitating CRC diagnosis, and promising prognostic biomarkers in predicting the survival of CRC patients.

Circular RNA Expression Profiles in Vaginal Epithelial Tissue of Women With Lubrication Disorders

INTRODUCTION

Recently, circular RNA (circRNA) has been proved to occupy a vital pathological position in many diseases by acting as microRNAs sponges. However, the role of circRNA in female sexual dysfunction (FSD), especially in lubrication disorders (LDs), remains unclear.

AIM

The aim of this study was to detect circRNA expression in LDs, analyzed target genes, and pathways regulated by the differently expressed circRNAs.

METHODS

In this study, next-generation sequencing was first conducted to produce circRNA expression profiles of FSD groups and normal control groups. Furthermore, differences in expression of 6 randomly selected circRNAs were confirmed through real-time quantitative polymerase chain reaction. Kyoto Encyclopedia of Genes and Genomes biological pathway analysis and Gene Ontology showed that immune processes and infection could be involved in the development of FSDs.

MAIN OUTCOME MEASURE

CircRNA expression in vaginal epithelial tissue obtained from women with LDs have been detected. Gene Ontology, Kyoto Encyclopedia of Genes and Genomes biological pathway analysis, and circRNA-microRNA interaction predictions were investigated.

RESULTS

Totally, 7,746 circRNAs of vaginal epithelial tissue from women of 2 groups were sequenced. Preliminary judgment revealed that there were 73 circRNAs that have significant differential expression, including 53 downregulated circRNAs and 20 upregulated circRNAs. Research results also displayed that the majority of circRNAs has multiple binding sites of microRNAs, including miR-137, which has been reported to be linked to FSD.

CLINICAL IMPLICATIONS

We predicted 10 circRNAs paired with hsa-miR-137-5p, but the mechanism of circRNA involvement in disease development remains to be further explored.

STRENGTHS & LIMITATIONS

For the first time, the research disclosed the potential pathogenesis of LDs. However, we only analyzed the expression profile of circRNA in FSD, no specific mechanism was further confirmed or proposed. We still have a preliminary understanding, and more research is needed to explore the target of FSD treatment.

CONCLUSION

The results suggest that circRNAs have different expression in the FSD groups and play a vital part in the occurrence and development of FSD. Zhang J, Xia H, Zhang A, et al. Circular RNA Expression Profiles in Vaginal Epithelial Tissue of Women With Lubrication Disorders. J Sex Med 2019;16:1696-1707.

Diagnostic performance of circular RNAs in human cancers: A systematic review and meta-analysis

BACKGROUND

Recently, accumulating evidence have revealed that circular RNA (circRNA) was deregulated in multiple types of cancer, suggesting that circRNA might serve as a novel candidate biomarker of cancer diagnosis. However, inconsistent results have become an obstacle in applying circRNAs to clinical practice. The aim of this study is to evaluate diagnostic value of circRNAs among cancers.

METHODS

A literature search was systematically performed among PubMed, Sciencedirect, Cochrane Library, Web of Science, Wanfang, and Chinese National Knowledge Infrastructure databases up to February 15, 2019. The pooled sensitivity (SEN), specificity (SPE), positive likelihood ratios, negative likelihood ratios, diagnostic odds ratio, and area under the SROC curve (AUC) were applied to evaluate diagnostic performance of circRNAs.

RESULTS

In total, the study included 64 studies with single circRNA and 13 studies with combined circRNAs. Overall, the study presented that a single circRNA had moderate diagnostic value, with a SEN of 0.75, a SPE of 0.76, and an AUC of 0.82. The plasma circRNAs had higher diagnostic accuracy than tissue (AUC: 0.87, 95% confidence interval [CI]: 0.83-0.89 for plasma/serum subgroup; AUC: 0.79, 95% CI: 0.75-0.82 for tissue subgroup). Furthermore, the combined circRNAs had good diagnostic efficacy for GC, with a SEN of 0.89, a SPE of 0.94, and an AUC of 0.97, respectively.

CONCLUSION

This study confirmed that circRNAs may be candidate biomarkers for cancer diagnosis. In particular, diagnosis of combined circRNAs will be a new alternative applied to clinical research and practice for cancer.

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.

Emerging roles of circular RNAs in colorectal cancer

Circular RNAs (circRNAs) are a newly discovered class of endogenous non-coding RNAs. Owing to the development of high-throughput sequencing, researchers have identified thousands of circRNAs. Emerging evidence suggests that circRNAs are involved in various tumor cell processes, including proliferation, apoptosis, invasion and migration. Because of their high stability and abundance, tissue-specific expression, and easy detection, circRNAs are considered ideal biomarkers for cancer diagnosis and prognosis. An increasing number of studies have recently demonstrated that circRNAs are closely associated with colorectal cancer (CRC). CRC is the third most common cancer and the second leading cause of cancer-related death globally. Thus, understanding the molecular mechanisms involved in the development and progression of CRC is vital. In this review, we summarize the current literature regarding human circRNAs related to CRC and present an overview of the potential clinical implications of circRNAs with respect to CRC.

Hsa_circ_0009361 acts as the sponge of miR-582 to suppress colorectal cancer progression by regulating APC2 expression

Circular RNA (circRNA) plays an important role in the development of human malignant tumors. Recently, an increasing number of circRNAs have been identified and investigated in various tumors. However, the expression pattern and biological function of circRNAs in colorectal cancer (CRC) still remain largely unexplored. In the present study, hsa_circ_0009361 was significantly down-regulated in CRC tissues and cells. Low expression level of hsa_circ_0009361 promoted the proliferation, epithelial-mesenchymal transition (EMT), migration, and invasion of CRC cells. Hsa_circ_0009361 was identified as the sponge of miR-582 by fluorescence in situ hybridization (FISH), RNA immunoprecipitation (RIP), and luciferase reporter assays. Overexpression of hsa_circ_0009361 up-regulated the expression of adenomatous polyposis coli 2 (APC2) and inhibited the activity of the Wnt/β-catenin pathway by competitively combining with miR-582. Exogenous miR-582 and APC2 interventions could reverse the multiple biological functions mediated by hsa_circ_0009361 in CRC cells. In vivo experiments also confirmed that hsa_circ_0009361 inhibited the growth and metastasis of CRC. Hsa_circ_0009361 acted as a tumor suppressive sponge of miR-582, which could up-regulate the expression of APC2, inhibit the Wnt/β-catenin signaling, and suppress the growth and metastasis of CRC. Collectively, the hsa_circ_0009361/miR-582/APC2 network could be employed as a potential therapeutic target for CRC patients.

Diagnostic value of circular RNAs as effective biomarkers for cancer: a systematic review and meta-analysis

Background: Increasing evidence has identified circular RNAs (circRNAs) as ideal molecular biomarkers for cancer diagnosis, therapy, and prognosis. However, the overall diagnostic efficiency of circRNAs remains unclear. Thus, this meta-analysis aimed to comprehensively evaluate the diagnostic accuracy of circRNA expression profiles for cancer.

Methods: A literature search of online databases was conducted to identify all eligible studies. The quality of the studies was assessed using the Quality Assessment of Diagnostic Accuracy Studies 2 tool. All statistical analyses were executed using STATA 14.0, Meta-DiSc 1.4, and Review Manager 5.2 software.

Results: A total of 32 studies, involving 2,400 cases and 2,295 controls, were included in the diagnostic meta-analysis. The pooled sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, diagnostic odds ratio, and area under the curve were 0.79 (95% CI: 0.73–0.84), 0.73 (95% CI: 0.67–0.79), 2.9 (95% CI: 2.5–3.5), 0.29 (95% CI: 0.24–0.36), 10 (95% CI: 8–13), and 0.83 (95% CI: 0.79–0.86), respectively. The overall analysis suggested that circRNAs are useful diagnostic biomarkers for cancer. Subgroup analysis indicated that plasma samples had a better diagnostic performance than cancer tissue samples for cancer detection. Studies involving ≥100 cases or gastric cancer showed higher sensitivities than those including <100 cases or other cancers.

Conclusion: This meta-analysis revealed that circRNAs were significantly correlated with cancer diagnosis. In addition, circRNAs had good diagnostic accuracy and might serve as effective diagnostic biomarkers for cancer.

Circular RNA circ_0002138 is down-regulated and suppresses cell proliferation in colorectal cancer

Circular RNAs (circRNAs) have been recently identified as widespread and diverse endogenous noncoding RNAs that may harbor vital functions in humans. However, the role of circRNAs in the process of tumorigenesis and development of colorectal cancer (CRC) remains hitherto vague. In this study, we investigated the expression level of circ_0002138 in 35 paired CRC tissues by quantitative real-time polymerase chain reaction (qRT-PCR) and found that circ_0002138 was stably down-regulated in CRC tissues compared to paired adjacent normal tissues (P < 0.001). Fisher's exact test was further conducted to analyze the relationship between circ_0002138 expression level and clinico pathological factors of CRC patients. Circ_0002138 expression was significantly correlated with age. To evaluate the diagnostic value of circ_0002138, a receiver operating characteristic (ROC) curve was used and the area under the ROC curve was 0.7249. Additionally, functional analysis demonstrated that circ_0002138 significantly inhibited CRC cell proliferation in vitro. Overall, our data suggest that circ_0002138 may become a novel potential biomarker for diagnosis and treatment target of CRC.

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.

Overexpressed circ_0067934 acts as an oncogene to facilitate cervical cancer progression via the miR-545/EIF3C axis

Circular RNAs were recently identified as a novel type of noncoding RNAs. An increasing number of reports have demonstrated their essential regulatory roles in various biological processes and human diseases, including cancer. However, the role of circRNA in cervical cancer (CC) remains largely unknown. In the current study, we investigated the physiological functions of circ_0067934 during CC development and progression. We found that circ_0067934 was overexpressed in CC tissues and cell lines. Circ_0067934 upregulation was associated with advanced stage, lymph node metastasis, and poor prognosis in CC patients. Knockdown of circ_0067934 suppressed the proliferation, colony formation, migration, invasion, and epithelial-mesenchymal transition of CC cells in vitro. Circ_0067934 loss also inhibited CC tumor growth in vivo. Mechanistically, silencing circ_0067934 increased miR-545 expression. MiR-545 repressed EIF3C expression through targeting its 3'-untranslated region. MiR-545 suppressed the proliferation, migration, and invasion of CC cells, whereas restoration of EIF3C could rescue the effects of circ_0067934 knockdown. Taken together, our findings revealed that circ_0067934 promotes CC progression via miR-545/EIF3C axis. Our study may provide a new insight into the pathogenesis of CC.

A novel circulating hsa_circ_0081001 act as a potential biomarker for diagnosis and prognosis of osteosarcoma

Chemo-resistance and lung metastasis have been the two obstacles in the osteosarcoma (OS) treatment, which is still lack of effective biomarkers for prediction, diagnosis and treatment. Circular RNA (circRNA) is a new type of endogenous noncoding RNA that could serve as ideal biomarkers in cancer because of its stable loop structure. However, little is known about the diagnostic value of circRNAs in OS as well as their associations with clinicopathologic characteristics of OS patients. In the current study, we identified a novel circRNA, hsa_circ_0081001, screened by the RNA sequencing in the three paired chemo-resistant and chemo-sensitive OS cell lines (MG63/DXR vs MG63, KHOS/DXR vs KHOS, U2OS/DXR vs U2OS), and found that hsa_circ_0081001 was significantly up-regulated in the OS cell lines, tissues and serums, associated with poor overall survival and cox multivariate analysis showed that hsa_circ_0081001 was a novel independent prognostic factor for OS patients. Then, receiver operating characteristic (ROC) curve analysis revealed that hsa_circ_0081001 could act as a biomarker for the OS diagnosis and prognosis prediction, better than alkaline phosphatase (ALP) and lactate dehydrogenase (LDH). In addition, we preliminarily found that hsa_circ_0081001 expression level may dynamically monitor and reflect the condition changes of OS patients in a small-scale prospective clinical pretest. In conclusion, our study suggested that circulating hsa_circ_0081001 could serve as a potential biomarker and therapeutic target for OS patients.

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.

Circular RNAs: Promising Biomarkers for Human Diseases

Circular RNA (circRNA) is a group of endogenous noncoding RNA characterized by a covalently closed cyclic structure lacking poly-adenylated tails. Recent studies have suggested that circRNAs play a crucial role in regulating gene expression by acting as a microRNA sponge, RNA binding protein sponge and translational regulator. CircRNAs have become a research hotspot because of their close association with the development of diseases. Some circRNAs are reportedly expressed in a tissue- and development stage-specific manner. Furthermore, due to other features of circRNAs including stability, conservation and high abundance in body fluids, circRNAs are believed to be potential biomarkers for various diseases. In the present review, we provide the current understanding of biogenesis and gene regulatory mechanisms of circRNAs, summarize the recent studies on circRNAs as potential diagnostic and prognostic biomarkers, and highlight the major advantages and limitations of circRNAs as novel biomarkers based on existing knowledge.

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.

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.

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.

Hsa_circ_0007534 as a blood-based marker for the diagnosis of colorectal cancer and its prognostic value

BACKGROUND

Many studies have shown that differentially expressed circular RNA (circRNA) in plasma can serve as biomarkers in non-invasive detection of cancers during screening. However, the clinical significance of plasma circRNA in the diagnosis of colorectal cancer (CRC) is still not clear. Therefore, we examined expression of hsa_circ_0007534 in plasma to verify whether it can be utilized to diagnose and monitor CRC in routine clinical practice.

METHODS

112 CRC patients and 46 healthy controls were recruited to participate in our study. The levels of hsa_circ_0007534 in plasma samples and tumor tissues were identified by real-time quantitative polymerase chain reaction (RT-qPCR). The diagnostic value was evaluated using receiver operating characteristics (ROC) curves and the area under the ROC curves (AUC). The Kaplan-Meier survival curve was used to evaluate whether the expression level of hsa_circ_0007534 was associated with overall survival rate.

RESULTS

Compared with the healthy control group, hsa_circ_0007534 expression was significantly increased in plasma from CRC patients. Increased hsa_circ_0007534 expression level in plasma was associated with progression of clinical classifications, metastatic phenotype, and poor differentiation in CRC patients. ROC analysis showed that hsa_circ_0007534 could distinguish CRC patients from healthy controls with high AUC (0.780), sensitivity (0.92) and specificity (0.522). Finally, high hsa_circ_0007534 expression was positively correlated with poor prognosis in CRC patients.

CONCLUSION

All of the results suggest that hsa_circ_0007534 may be a potential cancer marker of patients with CRC and may associate with poor prognosis.