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

The importance of the circRNA/Wnt axis in gliomas: Biological functions and clinical opportunities

Gliomas are among the most common cancers in the central nervous system, arising through various signaling pathways. One significant pathway is Wnt signaling, a tightly regulated process that plays a crucial role in gliomagenesis and development. The current study aims to explore the relationship between circular RNAs (circRNAs) and the Wnt/β-catenin signaling pathway in gliomas, considering the growing recognition of circRNAs in disease pathogenesis. A comprehensive review of recent research was conducted to investigate the roles of circRNAs in gliomas, focusing on their expression patterns and interactions with the Wnt signaling pathway. The analysis included studies examining circRNAs' function as microRNA sponges and their impact on glioma biology. The findings reveal that circRNAs are differentially expressed in gliomas and significantly influence the occurrence, growth, and metastasis of these tumors. Specifically, circRNAs interact with the Wnt signaling pathway, affecting glioma development and progression. This interaction highlights the importance of circRNAs in glioma pathophysiology. Understanding the regulatory network involving circRNAs and Wnt signaling offers valuable insights into glioma pathophysiology. CircRNAs hold promise as diagnostic and prognostic biomarkers and may serve as targets for novel therapeutic strategies in glioma treatment.

The closed loop of the circCLIP2/miR-361-3p/STAT2 signaling axis regulates the progression of cervical cancer

BACKGROUND

Circular RNAs (circRNAs) are involved in tumorigenesis and the progression of cancer through various pathways. However, the detailed regulatory mechanisms of circRNAs in cervical cancer are not fully understood. The present study was designed to explore the biological functions and potential mechanisms of circCLIP2 (has_circ_0001717) in cervical cancer.

METHODS

The expression profiles of circRNAs in cancerous and adjacent normal tissues of cervical cancer patients were examined using RNA sequencing. Gain- and loss-of-function experiments were carried out to determine the biological functions of circCLIP2 in the proliferation, invasion, migration and apoptosis of cervical cancer cells. qRT-PCR was also used to evaluate the expression of circCLIP2, miR-361-3p and STAT2 in cervical cancer cells. The protein levels of STAT2 were determined by western blotting.

RESULTS

CircCLIP2 was identified as the most down-regulated molecule in the cancerous tissues of cervical cancer patients compared to the adjacent normal tissues. Moreover, the levels of circCLIP2 was decreased in cervical cancer patients with metastasis and advanced tumour stage, and patients with high-circCLIP2-expression exhibited poorer survival rate. In addition, over-expression of circCLIP2 suppressed the proliferation, invasion and migration of cervical cancer cells, whereas cell apoptosis was enhanced. Moreover, down-regulated circCLIP2 functioned as the sponge of miR-361-3p, which reduced the expression of STAT2. Furthermore, knockdown of STAT2 inhibited the expression of circCLIP2 at the transcriptional level.

CONCLUSION

The circCLIP2/miR-361-3p/STAT2 signalling could mediate the progression of cervical cancer. CircCLIP2 may become a novel target for the diagnosis and treatment of cervical cancer.

Advances in CircRNAs in the Past Decade: Review of CircRNAs Biogenesis, Regulatory Mechanisms, and Functions in Plants

Circular RNA (circRNA) is a type of non-coding RNA with multiple biological functions. Whole circRNA genomes in plants have been identified, and circRNAs have been demonstrated to be widely present and highly expressed in various plant tissues and organs. CircRNAs are highly stable and conserved in plants, and exhibit tissue specificity and developmental stage specificity. CircRNAs often interact with other biomolecules, such as miRNAs and proteins, thereby regulating gene expression, interfering with gene function, and affecting plant growth and development or response to environmental stress. CircRNAs are less studied in plants than in animals, and their regulatory mechanisms of biogenesis and molecular functions are not fully understood. A variety of circRNAs in plants are involved in regulating growth and development and responding to environmental stress. This review focuses on the biogenesis and regulatory mechanisms of circRNAs, as well as their biological functions during growth, development, and stress responses in plants, including a discussion of plant circRNA research prospects. Understanding the generation and regulatory mechanisms of circRNAs is a challenging but important topic in the field of circRNAs in plants, as it can provide insights into plant life activities and their response mechanisms to biotic or abiotic stresses as well as new strategies for plant molecular breeding and pest control.

Molecular mechanisms of circular RNA translation

Circular RNAs (circRNAs) are covalently closed single-stranded RNAs without a 5' cap structure and a 3' poly(A) tail typically present in linear mRNAs of eukaryotic cells. CircRNAs are predominantly generated through a back-splicing process within the nucleus. CircRNAs have long been considered non-coding RNAs seemingly devoid of protein-coding potential. However, many recent studies have challenged this idea and have provided substantial evidence that a subset of circRNAs can associate with polysomes and indeed be translated. Therefore, in this review, we primarily highlight the 5' cap-independent internal initiation of translation that occurs on circular RNAs. Several molecular features of circRNAs, including the internal ribosome entry site, N6-methyladenosine modification, and the exon junction complex deposited around the back-splicing junction after back-splicing event, play pivotal roles in their efficient internal translation. We also propose a possible relationship between the translatability of circRNAs and their stability, with a focus on nonsense-mediated mRNA decay and nonstop decay, both of which are well-characterized mRNA surveillance mechanisms. An in-depth understanding of circRNA translation will reshape and expand our current knowledge of proteomics.

CircMCTP2 enhances the progression of bladder cancer by regulating the miR-99a-5p/FZD8 axis

BACKGROUND

CircRNAs and miRNAs are involved in the progression of tumor. CircMCTP2 is considered as a novel tumor promoter. However, the exact functions of circMCTP2 in bladder cancer are still unclear. This study was designed to explore the underlying mechanisms of circMCTP2-modulated tumor development in bladder cancer.

METHODS

The present study is an original research. The levels of circMCTP2 in a total of 39 bladder cancer specimens and cell lines were determined by RT-qPCR. The expression of FZD8 in T24 and RT-4 cells treated with miR-99a-5p mimics were examined using western blotting. In addition, the proliferative, migrative and invasive abilities of transfected cells were determined by CCK8 and Transwell assays. Furthermore, the apoptosis of transfected cells was evaluated using flow cytometry. Dual luciferase reporter assay was performed to elucidate the relationship between miR-99a-5p and circMCTP2/FZD8.

RESULTS

The levels of circMCTP2 were elevated in bladder cancer samples and cells, and this was related to worse survival rate. Downregulation of circMCTP2 suppressed growth and metastasis of cells, whereas the apoptotic rate of cells was enhanced. The levels of miR-99a-5rp was elevated after the downregulation of circMCTP2. Moreover, reverse correlation between the expression of miR-99a-5p and circMCTP2 was revealed in bladder cancer specimens. Additionally, FZD8 was the putative target of miR-99a-5p and the mimics of miR-99a-5p inhibited the proliferation, migration and invasion of bladder cancer cells via the FZD8/Wnt-b-catenin axis. Moreover, circMCTP2 regulated the growth and metastasis of bladder cancer cells potentially through regulating the miR-99a-5p/FZD8/Wnt-b-catenin axis. In summary, circMCTP2 was considered as an oncogenic factor through regulating the miR-99a-5p/FZD8/Wnt-b-catenin axis.

CONCLUSIONS

This novel signaling could regulate the biological behaviours of bladder cancer cells, and these findings highlighted circMCTP2 as a critical target for treating bladder cancer.

Applications of engineered exosomes in drugging noncoding RNAs for cancer therapy

Noncoding RNAs (ncRNAs) are engaged in key cell biological and pathological events, and their expression alteration is connected to cancer progression both directly and indirectly. A huge number of studies have mentioned the significant role of ncRNAs in cancer prevention and therapy that make them an interesting subject for cancer therapy. However, there are several limitations, including delivery, uptake, and short half-life, in the application of ncRNAs in cancer treatment. Exosomes are introduced as promising options for the delivery of ncRNAs to the target cells. In this review, we will briefly discuss the application and barriers of ncRNAs. After that we will focus on exosome-based ncRNAs delivery and their advantages as well as the latest achievements in drugging ncRNAs with exosomes.

RNA-RNA competitive interactions: a molecular civil war ruling cell physiology and diseases

The idea that proteins are the main determining factors in the functioning of cells and organisms, and their dysfunctions are the first cause of pathologies, has been predominant in biology and biomedicine until recently. This protein-centered view was too simplistic and failed to explain the physiological and pathological complexity of the cell. About 80% of the human genome is dynamically and pervasively transcribed, mostly as non-protein-coding RNAs (ncRNAs), which competitively interact with each other and with coding RNAs generating a complex RNA network regulating RNA processing, stability, and translation and, accordingly, fine-tuning the gene expression of the cells. Qualitative and quantitative dysregulations of RNA-RNA interaction networks are strongly involved in the onset and progression of many pathologies, including cancers and degenerative diseases. This review will summarize the RNA species involved in the competitive endogenous RNA network, their mechanisms of action, and involvement in pathological phenotypes. Moreover, it will give an overview of the most advanced experimental and computational methods to dissect and rebuild RNA networks.

Role of Circ-ITCH Gene Polymorphisms and Its Expression in Breast Cancer Susceptibility and Prognosis

INTRODUCTION/OBJECTIVE

Breast cancer (BC) is the first leading cause of cancer-related mortality in females worldwide. We have investigated the correlation between circ-ITCH gene polymorphisms, circ-ITCH expression, and their effect on β-catenin levels and BC development.

METHODS

Participants included 62 BC and 62 controls matched in terms of age. The circ-ITCH polymorphisms rs10485505 and rs4911154 were genotyped using whole blood samples. In addition, mRNA expression analysis of circ-ITCH was performed on BC tissues. The β-catenin levels in serum samples were measured using ELISA.

RESULTS

The qRT-PCR results demonstrated that circ-ITCH was significantly downregulated in BC compared to normal healthy tissues. The genotype distribution of rs10485505 and rs4911154 were significantly associated with BC risk. For rs10485505, genotype CT and TT were significantly associated with an increased BC risk. In contrast, there was a significant association between rs4911154, genotypes GA and AA, and an increased BC risk. Regarding the rs10485505 genotype, carriers of the T allele frequently have a poor prognosis compared to carriers of the CC genotype. Serum β-catenin in the BC patients' group was significantly higher than in the control group. The relative expression levels of circ-ITCH were remarkably decreased in the BC samples of patients carrying the A allele at rs4911154 compared to patients with a GG genotype. Conversely, β-catenin protein levels were increased in patients carrying the A allele, while rs10485505 genotype carriers of the CT and TT genotypes showed downregulation of circ-ITCH expression fold compared to the CC genotype. Contrarily, β-catenin levels markedly increased in TT and CT genotypes compared with the CC genotype.

CONCLUSIONS

Our research showed that the rs10485505 polymorphism (T allele) and the rs4911154 polymorphism (A allele) are associated with the risk and prognosis of BC. This finding may be due to the effect on the level of circ-ITCH mRNA expression in BC tissues as well as the level of β-catenin in BC patients.

NEDD4 E3 ubiquitin ligases: promising biomarkers and therapeutic targets for cancer

Accumulating evidence has demonstrated that NEDD4 E3 ubiquitin ligase family plays a pivotal oncogenic role in a variety of malignancies via mediating ubiquitin dependent degradation processes. Moreover, aberrant expression of NEDD4 E3 ubiquitin ligases is often indicative of cancer progression and correlated with poor prognosis. In this review, we are going to address association of expression of NEDD4 E3 ubiquitin ligases with cancers, the signaling pathways and the molecular mechanisms by which the NEDD4 E3 ubiquitin ligases regulate oncogenesis and progression, and the therapies targeting the NEDD4 E3 ubiquitin ligases. This review provides the systematic and comprehensive summary of the latest research status of E3 ubiquitin ligases in the NEDD4 subfamily, and proposes that NEDD4 family E3 ubiquitin ligases are promising anti-cancer drug targets, aiming to provide research direction for clinical targeting of NEDD4 E3 ubiquitin ligase therapy.

Characterization of cell-type specific circular RNAs associated with colorectal cancer metastasis

Colorectal cancer (CRC) is the most common gastrointestinal malignancy and a leading cause of cancer deaths in the United States. More than half of CRC patients develop metastatic disease (mCRC) with an average 5-year survival rate of 13%. Circular RNAs (circRNAs) have recently emerged as important tumorigenesis regulators; however, their role in mCRC progression remains poorly characterized. Further, little is known about their cell-type specificity to elucidate their functions in the tumor microenvironment (TME). To address this, we performed total RNA sequencing (RNA-seq) on 30 matched normal, primary and metastatic samples from 14 mCRC patients. Additionally, five CRC cell lines were sequenced to construct a circRNA catalog in CRC. We detected 47 869 circRNAs, with 51% previously unannotated in CRC and 14% novel candidates when compared to existing circRNA databases. We identified 362 circRNAs differentially expressed in primary and/or metastatic tissues, termed circular RNAs associated with metastasis (CRAMS). We performed cell-type deconvolution using published single-cell RNA-seq datasets and applied a non-negative least squares statistical model to estimate cell-type specific circRNA expression. This predicted 667 circRNAs as exclusively expressed in a single cell type. Collectively, this serves as a valuable resource, TMECircDB (accessible at https://www.maherlab.com/tmecircdb-overview), for functional characterization of circRNAs in mCRC, specifically in the TME.

Therapeutic and diagnostic applications of exosomal circRNAs in breast cancer

Circular RNAs (circRNAs) are regulatory elements that are involved in orchestrating gene expression and protein functions and are implicated in various biological processes including cancer. Notably, breast cancer has a significant mortality rate and is one of the most common malignancies in women. CircRNAs have been demonstrated to contribute to the pathogenesis of breast cancer including its initiation, progression, metastasis, and resistance to drugs. By acting as miRNA sponges, circRNAs can indirectly influence gene expression by disrupting miRNA regulation of their target genes, ultimately altering the course of cancer development and progression. Additionally, circRNAs can interact with proteins and modulate their functions including signaling pathways involved in the initiation and development of cancer. Recently, circRNAs can encode peptides that play a role in the pathophysiology of breast cancer and other diseases and their potential as diagnostic biomarkers and therapeutic targets for various cancers including breast cancer. CircRNAs possess biomarkers that differentiate, such as stability, specificity, and sensitivity, and can be detected in several biological specimens such as blood, saliva, and urine. Moreover, circRNAs play an important role in various cellular processes including cell proliferation, differentiation, and apoptosis, all of which are integral factors in the development and progression of cancer. This review synthesizes the functions of circRNAs in breast cancer, scrutinizing their contributions to the onset and evolution of the disease through their interactions with exosomes and cancer-related intracellular pathways. It also delves into the potential use of circRNA as a biomarker and therapeutic target against breast cancer. It discusses various databases and online tools that offer crucial circRNA information and regulatory networks. Lastly, the challenges and prospects of utilizing circRNAs in clinical settings associated with breast cancer are explored.

Circular RNA-mediated ceRNA network was identified in human lung adenocarcinoma by high-throughput sequencing

OBJECTIVES

Aberrantly expressed circular RNAs (circRNAs) have been detected in many types of tumors. Hence, they are currently investigated as candidate biomarkers for diagnostic and potential targets for therapy in cancers. The objective of this study was to assess the expression profile of circRNA in lung adenocarcinoma (LUAD).

METHODS

This study included 14 pairs of postoperative lung adenocarcinoma specimens, including cancer tissues and matched adjacent tissues. Second-generation sequencing was applied to the specimens to determine the circRNA expression in them among the 5242 distinct circRNAs detected.

RESULTS

We identified a total of 18 significantly dysregulated circRNAs in the LUAD tissues: upregulation in four and downregulation in 14. ROC (The receiver operating characteristic curve) further suggested that hsa_circ_0120106, has_circ_0007342, has_circ_0005937, and circRNA_0000826 could potentially be used as biomarkers in the diagnosis of LUAD. Furthermore, study of the circRNA-microRNA (miRNA)-messenger RNA (mRNA) revealed interactions between the 18 dysregulated circRNA and several cancer-related miRNAs. Finally, a further Kyoto Encyclopedia of Genes and Genomes analysis showed that the cell cycle phase transition, p53 signaling pathway, AMP-activated protein kinase (AMPK) relative signaling pathway, and so on were key putative pathways in the process of LUAD.

CONCLUSIONS

These findings demonstrated the correlation between abnormality in circRNA expression and LUAD, which lays the foundation of making CircRNAs candidate biomarkers in the diagnosis of LUAD.

Biological functions of circRNAs and their advance on skeletal muscle development in bovine

The development of skeletal muscle in animals is a complex biological process, which are strictly and precisely regulated by many genes and non-coding RNAs. Circular RNA (circRNA) was found as a novel class of functional non-coding RNA with ring structure in recent years, which appears in the process of transcription and is formed by covalent binding of single-stranded RNA molecules. With the development of sequencing and bioinformatics analysis technology, the functions and regulation mechanisms of circRNAs have attracted great attention due to its high stability characteristics. The role of circRNAs in skeletal muscle development have been gradually revealed, where circRNAs were involved in various biological processes, such as proliferation, differentiation, and apoptosis of skeletal muscle cells. In this review, we summarized the current studies advance of circRNAs involved in skeletal muscle development in bovine, and hope to gain a deeper understanding of the functional roles of the circRNAs in muscle growth. Our results will provide some theoretical supports and great helps for the genetic breeding of this species, and aiming at improving bovine growth and development and preventing muscle diseases.

Understanding the roles and regulation patterns of circRNA on its host gene in tumorigenesis and tumor progression

Circular RNAs (circRNAs) are a novel type of endogenous non-coding RNAs, which are covalently closed loop structures formed by precursor mRNAs (pre-mRNAs) through back-splicing. CircRNAs are abnormally expressed in many tumors, and play critical roles in a variety of tumors as oncogenes or tumor suppressor genes by sponging miRNAs, regulating alternative splicing and transcription, cis-regulating host genes, interacting with RNA binding proteins (RBPs) or encoding polypeptides. Among them, the regulation of circRNAs on their corresponding host genes is a critical way for circRNAs to exit their functions. Accumulating evidence suggests that circRNAs are able to regulate the expression of host genes at the transcriptional level, post-transcriptional level, translational level, post-translational level, or by encoding polypeptides. Therefore, this paper mainly summarized the roles and association of circRNAs and their corresponding host genes in tumorigenesis and tumor progression, generalized the circRNAs that function synergistically or antagonistically with their host genes, and elaborated the mechanisms of mutual regulation between circRNAs and their host genes. More importantly, this review provides specific references for revealing the potential application of circRNAs combined with their host genes in tumor diagnosis, treatment and prognosis.

Colon cancer transcriptome

Over the last four decades, methodological innovations have continuously changed transcriptome profiling. It is now feasible to sequence and quantify the transcriptional outputs of individual cells or thousands of samples using RNA sequencing (RNA-seq). These transcriptomes serve as a connection between cellular behaviors and their underlying molecular mechanisms, such as mutations. This relationship, in the context of cancer, provides a chance to unravel tumor complexity and heterogeneity and uncover novel biomarkers or treatment options. Since colon cancer is one of the most frequent malignancies, its prognosis and diagnosis seem to be critical. The transcriptome technology is developing for an earlier and more accurate diagnosis of cancer which can provide better protectivity and prognostic utility to medical teams and patients. A transcriptome is a whole set of expressed coding and non-coding RNAs in an individual or cell population. The cancer transcriptome includes RNA-based changes. The combined genome and transcriptome of a patient may provide a comprehensive picture of their cancer, and this information is beginning to affect treatment decision-making in real-time. A full assessment of the transcriptome of colon (colorectal) cancer has been assessed in this review paper based on risk factors such as age, obesity, gender, alcohol use, race, and also different stages of cancer, as well as non-coding RNAs like circRNAs, miRNAs, lncRNAs, and siRNAs. Similarly, they have been examined independently in the transcriptome study of colon cancer.

Hypoxia-responsive circular RNA circAAGAB reduces breast cancer malignancy by activating p38 MAPK and sponging miR-378 h

BACKGROUND

Breast cancer is a prevalent disease in women, with high prevalence worldwide. The hypoxic microenvironment of solid tumors develops during the progress of carcinogenesis and leads to greater malignancy and treatment resistance. Recently, accumulating evidence indicates that non-coding RNAs, such as circular RNAs (circRNAs), play a pivotal role in altering cellular functions. However, the underlying mechanisms of circRNAs in breast cancer are still unclear. Therefore, the purpose of this study was to investigate the role of a tumor-suppressive circRNA, circAAGAB, in breast cancer by assuming down-regulation of circAAGAB under hypoxia and the properties of a tumor suppressor.

METHODS

Firstly, circAAGAB was identified from expression profiling by next generation sequencing. Next, the stability of circAAGAB increased by interacting with the RNA binding protein FUS. Moreover, cellular and nuclear fractionation showed that most circAAGAB resided in the cytoplasm and that it up-regulated KIAA1522, NKX3-1, and JADE3 by sponging miR-378 h. Lastly, the functions of circAAGAB were explored by identifying its down-stream genes using Affymetrix microarrays and validated by in vitro assays.

RESULTS

The results showed that circAAGAB reduced cell colony formation, cell migration, and signaling through p38 MAPK pathway, as well as increased radiosensitivity.

CONCLUSION

These findings suggest that the oxygen-responsive circAAGAB acts as a tumor suppressor in breast cancer, and may contribute to the development of a more specific therapeutic regimen for breast cancer.

Biological functions, mechanisms, and clinical significance of circular RNA in colorectal cancer

Colorectal cancer (CRC) is a leading cause of cancer-related death worldwide due to the lack of effective diagnosis and prognosis biomarkers and therapeutic targets, resulting in poor patient survival rates. Circular RNA (circRNA) is a type of endogenous non-coding RNA (ncRNA) with a closed-loop structure that plays a crucial role in physiological processes and pathological diseases. Recent studies indicate that circRNAs are involved in the diagnosis, prognosis, drug resistance, and development of tumors, particularly in CRC. Therefore, circRNA could be a potential new target for improving CRC diagnosis, prognosis, and treatment. This review focuses on the origin and biological functions of circRNA, summarizes recent research on circRNA's role in CRC, and discusses the potential use of circRNAs as clinical biomarkers for cancer diagnosis and prognosis, as well as therapeutic targets for CRC treatment.

Circular RNAs: New layer of complexity evading breast cancer heterogeneity

Advances in high-throughput sequencing techniques and bioinformatic analysis have refuted the "junk" RNA hypothesis that was claimed against non-coding RNAs (ncRNAs). Circular RNAs (circRNAs); a class of single-stranded covalently closed loop RNA molecules have recently emerged as stable epigenetic regulators. Although the exact regulatory role of circRNAs is still to be clarified, it has been proven that circRNAs could exert their functions by interacting with other ncRNAs or proteins in their own physiologically authentic environment, regulating multiple cellular signaling pathways and other classes of ncRNAs. CircRNAs have also been reported to exhibit a tissue-specific expression and have been associated with the malignant transformation process of several hematological and solid malignancies. Along this line of reasoning, this review aims to highlight the importance of circRNAs in Breast Cancer (BC), which is ranked as the most prevalent malignancy among females. Notwithstanding the substantial efforts to develop a suitable anticancer therapeutic regimen against the heterogenous BC, inter- and intra-tumoral heterogeneity have resulted in an arduous challenge for drug development research, which in turn necessitates the investigation of other markers to be therapeutically targeted. Herein, the potential of circRNAs as possible diagnostic and prognostic biomarkers have been highlighted together with their possible application as novel therapeutic targets.

The Role of HECT E3 Ubiquitin Ligases in Colorectal Cancer

Colorectal cancer (CRC) is estimated to rank as the second reason for cancer-related deaths, and the prognosis of CRC patients remains unsatisfactory. Numerous studies on gastrointestinal cell biology have shown that the E3 ligase-mediated ubiquitination exerts key functions in the pathogenesis of CRC. The homologous to E6-associated protein C-terminus (HECT) family E3 ligases are a major group of E3 enzymes, featured with the presence of a catalytic HECT domain, which participate in multiple cellular processes; thus, alterations in HECT E3 ligases in function or expression are closely related to the occurrence and development of many human malignancies, including-but not limited to-CRC. In this review, we summarize the potential role of HECT E3 ligases in colorectal carcinogenesis and the related underlying molecular mechanism to expand our understanding of their pathological functions. Exploiting specific inhibitors targeting HECT E3 ligases could be a potential therapeutic strategy for CRC therapy in the future.

Recent Advances of Circular RNAs as Biomarkers for Osteosarcoma

Osteosarcoma is the most common primary malignant bone tumor in young adult, which is prone to early metastasis and poor prognosis. The current treatment methods need to be improved. Circular RNA is a covalently blocked circular, non-coding RNA that plays an essential role in the occurrence, development, clinical diagnosis, and treatment of various diseases. Recently, an increasing number of circRNAs have been identified in osteosarcoma. Understanding its role in osteosarcoma is conducive to the early detection, diagnosis, and treatment of osteosarcoma. In this paper, we reviewed the mechanism of action of circular RNA in the occurrence and development of osteosarcoma and its clinical application in recent years.

Convolution Neural Networks Using Deep Matrix Factorization for Predicting Circrna-Disease Association

CircRNAs have a stable structure, which gives them a higher tolerance to nucleases. Therefore, the properties of circular RNAs are beneficial in disease diagnosis. However, there are few known associations between circRNAs and disease. Biological experiments identify new associations is time-consuming and high-cost. As a result, there is a need of building efficient and achievable computation models to predict potential circRNA-disease associations. In this paper, we design a novel convolution neural networks framework(DMFCNNCD) to learn features from deep matrix factorization to predict circRNA-disease associations. Firstly, we decompose the circRNA-disease association matrix to obtain the original features of the disease and circRNA, and use the mapping module to extract potential nonlinear features. Then, we integrate it with the similarity information to form a training set. Finally, we apply convolution neural networks to predict the unknown association between circRNAs and diseases. The five-fold cross-validation on various experiments shows that our method can predict circRNA-disease association and outperforms state of the art methods.

XGBCDA: a multiple heterogeneous networks-based method for predicting circRNA-disease associations

BACKGROUND

Biological experiments have demonstrated that circRNA plays an essential role in various biological processes and human diseases. However, it is time-consuming and costly to merely conduct biological experiments to detect the association between circRNA and diseases. Accordingly, developing an efficient computational model to predict circRNA-disease associations is urgent.

METHODS

In this research, we propose a multiple heterogeneous networks-based method, named XGBCDA, to predict circRNA-disease associations. The method first extracts original features, namely statistical features and graph theory features, from integrated circRNA similarity network, disease similarity network and circRNA-disease association network, and then sends these original features to the XGBoost classifier for training latent features. The method utilizes the tree learned by the XGBoost model, the index of leaf that instance finally falls into, and the 1 of K coding to represent the latent features. Finally, the method combines the latent features from the XGBoost with the original features to train the final model for predicting the association between the circRNA and diseases.

RESULTS

The tenfold cross-validation results of the XGBCDA method illustrate that the area under the ROC curve reaches 0.9860. In addition, the method presents a striking performance in the case studies of colorectal cancer, gastric cancer and cervical cancer.

CONCLUSION

With fabulous performance in predicting potential circRNA-disease associations, the XGBCDA method has the promising ability to assist biomedical researchers in terms of circRNA-disease association prediction.

Variant calling enhances the identification of cancer cells in single-cell RNA sequencing data

Single-cell RNA-sequencing is an invaluable research tool that allows for the investigation of gene expression in heterogeneous cancer cell populations in ways that bulk RNA-seq cannot. However, normal (i.e., non tumor) cells in cancer samples have the potential to confound the downstream analysis of single-cell RNA-seq data. Existing methods for identifying cancer and normal cells include copy number variation inference, marker-gene expression analysis, and expression-based clustering. This work aims to extend the existing approaches for identifying cancer cells in single-cell RNA-seq samples by incorporating variant calling and the identification of putative driver alterations. We found that putative driver alterations can be detected in single-cell RNA-seq data obtained with full-length transcript technologies and noticed that a subset of cells in tumor samples are enriched for putative driver alterations as compared to normal cells. Furthermore, we show that the number of putative driver alterations and inferred copy number variation are not correlated in all samples. Taken together, our findings suggest that augmenting existing cancer-cell filtering methods with variant calling and analysis can increase the number of tumor cells that can be confidently included in downstream analyses of single-cell full-length transcript RNA-seq datasets.

Circular RNA expression profiles of ovarian granulosa cells in advanced-age women explain new mechanisms of ovarian aging

Aim: We aimed to determine the role of granulosa cells (GCs) circular RNA (circRNA) in ovarian aging. Methods: Nine women were recruited, including three diminished ovarian reserve young women, three advanced-aged women and three normal ovarian reserve young women. The circRNA expression profiles of GCs were characterized by CLEAR software. Key circRNA were validated by quantitative reverse transcription PCR. Results: GCs in advanced-age group females exhibited active MHC class II-related biological processes. A total of 3575 circRNAs were found in the advanced age group. Hsa-circ-0031584 appears to be one of the important molecules regulating the mitotic process of GCs. Conclusion: The expression profiles of circRNAs exhibited obvious stage specificity with age which might contribute to ovarian aging progression.

Circular RNAs regulate parental gene expression: A new direction for molecular oncology research

CircRNAs have been the focus of research in recent years. They are differentially expressed in various human tumors and can regulate oncogenes and tumor suppressor genes expression through various mechanisms. The diversity, stability, evolutionary conservatism and cell- or tissue-specific expression patterns of circRNAs also endow them with important regulatory roles in promoting or inhibiting tumor cells malignant biological behaviors progression. More interestingly, emerging studies also found that circRNAs can regulate not only other genes expression, but also their parental gene expression and thus influence tumors development. Apart from some conventional features, circRNAs have a certain specificity in the regulation of parental gene expression, with a higher proportion affecting parental gene transcription and easier translation into protein to regulate parental gene expression. CircRNAs are generally thought to be unable to produce proteins and therefore the protein-coding ability exhibited by circRNAs in regulating parental gene expression is unique and indicates that the regulatory effects of parental gene expression by circRNAs are not only a competitive binding relationship, but also a more complex molecular relationship between circRNAs and parental gene, which deserves further study. This review summarizes the molecular mechanisms of circRNAs regulating parental gene expression and their biological roles in tumorigenesis and development, aiming to provide new ideas for the clinical application of circRNAs in tumor-targeted therapy.

CircRNA ITCH: Insight Into Its Role and Clinical Application Prospect in Tumor and Non-Tumor Diseases

CircRNA E3 ubiquitin protein ligase (ITCH) (circRNA ITCH, circ-ITCH), a stable closed-loop RNA derived from the 20q11.22 region of chromosome 20, is a new circRNA discovered in the cytoplasm in recent decades. Studies have shown that it does not encode proteins, but regulates proteins expression at different levels. It is down-regulated in tumor diseases and is involved in a number of biological activities, including inhibiting cell proliferation, migration, invasion, and promoting apoptosis. It can also alter disease progression in non-tumor disease by affecting the cell cycle, inflammatory response, and critical proteins. Circ-ITCH also holds a lot of promise in terms of tumor and non-tumor clinical diagnosis, prognosis, and targeted therapy. As a result, in order to aid clinical research in the hunt for a new strategy for diagnosing and treating human diseases, this study describes the mechanism of circ-ITCH as well as its clinical implications.

RUNX3-regulated circRNA METTL3 inhibits colorectal cancer proliferation and metastasis via miR-107/PER3 axis

Colorectal cancer (CRC) is one of the most prevalent and lethal malignancies. Exploring the underlying molecular mechanisms is very helpful for the development of new therapy. Here, we investigated the function of circMETTL3/miR-107/PER3 in CRC. Human CRC tissues from diagnosed CRC patients and six CRC cell lines, one normal human colon cell line were used. qRT-PCR and western blotting were performed to determine expression levels of RUNX3, circMETTL3, miR-107, PER3, and proliferation-, and migration-related proteins. CCK-8, colony formation assay, transwell assay, and scratch wound assay were utilized to assess CRC cell proliferation and invasion. ChIP, EMSA, biotin-pull down, RIP assay, and dual luciferase reporter assay were performed to validate interactions of RUNX3/METTL3 promoter, circMETTL3/miR-107, and miR-107/PER3. FISH was used to characterize circMETTL3. MSP was employed to measure methylation level. Nude mouse xenograft model was used to determine the effects on tumor growth and metastasis in vivo. RUNX3, circMETTL3, and PER3 were diminished while miR-107 was elevated in CRC tissues and cells. Low levels of RUNX3 and circMETTL3 correlated with poor prognosis of CRC. Overexpression of RUNX3, circMETTL3, or PER3 suppressed while miR-107 mimics promoted, CRC cell proliferation and invasion, as well as tumor growth and metastasis in vivo. Mechanistically, RUNX3 bound to METTL3 promoter and activated circMETTL3 transcription. circMETTL3 directly bound with miR-107 which targeted PER3. circMETTL3/miR-107 regulated CRC cell proliferation and invasion via PER3. CircMETTL3, transcriptionally activated by RUNX3, restrains CRC development and metastasis via acting as a miR-107 sponge to regulate PER3 signaling.

The functional roles of the circRNA/Wnt axis in cancer

CircRNAs, covalently closed noncoding RNAs, are widely expressed in a wide range of species ranging from viruses to plants to mammals. CircRNAs were enriched in the Wnt pathway. Aberrant Wnt pathway activation is involved in the development of various types of cancers. Accumulating evidence indicates that the circRNA/Wnt axis modulates the expression of cancer-associated genes and then regulates cancer progression. Wnt pathway-related circRNA expression is obviously associated with many clinical characteristics. CircRNAs could regulate cell biological functions by interacting with the Wnt pathway. Moreover, Wnt pathway-related circRNAs are promising potential biomarkers for cancer diagnosis, prognosis evaluation, and treatment. In our review, we summarized the recent research progress on the role and clinical application of Wnt pathway-related circRNAs in tumorigenesis and progression.

Context-Dependent Regulation of Gene Expression by Non-Canonical Small RNAs

In recent functional genomics studies, a large number of non-coding RNAs have been identified. It has become increasingly apparent that noncoding RNAs are crucial players in a wide range of cellular and physiological functions. They have been shown to modulate gene expression on different levels, including transcription, post-transcriptional processing, and translation. This review aims to highlight the diverse mechanisms of the regulation of gene expression by small noncoding RNAs in different conditions and different types of human cells. For this purpose, various cellular functions of microRNAs (miRNAs), circular RNAs (circRNAs), snoRNA-derived small RNAs (sdRNAs) and tRNA-derived fragments (tRFs) will be exemplified, with particular emphasis on the diversity of their occurrence and on the effects on gene expression in different stress conditions and diseased cell types. The synthesis and effect on gene expression of these noncoding RNAs varies in different cell types and may depend on environmental conditions such as different stresses. Moreover, noncoding RNAs play important roles in many diseases, including cancer, neurodegenerative disorders, and viral infections.

hsa_circ_0000523/miR‑let‑7b/METTL3 axis regulates proliferation, apoptosis and metastasis in the HCT116 human colorectal cancer cell line

Circular RNAs (circRNAs/circs) have gained attention as a class of potential biomarkers for the early detection of multiple cancers. However, the functions and mechanisms of circRNAs in the oncogenesis of human colorectal cancer (CRC) remain to be elucidated. The present study aimed to investigate the roles of hsa_circ_0000523 and its parental gene methyltransferase-like 3 (METTL3) in regulating cell proliferation, apoptosis and invasion in the HCT116 human CRC cell line. To uncover the regulated function of hsa_circ_0000523 in HCT116 cells, a dual-luciferase reporter assay, flow cytometry, reverse transcription-quantitative PCR, Cell Counting Kit-8 assay, cell invasion and western blot assay were used. In HCT116 cells, hsa_circ_0000523 indirectly regulated METTL3 expression by suppressing the transcription of microRNA (miR)-let-7b. The expression of METTL3 promoted cell proliferation and suppressed apoptosis. In the present study, it was found that miR-let-7b promoted cell viability and inhibited apoptosis and invasion, while circ_0000523 exerted the opposite effects. Higher levels of METTL3 expression were associated with more aggressive tumor invasion. The present results suggest that circRNAs and METTL3 may be applied for highly sensitive diagnosis of CRC and for predicting prognosis in patients who have undergone therapy.

Circular RNA CircITCH (has-circ-0001141) suppresses hepatocellular carcinoma (HCC) progression by sponging miR-184

Aberrant expression of circular RNA (circRNA) is involved in the occurrence of various diseases and tumor development, in which plays a vital role, including hepatocellular carcinoma (HCC). Nevertheless, the regulation mechanism and biological function of circITCH in hepatocellular carcinoma (HCC) remain unclear. The expression level of circular RNA itchy E3 ubiquitin protein ligase (circ-ITCH) was identified and validated by real-time polymerase-chain reaction (RT-qPCR) in HCC cell lines. The stability of circITCH was confirmed by Ribonuclease R (RNase R) assay. Subsequently, through silencing and overexpression of circITCH to investigate the functional roles of circITCH in HCC proliferation, invasion, and apoptosis. We also carried out bioinformatics analysis, luciferase reporter assays to define the relationship between microRNA (miR)-184 and circITCH. Moreover, xenograft mouse models and immunohistochemistry were employed to assess the function of circITCH in HCC. CircITCH (hsa_circ_0001141) was a stable circRNA and downregulated in HCC cells. Overexpression of circITCH inhibited cell proliferation, migration, invasion, and promoted apoptosis in vitro and in vivo, whereas knockdown of circITCH had the opposite effects. Mechanistically, miR-184 could be sponged by circITCH, and its overexpression could mitigate the suppressive effects of circITCH overexpression on HCC progression. Through biological website to predict the target genes of miR-184 may be combined. Gene ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were performed to investigate mRNAs with significant functional enrichment and pathways, also which its relationship with HCC-related pathway and immune cells. Our findings reveal that circITCH served as a repressor to restrain HCC malignancy via miR-184. Therefore, circITCH may serve as a potential prognostic marker and therapeutic target for HCC.

Abbreviations: HCC: hepatocellular carcinoma; CircRNA: Circular RNA; miRNA: MicroRNA; Circ-ITCH: circular RNA itchy E3 ubiquitin protein ligase; RT-qPCR: real-time polymerase-chain reaction; RNase R: Ribonuclease R; CeRNA: competing endogenous RNAs; SiRNA: small interfering RNA

Recent progress of circular RNAs in different types of human cancer: Technological landscape, clinical opportunities and challenges (Review)

Circular RNAs (circRNAs) are a novel class of endogenous non‑coding RNAs that have been recently regarded as functionally active. CircRNAs are remarkably stable and known to possess several biological functions such as microRNA sponging, regulating transcription and splicing and occasionally acting as polypeptide‑producing templates. CircRNAs show tissue‑specific expression and have been reported to be associated with the progression of several types of malignancies. Given the recent progress in genome sequencing and bioinformatics techniques, a rapid increment in the biological role of circRNAs has been observed. Concurrently, the patent search from different patent databases shows that the patent number of circRNA is increasing very quickly. These phenomena reveal a rapid development of the technological landscape. In the present review, the recent progress on circRNAs in various kinds of cancer has been investigated and their function as biomarkers or therapeutic targets and their technological landscape have been appreciated. A new insight into circRNAs structure and functional capabilities in cancer has been reviewed. Continually increasing knowledge on their critical role during cancer progression is projecting them as biomarkers or therapeutic targets for various kinds of cancer. Thus, recent updates on the functional role of circRNAs in terms of the technological landscape, clinical opportunities (biomarkers and therapeutic targets), and challenges in cancer have been illustrated.

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

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

Circular RNA ITCH: An Emerging Multifunctional Regulator

In the last decade, numerous circRNAs were discovered by virtue of the RNA-Seq technique. With the deepening of experimental research, circRNAs have brought to light the key biological functions and progression of human diseases. CircRNA ITCH has been demonstrated to be a tumor suppressor in numerous cancers, and recently it was found to play an important role in bone diseases, diabetes mellitus, and cardiovascular diseases. However, the functions of circ-ITCH have not been completely understood. In this review, we comprehensively provide a conceptual framework to elucidate circ-ITCH biological functions of cell proliferation, apoptosis and differentiation, and the pathological mechanisms of inflammation, drug resistance/toxicity, and tumorigenesis. Finally, we summarize its clinical applications in various diseases. This research aimed at clarifying the role of circ-ITCH, which could be a promising therapeutic target.

MicroRNAs and 'Sponging' Competitive Endogenous RNAs Dysregulated in Colorectal Cancer: Potential as Noninvasive Biomarkers and Therapeutic Targets

The gastrointestinal (GI) tract in mammals is comprised of dozens of cell types with varied functions, structures, and histological locations that respond in a myriad of ways to epigenetic and genetic factors, environmental cues, diet, and microbiota. The homeostatic functioning of these cells contained within this complex organ system has been shown to be highly regulated by the effect of microRNAs (miRNA). Multiple efforts have uncovered that these miRNAs are often tightly influential in either the suppression or overexpression of inflammatory, apoptotic, and differentiation-related genes and proteins in a variety of cell types in colorectal cancer (CRC). The early detection of CRC and other GI cancers can be difficult, attributable to the invasive nature of prophylactic colonoscopies. Additionally, the levels of miRNAs associated with CRC in biofluids can be contradictory and, therefore, must be considered in the context of other inhibiting competitive endogenous RNAs (ceRNA) such as lncRNAs and circRNAs. There is now a high demand for disease treatments and noninvasive screenings such as testing for bloodborne or fecal miRNAs and their inhibitors/targets. The breadth of this review encompasses current literature on well-established CRC-related miRNAs and the possibilities for their use as biomarkers in the diagnoses of this potentially fatal GI cancer.

Lidocaine hampers colorectal cancer process via circITFG2/miR-1204/SOCS2 axis

BACKGROUND

Colorectal cancer (CRC) is a deadly disease with a poor prognosis. Lidocaine is preferred by surgical procedures due to the excellent anesthesia. Circular RNA integrin alpha FG-GAP repeat containing 2 (circITFG2) has been recognized as a momentous participator in CRC progression. The specific role of circITFG2 was further studied in this research.

METHODS

Quantitative real-time PCR (qRT-PCR) was devoted to examining the expression of circITFG2, microRNA-1204 (miR-1204) and SOCS2 mRNA in CRC cells. Western blot was used to determine SOCS2 protein expression in CRC cells. Cell viability, colony formation and apoptosis were detected by cell counting kit-8 (CCK-8) assay, colony formation assay and flow cytometry assay respectively. Cell migration and invasion were tested by wound healing assay and transwell assay. Dual-luciferase reporter system, RNA pull down and RNA-binding protein immunoprecipitation (RIP) assays were applied to verify the combination between miR-1204 and circITFG2 or SOCS2.

RESULTS

CircITFG2 was strikingly downregulated; however, lidocaine treatment induced a significant increase in the expression of circITFG2 and SOCS2 and a decrease in miR-1204 expression in CRC cells. Meanwhile, SOCS2 protein expression was upregulated by lidocaine treatment or miR-1204 silence in CRC cells and downregulated by circITFG2 knockdown or miR-1204 overexpression in lidocaine-treated CRC cells. CircITFG2 knockdown or miR-1204 overexpression abolished lidocaine-induced inhibition in proliferation, metastasis and promotion in apoptosis in CRC cells. CircITFG2 overexpression, SOCS3 overexpression or lidocaine treatment suppressed proliferation, metastasis and facilitated apoptosis in CRC cells. CircITFG2 sponged miR-1204 to regulate SOCS3 expression in lidocaine-treated CRC cells.

CONCLUSION

Lidocaine hindered CRC progression by circITFG2/miR-1204/SOCS2 axis. This finding might beat a path in improving CRC therapy.

Circ_0014235 confers Gefitinib resistance and malignant behaviors in non-small cell lung cancer resistant to Gefitinib by governing the miR-146b-5p/YAP/PD-L1 pathway

Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs), such as Gefitinib, have been recommended as the first-line treatment reagent for advanced EGFR-mutant non-small cell lung cancer (NSCLC). However, the mechanisms of drug resistance development are not fully determined. This study aimed to explore the role of circular RNA (circ_0014235) in Gefitinib-resistant NSCLC. The expression of circ_0014235, microRNA-146b-5p (miR-146b-5p) and Yes1 associated transcriptional regulator (YAP) mRNA was detected by quantitative real-time PCR (qPCR). Cell viability was detected by CCK-8 assay. Cell proliferation was assessed by colony formation assay and EdU assay. Cell cycle and cell apoptosis were determined by flow cytometry assay. The expression of marker proteins, YAP protein and programmed death ligand 1 (PD-L1) protein was detected by Western blot. The putative relationship between miR-146b-5p and circ_0014235 or YAP was ensured by dual-luciferase reporter assay and RIP assay. Animal models were established to explore the role of circ_0014235 in vivo. Circ_0014235 was highly expressed in Gefitinib-resistant NSCLC cells. Circ_0014235 downregulation reduced Gefitinib IC50, inhibited cell proliferation and induced cell apoptosis and cell cycle arrest in Gefitinib-resistant NSCLC cells, while these effects were reversed by the inhibition of miR-146b-5p, a target of circ_0014235. In addition, YAP was a target gene of miR-146b-5p, and circ_0014235 relieved miR-146b-5p-mediated inhibition on YAP by targeting miR-146b-5p. MiR-146b-5p restoration-blocked Gefitinib IC50 and cell malignant behaviors were recovered by YAP overexpression. YAP positively regulated PD-L1 expression, and YAP overexpression contributes to Gefitinib IC50 and cell malignant behaviors by upregulating PD-L1. Circ_0014235 confers Gefitinib resistance and malignant behaviors in Gefitinib-resistant NSCLC by governing the miR-146b-5p/YAP/PD-L1 pathway.

Circular RNAs in prostate cancer: Biogenesis,biological functions, and clinical significance

Circular RNAs (circRNAs) are covalently closed RNA molecules that play important regulatory roles in various tumors. Prostate cancer (PCa) is one of the most common malignant tumors in the world, with high morbidity and mortality. In recent years, more and more circRNAs have been found to be abnormally expressed and involved in the occurrence and development of PCa, including cell proliferation, apoptosis, invasion, migration, metastasis, chemotherapy resistance, and radiotherapy resistance. Most of the circRNAs regulate biological behaviors of cancer through a competitive endogenous RNA (ceRNA) regulatory mechanism, and some can exert their functions by binding to proteins. circRNAs are also associated with many clinicopathological features of PCa, including tumor grade, lymph node metastasis, and distant metastasis. In addition, circRNAs are potential diagnostic and prognostic biomarkers for PCa. Considering their critical regulatory roles in the progression of PCa, circRNAs would be the potential therapeutic targets. In this paper, the current research status of circRNAs in PCa is briefly reviewed.

CircITCH: A Circular RNA With Eminent Roles in the Carcinogenesis

Circular RNAs (circRNAs) are a group of long non-coding RNAs with enclosed structure generated by back-splicing events. Numerous members of these transcripts have been shown to affect carcinogenesis. Circular RNA itchy E3 ubiquitin protein ligase (circITCH) is a circRNA created from back splicing events in ITCH gene, a protein coding gene on 20q11.22 region. ITCH has a role as a catalyzer for ubiquitination through both proteolytic and non-proteolytic routes. CircITCH is involved in the pathetiology of cancers through regulation of the linear isoform as well as serving as sponge for several microRNAs, namely miR-17, miR-224, miR-214, miR-93-5p, miR-22, miR-7, miR-106a, miR-10a, miR-145, miR-421, miR-224-5p, miR-197 and miR-199a-5p. CircITCH is also involved in the modulation of Wnt/β-catenin and PTEN/PI3K/AKT pathways. Except from a single study in osteosarcoma, circITCH has been found to exert tumor suppressor role in diverse cancers. In the present manuscript, we provided a comprehensive review of investigations that reported function of circITCH in the carcinogenesis.

CircRNAs: Insights into Gastric Cancer

Background

Gastric cancer (GC) is recorded as the fifth most common cancer globally. The classic resemblance of early symptoms of chronic gastritis including nausea, dysphagia, and dyspepsia with GC is the current challenge limiting the early diagnosis of GC. The current diagnostic procedures of GC are limited due to their invasive nature. This directs the research question toward alternative approaches, specifically at the molecular level. Recent advances in molecular regulation of cancer suggest the prominence of circular RNAs (circRNAs) in the multistep process of tumourigenesis.

Summary

CircRNAs are a class of non-coding RNAs, abundant in eukaryotes, with key roles in regulating genes and miRNAs as well as the alteration of processes involved in pathological conditions. Research studies have demonstrated the participation of circRNAs in the initiation and progression of tumours. This review provides a comprehensive insight into the potential of circRNAs as disease biomarkers for the early detection and treatment of GC.

Key Messages

This study is an amalgamation of the implications and future prospects of circRNAs for the detection and potential treatment of GC.

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.

circ_CHFR regulates ox-LDL-mediated cell proliferation, apoptosis, and EndoMT by miR-15a-5p/EGFR axis in human brain microvessel endothelial cells

Oxidized low-density lipoprotein (ox-LDL) is a significant risk factor for various brain vascular diseases. Circular RNA (circRNA) is involved in the pathogenesis of brain vascular diseases. This study revealed the roles of circ_CHFR in ox-LDL-mediated cell proliferation, apoptosis, and endothelial-to-mesenchymal transition (EndoMT). Our results showed that circ_CHFR and EGFR expressions were dramatically upregulated, while miR-15a-5p expression was downregulated in ox-LDL-induced human brain microvessel endothelial cells (HBMECs) relative to control groups. circ_CHFR knockdown hindered the effects of ox-LDL exposure on cell proliferation, cell cycle, apoptosis, and EndoMT in HBMECs, whereas these impacts were abolished by miR-15a-5p inhibitor. In addition, circ_CHFR functioned as a sponge of miR-15a-5p and miR-15a-5p bound to EGFR. Thus, we concluded that circ_CHFR silencing hindered ox-LDL-mediated cell proliferation, apoptosis, and EndoMT by downregulating EGFR expression through sponging miR-15a-5p in HBMECs. Our findings provide a new mechanism for studying circRNA-directed therapy in ox-LDL-induced human brain vascular diseases.

circ-SIRT1 Promotes Colorectal Cancer Proliferation and EMT by Recruiting and Binding to eIF4A3

Circular RNA (circRNA), a recently identified type of endogenous noncoding RNA, has been implicated in the occurrence and development of a variety of tumors; however, whether circ-SIRT1, derived from pre-mRNA of the parental SIRT1 gene, is involved in colorectal cancer (CRC) remains unknown, as do the potential underlying mechanisms. The expression of circ-SIRT1 in CRC cells and tissue was detected by RT-qPCR. Colony formation and Cell Counting Kit-8 assays were used to evaluate the effect of circ-SIRT1 knockdown on the proliferative ability of CRC cells. Wound healing and Transwell assays were used to assess the effect of circ-SIRT1 knockdown on the migratory and invasive capacity of CRC cells. RNA immunoprecipitation and RNA pull-down assays were employed to validate the binding of circ-SIRT1 to EIF4A3. Western blot was used to identify the changes in the expression of EIF4A3 and EMT-related proteins. The RT-qPCR results showed that circ-SIRT1 was highly expressed in CRC cells and tissue and was positively correlated with the depth of tumor invasion. Knocking down circ-SIRT1 inhibited the proliferation and invasion of CRC cells and EMT. We further found that EIF4A3 could bind to circ-SIRT1, and that overexpressing circ-SIRT1 decreased the abundance of EIF4A3 at the mRNAs of the EMT marker proteins N-cadherin and vimentin. Combined, our findings suggested that circ-SIRT1 regulates the expression of EMT-related proteins by preventing EIF4A3 recruitment to the respective mRNAs. Our results further indicate that circ-SIRT1 functions as an oncogene in CRC by promoting the proliferation, invasion, and EMT of CRC cells through the circ-SIRT1/EIF4A3/N-cadherin/vimentin pathway.

Circular RNA hsa_circ_0001306 Functions as a Competing Endogenous RNA to Regulate FBXW7 Expression by Sponging miR-527 in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most common types of cancer worldwide. Circular RNAs (circRNAs) have been reported to regulate many types of cancers, including HCC. The purpose of this study was to investigate the potential roles of hsa_circ_0001306 in HCC. Firstly, the downregulation of hsa_circ_0001306 was identified by high‑throughput RNA sequencing and further verified by qRT-PCR. Secondly, we evaluated the effects of hsa_circ_0001306 on HCC cell proliferation, invasion, cell cycle. Finally, we used an animal model to validate the in vitro experimental results. The expression of hsa_circ_0001306 was closely related to tumor size. Knockdown of hsa_circ_0001306 could downregulate F-box and WD repeat domain containing 7(FBXW7), a target of miR-527, thereby promoting HCC cell proliferation and invasion. Furthermore, hsa_circ_0001306 siRNA increased the multiplication rate of HCC tumors. Mechanistic studies indicated that hsa_circ_0001306 acts as a ceRNA for miR-527, which resulted in the reduction of its endogenous target, FBXW7. Hsa_circ_001306 is significantly downregulated in HCC, and the hsa_circ_0001306/miR-527/FBXW7 axis plays an important role in HCC progression.

ceRNAs in Cancer: Mechanism and Functions in a Comprehensive Regulatory Network

Noncoding RNAs have been shown with powerful ability in post-transcriptional regulation, enabling intertwined RNA crosstalk and global molecular interaction in a large amount of dysfunctional conditions including cancer. Competing endogenous RNAs (ceRNAs) are those competitively binding with shared microRNAs (miRNAs), freeing their counterparts from miRNA-induced degradation, thus actively influencing and connecting with each other. Constantly updated analytical approaches boost outstanding advancement achieved in this burgeoning hotspot in multilayered intracellular communication, providing new insights into pathogenesis and clinical treatment. Here, we summarize the mechanisms and correlated factors under this RNA interplay and deregulated transcription profile in neoplasm and tumor progression, underscoring the great significance of ceRNAs for diagnostic values, monitoring biomarkers, and prognosis evaluation in cancer.

Circular RNA erythrocyte membrane protein band 4.1 assuages ultraviolet irradiation-induced apoptosis of lens epithelial cells by stimulating 5'-bisphosphate nucleotidase 1 in a miR-24-3p-dependent manner

Apoptosis of lens epithelial cells contributed to the formation of age-related cataract (ARC), and previous data revealed that circular RNA (circRNA) was responsible for the underneath mechanism. The study was organized to explore the role of circular RNA erythrocyte membrane protein band 4.1 (circ_EPB41) in ultraviolet (UV) irradiation-induced apoptosis of lens epithelial cells. SRA01/04 cells were irradiated with UV to mimic the ARC cell model. The RNA levels of circ_EPB41, microRNA-24-3p (miR-24-3p), and 3ʹ(2ʹ), 5ʹ-bisphosphate nucleotidase 1 (BPNT1) were detected by quantitative real-time polymerase chain reaction. Protein expression was checked by western blot. 5-Ethynyl-29-deoxyuridine, 3-(4,5-Dimethylthazol-2-yl)-2,5-diphenyltetrazolium bromide and DNA content quantitation assays were performed to investigate cell proliferation. Flow cytometry was conducted to analyze cell apoptosis. Dual-luciferase reporter assay was implemented to confirm the interaction among circ_EPB41, miR-24-3p, and BPNT1. Our data showed that circ_EPB41 and BPNT1 expression were downregulated in ARC tissues and UV-irradiated SRA01/04 cells as compared with normal anterior lens capsules and untreated SRA01/04 cells. Circ_EPB41 overexpression ameliorated the effects of UV irradiation on the proliferation and apoptosis of SRA01/04 cells. Besides, miR-24-3p, a target miRNA of circ_EPB41, attenuated circ_EPB41 introduction-mediated proliferation, and apoptosis of UV-irradiated SRA01/04 cells. MiR-24-3p regulated UV irradiation-induced effects by targeting BPNT1. Importantly, it was found that circ_EPB41 stimulated BPNT1 production by miR-24-3p. Taken together, the enforced expression of circ_EPB41 ameliorated UV irradiation-induced apoptosis of lens epithelial cells by miR-24-3p/BPNT1 pathway, providing us with a potential target for the therapy of UV-caused ARC.

Circular RNA ITCH attenuates the progression of nasopharyngeal carcinoma by inducing PTEN upregulation via miR-214

BACKGROUND

Circular RNA itchy E3 ubiquitin protein ligase (circ-ITCH) has previously been reported to play a key role in carcinogenesis. Nevertheless, the role of circ-ITCH in nasopharyngeal carcinoma (NPC) remains to be explored.

METHODS

Gene expression analysis was performed using a quantitative real-time polymerase chain reaction, western blotting and immunohistochemistry. The role of circ-ITCH in NPC was explored using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide, colony formation, transwell invasion, scratch healing and xenograft tumor assays. Furthermore, luciferase reporter assay was carried out to assess the interactions among circ-ITCH, microRNA-214 (miR-214) and phosphatase and tensin homolog (PTEN).

RESULTS

The levels of circ-ITCH and PTEN were decreased, whereas the level of miR-214 was increased in NPC tissues collected from 28 subjects compared to normal nasopharynx tissues collected from 15 subjects. Moreover, a negative correlation between circ-ITCH and miR-214 expression and a positive correlation between circ-ITCH and PTEN expression were observed in NPC tissues. Downregulation of circ-ITCH expression was also observed in NPC cell lines. In addition, upregulation of circ-ITCH markedly inhibited NPC cell proliferation, migration and invasion. Furthermore, circ-ITCH was confirmed to exert its function by sponging miR-214. PTEN was found to be a direct target gene of miR-214 and its expression was negatively correlated with miR-214 expression in NPC tissues. Moreover, our results showed that the circ-ITCH/miR-214 axis regulated NPC proliferation, migration and invasion through regulating the expression of PTEN. Upregulation of circ-ITCH or PTEN blocked miR-214-mediated promotion of NPC tumorigenesis in vitro. Additionally, upregulation of circ-ITCH also suppressed NPC tumorigenesis in vivo.

CONCLUSIONS

The present study demonstrated that circ-ITCH suppressed NPC tumorigenesis by upregulating PTEN expression through interacting with miR-214, thus proposing a novel mechanism for NPC inhibition.

The effective function of circular RNA in colorectal cancer

Colorectal cancer (CRC) is the 3rd most common type of cancer worldwide. Late detection plays role in one-third of annual mortality due to CRC. Therefore, it is essential to find a precise and optimal diagnostic and prognostic biomarker for the identification and treatment of colorectal tumorigenesis. Covalently closed, circular RNAs (circRNAs) are a class of non-coding RNAs, which can have the same function as microRNA (miRNA) sponges, as regulators of splicing and transcription, and as interactors with RNA-binding proteins (RBPs). Therefore, circRNAs have been investigated as specific targets for diagnostic and prognostic detection of CRC. These non-coding RNAs are also linked to metastasis, proliferation, differentiation, migration, angiogenesis, apoptosis, and drug resistance, illustrating the importance of understanding their involvement in the molecular mechanisms of development and progression of CRC. In this review, we present a detailed summary of recent findings relating to the dysregulation of circRNAs and their potential role in CRC.

Rs4911154 of circ-ITCH aggravated tumor malignancy of thyroid nodules via the circ-ITCH/miR-22-3p/CBL axis

Recent evidence revealed an inhibitory effect of circ-ITCH on the progression of papillary thyroid cancer via affecting the circ-ITCH/miR-22-3p/CBL axis. Rs4911154, an SNP located in circ-ITHC, was previously reported to be significantly associated with an increased risk of hepatocellular carcinoma. Ultrasound testing was used to evaluate the doubling time of thyroid nodules. 202 patients diagnosed with thyroid nodule disorders were divided into three groups according to their genotypes at rs4911154. We found that the A allele was correlated with a shortening doubling time of thyroid nodules. Moreover, the A allele contributed to reduced expression of circ-ITCH/CBL and increased expression of miR-22-3p. Besides, decreased tissue apoptosis was linked to the A allele. Luciferase assays indicated that miR-22-3p could effectively suppress the luciferase activities of CBL and circ-ITCH. Furthermore, manual up-regulation of miR-22-3p effectively suppressed the expression of CBL, while CBL siRNA apparently abolished circ-ITCH induced CBL upregulation, reduced proliferation and increased apoptosis of K1 and TPC-1 cells. A signaling pathway of circ-ITCH/miR-22-3p/CBL axis was established to explain the effect of SNP of circ-ITCH in thyroid tumor malignancy. Compared with the G allele, the A allele in rs4911154 contributed to the malignancy of thyroid nodules with decreased doubling time and down-regulated CBL expression.