Circular RNAs in cancer: an emerging key player

Unlocking the potential of extracellular vesicle circRNAs in breast cancer: From molecular mechanisms to therapeutic horizons

Breast cancer remains the leading cause of cancer-related morbidity and mortality among women worldwide, underscoring the urgent need for novel diagnostic and therapeutic strategies. This review explores the emerging roles of circular RNAs (circRNAs) within extracellular vesicles (exosomes) in breast cancer. circRNAs, known for their stability and tissue-specific expression, are aberrantly expressed in breast cancer and regulate critical cellular processes such as proliferation, migration, and apoptosis, positioning them as promising biomarkers. Exosomes facilitate intercellular communication by delivering circRNAs, reflecting the physiological and pathological state of their source cells. This review highlights the multifaceted roles of exosomal circRNAs in promoting tumor growth, metastasis, and drug resistance through their modulation of tumor metabolism, the tumor microenvironment, and immune responses. In particular, we emphasize their contributions to chemotherapy resistance and their potential as both diagnostic markers and therapeutic targets. By synthesizing current research, this review provides novel insights into the clinical applications of exosomal circRNAs, offering a foundation for future studies aimed at improving breast cancer management through non-invasive diagnostics and targeted therapies.

Exosomal non-coding RNAs (ncRNAs) as potential biomarkers in tumor early diagnosis

Exosomes, extracellular vesicles carrying a cargo rich in various non-coding RNAs (ncRNAs), have emerged as crucial mediators of intercellular communication. Their stability, abundance, and specificity make exosomal ncRNAs promising candidates for biomarker discovery. The discovery of exosomal ncRNAs has unveiled a novel avenue for the exploration of biomarkers in tumor early diagnosis. This review consolidates current knowledge on the role of exosomal ncRNAs as potential biomarkers in the early detection of various tumors. We provide an overview of recent studies demonstrating the diagnostic potential of exosomal ncRNAs across multiple cancer types, highlighting their sensitivity, specificity, and feasibility for early detection. This review underscores the potential of exosomal ncRNAs as non-invasive biomarkers for early tumor diagnosis, paving the way for improved clinical outcomes through timely intervention and personalized management strategies.

Circular RNAs in tumor immunity and immunotherapy

Circular RNAs (circRNAs) are unique noncoding RNAs that have a closed and stable loop structure generated through backsplicing. Due to their conservation, stability and tissue specificity, circRNAs can potentially be used as diagnostic indicators and therapeutic targets for certain tumors. Many studies have shown that circRNAs can act as microRNA (miRNA) sponges, and engage in interactions with proteins and translation templates to regulate gene expression and signal transduction, thereby participating in the occurrence and development of a variety of malignant tumors. Immunotherapy has revolutionized the treatment of cancer. Early researches have indicated that circRNAs are involved in regulating tumor immune microenvironment and antitumor immunity. CircRNAs may have the potential to be important targets for increasing sensitivity to immunotherapy and expanding the population of patients who benefit from cancer immunotherapy. However, few studies have investigated the correlation between circRNAs and tumor immunity. In this review, we summarize the current researches on circRNAs involved in antitumor immune regulation through different mechanisms and their potential value in increasing immunotherapy efficacy with the goal of providing new targets for cancer immunotherapy.

Circ_0004851 regulates the molecular mechanism of miR-296-3p/FGF11 in the influence of high iodine on PTC

The prevalence of papillary thyroid cancer (PTC) has been rising in recent years. Despite its relatively low mortality, PTC frequently metastasizes to lymph nodes and often recurs, posing significant health and economic burdens. The role of iodine in the pathogenesis and advancement of thyroid cancer remains poorly understood. Circular RNAs (circRNAs) are recognized to function as competing endogenous RNAs (ceRNAs) that modulate gene expression and play a role in various cancer stages. Consequently, this research aimed to elucidate the mechanism by which circRNA influences the impact of iodine on PTC. Our research indicates that high iodine levels can exacerbate the malignancy of PTC via the circ_0004851/miR-296-3p/FGF11 axis. These insights into iodine's biological role in PTC and the association of circRNA with the disease could pave the way for novel biomarkers and potentially effective therapeutic strategies to mitigate PTC progression.

Molecular and Therapeutic Roles of Non-Coding RNAs in Oral Cancer-A Review

Oral cancer (OC) is among the most common malignancies in the world. Despite advances in therapy, the worst-case scenario for OC remains metastasis, with a 50% survival rate. Therefore, it is critical to comprehend the pathophysiology of the condition and to create diagnostic and treatment plans for OC. The development of high-throughput genome sequencing has revealed that over 90% of the human genome encodes non-coding transcripts, or transcripts that do not code for any proteins. This paper describes the function of these different kinds of non-coding RNAs (ncRNAs) in OC as well as their intriguing therapeutic potential. The onset and development of OC, as well as treatment resistance, are linked to dysregulated ncRNA expression. These ncRNAs' potentially significant roles in diagnosis and prognosis have been suggested by their differing expression in blood or saliva. We have outlined every promising feature of ncRNAs in the treatment of OC in this study.

CircRNA-associated ceRNA regulatory networks as emerging mechanisms governing the development and biophysiopathology of epilepsy

The etiology of epilepsy is ascribed to the synchronized aberrant neuronal activity within the brain. Circular RNAs (circRNAs), a class of non-coding RNAs characterized by their circular structures and covalent linkage, exert a substantial influence on this phenomenon. CircRNAs possess stereotyped replication, transience, repetitiveness, and paroxysm. Additionally, MicroRNA (miRNA) plays a crucial role in the regulation of diverse pathological processes, including epilepsy. CircRNA is of particular significance due to its ability to function as a competing endogenous RNA, thereby sequestering or inhibiting miRNA activity through binding to target mRNA. Our review primarily concentrates on elucidating the pathological and functional roles, as well as the underlying mechanisms, of circRNA-miRNA-mRNA networks in epilepsy. Additionally, it explores the potential utility of these networks for early detection and therapeutic intervention.

Liquid biopsy in colorectal cancer: Onward and upward

Colorectal cancer (CRC) remains a leading cause of cancer-related deaths worldwide. In recent years, liquid biopsy has emerged as one of the most interesting areas of research in oncology, leading to innovative trials and practical changes in all aspects of CRC management. RNAs and cell free DNA (cfDNA) methylation are emerging as promising biomarkers for early diagnosis. Post-surgical circulating tumour DNA (ctDNA) can aid in evaluating minimal residual disease and personalising adjuvant treatment. In rectal cancer, ctDNA could improve response assessment to neoadjuvant therapy and risk stratification, especially in the era of organ-preservation trials. In the advanced setting, ctDNA analysis offers the opportunity to monitor treatment response and identify driver and resistance mutations more comprehensively than traditional tissue analysis, providing prognostic and predictive information. The aim of this review is to provide a detailed overview of the clinical applications and future perspectives of liquid biopsy in CRC.

Specific Circular RNA Signature of Endothelial Cells: Potential Implications in Vascular Pathophysiology

Circular RNAs (circRNAs) are a recently characterized family of gene transcripts forming a covalently closed loop of single-stranded RNA. The extent of their potential for fine-tuning gene expression is still being discovered. Several studies have implicated certain circular RNAs in pathophysiological processes within vascular endothelial cells and cancer cells independently. However, to date, no comparative study of circular RNA expression in different types of endothelial cells has been performed and analysed through the lens of their central role in vascular physiology and pathology. In this work, we analysed publicly available and original RNA sequencing datasets from arterial, veinous, and lymphatic endothelial cells to identify common and distinct circRNA expression profiles. We identified 4713 distinct circRNAs in the compared endothelial cell types, 95% of which originated from exons. Interestingly, the results show that the expression profile of circular RNAs is much more specific to each cell type than linear RNAs, and therefore appears to be more suitable for distinguishing between them. As a result, we have discovered a specific circRNA signature for each given endothelial cell type. Furthermore, we identified a specific endothelial cell circRNA signature that is composed four circRNAs: circCARD6, circPLXNA2, circCASC15 and circEPHB4. These circular RNAs are produced by genes that are related to endothelial cell migration pathways and cancer progression. More detailed studies of their functions could lead to a better understanding of the mechanisms involved in physiological and pathological (lymph)angiogenesis and might open new ways to tackle tumour spread through the vascular system.

Identification of potential hub genes and regulatory networks of smoking-related endothelial dysfunction in atherosclerosis using bioinformatics analysis

BACKGROUND

Endothelial dysfunction, the earliest stage of atherosclerosis, can be caused by smoking, but its molecular mechanism requires further investigation.

OBJECTIVE

This study aimed to use bioinformatics analysis to identify potential mechanisms involved in smoking-related atherosclerotic endothelial dysfunction.

METHODS

The transcriptome data used for this bioinformatics analysis were obtained from the Gene Expression Omnibus (GEO) database. The GSE137578 and GSE141136 datasets were used to identify common differentially expressed genes (co-DEGs) in endothelial cells treated with oxidized low-density lipoprotein (ox-LDL) and tobacco. The co-DEGs were annotated using Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomics (KEGG) databases. Additionally, a protein-protein interaction (PPI) network was constructed to visualize their interactions and screen for hub genes. GSE120521 dataset was used to verify the expression of hub genes in unstable plaques. The miRNA expression profile GSE137580 and online databases (starBase 2.0, TargetScan 8.0 and DGIdb v4.2.0) were used to predict the related non-coding RNAs and drugs.

RESULTS

A total of 232 co-DEGs were identified, including 113 up-regulated genes and 119 down-regulated genes. These DEGs were primarily enriched in detrimental autophagy, cell death, transcription factors, and cytokines, and were implicated in ferroptosis, abnormal lipid metabolism, inflammation, and oxidative stress pathways. Ten hub genes were screened from the constructed PPI network, including up-regulated genes such as FOS, HMOX1, SQSTM1, PTGS2, ATF3, DDIT3, and down-regulated genes MCM4, KIF15, UHRF1, and CCL2. Importantly, HMOX1 was further up-regulated in unstable plaques (p= 0.034). Finally, a regulatory network involving lncRNA/circRNA-miRNA-hub genes and drug-hub genes was established.

CONCLUSION

Atherosclerotic endothelial dysfunction is associated with smoking-induced injury. Through bioinformatics analysis, we identified potential mechanisms and provided potential therapeutic targets.

Exosomal Non-coding RNAs: A New Approach to Melanoma Diagnosis and Therapeutic Strategy

Malignant melanoma (MM) is a highly aggressive cancer with a poor prognosis. Currently, although a variety of therapies are available for treating melanoma, MM is still a serious threat to the patient's life due to numerous factors, such as the recurrence of tumors, the emergence of drug resistance, and the lack of effective therapeutic agents. Exosomes are biologically active lipid-bilayer extracellular vesicles secreted by diverse cell types that mediate intercellular signal communication. Studies found that exosomes are involved in cancer by carrying multiple bioactive molecules, including non-- coding RNAs (ncRNAs). The ncRNAs have been reported to play an important role in regulating proliferation, angiogenesis, immune regulation, invasion, metastasis, and treatment resistance of tumors. However, the functional role of exosomal ncRNAs in MM remains unknown. Therefore, this review summarizes the current state of melanoma diagnosis, treatment, and the application of exosomal ncRNAs in MM patients, which may provide new insights into the mechanisms involved in melanoma progression and serve as biomarkers for diagnosis and therapeutic targets.

Hsa_circ_0001946 Ameliorates Mechanical Stress-induced Intervertebral Disk Degeneration Via Targeting miR-432-5p and SOX9

STUDY DESIGN

Experimental analysis of circular RNA in intervertebral disk degeneration (IDD).

OBJECTIVE

This study aimed to explore the roles of hsa_circ_0001946 (circ-CDR1as) in mechanical stress-induced nucleus pulposus cell injury in IDD.

SUMMARY OF BACKGROUND DATA

Mechanical stress is an important pathogenic factor for IDD. Excessive compression stress leads to nucleus pulposus (NP) cell apoptosis and extracellular matrix (ECM) degradation and accelerated IDD. Circ-CDR1as is associated with various degenerative conditions, but its role in IDD is not clear. Herein, we explored the roles and mechanisms of circ-CDR1as in IDD in vitro.

MATERIALS AND METHODS

An in vitro model of IDD was constructed by treating NP cells with 1.0 MPa compression stress. Quantitative real-time polymerase chain reaction assay was used for detecting the expression of circ-CDR1as and miR-432-5p. Immunofluorescent analysis was performed for MMP13 detection. Western blot assay was performed for detecting apoptosis and ECM-related protein expression. Flow cytometry analysis was used for cell apoptosis analysis. The dual-luciferase reporter was used to analyze the interaction between miR-432-5p and circ-CDR1as or SOX9. Differences in means between groups were evaluated using the Student t test or one-way analysis of variance.

RESULTS

In compression-treated human NP cells, we found that circ-CDR1as was significantly downregulated. Functional experiments showed that circ-CDR1as overexpression reduced the compression-induced apoptosis and ECM degradation in NP cells. Further research indicated that circ-CDR1as could act as a molecular sponge for miR-432-5p, a miRNA that enhanced compression-induced damage of NP cells by inhibiting the expression of SOX9. The luciferase reporter experiments also showed that the mutual dialogue between circ-CDR1as and miR-432-5p regulated the expression of SOX9.

CONCLUSIONS

Circ-CDR1as binds to miR-432-5p and plays a protective role in mitigating compression-induced NP cell apoptosis and ECM degradation by targeting SOX9. Circ-CDR1as may provide a novel therapeutic target for the clinical management of IDD in the future.

The Role of Circular RNAs in Male Infertility and Reproductive Cancers: A Narrative Review

Infertility is a global health problem affecting about 15% of all couples, of which 50% are due to male infertility. Although the etiology of infertility is known in most infertile men, idiopathic male infertility remains a challenge. Therefore, there is a need for novel diagnostic methods to detect the underlying mechanisms and develop appropriate therapies. Recent studies have focused on the role of non-coding RNAs (ncRNAs) in male infertility. Circular RNAs (CircRNAs), a type of ncRNAs, are found to play a key role in the development of some pathological conditions, including cardiovascular diseases, diabetes, cancers, autoimmune diseases, etc. Several studies have reported the presence of CircRNAs and their target genes in the human reproductive system. In addition, their expression in testicular tissues, sperm cells, and seminal fluid has been identified. Abnormal expression of CircRNAs has been associated with azoospermia and asthenozoospermia in infertile men. The present narrative review provides a brief description of the role of CircRNAs in spermatogenic cells, male infertility, and reproductive cancers. In addition, some CircRNAs have been identified as potential biomarkers for disease detection and treatment.

Hsa_circ_0017956 Acts as miR-758-3p Sponge to Facilitate the Progression of Non-small-Cell Lung Cancer by Regulating FOXP4 Expression

Accumulating studies have demonstrated the important role of circular RNAs (circRNAs) in the progression of different human tumors, including non-small-cell lung cancer (NSCLC). The purpose of this study was to deeply study the function and mechanism of circ_0017956 in NSCLC. Real-time quantitative polymerase chain reaction (RT-qPCR) was applied to detect the expression of circ_0017956, microRNA-758-3p (miR-758-3p), and Forkhead Box P4 (FOXP4). Western blot was performed to determine the protein levels. Cell proliferation was examined by cell counting kit-8 (CCK-8) assay and 5-ethynyl-2'-deoxyuridine (EdU) assay. Flow cytometry was used to evaluate the apoptosis of NSCLC cells. Transwell assay was applied to detect cell migratory and invasive capacities. The angiogenesis ability was evaluated by tube formation experiment. The target relationship between miR-758-3p and circ_0017956 or FOXP4 was confirmed by dual-luciferase reporter assay. Animal experiment was conducted to assess the effect of circ_0017956 in vivo. Circ_0017956 and FOXP4 were upregulated, while miR-758-3p was downregulated in NSCLC tissues and cells. Silencing of circ_0017956 significantly suppressed cell proliferation, migration, invasion, and angiogenesis, but promoted cell apoptosis in NSCLC cells. Mechanically, circ_0017956 functioned as a sponge for miR-758-3p and miR-758-3p could directly interact with FOXP4. Moreover, silencing of miR-758-3p or overexpression of FOXP4 could overturn the anticancer influence of circ_0017956 interference on NSCLC cells. Besides that, circ_0017956 knockdown hindered tumor growth in vivo. Altogether, circ_0017956 promoted the progression of NSCLC by regulating FOXP4 through sponging miR-758-3p.

CircZNF609 promotes bladder cancer progression and inhibits cisplatin sensitivity via miR-1200/CDC25B pathway

Circular RNAs (circRNAs) have been extensively studied in tumor development and treatment. CircZNF609 (hsa_circ_0000615) has been shown to serve as an oncogene in all kinds of solid tumors and may act as the novel biomarker in tumor diagnosis and therapy in tumor early diagnosis and therapy. However, the underlying character and mechanism of circZNF609 in cisplatin chemosensitivity and bladder cancer (BCa) development were unknown. The expression level of cell division cycle 25B (CDC25B), microRNA 1200 (miR-1200), and circZNF609 in BCa cells and tissues depended on quantitative real-time PCR (qRT-PCR). CDC25B protein level was assayed with Western blot. Functional assays in vitro and in vivo had been conducted to inspect the important role of circZNF609 on BCa progression and cisplatin chemosensitivity in BCa. RNA sequencing and online databases were used to predict the interactions among circZNF609, miR-1200, and CDC25B. Mechanistic exploration was confirmed by RNA pull-down assay, RNA fluorescence in situ hybridization (FISH) and Dual luciferase reporter assay. CircZNF609 expression was increased significantly in BCa cell lines and tissues. For BCa patients, increased expression of circZNF609 was correlated with a worse survival. In vitro and in vivo, enforced expression of circZNF609 enhanced BCa cells proliferation, migration, and cisplatin chemoresistance. Mechanistically, circZNF609 alleviated the inhibition effect on target CDC25B expression by sponging miR-1200. CircZNF609 promoted tumor growth through novel circZNF609/miR-1200/CDC25B axis, implying that circZNF609 has significant potential to act as a new diagnostic biomarker and therapeutic target in BCa. Enhancing cisplatin sensitivity is an important direction for bladder cancer management. 1. This research reveals that circZNF609 improves bladder cancer progression and inhibits cisplatin sensitivity by inducing G1/S cell cycle arrest via a novel miR-1200/CDC25B cascades. 2. CircZNF609 was confirmed associated with worse survival of bladder cancer patients. 3. CircZNF609 act as a prognostic biomarker for bladder cancer treatment.

Highlighting functions of apoptosis and circular RNAs in colorectal cancer

Colorectal cancer (CRC) is known as one of the global problems that endangers the lives of thousands of people every year. Various treatments have been used to deal with this disease, but in some cases, they are not effective. Circular RNAs, as a novel class of noncoding RNAs, have different expression levels and various functions in cancer cells, such as gene regulation through microRNA sponging. They play an important role in various cellular processes, including differentiation, proliferation, invasion, and apoptosis. Changes in the process of apoptosis are closely related to the progression or inhibition of various malignancies. Induction of apoptosis in cancer cells is a promising target for tumor therapy. In this study, circRNAs were investigated as being central to the induction or inhibition of apoptosis in CRC. It is hoped that through targeted changes in the function of these biomolecules, better outcomes will be achieved in cancer treatment. Perhaps better outcomes for cancer treatment can be achieved by using new methods and modifying the expression of these nucleic acids. However, using this method may come with challenges and limitations.

Landscape of NcRNAs involved in drug resistance of breast cancer

Breast cancer (BC) leads to the most amounts of deaths among women. Chemo-, endocrine-, and targeted therapies are the mainstay drug treatments for BC in the clinic. However, drug resistance is a major obstacle for BC patients, and it leads to poor prognosis. Accumulating evidences suggested that noncoding RNAs (ncRNAs) are intricately linked to a wide range of pathological processes, including drug resistance. Till date, the correlation between drug resistance and ncRNAs is not completely understood in BC. Herein, we comprehensively summarized a dysregulated ncRNAs landscape that promotes or inhibits drug resistance in chemo-, endocrine-, and targeted BC therapies. Our review will pave way for the effective management of drug resistance by targeting oncogenic ncRNAs, which, in turn will promote drug sensitivity of BC in the future.

Circular RNA ARHGAP5 inhibits cisplatin resistance in cervical squamous cell carcinoma by interacting with AUF1

Cervical squamous cell carcinoma (CSCC) is one of the leading causes of cancer death in women worldwide. Patients with advanced cervical carcinoma always have a poor prognosis once resistant to cisplatin due to the lack of effective treatment. It is urgent to investigate the molecular mechanisms of cisplatin resistance. Circular RNAs (circRNAs) are known to exert their regulatory functions in a series of malignancies. However, their effects on CSCC remain to be elucidated. Here, we found that cytoplasmic circARHGAP5, derived from second and third exons of the ARHGAP5 gene, was downregulated in cisplatin-resistant tissues compared with normal cervix tissues and untreated cervical cancer tissues. In addition, experiments from overexpression/knockdown cell lines revealed that circARHGAP5 could inhibit cisplatin-mediated cell apoptosis in CSCC cells both in vitro and in vivo. Mechanistically, circARHGAP5 interacted with AU-rich element RNA-binding protein (AUF1) directly. Overexpression of AUF1 could also inhibit cell apoptosis mediated by cisplatin. Furthermore, we detected the potential targets of AUF1 related to the apoptotic pathway and found that bcl-2-like protein 11 (BIM) was not only negatively regulated by AUF1 but positively regulated by circARHGAP5, which indicated that BIM mRNA might be degraded by AUF1 and thereby inhibited tumor cell apoptosis. Collectively, our data indicated that circARHGAP5 directly bound to AUF1 and prevented AUF1 from interacting with BIM mRNA, thereby playing a pivotal role in cisplatin resistance in CSCC. Our study provides insights into overcoming cancer resistance to cisplatin treatment.

RNA helicase DDX5-induced circPHF14 promotes gastric cancer cell progression

As a well-established member of a strongly conserved protein family, DDX5 binds to RNA helicase in a specific manner, which can regulate mRNA transcription, protein translation and synthesis and precursor messenger RNA processing or alternative splicing. The effects of DDX5 on carcinogenesis and cancer progression are increasingly evident. Circular RNAs (circRNAs), a novel group of functionally non-coding RNAs (ncRNAs) with disordered expression, are associated with various pathological processes (e.g., tumors). circRNA pattern and its function regulated by DDX5 have not yet been determined. According to our findings, DDX5 was dramatically upregulated for stomach cancer tissues, and its overexpression contributed to the cell growth and invasion of GC cells. Based on the analysis of genome-wide circRNAs conducted with circRNA sequencing, DDX5 induces a large number of circRNAs. Further to screen several circRNAs from PHF14 for function, it was found that circPHF14 was essential for the growth and tumorigenesis of DDX5-positive gastric cancer cells. These findings suggest that in addition to the messenger RNA and microRNA patterns, DDX5 also effects a circRNA pattern, as demonstrated by circPHF14. DDX5-induced circRNAs have been found to be of crucial importance for the growth of DDX5-positive gastric cancer cells, providing a new therapeutic target.

Emerging landscape of circFNDC3B and its role in human malignancies

In recent years, more attention has been paid to expanding the abundance of Circular RNAs (circRNAs), while the circRNAs that have been found to have significant functions have not been studied in different diseases. CircFNDC3B is one of the most researched circRNAs generated from fibronectin type III domain-containing protein 3B (FNDC3B) gene. Accumulating researches have reported the multiple functions of circFNDC3B in different cancer types and other non-neoplastic diseases, and predicted that circFNDC3B might be a potential biomarker. Notably, circFNDC3B can play roles in different diseases by binding to various microRNAs (miRNAs), binding to RNA-binding proteins (RBPs), or encoding functional peptides. This paper systematically summarizes the biogenesis and function of circRNAs, reviews and discusses the roles and molecular mechanisms of circFNDC3B and its target genes in different cancers and non-neoplastic diseases, which will do favor to broaden our comprehension of the function of circRNAs and facilitate subsequent research on circFNDC3B.

Circular RNA circFAT1(e2) Facilitates Cell Progression through the miR-30e-5P/MYBL2 Pathway in Glioma

Objective

To explore the mechanism of glioma from MYB family genes from the perspective of the circRNA-miRNA-mRNA regulatory network.

Methods

First, the MYB family genes were analyzed by multiple bioinformatics analyses to identify one gene most associated with glioma. Then, the prognostic value and clinical characteristics of the gene were evaluated by bioinformatics analysis and experiments in glioma cells. Next, the target miRNA and circRNA were predicted and verified by dual-luciferase reporter assays. Besides, the functions of target circRNA in glioma were investigated by CCK-8 and Transwell assays. At last, the relation between the screened MYB gene, miRNA, and circRNA in glioma was identified by rescue experiments.

Results

After expression and Cox and survival analysis of six MYB family genes, MYBL2 was identified as the gene most associated with glioma. Then, we found that MYBL2 expression in primary gliomas was higher than those in other histologies, and it had variable expression according to clinical features. Furthermore, MYBL2 knockdown in glioma cells impairs cell growth, invasion, and migration in functional studies. Then, miR-30e-5p and circFAT1(e2) were identified as targets of MYBL2 by bioinformatics prediction and experimental verification. Finally, the relationship between circFAT1(e2), MYBL2, and miR-30e-5p was elucidated by rescue experiments.

Conclusion

circFAT1(e2) could promote glioma development by regulating MYBL2 and miR-30e-5p, and MYBL2 has diagnostic and prognostic values in glioma.

Non-coding RNAs as potential biomarkers of gallbladder cancer

Gallbladder cancer (GBC) performs strongly invasive and poor prognosis, and adenocarcinoma is the most common histological type in it. Statistically, the 5-year survival rate of patients with advanced GBC is less than 5%. Such dismal outcome might be caused by chemotherapy resistance and native biology of tumor cells, regardless of emerging therapeutic strategies. Early diagnosis, depending on biomarkers, receptors and secretive proteins, is more important than clinical therapy, guiding the pathologic stage of cancer and the choice of medication. Therefore, it is in urgent need to understand the specific pathogenesis of GBC and strive to find promising novel biomarkers for early screening in GBC. Non-coding RNAs (ncRNAs), especially microRNAs (miRNAs, miRs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs), are confirmed to participate in and regulate the occurrence and development of GBC. Exceptionally, lncRNAs and circRNAs could act as competing endogenous RNAs (ceRNAs) containing binding sites for miRNAs and crosstalk with miRNAs to target regulatory downstream protein-coding messenger RNAs (mRNAs), thus affecting the expression levels of specific proteins to participate in and regulate the development and progression of GBC. It follows that ncRNAs may become promising biomarkers and potential therapeutic targets for GBC. In this review, we mainly summarize the recent research progress of miRNAs and lncRNAs in regulating the development and progression of GBC, chemoresistance, and predicting the prognosis of patients, and highlight the potential applications of the lncRNA/circRNA-miRNA-mRNA cross-regulatory networks in early diagnosis, chemoresistance, and prognostic evaluation, aiming to better understand the pathogenesis of GBC and develop new diagnostic and therapeutic strategies.

Hsa_circ_0015278 Regulates FLT3-ITD AML Progression via Ferroptosis-Related Genes

AML with the FLT3-ITD mutation seriously threatens human health. The mechanism by which circRNAs regulate the pathogenesis of FLT3-ITD mutant-type AML through ferroptosis-related genes (FerRGs) remains unclear. Differentially expressed circRNAs and mRNAs were identified from multiple integrated data sources. The target miRNAs and mRNAs of the circRNAs were predicted using various databases. The PPI network, ceRNA regulatory network, GO, and KEGG enrichment analyses were performed. The "survival" and the "pROC" R packages were used for K-M and ROC analysis, respectively. GSEA, immune infiltration analysis, and clinical subgroup analysis were performed. Finally, circRNAs were validated by Sanger sequencing and qRT-PCR. In our study, 77 DECircs-1 and 690 DECircs-2 were identified. Subsequently, 11 co-up-regulated DECircs were obtained by intersecting DECircs-1 and DECircs-2. The target miRNAs of the circRNAs were screened by CircInteractome, circbank, and circAtlas. Utilizing TargetScan, ENCORI, and miRWalk, the target mRNAs of the miRNAs were uncovered. Ultimately, 73 FerRGs were obtained, and the ceRNA regulatory network was constructed. Furthermore, MAPK3 and CD44 were significantly associated with prognosis. qRT-PCR results confirmed that has_circ_0015278 was significantly overexpressed in FLT3-ITD mutant-type AML. In summary, we constructed the hsa_circ_0015278/miRNAs/FerRGs signaling axis, which provides new insight into the pathogenesis and therapeutic targets of AML with FLT3-ITD mutation.

The circRNA expression profile of colorectal inflammatory cancer transformation revealed potential predictive biomarkers

Colorectal cancer (CRC) is one of the most common malignant tumors in the world, and most colorectal cancer is transformed from colorectal adenoma (CRA). Identifying biomarkers for the early prediction of colorectal cancer would be an important finding. Circular RNA (circRNA) plays a key role in the occurrence and development of tumors, and its biological characteristics make it a potential biomarker for the early diagnosis of diseases. Therefore, we explored the relationship between circRNA and the malignant transformation from colorectal adenoma to colorectal cancer. We constructed inflammation-based tumorigenesis mouse models and performed high-throughput RNA sequencing to determine the expression profile of circRNAs in tissues at different stages of disease. Subsequent STEM analysis showed that with the development of the disease, 30 circRNAs were significantly downregulated, and 10 circRNAs were significantly upregulated. After qRT-PCR and Fish analysis verification, it was clear that mmu_circ_0008035 and mmu_circ_0000420 were significantly and continuously overexpressed in the development of colorectal cancer in our mouse model. Next, through homology analysis of circRNA in human and mouse and validation of clinical normal tissues, adenoma tissues and CRC tissues, we found biomarkers of has_circ0101338 ahashsa_circ0022426 that could predict the malignant transformation of human colorectal inflammation into CRC and have certain diagnostic value. In conclusion, our results may shed light on the mechanism of progression from precancerous adenoma to cancer and provide biomarkers that may be used in the early diagnosis of CRC.

CircHADHA-augmented autophagy suppresses tumor growth of colon cancer by regulating autophagy-related gene via miR-361

Colon cancer undergoes a traditional pathway from colon polyps to colon cancer. It is of great significance to investigate the key molecules involved in carcinogenesis from polyps to malignancies. Circular RNAs (circRNAs) are stably expressed in human body fluids such as plasma. Here, we demonstrated a differential expression pattern of plasma circRNAs in healthy individuals, colon polyp patients and colon cancer patients using circRNA Arraystar microarray. We explored that circRNA HADHA (circHADHA) was upregulated in plasma from polyp patients, whereas it was downregulated in plasma from colon cancer patients. Overexpression of circHADHA promoted autophagy in colon epithelial cells. Moreover, in colon cancer cells, overexpression of circHADHA promoted autophagy, whereas it inhibited cell proliferation and colony formation. CircHADHA increased the expression of ATG13 via miR-361 in both colon epithelial and cancer cells. ATG13 knockdown reduced autophagy even in the presence of circHADHA in colon cancer cells. Furthermore, the growth of circHADHA-overexpressing colon cancer cell-derived xenograft tumors was significantly decreased compared with control tumors in nude mice. In conclusion, circHADHA was differentially expressed in the plasma of healthy individuals, colon polyp patients and colon cancer patients. CircHADHA promoted autophagy by regulating ATG13 via miR-361 in both colon epithelial and cancer cells. CircHADHA suppressed tumor growth by inducing cell autophagy in colon cancer cells. CircHADHA potentially serves as a biomarker for screening of precursor colon cancer and a therapeutic target for colon cancer treatment.

Curcumin Targeting Non-Coding RNAs in Colorectal Cancer: Therapeutic and Biomarker Implications

Colorectal cancer is one of the most common gastrointestinal malignancies, with high incidence rates, a low rate of early diagnosis, and complex pathogenesis. In recent years, there has been progress made in its diagnosis and treatment methods, but tumor malignant proliferation and metastasis after treatment still seriously affect the survival and prognosis of patients. Therefore, it is an extremely urgent task of current medicine to find new anti-tumor drugs with high efficiency and safety and low toxicity. Curcumin has shown potent anti-tumor and anti-inflammatory effects and is considered a hot spot in the research and development of anti-tumor drugs due to its advantages of precise efficacy, lower toxic side effects, and less drug resistance. Recent studies have revealed that curcumin has anti-tumor effects exerted on the epigenetic regulation of tumor-promoting/tumor-suppressing gene expression through the alteration of expression levels of non-coding RNAs (e.g., lncRNAs, miRNAs, and circRNAs). Herein, we summarize the interaction between curcumin and non-coding RNAs on the occurrence and development of colorectal cancer. The information complied in this review will serve as a scientific and reliable basis and viewpoint for the clinical application of non-coding RNAs in colorectal cancer.

CircLIFR Inhibits Non-small Cell Lung Cancer Progression by Acting as a miR-429 Sponge to Enhance CELF2 Expression

Lung cancer is the most commonly diagnosed cancer and the leading reason for tumor-related mortality, while non-small cell lung cancer (NSCLC) is the most usual type of lung cancer. Circular RNAs (circRNAs) have emerged as vital regulators in the development of human cancers, including NSCLC. We aimed to explore the functions of circRNA leukemia inhibitory factor receptor (circLIFR) in NSCLC progression. Real-time quantitative polymerase chain reaction (RT-qPCR) was used to quantify the expression of circLIFR, microRNA-429 (miR-429), and Elav-like family member 2 (CELF2) in NSCLC tissues and cells. Cell proliferation capability of NSCLC cells was determined by Cell Counting Kit-8 (CCK-8) and colony formation assays. The flow cytometry assay was performed to evaluate cell-cycle distribution and apoptosis of NSCLC cells. The abilities of migration and invasion were measured by transwell assay. In addition, the activities of caspase 3 and caspase 9 were measured by the assay kits. The interaction relationship between miR-429 and circLIFR or CELF2 was analyzed by dual-luciferase reporter, RNA immunoprecipitation (RIP), and RNA pull-down assays. The expression levels of related proteins were examined by Western Blot assay. The xenograft experiment was established to explore the role of circLIFR in vivo. CircLIFR, circular, and stable transcript in NSCLC cells, was decreased more than 2 folds in NSCLC tissues and cells than controls (P < 0.0001). Importantly, overexpression of circLIFR impeded cell proliferation, migration, invasion, and inactivated protein kinase B (AKT)/phosphatase and tensin homolog (PTEN)-signaling pathways while enhanced apoptosis and cell-cycle arrest in NSCLC cells, which was overturned by upregulation of miR-429 or silencing of CELF2. Furthermore, the upregulation of circLIFR inhibited NSCLC tumor growth in vivo. Overexpression of circLIFR could suppress NSCLC progress by acting as a sponge of miR-429 to regulate the expression of CELF2 and PTEN/AKT-signaling pathways in NSCLC.

Integrative analysis of synovial sarcoma transcriptome reveals different types of transcriptomic changes

Background: Synovial sarcoma (SS) is a rare and aggressive cancer that can come from distinct soft tissue types including muscle and ligaments. However, the transcriptomic landscape of SS is still poorly understood. This study aimed to systematically dissect the changes in SS transcriptome from different perspectives.

Methods: We performed deep total RNA sequencing on ten paired Synovial sarcoma and tumor-adjacent tissues to systematically dissect the transcriptomic profile of SS in terms of gene expression, alternative splicing, gene fusion, and circular RNAs.

Results: A total of 2,309 upregulated and 1,977 downregulated genes were identified between SS and tumor-adjacent tissues. Those upregulated genes could lead to the upregulation of the cell cycle, ribosome, and DNA replication pathways, while the downregulated genes may result in the downregulation of a set of metabolic biological processes and signaling pathways. Moreover, 2,511 genes (including 21 splicing factors) were differentially alternative spliced, indicating that the deregulation of alternative splicing could be one important factor that contributes to tumorigenesis. Additionally, we identified the known gene fusions of SS18-SSX1/SSX2 as well as 11 potentially novel gene fusions. Interestingly, 49 circular RNAs were differentially expressed and their parental genes could function in muscle contraction and muscle system processes.

Conclusions: Collectively, our comprehensive dissection of the transcriptomic changes of SS from both transcriptional and post-transcriptional levels provides novel insights into the biology and underlying molecular mechanism of SS.

Circular RNA circTTBK2 facilitates non-small-cell lung cancer malignancy through the miR-873-5p/TEAD1/DERL1 axis

Aim: The underlying mechanisms by which circular RNAs (circRNAs) regulate non-small-cell lung cancer (NSCLC) progression remain elusive. This study investigated the role of circRNA circTTBK2 in NSCLC tumorigenesis. Materials & methods: Quantitative reverse transcriptase polymerase chain reaction analysis of circTTBK2 in NSCLC tissues and cell lines was performed. Cell proliferation, migration, invasion and tumorigenesis were confirmed in vitro and in vivo using CCK-8, EdU incorporation, Transwell assays and xenograft technique. The circTTBK2/miR-873-5p/TEAD1/DERL1 axis was verified by RNA immunoprecipitation, chromatin immunoprecipitation and luciferase reporter assays. Results: Overexpressed circTTBK2 in NSCLC tissues indicates poor prognosis of NSCLC patients. circTTBK2 harbors miR-873-5p, and miR-873-5p directly targets TEAD1. TEAD1 transcriptionally activates DERL1. Conclusion: This study revealed a novel machinery of circTTBK2/miR-873-5p/TEAD1/DERL1 for NSCLC tumorigenesis.

Lidocaine Suppresses Gastric Cancer Development Through Circ_ANO5/miR-21-5p/LIFR Axis

BACKGROUND

Lidocaine has been manifested to exert anti-tumor role in gastric cancer (GC) progression. However, the action mechanism by which Lidocaine functions in GC has not been fully elucidated.

AIM

The study aimed to reveal the molecular mechanism of Lidocaine in GC progression.

METHODS

Cell clonogenicity and viability were assessed by colony formation and methyl thiazolyl tetrazolium assays, respectively. Transwell assay was employed to detect cell migration and invasion. Flow cytometry was implemented to monitor cell apoptosis. Relative expression of circular RNA ANO5 (circ_ANO5), microRNA (miR)-21-5p and Leukemia inhibitory factor receptor (LIFR) was examined by quantitative reverse transcription-polymerase chain reaction. Western blot assay was performed to analyze the levels of LIFR and cell metastasis-related proteins. The target relationship between miR-21-5p and circ_ANO5 or LIFR was confirmed by dual-luciferase reporter assay. In addition, xenograft model was established to explore the role of Lidocaine in vivo.

RESULTS

Lidocaine inhibited cell proliferation, migration and invasion, while promoted apoptosis of GC cells. Lidocaine upregulated circ_ANO5 and LIFR expression, but downregulated miR-21-5p expression in GC cells. Additionally, expression of circ_ANO5 and LIFR was decreased, while miR-21-5p expression was increased in GC cells. Circ_ANO5 depletion or miR-21-5p overexpression attenuated Lidocaine-induced anti-proliferative and anti-metastatic effects on GC cells. Circ_ANO5 could sponge miR-21-5p, and miR-21-5p targeted LIFR. Moreover, Lidocaine suppressed the tumor growth in vivo.

CONCLUSION

Lidocaine might GC cell malignancy by modulating circ_ANO5/miR-21-5p/LIFR axis, highlighting a novel insight for GC treatment.

Hsa_circ_0046523 Mediates an Immunosuppressive Tumor Microenvironment by Regulating MiR-148a-3p/PD-L1 Axis in Pancreatic Cancer

Background

Circular RNAs (circRNAs) are a novel type of non-coding RNA, play an important role in the progression of tumors. However, the function and mechanism of circRNAs in regulating immune microenvironment of pancreatic cancer (PC) remain largely unclear.

Methods

The effects of hsa_circ_0046523 expression on proliferation, migration and invasion of PC cells were analyzed by CCK8 and Transwell assays. Flow cytometry was used to detect the proportion of CD4⁺ T cells, CD8⁺ T cells and Tregs in peripheral blood mononuclear cells (PBMCs) after co-culture, and the apoptosis, depletion and function of CD8⁺ T cells. The expression levels of immunoregulatory cytokines were detected by enzyme linked immunosorbent assay (ELISA). The dual-luciferase reporter was performed to determine the interaction between hsa_circ_0046523, miR-148a-3p, and PD-L1. Rescue experiments and PD-L1 blocking experiments were employed to investigate whether hsa_circ_0046523 exerts its biological function by miR-148a-3p/PD-L1 in PC. Furthermore, an immunocompetent murine PC model was established to confirm these findings.

Results

Hsa_circ_0046523 expression was remarkably upregulated in PC tissues and cell lines. Moreover, high expression of hsa_circ_0046523 was correlated with advanced pathological stage and poorer prognosis. Hsa_circ_0046523 overexpression promoted the proliferation, migration and invasion of PC cells in vitro. Co-culture experiments confirmed that forced expression of hsa_circ_0046523 could decrease the proportion of CD4⁺ and CD8⁺ T cells, as well as increase the proportion of Tregs among peripheral blood mononuclear cells (PBMCs). Meanwhile, hsa_circ_0046523 overexpression promoted the apoptosis and exhaustion of CD8⁺ T cells, inhibited CD8⁺ T cell function, increased the secretion of immunosuppressive cytokines IL-10 and TGF-β, and decreased the secretion of immune effector cytokines IFN-γ and IL-2 among PBMCs. Mechanistically, hsa_circ_0046523 exerted its biological function by binding to miR-148a-3p to upregulate PD-L1 expression in PC. Moreover, these immune modulating functions of miR-148a-3p/PD-L1 axis were also confirmed in an immunocompetent murine PC model.

Conclusions

Our study suggests that hsa_circ_0046523/miR-148a-3p/PD-L1 regulatory axis mediates PC immunosuppressive microenvironment and these molecules are expected to be new targets for remodeling tumor immune microenvironment of PC.

The circSPON2/miR-331-3p axis regulates PRMT5, an epigenetic regulator of CAMK2N1 transcription and prostate cancer progression

BACKGROUND

Prostate cancer (PCa) is the most frequently diagnosed malignancy in men, and its mechanism remains poorly understood. Therefore, it is urgent to discover potential novel diagnostic biomarkers and therapeutic targets that can potentially facilitate the development of efficient anticancer strategies.

METHODS

A series of functional in vitro and in vivo experiments were conducted to evaluate the biological behaviors of PCa cells. RNA pulldown, Western blot, luciferase reporter, immunohistochemistry and chromatin immunoprecipitation assays were applied to dissect the detailed underlying mechanisms. High-throughput sequencing was performed to screen for differentially expressed circRNAs in PCa and adjacent normal tissues.

RESULTS

Upregulation of protein arginine methyltransferase 5 (PRMT5) is associated with poor progression-free survival and the activation of multiple signaling pathways in PCa. PRMT5 inhibits the transcription of CAMK2N1 by depositing the repressive histone marks H4R3me2s and H3R8me2s on the proximal promoter region of CAMK2N1, and results in malignant progression of PCa both in vitro and in vivo. Moreover, the expression of circSPON2, a candidate circRNA in PCa tissues identified by RNA-seq, was found to be associated with poor clinical outcomes in PCa patients. Further results showed that circSPON2 induced PCa cell proliferation and migration, and that the circSPON2-induced effects were counteracted by miR-331-3p. Particularly, circSPON2 acted as a competitive endogenous RNA (ceRNA) of miR-331-3p to attenuate the repressive effects of miR-331-3p on its downstream target PRMT5.

CONCLUSIONS

Our findings showed that the epigenetic regulator PRMT5 aggravates PCa progression by inhibiting the transcription of CAMK2N1 and is modulated by the circSPON2/miR-331-3p axis, which may serve as a potential therapeutic target for patients with aggressive PCa.

The Emerging Roles of Circ-ABCB10 in Cancer

Circular RNAs (circRNAs) are non-coding RNAs (ncRNAs) without 5′ caps and 3′ tails, which are formed from precursor mRNAs (pre-mRNAs) that are inversely back-spliced by exons. CircRNAs are characterized by a covalently closed circular structure and are abundantly expressed in eukaryotic cells. With the development of RNA-sequencing, it was discovered that circRNAs play important roles in the regulation of numerous human genes and are related to the occurrence, development, and prognosis of diseases. Studies in various cancers have revealed that circRNAs have both positive and negative effects on the occurrence and development of tumors. Circ-ABCB10, a circular RNA originating from exons of ABCB10 located on chromosome 1q42, has been proven to play an important role in different types of cancers. Here, we report the primary findings of recent research studies by many contributors about the roles of circ-ABCB10 in cancer and clearly formulate its influence and functions in different aspects of cancer biology, which gives us a broad picture of circ-ABCB10. Thus, this study aimed to generalize the roles of circ-ABCB10 in the diagnosis and treatment of different types of tumors and its related miRNA genes. In this way, we wish to provide a sufficient understanding and assess the future development direction of the research on circ-ABCB10.

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

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

Liquid biopsy at the frontier of detection, prognosis and progression monitoring in colorectal cancer

Colorectal cancer (CRC) is one of the most common cancers worldwide and a leading cause of carcinogenic death. To date, surgical resection is regarded as the gold standard by the operator for clinical decisions. Because conventional tissue biopsy is invasive and only a small sample can sometimes be obtained, it is unable to represent the heterogeneity of tumor or dynamically monitor tumor progression. Therefore, there is an urgent need to find a new minimally invasive or noninvasive diagnostic strategy to detect CRC at an early stage and monitor CRC recurrence. Over the past years, a new diagnostic concept called “liquid biopsy” has gained much attention. Liquid biopsy is noninvasive, allowing repeated analysis and real-time monitoring of tumor recurrence, metastasis or therapeutic responses. With the advanced development of new molecular techniques in CRC, circulating tumor cells (CTCs), circulating tumor DNA (ctDNA), exosomes, and tumor-educated platelet (TEP) detection have achieved interesting and inspiring results as the most prominent liquid biopsy markers. In this review, we focused on some clinical applications of CTCs, ctDNA, exosomes and TEPs and discuss promising future applications to solve unmet clinical needs in CRC patients.

Circular RNA TLK1 Exerts Oncogenic Functions in Hepatocellular Carcinoma by Acting as a ceRNA of miR-138-5p

Mounting evidence has shown that circular RNAs (circRNAs) function as key regulators in carcinogenesis and cancer progression, and this study is aimed at investigating the regulatory functions of circRNA TLK1 (circ-TLK1) in hepatocellular carcinoma (HCC). We observed that circ-TLK1 was highly expressed in HCC samples, and its high expression was closely associated with poor clinicopathological variables of HCC patients. The results of functional experiments revealed that knockdown of circ-TLK1 remarkably inhibited the proliferation, migration, invasion, and EMT of HCC cells, while circ-TLK1 overexpression promoted these malignant behaviors. Moreover, we noted that circ-TLK1 was capable of binding to miR-138-5p and upregulating its target gene, SOX4 in HCC. Based on rescue assays, miR-138-5p inhibition partially suppressed the effects of circ-TLK1 knockdown on the malignant behaviors of HCC cells. In short, this study is the first to indicate that circ-TLK1 functions as an oncogene in HCC progression partly through acting as a ceRNA of miR-138-5p, which may be a promising target for HCC therapy.

Non-coding RNAs and glioblastoma: Insight into their roles in metastasis

Glioma, also known as glioblastoma multiforme (GBM), is the most prevalent and most lethal primary brain tumor in adults. Gliomas are highly invasive tumors with the highest death rate among all primary brain malignancies. Metastasis occurs as the tumor cells spread from the site of origin to another site in the brain. Metastasis is a multifactorial process, which depends on alterations in metabolism, genetic mutations, and the cancer microenvironment. During recent years, the scientific study of non-coding RNAs (ncRNAs) has led to new insight into the molecular mechanisms involved in glioma. Many studies have reported that ncRNAs play major roles in many biological procedures connected with the development and progression of glioma. Long ncRNAs (lncRNAs), microRNAs (miRNAs), and circular RNAs (circRNAs) are all types of ncRNAs, which are commonly dysregulated in GBM. Dysregulation of ncRNAs can facilitate the invasion and metastasis of glioma. The present review highlights some ncRNAs that have been associated with metastasis in GBM. miRNAs, circRNAs, and lncRNAs are discussed in detail with respect to their relevant signaling pathways involved in metastasis.

Genome-wide profiling of the expression of serum derived exosomal circRNAs in patients with hepatic alveolar echinococcosis

The patients with hepatic alveolar echinococcosis is poorly detected due to invasive and slow growth. Thus, early diagnosis of hepatic alveolar echinococcosis is so important for patients. Circular RNAs are crucial types of the non-coding RNA. Recent studies have provided serum-derived exosomal circRNAs as potential biomarkers for detection of various diseases. The clinical importance of exosomal circRNAs in hepatic alveolar echinococcosis have never been explored before. Here, we investigated the serum-derived exosomal circRNAs in the diagnosis of hepatic alveolar echinococcosis. Firstly, High-throughput Sequencing was performed using 9 hepatic alveolar echinococcosis and 9 control samples to detect hepatic alveolar echinococcosis related circRNAs. Afterwards, bioinformatic analyzes were performed to identify differentially expressed circRNAs and pathway analyzes were performed. Finally, validation of the determined circRNAs was performed using RT-PCR. The sequencing data indicated that 59 differentially expressed circRNAs; 31 up-regulated and 28 down-regulated circRNA in hepatic alveolar echinococcosis patients. The top 5 up-regulated and down-regulated circRNAs were selected for validation by RT-qPCR assay. As a result of the verification, circRNAs that were significantly up- and down-regulated showed an expression profile consistent with the results obtained. Importantly, our findings suggested that identified exosomal circRNAs could be a potential biomarker for the detection of hepatic alveolar echinococcosis serum and may help to understand the pathogenesis of hepatic alveolar echinococcosis.

The novel circular RNA HIPK3 accelerates the proliferation and invasion of hepatocellular carcinoma cells by sponging the micro RNA-124 or micro RNA-506/pyruvate dehydrogenase kinase 2 axis

Circular RNAs (circRNAs) have been confirmed to be associated with the progression of various cancers, including hepatocellular carcinoma (HCC). However, the role and mechanism of circHIPK3 in HCC are still unclear. To investigate its function, circHIPK3 expression was first determined by RT–qPCR in HCC tissues or cells. Functionally, cell proliferation and invasion were investigated by CCK-8, EdU, or Transwell assays. In terms of understanding the mechanism, the interaction of the circRNA HIPK3/micro RNA 124 (miRNA 124) or micro RNA 506 (miRNA506) /PDK2 regulatory loop was verified by dual-luciferase reporter gene assay. In addition, a xenograft tumor model was established to confirm the impact of circHIPK3 on the growth of HCC cells in vivo. We found that circHIPK3 was upregulated in HCC patients and associated with clinical characteristics, while miR-124 and miR-506 were downregulated in HCC patients. Additionally, we proved that knock down of circHIPK3 remarkably suppressed the proliferation and invasion of HCC cells. Mechanistically, circHIPK3 directly bound to miR-124 or miR-506 and inhibited their expression, and PDK2 was a target gene of miR-124 or miR-506. Moreover, circHIPK3 overexpression reversed the inhibitory effect of miR-124 or miR-506 on HCC progression. miR-124 or miR-506 could also suppress tumorigenesis of HCC cells by PDK2. Furthermore, in vivo evidence confirmed that knock down of circHIPK3 inhibited tumor formation. We suggest that circHIPK3 can accelerate the proliferation and invasion of HCC cells by sponging miR-124 or miR-506 to upregulate PDK2, which is the underlying mechanism of circHIPK3-induced HCC progression.

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

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

Systematic Review With Meta-Analysis: Diagnostic, Prognostic and Clinicopathological Significance of CircRNA Expression in Renal Cancer

Background

Renal cancer (RC) is one of the most common malignant tumors of the urinary system, and molecular targets for the specific diagnosis and treatment of RC have been widely explored. The purpose of this study was to systematically analyze circular RNAs (circRNAs), which may serve as novel tumor markers in terms of the diagnosis, prognosis and clinicopathological characteristics of RC.

Methods

PubMed and Web of Science were systematically searched for literature as up to July 30, 2021. All included studies were evaluated by the evaluation system, and the results were satisfactory. Hazard ratios (HRs) and odds ratios (ORs) were used to assess the association of circRNAs with diagnostic and clinicopathological indicators. The sensitivity (SEN), specificity (SPE), positive likelihood ratio, negative likelihood ratio, diagnostic odds ratio and area under the summary receiver operating characteristic curve (AUC) were combined to evaluate the diagnostic performance of circRNAs in RC.

Results

We included 22 studies that met the criteria, including 18 that were prognostic, 4 that were diagnostic, and 12 that were clinicopathologically relevant. In terms of prognosis, we found that upregulated circRNAs were positively associated with poor overall survival in patients with RC (HR=1.63, 95% CI=1.43–1.85). In terms of diagnosis, the combined SEN, SPE and AUC of circRNAs in the diagnosis of RC were 0.82, 0.84 and 0.89 (0.86–0.91), respectively. In terms of clinicopathological features, upregulated circRNAs were associated with the Fuhrman grade (OR=0.641, 95% CI=0.471–0.873), T stage (OR=0.236, 95% CI=0.141–0.396), TNM stage (OR=0.225, 95% CI=0.158–0.321) and lymphatic metastasis (OR=0.329, 95% CI=0.193–0.560).

Conclusion

Our meta-analysis confirms that circRNAs may be candidate biomarkers for the diagnosis, prognosis, and clinicopathological indicators of RC.

circHIPK3 Exacerbates Folic Acid-Induced Renal Tubulointerstitial Fibrosis by Sponging miR-30a

Renal tubulointerstitial fibrosis is a common pathological feature of progressive chronic kidney disease (CKD), and current treatment has limited efficacy. The circular RNA circHIPK3 is reported to participate in the pathogenesis of various human diseases. However, the role of circHIPK3 in renal fibrosis has not been examined. In this study, we aimed to determine whether and how circHIPK3 might participate in the pathogenesis of renal fibrosis. Mice received a peritoneal injection of folic acid (250 mg/kg). Of note, 30 days later, renal fibrosis was present on periodic acid-Schiff (PAS) and Masson staining, and mRNA and protein of profibrotic genes encoding fibronectin (FN) and collagen 1 (COL1) were increased. Renal circHIPK3 was upregulated, while miR-30a was downregulated, assessed by quantitative PCR (qPCR) and fluorescence in situ hybridization (FISH). The expression of transforming growth factor beta-1 (TGF-β1) was increased by qPCR analysis, immunoblotting, and immunofluorescence. Renal circHIPK3 negatively correlated with miR-30a, and kidney miR-30a negatively correlated with TGF-β1. Target Scan and miRanda algorithms predicted three perfect binding sites between circHIPK3 and miR-30a. We found that circHIPK3, miR-30a, and TGF-β1 colocalized in the cytoplasm of human tubular epithelial cells (HK-2 cells) on FISH and immunofluorescence staining. We transfected circHIPK3 and a scrambled RNA into HK-2 cells; miR-30a was downregulated, and the profibrotic genes such as TGF-β1, FN, and COL1 were upregulated and assessed by qPCR, immunoblotting, and immunofluorescence staining. Third, the upregulation of circHIPK3, downregulation of miR-30a, and overproduction of profibrotic FN and COL1 were also observed in HK-2 cells exposed to TGF-β1. Finally, renal biopsies from patients with chronic tubulointerstitial nephritis manifested similar expression patterns of circHIPK3, miR-30a, and profibrotic proteins, such as TGF-β1, FN, and COL1 as observed in the experimental model. A feed-forward cycle was observed among circHIPK3, miR-30a, and TGF-β1. Our results suggest that circHIPK3 may contribute to progressive renal fibrosis by sponging miR-30a. circHIPK3 may be a novel therapeutic target for slowing CKD progression.

Deciphering the tRNA-derived small RNAs: origin, development, and future

Transfer RNA (tRNA)-derived small RNAs (tsRNAs), a novel category of small noncoding RNAs, are enzymatically cleaved from tRNAs. Previous reports have shed some light on the roles of tsRNAs in the development of human diseases. However, our knowledge about tsRNAs is still relatively lacking. In this paper, we review the biogenesis, classification, subcellular localization as well as action mechanism of tsRNAs, and discuss the association between chemical modifications of tRNAs and the production and functions of tsRNAs. Furthermore, using immunity, metabolism, and malignancy as examples, we summarize the molecular mechanisms of tsRNAs in diseases and evaluate the potential of tsRNAs as new biomarkers and therapeutic targets. At the same time, we compile and introduce several resource databases that are currently publicly available for analyzing tsRNAs. Finally, we discuss the challenges associated with research in this field and future directions.

Circular RNAs as a Diagnostic Biomarker in Oral Squamous Cell Carcinoma: A Meta-Analysis

PURPOSE

Studies have found a positive correlation between various cancers and circular RNAs (circRNAs), which are newly discovered noncoding RNAs. However, limited scientific evidence is available to prove the clinical value of circRNAs in the presentation of oral squamous cell carcinoma (OSCC). This study aimed to comprehensively explore the potential of circRNAs as diagnostic indexes of OSCC.

METHODS

Online databases were systematically searched to identify published literature on the discovery of circRNAs in OSCC. Data were acquired from each reviewed study and collated to create a 2 × 2 eventuality table. Hierarchical analysis of the literature was conducted for the type of cancer, year of publication, and the sample size of each study. The diagnostic accuracy was calculated using indexes such as the pooled sensitivity and specificity and critically assessed using the Quality Assessment for Studies of Diagnostic Accuracy 2.

RESULTS

This meta-analysis included findings of 6 studies on 335 patients diagnosed with OSCC. These 6 studies examined 7 circRNAs, 5 in tissues and 2 in the saliva of patients with OSCC. When used as a diagnostic tool for OSCC, circRNAs manifested a sensitivity level of 0.72 (95% confidence interval: 0.67 to 0.76) and a degree of specificity of 0.81 (95% confidence interval: 0.76 to 0.85), with a general projected probability rate of 3.82 (95% confidence interval: 2.98 to 4.91) being positive and 0.35 (95% confidence interval: 0.29 to 0.41) being negative. The combined probability rate was 11.07 (95% confidence interval: 7.64 to 16.04), comprising a total of 0.76 (95% confidence interval: 0.72 to 0.79) of the region under the curve. A higher diagnostic value was found for salivary circRNAs (diagnostic odds ratio = 17.52; 95% CI: 10.11 to 30.35) than for tissue circRNAs (diagnostic odds ratio = 8.47; 95% CI: 5.6 to 12.83). This indicated that circRNAs showed a good discrimination ability as biomarkers of OSCC.

CONCLUSIONS

circRNAs showed high accuracy in the diagnosis of OSCC and could be used as prospective biomarkers to facilitate the diagnostic process.

The role of non-coding RNAs in chemotherapy for gastrointestinal cancers

Gastrointestinal (GI) cancers, including colorectal, gastric, hepatic, esophageal, and pancreatic tumors, are responsible for large numbers of deaths around the world. Chemotherapy is the most common approach used to treat advanced GI cancer. However, chemoresistance has emerged as a critical challenge that prevents successful tumor elimination, leading to metastasis and recurrence. Chemoresistance mechanisms are complex, and many factors and pathways are involved. Among these factors, non-coding RNAs (ncRNAs) are critical regulators of GI tumor development and subsequently can induce resistance to chemotherapy. This occurs because ncRNAs can target multiple signaling pathways, affect downstream genes, and modulate proliferation, apoptosis, tumor cell migration, and autophagy. ncRNAs can also induce cancer stem cell features and affect the epithelial-mesenchymal transition. Thus, ncRNAs could possibly act as new targets in chemotherapy combinations to treat GI cancer and to predict treatment response.

Epigenetic modifications in acute myeloid leukemia: The emerging role of circular RNAs (Review)

Canonical epigenetic modifications, which include histone modification, chromatin remodeling and DNA methylation, play key roles in numerous cellular processes. Epigenetics underlies how cells that posses DNA with similar sequences develop into different cell types with different functions in an organism. Earlier epigenetic research has primarily been focused at the chromatin level. However, the number of studies on epigenetic modifications of RNA, such as N1‑methyladenosine, 2'‑O‑ribosemethylation, inosine, 5‑methylcytidine, N6‑methyladenosine (m6A) and pseudouridine, has seen an increase. Circular RNAs (circRNAs), a type of RNA species that lacks a 5' cap or 3' poly(A) tail, are abundantly expressed in acute myeloid leukemia (AML) and may regulate disease progression. circRNAs possess various functions, including microRNA sponging, gene transcription regulation and RNA‑binding protein interaction. Furthermore, circRNAs are m6A methylated in other types of cancer, such as colorectal and hypopharyngeal squamous cell cancers. Therefore, the critical roles of circRNA epigenetic modifications, particularly m6A, and their possible involvement in AML are discussed in the present review. Epigenetic modification of circRNAs may become a diagnostic and therapeutic target for AML in the future.

CircSETDB1 knockdown inhibits the malignant progression of serous ovarian cancer through miR-129-3p-dependent regulation of MAP3K3

Background

Circular RNA (circRNA) is recently found to participate in the regulation of tumor progression, including ovarian cancer. However, the application of circRNA SET domain bifurcated histone lysine methyltransferase 1 (circSETDB1) as a therapeutic target in serous ovarian cancer (SOC) remains to be elucidated. Herein, circSETDB1 role in SOC malignant progression and underlying mechanism are revealed.

Methods

The expression of circSETDB1, microRNA-129-3p (miR-129-3p) and mitogen-activated protein kinase kinase kinase 3 (MAP3K3) messenger RNA (mRNA) was detected by quantitative real-time polymerase chain reaction. Protein abundance was determined by western blot analysis. Cell proliferation, apoptosis, invasion and migration were demonstrated by cell counting kit-8 and 5-Ethynyl-29-deoxyuridine assays, flow cytometry analysis, transwell invasion assay and wound-healing assay, respectively. The interaction between miR-129-3p and circSETDB1 or MAP3K3 was predicted by online database, and identified by mechanism assays. The effect of circSETDB1 knockdown on tumor formation in vivo was unveiled by mouse model experiment.

Results

CircSETDB1 and MAP3K3 expression were apparently upregulated, whereas miR-129-3p expression was downregulated in SOC tissues and cells in comparison with normal fallopian tube tissues or normal ovarian epithelial cells. CircSETDB1 knockdown inhibited cell proliferation, invasion and migration, but induced cell apoptosis in SOC cells. Additionally, miR-129-3p inhibitor impaired circSETDB1 silencing-mediated SOC malignant progression. MiR-129-3p repressed SOC cell processes via binding to MAP3K3. Furthermore, circSETDB1 knockdown suppressed tumor growth in vivo.

Conclusion

CircSETDB1 silencing repressed SOC malignant progression through miR-129-3p/MAP3K3 pathway. This study supports circSETDB1 as a new therapeutic target for SOC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13048-021-00875-0.

1. CircSETDB1 expression was increased in SOC tissues and cells.

2. CircSETDB1 silencing repressed the malignancy of SOC cells.

3. CircSETDB1 mediated SOC malignant progression by interacting with miR-129-3p.

4. MAP3K3 served as a target gene of miR-129-3p.

5. CircSETDB1 knockdown inhibited tumor formation in vivo.

Global identification of circular RNAs in imatinib (IM) resistance of chronic myeloid leukemia (CML) by modulating signaling pathways of circ_0080145/miR-203/ABL1 and circ 0051886/miR-637/ABL1

Imatinib (IM), targeting of BCR-ABL1 tyrosine kinase, is currently one of the first-line choices in the treatment of chronic myeloid leukemia (CML). This study aims to explore the molecular mechanisms underlying IM resistance in CML treatment. 108 CML patients were recruited and grouped according to their sensitivity to IM as the responder group (N = 66) and the non-responder group (N = 42). Real-time quantitative PCR (RT-qPCR) was performed to evaluate the expression of candidate circular RNAs (circRNAs), microRNA (miRNAs) and messenger RNA (mRNAs). No significant difference was noted regarding demographic and clinicopathological characteristics between the responder group and the non-responder group. The expression of circ_0080145, circ_0051886 and ABL1 mRNA was significantly increased, while the expression of miR-203 and miR-637 was decreased in the non-responder group as compared with the responders. By using in-silicon analysis, it was predicted that circ_0080145 and circ_0051886 targeted miR-203 and miR-637 respectively, and ABL1 was found to be shared direct target gene of miR-203 and miR-637. Ectopic over-expression of circ_0080145 and circ_0051886 respectively reduced the expression of miR-203 and miR-637. The expression of ABL1 mRNA/protein was most upregulated in culture cells co-transfected with circ_0080145 and circ_0051886 as compared with those cells individually transfected. This study established the signaling pathways of circ_0080145/miR-203/ABL1 and circ 0051886/miR-637/ABL1. The deregulation of circ_0080145 and circ_0051886 is, at least partially, responsible for the development of IM chemoresistance in CML by regulating expression of ABL1 via modulating expression of miR-203 and miR-637.

Circ-RNF121 regulates tumor progression and glucose metabolism by miR-1224-5p/FOXM1 axis in colorectal cancer

Aim

Previous studies have reported that circular RNA (circRNA) is associated with the pathogenesis of CRC. This study was designed to reveal the mechanism of circ-ring finger protein 121 (circ-RNF121) in colorectal cancer (CRC).

Materials and methods

The levels of circ-RNF121, microRNA-1224-5p (miR-1224-5p) and forkhead box M1 (FOXM1) were determined by quantitative real-time polymerase chain reaction (qRT-PCR). Protein level was detected by western blot. Cell proliferation was analyzed by 3-(4,5-Dimethylthazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and cell colony formation assays. Flow cytometry analysis was performed to investigate cell apoptosis. Cell migration and invasion were investigated by transwell and wound-healing assays. Cell glycolysis was detected using glucose, lactate and ADP/ATP ratio assay kits. The binding relationship between miR-1224-5p and circ-RNF121 or FOXM1 was predicted by starBase online database, and identified by dual-luciferase reporter assay. The impacts of circ-RNF121 silencing on tumor formation in vivo were disclosed by in vivo tumor formation assay.

Key findings

Circ-RNF121 and FOXM1 expression were dramatically upregulated, while miR-1224-5p expression was downregulated in CRC tissues or cells compared with control groups. Circ-RNF121 silencing repressed cell proliferation, migration, invasion and glycolysis but induced cell apoptosis in CRC, which were attenuated by miR-1224-5p inhibitor. Additionally, circ-RNF121 acted as a sponge of miR-1224-5p and miR-1224-5p bound to FOXM1. Circ-RNF121 silencing inhibited tumor growth in vivo. Furthermore, circ-RNF121 was secreted through being packaged into exosomes.

Significance

The finding provided a novel insight into studying circRNA-mediated CRC therapy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-02290-3.