Exosomal circRNA derived from gastric tumor promotes white adipose browning by targeting the miR-133/PRDM16 pathway

Circular RNA as a Potential Biomarker for Melanoma: A Systematic Review

Circular RNAs (circRNAs) are newly discovered RNAs with covalently looped structures. Due to their resistance to RNAase degradation and tissue-specific expression, circRNAs are expected to be potential biomarkers in early diagnosis and target treatment of many diseases. However, the role of circRNAs in melanoma still needs to be systematically reviewed for better understanding and further research. Based on published articles in PubMed, Embase, Cochrane Library, and Web of Science database, we systematically reviewed the implications and recent advances of circRNAs in melanoma, focusing on function, mechanism, and correlation with melanoma progression. According to inclusion and exclusion criteria, a total of 19 articles were finally included in this systematic review. Of the 19 studies, 17 used human samples, including melanoma tissues (n = 16) and blood serum of patients with melanoma (n = 1). The sample size of the study group ranged from 20 to 105 based on the reported data. Several studies explored the association between circRNAs and clinicopathological characteristics. circRNA dysregulation was commonly observed in melanoma patients. circRNAs function in melanoma by miRNA sponging and interaction with RNA binding proteins (RBP), ultimately controlling several important signaling pathways and cancer-related cellular processes, including proliferation, migration, invasion, metastasis, apoptosis, and glucose metabolism. circRNA expression could be associated with prognostic factors and drug responses, consolidating the potential clinical value in melanoma. Herein, we clarified the functional, prognostic, and predictive roles of circRNAs in melanoma in this systematic review, providing future directions for studies on melanoma-associated circRNAs.

Insights into circular RNAs: their biogenesis, detection, and emerging role in cardiovascular disease

Circular RNAs (circRNAs) are an evolutionarily conserved form of noncoding RNA with covalently closed loop structures. Initial studies established a functional role for circRNAs as potent microRNA sponges and many other studies have focussed solely on this. However, the biological functions of most circRNAs are still undetermined and other functional roles are gaining traction. These include protein sponges and regulators, and coding for proteins with an alternative mechanism of translation, potentially opening up a whole new transcriptome. The first step to gaining insight into circRNA function is accurate identification and various software platforms have been developed. Specialized detection software has now evolved into whole bioinformatics pipelines that can be used for detection, de novo identification, functional prediction, and validation of circRNAs. However, few cardiovascular circRNA studies have utilized these tools. This review summarizes current knowledge of circRNA biogenesis, bioinformatic detection tools and the emerging role of circRNAs in cardiovascular disease.

Identification of low-dose radiation-induced exosomal circ-METRN and miR-4709-3p/GRB14/PDGFRα pathway as a key regulatory mechanism in Glioblastoma progression and radioresistance: Functional validation and clinical theranostic significance

Glioblastoma is a central nervous malignancy with a very poor prognosis. This study attempted to explore the role of exosomes induced by low-dose radiation-induced (ldrEXOs) and ldrEXOs-derived circ-METRN in glioblastoma progression and radioresistance at the molecular, cellular, animal, and clinical levels. Results in the present study revealed that low-dose radiation stimulated the secretion of ldrEXOs which delivered high levels of circ-METRN. And circ-METRN-abundant ldrEXOs increased the expression of γ-H2AX, indicating an efficient DNA damage-repair process in glioblastoma cells. The ldrEXOs-derived circ-METRN enhanced the glioblastoma progression and radioresistance via miR-4709-3p/GRB14/PDGFRα pathway. Up-regulating PDGFRα can rescue the tumor-promoting function of ldrEXOs in groups previously treated with inhibition of GRB14. Additionally, in-vivo experiments revealed that treatments with ldrEXOs promoted the growth of xenografted tumors and shortened the survival period. Furthermore, clinical researches indicated that circ-METRN may be transported into the bloodstream by exosomes in the early stages of fractionated radiotherapy. It has important clinical values to detect the serum exosomal circ-METRN in the early stage of radiotherapy, which is not only conducive to predict radioresistance and prognosis but also to assist MRI diagnosis in detecting the very early recurrence of glioblastoma. In summary, this study reveals for the first time that low-dose radiation-induced exosomal circ-METRN plays an oncogenic role in glioblastoma progression and radioresistance through miR-4709-3p/GRB14/PDGFRα pathway, providing mechanistic insights into the roles of circRNAs and a valuable marker for therapeutic targets in glioblastoma.

CircRNA in cancer: Fundamental mechanism and clinical potential

Circular RNAs (CircRNAs) are a class of single-stranded noncoding RNAs that are formed in a circular conformation via non-canonical splicing or back-splicing events. Aberrant expressions of many circRNAs are observed in diverse cancers, indicating their crucial roles in tumorigenesis and tumor development. Recently, several pieces of evidence have revealed that many circRNAs are involved in the promotion or suppression of cancers to varying degrees via different molecular mechanisms. Here in this review, we present a summary of the characteristics, types, biogenesis, and functions of circRNAs, and outline a series of the most recently studied circRNAs and their functional mechanisms in multiple cancer types with future perspectives. With great advances in nucleic acid-based therapeutic tools, circRNAs could be further explored as targetable molecules in future cancer treatments.0.

Recent Advances on Extracellular Vesicles in Central Nervous System Diseases

Extracellular vesicles (EVs) are particles released by multiple cells, encapsulated by lipid bilayers and containing a variety of biological materials, including proteins, nucleic acids, lipids and metabolites. With the advancement of separation and characterization methods, EV subtypes and their complex and diverse functions have been recognized. In the central nervous system (CNS), EVs are involved in various physiological and pathological processes, such as regulation of neuronal firing, synaptic plasticity, formation and maintenance of myelin sheath, propagation of neuroinflammation, neuroprotection, and spread and removal of toxic protein aggregates. Activity-dependent alteration of constituents enables EVs to reflect the change of cell and tissue states, and the wide distribution of EVs in biological fluids endows them with potential as diagnostic and prognostic biomarkers for CNS diseases, including neurodegenerative disease, cerebrovascular disease, traumatic brain disease, and brain tumor. Favorable biocompatibility, ability of crossing the blood–brain barrier and protecting contents from degradation, give promising therapeutic effects of EVs, either collected from mesenchymal stem cells culture conditioned media, or designed as drug delivery vehicles loaded with specific agents. In this review, we summarized EVs’ basic biological properties, and mainly focused on their applications in CNS diseases.

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.

Circular RNA ITCH suppresses metastasis of gastric cancer via regulating miR-199a-5p/Klotho axis

Circular RNAs (circRNAs) are considered as a new regulatory factor in growth, metastasis and therapeutic resistance of human cancers. But the clinical significance and underlying mechanism of circular RNA ITCH (circ-ITCH) in gastric cancer (GC) remain unknown. In the present study, we found that circ-ITCH was down-regulated in GC cell lines, GC tissues and their serum-derived exosomes. The level of circ-ITCH was related to invasion depth. Functional assays showed that circ-ITCH overexpression inhibited the proliferation, migration, invasion and epithelial mesenchymal transition (EMT) of GC cells, whereas circ-ITCH knockdown appeared an opposite effect. Bioinformatic analysis and luciferase reporter assay confirmed that circ-ITCH acted as miR-199a-5p sponge and increased the level of Klotho. The expression level of miR-199-5p was up-regulated in GC tissues and negatively correlated with that of circ-ITCH. MiR-199a-5p mimics reversed the effects on inhibiting metastasis induced by circ-ITCH overexpression and decreased the level of Klotho in GC cells. Our findings indicate that circ-ITCH suppresses metastasis of GC by acting as the sponge of miR-199a-5p and increasing Klotho expression, which serves as a potential biomarker and targets for the diagnosis and therapy of GC.Abbreviations: CircRNAs: circular RNAs; GC: gastric cancer; circ-ITCH: circular RNA Itchy E3 ubiquitin protein ligase; ceRNA: competitive endogenous RNA; EMT: Epithelial-mesenchymal transition; siRNA: Small interfering RNA; TEM: transmission electron microscope; NTA: nanoparticle tracking analysis.

CircNRIP1 Modulates the miR-515-5p/IL-25 Axis to Control 5-Fu and Cisplatin Resistance in Nasopharyngeal Carcinoma

Background

The development of drug resistance leads many NPC patients to experience disease relapse following the completion of chemotherapy. It is thus essential that the mechanistic basis for such chemoresistance be clarified in an effort to identify approaches to sensitizing NPC tumors to treatment with cisplatin and related agents.

Methods

A qRT-PCR approach was used to measure the expression of circNRIP1 in NPC, while luciferase assays were used to identify interactions with downstream targets of circNRIP1 activity including miR-515-5p and IL-25. CCK8 assays were also utilized to detect IC50 values for cisplatin and 5-Fu.

Results

The expression of circNRIP1 was significantly increased in the serum of chemoresistant NPC patients. At a functional level, we determined that circNRIP1 is able to sequester miR-515-5p, thereby inhibiting its ability to post-transcriptionally suppress IL-25 expression. We observed a significant negative correlation between the expression of miR-515-5p and circNRIP1 in serum samples from chemoresistant NPC patients, consistent with a functional interaction between these two factors. We further found that 5-Fu and CDDP IC50 values in NPC cells in which circNRIP1 had been knocked down were restored following miR-515-5p inhibitor transfection. Similarly, changes in these IC50 values were reversed in NPC cells transfected with miR-515-5p mimics following the overexpression of IL-25 in these same cells.

Conclusion

These data highlight the circNRIP1/miR-515-5p/IL-25 as a novel regulator of 5-Fu and cisplatin resistance in NPC, suggesting that this pathway may be amenable to therapeutic targeting as an approach to treating this cancer type.

How progressive cancer endangers the heart: an intriguing and underestimated problem

Since it came into being as a discipline, cardio-oncology has focused on the prevention and treatment of cardiotoxicity induced by antitumor chemotherapy and radiotherapy. Over time, it has been proved that even more detrimental is the direct effect generated by cancer cells that release pro-cachectic factors in the bloodstream. Secreted molecules target different organs at a distance, including the heart. Inflammatory and neuronal modulators released by the tumor bulk, either as free molecules or through exosomes, contribute to the pathogenesis of cardiac disease. Progressive cancer causes cachexia and severe cardiac muscle wasting accompanied by cardiomyocyte atrophy, tissue fibrosis, and several functional impairments up to heart failure. The molecular mechanisms responsible for such a cardiac muscle wasting have been partially elucidated in animal models, but minimally investigated in humans, although severe cardiac dysfunction exacerbates global cachexia and hampers efficient anti-cancer treatments. This review provides an overview of cancer-induced structural cardiac and functional damage, drawing on both clinical and scientific research. We start by looking at the pathophysiological mechanisms and evolving epidemiology and go on to discuss prevention, diagnosis, and a multimodal policy of intervention aimed at providing overall prognosis and global care for patients. Despite much interest in the cardiotoxicity of cancer therapies, the direct tumor effect on the heart remains poorly explored. There is still a lack of diagnostic criteria for the identification of the early stages of cardiac disease in cancer patients, while the possibilities that there are for effective prevention are largely underestimated. Research on innovative therapies has claimed considerable advances in preclinical studies, but none of the molecular targets suitable for clinical application has been approved for therapy. These issues are critically discussed here.

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 RNA hsa_circ_0004277 Stimulates Malignant Phenotype of Hepatocellular Carcinoma and Epithelial-Mesenchymal Transition of Peripheral Cells

Accumulating evidence shows that exosomal circRNAs reflect the physiological status of donor cells, and various cell reactions are induced after exosomal circRNAs are captured by recipient cells. In this study, qRT-PCR was performed to detect circ-0004277 expression in hepatocellular carcinoma (HCC) cell lines, tissues, and plasma exosomes. The effects of circ-0004277 on the proliferation and migration of HCC cells were assessed by cell counting, 5-ethynyl-2'-deoxyuridine assays, Transwell migration assays, and tumor formation in nude mice. We found that circ-0004277 was significantly upregulated in HCC cells, tissues, and plasma exosomes compared to that in normal controls. Overexpression of circ-0004277 enhanced the proliferation, migration, and epithelial-mesenchymal transition (EMT) of HCC cells in vivo and in vitro. Furthermore, exosomes from HCC cells enhanced circ-0004277 expression in surrounding normal cells and stimulated EMT progression. ZO-1, a tight junction adapter protein, was downregulated in HCC tissues. In conclusion, our findings suggest that circ-0004277 promotes the malignant phenotype of HCC cells via inhibition of ZO-1 and promotion of EMT progression. In addition, exosomal circ-0004277 from HCC cells stimulates EMT of peripheral cells through cellular communication to further promote the invasion of HCC into normal surrounding tissues.

The Significance of Exosomal RNAs in the Development, Diagnosis, and Treatment of Gastric Cancer

Gastric cancer (GC) is one of the most common malignancies in the world. Exosomes, a subset of extracellular vesicles with an average diameter of 100 nm, contain and transfer a variety of functional macromolecules such as proteins, lipids, and nucleic acids. A large number of studies indicated that exosomes can play a significant role in the initiation and development of GC via facilitating intercellular communication between gastric cancer cells and microenvironment. Exosomal RNAs, one of the key functional cargos, are involved in the pathogenesis, development, and metastasis of GC. In addition, recent studies elucidated that exosomal RNAs may serve as diagnostic and prognostic biomarkers or therapeutic targets for GC. In this review, we summarized the function of exosomal RNA in the tumorigenesis, progression, diagnosis, and treatment of GC, which may further unveil the functions of exosome and promote the potentially diagnostic and therapeutic application of exosomes in GC.

CircRNAs: Emerging Bladder Cancer Biomarkers and Targets

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

Circular RNAs: Potential Applications as Therapeutic Targets and Biomarkers in Breast Cancer

Circular RNAs (circRNAs) are a class of non-coding RNAs that form a covalently closed loop. A number of functions and mechanisms of action for circRNAs have been reported, including as miRNA sponge, exerting transcriptional and translational regulation, interacting with proteins, and coding for peptides. CircRNA dysregulation has also been implicated in many cancers, such as breast cancer. Their relatively high stability and presence in bodily fluids makes cancer-associated circRNAs promising candidates as a new biomarker. In this review, we summarize the research undertaken on circRNAs associated with breast cancer, discuss circRNAs as biomarkers, and present circRNA-based therapeutic approaches.

Circular RNAs emerge as important regulators with great potential for clinical application in gastric cancer

Gastric cancer (GC) is a common digestive malignancy with a high-ranking morbidity and mortality. Therefore, it is urgent to identify novel indicators and develop new strategies for clinical diagnosis and treatment of GC. As a type of noncoding RNA, circular RNAs (circRNAs) have received increased attention in GC during recent years. To more comprehensively understand current research progress on circRNAs in GC, in this review, we introduce basic knowledge of circRNAs, summarize abnormally expressed circRNAs and discuss their functions and regulatory molecular mechanisms in GC. Then, we review potential applications of circRNAs for GC diagnosis, prognosis and treatment. Finally, we conclude by highlighting major advancements of circRNAs in GC research, and we discuss existing challenges and possible future research directions of GC-associated circRNAs.

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.

A circRNA-miRNA-mRNA regulatory network associated with the treatment response to tuberculosis

OBJECTIVES

The high morbidity and mortality of tuberculosis (TB) have severe socio-economic consequences, and there is an urgent need to explore the mechanisms driving TB development and progression. The aim of this study was to analyze the regulatory RNAs and target genes involved in TB, in order to identify key genetic biomarkers for diagnosing and treating TB.

METHODS

Circular RNAs (circRNAs), microRNAs (miRNAs) and messenger RNA (mRNAs) expression profiles of TB patients and healthy controls were downloaded from the GEO database. A circRNA-miRNA-mRNA competing endogenous RNA (ceRNA) network was constructed using the differentially expressed circRNAs (DEcircRNAs), miRNAs (DEmiRNAs), and mRNAs (DEmRNAs). The DEmRNAs in this network were functionally annotated using GO and KEGG analyses, and ordinal regression analysis was used to identify the genes correlated to the treatment response in TB patients.

RESULTS

We identified 133 DEmRNAs, 37 DEcircRNAs and 173 DEmiRNAs between the TB and healthy controls, from which 30 DECircRNAs, 27 DEmiRNAs and 35 DEmRNAs were used to construct the ceRNA network. CACNA1I, IGF2BP3, LPCAT2, SPOCK2 and IRF2 were significantly correlated with the anti-TB therapeutic response (P < 0.05).

CONCLUSION

A TB-associated DEcircRNA-miRNA-mRNA ceRNA network was constructed, of which some DEmRNAs potentially influence the treatment response.

Circular RNAs: Rising stars in lipid metabolism and lipid disorders

The underlying mechanisms of circular RNAs (circRNAs) in lipid metabolism regulation and the pathogenesis of lipid disorder diseases are clarified in this review. circRNAs are produced from host genes by back splicing and are mainly degraded by RNase L. circRNAs act as molecular sponges or scaffolds that bind with microRNAs or proteins and thus affect the intracorporeal processes of lipid metabolism. CircRNA_11897 and circSAMD4A facilitated adipogenesis while circH19 and circRNA_26852 accelerated adipolysis in adipose tissue. CircSAMD4A promoted the differentiation of preadipocytes, but circH19 and circFUT10 inhibited this differentiation. CircFUT10 also promoted the proliferation of preadipocytes. CiRS-133 fostered the browning of white adipose tissue. CircACC1, circRNA_021412, circRNA_0046366, and circRNA_0046367 promoted the mitochondrial β-oxidation of fatty acids in hepatocytes. CircRNA_021412 suppressed the synthesis of triglycerides in hepatocytes. CircScd1 inhibited hepatic lipid droplet formation. circ_0092317, circ_0003546, circ_0028198, circ_0092317, and circACC1 probably reduced cholesterol efflux from macrophages. circ_0037251 likely promoted lipid accumulation and inhibited lipophagy in macrophages. circRNAs participate in lipid metabolism regulation and affect the development of lipid disorder diseases.

Non-coding RNAs underlying chemoresistance in gastric cancer

BACKGROUND

Gastric cancer (GC) is a major health issue in the Western world. Current clinical imperatives for this disease include the identification of more effective biomarkers to detect GC at early stages and enhance the prevention and treatment of metastatic and chemoresistant GC. The advent of non-coding RNAs (ncRNAs), particularly microRNAs (miRNAs) and long-non coding RNAs (lncRNAs), has led to a better understanding of the mechanisms by which GC cells acquire features of therapy resistance. ncRNAs play critical roles in normal physiology, but their dysregulation has been detected in a variety of cancers, including GC. A subset of ncRNAs is GC-specific, implying their potential application as biomarkers and/or therapeutic targets. Hence, evaluating the specific functions of ncRNAs will help to expand novel treatment options for GC.

CONCLUSIONS

In this review, we summarize some of the well-known ncRNAs that play a role in the development and progression of GC. We also review the application of such ncRNAs in clinical diagnostics and trials as potential biomarkers. Obviously, a deeper understanding of the biology and function of ncRNAs underlying chemoresistance can broaden horizons toward the development of personalized therapy against GC.

Exosomal cargoes in OSCC: current findings and potential functions

Oral squamous cell carcinoma (OSCC) is the most prevalent malignancy in head and neck cancer, with high recurrence and mortality. Early diagnosis and efficient therapeutic strategies are vital for the treatment of OSCC patients. Exosomes can be isolated from a broad range of different cell types, implicating them as important factors in the regulation of human physiological and pathological processes. Due to their abundant cargo including proteins, lipids, and nucleic acids, exosomes have played a valuable diagnostic and therapeutic role across multiple diseases, including cancer. In this review, we summarize recent findings concerning the content within and participation of exosomes relating to OSCC and their roles in tumorigenesis, proliferation, migration, invasion, metastasis, and chemoresistance. We conclude this review by looking ahead to their potential utility in providing new methods for treating OSCC to inspire further research in this field.

Role of extracellular vesicles in tumour microenvironment

In recent years, it has been demonstrated that extracellular vesicles (EVs) can be released by almost all cell types, and detected in most body fluids. In the tumour microenvironment (TME), EVs serve as a transport medium for lipids, proteins, and nucleic acids. EVs participate in various steps involved in the development and progression of malignant tumours by initiating or suppressing various signalling pathways in recipient cells. Although tumour-derived EVs (T-EVs) are known for orchestrating tumour progression via systemic pathways, EVs from non-malignant cells (nmEVs) also contribute substantially to malignant tumour development. Tumour cells and non-malignant cells typically communicate with each other, both determining the progress of the disease. In this review, we summarise the features of both T-EVs and nmEVs, tumour progression, metastasis, and EV-mediated chemoresistance in the TME. The physiological and pathological effects involved include but are not limited to angiogenesis, epithelial-mesenchymal transition (EMT), extracellular matrix (ECM) remodelling, and immune escape. We discuss potential future directions of the clinical application of EVs, including diagnosis (as non-invasive biomarkers via liquid biopsy) and therapeutic treatment. This may include disrupting EV biogenesis and function, thus utilising the features of EVs to repurpose them as a therapeutic tool in immunotherapy and drug delivery systems. We also discuss the overall findings of current studies, identify some outstanding issues requiring resolution, and propose some potential directions for future research. Video abstract.

Exosomes derived from 5-fluorouracil-resistant colon cancer cells are enriched in GDF15 and can promote angiogenesis

Background: Angiogenesis is important for tumor proliferation and distant metastasis. However, the role of drug-resistant tumor cells in angiogenesis remains largely unknown. Current anti-angiogenic strategies also have limitations and it would be useful to develop novel targets and treatment strategies.

Methods: Differential ultracentrifugation was used to isolate conditioned medium-derived exosomes from 5-flurouracil (5-FU)-sensitive or -resistant colon cancer cells. Exosome endocytosis into human umbilical vein endothelial cells was observed via immunofluorescence. Differentially expressed proteins in the exosomes were confirmed via qRT-PCR and Western blotting. The angiogenic capacity of endothelial cells was evaluated using cell function assays and a rat model of abdominal aortic neovascularization. The underlying mechanisms were verified using qRT-PCR and Western blotting assays. Immunohistochemistry was used to evaluate in vivo angiogenesis.

Results: We observed that the conditioned medium and exosomes from 5-FU-resistant colon cancer cells could promote angiogenesis. Exosomal growth/differentiation factor 15 (GDF15) was a potent inducer of this angiogenesis in vitro by inhibiting the Smad signaling pathway, thus increasing periostin (POSTN) levels. Moreover, 5-FU-resistant colon cancer cells showed high microvascular density in vivo. TGF-β1, an activator of the Smad signaling pathway, could partly eliminate those effects.

Conclusions: Our study reveals the molecular regulation of angiogenesis in 5-FU-resistant colon cancer and suggests that the GDF15-POSTN axis may be a novel target for anti-angiogenic therapies in colon cancer.

Exosomal Secretion of Adipose Tissue during Various Physiological States

Exosomes are secreted extracellular vesicles containing a wide array of biologically active components. Recent studies have demonstrated that exosomes serve as an important vehicle for extracellular communication and exert systemic effects on the physiology of organisms. Adipose tissues (ATs) play a key role in balancing systemic energy homeostasis as a central hub for fatty acid metabolism. At the same time, proper endocrine function of ATs has also been shown to be crucial for regulating physiological and metabolic health. The endocrine function of ATs is partially mediated by AT-derived exosomes that regulate metabolic homeostasis, such as insulin signaling, lipolysis, and inflammation. During the pathogenesis of obesity, metabolic syndrome, and cancer, exosomes shed by the resident cells in ATs may also have a role in regulating the progression of these diseases along with associated pathologies. In this review, we summarize the contents of AT-derived exosomes and their effects on various cell populations along with possible underlying molecular mechanisms. We further discuss the potential applications of exosomes as a drug delivery tool and therapeutic target.

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.

RNA delivery by extracellular vesicles in mammalian cells and its applications

The term 'extracellular vesicles' refers to a heterogeneous population of vesicular bodies of cellular origin that derive either from the endosomal compartment (exosomes) or as a result of shedding from the plasma membrane (microvesicles, oncosomes and apoptotic bodies). Extracellular vesicles carry a variety of cargo, including RNAs, proteins, lipids and DNA, which can be taken up by other cells, both in the direct vicinity of the source cell and at distant sites in the body via biofluids, and elicit a variety of phenotypic responses. Owing to their unique biology and roles in cell-cell communication, extracellular vesicles have attracted strong interest, which is further enhanced by their potential clinical utility. Because extracellular vesicles derive their cargo from the contents of the cells that produce them, they are attractive sources of biomarkers for a variety of diseases. Furthermore, studies demonstrating phenotypic effects of specific extracellular vesicle-associated cargo on target cells have stoked interest in extracellular vesicles as therapeutic vehicles. There is particularly strong evidence that the RNA cargo of extracellular vesicles can alter recipient cell gene expression and function. During the past decade, extracellular vesicles and their RNA cargo have become better defined, but many aspects of extracellular vesicle biology remain to be elucidated. These include selective cargo loading resulting in substantial differences between the composition of extracellular vesicles and source cells; heterogeneity in extracellular vesicle size and composition; and undefined mechanisms for the uptake of extracellular vesicles into recipient cells and the fates of their cargo. Further progress in unravelling the basic mechanisms of extracellular vesicle biogenesis, transport, and cargo delivery and function is needed for successful clinical implementation. This Review focuses on the current state of knowledge pertaining to packaging, transport and function of RNAs in extracellular vesicles and outlines the progress made thus far towards their clinical applications.

Exosome-Shuttled circSHOC2 from IPASs Regulates Neuronal Autophagy and Ameliorates Ischemic Brain Injury via the miR-7670-3p/SIRT1 Axis

The aim of the present study was to investigate the neuroprotective roles and mechanisms of the circular RNA circSHOC2 in ischemic-preconditioned astrocyte-derived exosomes (IPAS-EXOs) against ischemic stroke. We established an ischemia model based on oxygen glucose deprivation (OGD) in vitro and isolated resultant exosomes from astrocytes. Neuronal viability and apoptosis were determined by Cell Counting Kit-8 (CCK-8) assays and TUNEL (terminal deoxynucleotidyltransferase-mediated deoxyuridine triphosphate nick end labeling) staining, respectively. Autophagy-related proteins were analyzed by western blotting. We found that exosomes derived from IPAS-preconditioned medium (IPAS-CM) exerted neuroprotection. Furthermore, circSHOC2 expression was significantly upregulated in exosomes released from IPAS-CM. Overexpression of circSHOC2 in neurons yielded the same protective effects as those from IPAS-EXOs in vitro, and similar results were also observed in the middle cerebral artery occlusion (MCAO) mouse model. Mechanistically, circSHOC2 reduced neuronal apoptosis via regulating autophagy. Furthermore, circSHOC2 was found to sponge miR-7670-3p, which regulated SIRT1 expression. Transfection with an miR-7670-3p small interfering RNA (siRNA) (siRNA-7670-3p) and incubation with circSHOC2 extracellular vesicles attenuated ischemia-induced neuronal apoptosis in vivo and in vitro, while silencing of SIRT1 reversed the protective effects of exosomal circSHOC2 on hypoxic cerebral neurons. Taken together, our findings indicate that circSHOC2 in IPAS-EXOs suppressed neuronal apoptosis and ameliorated neuronal damage by regulating autophagy and acting on the miR-7670-3p/SIRT1 axis, which might contribute to a therapeutic strategy for ischemic stroke treatment.

Circular RNAs as New Regulators in Gastric Cancer: Diagnosis and Cancer Therapy

Gastric cancer (GC) is one of the most commonly diagnosed cancers that causes high mortality in the world. Although the surgery tools and chemotherapies have significantly improved the overall survival of patients with GC, the early diagnosis of GC remains insufficient and many patients diagnosed with advanced stages of GC are not able to benefit from curative therapy. Circular RNAs (circRNAs), novel members of the non-coding cancer genome, are being explored with regards to various cancer types including GC. CircRNAs could work as miRNA sponges to regulate cell proliferation, cell migration, and cell cycle in GC. In addition, it was found that abnormal expression of circRNAs was associated with pathological characteristics in GC tissues, which could help to act as potential markers of early diagnosis or predictors of prognosis. Although various functional circRNAs have been discovered and characterized, the studies of circRNAs in GC are still at early stages compared with other RNAs. In order to provide a whole view to better understand the circRNAs in the occurrence and development of GC, we review the current knowledge on circRNAs in relation to their expression and regulation in GC as well as their potential to be diagnosis markers, and their role in drug resistance will be mentioned. It is helpful to address their possibility from basic research into practical application.

The emerging roles of exosomal circRNAs in diseases

Exosomes, the nanoscale phospholipid bilayer vesicles, enriched in selected proteins, nucleic acids and lipids, which they participated in a variety of biological processes in the body, including physiology and pathology. CircRNAs (circular RNAs) are a class of single-stranded closed molecules with tissue development specific expression patterns that have crucial regulatory functions in various diseases. Non-coding RNAs (such as microRNAs and long non‑coding RNAs) in exosomes have also been shown to play an important regulatory role in humans. However, little research has focused on exosomal circRNAs. Recently, CircRNAs have been identified to be enriched and stably expressed in exosomes. In this review, we summarize the biogenesis and biological functions of exosomes and circRNA, and further revealed the potential role of exosome-derived circRNA in different diseases. Besides, we propose its use as a diagnostic marker and therapeutic punctuation for diseases, especially in cancer.

Knockdown of circular RNA circMAT2B reduces oxygen-glucose deprivation-induced inflammatory injury in H9c2 cells through up-regulating miR-133

Myocardial infarction (MI) is the main cause of morbidity and mortality. Reperfusion ways can cause damage to cardiomyocytes. CircMAT2B, a novel circRNA, takes positive roles in regulating glucose metabolism under hypoxia. Therefore, we aimed to explore the effects of circMAT2B on MI. Oxygen-glucose deprivation (OGD)-induced H9c2 cell model was employed to stimulate MI. Ex-circMAT2B, si-circMAT2B, miR-133 inhibitor and relative control were transfected into H9c2 cells. qRT-PCR was employed to examine levels of circMAT2B and miR-133. Cell activity, apoptosis, ROS generation and release of inflammatory factors were assessed by CCK-8, flow cytometry, ROS species assay kit and ELISA, respectively. Moreover, the expression of apoptosis-related and pathway-related factors was detected through western blot analysis. The results showed that circMAT2B expression was notably up-regulated by OGD treatment. Moreover, circMAT2B knockdown could effectively decrease OGD-induced the increasing of apoptosis, ROS generation and the expression of IL-1β, IL-6 and TNF-α. Besides, miR-133 was positively regulated by si-circMAT2B. CircMAT2B knockdown attenuated OGD-induced H9c2 cell damage and alleviated OGD-induced the inhibition of PI3K/AKT and Raf/MEK/ERK pathways through up-regulating miR-133. In brief, circMAT2B knockdown works as an inflammatory inhibitor in OGD-induced H9c2 cells inflammatory injury through up-regulating miR-133.

Regulatory roles of circRNAs in adipogenesis and lipid metabolism: emerging insights into lipid-related diseases

Disorder of lipid metabolism has become an urgent health problem that brings about a variety of metabolic syndromes, including hepatic steatosis, adipose tissue dysfunction, diabetes and obesity. Circular RNAs (circRNAs), a class of emerging RNA molecules with unique structure and extensive effects, have been verified to participate in various biological programs through distinct mechanisms, especially in lipid-related processes. In this review, the biogenesis, characteristics, and functional mechanisms of circRNAs are discussed. Furthermore, the methods for circRNA identification and expression profiles of circRNAs associated with adipogenesis and lipid metabolism are described. Additionally, we emphasize the regulatory roles of circRNAs in adipogenesis, lipid metabolism, and lipid-related diseases. Finally, the diagnostic and therapeutic potential of circRNAs is highlighted, showing potential for the clinical application of circRNAs in the treatment of lipid-related diseases in the near future.

Circular RNA SIPA1L1 promotes osteogenesis via regulating the miR-617/Smad3 axis in dental pulp stem cells

BACKGROUND

Bone regeneration is preferred for bone loss caused by tumors, bone defects, fractures, etc. Recently, mesenchymal stem cells are considered as optimistic tools for bone defect therapy. Dental pulp stem cells (DPSCs) are a promising candidate for regenerative medicine and bone regeneration. Our previous study showed that upregulated circSIPA1L1 during osteogenesis of DPSCs is of significance. In this paper, the potential role of circSIPA1L1 in osteogenesis of DPSCs and its underlying mechanisms are explored.

METHODS

The circular structure of circSIPA1L1 was identified by Sanger sequencing and PCR. Regulatory effects of circSIPA1L1 and miR-617 on mineral deposition in DPSCs were assessed by alkaline phosphatase (ALP) and alizarin red S (ARS) staining and in vivo bone formation assay were conducted to verify the biological influences of circSIPA1L1 on DPSCs. Western blot was performed to detect the protein expression of Smad3. Localization of circSIPA1L1 and miR-617 was confirmed by FISH. Dual-luciferase reporter assay and rescue experiments were conducted to investigate the role of the circSIPA1L1/miR-617/Smad3 regulatory axis in osteogenesis of DPSCs.

RESULTS

Sanger sequencing and back-to-back primer experiments confirmed the closed-loop structure of circSIPA1L1. CircSIPA1L1 could promote the committed differentiation of DPSCs. MiR-617 was predicted to be the target binding circSIPA1L1 through MiRDB, miRTarBase, and TargetScan database analyses, which was further confirmed by dual-luciferase reporter assay. FISH results showed that circSIPA1L1 and miR-617 colocalize in the cytoplasm of DPSCs. MiR-617 exerted an inhibitory effect on the osteogenesis of DPSCs. Knockdown of circSIPA1L1 or upregulation of miR-617 downregulated phosphorylated Smad3. In addition, rescue experiments showed that knockdown of miR-617 reversed the inhibitory effect of circSIPA1L1 on osteogenesis of DPSCs.

CONCLUSION

CircRNASIPA1L1 promotes osteogenesis of DPSCs by adsorbing miR-617 and further targeting Smad3.

Exosome-Derived Circ-PVT1 Contributes to Cisplatin Resistance by Regulating Autophagy, Invasion, and Apoptosis Via miR-30a-5p/YAP1 Axis in Gastric Cancer Cells

Background: Emerging studies manifested that exosomal RNAs had pivotal roles in human cancer therapies. This article aimed to research the regulatory mechanism of exosomal circRNA-plasmacytoma variant translocation 1 (circ-PVT1) in cisplatin (DDP) resistance of gastric cancer (GC). Methods: Exosomes were isolated by ExoQuick^® method and ultracentrifugation and then identified through transmission electron microscope and the examination of exosome markers. Related proteins were detected using Western blot. Quantitative real-time polymerase chain reaction (qRT-PCR) was applied for measuring circ-PVT1, microRNA-30a-5p (miR-30a-5p), and Yes-associated protein 1 (YAP1) expression. The half inhibitory concentration (IC₅₀) of DDP was assessed by 3-(4, 5-dimethylthiazol-2-y1)-2, 5-diphenyl tetrazolium bromide (MTT). Cell apoptosis and invasion were, respectively, determined using flow cytometry and transwell assay. Target relationship was confirmed by dual-luciferase reporter assay. The impact of circ-PVT1 on DDP resistance was explored via xenograft tumor assay. Results: Exosomal circ-PVT1 was upregulated while miR-30a-5p was downregulated in DDP-resistant GC serums and cells. Circ-PVT1 knockdown repressed DDP resistance in DDP-resistant GC cells via promoting apoptosis and decreasing invasion or autophagy by negatively targeting miR-30a-5p. YAP1 was a direct target of miR-30a-5p. MiR-30a-5p overexpression inhibited DDP resistance via reducing YAP1. Circ-PVT1 modulated YAP1 expression by targeting miR-30a-5p. Circ-PVT1 depression expedited DDP sensitivity of GC via miR-30a-5p/YAP1 axis in vivo. Conclusion: Exosomal circ-PVT1 facilitated DDP resistance via modulating autophagy, invasion and apoptosis by miR-30a-5p/YAP1 axis in GC cells. Exosomal circ-PVT1 might be a prospective indicator in DDP therapy of GC.

Circular RNA circNHSL1 Contributes to Gastric Cancer Progression Through the miR-149-5p/YWHAZ Axis

Background

Gastric cancer (GC) is a considerable health burden around the world. Circular RNA Nance-Horan syndrome-like 1 (circNHSL1) is reported to be highly expressed in GC. Nevertheless, the function and molecule mechanism of circNHSL1 are still unclear.

Methods

The expression levels of circNHSL1, microRNA-149-5p (miR-149-5p) and YWHAZ were detected by real-time quantitative polymerase chain reaction (RT-qPCR). The subcellular fractionation identified the remarkable cytoplasmic localization of circNHSL1. Cell migration and invasion were measured by transwell assays. The levels of glutamine, glutamate and α-ketoglutarate (α-KG) were assessed by the corresponding kit. The protein levels of CD63, CD9, CD81, alanine, serine, cysteine-preferring transporter 2 (ASCT2), glutaminase 1 (GLS1), and tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein zeta (YWHAZ) were detected by Western blot assay. The binding relationship between miR-149-5p and circNHSL1 or YWHAZ was predicted by starBase 3.0 and then verified by RNA pull-down and dual-luciferase reporter assays. Xenograft tumor model examined the biological role of circNHSL1 in vivo. Exosomes were examined by a transmission electron microscope and nanoparticle tracking analysis (NTA).

Results

CircNHSL1 was highly expressed in GC cell-derived exosomes, GC tissues, and cells. Its knockdown impeded GC cell migration, invasion, and glutaminolysis. Mechanism analysis showed that circNHSL1 could affect YWHAZ expression by sponging miR-149-5p, thereby regulating GC progression. CircNHSL1 downregulation blocked GC tumor growth in vivo.

Conclusion

Our studies disclosed that circNHSL1 knockdown repressed migration, invasion, and glutaminolysis in vitro and inhibited tumor growth in vivo by miR-149-5p/YWHAZ axis in GC, implying an underlying circRNA-targeted therapy for GC treatment.

CircRNAs: biogenesis, functions, and role in drug-resistant Tumours

Targeted treatment, which can specifically kill tumour cells without affecting normal cells, is a new approach for tumour therapy. However, tumour cells tend to acquire resistance to targeted drugs during treatment. Circular RNAs (circRNAs) are single-stranded RNA molecules with unique structures and important functions. With the development of RNA sequencing technology, circRNAs have been found to be widespread in tumour-resistant cells and to play important regulatory roles. In this review, we present the latest advances in circRNA research and summarize the various mechanisms underlying their regulation. Moreover, we review the role of circRNAs in the chemotherapeutic resistance of tumours and explore the clinical value of circRNA regulation in treating tumour resistance.

Comprehensive Analysis of a circRNA-miRNA-mRNA Network to Reveal Potential Inflammation-Related Targets for Gastric Adenocarcinoma

Gastric cancer (GC) is the most common malignancy of the stomach. This study was aimed at elucidating the regulatory network of circRNA-miRNA-mRNA and identifying the precise inflammation-related targets in GC. The expression profiles of GSE83521, GSE78091, and GSE33651 were obtained from the GEO database. Interactions between miRNAs and circRNAs were investigated by the Circular RNA Interactome, and targets of miRNAs were predicted with miRTarBase. Then, a circRNA/miRNA/mRNA regulatory network was constructed. Also, functional enrichment analysis of selected differentially expressed genes (DEGs) was performed. The inflammation-/GC-related targets were collected in the GeneCards and GenLiP3 database, respectively. And a protein-protein interaction (PPI) network of DE mRNAs was constructed with STRING and Cytoscape to identify hub genes. The genetic alterations, neighboring gene networks, expression levels, and the poor prognosis of hub genes were investigated in cBioPortal, Oncomine, and Human Protein Atlas databases and Kaplan-Meier plotter, respectively. A total of 10 DE miRNAs and 33 DEGs were identified. The regulatory network contained 26 circRNAs, 10 miRNAs, and 1459 mRNAs. Functional enrichment analysis revealed that the selected 33 DEGs were involved in negative regulation of fat cell differentiation, response to wounding, extracellular matrix- (ECM-) receptor interaction, and regulation of cell growth pathways. THBS1, FN1, CALM1, COL4A1, CTGF, and IGFBP5 were selected as inflammation-related hub genes of GC in the PPI network. The genetic alterations in these hub genes were related to amplification and missense mutations. Furthermore, the genes RYR2, ERBB2, PI3KCA, and HELZ2 were connected to hub genes in this study. The hub gene levels in clinical specimens were markedly upregulated in GC tissues and correlated with poor overall survival (OS). Our results suggest that THBS1, FN1, CALM1, COL4A1, CTGF, and IGFBP5 were associated with the pathogenesis of gastric carcinogenesis and may serve as biomarkers and inflammation-related targets for GC.

Functions of Circular RNAs in Regulating Adipogenesis of Mesenchymal Stem Cells

The mesenchymal stem cells (MSCs) are known as highly plastic stem cells and can differentiate into specialized tissues such as adipose tissue, osseous tissue, muscle tissue, and nervous tissue. The differentiation of mesenchymal stem cells is very important in regenerative medicine. Their differentiation process is regulated by signaling pathways of epigenetic, transcriptional, and posttranscriptional levels. Circular RNA (circRNA), a class of noncoding RNAs generated from protein-coding genes, plays a pivotal regulatory role in many biological processes. Accumulated studies have demonstrated that several circRNAs participate in the cell differentiation process of mesenchymal stem cells in vitro and in vivo. In the current review, characteristics and functions of circRNAs in stem cell differentiation will be discussed. The mechanism and key role of circRNAs in regulating mesenchymal stem cell differentiation, especially adipogenesis, will be reviewed and discussed. Understanding the roles of these circRNAs will present us with a more comprehensive signal path network of modulating stem cell differentiation and help us discover potential biomarkers and therapeutic targets in clinic.

Analysis of exosomal circRNAs upon irradiation in pancreatic cancer cell repopulation

BACKGROUND

Pancreatic cancer is one of the most malignant tumors. However, radiotherapy can lead to tumor recurrence, which is caused by the residual surviving cells repopulation stimulated by some molecular released from dying cells. Exosomes may mediate cell-cell communication and transfer kinds of signals from the dying cells to the surviving cells for stimulating tumor repopulation. Circular RNAs (circRNAs) may be one vital kind of exosomal cargos involving in modulating cancer cell repopulation.

METHODS

Next generation sequencing (NGS) and bioinformatics were performed to analyze and annotate the expression and function of exosome-derived circRNAs in pancreatic cancer cells after radiation. Four circRNAs were chosen for qRT-PCR analysis to validate the sequencing results.

RESULTS

In this study, 3580 circRNAs were annotated in literatures and circBase among 12,572 identified circRNAs. There were 196 filtered differentially expressed circRNAs (the up-regulation and down-regulation respectively is 182 and 14, fold change > 2, p-value < 0.05). Regulation of metabolic process and lysine degradation were the main enriched biological processes and pathway according to Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis.

CONCLUSIONS

The hsa_circ_0002130-hsa_miR_4482-3p-NBN interaction network suggested potential sponging miRNA and target mRNA. Our results provided potential functions of circRNAs to explore molecular mechanisms and therapeutic targets in pancreatic cancer cell repopulation upon irradiation.

The Biological Role of Sponge Circular RNAs in Gastric Cancer: Main Players or Coadjuvants?

Circular RNAs (circRNAs) are a new class of long noncoding RNAs able to perform multiple functions, including sponging microRNAs (miRNAs) and RNA-Binding Proteins (RBPs). They play an important role in gastric carcinogenesis, but its involvement during gastric cancer (GC) development and progression are not well understood. We gathered miRNA and/or RBPs sponge circRNAs present in GC, and accessed their biological roles through functional enrichment of their target genes or ligand RBPs. We identified 54 sponge circRNAs in GC that are able to sponge 51 miRNAs and 103 RBPs. Then, we evaluated their host gene expression using The Cancer Genome Atlas (TCGA) database and observed that COL1A2 is the most overexpressed gene, which may be due to circHIPK3/miR-29b-c/COL1A2 axis dysregulation. We identified 27 GC-related pathways that may be affected mainly by circPVT1, circHIPK3 and circNF1. Our results indicate that circHIPK3/miR-107/BDNF/LIN28 axis may mediate chemoresistance in GC, and that circPVT1, circHIPK3, circNF1, ciRS-7 and circ_0000096 appear to be involved in gastrointestinal cancer development. Lastly, circHIPK3, circNRIP1 and circSMARCA5 were identified in different ethnic populations and may be ubiquitous modulators of gastric carcinogenesis. Overall, the studied sponge circRNAs are part of a complex RBP-circRNA-miRNA-mRNA interaction network, and are involved in the establishment, chemoresistance and progression of GC.

SPEN induces miR-4652-3p to target HIPK2 in nasopharyngeal carcinoma

SPEN family transcriptional repressor (SPEN), also known as the SMART/HDAC1-associated repressor protein (SHARP), has been reported to modulate the malignant phenotypes of breast cancer, colon cancer, and ovarian cancer. However, its role and the detail molecular basis in nasopharyngeal carcinoma (NPC) remain elusive. In this study, the SPEN mRNA and protein expression was found to be increased in NPC cells and tissues compared with nonmalignant nasopharyngeal epithelial cells and tissues. Elevated SPEN protein expression was found to promote the pathogenesis of NPC and lead to poor prognosis. Knockdown of SPEN expression resulted in inactivation ofPI3K/AKT and c-JUN signaling, thereby suppressing NPC migration and invasion. In addition, miR-4652-3p was found to be a downstream inducer of SPEN by targeting the homeodomain interacting protein kinase 2 (HIPK2) gene, a potential tumor suppressor that reduces the activation of epithelial-mesenchymal transition (EMT) signaling, thereby reducing its expression and leading to increased NPC migration, invasion, and metastasis. In addition, SPEN was found to induce miR-4652-3p expression by activating PI3K/AKT/c-JUN signaling to target HIPK2. Our data provided a new molecular mechanism for SPEN as a metastasis promoter through activation of PI3K/AKT signaling, thereby stimulating the c-JUN/miR-4652-3p axis to target HIPK2 in NPC.

Circular RNA is a popular molecule in tumors of the digestive system (Review)

Most tumors of the digestive system, including esophageal, gastric, liver and colorectal cancer, are malignant tumors that are associated with rates of high morbidity and mortality. The lack of effective methods for early diagnosis is an important cause of poor prognosis for these malignancies. Circular RNAs (circRNAs) belong to a family of endogenous, covalently closed non‑coding RNAs that are characterized as having no 5' cap structures or 3' poly‑A tails. Shortly following discovery, circRNAs were considered to be a product of mis‑splicing and have no significant biological function. However, in recent years, accumulating evidence is demonstrating that they serve key roles in tumorigenesis and have the potential to serve as diagnostic markers. The present article summarizes the biogenesis and function of circRNAs and reviews their role in seven common types of tumor of the digestive system whilst exploring their potential as tumor markers and the significant roles they can serve in the digestive system, in addition to providing a referencing point for future studies of digestive system malignancies.

Circular RNA profiling in plasma exosomes from patients with gastric cancer

Gastric cancer (GC) is among the most common cancer types worldwide with high mortality. Recent studies have shown that exosomes play a crucial role in the tumorigenesis of GC. The present study aimed to investigate the circular RNA (circRNA) profile in plasma exosomes from patients with gastric cancer (GC). Peripheral blood samples were collected from 5 patients with GC and 5 healthy donors, and exosomes were isolated from plasma. The high-throughput RNA sequencing (RNA-seq) method was applied to detect the differently expressed circRNAs (DE circRNAs). Subsequently, sequencing results were confirmed by reverse transcription quantitative (RT-q) PCR. The potential roles of DE circRNAs in GC were identified using Gene ontology (GO) and Kyoto Encyclopedia of Gene and Genome (KEGG) analysis. Furthermore, MiRanda software was used to predict circRNA-micro-RNA (miRNA) interactions. A total of 67,880 circRNAs were identified in all samples and 1,060 significantly DE circRNAs were screened, including 620 upregulated and 440 downregulated ones. These results were further confirmed by RT-qPCR. GO and KEGG analyses revealed that these circRNAs were significantly associated with ‘cell cycle’, ‘cytoskeleton organization’, ‘cellular response to DNA damage’, ‘regulation of GTPase activity’, ‘phosphatidylinositol signaling pathway’, ‘MAPK signaling pathway’, ‘thyroid hormone signaling pathway’, ‘chemokine signaling pathway’ and ‘Wnt signaling pathway’. In addition, a circRNA-miRNA-mRNA interaction network was established. Taken together, these findings may help better understanding the underlying mechanisms of GC and identifying new molecular alterations in GC, and allow the enrichment of the circRNA profiling in human GC.

Novel potential tumor biomarkers: Circular RNAs and exosomal circular RNAs in gastrointestinal malignancies

BACKGROUND

Circular RNAs (circRNAs) are structural ubiquitous RNA molecules. Accumulating evidences have elucidated that circRNAs play essential roles in the pathogenesis of diseases including cancers. Exosomal circRNAs are those circRNAs stably existing in exosomes and having high clinical values as novel potential diagnostic biomarkers of many diseases. Gastrointestinal (GI) malignancies, including pancreatic cancer, colorectal cancer, hepatocellular carcinoma (HCC), and gastric cancer, are leading causes of mortality worldwide and a major global health burden. However, no ideal tumor biomarkers of screening early GI cancers are currently available.

METHODS

We collected data through Web of Science. The search terms used were as follows: circular RNA, circRNA, exosomes, exosomal circRNAs, biomarkers, gastrointestinal malignancies, pancreatic cancer, hepatocellular carcinoma, HCC, gastric cancer, colorectal cancer, physiological functions, biogenesis, molecular mechanism. Only articles published in English were included.

RESULTS

We found that several circRNAs and exosomal circRNAs have been used as potential biomarkers to screen GI cancers including pancreatic cancer (hsa_circ_0001649, circ_0007534, circ_0030235, circRHOT1, circZMYM2, circ-LDLRAD3, chr14:101402109-101464448C, chr4:52729603-52780244C, circ-IARS, and circ-PDE8A), HCC (circSETD3, circADAMTS13, hsa_circ_0007874, hsa_circ_104135, circFBLIM1, cSMARCA5, circRNA-100338, and circPTGR1), colorectal cancer (hsa_circ_0001178, hsa_circ_0000826, hsa_circ_0004771, circDDX17, circITGA7, and circHIPK3), and gastric cancer (hsa_circ_0074362, circNRIP1, circAKT3, circ-DONSON, circPSMC3, circ-KIAA1244, circPVRL3, circPVT1, hsa_circ_0000096, ciRS-133, hsa_circ_0001017, and hsa_circ_0061276).

CONCLUSION

CircRNAs and exosomal circRNAs have the potential high clinical diagnostic values for GI malignancies.

Exosome biogenesis, secretion and function of exosomal miRNAs in skeletal muscle myogenesis

Exosomes are membrane-bound extracellular vesicles that are produced in the endosomal compartment of most mammalian cell types and then released. Exosomes are effective carriers for the intercellular material transfer of material that can influence a series of physiological and pathological processes in recipient cells. Among loaded cargoes, non-coding RNAs (ncRNAs) vary for the exosome-producing cell and its homeostatic state, and characterization of the biogenesis and secretion of exosomal ncRNAs and the functions of these ncRNAs in skeletal muscle myogenesis remain preliminary. In this review, we will describe what is currently known of exosome biogenesis, release and uptake of exosomal ncRNAs, as well as the varied functions of exosomal miRNAs in skeletal muscle myogenesis.

The Emerging Role and Promise of Circular RNAs in Obesity and Related Metabolic Disorders

Circular RNAs (circRNAs) are genome transcripts that are produced from back-splicing of specific regions of pre-mRNA. These single-stranded RNA molecules are widely expressed across diverse phyla and many of them are stable and evolutionary conserved between species. Growing evidence suggests that many circRNAs function as master regulators of gene expression by influencing both transcription and translation processes. Mechanistically, circRNAs are predicted to act as endogenous microRNA (miRNA) sponges, interact with functional RNA-binding proteins (RBPs), and associate with elements of the transcriptional machinery in the nucleus. Evidence is mounting that dysregulation of circRNAs is closely related to the occurrence of a range of diseases including cancer and metabolic diseases. Indeed, there are several reports implicating circRNAs in cardiovascular diseases (CVD), diabetes, hypertension, and atherosclerosis. However, there is very little research addressing the potential role of these RNA transcripts in the occurrence and development of obesity. Emerging data from in vitro and in vivo studies suggest that circRNAs are novel players in adipogenesis, white adipose browning, obesity, obesity-induced inflammation, and insulin resistance. This study explores the current state of knowledge on circRNAs regulating molecular processes associated with adipogenesis and obesity, highlights some of the challenges encountered while studying circRNAs and suggests some perspectives for future research directions in this exciting field of study.

Emerging Function and Clinical Significance of Exosomal circRNAs in Cancer

Exosomes are a type of extracellular vesicles (EVs) secreted by almost all cells, with a diameter range of 30-150 nm and a lipid bilayer membrane. Exosomes are now considered as vital mediators of intercellular communication and participate in multiple cellular processes, such as signal transduction and antigen presentation. Recently, circular RNAs (circRNAs), a novel class of noncoding RNAs (ncRNAs), have been found to be abundant and stable in exosomes. Increasing evidence indicates that exosome-derived circRNAs act as signaling molecules to regulate cancer growth, angiogenesis, invasion, metastasis, and sensitivity to chemotherapy. Moreover, circulating exosomal circRNAs can reflect the progression and malignant characteristics of cancer, implying their great potential as promising, non-invasive biomarkers for cancer diagnosis and prognosis. In this review, we summarize the recent progress on the functional roles of exosomal circRNAs in cancer progression, discussing their potential as promising biomarkers and therapeutic targets in cancer. Comprehensive elucidation of molecular mechanisms relevant to the implications of exosomal circRNAs in cancer progression will be conducive to the development of innovative diagnostic and therapeutic approaches in cancer.

Comprehensive landscape of extracellular vesicle-derived RNAs in cancer initiation, progression, metastasis and cancer immunology

Extracellular vesicles (EVs), a class of heterogeneous membrane vesicles, are generally divided into exosomes and microvesicles on basis of their origination from the endosomal membrane or the plasma membrane, respectively. EV-mediated bidirectional communication among various cell types supports cancer cell growth and metastasis. EVs derived from different cell types and status have been shown to have distinct RNA profiles, comprising messenger RNAs and non-coding RNAs (ncRNAs). Recently, ncRNAs have attracted great interests in the field of EV-RNA research, and growing numbers of ncRNAs ranging from microRNAs to long ncRNAs have been investigated to reveal their specific functions and underlying mechanisms in the tumor microenvironment and premetastatic niches. Emerging evidence has indicated that EV-RNAs are essential functional cargoes in modulating hallmarks of cancers and in reciprocal crosstalk within tumor cells and between tumor and stromal cells over short and long distance, thereby regulating the initiation, development and progression of cancers. In this review, we discuss current findings regarding EV biogenesis, release and interaction with target cells as well as EV-RNA sorting, and highlight biological roles and molecular mechanisms of EV-ncRNAs in cancer biology.

Circular RNA circSATB2 promotes progression of non-small cell lung cancer cells

BACKGROUND

Lung cancer has high morbidity and mortality worldwide with non-small cell lung cancer (NSCLC) accounting for 85% of the cases. Therapies for lung cancer have relatively poor outcomes and further improvements are required. Circular RNAs have been reported to participate in the occurrence and progression of cancer. Information on the functions and mechanism of circRNAs in lung cancer is limited and needs more exploration.

METHODS

We detected expression of genes and proteins by qPCR and western blot. Function of circSATB2 was investigated using RNA interference and overexpression assays. Location of circSATB2 was assessed by fluorescence in situ hybridization (FISH). Interaction of circSATB2, miR-326 and FSCN1 was confirmed by dual-luciferase reporter assay.

RESULTS

Data from the investigation showed that circSATB2 was highly expressed in NSCLC cells and tissues. circSATB2 positively regulated fascin homolog 1, actin-bundling protein 1 (FSCN1) expression via miR-326 in lung cancer cells. Furthermore, circSATB2 can be transferred by exosomes and promote the proliferation, migration and invasion of NSCLC cells, as well as induce abnormal proliferation in normal human bronchial epithelial cells. Also, circSATB2 was highly expressed in serumal exosomes from lung cancer patients with high sensitivity and specificity for clinical detection and was related to lung cancer metastasis.

CONCLUSIONS

circSATB2 participated in the progression of NSCLC and was differentially expressed in lung cancer tissue and serumal exosomes. circSATB2 may be potential biomarker for the diagnosis of NSCLC.