CircRNA has_circ_0078710 acts as the sponge of microRNA-31 involved in hepatocellular carcinoma progression

Noncoding RNAs and programmed cell death in hepatocellular carcinoma: Significant role of epigenetic modifications in prognosis, chemoresistance, and tumor recurrence rate

Hepatocellular carcinoma (HCC) is the most common type of liver cancer with a high death rate in the world. The molecular mechanisms related to the pathogenesis of HCC have not been precisely defined so far. Hence, this review aimed to address the potential cross-talk between noncoding RNAs (ncRNAs) and programmed cell death in HCC. All related papers in the English language up to June 2023 were collected and screened. The searched keywords in scientific databases, including Scopus, PubMed, and Google Scholar, were HCC, ncRNAs, Epigenetic, Programmed cell death, Autophagy, Apoptosis, Ferroptosis, Chemoresistance, Tumor recurrence, Prognosis, and Prediction. According to the reports, ncRNAs, comprising long ncRNAs, microRNAs, circular RNAs, and small nucleolar RNAs can affect cell proliferation, migration, invasion, and metastasis, as well as cell death-related processes, such as autophagy, ferroptosis, necroptosis, and apoptosis in HCC by regulating cancer-associated genes and signaling pathways, for example, phosphoinositide 3-kinase/Akt, extracellular signal-regulated kinase/MAPK, and Wnt/β-catenin signaling pathways. It seems that ncRNAs, as epigenetic regulators, can be utilized as biomarkers in diagnosis, prognosis, survival and recurrence rates prediction, chemoresistance, and evaluation of therapeutic response in HCC patients. However, more scientific evidence is suggested to be accomplished to confirm these results.

Circ0060467 sponges miR-6805 to promote hepatocellular carcinoma progression through regulating AIFM2 and GPX4 expression

BACKGROUND

Circular RNAs (circRNAs) represent a subset of non-coding RNAs implicated in the regulation of diverse biological processes, including tumorigenesis. However, the expression and functional implications of circ0060467 in hepatocellular carcinoma (HCC) remain elusive. In this study, we aimed to elucidate the role of circ0060467 in modulating the progression of HCC.

METHODS

Differentially expressed circRNAs in HCC tissues were identified through circRNA microarray assays. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) assays revealed the upregulation of circ0060467 in both HCC cell lines and tissues. Various assays were conducted to investigate the roles of circ0060467 in HCC progression. Additionally, RNA immunoprecipitation (RIP) assays and luciferase assays were carried out to assess the interactions between circ0060467, microRNA-6085 (miR-6085), apoptosis-inducing factor mitochondria-associated 2 (AIFM2), and glutathione peroxidase 4 (GPX4) in HCC.

RESULTS

Microarray and qRT-PCR analyses demonstrated a marked elevation of circ0060467 in HCC tissues and cell lines. Knockdown of circ0060467 suppressed HCC cell proliferation. Luciferase reporter and RIP assays confirmed the binding of circ0060467, AIFM2, and GPX4 to miR-6805. Subsequent experiments revealed that circ0060467 competes with AIFM2 and GPX4, thereby inhibiting cancer cell ferroptosis by binding to miR-6085 and promoting hepatocellular carcinoma progression.

CONCLUSIONS

Collectively, circ0060467 modulates the levels of AIFM2 and GPX4, crucial regulators of tumor cell ferroptosis, by acting as a sponge for miR-6085 in HCC. Thus, circ0060467 may represent a novel diagnostic marker and therapeutic target for HCC.

Emerging Role of Circular RNAs in Hepatocellular Carcinoma Immunotherapy

Hepatocellular carcinoma (HCC) is a highly fatal malignancy with limited therapeutic options and high recurrence rates. Recently, immunotherapeutic agents such as immune checkpoint inhibitors (ICIs) have emerged as a new paradigm shift in oncology. ICIs, such as programmed cell death protein 1 (PD-1) inhibitors, have provided a new source of hope for patients with advanced HCC. Yet, the eligibility criteria of HCC patients for ICIs are still a missing piece in the puzzle. Circular RNAs (circRNAs) have recently emerged as a new class of non-coding RNAs that play a fundamental role in cancer pathogenesis. Structurally, circRNAs are resistant to exonucleolytic degradation and have a longer half-life than their linear counterparts. Functionally, circRNAs possess the capability to influence various facets of the tumor microenvironment, especially at the HCC tumor-immune synapse. Notably, circRNAs have been observed to control the expression of immune checkpoint molecules within tumor cells, potentially impeding the therapeutic effectiveness of ICIs. Therefore, this renders them potential cancer-immune biomarkers for diagnosis, prognosis, and therapeutic regimen determinants. In this review, the authors shed light on the structure and functional roles of circRNAs and, most importantly, highlight the promising roles of circRNAs in HCC immunomodulation and their potential as promising biomarkers and immunotherapeutic regimen determinants.

Decoding hepatocarcinogenesis from a noncoding RNAs perspective

Being a leading lethal malignancy worldwide, the pathophysiology of hepatocellular carcinoma (HCC) has gained a lot of interest. Yet, underlying mechanistic basis of the liver tumorigenesis is poorly understood. The role of some coding genes and their respective translated proteins, then later on, some noncoding RNAs (ncRNAs) such as microRNAs have been extensively studied in context of HCC pathophysiology; however, the implication of long noncoding RNAs (lncRNAs) and circular RNAs (circRNAs) in HCC is indeed less investigated. As a subclass of the ncRNAs which has been elusive for long time ago, lncRNAs was found to be involved in plentiful cellular functions such as DNA, RNA, and proteins regulation. Hence, it is undisputed that lncRNAs dysregulation profoundly contributes to HCC via diverse etiologies. Accordingly, lncRNAs represent a hot research topic that requires prime focus in HCC. In this review, the authors discuss breakthrough discoveries involving lncRNAs and circRNAs dysregulation that have contributed to the contemporary concepts of HCC pathophysiology and how these concepts could be leveraged as potential novel diagnostic and prognostic HCC biomarkers. Further, this review article sheds light on future trends, thereby discussing the pathological roles of lncRNAs and circRNAs in HCC proliferation, migration, and epithelial-to-mesenchymal transition. Along this line of reasoning, future recommendations of how these targets could be exploited to achieve effective HCC-related drug development is highlighted.

Roles of Aging, Circular RNAs, and RNA Editing in the Pathogenesis of Amyotrophic Lateral Sclerosis: Potential Biomarkers and Therapeutic Targets

Amyotrophic lateral sclerosis (ALS) is an incurable motor neuron disease caused by upper and lower motor neuron death. Despite advances in our understanding of ALS pathogenesis, effective treatment for this fatal disease remains elusive. As aging is a major risk factor for ALS, age-related molecular changes may provide clues for the development of new therapeutic strategies. Dysregulation of age-dependent RNA metabolism plays a pivotal role in the pathogenesis of ALS. In addition, failure of RNA editing at the glutamine/arginine (Q/R) site of GluA2 mRNA causes excitotoxicity due to excessive Ca²⁺ influx through Ca²⁺-permeable α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors, which is recognized as an underlying mechanism of motor neuron death in ALS. Circular RNAs (circRNAs), a circular form of cognate RNA generated by back-splicing, are abundant in the brain and accumulate with age. Hence, they are assumed to play a role in neurodegeneration. Emerging evidence has demonstrated that age-related dysregulation of RNA editing and changes in circRNA expression are involved in ALS pathogenesis. Herein, we review the potential associations between age-dependent changes in circRNAs and RNA editing, and discuss the possibility of developing new therapies and biomarkers for ALS based on age-related changes in circRNAs and dysregulation of RNA editing.

Hsa_circ_0005050 regulated the progression of oral squamous cell carcinoma via miR-487a-3p/CHSY1 axis

Background/purpose

Circular RNAs (circRNAs) have been identified as potential functional modulators of the cellular physiology processes. This study aims to learn the potential molecular mechanisms of hsa_circ_0005050 (circ_0005050) in oral squamous cell carcinoma (OSCC).

Materials and methods

Quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) was used to examine the expression of circ_0005050, miR-487a-3p, and chondroitin sulfate synthase 1 (CHSY1). Dual-luciferase reporter system, RNA pull-down, and RNA Immunoprecipitation (RIP) assays were used to determine the binding between miR-487a-3p and circ_0005050 or CHSY1. Colony formation experiment and EdU assay were used to investigate proliferation. Wound-healing and transwell assays were used to detect the migration of cells. The apoptosis rate of OSCC cells was tested by flow cytometry. Protein levels of related factors were determined by Western blot. Tumor xenograft was established to determine the regulatory role of circ_0005050 on tumor growth in vivo, and Ki-67 expression was detected in this xenograft using Immunohistochemical (IHC).

Results

We implicated that circ_0005050 was apparently upregulated in OSCC tissues cells. In function experiments, repressing of circ_0005050 remarkably retarded OSCC growth in vitro. Furthermore, we conducted dual-luciferase reporter assays and RNA pull-down assays to verify that circ_0005050 sponged miR-487a-3p. Suppression of miR-487a-3p rescued the inhibition of proliferation in SCC15 and SCC25 cells induced by circ_0005050 knockdown. In addition, we found that overexpression of CHSY1 also reversed the inhibitory effect of circ_0005050 silencing on cell proliferation. Moreover, circ_0005050 knockdown inhibited tumor growth in vivo.

Conclusion

Circ_0005050 acted as an oncogenic factor in OSCC progression through miR-487a-3p/CHSY1 axis.

Circ_0061395 functions as an oncogenic gene in hepatocellular carcinoma by acting as a miR-1182 sponge

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors in liver cancer, with a high rate of metastasis and recurrence. Circular RNA_0061395 (circ_0061395) has been shown to be involved in the advance of HCC. However, the interaction between circ_0061395 and microRNA (miRNA) in HCC has not been studied. Quantitative real-time polymerase-chain reaction (qRT-PCR) was used to detect the expression of related genes in liver cancer tissues and cells. The stability of circ_0061395 was verified by RNase R digestion. Through detection of cell malignant behavior and apoptosis, the capping experiment was carried out to verify the regulatory relationship between miR-1182 and circ_0061395 or SPARC/osteonectin, CWCV and Kazal-like domains proteoglycan 1 (SPOCK1). The expression of related proteins was detected by western blot. The interaction of miR-1182 with circ_0061395 or SPOCK1 has been notarized by Dual-luciferase reporter analysis and RNA immunoprecipitation (RIP) assay. Xenotransplantation experiments using BALB/C nude mice were used to confirm the function of circ_0061395 in vivo. Circ_0061395 and SPOCK1 were significantly expressed in liver cancer tissues and cells. Silencing circ_0061395 reduced the proliferation, migration, invasion, tube formation and tumor spheroid formation rate of Huh-7 and SNU-387 cells. MiR-1182 was a target of circ_0061395. Silencing circ_0061395 inhibited the malignant behavior of HCC cells by releasing miR-1182. In addition, SPOCK1 was the target of miR-1182. Overexpression of SPOCK1 partially restored the inhibitory effect of miR-1182 on cell proliferation. Animal experiments confirmed the anti-tumor effect of silence circ_0061395. Circ_0061395 induced the changes of the expression of SPOCK1 by regulating miR-1182, thereby mediating the process of HCC, and at least partially promoting the development of HCC cells, providing a novel targeted therapy for HCC.

Circular RNA Controls Tumor Occurrence and Development via Cell Cycle Regulation

Circular RNAs (circRNAs) participate in the occurrence and development of various diseases through different mechanisms, such as by acting as a microRNA (miRNA) sponge, interacting with RNA-binding proteins, and regulating gene transcription and protein translation. For example, the abnormal expression of specific circRNAs in tumor cells can alter key regulatory factors and the cell cycle network, resulting in cell cycle disorders and the development and metastasis of tumors. Here, we summarize the mechanisms involved in the circRNA-mediated processes that lead to uncontrolled cell cycle and tumor cell proliferation. Extensive studies investigating the abnormal expression of circRNAs in different cancer types have been conducted. The unique characteristics of circRNAs and their ability to regulate the cell cycle through diverse mechanisms is extremely valuable in tumor diagnosis, treatment, and prognosis. Our review may assist in further understanding the circRNA-mediated regulation of the cell cycle in tumors and provide insights for research on circRNA-based therapeutic strategies and biological diagnosis for cancer.

The Sponge Interaction Between Circular RNA and microRNA Serves as a Fast-Evolving Mechanism That Suppresses Non-small Cell Lung Cancer (NSCLC) in Humans

Non-small cell lung cancer (NSCLC) is one of the most lethal cancer types in the world. Currently, the molecular mechanisms and pathways underlying NSCLC oncogenesis are poorly understood. Using multiple Omics data, we systematically explored the differentially expressed circular RNAs (circRNAs) in NSCLC. We also investigated potential microRNA sponges (that absorb circRNAs) in NSCLC and downstream target genes with experimental verifications. hsa_circ_0003497 was down-regulated in NSCLC and played an inhibitory role in tumorigenesis. In contrast, miR-197-3p was up-regulated in NSCLC. hsa_circ_0003497 directly interacts with miR-197-3p and releases a target gene of miR-197-3p termed CTNND1 (a known tumor suppressor gene). Evolutionary analysis reveals fast evolution of this hsa_circ_0003497-miR-197-3p-CTNND1-NSCLC axis in mammals. This work clarified the biological functions and molecular mechanisms of how hsa_circ_0003497 suppresses NSCLC through miR-197-3p and CTNND1. We discovered molecular markers for the prognosis of NSCLC and provided potential intervention targets for its treatment.

Circle RNA circ_0007331 promotes colorectal carcinoma by targeting miR-205-5p/high-mobility group A2 axis

Colorectal cancer (CRC) is a common malignancy of the gastrointestinal tract. CircRNAs have been reported to play regulatory roles in many cancers, including CRC. This study focuses on the role of circ_0007331 in CRC. Differentially expressed circRNAs in CRC were screened using the GEO database. RT-qPCR was used to analyze mRNA expression. StarBase and TargetScan were used to predict targeting relationships and then verified by the dual luciferase reporter assay along with the RNA pull-down assay. CCK-8 as well and transwell assays were used to measure cell viability, migration, and invasion. Protein levels were determined using western blotting. circ_0007331 is expressed more frequently in patients with CRC. The inhibition of circ_0007331 expression reduced the viability, colony formation, migration, and invasion of CRC cells. However, inhibition of miR-205-5p or elevation of high-mobility group A2 (HMGA2) can reverse the function of inhibited circ_0007331 in tumor cells. This study demonstrated that the circ_0007331/miR-205-5p/HMGA2 axis promotes CRC development. Thus, circ_0007331 may be a potential biomarker for CRC.

Circ_0078710 promotes the development of liver cancer by upregulating TXNDC5 via miR-431-5p

INTRODUCTION AND OBJECTIVES

Liver cancer, with high recurrence and metastasis rate, is a common malignant tumor. Circular RNA_0078710 (circ_0078710) has been shown to be take part in the advance of hepatocellular carcinoma. However, the interaction between circ_0091579 and microRNA-431-5p (miR-431-5p) in liver cancer has not been studied.

MATERIALS AND METHODS

The expressions of circ_0078710, miR-431-5p and Thioredoxin domain-containing 5 (TXNDC5) in liver cancer tissues and cells were detected by quantitative real-time polymerase chain reaction (qRT-PCR). The effect of cric_0078710 in liver cancer cells was assessed by Cell Counting Kit-8 (CCK-8) assay, Transwell, flow cytometry and Dual-luciferase reporter assay. Glycolysis metabolism was examined by lactate production, glucose uptake and ATP level. The protein levels of ki-67, bax and TXNEC5 were tested by western blot. The role of circ_0078710 in vivo was determined by animal study.

RESULTS

Circ_0078710 and TXNDC5 were notably expressed in liver cancer tissues and cells. Circ_0078710 knockdown diminished proliferation, migration, invasion and glycolytic metabolism of huh7 and Hep3B cells, and accelerated cell apoptosis. MiR-431-5p is the target of circ_0078710, and silence circ_0078710 can inhibit the malignant behavior and glycolysis of hepatocellular carcinoma (HCC) cells by releasing miR-431-5p. In addition, TXNDC5 was a target of miR-431-5p, and overexpression of TXNDC5 restored cell proliferation and glycolysis inhibition due to miR-431-5p. Animal experiments made clear the anti-tumor effect of circ_0078710 knockdown.

CONCLUSION

Circ_0078710 promotes the progression of liver cancer by regulating TXNDC5 expression by targeting miR-431-5p. These results demonstrate that circ_0078710 could be a remedy target for liver cancer.

Circular RNA circ_0008934 promotes hepatocellular carcinoma growth and metastasis through modulating miR-1305/TMTC3 axis

Circular RNAs (circRNAs) play important roles in the progression of hepatocellular carcinoma (HCC). However, the exact function of circ_0008934 in HCC is unknown. Our study aimed to investigate the expression characteristics of circ_0008934 in HCC and its effects on the proliferation and metastasis of HCC, and to explore the potential mechanism. In this study, circ_0008934 expression was found to be significantly upregulated in HCC tissues and cell lines by qRT-PCR. High level of circ_0008934 is closely associated with higher serum AFP (P < 0.001), larger tumor diameter (P = 0.012), microvascular invasion (P = 0.008) and poorer prognosis (P = 0.007) of HCC patients. Functionally, knockdown of circ_0008934 inhibited HCC cell proliferation, invasion and migration in vitro and vivo. Mechanically, circ_0008934 was a sponge of miR-1305 to facilitate the TMTC3 expression, and the TMTC3 expression in HCC tissues was negatively associated with the survival of HCC patients. Furthermore, rescued assays revealed that the circ_0008934 facilitated HCC proliferation, invasion and migration by regulating miR-1305/ TMTC3 signaling pathways. Overall, these results demonstrate that downregulation of circ_0008934 repress HCC growth and metastasis by upregulating miR-1305 to inhibit TMTC3, suggesting circ_0008934/ miR-1305/ TMTC3 regulatory axis may be a possible novel therapeutic target for HCC.

The expression of circ_0090049 in hepatocellular carcinoma and the molecular regulation mechanism of other biological functions

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors in liver cancer. Circular RNA_0090049 (circ_0090049) has been shown to be involved in the advance of HCC. However, the interaction between circ_0090049 and microRNA (miRNA) in HCC has not been studied. Quantitative real-time PCR was used to detect the expression of related genes. Through detection of cell proliferation, migration, invasion, and rate of tumor sphere formation, the capping experiment was carried out to verify the regulatory relationship between miRNA and circ_0090049 or circ_0090049 and ubiquitin-conjugating enzyme E2 T (UBE2T). The expression of related proteins was detected by Western blotting. The interaction of miRNA with circ_0090049 or UBE2T was notarized by Dual-luciferase reporter assay. Xenotransplantation experiments confirmed the function of circ_0090049 in vivo. Circ_0090049 and UBE2T were upregulated in liver cancer. Silencing circ_0090049 reduced the proliferation, migration, invasion, and tumor spheroid formation rate of Huh7 and HCCLM3 cells. MiR-605-5p and miR-548c-3p were identified as targets of circ_0090049, and UBE2T was the target of miR-605-5p and miR-548c-3p. Anti-miR-605-5p, anti-miR-548c-3p or UBE2T overexpression restored the inhibitory effect of circ_0090049 knockdown on HCC cells. Animal experiments confirmed the antitumor effect of silence circ_0090049. Circ_0090049 regulates the expression of UBE2T by regulating miR-605-5p or miR-548c-3p, thereby promoting the development of HCC cells.

Large-scale omics data reveal the cooperation of mutation-circRNA-miRNA-target gene network in liver cancer oncogenesis

Aims: Clarifying the initial trigger of the differentially expressed genes in cancers helps researchers understand the cellular system as a whole network. Materials & methods: We retrieve the transcriptome and translatome of tumor and normal tissues from ten liver cancer patients and define differentially expressed genes and tumor-specific mutations. We associate the oncogenesis with the mutations by target prediction and experimental verification. Results: Upregulated genes have tumor-specific mutations in 3'UTRs that abolish the binding of miRNAs. For downregulated genes, their corresponding miRNAs are mutually targeted by two circRNAs, with mutations in base-pairing regions. Transfection experiments support the oncogenic role of these mutations. Conclusions: The tumor-specific mutations serve as the initial trigger of liver cancer. The mutation-circRNA-miRNA-target gene chain is completed.

Circular RNAs in cell cycle regulation: Mechanisms to clinical significance

Circular RNAs (circRNAs), a type of non‐coding RNA, are single‐stranded circularized molecules characterized by high abundance, evolutionary conservation and cell development‐ and tissue‐specific expression. A large body of studies has found that circRNAs exert a wide variety of functions in diverse biological processes, including cell cycle. The cell cycle is controlled by the coordinated activation and deactivation of cell cycle regulators. CircRNAs exert mutifunctional roles by regulating gene expression via various mechanisms. However, the functional relevance of circRNAs and cell cycle regulation largely remains to be elucidated. Herein, we briefly describe the biogenesis and mechanistic models of circRNAs and summarize their functions and mechanisms in the regulation of critical cell cycle modulators, including cyclins, cyclin‐dependent kinases and cyclin‐dependent kinase inhibitors. Moreover, we highlight the participation of circRNAs in cell cycle‐related signalling pathways and the clinical value of circRNAs as promising biomarkers or therapeutic targets in diseases related to cell cycle disorder.

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.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Circular 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.

Biological roles and potential clinical values of circular RNAs in gastrointestinal malignancies

Circular RNAs (circRNAs), a class of endogenous RNA molecules, are produced by alternative splicing of precursor RNA and are covalently linked at the 5' and 3' ends. Recent studies have revealed that dysregulated circRNAs are closely related to the occurrence and progression of gastrointestinal malignancies. Accumulating evidence indicates that circRNAs, including circPVT1, circLARP4, circ-SFMBT2, cir-ITCH, circRNA_100782, circ_100395, circ-DONSON, hsa_circ_0001368, circNRIP1, circFAT1(e2), circCCDC66, circSMARCA5, circ-ZNF652, and circ_0030235 play important roles in the proliferation, differentiation, invasion, and metastasis of cancer cells through a variety of mechanisms, such as acting as microRNA sponges, interacting with RNA-binding proteins, regulating gene transcription and alternative splicing, and being translated into proteins. With the characteristics of high abundance, high stability, extensive functions, and certain tissue-, time- and disease-specific expressions, circRNAs are expected to provide novel perspectives for the diagnoses and treatments of gastrointestinal malignancies.

Circular RNA CHST15 Sponges miR-155-5p and miR-194-5p to Promote the Immune Escape of Lung Cancer Cells Mediated by PD-L1

Background

The effects of up-regulated CircCHST15 on lung cancer remained unclear. In this study, the role of CircCHST15 in lung cancer was investigated.

Methods

Dual-luciferase reporter verified the bioinformatics prediction that CircCHST15 targeted miR-155-5p and miR-194-5p. The correlation between CircCHST15 and PD-L1 was analyzed by Pearson analysis. CCK-8 and colony formation was performed to determine the viability and proliferation of lung cancer cells. After the lung cancer (subcutaneous-xenotransplant) model was established in mice, the T cell subtype and related cytokines in mouse tumor tissues were detected by flow cytometry and ELISA. Moreover, the expressions of CircCHST15, miR-155-5p, miR-194-5p, immune-related, and proliferation-related factors of the lung cancer cells or mice tumor tissues were detected by immunohistochemistry, RT-qPCR, or Western blot.

Results

CircCHST15 and PD-L1 were high-expressed in lung cancer, and the two was positively correlated. CircCHST15 targeted miR-155-5p and miR-194-5p, the later further targeted PD-L1. Lung cancer cell viability and proliferation were increased by miR-155-5p and inhibited by miR-194-5p. CircCHST15 located in the cytoplasm promoted tumor growth, down-regulated the expressions of miR-155-5p and miR-194-5p, and up-regulated the expressions of PD-L1, Ki-67, PCNA, CCL17, CCL22, IFN-γ, TNF-β, and IL-10. Also, CircCHST15 decreased the CD8⁺ cells in mouse blood and tumor, but increased the Tregs in mouse tumor. PD-L1 inhibitor showed an opposite effect to CircCHST15 on mouse tumors.

Conclusion

CircCHST15 sponged miR-155-5p and miR-194-5p to promote the PD-L1-mediated immune escape of lung cancer cells.

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.

Recent Update on the Role of Circular RNAs in Hepatocellular Carcinoma

After being overlooked for decades, circular RNAs (circRNAs) have recently generated considerable interest. circRNAs play a role in a variety of normal and pathological biological processes, including hepatocarcinogenesis. Many circRNAs contribute to hepatocarcinogenesis through sponging of microRNAs (miRs) and disruption of cellular signaling pathways that play a part in control of cell proliferation, metastasis and apoptosis. In most cases, overexpressed circRNAs sequester miRs to cause de-repressed translation of mRNAs that encode oncogenic proteins. Conversely, low expression of circRNAs has also been described in hepatocellular carcinoma (HCC) and is associated with inhibited production of tumor suppressor proteins. Other functions of circRNAs that contribute to hepatocarcinogenesis include translation of truncated proteins and acting as adapters to regulate influence of transcription factors on target gene expression. circRNAs also affect hepatocyte transformation indirectly. For example, the molecules regulate immune surveillance of cancerous cells and influence the liver fibrosis that commonly precedes HCC. Marked over- or under-expression of circRNA expression in HCC, with correlating plasma concentrations, has diagnostic utility and assays of these RNAs are being developed as biomarkers of HCC. Although knowledge in the field has recently surged, the myriad of described effects suggests that not all may be vital to hepatocarcinogenesis. Nevertheless, investigation of the role of circRNAs is providing valuable insights that are likely to contribute to improved management of a serious and highly aggressive cancer.

CircPAN3 ameliorates myocardial ischaemia/reperfusion injury by targeting miR-421/Pink1 axis-mediated autophagy suppression

Cardiovascular diseases are considered the leading cause of death worldwide. Myocardial ischaemia/reperfusion (I/R) injury is recognized as a critical risk factor for cardiovascular diseases. Although increasing advances have been made recently in understanding the mechanisms of I/R injury, they remain largely unknown. In this study, we found that the expression of circPAN3 (circular RNA PAN3) was decreased in a mouse model of myocardial I/R. Overexpression of circPAN3 significantly inhibited autophagy and alleviated cell apoptosis of cardiomyocytes, which was further verified in vivo by decreased autophagic vacuoles and reduced myocardial infarct sizes. Moreover, miR-421 (microRNA-421) was identified as a downstream target involved in circPAN3-mediated myocardial I/R injury. Additionally, miR-421 could negatively regulate Pink1 (phosphatase and tensin homologue-induced putative kinase 1) via a direct binding relationship. Furthermore, the mitigating effects of circPAN3 overexpression on myocardial I/R injury by suppressing autophagy and apoptosis were abolished by knockdown of Pink1. Our findings reveal a novel role for circPAN3 in modulating autophagy and apoptosis in myocardial I/R injury and the circPAN3-miR-421-Pink1 axis as a regulatory network, which might provide potential therapeutic targets for cardiovascular diseases.

Circ_0003998 enhances doxorubicin resistance in hepatocellular carcinoma by regulating miR-218-5p/EIF5A2 pathway

BACKGROUND

The involvement of circular RNAs (circRNAs) in chemoresistance of tumors has been identified. Herein, this study aims to investigate the role and the underlying mechanism of circ_0003998 in doxorubicin (DOX) resistance in hepatocellular carcinoma (HCC).

METHODS

The expression of circ_0003998 and microRNA (miR)-218-5p and eukaryotic translation initiation factor 5A-2 (EIF5A2) mRNA was detected using quantitative real-time polymerase chain reaction. Cell viability, migration and invasion were analyzed using cell counting kit-8, colony formation and transwell assay, respectively. The levels of matrix metallopeptidase 9 (MMP-9), E-cadherin, Vimentin, N-cadherin and EIF5A2 protein were detected using western blot. The interaction between miR-218-5p and circ_0003998 or EIF5A2 was confirmed by dual-luciferase reporter assay. In vivo experiments were performed using murine xenograft models.

RESULTS

Circ_0003998 was elevated in HCC tissues, DOX-resistant tissues and cells, and circ_0003998 knockdown promoted DOX-sensitivity in HCC by inhibiting resistant cell viability, migration, invasion and EMT in vitro and enhanced DOX cytotoxicity in vivo. Bioinformatics analysis revealed circ_0003998 inhibited miR-218-5p expression, which was clarified to be a target of circ_0003998, and circ_0003998 knockdown sensitized HCC cell to DOX by sponging miR-218-5p. EIF5A2 was a target of miR-218-5p, and miR-218-5p mitigated DOX resistance in HCC cells through modulating EIF5A2 expression. Additionally, circ_0003998 served as a competing endogenous RNA for miR-218-5p to regulate EIF5A2 expression.

CONCLUSION

Circ_0003998 knockdown sensitized HCC cell to DOX by regulating miR-218-5p/EIF5A2 axis, indicating new markers of poor response to DOX and potential therapeutic strategies for the chemotherapy of HCC.

CircSOD2 induced epigenetic alteration drives hepatocellular carcinoma progression through activating JAK2/STAT3 signaling pathway

Background

Emerging evidence suggests that circular RNAs play critical roles in disease development especially in cancers. Previous genome-wide RNA-seq studies found that a circular RNA derived from SOD2 gene was highly upregulated in hepatocellular carcinoma (HCC), however, the role of circSOD2 in HCC remains largely unknown.

Methods

The expression profiling of circSOD2 and microRNA in HCC patients were assessed by Real-Time Quantitative Reverse Transcription PCR (qRT-PCR). SiRNA or CRISPR-CAS9 were used to silence gene expression. The biological function of circSOD2 in HCC was investigated using in vitro and in vivo studies including, trans-well cell migration, cell apoptosis, cell cycle, CCK8, siRNA interference, western blots, and xenograft mouse model. The underlying molecular mechanism was determined by Chromatin Immunoprecipitation quantitative real time PCR (ChIP-qPCR), bioinformatic analysis, biotin-pull down, RNA immunoprecipitation, 5-mc DNA pulldown and luciferase assays.

Results

In accordance with previous sequencing results, here, we demonstrated that circSOD2 was highly expressed in HCC tumor tissues compared with normal liver tissues. Mechanically, we showed that histone writer EP300 and WDR5 bind to circSOD2 promoter and trigger its promoter H3K27ac and H3K4me3 modification, respectively, which further activates circSOD2 expression. SiRNA mediated circSOD2 suppression impaired liver cancer cell growth, cell migration, prohibited cell cycle progression and in vivo tumor growth. By acting as a sponge, circSOD2 inhibits miR-502-5p expression and rescues miR-502-5p target gene DNMT3a expression. As a DNA methyltransferase, upregulated DNMA3a suppresses SOCS3 expression by increasing SOCS3 promoter DNA methylation. This event further accelerates SOCS3 downstream JAK2/STAT3 signaling pathway activation. In addition, we also found that activated STAT3 regulates circSOD2 expression in a feedback way.

Conclusion

The novel signaling axis circSOD2/miR-502-5p/DNMT3a/JAK2/STAT3/circSOD2 provides a better understanding of HCC tumorigenesis. The molecular mechanism underlying this signaling axis offers new prevention and treatment of HCC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-020-01769-7.

Circular RNAs in liver diseases: Mechanisms and therapeutic targets

Circular RNAs (circRNAs) are formed from the genome through diverse back splicing and feature the closed loop. circRNAs are widely available in a variety of cells and characterized by conservation, structural stability, high abundance and tissue-specific or developmental-specific expression. Recent studies have shown that circRNAs are closely related to liver diseases, such as metabolic-associated fatty liver disease, hepatitis, liver cirrhosis and hepatocellular carcinoma. circRNAs play an important role in the progression of liver diseases, are potential diagnostic and prognostic markers, and have translational value in therapy. This article reviews the research on circRNAs in liver diseases, with a view to providing a theoretical basis and new ideas for future research and treatment of liver diseases.

The emerging roles of non-coding competing endogenous RNA in hepatocellular carcinoma

Accumulating evidence has emerged revealing that noncoding RNAs (ncRNAs) play essential roles in the occurrence and development of hepatocellular carcinoma (HCC). However, the complicated regulatory interactions among various ncRNAs in the development of HCC are not entirely understood. The newly discovered mechanism of competing endogenous RNAs (ceRNAs) uncovered regulatory interactions among different varieties of RNAs. In recent years, a growing number of studies have suggested that ncRNAs, including long ncRNAs, circular RNAs and pseudogenes, play major roles in the biological functions of the ceRNA network in HCC. These ncRNAs can share microRNA response elements to affect microRNA affinity with target RNAs, thus regulating gene expression at the transcriptional level and both physiological and pathological processes. The ncRNAs that function as ceRNAs are involved in diverse biological processes in HCC cells, such as tumor cell proliferation, epithelial-mesenchymal transition, invasion, metastasis and chemoresistance. Based on these findings, ncRNAs that act as ceRNAs may be promising candidates for clinical diagnosis and treatments. In this review, we discuss the mechanisms and research methods of ceRNA networks. We also reviewed the recent advances in studying the roles of ncRNAs as ceRNAs in HCC and highlight possible directions and possibilities of ceRNAs as diagnostic biomarkers or therapeutic targets. Finally, the limitations, gaps in knowledge and opportunities for future research are also discussed.

Epigenetic Associations between lncRNA/circRNA and miRNA in Hepatocellular Carcinoma

Simple Summary

Non-coding RNAs such as microRNAs, long non-coding RNAs, and circular RNAs contribute to the development and progression of hepatocellular carcinoma through epigenetic association. Long non-coding RNAs and circular RNAs act as competing endogenous RNAs that contain binding sites for miRNAs and thus compete with the miRNAs, which results in promotion of miRNA target gene expression, thereby leading to proliferation and metastasis of hepatocellular carcinoma. Competing endogenous RNAs have the potential to become diagnostic biomarkers and therapeutic targets for treatment of hepatocellular carcinoma.

Abstract

The three major members of non-coding RNAs (ncRNAs), named microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs), play an important role in hepatocellular carcinoma (HCC) development. Recently, the competing endogenous RNA (ceRNA) regulation model described lncRNA/circRNA as a sponge for miRNAs to indirectly regulate miRNA downstream target genes. Accumulating evidence has indicated that ceRNA regulatory networks are associated with biological processes in HCC, including cancer cell growth, epithelial to mesenchymal transition (EMT), metastasis, and chemoresistance. In this review, we summarize recent discoveries, which are specific ceRNA regulatory networks (lncRNA/circRNA-miRNA-mRNA) in HCC and discuss their clinical significance.

The Secret Garden of Neuronal circRNAs

High-throughput transcriptomic profiling approaches have revealed that circular RNAs (circRNAs) are important transcriptional gene products, identified across a broad range of organisms throughout the eukaryotic tree of life. In the nervous system, they are particularly abundant, developmentally regulated, region-specific, and enriched in genes for neuronal proteins and synaptic factors. These features suggested that circRNAs are key components of an important layer of neuronal gene expression regulation, with known and anticipated functions. Here, we review major recognized aspects of circRNA biogenesis, metabolism and biological activities, examining potential new functions in the context of the nervous system.

circ_0084927 promotes cervical carcinogenesis by sponging miR-1179 that suppresses CDK2, a cell cycle-related gene

Background

Cervical cancer (CC) is a malignant tumor found in the lowermost part of the womb. Evolving studies on CC have reported that circRNA plays a crucial role in CC progression. In this study, we investigated the main function of a novel circRNA, circ_0084927, and its regulatory network in CC development.

Methods

qRT-PCR was applied to evaluate the expression of circ_0084927, miR-1179, and CDK2 mRNA in CC tissues and cells. Dual-luciferase reporting experiments and RNA immunoprecipitation (RIP) assay were conducted to validate the target relationship of miR-1179 with circ_0084927 and CDK2 mRNA. CCK-8 and BrdU assays were also used to evaluate CC cell proliferation. The adhesion and apoptosis phenotypes of CC cells were measured using cell–matrix adhesion and caspase 3 activation assay. Flow cytometry was also employed to detect the CC cell cycle.

Results

Our results indicated that circ_0084927 was up-regulated in CC tissues and cells. Findings also revealed that circ_0084927 silence inhibited CC cell proliferation and adhesion while facilitating apoptosis and triggering cell cycle arrest. However, miR-1179 down-regulation appeared in CC tissues. Apart from observing that circ_0084927 abolished miR-1179’s inhibitory effects on cell proliferation and adhesion, it was found that CDK2 was up-regulated in CC tissues and was instrumental in cancer promotion. Also observed was that miR-1179 directly targeted CDK2, thereby inhibiting CDK2’s promotion on the malignant phenotypes of CC cells. Lastly, results indicated that circ_0084927 revoked the inhibitory effect of miR-1179 on CDK2 by sponging miR-1179.

Conclusion

circ_0084927 promoted cervical carcinogenesis by sequestering miR-1179, which directly targeted CDK2. Our results also provided novel candidate targets for CC treatment in that it revealed the circ_0084927/miR-1179/CDK2 regulatory network that strengthened CC aggressiveness.

Circular RNA is a popular molecule in tumors of the digestive system (Review)

Most tumors of the digestive system, including esophageal, gastric, liver and colorectal cancer, are malignant tumors that are associated with rates of high morbidity and mortality. The lack of effective methods for early diagnosis is an important cause of poor prognosis for these malignancies. Circular RNAs (circRNAs) belong to a family of endogenous, covalently closed non‑coding RNAs that are characterized as having no 5' cap structures or 3' poly‑A tails. Shortly following discovery, circRNAs were considered to be a product of mis‑splicing and have no significant biological function. However, in recent years, accumulating evidence is demonstrating that they serve key roles in tumorigenesis and have the potential to serve as diagnostic markers. The present article summarizes the biogenesis and function of circRNAs and reviews their role in seven common types of tumor of the digestive system whilst exploring their potential as tumor markers and the significant roles they can serve in the digestive system, in addition to providing a referencing point for future studies of digestive system malignancies.

Circular RNA circ-CSPP1 regulates CCNE2 to facilitate hepatocellular carcinoma cell growth via sponging miR-577

Objective

Circ-centro-some/spindle pole-associated protein (CSPP1) has been confirmed to be characterized in diverse human malignancies and its ectopic expression may regulate tumor progression and development. However, in hepatocellular carcinoma (HCC), its biological role, clinical significance and molecular mechanism are still unclear.

Methods

Circ-CSPP1 expression and its prognostic values in HCC tissues were detected by qRT-PCR or in situ hybridization (ISH), and enriched by using Rnase R. The functional experiments (Circ-CSPP1 was overexpressed or knocked down) were performed in HCC cells. The HCC cell growth was analyzed by CCK-8 assay, transwell, wound healing and colony formation assays. The interation between circ-CSPP1 and miR-577/miR-577 and cyclin E2 (CCNE2) were determined by dual luciferase assay or RNA binding protein immunoprecipitation (RIP) assay. The RNA fluorescence in situ hybridization (FISH) assay was used to detect the subcellular distribution. Finally, an in vivo nude mouse tumor model was constructed.

Results

In HCC patients and cells, circ-CSPP1 was aberrantly expressed, and its upregulation predicted poor prognosis, and closely correlated with tumor size and TNM stage. Circ-CSPP1 resisted RnaseR digestion, indicating it is a circular RNA structure. Moreover, overexpression of circ-CSPP1 promoted HCC cell viability, colony formation, migration, and invasion in vitro. Knockdown of circ-CSPP1 showed contrary results. Circ-CSPP1 acts as a miR-577 sponge and positively regulated the target of miR-577, CCNE2. Besides, miR-577 inhibitor rescued the suppressive effects of circ-CSPP1 knockdown on HCC cell growth, whereas was completely reversed by silencing of CCNE2. Finally, the in vivo experiments confirmed that circ-CSPP1 knockdown regulated xenograft tumor volume and downregulated CCNE2, p-Rb, E2F1 and c-myc expression.

Conclusion

These findings revealed that circ-CSPP1 contributed to HCC progression by positively regulating CCNE2 via miR-577, thus established its potential as new a prognostic and therapeutic marker for HCC patients.

Circular RNA Circ100084 functions as sponge of miR‑23a‑5p to regulate IGF2 expression in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) has become a major cause of cancer-related mortality worldwide. Circular RNAs (circRNAs) are non-coding RNAs that serve important roles in multiple cancers. However, the role of circRNAs in HCC remains largely unknown. In the present study, a circRNA microarray dataset of HCC samples, GSE97332, was downloaded from the gene expression omnibus database. Following data preprocessing, differentially expressed circRNAs between HCC tissues and normal tissues were determined using GEO2R. The circRNA-miRNA interactions were predicted by the miRanda database. The miRTarbase database was used to search for target genes of the miRNAs. A circRNA-miRNA-mRNA network was constructed using Cytoscape based on the obtained circRNA, miRNA and mRNA. In this network, the upregulated circRNA hsa_circRNA_100084 was found to be involved in a competing endogenous relationship of hsa_circRNA_100084-hsa-miR-23a-5p- insulin-like growth factor 2 (IGF2). The differential expression of hsa_circRNA_100084, hsa-miR-23a-5p and IGF2 in HCC tissues and liver cancer cells was validated by reverse transcription-quantitative PCR. Additionally, the interactions between hsa-miR-23a-5p with hsa_circRNA_100084 and IGF2 were validated by dual-luciferase reporter assays. Knocking down hsa_circRNA_100084 inhibited the proliferation, migration and invasion of liver cancer cells, while the simultaneous overexpression of IGF2 reversed the effects of hsa_circRNA_100084 knockdown. The results show that hsa_circRNA_100084 could promote the expression of IGF2 by acting as a sponge of hsa-miR-23a-5p in liver cancer cells.

PEX5, a novel target of microRNA-31-5p, increases radioresistance in hepatocellular carcinoma by activating Wnt/β-catenin signaling and homologous recombination

Rationale: Hepatocellular carcinoma (HCC) is the second leading cause of cancer-related death worldwide, with high recurrence and metastasis rates. Although radiation is an effective treatment for tumors, it is often limited by intrinsic radioresistance in HCC. The contributions of dysregulated microRNAs, including miR-31-5p, to HCC progression have been recently reported. However, the role of miR-31-5p in the radiation response of HCC is unknown. In this study, we aimed to investigate the impact of miR-31-5p on HCC radiosensitivity.

Methods: miR-31-5p expression in HCC tissues, paired adjacent tissues, and HCC cell lines was measured using quantitative real-time polymerase chain reaction and in situ hybridization. Bioinformatic analyses, gain- and loss-of-function experiments, and luciferase reporter assays were performed to validate peroxisomal biogenesis factor 5 (PEX5) as a direct target of miR-31-5p. The biofunctions of PEX5 and miR-31-5p in HCC were determined by Transwell, wound-healing, and Cell Counting Kit-8 (CCK8) assays. A colony formation assay was used to evaluate the radiosensitivity of HCC cells. The interaction among PEX5, β-catenin, Rac1, and JNK-2 was confirmed by coimmunoprecipitation. A xenograft tumor model was established to validate the effects of miR-31-5p and PEX5 on HCC progression and radiosensitivity in vivo.

Results: Low expression of miR-31-5p in HCC specimens, as observed in this study, predicted a poor clinical outcome. However, the expression pattern of PEX5, as a direct target of miR-31-5p, was opposite that of miR-31-5p, and high PEX5 expression indicated poor prognosis in HCC patients. Ectopic expression of PEX5 increased the proliferation, migration, and invasion abilities and enhanced the radioresistance of HCC cells in vitro and in vivo; however, these phenotypes were inhibited by miR-31-5p. Mechanistically, PEX5 stabilized cytoplasmic β-catenin and facilitated β-catenin nuclear translocation to activate Wnt/β-catenin signaling. Moreover, upon radiation exposure, PEX5 reduced excessive reactive oxygen species (ROS) accumulation and activated the homologous recombination (HR) pathway, which protected HCC cells from radiation-induced damage.

Conclusions: Our findings demonstrated a novel role for PEX5 as a miR-31-5p target and a mediator of the Wnt/β-catenin signaling and HR pathways, providing new insights into studying HCC radiation responses and implicating PEX5 and miR-31-5p as potential therapeutic targets in HCC.

The mechanistic, diagnostic and therapeutic novel nucleic acids for hepatocellular carcinoma emerging in past score years

Despite The Central Dogma states the destiny of gene as 'DNA makes RNA and RNA makes protein', the nucleic acids not only store and transmit genetic information but also, surprisingly, join in intracellular vital movement as a regulator of gene expression. Bioinformatics has contributed to knowledge for a series of emerging novel nucleic acids molecules. For typical cases, microRNA (miRNA), long noncoding RNA (lncRNA) and circular RNA (circRNA) exert crucial role in regulating vital biological processes, especially in malignant diseases. Due to extraordinarily heterogeneity among all malignancies, hepatocellular carcinoma (HCC) has emerged enormous limitation in diagnosis and therapy. Mechanistic, diagnostic and therapeutic nucleic acids for HCC emerging in past score years have been systematically reviewed. Particularly, we have organized recent advances on nucleic acids of HCC into three facets: (i) summarizing diverse nucleic acids and their modification (miRNA, lncRNA, circRNA, circulating tumor DNA and DNA methylation) acting as potential biomarkers in HCC diagnosis; (ii) concluding different patterns of three key noncoding RNAs (miRNA, lncRNA and circRNA) in gene regulation and (iii) outlining the progress of these novel nucleic acids for HCC diagnosis and therapy in clinical trials, and discuss their possibility for clinical applications. All in all, this review takes a detailed look at the advances of novel nucleic acids from potential of biomarkers and elaboration of mechanism to early clinical application in past 20 years.

The Regulatory Functions of Circular RNAs in Digestive System Cancers

Circular ribonucleic acids (circRNAs), which are a type of covalently closed circular RNA, are receiving increasing attention. An increasing amount of evidence suggests that circRNAs are involved in the biogenesis and development of multiple diseases such as digestive system cancers. Dysregulated circRNAs have been found to act as oncogenes or tumour suppressors in digestive system cancers. Moreover, circRNAs are related to ageing and a wide variety of processes in tumour cells, such as cell apoptosis, invasion, migration, and proliferation. Moreover, circRNAs can perform a remarkable multitude of biological functions, such as regulating splicing or transcription, binding RNA-binding proteins to enable function, acting as microRNA (miRNA) sponges, and undergoing translated into proteins. However, in digestive system cancers, circRNAs function mainly as miRNA sponges. Herein, we summarise the latest research progress on biological functions of circRNAs in digestive system cancers. This review serves as a synopsis of potential therapeutic targets and biological markers for digestive system cancer.

Biological Roles and Mechanisms of Circular RNA in Human Cancers

Circular RNA (circRNA) is an intriguing class of RNA with covalently closed-loop structure and is highly stable and conservative. As new members of the ncRNAs, the function, mechanism, potential diagnostic biomarker, and therapeutic target have raised increased attention. Most circRNAs are presented with characteristics of abundance, stability, conservatism, and often exhibiting tissue/developmental-stage-specific manner. Over 30,000 circRNAs have been identified with their unique structures to maintain stability more easily than linear RNAs. An increased numbers of circRNAs are dysregulated and involved in several biological processes of malignance, such as tumorigenesis, growth, invasion, metastasis, apoptosis, and vascularization. Emerging evidence suggests that circRNAs play important roles by acting as miRNA sponge or protein scaffolding, autophagy regulators, and interacting with RNA-binding protein (RBP), which may potentially serve as a novel promising biomarker for prevention, diagnosis and therapeutic target for treatment of human cancer with great significance either in scientific research or clinic arena. This review introduces concept, major features of circRNAs, and mainly describes the major biological functions and clinical relevance of circRNAs, as well as expressions and regulatory mechanisms in various types of human cancer, including pathogenesis, mode of action, potential target, signaling regulatory pathways, drug resistance, and therapeutic biomarkers. All of which provide evidence for the potential utilities of circRNAs in the diagnosis and treatment of cancer.

Circular RNA-0001283 Suppresses Breast Cancer Proliferation and Invasion via MiR-187/HIPK3 Axis

Background

Circular RNAs (circRNAs) are key regulators that take part in the carcinogenesis and development of breast cancer. The current study aimed to identify the expression of and explored the function of circRNA-0001283 in breast cancer.

Material/Methods

Breast cancer tissue samples were tested using high-throughput sequencing to identify the levels of relative genes; and proteins were addressed by using quantitative real-time polymerase chain reaction (qRT-PCR) and western-blot. Cell ability and cell apoptosis were investigated by Cell Counting Kit-8 (CCK-8) and flow cytometry. Invasion was detected by Transwell invasion assay. The identification of target genes was analyzed by dual-luciferase reporter assay.

Result

Downregulation of circRNA-0001283 expression was observed in breast cancer tissue samples. Ectopic expression of circRNA-0001283 remarkably suppressed cell viability and invasion, and induced apoptosis in breast cancer cells. Furthermore, circRNA-0001283 bound to miR-187 and decreased the expression of miR-187, which resulted in inhibition in cell growth and invasion. Finally, we showed that circRNA-0001283 positively regulated HIPK3 expression by sponging miR-187.

Conclusions

The results reveal a new functional circRNA-0001283 in breast cancer and may provide targets for developing novel therapeutic strategies for breast cancer.

Circ-ZKSCAN1 regulates FAM83A expression and inactivates MAPK signaling by targeting miR-330-5p to promote non-small cell lung cancer progression

Background

Circular RNAs (circRNAs) belong to a new type of endogenous non-coding RNA and plays a key role in carcinogenesis. Circ-ZKSCAN1 (hsa_circ_0001727) has been proven to be a tumor-dependent circRNA. However, its role in non-small cell lung cancer (NSCLC) has been underreported.

Methods

The expression patterns of circ-ZKSCAN1 were determined using qRT-PCR in NSCLC samples and cell lines. Cell proliferation was examined utilizing the CCK-8 assay. Cell migration and invasion were evaluated using the Transwell assay. The combination of circ-ZKSCAN1 and miR-330-5p in NSCLC cells was analyzed by RNA pull-down and luciferase reporter assay. We used the bioinformatics software circbank, CircInteractome, TargetScan and Miranda to predict circRNA-miRNA and miRNA-mRNA interactions.

Results

Our results showed that circ-ZKSCAN1 was significantly up-regulated in NSCLC, closely related to malignant characteristics and poor prognosis, and clinically related to tumor size and clinical stage. Subsequent experiments showed that circ-ZKSCAN1 could inhibit the growth of NSCLC cells in vitro and in vivo. Importantly, circ-ZKSCAN1 can act as a sponge of carcinogenic miR-330-5p to increase the expression of FAM83A, resulting in the inhibition of MAPK signal transduction pathway, thus promoting the progress of NSCLC. Interestingly, the increase in FAM83A expression caused by circ-ZKSCAN1 overexpression could in turn promote the expression of circ-ZKSCAN1.

Conclusions

Circ-ZKSCAN1 is a key positive regulator of NSCLC, and clarifies the potential molecular mechanism of the new circ-ZKSCAN1/miR-330-5p/FAM83A feedback loop in promoting the progress of NSCLC.

Role of miRNA sponges in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a leading cause of cancer-related deaths worldwide. HCC patients are commonly diagnosed at an advanced stage, for which highly effective therapies are limited. Hence, there is a growing need to discover promising biomarkers for HCC diagnosis, and in this context, microRNAs (miRNAs) hold great promise. MiRNAs function as gene expression regulators by directly binding messenger RNAs (mRNAs) and subsequently causing suppression of mRNA translation or degradation of target mRNAs. Two major types of noncoding RNAs act as competing endogenous sponges: circular RNAs and long non-coding RNAs.They can competitively bind to miRNA through miRNA response elements (MREs), thereby reducing the number of miRNAs binding mRNAs and regulating the expression of downstream target genes of miRNAs at the posttranscriptional level. The relationship between single miRNA sponge and HCC has been explored. However, comprehensive reviews on the sponge's function in HCC are lacking. In this review, we describe the methods to find endogenous sponges and construct exogenous sponges, and briefly compare endogenous and exogenous sponges. We also summarize the current progress on the functional role of miRNA sponges in HCC pathogenesis and present their potential value as diagnostic biomarkers and therapeutic targets. In-depth investigations on the function and mechanism of miRNA sponges in HCC will enrich our knowledge of HCC pathogenesis and contribute to the development of effective diagnostic biomarkers and therapeutic targets for HCC.

Circular RNA expression and circPTPRM promotes proliferation and migration in hepatocellular carcinoma

Circular RNAs (circRNAs) play a critical role during hepatocellular carcinoma (HCC) development. CircRNA PTPRM (circPTPRM) has not been reported to cause disease and its role in HCC is unclear. This study explored circRNA expression and the function of circPTPRM in HCC. RNA sequencing (RNA-seq) was performed on 3 randomly selected pairs of HCC tissues and their corresponding adjacent non-tumor tissues. Three differentially expressed circRNAs, circPTPRM, circSMAD2 and circPTBP3 were selected and verified by real-time quantitative reverse transcription-polymerase chain reactions in 30 pairs of tissue samples, In vitro cultured hepatoma cells, and normal liver cells. Clinical data analysis was performed to select target circRNAs. Anti-target circRNA siRNAs were transfected into hepatoma cell lines, and the biological behavior of hepatoma cells following silencing of the target circRNA were detected by cell proliferation, plate cloning, and transwell assays. There were 86 differentially expressed circRNAs from RNA-seq, of which 53 were significantly upregulated and 33 were significantly downregulated in HCC. CircPTPRM expression was significantly upregulated in HCC tissue (p = 0.023) based on the analysis of 30 paired samples. CircPTPRM expression positively correlated with HCC recurrence and metastasis (p = 0.039). CircPTPRM silencing reduced HCC cell proliferation, migration and invasion. CircRNAs were differentially expressed in HCC samples. CircPTPRM was significantly upregulated in HCC and may function during the tumorigenesis and metastasis of HCC.

Integration of Bioinformatic Predictions and Experimental Data to Identify circRNA-miRNA Associations

Circular RNAs (circRNAs) have recently emerged as a novel class of transcripts, characterized by covalently linked 3'-5' ends that result in the so-called backsplice junction. During the last few years, thousands of circRNAs have been identified in different organisms. Yet, despite their role as disease biomarker started to emerge, depicting their function remains challenging. Different studies have shown that certain circRNAs act as miRNA sponges, but any attempt to generalize from the single case to the "circ-ome" has failed so far. In this review, we explore the potential to define miRNA "sponging" as a more general function of circRNAs and describe the different approaches to predict miRNA response elements (MREs) in known or novel circRNA sequences. Moreover, we discuss how experiments based on Ago2-IP and experimentally validated miRNA:target duplexes can be used to either prioritize or validate putative miRNA-circRNA associations.

Circular RNAs in hepatocellular carcinoma: Biomarkers, functions and mechanisms

Hepatocellular carcinoma (HCC), a leading cause of cancer-related death with high invasive and metastatic potential, has a low survival rate. To improve the survival and quality of life in HCC patients, it is urgently needed to explore novel biomarkers for early diagnosis and prognosis of HCC, as well as therapeutic strategies. Circular RNAs (circRNAs) are a class of highly conserved, stable and abundant non-coding RNAs (ncRNAs) that can regulate gene expression at transcriptional or post-transcriptional levels. Recently, some circRNAs are identified to be potential biomarkers for HCC diagnosis and prognosis. Furthermore, some circRNAs are found to play oncogenic or suppressive roles in HCC progression by regulating various biological processes, including cell proliferation, migration, invasion and metastasis, epithelial-mesenchymal transition (EMT), as well as apoptosis. In this review, we summarize recent findings of deregulated circRNAs, their functions and molecular mechanisms in HCC, and discuss their potential roles as diagnostic biomarkers, prognostic biomarkers, as well as therapeutic targets for HCC.

Enhanced expression of circ_0000267 in hepatocellular carcinoma indicates poor prognosis and facilitates cell progression by sponging miR-646

Hepatocellular carcinoma (HCC) is a highly aggressive carcinoma worldwide. Circular RNAs (circRNAs) have been proved to be involved in the pathogenesis of several carcinomas. circ_0000267 was reported to be elevated in HCC tissue samples by circRNA microarray. In this study, quantitative reverse-transcription polymerase chain reaction was induced to further detect the expression of circ_0000267 in HCC tissues and cells. The clinical significance was also explored by Fisher's exact test, Kaplan-Meier curves and Cox regression analysis. Cell counting kit-8, colony formation, flow cytometry and transwell experiments were conducted on HCC cells to elucidate the functions of circ_0000267. Dual-luciferase reporter assay was induced to explore the mechanism of circ_0000267. Moreover, rescue experiments were also performed on HCC cells. As a result, circ_0000267 was enhanced in HCC tissues and cell lines. This upregulation is associated with patients' clinical severity and poor prognosis. Functionally, circ_0000267 could facilitate cell growth, migration and invasion and attenuate cell apoptosis in HCC cells. Mechanistically, circ_0000267 could directly sponge miR-646 to exert its oncogenic properties. In summary, we identified a novel HCC-associated circRNA in the progression of this fatal disease.

Circular RNA hsa_circ_0001649 inhibits hepatocellular carcinoma progression via multiple miRNAs sponge

Circular RNA (circRNA) exerts an essential role in tumor development. Hsa_circ_0001649 (circ-0001649) was produced at the SHPRH gene locus containing exon 26-29. This study analyzed the specific mechanism of circ-0001649 in influencing the development of hepatocellular carcinoma (HCC). Relative levels of circ-0001649 in HCC cell lines and tissues were examined by qRT-PCR. The direct binding between circ-0001649 and miR-127-5p/miR-612/miR-4688 were verified through Dual-luciferase reporter gene assay, RNA Binding Protein Immunoprecipitation (RIP) assay and western blot detection. In vitro and in vivo regulatory roles of circ-0001649 in proliferative and migratory abilities of HCC were evaluated by EdU, Transwell and tumourigenicity assay, respectively. Results showed that circ-0001649 was markedly decreased in hepatocellular carcinoma cell lines and tumor tissues. Overexpression of circ-0001649 greatly inhibited proliferation and migration of HCC in vitro and in vivo. More importantly, we confirmed that circ-0001649 regulated cellular behaviors of HCC cells by targeting SHPRH. Furthermore, we determined that circ-0001649 served as a ceRNA to sponge miR-127-5p, miR-612 and miR-4688, thus activating SHPRH. In summary, our study showed that circ-0001649 was lowly expressed in HCC and inhibited HCC progression via multiple miRNAs sponge.

Systematic Review and Meta-Analysis of the Utility of Circular RNAs as Biomarkers of Hepatocellular Carcinoma

Emerging studies have reported circRNAs were dysregulated in HCC. However, the clinical value of these circRNAs remains to be clarified. Herein, we aimed to comprehensively explore their association with the diagnosis, prognosis, and clinicopathological characteristics of HCC. PubMed, EMBASE, Web of Science, and Cochrane Library databases were comprehensively searched for eligible studies up to October 30, 2018. The diagnostic effect was evaluated by the pooled sensitivity, specificity, and other indexes. The pooled hazard ratio (HR) for overall survival (OS) and recurrence free survival (RFS) was calculated to assess the prognostic value. Ten studies on diagnosis, 12 on prognosis, and 23 on clinicopathology were identified from the databases. A total of 11 upregulated and 11 downregulated circRNAs showed an association with clinicopathological features of HCC. For the diagnosis analyses, the pooled sensitivity, specificity, positive likelihood ratio (PLR), negative likelihood ratio (NLR), and diagnostic odds ratio (DOR) of circRNAs for HCC were 0.74 (95%CI: 0.65-0.82) and 0.76 (95%CI: 0.70-0.81), 3.1 (95%CI: 2.5-3.8), 0.34 (95%CI: 0.25-0.47), and 9 (95%CI: 6-14), respectively. The area under SROC curve (AUC) was 0.81 (95% CI: 0.78-0.84), indicating moderate diagnostic accuracy. In stratified analyses, the diagnostic performance of circRNAs varied based on the source of control and specimen type. For the prognosis analyses, increased expression of upregulated circRNAs was associated with worse OS (HR: 3.67, 95%: 2.07-6.48), while high expression of downregulated circRNAs was associated with better OS (HR: 0.38, 95%: 0.30-0.48). In conclusion, this study reveals that circRNAs may serve as promising diagnostic and prognostic biomarkers for HCC. However, further investigations are still required to explore the clinical value of circRNAs.

Biogenesis and Function of Circular RNAs in Health and in Disease

Circular RNAs (circRNAs) are a class of non-coding RNA that were previously thought to be insignificant byproducts of splicing errors. However, recent advances in RNA sequencing confirmed the presence of circRNAs in multiple cell lines and across different species suggesting a functional role of this RNA species. CircRNAs arise from back-splicing events resulting in a circular RNA that is stable, specific and conserved. They can be generated from exons, exon-introns, or introns. CircRNAs have multifaceted functions. They are likely part of the competing endogenous RNA class. They can regulate gene expression by sponging microRNAs, binding proteins or they can be translated into a protein themselves. CircRNAs have been associated with health and disease, some with disease protective effects, some with disease promoting functions. The widespread expression and disease regulatory mechanisms endow circRNAs to be used as functional biomarkers and therapeutic targets for a variety of different disorders. In this concise article we provide an overview of the association of circRNAs with various diseases including cancer, cardiovascular and kidney disease as well as cellular senescence. We conclude with an assessment of the current status and future outlook of this new field of research that carries immense potential with respect to diagnostic and therapeutic approaches of a variety of diseases.

Reconstruction and analysis of circRNA‑miRNA‑mRNA network in the pathology of cervical cancer

The present study was performed with the aim of understanding the mechanisms of pathogenesis and providing novel biomarkers for cervical cancer by constructing a regulatory circular (circ)RNA‑micro (mi)RNA‑mRNA network. Using an adjusted P-value of <0.05 and an absolute log value of fold-change >1, 16 and 156 miRNAs from GSE30656 and The Cancer Genome Atlas (TCGA), 5,321 mRNAs from GSE63514, 4,076 mRNAs from cervical squamous cell carcinoma and endocervical adenocarcinoma (from TCGA) and 75 circRNAs from GSE102686 were obtained. Using RNAhybrid, Venn and UpSetR plot, 12 circRNA‑miRNA pairs and 266 miRNA‑mRNA pairs were obtained. Once these pairs were combined, a circRNA‑miRNA‑mRNA network with 11 circRNA nodes, 4 miRNA nodes, 153 mRNA nodes and 203 edges was constructed. By constructing the protein‑protein interaction network using Molecular Complex Detection scores >5 and >5 nodes, 7 hubgenes (RRM2, CEP55, CHEK1, KIF23, RACGAP1, ATAD2 and KIF11) were identified. By mapping the 7 hubgenes into the preliminary circRNA‑miRNA‑mRNA network, a circRNA‑miRNA‑hubgenes network consisting of 5 circRNAs (hsa_circRNA_000596, hsa_circRNA_104315, hsa_circRNA_400068, hsa_circRNA_101958 and hsa_circRNA_103519), 2 mRNAs (hsa‑miR‑15b and hsa‑miR‑106b) and 7 mRNAs (RRM2, CEP55, CHEK1, KIF23, RACGAP1, ATAD2 and KIF11) was constructed. There were 22 circRNA‑miRNA‑mRNA regulatory axes identified in the subnetwork. By analyzing the overall survival for the 7 hubgenes using the Gene Expression Profiling Interactive Analysis tool, higher expression of RRM2 was demonstrated to be associated with a significantly poorer overall survival. PharmGkb analysis identified single nucleotide polymorphisms (SNPs) of rs5030743 and rs1130609 of RRM2, which can be treated with cladribine and cytarabine. RRM2 was also indicated to be involved in the gemcitabine pathway. The 5 circRNAs (hsa_circRNA_000596, hsa_circRNA_104315, hsa_circRNA_400068, hsa_circRNA_101958 and hsa_circRNA_103519) may function as competing endogenous RNAs and serve critical roles in cervical cancer. In addition, cytarabine may produce similar effects to gemcitabine and may be an optional chemotherapeutic drug for treating cervical cancer by targeting rs5030743 and rs1130609 or other similar SNPs. However, the specific mechanism of action should be confirmed by further study.

Elevated expression of circular RNA circ_0008450 predicts dismal prognosis in hepatocellular carcinoma and regulates cell proliferation, apoptosis, and invasion via sponging miR-548p

Hepatocellular carcinoma (HCC) is one of the most frequent malignancies and a main cause of global cancer mortality. In the past decade, circular RNAs (circRNAs) have been proved to play key roles in various cancers. Previously, circ_0008450 was identified upregulated in HCC tissues by high-throughput circRNA sequencing. In this study, quantitative real-time polymerase chain reaction was used to evaluate the expression level of circ_0008450 in human HCC tumor and corresponding nontumor tissue samples, and the association between circ_0008450 expression and clinicopathologic features of patients with HCC was also analyzed. After that, the functions of circ_0008450 in biological behaviors of HCC cells were determined by cell counting kit-8, colony formation, flow cytometry, and the transwell assays. The mechanism of circ_0008450 was explored by the bioinformatic analysis and dual-luciferase reporter assay. The expression of circ_0008450 is upregulated in HCC tissue specimens and cell lines. Patients with a high circ_0008450 expression usually bear a lower 5-year survival rate. Silencing of circ_0008450 in Huh-7 cells inhibited cell viability, migration, and invasion, whereas cell apoptosis was increased. Conversely, its overexpression in HepG2 cells leads to absolutely inverse results. In addition, circ_0008450 was proved to be a sponge of miR-548p. The oncogenic role of circ_0008450 was partially attributed to its suppression on miR-548p. This study implies a new target for the treatment of HCC.