Novel circular RNA expression profiles reflect progression of patients with hypopharyngeal squamous cell carcinoma

RNA-Based Liquid Biopsy in Head and Neck Cancer

Head and neck cancer (HNC) is a prevalent and diverse group of malignancies with substantial morbidity and mortality rates. Early detection and monitoring of HNC are crucial for improving patient outcomes. Liquid biopsy, a non-invasive diagnostic approach, has emerged as a promising tool for cancer detection and monitoring. In this article, we review the application of RNA-based liquid biopsy in HNC. Various types of RNA, including messenger RNA (mRNA), microRNA (miRNA), long non-coding RNA (lncRNA), small nuclear RNA (snRNA), small nucleolar RNA (snoRNA), circular RNA (circRNA) and PIWI-interacting RNA (piRNA), are explored as potential biomarkers in HNC liquid-based diagnostics. The roles of RNAs in HNC diagnosis, metastasis, tumor resistance to radio and chemotherapy, and overall prognosis are discussed. RNA-based liquid biopsy holds great promise for the early detection, prognosis, and personalized treatment of HNC. Further research and validation are necessary to translate these findings into clinical practice and improve patient outcomes.

Profiling and functional analysis of differentially expressed circular RNAs identified in foot-and-mouth disease virus infected PK-15 cells

Circular RNAs (circRNAs) are a new type of endogenous noncoding RNA that exhibit a variety of biological functions. However, it is not clear whether they are involved in foot-and-mouth disease virus (FMDV) infection and host response. In this study, we established circRNA expression profiles in FMDV-infected PK-15 cells using RNA-seq (RNA-sequencing) technology analysis. The biological function of the differentially expressed circRNAs was determined by protein interaction network, Gene Ontology (GO), and Kyoto Encyclopedia of Gene and Genome (KEGG) pathway enrichment. We found 1100 differentially expressed circRNAs (675 downregulated and 425 upregulated) which were involved in various biological processes such as protein ubiquitination modification, cell cycle regulation, RNA transport, and autophagy. We also found that circRNAs identified after FMDV infection may be involved in the host cell immune response. RNA-Seq results were validated by circRNAs qRT-PCR. In this study, we analyzed for the first time circRNAs expression profile and the biological function of these genes after FMDV infection of host cells. The results provide new insights into the interactions between FMDV and host cells.

Hsa-circ_0058106 induces EMT and metastasis in laryngeal cancer via sponging miR-153 and inducing Twist1 nuclear translocation

PURPOSE

A new circular RNA (hsa-circ_0058106) has been found to be upregulated in laryngeal cancer, but its function remains unknown. Here, we explored its role in the metastasis of laryngeal cancer.

METHODS

The level of hsa-circ_0058106 in laryngeal cancer was detected by qRT-PCR. The effect of hsa-circ_0058106 silencing on the metastasis of laryngeal cancer was assessed using scratch wound healing and transwell assays, as well as nude mouse lung metastasis models. Fluorescence in situ hybridization was employed to analyze the cellular localization of hsa-circ_0058106. A luciferase activity assay was used to assess binding between hsa-circ_0058106 and miR-153. Interaction between hsa-circ_0058106 and Twist1 was confirmed using RNA pull-down and RNA immunoprecipitation assays.

RESULTS

A high level of hsa-circ_0058106 was found to be associated with lymph node metastasis and advanced clinical stages. Stable knockdown of hsa-circ_0058106 inhibited the migration and invasion of laryngeal cancer cells in vitro and in vivo. Moreover, we found that downregulation of hsa-circ_0058106 suppressed epithelial-mesenchymal transition (EMT), which was underscored by the observation that hsa-circ_0058106 silencing led to decreases in the expression of N-cadherin and Vimentin, and an increase in the expression of E-cadherin. Mechanistically, we found that hsa-circ_0058106 can specifically bind to miR-153 and regulate Snail1 expression by acting as a miR-153 sponge. In addition, we found that knockdown of hsa-circ_0058106 blocked the nuclear translocation of Twist1.

CONCLUSIONS

Our results indicate that hsa-circ_0058106 induces EMT and metastasis in laryngeal cancer by sponging miR-153 and inducing Twist1 nuclear translocation. These observations provide new insights into the regulatory effects of circRNAs in laryngeal cancer metastasis.

Circ_0058106 promotes proliferation, metastasis and EMT process by regulating Wnt2b/β-catenin/c-Myc pathway through miR-185-3p in hypopharyngeal squamous cell carcinoma

Hypopharyngeal squamous cell carcinoma (HSCC) accounts 95% of hypopharyngeal cancer, which is characterized by high early metastasis rate and poor prognosis. It is reported that circular RNA is involved in the occurrence and development of cancer; however, the role of circRNA in hypopharyngeal cancer has little been investigated. We performed hypopharyngeal carcinoma circRNA microarray and qRT-PCR verification. The results showed circ_0058106 expression level was significantly upregulated in tumor tissues than in corresponding normal tissues. We found that circ_0058106 upregulation promoted proliferation, migration and invasion of HSCC cells, while knockdown of circ_0058106 inhibited proliferation, migration and invasion of HSCC cells both in vitro and in vivo. Bioinformatics predicted circ_0058106 may interact with miR-185-3p. We verified circ_0058106 directly bound miR-185-3p and downregulated miR-185-3p expression by using dual-luciferase reporter assay and qRT-PCR. Moreover, we proved circ_0058106 promoted HSCC cells tumorigenesis and EMT process by regulating Wnt2b/β-catenin/c-Myc pathway via miR-185-3p. In conclusion, our findings firstly confirmed the carcinogenic effect of circ_0058106 in promoting HSCC cells tumorigenesis, metastasis, invasion and EMT process by regulating Wnt2b/β-catenin/c-Myc pathway through sponging miR-185-3p, indicating that circ_0058106 may be a new therapeutic target and prognostic marker for HSCC.

circFAT1 Promotes Cancer Stemness and Immune Evasion by Promoting STAT3 Activation

Cancer stemness and immune evasion are closely associated, and play critical roles in tumor development and resistance to immunotherapy. However, little is known about the underlying molecular mechanisms that coordinate this association. Here, it is reported that elevated circular RNA FAT1 (circFAT1) in squamous cell carcinoma (SCC) unifies and regulates the positive association between cancer stemness and immune evasion by promoting STAT3 activation. circFAT1 knockdown (KD) reduces tumorsphere formation of SCC cells in vitro and tumor growth in vivo. Bioinformatic analysis reveals that circFAT1 KD impairs the cancer stemness signature and activates tumor cell-intrinsic immunity. Mechanistically, circFAT1 binding to STAT3 in the cytoplasm prevents STAT3 dephosphorylation by SHP1 and promotes STAT3 activation, resulting in inhibition of STAT1-mediated transcription. Moreover, circFAT1 KD significantly enhances PD1 blockade immunotherapy by promoting CD8+ cell infiltration into tumor microenvironment. Taken together, the results demonstrate that circFAT1 is an important regulator of cancer stemness and antitumor immunity.

Research Progress of circRNAs in Head and Neck Cancers

Circular RNAs (circRNAs) are a novel type of non-coding RNAs. Because of their characteristics of a closed loop structure, disease- and tissue-specificity, and high conservation and stability, circRNAs have the potential to be biomarkers for disease diagnosis. Head and neck cancers are one of the most common malignant tumors with high incidence rates globally. Affected patients are often diagnosed at the advanced stage with poor prognosis, owing to the concealment of anatomic sites. The characteristics, functions, and specific mechanisms of circRNAs in head and neck cancers are increasingly being discovered, and they have important clinical significance for the early diagnosis, treatment, and prognosis evaluation of patients with cancer. In this study, the generation, characteristics, and functions of circRNAs, along with their regulatory mechanisms in head and neck cancers have been summarized. We report that circRNAs interact with molecules such as transcription and growth factors to influence specific pathways involved in tumorigenesis. We conclude that circRNAs have an important role to play in the proliferation, invasion, metastasis, energy and substance metabolism, and treatment resistance in cancers.

N6-methyladenosine modification of circCUX1 confers radioresistance of hypopharyngeal squamous cell carcinoma through caspase1 pathway

Hypopharyngeal squamous cell carcinoma (HPSCC) is one of the most common malignant tumors in otolaryngology head and neck surgery and is one of the worst prognostic malignant tumors. Endogenous circular RNA (circRNA) is more stable than mRNA, microRNA (miRNA), and long non-coding RNA (LncRNA) in exosomes, plasma, and urine, and participates in gene expression regulation to perform different functions. Therefore, circRNA is expected to become a biomarker and therapy target for many tumors. However, the expression and function of circRNA regulated by N6-methyladenosine (m6A) are still unclear in HNSCC. In this study, we demonstrated that a specific circRNA, circCUX1, was upregulated in HPSCC patients who are resistant to radiotherapy and predicts poor survival outcome. We further found that methyltransferase like 3 (METTL3) mediated the m6A methylation of circCUX1 and stabilizes its expression. Knockdown circCUX1 promotes the sensitivity of hypopharyngeal cancer cells to radiotherapy. In addition, circCUX1 binds to Caspase1 and inhibits its expression, resulting in a decrease in the release of inflammatory factors, thereby developing tolerance to radiotherapy. Our findings indicate that circCUX1 is a potential therapeutic target for radiotherapy tolerance in HPSCC patients.

Effect of the Up-Regulation of Circular RNA Hsa_circ_0069767 Derived from C-KIT on the Biological Behavior of Multiple Myeloma Cells

Purpose

Multiple myeloma (MM) is an incurable disease. This study focused on the expression of circular RNA circ_0069767 in MM and its influence on prognosis, in order to provide a potential target.

Patients and Methods

Totally 66 MM patients participated in this research. Using RT-PCR method to determine the expression level of circ_0069767 in 66 sorted samples from multiple myeloma patients and 21 normal control bone marrow samples, Kaplan–Meier was applied for survival analysis. We constructed stable over-expressing circ_0069767 and silenced circ_0069767 cell lines and used MTS experiment to detect cell viability, transwell experiment to detect cell migration and invasion ability and flow cytometry to detect cell apoptosis. Dual luciferase experiment, qRT-PCR experiment and Western blot were used to explore miRNA and downstream genes.

Results

The expression of circ_0069767 in MM was significantly higher than that of the normal control group. Patients with high expression of circ_0069767 had longer PFS and OS. Cell function experiments showed that overexpression of circ_0069767 in MM cells led to decreased proliferation, migration and invasion, but increased apoptosis; meanwhile, knockdown of circ_0069767 caused opposite biological behaviors. Circ_0069767 by sponging miR-636 in MM cells regulates the expression of K-RAS while the K-RAS gene remained unmutated.

Conclusion

Circ_0069767 plays an antitumor role and its expression can be used as a reliable prognostic indicator for MM patients.

The Research Progression and Clinical Significance of Circular RNAs in Head and Neck Cancers

With rapid development of science technique and molecular research, a large number of circular RNAs (circRNAs) were discovered. CircRNAs that are a heterogeneous endogenous group of non-coding RNA not only are abundantly and diffusely expressed in mammals but also participate in many biological processes, such as in tumor ingenuity and progress. CircRNAs have rarely open reports in the head and neck cancers (HNC), which are an aggressive malignant tumor with unsatisfactory overall survival rates. The diagnostics and treatments continue to improve while the survival rate of HNC patients has no more obvious improvement. Recent studies that are aimed at exploring the molecular mechanisms of occurrence and progression of circRNAs in HNC provide a valuable insight into potential novel diagnostic and therapeutic approaches. In this review, we summarize the increasing number of published researches on the research progression of circRNAs in HNC, as well as their possible clinical implications on HNC.

Prediction of the differentially expressed circRNAs to decipher their roles in the onset of human colorectal cancers

Circular RNAs belong to the class of endogenous long non-coding RNAs that play important roles in many physiological processes including tumorigenesis. One such process is the onset of colorectal cancers (CRC) which is one of the most prevalent cancers in the world. However, the involvement of the circRNAs in CRC progression is still obscure. In this study, we screened the differentially expressed circRNAs in CRC by taking 10 pairs of tumor and non-tumor transcriptomic data. Datasets were downloaded from EBI ENA database and differential expression analysis was performed. For functional characterization and pathway enrichment of differentially expressed circRNAs, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) were employed. Interactions with miRNAs and RNA binding proteins (RBPs) were predicted using miRanda, miRTarBase and starBase tools respectively. Our results identified total of 122 differentially expressed circRNAs in CRC onset, including 85 upregulated and 37 downregulated. GO and KEGG analyses revealed these circRNAs to be involved in many tumorigenic pathways. In addition, we predicted many miRNA and RBP targets of significantly expressed circRNAs that could exhibit the functional role in CRC progression. Combined analyses of miRanda, miRTarBase and KEGG pathway suggested that the possibly affected genes by circRNA-miRNA sponge to be associated with many cancer related pathways. From our findings we concluded 16 novel differentially expressed circRNAs that could play important roles in carcinogenesis of CRC. Our findings provide new insights in circRNA research and could therefore be useful in the development of potential biomarker and therapeutic approaches for CRC.

CircRNAs: potency of protein translation and feasibility of novel biomarkers and therapeutic targets for head and neck cancers

Circular RNAs (circRNAs), a new star noncoding RNA (ncRNA), show stability, conservation, abundance, and tissue and stage specificity. They act as key regulators of biological processes. They target the mRNAs of many other different genes or signaling pathways, and closely link associated genes into regulatory networks. Growing evidence has demonstrated that circRNAs may play an important role in the carcinogenesis, progression and chemoradiation resistance of many cancers including head and neck cancers (HNC). CircRNA, like other ncRNA, such as miRNA, lncRNA, usually is considered to be non-protein coding transcript. However, recent studies indicated that abnormal translation of circRNAs may be involved in human diseases. In this review, we collected the origin, classification, characteristics, function of circRNAs, exosmal circRNAs, and then synthesize current study results to highlight aberration of circRNAs in various types of HNC, and try to clarify the molecular mechanisms of circRNAs affecting the pathogenesis and progression of HNC, as well as pay particular attention to provide a new avenue to the diagnosis and treatment strategy for HNC.

Effect of up-regulation of circMATR3 on the proliferation, metastasis, progression and survival of hypopharyngeal carcinoma

Increasing number of circular RNAs (circRNAs) have been reported to play important role in gene regulation, carcinogenesis and pathogenesis in various cancers. However, the biological functions and underlying molecular mechanisms of circRNAs in hypopharyngeal squamous cell carcinoma (HSCC) remain elusive. Thus, secondary circRNA‐seq profiling was performed to identify the differentially expressed circRNAs between HSCC tissues and adjacent normal tissues, and the expression level of circMATR3 (derived from human gene matrin3 (MATR3), has_circRNA_0008922) was confirmed by qRT‐PCR. Proliferation of HSCC cells was detected by cell counting kit‐8 (CCK8) assay, apoptosis and the cell cycle were analysed by flow cytometry, and the migration and invasion of HSCC cells was determined by transwell assay. Bioinformatics analysis was conducted to predict possible pathways and potential miRNA targets of circMATR3. We found that circMATR3 was up‐regulated in HSCC tissues, and abundant circMATR3 expression was markedly correlated with late T classification, advanced clinical stage, greater lymph node metastasis, and poor prognosis. Furthermore, knock‐down of circMATR3 significantly inhibited proliferation, migration and invasion of HSCC cells, whereas silencing of circMATR3 induced cell apoptosis. Our analysis predicted that circMATR3 may participate in cancer‐related pathways by serving as miRNA sponges. In conclusion, our findings first identified the oncogenic roles of circMATR3 in promoting the progression of HSCC and demonstrated that circMATR3 may be a novel prognostic marker and therapeutic target for HSCC.

Diagnostic Significance of Downregulated circMORC3 as a Molecular Biomarker of Hypopharyngeal Squamous Cell Carcinoma: A Pilot Study

Background

Circular RNAs (circRNAs) have proven to be of great clinical significance as diagnostic biomarkers in various cancers. Here, we investigate the expression of circMORC3 in hypopharyngeal squamous cell carcinoma (HSCC), exploring whether it could serve as a diagnostic marker of HSCC.

Methods

CircMORC3 expression levels were detected in HSCC tissues and adjacent normal tissues using quantitative real-time polymerase chain reaction (qRT-PCR). The relationships between circMORC3 expression levels and clinicopathologic factors were explored. CircMORC3 expression levels in plasma from HSCC patients and non-tumor patients were also detected by qRT-PCR. Finally, receiver operating characteristic (ROC) curves were established to evaluate the diagnostic value of circMORC3 as a potential HSCC biomarker in tissues and plasma.

Results

The expression levels of circMORC3 were significantly lower in HSCC tissues than paired adjacent normal tissues, and the area under the ROC curve was 0.834. The decreased expression of circMORC3 was correlated to T stages and tumor sizes. Similarly, the circMORC3 expression levels in HSCC patient plasma were lower than non-tumor patient plasma, and the area under the ROC curve was 0.767.

Conclusion

Our results indicate that circMORC3 was downregulated in HSCC tissues and plasma, and it could serve as an early diagnostic HSCC biomarker.

Circ-SLC7A5, a potential prognostic circulating biomarker for detection of ESCC

Circular RNAs (circRNAs), resulting from the non-canonical splicing of linear pre-mRNAs, have permanently altered our perspectives toward cancer recently, especially in carcinogenesis and cancer progression. However, the roles of circRNAs in esophageal squamous cell carcinoma (ESCC) remain largely unknown. In the current study, circRNAs expression profiles are screened in ESCC, using plasma samples from 10 ESCC patients, including different TNM stages and 5 normal controls. Characteristics of circRNAs including length, types, and the possibility of binding to proteins are analyzed. Candidate tumor-related circRNAs are then quantitated in ESCC tissues, plasmas and cell lines. ESCC tissues can secret circRNAs into plasma and patients with high plasma circ-SLC7A5 are associated with high TNM stage, tending to have shorter overall survival than those with high levels. In addition, the biological characteristics of circ-SLC7A5 including location, miRNAs binding, m⁶A modification were analyzed. Our study reveals a novel prognosis biomarker of circ-SLC7A5, providing a preliminary landscape of circRNA expression for detection of ESCC.

HNRNPA2/B1 is upregulated in endocrine-resistant LCC9 breast cancer cells and alters the miRNA transcriptome when overexpressed in MCF-7 cells

MicroRNAs are dysregulated in breast cancer. Heterogeneous Nuclear Ribonucleoprotein A2/B1 (HNRNPA2/B1) is a reader of the N(6)-methyladenosine (m6A) mark in primary-miRNAs (pri-miRNAs) and promotes DROSHA processing to precursor-miRNAs (pre-miRNAs). We examined the expression of writers, readers, and erasers of m6A and report that HNRNPA2/B1 expression is higher in tamoxifen-resistant LCC9 breast cancer cells as compared to parental, tamoxifen-sensitive MCF-7 cells. To examine how increased expression of HNRNPA2/B1 affects miRNA expression, HNRNPA2/B1 was transiently overexpressed (~5.4-fold) in MCF-7 cells for whole genome miRNA profiling (miRNA-seq). 148 and 88 miRNAs were up- and down-regulated, respectively, 48 h after transfection and 177 and 172 up- and down-regulated, respectively, 72 h after transfection. MetaCore Enrichment analysis identified progesterone receptor action and transforming growth factor β (TGFβ) signaling via miRNA in breast cancer as pathways downstream of the upregulated miRNAs and TGFβ signaling via SMADs and Notch signaling as pathways of the downregulated miRNAs. GO biological processes for mRNA targets of HNRNPA2/B1-regulated miRNAs included response to estradiol and cell-substrate adhesion. qPCR confirmed HNRNPA2B1 downregulation of miR-29a-3p, miR-29b-3p, and miR-222 and upregulation of miR-1266-5p, miR-1268a, miR-671-3p. Transient overexpression of HNRNPA2/B1 reduced MCF-7 sensitivity to 4-hydroxytamoxifen and fulvestrant, suggesting a role for HNRNPA2/B1 in endocrine-resistance.

Hsa_circ_0001946 Inhibits Lung Cancer Progression and Mediates Cisplatin Sensitivity in Non-small Cell Lung Cancer via the Nucleotide Excision Repair Signaling Pathway

Background: Despite great advances in the diagnosis and treatment of non-small cell lung cancer (NSCLC), early diagnosis remains a challenge because patients usually have advanced lung cancer at the time they are diagnosed. The limited efficacy of conventional chemotherapy is another major problem in the treatment of NSCLC. Based on a published set of sequencing data, we find that hsa_circ_0001946 is a circRNA molecule with a significantly different expression level in three cell lines (human normal lung fibroblasts cell line MRC-5, human NSCLC cell line A549, cisplatin-resistant cell line A549/DDP), NSCLC tissues and paired adjacent normal tissues. We believe that hsa_circ_0001946 may have an effect on the progression of NSCLC and its sensitivity to cisplatin.

Methods: We focused on investigating the circular RNA, hsa_circ_0001946. RNA interference of hsa_circ_0001946 was carried out in A549 cell lines to determine the effect of reduced hsa_circ_0001946 expression on lung cancer progression and was analyzed by Cell Counting Kit-8 (CCK-8), 5-ethynyl-20-deoxyuridine, clone formation, Hoechst, wound healing, and transwell assays. The nucleotide excision repair (NER) signaling pathway was identified by Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis. Moreover, cellular responses to cisplatin were assessed through CCK-8 and flow cytometry assays. Western blot analysis and host-cell reactivation assay were used to determine the effect of hsa_circ_0001946 on NER signaling.

Results: In this study, we found that the reduced expression of hsa_circ_0001946 promoted the viability, proliferation, migration, and invasion of NSCLC cells, as well as inhibition of cell apoptosis. Our findings suggest that hsa_circ_0001946 can affect the sensitivity of NSCLC cells to the chemotherapeutic drug cisplatin via modulation of the NER signaling pathway.

Conclusions: Our study demonstrated the role of hsa_circ_0001946 in NSCLC pathogenesis, development, and chemosensitivity, and suggests that hsa_circ_0001946 may serve as a novel biomarker for the diagnosis and prediction of platinum-based chemosensitivity in patients with NSCLC.

Comprehensive analysis of circRNAs expression profiles in different periods of MDBK cells infected with bovine viral diarrhea virus

CircRNAs play an important regulatory role in the regulation of disease. However, we have a limited understanding of the role of circRNAs in the host's complex protective and pathological mechanisms of BVDV infection. Transcriptome analysis of circRNAs in host cells after BVDV infection may allow us to understand the biological functions of circRNAs in the regulation of BVDV infection. Here, we identified a total of 19,118 circRNAs from the MBDK cells (at 12 h, 24 h, and 48 h post-infection) infected with BVDV by using RNA-seq technology. We confirmed several circRNAs using RT-PCR and DNA sequencing, and qRT-PCR analysis was performed to identify several circRNAs expression and circRNAs resistance to RNase R digestion. GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) enrichment analysis showed that the host genes of differentially expressed circRNAs were involved in the regulation of cell proliferation, apoptosis, cycle and viral infection related signaling pathways. These results indicate that circRNA in host cells plays a broad regulatory role after BVDV infection and provides a valuable resource for studying circRNA biology in host cells after BVDV infection.

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

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

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

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

Function and clinical significance of circRNAs in solid tumors

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

The emerging role of circRNAs and their clinical significance in human cancers

Circular RNA (circRNA), a recently discovered subclass of non-coding RNAs (ncRNAs), forms a covalently closed loop with neither a 5' cap structure nor a 3' polyadenylated tail. Generated from precursor mRNA (pre-mRNA) through "backsplicing" (a type of alternative RNA splicing), the majority of circRNAs are located in the cytoplasm and are widespread among living organisms. They are stable and conserved and exhibit spatiotemporal-specific expression. CircRNAs are known to be involved in the development and progression of multiple diseases, including cancer, by acting as microRNA (miRNA) sponges and by regulating processes such as transcription and translation. The extensively aberrant expression profiles of circRNAs in multiple cancerous tissues make these molecules promising diagnostic biomarkers and therapeutic targets for cancer. Here, we briefly review the characteristics, biogenesis, classification, and functions of circRNAs, with a particular focus on the role of circRNAs in various cancers.

Microarray expression profiling and bioinformatics analysis of circular RNA expression in lung squamous cell carcinoma

Circular RNAs (circRNAs) are novel noncoding RNAs with a wide range of physiological and pathological activities. However, the expression profile and roles in lung squamous cell carcinoma (LSCC) remain largely unknown. Therefore, we investigated the expression profile of circRNAs in three LSCC and matched adjacent normal tissues using microarray. Total 216 differentially expressed circRNAs were identified, including 135 upregulated and 81 downregulated ones in LSCC tissues. Bioinformatics analysis revealed that these differentially expressed circRNAs were potentially implicated in carcinogenesis using Gene ontology (GO) and KEGG pathway analyses. By constructing miRNA-circRNA interaction network, a total of ten key circRNAs, including 6 upregulated and 4 downregulated circRNAs were further screened and then confirmed using qRT-PCR analysis in another 40 paired of LSCC tissues and adjacent normal tissues. In addition, Kaplan-Meier survival analysis demonstrated that the overall survival time of LSCC patients with high hsa_circRNA_103827 expression and low hsa_circRNA_000122 was significantly shorter (P<0.001). In conclusion, this study provides evidence that circRNAs are differentially expressed in LSCC and closely related to the carcinogenesis of LSCC. Among these, hsa_circRNA_103827 and hsa_circRNA_000122 might be served as potential prognostic biomarkers and therapeutic target for LSCC.

Circular RNAs in Blood

Recent advances in RNA sequencing and bioinformatic analysis have allowed the development of a new research field: circular RNAs (circRNAs). These members of the non-coding transcriptome are generated by backsplicing, which results in a covalently closed, single-stranded RNA molecule. To date, thousands of circRNAs have been identified in different human cell types. CircRNAs are evolutionarily conserved, highly stable, cell-/developmental stage-specific and have longer half-lives compared with linear RNAs. Interestingly, different studies have demonstrated that circRNAs are abundantly expressed in the bloodstream. In this chapter, we review the current knowledge of circRNA biology in blood cells and the cell-free compartment, including extracellular vesicles. The potential clinical application of blood circRNAs in the biomarker and therapy fields is also discussed. Finally, perspectives for future studies are proposed.

Circular RNA in Saliva

Although the type and amount of salivary components are influenced by many factors, due to easy, quick, cheap, and noninvasive sampling method alongside with the existence of the vast majority of the substances found in peripheral blood and urine in it, in recent years saliva has been considered as an ideal biofluid for disease research. Salivary circular RNA (circRNA), as an endogenous RNA molecule with a great variety of regulatory potency, is becoming a novel focus for detecting wide range of local or systemic diseases. Expectantly, with characterization of many more circRNAs in saliva, their motifs, and target sites, they can be used routinely in personalized medicine.

Circular RNAs: clinical relevance in cancer

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

Hsa_circ_0101996 combined with hsa_circ_0101119 in peripheral whole blood can serve as the potential biomarkers for human cervical squamous cell carcinoma

BACKGROUND

Previous study suggests changes in circRNAs in tumor tissues from cervical squamous cell carcinoma (CSCC) patients. However, little is known about the diagnostic value of circRNAs in CSCC. To assess the potential application of circRNAs as diagnostic tools in CSCC, the circulating circRNAs in peripheral whole blood were carried out.

METHODS

Five up-regulated circRNAs in peripheral whole blood from 87 patients with CSCC and 55 healthy controls were first identified by real-time quantitative polymerase chain reaction (RT-qPCR). The diagnostic value was evaluated using receiver operating characteristics (ROC) curves and the area under the ROC curves (AUC).

RESULTS

Compared with healthy controls, hsa_circ_0101996, hsa_circ_0104649, hsa_circ_0104443 and hsa_circ_0101119 expression were significantly up-regulated in peripheral whole blood from CSCC patients. ROC analysis showed that hsa_circ_0101996 and hsa_circ_0101119 could distinguish CSCC patients from healthy controls with high AUC (0.906 and 0.887, respectively). Intriguingly, the combination of hsa_circ_0101996 and hsa_circ_0101119 markedly improved AUC (0.964).

CONCLUSION

All of the findings suggest that hsa_circ_0101996 combined with hsa_circ_0101119 can serve as potential biomarkers for CSCC detection.

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: 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.

Biogenesis of circular RNAs and their roles in cardiovascular development and pathology

Circular RNAs (circRNAs) are a newly discovered type of RNA generated by back-splicing of precursor mRNA and found in many species. They are, expressed in a tissue-specific manner and fulfill regulatory activities in many biological processes. Recent research has revealed that circRNAs play critical roles in the development and pathologies of the cardiovascular system. Some of these circRNAs show aberrant expression and regulatory activities during heart disease including heart failure and cardiac infarction and hypertrophy. These findings suggest that circRNAs might be a suitable target for the treatment and prevention of heart disease. In this review, we summarize the latest research on the biogenesis and functions of circRNAs with emphasis on the regulatory roles of circRNAs in the development and pathologies of the cardiovascular system.