Comprehensive profile of differentially expressed circular RNAs reveals that hsa_circ_0000069 is upregulated and promotes cell proliferation, migration, and invasion in colorectal cancer

The mechanism and function of circular RNAs in human diseases

Circular RNAs (circRNAs) are a recently discovered form of RNA. Initially, circRNAs were believed to result from errors during the process of gene transcription. However, after further investigation, scientists suggested that circRNAs are of great biological significance. CircRNAs show stability, conservation, abundance, and tissue and stage specificity. They can also function as miRNA sponges, regulate gene expression, and interact with proteins to affect cell behavior. Emerging evidence has also demonstrated that circRNAs participate or show abnormal expression in diseases, including central nervous system diseases, cardiovascular diseases and cancers, indicating their marked potential in the prediction and prognosis of diseases and clinical treatment.

Changes in circular RNA expression patterns during human foetal brain development

Circular RNAs (circRNAs) are a recently identified class of long non-coding RNAs and their expression is regulated in a tissue- and developmental stage-specific manner. Recent studies indicate the potential regulatory role that circRNAs may have, particularly in the brain, where they are most abundant. This study aims to elucidate changes in circRNA patterns during human embryonic brain development. We detected a number of differentially expressed genes that showed distinct expression profiles for circular and linear transcripts despite having originated from the same genes, implicating a dichotomy in the regulation of these two RNA species. Altogether our study showed that circular and linear RNAs have independent expression patterns, and that circular transcriptomes from different developing stages have distinct characteristics in terms of transcript abundance and isoform diversity.

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.

Molecular roles and function of circular RNAs in eukaryotic cells

Protein-coding and noncoding genes in eukaryotes are typically expressed as linear messenger RNAs, with exons arranged colinearly to their genomic order. Recent advances in sequencing and in mapping RNA reads to reference genomes have revealed that thousands of genes express also covalently closed circular RNAs. Many of these circRNAs are stable and contain exons, but are not translated into proteins. Here, we review the emerging understanding that both, circRNAs produced by co- and posttranscriptional head-to-tail "backsplicing" of a downstream splice donor to a more upstream splice acceptor, as well as circRNAs generated from intronic lariats during colinear splicing, may exhibit physiologically relevant regulatory functions in eukaryotes. We describe how circRNAs impact gene expression of their host gene locus by affecting transcriptional initiation and elongation or splicing, and how they partake in controlling the function of other molecules, for example by interacting with microRNAs and proteins. We conclude with an outlook how circRNA dysregulation affects disease, and how the stability of circRNAs might be exploited in biomedical applications.

Circular RNA and its mechanisms in disease: From the bench to the clinic

The emerging recognition of the functional roles of circular RNAs (circRNAs) has given rise to a new perspective regarding our understanding of cellular physiology and disease pathogenesis. Unlike linear RNAs, circRNAs are covalently closed continuous loops that act as gene regulators in mammals, and their sequence composition determines the mode of circRNA biogenesis. The availability and integrated use of advanced genome analysis platforms have allowed the identification of a large number of these molecules. Their high abundance, stability and evolutionary conservation among species endow circRNAs with numerous potential functions, such as acting as microRNA (miRNA) sponges or binding to RNA-associated proteins to form RNA-protein complexes that regulate gene transcription. Moreover, circRNAs have been shown to be expressed in a tissue-specific manner and in pathological conditions, which has stimulated significant interest in their role in human disease and cancer. In this concise review, we outline the characteristics, functions and mechanisms of action of circRNAs as well as their involvement in different diseases. Although their exact roles and mechanisms of gene regulation remain to be clarified, circRNAs have potential applications as disease biomarkers and novel therapeutic targets.

Hsa_circ_0001649: A circular RNA and potential novel biomarker for colorectal cancer

The circRNAs are differentially expressed in a wide range of cancers in regulating their initiation and progression, and could be used to make a diagnosis for some diseases like tumor as a new biomarker. However, the correlation and the mechanism of action between circRNAs and colorectal cancer (CRC) are still unclear. In this study, by using qRT-PCRs, we detected the expression level of hsa_circ_0001649 in tissue and serum samples from CRC patients, and the cultured cell has been detected. We found that the hsa_circ_0001649 in CRC is significantly lower than the expression level of correspondent nontumorous tissues (n = 64, P < 0.01). We also tested the HCT116 cell lines, and the similar result is observed (n = 15, P < 0.01). Moreover, we detected the serum samples obtained before and after surgery, showing significantly the expression level of hsa_circ_0001649 in the same patient is up-regulated after surgery (n = 18, P < 0.01). Besides, we analyzed the correlation between clinicopathological date and the expression level of hsa_circ_0001649, we found that hsa_circ_0001649 expression level is closely associated with pathological differentiation (P = 0.037), and the result also illustrated that the expression level of hsa_circ_0001649 is no direct correlation with age, gender, TMN stage, lymphatic metastasis, CEA, CA19-9, and CA-724 levels. The area under the receiver operating characteristic (ROC) curve was 0.857. In conclusion, this study showed that the expression level of hsa_circ_0001649 was down-regulated in CRC and could use it as a new biomarker for specific and sensitive inspection of CRC.

Downregulated circular RNA hsa_circ_0001649 regulates proliferation, migration and invasion in cholangiocarcinoma cells

Cholangiocarcinoma (CCA) is one of the most aggressive malignancies with increasing worldwide incidence and is characterized by unfavorable prognosis due to its early invasive characteristics and poor response to chemotherapy or radiotherapy. Accumulating evidence has indicated that aberrantly expressed circular RNAs (circRNAs) are involved in cancer development and progression. However, their clinical values and biological roles in CCA remain unclear. Hsa_circ_0001649, a novel cancer-related circRNA, has been previously reported to be downregulated in hepatocellular carcinoma and gastric cancer. In the present study, qRT-PCR was carried out to measure the expression of hsa_circ_0001649 in CCA tissue samples and cell lines, and the correlation between hsa_circ_0001649 expression and clinicopathologic features was analyzed. The biological functions of hsa_circ_0001649 in CCA cells were evaluated both in vitro and in vivo. As a result, hsa_circ_0001649 was aberrantly downregulated in CCA tissues and cells, and this downregulation was associated with tumor size and differentiation grade in CCA. In addition, hsa_circ_0001649 overexpression caused tumor suppressive effects via inhibiting cell proliferation, migration and invasion; inducing cell apoptosis in KMBC and Huh-28 cells. On the contrary, silencing of hsa_circ_0001649 caused the opposite phenotypes. Furthermore, tumor xenograft study confirmed the in vitro results. Collectively, our findings suggest that hsa_circ_0001649 might be a rational CCA-related therapeutic target.

Circular RNA: An emerging non-coding RNA as a regulator and biomarker in cancer

Circular RNA (circRNA) is a type of covalently closed non-coding RNA that may regulate gene expression in eukaryotes. The recent application of high-throughput RNA sequencing and bioinformatics approaches has revealed a large number of circRNAs in human cells. Emerging evidence indicates that many circRNAs have cell-type specific expression and are linked to physiological development and various diseases. Specially, circRNAs can either serve as oncogenic stimuli or tumor suppressors in cancer. circRNAs have also been shown to be enriched and stable in extracellular fluid, indicating the potential of circRNAs as cancer biomarkers. Here, we summarize the current knowledge of circRNAs, including their classification, biogenesis, properties, and databases, as well as their function and clinical implications in cancer.

Circular RNAs as Biomarkers for Cancer

As a type of novel noncoding RNAs, circular RNAs (circRNAs) have attracted great interest due to its different characteristics from linear RNAs. They are abundantly and stably present in the transcriptome of eukaryotic cells, with development stage specificity and high conservatism. Because circRNAs are not easily degraded by exonuclease RNase R, they can exist more stably in body fluids than linear RNAs. Based on these unique conditions, circRNAs have great potential value as clinical diagnostic and prognostic markers. As the research deepens, more and more evidences suggest that circRNAs may be closely associated with many diseases, especially cancer. Numerous studies have demonstrated the abnormal expression of circRNAs in cancer, and they can regulate the occurrence and progression of cancer by targeting key genes. Abundant circRNAs in tissues and cells can be released into saliva and blood. It is undeniable that circRNAs are a class of promising future biomarkers for cancer diagnosis and prognosis. Here we summarize the researches on circRNAs and cancer over the past few years. We expect this summary to be a stepping stone to further exploration of possible circRNAs as cancer biomarkers.

Circular RNAs: Biogenesis, Function, and a Role as Possible Cancer Biomarkers

Circular RNAs (circRNAs) are a class of noncoding RNAs (ncRNAs) that form covalently closed continuous loop structures, lacking the terminal 5' and 3' ends. CircRNAs are generated in the process of back-splicing and can originate from different genomic regions. Their unique circular structure makes circRNAs more stable than linear RNAs. In addition, they also display insensitivity to ribonuclease activity. Generally, circRNAs function as microRNA (miRNA) sponges and have a regulatory role in transcription and translation. They may be also translated in a cap-independent manner in vivo, to generate specific proteins. In the last decade, next-generation sequencing techniques, especially RNA-seq, have revealed great abundance and also dysregulation of many circRNAs in various diseases, suggesting their involvement in disease development and progression. Regarding their high stability and relatively specific differential expression patterns in tissues and extracellular environment (e.g., body fluids), they are regarded as promising novel biomarkers in cancer. Therefore, we focus this review on describing circRNA biogenesis, function, and involvement in human cancer development and address the potential of circRNAs to be effectively used as novel cancer diagnostic and prognostic biomarkers.

Circular RNAs: clinical relevance in cancer

Circular RNAs, as recently discovered new endogenous non-coding RNAs, are important gene modulators with critical roles in tumor initiation and malignant progression. With the development of RNA sequencing and microarray technologies, numerous of functional circRNAs have been identified in cancerous tissues and cell lines. Mechanistically, circRNAs function as miRNA sponges, miRNA reservoirs or parental gene expression regulators. In this review, we discuss the properties and functions of circRNAs and their clinical implication as promising biomarkers for cancer research. Moreover, some emerging fields, such as exosome-loaded and immune response-associated circRNAs, are also discussed, suggesting novel insights into the carcinogenesis and therapy associated with these molecules.

Systematic review of circular RNAs as tumor biomarkers for tumor detection

AIM

To assess the diagnostic value of circRNAs in detection of tumors through a systematic review.

METHODS

Articles were searched in CNKI, WanFang database, PubMed and Web of Science databases up to May 5, 2017 with the Title/Abstract words ("circular RNA" or "circRNA" and "cancer" or "tumor" or "carcinoma"). Two investigators extracted the data and assessed the quality of included articles using the Newcastle-Ottawa Scale (NOS) independently.

RESULTS

Thirty-two studies were finally included, which covered hepatocellular carcinoma, gastric cancer, colorectal cancer, and other cancers. The NOS scores of all included studies were 7. Among them, few studies clearly indicated that circRNAs can serve as potential biomarkers and provided the ROC curve, AUC (area under the curve), sensitivity, and specificity.

CONCLUSION

CircRNAs have significant potential to serve as biomarkers for the diagnosis of tumors. Further studies with larger number of patients will be needed to validate these findings.

Circular RNAs: emerging cancer biomarkers and targets

CircRNAs are a class of RNA molecules that structurally form closed loops. CircRNAs are abundant in eukaryotic transcripts and show certain levels of tissue and cell specificity. CircRNAs have been suggested to regulate gene expression at transcriptional, post-transcriptional, and translational levels. An increasing number of studies have shown that circRNAs play important roles in the development and progression of diseases including cancer. In particular, circRNAs have shown great potential in cancer diagnosis, prognosis, and therapy. In this review, we provide an overview of the biogenesis and characteristics of circRNAs, succinctly describe their functions, and comprehensively discuss about the recent advances in the roles of circRNAs in cancer with an emphasis on their clinical values.

Current research on circular RNAs associated with colorectal cancer

Representing a novel type of endogenous noncoding RNAs, circular RNAs (circRNAs) have recently gained much attention for their involvement in multiple biological processes. CircRNAs are ubiquitously expressed in eukaryotic cells and modulate gene expression by acting as sponges of microRNAs (miRNAs) or other proteins, such as RNA-binding proteins (RBPs). Due to their unique structure, circRNAs are more stable than linear RNAs. Expression profiles of circRNAs are associated with clinicopathological characteristics of colorectal cancer patients, such as differentiation, TNM classification and distant metastasis. Furthermore, circRNAs play crucial roles in multiple processes associated with malignant phenotypes, including cell proliferation/cycle, apoptosis and invasion. Improvements in RNA-sequencing methods have helped researchers to elucidate molecular interactions between circRNAs and colorectal cancer. This review provides a comprehensive overview of the features and functions of circRNAs, as well as insights into their roles in the onset and development of colorectal cancer. Combined with the reported results, the identification of circRNAs associated with colorectal cancer will certainly contribute to early detection and help to design treatment strategies for colorectal cancer. Screening for circRNAs may provide an accessible, noninvasive yet highly sensitive diagnosis for colorectal cancer. Furthermore, a better understanding of the roles of circRNAs may also provide a novel predictive feature in colorectal cancer therapy and prognosis.

The expression profile and clinical significance of circRNA0003906 in colorectal cancer

Colorectal cancer (CRC) remains a major health problem worldwide and the detailed mechanisms of CRC still need further understanding. Circular RNAs (circRNAs), a special class of endogenous RNAs, have emerged recently as a new potential player in governing fundamental biological process and cancer progression. In this study, we chose circRNA0003906 as a targeted circRNA to evaluate its expression pattern and clinical value in CRC patients. circRNA0003906 expression level in 6 CRC cell lines and 122 paired CRC tissues was measured by quantitative real-time polymerase chain reaction. Then, the potential correlation between circRNA0003906 expression level and clinicopathological factors of CRC patients was analyzed. Additionally, a receiver operating characteristic curve was built to evaluate the diagnostic value of circRNA0003906. Our results showed that circRNA0003906 expression level was dramatically downregulated in both CRC tissues and cell lines. Moreover, the downregulation of circRNA0003906 level significantly correlated with lymphatic metastasis and poor differentiation. In addition, the area under the receiver operating characteristic curve of circRNA0003906 for CRC was 0.818 (P<0.001). Taking consideration of all of these results, circRNA0003906 may be potentially involved in the colorectal cancerogenesis and serve as a potential biomarker for the diagnosis and treatment of CRC.

The role of circRNAs in cancers

Circular RNAs (circRNAs) are recently regarded as a naturally forming family of widespread and diverse endogenous noncoding RNAs (ncRNAs) that may regulate gene expression in mammals. At present, above 30000 circRNAs have already been found, with their unique structures to maintain stability more easily than linear RNAs. Several previous literatures stressed on the important role of circRNAs, whose expression was relatively correlated with patients’ clinical characteristics and grade, in the carcinogenesis of cancer. CircRNAs are involved in many regulatory bioprocesses of malignance, including cell cycle, tumorigenesis, invasion, metastasis, apoptosis, vascularization, through adsorbing RNA as a sponge, binding to RNA-binding protein (RBP), modulating transcription, or influencing translation. Therefore, it is inevitable to further study the interactions between circRNAs and tumors and to develop novel circRNAs as molecular markers or potential targets, which will provide promising applications in early diagnosis, therapeutic evaluation, prognosis prediction of tumors and even gene therapy for tumors.

Circular RNAs in cancer: opportunities and challenges in the field

Circular RNA (circRNA) is a novel member of the noncoding cancer genome with distinct properties and diverse cellular functions, which is being explored at a steadily increasing pace. The list of endogenous circRNAs involved in cancer continues to grow; however, the functional relevance of the vast majority is yet to be discovered. In general, circRNAs are exceptionally stable molecules and some have been shown to function as efficient microRNA sponges with gene-regulatory potential. Many circRNAs are highly conserved and have tissue-specific expression patterns, which often do not correlate well with host gene expression. Here we review the current knowledge on circRNAs in relation to their implications in tumorigenesis as well as their potential as diagnostic and prognostic biomarkers and as possible therapeutic targets in future personalized medicine. Finally, we discuss future directions for circRNA cancer research and current caveats, which must be addressed to facilitate the translation of basic circRNA research into clinical use.

Deep Circular RNA Sequencing Provides Insights into the Mechanism Underlying Grass Carp Reovirus Infection

Grass carp hemorrhagic disease, caused by the grass carp reovirus (GCRV), is a major disease that hampers the development of grass carp aquaculture in China. The mechanism underlying GCRV infection is still largely unknown. Circular RNAs (circRNAs) are important regulators involved in various biological processes. In the present study, grass carp were infected with GCRV, and spleen samples were collected at 0 (control), 1, 3, 5, and 7 days post-infection (dpi). Samples were used to construct and sequence circRNA libraries, and a total of 5052 circRNAs were identified before and after GCRV infection, of which 41 exhibited differential expression compared with controls. Many parental genes of the differentially expressed circRNAs are involved in metal ion binding, protein ubiquitination, enzyme activity, and nucleotide binding. Moreover, 72 binding miRNAs were predicted from the differentially expressed circRNAs, of which eight targeted genes were predicted to be involved in immune responses, blood coagulation, hemostasis, and complement and coagulation cascades. Upregulation of these genes may lead to endothelial and blood cell damage and hemorrhagic symptoms. Our results indicate that an mRNA–miRNA–circRNA network may be present in grass carp infected with GCRV, providing new insight into the mechanism underlying grass carp reovirus infection.

Regulation of microRNAs function by circular RNAs in human cancer

Circular RNAs (circRNAs) are a newly validated class of endogenous non-coding RNA, generated from the ligation of exons, introns, or both, which arise via a diverse number of cellular mechanisms. Due to rapid advances in the development of combined high-throughput sequencing and bioinformatics analyzing tools, many circRNAs have recently been discovered, revealing an expansive number of ubiquitously expressed mammalian circRNAs. Interestingly, it has recently been confirmed that circRNAs bind to microRNAs (miRs), as miR “sponges”, acting to suppress miR function. As miRs are known to alter the development and progression of cancer, circRNAs may offer a novel diagnostic and prognostic biomarker for cancer. Indeed, recent evidence has shown that circRNAs are associated with many human cancers. Herein, we review the molecular characteristics and biogenesis of circRNAs, with a focus on newly identified circRNAs that may play an important role in human cancer, through their regulation of miR expression.

Recent progress in circular RNAs in human cancers

Circular RNAs (circRNAs) are a large class of endogenous RNAs, formed by exon skipping or back-splicing events as covalently closed loops, which are expressed abundantly in mammalian cells. Although their biological functions remain largely unknown, recent studies show that circRNAs have three main functions in mammalian cells. First, circRNAs can regulate transcription and RNA splicing. Second, circRNAs function as microRNA (miRNA) sponges. Third, they can be translated into protein driven by N⁶-methyladenosine modification. Taking advantage of RNA sequencing (RNA-seq) technology, the expressions of circRNAs were found to be dysregulated in all types of cancer cell lines, tumor tissues, and even plasma samples from patients, which correlated with certain clinical characteristics, suggesting the potential roles of circRNAs in tumor progression. Considering their conserved sequences and stable structures, circRNAs were deemed to be promising biomarkers for the early diagnosis and prognosis prediction of cancer. In this review, we describe briefly the formation and properties of circRNAs, and focus mainly on recent progress in research into their function, regulation, and clinical relevance in different cancers.

Circular RNAs play an important role in late-stage gastric cancer: Circular RNA expression profiles and bioinformatics analyses

Gastric cancer is one of the most common tumors of the digestive system. Here, analysis of the expression profiles of circular RNAs in advanced gastric adenocarcinoma and adjacent normal mucosa tissues revealed differential expression of 306 circular RNAs, among which 273 were predicted to exert regulatory effects on target microRNAs. The downstream pathway networks of circular RNA-microRNA were mapped and the node genes were identified. In particular, we found that the expression of hsa_circ_0058246 was elevated in tumor specimens of patients with poor clinical outcomes. Our collective findings indicate that circular RNAs play a critical role in gastric cancer tumorigenesis. Data from this study provide a new perspective on the molecular pathways underlying metastasis and recurrence of gastric cancer and highlight potential therapeutic targets that may contribute to more effective diagnosis and treatment of the disease.

Circular RNA circ-ABCB10 promotes breast cancer proliferation and progression through sponging miR-1271

Circular RNA (circRNA) is a key regulator in the development and progression of human cancers, however its role in breast cancer tumorigenesis is not well understood. The present study aims to investigate the expression profiles and potential modulation of circRNA on breast cancer carcinogenesis. Human circRNA microarray was performed to screen for abnormally expressed circRNA in breast cancer tissue. Results found circ-ABCB10, was significantly up-regulated in breast cancer tissue. And results were replicated in a larger sample size. In vitro, loss-of-function experiments showed circ-ABCB10 knockdown suppressed the proliferation and increased apoptosis of breast cancer cells. Bioinformatics prediction program predicted the complementary sequence within circ-ABCB10 and miR-1271, which was validated by luciferase reporter assay. Finally, miR-1271 rescued the function of circ-ABCB10 on breast cancer cells, confirming the sponge effect of circ-ABCB10 on miR-1271. Overall, results identified a new functional circ-ABCB10 in breast cancer tumorigenesis, and reveal the important regulatory role of circ-ABCB10 through sponging miR-1271, providing a novel insight for breast cancer pathogenesis.

Increased circular RNA UBAP2 acts as a sponge of miR-143 to promote osteosarcoma progression

Deregulated expression of circular RNA (circRNA) has been determined to be important in carcinogenesis and progression; however, in the most common type of primary malignant bone tumor osteosarcoma, the roles of circRNA in cancer development still remain to be elucidated. Here, we found that circRNA UBAP2 (circUBAP2) expression is significantly increased in human osteosarcoma tissues as compared to those in matched controls. Increased circUBAP2 expression was significantly correlated with human osteosarcoma progression and prognosis. Furthermore, increased circUBAP2 could promote osteosarcoma growth and inhibit apoptosis both in vitro and in vivo. Mechanistically, circUBAP2 was found to inhibit the expression of microRNA-143 (miR-143), thus enhancing the expression and function of anti-apoptotic Bcl-2, which is a direct target of miR-143. Together, our results suggest the roles of circUBAP2 in osteosarcoma development and implicate its potential in prognosis prediction and cancer therapy.

Circular RNAs: A novel type of biomarker and genetic tools in cancer

Circular RNAs (circRNAs) are a novel type of universal and diverse endogenous noncoding RNAs (ncRNAs) and they form a covalently closed continuous loop without 5′ or 3′ tails unlike linear RNAs. Most circRNAs are presented with characteristics of abundance, stability, conservatism, and often exhibiting tissue/developmental-stage-specific expression. CircRNAs are generated either from exons or introns by back splicing or lariat introns. CircRNAs play important roles as miRNA sponges, gene transcription and expression regulators, RNA-binding protein (RBP) sponges and protein/peptide translators. Emerging evidence revealed the function of circRNAs in cancer and may potentially serve as a required novel biomarker and therapeutic target for cancer treatment. In this review, we discuss about the origins, characteristics and functions of circRNA and how they work as miRNA sponges, gene transcription and expression regulators, RBP sponges in cancer as well as current research methods of circRNAs, providing evidence for the significance of circRNAs in cancer diagnosis and clinical treatment.

Decreased expression of hsa_circ_0003570 in hepatocellular carcinoma and its clinical significance

BACKGROUND

Circular RNAs (circRNAs) constitute a class of non-coding RNAs recently discovered to be widespread and abundant in mammalian cells. However, the expression features of most of circRNAs in hepatocellular carcinoma (HCC) are unraveled. In this study, we focused on hsa_circ_0003570, which was found to be down-regulated in HCC tissues in our previous microarray screening.

METHODS

The hsa_circ_0003570 levels in HCC cell lines, HepG2, SMMC-7721, MHCC97L, MHCC97H, and HCCLM3, and human normal hepatic cell line L02 were detected by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). Then, its levels in 107 paired HCC tissues and adjacent non-tumor tissues, 60 liver biopsy samples from patients with chronic liver diseases were detected by qRT-PCR. The receiver operating characteristic curve (ROC) was used to evaluate the diagnostic value of hsa_circ_0003570 for HCC.

RESULTS

Hsa_circ_0003570 was not only first found down-regulated in HCC cell lines (P<.001) but also in HCC tissues (P<.001). Moreover, hsa_circ_0003570 was gradually decreased from chronic hepatitis (CH), to liver cirrhosis (LC) and to HCC tissues (P<.01). Its expression levels were significantly correlated with tumor diameter (P=.035), differentiation (P=.013), microvascular invasion (P=.045), Barcelona Clinic Liver Cancer stages (P=.011), tumor-node-metastasis stages (P=.016), and serum alpha-fetoprotein levels (P=.031). The ROC curve demonstrated that hsa_circ_0003570 had poor performance for differentiating HCC from LC and CH, but had relatively good performance for differentiating LC from CH.

CONCLUSIONS

These results indicated that hsa_circ_0003570 expression levels were associated with HCC clinicopathological characteristics.

Circular RNA profiles in mouse lung tissue induced by radon

Background

Radon is a known human lung carcinogen, whose underlying carcinogenic mechanism remains unclear. Recently, circular RNA (circRNA), a class of endogenous non-protein coding RNAs that contain a circular loop, was found to exhibit multiple biological effects. In this study, circRNA profiles in mouse lung tissues between control and radon exposure were analyzed.

Methods

Six mice were exposed to radon at concentration of 100,000 Bq/m³, 12 h/d, for up to cumulative doses of 60 working level months (WLM). H&E staining and immunohistochemistry of caspase-3 were used to detect the damages in lung tissue. The lung tissue of control and exposed group were selected for circRNA microarray study. The circRNA/microRNA interaction was analyzed by starBase prediction software. 5 highest expressing circRNAs were selected by real-time PCR to validate the consistency in mouse lung tissue exposed to radon.

Results

Inflammatory reaction was found in mouse lung tissue exposed to radon, and caspase-3 expression was significantly increased. Microarray screening revealed 107 up-regulated and 83 down-regulated circRNAs, among which top 30 circRNAs with the highest fold changes were chosen for further analysis, with 5 microRNAs binding sites listed for each circRNA. Consistency of the top 5 circRNAs with the highest expressions were confirmed in mice exposed with 60WLM of radon.

Conclusion

Mouse lung tissue was severely injured when exposed to radon through pathological diagnosis and immunohistochemical analysis. A series of differentially expressed circRNAs demonstrated that they may play an important role in pulmonary toxicity induced by radon.

Screening differential circular RNA expression profiles reveals hsa_circ_0004018 is associated with hepatocellular carcinoma

Circular RNAs (circRNAs) have been emerged as an indispensable part of endogenous RNA network. However, the expression significance of circRNAs in hepatocellular carcinoma (HCC) is rarely revealed. The aim of this study was to determine the circRNA expression profile in HCC, and to investigate their clinical significances and relevant mechanisms for cancer progression. The global circRNA expression profile in HCC was measured by circRNA microarray. Levels of one representative circRNAs, hsa_circ_0004018, were confirmed by real-time reverse transcription-polymerase chain reaction. The expression levels of hsa_circ_0004018 in HCC were significantly lower compared with para-tumorous tissue (P<0.001). Our data further showed that lower expression of hsa_circ_0004018 was correlated with serum alpha-fetoprotein (AFP) level, tumor diameters, differentiation, Barcelona Clinic Liver Cancer stage and Tumor-node-metastasis stage. More importantly, we detected liver tissues from chronic hepatitis, cirrhosis and HCC patients; and found that hsa_circ_0004018 harbored HCC-stage-specific expression features in diverse chronic liver diseases (P<0.001). The area under receiver operating characteristic curve was up to 0.848 (95% CI=0.803–0.894, P<0.001). The sensitivity and specificity were 0.716 and 0.815, respectively. Finally, hsa_circ_0004018 might be involved in cancer-related pathways via interactions with miRNAs.