CiRS-7 promotes growth and metastasis of esophageal squamous cell carcinoma via regulation of miR-7/HOXB13. Cell Death Dis. 2018;9:838. [PMID: 30082829 PMCID: PMC6079012 DOI: 10.1038/s41419-018-0852-y]

Circ_0023984 Facilitates Esophageal Squamous Cell Carcinoma Progression by Regulating miR-433-3p/REV3L Axis

BACKGROUND

It has been revealed that circular RNAs (circRNAs) play an important role in regulating the malignant phenotype of tumor cells, thus involving in the progression of malignancies. However, the role of circ_0023984 in esophageal squamous cell carcinoma (ESCC) remains largely unclear.

METHODS

The quantitative real-time polymerase chain reaction and Western blot assays were used to detect the expression of circ_0023984, microRNA (miR)-443-3p, and protein reversionless 3-like (REV3L). In vitro and in vivo assays were performed using cell counting kit-8, colony formation, transwell, wound healing, flow cytometry, and xenograft assays. The interaction miR-433-3p and circ_0023984 or REV3L was confirmed by dual-luciferase reporter, pull-down or RIP assays.

RESULTS

Circ_0023984 was highly expressed in ESCC tissues and cells, knockdown of circ_0023984 suppressed cancer cell proliferation, migration, invasion, and promoted cell apoptosis in vitro. Mechanistic analysis confirmed that circ_0023984 functioned as a sponge for miR-433-3p to positively regulate the expression of REV3L that was verified to be a target of miR-433-3p. Circ_0023984 knockdown repressed the tumorigenesis of ESCC cells via targeting miR-433-3p. Additionally, miR-433-3p performed anti-proliferative, anti-migratory, and anti-invasive abilities in ESCC cells, which were reversed by REV3L overexpression. Pre-clinically, silencing of circ_0023984 suppresses the tumorigenesis and growth of xenografts in nude mice.

CONCLUSION

Circ_0023984 exerted an oncogenic role in ESCC tumorigenesis and aggressiveness through promoting cell growth, migration, and invasion via miR-433-3p/REV3L axis.

Medulloblastoma cerebrospinal fluid reveals metabolites and lipids indicative of hypoxia and cancer-specific RNAs

Medulloblastoma (MB) is the most common malignant brain tumor in children. There remains an unmet need for diagnostics to sensitively detect the disease, particularly recurrences. Cerebrospinal fluid (CSF) provides a window into the central nervous system, and liquid biopsy of CSF could provide a relatively non-invasive means for disease diagnosis. There has yet to be an integrated analysis of the transcriptomic, metabolomic, and lipidomic changes occurring in the CSF of children with MB. CSF samples from patients with (n = 40) or without (n = 11; no cancer) MB were subjected to RNA-sequencing and high-resolution mass spectrometry to identify RNA, metabolite, and lipid profiles. Differentially expressed transcripts, metabolites, and lipids were identified and their biological significance assessed by pathway analysis. The DIABLO multivariate analysis package (R package mixOmics) was used to integrate the molecular changes characterizing the CSF of MB patients. Differentially expressed transcripts, metabolites, and lipids in CSF were discriminatory for the presence of MB but not the exact molecular subtype. One hundred and ten genes and ten circular RNAs were differentially expressed in MB CSF compared with normal, representing TGF-β signaling, TNF-α signaling via NF-kB, and adipogenesis pathways. Tricarboxylic acid cycle and other metabolites (malate, fumarate, succinate, α-ketoglutarate, hydroxypyruvate, N-acetyl-aspartate) and total triacylglycerols were significantly upregulated in MB CSF compared with normal CSF. Although separating MBs into subgroups using transcriptomic, metabolomic, and lipid signatures in CSF was challenging, we were able to identify a group of omics signatures that could separate cancer from normal CSF. Metabolic and lipidomic profiles both contained indicators of tumor hypoxia. Our approach provides several candidate signatures that deserve further validation, including the novel circular RNA circ_463, and insights into the impact of MB on the CSF microenvironment.

Circ_0006948 Contributes to Cell Growth, Migration, Invasion and Epithelial-Mesenchymal Transition in Esophageal Carcinoma

BACKGROUND

Circular RNAs (circRNAs) can act as promoters or inhibitors in cancer progression. Has_circ_0006948 (circ_0006948) was reported to aggravate the malignant behaviors of esophageal carcinoma (EC).

AIMS

This study focused on investigating the molecular mechanism of circ_0006948 in EC progression.

METHODS

The quantitative real-time polymerase chain reaction was performed to detect the expression of circ_0006948, microRNA-4262 (miR-4262) and fibronectin type III domain containing 3B (FNDC3B). Cell growth analysis was conducted by Cell Counting Kit-8 and colony formation assays. Cell migration and invasion were assessed by transwell assay. Epithelial-mesenchymal transition (EMT)-associated proteins and FNDC3B protein expression were assayed using western blot. Dual-luciferase reporter and RNA pull-down assays were performed to validate the target combination. Xenograft tumor assay was used for investigating the role of circ_0006948 in vivo.

RESULTS

Circ_0006948 was upregulated in EC tissues and cells. Downregulating the expression of circ_0006948 or FNDC3B repressed cell growth, migration, invasion and EMT in EC cells. Target analysis indicated that miR-4262 was a target for circ_0006948 and FNDC3B was a downstream gene for miR-4262. Moreover, circ_0006948 could affect the expression of FNDC3B via sponging miR-4262. The effects of si-circ_0006948#1 on EC cells were partly restored by miR-4262 inhibition or FNDC3B overexpression. In addition, circ_0006948 also facilitated EC tumorigenesis in vivo by targeting the miR-4262/FNDC3B axis.

CONCLUSION

Taken together, circ_0006948 functioned as an oncogenic factor in EC by the miR-4262-mediated FNDC3B expression regulation.

Downstream of the HOX genes: explaining conflicting tumour suppressor and oncogenic functions in cancer

The HOX genes are a highly conserved group of transcription factors that have key roles in early development, but which are also highly expressed in most cancers. Many studies have found strong associative relationships between the expression of individual HOX genes in tumours and clinical parameters including survival. For the majority of HOX genes, high tumour expression levels seem to be associated with a worse outcome for patients, and in some cases this has been shown to result from the activation of pro-oncogenic genes and pathways. However, there are also many studies that indicate a tumour suppressor role for some HOX genes, sometimes with conclusions that contradict earlier work. In this review, we have attempted to clarify the role of HOX genes in cancer by focusing on their downstream targets as identified in studies that provide experimental evidence for their activation or repression. On this basis, the majority of HOX genes would appear to have a pro-oncogenic function, with the notable exception of HOXD10, which acts exclusively as a tumour suppressor. HOX proteins regulate a wide range of target genes involved in metastasis, cell death, proliferation, and angiogenesis, and activate key cell signalling pathways. Furthermore, for some functionally related targets, this regulation is achieved by a relatively small subgroup of HOX genes.

The Emerging Roles of Circular RNAs in the Chemoresistance of Gastrointestinal Cancer

Gastrointestinal (GI) cancer represents a major global health problem due to its aggressive characteristics and poor prognosis. Despite the progress achieved in the development of treatment regimens, the clinical outcomes and therapeutic responses of patients with GI cancer remain unsatisfactory. Chemoresistance arising throughout the clinical intervention is undoubtedly a critical barrier for the successful treatment of GI cancer. However, the precise mechanisms associated with chemoresistance in GI cancer remain unclear. In the past decade, accumulating evidence has indicated that circular RNAs (circRNAs) play a key role in regulating cancer progression and chemoresistance. Notably, circRNAs function as molecular sponges that sequester microRNAs (miRNAs) and/or proteins, and thus indirectly control the expression of specific genes, which eventually promote or suppress drug resistance in GI cancer. Therefore, circRNAs may represent potential therapeutic targets for overcoming drug resistance in patients with GI cancer. This review comprehensively summarizes the regulatory roles of circRNAs in the development of chemoresistance in different GI cancers, including colorectal cancer, gastric cancer and esophageal cancer, as well as deciphers the underlying mechanisms and key molecules involved. Increasing knowledge of the important functions of circRNAs underlying drug resistance will provide new opportunities for developing efficacious therapeutic strategies against GI cancer.

Downregulation of hsa_circRNA_0001400 Helps to Promote Cell Apoptosis Through Disruption of the circRNA_0001400-miR-326 Sponge in Cervical Cancer Cells

Background: In recent years, circular RNAs (circRNAs) have been reported to serve as essential regulators in several human cancers. Nevertheless, the function and mechanism of circRNAs in cervical cancer remain elusive. Methods: Flow cytometry assays were performed to measure cell apoptosis and cell cycle. Colony Formation and transwell chamber were performed to measure cell migration and invasion. Double luciferase reporter for gene analysis was used to detect the interaction between hsa-circRNA_0001400, miR-326, and Akt. Relative protein levels were determined by immunoblotting and relative gene levels were determined by quantitative real-time PCR. Tumor Xenograft Modeling was used to evaluate the effect of hsa_circRNA_0001400_siRNA in vivo. Results: In the present study, we showed that hsa_circRNA_0001400 was highly expressed in cervical cancer tissues relative to in matched normal tissue. We found that hsa_circRNA_0001400_siRNA significantly promoted the apoptosis of cervical cancer cells and arrested the cell cycle and migration of cervical cancer cells. We showed that hsa_circRNA_0001400_siRNA can inhibit the protein expression of Akt and that the inhibition of miR-326 could rescue the inhibition of Akt in cervical cancer cells. We found that has-miR-326 was downregulated in cervical cancer tissues and hsa_circRNA_0001400_siRNA could increase the gene expression of has-miR-326. We also observed that hsa_circRNA_0001400_siRNA inhibited the growth and angiogenesis of SiHa xenografts in nude mice. Conclusion: In conclusion, this study provides evidence that the hsa_circRNA_0001400-miR-326-Akt network promotes cervical cancer progression. Notably, our findings demonstrate the novel antitumor effects of hsa_circRNA_0001400_siRNA in cervical cancer.

miR-204-5p inhibits cell proliferation and induces cell apoptosis in esophageal squamous cell carcinoma by regulating Nestin

Esophageal cancer (EC) is a highly malignant gastrointestinal tumor, and esophageal squamous cell carcinoma (ESCC) is one of the most common histological types of EC. MicroRNAs (miRNAs) are small noncoding RNAs closely related to tumorigenesis and tumor progression. In addition, Nestin is an intermediate filament protein (class VI) and contributes to the progression of numerous tumors. However, the correlation between miRNAs and Nestin in ESCC remains unclear. This study aimed to investigate the relationship between miR-204-5p and Nestin in ESCC. First, Nestin-related miRNAs in ESCC were explored using RNA sequencing. In ESCC tissues and cell lines, the expression of miR-204-5p was decreased detected by quantitative real-time polymerase chain reaction (qPCR), whereas Nestin protein level was upregulated identified by Western blotting (WB). Besides, Nestin was the direct target of miR-204-5p in ESCC determined via the luciferase reported assay. Moreover, miR-204-5p regulated Nestin to inhibit ESCC cell proliferation detected by the colony formation assay and promote ESCC cell apoptosis identified using the flow cytometry and TUNEL assay. Furthermore, miR-204-5p suppressed tumorigenesis in vivo evaluated by the murine xenograft tumor model. In conclusion, these results indicated that miR-204-5p inhibited cell proliferation and induced cell apoptosis in ESCC through targeting Nestin, which might provide novel therapeutic targets for ESCC therapy.

Circular RNAs in prostate cancer: Biogenesis,biological functions, and clinical significance

Circular RNAs (circRNAs) are covalently closed RNA molecules that play important regulatory roles in various tumors. Prostate cancer (PCa) is one of the most common malignant tumors in the world, with high morbidity and mortality. In recent years, more and more circRNAs have been found to be abnormally expressed and involved in the occurrence and development of PCa, including cell proliferation, apoptosis, invasion, migration, metastasis, chemotherapy resistance, and radiotherapy resistance. Most of the circRNAs regulate biological behaviors of cancer through a competitive endogenous RNA (ceRNA) regulatory mechanism, and some can exert their functions by binding to proteins. circRNAs are also associated with many clinicopathological features of PCa, including tumor grade, lymph node metastasis, and distant metastasis. In addition, circRNAs are potential diagnostic and prognostic biomarkers for PCa. Considering their critical regulatory roles in the progression of PCa, circRNAs would be the potential therapeutic targets. In this paper, the current research status of circRNAs in PCa is briefly reviewed.

Circular RNA circPDSS1 promotes osteosarcoma progression by sponging miR-502-3p and miR-4436a

Osteosarcoma (OS) is a highly aggressive bone cancer. Patients with OS frequently develop drug resistance in clinical treatment, and the prognosis has not been improved significantly. There is an urgent need to identify novel markers and therapeutic targets. In this study, we focused on the highly expressed noncoding circular RNA circPDSS1 in OS, and studied its functional roles and downstream targets in OS cells by CCK-8, clone formation assay, transwell assays. Additionally, we performed luciferase reporter assay, RNA pull-down experiment and qRT-PCR to validate the micoRNA targets of circPDSS1. The involvement of circPDSS1 in tumorigenesis was also investigated in mouse xenografts model. The expression of circPDSS1 was significantly upregulated in OS tissues and cell lines. Patients with high circPDSS1 expression were associated with poorer progression-free survival (PFS) and overall survival (OS) as compared to those with low circPDSS1 expression. CircPDSS1 knockdown significantly inhibited the viability, clone formation ability and invasion ability of OS cells, and induced cell apoptosis, which were associated with the upregulation of proapoptotic proteins and the impairment of prosurvival signaling. Molecular mechanism study further demonstrated that circPDSS1 modulates OS cell functions by regulating the expression of miR-502-3p and miR-4436a. Our data suggest that circPDSS1 acts as a molecular sponge of miR-502-3p and miR-4436a regulates the proliferation and invasion of OS cells and promote the malignant progression of OS.

MiRNA-30e downregulation increases cancer cell proliferation, invasion and tumor growth through targeting RPS6KB1

Human esophagus carcinoma (EC) is one of the most common malignant tumors, especially in Africa and Asia including China. In EC initiation and progression, genetic and epigenetic aberrations have been reported to play a major role, but the underlying molecular mechanisms are largely unknown. In this study, the miR-30e levels were analyzed in human EC tissues and TCGA databases, and the results demonstrated that miR-30e expression in EC tissues was significantly decreased compared to adjacent normal tissues. To further investigate the role of miR-30e in cancer cells, we found that forced expression of miR-30e dramatically inhibited cell proliferation, invasion, tube formation, and colony formation of cancer cells. To determine the underlying mechanism of miR-30e, we found that RPS6KB1 was a direct target of miR-30e by binding to its 3′-UTR, which was verified by luciferase activity assay using reporters with wild-type miR-30e and its seed sequence mutant constructs and Western blotting assay. In vivo experiment showed that miR-30e overexpression significantly inhibited tumor growth and decreased RPS6KB1 expression in xenografts. In EC, high expression of RPS6KB1 in tumor tissues indicated poor prognosis of patients with less survival rate. High levels of RPS6KB1 and low levels of miR-30e closely correlated poor survival of patients with several other types of cancer. These findings show that miR-30e and its target RPS6KB1 are important in cancer development and clinical outcomes, and miR-30e/RPS6KB1 is a potential future therapeutic pathway for EC intervention.

CircRNAs: Insights into Gastric Cancer

Background

Gastric cancer (GC) is recorded as the fifth most common cancer globally. The classic resemblance of early symptoms of chronic gastritis including nausea, dysphagia, and dyspepsia with GC is the current challenge limiting the early diagnosis of GC. The current diagnostic procedures of GC are limited due to their invasive nature. This directs the research question toward alternative approaches, specifically at the molecular level. Recent advances in molecular regulation of cancer suggest the prominence of circular RNAs (circRNAs) in the multistep process of tumourigenesis.

Summary

CircRNAs are a class of non-coding RNAs, abundant in eukaryotes, with key roles in regulating genes and miRNAs as well as the alteration of processes involved in pathological conditions. Research studies have demonstrated the participation of circRNAs in the initiation and progression of tumours. This review provides a comprehensive insight into the potential of circRNAs as disease biomarkers for the early detection and treatment of GC.

Key Messages

This study is an amalgamation of the implications and future prospects of circRNAs for the detection and potential treatment of GC.

Biological and clinical implications of metastasis-associated circular RNAs in oesophageal squamous cell carcinoma

Oesophageal squamous cell carcinoma (OSCC) is a prevalent malignancy with high morbidity and mortality as a result of early metastasis and poor prognosis. Metastasis is a multistep process, involving various signalling pathways. Circular RNAs (circRNAs) are a class of covalently closed noncoding RNAs, the aberrant expression of which is reported to be involved in several biological events, including cell transformation, proliferation, migration, invasion, apoptosis and metastasis. Several studies have reported interactions between circRNAs and metastasis-associated signalling pathways. The abundance, stability and highly specific expression of candidate circRNAs make them potential biomarkers and therapeutic targets in OSCC. In this review article, we comprehensively describe metastasis-related circRNAs and their interactions with epithelial-mesenchymal transition-associated molecules. We also describe the molecular mechanisms and clinical relevance of circRNAs in OSCC progression and metastasis.

Dysregulated circular RNAs as novel biomarkers in esophageal squamous cell carcinoma: a meta-analysis

Introduction

Circular RNAs (circRNAs) play critical roles in tumorigenesis, but their clinical efficacy in esophageal squamous cell carcinoma (ESCC) still retains controversial. This meta‐analysis aims at evaluating the associations between circRNA expressions and clinicopathologic features as well as the diagnostic and prognostic values of circRNAs in ESCC.

Materials & Methods

PubMed, EMBASE, and other online databases were systematically searched to collect studies on circRNAs and clinicopathological features, diagnostic, and/or prognostic assessments of ESCC. The quality of included studies was evaluated using the Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS‐2) and Newcastle‐Ottawa Scale (NOS) scales. The included studies were quantitatively weighted and merged, and diagnostic indicators, hazard ratios (HRs) and the corresponding 95% confidence intervals (CIs) were calculated. P values were merged by Fisher᾽s method. Sources of heterogeneity were traced using subgroup, sensitivity, and meta‐regression analyses.

Results

As a result, 12 studies were included, representing 769 ESCC patients. The meta‐analysis showed that abnormal expressions of circRNAs were associated to TNM stage as well as lymph node and distant metastases in ESCC cases. CircRNA was used to distinguish ESCC patients from healthy controls, and the merged sensitivity, specificity, and the area under the curve (AUC) of ESCC were 0.78 (95% CI: 0.74–0.81), 0.79 (95% CI: 0.75–0.83), and 0.86, respectively. The survival analysis showed that upregulated oncogenic circRNA levels in ESCC tissues was associated with the shorter overall survival (OS) of the patients (univariate analysis: HR = 2.25, 95% CI: 1.71–2.95, p = 0.000, I² = 0.0%; multivariate analysis: HR = 2.50, 95% CI: 1.61–3.89, p = 0.000, I² = 0.0%), while the OS of ESCC patients presenting overexpressions of tumor‐suppressive circRNAs was significantly ameliorated (HR = 0.29, 95% CI: 0.20–0.42, p = 0.000, I² = 0.0%). The subgroup analyses based on circRNA biofunctions, sample size, and reference gene also revealed robust results.

Conclusion

CircRNAs can be used as promising molecular biomarkers for the early diagnosis and prognosis monitoring of ESCC.

CiRS-7/CDR1as; An oncogenic circular RNA as a potential cancer biomarker

Circular RNAs (circRNAs) as a new class of non-coding RNAs (ncRNAs) play role in gene regulation in multicellular organisms via various interactions with nucleic acids, proteins and particularly microRNAs. They have been found to be involved in a number of biological functions particularly in regulation of cell cycle, and extracellular interactions. Thus, dysregulation of circRNAs is found to be associated with several human diseases and especially numerous types of cancers. ciRS-7 is an example of circRNAs which have been studied in a number of human diseases like neurological diseases, diabetes mellitus, and importantly different malignancies. It has been found to regulate cell proliferation and malignant features in cancer cells. CiRS-7 is upregulated in several cancers and its overexpression promoted malignant phenotype of cancer cells via enhancing cell proliferation, migration, and invasion in vitro and in vivo. As a competing endogenous RNA (ceRNA), ciRS-7 is found to sponge miR-7 as the most common miRNA target in interaction together. Functional analyses show role of ciRS-7 in downregulation of miR-7 and involvement of a series of signaling pathways in turn through them it is believed that ciRS-7 regulates malignant behaviors of cancer cells. Clinical studies demonstrate upregulation of ciRS-7 in cancer tissues compared to their non-cancerous adjacent tissues, correlation with worse clinicopathological features in cancerous patients and an independent prognostic factor. In this review, we have an overview to the role of ciRS-7 in development and progression of cancer and also assess its potentials as a diagnostic and prognostic biomarker in human cancers.

The circular RNA circCPE regulates myoblast development by sponging miR-138

Background

Skeletal muscle development, a long-term and complex process, is controlled by a set of the myogenic genes. Circular RNAs (circRNAs), a class of noncoding RNA, have been shown to regulate various biological processes. Recent studies indicate circRNAs may be involved in myogenesis, but the role and regulatory mechanism of circRNAs in myogenesis is largely unknown. In the present study, circCPE was firstly found to promote the bovine myoblast proliferation and inhibit cell apoptosis and differentiation by influencing the expression of FOXC1 in a miR138-mediated manner. And in vivo experiments revealed that overexpression of circCPE attenuates skeletal muscle regeneration.

Results

We identified a novel circular RNA circCPE by analyzing circRNAs sequencing data of bovine muscle tissue. Sequencing verification, RNase R treatment and Actinomycin D treatment confirmed the circular nature of circCPE in bovine muscle. Functional assays showed that overexpression of circCPE could inhibit bovine myoblast apoptosis and differentiation, as well as facilitate cell proliferation. Moreover, in vivo experiments revealed that overexpression of circCPE attenuates skeletal muscle regeneration. In consideration of circRNA action as miRNAs sponge, we found that circCPE harbors miR-138 binding sites and absorbed miR-138. Mechanistically, the rescue experiments showed that the overexpression of circCPE can counteract the inhibitory effect of miR-138 on the cell proliferation and the accelerated effects on the differentiation and apoptosis. Subsequently, we found that circCPE sequester the inhibitory effect of miR-138 on FOXC1 so as to involve in myogenesis.

Conclusions

Collectively, we constructed a novel circCPE/miR-138/FOXC1 regulatory network in bovine myogenesis, which further provide stronger evidence that circRNA involved in muscle development acting as miRNA sponge.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-021-00618-7.

CircRNF111 Protects Against Insulin Resistance and Lipid Deposition via Regulating miR-143-3p/IGF2R Axis in Metabolic Syndrome

Abnormal expression of circRNAs (circular RNAs), a subclass of non-coding RNAs, has been documented in numerous human diseases. Herein, we explored whether circRNAs act as ceRNAs (competing endogenous RNAs) to modulate the pathological process-insulin resistance, as well as dyslipidemia of MetS (Metabolic Syndrome). The profile of circRNAs in serume of MetS and control samples was characterized by circRNA deep sequencing. We identified circRNF111 as a key downregulated circRNA involved in MetS. The decreased expression of circRNF111 in the serum samples of MetS was directly linked to excessive insulin resistance and dyslipidemia. Loss-of-function experiments showed that circRNF111 knockdown inhibited the glucose uptake and the Akt signaling pathway, meanwhile increased the deposition of triglycerides in adipogenic differentiated hADSCs (human adipose-derived stem cells). Mechanistically, circRNF111 sponged miR-143-3p and functioned via targeting miR-143-3p along with its downstream target gene IGF2R. The role along with the mechanism of circRNF111 sponging miR-143-3p in MetS was also explored in obese mice triggered by high-fat die. Therefore, our data suggest a protective role of the novel circRNA-circRNF111 in MetS progression. CircRNF111 inhibition enhances insulin resistance and lipid deposition in MetS through regulating miR-143-3p-IGF2R cascade. This provides a promising therapeutic approach for MetS.

Recent research progress on circular RNAs: Biogenesis, properties, functions, and therapeutic potential

Circular RNAs (circRNAs), an emerging family member of RNAs, have gained importance in research due to their new functional roles in cellular physiology and disease progression. circRNAs are usually available in a wide range of cells and have shown tissue-specific expression as well as developmental specific expression. circRNAs are characterized by structural stability, conservation, and high abundance in the cell. In this review, we discuss the different models of biogenesis. The properties of circRNAs such as localization, structure and conserved pattern, stability, and expression specificity are also been illustrated. Furthermore, we discuss the biological functions of circRNAs such as microRNA (miRNA) sponging, cell cycle regulation, cell-to-cell communication, transcription regulation, translational regulation, disease diagnosis, and therapeutic potential. Finally, we discuss the recent research progress and future perspective of circRNAs. This review provides an understanding of potential diagnostic markers and the therapeutic potential of circRNAs, which are emerging daily.

Biogenesis, Functions, and Role of CircRNAs in Lung Cancer

CircRNAs, a class of endogenous non-coding RNAs with closed-loop structures, have attracted increasing attention because of their good stability, high specificity of tissue expression, long half-life, and highly conserved sequence. CircRNAs have multiple biological functions, including miRNA sponge, transcription regulator, protein translation, interaction with protein, RNA maturation, and so on. These functions indicate the important role of circRNAs in tumorigenesis and malignant progression and their potential as potent diagnostic biomarkers and therapeutic molecules. In recent years, an increasing body of evidence suggests that circRNAs play a crucial role in proliferation, migration, invasion, and apoptosis of lung cancer cells. Therefore, circRNAs have gradually become a research focus in the diagnosis and treatment of lung cancer patients. This review summarizes the classification, biogenesis, and function of circRNAs, and discusses the role of circRNAs in the diagnosis, prognosis, and treatment of lung cancer patients.

Circ_0089823 reinforces malignant behaviors of non-small cell lung cancer by acting as a sponge for microRNAs targeting SOX4. Neoplasia 2021;23:887-897. [PMID: 34311177 PMCID: PMC8326602 DOI: 10.1016/j.neo.2021.06.011]

In recent years, increasing evidence indicates the significant roles of circRNAs in carcinogenesis. However, their roles in lung cancer remain largely unclear. We profiled the circRNA expression in 10 paired non-small cell lung cancer (NSCLC) and adjacent non-cancer tissues using high-throughput sequencing. A total of 183 up-regulated and 428 down-regulated circRNAs were identified in the NSCLC tissues (fold change ≥ 2, P < 0.05). Circ_0089823, an up-regulated circRNA (5.4-fold, P = 0.0017), was further investigated through loss-of-function and gain-of-function. The circ_0089823 level in NSCLC samples was related to the gender, tumor size, pathological type, TNM stage and smoking history. Knockdown of circ_0089823 suppressed cell proliferation, induced cell cycle arrest and apoptosis of NSCLC cells in vitro. Additionally, circ_0089823-silenced xenografts grew much slowly. On the contrary, its over-expression promoted the malignant behaviors of NSCLC cells. Furthermore, SOX4, a tumor-promoting transcription factor, was highly expressed in NSCLC tissues and positively regulated by circ_0089823. Bioinformatic analysis revealed several potential binding sites for miR-507, miR-557, miR-579-3p and miR-1287-5p in circ_0089823 and SOX4 3'-untranslated region, which was later confirmed by luciferase reporter assay. Interestingly, silencing SOX4 countervailed the effects of circ_0089823 over-expression on NSCLC cells. Here, we revealed that circ_0089823 might act as a sponge of microRNAs targeting SOX4, thus increasing the expression of SOX4, thereby reinforcing the malignant behaviors of NSCLC cells. This study indicates that circ_0089823 has the potential to become a candidate target for NSCLC treatment.

Circular RNA CircEYA3 induces energy production to promote pancreatic ductal adenocarcinoma progression through the miR-1294/c-Myc axis

BACKGROUND

Extensive studies have demonstrated the pivotal roles of circular RNAs (circRNAs) in the occurrence and development of different human cancers. However, the expression and regulatory roles of circRNAs in pancreatic ductal adenocarcinoma (PDAC) are unclear.

METHODS

CircEYA3 was explored based on Gene Expression Omnibus (GEO) dataset analysis. qRT-PCR was applied to determine the expression of circRNAs, miRNAs and mRNAs in PDAC cells and tissues. The biological roles of circEYA3 in vitro and in vivo were determined by performing a series of functional experiments. Further, dual luciferase reporter, fluorescence in situ hybridization (FISH), RNA pull-down assays, and RNA immunoprecipitation (RIP) assays were used to confirm the interaction of circEYA3 with miR-1294.

RESULTS

CircEYA3 was elevated in PDAC tissues and cells, and a higher level of circEYA3 was significantly associated with a poorer prognosis in patients with PDAC. Functionally, circEYA3 increased energy production via ATP synthesis to promote PDAC progression in vitro and in vivo. Mechanistically, circEYA3 functions as an endogenous miR-1294 sponge to elevate c-Myc expression, thus exerting its oncogenic functions.

CONCLUSION

CircEYA3 promotes the progression of PDAC through the miR-1294/c-Myc signalling axis, and circEYA3 may be an efficient molecular therapeutic target in PDAC.

Non-coding RNAs in necroptosis, pyroptosis and ferroptosis in cancer metastasis

Distant metastasis is the main cause of death for cancer patients. Recently, the newly discovered programmed cell death includes necroptosis, pyroptosis, and ferroptosis, which possesses an important role in the process of tumor metastasis. At the same time, it is widely reported that non-coding RNA precisely regulates programmed death and tumor metastasis. In the present review, we summarize the function and role of necroptosis, pyrolysis, and ferroptosis involving in cancer metastasis, as well as the regulatory factors, including non-coding RNAs, of necroptosis, pyroptosis, and ferroptosis in the process of tumor metastasis.

Circular RNA hsa_circ_0000277 sequesters miR-4766-5p to upregulate LAMA1 and promote esophageal carcinoma progression

Growing evidence has indicated that circular RNAs (circRNAs) play a pivotal role as functional RNAs in diverse cancers. However, most circRNAs involved in esophageal squamous cell carcinoma (ESCC) remain undefined, and the underlying molecular mechanisms mediated by circRNAs are largely unclear. Here, we screened human circRNA expression profiles in ESCC tissues and found significantly increased expression of hsa_circ_0000277 (termed circPDE3B) in ESCC tissues and cell lines compared to the normal controls. Moreover, higher circPDE3B expression in patients with ESCC was correlated with advanced tumor-node-metastasis (TNM) stage and dismal prognosis. Functional experiments demonstrated that circPDE3B promoted the tumorigenesis and metastasis of ESCC cells in vitro and in vivo. Mechanistically, bioinformatics analysis, a dual-luciferase reporter assay, and anti-AGO2 RNA immunoprecipitation showed that circPDE3B could act as a competing endogenous RNA (ceRNA) by harboring miR-4766-5p to eliminate the inhibitory effect on the target gene laminin α1 (LAMA1). In addition, LAMA1 was significantly upregulated in ESCC tissues and was positively associated with the aggressive oncogenic phenotype. More importantly, rescue experiments revealed that the oncogenic role of circPDE3B in ESCC is partly dependent on the miR-4766-5p/LAMA1 axis. Furthermore, bioinformatics analysis combined with validation experiments showed that epithelial-mesenchymal transition (EMT) activation was involved in the oncogenic functions of the circPDE3B-miR-4766-5p/LAMA1 axis in ESCC. Taken together, we demonstrate for the first time that the circPDE3B/miR-4766-5p/LAMA1 axis functions as an oncogenic factor in promoting ESCC cell proliferation, migration, and invasion by inducing EMT, implying its potential prognostic and therapeutic significance in ESCC.

Circular RNA CDR1as Inhibits the Metastasis of Gastric Cancer through Targeting miR-876-5p/GNG7 Axis

Circular RNA CDR1as has been demonstrated to participate in various cancer progressions as miRNA sponges. The exact underlying mechanisms of CDR1as on gastric cancer (GC) metastasis remain unknown. Here, we found that CDR1as knockdown facilitated GC cell migration and invasion while its overexpression inhibited the migration and invasion abilities of GC cells in vitro and in vivo. Moreover, epithelial-mesenchymal transition- (EMT-) associated proteins and MMP2 and MMP9 were downregulated by CDR1as. Bioinformatics analysis combined with dual-luciferase reporter gene assays, western blot, RT-qPCR analysis, and functional rescue experiments demonstrated that CDR1as served as a miR-876-5p sponge and upregulated the target gene GNG7 expression to suppress GC metastasis. In summary, our findings indicate that CDR1as suppresses GC metastasis through the CDR1as/miR-876-5p/GNG7 axis.

Circular RNAs in Hepatocellular Carcinoma: Emerging Functions to Clinical Significances

Hepatocellular carcinoma (HCC) is the most common primary cancer of the liver and carries high morbidity and mortality. Diagnosing HCC at an early stage is challenging. Therefore, finding new, highly sensitive and specific diagnostic biomarkers for the diagnosis and prognosis of HCC patients is extremely important. Circular RNAs (circRNAs) are a class of non-coding RNAs with covalently closed loop structures. They are characterized by remarkable stability, long half-life, abundance and evolutionary conservation. Recent studies have shown that many circRNAs are expressed aberrantly in HCC tissues and have important regulatory roles during the development and progression of HCC. Hence, circRNAs are promising biomarkers for the diagnosis and prognosis of HCC. This review: (i) summarizes the biogenesis, categories, and functions of circRNAs; (ii) focuses on current progress of dysregulated expression of circRNAs in HCC with regard to regulation of the tumor hallmarks, “stemness” of cancer cells, and immunotherapy; (iii) highlights circRNAs as potential biomarkers and therapeutic targets for HCC; and (iv) discusses some of the challenges, questions and future perspectives of circRNAs research in HCC.

CircRNA_2646 functions as a ceRNA to promote progression of esophageal squamous cell carcinoma via inhibiting miR-124/PLP2 signaling pathway

MicroRNA-124 (miR-124) has been predicted as a tumor suppressor in esophageal squamous cell carcinoma (ESCC). However, factors contributing to miR-124 reduction remain unclear. Circular RNAs (circRNAs) are a new family of non-coding RNAs with gene regulatory potential via interacting with miRNAs. We predicted three circRNAs, including CircRNA_14359, CircRNA_2646, and CircRNA_129, that could interact with miR-124 by bioinformatics analysis and determined their expressions in ESCC tissues and adjacent normal tissues. We found that CircRNA_2646 was up-regulated in ESCC, negatively correlated with the expression of miR-124 and positively associated with TNM stage and lymph node metastasis of ESCC. Luciferase reporter assay showed that CircRNA_2646 interacted with miR-124 in ESCC Eca109 and TE-1 cells. Moreover, ectopical overexpression of CircRNA_2646 accelerated cell proliferation, migration, invasion, and epithelial-to-mesenchymal transition (EMT), but restoration of miR-124 abrogated these functions and promoted Bcl-2-dependent cell apoptosis. Furthermore, it was found that the oncogene Proteolipid Protein 2 (PLP2) was the target gene of miR-124. In Eca109 and TE-1 cells, restoration of miR-124 decreased the level of PLP2 and inhibited PLP2-induced cell proliferation, migration, invasion, and EMT, but enhanced cell apoptosis. The in vivo study confirmed that CircRNA_2646 promoted ESCC development by repressing miR-124 and activating PLP2. Taken together, we identified that CircRNA_2646 functioned as an inhibitor in miR-124 signaling pathway in ESCC for carcinogenesis and could be a promising target for ESCC therapy.

Downregulation of TAF9B by miR-7-5p Inhibits the Progression of Osteosarcoma

Background

Osteosarcoma (OS) is a malignant bone tumor with high metastatic potential. As a regulatory factor of apoptosis, TATA-box binding protein (TBP) associated factor 9B (TAF9B) is rarely studied in tumors.

Methods

We investigated the role and mechanism of TAF9B in OS cells by overexpression and knockdown. CCK8, colony formation, transwell, and flow cytometry analysis were performed to detect proliferation, migration, invasion, and apoptosis.

Results

TAF9B overexpression promotes the proliferation, migration, and invasion of OS cells, while TAF9B knockdown gives the opposite result. TAF9B inhibits apoptosis by upregulating Bcl-2 and downregulating Bax and Cleaved-caspase-3. Through starBase analysis, it was found that miR-7-5p can bind to the 3ʹUTR region of TAF9B, which is further confirmed by the dual luciferase reporter system assay. MiR-7-5p downregulates the expression of TAF9B in MG63 and U2OS cells. The proliferation and invasion of OS cells are inhibited after miR-7-5p mimics transfection and are promoted after miR-7-5p inhibitor transfection. TAF9B rescues the inhibitory effect of miR-7-5p on OS cells. TAF9B also activates the AKT/mTOR signaling pathway.

Conclusion

According to our results, miR-7-5p inhibits the translation of TAF9B and then suppresses growth and metastasis through the AKT/mTOR signaling pathway in OS cells, thereby indicating the potential value of miR-7-5p and TAF9B as therapeutic targets for human OS.

A six-gene-based signature for breast cancer radiotherapy sensitivity estimation

Breast cancer (BRCA) represents the most common malignancy among women worldwide with high mortality. Radiotherapy is a prevalent therapeutic for BRCA that with heterogeneous effectiveness among patients. Here, we proposed to develop a gene expression-based signature for BRCA radiotherapy sensitivity estimation. Gene expression profiles of BRCA samples from the Cancer Genome Atlas (TCGA) and International Cancer Genome Consortium (ICGC) were obtained and used as training and independent testing dataset, respectively. Differential expression genes (DEGs) in BRCA samples compared with their paracancerous samples in the training set were identified by using the edgeR Bioconductor package. Univariate Cox regression analysis and LASSO Cox regression method were applied to screen optimal genes for constructing a radiotherapy sensitivity estimation signature. Nomogram combining independent prognostic factors was used to predict 1-, 3-, and 5-year OS of radiation-treated BRCA patients. Relative proportions of tumor infiltrating immune cells (TIICs) calculated by CIBERSORT and mRNA levels of key immune checkpoint receptors was adopted to explore the relation between the signature and tumor immune response. As a result, 603 DEGs were obtained in BRCA tumor samples, six of which were retained and used to construct the radiotherapy sensitivity prediction model. The signature was proved to be robust in both training and testing sets. In addition, the signature was closely related to the immune microenvironment of BRCA in the context of TIICs and immune checkpoint receptors’ mRNA levels. In conclusion, the present study obtained a radiotherapy sensitivity estimation signature for BRCA, which should shed new light in clinical and experimental research.

RAI14 Regulated by circNFATC3/miR-23b-3p axis Facilitates Cell Growth and Invasion in Gastric Cancer

Circular RNAs (circRNAs) have been proved to act crucial roles in multiple malignancies including gastric cancer (GC). Retinoic acid induced 14 (RAI14) acts as an oncogene in human cancers, but the underlying mechanisms by which RAI14 is regulated by circRNA/miRNA axis remain elusive. The clinical value of RAI14, miR-23b-3p and circNFATC3 was estimated by The Cancer Genome Atlas and fluorescence in situ hybridization. The interplay between miR-23b-3p and RAI14 or circNFATC3 was determined by qRT-PCR, Western blot, luciferase gene report and RIP assays. Biological function assays and a subcutaneous xenograft model were executed to unveil the role of circNFATC3/miR-23b-3p/RAI14 axis in GC cells. As a consequence, upregulation of RAI14 and circNFATC3 or downregulation of miR-23b-3p was associated with poor prognosis in patients with GC. Restored miR-23b-3p depressed cell proliferation, colony formation, and cell invasion by targeting RAI14, whereas RAI14 facilitated cell progression and reversed the anti-tumor effects of miR-23b-3p in GC cells. Then, circNFATC3 had a co-localization with miR-23b-3p in the cytoplasm in GC tissue cells and could act as a sponge of miR-23b-3p in GC cell line. Silencing of circNFATC3 inhibited cell growth and in vivo tumorigenesis by upregulating miR-23b-3p and downregulating RAI14. In conclusion, our findings indicated that RAI14 facilitated cell growth and invasion and was regulated by circNFATC3/miR-23b-3p axis in GC.

Upregulated long non‑coding RNA LincIN promotes tumor progression via the regulation of nuclear factor 90/microRNA‑7/HOXB13 in esophageal squamous cell carcinoma

Long non-coding RNA LincIN has been reported to be overexpressed and to be involved in the metastasis of breast cancer. However, the expression and role of LincIN in esophageal squamous cell carcinoma (ESCC) remain unsolved. In the present study, LincIN expression was examined in ESCC by RT-qPCR, and the roles of LincIN in ESCC were determined using cell growth, migration and invasion assays. In addition, the effects of LincIN on nuclear factor 90 (NF90) and microRNA/miR (miR)-7 were examined by RNA immunoprecipitation assay, RT-qPCR, dual-luciferase reporter assay and western blot analysis. The results revealed that LincIN expression was significantly increased in ESCC tissues and cell lines. The increased expression of LincIN was positively associated with invasion depth, lymph node metastasis, TNM stage and a poor prognosis. Functional assays revealed that the overexpression of LincIN promoted ESCC cell growth, migration and invasion. Mechanistic analysis revealed that LincIN physically bound to NF90, enhanced the binding between NF90 and primary miR-7 (pri-miR-7), and further enhanced the inhibitory effects of NF90 on miR-7 biogenesis. Therefore, LincIN downregulated miR-7 expression in ESCC. The expression of miR-7 inversely correlated with that of LincIN in ESCC tissues. By downregulating miR-7, LincIN increased the expression of HOXB13, a target of miR-7. The overexpression of miR-7 or the depletion of HOXB13 both attenuated the tumor-promoting roles of LincIN in ESCC cell growth, migration and invasion. On the whole, the findings of the present study suggest that LincIN is overexpressed and plays an oncogenic role in ESCC via the regulation of the NF90/miR-7/HOXB13 axis. Thus, LincIN may prove to be a promising prognostic biomarker and therapeutic target for ESCC.

Current Understanding of Circular RNAs in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a common and potentially fatal autoimmune disease that affects multiple organs. To date, its etiology and pathogenesis remains elusive. Circular RNAs (circRNAs) are a novel class of endogenous non-coding RNAs with covalently closed loop structure. Growing evidence has demonstrated that circRNAs may play an essential role in regulation of gene expression and transcription by acting as microRNA (miRNA) sponges, impacting cell survival and proliferation by interacting with RNA binding proteins (RBPs), and strengthening mRNA stability by forming RNA-protein complexes duplex structures. The expression patterns of circRNAs exhibit tissue-specific and pathogenesis-related manner. CircRNAs have implicated in the development of multiple autoimmune diseases, including SLE. In this review, we summarize the characteristics, biogenesis, and potential functions of circRNAs, its impact on immune responses and highlight current understanding of circRNAs in the pathogenesis of SLE.

CircRNAs: a new target for the diagnosis and treatment of digestive system neoplasms

A circRNA is a type of endogenous noncoding RNA that consists of a closed circular RNA molecule formed by reverse splicing; these RNAs are widely distributed in a variety of biological cells. In contrast to linear RNAs, circRNAs have no 5′ cap or 3′ poly(A) tail. They have a stable structure, a high degree of conservation, and high stability, and they are richly and specifically expressed in certain tissues and developmental stages. CircRNAs play a very important role in the occurrence and progression of malignant tumors. According to their origins, circRNAs can be divided into four types: exon-derived circRNAs (ecRNAs), intron-derived circRNAs (ciRNAs), circRNAs containing both exons and introns (EIciRNAs) and intergenic circRNAs. A large number of studies have shown that circRNAs have a variety of biological functions, participate in the regulation of gene expression and play an important role in the occurrence and progression of tumors. In this paper, the structure and function of circRNAs are reviewed, along with their biological role in malignant tumors of the digestive tract, in order to provide a reference for the diagnosis and treatment of digestive system neoplasms.

Circular RNA circ_0002137 regulated the progression of osteosarcoma through regulating miR-433-3p/ IGF1R axis

Current clinical treatment targeting osteosarcoma (OS) are limited for OS patients with pulmonary metastasis or relapse, which led to high mortality (70%‐85%) for advanced osteosarcoma patients. Although ongoing efforts have been made to illustrate the mechanisms of tumorigenesis and progression in OS; however, it was far for us to learn a comprehensive molecular mechanism implies in OS development. In our study, we implicated a circRNA hsa_circ_0002137, which was higher expressed in osteosarcoma tumours compared with paracancerous tissue. The dysregulated expression pattern was also found in osteosarcoma cell lines. The role of circ_0002137 was explored via down‐ or up‐regulated experiments. It was proved that down‐regulation of circ_0002137 suppressed the progress of OS, including cell invasion, cell cycle and cell apoptosis. Furthermore, the correlation between circ_0002137 and miR‐433‐3p was predicted using bioinformatic tools and verified utilizing RNA pull‐down assay and luciferase reporter assay. Interestingly, we found that the inhibitory effect of circ_0002137 on OS was dependent of insulin‐like growth factor‐1 receptor (IGF1R). In conclusion, it was demonstrated that circ_0002137 could restrain the progression of OS through regulating miR‐433‐3p/IGF1R axis, providing a comprehensive landscape of circ_0002137 in the generation and development of OS.

The Prognostic and Predictive Significance of circRNA CDR1as in Tumor Progression

Cerebellar degeneration-related protein 1 antisense (CDR1as) is an important member of the circRNAs family, also known as cirs-7. Its main function in vivo is to act as a mir-7 sponge. Accumulated studies show that CDR1as is closely related to various diseases, especially cancer. Our analysis show that CDR1as expression in human cancer is significantly associated with poor overall survival (hazard ratio [HR] = 2.50, 95% confidence interval [CI] = 2.06–3.04; p < 0.00001) and that high CDR1as expression is associated with the tumor node metastasis stage (odds ratio [OR] = 2.13, 95% CI = 1.63–2.78; p < 0.00001), and distant metastasis (OR = 3.50, 95% CI = 1.90–6.64; p < 0.00001). Furthermore, the results reveal the prognostic significance of CDR1as in neoplasms of the digestive system (HR = 1.69, 95% CI = 2.14–2.71; p < 0.001), colorectal cancer (HR = 1.34, 95% CI = 1.96–2.85; p < 0.001), and non-small cell lung cancer (HR = 2.40, 95% CI = 3.42–4.83; p = 0.008). In this study, we summarize in detail the latest research findings and demonstrate the function and regulatory mechanism of CDR1as in various cancer processes, and its potential as a biomarker for cancer prevention and prognosis.

Prognostic and Clinicopathological Significance of Circular RNA circ-ITCH Expression in Cancer Patients: A Meta-analysis

Circular RNAs are a class of RNAs with a covalently closed configuration, and several members of them have been reported to be capable of regulating various biological processes and predicting the outcome of disease. Among them, circular RNA circ-ITCH has been identified to be aberrantly expressed and associated with disease progression in diverse cancers. However, the correlation of circ-ITCH expression with clinicopathological features, as well as the prognosis of cancers, remains inconclusive. Therefore, a meta-analysis was performed to investigate the clinical significance of circ-ITCH in cancers by systematically summarizing all eligible literatures. Up to August 31, 2020, relevant articles were searched in PubMed, Web of Science, Cochrane library, Embase, CNKI, and Wanfang databases. Pooled hazard ratios (HRs) and odds ratios (ORs) with corresponding 95% confidence intervals (CIs) were calculated. A total of 1604 patients from 14 studies were included in this meta-analysis. The results showed that cancer patients with low circ-ITCH expression were more susceptible to develop lymph node metastasis (OR = 2.25, 95% CI: 1.67-3.02, p ≤ 0.01), larger tumor size (OR = 3.01, 95% CI: 2.01-4.52, p ≤ 0.01), advanced TNM stage (OR = 2.82, 95% CI: 1.92-4.14, p ≤ 0.01), and poor overall survival (OS) (HR = 2.45, 95% CI: 2.07-2.90, p ≤ 0.01, univariate analysis; HR = 2.69, 95% CI: 1.82-3.96, p ≤ 0.01, multivariate analysis). Thus, low circ-ITCH expression was significantly associated with aggressive clinicopathological features and unfavorable outcome in various cancers. Therefore, circ-ITCH may serve as a molecular therapy target and a prognostic marker in human cancers.

The expanding role of CDR1-AS in the regulation and development of cancer and human diseases

CircRNAs are a superabundant and highly conserved group of noncoding RNAs (ncRNAs) that are characterized by their high stability and integrity compared with linear forms of ncRNAs. Recently, their critical role in gene expression regulation has been shown; thus, it is not far-fetched to believe that their abnormal expression can be a cause of different kinds of diseases such as cancer, neurodegenerative, and autoimmune diseases. They can have a function in variety of biological processes such as microRNA (miRNA) sponging, interacting with RNA-binding proteins, or even an ability to translate to proteins. A huge challenge in finding diagnostic biomarkers is finding noninvasive biomarkers that can be detected in human fluids, especially blood samples. CircRNAs are becoming candidate biomarkers for diagnosis and prognosis of these diseases through their ability to transverse from the blood-brain barrier and their broad presence in circulating exosomes. The circRNA for miRNA-7 (ciRS-7) is newly recognized, and acknowledged to being related to human pathology and cancer progression. In this review, we first briefly summarize the latest studies about their characteristics, biogenesis, and their mechanisms of action in the regulation and development of human diseases. Finally, we provide a list of diseases that are linked to one member of this novel class of ncRNAs called ciRS-7.

Review on circular RNAs and new insights into their roles in cancer

Circular RNAs (circRNAs) are a very interesting class of conserved single-stranded RNA molecules derived from exonic or intronic sequences by precursor mRNA back-splicing. Unlike canonical linear RNAs, circRNAs form covalently closed, continuous stable loops without a 5'end cap and 3'end poly(A) tail, and therefore are resistant to exonuclease digestion. The majority of circRNAs are highly abundant, and conserved across different species with a tissue or developmental-stage-specific expression. circRNAs have been shown to play important roles as microRNA sponges, regulators of gene splicing and transcription, RNA-binding protein sponges and protein/peptide translators. Emerging evidence reveals that circRNAs function in various human diseases, particularly cancers, and may function as better predictive biomarkers and therapeutic targets for cancer treatment. In consideration of their potential clinical relevance, circRNAs have become a new research hotspot in the field of tumor pathology. In the present study, the current understanding of the biogenesis, characteristics, databases, research methods, biological functions subcellular distribution, epigenetic regulation, extracellular transport and degradation of circRNAs was discussed. In particular, the multiple databases and methods involved in circRNA research were first summarized, and the recent advances in determining the potential roles of circRNAs in tumor growth, migration and invasion, which render circRNAs better predictive biomarkers, were described. Furthermore, future perspectives for the clinical application of circRNAs in the management of patients with cancer were proposed, which could provide new insights into circRNAs in the future.

Genome-Wide Circular RNA Expression Patterns Reflect Resistance to Immunomodulatory Drugs in Multiple Myeloma Cells

Simple Summary

Multiple myeloma (MM) constitutes the second most common hematological malignancy and is caused by aberrant plasma cell proliferation in the bone marrow. While recent improvements in the treatment of MM has been observed using immunomodulatory drugs (IMiDs), patients often relapse due to acquired drug resistance and no cure for the disease is currently available. In this report, we profile circular RNA (circRNA) expression patterns in cultured MM cells being sensitive to IMiDs and their resistant counterparts. CircRNAs constitute a large class of non-coding RNA molecules with emerging roles in cancer development and progression, but have not previously been explored in this context. We found that global circRNA expression patterns reflect IMiD sensitivity, but the most downregulated circRNA in IMiD resistant MM cells did not seem to be a direct driver of IMiD resistance. Future studies should investigate other circRNA candidates identified here in the context of IMiD resistance.

Abstract

Immunomodulatory drugs (IMiDs), such as lenalidomide and pomalidomide, may induce significant remissions in multiple myeloma (MM) patients, but relapses are frequently observed and the underlying molecular mechanisms for this are not completely understood. Circular RNAs (circRNAs) constitute an emerging class of non-coding RNAs with important roles in cancer. Here, we profiled genome-wide expression patterns of circRNAs in IMiD-sensitive MM cells and their resistant counterparts as well as in IMiD-resistant cells treated with specific epigenetic drugs alone or in combination. We found that genome-wide circRNA expression patterns reflect IMiD sensitivity and ciRS-7 (also known as CDR1as) was the most downregulated circRNA upon acquired resistance. The depletion of ciRS-7 correlated with increased methylation levels of the promoter CpG island of its host gene, LINC00632. Expression of LINC00632 and ciRS-7 was partly restored by treatment with a combination of an EZH2 inhibitor (EPZ-6438) and a DNA methyl transferase inhibitor (5-azacytidine), which also restores the IMiD sensitivity of the cells. However, knockdown of ciRS-7 did not affect IMiD sensitivity and we found that ciRS-7 also becomes epigenetically silenced after prolonged cell culture without drug-exposure. In conclusion, we found that genome-wide circRNA expression patterns reflect IMiD sensitivity in an in vitro model of acquired resistance.

CircRNA ciRS-7: a Novel Oncogene in Multiple Cancers

circular RNA ciRS-7 (ciRS-7) is a type of endogenous circular RNA (circRNA) with a closed circular structure. Since Hansen first demonstrated that ciRS-7 could serve as a microRNA sponge in 2013, researchers have paid increased attention to this circRNA. ciRS-7 plays a crucial role in regulating RNA transcription, downstream gene expression, and protein production. Moreover, ciRS-7 acts as an oncogene and promotes tumor progression through competitively inhibiting miR-7 in various types of cancers. ciRS-7 has been identified to be closely associated with breast cancer, nasopharyngeal carcinoma, lung cancer, hepatocellular carcinoma, cervical cancer, osteosarcoma, melanoma, colorectal cancer, esophageal squamous cell carcinoma, gastric cancer, pancreatic cancer, laryngeal squamous cell carcinoma, and cholangiocarcinoma. In this review, we summarize the biological characteristics, molecular mechanisms, and future challenges of ciRS-7 in multiple tumors.

The Effect of Melatonin Modulation of Non-coding RNAs on Central Nervous System Disorders: An Updated Review

Melatonin is a hormone produced in and secreted by the pineal gland. Besides its role in regulating circadian rhythms, melatonin has a wide range of protective functions in the central nervous system (CNS) disorders. The mechanisms underlying this protective function are associated with the regulatory effects of melatonin on related genes and proteins. In addition to messenger ribonucleic acid (RNA) that can be translated into protein, an increasing number of non-coding RNAs in the human body are proven to participate in many diseases. This review discusses the current progress of research on the effects of melatonin modulation of non-coding RNAs (ncRNAs), including microRNA, long ncRNA, and circular RNA. The role of melatonin in regulating common pathological mechanisms through these ncRNAs is also summarized. Furthermore, the ncRNAs, currently shown to be involved in melatonin signaling in CNS diseases, are discussed. The information compiled in this review will open new avenues for future research into melatonin mechanisms and provide a further understanding of ncRNAs in the CNS.

LncRNA GIHCG Promotes the Development of Esophageal Cancer by Modulating miR-29b-3p/ANO1 Axis

Background

Esophageal cancer is one of the most frequent cancers with a higher mortality worldwide. Although many long non-coding RNAs (LncRNAs) are reported to play important roles in the progression of esophageal cancer, the function of lncRNA GIHCG in esophageal cancer remains unclear.

Methods

The expression of GIHCG in esophageal cancer tissues and cancer cell lines was detected by qRT-PCR. Cell proliferation was evaluated by Cell Counting Kit-8 (CCK-8) assay, EdU staining assay and colony formation assay. Cell invasion and migration were measured by transwell assay. Cell apoptosis was detected by a flow cytometer. Luciferase reporter assay and RIP assay were used to determine the interaction between GIHCG and miR-29b-3p, and their subsequent regulation of anoctamin 1 (ANO1). The expression of ANO1 in esophageal cancer tissues and cell lines was detected by Western blot. The effect of GIHCG/miR-29b-3p in tumor formation was assessed by the xenograft nude mice model in vivo.

Results

GIHCG was significantly upregulated in esophageal cancer tissues and relevant cancer cell lines. Downregulation of GIHCG significantly inhibited the growth, colony formation, invasion, migration and induced apoptosis of esophageal cancer cells in vitro. Bioinformatic analysis and RIP assay determined that GIHCG was a sponge of miR-29b-3p, and ANO1 was a direct target of miR-29b-3p. Moreover, functional experiments showed that GIHCG upregulated ANO1 expression by directly sponging miR-29b-3p. Furthermore, in vivo experiment revealed that knockdown of GIHCG significantly inhibited tumor growth in nude mice.

Conclusion

Our study revealed that lncRNA GIHCG promoted the progression of esophageal cancer by targeting the miR-29b-3p/ANO1 axis, suggesting that GIHCG might be a novel therapeutic target for esophageal cancer.

Cerina: systematic circRNA functional annotation based on integrative analysis of ceRNA interactions

Circular RNAs, a family of covalently circularized RNAs with tissue-specific expression, were recently demonstrated to play important roles in mammalian biology. Regardless of extensive research to predict, quantify, and annotate circRNAs, our understanding of their functions is still in its infancy. In this study, we developed a novel computational tool: Competing Endogenous RNA for INtegrative Annotations (Cerina), to predict biological functions of circRNAs based on the competing endogenous RNA model. Pareto Frontier Analysis was employed to integrate ENCODE mRNA/miRNA data with predicted microRNA response elements to prioritize tissue-specific ceRNA interactions. Using data from several circRNA-disease databases, we demonstrated that Cerina significantly improved the functional relevance of the prioritized ceRNA interactions by several folds, in terms of precision and recall. Proof-of-concept studies on human cancers and cardiovascular diseases further showcased the efficacy of Cerina on predicting potential circRNA functions in human diseases.

The Emerging Picture of the Roles of CircRNA-CDR1as in Cancer

Circular RNAs (circRNAs) are covalently closed circular structures without 5′ caps and 3′ tails, which are mainly formed from precursor mRNAs (pre-mRNAs) via back-splicing of exons. With the development of RNA sequencing and bioinformatic analysis, circRNAs were recently rediscovered and found to be widely expressed in the tree of life. Cerebellar degeneration-related protein 1 antisense RNA (CDR1as) is recognized as one of the most well-identified circRNAs. It contains over 70 miR-7 binding sites and can regulate gene activity by sponging miR-7. Increasing numbers of studies have recently demonstrated that CDR1as is abnormally expressed in many types of tumors, such as colorectal cancer, cholangiocarcinoma and osteosarcoma, and plays a vital role in the development of cancer. However, there are few reviews focusing on CDR1as and cancer. Hence, it is important to review and discuss the role of CDR1as in cancer. Here, we first review the main biological features of CDR1as. We then focus on the expression and roles of CDR1as in cancer. Finally, we summarize what is known on the role of CDR1as in cancer and discuss future prospects in this area of research.

Hsa_circ_0006571 promotes spinal metastasis through sponging microRNA-138 to regulate sirtuin 1 expression in lung adenocarcinoma

Background

Circular RNAs (circRNAs) are known to participate in lung cancer. However, their role in spinal metastasis (SM) of lung adenocarcinoma remains elusive. In this study, we determined that hsa_circ_0006571 serves as a sponge for miR-138, which targets sirtuin 1 (Sirt1) in the development of SM.

Methods

A human circRNA microarray was performed to compare SM and lung adenocarcinoma samples. The expression of hsa_circ_0006571 and miR-138 was determined using quantitative polymerase chain reaction (qPCR) in vitro and in vivo. Cell proliferation was performed by Cell Counting Kit-8 (CCK-8) and apoptosis was analyzed by Annexin V/PI staining. RNA-pulldown and RNA immunoprecipitation (RIP) were used to analyze the interaction between hsa_circ_0006571. Tumor metastasis was determined through a xenograft experiment in vivo.

Results

Hsa_circ_0006571 was observed to be significantly upregulated in SM tissues through circRNA microarray and qPCR. We detected a lower expression of miR-138 in SM tissues compared with lung adenocarcinoma. Hsa_circ_0006571 silencing suppressed lung cancer cell proliferation and migration while promoting apoptosis. Hsa_circ_0006571 interacted with miR-138 to promote expression of Sirt1, leading to activation of epithelial-mesenchymal transition (EMT). Xenograft experiments showed that downregulation of hsa_circ_0006571 delayed the SM of lung adenocarcinoma cells via the miR-138-Sirt1 axis.

Conclusions

Hsa_circ_0006571 promoted tumor cell migration and invasion via the miR-138/Sirt1 pathway. Our observations indicate that circRNAs are possible novel therapeutic targets for SM of lung adenocarcinoma.

Hypoxic Tumor-Derived Exosomal Circ0048117 Facilitates M2 Macrophage Polarization Acting as miR-140 Sponge in Esophageal Squamous Cell Carcinoma

Introduction

Hypoxia and tumor-associated macrophage (TAM) are key regulators in remodeling the microenvironment of esophageal squamous cell carcinoma (ESCC). Hypoxia could stimulate tumor cells to secrete more exosomes and activate TAMs to M2 type. Here, we investigated the function and the underlying mechanism of tumor-derived exosomal hsa-circ-0048117 in TAM polarization in ESCC. Collectively, these data indicate that PC cells generate miR-301a-3p-rich exosomes in a hypoxic microenvironment, which then polarize macrophages to promote malignant behaviors of PC cells.

Methods

Transmission electron microscopy (TEM) and nanoparticle tracking analysis (NTA) were used to analyze the physical characteristics of exosomes. High-throughput sequencing and bioinformatic analysis were performed to screen the potential exosomal circRNA. FISH, Ago2 RIP, pull-down and dual-luciferase reporter assay were conducted to figure out the correlation among hsa-circ-0048117, miR-140 and toll-like receptor 4 (TLR4). Flow cytometry and Western blot were used to evaluate their joint effect in macrophages polarization. Then, the invasion and migration ability were evaluated by transwell experiment. At last, serum exo-hsa-circ-0048117 in ESCC patients was compared and the correlation between its expression and T stage, N stage and TNM grades was analyzed.

Results

Hsa-circ-0048117 was significantly upregulated and enriched in exosomes secreted by hypoxia pre-challenged tumor cells and contributed to M2 macrophage polarization. Hsa-circ-0048117 depletion in macrophage led to inhibition of M2 polarization while restoration of hsa-circ-0048117 could rescue the process. Moreover, hsa-circ-0048117 could act as sponge of miR-140 by competing with TLR4 to facilitate the M2 macrophage polarization. Exo-hsa-circ-0048117 could be transmitted to macrophages to promote M2 polarization and M2 macrophages could enhance the ability of invasion and migration of tumor cells by secreting Arg1, IL-10 and TGF-β. Higher serum exo-hsa-circ-0048117 predicted an advanced T and N stage and positively correlated with TNM grade.

Conclusion

Our findings indicated that ESCC cells generate hsa-circ-0048117-rich exosomes in a hypoxic microenvironment; hsa-circ-0048117 was believed to promote M2 macrophage polarization which favors the malignant behaviors of ESCC cells. These results reminded us that exosomal hsa-circ-0048117 may play a key role in remodeling the microenvironment and modulating progression in ESCC.

The emerging prospects of circular RNA in tumor immunity

Circular RNA (circRNA), as a cluster of endogenous non-coding RNA (ncRNA) with tissue-specific expression in various eukaryotic species, may be involved in a variety of human physiological and pathological processes. With the continuous development of high-throughput sequencing in recent years, circRNA has been increasingly widely studied and become a hot spot in the field of tumor research. The immune system plays a crucial and complex role in tumor development. It is not only capable of inhibiting tumor progression, but it can also create conditions suitable for tumor development, thereby promoting tumor progression. Moreover, through ncRNA, tumor immunotherapy, as an essential means of tumor therapy, may regulate tumor immunity to achieve the purpose of treatment. This article reviews the role of circRNA in tumor immunity to supply a sufficient theoretical basis for tumor immunotherapy.

FTO demethylates m6A modifications in HOXB13 mRNA and promotes endometrial cancer metastasis by activating the WNT signalling pathway

Although many studies have confirmed the relationship between obesity and endometrial cancer (EC), the molecular mechanism between obesity and EC progression has not been elucidated. Overexpression of fat mass and the obesity associated protein FTO leads to weight gain, although recently it has been discovered that FTO can serve as a demethylase which erases N6-methyladenosine (m6A) modification and regulates the metabolization of mRNAs. In this study, we found high expression of FTO in metastatic EC and that this action promote both metastasis and invasion in vivo and in vitro. Mechanistically, FTO can catalyse demethylation modification in 3'UTR region of HOXB13 mRNA, thereby abolishing m6A modification recognition with the YTHDF2 protein. Decreasing HOXB13 mRNA decay and increasing HOXB13 protein expression was accompanied by WNT signalling pathway activation and the expression of downstream proteins, leading to tumour metastasis and invasion. We also found the WNT signalling pathway inhibitor ICG-001 can block HOXB13 gene-induced tumour metastasis, therefore ICG-001 may be a promising molecular intervention. This study provides insight into the relationship between obesity and the pathogenesis of endometrial cancer while highlighting future areas of research.

Circ0120816 acts as an oncogene of esophageal squamous cell carcinoma by inhibiting miR-1305 and releasing TXNRD1

BACKGROUND

Circular RNAs (circRNAs) have been discovered to participate in the carcinogenesis of multiple cancers. However, the role of circRNAs in esophageal squamous cell carcinoma (ESCC) progression is yet to be properly understood. This research aimed to investigate and understand the mechanism used by circRNAs to regulate ESCC progression.

METHODS

Bioinformatics analysis was first performed to screen dysregulated circRNAs and differentially expressed genes in ESCC. The ESCC tissue samples and adjacent normal tissue samples utilized in this study were obtained from 36 ESCC patients. All the samples were subjected to qRT-PCR analysis to identify the expression of TXNRD1, circRNAs, and miR-1305. Luciferase reporter assay, RNA immunoprecipitation assay and RNA pull-down assay were later conducted to verify the existing relationship among circ0120816, miR-1305 and TXNRD1. CCK-8, BrdU, cell adhesion, cell cycle, western blot and caspase 3 activity assays were also employed to evaluate the regulation of these three biological molecules in ESCC carcinogenesis. To evaluate the effect of circ0120816 on ESCC tumor growth and metastasis, the xenograft mice model was constructed.

RESULTS

Experimental investigations revealed that circ0120816 was the highest upregulated circRNA in ESCC tissues and that this non-coding RNA acted as a miR-1305 sponge in enhancing cell viability, cell proliferation, and cell adhesion as well as repressing cell apoptosis in ESCC cell lines. Moreover, miR-1305 was observed to exert a tumor-suppressive effect in ESCC cells by directly targeting and repressing TXNRD1. It was also noticed that TXNRD1 could regulate cyclin, cell adhesion molecule, and apoptosis-related proteins. Furthermore, silencing circ0120816 was found to repress ESCC tumor growth and metastasis in vivo.

CONCLUSIONS

This research confirmed that circ0120816 played an active role in promoting ESCC development by targeting miR-1305 and upregulating oncogene TXNRD1.

Circular RNA circTP63 enhances estrogen receptor-positive breast cancer progression and malignant behaviors through the miR-873-3p/FOXM1 axis

Circular RNAs (circRNAs) have been shown to play a functional role in a variety of cancers. However, few studies on circRNAs in estrogen receptor-positive breast cancer have been conducted. Here, we investigated the role of circRNA circTP63 in estrogen receptor-positive breast cancer progression and malignant behaviors. First, we observed increased expression of circTP63 in MCF7 cells relative to normal human mammary epithelial cell lines, such as DU4475 and MCF-10A, and the changed oncogenicity of MCF7 cells correlated with circTP63 overexpression and downregulation. Interestingly, a series of gain- and loss-of-function assays revealed that a higher level of FOXM1 was closely associated with MCF7 malignant behaviors induced by circTP63 overexpression. Further investigations showed that circTP63 sponged to miR-873-3p, which targeted FOXM1 mRNA and inhibited its expression. Mechanistically, circTP63 binds to miR-873-3p and prevents the targeting of FOXM1, thus inducing the progression and malignant behaviors of estrogen receptor-positive breast cancer, such as cell proliferation, cell cycle dysregulation, invasion, migration and even tumor growth. CircTP63 might be a potential biomarker or target to treat estrogen receptor-positive breast cancer patients in the future.

Analysis of the circRNAs expression profile in mouse lung with H7N9 influenza A virus infection

Influenza A virus is a single-stranded RNA virus that can cause great mortality and economic loss worldwide. Circular RNAs (circRNAs) are non-coding RNAs that have been shown to have important functions in the regulation of biological processes. However, their functions during the influenza A virus infection process remain unclear. Herein, RNA sequencing technology was used to identify circRNAs expressed in mouse lungs during infection with H7N9/PB2-627 K/701D (H7N9/Wild-type) virus and PB2 mutant viruses (H7N9/PB2-627E/701D and H7N9/PB2-627E/701 N). We identified 7126 circRNAs at different genomic locations during H7N9 influenza virus and its mutant virus infections, of which 186 were differentially expressed. Enrichment analysis revealed that the differentially expressed circRNAs were associated with the viral infection process. Our study shows that circRNA expression profiles were altered following H7N9 influenza A virus infection and the differentially expressed circRNAs may have an important immune-regulating function during viral infection.