Circular RNA circ-PRMT5 facilitates non-small cell lung cancer proliferation through upregulating EZH2 via sponging miR-377/382/498

Advanced approaches of the use of circRNAs as a replacement for cancer therapy

Cancer is a broad name for a group of diseases in which abnormal cells grow out of control and are characterized by their complexity and recurrence. Although there has been progress in cancer therapy with the entry of precision medicine and immunotherapy, cancer incidence rates have increased globally. Non-coding RNAs in the form of circular RNAs (circRNAs) play crucial roles in the pathogenesis, clinical diagnosis, and therapy of different diseases, including cancer. According to recent studies, circRNAs appear to serve as accurate indicators and therapeutic targets for cancer treatment. However, circRNAs are promising candidates for cutting-edge cancer therapy because of their distinctive circular structure, stability, and wide range of capabilities; many challenges persist that decrease the applications of circRNA-based cancer therapeutics. Here, we explore the roles of circRNAs as a replacement for cancer therapy, highlight the main challenges facing circRNA-based cancer therapies, and discuss the key strategies to overcome these challenges to improve advanced innovative therapies based on circRNAs with long-term health effects.

Oncogenic circ-SLC16A1 promotes progression of non-small cell lung cancer via regulation of the miR-1287-5p/profilin 2 axis

BACKGROUND

Circular RNAs (circRNAs) are single-stranded RNAs with covalently closed structures that have been implicated in cancer progression. However, the regulatory mechanisms remain largely unclear. So, the aim of this study was to reveal the role and regulatory mechanisms of circ-SLC16A1.

METHODS

In this study, next-generation sequencing was used to identify abnormally expressed circRNAs between cancerous and para-carcinoma tissues. Fluorescence in situ hybridization and quantitative reverse transcription polymerase chain reaction were performed to assess the expression patterns of circ-solute carrier family 16 member 1 (SLC16A1) in non-small cell lung cancer (NSCLC) cells and tissue specimens. The dual-luciferase reporter assay was utilized to identify downstream targets of circ-SLC16A1. Transwell migration, wound healing, 5-ethynyl-2'-deoxyuridine incorporation, cell counting, and colony formation assays were conducted to assess the proliferation and migration of NSCLC cells. A mouse tumor xenograft model was employed to determine the roles of circ-SLC16A1 in NSCLC progression and metastasis in vivo.

RESULTS

The results found that circ-SLC16A1 was upregulated in NSCLC cells and tissues. Downregulation of circ-SLC16A1 inhibited tumor growth by reducing proliferation, lung metastasis, and lymphatic metastasis of NSCLC cells, and arrested the cell cycle in the G1 phase. Also, silencing of circ-SLC16A1 promoted apoptosis of NSCLC cells. The results of bioinformatics analysis and the dual-luciferase reporter assay confirmed that microRNA (miR)-1287-5p and profilin 2 (PFN2) are downstream targets of circ-SLC16A1. PFN2 overexpression or circ-SLC16A1 inhibition restored proliferation and migration of NSCLC cells after silencing of circ-SLC16A1. PFN2 overexpression restored migration and proliferation of NSCLC cells post miR-1287-5p overexpression.

CONCLUSIONS

Collectively, these findings show that miR-1287-5p/PFN2 signaling was associated with downregulation of circ-SLC16A1 and reduced invasion and proliferation of NSCLC cells. So, circ-SLC16A1 is identified as a mediator of multiple pro-oncogenic signaling pathways in NSCLC and can be targeted to suppress tumor progression.

microRNA-382 as a tumor suppressor? Roles in tumorigenesis and clinical significance

MicroRNAs (miRNAs) are small single-stranded RNAs belonging to a class of non-coding RNAs with an average length of 18-22 nucleotides. Although not able to encode any protein, miRNAs are vastly studied and found to play role in various human physiologic as well as pathological conditions. A huge number of miRNAs have been identified in human cells whose expression is straightly regulated with crucial biological functions, while this number is constantly increasing. miRNAs are particularly studied in cancers, where they either can act with oncogenic function (oncomiRs) or tumor-suppressors role (referred as tumor-suppressor/oncorepressor miRNAs). miR-382 is a well-studied miRNA, which is revealed to play regulatory roles in physiological processes like osteogenic differentiation, hematopoietic stem cell differentiation and normal hematopoiesis, and liver progenitor cell differentiation. Notably, miR-382 deregulation is reported in pathologic conditions, such as renal fibrosis, muscular dystrophies, Rett syndrome, epidural fibrosis, atrial fibrillation, amelogenesis imperfecta, oxidative stress, human immunodeficiency virus (HIV) replication, and various types of cancers. The majority of oncogenesis studies have claimed miR-382 downregulation in cancers and suppressor impact on malignant phenotype of cancer cells in vitro and in vivo, while a few studies suggest opposite findings. Given the putative role of this miRNA in regulation of oncogenesis, assessment of miR-382 expression is suggested in a several clinical investigations as a prognostic/diagnostic biomarker for cancer patients. In this review, we have an overview to recent studies evaluated the role of miR-382 in oncogenesis as well as its clinical potential.

NGCICM: A Novel Deep Learning-Based Method for Predicting circRNA-miRNA Interactions

The circRNAs and miRNAs play an important role in the development of human diseases, and they can be widely used as biomarkers of diseases for disease diagnosis. In particular, circRNAs can act as sponge adsorbers for miRNAs and act together in certain diseases. However, the associations between the vast majority of circRNAs and diseases and between miRNAs and diseases remain unclear. Computational-based approaches are urgently needed to discover the unknown interactions between circRNAs and miRNAs. In this paper, we propose a novel deep learning algorithm based on Node2vec and Graph ATtention network (GAT), Conditional Random Field (CRF) layer and Inductive Matrix Completion (IMC) to predict circRNAs and miRNAs interactions (NGCICM). We construct a GAT-based encoder for deep feature learning by fusing the talking-heads attention mechanism and the CRF layer. The IMC-based decoder is also constructed to obtain interaction scores. The Area Under the receiver operating characteristic Curve (AUC) of the NGCICM method is 0.9697, 0.9932 and 0.9980, and the Area Under the Precision-Recall curve (AUPR) is 0.9671, 0.9935 and 0.9981, respectively, using 2-fold, 5-fold and 10-fold Cross-Validation (CV) as the benchmark. The experimental results confirm the effectiveness of the NGCICM algorithm in predicting the interactions between circRNAs and miRNAs.

Targeting pre-mRNA splicing in cancers: roles, inhibitors, and therapeutic opportunities

Accumulating evidence has indicated that pre-mRNA splicing plays critical roles in a variety of physiological processes, including development of multiple diseases. In particular, alternative splicing is profoundly involved in cancer progression through abnormal expression or mutation of splicing factors. Small-molecule splicing modulators have recently attracted considerable attention as a novel class of cancer therapeutics, and several splicing modulators are currently being developed for the treatment of patients with various cancers and are in the clinical trial stage. Novel molecular mechanisms modulating alternative splicing have proven to be effective for treating cancer cells resistant to conventional anticancer drugs. Furthermore, molecular mechanism-based combination strategies and patient stratification strategies for cancer treatment targeting pre-mRNA splicing must be considered for cancer therapy in the future. This review summarizes recent progress in the relationship between druggable splicing-related molecules and cancer, highlights small-molecule splicing modulators, and discusses future perspectives of splicing modulation for personalized and combination therapies in cancer treatment.

The pharmacological and biological importance of EZH2 signaling in lung cancer

Up to 18% of cancer-related deaths worldwide are attributed to lung tumor and global burden of this type of cancer is ascending. Different factors are responsible for development of lung cancer such as smoking, environmental factors and genetic mutations. EZH2 is a vital protein with catalytic activity and belongs to PCR2 family. EZH2 has been implicated in regulating gene expression by binding to promoter of targets. The importance of EZH2 in lung cancer is discussed in current manuscript. Activation of EZH2 significantly elevates the proliferation rate of lung cancer. Furthermore, metastasis and associated molecular mechanisms including EMT undergo activation by EZH2 in enhancing the lung cancer progression. The response of lung cancer to therapy can be significantly diminished due to EZH2 upregulation. Since EZH2 increases tumor progression, anti-cancer agents suppressing its expression reduce malignancy. In spite of significant effort in understanding modulatory function of EZH2 on other pathways, it appears that EZH2 can be also regulated and controlled by other factors that are described in current review. Therefore, translating current findings to clinic can improve treatment and management of lung cancer patients.

Hsa_circ_0079480 enhances cell proliferation, migration, and invasion in colorectal cancer through miR-498/ATP5E axis

Circular RNAs play critical roles in tumorigenesis. hsa_circ_0079480 was reported to be upregulated in colorectal cancer (CRC). However, its specific molecule in CRC is poorly understood. Hsa_circ_0079480, miR-498, and ATP5E expressions in CRC tissues and CRC cells were determined using quantitative real-time polymerase chain reaction assay. ATP5E protein level was assessed using Western blot. Cell proliferation, migration, and invasion were examined by 3-(4, 5-Dimethylthiazolyl2)-2, 5-diphenyltetrazolium bromide assay and Transwell assays, respectively. Dual-luciferase reporter gene assay was performed to analyze the interactions between hsa_circ_0079480, miR-498, and ATP5E. This study results showed that hsa_circ_0079480 and ATP5E expressions were significantly increased in CRC tissues and CRC cells, while miR-498 was downregulated. Hsa_circ_0079480 knockdown dramatically suppressed CRC cell proliferation, migration, and invasion. Meanwhile, it turned out that hsa_circ_0079480 knockdown inhibited CRC tumor growth in vivo. Hsa_circ_0079480 could negatively regulate miR-498 expression by directly targeting miR-498. MiR-498 overexpression dramatically inhibited CRC cell malignant behaviors. miR-498 negatively regulated ATP5E expression by directly binding to ATP5E. ATP5E knockdown suppressed CRC cell malignant behaviors. ATP5E overexpression mitigated the inhibitory effect of hsa_circ_0079480 on CRC cell malignant behaviors. Since hsa_circ_0079480 knockdown inhibited CRC cells malignant behaviors through regulation of the miR-498/ATP5E axis, it can be concluded that hsa_circ_0079480 might have great potential as therapeutic target for CRC.

Behind the scenes: How RNA orchestrates the epigenetic regulation of gene expression

Non-coding DNA accounts for approximately 98.5% of the human genome. Once labeled as "junk DNA", this portion of the genome has undergone a progressive re-evaluation and it is now clear that some of its transcriptional products, belonging to the non-coding RNAs (ncRNAs), are key players in cell regulatory networks. A growing body of evidence demonstrates the crucial impact of regulatory ncRNAs on mammalian gene expression. Here, we focus on the defined relationship between chromatin-interacting RNAs, particularly long non-coding RNA (lncRNA), enhancer RNA (eRNA), non-coding natural antisense transcript (ncNAT), and circular RNA (circRNA) and epigenome, a common ground where both protein and RNA species converge to regulate cellular functions. Through several examples, this review provides an overview of the variety of targets, interactors, and mechanisms involved in the RNA-mediated modulation of loci-specific epigenetic states, a fundamental evolutive strategy to orchestrate mammalian gene expression in a timely and reversible manner. We will discuss how RNA-mediated epigenetic regulation impacts development and tissue homeostasis and how its alteration contributes to the onset and progression of many different human diseases, particularly cancer.

Exosomal circular RNA: a signature for lung cancer progression

Membrane vesicles having a diameter of 30-150 nm are known as exosomes. Several cancer types secrete exosomes, which may contain proteins, circular RNAs (circRNAs), microRNAs, or DNA. CircRNAs are endogenous RNAs that do not code for proteins and can create continuous and covalently closed loops. In cancer pathogenesis, especially metastasis, exosomal circRNAs (exo-circRNAs) have a crucial role mainly due to the frequently aberrant expression levels within tumors. However, neither the activities nor the regulatory mechanisms of exo-circRNAs in advancing lung cancer (LC) are obvious. A better understanding of the regulation and network connections of exo-circRNAs will lead to better treatment for LCs. The main objective of the current review is to highlight the functions and mechanisms of exo-circRNAs in LC and assess the relationships between exo-circRNA dysregulation and LC progression. In addition, underline the possible therapeutic targets based on exo-circRNA modulating.

circPTN Promotes the Progression of Non-Small Cell Lung Cancer through Upregulation of E2F2 by Sponging miR-432-5p

Background

Non-small cell lung cancer (NSCLC) is one of the most prevalent cancers, accounting for around 80% of total lung cancer cases worldwide. Exploring the function and mechanism of circRNAs could provide insights into the diagnosis and treatment for NSCLC.

Methods

In this study, we collected tumor tissues and adjacent normal tissues from NSCLC patients to detect the expression level of circPTN and analyzed the association of its expression level with the clinicopathological parameter of NSCLC patients. Moreover, the functional engagement of circPTN in NSCLC cells was examined by cell counting kit-8 (CCK-8) cell proliferation assay, transwell migration and invasion assays, and tube formation assay. Quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting (WB) analysis were used to detect gene and protein expression, respectively. The molecular targets of cicrPTN were predicted using starBase online resources, which was validated by RNA immunoprecipitation (RIP) and dual-luciferase reporter assay.

Results

Compared with adjacent normal tissues, there was a remarkable increase of the circPTN levels in NSCLC tissues. A high level of circPTN expression was associated with more lymph node metastasis (LNM) and advanced TNM stages. Functionally, circPTN knockdown inhibited the proliferation, migration, and invasion and tube formation ability of NSCLC cells. We further demonstrated that circPTN regulated the malignant phenotype of NSCLC cells through targeting the miR-432-5p/E2F2 axis.

Conclusion

Together, our results suggest that circPTN, which is upregulated in NSCLC tissues, could serve as a prognostic marker for NSCLC patients. circPTN regulates the malignant progression of NSCLC cells through targeting the miR-432-5p/E2F2 axis, which may be employed as a potential strategy for the management of NSCLC.

Competing Endogenous RNA (ceRNA) Networks and Splicing Switches in Cervical Cancer: HPV Oncogenesis, Clinical Significance and Therapeutic Opportunities

Cervical cancer (CC) is the primary cause of female cancer fatalities in low-middle-income countries (LMICs). Persistent infections from the human papillomavirus (HPV) can result in cervical cancer. However, numerous different factors influence the development and progression of cervical cancer. Transcriptomic knowledge of the mechanisms with which HPV causes cervical cancer pathogenesis is growing. Nonetheless, there is an existing gap hindering the development of therapeutic approaches and the improvement of patient outcomes. Alternative splicing allows for the production of numerous RNA transcripts and protein isoforms from a single gene, increasing the transcriptome and protein diversity in eukaryotes. Cancer cells exhibit astounding transcriptome modifications by expressing cancer-specific splicing isoforms. High-risk HPV uses cellular alternative splicing events to produce viral and host splice variants and proteins that drive cancer progression or contribute to distinct cancer hallmarks. Understanding how viruses utilize alternative splicing to drive pathogenesis and tumorigenesis is essential. Although research into the role of miRNAs in tumorigenesis is advancing, the function of other non-coding RNAs, including lncRNA and circRNA, has been understudied. Through their interaction with mRNA, non-coding RNAs form a network of competing endogenous RNAs (ceRNAs), which regulate gene expression and promote cervical cancer development and advancement. The dysregulated expression of non-coding RNAs is an understudied and tangled process that promotes cervical cancer development. This review will present the role of aberrant alternative splicing and immunosuppression events in HPV-mediated cervical tumorigenesis, and ceRNA network regulation in cervical cancer pathogenesis will also be discussed. Furthermore, the therapeutic potential of splicing disruptor drugs in cervical cancer will be deliberated.

Immunomodulatory functions of the circ_001678/miRNA-326/ZEB1 axis in non-small cell lung cancer via the regulation of PD-1/PD-L1 pathway

High-throughput circRNA sequencing identified circRNA_001678 (circ_001678) as an upregulated circRNA in NSCLC tissues. Hence, the current study sought to investigate the function and the underlying mechanism of circRNA_001678 in immune escape of NSCLC. Briefly, commercially purchased NSCLC cell lines were adopted for in vitro experiment to evaluate the effects of circ_001678 over-expression or knockdown on cell biological functions, including proliferation, migration, and invasive abilities. In addition, the effects of circ_001678 on the in vivo tumorigenicity ability were evaluated for verification. Accordingly, we uncovered that circ_001678 over-expression augmented NSCLC progression in vitro and enhanced tumorigenicity ability in vivo. The interaction between circ_001678 and miR-326 predicted online was verified by means of luciferase and RNA pull-down assays. Furthermore, circ_001678 could sponge miR-326 to up-regulate ZEB1. On the other hand, the tumor-promoting effects of circ_001678 could be inhibited by anti-PD-L1/PD-1 treatment. Mechanistically, circ_001678 led to the activation of the PD-1/PD-L1 pathway to promote CD8+ T cell apoptosis, thereby inducing NSCLC cell immune escape via regulation of the miR-326/ZEB1 axis. To conclude, our findings revealed that circ_001678 sponges miR-326 to up-regulate ZEB1 expression and induce the PD-1/PD-L1 pathway-dependent immune escape, thereby promoting the malignant progression of NSCLC.

Role of circular RNAs in the diagnosis, regulation of drug resistance and prognosis of lung cancer (Review)

Lung cancer is one of the most common malignant tumors in China and is the highest cause of mortality among male and female patients, both in urban and rural areas. A subset of patients with lung cancer only display chest tightness without any other obvious symptoms. This is because most symptoms do not manifest during the early stages of disease development. Consequently, most patients with lung cancer are diagnosed when the disease is in the advanced stages, when they are already unfit for surgical treatment. Furthermore, the prognosis of patients with lung cancer is poor. The 5-year survival rate of patients with stage IA lung cancer is 85%, compared with 6% in those with stage IV. This requires the development of strategies for early diagnosis, treatment and prognosis to improve the management of lung cancer. Circular RNAs (circRNAs) belong to a class of closed circular non-coding RNAs formed by reverse splicing of a precursor mRNA. These RNAs are highly stable, ubiquitously expressed, conserved, and show high specificity. CircRNAs regulate biological processes, such as the proliferation, differentiation and invasion of lung cancer cells. Therefore, they can be used as biomarkers for the early diagnosis and prognosis prediction of lung cancer, as well as novel targets for therapy design. In the present review, the biological characteristics and functions of circRNAs, as well as their application in the diagnosis, control of drug resistance and effect on the prognosis of patients with lung cancer, will be discussed.

Noncoding RNAs in Thyroid-Follicular-Cell-Derived Carcinomas

Simple Summary

Thyroid tumors represent the most common neoplastic pathology of the endocrine system. Mutations occurring in oncogenes and tumor suppressor genes are responsible for thyroid carcinogenesis; however, the complete mutational landscape characterizing these neoplasias has not been completely unveiled. It has been established that only the 2% of the human genome codes for proteins, suggesting that the vast majority of the genome has regulatory capabilities, which, if altered, could account for the onset of cancer. Hence, many scientific efforts are currently focused on the characterization of the heterogeneous class of noncoding RNAs, which represent an abundant part of the transcribed noncoding genome. In this review, we mainly focus on the involvement of microRNAs, long noncoding RNAs, and pseudogenes in thyroid cancer. The determination of the diagnosis, prognosis, and treatment of thyroid cancers based on the evaluation of the noncoding RNA network could allow the implementation of a more personalized approach to fighting these pathologies.

Abstract

Among the thyroid neoplasias originating from follicular cells, we can include well-differentiated carcinomas, papillary (PTC) and follicular (FTC) thyroid carcinomas, and the undifferentiated anaplastic (ATC) carcinomas. Several mutations in oncogenes and tumor suppressor genes have already been observed in these malignancies; however, we are still far from the comprehension of their full regulation-altered landscape. Even if only 2% of the human genome has the ability to code for proteins, most of the noncoding genome is transcribed, constituting the heterogeneous class of noncoding RNAs (ncRNAs), whose alterations are associated with the development of several human diseases, including cancer. Hence, many scientific efforts are currently focused on the elucidation of their biological role. In this review, we analyze the scientific literature regarding the involvement of microRNAs (miRNAs), long noncoding RNAs (lncRNAs), and pseudogenes in FTC, PTC, and ATC. Recent findings emphasized the role of lncRNAs in all steps of cancer progression. In particular, lncRNAs may control progression steps by regulating the expression of genes and miRNAs involved in cell proliferation, apoptosis, epithelial–mesenchymal transition, and metastatization. In conclusion, the determination of the diagnosis, prognosis, and treatment of cancer based on the evaluation of the ncRNA network could allow the implementation of a more personalized approach to fighting thyroid tumors.

CircRNA hsa_circ_0070659 predicts poor prognosis and promotes non-small cell lung cancer (NSCLC) progression via microRNA-377 (miR-377) / Ras-Associated Binding Protein 3C (RAB3C) pathway

A large number of circular RNAs (circRNAs) are dysregulated in lung cancer and affect the progression and prognosis of lung disease. Herein, this study selected specific circular RNA (circ_0070659) by bioinformatics analysis and aimed to investigate the role of circ_0070659 in non-small cell lung cancer (NSCLC). The differentially expressed circRNA (hsa_circ_0070659) in NSCLC was screened from public databases (GEO), and real-time quantitative polymerase chain reaction (RT-qPCR) was carried out to identify the circ_0070659 levels in cancer tissues and cells. NSCLC cell proliferation, migration, and invasion abilities after circ_0070659 silencing was detected by colony formation assay, Cell Counting Kit-8 (CCK-8) assay and Transwell assay. Targeted binding between microRNA-377 (miR-377) and circ_0070659 or Ras-Associated Binding Protein 3C (RAB3C) was verified by western blot, dual-luciferase reporter assay, and RNA pull-down assay. Our experimental results showed that circ_0070659 levels were largely increased in tumor tissues and cells. Biologically, knockdown of circ_0070659 obviously inhibited proliferation, migration, and invasion of NSCLC cells. Mechanistically, circ_0070659 promoted RAB3C-mediated proliferation and invasion through sponging miR-377. Furthermore, miR-377 inhibitor reversed the inhibitory ability of circ_0070659 silencing on malignant biological behavior of NSCLC cells. Our study revealed a novel signaling pathway that circ_0070659/miR-377/RAB3C axis regulates tumor progression, and it may become a new therapeutic target for NSCLC.

Circular RNA_0120376 regulates microRNA-148b-3 and centrosomal protein 55 to promote non-small cell lung cancer development

Circular RNAs (circRNAs) are non-coding RNAs with covalent closed-loop structures that are vital in regulating diverse pathological processes. This work is aimed to investigate the role of circ_0120376 in non-small cell lung cancer (NSCLC). Circ_0120376, microRNA (miR)-148b-3p, and centrosomal protein 55 (CEP55) mRNA expression in NSCLC tissues and cells were determined using qRT-PCR. The influences of circ_0120376 and miR-148b-3p on the proliferation of NSCLC cell lines were analyzed by CCK-8 and colony formation assays. Apoptosis was analyzed by flow cytometry. Cell migration and invasion were analyzed using the Transwell experiment. Binding relationships between circ_0120376 and miR-148b-3p and between miR-148b-3p and CEP55 3'UTR were investigated using the dual-luciferase reporter experiment and the RIP experiment. Western blot was conducted to analyze the regulatory effect of circ_0120376 and miR-148b-3p on CEP55 expression. We found that circ_0120376 was markedly overexpressed in NSCLC, and its overexpression was positively associated with increased T stage and lymph node metastasis of the patients. Functional experiments unveiled that circ_0120376 enhanced the proliferation, migration and invasion of NSCLC cells and impeded apoptosis, while knocking down circ_0120376 remarkably suppressed the malignant features of NSCLC cells mentioned above. Circ_0120376 could adsorb miR-148b-3p to reduce miR-148b-3p expression, and circ_0120376 could increase CEP55 expression via adsorbing miR-148b-3p. In summary, circ_0120376 contributes to the malignancy of NSCLC cells through a ceRNA mechanism via regulating miR-148b-3p/CEP55 axis. Circ_0120376 is likely to be a potential diagnostic biomarker and therapeutic target for NSCLC.

Circ_0016760 Serves as a Cancer Promoter in Non-small Cell Lung Cancer Through miR-876-3p/NOVA2 Axis

Non-small cell lung cancer (NSCLC) is a serious threaten to human health globally. Circular RNAs (circRNAs) were testified to alter the progression of NSCLC. This work intended to investigate the functional role of circ_0016760 in NSCLC development and the potential mechanism. Expression of circ_0016760, microRNA (miR)-876-3p and NOVA alternative splicing regulator 2 (NOVA2) was determined via quantitative reverse transcription-PCT (qRT-PCR) or western blotting. Cell viability, clonogenicity and apoptosis were assessed by Cell Counting Kit-8 (CCK-8) assay, colony formation assay and flow cytometry, respectively. Transwell assay was performed to examine cell migration and invasion. Western blotting was also conducted to detect the levels of epithelial-to-mesenchymal transition (EMT)-related proteins. Role of circ_0016760 in vivo was evaluated via xenograft model assay. Moreover, the interaction between miR-876-3p and circ_0016760 or NOVA2 was verified by dual-luciferase reporter assay or RNA Immunoprecipitation (RIP) assay. Circ_0016760 and NOVA2 were upregulated, while miR-876-3p expression was decreased in NSCLC tissues and cells. Circ_0016760 depletion suppressed NSCLC cell proliferation and metastasis in vitro, as well as hampered tumor growth in vivo. Circ_0016760 acted as a sponge of miR-876-3p, and miR-876-3p could target NOVA2. Circ_0016760 might play vital roles in NSCLC by regulating miR-876-3p/NOVA2 axis. Circ_0016760 could promote the malignant development of NSCLC through miR-876-3p/NOVA2 axis, at least in part.

The long and short non-coding RNAs modulating EZH2 signaling in cancer

Non-coding RNAs (ncRNAs) are a large family of RNA molecules with no capability in encoding proteins. However, they participate in developmental and biological processes and their abnormal expression affects cancer progression. These RNA molecules can function as upstream mediators of different signaling pathways and enhancer of zeste homolog 2 (EZH2) is among them. Briefly, EZH2 belongs to PRCs family and can exert functional roles in cells due to its methyltransferase activity. EZH2 affects gene expression via inducing H3K27me3. In the present review, our aim is to provide a mechanistic discussion of ncRNAs role in regulating EZH2 expression in different cancers. MiRNAs can dually induce/inhibit EZH2 in cancer cells to affect downstream targets such as Wnt, STAT3 and EMT. Furthermore, miRNAs can regulate therapy response of cancer cells via affecting EZH2 signaling. It is noteworthy that EZH2 can reduce miRNA expression by binding to promoter and exerting its methyltransferase activity. Small-interfering RNA (siRNA) and short-hairpin RNA (shRNA) are synthetic, short ncRNAs capable of reducing EZH2 expression and suppressing cancer progression. LncRNAs mainly regulate EZH2 expression via targeting miRNAs. Furthermore, lncRNAs induce EZH2 by modulating miRNA expression. Circular RNAs (CircRNAs), like lncRNAs, affect EZH2 expression via targeting miRNAs. These areas are discussed in the present review with a focus on molecular pathways leading to clinical translation.

Circ_0000658 knockdown inhibits epithelial-mesenchymal transition in bladder cancer via miR-498-induced HMGA2 downregulation

BACKGROUND

Epithelial-mesenchymal transition (EMT) has been associated with the angiogenesis and oncogenic phenotypes of multiple malignant tumors including bladder cancer (BCa). Circular RNAs (circRNAs) are recognized as crucial regulators in the EMT. This study aims to illustrate the possible role of circular RNA_0000658 (circ_0000658) in BCa and the underlying molecular mechanism.

METHODS

The expression of circ_0000658, microRNA (miR)-498, and high mobility group AT-hook 2 (HMGA2) was assessed in cancer and adjacent normal tissue collected from BCa patients and human BCa cell lines (MGH-U3, T24, 5637 and SW780). BCa cells were transduced with a series of overexpression or shRNA plasmids to clarify the function of circ_0000658 and miR-498 on the oncogenic phenotypes and EMT of BCa cells. Further, we established nude mice xenografted with BCa cells to validate the roles of circ_0000658 on tumor growth in vivo.

RESULTS

Circ_0000658 was highly expressed in BCa tissue samples and cell lines, which indicated a poor prognosis of BCa patients. Circ_0000658 competitively bound to miR-498 and thus restricted miR-498 expression. Meanwhile, circ_0000658 weakened the binding of miR-498 to the target gene HMGA2 and upregulated the HMGA2 expression. Circ_0000658 elevation or miR-498 knockdown augmented oncogenic phenotypes and EMT of BCa cells, corresponding to a reduction in the expression of β-catenin and E-cadherin as well as an increase in the expression of N-cadherin, Slug, Snail, ZEB1 and Twist. Inhibition of HMGA2 reversed the effects of circ_0000658 overexpression on tumor growth in vivo.

CONCLUSION

Altogether, our study uncovered the tumor-promoting role of circ_0000658 in BCa via the miR-498/HMGA2 axis.

A novel identified circ-ANKHD1 targets the miR-27a-3p/SFRP1 signaling pathway and modulates the apoptosis of granulosa cells

The specific expression profile and function of circular RNAs (circRNAs) in mammalian ovarian follicles, especially during the atresia process, are unclear. In this study, we verified and explored the expression and function of circ-ANKHD1 in granulosa cells. Our results showed that abundance of circ-ANKHD1 was significantly lower in the granulosa cells than that of ANKHD1. The expression of ANKHD1 was highest in the granulosa cells from follicles with a diameter of 5-6 mm and lowest in that with a diameter of 3-4 mm. Furthermore, the expression level of circ-ANKHD1 in the ovarian tissue of 1-day-old piglets was significantly higher than that of 17-month-old multiparous sows. The luciferase reporter assay showed the potential interaction between circ-ANKHD1 and miR-27a-3p/miR-142-5p. Furthermore, circ-ANKHD1 overexpression up-regulated SFRP1 expression, while miR-27a-3p overexpression suppressed SFRP1 expression in granulosa cells. Circ-ANKHD1 overexpression significantly decreased the cell apoptotic rates of the granulosa cells and repressed the cell population at G0/G1 and S phases but increased cell population at G2/M phase. Finally, circ-ANKHD1 overexpression increased the mRNA expression levels of Bcl-2 and cyclin D1 in the granulosa cells, while there are no effects on the mRNA expression levels of caspase-3, p53, Bax, and proliferating cell nuclear antigen. In conclusion, our study for the first time identified a novel circRNA, circ-ANKHD1 that may be associated with the biological functions of granulosa cells. Circ-ANKHD1 may promote the granulosa cell proliferation, but attenuate apoptosis, and these effects may be associated with modulation of miR-27a-3p/SFRP1.

Circ_0016760 accelerates non-small-cell lung cancer progression through miR-646/AKT3 signaling in vivo and in vitro

BACKGROUND

Currently, the prognosis of non-small-cell lung cancer (NSCLC) patients remains dismal due to recurrence and metastasis. The purpose of our study was to explore the role of circular RNA_0016760 (circ_0016760) in NSCLC progression and its associated mechanism.

METHODS

Quantitative real-time polymerase chain reaction (qRT-PCR) was implemented to measure the expression of circ_0016760, microRNA-646 (miR-646) and AK strain thymoma serine/threonine kinase 3 (AKT3). The protein level of AKT3 was examined by Western blot assay. Cell Counting Kit 8 assay, transwell assays, and flow cytometry were conducted to analyze cell proliferation, metastasis, and apoptosis. Dual-luciferase reporter assay was used to confirm the interactions that were predicted by bioinformatics software (Circular RNA Interactome and TargetScan). A xenograft tumor model was built to investigate the role of circ_0016760 in vivo.

RESULTS

Circ_0016760 and AKT3 were highly expressed in NSCLC tissue specimens and cell lines. Circ_0016760 interference suppressed cell proliferation, migration, and invasion and promoted the apoptosis of NSCLC cells. Circ_0016760 interacted with miR-646 and negatively regulated its expression. MiR-646 silencing partly counteracted circ_0016760 knockdown-mediated influences in NSCLC cells. MiR-646 bound to the AKT3 3' untranslated region in NSCLC cells, and miR-646 overexpression-induced effects in NSCLC cells were partly overturned by the addition of AKT3 overexpression plasmid. Circ_0016760 silencing reduced the expression of AKT3 through enhancing miR-646 expression. Circ_0016760 knockdown suppressed NSCLC tumor growth in vivo.

CONCLUSION

Circ_0016760 played an oncogenic role to promote the proliferation, migration, and invasion and restrained the apoptosis of NSCLC cells via miR-646/AKT3 signaling.

Regulatory roles of phytochemicals on circular RNAs in cancer and other chronic diseases

As novel non-coding RNAs (ncRNAs), circular RNAs (circRNAs) play an essential role in the pathogenesis of many chronic diseases, and the regulation of these functional molecules has become a research hotspot gradually. Within the past decade, phytochemicals were reported to regulate the expression of long non-coding RNAs (lncRNAs) and microRNAs (miRNAs) in various chronic diseases, and more recently, most studies focus on the regulatory roles of phytochemicals on circRNAs. Abnormal expression of circRNAs has been identified in chronic diseases like cancer, heart failure, depression and atherosclerosis, and numerous studies have revealed the modulation of circRNAs by phytochemicals including berberine, celastrol, cinnamaldehyde, curcumin, et al. The expression of circRNAs, such as circSATB2 and circFOXM1, were modulated by phytochemicals, and these regulations further affected cell proliferation, apoptosis, migration, invasion, autophagy, chemosensitivity, radiosensitivity and other biological processes. Mechanismly, the circRNAs mainly functioned as miRNA sponge, subsequently affecting miRNA-mediated regulation of target genes and related cell signaling pathways. In this review, we summarized the impact of phytochemicals on circRNAs expression and biological function, and discussed the mechanisms underlying phytochemicals regulating circRNAs in cancer and other chronic diseases.

Targeting protein arginine methyltransferase 5 in cancers: Roles, inhibitors and mechanisms

The protein arginine methyltransferase 5 (PRMT5) as the major type II arginine methyltransferase catalyzes the mono- and symmetric dimethylation of arginine residues in both histone and non-histone proteins. Recently, increasing evidence has demonstrated that PRMT5 plays an indispensable role in the occurrence and development of various human cancers by promoting the cell proliferation, invasion, and migration. It has become a promising and valuable target in the cancer epigenetic therapy. This review is to summarize the clinical significance of PRMT5 in the cancers such as lung cancer, breast cancer and colorectal cancer, and the drug discovery targeting PRMT5. Importantly, the existing PRMT5 inhibitors representing different molecular mechanisms, and their pharmacological effect, mechanism of action and biological affinity are analyzed. Clinical status, current problems and future perspective of PRMT5 inhibitors for the treatment of cancers are also discussed, all of which provides crucial help for the future discovery of PRMT5 targeted drugs for cancer treatment.

Knockdown of MIR9‑3HG inhibits proliferation and promotes apoptosis of cervical cancer cells by miR‑498 via EP300

Cervical cancer is a serious gynecological cancer and one of the primary causes of mortality in female patients with cancer. Despite advances in cancer research, the molecular mechanism underlying cancer remains poorly understood. High levels of MIR9-3 host gene (HG) are associated with the occurrence and development of cervical cancer. However, the specific role of MIR9-3HG during the development of cervical cancer is unclear. In the present study, the expression of MIR9-3HG was silenced in C33A and SiHa cervical cancer cell lines. Proliferation and apoptosis were measured in these cells using 5-ethynyl-2′-deoxyuridine assay and flow cytometry, respectively. In addition, targeting microRNAs (miRs) of MIR9-3HG and mRNAs of miR-498 were predicted using public databases. The predicted interactions between these molecules were validated using RNA immunoprecipitation, RNA pull-down and luciferase reporter assays. Lastly, C33A cells transfected with short hairpin MIR-3HG alone or in combination with miR-498 inhibitor or PC-EP300 were subcutaneously injected into mice. The levels of miR-498, EP300 and Ki67 in tumor tissue were measured via reverse transcription-quantitative PCR or western blotting. MIR9-3HG knockdown inhibited the proliferation of cervical cancer cells, whilst promoting apoptosis. MIR9-3HG sponged miR-498 and inhibited its expression. Additionally, miR-498 interacted with EP300 and inhibited its expression. Transfection with miR-498 inhibitor significantly decreased apoptosis levels; this effect was abolished following EP300 silencing in vitro. In vivo, both miR-498 inhibition and EP300 overexpression reversed the inhibition of tumor growth mediated by MIR-3HG knockdown. MIR9-3HG promoted the proliferation cervical cancer cells via EP300 and miR-498. These in vitro and in vivo findings demonstrate the regulatory role of the MIR9-3HG/miR-498/EP300 axis in cervical cancer cell growth. Thus, the present study identified novel molecular targets for the diagnosis and treatment of cervical cancer and provided new insight into the pathogenesis of cervical cancer.

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.

Circular RNAs in Lung Cancer: Recent Advances and Future Perspectives

Globally, lung cancer is the most commonly diagnosed cancer and carries with it the greatest mortality rate, with 5-year survival rates varying from 4–17% depending on stage and geographical differences. For decades, researchers have studied disease mechanisms, occurrence rates and disease development, however, the mechanisms underlying disease progression are not yet fully elucidated, thus an increased understanding of disease pathogenesis is key to developing new strategies towards specific disease diagnoses and targeted treatments. Circular RNAs (circRNAs) are a class of non-coding RNA widely expressed in eukaryotic cells, and participate in various biological processes implicated in human disease. Recent studies have indicated that circRNAs both positively and negatively regulate lung cancer cell proliferation, migration, invasion and apoptosis. Additionally, circRNAs could be promising biomarkers and targets for lung cancer therapies. This review systematically highlights recent advances in circRNA regulatory roles in lung cancer, and sheds light on their use as potential biomarkers and treatment targets for this disease.

Circ-PRMT5 enhances the proliferation, migration and glycolysis of hepatoma cells by targeting miR-188-5p/HK2 axis

INTRODUCTION AND OBJECTIVES

Circular RNA (circRNA) has been demonstrated as a critical regulator in human cancer, including hepatocellular carcinoma (HCC). Nevertheless, the role of circ-PRMT5 in HCC remains largely unknown.

PATIENTS OR MATERIALS AND METHODS

The real-time quantitative polymerase chain reaction (RT-qPCR) was performed to assess the expression levels of circ-PRMT5, miR-188-5p and anti-Hexokinase II (HK2) in HCC tissues and cells. The cell proliferation, migration and glycolysis were determined by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl-2H-tetrazol-3-ium bromide (MTT), transwell migration assay, and indicated kits, respectively. The interaction relationship between miR-188-5p and circ-PRMT5 or HK2 was analyzed by the bioinformatics database, dual-luciferase reporter assay, and RNA immunoprecipitation (RIP) assay. The western blot assay was used to analyze the expression level of HK2. The functional role of circ-PRMT5 in vivo was assessed by a xenograft experiment.

RESULTS

Circ-PRMT5 was elevated in HCC tissues and cells than matched control groups. Furthermore, loss-of-functional experiments revealed that the silencing of circ-PRMT5 could repress proliferation, migration, glycolysis in vitro and tumor growth in vivo. Moreover, we also confirmed that overexpression of circ-PRMT5 abolished the effects on HCC cells induced by upregulating miR-188-5p. In addition, overexpression of miR-188-5p could repress the development of HCC. More importantly, HK2 was a target gene of miR-188-5p, and miR-188-5p regulated proliferation, migration, glycolysis of HCC cells by specifically binding to HK2. Mechanistically, circ-PRMT5 could act as a sponge of miR-188-5p to regulate the expression of HK2.

CONCLUSION

In summary, circ-PRMT5 might play a key role in proliferation, migration, glycolysis of HCC cells via miR-188-5p/HK2 axis, which indicated that circ-PRMT5 might be a potential therapeutic target for HCC treatment.

Clinicopathological and prognostic significance of circRNAs in lung cancer: A systematic review and meta-analysis

BACKGROUND

Circular RNAs (circRNAs) regulate multiple pathways during lung cancer pathogenesis. Apart from functional significance, many circRNAs have been shown to be associated with clinicopathological characteristics and predict lung cancer prognosis. Our aim is to summarize the expanding knowledge of clinical roles of circRNAs in lung cancer.

METHODS

A thorough search of literature was conducted to identify articles about the correlation between circRNA expression and its prognostic and clinicopathological values. Biological mechanisms were summarized.

RESULTS

This study included 35 original articles and 32 circRNAs with prognostic roles for lung cancer. Increased expression of 25 circRNAs and decreased expression of 7 circRNAs predicted poor prognosis. For non-small cell lung cancer, changes of circRNAs were correlated with tumor size, lymph node metastasis, distant metastasis, tumor node metastasis (TNM) stage, and differentiation, indicating the major function of circRNAs is to promote lung cancer invasion and migration. Particularly, meta-analysis of ciRS-7, hsa_circ_0020123, hsa_circ_0067934 showed increase of the 3 circRNAs was associated with positive lymph node metastasis. Increase of ciRS-7 and hsa_circ_0067934 was also related with advanced TNM stage. The biological effects depend on the general function of circRNA as microRNA sponge.

CONCLUSIONS

CircRNAs have the potential to function as prognostic markers and are associated with lung cancer progression and metastasis.

Insights Into circRNAs: Functional Roles in Lung Cancer Management and the Potential Mechanisms

Lung cancer is the most prevalent cancer globally. It is also the leading cause of cancer-related death because of the late diagnosis and the frequent resistance to therapeutics. Therefore, it is impending to identify novel biomarkers and effective therapeutic targets to improve the clinical outcomes. Identified as a new class of RNAs, circular RNAs (circRNAs) derive from pre-mRNA back splicing with considerable stability and conservation. Accumulating research reveal that circRNAs can function as microRNA (miRNA) sponges, regulators of gene transcription and alternative splicing, as well as interact with RNA-binding proteins (RBPs), or even be translated into proteins directly. Currently, a large body of circRNAs have been demonstrated differentially expressed in physiological and pathological processes including cancer. In lung cancer, circRNAs play multiple roles in carcinogenesis, development, and response to different therapies, indicating their potential as diagnostic and prognostic biomarkers as well as novel therapeutics. In this review, we summarize the multi-faceted functions of circRNAs in lung cancer and the underlying mechanisms, together with the possible future of these discoveries in clinical application.

Insights Into the Role of CircRNAs: Biogenesis, Characterization, Functional, and Clinical Impact in Human Malignancies

Circular RNAs (circRNAs) are an evolutionarily conserved novel class of non-coding endogenous RNAs (ncRNAs) found in the eukaryotic transcriptome, originally believed to be aberrant RNA splicing by-products with decreased functionality. However, recent advances in high-throughput genomic technology have allowed circRNAs to be characterized in detail and revealed their role in controlling various biological and molecular processes, the most essential being gene regulation. Because of the structural stability, high expression, availability of microRNA (miRNA) binding sites and tissue-specific expression, circRNAs have become hot topic of research in RNA biology. Compared to the linear RNA, circRNAs are produced differentially by backsplicing exons or lariat introns from a pre-messenger RNA (mRNA) forming a covalently closed loop structure missing 3′ poly-(A) tail or 5′ cap, rendering them immune to exonuclease-mediated degradation. Emerging research has identified multifaceted roles of circRNAs as miRNA and RNA binding protein (RBP) sponges and transcription, translation, and splicing event regulators. CircRNAs have been involved in many human illnesses, including cancer and neurodegenerative disorders such as Alzheimer’s and Parkinson’s disease, due to their aberrant expression in different pathological conditions. The functional versatility exhibited by circRNAs enables them to serve as potential diagnostic or predictive biomarkers for various diseases. This review discusses the properties, characterization, profiling, and the diverse molecular mechanisms of circRNAs and their use as potential therapeutic targets in different human malignancies.

Development and validation of a novel circular RNA as an independent prognostic factor in acute myeloid leukemia

BACKGROUND

Although there are many clinical and molecular biomarkers in acute myeloid leukemia (AML), the novel and reliable biomarkers are still required to predict the overall survival at the time of disease diagnosis.

METHODS

In order to identify independent predictors, we firstly selected 60 cytogenetically normal AML (CN-AML) patients using the propensity score analysis to balance the confounders and performed circular RNA (circRNA) sequencing. Next, one outcome related to circRNA was selected and validated in the independent cohort of 218 CN-AML patients. We then constructed circRNA-miRNA-mRNA regulated network and performed cellular metabolomic analysis to decipher the underlying biological insights.

RESULTS

We identified 308 circRNAs as independent candidate predictors of overall survival. Hsa_circ_0075451 expression was validated as an independent predictor with a weak predictive ability for overall survival. The regulated network of this circular RNA indicated 84 hub genes that appear to be regulated by 10 miRNAs sponged by hsa_circ_0075451. The regulatory axis of hsa_circ_0075451 -| miR-330-5p/miR-326 -| PRDM16 was validated by the dual luciferase report assay, fluorescence in situ hybridization, and ShRNA interference assay.

CONCLUSIONS

Our data demonstrates that hsa_circ_0075451 expression may independently contribute to the poor prognosis of AML and present a novel therapeutic target.

Circ_0031242 Silencing Mitigates the Progression and Drug Resistance in DDP-Resistant Hepatoma Cells by the miR-924/POU3F2 Axis

Background

Circular RNAs (circRNAs) have been implicated in the progression and chemoresistance development of hepatocellular carcinoma (HCC). However, the precise parts of circ_0031242 in HCC chemoresistance are still not fully understood.

Methods

The levels of circ_0031242, miR-924 and POU class 3 homeobox 2 (POU3F2) were detected by quantitative real-time polymerase chain reaction (qRT-PCR) assay or Western blot analysis. IC₅₀ value for cisplatin (DDP) and cell viability were measured by the cell counting kit-8 (CCK-8) assay. Cell migration, invasion and apoptosis were assessed by transwell assay and flow cytometry, respectively. Targeted correlations among circ_0031242, miR-924 and POU3F2 were verified by the dual-luciferase reporter and RNA immunoprecipitation (RIP) assays.

Results

Our data revealed that circ_0031242 was associated with HCC resistance to DDP. The silencing of circ_0031242 diminished DDP resistance, suppressed cell viability, migration, invasion and promoted apoptosis of DDP-resistant HCC cells (Huh7-R and SNU-387-R) in vitro, as well as enhanced DDP sensitivity in vivo. Mechanistically, circ_0031242 directly interacted with miR-924 by binding to miR-924. Moreover, miR-924 was a downstream effector of circ_0031242 function. POU3F2 was a direct target of miR-924, and miR-924 overexpression regulated DDP-resistant HCC cell progression and DDP resistance by down-regulating POU3F2. Furthermore, circ_0031242 modulated POU3F2 expression through sponging miR-924.

Conclusion

Our findings identified that circ_0031242 functioned as an important regulator in DDP-resistant HCC cell progression and DDP resistance through the miR-924/POU3F2 axis, illuminating circ_0031242 as a potential therapeutic target for the chemoresistant HCC.

Circular RNAs in Human Cancer

Circular RNAs (circRNAs) are a class of endogenous single-stranded covalently closed RNAs, primarily produced from pre-mRNAs via non-canonical back-splicing. circRNAs are highly conserved, stable, and expressed in tissue- and development-specific pattern. circRNAs play essential roles in physiological process as well as cancer biology. By the advances of deep sequencing and bioinformatics, the number of circRNAs have increased explosively. circRNAs function as miRNA/protein sponge, protein scaffold, protein recruitment, enhancer of protein function, as well as templates for translation involved in the regulation of transcription/splicing, translation, protein degradation, and pri-miRNA processing in human cancers and contributed to the pathogenesis of cancer. Numerous circRNAs may function in diverse manners. In this review, we survey the current understanding of circRNA functions in human cancer including miRNA sponge, circRNA-protein interaction, and circRNA-encoded protein, and summarize available databases for circRNA annotation and functional prediction.

Circ-FOXM1 knockdown suppresses non-small cell lung cancer development by regulating the miR-149-5p/ATG5 axis

Circular RNAs (circRNAs) have been reported to be related to the development of human cancers. However, the function of circ-FOXM1 in non-small cell lung cancer (NSCLC) was largely unknown. Here, we revealed the role and functional mechanism of circ-FOXM1 in NSCLC progression. The relative expression of circ-FOXM1, microRNA-149-5p (miR-149-5p), and autophagy-related 5 (ATG5) was determined by quantitative real-time polymerase chain reaction (RT-qPCR). Cell Counting Kit-8 (CCK-8), flow cytometry, and transwell assay were employed to assess cell viability, apoptosis, and migration, respectively. The relative protein expression was detected by western blot. Furthermore, mouse xenograft was carried out to analyze the effect of circ-FOXM1 on tumor growth in vivo. In addition, the interaction between miR-149-5p and circ-FOXM1 or ATG5 was predicted by Starbase3.0 and confirmed by the dual-luciferase reporter assay and RNA pull-down assay. Circ-FOXM1 and ATG5 levels were upregulated, while the miR-149-5p level was downregulated in NSCLC tissues and cells. Circ-FOXM1 knockdown suppressed NSCLC cell viability, migration, and autophagy, and induced cell apoptosis. Interestingly, circ-FOXM1 targeted miR-149-5p to upregulate the ATG5 level. Moreover, circ-FOXM1 exerted function through repressing miR-149-5p expression, and miR-149-5p exerted function via inhibiting ATG5 expression. Our results suggested that circ-FOXM1 knockdown attenuated the development of NSCLC through modulating the miR-149-5p/ATG5 axis, providing a theoretical basis for the therapy of NSCLC.

Circular RNA circ_0068,888 protects against lipopolysaccharide-induced HK-2 cell injury via sponging microRNA-21-5p

Our previous findings revealed that hsa_circ_0068,888 was markedly down-regulated in the plasma of patients with sepsis-associated acute kidney injury (AKI). However, its molecular mechanism in AKI remains unclear. Herein, we explored the role of hsa_circ_0068,888 in AKI. Human renal proximal tubular cell line HK-2 was stimulated with lipopolysaccharide (LPS) to mimic AKI in vitro. Decreased hsa_circ_0068,888 expression was observed in AKI cell model. The overexpression of hsa_circ_0068,888 significantly increased the viability of LPS-stimulated HK-2 cells, whereas hsa_circ_0068,888 downregulation showed the opposite effect. Furthermore, LPS triggered inflammatory response and oxidative stress, which was inhibited by hsa_circ_0068,888 overexpression and enhanced by hsa_circ_0068,888 down-regulation. Hsa_circ_0068,888 overexpression suppressed the activation of nuclear factor-κB (NF-κB) pathway triggered by LPS as evidenced by decreased p-p65 protein level and nuclear translocation of p65 in hsa_circ_0068,888 overexpressed cells. Additionally, we proved that hsa_circ_0068,888 targeted microRNA-21-5p (miR-21-5p). The expression of miR-21-5p was markedly increased and was negatively regulated by hsa_circ_0068,888 in LPS-stimulated HK-2 cells. Furthermore, we demonstrated that miR-21-5p overexpression reversed the effects on cell viability, inflammatory response, oxidative stress, and NF-κB pathway induced by hsa_circ_0068,888 overexpression in LPS-stimulated HK-2 cells. Overall, these results implied that hsa_circ_0068,888 shows a protective effect on AKI by sponging miR-21-5p. Hence, up-regulation of hsa_circ_0068,888 might be a potential strategy in treatment for AKI.

Circ-PRMT5 promotes breast cancer by the miR-509-3p/TCF7L2 axis activating the PI3K/AKT pathway

BACKGROUND

Breast cancer is the most prevalent malignancy occurring in females. In recent years, emerging evidence has suggested that circular RNAs are involved in the development of multiple cancers. Circ-PRMT5 has recently attracted attention as a tumor-promoting circular RNA. In the present study, we focused on exploring the biological effects of circ-PRMT5 in breast cancer.

METHODS

A quantitative real-time polymerase chain reaction was used to determine the expression of circ-PRMT5 in breast cancer. In vitro experiments, including cell-counting kit-8, 5-ethynyl-2'-deoxyuridine, flow cytometry and tube formation assays, were performed to test the effects of circ-PRMT5 on the cellular progression of breast cancer. Bioinformatic analysis, luciferase reporter, radioimmunoprecipitation and RNA-pull down assays were performed to predict the potential microRNAs interacting with circ-PRMT5 and mRNAs that can be targeted by miR-509-3p.

RESULTS

Circ-PRMT5 is up-regulated in breast cancer tissues and cells. Importantly, an elevation of circ-PRMT5 indicates a poor prognosis in patients with breast cancer. Functionally, knockdown of circ-PRMT5 suppresses cell proliferation and angiogenesis and increases cell apoptosis in breast cancer. Mechanistically, we identified that circ-PRMT5 up-regulates TCF7L2 expression by acting as a miR-509-3p sponge. The negative expression correlation between miR-509-3p and circ-PRMT5 or TCF7L2 in clinical tissues was further demonstrated. Rescue assays showed that TCF7L2 overexpression reverses the antitumoral effects of circ-PRMT5 knockdown on breast cancer cell processes. Additionally, we demonstrated that circ-PRMT5 activates the phosphoinositide 3-kinase (PI3K)/AKT pathway by up-regulation of TCF7L2.

CONCLUSIONS

Overall, our data indicate that the circ-PRMT5/miR-509-3p/TCF7L2 axis can aggravate the malignant character of breast cancer cells by the regulation of the PI3K/AKT pathway.

CircRNAs as promising biomarker in diagnostic and prognostic of lung cancer: An updated meta-analysis

BACKGROUND

As a class of endogenous non-coding RNAs with closed-loop structure, circular RNAs (circRNAs) are receiving more and more attention. CircRNAs have been reported to be widely expressed in various human cancers and are implicated in tumorigenesis and progression. The present study aimed to systematically evaluate the clinicopathological, diagnostic and prognostic values of circRNAs in lung cancer.

METHODS

We searched literature from PubMed, Web of science, Cochrane Library, EMBASE and Ovid online databases up to May 29, 2020. Statistical analyses were undertaken based on Stata 11.0, Meta-DiSc 1.4, and RevMan 5.3 software.

RESULTS

Finally, a total of 63 eligible articles were included in our meta-analysis, including 18 studies for diagnosis, 22 studies for prognosis and 57 studies for clinicopathological features. In terms of diagnostic values, circRNAs could discriminate between lung cancer patients and the normal individuals with a relatively high pooled area under the curve (AUC) of 0.83 (95%CI, 0.80-0.86). For the prognostic values, we found that elevated expression of oncogenic circRNAs could predict poor survival outcomes based on multivariate analysis (HR = 2.430, 95%CI = 2.003-2.948, P < 0.001 for OS; HR = 2.228, 95%CI = 1.289-3.853, P = 0.004 for DFS) while tumor-suppressor circRNAs was correlated with better OS in univariate analysis (HR = 0.627, 95%CI = 0.519-0.757, P < 0.001). The pooled results suggested that elevated expression of carcinogenic circRNAs was associated with tumor size (OR = 1.676, 95%CI = 1.209-2.323, P = 0.002), smoking statue (OR = 1.260, 95%CI = 1.062-1.494, P = 0.008), TNM stage (OR = 2.345, 95%CI = 1.617-3.399, P < 0.001), differentiation grade (OR = 1.843, 95%CI = 1.228-2.765, P = 0.003), and lymphatic metastasis (OR = 2.097, 95%CI = 1.482-2.967, P < 0.001). Moreover, the expression of tumor-suppressor circRNAs was related to the improved clinicopathological features (lymphatic metastasis: OR = 0.536, 95%CI = 0.311-0.926, P = 0.025).

CONCLUSIONS

Our meta-analysis demonstrated that circRNAs could be used as feasible and important biomarkers for diagnosis, prognosis and clinicopathological features in lung cancer.

Hsa_circ_0046263 Drives the Carcinogenesis and Metastasis of Non-Small Cell Lung Cancer Through the Promotion of NOVA2 by Absorbing Mir-940 as a Molecular Sponge

Background

Circular RNAs (circRNAs) have increasingly been investigated in different cancers due to their regulatory roles. In this study, hsa_circ_0046263 will be detailedly researched in non-small cell lung cancer (NSCLC).

Methods

The analyses of hsa_circ_0046263, microRNA-940 (miR-940), and neuro-oncological ventral antigen 2 (NOVA2) levels were administrated by quantitative real-time polymerase chain reaction (qRT-PCR). The proliferation detection was conducted using Cell Counting Kit-8 (CCK-8) and colony formation assays. Cell cycle and apoptosis were evaluated by flow cytometry. Transwell assay for migration and invasion was used to determine cell metastatic capacity. Overall protein levels were examined adopting Western blot. Target binding analysis was completed via dual-luciferase reporter and RNA immunoprecipitation (RIP) assays. The effect of hsa_circ_0046263 on NSCLC in vivo was studied by xenograft model in mice.

Results

Hsa_circ_0046263 was overtly upregulated in NSCLC with important prognostic value. In vitro experiments indicated that hsa_circ_0046263 knockdown caused inhibitory effects on NSCLC cell proliferation, cell cycle, and metastasis but stimulative effect on apoptosis. Molecular mechanism analysis demonstrated that hsa_circ_0046263 served as a miR-940 sponge to act in the development of NSCLC. Moreover, miR-940 targeted NOVA2 and NOVA2 was regulated by hsa_circ_0046263/miR-940 axis. NOVA2 overexpression also neutralized the miR-940-mediated progression inhibition of NSCLC cells. In vivo assays suggested that hsa_circ_0046263 enhanced NSCLC tumorigenesis by targeting miR-940/NOVA2 axis.

Conclusion

Hsa_circ_0046263 was identified as a cancer-promoting factor in NSCLC via sponging miR-940 and upregulating NOVA2, which presented a clear mechanism of NSCLC occurrence and progression.

Pre-clinical investigation of STAT3 pathway in bladder cancer: Paving the way for clinical translation

Effective cancer therapy requires identification of signaling networks and investigating their potential role in proliferation and invasion of cancer cells. Among molecular pathways, signal transducer and activator of transcription 3 (STAT3) has been of importance due to its involvement in promoting proliferation, and invasion of cancer cells, and mediating chemoresistance. In the present review, our aim is to reveal role of STAT3 pathway in bladder cancer (BC), as one of the leading causes of death worldwide. In respect to its tumor-promoting role, STAT3 is able to enhance the growth of BC cells via inhibiting apoptosis and cell cycle arrest. STAT3 also contributes to metastasis of BC cells via upregulating of MMP-2 and MMP-9 as well as genes in the EMT pathway. BC cells obtain chemoresistance via STAT3 overexpression and its inhibition paves the way for increasing efficacy of chemotherapy. Different molecular pathways such as KMT1A, EZH2, DAB2IP and non-coding RNAs including microRNAs and long non-coding RNAs can function as upstream mediators of STAT3 that are discussed in this review article.

LINC00152 upregulates ZEB1 expression and enhances epithelial-mesenchymal transition and oxaliplatin resistance in esophageal cancer by interacting with EZH2

BACKGROUND

Expression of the long non-coding mRNA LINC00152 has been reported to correlate with cancer cell resistance to oxaliplatin (L-OHP). However, little is known regarding the molecular mechanism of LINC00152 in esophageal cancer (EC). Hence, we intended to characterize the role of LINC00152 in EC, with a special focus on epithelial-mesenchymal transition (EMT) and L-OHP resistance.

METHODS

We collected EC tissues and identified EC cell lines with higher L-OHP resistance, and then characterized expression patterns of LINC00152, Zeste Homologue 2 (EZH2), Zinc finger e-box binding homeobox (ZEB1) and EMT-related genes using RT-qPCR and Western blot analysis. Furthermore, their functional significance was identified by gain and loss-of-function experiments. The relationship among LINC00152, EZH2 and ZEB1 was examined using RIP, RNA pull-down and ChIP assays. Additionally, resistance of EC cells to L-OHP was reflected by CCK-8 assay to detect cell viability. Animal experiments were also conducted to detect the effects of the LINC00152/EZH2/ZEB1 on EMT and L-OHP resistance.

RESULTS

LINC00152, EZH2 and ZEB1 were highly expressed in EC tissues and Kyse-150/TE-1 cells. As revealed by assays in vitro and in vivo, LINC00152 positively regulated ZEB1 expression through interaction with EZH2 to enhance EMT and L-OHP resistance in EC cells. In contrast, silencing of LINC00152 contributed to attenuated EMT and drug resistance of EC cells to L-OHP.

CONCLUSIONS

Our study demonstrates that LINC00152/EZH2/ZEB1 axis can regulate EMT and resistance of EC cells to L-OHP, thus presenting a potential therapeutic target for EC treatment.

Hsa_circ_0001869 promotes NSCLC progression via sponging miR-638 and enhancing FOSL2 expression

Accumulating studies suggest that circular RNAs (circRNAs) function as key regulators in human cancers. We found that hsa_circ_0001869 participated in non-small cell lung cancer (NSCLC) progression. However, its expression and function during NSCLC remain unknown. The data advised that hsa_circ_0001869 expression was increased in NSCLC cell lines and tissues. High hsa_circ_0001869 expression had negatively correlation with the NSCLC patients prognosis. Bioinformatics and luciferase report analyses confirmed that miR-638 and FOSL2 were hsa_circ_0001869 downstream target. hsa_circ_0001869 downregulation decreased tumor proliferation, invasion and migration by promoting miR-638 expression and decreasing FOSL2 expression. As a result of overexpression of FOSL2 or silencing of miR-638, the recovery of proliferation, migration, and invasion after hsa_circ_0001869 silencing. Overexpression of FOSL2 also led to recovery of migration, invasion and proliferation after upregulation of miR-638. In vivo studies confirmed that overexpression of FOSL2 or silencing of miR-638 led to the recovery of tumor growth ability regarding A549 cells after hsa_circ_0001869 knockdown. Present investigation discovered that hsa_circ_0001869 enhanced NSCLC progression via sponging miR-638 and promoting FOSL2 expression. hsa_circ_0001869 downregulation suppressed tumor growth and invasion ability.

CircFAT1 promotes hepatocellular carcinoma progression via miR-30a-5p/REEP3 pathway

As newly found non‐coding RNAs, circular RNAs (circRNAs) are involved in multiple biological processes. Emerging evidence has illustrated the pivotal roles of circRNAs in various human cancers. However, the function of circFAT1 in hepatocellular carcinoma (HCC) remains largely unclear. In the present study, we found that circFAT1 expression is up‐regulated in HCC tissues and cells. In addition, circFAT1 level is positively correlated with TNM stage and tumour size. To further explore the function of circFAT1 in HCC, in vitro and in vivo experiments were performed. The results show that circFAT1 inhibition reduces the proliferation and invasion of HCC cells and tumorigenesis in vivo, whereas REEP3 overexpression reverses these processes. In conclusion, circFAT1 sponges miR‐30a‐5p to regulate the expression of REEP3, thus promoting hepatocarcinogenesis. New HCC diagnosis or treatment strategies may be developed from circFAT1 as a target.

Soy isoflavone genistein inhibits hsa_circ_0031250/miR-873-5p/FOXM1 axis to suppress non-small-cell lung cancer progression

The foods of plants provide the rich nutrition and have protective function in human diseases, including cancers. Genistein is a major isoflavone constituent in soybeans, which has an anti-cancer role in non-small-cell lung cancer (NSCLC). Nevertheless, the mechanism underlying the anti-cancer function of genistein in NSCLC remains largely unknown. NSCLC cells (H292 and A549) were exposed to genistein. Circular RNA hsa_circ_0031250 (circ_0031250), microRNA (miR)-873-5p and forkhead box M1 (FOXM1) abundances were examined via quantitative reverse transcription polymerase chain reaction and Western blotting. The function of genistein, circ_0031250, miR-873-5p, and FOXM1 on NSCLC progression was investigated via Cell Counting Kit-8, colony formation, transwell well, wound healing, flow cytometry, Western blotting and xenograft model. The target relationship was analyzed by dual-luciferase reporter analysis and RNA immunoprecipitation. Results showed that genistein inhibited NSCLC cell viability in dose-time-dependent patterns. circ_0031250 abundance was elevated in NSCLC samples and cell lines, and it was reduced via genistein exposure. circ_0031250 knockdown aggravated genistein-caused suppression of cell proliferation, migration and invasion and elevation of apoptosis. miR-873-5p expression was decreased in NSCLC samples and cells. miR-873-5p was targeted via circ_0031250, and miR-873-5p knockdown attenuated the influence of circ_0031250 silence on NSCLC progression in the presence of genistein. FOXM1 was regulated via circ_0031250/miR-873-5p axis. miR-873-5p constrained cell proliferation, migration and invasion and increased apoptosis via regulating FOXM1 in genistein-treated cells. circ_0031250 knockdown enhanced the inhibitive function of genistein on NSCLC cell growth in xenograft model. Collectively, genistein repressed NSCLC progression by modulating circ_0031250/miR-873-5p/FOXM1 axis.

Circular RNAs: Emerging Role in Cancer Diagnostics and Therapeutics

Circular RNAs (circRNAs) are rapidly coming to the fore as major regulators of gene expression and cellular functions. They elicit their influence via a plethora of diverse molecular mechanisms. It is not surprising that aberrant circRNA expression is common in cancers and they have been implicated in multiple aspects of cancer pathophysiology such as apoptosis, invasion, migration, and proliferation. We summarize the emerging role of circRNAs as biomarkers and therapeutic targets in cancer.

Circular RNA PRMT5 confers cisplatin-resistance via miR-4458/REV3L axis in non-small-cell lung cancer

Multifactor and multistep processes were elucidated to participate in the progression of non-small-cell lung cancer (NSCLC). Circular RNA 0031250 (circ-PRMT5) was a vital factor in NSCLC. However, the role of circ-PRMT5 in cisplatin (DDP)-resistance needed to be further highlighted. Expression profiles of circ-PRMT5, microRNA (miR)-4458, and EV3-like DNA-directed polymerase ζ catalytic subunit (REV3L) were detected using quantitative real-time polymerase chain reaction. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, flow cytometry, and transwell assays were performed to determine the half-maximal inhibitory concentration of DDP, cell viability, apoptosis, and invasion in vitro. Besides, the protein levels of REV3L and indicated proteins were examined by adopting western blot. Dual-luciferase reporter assay was performed to analyze the interaction between miR-4458 and circ-PRMT5 or REV3L. The functional role of circ-PRMT5 was explored using a xenograft tumor model. Levels of circ-PRMT5 and REV3L were markedly increased, while miR-4458 was downregulated in resistant tissues and cells. Knockdown of circ-PRMT5 enhanced cell apoptosis, DDP-sensitivity, and declined metastasis in NSCLC with DDP resistance. Besides, miR-4458 inhibition or REV3L upregulation could revert circ-PRMT5 absence-mediated effect on DDP-sensitivity in vitro. Mechanically, circ-PRMT5 was a sponge of miR-4458 to regulate REV3L. Importantly, circ-PRMT5 silencing could interact with DDP treatment expedite the decrease of tumor growth in vivo. Circ-PRMT5 promoted DDP resistance via REV3L by sponging miR-4458 in NSCLC, thus providing a novel therapeutic strategy for patients with NSCLC.

The role of protein arginine methyltransferases in kidney diseases

The methylation of arginine residues by protein arginine methyltransferases (PRMTs) is a crucial post-translational modification for many biological processes, including DNA repair, RNA processing, and transduction of intra- and extracellular signaling. Previous studies have reported that PRMTs are extensively involved in various pathologic states, including cancer, inflammation, and oxidative stress reaction. However, the role of PRMTs has not been well described in kidney diseases. Recent studies have shown that aberrant function of PRMTs and its metabolic products-symmetric dimethylarginine (SDMA) and asymmetric dimethylarginine (ADMA)-are involved in several renal pathological processes, including renal fibrosis, acute kidney injury (AKI), diabetic nephropathy (DN), hypertension, graft rejection and renal tumors. We aim in this review to elucidate the possible roles of PRMTs in normal renal function and various kidney diseases.

LncRNA DDX11-AS1: a novel oncogene in human cancer

Long noncoding RNA (lncRNA) is a newly identified type of noncoding RNA with a length of more than 200 nucleotides. The latest research shows that lncRNAs play important roles in the occurrence and development of human tumours by acting both as carcinogenic genes and as tumour suppressor genes. LncRNAs plays a role in various biological processes, such as cell growth, apoptosis, migration and invasion. The newly discovered lncRNA DDX11-AS1 is abnormally highly expressed in various malignant tumours, such as hepatocellular carcinoma, colorectal cancer, osteosarcoma, bladder cancer, NSCLC and gastric cancer. DDX11-AS1 mainly regulates the expression of related genes through direct or indirect ways to perform its functions in carcinogenicity. These results indicate that DDX11-AS1 may be a marker or therapeutic target of tumours. This review summarizes the biological function and mechanism of DDX11-AS1 in the process of tumour development.

Circular RNA circ-LDLRAD3 serves as an oncogene to promote non-small cell lung cancer progression by upregulating SLC1A5 through sponging miR-137

Circular RNAs (circRNAs) are closely associated with the development of non-small cell lung cancer (NSCLC); however, it is still unclear whether circular RNA circ-LDLRAD3 participated in the regulation of NSCLC progression. In this study, we found that circ-LDLRAD3 was high-expressed and miR-137 was low-expressed in NSCLC tissues and cells compared to their normal counterparts, which showed negative correlations in NSCLC tissues. Further experiments validated that miR-137 could be sponged and inhibited by circ-LDLRAD3 in NSCLC cells. In addition, knock-down of circ-LDLRAD3 and miR-137 overexpression promoted NSCLC cell apoptosis, and inhibited cell proliferation and invasion. Similarly, upregulation of circ-LDLRAD3 or miR-137 ablation had opposite effects on the above cell functions. Besides, the glutamine transporter SLC1A5 was validated to be the downstream target of circ-LDLRAD3 and miR-137, and upregulated circ-LDLRAD3 increased SLC1A5 expression levels by downregulating miR-137. Furthermore, the effects of downregulated circ-LDLRAD3 on cell proliferation, apoptosis and mobility were all reversed by knocking down miR-137 and overexpressing SLC1A5. Taken together, this in vitro study found that knock-down of circ-LDLRAD3 inhibited the development of NSCLC by regulating miR-137/SLC1A5 axis.

Circular RNA circ_0000284 plays an oncogenic role in the progression of non-small cell lung cancer through the miR-377-3p-mediated PD-L1 promotion

Background

Circular RNAs (circRNAs), a subgroup of non-coding RNAs, are recognized as pivotal mediators in various types of cancers. CircRNA_0000284 (circ_0000284) was manifested to participate in the development of non-small cell lung cancer (NSCLC). The novel functional mechanism of circ_0000284 in NSCLC was investigated in our current study.

Methods

We exploited quantitative real-time polymerase chain reaction (qRT-PCR) to analyze the relative RNA (circRNA, miRNA and mRNA) expression. The assessment of cell proliferation and colony formation was executed by Cell Counting Kit-8 (CCK-8) and colony formation assay, respectively. Transwell assay was implemented to examine cell migration and invasion. All protein levels were assayed using western blot. The role of circ_0000284 in vivo was evaluated via xenograft model. The target relation was estimated by dual-luciferase reporter and RNA immunoprecipitation (RIP) assays.

Results

As for the biological characterization, circ_0000284 was highly stable and localized in the cytoplasm. Circ_0000284 was up-regulated in NSCLC and could predict poor prognosis of NSCLC patients. Both in vitro and in vivo, down-regulation of circ_0000284 refrained tumorigenesis of NSCLC. Besides, microRNA-377-3p (miR-377-3p) was a miRNA target of circ_0000284, and targeted programmed death-ligand 1 (PD-L1). Circ_0000284 was a cancer-promoting circRNA in NSCLC via regulating the miR-377-3p/PD-L1 axis.

Conclusion

Thus, our results unraveled that circ_0000284 facilitated the progression of NSCLC by up-regulating the PD-L1 expression as a competing endogenous RNA (ceRNA) of miR-377, possibly developing a different perspective in understanding the molecular pathogenesis of NSCLC.