CircRNA_ACAP2 Suppresses EMT in Head and Neck Squamous Cell Carcinoma by Targeting the miR-21-5p/STAT3 Signaling Axis

Circular RNA CircACAP2 regulates temporomandibular joint osteoarthritis via miR-21-5p/PLAG1 axis

OBJECTIVES

The pathogenesis of temporomandibular joint osteoarthritis (TMJOA) remains not fully understood. Our previous studies demonstrated that miR-21-5p may participate in the TMJOA development and the interaction between circRNA-ACAP2 (CircACAP2) and miR-21-5p. Our present study aimed to explore the biological functions and regulatory mechanisms of CircACAP2 in TMJOA.

MATERIALS AND METHODS

The differential expression pattern of CircACAP2 in OA and normal tissues or cells was detected. CircACAP2 biological functions experiments were performed in chondrocytes by overexpression and interference techniques. The interaction of CircACAP2 with miR-21-5p and downstream target mRNA, polymorphic adenoma gene 1 (PLAG1), was predicted by bioinformatic databases and then demonstrated by dual-luciferase reporter assay. The biological role of CircACAP2 in TMJOA was investigated and validated in a mouse model.

RESULTS

The expression level of CircACAP2 was markedly reduced in OA cartilage and directly related to chondrocyte proliferation and apoptosis as well as ECM metabolism in the cartilage. CircACAP2 functioned in chondrocytes via targeting miR-21-5p and PLAG1. Overexpressing of CircACAP2 alleviated TMJOA in mouse models.

CONCLUSIONS

The present study unveiled that CircACAP2/miR-21-5p/PLAG1 axis may play an important regulatory role in TMJOA progression, which may highlight a potentially effective intervention and therapeutic strategy for the treatment of TMJOA.

Competing endogenous RNAs in head and neck squamous cell carcinoma: a review

Our understanding of RNA biology has evolved with recent advances in research from it being a non-functional product to molecules of the genome with specific regulatory functions. Competitive endogenous RNA (ceRNA), which has gained prominence over time as an essential part of post-transcriptional regulatory mechanism, is one such example. The ceRNA biology hypothesis states that coding RNA and non-coding RNA co-regulate each other using microRNA (miRNA) response elements. The ceRNA components include long non-coding RNAs, pseudogene and circular RNAs that exert their effect by interacting with miRNA and regulate the expression level of its target genes. Emerging evidence has revealed that the dysregulation of the ceRNA network is attributed to the pathogenesis of various cancers, including the head and neck squamous cell carcinoma (HNSCC). This is the most prevalent cancer developed from the mucosal epithelium in the lip, oral cavity, larynx and pharynx. Although many efforts have been made to comprehend the cause and subsequent treatment of HNSCC, the morbidity and mortality rate remains high. Hence, there is an urgent need to understand the holistic progression of HNSCC, mediated by ceRNA, that can have immense relevance in identifying novel biomarkers with a defined therapeutic intervention. In this review, we have made an effort to highlight the ceRNA biology hypothesis with a focus on its involvement in the progression of HNSCC. For the identification of such ceRNAs, we have additionally highlighted a number of databases and tools.

Exploring the evolving roles and clinical significance of circRNAs in head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) represents the predominant malignancies in the head and neck region, and has limited therapeutic alternatives. Circular RNAs (circRNAs), a substantial category of non-coding RNA molecules, exert influential roles in human disease development and progression, employing various mechanisms such as microRNA sponging, interaction with RNA-binding proteins, and translational capabilities. Accumulating evidence highlights the differential expression of numerous circRNAs in HNSCC, and numerous dysregulated circRNAs underscore their crucial involvement in malignant advancement and resistance to treatment. This review aims to comprehensively outline the characteristics, biogenesis, and mechanisms of circRNAs, elucidating their functional significance in HNSCC. In addition, we delve into the clinical implications of circRNAs, considering their potential as biomarkers or targets for diagnosis, prognosis, and therapeutic applications in HNSCC. The discussion extends to exploring future challenges in the clinical translation of circRNAs, emphasizing the need for further research.

Circular RNAs in EMT-driven metastasis regulation: modulation of cancer cell plasticity, tumorigenesis and therapy resistance

The non-coding RNAs comprise a large part of human genome lack of capacity in encoding functional proteins. Among various members of non-coding RNAs, the circular RNAs (circRNAs) have been of importance in the pathogenesis of human diseases, especially cancer. The circRNAs have a unique closed loop structure and due to their stability, they are potential diagnostic and prognostic factors in cancer. The increasing evidences have highlighted the role of circRNAs in the modulation of proliferation and metastasis of cancer cells. On the other hand, metastasis has been responsible for up to 90% of cancer-related deaths in patients, requiring more investigation regarding the underlying mechanisms modulating this mechanism. EMT enhances metastasis and invasion of tumor cells, and can trigger resistance to therapy. The cells demonstrate dynamic changes during EMT including transformation from epithelial phenotype into mesenchymal phenotype and increase in N-cadherin and vimentin levels. The process of EMT is reversible and its reprogramming can disrupt the progression of tumor cells. The aim of current review is to understanding the interaction of circRNAs and EMT in human cancers and such interaction is beyond the regulation of cancer metastasis and can affect the response of tumor cells to chemotherapy and radiotherapy. The onco-suppressor circRNAs inhibit EMT, while the tumor-promoting circRNAs mediate EMT for acceleration of carcinogenesis. Moreover, the EMT-inducing transcription factors can be controlled by circRNAs in different human tumors.

EIF4A3-regulated hsa_circ_0001445 can inhibit the progression of laryngeal squamous cell carcinoma via hsa-miR-432-5p-dependent up-regulation of RGMA expression

Laryngeal squamous cell carcinoma (LSCC) is a common malignant tumor in the head and neck, the 5-year relative survival rate of patients diagnosed with laryngeal cancer was estimated to be 61% from 2012 to 2018. An increasing number of studies have shown that circular RNAs (circRNAs) play a key role in the occurrence and development of cancer and may function as cancer biomarkers and new therapeutic targets. At present, the research on the relationship between circRNAs and LSCC is still in its infancy and needs further exploration. In this study, we found a circRNA (hsa_circ_0001445) associated with LSCC based on bioinformatics analysis. Quantitative real-time polymerase chain reaction (qRT-PCR) assay indicated that the expression of hsa_circ_0001445 was down-regulated in LSCC tissues and cell lines. Notably, the expression of hsa_circ_0001445 was negatively correlated with aggressive clinicopathological features and poor prognosis. Then, functional experiments found that overexpression of hsa_circ_0001445 inhibited the proliferation, migration and invasion of LSCC cells and tumor growth in vivo. Mechanistically, RNA immunoprecipitation (RIP), biotin-labeled probe pull-down, luciferase reporter assay and western blot experiments were employed and found that EIF4A3 reduced the expression of hsa_circ_0001445, and the direct binding of hsa_circ_0001445 to hsa-miR-432-5p attenuated the inhibitory effect of hsa-miR-432-5p on RGMA. In summary, our research suggests that hsa_circ_0001445 may be used as a potential prognostic biomarker and therapeutic target for LSCC.

CircRNA_0026344 via miR-21 is involved in cigarette smoke-induced autophagy and apoptosis of alveolar epithelial cells in emphysema

Cigarette smoke (CS), a main source of indoor air pollution, is a primary risk factor for emphysema, and aberrant cellular autophagy is related to the pathogenesis of emphysema. Circular RNAs (circRNAs) affect the expression of mRNAs via acting as microRNA (miRNA) sponges, but their role in emphysema progression is not established. In the present investigation, CS, acting on alveolar epithelial cells, caused higher levels of miR-21, p-ERK, and cleaved-caspase 3 and led to lower levels of circRNA_0026344 and PTEN, which induced autophagy and apoptosis. miR-21 suppressed the expression of PTEN, which was involved in the regulation of autophagy and apoptosis. Further, in alveolar epithelial cells, overexpression of circRNA_0026344 blocked cigarette smoke extract (CSE)-induced autophagy and apoptosis, but this blockage was reversed by upregulation of miR-21 with a mimic. These results demonstrated that, in alveolar epithelial cells, CS decreases circRNA_0026344 levels, which sponge miR-21 to inhibit the miR-21 target, PTEN, which, in turn, activates ERK and thereby promotes autophagy and apoptosis, leading to emphysema. Thus, for emphysema, circRNA_0026344 regulates the PTEN/ERK axis by sponging miR-21, which is associated with the CS-induced autophagy and apoptosis of alveolar epithelial cells. In sum, the present investigation identifies a novel mechanism for CS-induced emphysema and provides information useful for the diagnosis and treatment of CS-induced emphysema.

An Isoxazoloquinone Derivative Inhibits Tumor Growth by Targeting STAT3 and Triggering Its Ubiquitin-Dependent Degradation

BACKGROUND

Triple-negative breast cancer (TNBC) is the most aggressive breast cancer subtype, with shorter five-year survival than other breast cancer subtypes, and lacks targeted and hormonal treatment strategies. The signal transducer and activator of transcription 3 (STAT3) signaling is up-regulated in various tumors, including TNBC, and plays a vital role in regulating the expression of multiple proliferation- and apoptosis-related genes.

RESULTS

By combining the unique structures of the natural compounds STA-21 and Aulosirazole with antitumor activities, we synthesized a class of novel isoxazoloquinone derivatives and showed that one of these compounds, ZSW, binds to the SH2 domain of STAT3, leading to decreased STAT3 expression and activation in TNBC cells. Furthermore, ZSW promotes STAT3 ubiquitination, inhibits the proliferation of TNBC cells in vitro, and attenuates tumor growth with manageable toxicities in vivo. ZSW also decreases the mammosphere formation of breast cancer stem cells (BCSCs) by inhibiting STAT3.

CONCLUSIONS

We conclude that the novel isoxazoloquinone ZSW may be developed as a cancer therapeutic because it targets STAT3, thereby inhibiting the stemness of cancer cells.

A Circular RNA, hsa_circ_0018180 (circPARD3), Triggers Glycolysis and Promotes Malignancy of Head and Neck Squamous Cell Carcinoma Through the miR-5194/ENO1 Axis

Emerging evidence has demonstrated the pivotal roles of circular RNAs (circRNAs) in the modulation of malignancy and pathological progression among multiple human cancers. Glucose metabolism reprogramming is a widely identified characteristic for contributing to facilitate tumorigenesis. Nonetheless, their contributions to head and neck squamous cell carcinoma (HNSCC) cell glycolysis remain to be further elucidated. Herein, we aim to investigate the role of circRNA, hsa_circ_0018180 (also named as circPARD3) in HNSCC. Expression patterns of circPARD3 in HNSCC tissues and different cell lines were determined by qRT-PCR assay, as well as its correlation with the prognosis of survival. CCK-8, EdU incorporation, and transwell assays were carried out to assess the cell viability, proliferation, migration, and invasion, respectively. Glucose uptake and lactate production were evaluated by preforming glycolysis. Mechanistically, the circPARD3/miR-5194/ENO1 axis was verified by RNA immunoprecipitation (RIP) and luciferase reporter assays. Western blot analysis was employed to measure the epithelial-mesenchymal transition (EMT)-associated biomarkers. Upregulated circPARD3 observed in HNSCC tissues and cell lines indicated the poor prognosis of patients. Stable knockdown of circPARD3 dramatically exerted the suppressive effects on cell viability, proliferation, migration, and invasion, as well as glucose uptake and lactate production. Mechanistically, circPARD3 harbored miR-5194, serving as a miRNA sponge, thereby increasing ENO1 expression. Moreover, ENO1 evidently reversed miR-5194-mediated attenuated malignant behaviors. Collectively, our study identified an oncogenic role of circPARD3 in HNSCC through a novel machinery of circPARD3/miR-5194/ENO1 and provided a promising therapeutic target for HNSCC.

Identification of circRNA-lncRNA-miRNA-mRNA competitive endogenous RNA networks as prognostic bio-markers in head and neck squamous cell carcinoma

BACKGROUND

Head and neck squamous cell carcinoma (HNSCC) is one of the most prevalent neoplasms of malignancy. The pathogenesis of HNSCC is involved in the change of gene expression and the abnormal interaction between genes.

OBJECTIVE

The purpose of our research is to find genes that affect the survival time of patients and construct circRNA-lncRNA-miRNA-mRNA network. This paper aims to reveal the development mechanism of HNSCC and provide new ideas for clinical prognosis prediction.

METHODS

Transcriptome data were obtained from TCGA and GEO databases. A total of 556 samples were included. We screened the differentially expressed lncRNAs, circRNAs and mRNAs to predict interactions between lncRNA-miRNA, circRNA-miRNA and miRNA-mRNA. Then, we selected the hub mRNAs to predict the prognosis of patients.

RESULTS

We identified 8 hub prognostic mRNAs (FAM111A, IFIT2, CAV1, KLF9, OCIAD2, SLCO3A1, S100A16 and APOL3) by a series of bioinformatics analyses and established the prognostic ceRNA network of 8 mRNAs, 3 miRNAs, 2 circRNAs and 1 lncRNAs according to the targeting relationship by using databases.

CONCLUSION

We established the circRNA-lncRNA-miRNA-mRNA gene interaction network in HNSCC. We illuminated the molecular mechanism underlying the gene regulation associated with the pathogenesis of HNSCC and predicted the biomarkers related to prognosis.

circFOXO3 Induced by KLF16 Modulates Clear Cell Renal Cell Carcinoma Growth and Natural Killer Cell Cytotoxic Activity through Sponging miR-29a-3p and miR-122-5p

Renal cell carcinoma (RCC) is one of the most common urological malignancies with high incidence and metastatic relapse. Clear cell RCC (ccRCC) comprises nearly 70% of all RCC cases and is responsible for the majority of morbidity and mortality of RCC. Due to the poor diagnosis strategy and unsatisfactory clinical intervention, ccRCC causes a huge economic burden and poor patient quality of life; therefore, novel diagnostic or therapeutic targets for ccRCC are urgently needed. This study investigated the biological role of circFOXO3 in ccRCC development, showing that circFOXO3 is highly expressed in RCC cells and tissues and inhibits the viability of ccRCC cells. circFOXO3 dysregulation regulates NK cell cytotoxicity towards RCC cells by directly sponging miR-29a-3p and miR-122-5p. Overexpression of miR-29a-3p or miR-122-5p attenuated NK cell toxicity towards RCC cells and the transcriptional factor Kruppel-Like Factor 16 (KLF16) regulates circFOXO3 expression in RCC cells. In conclusion, this study has partially elucidated the function of circFOXO3 in ccRCC development, providing potential novel therapeutic targets for ccRCC.

Emerging roles of PIWI-interacting RNAs (piRNAs) and PIWI proteins in head and neck cancer and their potential clinical implications

Head and neck squamous cell carcinoma (HNSCC) are among the well-known neoplasms originating in the oral cavity, pharynx, and larynx. Despite advancements in chemotherapy, radiotherapy, and surgery, the survival rates of the patients are low, which has posed a major therapeutic challenge. A growing number of non-coding RNAs (ncRNAs), for instance, microRNAs, have been identified whose abnormal expression patterns have been implicated in HNSCC. However, more recently, several seminal research has shown that piwi-interacting RNAs (piRNAs), a promising and young class of small ncRNA, are linked to the emergence and progression of cancer. They can regulate transposable elements (TE) and gene expression through multiple mechanisms, making them potentially more powerful regulators than miRNAs. Hence, they can be more promising ncRNAs candidates for cancer therapeutic intervention. Here, we surveyed the roles and clinical implications of piRNAs and their PIWI proteins partners in tumorigenesis and associated molecular processes of cancer, with a particular focus on HNSCC, to offer a new avenue for diagnosis, prognosis, and therapeutic interventions for the malignancy, improving patient's outcomes.

CircSLC8A1 Exacerbates Hypoxia-Induced Myocardial Injury via Interacting with MiR-214-5p to Upregulate TEAD1 Expression

Circular RNAs (circRNAs) act as important regulators in myocardial infarction (MI). This study aimed to explore the regulatory mechanism of circRNA solute carrier family 8 member A1 antisense RNA 1 (circSLC8A1) in hypoxia-induced myocardial injury.Exosomes were isolated by ultracentrifugation and identified by microscopic observation or protein detection. Protein levels were examined by Western blot. CircSLC8A1, microRNA-214-5p (miR-214-5p), and TEA domain transcription factor 1 (TEAD1) levels were determined via quantitative real-time polymerase chain reaction (qRT-PCR). Cell viability and apoptosis were analyzed by 3-(4,5-dimethylthiazol-2-y1)-2,5-diphenyl tetrazolium bromide (MTT) and flow cytometry, respectively. Inflammatory cytokines were measured using enzyme-linked immunosorbent assay (ELISA). Oxidative stress was assessed by reactive oxygen species (ROS) production, malondialdehyde (MDA) level, and superoxide dismutase (SOD) activity through the corresponding detection kits. Target analysis was performed by dual-luciferase reporter assay, RNA immunoprecipitation (RIP) assay, and pull-down assay.Exosomes released circSLC8A1 from hypoxic cardiomyocytes. Exosomal circSLC8A1 exacerbated hypoxia-induced repression of cell viability but promotion of cell apoptosis, inflammation, and oxidative stress. Knockdown of circSLC8A1 ameliorated hypoxia-mediated cell injury. CircSLC8A1 directly targeted miR-214-5p and miR-214-5p downregulation reverted the effects of si-circSLC8A1 on hypoxia-treated cardiomyocytes. TEAD1 was a target of miR-214-5p and circSLC8A1 upregulated TEAD1 level via targeting miR-214-5p. In addition, miR-214-5p inhibited hypoxia-caused cell injury by downregulating the expression of TEAD1.These results suggested that circSLC8A1 aggravated cell damages in hypoxia-treated cardiomyocytes by the regulation of TEAD1 via sponging miR-214-5p.

The Expression Profile, Clinical Application and Potential Tumor Suppressing Mechanism of hsa_circ_0001675 in Head and Neck Carcinoma

Purpose

This study sought to identify circular RNAs (circRNA) that participate in the regulation of head and neck cancer (HNC), analyze their clinical application, and predict their molecular mechanism during HNC.

Materials and Methods

High-throughput sequencing was used to analyze circRNA expression in 18 matched HNC and adjacent normal tissues. Target circRNAs with significantly differential expression were obtained. In 103 HNC and adjacent normal tissues, real-time fluorescent quantitative PCR (qRT-PCR) was used to verify the differential expression of target circRNAs. This data was combined with clinicopathological information to analyze the diagnostic value of target circRNA. Bioinformatics was used to find target circRNAs that acted as competitive endogenous RNA (ceRNA) and construct a circRNA-miRNA-mRNA regulatory network. mRNA expression was verified by immunohistochemistry (IHC).

Results

A total of 714 differentially expressed circRNAs were detected in HNC, and the low expression of hsa_circ_0001675 was particularly significant (fold change [FC] = -4.85, P = 6.305E-05). hsa_circ_0001675 had significantly lower expression in HNC than in normal tissue (P < 0.01). Low hsa_circ_0001675 expression was positively associated with tumor invasion and clinical staging (P < 0.05), and its area under the ROC curve (AUC) was 0.7776. Low hsa_circ_0001675 expression also correlated with the overall survival (OS) rate and the progression-free survival (PFS) rate of HNC patients (P < 0.001). Bioinformatics was used to construct a ceRNA network of hsa_circ_0001675 with six differentially expressed miRNAs (hsa-miR-330-5p, hsa-miR-498, hsa-miR-532-3p, hsa-miR-577, hsa-miR-1248, and hsa-miR-1305) and 411 differentially expressed mRNAs and found that the neuroactive ligand-receptor interaction, and the cAMP and calcium signaling pathways were particularly enriched. Further bioinformatics and IHC analysis showed that miR577/TESC is the likely downstream signaling pathway for hsa_circ_0001675.

Conclusion

This study showed that hsa_circ_0001675 is downregulated in HNC and could be an effective biomarker for HNC diagnosis. In addition, hsa_circ_0001675 may have a potential ceRNA mechanism and suppress HNC disease progression through the hsa_circ_0001675-miRNA-mRNA axis.

Circ_SAR1A regulates the malignant behavior of lung cancer cells via the miR-21-5p/TXNIP axis

Background

Lung cancer is one of the most common malignancies globally and a significant component of cancer‐related deaths. The lack of early diagnosis accounts for detecting approximately 75% of cancer patients at an intermediate to an advanced stage, with a low 5‐year survival rate. Therefore, a more comprehensive understanding of the molecular mechanisms of lung cancer development is necessary to find reliable and effective therapeutic and diagnostic biomarkers.

Methods

circ_SAR1A, miR‐21‐5p, and TXNIP in lung cancer tissues, animal xenografts, and cell lines were validated by qRT‐PCR and western blotting analyses. RNase R digestion and nuclear/cytoplasm fractionation experiments were utilized to determine the stability and localization of circ_SAR1A in lung cancer cells. The binding between miR‐21‐5p and circ_SAR1A or TXNIP was confirmed by luciferase reporter, RNA pull‐down, Spearman's correlation, and rescue assays. CCK‐8, colony formation, flow cytometry, Transwell, and western blotting were utilized to illustrate the malignant behavior of lung cancer cells.

Results

circ_SAR1A and TXNIP were down‐regulated while miR‐21‐5p was up‐regulated in lung cancer samples and cells. circ_SAR1A was located predominantly in the cytoplasm; it inhibited lung cancer growth in vitro and in vivo by sponging to miR‐21‐5p. miR‐21‐5p silencing suppressed lung cancer malignancy by targeting TXNIP.

Conclusions

circ_SAR1A is a critical negative regulator of lung carcinogenesis. circ_SAR1A/miR‐21‐5p/TXNIP attenuation inhibited lung cancer progression, presenting an ideal diagnostic and a potential therapeutic target.

Circular RNAs in Intervertebral Disc Degeneration: An Updated Review

Low back pain, a common medical condition, could result in severe disability and inflict huge economical and public health burden. Its pathogenesis is attributed to multiple etiological factors, including intervertebral disc degeneration (IDD). Emerging evidence suggests that circular RNAs (circRNAs), a major type of regulatory non-coding RNA, play critical roles in cellular processes that are pertinent to IDD development, including nucleus pulposus cell proliferation and apoptosis as well as extracellular matrix deposition. Increasing number of translational studies also indicated that circRNAs could serve as novel biomarkers for the diagnosis of IDD and/or predicting its clinical outcomes. Our review aims to discuss the recent progress in the functions and mechanisms of newly discovered IDD-related circRNAs.

The circ_0032822 Promotes the Proliferation of Head and Neck Squamous Cell Carcinoma Cells Through miR-141/EF3 Signaling Axis

Head and neck squamous cell carcinoma (HNSCC) refers to an epithelial malignant tumor that originates in the head and neck, and over 600,000 new cases are reported every year, However, the overall prognosis is still poor due to local recurrence and distant metastasis after surgery. The circ_0032822 has been reported upregulated in human oral squamous cell carcinoma; however, the detailed function or mechanism remains unknown. In this study, we confirmed the upregulation of circ_0032822 in HNSCC tumor tissues. Functionally, the overexpression of circ_0032822 significantly promoted the proliferation of HNSCC cell lines along with the S phase arrest and reduced apoptosis, while downregulation of circ_0032822 has the opposite effect in vitro. Mechanistic analysis showed that circ_0032822 acted as a competing endogenous RNA of miR-141 to diminish the repressive effect of miR-141 on its target E2F3. In conclusion, we demonstrated that circ_0032822 functions as a tumor oncogene in HNSCC and that its function is regulated via the miR-141/E2F3 axis.

Regulation of cell signaling pathways by circular RNAs and microRNAs in different cancers: Spotlight on Wnt/β-catenin, JAK/STAT, TGF/SMAD, SHH/GLI, NOTCH and Hippo pathways

Groundbreaking discoveries in molecular oncology have leveraged our understanding altogether to a new level. Mapping of plethora of cell signaling pathways has enabled researchers to drill down deep into the intermeshed regulatory networks which crosstalk to promote carcinogenesis and metastasis. More importantly, discovery of non-coding RNAs has added new layers of complexity to already complicated nature of cell signaling pathways. The discovery of circular RNAs (circRNAs) has opened the door to an ever-widening understanding of cellular processes that are controlled or influenced by circRNAs. In this review, we have summarized most recent advancements in our understanding related to interplay between circular RNAs and microRNAs for the regulation of NOTCH, Wnt/β-catenin, Hippo, SHH/GLI, JAK/STAT and TGF/SMAD pathways in different cancers.

Underlying metastasis mechanism and clinical application of exosomal circular RNA in tumors (Review)

Circular RNA (circRNA) is a long non-coding RNA molecule with a closed loop structure lacking a 5′cap and 3′tail. circRNA is stable, difficult to cleave and resistant to RNA exonuclease or RNase R degradation. circRNA molecules have several clinical applications, especially in tumors. For instance, circRNA may be used for non-invasive diagnosis, therapy and prognosis. Exosomes play a crucial role in the development of tumors. Exosomal circRNA in particular has led to increased research interest into tumorigenesis and tumor progression. Additionally, exosomal circRNA plays a role in cell-cell communication. Exosomal circRNA facilitates tumor metastasis by altering the tumor microenvironment and the pre-metastatic niche. Additionally, studies have revealed the mechanism by which exosomal circRNA affects malignant progression through signal transduction. Moreover, exosomal circRNA promotes tumor metastasis by regulating gene expression, RNA transcription and protein translation. In this review, the biological features and clinical application of exosomal circRNA are described, highlighting the underlying mechanisms through which they regulate tumor metastasis. The application of circRNA as clinical diagnostic biomarkers and in the development of novel therapeutic strategies is also discussed.