Microarray is an efficient tool for circRNA profiling

Regulatory effect and mechanism of CircSEC24A in IL-1β-induced osteoarthritis

Osteoarthritis (OA) is a chronic joint disease characterized by articular cartilage degeneration and damage. Increasing circular RNAs (circRNAs) have been identified to participate in the pathogenesis of OA. Hsa_circ_0128006 (also known as circSEC24) was reported as an upregulated circRNA in OA tissues, but its biological role and underlying mechanism in OA are still to be discussed. circSEC24A and NAMPT expression levels were upregulated, and miR-515-5p was reduced in OA cartilage tissues and IL-1β-treated CHON-001 cells. The absence of circSEC24A overturned IL-1β-induced suppression of cell viability and promotion of oxidative stress, apoptosis, extracellular matrix (ECM) degradation, and inflammation in CHON-001 cells. Mechanistically, circSEC24A acted as a molecular sponge for miR-515-5p to affect NAMPT expression. CircSEC24A knockdown could attenuate IL-1β-triggered CHON-001 cell injury partly via the miR-515-5p/NAMPT axis, providing new insight into the underlying application of circSEC24A in OA treatment.

The multifaceted roles of circular RNAs in cancer hallmarks: From mechanisms to clinical implications

Circular RNAs (circRNAs) represent a distinct class of covalently closed RNA species lacking conventional 5' to 3' polarity. Derived predominantly from pre-mRNA transcripts of protein-coding genes, circRNAs arise through back-splicing events of exon-exon or exon-intron junctions. They exhibit tissue- and cell-specific expression patterns and play crucial roles in regulating fundamental cellular processes such as cell cycle dynamics, proliferation, apoptosis, and differentiation. CircRNAs modulate gene expression through a plethora of mechanisms at epigenetic, transcriptional, and post-transcriptional levels, and some can even undergo translation into functional proteins. Recently, aberrant expression of circRNAs has emerged as a significant molecular aberration within the intricate regulatory networks governing hallmarks of cancer. The tumor-specific expression patterns and remarkable stability of circRNAs have profound implications for cancer diagnosis, prognosis, and therapy. This review comprehensively explores the multifaceted roles of circRNAs across cancer hallmarks in various tumor types, underscoring their growing significance in cancer diagnosis and therapeutic interventions. It also details strategies for leveraging circRNA-based therapies and discusses the challenges in using circRNAs for cancer management, emphasizing the need for further research to overcome these obstacles.

Circular RNAs in human diseases

Circular RNAs (circRNAs) are a unique class of RNA molecules formed through back-splicing rather than linear splicing. As an emerging field in molecular biology, circRNAs have garnered significant attention due to their distinct structure and potential functional implications. A comprehensive understanding of circRNAs' functions and potential clinical applications remains elusive despite accumulating evidence of their involvement in disease pathogenesis. Recent research highlights their significant roles in various human diseases, but comprehensive reviews on their functions and applications remain scarce. This review provides an in-depth examination of circRNAs, focusing first on their involvement in non-neoplastic diseases such as respiratory, endocrine, metabolic, musculoskeletal, cardiovascular, and renal disorders. We then explore their roles in tumors, with particular emphasis on exosomal circular RNAs, which are crucial for cancer initiation, progression, and resistance to treatment. By detailing their biogenesis, functions, and impact on disease mechanisms, this review underscores the potential of circRNAs as diagnostic biomarkers and therapeutic targets. The review not only enhances our understanding of circRNAs' roles in specific diseases and tumor types but also highlights their potential as novel diagnostic and therapeutic tools, thereby paving the way for future clinical investigations and potential therapeutic interventions.

circ_0000337 Promotes the Progression of Cervical Cancer by miR-155-5p/RAB3B Axis

Current study aims to investigate the biological function of circular RNA (circRNA, circ_0000337) in cervical cancer (CC). Bioinformatic analyses were used to predict targets for circ_0000337 and miR-155-5p, and analyze the gene expression differences between cervical squamous cell carcinoma and endocervical adenocarcinoma (CESC) tissues and normal tissues. Quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot were applied to assess mRNA and protein expressions of circ_0000337, microRNA-155-5p (miR-155-5p) and member RAS oncogene family (RAB3B), respectively. Following the establishment of gain/loss-of-function models, CCK-8 was performed to evaluate cell proliferation. Bioinformatics analysis, dual-luciferase reporter assay and RNA immunoprecipitation (RIP) were used to identify the interaction in circ_0000337, miR-155-5p, and RAB3B. Circ_0000337 and RAB3B were upregulated, while miR-155-5p was downregulated in CC tissues and cell lines. circ_0000337 overexpression promoted cell proliferation, circ_0000337 knock down inhibited cell proliferation by sponging miR-155-5p. RAB3B was a target of miR-155-5p which was positively regulated by circ_0000337. In the collected CC tissues, there was a negative correlation between miR-155-5p and circ_0000337 or RAB3B, and a positive correlation between circ_0000337 and RAB3B. miR-155-5p was positively, while RAB3B was negatively correlated with OS in patients with CC, and they were negatively correlated. In conclusion, circ_0000337 upregulates RAB3B by sponging miR-155-5p to promote CC cell proliferation.

Current advances in circular RNA detection and investigation methods: Are we running in circles?

Circular RNAs (circRNAs), characterized by their closed-loop structure, have emerged as significant transcriptomic regulators, with roles spanning from microRNA sponging to modulation of gene expression and potential peptide coding. The discovery and functional analysis of circRNAs have been propelled by advancements in both experimental and bioinformatics tools, yet the field grapples with challenges related to their detection, isoform diversity, and accurate quantification. This review navigates through the evolution of circRNA research methodologies, from early detection techniques to current state-of-the-art approaches that offer comprehensive insights into circRNA biology. We examine the limitations of existing methods, particularly the difficulty in differentiating circRNA isoforms and distinguishing circRNAs from their linear counterparts. A critical evaluation of various bioinformatics tools and novel experimental strategies is presented, emphasizing the need for integrated approaches to enhance our understanding and interpretation of circRNA functions. Our insights underscore the dynamic and rapidly advancing nature of circRNA research, highlighting the ongoing development of analytical frameworks designed to address the complexity of circRNAs and facilitate the assessment of their clinical utility. As such, this comprehensive overview aims to catalyze further advancements in circRNA study, fostering a deeper understanding of their roles in cellular processes and potential implications in disease. This article is categorized under: RNA Methods > RNA Nanotechnology RNA Methods > RNA Analyses in Cells RNA Methods > RNA Analyses In Vitro and In Silico.

Circular RNAs: characteristics, functions, mechanisms, and potential applications in thyroid cancer

Thyroid cancer (TC) is one of the most common endocrine malignancies, and its incidence has increased globally. Despite extensive research, the underlying molecular mechanisms of TC remain partially understood, warranting continued exploration of molecular markers for diagnostic and prognostic applications. Circular RNAs (circRNAs) have recently garnered significant attention owing to their distinct roles in cancers. This review article introduced the classification and biological functions of circRNAs and summarized their potential as diagnostic and prognostic markers in TC. Further, the interplay of circRNAs with PI3K/Akt/mTOR, Wnt/β-catenin, MAPK/ERK, Notch, JAK/STAT, and AMPK pathways is elaborated upon. The article culminates with an examination of circRNA's role in drug resistance of TC and highlights the challenges in circRNA research in TC.

CircRNA and Stroke: New Insight of Potential Biomarkers and Therapeutic Targets

Stroke, the second-largest cause of death and the leading cause of disability globally, presents significant challenges in terms of prognosis and treatment. Identifying reliable prognosis biomarkers and treatment targets is crucial to address these challenges. Circular RNA (circRNA) has emerged as a promising research biomarkers and therapeutic targets because of its tissue specificity and conservation. However, the potential role of circRNA in stroke prognosis and treatment remains largely unexplored. This review briefly elucidate the mechanism underlying circRNA's involvement in stroke pathophysiology. Additionally, this review summarizes the impact of circRNA on different forms of strokes, including ischemic stroke and hemorrhagic stroke. And, this article discusses the positive effects of circRNA on promoting cerebrovascular repair and regeneration, maintaining the integrity of the blood-brain barrier (BBB), and reducing neuronal injury and immune inflammatory response. In conclusion, the significance of circRNA as a potential prognostic biomarker and a viable therapeutic target was underscored.

Circular RNAs: Regulators of endothelial cell dysfunction in atherosclerosis

Endothelial cell (EC) dysfunction is associated with atherosclerosis. Circular RNAs (circRNAs) are covalently closed loops formed by back-splicing, are highly expressed in a tissue-specific or cell-specific manner, and regulate ECs mainly through miRNAs (mircoRNAs) or protein sponges. This review describes the regulatory mechanisms and physiological functions of circRNAs, as well as the differential expression of circRNAs in aberrant ECs. This review focuses on their roles in inflammation, proliferation, migration, angiogenesis, apoptosis, senescence, and autophagy in ECs from the perspective of signaling pathways, such as nuclear factor κB (NF-κB), nucleotide-binding domain, leucine-rich-repeat family, pyrin-domain-containing 3 (NLRP3)/caspase-1, Janus kinase/signal transducer and activator of transcription (JAK/STAT), and phosphoinositide-3 kinase/protein kinase B (PI3K/Akt). Finally, we address the issues and recent advances in circRNAs as well as circRNA-mediated regulation of ECs to improve our understanding of the molecular mechanisms underlying the progression of atherosclerosis and provide a reference for studies on circRNAs that regulate EC dysfunction and thus affect atherosclerosis.

Research progress and potential application of microRNA and other non-coding RNAs in forensic medicine

At present, epigenetic markers have been extensively studied in various fields and have a high value in forensic medicine due to their unique mode of inheritance, which does not involve DNA sequence alterations. As an epigenetic phenomenon that plays an important role in gene expression, non-coding RNAs (ncRNAs) act as key factors mediating gene silencing, participating in cell division, and regulating immune response and other important biological processes. With the development of molecular biology, genetics, bioinformatics, and next-generation sequencing (NGS) technology, ncRNAs such as microRNA (miRNA), circular RNA (circRNA), long non-coding RNA (lncRNA), and P-element induced wimpy testis (PIWI)-interacting RNA (piRNA) are increasingly been shown to have potential in the practice of forensic medicine. NcRNAs, mainly miRNA, may provide new strategies and methods for the identification of tissues and body fluids, cause-of-death analysis, time-related estimation, age estimation, and the identification of monozygotic twins. In this review, we describe the research progress and application status of ncRNAs, mainly miRNA, and other ncRNAs such as circRNA, lncRNA, and piRNA, in forensic practice, including the identification of tissues and body fluids, cause-of-death analysis, time-related estimation, age estimation, and the identification of monozygotic twins. The close links between ncRNAs and forensic medicine are presented, and their research values and application prospects in forensic medicine are also discussed.

Circular RNAs and cervical cancer: friends or foes? A landscape on circRNA-mediated regulation of key signaling pathways involved in the onset and progression of HPV-related cervical neoplasms

Cervical cancer (CC) is a common gynecologic malignancy, accounting for a significant proportion of women death worldwide. Human papillomavirus (HPV) infection is one of the major etiological causes leading to CC onset; however, genetic, and epigenetic factors are also responsible for disease expansion. Circular RNAs (circRNAs), which are known as a particular subset of non-coding RNA (ncRNA) superfamily, with covalently closed loop structures, have been reported to be involved in the progression of diverse diseases, especially neoplasms. In this framework, abnormally expressed circRNAs are in strong correlation with CC pathogenesis through regulating substantial signaling pathways. Also, these RNA molecules can be considered as promising biomarkers and therapeutic targets for CC diagnosis/prognosis and treatment, respectively. Herein, we first review key molecular mechanisms, including Wnt/β-catenin, MAPK, and PI3K/Akt/mTOR signaling pathways, as well as angiogenesis and metastasis, by which circRNAs interfere with CC development. Then, diagnostic, prognostic, and therapeutic potentials of these ncRNA molecules will be highlighted in depth.

Circular RNAs and their roles in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal lung disease with limited treatment options. Circular RNAs (circRNAs) have emerged as a novel class of non-coding RNAs with diverse functions in cellular processes. This review paper aims to explore the potential involvement of circRNAs in the pathogenesis of IPF and their diagnostic and therapeutic implications. We begin by providing an overview of the epidemiology and risk factors associated with IPF, followed by a discussion of the pathophysiology underlying this complex disease. Subsequently, we delve into the history, types, biogenesis, and functions of circRNAs and then emphasize their regulatory roles in the pathogenesis of IPF. Furthermore, we examine the current methodologies for detecting circRNAs and explore their diagnostic applications in IPF. Finally, we discuss the potential utility of circRNAs in the treatment of IPF. In conclusion, circRNAs hold great promise as novel biomarkers and therapeutic targets in the management of IPF.

Construction of Fluorescent G-Quadruplex Nanowires for Label-Free and Accurate Monitoring of Circular RNAs in Breast Cancer Cells and Tissues with Low Background

Circular RNAs (circRNAs) represent an emerging category of endogenous transcripts characterized by long half-life time, covalently closed structures, and cell-/tissue-specific expression patterns, making them potential disease biomarkers. Herein, we demonstrate the construction of fluorescent G-quadruplex nanowires for label-free and accurate monitoring of circular RNAs in breast cancer cells and tissues by integrating proximity ligation-rolling circle amplification cascade with lighting up G-quadruplex. The presence of target circRNA facilitates the SplintR ligase-mediated ligation of the padlock probe. Upon the addition of primers, the ligated padlock probe can serve as a template to initiate subsequent rolling circle amplification (RCA), generating numerous long G-quadruplex nanowires that can incorporate with thioflavin T (ThT) to generate a remarkably improved fluorescence signal. Benefiting from good specificity of SplintR ligase-mediated ligation reaction and exponential amplification efficiency of RCA, this strategy can sensitively detect target circRNA with a limit of detection of 4.65 × 10-18 M. Furthermore, this method can accurately measure cellular circRNA expression with single-cell sensitivity and discriminate the circRNA expression between healthy para-carcinoma tissues and breast cancer tissues, holding great potential in studying the pathological roles of circRNA and clinic diagnostics.

Astragaloside IV regulates circ_0001615 and miR-873-5p/LASP1 axis to suppress colorectal cancer cell progression

Astragaloside IV (AS-IV) has exhibited pivotal anti-cancer efficacy in multiple types of cancer, including colorectal cancer (CRC). Meanwhile, circular RNA (circRNA) circ_0001615 has been reported to be involved in the malignant development of CRC. Herein, this study is expected to figure out the interaction between circ_0001615 and AS-IV on CRC progression. The 50% inhibition concentration (IC50), proliferation, apoptosis, and migration were detected by Cell Counting Kit-8 (CCK-8), 5-ethynyl-2'-deoxyuridine (EdU), flow cytometry, and wound healing assays. The expression of related proteins was examined by western blot. Circ_0001615, microRNA-873-5p (miR-873-5p), and LIM and SH3 protein 1 (LASP1) levels were detected by real-time quantitative polymerase chain reaction (RT-qPCR). The binding between miR-873-5p and circ_0001615, or LASP1, was predicted by Starbase, followed by verification by dual-luciferase reporter and RNA immunoprecipitation (RIP) assays. The biological role of circ_0001615 and AS-IV on CRC tumor growth was detected by the xenograft tumor model in vivo. According to the IC50 of AS-IV in CRC cells, the 100 ng/mL AS-IV treatment for 24 h was chosen for the following research: Our data confirmed that AS-IV is a beneficial anti-cancer agent in CRC cells. Furthermore, circ_0001615 and LASP1 expression were increased, and miR-873-5p was decreased in CRC patients and cell lines, whereas their expression exhibited an opposite trend in AS-IV-treated cells. Functionally, applying AS-IV might act as a beneficial anti-cancer effect by downregulating circ_0001615 in CRC cells in vitro. Mechanically, circ_0001615 serves as a sponge for miR-873-5p to affect LASP1 expression. In addition, AS-IV inhibited CRC cell growth in vivo by modulating circ_0001615. Overall, AS-IV could mitigate CRC development, at least in part, through the circ_0001615/miR-873-5p/LASP1 axis. These findings support a theoretical basis for an in-depth study of the function of AS-IV and the clinical treatment of CRC.

Circular RNAs: Biogenesis, Functions, and Role in Myocardial Hypertrophy

Circular RNAs (circRNAs) are a large class of endogenous single-stranded covalently closed RNA molecules. High-throughput RNA sequencing and bioinformatic algorithms have identified thousands of eukaryotic circRNAs characterized by high stability and tissue-specific expression pattern. Recent studies have shown that circRNAs play an important role in the regulation of physiological processes in the norm and in various diseases, including cardiovascular disorders. The review presents current concepts of circRNA biogenesis, structural features, and biological functions, describes the methods of circRNA analysis, and summarizes the results of studies on the role of circRNAs in the pathogenesis of hypertrophic cardiomyopathy, the most common inherited heart disease.

Circular RNAs: An emerging precise weapon for diabetic nephropathy diagnosis and therapy

Diabetic nephropathy (DN) is a prevalent chronic microvascular complication associated with diabetes mellitus and represents a major cause of chronic kidney disease and renal failure. Current treatment strategies for DN primarily focus on symptom alleviation, lacking effective approaches to halt or reverse DN progression. Circular RNA (circRNA), characterized by a closed-loop structure, has emerged as a novel non-coding RNA regulator of gene expression, attributed to its conservation, stability, specificity, and multifunctionality. Dysregulation of circRNA expression is closely associated with DN progression, whereby circRNA impacts kidney cell injury by modulating cell cycle, differentiation, cell death, as well as influencing the release of inflammatory factors and stromal fibronectin expression. Consequently, circRNA is considered a predictive biomarker and a potential therapeutic target for DN. This review provides an overview of the latest research progress in the classification, functions, monitoring methods, and databases related to circRNA. The paper focuses on elucidating the impact and underlying mechanisms of circRNA on kidney cells under diabetic conditions, aiming to offer novel insights into the prevention, diagnosis, and treatment of DN.

Non-Coding RNAs in Human Cancer and Other Diseases: Overview of the Diagnostic Potential

Non-coding RNAs (ncRNAs) are abundant single-stranded RNA molecules in human cells, involved in various cellular processes ranging from DNA replication and mRNA translation regulation to genome stability defense. MicroRNAs are multifunctional ncRNA molecules of 18-24 nt in length, involved in gene silencing through base-pair complementary binding to target mRNA transcripts. piwi-interacting RNAs are an animal-specific class of small ncRNAs sized 26-31 nt, responsible for the defense of genome stability via the epigenetic and post-transcriptional silencing of transposable elements. Long non-coding RNAs are ncRNA molecules defined as transcripts of more than 200 nucleotides, their function depending on localization, and varying from the regulation of cell differentiation and development to the regulation of telomere-specific heterochromatin modifications. The current review provides recent data on the several forms of small and long non-coding RNA's potential to act as diagnostic, prognostic or therapeutic target for various human diseases.

An interaction between eIF4A3 and eIF3g drives the internal initiation of translation

An RNA structure or modified RNA sequences can provide a platform for ribosome loading and internal translation initiation. The functional significance of internal translation has recently been highlighted by the discovery that a subset of circular RNAs (circRNAs) is internally translated. However, the molecular mechanisms underlying the internal initiation of translation in circRNAs remain unclear. Here, we identify eIF3g (a subunit of eIF3 complex) as a binding partner of eIF4A3, a core component of the exon-junction complex (EJC) that is deposited onto spliced mRNAs and plays multiple roles in the regulation of gene expression. The direct interaction between eIF4A3-eIF3g serves as a molecular linker between the eIF4A3 and eIF3 complex, thereby facilitating internal ribosomal entry. Protein synthesis from in vitro-synthesized circRNA demonstrates eIF4A3-driven internal translation, which relies on the eIF4A3-eIF3g interaction. Furthermore, our transcriptome-wide analysis shows that efficient polysomal association of endogenous circRNAs requires eIF4A3. Notably, a subset of endogenous circRNAs can express a full-length intact protein, such as β-catenin, in an eIF4A3-dependent manner. Collectively, our results expand the understanding of the protein-coding potential of the human transcriptome, including circRNAs.

Microarray Expression Profile and Bioinformatic Analysis of Circular RNA in Human Arteriosclerosis Obliterans

Background

Arteriosclerosis obliterans (ASO) is the leading cause of nontraumatic lower-extremity amputations. Multiple researches have suggested that circular RNAs (circRNAs) played vital regulatory functions in cancer and cardiovascular disease. Nevertheless, the underlying effect and pathological mechanism of circRNAs in the formation and progression of ASO are still indistinct.

Methods and Results

This study used microarray analysis to investigate the expression portrait of circRNAs in normal lower extremity arteries and ASO arteries. Bioinformatics analysis was conducted using the KEGG database to study the enrichment of differentially expressed circRNAs (DE circRNAs) and predict their functions. The accuracy of microarray assay was verified by evaluating expression of the top 5 upregulated and 5 downregulated circRNAs (raw density of normal group ≥200) using RT-qPCR. A circRNA-miRNA-mRNA interaction network was further predicted using software. Compared to the normal lower extremity group, the ASO arteries with HE and EVG staining presented hyperplastic fibrous membrane and luminal stenosis. A total of 12,735 circRNAs were identified, including 1196 DE circRNAs with 276 upregulated and 920 downregulated in ASO group based on |log2(FC)| > 1 and padj < 0.05. Among selected 10 circRNAs, RT-qPCR confirmed that hsa_circ_0003266, hsa_circ_0118936 and hsa_circ_0067161 were upregulated while hsa_circ_0091934 and hsa_circ_0092022 were downregulated in ASO group (p < 0.05). GO analysis presented that the DE circRNAs were primarily enriched in protein binding, intracellular part and organelle organization. KEGG pathway analysis indicated that MAPK signaling pathway, human T-cell leukemia virus 1 infection, proteoglycans in cancer were associated with the DE circRNAs. The circRNA-miRNA-mRNA interactive network revealed that both mRNAs and miRNAs linked to circRNAs played an indispensable role in ASO.

Conclusion

This study described the expression portrait of circRNAs in human ASO arteries, and revealed the molecular background for further investigations of the circRNA regulatory mechanism in the formation and progression of ASO.

Circular RNAs: Diagnostic and Therapeutic Perspectives in CNS Diseases

Circular RNAs (circRNAs) are a class of regulatory non-coding RNAs characterized by the presence of covalently closed ends. A growing body of evidence suggests that circRNAs play important roles in physiology and pathology. In particular, accumulating data on circRNA functions in various central nervous system (CNS) diseases and their correlations indicate that circRNAs are critical contributors to the onset and development of brain disorders. In this review, we focus on the regulatory and functional roles of circRNAs in CNS diseases, highlighting their diagnostic and therapeutic potential, with the aim of providing new insights into CNS diseases.

Rapid diagnosis of acute myocardial infarction based on reverse transcription-accelerated strand exchange amplification of miR-208a

Acute myocardial infarction (AMI) is a prevalent cardiovascular disease associated with high morbidity and mortality, posing a significant threat to human health. Therefore, early diagnosis of AMI has become a focal point of research. MiR-208 is specifically expressed in the heart and is involved in the regulation of cardiomyocyte hypertrophy, cardiac fibrosis, and other myocardial gene expressions. It is expected to be applied in the clinical detection of AMI due to its release by damaged myocardial cells within 3 hours of AMI. In this study, we developed a denatured bubble-mediated reverse transcription-accelerated strand exchange amplification (RT-ASEA) method to detect the early biomarker miR-208a of AMI. The novel approach allowed rapid amplification of miR-208a in 15 minutes, with good performance in terms of repeatability (CV < 6%), determination limit (1 × 100 pmol L-1), and linearity (R2 = 0.9690). Based on the analysis of 42 clinical samples, a strong correlation was observed between the Ct value of miR-208a detected by the RT-ASEA method and the cTnI concentration, considered the gold standard for diagnosis of AMI. The research suggested that the RT-ASEA method could be applied to distinguish between AMI and healthy groups. The area under the receiver operating characteristic curve (AUC) was 0.9976, with a sensitivity of 96% and a specificity of 100%. Optimized RT-ASEA is a reliable and efficient method for miRNA detection. Furthermore, this study provides crucial data support for the development of miR-208a as an early biomarker for AMI, which is of great significance in life and health.

Hsa_circ_0000078 Regulates miR-205-5p/EREG Pathway to Inhibit Cervical Cancer Progression

It is well established that circular RNAs (circRNAs) play a role in tumor initiation and tumorigenesis. The goal of this study was to reveal the detailed functions and regulatory mechanisms of circ_0000078 in cervical cancer (CC). Circ_0000078, miR-205-5p, and epiregulin (EREG) mRNA expression levels were examined using RT-qPCR. Western blotting was performed to quantify EREG protein. Cell proliferation, apoptosis, migration, and invasion were examined by performing CCK-8, caspase 3 activity, wound healing, and transwell assays, respectively. The effect of circ_0000078 on tumor growth in vivo was confirmed in a xenograft model. The putative relationship between miR-205-5p and circ_0000078 or EREG, as predicted by bioinformatics analysis, was evaluated by dual-luciferase and RNA immunoprecipitation assays. Aberrant downregulation of circ_0000078 and EREG as well as upregulation of miR-205-5p were observed in cervical tumor samples and cancer cells. Ectopic expression of circ _0000078 not only restrained cancer cell growth, survival, migration, and invasiveness, but also decelerated tumor formation and development in a mouse model. miR-205-5p, acts as a target of circ_0000078 and directly binds to EREG to repress its expression. Overexpression of miR-205-5p reversed the inhibitory effects of circ_0000078 upregulation on cancer cell behavior and also partially abolished the anti-cancer effects of EREG upregulation in vitro. Circ_0000078 inhibits the growth of cancer by interfering with the miR-205-5p/EREG network, acting as a tumor suppressor in CC. These results provide a better understanding of the pathogenesis of this disease.

Going circular: history, present, and future of circRNAs in cancer

To date, thousands of highly abundant and conserved single-stranded RNA molecules shaped into ring structures (circRNAs) have been identified. CircRNAs are multifunctional molecules that have been shown to regulate gene expression transcriptionally and post-transcriptionally and exhibit distinct tissue- and development-specific expression patterns associated with a variety of normal and disease conditions, including cancer pathogenesis. Over the past years, due to their intrinsic stability and resistance to ribonucleases, particular attention has been drawn to their use as reliable diagnostic and prognostic biomarkers in cancer diagnosis, treatment, and prevention. However, there are some critical caveats to their utility in the clinic. Their circular shape limits their annotation and a complete functional elucidation is lacking. This makes their detection and biomedical application still challenging. Herein, we review the current knowledge of circRNA biogenesis and function, and of their involvement in tumorigenesis and potential utility in cancer-targeted therapy.

circRNA landscape in dorsal root ganglia from mice with collagen antibody-induced arthritis

Circular RNAs are a novel class of RNA molecules that are covalently closed into a ring structure. They are an epigenetic regulatory mechanism, and their best-studied function is regulation of microRNA activity. As such circular RNAs may be involved in the switch from acute to chronic pain. They have previously been studied in the context of neuropathic pain models, but their importance in inflammation-induced chronic pain models is unexplored. Microarray analysis of dorsal root ganglia collected in the late phase of collagen antibody-induced arthritis (day 59) were used to elucidate the relevance of circular RNAs in the mechanical hypersensitivity caused by this model. 120 circular RNA genes were found to be significantly differentially regulated in female BALB/c mice with collagen antibody-induced arthritis. Six genes were chosen for RT-qPCR analysis in the late (day 54-60) as well as the inflammatory (day 11-12) phase of this model. This validated an increase in circNufip1 expression in the late phase of collagen antibody-induced arthritis. Additionally, it was found that circVps13 and circMicall1 are upregulated in the inflammatory phase. Interestingly, no changes were found in dorsal root ganglia from mice injected with Freund's Complete Adjuvant (day 3) nor mice with spared nerve injury (day 20), despite their similarities to inflammatory and late phase collagen antibody-induced arthritis, respectively. This study provides evidence that mild circular RNA changes occur in dorsal root ganglia of mice with collagen antibody-induced arthritis that are, bioinformatically, predicated to be involved in processes relevant to sensitization.

CircRNAs in colorectal cancer: potential biomarkers and therapeutic targets

Globally, colorectal cancer (CRC) is the third most prevalent cancer and the second leading cause of cancer-related deaths. Circular RNAs (circRNAs) are single-stranded RNA with covalently closed-loop structures and are highly stable, conserved, and abundantly expressed in various organs and tissues. Recent research found abnormal circRNA expression in CRC patients' blood/serum, cells, CRC tissues, and exosomes. Furthermore, mounting data demonstrated that circRNAs are crucial to the development of CRC. CircRNAs have been shown to exert biological functions by acting as microRNA sponges, RNA-binding protein sponges, regulators of gene splicing and transcription, and protein/peptide translators. These characteristics make circRNAs potential markers for CRC diagnosis and prognosis, potential therapeutic targets, and circRNA-based therapies. However, further studies are still necessary to improve the understanding of the roles and biological mechanisms of circRNAs in the development of CRC. In this review, up-to-date research on the role of circRNAs in CRC was examined, focusing on their potential application in CRC diagnosis and targeted therapy, which would advance the knowledge of the functions of circRNAs in the development and progression of CRC.

CircBCL11B acts as a ceRNA to facilitate 1,2-dichloroethane-induced astrocyte swelling via miR-29b-3p/AQP4 axis in SVG p12 cells

1,2-Dichloroethane (1,2-DCE) is a pervasive environmental pollutant found in ambient and residential air, as well as ground and drinking water. Brain edema is the primary pathological consequence of 1,2-DCE overexposure. We found that microRNA (miRNA)-29b dysregulation after 1,2-DCE exposure can aggravate brain edema by suppressing aquaporin 4 (AQP4). Moreover, circular RNAs (circRNAs) can regulate the expression of downstream target genes through miRNA, and affect protein function. However, circRNAs' role in 1,2-DCE-induced brain edema via miR-29b-3p/AQP4 axis remains unclear. To address the mechanism's bottleneck, we explored the circRNA-miRNA-mRNA network underlying 1,2-DCE-driven astrocyte swelling in SVG p12 cells by circRNA sequencing, electron microscopy and isotope ³H labeling combined with the 3-O-methylglucose uptake method. The results showed that 25 and 50mM 1,2-DCE motivated astrocyte swelling, characterized by increased water content, enlarged cell vacuoles, and mitochondrial swelling. This was accompanied by miR-29b-3p downregulation and AQP4 upregulation. We verified that AQP4 were negatively regulated by miR-29b-3p in 1,2-DCE-induced astrocyte swelling. Also, circRNA sequencing highlighted that circBCL11B was upregulated by 1,2-DCE. This was manifested as circBCL11B overexpression playing an endogenous competitive role via upregulating AQP4 by binding to miR-29b-3p, thus leading to astrocyte swelling. Conversely, circBCL11B knockdown reversed the 1,2-DCE-motivated AQP4 upregulation and alleviated the cell swelling. Finally, we demonstrated that the circBCL11B was targeted to miR-29b-3p by fluorescence in situ hybridization and dual-luciferase reporter assay. In conclusion, our findings indicate that circBCL11B acts as a competing endogenous RNA to facilitate 1,2-DCE-caused astrocyte swelling via miR-29b-3p/AQP4 axis. These observations provide new insight into the epigenetic mechanisms underlying 1,2-DCE-induced brain edema.

The function and mechanisms of action of circular RNAs in Urologic Cancer

Kidney, bladder, and prostate cancer are the three major tumor types of the urologic system that seriously threaten human health. Circular RNAs (CircRNAs), special non-coding RNAs with a stabile structure and a unique back-splicing loop-forming ability, have received recent scientific attention. CircRNAs are widely distributed within the body, with important biologic functions such as sponges for microRNAs, as RNA binding proteins, and as templates for regulation of transcription and protein translation. The abnormal expression of circRNAs in vivo is significantly associated with the development of urologic tumors. CircRNAs have now emerged as potential biomarkers for the diagnosis and prognosis of urologic tumors, as well as targets for the development of new therapies. Although we have gained a better understanding of circRNA, there are still many questions to be answered. In this review, we summarize the properties of circRNAs and detail their function, focusing on the effects of circRNA on proliferation, metastasis, apoptosis, metabolism, and drug resistance in kidney, bladder, and prostate cancers.

Challenges and opportunities for circRNA identification and delivery

Circular RNAs (circRNAs) are evolutionarily conserved noncoding RNAs with tissue-specific expression patterns, and exert unique cellular functions that have the potential to become biomarkers in therapeutic applications. Therefore, accurate and sensitive detection of circRNA with facile platforms is essential for better understanding of circRNA biological processes and circRNA-related disease diagnosis and prognosis; and precise regulation of circRNA through efficient delivery of circRNA or siRNA is critical for therapeutic purposes. Here, we reviewed the current development of circRNA identification methodologies, including overviewing the purification steps, summarizing the sequencing methods of circRNA, as well as comparing the advantages and disadvantages of traditional and new detection methods. Then, we discussed the delivery and manipulation strategies for circRNAs in both research and clinic treatment. Finally, the challenges and opportunities of analyzing circRNAs were addressed.

Circular RNA circ_0000741/miR-379-5p/TRIM14 signaling axis promotes HDAC inhibitor (SAHA) tolerance in glioblastoma

BACKGROUND

Histone deacetylase (HDAC) inhibitor-based therapeutic drug tolerance is a major obstacle to glioblastoma (GBM) treatment. Meanwhile, non-coding RNAs have been reported to be involved in the regulation of HDAC inhibitor (SAHA) tolerance in some human tumors. However, the relationship between circular RNAs (circRNAs) and SAHA tolerance is still unknown. Herein, we explored the role and mechanism of circ_0000741 on SAHA tolerance in GBM.

METHODS

Circ_0000741, microRNA-379-5p (miR-379-5p), and tripartite motif-containing 14 (TRIM14) level were detected by real-time quantitative polymerase chain reaction (RT-qPCR). (4-5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT), 5-ethynyl-2'-deoxyuridine (EdU), Colony formation, flow cytometry, and transwell assays were used to detect SAHA tolerance, proliferation, apoptosis, and invasion in SAHA-tolerant GBM cells. Western blot analysis of protein levels of E-cadherin, N-cadherin, and TRIM14. After Starbase2.0 analysis, the binding between miR-379-5p and circ_0000741 or TRIM14 was proved using a dual-luciferase reporter. The role of circ_0000741 on drug tolerance was assessed using a xenograft tumor model in vivo.

RESULTS

Circ_0000741 and TRIM14 were upregulated, and miR-379-5p was reduced in SAHA-tolerant GBM cells. Furthermore, circ_0000741 absence reduced SAHA tolerance, suppressed proliferation, invasion, and induced apoptosis in SAHA-tolerant GBM cells. Mechanistically, circ_0000741 might affect TRIM14 content via sponging miR-379-5p. Besides, circ_0000741 silencing enhanced the drug sensitivity of GBM in vivo.

CONCLUSION

Circ_0000741 might accelerate SAHA tolerance by regulating the miR-379-5p/TRIM14 axis, which provided a promising therapeutic target for GBM treatment.

Microarray profiling identifies hsa_circ_0082003 as a novel tumor promoter for papillary thyroid carcinoma

BACKGROUND

Circular RNAs (circRNAs) are non-coding RNAs that have essential regulatory roles in the development of various tumors. This study explored whether circRNAs are involved in the progression of papillary thyroid carcinoma (PTC).

METHODS

Differentially expressed circRNAs (DECs) in four pairs of PTC and matched normal thyroid tissues were screened using a circRNA microarray. The potential functions of dysregulated circRNAs were predicted by bioinformatic analyses. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) was used to determine hsa_circ_0082003 expression in 80 pairs of PTC and matched normal thyroid tissues. Cell counting kit-8, colony formation, wound healing, and Transwell assays were performed to evaluate the biological functions of hsa_circ_0082003 in PTC cells. The role of hsa_circ_0082003 in PTC tumorigenesis in vivo was validated in nude mice.

RESULTS

In total, 3150 DECs (2317 upregulated and 833 downregulated) were identified. Pathway enrichment analyses indicated that the dysregulated circRNAs may play roles in PTC development. RT-qPCR validation demonstrated that hsa_circ_0082003 expression was significantly increased in PTC tissues and correlated with poor clinicopathological parameters. Receiver operating characteristic curve analysis showed that hsa_circ_0082003 had good performance for diagnosing PTC and judging whether it was accompanied by lymph node metastasis. Knockdown of hsa_circ_0082003 inhibited PTC cell proliferation, migration, and invasion. Tumor formation assays in vivo showed that downregulation of hsa_circ_0082003 significantly suppressed the growth of PTC.

CONCLUSION

Hsa_circ_0082003 may serve as a novel diagnostic biomarker and potential therapeutic target for PTC.

Circularized RNA as novel therapeutics in cancer

Circular RNAs (CircRNAs) regulate gene expression by functioning as microRNA sponges, regulating protein stability, and gilding proteins for gene transcription and translation. Also, limited circRNAs harbour protein-coding ability through cap-independent pathways. These molecular mechanisms of circRNAs contribute to their importance in several cellular processes. Particularly, the dysregulation of circRNAs also plays a critical role in disease development. Targeting disease-causing circRNAs by restoring their normal expression by gain-of-function or loss-of-function approach and regulating their molecular activities could be potential direction for the development of anti-cancer therapies. Furthermore, due to unique covalently closed circular structure, the superior stability of circRNAs also grants them as novel therapeutic tools replacing the therapeutic small interfering RNAs and messenger RNAs. Here, we will review the functional and molecular mechanisms of circRNAs in pathogenesis, the current methods for targeting the dysregulated circRNAs, and the potential of using synthetic circRNAs in disease treatment and prevention.

Tetrahedron supported CRISPR/Cas13a cleavage for electrochemical detection of circular RNA in bladder cancer

As a diagnostic biomarker, the detection of circular RNA (circRNA) is vital for the early screening of bladder cancer. Usually, the low abundance of circRNA in clinic samples results in the necessarily complicated extraction before detection. In this work, a tetrahedron supported CRISPR/Cas13a cleavage has been explored for direct electrochemical detection of circRNA in urine from bladder cancer. CRISPR/Cas13a system has been reasonably designed to recognize the characteristic back-splice junction site of circRNA. The activated CRISPR/Cas13a by circRNA can cleave uracil bases composed of DNA tetrahedron immobilized on the surface of gold electrode, resulting in the breakage of DNA tetrahedron and the release of electrochemical active molecule methylene blue. By virtue of highly catalytic efficiency of CRISPR/Cas13a and rigid structure of tetrahedron, the developed electrochemical biosensor can directly detect circRNA in 25 μL urine sample with the lowest detection limit of 0.089 fM and linear detection range from 10 fM to 50 nM in less than 10 min, so as to avoid complicated extraction process and benefit for on-site detection.

Circular RNAs-New Kids on the Block in Cancer Pathophysiology and Management

The ever-increasing number of cancer cases and persistently high mortality underlines the urgent need to acquire new perspectives for developing innovative therapeutic approaches. As the research on protein-coding genes brought significant yet only incremental progress in the development of anticancer therapy, much attention is now devoted to understanding the role of non-coding RNAs (ncRNAs) in various types of cancer. Recent years have brought about the awareness that ncRNAs recognized previously as "dark matter" are, in fact, key players in shaping cancer development. Moreover, breakthrough discoveries concerning the role of a new group of ncRNAs, circular RNAs, have evidenced their high importance in many diseases, including malignancies. Therefore, in the following review, we focus on the role of circular RNAs in cancer, particularly in cancer stem-like cells, summarize their mechanisms of action, and provide an overview of the state-of-the-art toolkits to study them.

Circ_CSPP1 Regulates the Development of Non-small Cell Lung Cancer via the miR-486-3p/BRD9 Axis

In this study, we explored the role of circ_CSPP1 in non-small cell lung cancer (NSCLC) using NSCLC cell lines (A549 and H1299) and human bronchial epithelioid cells (16HBE). The differential expression of circ_CSPP1, miR-486-3p and BRD9 in NSCLC by quantitative real-time polymerase chain reaction (qRT-PCR) and western blot in A549 cells, H1299 cells, 16HBE cells, NSCLC tissues and healthy lung tissues. Dual-luciferase reporter assay was conducted to verify the interaction between circ_CSPP1 and miR-486-3p or miR-486-3p and BRD9. The effect of circ_CSPP1/miR-486-3p/BRD9 axis on NSCLC cell proliferation was evaluated using cell counting kit-8 assay, colony formation assay, and 5-ethynyl-2'-deoxyuridine assay. Additionally, transwell assays were performed to evaluate the effect of circ_CSPP1/miR-486-3p/BRD9 axis on A549 and H1299 cell migration and invasion. The effect of circ_CSPP1 on tumor tumorigenesis of A549 cells in vivo was determined by xenograft tumor model and immunohistochemistry assay. Circ_CSPP1 and BRD9 expression were upregulated, while miR-486-3p expression was downregulated in tumor tissues of NSCCL patients and A549 and H1299 cells. Circ_CSPP1 specifically bound miR-486-3p, and miR-486-3p could target BRD9. Circ_CSPP1 upregulation promoted proliferation, invasion and migration of NSCLC cells, circ_CSPP1 knockdown or miR-486-3p upregulation had the opposite effects. Circ_CSPP1 knockdown-induced effects were reverted by miR-486-3p inhibition. Similarly, the effects of miR-486-3p upregulation on NSCLC cell proliferation, invasion and migration were reversed by BRD9 overexpression. In addition, circ_CSPP1 silencing inhibited tumor growth in nude mice. Circ_CSPP1 promoted A549 and H1299 cell malignancy by competitively inhibiting BRD9 and binding to miR-486-3p.

Silencing CircEIF3I/miR-526b-5p Axis Epigenetically Targets HGF/c-Met Signal to Hinder the Malignant Growth, Metastasis and Angiogenesis of Hepatocellular Carcinoma

BACKGROUND

Hepatocyte growth factor (HGF)/c-mesenchymal-epithelial transition factor (c-Met) is important for the diagnosis and prognosis of hepatocellular carcinoma (HCC). Circular RNAs (circRNAs) are key regulators of HCC progression, and this study focused on circRNA eukaryotic translation initiation factor 3 subunit I (circEIF3I) with HGF/c-Met in HCC.

METHODS

Levels of circEIF3I, microRNA (miR)-526b-5p, HGF, E-cadherin, N-cadherin, and Vimentin were detected by Gene Expression Omnibus database, quantitative PCR and western blotting. Cell functions were measured by detecting cell growth (cell proliferation assay with WST-1 and EdU, colony formation assay, flow cytometry, caspase 3 activity assay, and nude mouse tumorigenicity assay), metastasis (transwell assay and western blotting), angiogenesis (endothelial tube formation assay). Molecular interaction was determined dual-luciferase reporter assay, RNA immunoprecipitation, and Pearson correlation analysis.

RESULTS

Expression of circEIF3I was upregulated in HCC tissues. Knockdown of circEIF3I suppressed cell proliferation epithelial-mesenchymal transition, migration, invasion and tube formation ability but promoted apoptosis of HCC cells. CircEIF3I could sponge miR-526b-5pto regulate downstream HGF. Functionally, circEIF3I regulation in HCC cell progression was associated with miR-526b-5p sponging function and HGF upregulation could attenuate tumor-inhibiting roles of miR-526b-5p. HCC tumor growth was delayed by interfering circEIF3I.

CONCLUSION

CircEIF3I was an oncogenic circRNA in HCC-, and interfering circEIF3I exhibited anti-HCC activity via circEIF3I-miR-526b-5p-HGF/c-Met pathway.

Circular RNAs: biology and clinical significance of breast cancer

Circular RNAs (circRNAs) are novel noncoding RNAs with covalently closed-loop structures that can regulate eukaryotic gene expression. Due to their stable structure, circRNAs are widely distributed in the cytoplasm and have important biological functions, including as microRNA sponges, RNA-binding protein conjugates, transcription regulators, and translation templates. Breast cancer is among the most common malignant cancers diagnosed in women worldwide. Despite the development of comprehensive treatments, breast cancer still has high mortality rates. Recent studies have unmasked critical roles for circRNAs in breast cancer as regulators of tumour initiation, progression, and metastasis. Further, research has revealed that some circRNAs have the potential for use as diagnostic and prognostic biomarkers in clinical practice. Herein, we review the biogenesis and biological functions of circRNAs, as well as their roles in different breast cancer subtypes. Moreover, we provide a comprehensive summary of the clinical significance of circRNAs in breast cancer. CircRNAs are believed to be a hot focus in basic and clinical research of breast cancer, and innovative future research directions of circRNAs could be used as biomarkers, therapeutic targets, or novel drugs.Abbreviations: CeRNA: Competitive endogenous RNA; ciRNA: Circular intronic RNA; circRNA: Circular RNA; EIciRNA: Exon-intron circRNA; EMT: Epithelial-mesenchymal transition; IRES: Internal ribosome entry site; lncRNA: Long non-coding RNA; miRNA: MicroRNA; MRE: MiRNA response element; ncRNA: Non-coding RNA; RBP: RNA-binding protein; RNA-seq: RNA sequencing; RT-PCR: Reverse transcription-polymerase chain reaction.

Circular RNAs expression profiles and bioinformatics analysis in bronchopulmonary dysplasia

BACKGROUND

Bronchopulmonary dysplasia (BPD) has long been considered the most challenging chronic lung disease for neonatologists and researchers due to its complex pathological mechanisms and difficulty in prediction. Growing evidence indicates that BPD is associated with the dysregulation of circular RNAs (circRNAs). Therefore, we aimed to explore the expression profiles of circRNAs and investigate the underlying molecular network associated with BPD.

METHODS

Peripheral blood was collected from very-low-birth-weight (VLBW) infants at 5-8 days of life to extract PBMCs. Microarray analysis and qRT-PCR tests were performed to determine the differentially expressed circRNAs (DEcircRNAs) between BPD and non-BPD VLBW infants. Simultaneous analysis of GSE32472 was conducted to obtain differentially expressed mRNAs (DEmRNA) from BPD infants. The miRNAs were predicted by DEcircRNAs and DEmRNAs of upregulated, respectively, and then screened for overlapping ones. GO and KEGG analysis was performed following construction of the competing endogenous RNA regulatory network (ceRNA) for further investigation.

RESULTS

A total of 65 circRNAs (52 upregulated and 13 downregulated) were identified as DEcircRNAs between the two groups (FC >2.0 and p.adj <0.05). As a result, the ceRNA network was constructed based on three upregulated DEcircRNAs validated by qRT-PCR (hsa_circ_0007054, hsa_circ_0057950, and hsa_circ_0120151). Bioinformatics analysis indicated these DEcircRNAs participated in response to stimulus, IL-1 receptor activation, neutrophil activation, and metabolic pathways.

CONCLUSIONS

In VLBW infants with a high risk for developing BPD, the circRNA expression profiles in PBMCs were significantly altered in the early post-birth period, suggesting immune dysregulation caused by infection and inflammatory response already existed.

Mechanisms of circular RNA degradation

Circular RNAs (CircRNAs) are a class of noncoding RNAs formed by backsplicing during cotranscriptional and posttranscriptional processes, and they widely exist in various organisms. CircRNAs have multiple biological functions and are associated with the occurrence and development of many diseases. While the biogenesis and biological function of circRNAs have been extensively studied, there are few studies on circRNA degradation and only a few pathways for specific circRNA degradation have been identified. Here we outline basic information about circRNAs, summarize the research on the circRNA degradation mechanisms and discusses where this field might head, hoping to provide some inspiration and guidance for scholars who aim to study the degradation of circRNAs.

New insights into the role of circular RNAs in ovarian cancer

Ovarian cancer (OC) is one of the most aggressive tumors in women and has a poor prognosis and the highest mortality rate. Circular RNAs (circRNAs) are a type of endogenous non-coding RNAs that have recently attracted interest in cancer research. Increasing evidence has demonstrated that circRNAs play an oncogenic or suppressive role in tumorigenesis and progression, and show tissue- or developmental-stage-specific expression. Due to high stability, conservation, abundance, and specificity, circRNAs are considered promising biomarkers for the diagnosis and prognosis of cancer. Herein, we have summarized the expression profiles of circRNAs in OC tissues, serums, and cell lines. Moreover, we discuss how circRNAs participate in the regulation of multiple biological processes in OC, including cell proliferation, apoptosis, migration, invasion, autophagy, epithelial-to-mesenchymal transition, glucose metabolism, angiogenesis, immune response, and chemotherapy resistance, by sponging microRNAs and interacting with proteins.

Circular RNAs: Biomarkers of cancer

Circular RNAs (circRNAs) are a class of single-stranded closed RNAs that are produced by the back splicing of precursor mRNAs. The formation of circRNAs mainly involves intron-pairing-driven circularization, RNA-binding protein (RBP)-driven circularization, and lariat-driven circularization. The vast majority of circRNAs are found in the cytoplasm, and some intron-containing circRNAs are localized in the nucleus. CircRNAs have been found to function as microRNA (miRNA) sponges, interact with RBPs and translate proteins, and play an important regulatory role in the development and progression of cancer. CircRNAs exhibit tissue- and developmental stage-specific expression and are stable, with longer half-lives than linear RNAs. CircRNAs have great potential as biomarkers for cancer diagnosis and prognosis, which is highlighted by their detectability in tissues, especially in fluid biopsy samples such as plasma, saliva, and urine. Here, we review the current studies on the properties and functions of circRNAs and their clinical application value.

A circular RNA derived from GLIS3 accelerates the proliferation of glioblastoma cells through competitively binding with miR-449c-5p to upregulate CAPG and GLIS3

Background

Glioblastoma (GBM) is an aggressive and malignant brain tumor with extremely poor prognosis. Despite advances in treatment, the pathogenesis of GBM remains elusive. Mounting studies have revealed the critical role of circular RNAs (circRNAs) in the development and progression of human cancers including GBM, but the comprehension of their functions is still insufficient. In this study, we investigated the expression profile of a circRNA derived from GLIS family zinc finger 3 (GLIS3) in GBM and normal astrocytes. CircGLIS3 expression was detected through quantitative real-time polymerase chain reaction (qRT-PCR) analysis. Functional experiments were performed to analyze the influence of circGLIS3 on GBM cell proliferation and apoptosis. In addition, mechanism assays were to uncover the potential regulatory mechanism of circGLIS3.

Results

CircGLIS3 was up-regulated in GBM cells and knockdown of circGLIS3 significantly hampered proliferation and promoted apoptosis of GBM cells. Furthermore, circGLIS3 positively regulated CAPG and GLIS3 by sponging miR-449c-5p to affect GBM cell proliferation and apoptosis.

Conclusions

In summary, our study identified that circGLIS3 could promote proliferation and inhibit apoptosis of GBM cells via targeting miR-449c-5p/GLIS3/CAPG axis in vitro. This study could offer a novel molecular perspective for further investigation into mechanisms essential to GBM progression.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12868-022-00736-6.

CircDUSP22 Overexpression Restrains Pancreatic Cancer Development via Modulating miR-1178-3p and Downstream BNIP3

Aberrant expression of circular RNAs (circRNAs) is important in carcinogenesis, however, many differentially expressed circRNAs have not been functionally characterized. This study aimed to unveil the role of circRNA-dual specificity phosphatase 22 (circDUSP22) in pancreatic cancer (PaCa). Expression analyses of circDUSP22, miR-1178-3p and BCL2 interacting protein 3 (BNIP3) were carried out using quantitative real-time PCR (qRT-PCR) or western blotting. Cell growth was assessed by MTT, EdU and colony formation assays. Cell cycle distribution and cell apoptosis were investigated using flow cytometry assay. The assumed binding relationship between miR-1178-3p and circDUSP22 or BNIP3 was testified by dual-luciferase reporter and pull-down assays. The effect of circDUSP22 in vivo was identified by animal studies. The decreased expression of circDUSP22 was observed in PaCa samples and cells. CircDUSP22 ectopic expression in vitro blocked PaCa cell proliferation, arrested cell cycle and provoked cell apoptosis. CircDUSP22 targeted miR-1178-3p, whose expression was reinforced in PaCa. The inhibitory cell growth caused by circDUSP22 ectopic expression was reversed by miR-1178-3p enrichment. In addition, miR-1178-3p targeted BNIP3, whose expression was declined in PaCa. The inhibitory cell growth caused by circDUSP22 ectopic expression was reversed by BNIP3 knockdown. CircDUSP22 overexpression in vivo decelerated tumor growth. CircDUSP22 upregulation blocked PaCa development partly by targeting miR-1178-3p and increasing BNIP3, implying the potential implication of circDUSP22 in targeted therapy of PaCa.

Promising Roles of Circular RNAs as Biomarkers and Targets for Potential Diagnosis and Therapy of Tuberculosis

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb) infection, remains one of the most threatening infectious diseases worldwide. A series of challenges still exist for TB prevention, diagnosis and treatment, which therefore require more attempts to clarify the pathological and immunological mechanisms in the development and progression of TB. Circular RNAs (circRNAs) are a large class of non-coding RNA, mostly expressed in eukaryotic cells, which are generated by the spliceosome through the back-splicing of linear RNAs. Accumulating studies have identified that circRNAs are widely involved in a variety of physiological and pathological processes, acting as the sponges or decoys for microRNAs and proteins, scaffold platforms for proteins, modulators for transcription and special templates for translation. Due to the stable and widely spread characteristics of circRNAs, they are expected to serve as promising prognostic/diagnostic biomarkers and therapeutic targets for diseases. In this review, we briefly describe the biogenesis, classification, detection technology and functions of circRNAs, and, in particular, outline the dynamic, and sometimes aberrant changes of circRNAs in TB. Moreover, we further summarize the recent progress of research linking circRNAs to TB-related pathogenetic processes, as well as the potential roles of circRNAs as diagnostic biomarkers and miRNAs sponges in the case of Mtb infection, which is expected to enhance our understanding of TB and provide some novel ideas about how to overcome the challenges associated TB in the future.

CircRNA 0009043 suppresses non-small-cell lung cancer development via targeting the miR-148a-3p/DNAJB4 axis

Background

Circular RNAs (circRNAs) are important regulators of the development and progression of non-small-cell lung cancer (NSCLC) and many other malignancies. The functional importance of circ_0009043 in NSCLC, however, has yet to be established.

Methods

The expression of circ_0009043, miR-148a-3p, and DnaJ heat shock protein family (Hsp40) member B4 (DNAJB4) in NSCLC cells was assessed via qPCR. The proliferative activity of these cells was examined through EdU uptake and CCK-8 assays, while flow cytometry approaches were used to examine apoptotic cell death rates. Protein expression was measured through Western immunoblotting. Interactions between miR-148a-3p and circ_0009043 or DNAJB4 were detected through RNA immunoprecipitation (RIP) and dual-luciferase reporter assays. The in vivo importance of circ_0009043 as a regulator of oncogenic activity was assessed using murine xenograft models.

Results

Both NSCLC cells and tissue samples were found to exhibit circ_0009043 upregulation, and lower circ_0009043 expression levels were found to be related to poorer NSCLC patient overall survival. Knocking down circ_0009043 resulted in the enhancement of NSCLC cell proliferative activity and the suppression of apoptotic tumor cell death in vitro, while also driving more rapid in vivo tumorigenesis. Mechanistically, circ_0009043 was found to function as a molecular sponge that sequestered miR-148a-3p, which was in turn able to directly suppress DNAJB4 expression. When miR-148a-3p was overexpressed, this reversed the impact of knocking down circ_0009043 on the apoptotic death and proliferation of NSCLC cells. Conversely, miR-148a-3p inhibition resulted in the suppression of NSCLC cell apoptosis and the enhancement of tumor cell growth, while the downregulation of DNAJB4 reversed these changes.

Conclusion

Circ_0009043 acts as a tumor suppressor in NSCLC cells, promoting DNAJB4 upregulation via the sequestration of miR-148a-3p.

Roles of circRNAs in hematological malignancies

As one of the leading causes of death, hematologic malignancies are associated with an ever-increasing incidence, and drug resistance and relapse of patients after treatment represent clinical challenges. Therefore, there are pressing demands to uncover biomarkers to indicate the development, progression, and therapeutic targets for hematologic malignancies. Circular RNAs (circRNAs) are covalently closed circular-single-stranded RNAs whose biosynthesis is regulated by various factors and is widely-expressed and evolutionarily conserved in many organisms and expressed in a tissue−/cell-specific manner. Recent reports have indicated that circRNAs plays an essential role in the progression of hematological malignancies. However, circRNAs are difficult to detect with low abundance using conventional techniques. We need to learn more information about their features to develop new detection methods. Herein, we sought to retrospect the current knowledge about the characteristics of circRNAs and summarized research on circRNAs in hematological malignancies to explore a potential direction.

Target-Initiated Cascade Signal Amplification Lights up a G-Quadruplex for a Label-Free Detection of Circular Ribonucleic Acids

Circular ribonucleic acids (circRNAs) are a type of RNA that originates through back-splicing events from linear primary transcripts. CircRNAs display high structural resistance and tissue specificity. Accurate quantification of the circRNA expression level is of vital importance to disease diagnosis. Herein, we construct a label-free fluorescent biosensor for ultrasensitive analysis of circRNAs based on the integration of target-initiated cascade signal amplification strategy with a light-up G-quadruplex. This assay involves only one assistant probe that targets the circRNA-specific back-splice junction. When circRNA is present, it hybridizes with the assistant probe to initiate the duplex-specific nuclease (DSN)-catalyzed cyclic cleavage reaction, producing abundant triggers with 3'OH termini. Then, terminal deoxynucleotidyl transferase (TdT) catalyzes the addition of dGTP and dATP at the 3'-OH termini of the resultant triggers to obtain abundant long G-rich DNA sequences that can form efficient G-quadruplex products. The addition of Thioflavin T (ThT) can light up G-quadruplex, generating an enhanced fluorescence. This assay may be performed isothermally without the involvement of any nucleic acid templates, exogenous primers, and specific labeled probes. Importantly, this biosensor can discriminate target circRNA from one-base mismatched circRNA and exhibits good performance in human serum. Moreover, it can accurately detect circRNA in cancer cells at a single-cell level and even differentiate the circRNA levels in the tissues of healthy persons and nonsmall cell lung cancer (NSCLC) patients, with promising applications in circRNA-related cancer diagnosis and therapeutics.

Novel Insight of CircRNAs in Cervical Cancer: Potential Biomarkers and Therapeutic Target

Cervical cancer (CC) is a prominent cancer around the globe, with a high incidence, and fatality rate. Numerous recent investigations have shown that various non-coding RNAs are associated with the progression of CC. Circular RNAs, a novel class of non-coding RNAs, have a single chain covalent closed-loop structure and are involved in cell growth and other physiological processes. These dysregulated circRNAs seem to have environment-specific functions. They have been demonstrated in certain studies to have a dual involvement in oncogene production and tumor inhibition in different cell settings. Simultaneously, some evidence indicates that circRNAs are abnormally expressed in CC and contributes to its progression. Thus, the distinctive expression profile of circRNAs is associated with the diagnosis, prognosis, and treatment outcomes of CC. We summarized numerous CC-specific circles and their function in revealing the molecular processes of carcinogenesis and progression in CC in this review. Taken together, these data suggest that circRNA may be used as an early detection biomarker and potential therapeutic target in patients with CC.

Roles of circRNAs in the Tumorigenesis and Metastasis of HCC: A Mini Review

Circular RNAs (circRNAs) are a class of non-coding RNAs with loop structures that are stable and widely distributed in different tumor tissues. The development of high-throughput sequencing and in silico tools has enabled the discovery of numerous functional circRNAs. Hepatocellular carcinoma (HCC) is a malignant tumor, and the mechanism involved in its progression has remained unclear. In recent years, an increasing number of circRNAs have been identified in HCC, contributing to tumorigenesis and metastasis and with the potential role as biomarkers through competitive endogenous RNAs (ceRNAs) as miRNA sponges or by interacting with RNA binding proteins (RBPs). In this review, we summarize the regulatory roles of circRNAs in HCC development as well as the use of bioinformatics tools in the annotation and prioritization of circRNA and highlight the participation of exosomal circRNAs in HCC metastasis and drug resistance.

Current advances and future perspectives on the functional roles and clinical implications of circular RNAs in esophageal squamous cell carcinoma: more influential than expected

Esophageal squamous cell carcinoma (ESCC) is one of the most aggressive gastrointestinal cancers with high incidence and mortality. Therefore, it is necessary to identify novel sensitive and specific biomarkers for ESCC detection and treatment. Circular RNAs (circRNAs) are a type of noncoding RNAs featured by their covalently closed circular structure. This special structure makes circRNAs more stable in mammalian cells, coupled with their great abundance and tissue specificity, suggesting circRNAs may present enormous potential to be explored as valuable prognostic and diagnostic biomarkers for tumor. Mounting studies verified the critical roles of circRNAs in regulating ESCC cells malignant behaviors. Here, we summarized the current progresses in a handful of aberrantly expressed circRNAs, and elucidated their biological function and clinical significance in ESCC, and introduced a series of databases for circRNA research. With the improved advancement in high-throughput sequencing and bioinformatics technique, new frontiers of circRNAs will pave the path for the development of precision treatment in ESCC.