cir-ITCH plays an inhibitory role in colorectal cancer by regulating the Wnt/β-catenin pathway

Hsa_circ_0003998 promotes cell proliferation and invasion by targeting miR-326 in non-small cell lung cancer

Background

Circular RNAs represent a new class of noncoding RNAs involved in the development of cancer. However, little is known about their role in non-small cell lung cancer (NSCLC).

Methods

We examined hsa_circ_0003998 levels in 60 NSCLC tissues by quantitative real-time polymerase chain reaction and analyzed the clinicopathologic significance of hsa_circ_0003998 expression. The effect of small interfering RNA-mediated hsa_circ_0003998 knockdown on proliferation and invasion was analyzed in A549 and H1299 cells in vitro. Moreover, the target genes of hsa_circ_0003998 were further explored by bioinformatic analysis, dual luciferase reporter assays, and rescue experiments.

Results

Hsa_circ_0003998 upregulation was associated with larger tumor size and lymph node metastasis and also correlated with shorter overall survival of NSCLC patients. Functional experiments showed knockdown of hsa_circ_0003998 restrained cell proliferation and invasion in NSCLC cells. In particular, hsa_circ_0003998 upregulated the expression of miR-326 target gene Notch1 through sponging miR-326. Furthermore, the tumor-inhibiting effect of hsa_circ_0003998 silencing was blocked by miR-326 inhibitor.

Conclusion

hsa_circ_0003998/miR-326/Notch1 pathway regulates the progression of NSCLC.

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

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

Advances in circular RNAs and their roles in breast Cancer

Circular RNAs (circRNAs) are a type of noncoding RNAs with a closed loop structure. With the development of high-throughput sequencing, massive circRNAs have been discovered in tumorous tissues. Emerging evidence suggests that the biological functions of circRNAs including serving as ceRNAs or miRNA sponges, interacting with proteins, regulating gene transcription and translation, suggesting that circRNAs will be novel biomarkers and targets for the diagnosis and prognosis of diseases. Breast cancer is the most frequently occurring cancer and the leading cause of cancer-related death among women worldwide. It is vital to understand the molecular pathways involved in the pathogenesis of proliferation and progression. In this review, we summarize the current knowledge on human circRNAs and their potential clinical implications on breast cancer.

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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

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

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

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

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.

Advances of circular RNAs in carcinoma

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

Circular RNA IARS (circ-IARS) secreted by pancreatic cancer cells and located within exosomes regulates endothelial monolayer permeability to promote tumor metastasis

BACKGROUND

Recent studies show that exosomes are involved in intercellular communication and that abundant circular RNAs (circRNAs) are present within exosomes. However, whether these exosomal circRNAs contribute to tumor invasion and metastasis remains unclear, as do their associated mechanisms.

METHODS

Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) was used to measure the expression levels of circ-IARS in 85 pancreatic ductal adenocarcinoma (PDAC) tissues, plasma exosomes, and Hs 766 T, Hs 766 T-L2 and human microvascular vein endothelial (HUVECs) cells. RhoA, ZO-1 and RhoA-GTP levels were detected by qRT-PCR and western blotting (WB); RhoA activity analysis was also performed. Transwell assays were performed to examine changes in endothelial monolayer permeability, and immunofluorescence and WB were employed to evaluate F-actin expression and focal adhesion. Finally, an animal experiment was performed to detect the contribution of circ-IARS to cancer metastasis.

RESULTS

circ-IARS expression was up-regulated in pancreatic cancer tissues and in plasma exosomes of patients with metastatic disease. Circ-IARS was found to enter HUVECs through exosomes and promote tumor invasion and metastasis. Circ-IARS expression was positively correlated with liver metastasis, vascular invasion, and tumor-node-metastasis (TNM) stage and negatively correlated with postoperative survival time. Overexpression of circ-IARS significantly down-regulated miR-122 and ZO-1 levels, up-regulated RhoA and RhoA-GTP levels, increased F-actin expression and focal adhesion, enhanced endothelial monolayer permeability, and promoted tumor invasion and metastasis.

CONCLUSIONS

circ-IRAS accesses HUVECs via exosomes derived from pancreatic cancer cells followed by increased endothelial monolayer permeability. Furthermore, this process promotes tumor invasion and metastasis. The results of this study suggest that the presence of circRNAs in exosomes may be important indicator for early diagnosis and prognostic prediction in PDAC.

Function and clinical significance of circRNAs in solid tumors

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

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

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

A 360° view of circular RNAs: From biogenesis to functions

The first circular RNA (circRNA) was identified more than 40 years ago, but it was only recently appreciated that circRNAs are common outputs of many eukaryotic protein-coding genes. Some circRNAs accumulate to higher levels than their associated linear mRNAs, especially in the nervous system, and have clear regulatory functions that result in organismal phenotypes. The pre-mRNA splicing machinery generates circRNAs via backsplicing reactions, which are often facilitated by intronic repeat sequences that base pair to one another and bring the intervening splice sites into close proximity. When spliceosomal components are limiting, circRNAs can become the preferred gene output, and backsplicing reactions are further controlled by exon skipping events and the combinatorial action of RNA binding proteins. This allows circRNAs to be expressed in a tissue- and stage-specific manner. Once generated, circRNAs are highly stable transcripts that often accumulate in the cytoplasm. The functions of most circRNAs remain unknown, but some can regulate the activities of microRNAs or be translated to produce proteins. Circular RNAs can further interface with the immune system as well as control gene expression events in the nucleus, including alternative splicing decisions. Circular RNAs thus represent a large class of RNA molecules that are tightly regulated, and it is becoming increasingly clear that they likely impact many biological processes. This article is categorized under: RNA Processing > Splicing Mechanisms RNA Structure and Dynamics > Influence of RNA Structure in Biological Systems RNA Evolution and Genomics > RNA and Ribonucleoprotein Evolution RNA Evolution and Genomics > Computational Analyses of RNA.

Circular RNAs in digestive system cancer: potential biomarkers and therapeutic targets

Circular RNAs (circRNAs) are a series of special closed circular RNA molecules with stability and conservatism. In recent years, advances in high-throughput RNA sequencing technology have led to explosive discovery of circRNAs in different types of species and cells. Moreover, circRNAs can accomplish a remarkable multitude of biological functions, such as regulating transcription or splicing, serving as miRNA sponges, interacting with RNA-binding proteins, and translating proteins. Meanwhile, circRNAs involve in the biogenesis and development of many diseases, including cardiovascular disorders, nervous system disorders, cancers, etc. Herein, we discuss the latest research progress of circRNA, as well as their diagnostic and prognostic significance in digestive system cancers. In addition, this paper highlights that circRNAs might serve as potential therapeutic targets for novel drugs by taking digestive system cancer as an illustrative example.

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.

A novel plasma circular RNA circFARSA is a potential biomarker for non-small cell lung cancer

Emerging evidence indicates that circular RNAs (circRNAs) are implicated in cancer development. This study aimed to evaluate whether circulating circRNAs may serve as novel biomarkers for non-small cell lung cancer (NSCLC). We used RNA sequencing (RNA-seq) and quantitative real-time PCR to explore cancer-related circRNAs. Bioinformatics and functional analyses were performed to reveal biological effects of circRNAs on lung cancer cells. A total of 5471 distinct circRNAs were identified by total RNA-seq, in which 185 were differentially expressed between cancerous and adjacent normal tissues. A circRNA derived from exon 5-7 of the FARSA gene, termed circFARSA, was observed to increase in cancerous tissues (P = 0.016), and was more abundant in patients' plasma than controls (P < 0.001). Overexpression of circFARSA in A549 cell line significantly promoted cell migration and invasion. In silico analysis suggested that circFARSA might sponge miR-330-5p and miR-326, thereby relieving their inhibitory effects on oncogene fatty acid synthase. Summarily, this study revealed circRNA profile of NSCLC for the first time and provided the evidence of plasma circFARSA as a potential noninvasive biomarker for this malignancy.

Circular RNAs in Cancer - Lessons Learned From microRNAs

Circular RNAs (circRNA) are RNA molecules built from fragments of linear pre-messenger RNAs and other linear RNA species through a process termed "back-splicing" in which the 3' and 5' ends are joined together giving rise to a covalently uninterrupted loop. circRNAs are not new members of the RNA world; they were first discovered in the early 1990s. The novelty is their abundance in the mammalian cells, as recently thousands of circRNAs were discovered and annotated. The biogenesis of circRNAs is a partially characterized process, regulated by three different mechanisms: exon skipping, intron pairing, and RNA-binding proteins. On the other hand, the function of circRNAs remains largely unknown and only a handful of singular reports describe in detail the biological roles of some circular transcripts. In a very short period of time, numerous circRNAs were associated with various cancer types and were also identified in bodily fluids with the potential of being disease-specific biomarkers. In this review, we briefly describe the biogenesis and function of circRNAs and present the circular transcripts that were more than once reported in literature to be associated with cancer. Finally, we point out some of the difficulties encountered in the study of circRNAs in cancer, as we consider that taking these into account could accelerate and improve our understanding of the biologic and translational use of circRNAs in human diseases.

Leptin promotes the growth of breast cancer by upregulating the Wnt/β-catenin pathway

The present study aimed to investigate the role of leptin in the growth of breast cancer. In the present study, expression of leptin in tumor tissues and adjacent tissues was detected by reverse transcription-quantitative polymerase chain reaction. Serum leptin in patients with breast cancer and normal healthy controls was detected by ELISA. Different concentrations of leptin were used to treat breast cancer cells, and cell proliferation was detected by cell proliferation assay. Interactions between leptin and Wnt/β-catenin were evaluated by western blotting. It was demonstrated that expression of leptin mRNA was significantly higher in tumor tissues than in adjacent tissues in 43 out of 48 patients. Serum level of leptin was significantly higher in patients with breast cancer than in normal controls. Leptin promoted the proliferation of breast cancer cells in a dose-dependent manner. Leptin significantly increased the expression level of β-catenin in breast cancer cells. Treatment with Wnt inhibitor reduced the enhancing effects of leptin on proliferation of breast cancer cells. The results of the present study therefore indicate that leptin may promote the growth of breast cancer by upregulating the Wnt/β-catenin pathway.

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.

Identification of the tumor-suppressive function of circular RNA ITCH in glioma cells through sponging miR-214 and promoting linear ITCH expression

Circular RNAs (circRNAs) is a class of endogenous noncoding RNAs that, unlike linear RNAs, form covalently closed continuous loops and have recently shown huge capabilities as gene regulators in mammals. However, little is known about their roles in cancer initiation and progression, such as glioma. In this study, we determined the expression level of circRNA ITCH (cir-ITCH) in glioma specimens and further investigated its functional role in glioma cells. By performing Taq-man based RT-qPCR, we identified that cir-ITCH was downregulated in glioma tissues and cell lines. Receiver operating curve analysis suggested cir-ITCH showed a relatively high diagnostic accuracy. Kaplan-Meier assay revealed that decreased cir-ITCH level was associated with poor survival of glioma patients. The functional relevance of cir-ITCH was further examined by biological assays. Cir-ITCH significantly promoted the capacities of cell proliferation, migration and invasion of glioma cells. The linear isomer of cir-ITCH, ITCH gene was then identified as the down stream target. Subsequently, RNA immunoprecipitation clearly showed that cir-ITCH sponged miR-214, which further promoted the ITCH expression. Finally, the gain and loss functional assays indicate that cir-ITCH plays an anti-oncogenic role through sponging miR-214 and regulating ITCH-Wnt/β-catenin pathway. These results suggest that cir-ITCH is a tumor-suppressor gene in glioma and may serve as a promising prognostic biomarker for glioma patients. Therefore, restoration of cir-ITCH expression could be a future direction to develop a novel treatment strategy.

Identification and functional characterization of circRNA-0008717 as an oncogene in osteosarcoma through sponging miR-203

Circular RNA (circRNA) is a key regulator in the development and progression of human cancers, however its role in osteosarcoma tumorigenesis is not well understood. The present study aims to investigate the expression profiles and potential modulation of circRNA on osteosarcoma carcinogenesis. Human circRNA microarray was performed to screen for abnormally expressed circRNA in osteosarcoma tissue and circRNA-0008717 was identified as one circRNA significantly upregulated in osteosarcoma tissue. Osteosarcoma patients with high circRNA-0008717 expression had shortened survival. Gain and loss functional assays suggested that knockdown of circRNA-0008717 suppressed cell proliferation, migration and invasion, but promoted cell apoptosis. By using biotin-labeled circRNA-0008717 probe to perform RNA precipitation in osteosarcoma cells, we identified miR-203 as the circ0008717-associated microRNA. Subsequently, Bmi-1 was identified as the functional target of miR-203. In addition, overexpression of circRNA-0008717 in osteosarcoma could elevate Bmi-1 expression, resulting in the promotion of osteosarcoma cell proliferation and invasion. Furthermore, the tumor promoting effect of circRNA-0008717 was abolished by miR-203 mimics or Bmi-1 silencing vector. In conclusion, circRNA-0008717 plays an oncogenic role in osteosarcoma and may serve as a promising prognostic biomarker for osteosarcoma patients. Therefore, silence of circRNA-0008717 could be a future direction to develop a novel treatment strategy.

Polymorphisms and expression pattern of circular RNA circ-ITCH contributes to the carcinogenesis of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) ranks the sixth most common cancer and the third cause of cancer-related mortality worldwide. Recent studies identified that circ-ITCH Suppresses mutiple cancers proliferation via inhibiting the Wnt/beta-Catenin pathway. In current study, conducted a genetic association study together with epidemiological follow-up study to delineate the role of circ-ITCH in the development and progression of HCC. we found rs10485505 (adjusted OR =1.18; 95% CI=1.06-1.31; P value =3.1×10^-3) and rs4911154 (adjusted OR =1.27; 95% CI=1.14-1.43; P value =3.7×10^-5) were significantly associated with increased HCC risk. The expression level of circ-ITCH was significantly lower in HCC tissues, compared with that in adjacent tissues (P value < 0.001). Cox regression analysis indicated that high expression of circ-ITCH was associated with favorable survival of HCC (HR=0.45; 95% CI=0.29-0.68; P value < 0.001). These results indicate that circ-ITCH may have an inhibitory effect on HCC, and could serve as susceptibility and prognostic biomarkers for HCC patients.

The Emerging Role of Circular RNAs in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) ranks the third leading cause of cancer death in the world and has a notably low survival rate. Circular RNAs (circRNAs) are newly classed non-coding RNA (ncRNA) members that are capable of regulating gene expression at transcription or post-transcription levels. Recent studies demonstrate that some circRNAs are differentially expressed in HCC, and the deregulation of these circRNAs is associated with the clinical pathological and prognostic significance. They also play essential roles in HCC progression, and contribute to cell proliferation, migration, invasion and metastasis by targeting different microRNAs (miRNAs) and protein-coding genes. In this review, we concentrate on recent progress of some important circRNAs in HCC, with an emphasis on their deregulation, functions and regulatory mechanisms, and discuss their potential utility as diagnostic and/or prognostic biomarkers or therapeutic targets for HCC.

The differentially expressed circular ribonucleic acids of primary hepatic carcinoma following liver transplantation as new diagnostic biomarkers for primary hepatic carcinoma

Recent studies have shown that circular ribonucleic acids have differential expression in some diseases. This study compared the expression levels of five circular ribonucleic acids between patients of primary hepatic carcinoma following liver transplantation and healthy individuals for searching a new diagnostic biomarker about primary hepatic carcinoma. We chose differentially expressed targeted circular ribonucleic acids according to fold change ≥2.0 or ≤-2.0 between circular ribonucleic acids microarray of perioperative liver transplantation and normal controls. Then we used the Arraystar home-made micro-ribonucleic acid target prediction software based on TargetScan and miRanda to predict circular ribonucleic acid/micro-ribonucleic acid interactions. And we assess the expression levels of hsa_circ_100571, hsa_circ_400031, hsa_circ_102032, hsa_circ_103096, and hsa_circ_102347 in the peripheral blood of normal controls and liver transplantation patients before transplantation and on the first, third, and seventh days after transplantation by real-time quantitative polymerase chain reaction. We chose five circular ribonucleic acids, two of which have been correlated with micro-ribonucleic acid-related carcinoma recurrence after liver transplantation, hepatocellular carcinoma and analyzed their expression with 2^-△△Ct method. The expression level of hsa_circ_100571 and hsa_circ_400031 on day 1 after liver transplantation was higher than pre-transplantation (p < 0.01), and these levels showed a declining trend on post-transplantation. The expression level of hsa_circ_102032 and hsa_circ_103096 on day 1 after liver transplantation was lower than pre-transplantation (p < 0.01) and decreased on post-transplantation. There were the significantly different expressions between the post-transplantation day 7 and normal control (p < 0.01). The expression level of hsa_circ_102347 on day 1 after liver transplantation was lower than pre-transplantation (p < 0.01). This expression showed a declining trend on post-transplantation, and the postoperative day 7 level was similar to normal control (p > 0.05). Five types of circular ribonucleic acid-related micro-ribonucleic acids had varying degrees of upregulation and downregulation between perioperative transplantation of primary hepatic carcinoma patients and normal controls; the hsa_circ_102347 is most likely to have association with primary hepatic carcinoma.

Long Noncoding RNA GAPLINC Promotes Cells Migration and Invasion in Colorectal Cancer Cell by Regulating miR-34a/c-MET Signal Pathway

BACKGROUND

Gastric adenocarcinoma predictive long intergenic noncoding RNA (GAPLINC) has been detected in colorectal cancer (CRC) cells and reportedly performs many functions related to tumor proliferation and metastasis. Aim The present study aimed to comprehensively explore the biological functions of GAPLINC and their underlying mechanism in CRC cell.

METHODS

The human cancer LncRNA PCR array was used to detect the differentially expressed long noncoding RNAs in human CRC samples. Real-time PCR, dual-luciferase assay, RNA pull-down assay, Transwell assay, and western blot analysis were performed to explore the molecular mechanism underlying GAPLINC functions related to migration and invasion of a human CRC cell line (HCT116).

RESULTS

Compared to the non-cancerous tissues, GAPLINC expression was obviously increased in CRC tissues. In HCT116, silencing of GAPLINC weakened cell migration and invasion, while overexpression of GAPLINC significantly promoted cell migration and invasion. Through dual-luciferase, RNA pull-down, and Transwell assays, we verified that miR-34a was the downstream molecule of GAPLINC and that miR-34a negatively regulated the migration and invasion of HCT116 cell. Furthermore, we found that GAPLINC positively regulated the miR-34a target gene c-MET in CRC tissues.

CONCLUSIONS

Our findings revealed that GAPLINC was up-regulated in CRC tissues and was involved in the migration and invasion of CRC cells by regulating miR-34a/c-MET signaling pathway.

Hsa_circ_0005986 inhibits carcinogenesis by acting as a miR-129-5p sponge and is used as a novel biomarker for hepatocellular carcinoma

Circular RNAs (circRNAs), a class of long-time-ignored noncoding RNA, have been revealed as multifunctional RNAs in recent years. However, the diagnostic values and the mechanism of most circRNAs in hepatocellular carcinoma (HCC) remain unknown. In this study, we revealed that the expression level of hsa_circ_0005986 in HCC was significantly lower than that in adjacent non-tumorous tissues (P < 0.001). Its levels in HCC cell lines, HepG2, SMMC7721, Huh7, MHCC97L, MHCC97H, and HCCLM3 were significantly lower than those in human normal hepatic cell line L02 (P < 0.001). In addition, the low expression level of hsa_circ_0005986 was correlated with chronic hepatitis B family history (P = 0.001), tumor diameters (P < 0.001), microvascular invasion (P = 0.026), and Barcelona Clinic Liver Cancer (BCLC) stage (P < 0.001). Further experiments demonstrated that both hsa_circ_0005986 and Notch1mRNA were targets of miR-129-5p, and that hsa_circ_0005986 downregulation liberated miR-129-5p and decreased the expression level of Notch1mRNA. More importantly, hsa_circ_0005986 downregulation accelerated cell proliferation by promoting the G0/G1 to S phase transition. We conclude that hsa_circ_0005986 function as microRNA sponge in tumorigenesis and can be used as a novel biomarker for HCC.

Long non-coding RNA TUG1 promotes endometrial cancer development via inhibiting miR-299 and miR-34a-5p

It is generally known that the human genome makes a large amount of noncoding RNAs compared with coding genes. Long non-coding RNAs (lncRNAs) which composed of more than 200 nucleotides have been described as the largest subclass of the non-coding transcriptome in human noncoding RNAs. Existing research shows that lncRNAs exerted biological functions in various tumors via participating in both oncogenic and tumor suppressing pathways. The previous studies indicated that lncRNA taurine upregulated 1 (TUG1) play important roles in the initiation and progression of malignancies. In this study,based on previous research, we investigated the expression and biological role of the lncRNA-TUG1. We analyzed the relationship between lncRNA-TUG1and endometrial carcinoma (EC) in a total 104 EC carcinoma specimens, compared with that in normal tissues. We found that lncRNA-TUG1 expression in cancer tissues was significantly higher than that in adjacent tissues. Through a series of experiments, the results demonstrated that lncRNA-TUG1 enhances the evolution and progression of EC through inhibiting miR-299 and miR-34a-5p.

The novel roles of circular RNAs in metabolic organs

Circular RNAs (circRNAs) with a covalently closed loop structure which was different with linear RNAs, recently re-merged as novel regulator and exerted function in multiple biological processes. Through deep RNA sequencing (RNA-seq) technology coupled with bioinformatic analyses, a number of circRNAs has been identified. Moreover, circRNAs exhibit tissue- and development-specific expression indicating their potential biological significance. Actually, function of circRNAs as miRNA sponge has been well demonstrated in some diseases, besides, circRNAs also could function as RNA binding protein sponge and regulate alternative splicing and gene transcription. Notably, Emerging evidences showed that circRNAs played a pivotal role on the development of diseases including atherosclerotic vascular disease, neurological disorders and liver diseases, and served as diagnostic or predictive biomarkers of some diseases. This review mainly discusses the current advance of circRNAs as regulator involved in many diseases, and highlights circRNAs which have been well elucidated biological and pathogenic mechanism.

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.

Profiling and Bioinformatic Analyses Indicate Differential circRNA and miRNA/isomiR Expression and Interactions

As a novel class of noncoding RNAs, circular RNAs (circRNAs) have been reported to play a role in various biological processes. Some circRNAs may serve as microRNA (miRNA) sponges, regulating transcription or splicing. Herein, we investigated the expression profiles and interactions of miRNAs/isomiRs and circRNAs in male patients with esophageal cancer. We found that some miRNA genes generated two deregulated miRNA products (miR-#-5p and miR-#-3p), and these products were consistently abnormally expressed. Some circRNAs were predicted to be miRNA sponges for specific miRNAs. Some of these typically showed opposing expression patterns in cancer tissues: one upregulated and the other downregulated. Although fewer miRNAs were predicted to interact with circRNAs, the number of predicted interactions would be substantially increased if detailed isomiRs were involved. High sequence similarity across multiple isomiRs suggested that they might interact with circRNAs, similar to the interaction of homologous miRNAs with circRNAs. At the isomiR level, due to the characteristics of the sequences and expression patterns involved, the cross-talk between different ncRNAs is complicated despite simplification of the isomiRs involved through clustering. We expect that our results may provide methods for further study of the cross-talk among ncRNAs and elucidate their biological roles in human diseases.

Circular RNAs: a new frontier for cancer diagnosis and therapy

In recent years, circular RNAs (circRNAs) have attracted considerable attention because they play a significant role in many fields of cancer biology. Additionally, it has become increasingly clear that circRNAs have the potential to make contributions to the successful application of individualized cancer medicine. This brief review introduces circRNAs by describing their potential as a biomarker and therapeutic target and discussing the possible strategies to target them. This review also presents the challenges that are encountered by circRNAs for their definitive entry into clinical practice. Clearly, our understanding of circRNAs helps to add a new dimension to the molecular structure of cancer and will provide many new opportunities for cancer treatment.

circRNAs in Cancer

Exonic circular RNAs (circRNAs) are mostly generated from exons of protein-coding genes and, in many cases, are more abundant that the linear product from their hosting gene. Certain circRNAs are very abundant in the brain and in non-dividing cells; and many also show physiological-specific and tissue-specific expression. Moreover, recent work has demonstrated that some circRNAs are functional. Lately an important number of research articles have pointed a relation between cancer and certain circRNAs. In this review, we describe general advances in the field regarding circRNA biogenesis and functions in relationship with cancer. Also, we summarize some necessary precautions to work with circRNA that are particularly relevant to cancer-related studies.

Circular RNA circ-ITCH inhibits bladder cancer progression by sponging miR-17/miR-224 and regulating p21, PTEN expression

BACKGROUND

Circ-ITCH is a circRNA generated from several exons of itchy E3 ubiquitin protein ligase (ITCH) and tumor suppressor served as a sponge for certain miRNAs targeting their parental transcripts of ITCH. However, the role of circ-ITCH in bladder cancer (BCa) was not reported. In the present study, we investigated the role of circ-ITCH in BCa.

METHODS

Quantitative real-time PCR was used to detect the expression of circ-ITCH and survival analysis was adopted to explore the association between circ-ITCH expression and the prognosis of BCa. BCa cells were stably transfected with lentivirus approach and cell proliferation, migration, invasion, cell cycle and cell apoptosis, as well as tumorigenesis in nude mice were performed to assess the effect of circ-ITCH in BCa. Biotin-coupled probe pull down assay, Biotin-coupled miRNA capture, Fluorescence in situ hybridization and Luciferase reporter assay were conducted to confirm the relationship between the circ-ITCH and the microRNA.

RESULTS

In the present study, we found that circ-ITCH, is down-regulated in BCa tissues and cell lines. BCa patients with low circ-ITCH expression had shortened survival. Enforced- expression of circ-ITCH inhibited cells proliferation, migration, invasion and metastasis both in vitro and in vivo. Mechanistically, we demonstrated that circ-ITCH up-regulates the expression of miR-17 and miR-224 target gene p21 and PTEN through 'sponging' miR-17 and miR-224, which suppressed the aggressive biological behaviors of BCa.

CONCLUSIONS

circ-ITCH acts as a tumor suppressor by a novel circ-ITCH/miR-17, miR-224/p21, PTEN axis, which may provide a potential biomarker and therapeutic target for the management of BCa.

Potential functions and implications of circular RNA in gastrointestinal cancer

Circular RNAs (circRNAs) are a novel type of endogenous non-coding RNA that have gained attention from researchers for their involvement in multiple biological processes. circRNAs are ubiquitously expressed in eukaryotic cells and regulate gene expression at the transcriptional or post-transcriptional level by interacting with microRNAs (miRNAs) or other molecules. The present review provides an overview of circRNAs, as well as insights into their roles in the development and progression of gastrointestinal cancer. Furthermore, combined with reported data, the present review investigates the potential of circRNAs to become diagnostic or predictive biomarkers of gastrointestinal cancer and may provide novel insights into the treatment of associated cancer types.

Circular RNAs Act as miRNA Sponges

Majority of RNAs expressed in animal cells lack protein-coding ability. Unlike other cellular RNAs, circular (circ)RNAs include a large family of noncoding (nc)RNAs that lack the 5' or 3' ends. The improvements in high-throughput RNA sequencing and novel bioinformatics tools have led to the identification of thousands of circRNAs in various organisms. CircRNAs can regulate gene expression by influencing the transcription, the mRNA turnover, and translation by sponging RNA-binding proteins and microRNAs. Given the broad impact of circRNA on miRNA activity, there is huge interest in understanding the impact of miRNA sponging by circRNA on gene regulation. In this review, we summarize our current knowledge of the miRNA-circRNA interaction and mechanisms that influence gene expression.

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.

Emerging Role of Circular RNAs as Potential Biomarkers for the Diagnosis of Human Diseases

In the eukaryotic transcriptome, the evolutionary conserved circular RNAs naturally occur from the family of noncoding RNAs. Circular RNAs possess a unique feature to interact with nucleic acids and ribonucleoproteins and are establishing themselves as an obligatory composition for the regulatory messages which are encoded by the genome. The back-splicing mechanism leads to the formation of circularized RNA, and because of this they become resistant to exonuclease-mediated degradation. The differential and aberrant expression of circular RNAs can be detected with the help of various profiling methods by using serum, plasma, and tissue samples. In this chapter, we have highlighted the role of circular RNAs as putative biomarker for the detection of various human diseases along with its profiling methods. Here we have discussed the differentially expressed circular RNAs in neurological disorders and infectious diseases along with cancer diseases. For instance, in case of pulmonary tuberculosis, hsa_circRNA_001937 was upregulated, while hsa_circRNA_102101 got downregulated; Hsa_circ_000178 was depicted to get upregulated in breast cancer which is associated with disease progression. Furthermore, it has been observed that circRNAs are abundantly present within the mammalian brain tissues. In epileptic condition, Circ-EFCAB2 was observed to get notably upregulated within patients. Taking the above conditions into consideration, circular RNAs have proven themselves as promising noninvasive biomarker for the detection of human diseases.

Competing endogenous RNA networks in human cancer: hypothesis, validation, and perspectives

Non-coding RNAs represent a majority of the human transcriptome. However, less is known about the functions and regulatory mechanisms of most non-coding species. Moreover, little is known about the potential non-coding functions of coding RNAs. The competing endogenous RNAs (ceRNAs) hypothesis is proposed recently. This hypothesis describes potential communication networks among all transcript RNA species mediated by miRNAs and miRNA-recognizing elements (MREs) within RNA transcripts. Here we review the evolution of the ceRNA hypothesis, summarize the validation experiments and discusses the significance and perspectives of this hypothesis in human cancer.

CD90 promotes cell migration, viability and sphere‑forming ability of hepatocellular carcinoma cells

Cluster of differentiation (CD)90 (Thy-1) was proposed as a marker for the liver cancer stem cells that are responsible for tumorigenic activity, however its involvement in the progression of hepatocellular carcinoma (HCC) remains unknown. The aim of the present study was to determine the effect of CD90 on the biological functions of HCC and to investigate the associated circular RNA (circRNA) involved in this process. The analysis of the in vitro data demonstrated that CD90⁺ cells isolated from SK-Hep-1 cells exhibited increased viability, migration and invasive abilities compared with CD90⁻ cells. In addition, circRNA expression profiles in CD90⁺ and CD90⁻ cells were screened using a microarray assay and hsa_circ_0067531 and hsa_circ_0057096 were identified to be expressed at significantly different levels. It was additionally demonstrated that the expression of hsa_circ_0067531 in HCC tissues was significantly decreased compared with normal adjacent tissues. Overall, the results of the present study suggested that CD90 may be used as a potential biomarker for HCC. Furthermore, it was demonstrated that hsa_circ_0067531 may affect the biological functions of CD90⁺ HCC cells and may be a promising candidate to aid in the diagnosis and therapy of HCC.

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 RNA expression is abundant and correlated to aggressiveness in early-stage bladder cancer

The functions and biomarker potential of circular RNAs (circRNAs) in various cancer types are a rising field of study, as emerging evidence relates circRNAs to tumorigenesis. Here, we profiled the expression of circRNAs in 457 tumors from patients with non-muscle-invasive bladder cancer (NMIBC). We show that a set of highly expressed circRNAs have conserved core splice sites, are associated with Alu repeats, and enriched with Synonymous Constraint Elements as well as microRNA target sites. We identified 113 abundant circRNAs that are differentially expressed between high and low-risk tumor subtypes. Analysis of progression-free survival revealed 13 circRNAs, among them circHIPK3 and circCDYL, where expression correlated with progression independently of the linear transcript and the host gene. In summary, our results demonstrate that abundant circRNAs possess multiple biological features, distinguishing them from low-expressed circRNAs and non-circularized exons, and suggest that circRNAs might serve as a new class of prognostic biomarkers in NMIBC.

Expression levels of non-coding “circular” RNA molecules could be used as a prognostic biomarker for patients with early-stage bladder cancer. A team led by Trine Line Hauge Okholm and Jakob Skou Pedersen from Aarhus University Hospital, Denmark, profiled the expression of these loop-forming, potentially gene-regulating RNAs in biopsied tumor samples from 457 patients with bladder cancer that had not invaded nearby muscle tissue. They identified a suite of 113 circular RNAs that were abundant and differentially expressed between patients with different molecular subtypes of bladder cancer. The researchers also found a smaller set of 13 circular RNAs for which expression levels correlated with disease progression. These non-coding RNA molecules, by indicating likely patient outcomes, could potentially serve as future diagnostic aids to inform treatment strategies and decisions.

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.

Identification and comparison of novel circular RNAs with associated co-expression and competing endogenous RNA networks in pulmonary tuberculosis

Pulmonary tuberculosis (PTB) is caused by Mycobacterium tuberculosis and is one of the most serious diseases worldwide. Circular RNAs (circRNAs) are a large class of non-coding RNAs that were identified with potential regulatory roles in disease pathogenesis and progression. In this study, we used whole transcriptome sequencing to identify circRNAs from 3 PTB patients and 3 healthy individuals to determine the expression pattern of circRNAs in blood and the circRNA molecular regulatory networks in PTB pathogenesis. One hundred and seventy differentially expressed (≥ 2-fold change) circRNAs were dysregulated in PTB, compared with in healthy individuals. Quantitative real-time polymerase chain reaction was used to validate the RNA sequencing analysis from 20 PTB patients, and the results were consistent with the sequencing data. Gene Ontology annotation and Kyoto Encyclopedia of Genes and Genomes pathway analysis were applied to explore the potential circRNA functions of the significantly deregulated genes. Several immunity pathways, including endocytosis pathways in cancer, mitogen-activated protein kinase signaling pathway, human T-lymphotropic virus type 1 infection, and ubiquitin-mediated proteolysis, were involved in PTB pathogenesis. Competing endogenous RNAs (ceRNA) were constructed and inferred that aberrant expression of circRNA-associated ceRNA resulted in extensive variation in gene expression by miRNA-mediated circRNA-mRNA crosstalk interactions. Our study revealed that the circRNA-miRNA-mRNA network may shed light on the biological functions of circRNAs in PTB and provide useful information for exploring potential roles of circRNA in PTB.

Genome-wide analysis of circular RNAs in prenatal and postnatal muscle of sheep

Circular RNAs (circRNAs), a type of non-coding RNA with circular structure, were generated by back splicing and widely expressed in animals and plants. Recent studies have shown that circRNAs extensively participate in cell proliferation, cell differentiation, cell autophagy and other biological processes. However, the role and expression of circRNAs in the development and growth of muscle have not been studied in sheep. In our study, we first used RNA-seq to study the circRNAs in prenatal and postnatal longissimus dorsi muscle of sheep. A total of 6113 circRNAs were detected from the RNA-seq data. Several circRNAs were identified using reverse transcription PCR, DNA sequencing and RNase R digestion experiments. The expression levels of several circRNAs in prenatal and postnatal muscle were confirmed by Real-Time RT-PCR. The gene ontology (GO) and KEGG enrichment analysis of the host gene of the circRNAs showed that these circRNAs were mainly involved in the growth and development of muscle related signaling pathways. These circRNAs might sponge microRNAs (miRNAs) in predicted circRNA-miRNA-mRNA networks. The circRNAs expression profiles in muscle provided an important reference for the study of circRNAs in sheep.

Circular RNAs function as competing endogenous RNAs in multiple types of cancer

Circular (circ)RNAs, naturally formed endogenous non-coding RNAs, have received extensive attention in recent years due to their special loop structures and specific function. circRNAs are formed with covalently closed continuous loops and are mainly generated by back-splicing processes or lariat introns from exons and/or introns. Usually, circRNAs are stable, abundant, and evolutionarily conserved in the cytoplasm. circRNAs often exhibit abnormal expression in different diseases, notably in human cancers, and the presence of abundant circRNAs in serum, saliva and exosomes renders them potential diagnostic or predictive biomarkers for diseases, including multiple types of cancer. Presently, certain circRNAs have been reported to function as microRNA sponges and RNA-binding protein sponges to regulate downstream gene transcription, which suggests a potential for circRNAs in cancer diagnosis, prognosis and clinical therapy. The present study assessed the latest advances in the study of circRNAs in cancer, summarized the functions of circRNAs in different types of cancer, highlighted the competing endogenous RNA function of circRNAs in the occurrence and development of human malignancies, and provided evidence for the future application of circRNAs in the diagnosis, prognosis and treatment of multiple types of cancer.

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.