Circular RNA Hsa_circ_0066755 as an Oncogene via sponging miR-651 and as a Promising Diagnostic Biomarker for Nasopharyngeal Carcinoma

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

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

Emerging roles of circular RNAs in nasopharyngeal carcinoma: functions and implications

Nasopharyngeal carcinoma (NPC) is a distinct malignancy primarily prevalent in Southern China and Southeast Asia. Circular RNAs (circRNAs), a class of non-coding RNAs, are evolutionarily conserved and exhibit remarkable stability. Their dysregulation has been observed in various cancers, including NPC. In this review, we investigate the pivotal role of circRNAs in NPC, focusing specifically on their involvement in tumor proliferation, apoptosis, metastasis, angiogenesis, stemness, metabolism, and the tumor microenvironment. We highlight the diagnostic and prognostic potential of circRNAs in NPC, emphasizing their utility as biomarkers for early detection, disease monitoring, and prediction of treatment outcomes. Additionally, we explore the therapeutic implications of circRNAs in NPC, highlighting their potential for targeted therapies.

circRNA: a promising all-around star in the future

circRNA is a type of RNA molecule with a circular structure. From initially thinking it was useless to now discovering that it has important and complex functions, the importance of circRNA is increasingly being recognized. circRNA was first discovered as an ncRNA with a molecular sponge function. Clinically, due to its special molecular structure, researchers are generally interested in its potential as a biomarker. Recently, circRNA has been proven to have many functions other than encoding proteins. In the clinical setting, circRNA also has strong potential for application in vaccine preparation and targeted therapy. This article discusses the synthesis of circRNA, introduces its functions and discusses its future development prospects.

Circular RNA SMARCA5 Modulates Epithelial-Mesenchymal Transformation, Proliferation, and Metastasis of Nasopharyngeal Carcinoma Cells via microRNA-582-3p/Phosphatase and Tensin Homolog Axis

The action mechanism in which circular RNA (circ) SMARCA5 targeted nasopharyngeal carcinoma (NPC) cell proliferation, migration, invasion, and apoptosis via microRNA (miR)-582-3p/phosphatase and tensin homolog (PTEN) axis was explored. The examination was performed via reverse transcription-quantitative polymerase chain reaction (RT-qPCR), discovering that circSMARCA5 was elevated while miR-582-3p was silenced in NPC tissues and cells. E-cadherin and N-cadherin were detected. The results illustrated transfection with si-circSMARCA5 or miR-582-3p-mimic was available to repress cancer cell advancement, and E-cadherin was augmented. Transfection with pcDNA 3.1-circSMARCA5 or miR-582-3p-inhibitor was available to accelerate cancer cell advancement, and N-cadherin was augmented. MiR-582-3p-inhibitor blocked the suppression of si-circSMARCA5 on NPC. The si-PTEN blocked the malignant behavior of pcDNA 3.1-circSMARCA5 against NPC. The binding sites between circSMARCA5 and miR-582-3p and between miR-582-3p and PTEN were verified. Linear analysis results illuminated the expression pattern of circSMARCA5 was opposite to miR-582-3p, while the expression pattern of circSMARCA5 was positively associated with PTEN. In brief, the results of the research clarified circSMARCA5 modulated NPC cells' vital movement via the miR-582-3p/PTEN molecular axis.

Circ_0000285 regulates nasopharyngeal carcinoma progression through miR-1278/FNDC3B axis

BACKGROUND

Nasopharyngeal carcinoma (NPC) is cancer with high mortality and poor prognosis. Circular RNAs (circRNAs) have been identified in a wide variety of cancers. But the functional mechanism of circ_000285 in NPC remains unclear.

PURPOSE

To decipher the biological function and molecular mechanism of circ_000285 in NPC.

METHODS

Quantitative PCR (RT-qPCR) was applied for detecting the expression of circ_0000285, miR-1278, and FNDC3B. Western blot was used to measure the protein levels of Fibronectin type III domain containing 3B (FNDC3B), Bcl2 associated X (Bax), and B cell leukemia/lymphoma 2 (Bcl2). Cell proliferation, migration, and invasion were analyzed by colony formation, 5-ethynyl-2'-deoxyuridine (EdU), and transwell assays. Cell apoptosis was detected by flow cytometry assays. ELISA assay was used to analyze Caspase-3 activity. Bioinformatics was used to predict, and the target relationship between miR-1278 and circ_0000285 or FNDC3B was verified by luciferase reporter assay. Tumor xenograft models were established to examine how circ_0000285 functions during the mediation of NPC tumor growth in vivo.

RESULTS

Increased circ_0000285 and FNDC3B expressions, and a decreased miR-1278 expression were observed in NPC tissues and cell lines. Knockdown of circ_0000285 inhibited NPC cell proliferation, migration, invasion, and while promoting NPC cell apoptosis in vitro. Circ_0000285 knockdown-mediated anti-tumor effects in NPC cells could be largely reversed by silencing of miR-1278 or overexpression of FNDC3B. Circ_0000285 could up-regulate FNDC3B expression by sponging miR-1278 in NPC cells. Knockdown of circ_0000285 could inhibit tumor growth in vivo.

CONCLUSION

Circ_0000285 upregulates FNDC3B expression by adsorbing miR-1278 to promote NPC development.

Cystathionine γ-lyase mediates cell proliferation, migration, and invasion of nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is an epithelia-derived malignancy with a distinctive geographic distribution. Cystathionine γ-lyase (CSE) is involved in cancer development and progression. Nevertheless, the role of CSE in the growth of NPC is unknown. In this study, we found that CSE levels in human NPC cells were higher than those in normal nasopharyngeal cells. CSE overexpression enhanced the proliferative, migrative, and invasive abilities of NPC cells and CSE downregulation exerted reverse effects. Overexpression of CSE decreased the expressions of cytochrome C, cleaved caspase (cas)-3, cleaved cas-9, and cleaved poly-ADP-ribose polymerase, whereas CSE knockdown exhibited reverse effects. CSE overexpression decreased reactive oxygen species (ROS) levels and the expressions of phospho (p)-extracellular signal-regulated protein kinase 1/2, p-c-Jun N-terminal kinase, and p-p38, but promoted the expressions of p-phosphatidylinositol 3-kinase (PI3K), p-AKT, and p-mammalian target of rapamycin (mTOR), whereas CSE knockdown showed oppose effects. In addition, CSE overexpression promoted NPC xenograft tumor growth and CSE knockdown decreased tumor growth by modulating proliferation, angiogenesis, cell cycle, and apoptosis. Furthermore, DL-propargylglycine (an inhibitor of CSE) dose-dependently inhibited NPC cell growth via ROS-mediated mitogen-activated protein kinase (MAPK) and PI3K/AKT/mTOR pathways without significant toxicity. In conclusion, CSE could regulate the growth of NPC cells through ROS-mediated MAPK and PI3K/AKT/mTOR cascades. CSE might be a novel tumor marker for the diagnosis and prognosis of NPC. Novel donors/drugs that inhibit the expression/activity of CSE can be developed in the treatment of NPC.

Circ_0000467 modulates malignant characteristics of colorectal cancer via sponging miR-651-5p and up-regulating DNMT3B

Circular RNAs (circRNAs) are widely expressed in cancer tissues and participate in modulating the progression of malignant tumors, playing a pro- or anti-cancer role. This work is conducted to probe the precise role of circ_0000467 in colorectal cancer (CRC) and its regulatory mechanism. The differentially expressed circRNAs in CRC tissues and paracancerous tissues were screened by bioinformatics analysis. The expression levels of circ_0000467, miR-651-5p and DNA methyltransferases 3B (DNMT3B) mRNA in CRC tissues and cells were detected by qRT-PCR. circ_0000467 knockdown cell model was constructed to investigate the effects of circ_0000467 on CRC cell growth, migration and invasion by CCK-8 and Transwell experiments. Western blot was performed to examine DNMT3B protein expression in CRC cells. Dual-luciferase reporter gene experiment was executed to validate the targeting relationship between circ_0000467 and miR-651-5p, miR-651-5p and DNMT3B. Circ_0000467 expression and DNMT3B mRNA expression were increased and miR-651-5p expression was down-regulated in CRC tissues and cell lines. Knockdown of circ_0000467 repressed CRC cell growth, migration and invasion. Dual-luciferase reporter gene experiments validated that miR-651-5p was a direct target of circ_0000467 and miR-651-5p could specifically bind with DNMT3B 3'UTR. Functional compensation experiments showed that the regulatory effect of circ_0000467 on CRC cells' behaviors could be partially counteracted by miR-651-5p. Circ_0000467 may enhance the growth and metastasis of CRC cells by targeting miR-651-5p and up-regulating DNMT3B expression. Circ_0000467 may be a potential diagnostic biomarker and therapeutic target for CRC.

A microRNA Prognostic Signature in Patients with Diffuse Intrinsic Pontine Gliomas through Non-Invasive Liquid Biopsy

Simple Summary

Diffuse intrinsic pontine glioma (DIPG) is a neuro-radiologically defined tumor of the brainstem, primarily affecting children, with most diagnoses occurring between 5 and 7 years of age. Surgical removal in DIPGs is not feasible. Subsequent tumor progression is almost universal and no biomarker for predicting the course of the disease has entered into clinical practice so far. Under these premises, it is essential to develop reliable biomarkers that are able to improve outcomes and stratify patients using non-invasive methods to determine tumor profiles. We designed a study assessing circulating miRNA expression by a high-throughput platform and divided patients into training and validation phases in order to disclose a potential signature with clinical impact. Our results for the first time have proved the usefulness of blood-circulating nucleic acids as powerful, easy-to-assay molecular markers of disease status in DIPG.

Abstract

Diffuse midline gliomas (DMGs) originate in the thalamus, brainstem, cerebellum and spine. This entity includes tumors that infiltrate the pons, called diffuse intrinsic pontine gliomas (DIPGs), with a rapid onset and devastating neurological symptoms. Since surgical removal in DIPGs is not feasible, the purpose of this study was to profile circulating miRNA expression in DIPG patients in an effort to identify a non-invasive prognostic signature with clinical impact. Using a high-throughput platform, miRNA expression was profiled in serum samples collected at the time of MRI diagnosis and prior to radiation and/or systemic therapy from 47 patients enrolled in clinical studies, combining nimotuzumab and vinorelbine with concomitant radiation. With progression-free survival as the primary endpoint, a semi-supervised learning approach was used to identify a signature that was also tested taking overall survival as the clinical endpoint. A signature comprising 13 circulating miRNAs was identified in the training set (n = 23) as being able to stratify patients by risk of disease progression (log-rank p = 0.00014; HR = 7.99, 95% CI 2.38–26.87). When challenged in a separate validation set (n = 24), it confirmed its ability to predict progression (log-rank p = 0.00026; HR = 5.51, 95% CI 2.03–14.9). The value of our signature was also confirmed when overall survival was considered (log-rank p = 0.0021, HR = 4.12, 95% CI 1.57–10.8). We have identified and validated a prognostic marker based on the expression of 13 circulating miRNAs that can shed light on a patient’s risk of progression. This is the first demonstration of the usefulness of nucleic acids circulating in the blood as powerful, easy-to-assay molecular markers of disease status in DIPG. This study provides Class II evidence that a signature based on 13 circulating miRNAs is associated with the risk of disease progression.

Emerging functions of circular RNA in the regulation of adipocyte metabolism and obesity

As noncoding RNAs, circular RNAs (circRNAs) are covalently enclosed endogenous biomolecules in eukaryotes that have tissue specificity and cell specificity. circRNAs were once considered a rare splicing byproduct. With the development of high-throughput sequencing, it has been confirmed that they are expressed in thousands of mammalian genes. To date, only a few circRNA functions and regulatory mechanisms have been verified. Adipose is the main tissue for body energy storage and energy supply. Adipocyte metabolism is a physiological process involving a series of genes and affects biological activities in the body, such as energy metabolism, immunity, and signal transmission. When adipocyte formation is dysregulated, it will cause a series of diseases, such as atherosclerosis, obesity, fatty liver, and diabetes. In recent years, many noncoding RNAs involved in adipocyte metabolism have been revealed. This review provides a comprehensive overview of the basic structure and biosynthetic mechanism of circRNAs, and further discusses the circRNAs related to adipocyte formation in adipose tissue and liver. Our review will provide a reference for further elucidating the genetic regulation mechanism of circRNAs involved in adipocyte metabolism.

Diagnostic and prognostic value of circRNAs expression in head and neck squamous cell carcinoma: A meta-analysis

Background

Circular RNAs (circRNAs) have been found to have potential biological applications against tumors in humans. This study aimed to evaluate the diagnostic, prognostic, and clinicopathological value of circRNAs in head and neck squamous cell carcinoma (HNSCC).

Methods

The PubMed, Web of Science, EMBASE, and the Cochrane Library were comprehensively searched for the relevant studies before October 20, 2021. Statistical analysis was performed based on STATA 15.0, Meta‐DiSc 1.4, and RevMan 5.3 software.

Results

A total of 55 reports regarding 56 kinds of circRNA were studied in this meta‐analysis, including 23, 38, and 26 articles on diagnosis, prognosis, and clinicopathological features, respectively. The pooled sensitivity, specificity, and area under the curve (AUC) of the summary receiver‐operating characteristic curve (SROC) were 0.78, 0.84, and 0.87, respectively. Besides, the upregulation of oncogenic circRNAs was significantly associated with poorer overall survival (OS) (HR=2.25, p < 0.05) and disease‐free interval (DFS) (HR=1.92, p < 0.05). In contrast, the elevated expression of tumor suppressor circRNAs was associated with a favorable prognosis (HR=0.50, p < 0.05). In addition, the high expression of oncogenic circRNAs was associated with the tumor size (OR=3.59, p < 0.05), degree of differentiation (OR=1.89, p < 0.05), TNM stage (OR=2.35, p < 0.05), lymph node metastasis (OR=1.85, p < 0.05), and distant metastasis (OR=3.42, p < 0.05). Moreover, the expression of tumor suppressor circRNAs was associated with improved clinicopathological features (lymph node metastasis: OR=0.25, p < 0.05).

Conclusions

CircRNAs could serve as potential predictive indicators and be useful for the diagnosis, prognosis, and identification of clinicopathological features in HNSCC.

CircTMTC1 contributes to nasopharyngeal carcinoma progression through targeting miR-495-MET-eIF4G1 translational regulation axis

Nasopharyngeal carcinoma (NPC) is the most common primary malignancy arising from the epithelial cells of nasopharynx. CircTMTC1 is upregulated in NPC patients, but its role and molecular mechanism in NPC are unknown. Normal nasopharyngeal epithelium and tumor tissues were collected. The expression of circTMTC1, miR-495, MET/eIF4G1 pathway-related molecules were examined. Colony formation and transwell assays were used to assess cell proliferation, migration, and invasion. Cell apoptosis was analyzed by annexin V and propidium iodide (PI) staining. Gene interaction was examined by RNA immunoprecipitation (RIP) and luciferase activity assays. Subcutaneous and intravenous xenograft mouse models were established to analyze NPC growth and metastasis in vivo. CircTMTC1 was highly expressed and miR-495 was downregulated in NPC, which were associated with poor prognosis of NPC. Both circTMTC1 knockdown and miR-495 overexpression inhibited NPC cell proliferation, migration, invasion, and epithelial-mesenchymal transition (EMT) and promoted cell apoptosis. CircTMTC1 directly targeted miR-495 to promote the expression of its downstream target gene MET. miR-495 knockdown enhanced the expression of c-Myc, Cyclin D1, and survivin and accelerated NPC cell proliferation, migration, invasion, and EMT through targeting MET and activating the MET-eIF4G1 axis. CircTMTC1 silence inhibited NPC growth and lung metastasis by targeting the miR-495-MET-eIF4G1 translational regulation axis in vivo. CircTMTC1 accelerates NPC progression through targeting miR-495 and consequently activating the MET-eIF4G1 translational regulation axis, suggesting potential therapeutic targets for NPC treatment.

SNHG8 promotes cell proliferation, migration, and invasion of nasopharyngeal carcinoma cells as an oncogene through miR-588/HMGA2 axis

Nasopharyngeal carcinoma (NC) poses a threat to the life of patients. Long non-coding RNA (LncRNA) is a novel kind of non-coding RNA, which plays a pivotal role through sponge microRNA (miRNA). Abnormal expression of small nucleolar RNA host gene 8 (SNHG8) is involved in various tumors; however, the role of SNHG8 in NC remains unknown. Quantitative real-time PCR (qRT-PCR) and Western blotting was employed to detect the expression levels of SNHG8, miR-588, and high mobility group A2 (HMGA2). Cell proliferation, migration, and invasion were analyzed by CCK-8 and transwell assays. miR-588 binding sites in SNHG8 were predicted by LncBase analysis. Luciferase reporter and RNA pull-down assay were used to confirm the interaction of SNHG8 and miR-588. SNHG8 was highly expressed in NC cells. The prognosis of the patients with NC in the high expression levels of SNHG8 was poorer than that in the low expression levels. The expression of SNHG8 was closely related to tumor size, TNM stage, and distal metastasis. Knockdown of SNHG8 inhibited cell proliferation, migration, and invasion of NC. SNHG8 targeted miR-588. Inhibition of miR-588 could partially reverse the knockdown of SNHG8 in NC cells, and miR-588 targeted HMGA2. In conclusion, SNHG8 promotes proliferation, migration, and invasion of NC cells through miR-588/HMGA2 in NC as an oncogene.

Prognostic value of EGFR and p-EGFR in nasopharyngeal carcinoma: A systematic review and meta-analysis

PURPOSE

To evaluate the prognostic effect and clinical significance of epidermal growth factor receptor and its phosphorlated form (EGFR/p-EGFR) in nasopharyngeal carcinoma.

METHODS

A systematic review and meta-analysis was designed. We visited PubMed, Embase, China National Knowledge Infrastructure Database, Database of Chinese sci-tech periodicals, WanFang Database, and China Biology Medicine disc to search for Chinese and English publications of prospective studies and retrospective studies investigating the association of EGFR/p-EGFR and nasopharyngeal carcinoma prognosis from inception to April 2021. The inclusion criteria were that the samples should be pathologically confirmed as nasopharyngeal carcinoma and the expression of EGFR/p-EGFR should be detected via immunohistochemistry; the study should analyze the prognostic significance of EGFR/p-EGFR in nasopharyngeal carcinoma; hazard ratio (HR) and 95% confidence interval (CI) should be reported in the study or could be derived from survival curves; and the outcomes of the study should include overall survival (OS), disease-free survival (DFS), progression-free survival (PFS), and distant metastasis-free survival (DMFS).

RESULTS

A total of 18 studies evaluating 1451 samples were included. For studies that reported OS as an outcome, EGFR overexpression indicated worse OS of nasopharyngeal carcinoma patients. The heterogeneity between studies was high (I2 = 91%, P < .01), and a random-effect model was used to combine the effect size (HR = 1.71, 95% CI [1.21, 2.41], P < .01). Further sensitivity analysis and prespecified subgroup analysis were performed to detect the source of heterogeneity, and the results showed that the heterogeneity could not be eliminated. Publication bias assessed by funnel plots and Begg test and Egger test was low (Begg test: P = .846 and Egger test: P = .074). p-EGFR was not correlated with the OS of nasopharyngeal carcinoma patients (HR = 1.01, 95% CI [0.88, 1.15], P = .92). For studies that reported DFS, EGFR overexpression was associated with worse DFS in patients with nasopharyngeal carcinoma (HR = 2.53, 95% CI [1.84, 3.47], P < .01). For studies that reported PFS, EGFR overexpression was not correlated with the PFS of nasopharyngeal carcinoma patients (HR = 1.86, 95% CI [0.90, 3.82], P = .09). For studies that reported DMFS, EGFR overexpression was not correlated with the DMFS of nasopharyngeal carcinoma patients, and high heterogeneity between studies was detected (I2 = 97%, P < .01). A random-effect model was used to combine the effect size (HR = 1.80, 95% CI [0.56, 5.76], P = .32). A sensitivity analysis was conducted. Publication bias was detected to be low (Begg test: P = .817 and Egger test: P = .954). There was no correlation between p-EGFR overexpression and DMFS in patients with nasopharyngeal carcinoma (HR = 1.20, 95% CI [0.95, 1.52], P = .12).

CONCLUSION

In nasopharyngeal carcinoma patients, EGFR overexpression could be used as a biomarker that predicts poor OS and DFS, but not a prognostic biomarker for PFS and DMFS. The overexpression of p-EGFR was not shown to be associated with the prognosis of nasopharyngeal carcinoma patients and could not be used as a prognostic biomarker.

ETHICS AND DISSEMINATION

This study was registered on the International Platform of Registered Systematic Review and Meta-analysis Protocols (INPLASY), and reported as stated by the Preferred Reporting Items for Systematic reviews and Meta-Analyses. Neither ethical approval nor informed consent was required since this study was conducted based on previous publications.

INPLASY REGISTRATION NUMBER

INPLASY 202150010.

Hsa_circ_0007637 Facilitates Nasopharyngeal Carcinoma Progression by Sponging miR-636/TPD52 Axis

Purpose

Hsa_circ_0007637 was discovered to be differentially expressed in nasopharyngeal carcinoma (NPC). However, the exact function and mechanism of Hsa_circ_0007637 on NPC have not been studied. This study firstly researched the function and mechanism of Hsa_circ_0007637 on NPC progression.

Methods

Hsa_circ_0007637, miR-636 and TPD52 expressions in 80 NPC patients were detected by quantitative real-time polymerase chain reaction. Hsa_circ_0007637 effect on NPC cell proliferation, apopticosis, invasion and migration was investigated by cell counting kit-8 assay, flow cytometry, transwell experiment and wound healing assay accordingly. Dual-luciferase reporter gene assay, RNA immunoprecipitation experiment and RNA fluorescence in situ hybridization experiment were performed to identify the binding between Hsa_circ_0007637 and miR-636. Dual-luciferase reporter gene assay and RNA pull down assay were conducted to verify the binding between miR-636 and TPD52. TPD52 protein expression in NPC cells was determined by Western blot. In vivo study was performed using nude mice. Immunohistochemistry was performed to assess TPD52 and Ki67 expression in tissues.

Results

Hsa_circ_0007637 was overexpressed in NPC tissues and cells. High Hsa_circ_0007637 expression predicted a poor outcome for NPC patients. Hsa_circ_0007637 knockdown decreased proliferation, invasion, migration and increased apoptosis of NPC cells (P < 0.01). Hsa_circ_0007637 could enhance TPD52 expression via sponging miR-636. miR-636 overexpression or TPD52 knockdown weakened the promoting effect of Hsa_circ_0007637 on NPC cells malignant phenotype (P < 0.01). Hsa_circ_0007637 knockdown suppressed NPC cells growth in vivo (P < 0.01).

Conclusion

Hsa_circ_0007637 facilitates NPC progression by sponging miR-636/TPD52 axis.

Circular RNA circ_0008450 regulates the proliferation, migration, invasion, apoptosis and chemosensitivity of CDDP-resistant nasopharyngeal carcinoma cells by the miR-338-3p/SMAD5 axis

Circular RNAs have recently been implicated in the tumorigenesis and chemoresistance of nasopharyngeal carcinoma (NPC). In this report, we identified the precise action of circ_0008450 in NPC progression and cisplatin (CDDP) resistance. The levels of circ_0008450, microRNA (miR)-338-3p and SMAD family member 5 (SMAD5) were gauged by quantitative real-time PCR or western blot. Cell proliferation and IC50 value for CDDP were detected by the Cell Counting Kit-8 assay. Cell colony formation, cell cycle progression, apoptosis, migration and invasion were assessed by colony formation, flow cytometry and transwell assays, respectively. Targeted relationships among circ_0008450, miR-338-3p and SMAD5 were determined by dual-luciferase reporter and RNA immunoprecipitation assays. Tumor models were assayed to evaluate the role of circ_0008450 in tumor growth. Our data indicated that up-regulated circ_0008450 was correlated with NPC CDDP resistance. Moreover, the knockdown of circ_0008450 suppressed cell proliferation, migration, invasion, and promoted apoptosis and CDDP sensitivity in vitro, as well as weakened tumor growth in vivo. Mechanistically, circ_0008450 directly bound to miR-338-3p, and the regulatory effects of circ_0008450 on cell malignant behaviors and CDDP sensitivity were mediated by miR-338-3p in vitro. SMAD5 was a direct target of miR-338-3p and circ_0008450 mediated SMAD5 expression through miR-338-3p. Furthermore, the enforced level of miR-338-3p regulated cell malignant behaviors and CDDP sensitivity in vitro via down-regulating SMAD5. Additionally, the phosphatidylinositol 3-kinase (PI3K)/AKT signaling pathway was modulated by the circ_0008450/miR-338-3p axis in the two CDDP-resistant NPC cell lines. Our current study suggested that circ_0008450 modulated the malignant behaviors and drug sensitivity of CDDP-resistant NPC cells at least in part by targeting the miR-338-3p/SMAD5 axis, providing potential targets for improving the treatment of chemoresistant NPC.

Circular RNAs: Functions and mechanisms in nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a malignant epithelial tumor of the nasopharyngeal mucosa with a high incidence rate in southern China and Southeast Asia and an evident ethnic and geographical distribution. Circular RNAs (circRNAs) are single-stranded noncoding RNAs with covalent, closed-loop structures. They are characterized by high stability and abundance, are evolutionarily conserved, and exhibit tissue/developmental stage specificity. Previous studies have shown that circRNAs are associated with the occurrence and development of various malignant tumors. However, the expression patterns and clinical significance of circRNAs in NPC remain ambiguous. Hence, the present review focuses on the biogenesis and regulation of circRNAs, and the functional roles of abnormally expressed circRNAs in NPC. In addition, the current review discusses the possibility of utilizing circRNAs as potential clinical biomarkers for the diagnosis and prognosis of NPC.

The potential of using blood circular RNA as liquid biopsy biomarker for human diseases

Circular RNA (circRNA) is a novel class of single-stranded RNAs with a closed loop structure. The majority of circRNAs are formed by a back-splicing process in pre-mRNA splicing. Their expression is dynamically regulated and shows spatiotemporal patterns among cell types, tissues and developmental stages. CircRNAs have important biological functions in many physiological processes, and their aberrant expression is implicated in many human diseases. Due to their high stability, circRNAs are becoming promising biomarkers in many human diseases, such as cardiovascular diseases, autoimmune diseases and human cancers. In this review, we focus on the translational potential of using human blood circRNAs as liquid biopsy biomarkers for human diseases. We highlight their abundant expression, essential biological functions and significant correlations to human diseases in various components of peripheral blood, including whole blood, blood cells and extracellular vesicles. In addition, we summarize the current knowledge of blood circRNA biomarkers for disease diagnosis or prognosis.

Plasma circRNAs as Biomarkers in Cancer

The incidence and mortality of cancer are increasing each year. At present, the sensitivity and specificity of the blood biomarkers that were used in clinical practice are low, which make the detection rate of cancer decrease. With advances in bioinformatics and technology, some non-coding RNA as biomarkers can be easily detected through some traditional and new technologies. Circular RNAs (circRNAs) are non-coding RNAs, that is, they do not encode proteins, and have important regulatory functions. CircRNAs can remain stable in bodily fluids, such as in saliva, blood, urine, and especially plasma. The difference in the expression of plasma circRNAs between cancer patients and normal people may suggest that plasma circRNAs may play an important role in the occurrence and development of cancer. In this review, we summarized the clinical effect of plasma circRNAs in several high-incidence cancers. CircRNAs may be effective biomarkers for tumour diagnosis, treatment selection and prognosis evaluation.

Cancer-Derived Exosomal miR-651 as a Diagnostic Marker Restrains Cisplatin Resistance and Directly Targets ATG3 for Cervical Cancer

Objective

Cancer-derived exosomes can facilitate drug resistance in cervical cancer. However, the mechanisms remain elusive. Herein, we observed the roles of exosomal miR-651 in cisplatin resistance of cervical cancer.

Methods

Circulating miR-651 was detected in cervical cancer and healthy individuals. The diagnostic efficacy was determined. When transfected with miR-651 mimics, cisplatin resistance, apoptosis, and proliferation were assessed. The cancer-derived exosomes were separated and identified. We observed the uptake of PKH67-labeled exosomes by HeLa/S cells. After coculture with exosomes secreted by HeLa/S or HeLa/DDP cells, malignant behaviors were examined in HeLa/S cells. The interactions between ATG3 and miR-651 were validated by dual luciferase report. Biological behaviors were investigated for HeLa/S cells cocultured with exosomes secreted by miR-651 mimic-transfected HeLa/DDP cells.

Results

Downregulated circulating miR-651 was found in cancer subjects than healthy individuals. It possessed high sensitivity and accuracy in diagnosing cervical cancer (AUC = 0.9050). Lower miR-651 expression was confirmed in HeLa/DDP than HeLa/S cells. Forced miR-651 lessened cisplatin resistance and proliferation and elevated apoptosis in HeLa cells. ATG3 was a direct target of miR-651. The exosomes isolated from HeLa cells were rich in CD63, CD9, and CD81 proteins, thereby identifying the isolated exosomes. Exosomes secreted by HeLa/DDP cells can be absorbed by HeLa/S cells. When being cocultured with exosomes secreted by HeLa/DDP cells, malignant behaviors of HeLa/S cells were enhanced, which were ameliorated by miR-651 mimic exosomes.

Conclusion

Our findings showed that cancer-derived exosomal miR-651 restrained cisplatin resistance and directly targeted ATG3, indicating that exosomal miR-651 could be a therapeutic agent.

CircRNAs and their regulatory roles in cancers

Circular RNAs (circRNAs), a novel type of non-coding RNAs (ncRNAs), have a covalently closed circular structure resulting from pre-mRNA back splicing via spliceosome and ribozymes. They can be classified differently in accordance with different criteria. As circRNAs are abundant, conserved, and stable, they can be used as diagnostic markers in various diseases and targets to develop new therapies. There are various functions of circRNAs, including sponge for miR/proteins, role of scaffolds, templates for translation, and regulators of mRNA translation and stability. Without m7G cap and poly-A tail, circRNAs can still be degraded in several ways, including RNase L, Ago-dependent, and Ago-independent degradation. Increasing evidence indicates that circRNAs can be modified by N-6 methylation (m6A) in many aspects such as biogenesis, nuclear export, translation, and degradation. In addition, they have been proved to play a regulatory role in the progression of various cancers. Recently, methods of detecting circRNAs with high sensitivity and specificity have also been reported. This review presents a detailed overview of circRNAs regarding biogenesis, biomarker, functions, degradation, and dynamic modification as well as their regulatory roles in various cancers. It’s particularly summarized in detail in the biogenesis of circRNAs, regulation of circRNAs by m6A modification and mechanisms by which circRNAs affect tumor progression respectively. Moreover, existing circRNA detection methods and their characteristics are also mentioned.

Hsa-circ_0000064 accelerates the malignant progression of gastric cancer via sponging microRNA-621

Gastric cancer (GC) is one of the most common digestive system tumors in the world. Many circular RNAs (circRNAs) are involved in the progression of GC. The purpose of this study was to delve into the expression characteristics and biological functions of circ_0000064 in GC, and further study its mechanisms. Quantitative real-time polymerase chain reaction (qRT-PCR) was performed to detect circ_0000064 expression in 61 GC tissues and cell lines. Circ_0000064 knockdown was successfully modeled with siRNA. The effects of circ_0000064 on the biological functions of GC cells were analyzed by CCK-8, BrdU, and Transwell assays. Bioinformatics and dual-luciferase reporter gene assay were adopted to explore the relations between circ_0000064 and microRNA-621 (miR-621). Western blot was used to examine the regulatory function of circ_0000064 and miR-621 on SYF2 pre-mRNA splicing factor 2. Cric_0000064 expression was elevated in GC tissues and cell lines. Knocking down cric_0000064 could inhibit the viability, migration, and invasion of GC cells. Dual-luciferase reporter gene assay showed that miR-621 could bind circ_0000064 and SYF2 3'UTR; in addition, miR-621 overexpression or SYF2 knockdown could partially weaken the cancer-promoting effect of circ_0000064 on GC cells. Circ_0000064 expression was negatively correlated with miR-621 expression in GC tissues while positively with SYF2 expression. Circ_0000064 can participate in the GC progression via modulating miR-621/SYF2 axis. This implies that circ_0000064 may be a new diagnosed biomarker or a new therapeutic target of GC.

Research Progress of circRNAs in Head and Neck Cancers

Circular RNAs (circRNAs) are a novel type of non-coding RNAs. Because of their characteristics of a closed loop structure, disease- and tissue-specificity, and high conservation and stability, circRNAs have the potential to be biomarkers for disease diagnosis. Head and neck cancers are one of the most common malignant tumors with high incidence rates globally. Affected patients are often diagnosed at the advanced stage with poor prognosis, owing to the concealment of anatomic sites. The characteristics, functions, and specific mechanisms of circRNAs in head and neck cancers are increasingly being discovered, and they have important clinical significance for the early diagnosis, treatment, and prognosis evaluation of patients with cancer. In this study, the generation, characteristics, and functions of circRNAs, along with their regulatory mechanisms in head and neck cancers have been summarized. We report that circRNAs interact with molecules such as transcription and growth factors to influence specific pathways involved in tumorigenesis. We conclude that circRNAs have an important role to play in the proliferation, invasion, metastasis, energy and substance metabolism, and treatment resistance in cancers.

Diagnostic and Prognostic Value of Circulating CircRNAs in Cancer

Cancer has been regarded as one of the leading causes of mortality worldwide. Diagnostic and prognostic biomarkers with high sensitivity and specificity for cancer play a crucial role in preventing or treating cancer. Circular RNAs (circRNAs), which hold great potential for the management of cancer patients due to their abundance, stable property, and high specificity in serum, plasma, and other body fluids, can be used as non-invasive and blood-based biomarkers in cancer diagnosis and prognosis. There are four types of circRNAs including exonic circRNAs (ecircRNA), intronic circRNAs, exon-intron circRNAs (EIciRNA), and intergenic circRNAs. CircRNAs can act as miRNA sponges, affect protein translation, interplay with RNA binding proteins, regulate protein recruitment, and modulate protein scaffolding and assembly. Therefore, the multifunctionalities of circRNAs make them ideal for detecting and predicting cancer. Indeed, circRNAs manifest high sensitivity and specificity in more than ten types of cancer. This review aims to consolidate the types and functions of circRNAs, as well as discuss the diagnostic and prognostic value of circulating circRNAs in cancer.

Downregulation of circ_0000673 Promotes Cell Proliferation and Migration in Endometriosis via the Mir-616-3p/PTEN Axis

Endometriosis is a common gynecological disease, affecting up to 10% of women of reproductive age and approximately 50% of women with infertility. Circular RNAs (circRNAs) have been shown to be involved in a number of diseases. Dysregulated expression of circRNAs in endometriosis has been reported, and circ_0000673 was significantly downregulated. However, the details of its role in the pathogenesis of endometriosis are still poorly understood. We investigated the location and effects of the downregulation of circ_0000673 in endometriosis. We demonstrated that knockdown of circ_0000673 significantly increased the proliferation and migration of eutopic and normal endometrial cells. Bioinformatics analysis predicted that circ_0000673 might act as a sponge for miR-616-3p. We found that the effect of circ_0000673 knockdown could be recovered by miR-616-3p inhibitor and enhanced by miR-616-3p mimics. qPCR and western blot assays showed that circ_0000673 knockdown could decrease the expression of PTEN and increase the expression of PI3K and p-AKT. PTEN was confirmed to be a target of miR-616-3p. These results demonstrated that the downregulation of circ_0000673 could promote the progression of endometriosis by inactivating PTEN via the deregulation of miR-616-3p.