Oncogenic Role of Fusion-circRNAs Derived from Cancer-Associated Chromosomal Translocations

CircGLIS3 promotes gastric cancer progression by regulating the miR-1343-3p/PGK1 pathway and inhibiting vimentin phosphorylation

BACKGROUND

Circular RNAs (circRNAs) have been proved to play crucial roles in the development of various cancers. However, the molecular mechanism of circGLIS3 involved in gastric cancer (GC) tumorigenesis has not been elucidated.

METHODS

The higher expression level of circGLIS3 was identified in GC through RNA sequencing and subsequent tissue verification using Quantitative real-time PCR (qRT-PCR). A series of functional experiments in vitro and in vivo were performed to evaluated the effects of circGLIS3 on tumor growth and metastasis in GC. The interaction and regulation of circGLIS3/miR-1343-3p/PGK1 axis was confirmed by RNA pulldown, western blot, and rescue experiments. RIP and western blot were performed to demonstrate the role of circGLIS3 in regulating phosphorylation of VIMENTIN. We then used qRT-PCR and co culture system to trace circGLIS3 transmission via exosomal communication and identify the effect of exosomal circGLIS3 on gastric cancer and macrophages. Finally, RIP experiments were used to determine that EIF4A3 regulates circGLIS3 expression.

RESULTS

CircGLIS3(hsa_circ_0002874) was significantly upregulated in GC tissues and high circGLIS3 expression was associated with advanced TNM stage and lymph node metastasis in GC patients. We discovered that overexpression of circGLIS3 promoted GC cell proliferation, migration, invasion in vitro and in vivo, while suppression of circGLIS3 exhibited the opposite effect. Mechanistically, circGLIS3 could sponge miR-1343-3p and up-regulate the expression of PGK1 to promote GC tumorigenesis. We also found that circGLIS3 reduced the phosphorylation of VIMENTIN at ser 83 site by binding with VIMENTIN. Moreover, it was proven that exosomal circGLIS3 could promote gastric cancer metastasis and the M2 type polarization of macrophages. In the final step, the mechanism of EIF4A3 regulating the generation of circGLIS3 was determined.

CONCLUSION

Our findings demonstrate that circGLIS3 promotes GC progression through sponging miR-1343-3p and regulating VIMENTIN phosphorylation. CircGLIS3 is a potential therapeutic target for GC patients.

Nuclear export of circular RNA

Circular RNAs (circRNAs), which are increasingly being implicated in a variety of functions in normal and cancerous cells1-5, are formed by back-splicing of precursor mRNAs in the nucleus6-10. circRNAs are predominantly localized in the cytoplasm, indicating that they must be exported from the nucleus. Here we identify a pathway that is specific for the nuclear export of circular RNA. This pathway requires Ran-GTP, exportin-2 and IGF2BP1. Enhancing the nuclear Ran-GTP gradient by depletion or chemical inhibition of the major protein exporter CRM1 selectively increases the nuclear export of circRNAs, while reducing the nuclear Ran-GTP gradient selectively blocks circRNA export. Depletion or knockout of exportin-2 specifically inhibits nuclear export of circRNA. Analysis of nuclear circRNA-binding proteins reveals that interaction between IGF2BP1 and circRNA is enhanced by Ran-GTP. The formation of circRNA export complexes in the nucleus is promoted by Ran-GTP through its interactions with exportin-2, circRNA and IGF2BP1. Our findings demonstrate that adaptors such as IGF2BP1 that bind directly to circular RNAs recruit Ran-GTP and exportin-2 to export circRNAs in a mechanism that is analogous to protein export, rather than mRNA export.

The pathological mechanisms of circRNAs in mediating intervertebral disc degeneration

Lower back pain (LBP) is a worldwide health problem associated with significant economic and social burden. Intervertebral disc degeneration (IVDD) is a leading cause of LBP. Several studies show that the death of nucleus pulposus cells (NPCs), abnormal metabolism of the extracellular matrix (ECM), and inflammatory response are the key mechanisms behind the pathogenesis of IVDD. Circular RNAs (circRNAs) are key regulators of gene expression and play a significant role in regulating NPCs death, ECM homeostasis, and inflammatory response by acting as microRNAs (miRNAs) sponges in IVDD. However, the regulatory role of circRNAs in mediating IVDD remains unknown. This review comprehensively describes the normal anatomic structure and function of IVD, the pathogenesis of IVDD, the characteristics, synthesis, mechanisms, and function of circRNAs. Moreover, we highlighted the 23 circRNAs that mediate ECM metabolism, 16 circRNAs that mediate NPCs apoptosis, circ_0004354 and circ_0040039 that mediate NPCs pyroptosis, and 5 circRNAs that mediate inflammatory response in IVDD. In addition, this review presents suggestions for future studies, such as the need for further investigation on ferroptosis-related circRNAs in IVDD. This review could provide novel insights into the pathogenesis and treatment of IVDD.

Circular RNA in Multiple Sclerosis: Pathogenicity and Potential Biomarker Development: A Systematic Review

Multiple sclerosis (MS) is a complex autoimmune disorder of the CNS that affects millions of people worldwide. The causes of the disease remain unknown despite extensive efforts to understand it. CircRNAs are a unique class of endogenous non-coding RNA that are abundant, stable, conserved, and specifically expressed molecules, making them a promising biomarker of diseases. This review investigates the role of circRNA in MS pathogenicity and their potential as a biomarker through a comprehensive literature search conducted in 8 scientific databases. The studies found that there are differentially expressed circRNAs in MS patients compared to healthy controls (HC), and this difference is even more pronounced in different MS subtypes. Enrichment of circRNAs in linkage disequilibrium (LD) blocks that harbor MS-associated SNPs suggests that these SNPs manipulate the levels of circRNAs in the surrounding area, contributing to disease pathogenicity. While circRNA shows promise as an indicator or biomarker for MS disease pathology, further research is needed to fully explore its potential and impact on human biology.

Prognostic Value of hsa_circ_0007615 in Epithelial Ovarian Cancer and its Regulatory Effect on Tumor Progression

This study aimed to interrogate the functional and clinical significance of hsa_circ_0007615 in epithelial ovarian cancer (EOC). GSE192410 was screened for upregulated circRNAs in ovarian cancer. The expression levels of hsa_circ_0007615 were evaluated in a patient cohort comprising 113 EOC tissues and matched normal tissues. Subsequently, the prognostic value was confirmed by the relevance of hsa_circ_0007615 with clinical parameters, Kaplan-Meier analysis and Cox proportional risk model. Cell functional analyses were performed in EOC cell lines using a cell proliferation kit, transwell and cell death kit. Our data revealed that hsa_circ_0007615 was significantly upregulated in EOC tissues and cell lines, compared with normal ones. Multivariate survival analysis revealed that hsa_circ_0007615 emerged as an independent risk factor for overall survival and recurrence of EOC patients. Knockdown of hsa_circ_0007615 in EOC cells led to the blocking of cell proliferation, migration and invasion, but an increase of cell death presenting as ferroptosis. Tumor suppressive effects of hsa_circ_0007615 knockdown can be abolished by miR-874-3p inhibition. TUBB3 was a targeting gene of miR-874-3p. Hsa_circ_0007615 has the functional and clinical significance of EOC. Mechanistically, hsa_circ_0007615 may contribute to EOC by sponging miR-874-3p and moderating TUBB3.

The dark side of circular RNA, a new driver of genome instability

Circular RNAs (circRNAs) are covalently closed RNA molecules whose functions are still largely uncharacterized. In the July issue of Cancer Cell, Conn et al.1 demonstrate that circRNA can bind cognate DNA loci, forming circRNA-DNA hybrids (circR loops), driving genetic rearrangements of MLL/KMT2A, which are associated with the most aggressive acute leukemias.

Head and neck cancer treatment in the era of molecular medicine

Head and neck cancers are a heterogeneous group of highly aggressive tumors and collectively represent the sixth most common cancer worldwide. Most head and neck cancers are squamous cell carcinomas (HNSCCs). Current multimodal treatment concepts combine surgery, chemotherapy, irradiation, immunotherapy, and targeted therapeutics. Recent scientific advancements have enabled a more precise molecular characterization of HNSCC and revealed novel therapeutic targets and prognostic/predictive biomarkers. Notably, HNSCC is characterized by complex relations between stromal, epithelial, and immune cells within the tumor microenvironment (TME). The TME consists of different subsets of immune cells that infiltrate the tumors and interact with the tumor cells or with each other. Understanding multiple pivotal factors in HNSCC tumorigenesis and tumor progression may help define novel targets and develop more effective therapies for patients. This review provides a comprehensive overview of the latest advances in the molecular biology of HNSCC and their effects on clinical oncology; it is meant for a broad readership in the head and neck cancers field.

Preleukemic Fusion Genes Induced via Ionizing Radiation

Although the prevalence of leukemia is increasing, the agents responsible for this increase are not definitely known. While ionizing radiation (IR) was classified as a group one carcinogen by the IARC, the IR-induced cancers, including leukemia, are indistinguishable from those that are caused by other factors, so the risk estimation relies on epidemiological data. Several epidemiological studies on atomic bomb survivors and persons undergoing IR exposure during medical investigations or radiotherapy showed an association between radiation and leukemia. IR is also known to induce chromosomal translocations. Specific chromosomal translocations resulting in preleukemic fusion genes (PFGs) are generally accepted to be the first hit in the onset of many leukemias. Several studies indicated that incidence of PFGs in healthy newborns is up to 100-times higher than childhood leukemia with the same chromosomal aberrations. Because of this fact, it has been suggested that PFGs are not able to induce leukemia alone, but secondary mutations are necessary. PFGs also have to occur in specific cell populations of hematopoetic stem cells with higher leukemogenic potential. In this review, we describe the connection between IR, PFGs, and cancer, focusing on recurrent PFGs where an association with IR has been established.

CircFOXK2 promotes hepatocellular carcinoma progression and leads to a poor clinical prognosis via regulating the Warburg effect

BACKGROUND

The Warburg effect is well-established to be essential for tumor progression and accounts for the poor clinical outcomes of hepatocellular carcinoma (HCC) patients. An increasing body of literature suggests that circular RNAs (circRNAs) are important regulators for HCC. However, few circRNAs involved in the Warburg effect of HCC have hitherto been investigated. Herein, we aimed to explore the contribution of circFOXK2 to glucose metabolism reprogramming in HCC.

METHODS

In the present study, different primers were designed to identify 14 circRNAs originating from the FOXK2 gene, and their differential expression between HCC and adjacent liver tissues was screened. Ultimately, circFOXK2 (hsa_circ_0000817) was selected for further research. Next, the clinical significance of circFOXK2 was evaluated. We then assessed the pro-oncogenic activity of circFOXK2 and its impact on the Warburg effect in both HCC cell lines and animal xenografts. Finally, the molecular mechanisms of how circFOXK2 regulates the Warburg effect of HCC were explored.

RESULTS

CircFOXK2 was aberrantly upregulated in HCC tissues and positively correlated with poor clinical outcomes in patients that underwent radical hepatectomy. Silencing of circFOXK2 significantly suppressed HCC progression both in vitro and in vivo. Mechanistically, circFOXK2 upregulated the expression of protein FOXK2-142aa to promote LDHA phosphorylation and led to mitochondrial fission by regulating the miR-484/Fis1 pathway, ultimately activating the Warburg effect in HCC.

CONCLUSIONS

CircFOXK2 is a prognostic biomarker of HCC that promotes the Warburg effect by promoting the expression of proteins and miRNA sponges that lead to tumor progression. Overall, circFOXK2 has huge prospects as a potential therapeutic target for patients with HCC.

cRNAsp12 Web Server for the Prediction of Circular RNA Secondary Structures and Stabilities

Circular RNAs (circRNAs) are a novel class of non-coding RNA that, unlike linear RNAs, form a covalently closed loop without the 5' and 3' ends. Growing evidence shows that circular RNAs play important roles in life processes and have great potential implications in clinical and research fields. The accurate modeling of circRNAs structure and stability has far-reaching impact on our understanding of their functions and our ability to develop RNA-based therapeutics. The cRNAsp12 server offers a user-friendly web interface to predict circular RNA secondary structures and folding stabilities from the sequence. Through the helix-based landscape partitioning strategy, the server generates distinct ensembles of structures and predicts the minimal free energy structures for each ensemble with the recursive partition function calculation and backtracking algorithms. For structure predictions in the limited structural ensemble, the server also provides users with the option to set the structural constraints of forcing the base pairs and/or forcing the unpaired bases, such that only structures that meet the criteria are enumerated recursively.

circRNA_0067717 promotes paclitaxel resistance in nasopharyngeal carcinoma by acting as a scaffold for TRIM41 and p53

PURPOSE

Circular RNAs (circRNAs) play important roles in tumour progression. This study aimed to explore the mechanism of hsa_circ_0067717 (termed circRNA_0067717) promoting paclitaxel resistance in nasopharyngeal carcinoma (NPC).

METHODS

We assayed CNE-1 and HNE-2 parental cell lines and the corresponding paclitaxel-resistant NPC cell lines using circRNA microarrays. RNA pull-down assay, RNA immunoprecipitation, and RNA fluorescence in situ hybridization were used to identify the molecular mechanisms.

RESULTS

Here, we confirm that circRNA_0067717 is significantly upregulated in NPC paclitaxel-resistant cells and is associated with paclitaxel resistance in NPC. Mechanistically, circRNA_0067717 functions as a scaffold for TRIM41 protein (a ubiquitin E3 ligase) and p53 protein. In nasopharyngeal carcinoma paclitaxel-resistant cells, the highly expressed circRNA_0067717 can bind to more TRIM41 and p53 protein, promoting TRIM41-induced p53 ubiquitination and degradation, resulting in a decrease in p53 protein level. Moreover, the 1-176 nt area of circRNA_0067717 and the 301-425 nt region of circRNA_0067717 are the binding sites for p53 and TRIM41, respectively. The resistance of NPC cells to paclitaxel can be reduced by blocking these binding regions of circRNA_0067717.

CONCLUSION

We demonstrate that circRNA_0067717 acts as a scaffold for TRIM41 and p53, enhancing paclitaxel chemoresistance in NPC by promoting TRIM41-induced p53 degradation via ubiquitination.

Hsa_circ_0000851 promotes PDK1/p-AKT-mediated cell proliferation and migration by regulating miR-1183 in triple-negative breast cancer

Breast cancer (BC) is the most common cause of cancer-related mortality in women worldwide. Circular RNAs (circRNAs), a type of non-coding RNA, have garnered interest because of their unique looped structure. In recent years, circRNAs have been shown to be involved in various diseases, including carcinogenesis, and to serve as biomarkers for early risk assessment and survival prediction of different tumour types. This study aimed to identify a novel circRNA, hsa_circ_0000851, generated from the sixth intron of the oncogene TCF4, reported to be involved in BC pathogenesis. Our study showed that hsa_circ_0000851 was mainly located in the cytoplasm of BC cells and upregulated in BC cell lines and tissue samples. Higher hsa_circ_0000851 expression levels resulted in increased proliferation of BC cells both in vitro and in vivo, while treatment of BC cells with hsa_circ_0000851 siRNA decreased their proliferation. We found that hsa_circ_0000851 bound directly to miR-1183, accelerating the expression of its target gene PDK1, which facilities BC cell proliferation and migration through PDK1/p-AKT.

Discovery of fusion circular RNAs in leukemia with KMT2A::AFF1 rearrangements by the new software CircFusion

Chromosomal translocations in cancer genomes, key players in many types of cancers, generate chimeric proteins that drive oncogenesis. Genomes with chromosomal rearrangements can also produce fusion circular RNAs (f-circRNAs) by backsplicing of chimeric transcripts, as first shown in leukemias with PML::RARα and KMT2A::MLLT3 translocations and later in solid cancers. F-circRNAs contribute to the oncogenic processes and reinforce the oncogenic activity of chimeric proteins. In leukemia with KMT2A::AFF1 (MLL::AF4) fusions, we previously reported specific alterations of circRNA expression, but nothing was known about f-circRNAs. Due to the presence of two chimeric sequences, fusion and backsplice junctions, the identification of f-circRNAs with available tools is challenging, possibly resulting in the underestimation of this RNA species, especially when the breakpoint is not known. We developed CircFusion, a new software tool to detect linear fusion transcripts and f-circRNAs from RNA-seq data, both in samples for which the breakpoints are known and when the information about the joined exons is missing. CircFusion can detect linear and circular chimeric transcripts deriving from the main and reciprocal translocations also in the presence of multiple breakpoints, which are common in malignant cells. Benchmarking tests on simulated and real datasets of cancer samples with previously experimentally determined f-circRNAs showed that CircFusion provides reliable predictions and outperforms available methods for f-circRNA detection. We discovered and validated novel f-circRNAs in acute leukemia harboring KMT2A::AFF1 rearrangements, leading the way to future functional studies aimed to unveil their role in this malignancy.

Circular RNAs: typical biomarkers for bone-related diseases

Bone is a connective tissue that has important functions in the human body. Cells and the extracellular matrix (ECM) are key components of bone and are closely related to bone-related diseases. However, the outcomes of conventional treatments for bone-related diseases are not promising, and hence it is necessary to elucidate the exact regulatory mechanisms of bone-related diseases and identify novel biomarkers for diagnosis and therapy. Circular RNAs (circRNAs) are single-stranded RNAs that form closed circular structures without a 5' cap or 3' tail and polycyclic adenylate tails. Due to their high stability, circRNAs have the potential to be typical biomarkers. Accumulating evidence suggests that circRNAs are involved in bone-related diseases, including osteoarthritis, osteoporosis, osteosarcoma, multiple myeloma, intervertebral disc degeneration, and rheumatoid arthritis. Herein, we summarize the recent research progress on the characteristics and functions of circRNAs, and highlight the regulatory mechanism of circRNAs in bone-related diseases.

The function and clinical implication of circular RNAs in lung cancer

Lung cancer is the leading cause of cancer-related deaths worldwide. Despite the recent advent of promising new targeted therapies, lung cancer diagnostic strategies still have difficulty in identifying the disease at an early stage. Therefore, the characterizations of more sensible and specific cancer biomarkers have become an important goal for clinicians. Circular RNAs are covalently close, endogenous RNAs without 5' end caps or 3'poly (A) tails and have been characterized by high stability, abundance, and conservation as well as display cell/tissue/developmental stage-specific expressions. Numerous studies have confirmed that circRNAs act as microRNA (miRNA) sponges, RNA-binding protein, and transcriptional regulators; some circRNAs even act as translation templates that participate in multiple pathophysiological processes. Growing evidence have confirmed that circRNAs are involved in the pathogenesis of lung cancers through the regulation of proliferation and invasion, cell cycle, autophagy, apoptosis, stemness, tumor microenvironment, and chemotherapy resistance. Moreover, circRNAs have emerged as potential biomarkers for lung cancer diagnosis and prognosis and targets for developing new treatments. In this review, we will summarize recent progresses in identifying the biogenesis, biological functions, potential mechanisms, and clinical applications of these molecules for lung cancer diagnosis, prognosis, and targeted therapy.

Local data commons: the sleeping beauty in the community of data commons

Background

Public Data Commons (PDC) have been highlighted in the scientific literature for their capacity to collect and harmonize big data. On the other hand, local data commons (LDC), located within an institution or organization, have been underrepresented in the scientific literature, even though they are a critical part of research infrastructure. Being closest to the sources of data, LDCs provide the ability to collect and maintain the most up-to-date, high-quality data within an organization, closest to the sources of the data. As a data provider, LDCs have many challenges in both collecting and standardizing data, moreover, as a consumer of PDC, they face problems of data harmonization stemming from the monolithic harmonization pipeline designs commonly adapted by many PDCs. Unfortunately, existing guidelines and resources for building and maintaining data commons exclusively focus on PDC and provide very little information on LDC.

Results

This article focuses on four important observations. First, there are three different types of LDC service models that are defined based on their roles and requirements. These can be used as guidelines for building new LDC or enhancing the services of existing LDC. Second, the seven core services of LDC are discussed, including cohort identification and facilitation of genomic sequencing, the management of molecular reports and associated infrastructure, quality control, data harmonization, data integration, data sharing, and data access control. Third, instead of commonly developed monolithic systems, we propose a new data sharing method for data harmonization that combines both divide-and-conquer and bottom-up approaches. Finally, an end-to-end LDC implementation is introduced with real-world examples.

Conclusions

Although LDCs are an optimal place to identify and address data quality issues, they have traditionally been relegated to the role of passive data provider for much larger PDC. Indeed, many LDCs limit their functions to only conducting routine data storage and transmission tasks due to a lack of information on how to design, develop, and improve their services using limited resources. We hope that this work will be the first small step in raising awareness among the LDCs of their expanded utility and to publicize to a wider audience the importance of LDC.

The emerging roles and potential applications of circular RNAs in ovarian cancer: a comprehensive review

Ovarian cancer (OC) is among the most common human malignancies and the first cause of deaths among gynecologic cancers. Early diagnosis can help improving prognosis in those patients, and accordingly exploring novel molecular mechanisms may lead to find therapeutic targets. Circular RNAs (circRNAs) comprise a group of non-coding RNAs in multicellular organisms, which are identified with characteristic circular structure. CircRNAs have been found with substantial functions in regulating gene expression through interacting with RNA-binding proteins, targeting microRNAs, and transcriptional regulation. They have been found to be involved in regulating several critical processes such as cell growth, and death, organ development, signal transduction, and tumorigenesis. Accordingly, circRNAs have been implicated in a number of human diseases including malignancies. They are particularly reported to contribute to several hallmarks of cancer leading to cancer development and progression, although a number also are described with tumor-suppressor function. In OC, circRNAs are linked to regulation of cell growth, invasiveness, metastasis, angiogenesis, and chemoresistance. Notably, clinical studies also have shown potentials in diagnosis, prediction of prognosis, and therapeutic targets for OC. In this review, I have an overview to the putative mechanisms, and functions of circRNAs in regulating OC pathogenesis in addition to their clinical potentials.

rtcisE2F promotes the self-renewal and metastasis of liver tumor-initiating cells via N6-methyladenosine-dependent E2F3/E2F6 mRNA stability

Liver cancer is highly heterogeneous, and the tumor tissue harbors a variety of cell types. Liver tumor initiating cells (TICs) well contribute to tumor heterogeneity and account for tumor initiation and metastasis, but the molecular mechanisms of liver TIC self-renewal are elusive. Here, we identified a functional read-through rt-circRNA, termed rtcisE2F, that is highly expressed in liver cancer and liver TICs. rtcisE2F plays essential roles in the self-renewal and activities of liver TICs. rtcisE2F targets E2F6 and E2F3 mRNAs, attenuates mRNA turnover, and increases E2F6/E2F3 expression. Mechanistically, rtcisE2F functions as a scaffold of N-methyladenosine (m⁶A) reader IGF2BP2 and E2F6/E2F3 mRNA. rtcisE2F promotes the association of E2F6/E2F3 mRNAs with IGF2BP2, and inhibits their association with another m⁶A reader, YTHDF2. IGF2BP2 inhibits E2F6/E2F3 mRNA decay, whereas YTHDF2 promotes E2F6/E2F3 mRNA decay. By switching m⁶A readers, rtcisE2F enhances E2F6/E2F3 mRNA stability. E2F6 and E2F3 are both required for liver TIC self-renewal and Wnt/β-catenin activation, and inhibition of these pathways is a potential strategy for preventing liver tumorigenesis and metastasis. In conclusion, the rtcisE2F-IGF2BP2/YTHDF2-E2F6/E2F3-Wnt/β-catenin axis drives liver TIC self-renewal and initiates liver tumorigenesis and metastasis, and may provide a strategy to eliminate liver TICs.

Comprehensive elaboration of circular RNA in multiple myeloma

Circular RNAs (circRNAs), a novel category of endogenous non-coding RNAs, are usually well conserved across different species with a covalent closed-loop structure. Existing and emerging evidence confirms that circRNAs can function as regulators of alternative splicing, microRNA and RNA-binding protein sponges and translation, as well as gene transcription. In consideration of their multi-faceted functions, circRNAs are critically involved in hematological malignancies including multiple myeloma (MM). In particular, circRNAs have been found to play vital roles in tumor microenvironment and drug resistance, which may grant them potential roles as biomarkers for MM diagnosis and targeted therapy. In this review, we comprehensively elaborate the current state-of-the-art knowledge of circRNAs in MM, and then focus on their potential as biomarkers in diagnosis and therapy of MM.

Hsa_Circ_0066351 Acts as a Prognostic and Immunotherapeutic Biomarker in Colorectal Cancer

Circular RNA (circRNA), a novel class of non-coding RNA, has been reported in various diseases, especially in tumors. However, the key signatures of circRNA-competitive endogenous RNA (ceRNA) network are largely unclear in colorectal cancer (CRC). We first characterized circRNAs profile by using circRNA-seq analysis from real-word dataset. The expression level of hsa_circ_0066351 in CRC tissues and cell lines was detected by quantitative real-time PCR. Then, cell proliferation assay was used to confirm the proliferation function of hsa_circ_0066351. Next, Cytoscape was used to construct circRNA–miRNA–mRNA networks. Last but not least, the landscape of hsa_circ_0066351–miRNA–mRNA in CRC had been investigated in the bulk tissue RNA-Seq level and single-cell Seq level. We proved that hsa_circ_0066351 was significantly downregulated in CRC cell lines and tissues (P < 0.001), and was negatively associated with distant metastasis (P < 0.01). Significantly, the expression of hsa_circ_0066351 was associated with better survival in patients with CRC. Function assays showed that hsa_circ_0066351 could inhibit CRC cells proliferation. In addition, a ceRNA network, including hsa_circ_0066351, two miRNAs, and ten mRNAs, was constructed. Our analyses showed that these ten mRNAs were consistently downregulated in pan-cancer and enriched in tumor suppressive function. A risk score model constructed by these ten downstream genes also indicated that they were related to the prognosis and immune response in CRC. In conclusion, we demonstrated that a novel circRNA (hsa_circ_0066351) inhibited CRC proliferation, and revealed a potential prognostic and immunotherapeutic biomarker in CRC.

RGCNCDA: Relational graph convolutional network improves circRNA-disease association prediction by incorporating microRNAs

Recently, a large number of studies have indicated that circRNAs with covalently closed loops play important roles in biological processes and have potential as diagnostic biomarkers. Therefore, research on the circRNA-disease relationship is helpful in disease diagnosis and treatment. However, traditional biological verification methods require considerable labor and time costs. In this paper, we propose a new computational method (RGCNCDA) to predict circRNA-disease associations based on relational graph convolutional networks (R-GCNs). The method first integrates the circRNA similarity network, miRNA similarity network, disease similarity network and association networks among them to construct a global heterogeneous network. Then, it employs the random walk with restart (RWR) and principal component analysis (PCA) models to learn low-dimensional and high-order information from the global heterogeneous network as the topological features. Finally, a prediction model based on an R-GCN encoder and a DistMult decoder is built to predict the potential disease-associated circRNA. The predicted results demonstrate that RGCNCDA performs significantly better than the other six state-of-the-art methods in a 5-fold cross validation. Furthermore, the case study illustrates that RGCNCDA can effectively discover potential circRNA-disease associations.

iGRLCDA: identifying circRNA-disease association based on graph representation learning

While the technologies of ribonucleic acid-sequence (RNA-seq) and transcript assembly analysis have continued to improve, a novel topology of RNA transcript was uncovered in the last decade and is called circular RNA (circRNA). Recently, researchers have revealed that they compete with messenger RNA (mRNA) and long noncoding for combining with microRNA in gene regulation. Therefore, circRNA was assumed to be associated with complex disease and discovering the relationship between them would contribute to medical research. However, the work of identifying the association between circRNA and disease in vitro takes a long time and usually without direction. During these years, more and more associations were verified by experiments. Hence, we proposed a computational method named identifying circRNA-disease association based on graph representation learning (iGRLCDA) for the prediction of the potential association of circRNA and disease, which utilized a deep learning model of graph convolution network (GCN) and graph factorization (GF). In detail, iGRLCDA first derived the hidden feature of known associations between circRNA and disease using the Gaussian interaction profile (GIP) kernel combined with disease semantic information to form a numeric descriptor. After that, it further used the deep learning model of GCN and GF to extract hidden features from the descriptor. Finally, the random forest classifier is introduced to identify the potential circRNA-disease association. The five-fold cross-validation of iGRLCDA shows strong competitiveness in comparison with other excellent prediction models at the gold standard data and achieved an average area under the receiver operating characteristic curve of 0.9289 and an area under the precision-recall curve of 0.9377. On reviewing the prediction results from the relevant literature, 22 of the top 30 predicted circRNA-disease associations were noted in recent published papers. These exceptional results make us believe that iGRLCDA can provide reliable circRNA-disease associations for medical research and reduce the blindness of wet-lab experiments.

Exploring clinical implications and role of non-coding RNAs in lung carcinogenesis

Lung cancer is the utmost familiar category of cancer with greatest fatality rate worldwide and several regulatory mechanisms exercise cellular control on critical oncogenic trails implicated in lung associated carcinogenesis. The non-coding RNAs (ncRNAs) are shown to play a variety of regulatory roles, including stimulating cell proliferation, inhibiting programmed cell death, enhancing cancer cell metastatic ability and acquiring resistance to drugs. Furthermore, ncRNAs exhibit tissue-specific expression as well as great stability in bodily fluids. As a consequence, they are strong contenders for cancer based theragnostics. microRNA (miRNA) alters gene expression primarily by either degrading or interfering with the translation of targeted mRNA and long non-coding RNAs (lncRNAs) can influence gene expression by targeting transcriptional activators or repressors, RNA polymers and even DNA-duplex. lncRNAs are typically found to be dysregulated in lung cancer and hence targeting ncRNAs could be a viable strategy for developing potential therapies as well as for overcoming chemoresistance in lung cancer. The purpose of this review is to elucidate the role of ncRNAs, revisiting the recent studies in lung cancer.

Gastric cancer: An epigenetic view

Gastric cancer (GC) poses a serious threat worldwide with unfavorable prognosis mainly due to late diagnosis and limited therapies. Therefore, precise molecular classification and search for potential targets are required for diagnosis and treatment, as GC is complicated and heterogeneous in nature. Accumulating evidence indicates that epigenetics plays a vital role in gastric carcinogenesis and progression, including histone modifications, DNA methylation and non-coding RNAs. Epigenetic biomarkers and drugs are currently under intensive evaluations to ensure efficient clinical utility in GC. In this review, key epigenetic alterations and related functions and mechanisms are summarized in GC. We focus on integration of existing epigenetic findings in GC for the bench-to-bedside translation of some pivotal epigenetic alterations into clinical practice and also describe the vacant field waiting for investigation.

The Circ_0001367/miR-545-3p/LUZP1 Axis Regulates Cell Proliferation, Migration and Invasion in Glioma Cells

Glioma is the most common primary intracranial malignant tumour in adults. It has a high incidence and poses a serious threat to human health. Circular RNA is a hotspot of cancer research. In this study, we aimed to explore the role of circ_0001367 in gliomagenesis and the underlying mechanism. First, qRT-PCR was conducted, which showed that circ_0001367 level was downregulated in glioma tissues and cells. Next, gain-of-function and loss-of-function assays were performed, which indicated that circ_0001367 inhibited the proliferation, migration and invasion of glioma cells. Subsequent bioinformatics analysis, dual-luciferase reporter assays, RNA immunoprecipitation assays and cell function assays demonstrated that circ_0001367 inhibited the proliferation, migration and invasion of glioma cells by absorbing miR-545-3p and thereby regulating the expression of leucine zipper protein (LUZP1). Finally, an in vivo experiment was conducted, which demonstrated that circ_0001367 inhibited glioma growth in vivo by modulating miR-545-3p and LUZP1. Taken together, the results of this study demonstrate that the circ_0001367/miR-545-3p/LUZP1 axis may be a novel target for glioma therapy.

CircEpc1 Promotes Ricin Toxin-Induced Inflammation via Activation of NF-κB and MAPK Signaling Pathways by Sponging miR-5114

Increasing studies have concentrated on investigating circular RNAs (circRNAs) as pivotal regulators in the progression of numerous diseases and biological processes and abundant evidence shows that circRNAs are participated in the regulation of innate immune responses. Several studies showed that Ricin Toxin (RT) could induce inflammatory injury. There was no research on the particular functions and underlying mechanisms of circRNAs in RT-induced inflammation. In this study, RNA sequencing performed on RT-treated and normal RAW264.7 macrophage cells was used to investigated the differentially expressed circRNAs. Based on the dataset, the expression of circEpc1 (mmu_circ_0,000,842) was identified higher in RT-treated cells. Moreover, gain-and-loss function assays showed that circEpc1 function as a promoter in RT-induced inflammation in vivo and in vitro. Mechanistically, circEpc1 acted as a miR-5114 sponge to relieve the suppressive effect of miR-5114 on its target NOD2 and thereby activating NF-κB and MAPK signaling pathways. Our results illuminated a link between RT-induced inflammation and the circEpc1 regulatory loop and provided novel insight into the functions of circRNA in innate immune, which may emerge as a potential target in immunotherapy to control the RT-induced inflammatory injury.

From circRNAs to fusion circRNAs in hematological malignancies

Circular RNAs (circRNAs) represent a type of endogenous noncoding RNA generated by back-splicing events. Unlike the majority of RNAs, circRNAs are covalently closed, without a 5' end or a 3' poly(A) tail. A few circRNAs can be associated with polysomes, suggesting a protein-coding potential. CircRNAs are not degraded by RNA exonucleases or ribonuclease R and are enriched in exosomes. Recent developments in experimental methods coupled with evolving bioinformatic approaches have accelerated functional investigation of circRNAs, which exhibit a stable structure, a long half-life, and tumor specificity and can be extracted from body fluids and used as potential biological markers for tumors. Moreover, circRNAs may regulate the occurrence and development of cancers and contribute to drug resistance through a variety of molecular mechanisms. Despite the identification of a growing number of circRNAs, their effects in hematological cancers remain largely unknown. Recent studies indicate that circRNAs could also originate from fusion genes (fusion circRNAs, f-circRNAs) next to chromosomal translocations, which are considered the primary cause of various cancers, notably hematological malignancies. This Review will focus on circRNAs and f-circRNAs in hematological cancers.

Effect and mechanism of circRNAs in tumor angiogenesis and clinical application

Tumor blood vessels provide oxygen and necessary nutrients for the tumor, which provides the basis for tumor metastasis. Therefore, tumor angiogenesis plays a very important role in tumor growth and metastasis. In contrast to linear RNAs, circRNAs represent a type of closed-loop RNA with diverse biological functions. At the same time, circRNAs have strong stability, timeliness, tissue specificity and disease specificity. With the rapid development of next-generation sequencing and bioinformatics, there have been an increasing number of studies on circRNAs. At present, a large number of studies have reported that circRNAs regulate tumor growth, invasion, metastasis, tumor metabolism, tumor immunity and other biological functions. Increasing evidence has shown that circRNAs also play an important role in tumor angiogenesis. In this review, we briefly introduced tumor angiogenesis and circRNAs and outlined the main ways that circRNAs affect tumor angiogenesis from multiple aspects. Finally, we further explored the potential clinical application value of circRNAs in the context of tumor angiogenesis.

CircRFWD2 Promotes Osteogenic Differentiation of human Dental Pulp Stem Cells by Targeting miR-6817-5p Through BMP-Smad and p38 MAPK Pathway

Dental pulp stem cells (DPSCs) are one promising cell source of mesenchymal stem cells in bone tissue engineering. However, it remains unknown that the molecules and signaling pathways involved in osteogenesis of DPSCs. Hence, this study investigated the functional roles and underlying mechanisms of circRFWD2 during osteogenesis of DPSCs. Knockdown of circRFWD2 suppressed osteogenesis of DPSCs significantly. Mechanistically, circRFWD2 could crosstalk with miR-6817-5p, which was an inhibitor of DPSCs osteogenesis. MiR-6817-5p functioned as a sponge of BMPR2, which regulated the phosphorylation of Smad5 and p38 to impact osteogenesis activity of DPSCs. Collectively, circRFWD2/miR-6817-5p/BMPR2 axis could regulate DPSCs osteogenesis via BMP-Smad and p38 MAPK pathway, which are novel mechanisms in the osteogenic differentiation of DPSCs and suggest potential therapeutic methods for bone defects regeneration.

The Role of Circular RNAs in DNA Damage Response and Repair

Circular RNAs (circRNA) comprise a distinct class of non-coding RNAs that are abundantly expressed in the cell. CircRNAs have the capacity to regulate gene expression by interacting with regulatory proteins and/or other classes of RNAs. While a vast number of circRNAs have been discovered, the majority still remains poorly characterized. Particularly, there is no detailed information on the identity and functional role of circRNAs that are transcribed from genes encoding components of the DNA damage response and repair (DDRR) network. In this article, we not only review the available published information on DDRR-related circRNAs, but also conduct a bioinformatic analysis on data obtained from public repositories to uncover deposited, yet uncharacterized circRNAs derived from components of the DDRR network. Finally, we interrogate for potential targets that are regulated by this class of molecules and look into potential functional implications.

A DOCK1 Gene-Derived Circular RNA Is Highly Expressed in Luminal Mammary Tumours and Is Involved in the Epithelial Differentiation, Growth, and Motility of Breast Cancer Cells

Circular RNAs are regulatory molecules involved in numerous cellular processes and may be involved in tumour growth and diffusion. Here, we define the expression of 15 selected circular RNAs, which may control the process of epithelial-to-mesenchymal transition, using a panel of 18 breast cancer cell lines recapitulating the heterogeneity of these tumours and consisting of three groups according to the mesenchymal/epithelial phenotype. A circular RNA from the DOCK1 gene (hsa_circ_0020397) shows low/undetectable levels in triple-negative mesenchymal cell lines, while its content is high in epithelial cell lines, independent of estrogen receptor or HER2 positivity. RNA-sequencing experiments performed on the triple-negative/mesenchymal MDA-MB-231 and MDA-MB-157 cell lines engineered to overexpress hsa_circ_0020397 demonstrate that the circRNA influences the expression of 110 common genes. Pathway analysis of these genes indicates that overexpression of the circular RNA differentiates the two mesenchymal cell lines along the epithelial pathway and increases cell-to-cell adhesion. This is accompanied by growth inhibition and a reduction in the random/directional motility of the cell lines. The upregulated AGR2, ENPP1, and PPP1R9A genes as well as the downregulated APOE, AQP3, CD99L2, and IGFBP4 genes show an opposite regulation by hsa_circ_0020397 silencing in luminal CAMA1 cells. The results provide novel insights into the role played by specific circular RNAs in the generation/progression of breast cancer.

F-circEA1 regulates cell proliferation and apoptosis through ALK downstream signaling pathway in non-small cell lung cancer

Studies have confirmed that circular RNA (circRNA) has a stable closed structure, which plays an important role in the progression of tumors. Cancers with positive fusion genes can produce associated fusion circRNA (F-cirRNA). However, there are no reports concerning a role for F-circRNA of the echinoderm microtubule associated-protein like 4-anaplastic lymphoma kinase variant 1 (EML4-ALK1) in non-small cell lung cancer (NSCLC). Our study confirmed the existence of fusion circEA1 (F-circEA1) in NCI-H3122 cells (carrying the EML4-ALK1 gene), F-circEA1 was expressed both in the cytoplasm and nucleus as determined by fluorescence in situ hybridization (FISH) and Sanger sequencing. CCK8 and transwell assays showed that F-circEA1 was beneficial to cell proliferation, metastasis, and invasion. Overexpression of F-circEA1 can also promote cell proliferation, migration and invasion in A549 and SPCA1 cells (non-small cell lung cancer cell line not carrying the EML4-ALK1 gene). Interference with F-circEA1, induced cell cycle arrest and promoted apoptosis as determined by flow cytometry, and increased drug sensitivity to crizotinib in H3122 cells. F-circEA1 directly affected the expression of parental gene EML4-ALK1. Further research found that F-circEA1 can affect the downstream signaling pathway of ALK. In vivo, the growth rate of xenogeneic tumors was reduced and the protein expression level of EML4-ALK1 was significantly decreased in transplanted tumors measured by immunohistochemistry (IHC) after interference with F-circEA1. In conclusion, F-circEA1 can be considered as a proto-oncogene that regulates cell proliferation and apoptosis by affecting the expression of the parental gene EML4-ALK1 and its ALK downstream signaling pathway in non-small cell lung cancer.

BUB1B and circBUB1B_544aa aggravate multiple myeloma malignancy through evoking chromosomal instability

Multiple myeloma (MM) is an incurable plasma cell malignancy in the bone marrow characterized by chromosome instability (CIN), which contributes to the acquisition of heterogeneity, along with MM progression, drug resistance, and relapse. In this study, we elucidated that the expression of BUB1B increased strikingly in MM patients and was closely correlated with poor outcomes. Overexpression of BUB1B facilitated cellular proliferation and induced drug resistance in vitro and in vivo, while genetic targeting BUB1B abrogated this effect. Mechanistic studies unveiled that enforced expression of BUB1B evoked CIN resulting in MM poor outcomes mainly through phosphorylating CEP170. Interestingly, we discovered the existence of circBUB1B_544aa containing the kinase catalytic center of BUB1B, which was translated by a circular RNA of BUB1B. The circBUB1B_544aa elevated in MM peripheral blood samples was closely associated with MM poor outcomes and played a synergistic effect with BUB1B on evoking CIN. In addition, MM cells could secrete circBUB1B_544aa and interfere the MM microenvironmental cells in the same manner as BUB1B full-length protein. Intriguingly, BUB1B siRNA, targeting the kinase catalytic center of both BUB1B and circBUB1B_544aa, significantly inhibited MM malignancy in vitro and in vivo. Collectively, BUB1B and circBUB1B_544aa are promising prognostic and therapeutic targets of MM.

circAMOTL1L Suppresses Renal Cell Carcinoma Growth by Modulating the miR-92a-2-5p/KLLN Pathway

Accumulating evidence indicates that the dysregulation of circular RNAs (circRNAs) contributes to tumor progression; however, the regulatory functions of circRNAs in renal cell carcinoma (RCC) remain largely unknown. In this study, the function and underlying mechanism of circAMOTL1L in RCC progression were explored. qRT-PCR showed the downregulation of circAMOTL1L in RCC tissues and cell lines. The decrease in circAMOTL1L expression correlated with the tumor stage, metastasis, and poor prognosis in patients with RCC. Functional experiments revealed that circAMOTL1L inhibited cell proliferation and increased apoptosis in RCC cells. Subcutaneous implantation with circAMOTL1L-overexpressing cells in nude mice decreased the growth ability of the xenograft tumors. Mechanistically, circAMOTL1L served as a sponge for miR-92a-2-5p in upregulating KLLN (killin, p53-regulated DNA replication inhibitor) expression validated by bioinformatics analysis, oligo pull-down, and luciferase assays. Further, reinforcing the circAMOTL1L-miR-92a-2-5p-KLLN axis greatly reduced the growth of RCC in vivo. Conclusively, our findings demonstrate that circAMOTL1L has an antioncogenic role in RCC growth by modulating the miR-92a-2-5p-KLLN pathway. Thus, targeting the novel circAMOTL1L-miR-92a-2-5p-KLLN regulatory axis might provide a therapeutic strategy for RCC.

Circular RNAs in cardiovascular diseases

In eukaryotes, precursor mRNAs (pre-mRNAs) produce a unique class of biologically active molecules namely circular RNAs (circRNAs) with a covalently closed-loop structure via back-splicing. Because of this unconventional circular form, circRNAs exhibit much higher stability than linear RNAs due to the resistance to exonuclease degradation and thereby play exclusive cellular regulatory roles. Recent studies have shown that circRNAs are widely expressed in eukaryotes and display tissue- and disease-specific expression patterns, including in the cardiovascular system. Although numerous circRNAs are discovered by in silico methods, a limited number of circRNAs have been studied. This review intends to summarize the current understanding of the characteristics, biogenesis, and functions of circRNAs and delineate the practical approaches for circRNAs investigation. Moreover, we discuss the emerging roles of circRNAs in cardiovascular diseases.

The Emerging Functions of Circular RNAs in Bladder Cancer

Simple Summary

The role of circular RNAs has made breakthroughs in understanding the mechanisms of tumor development. Bladder cancer has an increasing incidence, high recurrence rate, high metastatic potential, poor prognosis, and susceptibility to chemotherapy resistance. Thus, it is essential to identify molecules related to the tumorigenesis of bladder cancer. In this review, we summarize current knowledge about the expression of circular RNAs in bladder cancer and their implications in vesical carcinogenesis. We further discuss the limitations of existing studies and provide an outlook for future studies in the hopes of better revealing the association between circular RNAs and bladder cancer.

Abstract

Bladder cancer (BC) is among the top ten most common cancer types worldwide and is a serious threat to human health. Circular RNAs (circRNAs) are a new class of non-coding RNAs generated by covalently closed loops through back-splicing. As an emerging research hotspot, circRNAs have attracted considerable attention due to their high conservation, stability, abundance, and specificity of tissue development. Accumulating evidence has revealed different form of circRNAs are closely related to the malignant phenotype, prognosis and chemotherapy resistance of BC, suggesting that different circRNAs may be promising biomarkers and have therapeutic significance in BC. The intention of this review is to summarize the mechanisms of circRNA-mediated BC progression and their diagnostic and prognostic value as biomarkers, as well as to further explore their roles in chemotherapy resistance.

CircRNAs: Decrypting the novel targets of fibrosis and aging

Fibrosis is a typical aging-related pathological process involving almost all organs. It is usually initiated by organic injury and leads to the gradual decline of organ function or even loss. Circular RNAs (circRNAs) are being hailed as a newly rediscovered class of covalently closed transcripts without a 5' cap or 3' tail which draw increasing attention. In particular, circRNAs have been identified to be involved in the multifaceted processes of fibrosis in various organs, including the heart, liver, lung, and kidney. As more and more circRNAs are functionally characterized, they have become novel therapies for fibrosis. In this review, we systematically summarized current studies regarding the roles of circRNAs in fibrosis and shed light on the basis of circRNAs as a potential treatment for fibrosis.

Insights into the Evolving Roles of Circular RNAs in Cancer

The majority of RNAs transcribed from the human genome have no coding capacity and are termed non-coding RNAs (ncRNAs). It is now widely accepted that ncRNAs play key roles in cell regulation and disease. Circular RNAs (circRNAs) are a form of ncRNA, characterised by a closed loop structure with roles as competing endogenous RNAs (ceRNAs), protein interactors and transcriptional regulators. Functioning as key cellular regulators, dysregulated circRNAs have a significant impact on disease progression, particularly in cancer. Evidence is emerging of specific circRNAs having oncogenic or tumour suppressive properties. The multifaceted nature of circRNA function may additionally have merit as a novel therapeutic target, either in treatment or as a novel biomarker, due to their cell-and disease-state specific expression and long-term stability. This review aims to summarise current findings on how circRNAs are dysregulated in cancer, the effects this has on disease progression, and how circRNAs may be targeted or utilised as future potential therapeutic options.

The Landscape of Regulatory Noncoding RNAs in Ewing's Sarcoma

Ewing’s sarcoma (ES) is a pediatric sarcoma caused by a chromosomal translocation. Unlike in most cancers, the genomes of ES patients are very stable. The translocation product of the EWS-FLI1 fusion is most often the predominant genetic driver of oncogenesis, and it is pertinent to explore the role of epigenetic alterations in the onset and progression of ES. Several types of noncoding RNAs, primarily microRNAs and long noncoding RNAs, are key epigenetic regulators that have been shown to play critical roles in various cancers. The functions of these epigenetic regulators are just beginning to be appreciated in ES. Here, we performed a comprehensive literature review to identify these noncoding RNAs. We identified clinically relevant tumor suppressor microRNAs, tumor promoter microRNAs and long noncoding RNAs. We then explored the known interplay between different classes of noncoding RNAs and described the currently unmet need for expanding the noncoding RNA repertoire of ES. We concluded the review with a discussion of epigenetic regulation of ES via regulatory noncoding RNAs. These noncoding RNAs provide new avenues of exploration to develop better therapeutics and identify novel biomarkers.

Circular RNA circβ-catenin aggravates the malignant phenotype of non-small-cell lung cancer via encoding a peptide

Background

More and more evidences demonstrate that circular RNAs (circNRAs) can encode protein. As a circRNA with translation capabilities, outcomes of circβ‐catenin in non‐small cell lung cancer (NSCLC) still need to be explored.

Method

The research methods of circβ‐catenin in the article include qRT‐PCR, wound healing assay, CCK‐8, colony formation, and Transwell assay. Western blotting and immunofluorescence were provided to detect protein expression levels and peptide encoded by circβ‐catenin, respectively.

Results

A prominently higher circβ‐catenin expression was found in NSCLC tissues. Silencing of circβ‐catenin was able to inhibit NSCLC cell migrating, invasive, and proliferative phenotypes. Overexpression of circβ‐catenin could enhance the migrating, invasive, and proliferative phenotypes of NSCLC cells. Importantly, circβ‐catenin was found to encode a peptide in NSCLC cells. Silencing or overexpression of circβ‐catenin could reduce or increase β‐catenin protein expression via suppressing the degradation of β‐catenin.

Conclusion

Circβ‐catenin could promote NSCLC cell malignant phenotypes via peptide‐regulated β‐catenin pathway. Our study provided a new understanding for the mechanisms of NSCLC.

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.

Circular RNAs regulate cancer-related signaling pathways and serve as potential diagnostic biomarkers for human cancers

Circular RNAs (circRNAs) are RNAs that have an important role in various pathological processes, including cancer. After the usage of high-throughput RNA sequencing, many circRNAs were found to be differentially expressed in various cancer cell lines and regulate cell signaling pathways by modulating particular gene expressions. Understanding their role in these pathways and what cancers they are found in can set the stage for identifying diagnostic and prognostic biomarkers and therapeutic targets of cancer. This paper will discuss which circRNAs are found in different cancers and what mechanisms they use to upregulate or downregulate certain cellular components.

CircRNA NALCN acts as an miR-493-3p sponge to regulate PTEN expression and inhibit glioma progression

Background

An increasing number of studies have shown that circular RNAs (circRNAs) play important roles in the regulation of tumor progression. Therefore, we explored the expression characteristics, function, and related mechanism of the newly identified circNALCN in glioma.

Methods

RNA sequencing was used to analyze the expression profiles of circRNAs in brain tissue from five glioma cases and four normal controls. Quantitative real-time polymerase chain reaction was implemented to examine the levels of circNALCN, miR-493-3p, and phosphatase and tensin homolog (PTEN). Cell counting kit 8 assays were performed to analyze cell proliferation, and cell migration was assessed by the wound healing test and Transwell assay. Dual-luciferase reporter, fluorescence in situ hybridization, and RNA pulldown assays were performed to confirm the role of circNALCN as an miR-493-3p sponge, weakening the inhibitory effect of miR-493-3p on target PTEN expression.

Results

The downregulated expression of circNALCN was observed in both glioma tissues and cell lines. CircNALCN expression was negatively correlated with World Health Organization grade and overall survival in patients with glioma. Functionally, the overexpression of circNALCN significantly inhibited the proliferation and migration of glioma cells, whereas miR-493-3p mimics counteracted these effects. The mechanistic analysis demonstrated that circNALCN acted as a competing endogenous RNA for miR-493-3p to relieve the repressive effects of miR-493-3p on its target, PTEN, suppressing glioma tumorigenesis.

Conclusions

CircNALCN inhibits the progression of glioma through the miR-493-3p/PTEN axis, providing a developable biomarker and therapeutic target for glioma patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-02001-y.

Emerging role of circular RNAs in breast cancer

Circular RNAs (cirRNAs) are generally considered as non-coding RNAs which can act as molecular sponges for miRNAs, exert regulatory roles in transcription or splicing, and interplay with RNA binding proteins. These single-stranded transcripts can affect tumor growth, the metastatic ability of cancer cells, stemness properties, and resistance to therapeutic options. Recent investigations have shown the crucial effects of circrNAs in the evolution of breast cancer. Signature of circRNAs in breast cancer samples has been mostly assessed through microarray-based methods revealing up-regulation of some circRNAs such as circ-TFF1, circACAP2, circ-TFCP2L1, hsa_circ_0000519, circDENND4C, circPLK1 and circRNA_069718, while down-regulation of other circRNAs such as hsa_circ_0000375, circYap, hsa_circ_0025202, circTADA2A-E6, circASS1 and circRNA_BARD1 in breast cancer samples. Mechanistically, these transcripts mainly affect breast cancer tumorigenesis via serving as sponges for miRNAs. In the current manuscript, we explore the results of researches that appraised the role of circRNAs in breast cancer.

Current research on circular RNAs and their potential clinical implications in breast cancer

Breast cancer (BC) is one of the most common cancers and the leading causes of death among women worldwide, and its morbidity rate is growing. Discovery of novel biomarkers is necessary for early BC detection, treatment, and prognostication. Circular RNAs (circRNAs), a novel type of endogenous non-coding RNAs with covalently closed continuous loops, have been found to have a crucial role in tumorigenesis. Studies have demonstrated that circRNAs are aberrantly expressed in the tumor tissues and plasma of patients with BC, and they modulate gene expression affecting the proliferation, metastasis, and chemoresistance of BC by specifically binding and regulating the expression of microRNAs (miRNAs). Therefore, circRNAs can be used as novel potential diagnostic and prognostic markers, and therapeutic targets for BC. This article summarizes the properties, functions, and regulatory mechanisms of circRNAs, particularly current research on their association with BC proliferation, metastasis, and chemoresistance.

[Expression of circ-KEL in acute myeloid leukemia and its regulatory mechanisms in leukemic cells]

Objective: To explore the expression of circ-KEL in patients with acute myeloid leukemia (AML) and the effect and mechanism of circ-KEL on leukemic cells. Methods: The expression of circ-KEL was detected by quantitative real-time polymerase chain reaction in bone marrow mononuclear cells collected from 116 patients with AML and 40 healthy donors. The correlation of circ-KEL expression with the clinical characteristics of patients with AML was further systematically analyzed. The modulations among circ-KEL, miR-335-5p, and LRG1 were predicted through bioinformatics analysis and validated by dual luciferase assay. Cell proliferation and apoptosis were detected using CCK8 and flow cytometry. Results: The expression of circ-KEL was significantly elevated in patients with AML compared with the healthy controls (Relative expression level, -Δct, AML: -7.117±1.831; control: -8.669±1.771, P<0.001) . Moreover, patients with high circ-KEL expression have significantly worse overall survival. The level of circ-KEL in patients with AML was downregulated after chemo-treatment. In addition, circ-KEL could serve as the sponge of miR-335-5p and regulate LRG1. Bioinformatics analysis showed that miR-335-5p correlates with good prognosis and was negatively associated with LRG1. LRG1 could promote cell proliferation and inhibit cell apoptosis. Our results also exhibited the higher expression of LRG1 in patients with AML. Moreover, circ-KEL exerted functional effects via sponging miR-335-5p and regulating LRG1. Conclusion: circ-KEL expresses highly in patients with AML and correlates with poor prognosis, suggesting its important role in the genesis and progress of AML.

CircNFIX promotes progression of pituitary adenoma via CCNB1 by sponging miR-34a -5p

Previous studies have shown that CCNB1 affects the invasiveness of pituitary adenomas, and it is of great significance to find the upstream mechanism of regulating CCNB1.In this study, we explored a significantly overexpressed circRNA in invasive pituitary adenomas. Based on bioinformatics analysis and mechanism experiments, we determined that circNFIX (has-circ_0005660) affects cell invasion, migration and proliferation in pituitary adenomas by sponging miR-34a-5p through CCNB1. In pituitary adenoma tissues, the expression of circNFIX and CCNB1 was upregulated, while miR-34a-5p expression was downregulated. The silencing of circNFIX or overexpression of miR-34a-5p inhibited cell invasion, migration and proliferation. Inhibition of miR-34a-5p expression reversed the inhibitory effect of circNFIX silencing on the progression of pituitary adenoma. In conclusion, CircNFIX affects cell invasion, migration, and proliferation in pituitary adenomas by sponging miR-34a-5p through CCNB1. Therefore, circNFIX is expected to serve as a potential target for the treatment of pituitary adenomas.