Three isoforms of exosomal circPTGR1 promote hepatocellular carcinoma metastasis via the miR449a-MET pathway

The functional roles, cross-talk and clinical implications of m6A modification and circRNA in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related deaths worldwide. HCC has high rates of death and recurrence, as well as very low survival rates. N6-methyladenosine (m6A) is the most abundant modification in eukaryotic RNAs, and circRNAs are a class of circular noncoding RNAs that are generated by back-splicing and they modulate multiple functions in a variety of cellular processes. Although the carcinogenesis of HCC is complex, emerging evidence has indicated that m6A modification and circRNA play vital roles in HCC development and progression. However, the underlying mechanisms governing HCC, their cross-talk, and clinical implications have not been fully elucidated. Therefore, in this paper, we elucidated the biological functions and molecular mechanisms of m6A modification in the carcinogenesis of HCC by illustrating three different regulatory factors ("writer", "eraser", and "reader") of the m6A modification process. Additionally, we dissected the functional roles of circRNAs in various malignant behaviors of HCC, thereby contributing to HCC initiation, progression and relapse. Furthermore, we demonstrated the cross-talk and interplay between m6A modification and circRNA by revealing the effects of the collaboration of circRNA and m6A modification on HCC progression. Finally, we proposed the clinical potential and implications of m6A modifiers and circRNAs as diagnostic biomarkers and therapeutic targets for HCC diagnosis, treatment and prognosis evaluation.

Insights into the Evolving Roles of Circular RNAs in Cancer

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

Exosomal circEIF3K from cancer-associated fibroblast promotes colorectal cancer (CRC) progression via miR-214/PD-L1 axis

Background

Tumor microenvironment (e.g., cancer-associated fibroblast) plays a key role in cancer tumorigenesis and metastasis. However, the detailed mechanism of whether hypoxia promotes CRC progression via tumor microenvironment remains unclear.

Methods

In this study, circEIF3K exosome was examined by NanoSight Tracking Analysis and RT-qPCR. We used cell colony formation assay, transwell assay and tube formation assay to determine proliferation, invasion and metastasis of HCT116 or SW620 cells. Xenograft tumor assay was employed to show in vivo tumor growth of HCT116 cells.

Results

We found that hypoxia could induce secretion of circEIF3K exosome. Conditioned medium (CM) and exosome from circEIF3K knockdown CAF significantly attenuated proliferation, invasion and tube formation of HCT116 or SW620 cells, which could be reverted by miR-214 under hypoxia treatment. Besides, we observed that circEIF3K knockdown evidently impaired tumor growth in mice. TCGA dataset analysis showed that low expression of circEIF3K was observed in normal tissues and associated with prolonged survival time. Finally, PD-L1 was confirmed as important target for miR-214 in CRC.

Conclusion

In conclusion, our study reveals that a novel axis circEIF3K/miR-214/PD-L1 mediates hypoxia-induced CRC progression via CAF, providing the rationale for developing new targeted therapeutics to treat CRC.

Exosome encapsulated ncRNAs in the development of HCC: potential circulatory biomarkers and clinical therapeutic targets

Hepatocellular carcinoma (HCC) is the sixth most deadly malignant cancer in the world and has the third highest mortality rate among cancer-related deaths worldwide. Its poor prognosis can be attributed to late diagnosis, high risk of recurrence and drug resistance. Therefore, finding a new biomarker to help us in the early diagnosis, and exploring the molecular mechanisms involved in recurrence and drug resistance is a reasonable research direction for clinical treatment of HCC. At present, the exosomes related to HCC have been confirmed to carry ncRNAs, transfer them to target cells, and bind corresponding target molecules. Furthermore, they affect the proliferation and metastasis of hepatocellular carcinoma by promoting angiogenesis, epithelial-mesenchymal transition (EMT), and inhibiting the function of the body's immune system. They play an important role in the recurrence and resistance of HCC. Besides, exosomes are stably expressed in body fluids such as sera, are easy to collect and cause little harm to the human body. They are the best candidates for liquid biopsy. Therefore, exosomal ncRNAs have application prospects as biomarkers and targeted molecules for therapy. This article summarizes the current research involving ncRNAs in HCC-related exosomes.

Exosomal non-coding RNAs in Hepatobiliary Cancer: A Rising Star

Hepatobiliary cancers are a heterogeneous group of malignancies with a dismal prognosis. Despite intensive research efforts focused on these tumors, methods for early diagnosis and effective targeted therapies are still lacking. Exosomes, released by most cells, exist in all kinds of body fluids and play an important role in cell-to-cell communication. They are small membranous vesicles containing biological molecules, such as noncoding RNAs (ncRNAs), which are not translated into proteins, but they exert effects on the regulation of gene transcription and translation. There is growing evidence for the essential roles of ncRNAs in exosomes in both physiological and pathological conditions of hepatobiliary cancers. They have been identified as sensitive diagnostic biomarkers as well as potential therapeutic targets. The present review discusses recent findings in the crosstalk between hepatobiliary cancers cells and the surrounding cells of the microenvironment and discuss their potential clinical usage.

Emerging Role of Extracellular Vesicles in Biomarking the Gastrointestinal Diseases

INTRODUCTION

Extracellular vesicles (EVs) play an important role in cell-cell communication and regulation of various cellular functions under physiological and pathophysiological conditions through transferring their cargo to recipient cells. Molecular constituents of EVs are a fingerprinting profile of secreting cells which can be used as promising prognostic, diagnostic, and drug-response biomarkers in clinical settings.

AREAS COVERED

The present study provides a brief introduction about the biology of EVs and reviews methodologies used for EV isolation and characterization as well as high-throughput strategies to analyze EV contents. Furthermore, this review highlights the importance and unique role of EVs in the development and progression of gastrointestinal (GI) diseases, especially GI cancers, and then discusses their potential use, particularly those isolated from body fluids, in diagnosis and prognosis of GI diseases.

EXPERT OPINION

In-depth analysis of EV content can lead to the identification of new potential biomarkers for early diagnosis and prognosis prediction of GI diseases. The use of a more targeted approach by establishing more reproducible and standardized methods to decrease variations and obtain desired EV population as well as revisiting large pools of identified biomarkers and their evaluation in larger patient cohorts can result in the introduction of more reliable biomarkers in clinic.

The Potential of Serum Exosomal hsa_circ_0028861 as the Novel Diagnostic Biomarker of HBV-Derived Hepatocellular Cancer

Hepatitis B virus (HBV)-derived hepatocellular cancer (HCC) is a serious threat to human health, especially in China. There is no highly sensitive and specific HCC biomarker at present, which makes it difficult to detect HCC at the early stage. Serum exosomal circular RNAs (circRNAs) have been reported as novel diagnostic and prognostic biomarkers of cancers. In the present study, we aimed to explore the diagnostic performance of serum exosomal circRNAs for HBV-derived HCC screening. At first, many circRNAs were found to be differentially expressed in the serum exosomes of HCC individuals by microarray analysis. The validation of dysregulated circRNAs by qRT-PCR revealed that serum exosomal hsa_circ_0028861 was decreased in HCC compared to chronic HBV and cirrhosis. Then, hsa_circ_0028861 was identified as a novel biomarker for HCC diagnosis with an area under the ROC curve (AUC) of 0.79 for discriminating HCC from chronic HBV and cirrhosis individuals. Hsa_circ_0028861 was capable of detecting small (AUC = 0.81), early-stage (AUC = 0.82) and AFP-negative [AFP (-)] (AUC = 0.78) tumors as well. The combination of hsa_circ_0028861 and AFP exhibited better diagnostic ability (AUC = 0.86 for discriminating HCC from chronic HBV and cirrhosis). Moreover, bioinformatics prediction suggested that hsa_circ_0028861 might influence HCC progression by regulating its targeted microRNAs (miRNAs) and downstream tumor-related signaling pathways. Collectively, our study reveals a novel diagnostic tool for HBV-derived HCC.

USO1 isoforms differentially promote liver cancer progression by dysregulating the ER-Golgi network

Alternative splicing of RNA transcripts plays an important role in cancer development and progression. Recent advances in RNA-seq technology have made it possible to identify alternately spliced events in various types of cancer; however, research on hepatocellular carcinoma (HCC) is still limited. Here, by performing RNA-Seq profiling of HCC transcripts at isoform level, we identified tumor-specific and molecular subtype-dependent expression of the USO1 isoforms, which we designated as a normal form USO1-N (XM_001290049) and a tumor form USO1-T (NM_003715). The expression of USO1-T, but not USO1-N, was associated with worse prognostic outcomes of HCC patients. We confirmed that the expression of USO1-T promoted an aggressive phenotype of HCC, both in vitro and in vivo. In addition, structural modeling analyses revealed that USO1-T lacks an ARM10 loop encoded by exon 15, which may weaken the dimerization of USO1 and its tethering to GM130. We demonstrated that USO1-T ensured unstacking of the Golgi and accelerated the trafficking from ER to Golgi and plasma membrane in multiple liver cancer cells. ERK and GRASP65 were found to be involved in the USO1-T mediated Golgi dysfunction. Conclusively, we provide new mechanophysical insights into the USO1 isoforms that differentially regulate the ER-Golgi network, promoting the heterogeneous HCC progression.

Current Molecular Biology and Therapeutic Strategy Status and Prospects for circRNAs in HBV-Associated Hepatocellular Carcinoma

Circular RNAs (circRNAs) are newly classified noncoding RNA (ncRNA) members with a covalently closed continuous loop structure that are involved in immune responses against hepatitis B virus (HBV) infections and play important biological roles in the occurrence and pathogenesis of HCC progression. The roles of circRNAs in HBV-associated HCC (HBV-HCC) have gained increasing attention. Substantial evidence has revealed that both tissue and circulating circRNAs may serve as potential biomarkers for diagnostic, prognostic and therapeutic purposes. So far, at least four circRNA/miRNA regulatory axes such as circRNA_101764/miR-181, circRNA_100338/miR-141-3p, circ-ARL3/miR-1305, circ-ATP5H/miR-138-5p, and several circulating circRNAs were reported to be associated with HBV-HCC development. Notably, TGF/SMAD, JAK/STAT, Notch and Wnt/β-catenin signaling pathways may play pivotal roles in this HBV-driven HCC via several circRNAs. Moreover, in non-HBV HCC patients or HCC patients partially infected by HBV, numerous circRNAs have been identified to be important regulators impacting the malignant biological behavior of HCC. Furthermore, the role of circRNAs in HCC drug resistance has become a focus of research with the aim of reversing chemoresistance and immune resistance. Herein, we review the molecular biology of circRNAs in HBV-HCC and their potential in therapeutic strategies.

Exosomal circRNA in Digestive System Tumors: The Main Player or Coadjuvants?

Exosomes are a type of extracellular microvesicles with a diameter of 40–160 nm. Circular RNA (circRNA) is a type of closed circular RNA molecule that is highly conserved in evolution. Exosomal circRNA plays a vital role in the proliferation, invasion, migration, and drug resistance of digestive system tumors. In this study, we used The Cancer Genome Atlas (TCGA) database, UALCAN, Python crawler, miRTargetLink Human, Database for Annotation, Visualization, and Integrated Discovery (DAVID), micBioinformatic online tool, and Cytoscape software (3.7.1). The results showed that circ-RanGAP1 in gastric cancer, circUHRF1 in hepatocellular carcinoma, and circFMN2 in colorectal cancer regulate the malignant behavior of tumors and affect the expression of their host gene through sponging miR-877-3p, miR-449c-5p, and miR-1182, respectively. Twenty exosomal circRNAs regulate 6,570 target genes through sponging 23 miRNAs. Firstly, 270 of those target genes are regulated by two or more miRNAs, which are highly correlated with 83 tumor-related pathways and six Kyoto Encyclopedia of Genes and Genomes pathways. Secondly, 1,146 target genes were significantly differentially expressed in corresponding digestive system tumors, and functional enrichment analysis revealed that 78 of those were involved in 20 cancer-related pathways. In short, the bioinformatics analysis showed that these exosomal circRNAs are stably expressed in body fluids, and regulate the occurrence and development of gastric cancer, hepatocellular carcinoma, colorectal cancer, and other digestive system tumors through sponging miRNAs. Exosomal circRNAs may be used as biomarkers for the diagnosis of disease and identification of effective therapeutic targets in the future, as well as improve the prognosis of patients with digestive system tumors.

The Role of Extracellular Vesicles in Disease Progression and Detection of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the most common primary liver malignancy and one of the leading causes of cancer-related death worldwide. Despite the improvements in surveillance and treatment, the prognosis of HCC remains poor. Extracellular vesicles (EVs) are a heterogeneous group of phospholipid bilayer-enclosed particles circulating in the bloodstream and mediating intercellular communication. Emerging studies have shown that EVs play a crucial role in regulating the proliferation, immune escape, and metastasis of HCC. In addition, because EVs are present in the circulation at relatively early stages of disease, they are getting attention as an attractive biomarker for HCC detection. Over the past decade, dedicated efforts have been made to isolate EVs more efficiently and make them useful tools in different clinical settings. In this review article, we provide an overview of the EVs isolation methods and highlight the role of EVs as mediators in the pathogenesis and progression of HCC. Lastly, we summarize the potential applications of EVs in early-stage HCC detection.

Circular RNA 0006602 in plasma exosomes: a new potential diagnostic biomarker for hepatocellular carcinoma

Circular RNAs (circRNAs) in exosomes exhibit stable expression and are not easily degraded in plasma; a characteristic that makes them ideal as novel non-invasive tumor diagnostic markers. In this study, we examined different expression of circRNA in plasma exosomes of primary hepatocellular carcinoma patient and healthy volunteer by full transcriptome sequencing. Five circRNAs with up-regulated expression were selected, and large sample size verified their expression. Among them, it is further confirmed that exo_circ_0006602 is up-regulated in the large sample cohort. In addition, the expression level of exo_circ_0006602 was correlated with HBsAg (P<0.011), HBeAg (P=0.048), liver cirrhosis (P=0.001) and Edmondson-Steiner grade (P<0.001). The receiver operating characteristic (ROC) was used to evaluate the accuracy of exo_circ_0006602 as a diagnostic marker. The AUC value of exo_circ_0006602 was significantly highter than common serum tumor markers AFP and CEA. Exo_circ_0006602 combined with AFP can significantly improve the diagnostic accuracy. Cell function experiments show that exo_circ_0006602 can significantly improve the proliferation and invasion ability of liver cancer cell lines and also promoted the expression of tumor proliferation-related protein Snail. In conclusion, our results suggested that exo_circ_0006602 can be used as a potential non-invasive biomarker for the early diagnosis and screening of liver cancer, the sensitivity and specificity of diagnosis are higher than traditional tumor markers.

The Role of Extracellular Vesicles as Shuttles of RNA and Their Clinical Significance as Biomarkers in Hepatocellular Carcinoma

Extracellular vesicles (EVs) have attracted interest as mediators of intercellular communication following the discovery that EVs contain RNA molecules, including non-coding RNA (ncRNA). Growing evidence for the enrichment of peculiar RNA species in specific EV subtypes has been demonstrated. ncRNAs, transferred from donor cells to recipient cells, confer to EVs the feature to regulate the expression of genes involved in differentiation, proliferation, apoptosis, and other biological processes. These multiple actions require accuracy in the isolation of RNA content from EVs and the methodologies used play a relevant role. In liver, EVs play a crucial role in regulating cell-cell communications and several pathophysiological events in the heterogeneous liver class of cells via horizontal transfer of their cargo. This review aims to discuss the rising role of EVs and their ncRNAs content in regulating specific aspects of hepatocellular carcinoma development, including tumorigenesis, angiogenesis, and tumor metastasis. We analyze the progress in EV-ncRNAs' potential clinical applications as important diagnostic and prognostic biomarkers for liver conditions.

The role of circular RNAs in the development of hepatocellular carcinoma

Circular RNAs (circRNAs) are a group of regulatory non-coding transcripts, which partake in the pathobiology of hepatocellular carcinoma (HCC). Numerous micro-array based investigations have discovered aberrant expression of circRNAs in HCC samples in comparison with para-cancerous sections. Furthermore, a number of in vitro and in vivo experimentations have aimed at understanding the molecular pathways of circRNAs contribution in the evolution of HCC. CircRNAs have interplay with a number of transcription factors such as ZEB1 that possibly mediates the effects of these transcripts in the epithelial-mesenchymal transition. Moreover, circRNAs functionally interact with miRNAs. CircRNA_0000502/ miR-124, circ_0001955/ miR-145-5p, circ_0001955/ miR-516a-5p and hsa_circ_0001955/miR-145-5p are examples of such interactions in the context of HCC. CircRNAs not only predict the course of HCC, but also, they can differentiate HCC samples from non-malignant liver tissues. In this review article, we have provided an inclusive summary of researches that quantified circRNAs profile in HCC. We also provide evidence for application of circRNAs as HCC biomarkers.

Exosomal S100A4 derived from highly metastatic hepatocellular carcinoma cells promotes metastasis by activating STAT3

Intercellular cross-talk plays important roles in cancer progression and metastasis. Yet how these cancer cells interact with each other is still largely unknown. Exosomes released by tumor cells have been proved to be effective cell-to-cell signal mediators. We explored the functional roles of exosomes in metastasis and the potential prognostic values for hepatocellular carcinoma (HCC). Exosomes were extracted from HCC cells of different metastatic potentials. The metastatic effects of exosomes derived from highly metastatic HCC cells (HMH) were evaluated both in vitro and in vivo. Exosomal proteins were identified with iTRAQ mass spectrum and verified in cell lines, xenograft tumor samples, and functional analyses. Exosomes released by HMH significantly enhanced the in vitro invasion and in vivo metastasis of low metastatic HCC cells (LMH). S100 calcium-binding protein A4 (S100A4) was identified as a functional factor in exosomes derived from HMH. S100A4rich exosomes significantly promoted tumor metastasis both in vitro and in vivo compared with S100A4low exosomes or controls. Moreover, exosomal S100A4 could induce expression of osteopontin (OPN), along with other tumor metastasis/stemness-related genes. Exosomal S100A4 activated OPN transcription via STAT3 phosphorylation. HCC patients with high exosomal S100A4 in plasma also had a poorer prognosis. In conclusion, exosomes from HMH could promote the metastatic potential of LMH, and exosomal S100A4 is a key enhancer for HCC metastasis, activating STAT3 phosphorylation and up-regulating OPN expression. This suggested exosomal S100A4 to be a novel prognostic marker and therapeutic target for HCC metastasis.

Non-coding RNAs and lipids mediate the function of extracellular vesicles in cancer cross-talk

Research on extracellular vesicles (EVs) has been expanded, especially in the field of cancer. The cargoes in EVs, especially those in small EVs such as exosomes include microRNAs (miRNAs), mRNA, proteins, and lipids, are assumed to work cooperatively in the tumor microenvironment. In 2007, it was reported that miRNAs were abundant among the non-coding RNAs present in exosomes. Since then, many studies have investigated the functions of miRNAs and have tried to apply these molecules to aid in the diagnosis of cancer. Accordingly, many reviews of non-coding RNAs in EVs have been published for miRNAs. This review focuses on relatively new cargoes, covering long noncoding (lnc) RNAs, circular RNAs, and repeat RNAs, among non-coding RNAs. These RNAs, regardless of EV or cell type, have newly emerged due to the innovation of sequencing technology. The poor conservation, low quantity, and technical difficulty in detecting these RNA types have made it difficult to elucidate their functions and expression patterns. We herein summarize a limited number of studies. Although lipids are major components of EVs, current research on EVs focuses on miRNA and protein biology, while the roles of lipids in exosomes have not drawn attention. However, several recent studies revealed that phospholipids, which are components of the EV membrane, play important roles in the intercommunication between cells and in the generation of lipid mediators. Here, we review the reported roles of these molecules, and describe their potential in cancer biology.

Genomic Landscape of Liquid Biopsy for Hepatocellular Carcinoma Personalized Medicine

Hepatocellular carcinoma (HCC) is the sixth most frequently diagnosed cancer and the third leading cause of cancer-related deaths worldwide. Advanced-stage HCC patients have poor survival rates and this requires the discovery of novel clear biomarkers for HCC early diagnosis and prognosis, identifying risk factors, distinguishing HCC from non-HCC liver diseases, and assessment of treatment response. Liquid biopsy has emerged as a novel minimally invasive approach to enable monitoring tumor progression, metastasis, and recurrence. Since the liquid biopsy analysis has relatively high specificity and low sensitivity in cancer early detection, there is a risk of bias. Next-generation sequencing (NGS) technologies provide accurate and comprehensive gene expression and mutational profiling of liquid biopsies including cell-free circulating tumor DNA (ctDNA), circulating tumor cells (CTCs), and genomic components of extracellular vesicles (EVs) including micro-RNAs (miRNAs), long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs). Since HCC is a highly heterogeneous cancer, HCC patients can display various genomic, epigenomic, and transcriptomic patterns and exhibit varying sensitivity to treatment options. Identification of individual variabilities in genomic signatures in liquid biopsy has the potential to greatly enhance precision oncology capabilities. In this review, we highlight and critically discuss the latest progress in characterizing the genomic landscape of liquid biopsy, which can advance HCC personalized medicine.

Circular RNAs and Hepatocellular Carcinoma: New Epigenetic Players With Diagnostic and Prognostic Roles

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related death worldwide. Due to the lack of potent diagnosis and prognosis biomarkers and effective therapeutic targets, the overall prognosis of survival is poor in HCC patients. Circular RNAs (circRNAs) are a class of novel endogenous non-coding RNAs with covalently closed loop structures and implicated in diverse physiological processes and pathological diseases. Recent studies have demonstrated the involvement of circRNAs in HCC diagnosis, prognosis, development, and drug resistance, suggesting that circRNAs may be a class of novel targets for improving HCC diagnosis, prognosis, and treatments. In fact, some artificial circRNAs have been engineered and showed their therapeutic potential in treating HCV infection and gastric cancer. In this review, we introduce the potential of circRNAs as biomarkers for HCC diagnosis and prognosis, as therapeutic targets for HCC treatments and discuss the challenges in circRNA research and chances of circRNA application.

Current perspectives on exosomes in the diagnosis and treatment of hepatocellular carcinoma (review)

The prognosis of hepatocellular carcinoma (HCC), a malignant tumor, is poor. Tumor recurrence and metastasis are the major challenges for the treatment of HCC. Various studies have demonstrated that exosomes, which are loaded with various biomolecules including nucleic acids, lipids, and proteins are involved in the recurrence and metastasis of HCC. Additionally, exosomes mediate various biological processes, such as immune response, cell apoptosis, angiogenesis, thrombosis, autophagy, and intercellular signal transduction. In cancer, exosomes regulate cancer cell differentiation, development, and drug resistance. Circular RNAs, microRNAs, and proteins in the exosomes can serve as early diagnostic and prognostic markers for HCC. As exosomes are characterized by low immunogenicity and high stability in the tissues and circulation, they can be used to deliver the drugs in cancer therapies.

Hsa‑circRNA‑G004213 promotes cisplatin sensitivity by regulating miR‑513b‑5p/PRPF39 in liver cancer

In recent years, increasing evidence has confirmed that exosomal circular RNAs (circRNAs) serve a crucial role in the prognostic prediction and diagnosis of liver cancer (LC). The present study compared the expression patterns of exosomal circRNAs during transarterial chemoembolization (TACE). CircRNA sequencing analysis identified 390 differentially expressed circRNAs between the prior TACE and following the first TACE operation groups and 489 differentially expressed circRNAs between the prior to TACE and following the second TACE operation groups. Gene Ontology analysis of the differentially expressed circRNAs demonstrated that they were associated with fatty acid metabolism, receptor binding and membrane protein complexes. Kyoto Encyclopedia of Genes and Genomes pathway analysis predicted that protein digestion and absorption pathways were activated following TACE. A novel gene was screened out; hsa‑circRNA‑G004213 (circ‑G004213) was significantly upregulated following TACE (fold change >10, P < 0.01). Further analysis found circ‑G004213 significantly increased the cisplatin sensitivity of HepG2 cells and positively associated with the prognosis of tumor‑bearing mice. Based on the potential downstream miRNAs and mRNAs, the circRNA‑miRNA‑mRNA network was constructed. It was demonstrated that circ‑G004213 regulated cisplatin resistance via the miR‑513b‑5p/PRPF39 axis. Finally, the present study confirmed that circ‑G004213 was positively associated with the prognosis of patients with LC following TACE. Therefore, circ‑G004213 may be used as an indicator for predicting the efficacy of TACE.

Exosomal Non-coding RNAs-Mediated Crosstalk in the Tumor Microenvironment

Exosomes are secreted by different types of cells in tumor microenvironment (TME) and participate in multiple biological processes of tumors. Non-coding RNAs (ncRNAs) enveloped in exosomes and released to the TME are shown to be involved in tumorigenesis and development, as well as act as important intracellular communication mediators. However, the understanding on the exact regulatory functions and substrates of exosomal RNA is still at an early stage. In this review, we provided an overview on recent studies on exosomes mediating the modulation of both tumor cells and immune cells, then summarized the exosomal ncRNAs [such as microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs)] secreted by tumor cells and stromal cells that exhibited potential capabilities to regulate tumor cell growth, progression, metastasis, drug resistance, and immune response. Our review may hopefully inspire a deeper understanding on the ncRNAs’ function as useful biomarkers for the diagnosis, prognosis, and as novel targets therapy for cancer.

Circular RNA expression profile of lung squamous cell carcinoma: identification of potential biomarkers and therapeutic targets

Emerging evidences indicated that exosomal circular RNAs (circRNAs) could serve as diagnostic biomarkers for cancers. However, the expression profiles and clinical significance of circRNAs in lung squamous cell carcinoma (LUSC) remain largely unknown. Herein, we analyzed circRNAs expression profile in six pairs of plasma exosome samples of LUSC patients using high-throughput sequencing. A total of 252 differentially expressed exosomal circRNAs were identified, including 133 up-regulated circRNAs and 119 down-regulated circRNAs. Subsequently, the circRNAs–miRNAs–mRNAs interaction network was built to investigate potential function of circRNAs. Three up-regulated circRNAs (hsa_circ_0014235, hsa_circ_0025580 and hsa_circ_0026403) were implied to participate in cancer-related pathways. QRT-PCR experiment confirmed the up-regulation of hsa_circ_0014235 and hsa_circ_0025580. Finally, clinical studies indicated that hsa_circ_0014235 and hsa_circ_0025580 could serve as novel diagnostic biomarkers for LUSC. Taken together, our study revealed exosomal circRNAs expression profile in LUSC for the first time and showed the important diagnostic potential for circRNAs in LUSC.

Exosomes in hepatocellular carcinoma microenvironment and their potential clinical application value

Hepatocellular carcinoma (HCC) has become a challenging disease in the world today. Due to the limitations on the current diagnosis and treatment as well as its high metastatic ability and high recurrence rate, HCC gradually becomes the second deadliest tumor. Exosomes are one of the types of cell-derived vesicles and can carry intracellular materials such as genetic materials, lipids, and proteins. In recent years, it has been verified that exosomes are linked to numerous physiological and pathological processes, including HCC. However, how exosomes affect HCC progression remains largely unknown. In this review, the exosome-mediated cellular material transfer between cells of different types in the HCC microenvironment and their effects on the behaviors and functions of recipient cells are studied. Furthermore, we also addressed the underlying molecular mechanisms. We believe that new light on the diagnosis of this cancer as well as its treatment strategies will be shed after a collation of literature in this area.

Exosomal Non-Coding RNAs: Regulatory and Therapeutic Target of Hepatocellular Carcinoma

Exosomes are small extracellular vesicles secreted by most somatic cells, which can carry a variety of biologically active substances to participate in intercellular communication and regulate the pathophysiological process of recipient cells. Recent studies have confirmed that non-coding RNAs (ncRNAs) carried by tumor cell/non-tumor cell-derived exosomes have the function of regulating the cancerous derivation of target cells and remodeling the tumor microenvironment (TME). In addition, due to the unique low immunogenicity and high stability, exosomes can be used as natural vehicles for the delivery of therapeutic ncRNAs in vivo. This article aims to review the potential regulatory mechanism and the therapeutic value of exosomal ncRNAs in hepatocellular carcinoma (HCC), in order to provide promising targets for early diagnosis and precise therapy of HCC.

Peripheral Blood Genetic Biomarkers for the Early Diagnosis of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide and has high mortality. Biomarkers related to HCC, such as alpha-fetoprotein, and imaging technology, such as ultrasound and computed tomography, have been used to screen and monitor HCC, but HCC is still difficult to diagnose effectively in the early stage due to the low sensitivity of the above mentioned traditional methods. There is an urgent need for noninvasive biomarkers to facilitate the screening and early diagnosis of HCC. With the advancement of next-generation sequencing, genetic biomarkers are becoming the core of cancer diagnosis. Genetic biomarkers such as peripheral blood circulating tumor DNA, microRNAs, long noncoding RNAs, circular RNAs, and exosomes have become the focus of early HCC diagnostics. HCC genetic biomarkers have been implemented in clinical practice. In this review, we describe the available literature on peripheral blood genetic biomarkers in the diagnosis of early HCC.

Exosome in Hepatocellular Carcinoma: an update

Hepatocellular carcinoma (HCC) is a common malignant tumor in the digestive tract with limited therapeutic choices. Intercellular communication among cancer cells and their microenvironment is crucial to disease progression. Exosomes are extracellular vesicles secreted by multiple types of cells into the extracellular space, which contain a variety of active components of secretory cells, including lipids, proteins, RNA and DNA. This vesicle structure involves in the exchange of materials and information between cells and plays an important role in the development of many diseases. Studies have shown that exosomes participate in the communication between HCC cells and non-HCC cells and regulate the occurrence and development of hepatocellular carcinoma. Therefore, exosomes may be specific biomarkers for early diagnosis and metastasis of HCC, which are also potential targets for the treatment of HCC. This review summarizes the characteristic, types and biological functions of exosomes and discusses their research progress and application prospects in the diagnosis and treatment of HCC.

The Latest Overview of circRNA in the Progression, Diagnosis, Prognosis, Treatment, and Drug Resistance of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the main causes of tumor-related deaths worldwide. Due to the lack of obvious early symptoms and the lack of sensitive screening indicators in the early stage of HCC, the vast majority of patients are diagnosed with advanced or metastatic HCC, resulting in dissatisfactory treatment result. Therefore, it is urgent to determine effective and sensitive diagnostic and prognostic indicators and to determine new therapeutic targets. Circular RNA (circRNA) is a type of non-coding RNA that has been neglected for a long time. In recent years, it has been proved to play an important role in the development of many human diseases. Increasing evidence shows that change in circRNA expression has an extensive effect on the biological behavior of HCC. In this study, we comprehensively tracked the latest progress of circRNA in the pathogenesis of HCC, and reviewed its role as a biomarker for diagnosis and prognosis prediction in patients with HCC. In addition, we also summarized the potential of circRNA as therapeutic target in HCC and its relationship with HCC drug resistance, providing clues for the clinical development of circRNA-based therapeutic strategies.

Role of circular RNAs in colorectal tumor microenvironment

Circular RNAs (circRNAs) are a class of endogenous noncoding RNA, which were previously considered as a byproduct of RNA splicing error. Numerous studies have demonstrated the altered expression of circRNAs in organ tissues during pathological conditions and their involvements in disease pathogenesis and progression, including cancers. In colorectal cancer (CRC), multiple circRNAs have been identified and characterized as "oncogenic", given their involvements in the downregulation of tumor suppressor genes and induction of tumor initiation, progression, invasion, and metastasis. Additionally, other circRNAs have been identified in CRC and characterized as "tumor suppressive" based on their ability of inhibiting the expression of oncogenic genes and suppressing tumor growth and proliferation. circRNAs could serve as potential diagnostic and prognostic biomarkers, and therapeutic targets or vectors to be utilized in cancer therapies. This review briefly describes the dynamic changes of the tumor microenvironment inducing immunosuppression and tumorigenesis, and outlines the biogenesis and characteristics of circRNAs and recent findings indicating their roles and functions in the CRC tumor microenvironment. It also discusses strategies and technologies, which could be employed in the future to overcome current cancer therapy challenges associated with circRNAs.

The Roles of circRNAs in Liver Cancer Immunity

Circular RNAs (circRNAs) are stable covalently closed non-coding RNAs (ncRNAs). Many studies indicate that circRNAs are involved in the pathological and physiological processes of liver cancer. However, the functions of circRNAs in liver cancer immunity are less known. In this review, we summarized the functions of circRNAs in liver cancer, including proliferative, metastasis and apoptosis, liver cancer stemness, cell cycle, immune evasion, glycolysis, angiogenesis, drug resistance/sensitizer, and senescence. Immune escape is considered to be one of the hallmarks of cancer development, and circRNA participates in the immune escape of liver cancer cells by regulating natural killer (NK) cell function. CircRNAs may provide new ideas for immunotherapy in liver cancer.

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.

Recent Update on the Role of Circular RNAs in Hepatocellular Carcinoma

After being overlooked for decades, circular RNAs (circRNAs) have recently generated considerable interest. circRNAs play a role in a variety of normal and pathological biological processes, including hepatocarcinogenesis. Many circRNAs contribute to hepatocarcinogenesis through sponging of microRNAs (miRs) and disruption of cellular signaling pathways that play a part in control of cell proliferation, metastasis and apoptosis. In most cases, overexpressed circRNAs sequester miRs to cause de-repressed translation of mRNAs that encode oncogenic proteins. Conversely, low expression of circRNAs has also been described in hepatocellular carcinoma (HCC) and is associated with inhibited production of tumor suppressor proteins. Other functions of circRNAs that contribute to hepatocarcinogenesis include translation of truncated proteins and acting as adapters to regulate influence of transcription factors on target gene expression. circRNAs also affect hepatocyte transformation indirectly. For example, the molecules regulate immune surveillance of cancerous cells and influence the liver fibrosis that commonly precedes HCC. Marked over- or under-expression of circRNA expression in HCC, with correlating plasma concentrations, has diagnostic utility and assays of these RNAs are being developed as biomarkers of HCC. Although knowledge in the field has recently surged, the myriad of described effects suggests that not all may be vital to hepatocarcinogenesis. Nevertheless, investigation of the role of circRNAs is providing valuable insights that are likely to contribute to improved management of a serious and highly aggressive cancer.

Circulating Long and Circular Noncoding RNA as Non-Invasive Diagnostic Tools of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most common causes of cancer-related death worldwide, partially due to late diagnosis of the disease. Growing evidence in the field of biomarker discovery has shown the promising use of nucleic acid in the early detection of many cancers, including HCC. Here, we review data on how various long noncoding RNAs (lncRNAs) and circular RNAs (circRNAs) could be used as a diagnostic tool for HCC being differentially expressed in HCC compared to non-HCC patients. These non-coding RNAs (ncRNAs) showed high stability in the blood being present as free-circulating molecules or encapsulated into exosomes. This review reports some recent evidence on the use of lncRNAs and circRNAs as possible diagnostic biomarkers for HCC. Further, their pathophysiological mechanism in liver carcinogenesis was also described, elucidating the complex regulatory networks making these ncRNAs of particular relevance for the study of liver malignancy cancer.

Exosomal circRNAs: A new star in cancer

As a disease that seriously endangers human health, cancer still lacks effective treatment because of its complicated mechanism of action. Currently, an emerging class of RNAs, named circular RNAs (circRNAs), has been found to be closely related to cancer. CircRNAs have a stable closed loop structure which would be hardly degraded in blood or body fluids. Exosomes are found naturally in a variety of cells, mediating cell-to-cell communication, or participating in multiple processes of tumor development. Researchers have found that abnormally expressed circRNAs may be associated with the occurrence and development of malignancies. As a kind of exosome-derived non-coding RNAs, exosomal circRNAs have also played important roles in cancer progression and acted as diagnostic and prognostic biomarkers for cancer, and thus arousing more and more attention. This article reviews the functions, mechanisms and values of the exosomal circRNAs in tumors in order to provide new ideas and novel biomarkers for the diagnosis and treatment of cancer.

Exosomal circRNAs as novel cancer biomarkers: Challenges and opportunities

Identifying high specificity and sensitivity biomarkers has always been the focus of research in the field of non-invasive cancer diagnosis. Exosomes are extracellular vesicles with a lipid bilayer membrane that can be released by all types of cells, which contain a variety of proteins, lipids, and a variety of non-coding RNAs. Increasing research has shown that the lipid bilayer can effectively protect the nucleic acid in exosomes. In cancers, tumor cell-derived exosomal circRNAs can act on target cells or organs through the transport of exosomes, and then participate in the regulation of tumor development and metastasis. Since exosomes exist in various body fluids and circRNAs in exosomes exhibit high stability, exosomal circRNAs have the potential as biomarkers for early and minimally invasive cancer diagnosis and prognosis judgment. In this review, we summarized circRNAs and their biological roles in cancers, with the emerging value biomarkers in cancer diagnosis, disease judgment, and prognosis observation. In addition, we briefly compared the advantages of exosomal circRNAs as biomarkers and the current obstacles in the exosome isolation technology, shed light to the future development of this technology.

Circular RNAs in body fluids as cancer biomarkers: the new frontier of liquid biopsies

Cancer is a leading cause of death worldwide, particularly because of its high mortality rate in patients who are diagnosed at late stages. Conventional biomarkers originating from blood are widely used for cancer diagnosis, but their low sensitivity and specificity limit their widespread application in cancer screening among the general population. Currently, emerging studies are exploiting novel, highly-accurate biomarkers in human body fluids that are obtainable through minimally invasive techniques, which is defined as liquid biopsy. Circular RNAs (circRNAs) are a newly discovered class of noncoding RNAs generated mainly by pre-mRNA splicing. Following the rapid development of high-throughput transcriptome analysis techniques, numerous circRNAs have been recognized to exist stably and at high levels in body fluids, including plasma, serum, exosomes, and urine. CircRNA expression patterns exhibit distinctly differences between patients with cancer and healthy controls, suggesting that circRNAs in body fluids potentially represent novel biomarkers for monitoring cancer development and progression. In this study, we summarized the expression of circRNAs in body fluids in a pan-cancer dataset and characterized their clinical applications in liquid biopsy for cancer diagnosis and prognosis. In addition, a user-friendly web interface was developed to visualize each circRNA in fluids (https://mulongdu.shinyapps.io/circrnas_in_fluids/).

Cisplatin-resistant osteosarcoma cell-derived exosomes confer cisplatin resistance to recipient cells in an exosomal circ_103801-dependent manner

Studies have shown that exosomes can mediate the chemoresistance of drug-resistant cells by transmitting circular RNAs (circRNAs). However, the role of exosome-derived hsa_circ_103801 (exosomal hsa_circ_103801) in osteosarcoma (OS) remains unclear. The level of hsa_circ_103801 was upregulated in the serum exosomes from patients with OS, and OS patients with high hsa_circRNA_103801 expression had a shorter survival time relative to patients with low hsa_circ_103801 expression. The expression of hsa_circ_103801 was upregulated in cisplatin-resistant MG63 (MG63/CDDP) cells compared with that in MG63 cells. In addition, hsa_circ_103801 was highly enriched in exosomes derived from CDDP-resistant OS cells and could be delivered to MG63 and U2OS cells through exosomes. Exosomes derived from CDDP-resistant cells were shown to reduce the sensitivity of MG63 and U2OS cells to CDDP, inhibit apoptosis, and increase the expression of multidrug resistance-associated protein 1 and P-glycoprotein. Moreover, exosomal hsa_circ_103801 could strengthen the promotive effect of exosomes on the chemoresistance of MG63 and U2OS cells to CDDP. Hence, serum exosomal hsa_circ_103801 may serve as an effective prognostic biomarker for OS, and exosomal hsa_circ_103801 could be a potential target for overcoming OS chemoresistance.

Exosomal circRNAs: Sorting Mechanisms, Roles and Clinical Applications in Tumors

Exosomes are a group of nano-sized membrane vesicles and are important mediators of intercellular communication, particularly in tumor microenvironment. Recently, researchers have found that circular RNAs (circRNAs), with the great research significance, are enriched and stable in exosomes. In this review, we summarize the research significance of exosomal circRNAs, sorting mechanisms and their functioning mechanisms in tumor progression. Their clinical applications as clinical tumor biomarkers and as therapeutic targets in inhibiting tumor metastasis, anti-cancer immunity response and drug resistance have been widely discussed.

Extracellular vesicles as biomarkers in liver diseases: A clinician's point of view

Extracellular vesicles are membrane-bound vesicles containing proteins, lipids, RNAs and microRNAs. They can originate from both healthy and stressed cells, and provide a snapshot of the cell of origin in physiological and pathological circumstances. Various processes that may give rise to the release of extracellular vesicles occur in liver diseases, including hepatocyte apoptosis, hepatic stellate cell activation, liver innate immune system activation, systemic inflammation, and organelle dysfunction (mitochondrial dysfunction and endoplasmic reticulum stress). Numerous studies have therefore investigated the potential role of extracellular vesicles as biomarkers in liver diseases. This review provides an overview of the methods that can be used to measure extracellular vesicle concentrations in clinical settings, ranging from plasma preparation to extracellular vesicle measurement techniques, as well as looking at the challenges of using extracellular vesicles as biomarkers. We also provide a comprehensive review of studies that test extracellular vesicles as diagnostic, severity and prognostic biomarkers in various liver diseases, including non-alcoholic and alcoholic steatohepatitis, viral hepatitis B and C infections, cirrhosis, primary liver cancers, primary sclerosing cholangitis and acute liver failure. In particular, extracellular vesicles could be useful tools to evaluate activity and fibrosis in non-alcoholic fatty liver disease, predict risk of hepatitis B virus reactivation, predict complications and mortality in cirrhosis, detect early hepatocellular carcinoma, detect malignant transformation in primary sclerosing cholangitis and predict outcomes in acute liver failure. While most studies draw on data derived from pilot studies, which still require clinical validation, some extracellular vesicle subpopulations have already been evaluated in solid prospective studies.

The emerging roles of exosomes in anti-cancer drug resistance and tumor progression: An insight towards tumor-microenvironment interaction

The tumor microenvironment (TME) is a complex network of cellular organization consisting of fibroblasts, adipocytes, pericytes, immune cells endothelial cells, and extracellular matrix proteins. Besides communicating with each other, tumor cells are also involved in the tumor stroma interaction. Presently, most of the studies have focused on the contribution of TME in supporting tumor growth through intercellular communication by physical contact between the cells or through paracrine signaling cascades of growth factors and cytokines. The crosstalk between the tumor and TME has a pivotal role in the development of anti-cancer drug resistance. Drug resistance, be it against targeted or non-targeted drugs, has emerged as a major hurdle in the successful therapeutic intervention of cancer. Among the several mechanisms involved in the development of the resistance to anti-cancer therapies, exosomes have recently come into the limelight. Exosomes are the nano-sized vesicles, originated from the endolysosomal compartments and have the inherent potential to shuttle diverse biomolecules like proteins, lipids, and nucleic acids to the recipient cells. There are also instances where the pharmacological compounds are transferred between the cells via exosomes. For instance, the transfer of the cargoes from the drug-resistant tumor cells immensely affects the recipient drug-sensitive cells in terms of their proliferation, survival, migration, and drug resistance. In this review, we have discussed multiple aspects of the exosome-mediated bidirectional interplay between tumor and TME. Furthermore, we have also emphasized the contribution of exosomes promoting drug resistance and therapeutic strategies to mitigate the exosome induced drug resistance as well.

Advances on liver cell-derived exosomes in liver diseases

Exosomes are extracellular vesicles with diameters ranging from 30 to 150 nm, which contain several donor cell‐associated proteins as well as mRNA, miRNA, and lipids and coordinate multiple physiological and pathological functions through horizontal communication between cells. Almost all types of liver cells, such as hepatocytes and Kupffer cells, are exosome‐releasing and/or exosome‐targeted cells. Exosomes secreted by liver cells play an important role in regulating general physiological functions and also participate in the onset and development of liver diseases, including liver cancer, liver injury, liver fibrosis and viral hepatitis. Liver cell‐derived exosomes carry liver cell‐specific proteins and miRNAs, which can be used as diagnostic biomarkers and treatment targets of liver disease. This review discusses the functions of exosomes derived from different liver cells and provides novel insights based on the latest developments regarding the roles of exosomes in the diagnosis and treatment of liver diseases.

Isolation and characterization of exosomes for cancer research

Exosomes are a subset of extracellular vesicles that carry specific combinations of proteins, nucleic acids, metabolites, and lipids. Mounting evidence suggests that exosomes participate in intercellular communication and act as important molecular vehicles in the regulation of numerous physiological and pathological processes, including cancer development. Exosomes are released by various cell types under both normal and pathological conditions, and they can be found in multiple bodily fluids. Moreover, exosomes carrying a wide variety of important macromolecules provide a window into altered cellular or tissue states. Their presence in biological fluids renders them an attractive, minimally invasive approach for liquid biopsies with potential biomarkers for cancer diagnosis, prediction, and surveillance. Due to their biocompatibility and low immunogenicity and cytotoxicity, exosomes have potential clinical applications in the development of innovative therapeutic approaches. Here, we summarize recent advances in various technologies for exosome isolation for cancer research. We outline the functions of exosomes in regulating tumor metastasis, drug resistance, and immune modulation in the context of cancer development. Finally, we discuss prospects and challenges for the clinical development of exosome-based liquid biopsies and therapeutics.

Circular RNAs in liver diseases: Mechanisms and therapeutic targets

Circular RNAs (circRNAs) are formed from the genome through diverse back splicing and feature the closed loop. circRNAs are widely available in a variety of cells and characterized by conservation, structural stability, high abundance and tissue-specific or developmental-specific expression. Recent studies have shown that circRNAs are closely related to liver diseases, such as metabolic-associated fatty liver disease, hepatitis, liver cirrhosis and hepatocellular carcinoma. circRNAs play an important role in the progression of liver diseases, are potential diagnostic and prognostic markers, and have translational value in therapy. This article reviews the research on circRNAs in liver diseases, with a view to providing a theoretical basis and new ideas for future research and treatment of liver diseases.

Circular RNAs: Emerging Role in Cancer Diagnostics and Therapeutics

Circular RNAs (circRNAs) are rapidly coming to the fore as major regulators of gene expression and cellular functions. They elicit their influence via a plethora of diverse molecular mechanisms. It is not surprising that aberrant circRNA expression is common in cancers and they have been implicated in multiple aspects of cancer pathophysiology such as apoptosis, invasion, migration, and proliferation. We summarize the emerging role of circRNAs as biomarkers and therapeutic targets in cancer.

EVs as Potential New Therapeutic Tool/Target in Gastrointestinal Cancer and HCC

For more than a decade, extracellular vesicles (EVs) have been in focus of science. Once thought to be an efficient way to eliminate undesirable cell content, EVs are now well-accepted as being an important alternative to cytokines and chemokines in cell-to-cell communication route. With their cargos, mainly consisting of functional proteins, lipids and nucleic acids, they can activate signalling cascades and thus change the phenotype of recipient cells at local and systemic levels. Their substantial role as modulators of various physiological and pathological processes is acknowledged. Importantly, more and more evidence arises that EVs play a pivotal role in many stages of carcinogenesis. Via EV-mediated communication, tumour cells can manipulate cells from host immune system or from the tumour microenvironment, and, ultimately, they promote tumour progression and modulate host immunity towards tumour's favour. Additionally, the role of EVs in modulating resistance to pharmacological and radiological therapy of many cancer types has become evident lately. Our understanding of EV biology and their role in cancer promotion and drug resistance has evolved considerably in recent years. In this review, we specifically discuss the current knowledge on the association between EVs and gastrointestinal (GI) and liver cancers, including their potential for diagnosis and treatment.

The functions and clinical significance of circRNAs in hematological malignancies

With covalently closed circular structures, circular RNAs (circRNAs) were once misinterpreted as by-products of mRNA splicing. Being abundant, stable, highly conserved, and tissue-specific, circRNAs are recently identified as a type of regulatory RNAs. CircRNAs bind to certain miRNAs or proteins to participate in gene transcription and translation. Emerging evidence has indicated that the dysregulation of circRNAs is closely linked to the tumorigenesis and treatment response of hematological malignancies. CircRNAs play critical roles in various biological processes, including tumorigenesis, drug resistance, tumor metabolism, autophagy, pyroptosis, and ferroptosis. The N6-methyladenosine modification of circRNAs and discovery of fusion-circRNAs provide novel insights into the functions of circRNAs. Targeting circRNAs in hematological malignancies will be an attractive treatment strategy. In this review, we systematically summarize recent advances toward the novel functions and molecular mechanisms of circRNAs in hematological malignancies, and highlight the potential clinical applications of circRNAs as novel biomarkers and therapeutic targets for future exploration.

The Potential of Circular RNAs as Cancer Biomarkers

Circular RNA (circRNA) is a covalently closed RNA structure that has several proposed functions related to cancer development. Recently, cancer-specific and tissue-specific circRNAs have been identified by high-throughput sequencing and are curated in publicly available databases. CircRNAs have features that are ideal properties of biomarkers, including conservation, abundance, and stability in plasma, saliva, and urine. Many circRNAs with predictive and prognostic significance in cancer have been described, and functional mechanisms for some circRNAs have been suggested. CircRNA also has great potential as a noninvasive biomarker for early cancer detection, although further investigation is necessary before clinical application is feasible.See all articles in this CEBP Focus section, "NCI Early Detection Research Network: Making Cancer Detection Possible."

Emerging Roles of Exosomal Circular RNAs in Cancer

Circular RNA (circRNA) is a type of non-coding RNA that forms a covalently closed continuous loop. The expression pattern of circRNA varies among cell types and tissues, and many circRNAs are aberrantly expressed in various cancers. Aberrantly expressed circRNAs have been shown to play crucial roles in carcinogenesis, functioning as microRNA sponges or new templates for protein translation. Recent research has shown that circRNAs are enriched in exosomes. Exosomes are secretory vesicles that mediate intercellular communication through the delivery of cargo, including proteins, lipids, DNA, and RNA. Exosome-mediated crosstalk between cancer cells and the tumor microenvironment promotes the epithelial-mesenchymal transition, angiogenesis, and immune escape, and thus may contribute to cancer invasion and metastasis. In this review, we discuss the biological functions of exosomal circRNAs and their significance in cancer progression. Additionally, we discuss the potential clinical applications of exosomal circRNAs as biomarkers and in cancer therapy.

Circular RNAs and cancer: Opportunities and challenges

Circular RNAs (circRNAs) are covalently circularized RNA moieties that despite being relatively abundant were only recently identified and have only begun to be investigated within the last couple of years. Even though there are many thousands of genes that appear capable of producing circRNAs, and the fact that many circRNAs appear to be highly evolutionarily conserved, the function of all but a few remain to be fully explored. What has been determined, however, is that circRNAs play key regulatory roles in many aspects of biology with focus being given to their function in cancer. Most of the studies to date have found that circRNAs act as master regulator of gene expression most often than not acting to regulate levels though sequestration or "sponging" of other gene expression regulators, particularly miRNAs. They can also function directly modulating transcription, or by interfering with splicing mechanisms. Some circRNAs can also be translated into functional proteins or peptides. A combination of tissue and developmental stage specific expression along with an innate resistance to RNAse activity means that circRNAs show perhaps their greatest potential as novel biomarkers of cancer. In this chapter we consider the current state of knowledge regarding these molecules, their synthesis, function, and association with cancer. We also consider some of the challenges that remain to be overcome to allow this emerging class of RNAs to fulfill their potential in clinical practice.