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

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

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

Interactions between circRNAs and miR-141 in Cancer: From Pathogenesis to Diagnosis and Therapy

The function of non-coding RNAs (ncRNAs) in the pathogenesis and development of cancer is indisputable. Molecular mechanisms underlying carcinogenesis involve the aberrant expression of ncRNAs, including circular RNAs (circRNAs), and microRNAs (miRNAs). CircRNAs are a class of single-stranded, covalently closed RNAs responsible for maintaining cellular homeostasis through their diverse functions. As a part of the competing endogenous RNA (ceRNAs) network, they play a central role in the regulation of accessibility of miRNAs to their mRNA targets. The interplay between these molecular players is based on the primary role of circRNAs that act as miRNAs sponges, and the circRNA/miRNA imbalance plays a central role in different pathologies including cancer. Herein, we present the latest state of knowledge about interactions between circRNAs and miR-141, a well-known member of the miR-200 family, in malignant transformation, with emphasis on the biological role of circRNA/miR-141/mRNA networks as a future target for novel anti-cancer therapies.

Advances in epigenetic modifications and cervical cancer research

Cervical cancer (CC) is an important public health problem for women, and perspectives and information regarding its prevention and treatment are quickly evolving. Human papilloma virus (HPV) has been recognized as a major contributor to CC development; however, HPV infection is not the only cause of CC. Epigenetics refers to changes in gene expression levels caused by non-gene sequence changes. Growing evidence suggests that the disruption of gene expression patterns which were governed by epigenetic modifications can result in cancer, autoimmune diseases, and various other maladies. This article mainly reviews the current research status of epigenetic modifications in CC based on four aspects, respectively DNA methylation, histone modification, noncoding RNA regulation and chromatin regulation, and we also discuss their functions and molecular mechanisms in the occurrence and progression of CC. This review provides new ideas for early screening, risk assessment, molecular targeted therapy and prognostic prediction of CC.

MicroRNAs Improve Cancer Treatment Outcomes Through Personalized Medicine

MicroRNAs (miRNAs) are short non-coding RNAs that repress or degrade mRNA targets to downregulate genes. In cancer occurrence, the expression of miRNAs is altered. Depending on the involvement of a certain miRNA in the pathogenetic growth of a tumor, It may be up or downregulated. The "oncogenic" action of miRNAs corresponds with upregulation, which leads to tumor proliferation and spread meanwhile the miRNAs that have been downregulated bring tumorsuppressive outcomes. Oncogenes and tumor suppressor genes are among the genes whose expression is under their control, demonstrating that classifying them solely as oncogenes or tumor suppressor genes alone is not only hindering but also incorrect. Apart from basic tumors, miRNAs may be found in nearly all human fluids and can be used for cancer diagnosis as well as clinical outcome prognostics and better response to treatment strategies. The overall variance of these tiny noncoding RNAs influences patient-specific pharmacokinetics and pharmacodynamics of anti-cancer medicines, driving a growing demand for personalized medicine. By now, microRNAs from tumor biopsies or blood are being widely investigated as substantial biomarkers for cancer in time diagnosis, prognosis, and, progression. With the rise of COVID-19, this paper also attempts to study recent research on miRNAs involved with deaths in lung cancer COVID patients. With the discovery of single nucleotide polymorphisms, personalized treatment via microRNAs has lately become a reality. The present review article describes the highlights of recent knowledge of miRNAs in various cancers, with a focus on miRNA translational applications as innovative potential diagnostic and prognostic indicators that expand person-to-person therapy options.

CircRNA has_circ_0017109 promotes lung tumor progression via activation of Wnt/β-catenin signaling due to modulating miR-671-5p/FZD4 axis

INTRODUCTION

Accumulating evidence highlights the critical roles of circular RNAs (circRNAs) in the malignant progression of cancers. In this study, we investigated the expression pattern of a newly identified circRNA (hsa_circ_0017109) in non-small cell lung cancer (NSCLC), and examined its downstream molecular targets.

METHODS

Quantitative real-time PCR (qRT-PCR) and Western blotting (WB) were conducted to quantify gene and protein expression. In vitro functional assays such as colony formation assay, cell counting kit-8 (CCK-8) and flow cytometry were used to study cell proliferation and apoptosis. RNA pull-down assay, luciferase reporter assay and RNA immunoprecipitation were performed to validate molecular interaction. Mouse xenograft model of NSCLC cells was used to assess the role of circ_0017109 in tumorigenesis.

RESULTS

Circ_0017109 was upregulated in NSCLC tumor samples and cells. Silencing circ_0017109 impaired cell proliferation and promoted apoptosis in NSCLC cells, and circ_0017109 knockdown suppressed in vivo tumorigenesis of NSCLC cells in mouse xenograft model. MiR-671-5p was identified as a target of circ_0017109, and circ_0017109 negatively impacted on miR-671-5p expression. MiR-671-5p downregulated FZD4 and dampened the activity of Wnt/β-catenin signaling pathway. Circ_0017109 modulated FZD4 expression by suppressing miR-671-5p activity.

CONCLUSIONS

Elevated circ_0017109 expression promotes tumor progression of NSCLC by modulating miR-671-5p/FZD4/β-catenin axis.

Epigenomic reprogramming in iAs-mediated carcinogenesis

Arsenic is a naturally occurring metal carcinogen found in the Earth's crust. Millions of people worldwide are chronically exposed to arsenic through drinking water and food. Exposure to inorganic arsenic has been implicated in many diseases ranging from acute toxicities to malignant transformations. Despite the well-known deleterious health effects of arsenic exposure, the molecular mechanisms in arsenic-mediated carcinogenesis are not fully understood. Since arsenic is non-mutagenic, the mechanism by which arsenic causes carcinogenesis is via alterations in epigenetic-regulated gene expression. There are two possible ways by which arsenic may modify the epigenome-indirectly through an arsenic-induced generation of reactive oxygen species which then impacts chromatin remodelers, or directly through interaction and modulation of chromatin remodelers. Whether directly or indirectly, arsenic modulates epigenetic gene regulation and our understanding of the direct effect of this modulation on chromatin structure is limited. In this chapter we will discuss the various ways by which inorganic arsenic affects the epigenome with consequences in health and disease.

A Review and In Silico Analysis of Tissue and Exosomal Circular RNAs: Opportunities and Challenges in Thyroid Cancer

Simple Summary

Thyroid cancer is the most common endocrine neoplasm. Recently, knowledge of the molecular genetic changes of thyroid cancer has dramatically improved. Understanding the roles of these molecular changes in thyroid cancer tumorigenesis and progression is essential in developing a successful treatment strategy and improving disease outcomes. As a family of non-coding RNAs, circular RNAs (circRNAs) have been involved in several aspects of the physiological and pathological processes of the cells. The roles of circRNAs in cancer development and progress are evident. In the current review, we aimed to explore the clinical potential of circRNAs as potential diagnostic, prognostic, and therapeutic targets in thyroid cancer. Furthermore, screening the genome-wide circRNAs and performing functional enrichment analyses for all associated dysregulated circRNAs in thyroid cancer have been done. Given the unique advantages circRNAs have, such as superior stability, higher abundance, and presence in different body fluids, this family of non-coding RNAs could be promising diagnostic and prognostic biomarkers and potential therapeutic targets for thyroid cancer.

Abstract

Thyroid cancer (TC) is the most common endocrine tumor. The genetic and epigenetic molecular alterations of TC have become more evident in recent years. However, a deeper understanding of the roles these molecular changes play in TC tumorigenesis and progression is essential in developing a successful treatment strategy and improving patients’ prognoses. Circular RNAs (circRNAs), a family of non-coding RNAs, have been implicated in several aspects of carcinogenesis in multiple cancers, including TC. In the current review, we aimed to explore the clinical potential of circRNAs as putative diagnostic, prognostic, and therapeutic targets in TC. The current analyses, including genome-wide circRNA screening and functional enrichment for all deregulated circRNA expression signatures, show that circRNAs display atypical contributions, such as sponging for microRNAs, regulating transcription and translation processes, and decoying for proteins. Given their exceptional clinical advantages, such as higher stability, wider abundance, and occurrence in several body fluids, circRNAs are promising prognostic and theranostic biomarkers for TC.

The role of CircRNA/miRNA/mRNA axis in breast cancer drug resistance

Multidrug resistance is one of the major obstacles in the treatment of cancers. This undesirable feature increases the mortality rate of cancers, including breast cancer. Circular RNA (CircRNA)/microRNA (miRNA)/messenger RNA (mRNA) is one of the important axes with major roles in the promotion and resistance of breast cancer. This heterogeneous pathway includes mRNA of oncogenes and tumor suppressors, which are controlled by miRNAs and CircRNAs. Unfortunately, this network could be easily deregulated, resulting in drug resistance and tumor development. Therefore, understanding these dysregulations may thus help to identify effective therapeutic targets. On this basis, we try to review the latest findings in the field, which could help us to better comprehend this significant axis in breast cancer.

hsa_circ_0000285 facilitates thyroid cancer progression by regulating miR-127-5p/CDH2

Thyroid cancer (THCA) is a leading endocrine cancer and becomes the fifth most commonly diagnosed malignancy in females. It is confirmed that circular RNAs (circRNAs) perform regulatory potencies in the pathological progress of THCA. Our purpose was to certify the trait of hsa_circ_0000285 (circ_0000285) and investigate its modulatory mechanism in THCA progression. We identified the expression profile of hsa_circ_0000285 in THCA by conducting qRT-PCR assay. Therewith, the potential of hsa_circ_0000285 in THCA development was determined with a set of functional experiments, including CCK-8, wound healing assay, Western blot, and xenograft model. The molecular mechanism underlying hsa_circ_0000285 was investigated with bioinformatic analysis, RIP and dual-luciferase reporter experiments. As opposed to normal samples and cells, hsa_circ_0000285 level was overtly increased in THCA specimens and cells. The downregulation of hsa_circ_0000285 weakened the proliferative and migratory capacity of THCA cells and promoted cell apoptosis. In addition, hsa_circ_0000285 silence suppressed the tumor growth of xenograft model mice in vivo. Notably, we demonstrated that hsa_circ_0000285 might target miR-127-5p/CDH2 axis in THCA. Afterward, our findings manifested that miR-127-5p attenuation blocked the function of hsa_circ_0000285 depletion in THCA cells. In the final step, CDH2 was proven to mediate the repressive potency of miR-127-5p in the malignant behaviors of THCA. Mechanistically, hsa_circ_0000285 induced the development of THCA via functioning as a competing endogenous RNA (ceRNA) of miR-127-5p to enhance CDH2 expression, which provided a new perspective for THCA therapy.

Specific expression and functions of circular RNAs

In recent years, circular RNAs (circRNAs), a new class of RNA molecules characterized by their covalently closed circular structure, have become a new research paradigm in RNA biology. Many circRNAs are conserved among eukaryotes, localize in specific subcellular compartments, and play different biological roles. Accumulating evidence shows that circRNAs regulate a diversity of cellular processes by acting as miRNA sponges, anchors for circRNA binding proteins (cRBPs), transcriptional regulators, molecular scaffolds, and sources for translation of small proteins/peptides. The emergence of the biological functions of circRNAs has brought a new perspective to our understanding of cellular physiology and disease pathogenesis. Recent studies have shown that the expression of circRNAs is tissue- and cell type-specific and specifically regulated through development or disease progression, where they exert specific biological functions. However, the mechanisms underlying these remain largely unknown. A deeper understanding of how the specific expression of circRNAs is regulated to exert specific biological functions will enable the use of circRNA as a biomarker in clinical practice and the development of new therapeutic approaches. This review aims to summarize recent developments in circRNA biogenesis, functions, and molecular mechanisms. We also provide some specific circRNAs as examples to show their tissue-specific distribution and evaluate the possibility of applying circRNA technologies in molecular research and therapeutics.

Silencing circRNA protein kinase C iota (circ-PRKCI) suppresses cell progression and glycolysis of human papillary thyroid cancer through circ-PRKCI/miR-335/E2F3 ceRNA axis

The circular RNA PRKCI (circ-PRKCI; ID: hsa_circ_0122683) is highly expressed in human papillary thyroid cancer (PTC) tumors according to GSE93522 dataset. However, its role in PTC tumorigenesis remains to be documented. Here, quantitative real-time PCR showed that expression of circ-PRKCI was abnormally upregulated in human PTC patients' tumors and cells, and higher circ-PRKCI might predict lymph node metastasis and recurrence. Functionally, cell behaviors were measured by 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide assay, colony formation assay, fluorescence-activated cell sorting method, scratch wound assay, transwell assay, western blotting, and assay kits for glucose and lactate. As a result, circ-PRKCI knockdown could suppress cell cycle progression of PTC cells and restrain the abilities of cell proliferation, colony formation, wound closure, invasion, glucose consumption and lactate production, accompanied with decreased levels of matrix metalloproteinase-2 (MMP2), MMP9 and Snail. Moreover, above-mentioned inhibition could be imitated by overexpressing microRNA-335-5p (miR-335). Molecularly, circ-PRKCI functioned as a sponge for miR-335 and miR-335 could further targeted E2F transcription factor-3 (E2F3), according to dual-luciferase reporter assay and RNA immunoprecipitation. However, downregulating miR-335 diminished the effects of circ-PRKCI role on cell growth, metastasis and glycolysis in PTC cells; besides, there was a counteractive effect between miR-335 upregulation and E2F3 upregulation in PTC cells as well. Furthermore, xenograft experiment revealed that silencing circ-PRKCI could retard tumor growth of PTC cells in vivo. Collectively, circ-PRKCI exerted oncogenic role in PTC by antagonizing cell progression and glycolysis via regulating miR-335/E2F3 axis, suggesting circ-PRKCI was a potential biomarker and target for PTC.

Up-regulation of circ_0000353 impedes the proliferation and metastasis of non-small cell lung cancer cells via adsorbing miR-411-5p and increasing forkhead box O1

BACKGROUND

Non-small cell lung cancer (NSCLC) is the most common malignant tumor worldwide. This work focuses on investigating the role of circ_0000353 in NSCLC and its potential mechanism of action.

METHODS

The expression levels of circ_0000353 and miR-411-5p in NSCLC and their matched normal lung tissues were detected by real-time PCR (RT-PCR). The correlation between the circ_0000353 expression and the clinicopathological parameters of NSCLC patients was also analyzed. CCK-8, BrdU and colony formation assays were adopted to detect the role of circ_0000353 in the proliferation of NSCLC cells. The metastasis of NSCLC cells was measured by Transwell assay. The dual-luciferase reporter gene assay was used to confirm the targeting relationship between circ_0000353 and miR-411-5p. The expression level of FOXO1 was detected by western blot.

RESULTS

Circ_0000353 was significantly down-regulated in NSCLC tissues and cell lines, and the decreased expression was significantly linked to the increased clinical stage, larger tumor volume, and metastasis. The circ_0000353 over-expression restrained the proliferation, migration, and invasion of NSCLC cells in vitro. Additionally, up-regulation of miR-411-5p was observed in NSCLC tissues and cell lines, and luciferase assay and RT-PCR assay showed that circ_0000353 over-expression could target miR-411-5p and suppress its expression. Further studies confirmed that circ_0000353 and miR-411-5p modulated the FOXO1 expression.

CONCLUSION

Circ_0000353 repressed the proliferation, migration, and invasion of NSCLC cells via inhibition of miR-411-5p and up-regulation of FOXO1.

CircMYLK promotes the growth, migration, invasion, and survival of bladder cancer cells by upregulating CCND3 level via competitively binding to miR-34a

Bladder cancer is one of the most common types of urothelial carcinoma with a rising incidence rate worldwide. Circular RNAs (circRNAs) are involved in the development of numerous cancers, including bladder cancer. We aimed to uncover the role and associated mechanism of circMYLK in bladder cancer. The expression levels of circMYLK, miRNA-34a (miR-34a) and Cyclin D3 (CCND3) mRNA were investigated using real-time quantitative polymerase chain reaction. The protein level of CCND3 was investigated using western blot. In functional assays, flow cytometry assays were utilized for cell cycle analysis and cell apoptosis analysis. Transwell assays were used for cell migration and invasion analysis. Caspase-3 activity was examined to monitor cell apoptosis. The putative relationship between miR-34a and circMYLK or CCND3 was validated by dual-luciferase reporter assay and RNA immunoprecipitation assay. CircMYLK was highly expressed in bladder cancer tissues and cells. CircMYLK downregulation inhibited bladder cancer cell migration and invasion, and promoted cancer cell apoptosis and cell cycle arrest. MiR-34a, a target of circMYLK, was downregulated in bladder cancer tissues and cells. MiR-34a inhibition reversed the effects of circMYLK downregulation and then recovered bladder cell malignant behaviors. Further analysis showed that CCND3 was a downstream target of miR-34a, and CCND3 was upregulated in bladder cancer tissues and cells. MiR-34a overexpression blocked bladder cancer cell migration and invasion, and induced cell apoptosis and cycle arrest, while these effects were abolished by CCND3 overexpression. CircMYLK contributed to the malignant development of bladder cancer cells partly through the miR-34a/CCND3 regulatory network, showing the significance of circMYLK in bladder cancer pathogenesis.

Biological roles and potential clinical values of circular RNAs in gastrointestinal malignancies

Circular RNAs (circRNAs), a class of endogenous RNA molecules, are produced by alternative splicing of precursor RNA and are covalently linked at the 5' and 3' ends. Recent studies have revealed that dysregulated circRNAs are closely related to the occurrence and progression of gastrointestinal malignancies. Accumulating evidence indicates that circRNAs, including circPVT1, circLARP4, circ-SFMBT2, cir-ITCH, circRNA_100782, circ_100395, circ-DONSON, hsa_circ_0001368, circNRIP1, circFAT1(e2), circCCDC66, circSMARCA5, circ-ZNF652, and circ_0030235 play important roles in the proliferation, differentiation, invasion, and metastasis of cancer cells through a variety of mechanisms, such as acting as microRNA sponges, interacting with RNA-binding proteins, regulating gene transcription and alternative splicing, and being translated into proteins. With the characteristics of high abundance, high stability, extensive functions, and certain tissue-, time- and disease-specific expressions, circRNAs are expected to provide novel perspectives for the diagnoses and treatments of gastrointestinal malignancies.

Insights Into the Role of CircRNAs: Biogenesis, Characterization, Functional, and Clinical Impact in Human Malignancies

Circular RNAs (circRNAs) are an evolutionarily conserved novel class of non-coding endogenous RNAs (ncRNAs) found in the eukaryotic transcriptome, originally believed to be aberrant RNA splicing by-products with decreased functionality. However, recent advances in high-throughput genomic technology have allowed circRNAs to be characterized in detail and revealed their role in controlling various biological and molecular processes, the most essential being gene regulation. Because of the structural stability, high expression, availability of microRNA (miRNA) binding sites and tissue-specific expression, circRNAs have become hot topic of research in RNA biology. Compared to the linear RNA, circRNAs are produced differentially by backsplicing exons or lariat introns from a pre-messenger RNA (mRNA) forming a covalently closed loop structure missing 3′ poly-(A) tail or 5′ cap, rendering them immune to exonuclease-mediated degradation. Emerging research has identified multifaceted roles of circRNAs as miRNA and RNA binding protein (RBP) sponges and transcription, translation, and splicing event regulators. CircRNAs have been involved in many human illnesses, including cancer and neurodegenerative disorders such as Alzheimer’s and Parkinson’s disease, due to their aberrant expression in different pathological conditions. The functional versatility exhibited by circRNAs enables them to serve as potential diagnostic or predictive biomarkers for various diseases. This review discusses the properties, characterization, profiling, and the diverse molecular mechanisms of circRNAs and their use as potential therapeutic targets in different human malignancies.

Protein-Related Circular RNAs in Human Pathologies

Circular RNAs (circRNAs) are a distinct family of RNAs derived from alternative splicing which play a crucial role in regulating gene expression by acting as microRNA (miRNA) and RNA binding protein (RBP) sponges. However, recent studies have also reported the multifunctional potential of these particles. Under different conditions, circRNAs not only regulate protein synthesis, destination, and degradation but can serve as protein scaffolds or recruiters and are also able to produce short peptides with active biological functions. circRNAs are under ongoing investigation because of their close association with the development of diseases. Some circRNAs are reportedly expressed in a tissue- and development stage-specific manner. Furthermore, due to other features of circRNAs, including their stability, conservation, and high abundance in bodily fluids, they are believed to be potential biomarkers for various diseases, including cancers. In this review, we focus on providing a summary of the current knowledge on circRNA-protein interactions. We present the properties and functions of circRNAs, the possible mechanisms of their translation abilities, and the emerging functions of circRNA-derived peptides in human pathologies.

Circular RNAs: New Epigenetic Signatures in Viral Infections

Covalent closed circular RNAs (circRNAs) can act as a bridge between non-coding RNAs and coding messenger RNAs. CircRNAs are generated by a back-splicing mechanism during post-transcriptional processing and are abundantly expressed in eukaryotic cells. CircRNAs can act via the modulation of RNA transcription and protein production, and by the sponging of microRNAs (miRNAs). CircRNAs are now thought to be involved in many different biological and pathological processes. Some studies have suggested that the expression of host circRNAs is dysregulated in several types of virus-infected cells, compared to control cells. It is highly likely that viruses can use these molecules for their own purposes. In addition, some viral genes are able to produce viral circRNAs (VcircRNA) by a back-splicing mechanism. However, the viral genes that encode VcircRNAs, and their functions, are poorly studied. In this review, we highlight some new findings about the interaction of host circRNAs and viral infection. Moreover, the potential of VcircRNAs derived from the virus itself, to act as biomarkers and therapeutic targets is summarized.

Biogenesis, Features, Functions, and Disease Relationships of a Specific Circular RNA: CDR1as

In 2011, Hansen discovered the natural antisense transcript (NAT) of the cerebellar degeneration-related protein 1 gene (CDR1), and further described CDR1 NAT as a circular RNA (CircRNA). CDR1 antisense RNA (CDR1as), which is the official name of CDR1 NAT, is conserved and extensively expressed in most eutherian mammal brains and other specialized tissues. Further studies have elucidated its biogenesis, features, functions, and relationships with diseases. CDR1as is involved in many disease processes as a microRNA (miR) sponge. Therefore, it seems that further research on CDR1as could facilitate the diagnosis and treatment of some diseases, such as cancer and diabetes. However, a detailed analysis of the results of studies on CDR1as revealed that they are inconsistent and make unclear conclusions. In this review, we gathered and analyzed the recent studies about CDR1as in detail and aimed to elucidate accurate conclusions from them.

Functions and clinical significance of circular RNAs in glioma

CircRNAs are a class of single-stranded RNA molecules with a covalently closed loop structure and have been characterized by high stability, abundance, conservation, and display tissue/developmental stage-specific expression, furthermore, based on the abundance in distinct body fluids or exosomes, circRNAs present novel biomarkers and targets for the diagnosis and prognosis of cancers. Recently, the regulatory mechanisms of biogenesis and molecular functions, including miRNAs and RBPs sponge, translation as well as transcriptional and splicing regulation, have been gradually uncovered, although various aspects remained to be elucidated in combination with deep-sequence and bioinformatics. Accumulating studies have indicated that circRNAs are more enriched in neuronal tissues partly due to the abundance of specific genes promoting circularization, suggesting dysregulation of circRNAs is closely related to diseases of the nervous system, including glioma. In this review, we elaborate on the biogenesis, functions, databases as well as novel advances especially involved in the molecular pathways, highlight its great value as diagnostic or therapeutic targets in glioma.

Circ_0000267 promotes gastric cancer progression via sponging MiR-503-5p and regulating HMGA2 expression

Background

Circular RNAs (circRNAs) are a class of newly discovered RNAs that attach great importance to modulate gene expression and biological function. Nonetheless, in gastric cancer (GC), the expression and function of circRNA are much less explored. In this study, circ_0000267 expression in GC was investigated and the function and mechanism of circ_0000267 was probed.

Materials and Methods

Quantitative real‐time PCR (qRT‐PCR) was employed to detect circ_0000267, miR‐503‐5p, and HMGA2 expression. Immunohistochemistry and western blot were adopted to detect HMGA2 and epithelial–mesenchymal transition (EMT)‐related proteins (E‐cadherin and N‐cadherin) expression in GC tissues and cells, respectively. GC cell lines with circ_0000267 overexpressed and knocked down were constructed, and CCK‐8 assay, BrdU assay, scratch healing assay, and transwell assay were employed to assess the effect of circ_0000267 on the proliferation and metastasis of GC cells. Besides, dual‐luciferase reporter gene assay was adopted to verify the targeting relationship between circ_0000267 and miR‐503‐5p.

Results

Circ_0000267 showed a significant upregulation in GC tissues and cell lines, and its high expression level was extremely linked to the increased tumor diameter and local lymph node metastasis. Circ_0000267 overexpression accelerated GC cell proliferation, metastasis, and EMT processes, while knocking down circ_0000267 led to the opposite effect. From the perspective of mechanism, circ_0000267 promoted the progression of GC through adsorbing miR‐503‐5p and upregulating HMGA2 expression.

Conclusion

Circ_0000267 is an oncogenic circRNA that affects the progression of GC, which participates in promotion of GC proliferation, migration, invasion, and EMT via modulating the miR‐503‐5p/HMGA2 axis.

Circular RNA circSLC26A4 Accelerates Cervical Cancer Progression via miR-1287-5p/HOXA7 Axis

Circular RNAs (circRNAs) are group of noncoding RNAs derived from back-splicing events. Accumulating evidence certifies the critical roles of circRNAs in human tumorigenesis. However, the role and biogenesis of circRNAs in cervical cancer are still unclear. Here, a novel identified circRNA, circSLC26A4, was found to be upregulated in cervical cancer tissue and cells. Clinically, the high expression of circSLC26A4 was related to the poor survival of cervical cancer patients. Functionally, cellular experiments indicated that circSLC26A4 knockdown repressed the proliferation, invasion, and tumor growth in vitro and in vivo. Furthermore, circSLC26A4 acted as the sponge of miR-1287-5p; moreover, miR-1287-5p targeted the 3′ UTR of HOXA7 mRNA. Mechanistically, RNA binding protein (RBP) quaking (QKI) was identified to interact with the QKI response elements (QREs) in SLC26A4 gene introns, thereby promoting circSLC26A4 biogenesis. In conclusion, these findings demonstrate that circSLC26A4 facilitates cervical cancer progression through the QKI/circSLC26A4/miR-1287-5p/HOXA7 axis, which might bring novel therapeutic strategies for cervical cancer.

Clinical significance of hsa_circ_0000419 in gastric cancer screening and prognosis estimation

Gastric cancer (GC) is an aggressive malignancy that seriously threatens human health. Accumulating studies have shown that circular RNAs (circRNAs) can be used as diagnostic biomarkers and promising therapeutic targets with significant clinical implications. However, the roles of circRNAs in GC remain largely elusive. In this study, hsa_circ_0000419 levels in GC cell lines, tissues and plasma were detected, and their clinicopathological correlation was analyzed. Receiver operating characteristic (ROC) curve and Kaplan-Meier survival curve were established for its clinical values evaluation. Potential biological functions were further predicted and annotated by bioinformatics analysis. Hsa_circ_0000419 levels were significantly decreased in GC cell lines, cancer tissues and plasma from GC patients. GC tissues hsa_circ_0000419 levels were associated with cell differentiation, Borrmann type, overall survival and disease-free survival, whereas plasma hsa_circ_0000419 were significantly correlated with tumor stage, lymphatic and distal metastasis, venous and perineural invasion. Plasma hsa_circ_0000419 exists in exosomes and maintain good stability. Bioinformatics analysis showed that hsa_circ_0000419 involved in gastric tumorigenesis and progression via its interaction with microRNAs. Collectively, our study suggests that hsa_circ_0000419 is a novel biomarker for GC screening as well as an important indicator for prognostic estimation of patients with advanced GC.

CircRNAs: From anonymity to novel regulators of gene expression in cancer (Review)

Circular RNAs (circRNAs) are a group of non‑coding RNAs, formed mostly through a unique backsplicing mechanism. Originally proposed to be a by‑product from errors in splicing, recent studies have shown they exhibit a range of roles in regulating gene expression, including sponging of microRNAs (miRNAs), interactions with RNA‑binding proteins and regulation of transcription. Though research is still in its infancy, evidence suggests circRNA levels are tightly regulated in the cell, reinforced by dysregulated circRNAs levels being implicated in a range of diseases, including cancer and viral infection. There is growing interest in circRNAs playing specific roles in cancers, either oncogenic or as tumour suppressors, with particular focus on their potential as novel biomarkers. This review will provide an overview of circRNA biogenesis and regulation, and their potential roles in the cell, with a focus on their dysregulation in cancer.

Star Circular RNAs In Human Cancer: Progress And Perspectives

Circular RNAs (circRNAs) are a recently discovered subclass of non-coding RNAs (ncRNAs) characterized by a covalently closed loop structure created by reverse splicing. Because they do not have a 5' cap structure and a 3' poly A tail, circRNAs have higher stability, abundance and evolutionary conservation than linear RNA between species. These features produce various potential biological functions of circRNAs, such as miRNA sponges, RNA-binding proteins that form RNA protein complexes. In recent years, more and more studies have shown that circRNAs play a vital role in the occurrence and development of human diseases. At the same time, their enormous potential as a biomarker and therapeutic target is also evolving. The purpose of this review is to summarize existing cancer-associated circRNAs and to try to find circRNAs that are abnormally expressed in many cancers. Therefore, we reviewed previous circRNAs studies related to cancer and selected them by statistics. The eight circRNAs that have the highest frequency in different cancers or involve key pathways are called star circRNAs. Here, we review the classification, features, and functions of emerging star circRNAs, with particular attention to the role of circRNAs in various cancers.

Clinical significances of hsa_circ_0067582 and hsa_circ_0005758 in gastric cancer tissues

BACKGROUND

Circular RNAs (circRNAs) are a special class of endogenous noncoding RNAs that have numerous biological functions in normal situation and diseases including cancers. However, the clinical significance of circRNAs in gastric cancer (GC) remains largely unknown. Here, we chose two representative circRNAs, hsa_circ_0067582 and hsa_circ_0005758, to investigate their clinical significance in GC patients.

METHODS

Using real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR), we explored the expression levels of hsa_circ_0067582 and hsa_circ_0005758 in tissues with different stages of gastric tumorigenesis. Then, the relationships between their expression levels and GC patients' clinicopathological factors were further investigated. Receiver operating characteristic (ROC) curves were established for evaluating diagnostic values of hsa_circ_0067582 and hsa_circ_0005758.

RESULTS

Compared with healthy control tissues, both hsa_circ_0067582 and hsa_circ_0005758 were significantly decreased in GC tissues. Besides, hsa_circ_0067582 expression was associated with GC patients' tissue CEA level (P <.001) and stages (P = .037); and hsa_circ_0005758 expression was relevant to tissue CEA level (P < .001) and perineural invasion (P = .048). The area under the ROC curve (AUC) of hsa_circ_0067582 was up to 0.671. The cutoff value was set at 10.61, with which the sensitivity and specificity were 55.2% and 75.0%, respectively. Similar to hsa_circ_0005758, the AUC of hsa_circ_0005758 was 0.721. The cutoff value was set at 10.20, with which the sensitivity and specificity were 75.0% and 67.7%, respectively.

CONCLUSION

These results showed that both hsa_circ_0067582 and hsa_circ_0005758 may play an important role in gastric carcinogenesis; and they may be potential indicators for GC diagnosis.

Current Status of Functional Studies on Circular RNAs in Bladder Cancer and their Potential Role as Diagnostic and Prognostic Biomarkers: A Review

Worldwide, bladder cancer represents the ninth most common malignancy and is the 13^th cause of cancer-associated death. Although surgery combined with chemotherapy and radiotherapy has improved patient outcomes, the prognosis remains poor for most patients with muscle-invasive bladder cancer. The exact mechanisms and critical regulators of bladder cancer remain unknown. Circular RNAs (circRNAs) are a distinct type of endogenous non-coding RNA. Recent studies have shown that circRNAs participate in many processes, including proliferation, invasion, migration, and apoptosis in multiple types of malignancy, including bladder cancer. Some circRNAs are dysregulated in bladder cancer and play essential roles in cancer progression. Importantly, some circRNAs may serve as diagnostic and prognostic biomarkers for bladder cancer. This review aims to summarize the findings from recent studies that have focused on the roles of human circRNAs in bladder cancer and discusses the clinical roles for circRNAs, including their potential roles as diagnostic or prognostic biomarkers.