The Biogenesis, Functions, and Challenges of Circular RNAs

Circular RNAs as novel regulators, biomarkers and potential therapies in fibrosis

Fibrosis is the excess deposition of extracellular matrix components which ultimately leads to the disruption of organ architecture and loss of function. Circular RNAs (circRNAs) are a newly discovered type of long noncoding RNAs with single-stranded covalently closed loops. It is known that circRNAs are novel regulators of gene expression via various ways, including miRNA sponge, protein sponge, regulation of transcription and post transcription. Recently, a growing body of evidence suggests that circular RNAs are also involved in tissue fibrosis in several organs. In this review, we summarized current studies of circular RNAs in fibrosis and hopefully aid in better understanding the molecular mechanism of fibrosis and provide a basis to explore new therapeutic targets of fibrosis.

Expression profiles of circRNAs and the potential diagnostic value of serum circMARK3 in human acute Stanford type A aortic dissection

CircRNAs are involved in a variety of human diseases, however, the expression profiles and the potential diagnostic value of circRNAs in human acute Stanford type A aortic dissection (AAAD) remains largely unknown. In this study, high-throughput RNA sequencing (RNA-Seq) was used to investigate the differentially expressed circRNAs, microRNAs (miRs) and mRNAs in human AAAD tissues (n = 10) compared with normal aortic tissues (n = 10). The results of RNA-Seq revealed that 506 circRNAs were significantly dysregulated (P<0.05, false discovery rate, FDR<0.05, fold change>2). The subsequent weighted gene correlation network analysis and the following co-expression network analysis revealed that tyrosine-protein kinase Fgr might play important roles in the occurrence and development of AAAD. According to the circRNA-miRNA-mRNA network, we found that the upstream regulatory molecule of Fgr is circMARK3. Finally, a receiver operating characteristic (ROC) curve was used to evaluate the diagnostic value of the serum circMARK3 as biomarkers for AAAD (cutoff value = 1.497, area under the curve = 0.9344, P < 0.0001, sensitivity = 90.0%, specificity = 86.7%). These results provided a preliminary landscape of circRNAs expression profiles and indicated that circMARK3 was a potential biomarker for AAAD diagnosis.

The emerging role of circular RNAs in breast cancer

Breast cancer (BCa) is one of the most frequently diagnosed cancers and leading cause of cancer deaths among females worldwide. Circular RNAs (circRNAs) are a new class of endogenous regulatory RNAs characterized by circular shape resulting from covalently closed continuous loops that are capable of regulating gene expression at transcription or post-transcription levels. With the unique structures, circRNAs are resistant to exonuclease RNase R and maintain stability more easily than linear RNAs. Recently, an increasing number of circRNAs are discovered and reported to show different expression in BCa and these dysregulated circRNAs were correlated with patients’ clinical characteristics and grade in the progression of BCa. CircRNAs participate in the bioprocesses of carcinogenesis of BCa, including cell proliferation, apoptosis, cell cycle, tumorigenesis, vascularization, cell invasion, migration as well as metastasis. Here we concentrated on biogenesis and function of circRNAs, summarized their implications in BCa and discussed their potential as diagnostic and therapeutic targets for BCa.

circGFRA1 Promotes Ovarian Cancer Progression By Sponging miR-449a

Backgroud: Increasing studies show that circular RNAs (circRNAs) play important roles in tumor progression. However, the function of circRNAs in ovarian cancer is mostly unclear. Methods: We detected the expression of circGFRA1 by quantitative real-time PCR (qRT-PCR) in 50 pairs of ovarian cancer tissues and adjacent normal tissues. Then, we explored the function of circGFRA1 in ovarian cancer progression, such as cell proliferation, apoptosis and invasion. Moreover, we performed luciferase reporter and RNA immunoprecipitation (RIP) assay to study the competing endogenous RNA (ceRNA) function of circGFRA1 in ovarian cancer progression. Results: qRT-PCR showed that circGFRA1 was overexpressed in ovarian cancer tissues. Inhibition of circGFRA1 suppressed cell proliferation and invasion, but induced cell apoptosis in ovarian cancer. Luciferase reporter and RIP assay revealed that circGFRA1 could regulate the expression of GFRA1 by sponging miR-449a. Conclusions: In summary, circGFRA1 regulated GFRA1 expression and ovarian cancer progression by sponging miR-449a. circGFRA1 could be a potential diagnostic biomarker and therapeutic target for ovarian cancer.

Epigenetics and vascular diseases

Cardiovascular disease remains the number one cause of death and disability worldwide despite significant improvements in diagnosis, prevention, and early intervention efforts. There is an urgent need for improved understanding of cardiovascular processes responsible for disease development in order to develop more effective therapeutic strategies. Recent knowledge gleaned from the study of epigenetic mechanisms in the vasculature has uncovered new potential targets for intervention. Herein, we provide an overview of epigenetic mechanism, and review recent findings related to epigenetics in vascular diseases, highlighting classical epigenetic mechanism such as DNA methylation and histone modification as well as the newly discovered non-coding RNA mechanisms.

Differential expression profiles and functional analysis of circular RNAs in children with fulminant myocarditis

Aim: To assess differential expression profiles of circular RNAs (circRNAs) and explore their possible functions in children with fulminant myocarditis. Materials & methods: circRNA microarray experiments were carried out for determining differential expression profiles of circRNAs in three children with fulminant myocarditis and three healthy volunteers. Functional analysis and circRNA-miRNA-mRNA interaction network building were conducted to study biological functions. Results: This work identified 2281 upregulated and 892 downregulated circRNAs. Further assessment confirmed hsa_circ_0071542 upregulation (2.5-fold) in fulminant myocarditis. Functional analysis demonstrated the differentially expressed circRNAs mainly contributed to inflammation and immunity. Conclusion: circRNAs might have substantial roles in pediatric fulminant myocarditis, and hsa_circ_0071542 could serve as a promising biomarker.

Functions and Potential Applications of Circular RNAs in Cancer Stem Cells

Circular RNAs (circRNAs) were discovered in the 1970s, but they have drawn increasing attention in recent years. Currently, we know that circRNAs are not "wrongly spliced" during transcription but play important roles in the initiation and development of various diseases, including cancers. Recently, a growing number of studies have suggested that cancer stem cells (CSCs) may contribute to the origination and maintenance of cancers. This review briefly introduces the major functions of circRNAs, including interacting with other noncoding RNAs, competing with pre-mRNA splicing, binding with proteins to form a scaffold, promoting protein nuclear translocation and even translating proteins in a cap-independent manner. Furthermore, we describe the regulatory mechanism of circRNAs in CSC phenotypes and discuss the potential clinical applications of circRNAs in CSC-targeted therapy, including functioning as new biomarkers, acting as vaccines and breaking the therapeutic resistance of CSCs. Finally, we discuss the major limitations and challenges in the field, which will be beneficial for the future clinical use of circRNAs.

The Role of CDR1as in Proliferation and Differentiation of Human Umbilical Cord-Derived Mesenchymal Stem Cells

Mesenchymal stem cells derived from human umbilical cord (hucMSCs) are considered a promising tool for regenerative medicine. circRNAs as newly discovered noncoding RNAs are involved in multiple biological processes. However, little has been known about the function of circRNAs in the proliferation and differentiation of hucMSCs. In this study, we selected several circRNAs expressed in MSCs from circBase and found that CDR1as expression level was markedly significant. We observed that, compared with that of uninduced hucMSCs, the CDR1as expression level of induced hucMSCs decreased with cell induction differentiation. By using siRNA to knock down CDR1as of hucMSCs, we discovered that proliferation was inhibited but the apoptosis increased. In addition, we found that the expression of stemness transcription factors (STFs) was downregulated after CDR1as knockdown and the adipogenesis and osteogenesis potential of hucMSCs was impaired. Our findings suggest that CDR1as takes a part in maintaining proliferation and differentiation of hucMSCs, providing clues for MSC modification and further for stem cell therapy and tissue regeneration.

CircABCC2 Regulates Hepatocellular Cancer Progression by Decoying MiR-665

Background: Numerous studies have shown that circular RNAs (circRNAs) play vital roles in tumor progression. However, how circRNAs function in hepatocellular cancer (HCC) remains mostly unclear.

Methods: We analyzed HCC circRNA expression via a microarray, and the expression of an upregulated circRNA, circABCC2, was detected. We next explored the function of circABCC2 in HCC via a series of experiments. We performed RNA immunoprecipitation (RIP) and luciferase assays to explore the competing endogenous RNA (ceRNA) function of circABCC2 in HCC.

Results: qRT-PCR verified that circABCC2 was overexpressed in HCC. Inhibition of circABCC2 suppressed HCC cell proliferation and invasion, but promoted apoptosis. Luciferase assays and RIP showed that circABCC2 and ABCC2 could directly bind to miR-665 and that circABCC2 could regulate ABCC2 expression by sponging miR-665.

Conclusions: In summary, circABCC2 regulates ABCC2 expression and HCC progression by sponging miR-665. circABCC2 could be used as a biomarker and therapeutic target in HCC.

Noncoding RNAs in cancer therapy resistance and targeted drug development

Noncoding RNAs (ncRNAs) represent a large segment of the human transcriptome and have been shown to play important roles in cellular physiology and disease pathogenesis. Increasing evidence on the functional roles of ncRNAs in cancer progression emphasizes the potential of ncRNAs for cancer treatment. Here, we summarize the roles of ncRNAs in disease relapse and resistance to current standard chemotherapy and radiotherapy; the current research progress on ncRNAs for clinical and/or potential translational applications, including the identification of ncRNAs as therapeutic targets; therapeutic approaches for ncRNA targeting; and ncRNA delivery strategies in potential clinical translation. Several ongoing clinical trials of novel RNA-based therapeutics were also emphasized. Finally, we discussed the perspectives and obstacles to different target combinations, delivery strategies, and system designs for ncRNA application. The next approved nucleic acid drug to treat cancer patients may realistically be on the horizon.

Circular RNA 0047905 acts as a sponge for microRNA4516 and microRNA1227-5p, initiating gastric cancer progression

Several lines of evidence suggest that circular RNAs (circRNAs) play important roles in oncogenesis and tumor progression. However, our knowledge of the role of circRNAs in gastric cancer (GC) remains limited. We investigated the possibility that circular RNA 0047905 (circRNA0047905) might act as a tumor promoter in the pathogenesis of gastric cancer by profiling miRNA expression in GC tissues and paired noncancerous mucosa tissues using miRNA microarrays. Next, a ceRNA network was constructed according to common miRNAs binding circRNAs and mRNAs. Mechanistically, we demonstrated that circRNA0047905 directly binds miR4516 and miR1227-5p, relieving suppression for targets SERPINB5 and MMP11. We observed that down-regulated circRNA0047905 expression in gastric cancer cells inhibited Akt/CREB signaling pathway activation. RNA scope in situ hybridization revealed expression of circRNA0047905 in GC. Our data suggest that circRNA0047905 is a promising target for GC diagnosis and therapy.

Circular RNA expression profile in peripheral blood mononuclear cells from Crohn disease patients

Crohn disease (CD) is a multifactorial autoimmune disease which is characterized by chronic and recurrent gastrointestinal tract inflammatory disorder. However, the molecular mechanisms of CD remain unclear. Increasing evidences have demonstrated that circular RNAs (circRNAs) participate in the pathogenesis of a variety of disease and were considered as ideal biomarkers in human disease. This study aimed to investigate circRNA expression profiles and detect new biomarkers in inflammatory bowel disease (IBD). Differentially expression of circRNAs between CD and HCs (health controls) were screened by microarray analysis. Peripheral blood mononuclear cells (PBMCs) from 5 CD patients and 5 HCs were included in the microarray analysis. Then, the differences were validated by quantitative polymerase chain reaction (qPCR) following reverse transcription polymerase chain reaction (RT-PCR) in the patients of CD and sex- and age-matched HCs. The most differential expressed circRNA was further validated in ulcerative colitis (UC) patients. Statistical significance between CD, UC, and HCs was analyzed by Student t test for unpaired samples or one-way analysis of variance (ANOVA). Diagnostic value of each circRNA was assessed by receiver operating characteristic (ROC) curve. We identified 155 up-regulated circRNAs and 229 down-regulated ones by microarray analysis in PBMCs from CD patients compared with HCs. Besides, 4 circRNAs (092520, 102610, 004662, and 103124) were significantly up-regulated validated by RT-PCR and qPCR between CD and HCs. ROC curve analysis suggested important values of circRNAs (092520, 102610, 004662, and 103124) in CD diagnosis, with area under the curve (AUC) as 0.66, 0.78, 0.85, and 0.74, respectively. Then, we further identified that the relative expression levels of circRNA_004662 was upregulated significantly in CD patients compared with UC patients. Herein, the upregulation of the 4 circRNAs (092520, 102610, 004662, or 103124) in PBMCs can be served as potential diagnostic biomarkers of CD, and circRNA_004662 might be a novel candidate for differentiating CD from UC. Moreover, a circRNA-microRNA-mRNA network predicted that circRNA_004662 appeared to be correlated with mammalian target of rapamycin (mTOR) pathway.

A transcriptomic regulatory network among miRNAs, piRNAs, circRNAs, lncRNAs and mRNAs regulates microcystin-leucine arginine (MC-LR)-induced male reproductive toxicity

Microcystin-leucine arginine (MC-LR) which is produced by cyanobacteria is a potent toxin for the reproductive system. Our previous work has demonstrated that both acute and chronic reproductive toxicity engendered by MC-LR can result in the decline of sperm quality and damage of testicular structures in male mice. The present study was designed to investigate the impact of chronic low-dose exposure to MC-LR on the regulation of RNA networks including mRNA, microRNA (miRNA), piwi-associated RNA (piRNA), covalently closed circular RNA (circRNA) and long non-coding RNA (lncRNA) in testicular tissues. By high-throughput sequencing analysis, 1091 mRNAs, 21 miRNAs, 644 piRNAs, 278 circRNAs and 324 lncRNAs were identified to be significantly altered in testicular tissues treated with MC-LR. We performed gene ontology (GO) analysis to ascertain the biological functions of differentially expressed genes. Among the altered 21 miRNAs and 644 piRNAs, the miRNA chr13_8977, which is a newly discovered species, and the piRNA mmu_piR_027558 were dramatically down-regulated after exposure to MC-LR. Consistently, both mRNA levels and protein expression levels of their predicted targets were increased significantly when chr13_8977 and mmu_piR_027558 were each down-regulated. Testicular structures, germ cell apoptosis and sperm quality were also affected by the altered expression of chr13_8977 and mmu_piR_027558 severally. We further investigated the differential expression of circRNAs and lncRNAs and their biological functions in testicular tissues following treatment with chronic low-dose exposure to MC-LR. We also constructed a competing endogenous RNA (ceRNA) network to predict the functions of the altered expressed RNAs using MiRanda. Our study suggested a crucial role for the potential network regulation of miRNAs, piRNAs, circRNAs, lncRNAs and mRNAs impacting the cytotoxicity of MC-LR in testicular tissues, which provides new perspectives in the development of diagnosis and treatment strategies for MC-LR-induced male reproductive toxicity.

Circular PVT1: an oncogenic non-coding RNA with emerging clinical importance

The importance of circular RNAs (circRNAs) in pathological processes like cancer is evident. Among the circRNAs, recent studies have brought circPVT1 under focus as the most potent oncogenic non-coding RNA. Recent studies on various aspects of circPVT1, including its biogenesis, molecular alteration and its probable role in oncogenesis, have been conducted for research and clinical interest. In this review, a first attempt has been made to summarise the available data on circPVT1 from PubMed and other relevant databases with special emphasis on its role in development, progression and prognosis of various malignant conditions. CircPVT1 is derived from the same genetic locus encoding for long non-coding RNA lncPVT1; however, existing literature suggested circPVT1 and lncPVT1 are transcripted independently by different promoters. The interaction between circRNA and microRNA has been highlighted in majority of the few malignancies in which circPVT1 was studied. Besides its importance in diagnostic and prognostic procedures, circPVT1 seemed to have huge therapeutic potential as evident from differential drug response of cancer cell line as well as primary tumors depending on expression level of the candidate. circPVT1 in cancer therapeutics might be promising as a biomarker to make the existing treatment protocol more effective and also as potential target for designing novel therapeutic intervention.

Non-Coding RNAs in Caenorhabditis elegans Aging

Non-coding RNAs (ncRNAs) comprise various RNA species, including small ncRNAs and long ncRNAs (lncRNAs). ncRNAs regulate various cellular processes, including transcription and translation of target messenger RNAs. Recent studies also indicate that ncRNAs affect organismal aging and conversely aging influences ncRNA levels. In this review, we discuss our current understanding of the roles of ncRNAs in aging and longevity, focusing on recent advances using the roundworm Caenorhabditis elegans. Expression of various ncRNAs, including microRNA (miRNA), tRNA-derived small RNA (tsRNA), ribosomal RNA (rRNA), PIWI-interacting RNA (piRNA), circular RNA (circRNA), and lncRNA, is altered during aging in C. elegans. Genetic modulation of specific ncRNAs affects longevity and aging rates by modulating established aging-regulating protein factors. Because many aging-regulating mechanisms in C. elegans are evolutionarily conserved, these studies will provide key information regarding how ncRNAs modulate aging and lifespan in complex organisms, including mammals.

Circular RNAs and RNase L in PKR activation and virus infection

Circular RNAs (circRNAs) from back-splicing have been found in every cell and tissue. By binding to miRNAs and proteins or even by encoding small proteins, circRNAs are now emerging as important regulators in modulating transcription, RNA splicing and interference. The highlighted discovery reports an important role of circRNAs in antiviral innate immunity by binding PKR as PKR inhibitors. Rapid degradation of circRNAs by activated RNase L from virus infection or poly I:C stimulation is required to free PKR for its activation. Systemic lupus erythematosus patients remark with circRNA reduction and aberrant PKR activation.

Transforming activity of an oncoprotein-encoding circular RNA from human papillomavirus

Single-stranded circular RNAs (circRNAs), generated through ‘backsplicing’, occur more extensively than initially anticipated. The possible functions of the vast majority of circRNAs remain unknown. Virus-derived circRNAs have recently been described in gamma-herpesviruses. We report that oncogenic human papillomaviruses (HPVs) generate circRNAs, some of which encompass the E7 oncogene (circE7). HPV16 circE7 is detectable by both inverse RT-PCR and northern blotting of HPV16-transformed cells. CircE7 is N⁶-methyladenosine (m⁶A) modified, preferentially localized to the cytoplasm, associated with polysomes, and translated to produce E7 oncoprotein. Specific disruption of circE7 in CaSki cervical carcinoma cells reduces E7 protein levels and inhibits cancer cell growth both in vitro and in tumor xenografts. CircE7 is present in TCGA RNA-Seq data from HPV-positive cancers and in cell lines with only episomal HPVs. These results provide evidence that virus-derived, protein-encoding circular RNAs are biologically functional and linked to the transforming properties of some HPV.

The authors identify circular RNAs (circRNA) from human papillomavirus and show that circRNA-encoded E7 contributes to cancer cell growth in vitro and in tumor xenografts. Furthermore, circE7 is present in TCGA RNA-Seq data from HPV-positive cancers.

Microarray analysis reveals the changes of circular RNA expression and molecular mechanism in acute lung injury mouse model

Acute lung injury (ALI) is a severe disease with sudden onset, rapid progression, poor treatment response, and high mortality. An increasing number of studies had found that circular RNAs (circRNAs) has significant functions in various diseases, while the role of circRNAs in ALI is not yet clear. The purpose of this study was to find circRNAs related to ALI and their mechanism of action. Expression profiles of lung circRNAs and messenger RNAs (mRNAs) were analyzed by microarray in the ALI mice models and healthy controlled mice. Differentially expressed RNAs were identified, function and pathways were analyzed by bioinformatics analysis. Moreover, the results of the microarray were verified by real-time PCR. We identified 2262 differentially expressed mRNAs and 581 circRNAs between ALI mice and control. Validation of candidate circRNAs by real-time PCR indicates that the majority of circRNAs identified by microarray are reliable and worthy of further study. ALI induced circRNAs primarily function in the metabolic regulatory process. Moreover, differentially expressed circRNAs were mainly involved in signaling pathways of mitogen-activated protein kinases, focal adhesion, FoxO, neurotrophin, and Wnt. In addition, a competitive endogenous RNA network was constructed to further interpret the molecular mechanism of ALI. This study observed significantly changed circRNAs profiles in LPS-induced mouse model and revealed a potential role of circRNAs in ALI.

Circular exonic RNAs: When RNA structure meets topology

Although RNA circularization was first documented in the 1990s, the extent to which it occurs was not known until recent advances in high-throughput sequencing enabled the widespread identification of circular RNAs (circRNAs). Despite this, many aspects of circRNA biogenesis, structure, and function yet remain obscure. This review focuses on circular exonic RNAs, a subclass of circRNAs that are generated through backsplicing. Here, I hypothesize that RNA secondary structure can be the common factor that promotes both exon skipping and spliceosomal RNA circularization, and that backsplicing of double-stranded regions could generate topologically linked circRNA molecules. CircRNAs manifest themselves by the presence of tail-to-head exon junctions, which were previously attributed to post-transcriptional exon permutation and repetition. I revisit these observations and argue that backsplicing does not automatically imply RNA circularization because tail-to-head exon junctions give only local information about transcript architecture and, therefore, they are in principle insufficient to determine globally circular topology. This article is part of a Special Issue entitled: RNA structure and splicing regulation edited by Francisco Baralle, Ravindra Singh and Stefan Stamm.

Computational approaches for the discovery of splicing regulatory RNA structures

Global RNA structure and local functional motifs mediate interactions important in determining the rates and patterns of mRNA splicing. In this review, we overview approaches for the computational prediction of RNA secondary structure with a special emphasis on the discovery of motifs important to RNA splicing. The process of identifying and modeling potential splicing regulatory structures is illustrated using a recently-developed approach for RNA structural motif discovery, the ScanFold pipeline, which is applied to the identification of a known splicing regulatory structure in influenza virus.

Intriguing circles: Conflicts and controversies in circular RNA research

Circular RNAs (circRNAs) are covalently closed RNA circles without a 5' cap or 3' tail. Since the landmark discovery of ciRS-7/CDR1as functioning as a miR-7 sponge in 2013, circRNAs have become a hot topic in RNA research. CircRNAs have been found to play active roles in cancer, cardiovascular diseases, neurological disorders, and many other diseases. They can function as microRNA (miRNA) sponges, protein scaffolds, and even translation templates. However, as circRNA research expands, many divergent views have emerged. For example, are most circRNAs competent in serving as miRNA sponges? What kinds of circRNAs are most likely to sponge miRNAs? Apart from sponging miRNAs, what could the functions of most circRNAs be? What are the features of circRNAs that are translatable? Many researchers have claimed that circRNAs are abundant, stable, conserved, and specific molecules, which hold great potential in serving as biomarkers. However, circRNA abundance is variable and some circRNAs are abundant while others are not. In addition, their stability and conservation may vary under different circumstances. Furthermore, it is unclear whether circRNA biogenesis is more likely to be regulated by RNA binding proteins or transcription factors. All of these are open questions that remain to be answered by researchers in this field. Discussing and investigating these questions will advance the understanding of this class of novel molecules and may propel inspiring new ideas for future studies. This article is categorized under: Regulatory RNAs/RNAi/Riboswitches > Regulatory RNAs RNA in Disease and Development > RNA in Disease RNA Methods > RNA Analyses in Cells RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications.

Circbank: a comprehensive database for circRNA with standard nomenclature

Circular RNAs (circRNAs) represent a new type of regulatory RNA which forms a covalently closed continuous loop from back-splicing events, a process in which the downstream 5' splice site and the 3' splice site are covalently linked. Emerging evidence indicates that circRNAs exert a new layer of transcriptional and post-transcriptional regulation of gene expression. However, there is no standard nomenclature of circRNA, although the study of circRNAs has exploded in the past few years. Here we present circbank ( www.circbank.cn ), a comprehensive database for human circRNAs, where a novel naming system of circRNAs based on the host genes of circRNAs was implemented. In addition to the new naming system, circbank collected other five features of circRNAs including the miRNA binding site, conservation of circRNAs, m⁶A modification of circRNAs, mutation of circRNAs and protein-coding potential of circRNAs. Circbank is publicly available and allows users to query, browse and download circRNAs with all six features we provided, based on different search criteria. The database may serve as a resource to facilitate the research of function and regulation of circRNAs.

Comprehensive circRNA/miRNA/mRNA analysis reveals circRNAs protect against toxicity induced by BPA in GC-2 cells

Aim: To identify the circRNAs expression pattern and roles in bisphenol A (BPA) induced germ cell apoptosis. Materials & methods: We performed circRNA/miRNA/mRNA-Seq in 120 μM BPA treated and nontreated GC-2 cells. Bioinformatic analysis, qPCR, apoptosis assays, luciferase report were done in the function analysis. Results: A large number of apoptosis related circRNAs/miRNAs/mRNAs were differentially expressed with competing endogenous RNA network constructed. Interestingly, most investigated upregulated circRNAs, including circDcbld2, circMapk1, circMpp6 and circTbc1d20 showed protective effects in antagonizing BPA toxicity, with the effects individually and synergistically observed. CircMapk1 may take its role by sponging miR-214-3p. Conclusion: circRNAs can play protective roles via sponging miRNAs in toxicity. Some circRNAs may serve as novel targets for BPA toxicity intervention or as biomarkers.

Circular RNA CircCACTIN Promotes Gastric Cancer Progression by Sponging MiR-331-3p and Regulating TGFBR1 Expression

Background: Circular RNAs (circRNAs) are a new class of RNAs that play a significant role in regulating gene expression and biological function. However, the expression profile and function of circRNAs in gastric cancer (GC) remain mostly uncertain. In the present study, we researched the expression profile of circRNAs in human GC tissues and explored the role of circCACTIN (hsa_circ_0092303).

Methods: Circular RNA microarray assays were performed to detect circular RNA expression profiles of GC and circCACTIN was identified for further investigation. Quantitative real-time PCR was used to detect the expression of circCACTIN, miR-331-3p and TGFBR1 in GC specimens and cell lines. CircCACTIN was stably silenced and overexpressed in GC cells, and cell proliferation, migration, invasion, epithelial-mesenchymal transition (EMT), as well as tumorigenesis in nude mice were performed to assess the effect of circCACTIN on GC.

Results: CircCACTIN expression was obviously up-regulated in GC tissues and cell lines. Knockdown of circCACTIN inhibited GC cells proliferation, migration, invasion and EMT. Enforced-expression of circCACTIN promoted GC cells migration, invasion and EMT, but had no effect on GC cells proliferation. Moreover, in vivo experiments, circCACTIN up-regulation promoted GC tumor growth and EMT, and circCACTIN down-regulation inhibited GC tumor growth and EMT. Binding interactions were detected between circCACTIN and miR-331-3p, and between miR-331-3p and TGFBR1 by Dual-luciferase reporter assays. Mechanistically, we demonstrated that circCACTIN promoted gastric cancer progression by sponging miRNA-331-3p and regulating TGFBR1 mRNA expression.

Conclusion: The circCACTIN/miR-331-3p/TGFBR1 axis affected the proliferation, migration, invasion and EMT of GC through the mechanism of competing endogenous RNAs (ceRNA). Furthermore, our results identified circCACTIN as a novel oncogenic circRNA in GC.

Analysis of Circular RNA Expression Profile in HEK 293T Cells Exposed to Ionizing Radiation

Radiation therapy is one of the most common cancer treatments. It is important to understand how cells respond to ionizing radiation (IR) to improve therapeutic efficacy. Circular RNAs (circRNAs) recently have been found to regulate a variety of cellular processes. However, it is poorly defined that their expression pattern and their identity in cells following IR exposure. Here, we performed high-throughput sequencing and comprehensive analysis of circRNA expression in human embryonic kidney (HEK) 293T cells before and after irradiation. We identified totally 5592 circRNAs and discovered 1038 new circRNAs. We found 158 circRNAs with significantly differential expression after IR exposure. Among them, there were 61 upregulated and 97 downregulated circRNAs. Using Gene Ontology, Kyoto Encyclopedia of Genes and Genomes pathway, and circRNA-microRNA-messenger RNA network analyses, we found the differentially expressed circRNAs might be involved in the signal pathways of oxidative phosphorylation, epithelial growth factor receptor (EGFR) tyrosine kinase inhibitor resistance, and mammalian target of rapamycin (mTOR) signaling.

Circular RNA hsa_circ_0068871 regulates FGFR3 expression and activates STAT3 by targeting miR-181a-5p to promote bladder cancer progression

BACKGROUND

FGFR3 plays an important role in the development of bladder cancer (BCa). Hsa_circ_0068871 is a circRNA generated from several exons of FGFR3. However, the potential functional role of hsa_circ_0068871 in BCa remains largely unknown. Here we aim to evaluate the role of hsa_circ_0068871 in BCa.

METHODS

We selected miR-181a-5p as the potential target miRNA of hsa_circ_0068871. The expression levels of hsa_circ_0068871 and miR-181a-5p were examined in BCa tissues and paired adjacent normal tissues by quantitative real-time PCR. To characterize the function of hsa_circ_0068871, BCa cell lines were stably infected with lentivirus targeting hsa_circ_0068871, followed by examinations of cell proliferation, migration and apoptosis. In addition, xenografts experiment in nude mice were performed to evaluate the effect of hsa_circ_0068871 in BCa. Biotinylated RNA probe pull-down assay, fluorescence in situ hybridization and luciferase reporter assay were conducted to confirm the relationship between hsa_circ_0068871, miR-181a-5p and FGFR3.

RESULTS

Hsa_circ_0068871 is over-expressed in BCa tissues and cell lines, whereas miR-181a-5p expression is repressed. Depletion of has_circ_0068871 or upregulation of miR-181a-5p inhibited the proliferation and migration of BCa cells in vitro and in vivo. Mechanistically, hsa_circ_0068871 upregulated FGFR3 expression and activated STAT3 by targeting miR-181a-5p to promote BCa progression.

CONCLUSIONS

Hsa_circ_0068871 regulates the miR-181a-5p/FGFR3 axis and activates STAT3 to promote BCa progression, and it may serve as a potential biomarker.

Circular RNA DOCK1 promotes bladder carcinoma progression via modulating circDOCK1/hsa-miR-132-3p/Sox5 signalling pathway

Objectives

To reveal the role of circular RNA (circRNA) DOCK1 (circDOCK1) as a potential biomarker and therapeutic target and its competing endogenous RNA mechanism in bladder carcinoma (BC).

Methods

The next‐generation sequencing (NGS) technology was introduced to screen the circRNA expression profiles of BC using microarray. qPCR and Western blots assay were employed to measure the gene expression in different groups. Cell counting kit‐8, EdU and transwell assays were applied to detect the cell viability, proliferation and migration potential, respectively. Luciferase reporter assay was used to test the binds between hsa‐miR‐132‐3p/Sox5. Xenografted tumour growth of nude mice was performed to test the role of circDOCK1 in vivo.

Results

CircDOCK1 was upregulated in BC tissues and cell lines. Repression of circDOCK1 reduced cell viability, inhibited cell proliferation and curbed the cell migration potential of BC cell. CircDOCK1 played its role via regulation of circDOCK1/hsa‐miR‐132‐3p/Sox5 pathway in BC cells. Suppression circDOCK1 inhibited the tumour growth in vivo.

Conclusion

In this study, we revealed that circDOCK1 affected the progression of BC via modulation of circDOCK1/hsa‐miR‐132‐3p/Sox5 pathway both in vitro and in vivo and providing a potential biomarker and therapeutic targets for BC.

N6-Methyladenosine (m6A): A Promising New Molecular Target in Acute Myeloid Leukemia

Recent studies have uncovered an important role for RNA modifications in gene expression regulation, which led to the birth of the epitranscriptomics field. It is now acknowledged that RNA modifiers play a crucial role in the control of differentiation of stem and progenitor cells and that changes in their levels are a relevant feature of different types of cancer. To date, among more than 160 different RNA chemical modifications, the more relevant in cancer biology is the reversible and dynamic N⁶-methylation of adenosine, yielding N⁶-methyladenosine (m⁶A). m⁶A is the more abundant internal modification in mRNA, regulating the expression of the latter at different levels, from maturation to translation. Here, we will describe the emerging role of m⁶A modification in acute myeloid leukemia (AML), which, among first, has demonstrated how mis-regulation of the m6A modifying system can contribute to the development and progression of cancer. Moreover, we will discuss how AML is paving the way to the development of new therapeutic options based on the inhibition of m⁶A deposition.

Engineering of hairpin ribozyme variants for RNA recombination and splicing

The hairpin ribozyme is a small, naturally occurring RNA that catalyzes the reversible cleavage of RNA substrates. Among the small endonucleolytic ribozymes, the hairpin ribozyme possesses the unique feature of the internal equilibrium between cleavage and ligation being shifted toward ligation. This allows control of the reaction outcome by structural design: fragments that are strongly bound to the ribozyme are preferentially ligated, whereas substrates that easily dissociate upon cleavage, such that they are not available for religation, are preferentially cleaved. We have made use of this characteristic feature in engineering a number of hairpin ribozyme variants by programmed conformational design that carry out cascades of cleavage and ligation reactions, and as a result mediate more complex RNA processing reactions. Here, we review our work on the engineering of hairpin ribozyme variants for RNA recombination and regular and back-splicing, and discuss the relevance of such activities in early life.

Circular RNAs and their roles in head and neck cancers

Circular RNAs are abundant endogenous non-coding RNA with no 5′ cap and 3′ polyadenylation tail that modify liner mRNAs and have no terminal structures. Our knowledge of the biogenesis of circular RNAs has been expanded, and circular RNAs were shown to be key regulators of various diseases, especially cancers. Head and neck cancers are the sixth most popular cancers worldwide, and the overall survival rates remain unsatisfactory. Recent studies have indicated that circular RNAs are involved in the tumorigenesis, progression, invasion and chemosensitivity of head and neck cancers and that some circular RNAs could serve as diagnostic and prognostic biomarkers. In this study, we summarize research advances in the regulation of circular RNA biogenesis, their characteristics and functions, the involvement of circular RNAs in the pathophysiology of head and neck cancers and their potential clinical utilization, as well as the likely directions of future studies.

Circular RNAs as promising biomarkers in cancer: detection, function, and beyond

Circular RNAs (circRNAs) are 3′–5′ covalently closed RNA rings produced from back-splicing of precursor mRNA in eukaryotes. Recent studies, using both computational and experimental approaches, have allowed advanced characterization of circRNAs, leading the research field into a new era and shedding light on the contribution of circRNAs to disease.

circEPSTI1 regulates ovarian cancer progression via decoying miR-942

Increasing studies show that circular RNAs (circRNAs) play vital roles in tumour progression. But, how circRNAs function in ovarian cancer is mostly unclear. Here, we detected the expression of circEPSTI1 in ovarian cancer and explored the function of circEPSTI1 in ovarian cancer via a series of experiments. Then, we performed luciferase assay and RNA immunoprecipitation (RIP) assay to explore the competing endogenous RNA (ceRNA) function of circEPSTI1 in ovarian cancer. qRT-PCR verified that circEPSTI1 was overexpressed in ovarian cancer. Inhibition of circEPSTI1 suppressed ovarian cancer cell proliferation, invasion but promoted cell apoptosis. Luciferase assays and RIP assay showed that circEPSTI1 and EPSTI1 (epithelial stromal interaction 1) could directly bind to miR-942. And circEPSTI1 could regulate EPSTI1 expression via sponging miR-942. In summary, circEPSTI1 regulated EPSTI1 expression and ovarian cancer progression by sponging miR-942. circEPSTI1 could be used as a biomarker and therapeutic target in ovarian cancer.

Up-regulation of circular RNA hsa_circ_0037909 promotes essential hypertension

Aims

Essential hypertension (EH) is a high prevalence disease facing a public health challenge. People were little known about the genetics of diagnosing the cause of EH. Circular RNAs that have a continuous cycle of covalent closure, without affected by RNA exonuclease, and are more stable and hard to degrade may involve into the molecule regulation mechanism of EH as an important biomedical.

Methods

qRT‐PCR was used to analyze circRNAs in total volume of human blood and the induced human aortic endothelial cells (HAECs) and human umbilical vein endothelial cells (HUVECs). Our case‐control study was involved with 48 pairs of case controls with sex and age (±3 years) match. We conducted t test, Pearson's χ² test, and receiver operating characteristics (ROC) curve analysis for the corresponding analysis.

Results

The expression level of hsa_circ_0037909 in EH patients was significantly higher than that in the healthy controls (P = 0.007), and the expression level of hsa‐miR‐637 in EH patients was significantly lower in than that in the healthy controls (P = 0.039); the same result appears in the HAECs and HUVECs. Hsa‐miR‐637 (adjusted P = 0.018), hsa_circ_0037909 (adjusted P = 0.005), HDL (adjusted P = 0.024), and serum creatinine (adjusted P = 0.014) were brought into the model which performed logistic regression analysis. The combination of two RNAs was excellent (P < 0.001) through ROC curve analysis. Hsa_circ_0037909 was significantly positively correlated with serum creatinine (P < 0.001) and low‐density lipoprotein (LDL) (P = 0.017).

Conclusions

Our findings suggested that the combination of hsa_circ_0037911 and hsa‐miR‐637 may be a significant important biomarker for early diagnosis of EH. Hsa_circ_0037909 may affect serum creatinine or LDL leading to the formation of EH.

Low Expression of hsa_circ_0018069 in Human Bladder Cancer and Its Clinical Significance

Abnormal expression of noncoding RNA molecules such as circRNA plays an important role in the development of malignant tumors. circRNAs are stable in structure and can be useful as ideal tumor markers. Advanced bladder cancer has poor treatment options and prognosis. Thus, we examined circRNAs to further understand the pathogenesis and development of bladder cancer and to identify molecular markers for the early diagnosis of bladder carcinoma. We found that hsa_circ_0018069 was differentially expressed in our RNA sequencing data. We used qRT-PCR to detect its expression in T24 and Biu-87 cell lines and in 41 paired samples of bladder cancer and adjacent normal tissue and analyzed the correlation between expression of hsa_circ_0018069 and the clinical characteristics of patients with bladder cancer. We then performed a bioinformatics analysis to reveal the mechanism of hsa_circ_0018069 in tumorigenesis of bladder cancer. The expression of hsa_circ_0018069 was significantly reduced in T24 and Biu-87 cells and was also significantly downregulated in bladder cancer tissues. Decreased expression of hsa_circ_0018069 was related to the grade stage (P=0.024), T stage (P=0.027), and muscular invasion depth (P=0.022) of bladder cancer. Bioinformatics analysis showed that hsa_circ_0018069 was coexpressed with protein-coding mRNAs that participate in cytoskeletal protein binding and cell-substrate junction assembly and play an anticancer role through focal adhesion and calcium signaling pathways. ceRNA analysis showed that hsa_circ_0018069 functions in ErbB, Ras, FoxO, and the focal adhesion signaling pathway by harboring miR-23c, miR-34a-5p, miR-181b-5p, miR-454-3p, and miR-3666. hsa_circ_0018069 may thus play an important role in the occurrence and progression of bladder cancer and serve as a valuable biomarker for the early diagnosis of this disease.

Circular RNA expression profiles in neonatal rats following hypoxic-ischemic brain damage

Circular RNAs (circRNAs) have been studied in a number of diseases. However, the roles of circRNAs in hypoxic‑ischemic brain damage (HIBD) remains unknown. In the present study, high throughput sequencing was used to profile altered circRNAs in HIBD rats. A total of 66 circRNAs were identified to be differentially expressed (fold‑change >2 and P‑value <0.05) in HIBD rats compared with the control group, including 20 upregulated and 46 downregulated circRNAs. Gene ontology and Kyoto Encyclopedia of Genes and Genomes pathway analysis indicated that numerous mRNAs transcribed from the host genes of altered circRNAs were involved in brain damage and neural regeneration. The interaction of circRNA/microRNA was predicted based on TargetScan and miRanda. The results of this study demonstrated an altered circRNA expression pattern in HIBD rats and suggests important roles in HIBD physiological and pathological processes. These findings suggest a novel focus for future studies investigating the molecular mechanism underlying HIBD and possibilities for the treatment of HIBD through modulating circRNAs.

MicroRNA in Brain pathology: Neurodegeneration the Other Side of the Brain Cancer

The mammalian brain is made up of billions of neurons and supporting cells (glial cells), intricately connected. Molecular perturbations often lead to neurodegeneration by progressive loss of structure and malfunction of neurons, including their death. On the other side, a combination of genetic and cellular factors in glial cells, and less frequently in neurons, drive oncogenic transformation. In both situations, microenvironmental niches influence the progression of diseases and therapeutic responses. Dynamic changes that occur in cellular transcriptomes during the progression of developmental lineages and pathogenesis are controlled through a variety of regulatory networks. These include epigenetic modifications, signaling pathways, and transcriptional and post-transcriptional mechanisms. One prominent component of the latter is small non-coding RNAs, including microRNAs, that control the vast majority of these networks including genes regulating neural stemness, differentiation, apoptosis, projection fates, migration and many others. These cellular processes are also profoundly dependent on the microenvironment, stemness niche, hypoxic microenvironment, and interactions with associated cells including endothelial and immune cells. Significantly, the brain of all other mammalian organs expresses the highest number of microRNAs, with an additional gain in expression in the early stage of neurodegeneration and loss in expression in oncogenesis. However, a mechanistic explanation of the concept of an apparent inverse correlation between the odds of cancer and neurodegenerative diseases is only weakly developed. In this review, we thus will discuss widespread de-regulation of microRNAome observed in these two major groups of brain pathologies. The deciphering of these intricacies is of importance, as therapeutic restoration of pre-pathological microRNA landscape in neurodegeneration must not lead to oncogenesis and vice versa. We thus focus on microRNAs engaged in cellular processes that are inversely regulated in these diseases. We also aim to define the difference in microRNA networks between pro-survival and pro-apoptotic signaling in the brain.

circHIPK3 regulates lung fibroblast-to-myofibroblast transition by functioning as a competing endogenous RNA

Myofibroblasts predominantly emerging through fibroblast-to-myofibroblast transition (FMT) are considered to be the key collagen-producing cells in pulmonary fibrosis. Circular RNAs (circRNAs) are important players involved in many biological processes. circHIPK3 has been identified as the one of the most abundant circRNAs in human lung. In this study, we characterized the role of circHIPK3 in pulmonary fibrosis. We revealed that circHIPK3 is upregulated in bleomycin-induced pulmonary fibrosis mice model, FMT-derived myofibroblasts. circHIPK3 silencing can ameliorate FMT and suppress fibroblast proliferation in vivo and vitro. Fundamentally, circHIPK3 regulates FMT by functioning as an endogenous miR-338-3p sponge and inhibit miR-338-3p activity, thereby leading to increased SOX4 and COL1A1 expression. Moreover, dysregulated circHIPK3 expression was detected in the clinical samples of patients with idiopathic pulmonary fibrosis. Intervention of circHIPK3 may represent a promising therapy for pulmonary fibrosis.

Integrative Analysis Reveals Key Circular RNA in Atrial Fibrillation

Circular RNAs (circRNAs) are an emerging class of RNA species that may play a critical regulatory role in gene expression control, which can serve as diagnostic biomarkers for many diseases due to their abundant, stable, and cell- or tissue-specific expression. However, the association between circRNAs and atrial fibrillation (AF) is still not clear. In this study, we used RNA sequencing data to identify and quantify the circRNAs. Differential expression analysis of the circRNAs identified 250 up- and 126 down-regulated circRNAs in AF subjects compared with healthy donors, respectively. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of the parental genes of the dysregulated circRNAs indicated that the up-regulated parental genes may participate in the process of DNA damage under oxidative stress. Furthermore, to annotate the dysregulated circRNAs, we constructed and merged the competing endogenous RNA (ceRNA) network and protein-protein interaction (PPI) network, respectively. In the merged network, 130 of 246 dysregulated circRNAs were successfully characterized by more than one pathway. Notably, the five circRNAs, including chr9:15474007-15490122, chr16:75445723-75448593, hsa_circ_0007256, chr12:56563313-56563992, and hsa_circ_0003533, showed the highest significance by the enrichment analysis, and four of them were enriched in cytokine-cytokine receptor interaction. These dysregulated circRNAs may mainly participate in biological processes of inflammatory response. In conclusion, the present study identified a set of dysregulated circRNAs, and characterized their potential functions, which may be associated with inflammatory responses in AF. To our knowledge, this is the first study to uncover the association between circRNAs and AF, which not only improves our understanding of the roles of circRNAs in AF, but also provides candidates of potentially functional circRNAs for AF researchers.

A two-circular RNA signature as a noninvasive diagnostic biomarker for lung adenocarcinoma

BACKGROUND

Recently, circular RNAs (circRNAs) have been reported to be microRNA sponges and play essential roles in cancer development. This study aimed to evaluate whether circulating circRNAs could be used as diagnostic biomarkers for lung adenocarcinoma (LUAD).

METHODS

The Gene Expression Omnibus (GEO) dataset was used to investigate differentially expressed circRNAs (DEcircRNAs) in paired LUAD tissues and adjacent nontumor tissues. The expression levels of the host genes were analyzed in The Cancer Genome Atlas (TCGA)-LUAD dataset, and the prognostic value was assessed using the Kaplan-Meier plotter. Quantitative real-time PCR (qRT-PCR) was performed to validate the expression of candidate circRNAs in the LUAD plasma and cells. The CCK8 assay was used to measure the function of circRNAs in cell proliferation. Competing endogenous RNA (ceRNA) network, gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were performed to predict the possible mechanisms and functions of circRNAs in LUAD.

RESULTS

Two upregulated and two downregulated circRNAs were identified as candidate circRNAs using bioinformatics analysis. qRT-PCR demonstrated that hsa_circ_0005962 was upregulated in LUAD plasma and cells, whereas hsa_circ_0086414 was downregulated. Receiver operating characteristic (ROC) curve analysis confirmed that a signature comprising the two circRNAs had good diagnostic potential, with an area under the ROC curve (AUC) of 0.81 (P < 0.0001). In addition, we observed that overexpression of plasma hsa_circ_0086414 was related to EGFR mutations (P = 0.001). Plasma hsa_circ_0005962 displayed significantly different expression before and after surgery in patients with LUAD (P < 0.0001). In vitro experiments suggested that hsa_circ_0005962 promoted LUAD cell proliferation. For future studies, we predicted the circRNA-miRNA-mRNA network for hsa_circ_0005962. Bioinformatics analysis revealed that hsa_circ_0005962 might be involved in LUAD development.

CONCLUSION

A circRNA signature was identified as a potential noninvasive biomarker for LUAD diagnosis.

Insights into the biogenesis and potential functions of exonic circular RNA

Circular RNAs (circRNAs) exhibit unique properties due to their covalently closed nature. Models of circRNAs synthesis and function are emerging but much remains undefined about this surprisingly prevalent class of RNA. Here, we identified exonic circRNAs from human and mouse RNA-sequencing datasets, documenting multiple new examples. Addressing function, we found that many circRNAs co-sediment with ribosomes, indicative of their translation potential. By contrast, circRNAs with potential to act as microRNA sponges were scarce, with some support for a collective sponge function by groups of circRNAs. Addressing circRNA biogenesis, we delineated several features commonly associated with circRNA occurrence. CircRNA-producing genes tend to be longer and to contain more exons than average. Back-splice acceptor exons are strongly enriched at ordinal position 2 within genes, and circRNAs typically have a short exon span with two exons being the most prevalent. The flanking introns either side of circRNA loci are exceptionally long. Of note also, single-exon circRNAs derive from unusually long exons while multi-exon circRNAs are mostly generated from exons of regular length. These findings independently validate and extend similar observations made in a number of prior studies. Furthermore, we analysed high-resolution RNA polymerase II occupancy data from two separate human cell lines to reveal distinctive transcription dynamics at circRNA-producing genes. Specifically, RNA polymerase II traverses the introns of these genes at above average speed concomitant with an accentuated slow-down at exons. Collectively, these features indicate how a perturbed balance between transcription and linear splicing creates important preconditions for circRNA production. We speculate that these preconditions need to be in place so that looping interactions between flanking introns can promote back-splicing to raise circRNA production to appreciable levels.

Circular RNA circNRIP1 acts as a microRNA-149-5p sponge to promote gastric cancer progression via the AKT1/mTOR pathway

BACKGROUND

CircRNA has emerged as a new non-coding RNA that plays crucial roles in tumour initiation and development. 'MiRNA sponge' is the most reported role played by circRNAs in many tumours. The AKT/mTOR axis is a classic signalling pathway in cancers that sustains energy homeostasis through energy production activities, such as the Warburg effect, and blocks catabolic activities, such as autophagy. Additionally, the AKT/mTOR axis exerts a positive effect on EMT, which promotes tumour metastasis.

METHODS

We detected higher circNRIP1 expression in gastric cancer by performing RNA-seq analysis. We verified the tumour promotor role of circNRIP1 in gastric cancer cells through a series of biological function assays. We then used a pull-down assay and dual-luciferase reporter assay to identify the downstream miR-149-5p of circNRIP1. Western blot analysis and immunofluorescence assays were performed to demonstrate that the circNRIP1-miR-149-5p-AKT1/mTOR axis is responsible for the altered metabolism in GC cells and promotes GC development. We then adopted a co-culture system to trace circNRIP1 transmission via exosomal communication and RIP experiments to determine that quaking regulates circNRIP1 expression. Finally, we confirmed the tumour suppressor role of microRNA-133a-3p in vivo in PDX mouse models.

RESULTS

We discovered that knockdown of circNRIP1 successfully blocked proliferation, migration, invasion and the expression level of AKT1 in GC cells. MiR-149-5p inhibition phenocopied the overexpression of circNRIP1 in GC cells, and overexpression of miR-149-5p blocked the malignant behaviours of circNRIP1. Moreover, it was proven that circNRIP1 can be transmitted by exosomal communication between GC cells, and exosomal circNRIP1 promoted tumour metastasis in vivo. We also demonstrated that quaking can promote circNRIP1 transcription. In the final step, the tumour promotor role of circNRIP1 was verified in PDX models.

CONCLUSIONS

We proved that circNRIP1 sponges miR-149-5p to affect the expression level of AKT1 and eventually acts as a tumour promotor in GC.

Potential ceRNA networks involved in autophagy suppression of pancreatic cancer caused by chloroquine diphosphate: A study based on differentially‑expressed circRNAs, lncRNAs, miRNAs and mRNAs

Autophagy has been reported to be involved in the occurrence and development of pancreatic cancer. However, the mechanism of autophagy‑associated non‑coding RNAs (ncRNAs) in pancreatic cancer remains largely unknown. In the present study, microarrays were used to detect differential expression of mRNAs, microRNAs (miRNAs), long ncRNAs (lncRNAs) and circular RNAs (circRNAs) post autophagy suppression by chloroquine diphosphate in PANC‑1 cells. Collectively, 3,966 mRNAs, 3,184 lncRNAs and 9,420 circRNAs were differentially expressed. Additionally, only two miRNAs (hsa‑miR‑663a‑5p and hsa‑miR‑154‑3p) were underexpressed in the PANC‑1 cells in the autophagy‑suppression group. Furthermore, miR‑663a‑5p with 9 circRNAs, 8 lncRNAs and 46 genes could form a prospective ceRNA network associated with autophagy in pancreatic cancer cells. In addition, another ceRNA network containing miR‑154‑3p, 5 circRNAs, 2 lncRNAs and 11 genes was also constructed. The potential multiple ceRNA, miRNA and mRNA associations may serve pivotal roles in the autophagy of pancreatic cancer cells, which lays the theoretical foundation for subsequent investigations on pancreatic cancer.

Deregulation of Circular RNAs in Cancer From the Perspectives of Aberrant Biogenesis, Transport and Removal

CircRNAs (circular RNAs) are a class of RNAs generated from circularization with multiple novel functions. Recent studies have revealed the aberrant expression and aberrant functions of circRNAs in various tumors; thus, circRNAs have been recognized as promising cancer biomarkers. However, the underlying mechanisms behind their aberrant expression and functions remain unclear. In this review, we discuss at length the cancer-specific deregulation of circRNAs and the potential underlying aberrant events in circRNA biogenesis, localization and removal in cancer cells.

Diverse roles of noncoding RNAs in vascular calcification

Vascular calcification occurs when calcium phosphate crystals are abnormally deposited in the vessel walls, thus hardening and narrowing the arteries. This condition is commonly observed in patients with diseases such as atherosclerosis, chronic kidney disease, diabetes, and cardiovascular diseases. Despite many studies being conducted, the molecular mechanism involved in vascular calcification is unknown. From recent studies, it is clear that several types of noncoding RNAs are involved in human diseases. It has also been shown that the noncoding RNAs, including microRNAs, long noncoding RNAs, and circular RNAs, are involved in the progression of vascular calcification. With the development of therapeutic approaches based on the manipulation of noncoding RNAs, it is speculated that the modulation of these molecules could be another strategy to treat vascular calcification in the future. In this review, we summarize the roles of various noncoding RNAs in vascular calcification and the technologies to modulate the noncoding RNAs for therapeutic purpose.

The novel roles of circRNAs in human cancer

Covalently closed single-stranded circular RNAs (circRNAs) consist of introns or exons and are widely present in eukaryotic cells. CircRNAs generally have low expression levels and relatively stable structures compared with messenger RNAs (mRNAs), most of which are located in the cytoplasm and often act in cell type and tissue-specific manners, indicating that they may serve as novel biomarkers. In recent years, circRNAs have gradually become a hotspot in the field of RNA and cancer research, but the functions of most circRNAs have not yet been discovered. Known circRNAs can affect the biogenesis of cancers in diverse ways, such as functioning as a microRNA (miRNA) sponges, combining with RNA binding proteins (RBPs), working as a transcription factor and translation of proteins. In this review, we summarize the characteristics and types of circRNAs, introduce the biogenesis of circRNAs, discuss the emerging functions and databases on circRNAs and present the current challenges of circRNAs studies.

A circular RNA hsa_circ_0079929 inhibits tumor growth in hepatocellular carcinoma

Purpose

Most recently, circular RNAs (circRNAs) were considered playing regulatory roles in tumor initiation and development. The specific function of circRNAs in hepatocellular carcinoma (HCC) remains unknown. This study was designed to detect specific roles of a circRNA hsa_circ_0079299 in HCC.

Methods

The expression of hsa_circ_0079299 in HCC and tumor cell lines was detected using quantitative PCR (qPCR). Cell proliferation, migration, cell cycle and apoptosis after overexpression of the circRNA were measured using cell counting kit-8 (CCK8) assay, colony formation, 5-ethynyl-2′-deoxyuridine (EdU) assay, wound healing assay, transwell culture system and flow cytometry. Western blotting assay detected the protein expression of PI3K/AKT/mTOR signaling pathway and cyclin B1 (CCNB1). Overexpression of the circRNA in vivo was measured by nude mice tumorigenesis.

Results

The expression of hsa_circ_0079299 was lower in HCC tissues. Overexpression of hsa_circ_0079299 suppressed tumor growth in vitro and in vivo, retarded cell cycle progression while had no effect on cell migration and apoptosis. The inhibitory effect of hsa_circ_0079299 was partly mediated by PI3K/AKT/mTOR signaling pathway.

Conclusion

Our study shows that tumor suppressive role of hsa_circ_0079299 in HCC provides new recognition of circRNAs in cancers.