Circular RNA FAM114A2 suppresses progression of bladder cancer via regulating ∆NP63 by sponging miR-762

Therapeutic importance and diagnostic function of circRNAs in urological cancers: from metastasis to drug resistance

Circular RNAs (circRNAs) are a member of non-coding RNAs with no ability in encoding proteins and their aberrant dysregulation is observed in cancers. Their closed-loop structure has increased their stability, and they are reliable biomarkers for cancer diagnosis. Urological cancers have been responsible for high mortality and morbidity worldwide, and developing new strategies in their treatment, especially based on gene therapy, is of importance since these malignant diseases do not respond to conventional therapies. In the current review, three important aims are followed. At the first step, the role of circRNAs in increasing or decreasing the progression of urological cancers is discussed, and the double-edged sword function of them is also highlighted. At the second step, the interaction of circRNAs with molecular targets responsible for urological cancer progression is discussed, and their impact on molecular processes such as apoptosis, autophagy, EMT, and MMPs is highlighted. Finally, the use of circRNAs as biomarkers in the diagnosis and prognosis of urological cancer patients is discussed to translate current findings in the clinic for better treatment of patients. Furthermore, since circRNAs can be transferred to tumor via exosomes and the interactions in tumor microenvironment provided by exosomes such as between macrophages and cancer cells is of importance in cancer progression, a separate section has been devoted to the role of exosomal circRNAs in urological tumors.

Bladder cancer: non-coding RNAs and exosomal non-coding RNAs

Bladder cancer (BCa) is a highly prevalent type of cancer worldwide, and it is responsible for numerous deaths and cases of disease. Due to the diverse nature of this disease, it is necessary to conduct significant research that delves deeper into the molecular aspects, to potentially discover novel diagnostic and therapeutic approaches. Lately, there has been a significant increase in the focus on non-coding RNAs (ncRNAs), including microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs), due to their growing recognition for their involvement in the progression and manifestation of BCa. The interest in exosomes has greatly grown due to their potential for transporting a diverse array of active substances, including proteins, nucleic acids, carbohydrates, and lipids. The combination of these components differs based on the specific cell and its condition. Research indicates that using exosomes could have considerable advantages in identifying and forecasting BCa, offering a less invasive alternative. The distinctive arrangement of the lipid bilayer membrane found in exosomes is what makes them particularly effective for administering treatments aimed at managing cancer. In this review, we have tried to summarize different ncRNAs that are involved in BCa pathogenesis. Moreover, we highlighted the role of exosomal ncRNAs in BCa.

CircFAM114A2 Suppresses Cell Proliferation, Migration, and Invasion of Colorectal Cancer Through Sponging miR-647 to Upregulate DAB2IP Expression

BACKGROUND

Increasing evidence had proved that some circular RNA (circRNA) exerted critical roles in tumors progression by functioning as "microRNAs (miRNAs) sponges" to regulate their targeted genes.

METHODS

circFAM114A2 and miR-647 expression was measured in CRC tissues and cells by quantitative real-time polymerase chain reaction (qRT-PCR), and the prognostic value of circFAM114A2 evaluated by Kaplan-Meier survival curve. Subsequently, wounding healing and transwell assays were performed to assess cell proliferation, migration, and invasion. RNA pull-down and dual-luciferase reporter assays were used to confirm the interactions between circFAM114A2, miR-647, and DAB2IP.

RESULTS

CircFAM114A2 was notably downregulated in CRC tissues and cells, and low circFAM114A2 expression indicated the poor prognosis of CRC patients. Next, overexpression of circFAM114A2 suppressed CRC cells proliferation, migration, and invasion in vitro and impede CRC tumor growth in vivo. Mechanically, circFAM114A2 competitively bound to miR-647 and upregulated its target gene DAB2IP expression in CRC cells.

CONCLUSION

Our results indicated that circFAM114A2/miR-647/DAP2IP axis played an important role in CRC progression, suggesting that circFAM114A2 might be a novel therapeutic target in patients with CRC.

Dysregulation and antimetastatic function of circLRIG1 modulated by miR-214-3p/LRIG1 axis in bladder carcinoma

CircLRIG1, a newly discovered circRNA, has yet to have its potential function and biological processes reported. This study explored the role of circLRIG1 in the development and progression of bladder carcinoma and its potential molecular mechanisms. Techniques such as qRT-PCR, Western blot, various cellular assays, and in vivo models were used to investigate mRNA and protein levels, cell behavior, molecular interactions, and tumor growth. The results showed that both circLRIG1 and LRIG1 were significantly reduced in bladder carcinoma tissues and cell lines. Low circLRIG1 expression was associated with poor patient prognosis. Overexpressing circLRIG1 inhibited bladder carcinoma cell growth, migration, and invasion, promoted apoptosis, and decreased tumor growth and metastasis in vivo. Importantly, circLRIG1 was found to sponge miR-214-3p, enhancing LRIG1 expression, and its overexpression also modulated protein levels of E-cadherin, N-cadherin, Vimentin, and LRIG1. Similar effects were observed with LRIG1 overexpression. Notably, a positive correlation was found between circLRIG1 and LRIG1 expression in bladder carcinoma tissues. Additionally, the tumor-suppressing effect of circLRIG1 was reversed by overexpressing miR-214-3p or silencing LRIG1. The study concludes that circLRIG1 suppresses bladder carcinoma progression by enhancing LRIG1 expression via sponging miR-214-3p, providing a potential strategy for early diagnosis and treatment of bladder carcinoma.

Epigenetic Regulation in Urothelial Carcinoma

Urothelial carcinoma (UC) is a common malignancy that remains a clinical challenge: Non-muscle-invasive urothelial carcinoma (NMIUC) has a high rate of recurrence and risk of progression, while muscle-invasive urothelial carcinoma (MIUC) has a high mortality. Although some new treatments, such as immunotherapies, have shown potential effects on some patients, most cases of advanced UC remain incurable. While treatments based on epigenetic mechanisms, whether combined with traditional platinum-based chemotherapy or emerging immunotherapy, show therapeutic advantages. With the advancement of sequencing and bioinformatics, the study of epigenomics, containing DNA methylation, histone modifications, chromatin remodeling, and non-coding RNA, is increasingly linked with the occurrence and progression of UC. Since the epigenetics of UC is a constantly developing field of medicine, this review aims to summarize the latest research on epigenetic regulation of UC, generalize the mechanism of epigenetics in UC, and reveal the potential epigenetic therapies in the clinical setting, in order to provide some new clues on the discovery of new drugs based on the epigenetics.

A novel cuproptosis pattern and tumor immune microenvironment characterization in urothelial carcinoma of the bladder

Background

Urothelial carcinoma of the bladder (UCB) is the most prevalent malignant tumor of the urinary system worldwide, which has a significant recurrence rate despite multiple treatment options available. As a unique and novel copper-dependent programmed cell death mechanism, the comprehensive impact of cuproptosis on the tumor immune microenvironment, clinicopathological characteristics and the prognosis of patients remains largely unclear.

Methods

A total of 568 UCB samples were thoroughly examined for cuproptosis patterns using data downloaded from TCGA and GEO, based on 10 cuproptosis-related genes reported previously. Then, the univariate COX regression analysis was performed on the genes that differed across the various patterns. To measure individual cuproptosis pattern, a cuproptosis score system was constructed using a principal component analysis algorithm. To validate the scoring system, immunohistochemical staining was performed on tumor tissues with different pathological grades, and experiments in vitro were conducted about the differentially expressed genes related to prognosis. Finally, the capacity of scoring system to predict the response to immunotherapy was verified by using data from IMvigor 210 cohort.

Results

Four unique cuproptosis clusters and two gene clusters were finally found by the investigation. The clinical features and prognosis of patients, as well as the mRNA transcriptome, pathway enrichment, and immune cell infiltration in TME, varied dramatically between various cuproptosis clusters and gene clusters. To identify individual cuproptosis patterns in UCB patients, we also established a cuproptosis scoring system. After validation with multiple methods, it was indicated that the score system could predict the prognosis of UCB patients and was significantly connected to clinical features such TNM category, tumor grade, molecular type and ultimate survival status. The clinical outcomes of UCB patients were predicted effectively according to the tumor mutation burden in conjunction with the scoring system. Furthermore, we found that the cuproptosis score had a significant correlation with the response to immunotherapy and the sensitivity to chemotherapy.

Conclusion

This study revealed the potential impact of cuproptosis on the UCB tumor immune microenvironment and clinical pathological characteristics. The cuproptosis score system could effectively predict the prognosis of patients and the response to chemotherapy and immunotherapy.

Research progress of circular RNA molecules in aging and age-related diseases

Circular RNAs (circRNAs) are a class of single-chain endogenous closed circular RNAs that do not have a poly(A) tail at the 3' end and a cap structure at the 5' end and are connected end-to-end by covalent bonds. CircRNAs, which are pervasive, diverse, stable, and conversed, have functions in transcriptional control and protein translation and play vital roles in modulating cell senescence, individual aging, as well as the occurrence and development of age-related diseases. Studies in recent years were reviewed from aspects including the biosynthesis mechanisms, classification, expression, biomedical functions, associations with aging and age-related diseases, and potential clinical applications of circRNAs. It will provide the theoretic basis for exploring the molecular biological mechanisms of aging, using circRNA as the therapeutic target to delay aging, and finding therapeutic strategies to prevent and treat age-related diseases.

Exosomes from human induced pluripotent stem cells-derived keratinocytes accelerate burn wound healing through miR-762 mediated promotion of keratinocytes and endothelial cells migration

Background

The use of keratinocytes derived from induced pluripotent stem cells (iPSCs-KCs) may represent a novel cell therapy strategy for burn treatment. There is growing evidence that extracellular vesicles, including exosomes, are primary mediators of the benefits of stem cell therapy. Herein, we thus explored the effects of exosomes produced by iPSCs-derived keratinocytes (iPSCs-KCs-Exos) in a model of deep second-degree burn wound healing and evaluated the mechanistic basis for the observed activity.

Methods

iPSCs-KCs-Exos were isolated from conditioned medium of iPSCs-KCs and verified by electron micrograph and size distribution. Next, iPSCs-KCs-Exos were injected subcutaneously around wound sites, and its efficacy was evaluated by measuring wound closure areas, histological examination, and immunohistochemistry staining. The effects of iPSCs-KCs-Exos on proliferation and migration of keratinocytes and endothelial cells in vitro were assessed by EdU staining, wound healing assays, and transwell assay. Then, high-throughput microRNA sequencing was used to explore the underlying mechanisms. We assessed the roles of miR-762 in iPSCs-KCs-Exos-induced regulation of keratinocytes and endothelial cells migration. Furthermore, the target gene which mediated the biological effects of miR-762 in keratinocytes and endothelial cells was also been detected.

Results

The analysis revealed that iPSCs-KCs-Exos application to the burn wound drove the acceleration of wound closure, with more robust angiogenesis and re-epithelialization being evident. Such iPSCs-KCs-Exos treatment effectively enhanced endothelial cell and keratinocyte migration in vitro. Moreover, the enrichment of miR-762 was detected in iPSCs-KCs-Exos and was found to target promyelocytic leukemia (PML) as a means of regulating cell migration through a mechanism tie to integrin beta1 (ITGB1).

Conclusion

These results thus provide a foundation for the further study of iPSCs-KCs-Exos as novel cell-free treatments for deep second-degree burns.

Graphical Abstract

circDHTKD1 promotes lymphatic metastasis of bladder cancer by upregulating CXCL5

Lymph node (LN) metastasis is associated with unfavorable prognosis of bladder cancer (BCa). Although lymphangiogenesis is functionally important in LN metastasis of tumors, the potential mechanism in BCa remains unclear. Here, we clarified a regulatory mechanism of circRNA-mediated lymphangiogenesis and LN metastasis in BCa based on next-generation sequencing data. We revealed that circDHTKD1 was positively associated with LN metastasis and significantly upregulated in BCa. By analyzing the co-expression patterns of circDHTKD1 and differentially expressed mRNAs, we identified that circDHTKD1 facilitated lymphangiogenesis by upregulating CXCL5. Mechanistically, circDHTKD1 directly interacted with miR-149-5p, and antagonized the repression of miR-149-5p on CXCL5. Furthermore, circDHTKD1-induced CXCL5 expression recruited and activated neutrophils, which participated in lymphangiogenesis by secreting VEGF-C. Our study supports circDHTKD1 as a promising diagnostic and therapeutic target for LN metastasis in BCa.

Circular RNAs in cardiovascular diseases

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

The Role of Circular RNAs in the Carcinogenesis of Bladder Cancer

Circular RNAs (circRNAs) are a group of transcripts with enclosed configurations which can regulate gene expression. These transcripts have important roles in normal development and in the pathogenesis of disorders. Recent evidence has supported involvement of circRNAs in the development of bladder cancer. Several circRNAs such as circ_0058063, hsa-circRNA-403658, circPDSS1, circCASC15, circRNA-MYLK, and circRNA_103809 have been upregulated in bladder cancer samples. On the other hand, hsa_circ_0137606, BCRC-3, circFUT8, hsa_circ_001598, circSLC8A1, hsa_circ_0077837, hsa_circ_0004826, and circACVR2A are among downregulated circRNAs in bladder cancer. Numerous circRNAs have diagnostic or prognostic value in bladder cancer. In this review, we aim to outline the latest findings about the role of circRNAs in bladder cancer and introduce circRNAs for further investigations as therapeutic targets.

circKL inhibits the growth and metastasis of kidney cancer by sponging miR‑182‑5p and upregulating FBXW7

Circular RNAs (circRNAs) are a type of non-coding RNA with important roles in the regulation of various biological processes involved in malignant progression. However, the potential molecular mechanisms and roles of circRNAs in kidney cancer have remained to be fully elucidated. In a previous study by our group, high-throughput microarray sequencing data were analyzed to determine the differentially expressed circRNAs in kidney cancer. In this analysis, a novel circRNA (hsa_circ_0100312, named circKL) was identified as a frequently downregulated circRNA in kidney cancer cells and tissues by reverse transcription-quantitative PCR. In the present study, Cell Counting Kit-8, colony formation, Transwell, wound-healing and mouse xenograft assays as well as a lung metastasis experiment were performed to confirm the functions of circKL. The experiments confirmed that circKL overexpression significantly inhibited the proliferation, migration, tumor growth and metastasis of kidney cancer both in vitro and in vivo. The potential molecular mechanisms of circKL were investigated by performing dual-luciferase and RNA immunoprecipitation assays. Western blot assays confirmed that overexpression of circKL significantly increased the protein level of F-box and WD repeat domain containing 7 (FBXW7). All results suggested that circKL suppressed the growth and migration of kidney cancer by sponging microRNA (miR)-182-5p and upregulating FBXW7 expression. Overall, the circKL/miR-182-5p/FBXW7 axis was indicated to have a key role in the growth and metastasis of kidney cancer and may be targeted as a novel therapeutic strategy.

Circular RNA circ_0000515 adsorbs miR-542-3p to accelerate bladder cancer progression via up-regulating ILK expression

Background: Bladder cancer (BC) is a common cause of cancer-relevant deaths globally. This study is designed to delve into expressions, biological functions and molecular mechanisms of circ_0000515 in BC.

Methods: Quantitative real-time polymerase chain reaction was accomplished to examine circ_0000515, miR-542-3p and integrin-linked kinase (ILK) mRNA expressions in BC tissues and cell lines. In RT-4 and RT-112 cells with circ_0000515 depletion and UMUC3 and BIU-87 cells with this circ RNA overexpression, a cell counting kit-8 assay was adopted to monitor the viability. Besides, transwell assay was conducted to detect cell migration and aggressiveness, and luciferase reporter gene assay was applied to probe the interplay among circ_0000515, miR-542-3p and ILK mRNA. Additionally, Besides, the regulatory function of circ_0000515 on miR-542-3p expression was under the assay of quantitative real-time polymerase chain reaction, and western blot was fulfilled to determine the regulative function of circ_0000515/miR-542-3p axis on ILK protein expressions. A xenograft animal was modeled to examine lung metastasis in vivo.

Results: Circ_0000515 and ILK expressions were significantly elevated in BC tissues and cell lines, while that of miR-542-3p was dramatically suppressed. Knocking down circ_0000515 could significantly repress the growth, migration and aggressiveness of BC cells while overexpression of circ_0000515 showed opposite effects. Moreover, circ_0000515 knockdown inhibited pulmonary metastasis in vivo. Circ_0000515 was validated to adsorb miR-542-3p, and ILK was testified as the downriver target of miR-542-3p. Circ_0000515 could ascend ILK expression through repressing that of miR-542-3p.

Conclusions: Circ_0000515, as a tumor promoter, strengthens the viability, migration and aggressiveness of BC cells via modulating miR-542-3p/ILK axis.

circKDM4C enhances bladder cancer invasion and metastasis through miR-200bc-3p/ZEB1 axis

Circular RNAs (circRNAs) play essential roles in human bladder cancer (BCa) development, however, unusual expression patterns and functional dysfunction of circRNAs in BCa have not been evaluated. In this study, we validated that circKDM4C (hsa_circ_0001839), derived from the KDM4C gene, is elevated in BCa cell lines as well as tissues. Functionally, overexpression of circKDM4C significantly enhances, and silencing of circKDM4C suppresses migration and invasion capabilities of BCa cells. Mechanistically, circKDM4C can directly interact with miR-200b-3p and miR-200c-3p as a miRNA sponge, which enhances the expression of ZEB1 and promotes mesenchymal phenotype. Conclusively, our findings indicate that circKDM4C may act as a pro-oncogenic factor in BCa invasion and metastasis via the circKDM4C/miR-200bc-3p/ZEB1 axis, which is a potential biomarker or therapeutic target for bladder cancer.

CircFAM114A2 Promotes Cisplatin Sensitivity via miR-222-3p/P27 and miR-146a-5p/P21 Cascades in Urothelial Carcinoma

INTRODUCTION

Circular RNAs (circRNAs) are non-coding RNAs that have the structure of a covalently closed loop. Increasing data have proven that circRNAs can influence the progression and chemotherapy sensitivity of tumors. Therefore, the underlying function and mechanisms of more circRNAs in progression and chemotherapy resistance are important.

METHODS

We conducted RNA sequencing on five pairs of urothelial carcinoma samples and screened for circRNAs. CircFAM114A2 was found to be low expressed in urothelial carcinoma. The functions of circFAM114A2 in urothelial carcinoma were explored by cell cycle assay, IC50 determination assay, cell proliferation assay, apoptosis assay, and tumorigenesis assay.

RESULTS

We discovered that the levels of circFAM114A2 were decreased in urothelial carcinoma cell lines and tissues. According to follow-up data, urothelial carcinoma patients with higher circFAM114A2 expression had better survival. Importantly, the levels of circFAM114A2 were associated with the histological grade of urothelial carcinoma. CircFAM114A2 could inhibit cell proliferation and block more urothelial carcinoma cells in the G1 phase and then increase the sensitivity of urothelial carcinoma to cisplatin chemotherapy. Mechanistically, circFAM114A2 directly sponged miR-222-3p/miR-146a-5p and subsequently influenced the expressions of the downstream target genes P27/P21, which, in turn, inhibited the progression of urothelial carcinoma and increased the sensitivity of cancer cells to cisplatin chemotherapy.

CONCLUSION

CircFAM114A2 could inhibit progression and promote cisplatin sensitivity in urothelial carcinoma through novel circFAM114A2/miR-222-3p/P27 and circFAM114A2/miR-146a-5p/P21 pathways. CircFAM1142 has therefore great potential as a prognostic biomarker and therapeutic target for urothelial carcinoma.

CircMMP1 promotes colorectal cancer growth and metastasis by sponging miR-1238 and upregulating MMP family expression

Background

Circular RNAs (circRNAs) are a type of non-coding RNA which play an important role in the regulation of biological processes of various malignant tumors. However, the potential molecular mechanisms and roles of circRNAs in colorectal cancer (CRC) remain unelucidated.

Methods

In the current study, we analyzed the data of high-throughput microarray sequencing to screen differentially expressed circRNAs in CRC. Cell counting kit-8 (CCK-8), colony-formation, transwell, mouse xenograft models and immunohistochemistry assays were used to explore the function of circRNAs. TargetScan database, quantitative real-time polymerase chain reaction (qRT-PCR), double luciferase and RNA immunoprecipitation (RIP) were used to explore the molecular mechanism.

Results

We identified circMMP1 (hsa_circ_0024109) as a frequently upregulated circRNA in both CRC tissues and cells. Both in vitro and in vivo experiments demonstrated that circMMP1 knockdown significantly inhibited the proliferation and metastasis of CRC. The results demonstrated that circMMP1 promoted the growth and metastasis of CRC by sponging miR-1238 and upregulating the expression of matrix metalloproteinase 1 (MMP1), MMP2, and MMP9 expression.

Conclusions

In conclusion, our study identified the biological role of the circMMP1-miR-1238-MMP1/MMP2/MMP9 axis in the growth and metastasis of CRC, which is crucial for the monitoring and treatment of CRC. Further research on circMMP1 may provide a theoretical basis for diagnostic biomarkers of early CRC screening.

The Emerging Functions of Circular RNAs in Bladder Cancer

Simple Summary

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

Abstract

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

The evolutionarily conserved gene, Fam114a2, is dispensable for fertility in mouse

Family with sequence similarity 114 member A2 (Fam114a2) is sperm binding protein that is highly conserved in mammals with homologs both in fungi and plants. Previous studies have demonstrated that miR-762 and P63 are two crucial players of spermatogenesis, and CricFM114A2 regulates their expression. Thus, the current study was focused on describing the role of Fam114a2 in spermatogenesis by generating Fam114a2 knockout (Fam114a2^-/-) mice using CRISPR/Cas9 genome editing techniques. We identified that Fam114a2^-/- mouse has normal fertility and normal morphology of sperm. Furthermore, histological investigation of testicular and epididymis tissues showed no subtle difference, and seminiferous tubules comprised of all stages of germ cells, including mature spermatozoa in Fam114a2^-/- mice. Moreover, cytological investigation of spermatocytes in the progression of prophase I also did not display any notable difference in Fam114a2^-/- mice. Additionally, normal expression of p63 and miR-762 was observed in Fam114a2^+/+ and Fam114a2^-/- testis indicating that Fam114a2 is not involved in the direct regulation of in mice spermatogenesis. Moreover, the removal of Fam114a2 in mouse did not affect the expression of its paralogue Fam114a1 in multiple tissues. Taken together our data determined that Fam114a2 is not essential for male fertility and spermatogenesis in mice.

The Roles of CircRNAs in Bladder Cancer: Biomarkers, Tumorigenesis Drivers, and Therapeutic Targets

Bladder cancer (BCa) is the most prevalent malignancy of the urinary system. Circular RNAs (circRNAs), a novel subtype of non-coding RNAs, play a crucial role in physiological and developmental processes. CircRNAs mainly function as regulators of splicing process and transcription, microRNA sponges, and protein brackets. Recent advances in understanding the pathogenesis of BCa have led to the identification of an abundance of dysregulated circRNAs associated with BCa. These aberrantly expressed circRNAs eventually lead to abnormalities in biological, genetic, and epigenetic information. In this review, we introduce the potential of circRNAs as biomarkers for BCa diagnosis and prognosis. Notably, diverse mechanisms have been proposed for circRNAs driving carcinogenesis, including increasing cell proliferation, promoting invasive and migratory capacity, enhancing endothelial–mesenchymal transition, sustaining stemness, and enabling resistance to chemotherapy. Importantly, a full understanding of circRNA mechanisms is needed to mine promising therapeutic approaches for targeting BCa. In this paper, we present the latest advances in circRNAs and systemically summarize the characteristics and mechanisms of circRNAs in BCa, providing potential perspectives for BCa treatment.

Circular RNA TAF4B Promotes Bladder Cancer Progression by Sponging miR-1298-5p and Regulating TGFA Expression

BACKGROUND

Bladder cancer (Bca) is the most common malignant tumor of the urinary system. Circular RNAs (circRNAs) have been recognized as key regulators in tumorigenesis. However, the molecular mechanisms underlying circRNAs involved in the progression of BCa remain largely unknown.

METHODS

We detected the expression level of circular RNA TAF4B (circTAF4B) by qRT-PCR assay. Cell proliferation was evaluated by CCK-8 and colony formation assays. Wound healing and Transwell assays were performed to measure cell migration and invasion capability. Moreover, we performed qRT-PCR and western blotting assays to determine the expression levels of epithelial-mesenchymal transition (EMT) markers. A nuclear/cytoplasmic fractionation assay was used to measure the subcellular location of circTAF4B. RNA pull-down and dual-luciferase reporter assays were used to detect the target microRNA of circTAF4B. A mouse xenograft model was produced to analyze the effect of circTAF4B on the tumorigenesis of BCa.

RESULTS

In this study, we identified a novel circular RNA, circTAF4B, that is significantly upregulated in BCa and correlated with poor prognosis. Downregulated circTAF4B abolished the growth, metastasis and EMT process in BCa cells. Mechanistically, we found that circTAF4B facilitated the expression of transforming growth factor A (TGFA) by sponging miR-1298-5p. Finally, circTAF4B enhanced the proliferation and EMT process of BCa cells in vivo.

CONCLUSION

In summary, our study demonstrated that circTAF4B played a carcinogenic role in the growth, metastasis, and EMT process of BCa by regulating the miR-1298-5p/TGFA axis. Thus, circTAF4B may become a diagnostic and therapeutic target for BCa.

Circular RNAs Interaction with MiRNAs: Emerging Roles in Breast Cancer

Despite significant advances in cancer therapy strategies, breast cancer is one of the most common and lethal malignancies worldwide. Characterization of a new class of RNAs using next-generation sequencing opened new doors toward uncovering etiopathogenesis mechanisms of breast cancer as well as prognostic and diagnostic biomarkers. Circular RNAs (circRNAs) are a novel class of RNA with covalently closed and highly stable structures generated primarily from the back-splicing of precursor mRNAs. Although circRNAs exert their function through various mechanisms, acting as a sponge for miRNAs is their primary mechanism of function. Furthermore, growing evidence has shown that aberrant expression of circRNAs is involved in the various hallmarks of cancers. This paper reviews the biogenesis, characteristics, and mechanism of functions of circRNAs and their deregulation in various cancers. Finally, we focused on the circRNAs roles as a sponge for miRNAs in the development, metastasis, angiogenesis, drug resistance, apoptosis, and immune responses of breast cancer.

The biological function and diagnostic value of miR-762 in nasopharyngeal carcinoma

BACKGROUND

Low diagnostic efficiency and high metastasis and recurrence of nasopharyngeal carcinoma (NPC) result in bad survival. A novel diagnostic biomarker is of great importance for the improvement of NPC management. This study aimed to state the biological function and diagnostic values of miR-762 in NPC to provide a novel insight into the detection and therapy of NPC.

METHODS

The expression of miR-762 in NPC and healthy samples was detected by quantitative real-time polymerase chain reaction and its diagnostic value was evaluated by the receiver operating characteristic (ROC) analysis. The functional roles of miR-762 in the proliferation, migration, and invasion of NPC cells were assessed by CCK8 and Transwell assay.

RESULTS

The significant upregulation of miR-762 was observed in NPC serum compared with healthy controls, which was associated with the TNM stage and lymph node metastasis of NPC patients. The ROC curve showed that miR-762 could be a diagnostic biomarker for NPC with high accuracy and specificity. Additionally, miR-762 served as a tumor promoter, which could promote cell proliferation, migration, and invasion of NPC.

CONCLUSION

The upregulation of miR-762 in NPC is associated with the disease progression and diagnosis of NPC. miR-762 might be involved in the tumor progression of NPC, which provides a potential therapeutic target for the treatment and management of NPC.

Circular RNA_0000629 Suppresses Bladder Cancer Progression Mediating MicroRNA-1290/CDC73

Background

Recent studies showed circular RNAs (circRNAs) played regulatory roles in bladder cancer (BC). However, the relevance of circ_0000629, a newly identified circRNA, has not been determined yet. We aimed to characterize the function of circ_0000629 in BC and the relevant mechanism.

Methods

First, we downloaded circRNA-related microarrays GSE147985 and GSE92675 from the GEO database, followed by a validation in our clinically obtained samples. We then overexpressed circ_0000629 in T24 and SW780 cells and evaluated the effects of circ_0000629 on BC cell proliferatory, apoptotic, and metastatic abilities. We further detected the subcellular localization of circ_0000629 in T24 and SW780 cells by the fractionation and export assay and FISH experiments. Integrated microarray analyses and bioinformatics website prediction were utilized to screen out the downstream microRNA (miRNA)/mRNA. The effects of miR-1290 and CDC73 on BC cell growth and metastasis was verified by functional rescue experiments. In addition, mice xenografts were built to measure the effect of circ_0000629 on tumor growth in vivo.

Results

Circ_0000629 and CDC73 were reduced, and miR-1290 was significantly overexpressed in BC tissues and cells. Moreover, circ_0000629 significantly inhibited the development and metastasis of BC cells, but further overexpression of miR-1290 or knockdown of CDC73 attenuated the inhibitory effect of circ_0000629 on BC cells. Circ_0000629 localized in the cytoplasm and regulated CDC73 expression by sponging miR-1290. Further, overexpressed circ_0000629 reduced the BC tumor growth in vivo.

Conclusion

Circ_0000629 promotes the expression of CDC73 by competitively binding to miR-1290, thereby inhibiting the growth and metastasis of BC cells.

Functions of circular RNAs in bladder, prostate and renal cell cancer (Review)

Circular RNAs (circRNAs) are a class of non-coding RNAs formed by covalently closed loops through back-splicing and exon-skipping. circRNAs have been confirmed to play a vital role in various biological functions, acting as microRNA sponges and reservoirs, as well as combining with RNA-binding proteins during the progression of multiple cancer types. Therefore, the present review evaluated recent research articles in PubMed that were published between November 2017 and September 2020. Key word search strings included: ‘Circular RNA (circRNA) AND bladder cancer (BC)’, ‘circular RNA (circRNA) AND prostate cancer (PCa)’ and ‘circular RNA (circRNA) AND renal cell cancer (RCC)’. In total, >58 circRNAs were found to be implicated in urological cancers, with several of the circRNAs targeting common carcinogenic pathways, such as the AKT, TGF-β, MAPK, VEGF and even metabolic pathways. circRNAs are important modulators of BC, PCa and RCC. circRNAs are functionally implicated in the pathogenesis of these cancer types, and have been found to act as biomarkers for the diagnosis and prognosis of urological cancer. However, to the best of our knowledge, the functions of circRNAs in tumors of the urinary system remain largely unknown and require further research.

CircRNAs: Emerging Bladder Cancer Biomarkers and Targets

Circular RNAs (circRNAs) are newly discovered intriguing RNAs due to the covalently closed loop structure, high stability, tissue specificity, and functional diversity. In recent years, a large number of circRNAs have been identified through high-throughput sequencing technology and bioinformatics methods, the abnormal expression of circRNAs are closely related to many diseases including bladder cancer (BC). CircRNAs have been proven to have several functions, such as acting as a regulator of parental gene transcription, miRNA sponge and interacting with proteins to regulate its expression. In addition, some circRNAs have been identified to encode proteins. CircRNAs have the characteristics of high abundance, high stability, wide distribution in body fluids, tissue specificity, and developmental stage specificity, which determine that circRNAs has great potential to be utilized as biomarkers for BC. Herein, we briefly summarize the biogenesis, functions and roles, and the current research progress of circRNAs in BC with a focus on the potential application for BC diagnosis, treatment, and prognosis.

Circular RNA circGSE1 Promotes Cervical Cancer Progression Through miR-138-5p/Vimentin

Background

A growing number of studies have identified that circular RNAs (circRNAs) play a vital role in the progression of various tumors. However, the underlying functions and mechanisms of circRNAs in cervical cancer have not been clarified.

Methods

qRT-PCR was used to detect the level of circGSE1 in cervical cancer tissues and matched normal tissues. In vitro cell wound healing, transwell migration and invasion assays were employed to assess the effects of circGSE1 on cell mobility. The pull-down, luciferase reporter, RIP and rescue assays were performed to evaluate the interaction between circGSE1and miR-138-5p and the regulation of miR-138-5p on Vimentin.

Results

We found that circGSE1 was significantly higher in cervical cancer tissues than that in matched normal tissues. Further analyses revealed that the level of circGSE1 was positively correlated with tumor differentiation, FIGUREO stage, depth of stromal invasion, lymph node metastasis and infiltration of parauterine organ. Kaplan–Meier survival analysis showed that high circGSE1 predicted worse overall survival and disease-free survival. Down-regulated circGSE1 evidently inhibited cell migration and metastasis of cervical cancer, while up-regulated circGSE1 significantly promoted cell migration and metastasis. The pull-down, luciferase reporter and RIP assays revealed that circGSE1 directly bound to and sponge miR-138-5p. MiR-138-5p inhibited the expression of Vimentin through directly binding to 3ʹUTR of Vimentin mRNA. In addition, miR-138-5p suppressed cell migration and invasion through inhibiting Vimentin expression, and circGSE1 promoted cell migration and invasion through sponging miR-138-5p and enhancing Vimentin expression.

Conclusion

CircGSE1 promotes the progression and may act as a novel diagnostic biomarker for disease progression of cervical cancer.

Expression profiles, biological functions and clinical significance of circRNAs in bladder cancer

Circular RNAs (circRNAs), which are single-stranded closed-loop RNA molecules lacking terminal 5′ caps and 3′ poly(A) tails, are attracting increasing scientific attention for their crucial regulatory roles in the occurrence and development of various diseases. With the rapid development of high-throughput sequencing technologies, increasing numbers of differentially expressed circRNAs have been identified in bladder cancer (BCa) via exploration of the expression profiles of BCa and normal tissues and cell lines. CircRNAs are critically involved in BCa biological behaviours, including cell proliferation, tumour growth suppression, cell cycle arrest, apoptosis, invasion, migration, metastasis, angiogenesis, and cisplatin chemoresistance. Most of the studied circRNAs in BCa regulate cancer biological behaviours via miRNA sponging regulatory mechanisms. CircRNAs have been reported to be significantly associated with many clinicopathologic characteristics of BCa, including tumour size, grade, differentiation, and stage; lymph node metastasis; tumour numbers; distant metastasis; invasion; and recurrence. Moreover, circRNA expression levels can be used to predict BCa patients’ survival parameters, such as overall survival (OS), disease-free survival (DFS), and progression-free survival (PFS). The abundance, conservation, stability, specificity and detectability of circRNAs render them potential diagnostic and prognostic biomarkers for BCa. Additionally, circRNAs play crucial regulatory roles upstream of various signalling pathways related to BCa carcinogenesis and progression, reflecting their potential as therapeutic targets for BCa. Herein, we briefly summarize the expression profiles, biological functions and mechanisms of circRNAs and the potential clinical applications of these molecules for BCa diagnosis, prognosis, and targeted therapy.

Identification of a potentially functional circRNA-miRNA-mRNA ceRNA regulatory network in bladder cancer by analysis of microarray data

Background

Circular RNAs (circRNAs) have received increasing attention in cancer development. However, a substantial number of circRNAs still require characterization. The purpose of this study is to uncover novel circRNAs and their molecular mechanism in bladder cancer (BCa).

Methods

A combinative strategy of extensive data mining and computational biology was employed to identify BCa-related circRNAs and explore their potential mechanisms of action.

Results

Three differentially expressed circRNAs (has_circ_0023642, has_circ_0047322, has_circ_0041151) were obtained from the microarray dataset (GSE92675). Four miRNAs (miR-616, miR-515-5p, miR-647, miR-1178) with potential binding sites with these three circRNAs were identified. Pathway analysis demonstrated that all four miRNAs were closely associated with some cancer-related pathways. Survival analysis indicated that these miRNAs might potentially play a role in tumor-suppressive functions in BCa. Subsequently, 181 overlapping genes were identified from 472 up-regulated genes in BCa (TCGA database), and 10,017 predicted target genes of the four miRNAs obtained. A circRNA-miRNA-mRNA network was constructed on the identified three circRNAs, four miRNAs, and 181 overlapping genes. Besides, six hub genes (CENPA, HIST1H2BJ, HIST1H2BO, HIST1H3H, HIST1H3B, HIST1H3F) were identified from establishing a protein-protein interaction (PPI) network on the same overlapping genes. Furthermore, a circRNA-miRNA-hub gene sub-network was built to delineate the links among the differential circRNAs, miRNA, and hub genes.

Conclusions

Our study provided significant insights into the molecular mechanisms that regulate the progression of BCa from the circRNA-miRNA-mRNA network view.

Identification of Circulating miR-762 as a Novel Diagnostic and Prognostic Biomarker for Non-Small Cell Lung Cancer

Background:

MicroRNAs (miRNAs) have been demonstrated to play critical roles in tumorigenesis of non-small cell lung cancer (NSCLC), and circulating miRNAs are a valuable source of biomarkers for the clinical management of NSCLC. The aim of this study was to determine the value of serum miR-762 as a diagnostic and prognostic biomarker for NSCLC.

Methods:

We examined circulating miR-762 expression in 148 NSCLC patients and 60 healthy individuals using the quantitative real-time polymerase chain reaction (qRT-PCR). The effect of miR-762 downregulation on the proliferative capacity of NSCLC cells were also explored.

Results:

The serum miR-762 levels were significantly upregulated in NSCLC patients compared to the healthy individuals. Receiver operating characteristics (ROC) curve analysis revealed that circulating miR-762, carcinoembryonic antigen (CEA), CYFRA21-1 and a combination of these 3 biomarkers yield the areas under the curve (AUC) of 0.874, 0.826, 0.41 and 0.969, respectively. Interestingly, circulating miR-762 identified the NSCLC patients at the clinical stage I from healthy controls with an AUC value of 0.920. In addition, serum miR-762 expression was significantly correlated with clinical stage, lymph node metastasis, histological grade and gefitinib-resistance. The survival analysis showed that NSCLC patients in the high serum miR-762 group suffered worse overall survival and relapse-free survival than those in the low serum miR-762 group. The multivariate Cox proportional hazards regression analysis revealed high circulating miR-762 was an independent unfavorable prognostic factor. Downregulation of miR-762 significantly suppressed the proliferative capacity of NSCLC cells in vitro, and bioinformatic analysis of the potential downstream targets of miR-762 identified many important cancer-associated pathways.

Conclusions:

In conclusion, serum miR-762 might serve as a promising diagnostic and prognostic biomarker for the NSCLC.

Circ_0123996 promotes cell proliferation and fibrosisin mouse mesangial cells through sponging miR-149-5p and inducing Bach1 expression

Diabetic nephropathy (DN) is a serious microvascular complication of diabetes across the world. Recently, many circular RNAs (circRNAs) can exert a crucial role in DN progression. Our investigation was designed to study whether circ_0123996 was associated with DN and aimed to find out the underlying mechanisms. We observed that circ_0123996 expression was significantly increased in Type 2 diabetes (T2D) with DN in comparison to those patients without DN. Consistently, circ_0123996 was also obviously elevated in DN mice models and high glucose (HG)-incubated MMCs. Then, it was proved transfection of circ_0123996 siRNA in mice mesangial cells (MMCs) restrained MMCs proliferation greatly. In addition, it was demonstrated that decrease of circ_0123996 alleviated fibrosis-related protein expression including FN and Col-4 in MMCs. Next, it was confirmed by our study that circ_0123996 can serve as a sponge for miR-149-5p. miR-149-5p has been identified in several diseases including diabetes. At present, we observed that miR-149-5p was decreased in DN. Overexpression of miR-149-5p greatly repressed the effect of circ_0123996 on MMCs. BTB and CNC homology 1 (Bach1) is reported in various disease including some vascular diseases.Here, Bach1 was confirmed as a target of miR-149-5p. Circ_0123996 upregulated Bach1 expression and restrained MMCs proliferation and fibrosis through sponging miR-149-5p. Thus, it was revealed that circ_0123996 was involved in DN via sponging miR-149-5p and modulating Bach1 expression.

Seeing Is Believing: Visualizing Circular RNAs

Advancement in the RNA sequencing techniques has discovered hundreds of thousands of circular RNAs (circRNAs) in humans. However, the physiological function of most of the identified circRNAs remains unexplored. Recent studies have established that spliceosomal machinery and RNA-binding proteins modulate circRNA biogenesis. Furthermore, circRNAs have been implicated in regulating crucial cellular processes by interacting with various proteins and microRNAs. However, there are several challenges in understanding the mechanism of circRNA biogenesis, transport, and their interaction with cellular factors to regulate cellular events because of their low abundance and sequence similarity with linear RNA. Addressing these challenges requires systematic studies that directly visualize the circRNAs in cells at single-molecule resolution along with the molecular regulators. In this review, we present the design, benefits, and weaknesses of RNA imaging techniques such as single-molecule RNA fluorescence in situ hybridization and BaseScope in fixed cells and fluorescent RNA aptamers in live-cell imaging of circRNAs. Furthermore, we propose the potential use of molecular beacons, multiply labeled tetravalent RNA imaging probes, and Cas-derived systems to visualize circRNAs.

Hsa_circRNA_100146 Acts as a Sponge of miR-149-5p in Promoting Bladder Cancer Progression via Regulating RNF2

Background

Mounting evidence has demonstrated that circular RNAs (circRNAs) play indispensable roles in the progression of bladder cancer. Public database mining showed that hsa_circRNA_100146 (circRNA_100146) was highly expressed in bladder cancer. This study aimed to characterize the biological role of circRNA_100146 and clarify the underlying mechanism in bladder cancer.

Methods

We evaluated the relationship between circRNA_100146 expression and clinicopathological features. Furthermore, gain- and loss-of-function studies were conducted in bladder cancer cells via transfection with gene-carrying plasmids (over-expression) or specific short hairpin RNAs (knockdown). Moreover, computational algorithms and dual-luciferase reporter assays were performed to explore the possible mechanisms of action. Additionally, in vivo xenograft experiments were performed to further analyze the effect of circRNA_100146 on tumor growth.

Results

Our data showed that circRNA_100146 expression was increased in bladder cancer tissues and cell lines, and that high expression of circRNA_100146 was correlated with poor patient prognosis. Upregulation of circRNA_100146 promoted cell proliferation, migration, and invasion, and inhibited cell apoptosis, whereas knockdown of circRNA_100146 displayed opposite effects on bladder cancer cells. Notably, circRNA_100146 could combine with miR-149-5p and promote ring finger protein 2 (RNF2) expression, thereby facilitating the progression of bladder cancer. Furthermore, overexpression of RNF2 reversed the effects of circRNA_100146 knockdown on the biological behaviors of bladder cancer cells. The in vivo experiments revealed that downregulation of circRNA_100146 dramatically delayed tumor growth.

Conclusion

Our findings indicate that circRNA_100146 functions as a sponge of miR-149-5p in promoting bladder cancer progression by regulating RNF2 expression and that circRNA_100146 may serve as a novel biomarker in human bladder cancer.

Circular RNAs and Bladder Cancer

Bladder cancer (BC) is the most common urinary system malignancy and is a serious threat to human health. Circular RNAs (circRNAs) are members of a newly defined class of noncoding RNAs (ncRNAs) that can regulate gene expression at the transcriptional or posttranscriptional level. Studies have shown that circRNAs are related to the clinicopathological characteristics, prognosis, and chemosensitivity of BC, and basic research has further confirmed that changes in the expression of circRNAs in BC are closely related to various tumor biological functions. CircRNAs promote tumor development by interacting with miRNAs to regulate transcription factors and both classical and nonclassical tumor signaling pathways. The nonclassical signaling pathways are related to cell cycle progression, epithelial–mesenchymal transition (EMT), extracellular matrix maintenance, and tumor stem cell maintenance. In this article, the relationships between circRNAs and the clinical characteristics of BC are reviewed, and the molecular mechanisms by which circRNAs promote tumor development are explored.

hsa_circRNA6448-14 promotes carcinogenesis in esophageal squamous cell carcinoma

Circular RNAs (circRNAs) play important roles in cancer progression. hsa_circRNA6448-14 originates from exon 5 to exon 11 of the TGFBI gene. We investigated the roles of hsa_circRNA6448-14 in esophageal squamous cell carcinoma (ESCC) with microarrays and quantitative real-time polymerase chain reaction (qRT-PCR), Kaplan-Meier analysis, loss-of-function and gain-of-function assays, and pull-down assays for miRNA binding. The hsa_circRNA6448-14-miRNA-mRNA network was drawn using Circos. hsa_circRNA6448-14 was significantly upregulated in ESCC tissues and cell lines. As a diagnostic biomarker, hsa_circRNA6448-14 had an area under the curve (AUC), sensitivity, and specificity of 0.906, 82.9%, and 85.5%, respectively. hsa_circRNA6448-14 upregulation was correlated with poor differentiation, advanced pTNM stage, poor disease-free survival (DFS), and poor overall survival (OS). Elevated hsa_circRNA6448-14 promoted cell proliferation, migration, invasion, and inhibited apoptosis in vitro. hsa_circRNA6448-14 functioned as a miRNA sponge to competitively bind miR-455-3p, and hsa_circRNA6448-14 expression negatively correlated with that of miR-455-3p. hsa_circRNA6448-14 promoted carcinogenesis in ESCC, suggesting that hsa_circRNA6448-14 could serve as a diagnostic and prognostic biomarker for ESCC.

The Regulatory Role of circRNA_101308 in Cervical Cancer and the Prediction of Its Mechanism

Purpose

Accumulating evidence indicates that circular RNAs (circRNAs) are closely involved in canceration and cancer progression. However, the role of circRNAs in cervical cancer (CC) is largely unknown. Here, we characterized the role of circRNA_101308 in CC.

Materials and Methods

The expression of circRNA_101308 in CC tissues was measured by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). Then, circRNA_101308 was overexpressed in CC cells to detect its function by proliferation and apoptosis assays, Transwell assays and animal experiments. The potential mechanism of circRNA_101308 in CC was explored by RNA pull-down, Gene Ontology (GO) and pathway analyses.

Results

CircRNA_101308 was significantly downregulated in CC tissues. The level of circRNA_101308 was much lower in CC patients with lymph node metastasis or deep myometrial invasion compared to those patients without lymph node metastasis and superficial myometrial invasion. CircRNA_101308 overexpression inhibited CC cell proliferation, invasion and migration. MiR-26a-5p, miR-196a-5p, miR-196b-5p, miR-335-3p, and miR-1307-3p were found to be sponged by circRNA_101308 in CC cells. Further, GO and pathway analyses predicted the potential functional processes and pathways of circRNA_101308 in CC.

Conclusion

CircRNA_101308 is downregulated and acts as a tumor suppressor in CC. CircRNA_101308 can participate in many different processes by sponging different miRNAs in CC cells. This exploration of circRNA_101308 provides new directions for research on cancer development and the clinical treatment of CC.

The Biogenesis, Functions, and Roles of circRNAs in Bladder Cancer

Bladder cancer (BCa) is the 10th most prevalent malignancy worldwide and remains a crucial cause of cancer-related morbidity and mortality. Circular RNAs (circRNAs), a large class of endogenous non-coding RNAs, contain unique covalent closed structures and their biogenesis and turnover are regulated by multiple factors. Recently, multiple circRNAs have been found to serve as important factors in several biological processes such as tumorigenesis. An increasing amount of research discovered that circRNAs are dysregulated in multiple cancer tissues compared with matched normal tissues, especially in BCa, indicating that circRNAs can act as biomarkers for the diagnosis and prognosis of BCa. In this review, we focus on the biogenesis, properties, turnover, and functions of circRNAs, summarizing their potential functions and clinical implications in BCa.