Circular RNAs: Promising biomarkers for cancer diagnosis and prognosis

Clinical value and potential circulating of miR-99a as tumor suppressor biomarker in serum of oral squamous cell carcinoma and erosive atrophic lichen planus

OBJECTIVES

Oral squamous cell carcinoma (OSCC) is the most common type of oral neoplasms that consist of more over 90% of oral cancers. It was demonstrated that erosive atrophic oral lichen planus (OLP) has potential of malignancy transformation into OSCC. The microRNAs are non-coding regulator sequences involved in cancer process. The miR-99a involve in growth, proliferation, migration, invasion, and metastasis of tumor cells. Therefore, we evaluated miR-99a expression in serum of OSCC and erosive atrophic OLP patients in comparison to healthy control individuals to more investigate about level of miR-99a expression in potential premalignant disorder (erosive atrophic OLP) in comparison to malignant transformation form (OSCC). Gene ontology (GO) and pathway analyses were performed to better understand the importance of miR-99a in OSCC.

MATERIALS AND METHODS

In this cross-sectional study, total 90 serum samples from OSCC patients (n = 30), erosive atrophic OLP (n = 30) and healthy control individuals (n = 30) were collected, and then evaluated for miR-99a expression by qPCR. Pathway analysis and protein-protein interaction were done using STRING (v: 12.0), and (GO) terms and related genes were extracted from the GO online search tool. The statistical analysis was evaluated by Kruskal Wallis, Chi-Square, Kruskal Wallis, Spearman and Mann-Whitney tests. The p-value less than 0.05 was considered statistically significant.

RESULTS

miR-99a expression down regulated in OSCC in comparison to erosive atrophic OLP and control groups (p < 0.05). The miR-99a up regulated in grade I more than grades II and III (p < 0.05). We showed upregulation of miR-99a in early stage more than advanced stage (p < 0.05). Expression of miR-99a reduced accordance to the increasing of tumor size and lymph involvement levels (p < 0.05). The 165 determined targets were classified into three domains. The most significant enrichment in biological processes, cellular components, and molecular functions was in the cellular nitrogen compound biosynthetic process, cytosolic ribosome, and protein binding, respectively.

CONCLUSIONS

We highlighted tumor suppressive role of miR-99a in OSCC patients. It seems that miR-99a can be considered a valuable biomarker for the early diagnosis of erosive atrophic OLP before transformation.

CLINICAL RELEVANCE

Our results may help to better understand the prognostic factor for oral squamous cell carcinoma to evaluate survival and subsequent tumor development. And it may also help to understand the pathogenesis of OSCC.

Circ_MACF1 targets miR-421 to upregulate FMO2 to suppress paclitaxel resistance and malignant cellular behaviors in lung adenocarcinoma

BACKGROUND

Chemoresistance remains an enormous challenge in the treatment of lung adenocarcinoma (LADC). Circular RNAs (circRNAs) exhibit important regulation in tumor progression and chemoresistance. This research focused on exploring the regulatory function and mechanism of circ_MACF1 (has_circ_0011780) in paclitaxel (PTX) resistance in LADC.

METHODS

Circ_MACF1, miR-421 and flavin-containing monooxygenase 2 (FMO2) were determined by RT-qPCR. MTT was applied to detect IC50 of PTX. The proliferation analysis was performed using EdU and colony formation assay. Cell apoptosis and motility were examined using flow cytometry and transwell assay, respectively. Western blot was administered for protein detection. A dual-luciferase reporter assay was performed for confirming target interaction. PTX sensitivity in vivo was researched via xenograft tumor assay.

RESULTS

Expression of circ_MACF1 was decreased in PTX-resistant LADC tissues and cells. Circ_MACF1 overexpression reduced chemoresistance, proliferation, motility and accelerated apoptosis in PTX-resistant LADC cells. Circ_MACF1 targeted miR-421 and miR-421 upregulation reverted circ_MACF1-evoked effects. FMO2 served as a downstream target of miR-421 and circ_MACF1 sponged miR-421 to elevate the expression of FMO2. MiR-421 enhanced PTX resistance and LADC progression via targeting FMO2. FMO2 knockdown enhanced IC50 of PTX and cell proliferation. In vivo, circ_MACF1 elevated PTX sensitivity of LADC by mediating miR-421/FMO2 axis.

CONCLUSION

These findings elucidated that circ_MACF1 inhibited PTX resistance by absorbing miR-421 to upregulate FMO2 in LADC.

CircCDK1 blocking IGF2BP2-mediated m6A modification of CPPED1 promotes laryngeal squamous cell carcinoma metastasis via the PI3K/AKT signal pathway

BACKGROUND

Circular RNA (circRNA) is a novel noncoding RNA (ncRNA) that plays a critical role in various cancers. However, the clinical significance, biological function, and molecular mechanisms of circRNAs in laryngeal squamous cell carcinoma (LSCC) remain unclear.

METHODS

A circRNA array was performed to identify the differentially expressed circRNAs. In vitro and in vivo assays were proceeded to verify the biological function of circCDK1 in LSCC. RNA pulldown assays and RNA immunoprecipitation (RIP) were used to confirm the binding between circCDK1 and insulin-like growth factor 2 mRNA binding protein 2(IGF2BP2). The MeRIP assay was then used to identified the N6-methyladenisine (m6A) methylation of calcineurin like phosphatase domain containing1 (CPPED1).

RESULTS

Hsa_circ_0005774 (circCDK1) was found upregulated in LSCC tissues compared to adjacent normal tissues. The level of circCDK1 was positively correlated with poor prognosisof LSCC patients. In vitro and in vivo, circCDK1 promoted migration and invasion of LSCC cells. Mechanistically, eukaryotic translation initiation factor4A3(EIF4A3) induced biogenesis of circCDK1 by binding to its flanking. By competitively binding to IGF2BP2, circCDK1 blocked the m6A modification of CPPED1 in IGF2BP2-dependent manner. Moreover, the circCDK1-mediated decrease of CPPED1 activated the PI3K/AKT signal pathway to facilitate progression of LSCC.

CONCLUSIONS

Our findings demonstrated that EIF4A3-induced upregulation of circCDK1 promoted LSCC metastasis via EIF4A3-circCDK1-IGF2BP2-CPPED1 to activate PI3K-AKT signal pathway. CircCDK1 might serve as a new diagnostic and prognostic marker or potential therapeutic target for LSCC.

Identification of Novel Circular RNA Targets in Key Penumbra Region of Rats After Cerebral Ischemia-Reperfusion Injury

Circular RNAs (circRNAs) are abundantly and stably expressed in the brain of mammals and humans. Some circRNAs are implicated in ischemic stroke. Therefore, we aimed to detect how circRNAs change in the key penumbra area during cerebral ischemia-reperfusion (CI/R) injury. Rats were subjected to transient middle cerebral artery occlusion (tMCAO), during which the permanent blocking period was 2 h and reperfusion time was 24 or 72 h. Then modified neurologic severity score (mNSS), triphenyl tetrazolium chloride (TTC) staining and HE staining were used to exhibiting damage between rats in different groups. The penumbra regions of all rats were dissected and total RNA was further processed for high-throughput sequencing. CircRNA expression profiles were screened and bioinformatics analyses were conducted to investigate these differentially expressed circRNAs. Some of them were verified by reverse transcription-quantitative polymerase chain reaction (RT-qPCR), followed by the establishment of a circRNA-miRNA-mRNA network and the detection of their downstream molecules. A total of 99 and 98 circRNAs were differentially expressed at CI/R 24 h and CI/R 72 h, respectively. Notably, 21 circRNAs significantly changed at both reperfusion points. Three circRNAs, namely circ.7225, circ.5415, and circ.20623 were found to be associated with CI/R injury and might be preferred targets. Common downstream miR-298-5p and Bcl-3 were found to make up the circRNA-miRNA-mRNA network. Novel circRNA targets came to light in the penumbra of rats during CI/R injury and might establish the circRNA-miRNA-mRNA relationship, thus serving as potential biomarkers for ischemic stroke treatment.

Circular RNAs: Emerging roles and new insights in human cancers

Circular RNAs (circRNAs) are single-stranded, covalently closed RNA molecules formed by mRNA exon back-splicing. Although the circRNA functions remain largely unknown, their currently known biological activities include: acting as competing endogenous RNA (ceRNA) to adsorb microRNA (miRNA), binding proteins, regulating transcription or splicing, and ability to be translated into proteins or peptides. A growing number of studies have found that many circRNAs are abnormally expressed in various cancers, and their dysregulation is highly correlated with tumor progression. Therefore, diagnosis and treatment using circRNAs as biomarkers and therapeutic targets, respectively, has gradually become an attractive research topic. In this review, we introduced the canonical biogenesis pathways and degradation mechanisms of circRNAs. In addition, we examined the biological functions of circRNAs in vivo. Finally, we discussed the current clinical applications and challenges faced by circRNA, and proposed future directions for this promising research field.

The Regulation of Ferroptosis by Noncoding RNAs

As a novel form of regulated cell death, ferroptosis is characterized by intracellular iron and lipid peroxide accumulation, which is different from other regulated cell death forms morphologically, biochemically, and immunologically. Ferroptosis is regulated by iron metabolism, lipid metabolism, and antioxidant defense systems as well as various transcription factors and related signal pathways. Emerging evidence has highlighted that ferroptosis is associated with many physiological and pathological processes, including cancer, neurodegeneration diseases, cardiovascular diseases, and ischemia/reperfusion injury. Noncoding RNAs are a group of functional RNA molecules that are not translated into proteins, which can regulate gene expression in various manners. An increasing number of studies have shown that noncoding RNAs, especially miRNAs, lncRNAs, and circRNAs, can interfere with the progression of ferroptosis by modulating ferroptosis-related genes or proteins directly or indirectly. In this review, we summarize the basic mechanisms and regulations of ferroptosis and focus on the recent studies on the mechanism for different types of ncRNAs to regulate ferroptosis in different physiological and pathological conditions, which will deepen our understanding of ferroptosis regulation by noncoding RNAs and provide new insights into employing noncoding RNAs in ferroptosis-associated therapeutic strategies.

Circular non-coding RNA circ_0072088 serves as a ceRNA, targeting the miR-1225-5p/WT1 axis to regulate non-small cell lung cancer cell malignant behavior

BACKGROUND

Circular RNA (circRNA) circ_0072088 has been reported to be associated with NSCLC cell growth, migration, and invasion. However, the role and mechanism of circ_0072088 on NSCLC development have not yet been determined.

METHODS

Circ_0072088, microRNA-1225 (miR-1225-5p), and Wilms' tumor (WT1) suppressor gene level was detected by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). Migration, invasion, and apoptosis were detected using transwell and flow cytometry assays. Matrix metallopeptidase 9 (MMP9), hexokinase 2 (HK2), and WT1 were examined using western blot assay. The biological role of circ_0072088 on NSCLC tumor growth was examined by the xenograft tumor model in vivo. Circular RNA Interactome and TargetScan were used to predict the binding between miR-1225-5p and circ_0072088 or WT1, followed by confirmation using a dual-luciferase reporter.

RESULTS

Circ_0072088 and WT1 were highly expressed in NSCLC tissues and cells, and miR-1225-5p was decreased. Knockdown of circ_0072088 might repress migration, invasion, and glycolysis, and facilitate apoptosis of NSCLC cells in vitro. Circ_0072088 silencing also blocked NSCLC tumor growth in vivo. Mechanistically, circ_0072088 acted as a sponge of miR-1225-5p to regulate WT1 expression.

CONCLUSION

Circ_0072088 knockdown could inhibit cell growth, migration, invasion, and glycolysis partially by regulating the miR-1225-5p/WT1 axis, thus providing a promising therapeutic target for NSCLC treatment.

Application prospect of circular RNA-based neoantigen vaccine in tumor immunotherapy

Neoantigen is a protein produced by mutant gene, which is only expressed in tumor cells. It is an ideal target for therapeutic tumor vaccines. Although synthetic long peptide (SLP)-based neoantigen vaccine, DNA-based neoantigen vaccine, and mRNA-based neoantigen vaccine are all in the development stage, they have some inherent shortcomings. Therefore, researchers turned their attention to a new type of "non-coding RNA (ncRNA)", circular RNA (circRNA), for potential better choice. Because of its unique high stability and protein-coding capacity, circRNA is a promising target in the field of neoantigen vaccine. In this paper, we reviewed the feasibility of circRNA encoding neoantigens, summarized the construction process, explained the mechanism of circRNA vaccine in vitro, and discussed the advantages and disadvantages of circRNA vaccine and possible combination with other immunotherapies.

Circular RNA circ_0079593 facilitates glioma development via modulating miR-324-5p/XBP1 axis

Glioma is a common brain tumor with high mortality. Circular RNAs (circRNAs) play crucial roles in tumor occurrence and development. However, the function and molecular basis of circ_0079593 in glioma remain unknown. Quantitative real-time PCR (qPCR) and Western blot were used for expression determination of circ_0079593, microRNA-324-5p (miR-324-5p) and X-box binding protein 1 (XBP1). Cell Counting Kit-8 (CCK-8), colony formation, flow cytometry, transwell assays, and tube formation assay were employed to evaluate cell functions. Glycolysis was determined via detecting glucose consumption, lactate production and ATP level. The binding relationship between miR-324-5p and circ_0079593 or XBP1 was validated by dual-luciferase reporter assay and RNA Immunoprecipitation (RIP) assay. Besides, xenograft assay was applied to test tumor growth in vivo. Circ_0079593 and XBP1 levels were elevated, while miR-324-5p level was declined in glioma. Silencing of circ_0079593 restrained proliferation, mobility, angiogenesis and glycolysis and induced apoptosis in glioma cells. Circ_0079593 accelerated glioma progression via sequestering miR-324-5p, one of the targets of circ_0079593. XBP1 was a target gene of miR-324-5p, and miR-324-5p alleviated the malignant growth of glioma by repressing XBP1. Furthermore, silence of circ_0079593 hindered tumor growth in vivo. Circ_0079593 contributed to the malignant evolution of glioma via modulating miR-324-5p and downstream XBP1 gene, suggesting that circ_0079593 might be a promising therapeutic target for glioma. Circ_0079593 was boosted in glioma. Circ_0079593 depletion restrained glioma progression. Circ_0079593 triggered glioma development via miR-324-5p/XBP1 axis. Circ_0079593 silence suppressed glioma tumorigenesis in vivo.

Knockdown circZNF131 Inhibits Cell Progression and Glycolysis in Gastric Cancer Through miR-186-5p/PFKFB2 Axis

Gastric cancer (GC) is a prevalent and heterogeneous malignancy in the digestive system. Increasing studies have suggested that circular RNAs are implicated in GC pathogenesis. This study aimed to explore the biological role and underlying mechanism of circRNA zinc finger protein 131 (circZNF131) in GC. The expression pattern of circZNF131, microRNA-186-5p (miR-186-5p), and 6-phosphofructo-2-kinase/fructose-2, 6-bisphosphatase 2 (PFKFB2) mRNA in GC tissues and cells was detected by quantitative real-time polymerase chain reaction. The stability of circZNF131 was verified using ribonuclease R assay. Functional experiments were performed by colony formation assay for cloning ability analysis, transwell assay and wounding healing assay for cell metastasis, and flow cytometry for cell apoptosis. Glycolysis metabolism was investigated by determining the levels of glucose uptake and lactate production. The protein detection of apoptosis- or glycolysis-associated markers, PFKFB2, and Ki-67 was implemented by western blot or immunohistochemistry. Dual-luciferase reporter assay was conducted to identify the interaction between miR-186-5p and circZNF131 or PFKFB2. The role of circZNF131 on tumor growth in nude mice was investigated via xenograft tumor assay. Expression analysis indicated that circZNF131 was upregulated in GC tissues and cells in a stable structure. Functional analyses showed that circZNF131 knockdown suppressed GC cell colony formation ability, migration, invasion and glycolysis metabolism, and induced cell apoptosis. Mechanically, miR-186-5p was a target of circZNF131, and miR-186-5p could bind to PFKFB2. Rescue experiments presented that miR-186-5p inhibition reversed the effects of circZNF131 knockdown on GC cell growth and glycolysis, and PFKFB2 overexpression abolished the impacts of miR-186-5p restoration on GC cell progression. Moreover, circZNF131 could positively modulate PFKFB2 expression via sponging miR-186-5p. In vivo, circZNF131 knockdown hindered GC tumor growth by regulating the miR-186-5p/PFKFB2 axis. circZNF131 could exert an oncogenic role in GC malignant development through the miR-186-5p/PFKFB2 axis, which might provide novel targets for GC treatment.

Transfer RNA-Derived Small RNAs: Novel Regulators and Biomarkers of Cancers

Transfer RNA-derived small RNAs (tsRNAs) are conventional non-coding RNAs (ncRNAs) with a length between18 and 40 nucleotides (nt) playing a crucial role in treating various human diseases including tumours. Nowadays, with the use of high-throughput sequencing technologies, it has been proven that certain tsRNAs are dysregulated in multiple tumour tissues as well as in the blood serum of cancer patients. Meanwhile, data retrieved from the literature show that tsRNAs are correlated with the regulation of the hallmarks of cancer, modification of tumour microenvironment, and modulation of drug resistance. On the other side, the emerging role of tsRNAs as biomarkers for cancer diagnosis and prognosis is promising. In this review, we focus on the specific characteristics and biological functions of tsRNAs with a focus on their impact on various tumours and discuss the possibility of tsRNAs as novel potential biomarkers for cancer diagnosis and prognosis.

Plasma circRNA microarray profiling identifies novel circRNA biomarkers for the diagnosis of ovarian cancer

Background

Circular RNA (circRNA), a class of RNA with a covalent closed circular structure that widely existed in serum and plasma, has been considered an ideal liquid biopsy marker in many diseases. In this study, we employed microarray and qRT-PCR to evaluate the potential circulating circRNAs with diagnostic efficacy in ovarian cancer.

Methods

We used microarray to explore the circRNA expression profile in ovarian cancer patients’ plasma and quantitative real-time (qRT)-PCR approach to assessing the candidate circRNA’s expression. Then the receiver operating characteristic (ROC) curve was employed to analyze the diagnostic values of candidate circRNAs. The diagnostic model circCOMBO was a combination of hsa_circ_0003972 and hsa_circ_0007288 built by binary logistic regression. Then bioinformatic tools were used to predict their potential mechanisms.

Results

Hsa_circ_0003972 and hsa_circ_0007288 were downregulated in ovarian cancer patients’ plasma, tissues, and cell lines, comparing with the controls. Hsa_circ_0003972 and hsa_circ_0007288 exhibited diagnostic values with the Area Under Curve (AUC) of 0.724 and 0.790, respectively. circCOMBO showed a better diagnostic utility (AUC: 0.781), while the combination of circCOMBO and carbohydrate antigen 125 (CA125) showed the highest diagnostic value (AUC: 0.923). Furthermore, the higher expression level of hsa_circ_0007288 in both plasma and ovarian cancer tissues was associated with lower lymph node metastasis potential in ovarian cancer.

Conclusions

Our results revealed that hsa_circ_0003972 and hsa_circ_0007288 may serve as novel circulating biomarkers for ovarian cancer diagnosis.

Supplementary information

The online version contains supplementary material available at 10.1186/s13048-022-00988-0.

Hsa_circ_0003945 promotes progression of hepatocellular carcinoma by mediating miR-34c-5p/LGR4/β-catenin axis activity

Accumulating evidence suggests that circular RNAs (circRNAs) play essential roles in regulating cancer progression, but many circRNAs in hepatocellular carcinoma (HCC) remain unknown. Dysregulated circRNAs in HCC were identified through bioinformatics analysis of Gene Expression Omnibus data sets. Quantitative real‐time PCR (qRT‐PCR), Sanger sequencing, RNase R digestion and actinomycin D treatment were conducted to confirm the characterization of circRNAs. CCK‐8, wound‐healing and Transwell assays were performed to assess the functional roles of Hsa_circ_0003945 (Circ_0003945) in HCC cell lines. Subcellular fractionation and fluorescence in situ hybridization (FISH) were performed to locate Circ_0003945 in HCC cells. Dual‐luciferase reporter assay was executed to verify the binding of Circ_0003945 to microRNAs (miRNAs) or the miRNAs to their target genes. In this study, we found that Circ_0003945 was upregulated in HCC tissue, and higher Circ_0003945 expression was positively correlated with tumour size and tumour stage. Furthermore, high plasma levels of circulating Circ_0003945 were confirmed in HCC patients compared with those in non‐HCC groups. The functional experiments revealed that overexpression or knockdown of Circ_0003945 promoted or attenuated tumour growth and migration, respectively. Mechanistically, Circ_0003945 might exert as a miR‐34c‐5p sponge to upregulate the expression of leucine‐rich repeat‐containing G protein‐coupled receptor 4 (LGR4), activating the β‐catenin pathway, and finally facilitating HCC progression. Additionally, a β‐catenin activator could reverse the effect of Circ_0003945 knockdown. In conclusion, Circ_0003945 exerts a tumour‐promoting role in HCC cells by regulating the miR‐34c‐5p/LGR4/β‐catenin axis, which may be a potential target for HCC therapy.

Decreased Expression of circ_0000160 in Breast Cancer With Axillary Lymph Node Metastasis

Background: Circular RNAs (circRNAs) have been shown to play important roles in the development and progression of human cancers. Emerging evidence shows that circRNAs have the potential to be promising biomarkers for cancer diagnosis and prognosis. However, the roles of circRNAs in breast cancer axillary lymph node metastasis (ALNM) remain to be determined.

Methods: Transcriptome sequencing was utilized to screen the differentially expressed circRNAs in three breast cancer tissues with ALNM and three without ALNM. Differentially expressed circRNAs were further verified by quantitative real-time PCR. Moreover, receiver operating characteristic (ROC) curve analysis was performed to calculate the value of circRNAs to distinguish breast cancer tissues with ALNM and those without ALNM. To explore the potential mechanism of the circRNAs, a circRNA–miRNA–mRNA network was constructed based on the CircInteractome, circBank, and mirDIP online software.

Results: In total, 31 differentially expressed circRNAs were identified by transcriptome sequencing; among them, 21 were upregulated and 10 were downregulated in breast cancer with ALNM compared to those without ALNM. Circ_0000160 was validated to be downregulated in breast cancer tissues with ALNM compared with those without ALNM. The ROC curve showed the ability of circ_0000160 to distinguish breast cancer tissues with ALNM and those without ALNM, with an area under the curve of 0.7435. Furthermore, bioinformatics analysis revealed that the predicted mRNAs for circ_0000160 may be related to lymph node metastasis. The predicted mRNAs for circ_0000160 may be involved in many cancer-related pathways.

Conclusion: A decreased expression of circ_0000160 was found in breast cancer with axillary lymph node metastasis. Circ_0000160 may have the potential to distinguish breast cancer with axillary lymph node metastasis from those without axillary lymph node metastasis.

CircFISH: A Novel Method for the Simultaneous Imaging of Linear and Circular RNAs

Simple Summary

Circular RNAs are a recently appreciated class of regulatory non-coding RNAs. Although a number of high-resolution methods have been developed for the imaging of RNAs in cells and tissues, there is no reliable method for the simultaneous imaging of circular RNAs distinctly from their linear counterparts. Here, we report circFISH as a simple and single-molecule resolution method that will simultaneously image linear and circular RNAs in fixed cells and tissues. We demonstrate that multiple circular RNAs can be imaged using circFISH. We also show the ability of circFISH to work seamlessly with protein and other organelle imaging. We optimized the method to work across sample types, making it a versatile tool for the functional characterization of circular RNAs.

Abstract

Circular RNAs (circRNAs) are regulatory RNAs which have recently been shown to have clinical significance in several diseases, including, but not limited to, various cancers, neurological diseases and cardiovascular diseases. The function of such regulatory RNAs is largely dependent on their subcellular localization. Several circRNAs have been shown to conduct antagonistic roles compared to the products of the linear isoforms, and thus need to be characterized distinctly from the linear RNAs. However, conventional fluorescent in situ hybridization (FISH) techniques cannot be employed directly to distinguish the signals from linear and circular isoforms because most circRNAs share the same sequence with the linear RNAs. In order to address this unmet need, we adapted the well-established method of single-molecule FISH by designing two sets of probes to differentiate the linear and circular RNA isoforms by virtue of signal colocalization. We call this method ‘circular fluorescent in situ hybridization’ (circFISH). Linear and circular RNAs were successfully visualized and quantified at a single-molecule resolution in fixed cells. RNase R treatment during the circFISH reduced the levels of linear RNAs while the circRNA levels remain unaltered. Furthermore, cells with shRNAs specific to circRNA showed the loss of circRNA levels, whereas the linear RNA levels were unaffected. The optimization of the in-situ RNase R treatment allowed the multiplexing of circFISH to combine it with organelle staining. CircFISH was found to be compatible with multiple sample types, including cultured cells and fresh-frozen and formalin-fixed tissue sections. Thus, we present circFISH as a versatile method for the simultaneous visualization and quantification of the distribution and localization of linear and circular RNA in fixed cells and tissue samples.

Circular RNA: A promising new star for the diagnosis and treatment of colorectal cancer

Background

Colorectal cancer (CRC) is one of the most common malignant tumors of the digestive tract. According to the research of circular RNAs in the CRC field, compared with linear RNAs, circular RNAs are a special type of noncoding RNA that are covalently closed circular structures, which have no 5' cap structure and 3' polyA tail and are not affected by RNA exonuclease and actinomycin D.

Biological functions

Notably, circular RNAs have a high degree of stability and potential effect on gene regulation. Meanwhile, circular RNAs are involved in the sponge action of microRNAs and mediate protein translation and direct binding, alternative splicing, and histone modification.

Relationships with CRC

Studies have shown that circular RNAs are related to the proliferation, invasion, recurrence, metastasis, ferroptosis, apoptosis, and chemotherapy resistance of CRC.

Conclusions

This article provides a brief review based on the source, structural characteristics, mechanisms, biological functions of circular RNAs, and the relationships between CRC.

Mechanisms Regulating Abnormal Circular RNA Biogenesis in Cancer

Simple Summary

Circular RNAs (circRNAs) are circular RNA molecules without a 5′ cap and a 3′ poly(A) tail structure, which play an important role in tumor development, invasion and metastasis, etc. However, the mechanism of circRNA dysregulation in cancer remains unclear. Different from the classic splicing of linear RNA, circRNA is formed by back-splicing and is regulated by many cis-acting elements and trans-acting proteins. Exploring how the dysregulation of cis-regulatory elements and trans-acting proteins in tumor cells affects the biogenesis of circRNA, which in turn affects the development and prognosis of cancer, is of great significance for circRNA to become a cancer biomarker and therapeutic target.

Abstract

Circular RNAs (circRNAs), which are a class of endogenous RNA with covalently closed loops, play important roles in epigenetic regulation of gene expression at both the transcriptional and post-transcriptional level. Accumulating evidence demonstrated that numerous circRNAs were abnormally expressed in tumors and their dysregulation was involved in the tumorigenesis and metastasis of cancer. Although the functional mechanisms of many circRNAs have been revealed, how circRNAs are dysregulated in cancer remains elusive. CircRNAs are generated by a “back-splicing” process, which is regulated by different cis-regulatory elements and trans-acting proteins. Therefore, how these cis and trans elements change during tumorigenesis and how they regulate the biogenesis of circRNAs in cancer are two questions that interest us. In this review, we summarized the pathways for the biogenesis of circRNAs; and then illustrated how circRNAs dysregulated in cancer by discussing the changes of cis-regulatory elements and trans-acting proteins that related to circRNA splicing and maturation in cancer.

Scutellaria barbata D.Don and Oldenlandia diffusa (Willd.) Roxb crude extracts inhibit hepatitis-B-virus-associated hepatocellular carcinoma growth through regulating circRNA expression

ETHNOPHARMACOLOGICAL RELEVANCE

Scutellaria barbata D.Don (SB) and Oldenlandia diffusa (Willd.) Roxb are commonly known as Ban Zhi Lian and Bai Hua She Cao in Chinese herbal medicines, respectively. As a pair of herbs, they have traditionally been used as ethnomedicines for clearing away heat and toxins, removing blood stasis, and promoting blood circulation, diuresis, and detumescence.

AIM OF THE STUDY

The aim of the present study was to determine the active ingredients in SB and OD extracts and to investigate whether these extracts can inhibit the growth of hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC) cell lines (HepG2.2.15 and Hep3B) in vitro and in vivo, as well as to explore their mechanisms of action.

MATERIALS AND METHODS

We determined the levels of total flavonoids, luteolin, and apigenin in SB and OD extracts via ultraviolet-visible spectrophotometry and high-performance liquid chromatography. The effects of SB and OD extracts on HBV-associated HCC cell growth were assessed by HepG2.2.15 and Hep3B cells phenotype and RNA sequencing of Hep3B cells in vitro, and xenograft models in vivo.

RESULTS

The extracts of SB and OD contained total flavonoids. There were active ingredients of luteolin and apigenin in SB, but not in OD. The extracts of SB and OD significantly inhibited HCC growth, migration, invasion, and HBV activity in vitro and in vivo, as well as altered circRNA expression in Hep3B cells. Moreover, we constructed a circRNA-miRNA-mRNA co-expression network.

CONCLUSIONS

The extracts of SB and OD may inhibit HCC cell growth and HBV activity in vitro and in vivo through altering circRNA-miRNA-gene expression and that the efficacies of these extracts may be related to the presence of luteolin and apigenin.

Circular RNA: A novel type of biomarker for glioma (Review)

With the rapid development of sequencing technologies, the characteristics and functions of circular RNAs (circRNAs) in different tissues, and their underlying pathophysiological mechanisms, have been identified. circRNAs are significantly enriched in the brain and are continually expressed from the embryonic stage to the adult stage in rats. Previous studies have reported that certain circRNAs are differentially expressed in glioma and regulate a number of biological processes, such as cell proliferation, metastasis and oncogenesis of glioma. Furthermore, certain circRNAs have been associated with tumor size, World Health Organization tumor grade and poor prognosis in patients with glioma. It has been hypothesized that circRNAs may be involved in the onset and progression of glioma through transcriptional regulation, protein translation and binding to microRNAs. These properties and functions suggest the potential of circRNAs as prognostic biomarkers and therapeutic targets for glioma. For the present review, published studies were examined from PubMed, Embase, Cochrane Central and the reference lists of the retrieved articles. The aim of the present review was to summarize the progress of circRNA research in glioma, discuss the potential diagnostic and prognostic values, and the roles of circRNAs in glioma, and provide a novel theoretical basis and research concepts for the prediction, diagnosis and treatment of glioma.

Curcumin restrains hepatocellular carcinoma progression depending on the regulation of the circ_0078710/miR-378b/PRIM2 axis

PURPOSE

Curcumin has shown anti-tumor activity in multiple malignancies. The aim of our study was to explore the molecular mechanism behind the anti-tumor activity of curcumin in hepatocellular carcinoma (HCC).

METHODS

The proliferation, migration, invasion, and apoptosis were analyzed by 5-ethynyl-2'-deoxyuridine (EDU) assay, transwell migration assay, transwell invasion assay, and flow cytometry. Western blot assay and reverse transcription-quantitative polymerase chain reaction (RT-qPCR) were conducted to analyze protein and RNA expression. Dual-luciferase reporter assay, RNA immunoprecipitation (RIP) assay, and RNA-pull down assay were performed to confirm the interaction between microRNA-378b (miR-378b) and circular RNA_0078710 (circ_0078710) or DNA primase, polypeptide 2 (PRIM2). Tumor xenograft assay was conducted to assess the roles of curcumin and circ_0078710 in vivo.

RESULTS

Curcumin stimulation restrained the proliferation, migration, and invasion, and triggered the apoptosis of HCC cells. Curcumin down-regulated the expression of circ_0078710 in HCC cells in a dose-dependent manner. Circ_0078710 knockdown aggravated curcumin-mediated anti-tumor effects in HCC cells. Circ_0078710 acted as a molecular sponge for miR-378b. Circ_0078710 interference-induced effects in curcumin-stimulated HCC cells were partly abolished by the silence of miR-378b. MiR-378b bound to the 3' untranslated region (3'UTR) of PRIM2. PRIM2 overexpression partly reversed circ_0078710 interference-mediated influences in curcumin-treated HCC cells. Circ_0078710 silencing aggravated curcumin-mediated suppressive effect in tumor growth in vivo.

CONCLUSIONS

Circ_0078710 silencing aggravated curcumin-mediated anti-tumor effects through mediating the miR-378b/PRIM2 signaling in HCC cells.

Circular RNA 0014715 Facilitates Cell Proliferation and Inhibits Apoptosis in Esophageal Squamous Cell Carcinoma

Background

Circular RNAs (circRNAs) have recently been verified to have multiple biological functions and participate in diverse biological processes in different malignant tumors, including esophageal squamous cell carcinoma (ESCC). Nonetheless, the function of circular RNA 0014715 (hsa_circ_0014715, circ_0014715) in ESCC has not been described.

Materials and Methods

We investigated clinical data from sixty-seven patients undergoing surgery for esophageal cancer. The clinical data were collected. And we analyzed the correlation between the clinical characteristics of these patients and the expression of circ_0014715. Besides, we explored the expression of circ_0014715 in ESCC cell lines. We used cell counting kit-8, colony formation, transwell assay, and flow cytometry to detect changes in cell proliferation, migration, apoptosis, and cell cycle progression.

Results

We found that circ_0014715 was highly expressed in esophageal squamous cell carcinoma tissues and cell lines. The correlation analysis of clinicopathological features and gene expression revealed that high expression of circ_0014715 was related to nerve invasion, vascular invasion, more advanced tumor-node-metastasis (TNM) stage and poor differentiation grade. Receiver operating characteristic (ROC) curves revealed that circ_0014715 might have diagnostic value for ESCC. Experiments with cultured cells showed that knockdown of circ_0014715 significantly restrained cell proliferation, migration, invasion, wound healing and accelerated cell apoptosis. And cell cycle arrest at G2 phase was observed via flow cytometry. Overexpression of circ_0014715 caused the opposite effects. Collectively, these studies show that circ_0014715 is closely connected with the pathogenesis and development of ESCC. The excess expression of circ_0014715 may have promoting effects on the progression of esophageal cell carcinoma.

Conclusion

Our finding revealed that circ_0014715 promoted tumor growth and cell proliferation. All of these suggest that targeting circ_0014715 has potential therapeutic value in the treatment of ESCC.

CircC16orf62 promotes hepatocellular carcinoma progression through the miR-138-5p/PTK2/AKT axis

Circular RNA (circRNAs) functions vital in the pathogenesis and progression of hepatocellular carcinoma (HCC). However, the expressions and functions of certain circRNAs on metastasis and proliferation of that cancer is still unclear. Bioinformation analysis and qRT-PCR indicated that CircC16orf62 was prominent upregulated in HCC of which the expression level was positively associated to cancer’s malignant progression. Gain or loss-of-function studies indicated that the reduction of CircC16orf62 expression promotes the proliferation, invasion, and glycolysis of HCC in vitro and in vivo. The bioinformatic analysis found that miR-138-5p and PTK2 were the downstream target of CircC16or62. Then, the FISH(Fluorescence immunoin situ hybridization) and cell nucleoplasmic separation determined that CircC16orf62 located in the cell cytoplasm. Plasmid vectors or siRNAs were used to change the expression of CircC16orf62, miR-138-5p, and PTK2 in PC cell lines. CircC16orf62 functioned as a molecular sponge for miR-138-5p, and a competitive endogenous RNA for PTK2, promoting AKT/mTOR pathway activation. Our observations lead us to conclude that CircC16orf62 functions as an oncogene in HCC progression, behaving as a competitive endogenous RNA for miR-138-5p binding, thus activating the AKT/mTOR pathway. In conclusion, CircC16orf62 is an oncogene through the miR-138-5p/PTK2/Akt axis in HCC cells, indicating CircC16orf62 can be a therapeutic target with potentiality for liver cancer and a predictive marker for people with HCC.

Non-coding RNAs in Wilms' tumor: biological function, mechanism, and clinical implications

Non-coding RNAs are involved with maintenance and regulation of physiological mechanisms and are involved in pathological processes, such as cancer. Among the small ncRNAs, miRNAs are the most explored in tumorigenesis, metastasis development, and resistance to chemotherapy. These small molecules of ~ 22 nucleotides are modulated during early renal development, involved in the regulation of gene expression and Wilms' tumor progression. Wilms' tumors are embryonic tumors with few mutations and complex epigenetic dysregulation. In recent years, the small ncRNAs have been explored as potentially related both in physiological development and in the tumorigenesis of several types of cancer. Besides, genes regulated by miRNAs are related to biological pathways as PI3K, Wnt, TGF-β, and Hippo signaling pathways, among others, which may be involved with the underlying mechanisms of resistance to chemotherapy, and in this way, it has emerged as potential targets for cancer therapies, including for Wilms' tumors.