A Noncoding Regulatory RNAs Network Driven by Circ-CDYL Acts Specifically in the Early Stages Hepatocellular Carcinoma

Regulation of cell signaling pathways by circular RNAs and microRNAs in different cancers: Spotlight on Wnt/β-catenin, JAK/STAT, TGF/SMAD, SHH/GLI, NOTCH and Hippo pathways

Groundbreaking discoveries in molecular oncology have leveraged our understanding altogether to a new level. Mapping of plethora of cell signaling pathways has enabled researchers to drill down deep into the intermeshed regulatory networks which crosstalk to promote carcinogenesis and metastasis. More importantly, discovery of non-coding RNAs has added new layers of complexity to already complicated nature of cell signaling pathways. The discovery of circular RNAs (circRNAs) has opened the door to an ever-widening understanding of cellular processes that are controlled or influenced by circRNAs. In this review, we have summarized most recent advancements in our understanding related to interplay between circular RNAs and microRNAs for the regulation of NOTCH, Wnt/β-catenin, Hippo, SHH/GLI, JAK/STAT and TGF/SMAD pathways in different cancers.

Circular RNA hsa_circ_101555 promotes hepatocellular carcinoma cell proliferation and migration by sponging miR-145-5p and regulating CDCA3 expression

Circular RNAs have been reported to play significant roles in regulating pathophysiological processes while also guiding clinical diagnosis and treatment of hepatocellular carcinoma (HCC). However, only a few circRNAs have been identified thus far. Herein, we investigated the role of a specific closed-loop structure of hsa_circ_101555 that was generated by back-splicing of the host gene casein kinase 1 gamma 1 (CSNK1G1) in the development and proliferation of HCC. We investigated the expression of Hsa_circ_101555 in HCC and normal tissues using bioinformatics. The expression level of hsa_circ_101555 was further detected by fluorescence in situ hybridization and qRT-PCR in ten HCC patients. Transwell, migration, WST-1 assays, and colony formation assays were used to evaluate the role of hsa_circ_101555 in HCC development and proliferation. The regulatory mechanisms of hsa_circ_101555 in miR-145-5p and CDCA3 were determined by dual luciferase reporter assay. A mouse xenograft model was also used to determine the effect of hsa_circ_101555 on HCC growth in vivo. hsa_circ_101555 showed greater stability than the linear RNA; while in vitro and in vivo results demonstrated that hsa_circ_101555 silencing significantly suppressed cell proliferation, migration, and invasion of HCC cells. Rescue experiments further demonstrated that suppression of miR-145-5p significantly attenuated the biological effects of hsa_circ_101555 knockdown in HCC cells. We also identified a putative oncogene CDCA3 as a potential miR-145-5p target. Thus, our results demonstrated that hsa_circ_101555 might function as a competing endogenous RNA of miR-145-5p to upregulate CDCA3 expression in HCC. These findings suggest that hsa_circ_101555 may be a potential therapeutic target for patients with HCC.

Ferroptosis is involved in the progression of hepatocellular carcinoma through the circ0097009/miR-1261/SLC7A11 axis

Background

Circular RNAs (circRNAs) are a class of non-coding RNAs that have been demonstrated to play important roles in tumorigenesis. However, how circRNAs regulate the progression of hepatocellular cancer (HCC) remains unclear.

Methods

In the present study, circRNA microarray analyses were performed with HCC tissues to identify circRNAs that are differentially expressed. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis was conducted on HCC cell lines and tissues, and circ0097009 was found to be significantly upregulated. The functions of circ0097009 in HCC were investigated by a series of experiments, including cell proliferation, invasion, and mouse xenograft assays. Additionally, luciferase assays and RNA immunoprecipitation (RIP) assays were used to explore the interactions of circ0097009, microRNA-1261 (miR-1261), and solute carrier family 7 member 11 (SLC7A11) in HCC.

Results

Microarray analysis and qRT-PCR verified that circRNA, circ0097009, was significantly upregulated in HCC tissues and cell lines. Knockdown of circ0097009 inhibited the proliferation and invasion of HCC cells. Luciferase reporter assays showed that circ0097009 and SLC7A11 directly bound to miR-1261. Subsequent experiments showed that circ0097009 and SLC7A11 reciprocally regulated their expression via miR-1261 sponging by circ0097009.

Conclusions

Circ0097009 acts as a competing endogenous RNA to regulate the expression of SLC7A11, a key regulator of cancer cell ferroptosis, by sponging miR-1261 in HCC. Circ0097009 may be used as a diagnostic biomarker for HCC and as a potential target for HCC therapy.

The role of miRNA, lncRNA and circRNA in the development of intervertebral disk degeneration (Review)

Intervertebral disc degeneration (IVDD) is a degenerative musculoskeletal disorder with multiple causative factors, such as age, genetics, mechanics and life style. IVDD contributes to non-specific lower back pain (NLBP), which is a globally prevalent and debilitating musculoskeletal disorder. NLBP has a substantial impact on medical resources and creates an economic burden for the public. Dysregulated phenotypes of nucleus pulposus (NP) cells and endplate chondrocytes, such as proliferation, senescence and apoptosis, along with aberrant expression of extracellular matrix components, including type II collagen and aggrecan, are involved in the pathological process of IVDD. Evidence indicates that non-coding RNAs, mainly microRNAs (miRNAs), long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs), play a vital role in the development of IVDD. In the present review, the potential molecular mechanisms of miRNAs, lncRNAs and circRNAs in the initiation and progression of IVDD were described based on the latest literature. Furthermore, ways to influence the functions of NP cells and endplate chondrocytes in IVDD were also summarized. The presented insights suggested that non-coding RNAs may function as potential targets for the treatment of IVDD.

Functions of circular RNAs in bladder, prostate and renal cell cancer (Review)

Circular RNAs (circRNAs) are a class of non-coding RNAs formed by covalently closed loops through back-splicing and exon-skipping. circRNAs have been confirmed to play a vital role in various biological functions, acting as microRNA sponges and reservoirs, as well as combining with RNA-binding proteins during the progression of multiple cancer types. Therefore, the present review evaluated recent research articles in PubMed that were published between November 2017 and September 2020. Key word search strings included: ‘Circular RNA (circRNA) AND bladder cancer (BC)’, ‘circular RNA (circRNA) AND prostate cancer (PCa)’ and ‘circular RNA (circRNA) AND renal cell cancer (RCC)’. In total, >58 circRNAs were found to be implicated in urological cancers, with several of the circRNAs targeting common carcinogenic pathways, such as the AKT, TGF-β, MAPK, VEGF and even metabolic pathways. circRNAs are important modulators of BC, PCa and RCC. circRNAs are functionally implicated in the pathogenesis of these cancer types, and have been found to act as biomarkers for the diagnosis and prognosis of urological cancer. However, to the best of our knowledge, the functions of circRNAs in tumors of the urinary system remain largely unknown and require further research.

Notch Signaling Regulation in HCC: From Hepatitis Virus to Non-Coding RNAs

The Notch family includes evolutionary conserved genes that encode for single-pass transmembrane receptors involved in stem cell maintenance, development and cell fate determination of many cell lineages. Upon activation by different ligands, and depending on the cell type, Notch signaling plays pleomorphic roles in hepatocellular carcinoma (HCC) affecting neoplastic growth, invasion capability and stem like properties. A specific knowledge of the deregulated expression of each Notch receptor and ligand, coupled with resultant phenotypic changes, is still lacking in HCC. Therefore, while interfering with Notch signaling might represent a promising therapeutic approach, the complexity of Notch/ligands interactions and the variable consequences of their modulations raises concerns when performed in undefined molecular background. The gamma-secretase inhibitors (GSIs), representing the most utilized approach for Notch inhibition in clinical trials, are characterized by important adverse effects due to the non-specific nature of GSIs themselves and to the lack of molecular criteria guiding patient selection. In this review, we briefly summarize the mechanisms involved in Notch pathway activation in HCC supporting the development of alternatives to the γ-secretase pan-inhibitor for HCC therapy.

Identification of Plasma hsa_circ_0005397 and Combined With Serum AFP, AFP-L3 as Potential Biomarkers for Hepatocellular Carcinoma

Background: Mounting evidence has demonstrated that circular RNA (circRNA) plays crucial roles in the occurrence and development of hepatocellular carcinoma (HCC). However, the expression pattern and clinical application value of plasma circRNA in HCC are still largely unknown. Herein, we explored the role of plasma hsa_circ_0005397 in diagnosis and prognosis of HCC.

Methods: The expression level of plasma hsa_circ_0005397 was measured by quantitative real-time polymerase chain reaction (qRT-PCR). The identification and origin of plasma hsa_circ_0005397 were confirmed by RNase R assay, Sanger sequencing and HCC cell culture. In addition, its diagnostic value was assessed by receiver operating characteristic (ROC) curve and prognostic value was evaluated by dynamics monitoring and Kaplan–Meier curve analyses in HCC patients.

Results: The expression of plasma hsa_circ_0005397 was higher in patients with HCC than that in patients with benign liver diseases and healthy controls (both p < 0.05). Moreover, it was closely correlated with tumor size (p = 0.020) and TNM stage (p = 0.006) of HCC patients. The area under the ROC curve of plasma hsa_circ_0005397 was 0.737 and 95% confidence interval was 0.671–0.795. Furthermore, the combination of plasma hsa_cic_0005397, serum AFP and AFP-L3 could improve the diagnostic sensitivity of HCC. Additionally, dynamic monitoring plasma hsa_cic_0005397 might help us predict recurrence or metastasis in HCC patients after surgical resection. Besides, the increased plasma hsa_cic_0005397 was closely correlated with shorter overall survival of HCC patients (p = 0.007).

Conclusion: Plasma has_circ_0005397 represents a novel noninvasive biomarker for HCC. Moreover, the combination of plasma hsa_cic_0005397, serum AFP and AFP-L3 might improve the diagnostic value for HCC.

The Latest Overview of circRNA in the Progression, Diagnosis, Prognosis, Treatment, and Drug Resistance of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the main causes of tumor-related deaths worldwide. Due to the lack of obvious early symptoms and the lack of sensitive screening indicators in the early stage of HCC, the vast majority of patients are diagnosed with advanced or metastatic HCC, resulting in dissatisfactory treatment result. Therefore, it is urgent to determine effective and sensitive diagnostic and prognostic indicators and to determine new therapeutic targets. Circular RNA (circRNA) is a type of non-coding RNA that has been neglected for a long time. In recent years, it has been proved to play an important role in the development of many human diseases. Increasing evidence shows that change in circRNA expression has an extensive effect on the biological behavior of HCC. In this study, we comprehensively tracked the latest progress of circRNA in the pathogenesis of HCC, and reviewed its role as a biomarker for diagnosis and prognosis prediction in patients with HCC. In addition, we also summarized the potential of circRNA as therapeutic target in HCC and its relationship with HCC drug resistance, providing clues for the clinical development of circRNA-based therapeutic strategies.

pH-responsive delivery vehicle based on RGD-modified polydopamine-paclitaxel-loaded poly (3-hydroxybutyrate-co-3-hydroxyvalerate) nanoparticles for targeted therapy in hepatocellular carcinoma

A limitation of current anticancer nanocarriers is the contradiction between multiple functions and favorable biocompatibility. Thus, we aimed to develop a compatible drug delivery system loaded with paclitaxel (PTX) for hepatocellular carcinoma (HCC) therapy. A basic backbone, PTX-loaded poly (3-hydroxybutyrate-co-3-hydroxyvalerate) PHBV nanoparticle (PHBV-PTX-NPs), was prepared by emulsion solvent evaporation. As a gatekeeper, the pH-sensitive coating was formed by self-polymerization of dopamine (PDA). The HCC-targeted arginine-glycine-aspartic acid (RGD)-peptide and PDA-coated nanoparticles (NPs) were combined through the Michael addition. Subsequently, the physicochemical properties of RGD-PDA-PHBV-PTX-NPs were characterized by dynamic light scattering-autosizer, transmission electron microscope, fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetry and X-ray spectroscopy. As expected, the RGD-PDA-PHBV-PTX-NPs showed robust anticancer efficacy in a xenograft mouse model. More importantly, they exhibited lower toxicity than PTX to normal hepatocytes and mouse in vitro and in vivo, respectively. Taken together, these results indicate that the RGD-PDA-PHBV-PTX-NPs are potentially beneficial for easing conflict between multifunction and biocompatible characters of nanocarriers.

Circular RNA circARPP21 Acts as a Sponge of miR-543 to Suppress Hepatocellular Carcinoma by Regulating LIFR

Background

A large body of evidence has shown that circular RNAs (circRNAs) play a significant role in the progression of some malignant cancers, including hepatocellular carcinoma (HCC). However, the complex mechanism of circRNAs in hepatocellular carcinoma has not been clarified.

Methods

We identified circRNAs by microarray analysis and quantitative real-time polymerase chain reaction (RT-qPCR). We also carried out bioinformatics analysis, luciferase reporter assays, and RNA pull-down assays to define the relationship between microRNA (miR)-543 and circARPP21. Through silencing and overexpression of circARPP21, we investigated the effects of circARPP21 on proliferation, migration, and invasion abilities of HCC cells in vitro and in vivo.

Results

In this study, we found that a novel circRNA, circARPP21 (hsa_circ_0123629), exerts a strong effect on HCC progression. Reduced expression of circARPP21 in HCC patients is correlated with larger tumor size, higher tug-lymph node metastasis (TNM) stage, and poor prognosis as indicated by elevated levels of alpha-fetoprotein (AFP). Conversely, higher expression of circARPP21 can increase leukemia inhibitory factor receptor (LIFR) expression by sponging miR-543. Finally, overexpression of miR-543 can reverse the anti-proliferation and anti-metastasis effects of circARPP21.

Conclusion

The circARPP21/miR-543/LIFR axis suppresses the proliferation, invasion, and migration of hepatocellular carcinoma cells. In addition, circARPP21 can serve as a biomarker in HCC, thus offering a potential new approach to HCC therapy.

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.

Identification of an autophagy-related gene signature predicting overall survival for hepatocellular carcinoma

The poor prognosis of hepatocellular carcinoma (HCC) calls for the development of accurate prognostic models. The growing number of studies indicating a correlation between autophagy activity and HCC indicates there is a commitment to finding solutions for the prognosis of HCC from the perspective of autophagy. We used a cohort in The Cancer Genome Atlas (TCGA) to evaluate the expression of autophagy-related genes in 371 HCC samples using univariate Cox and lasso Cox regression analysis, and the prognostic features were identified. A prognostic model was established by combining the expression of selected genes with the multivariate Cox regression coefficient of each gene. Eight autophagy-related genes were selected as prognostic features of HCC. We established the HCC prognostic risk model in TCGA dataset using these identified prognostic genes. The model's stability was confirmed in two independent verification sets (GSE14520 and GSE36376). The model had a good predictive power for the overall survival (OS) of HCC (hazard ratio = 2.32, 95% confidence interval = 1.76-3.05, P<0.001). Moreover, the risk score computed by the model did not depend on other clinical parameters. Finally, the applicability of the model was demonstrated through a nomogram (C-index = 0.701). In the present study, we established an autophagy-related risk model having a high prediction accuracy for OS in HCC. Our findings will contribute to the definition of prognosis and establishment of personalized therapy for HCC patients.

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.

Circular RNA CircCDYL Regulates Proliferation and Apoptosis in Non-Small Cell Lung Cancer Cells by Sponging miR-185-5p and Upregulating TNRC6A

Aim

A series of research reveal that circular RNA (circRNA) plays a vital role in regulating the development of tumor cells. In this research, we would explore the role and mechanism of circCDYL in non-small cell lung cancer (NSCLC).

Methods

RT-PCR was performed to detect the expression of circCDYL in NSCLC tissues, plasma, and cell lines. The tumor cell proliferation ability was evaluated by clone formation assay, and cell cycle determination. Flow cytometry was used to detect apoptosis in NSCLC cell lines. Western blot and RT-PCR were used to assess the expression of proteins and genes. Luciferase assay was performed to confirm the relationship of circRNA-miRNA-mRNA.

Results

The decreased level of circCDYL was observed in NSCLC patients' tissues and plasma, which was also downregulated in NSCLC cell lines. Forced expression of circCDYL inhibited cell viability, proliferation and induced apoptosis in A549 cells. Luciferase assay verified that circCDYL could bind with miR-185-5p and confirmed that TNRC6A was a downstream target of miR-185-5p. Overexpression of miR-185-5p or silencing of TNRC6A could inhibit the anti-tumor effect of circCDYL in A549 cells via regulating the ERK1/2 signal.

Conclusion

Here, we revealed that circCDYL inhibited proliferation and induced apoptosis in NSCLC cell lines via regulating ERK1/2 signal, and the mechanism of this progression may target miR-185-5p/TNRC6A, which provided a theoretical basis for clinical therapy.

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.

A PCR-free screen-printed magnetic electrode for the detection of circular RNA from hepatocellular cancer based on a back-splice junction

Circular RNA (circRNA) has the potential to be applied to disease diagnosis and therapy. However, the currently available circRNA detection techniques are limited. This work proposes a sensitive and selective approach for circRNA detection based on gold nanoparticle-modified screen-printed magnetic electrodes (AuNPs-SPME). Magnetic beads (MBs) with capture probes based on specific back-splice junction (BSJ) sites were employed to identify and selectively isolate the target circRNA, which could be directly adsorbed onto the AuNPs-SPME. Then, the circRNA attached to the surface was detected by changes in the methylene blue redox signal. The simple and time-saving AuNPs-SPME is highly sensitive (LOD = 1.0 pM) to circCDYL, one of the biomarkers of hepatocellular cancer (HCC). The analytical performance of the method presented has also been verified in human serum samples, holding great promise for clinical diagnosis.

Functional magnetic beads with capture probes based on specific back-splice junction sites were employed to identify and selectively isolate target circRNA.

A novel HDGF-ALCAM axis promotes the metastasis of Ewing sarcoma via regulating the GTPases signaling pathway

Ewing sarcoma (ES) is a type of highly aggressive pediatric tumor in bones and soft tissues and its metastatic spread remains the most powerful predictor of poor outcome. We previously identified that the transcription factor hepatoma-derived growth factor (HDGF) promotes ES tumorigenesis. However, the mechanisms underlying ES metastasis remain unclear. Here, we show that HDGF drives ES metastasis in vitro and in vivo, and HDGF reduces metastasis-free survival (MFS) in two independent large cohorts of human ES patients. Integrative analyses of HDGF ChIP-seq and gene expression profiling in ES cells reveal that HDGF regulates multiple metastasis-associated genes, among which activated leukocyte cell adhesion molecule (ALCAM) emerges as a major HDGF target and a novel metastasis-suppressor in ES. HDGF down-regulates ALCAM, induces expression and activation of the downstream effectors Rho-GTPase Rac1 and Cdc42, and promotes actin cytoskeleton remodeling and cell-matrix adhesion. In addition, repression of ALCAM and activation of Rac1 and Cdc42 are required for the pro-metastatic functions of HDGF in vitro. Moreover, analyses in murine models with ES tumor orthotopic implantation and experimental metastasis, as well as in human ES samples, demonstrate the associations among HDGF, ALCAM, and GTPases expression levels. Furthermore, high HDGF/low ALCAM expression define a subgroup of patients harboring the worst MFS. These findings suggest that the HDGF/ALCAM/GTPases axis represents a promising therapeutic target for limiting ES metastasis.

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.

Hepatoma-derived growth factor participates in concanavalin A-induced hepatitis

Hepatitis is an important health problem worldwide. Novel molecular targets are in demand for detection and management of hepatitis. Hepatoma-derived growth factor (HDGF) has been delineated to participate in hepatic fibrosis and liver carcinogenesis. However, the relationship between hepatitis and HDGF remains unclear. This study aimed to elucidate the role of HDGF during hepatitis using concanavalin A (ConA)-induced hepatitis model. In cultured hepatocytes, ConA treatment-elicited HDGF upregulation at transcriptional level and promoted HDGF secretion while reducing intracellular HDGF protein level and cellular viability. Similarly, mice receiving ConA administration exhibited reduced hepatic HDGF expression and elevated circulating HDGF level, which was positively correlated with serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels. By using HDGF knockout (KO) mice, it was found the ConA-evoked cell death was prominently alleviated in KO compared with control. Besides, it was delineated HDGF ablation conferred protection by suppressing the ConA-induced neutrophils recruitment in livers. Above all, the ConA-mediated activation of tumor necrosis factor-α (TNF-α)/interleukin-1β (IL-1β)/interleukin-6 (IL-6)/cyclooxygenase-2 (COX-2) inflammatory signaling was significantly abrogated in KO mice. Treatment with recombinant HDGF (rHDGF) dose-dependently stimulated the expression of TNF-α/IL-1β/IL-6/COX-2 in hepatocytes, further supporting the pro-inflammatory function of HDGF. Finally, application of HDGF antibody not only attenuated the ConA-mediated inflammatory cascade in hepatocytes, but also ameliorated the ConA-induced hepatic necrosis and AST elevation in mice. In summary, HDGF participates in ConA-induced hepatitis via neutrophils recruitment and may constitute a therapeutic target for acute hepatitis.

Competing Endogenous RNA (ceRNA) Network Analysis of Autophagy-Related Genes in Hepatocellular Carcinoma

Purpose

Autophagy plays an important role in the occurrence and development of hepatocellular carcinoma (HCC). We aimed to develop an autophagy-related genes signature predicting the prognosis of HCC and to depict a competing endogenous RNA (ceRNA) network.

Methods

Differentially expressed autophagy-related genes (DE-ATGs), miRNAs and lncRNAs and clinical data of HCC patients were extracted from TCGA. The GO and KEGG analysis were performed to investigate the gene function. Univariate and multivariate Cox regression analysis were used to identify a prognostic signature with the DE-ATGs. And a nomogram, adapted to the clinical characteristics, was established. Then, we established a ceRNA network related to autophagy genes.

Results

We screened out 27 differentially expressed genes which were enriched in GO and KEGG pathways related to autophagy and cancers. In univariate and multivariate Cox regression analysis, BIRC5, HSPB8, and SQSTM1 were screened out to establish a prognostic risk score model (AUC=0.749, p<0.01). Kaplan-Meier survival analysis showed that the overall survival of high-risk patients was significantly worse. Furthermore, the signature was validated in the other two independent databases. The nomogram, including the autophagy-related risk signature, gender, stage and TNM, was constructed and validated (C-index=0.736). Finally, the ceRNA network was established based on DE-ATGs, differentially expressed miRNAs and lncRNAs.

Conclusion

We constructed a reliable prognostic model of HCC with autophagy-related genes and depicted a ceRNA network of DE-ATGs in HCC which provides a basis for the study of post-transcriptional modification and regulation of autophagy-related genes in HCC.

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.

Circular RNAs in cancer: limitations in functional studies and diagnostic potential

Circular RNAs (circRNAs) are a large class of noncoding RNAs, generated from a process called back-splicing, that possess critical regulatory functions in many cellular events. A large body of literature has reported various circRNA functions and their underlying mechanisms, including sponging miRNA, exerting transcriptional and translational regulation, interacting with proteins, and translating into peptides and proteins. CircRNA dysregulation has been implicated in many cancers, including lung, breast, liver, gastric, colorectal, and ovarian cancer. They are detectable in bodily fluids and relatively stable, making them potential cancer biomarker candidates. Furthermore, targeting circRNA expression levels is a potential therapeutic approach for treating cancers. In this review, we describe the functional mechanisms of circRNAs and discuss limitations of current mechanism studies. Following this, we outline the potential of circRNAs to be effective biomarkers in various cancers and present circRNA-based therapeutic approaches. Finally, we discuss challenges in using circRNAs as diagnostic and therapeutic tools and propose future research directions.

Comprehensive analysis of TGF-β-induced mRNAs and ncRNAs in hepatocellular carcinoma

Transforming growth factor β (TGF-β) is a potent inducer of epithelial-mesenchymal transition (EMT) in hepatocellular carcinoma (HCC), and plays a critical role in its tumorigenesis and progression. Accumulating evidence indicates that protein-coding mRNAs, as well as non-coding RNAs (ncRNAs), may play key roles in the tumorigenesis and progression of HCC. In this study, we first report on the differential expression of lncRNAs, mRNAs, miRNAs, and circRNAs in Huh7 cells treated with TGF-β or DMSO for 7 days. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were performed for significantly differentially expressed RNAs (DE RNAs). Then the competing endogenous RNA (ceRNA) network based on these DE RNAs was predicted and constructed. Among them, we identified that lncRNA SLC7A11-AS1 and hsa_circ_0006123 are involved in the EMT process induced by TGF-β and may promotes the metastasis of HCC. This knowledge may pave the way to develop novel clinical diagnostics and therapeutic approaches. Our study might open a new avenue for future investigations of the molecular mechanisms driving the EMT process induced by TGF-β in HCC.

Circular RNAs in gastrointestinal cancer: Current knowledge, biomarkers and targeted therapy (Review)

Circular RNAs (circRNAs) are a type of endogenous non‑coding RNAs that are connected at the 3' and 5' ends by exon or intron cyclization, which forms a covalently closed loop. They are stable, well conserved, exhibit specific expression in mammalian cells and can function as microRNA (miRNA or miR) sponges to regulate the target genes of miRNAs, which influences biological processes. Such as tumor proliferation, invasion, metastasis, apoptosis and tumor stage. circRNAs represent promising candidates for clinical diagnosis and treatment. In the present review, the biogenesis, classification and functions of circRNAs in tumors are briefly summarized and discussed. In addition, the participation of circRNAs in signal transduction pathways regulating gastrointestinal cancer cellular functions is highlighted.

Emerging role of circular RNA in intervertebral disc degeneration: Knowns and unknowns (Review)

Lower back pain (LBP) is one of the predominant factors contributing to dyskinesia and remains a serious social and economic burden worldwide. Intervertebral disc degeneration (IDD) is the leading cause of LBP; the existing IDD treatments cannot completely prevent IDD. Circular RNAs (circRNAs) are non‑coding RNAs resulting from back‑splicing with unique structural characteristics and functions. Accumulating evidence suggests that circRNAs are involved in the pathological process of IDD and modulate a range of IDD‑related genes or proteins. However, the underlying circRNA‑mediated regulatory mechanisms remain poorly understood. The aim of the present review is to describe the current understanding of circRNA characteristics, classification, biogenesis and function in relation to its specific roles in IDD. Additionally, the limitations on the current knowledge in the field and the future direction of IDD‑related research are also discussed.

The roles of circRNAs in cancers: Perspectives from molecular functions

Circular RNAs (circRNAs), characteristic of covalently closed loops generated by back-splicing, are a subclass of single-stranded RNA molecules. Owing to the circular structures, circRNAs are protected from exonuclease-induced degradation, which makes them more stable compared with linear RNAs. With the development of high-throughput sequencing technology and bioinformatics, the roles of circRNAs in a variety of physiological and pathophysiological processes have been increasingly revealed. Although the functions of most circRNAs remain largely elusive, accumulating studies have identified them as microRNA(miRNA) sponges, protein regulators, transcriptional regulators, protein templates, and so forth. In this review, we briefly describe the biogenesis of circRNAs and provide an overview on their functions in cancers, including miRNA sponges, protein regulators, transcriptional regulators, protein templates. Furthermore, we discuss the potential application of circRNAs as biomarkers and give insight into future perspectives.

Circular RNAs and cancer: Opportunities and challenges

Circular RNAs (circRNAs) are covalently circularized RNA moieties that despite being relatively abundant were only recently identified and have only begun to be investigated within the last couple of years. Even though there are many thousands of genes that appear capable of producing circRNAs, and the fact that many circRNAs appear to be highly evolutionarily conserved, the function of all but a few remain to be fully explored. What has been determined, however, is that circRNAs play key regulatory roles in many aspects of biology with focus being given to their function in cancer. Most of the studies to date have found that circRNAs act as master regulator of gene expression most often than not acting to regulate levels though sequestration or "sponging" of other gene expression regulators, particularly miRNAs. They can also function directly modulating transcription, or by interfering with splicing mechanisms. Some circRNAs can also be translated into functional proteins or peptides. A combination of tissue and developmental stage specific expression along with an innate resistance to RNAse activity means that circRNAs show perhaps their greatest potential as novel biomarkers of cancer. In this chapter we consider the current state of knowledge regarding these molecules, their synthesis, function, and association with cancer. We also consider some of the challenges that remain to be overcome to allow this emerging class of RNAs to fulfill their potential in clinical practice.

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.

Hepatocellular Carcinoma-associated microRNAs Induced by Hepatoma-derived Growth Factor Stimulation

BACKGROUND/AIM

Hepatoma-derived growth factor (HDGF) is involved in the progression of hepatocellular carcinoma (HCC). The present study assessed the epigenomic changes in hepatoma-derived cells through HDGF stimulation.

MATERIALS AND METHODS

We used two hepatoma-derived cell lines (HepG2 and SK-Hep1) and searched for microRNAs whose expression commonly changed in response to HDGF administration. We further explored a genetic database to investigate the association of the candidate microRNAs with the survival of HCC patients.

RESULTS

Despite both HepG2 and SK-Hep1 cells being categorized as hepatoma-derived cells, the microRNA profile differed between these two lines. However, HepG2 and SK-Hep1 cells shared 30 up-regulated and 2 down-regulated microRNAs. Of these, miR-6072 and miR-3137 were significantly associated with a poor prognosis in HCC patients.

CONCLUSION

We identified two candidate microRNAs whose expression increased in response to HDGF stimulation. Both these molecules were associated with a poor prognosis of HCC patients.

Upregulated hsa_circ_0005785 Facilitates Cell Growth and Metastasis of Hepatocellular Carcinoma Through the miR-578/APRIL Axis

Although accumulating documents have expounded the pivotal position of circular RNAs (circRNAs) in hepatocarcinogenesis and progression, the overwhelming majority of their functions and molecular mechanisms in hepatocellular carcinoma (HCC) are elusive. Herein, we explored the functions and potential mechanisms of hsa_circ_0005785 in HCC, which was aberrantly overexpressed in HCC and related to HCC patients' TNM stage and overall survival. Moreover, hsa_circ_0005785 depletion could repress proliferation and metastasis of the HCC cell in vitro, lead to cell apoptosis and cell-cycle arrest, and restrain HCC cell growth in vivo. Furthermore, mechanism analyses discovered that hsa_circ_0005785 adsorbed miR-578 by playing a miRNA sponge role, which resulted in the derepression of a proliferation-inducing ligand (APRIL) expression, miR-578's mRNA target. Besides, hsa_circ_0005785 reversed the suppressive influence of miR-578 on HCC and accelerated tumor malignant progression through the miR-578/APRIL axis. Taken together, our current study revealed an oncogenic role of hsa_circ_0005785 in the tumorigenesis of HCC. Moreover, targeting to the hsa_circ_0005785/miR-578/APRIL regulatory pathway might be a promising diagnostic and therapeutic strategy for HCC clinical practice.

CircularRNA-9119 protects hepatocellular carcinoma cells from apoptosis by intercepting miR-26a/JAK1/STAT3 signaling

Hepatocellular carcinoma (HCC) is a more common malignancy than the majority of cancers and ranks second in the world’s top causes of cancer-related mortality. The objective of the study was to investigate and explain how circularRNA-9119 (circ9119) regulated the properties of HCC cell lines. Cancer cells isolated from HCC patients and HCC cell lines showed clearly upregulated expression of circ9119 and Janus kinase 1 (JAK1) with decreased levels of miR-26a compared to healthy controls and normal hepatic cells. To determine the function of circ9119, circ9119 was silenced in HCC cells, resulting in significantly less proliferation of HCC cells and increasing apoptosis. Circ9119 silencing also resulted in the upregulation of miR-26a. Bioinformatics prediction and dual-luciferase reporter assays showed that circ9119 targeted miR-26a. Further studies revealed that miR-26a had the opposite effect on circ9119; the inhibition of miR-26a antagonized circ9119 silencing, leading to reduced cell proliferation and increased apoptosis, while the ectopic overexpression of miR-26a impaired cell growth. Additionally, we found that the JAK1 3′-UTR was targeted by miR-26a; a decrease in the levels of JAK1 protein and mRNA followed transfection of a miR-26a mimic. Administration of the JAK1 inhibitor, baricitinib, caused the activation of signal transducer and activator of transcription 3 (STAT3) and revealed an effect similar to that of circ9119 silencing on cell proliferation and apoptosis. These results showed that circ9119 could modulate apoptosis, and broadly, cell proliferation by competitively binding miR-26a, which targeted JAK1-STAT3, in HCC cell lines. This study is a novel description of circ9119 regulation of HCC.

CircCDK14 protects against Osteoarthritis by sponging miR-125a-5p and promoting the expression of Smad2

Rationale: Osteoarthritis (OA) is the most common joint disease worldwide. Previous studies have identified the imbalance between extracellular matrix (ECM) catabolism and anabolism in cartilage tissue as the main cause. To date, there is no cure for OA despite a few symptomatic treatments. This study aimed to investigate the role of CircCDK14, a novel circRNA factor, in the progression of OA, and to elucidate its underlying molecular mechanisms.

Methods: The function of CircCDK14 in OA, as well as the interaction between CircCDK14 and its downstream target (miR-125a-5p) and mRNA target (Smad2), was evaluated by western blot (WB), immunofluorescence (IF), RNA immunoprecipitation (RIP), quantitative RT-PCR, luciferase assay and fluorescence in situ hybridization (FISH). Rabbit models were introduced to examine the function and mechanism of CircCDK14 in OA in vivo.

Results: In our present study, we found that CircCDK14, while being down-regulated in the joint wearing position, regulated metabolism, inhibited apoptosis and promoted proliferation in the cartilage. Mechanically, the protective effect of CircCDK14 was mediated by miR-125a-5p sponging, which downregulated the Smad2 expression and led to the dysfunction of TGF-β signaling pathway. Intra-articular injection of adeno-associated virus-CircCDK14 also alleviated OA in the rabbit model.

Conclusion: Our study revealed an important role of CircCDK14/miR-125a-5p/Smad2 axis in OA progression and provided a potential molecular therapeutic strategy for the treatment of OA.

Hypoxia-induced miR-3677-3p promotes the proliferation, migration and invasion of hepatocellular carcinoma cells by suppressing SIRT5

Hepatocellular carcinoma (HCC), with life‐threatening malignant behaviours, often develops distant metastases and is the fourth most common primary cancer in the world, having taken millions of lives in Asian countries such as China. The novel miR‐3677‐3p is involved in a high‐expression‐related poor prognosis in HCC tissues and cell lines, indicating oncogenesis functions in vitro and in vivo. Initially, we confirmed the inhibition of proliferation, migration and invasion in miR‐3677‐3p knock‐down MHCC‐97H and SMMC‐7721 cell lines, which are well known for their high degree of invasiveness. Then, we reversed the functional experiments in the low‐miR‐3677‐3p‐expression Hep3B cell line via overexpressing miR‐3677‐3p. In nude mice xenograft and lung metastasis assays, we found suppressor behaviours, smaller nodules and low density of organ spread, after injection of cells transfected with shRNA‐miR‐3677‐3p. A combination of databases (Starbase, TargetScan and MiRgator) illustrated miR‐3677‐3p targets, and it was shown to suppress the expression of SIRT5 in a dual‐luciferase reporter system. To clarify the conclusions of previous ambiguous research, we up‐regulated SIRT5 in Hep3B cells, and rescue tests were established for confirmation that miR‐3677‐3p suppresses SIRT5 to enhance the migration and invasion of HCC. Interestingly, we discovered hypoxia‐induced miR‐3677‐3p up‐regulation benefited HCC malignancy and invasiveness. In conclusion, the overexpression of miR‐3677‐3p mediated SIRT5 inhibition, which could increase proliferation, migration and invasion of HCC in hypoxic microenvironments.

Circular RNA circZNF566 promotes hepatocellular carcinoma progression by sponging miR-4738-3p and regulating TDO2 expression

As a recently discovered noncoding RNA, circular RNAs (circRNAs) have been identified to play key roles in cancer biology; however, the detailed functions and mechanisms of circRNAs in hepatocellular carcinoma (HCC) remain largely unclarified. RNA-seq analysis was used to screen the expression profiles of circRNAs in HCC. CircZNF566 expression in HCC tissues and cell lines was detected by qRT-PCR. In vitro CCK-8, colony formation, wound healing, transwell migration, and invasion assays and in vivo tumorigenesis and metastasis assays were conducted to determine the functions of circZNF566. Luciferase reporter, RNA immunoprecipitation (RIP) and RNA pull-down assays were also performed to confirm the relationship between circZNF566 and miR-4738-3p. Bioinformatics analysis and luciferase reporter assays were employed to determine whether miR-4738-3p regulates tryptophan 2,3-dioxygenase (TDO2) expression. Finally, immunohistochemistry (IHC) was used to detect the level of TDO2 and determine its prognostic value. CircZNF566 was significantly upregulated in HCC tissues and cell lines. High circZNF566 expression in HCC tissues was positively correlated with clinicopathological features and poor prognosis. Functionally, in vitro experiments showed that circZNF566 promoted HCC cell migration, invasion, and proliferation, whereas in vivo experiments showed that circZNF566 promoted tumorigenesis and metastasis. Mechanistically, circZNF566 acted as a miR-4738-3p sponge to relieve the repressive effect of miR-4738-3p on its target TDO2. In addition, miR-4738-3p suppressed HCC cell migration, invasion, and proliferation, while TDO2 was positively correlated with pathological features and poor prognosis and promoted cell migration, invasion, and proliferation in HCC. CircZNF566 is a novel tumor promoter in HCC and functions through the circZNF566/ miR-4738-3p /TDO2 axis; in addition, circZNF566 may serve as a novel diagnostic marker, prognostic indicator, and target for the treatment of HCC.

Circular RNA (circRNA) CDYL Induces Myocardial Regeneration by ceRNA After Myocardial Infarction

Background

The aim of the study was to assess the effect of circRNA CDYL on myocardial angiogenesis after acute myocardial infarction (AMI).

Material/Methods

We compared changes in circRNA CDYL and myocardial angiogenesis in myocardial infarction tissue and normal heart tissue by establishing a myocardial infarction mouse model to clarify the relationship between circRNA CDYL and changes in myocardial infarction and myocardial angiogenesis. Secondly, we used the RegRNA website to predict downstream miRNA, and we performed gain-of-function and loss-of-function experiments.

Results

CircCDYL was downregulated in myocardial tissues and hypoxia myocardial cells, and overexpression and downregulation of circCDYL improved and aggravated, respectively, heart function after AMI. CircCDYL overexpression and downregulation can promote and inhibit, respectively, proliferation of cardiomyocytes in vitro. Finally, we found that circCDYL can sponge miR-4793-5p and regulate its expression, and then miR-4793-5p regulates APP expression.

Conclusions

CircCDYL can promote the proliferation of cardiomyocytes through the miR-4793-5p/APP pathway.

Role of circular RNAs in digestive system malignancies

Gastrointestinal malignancies have very high morbidity and mortality worldwide, seriously endangering human life and health. However, there are still many challenges in their early diagnosis and effective treatment. Circular RNAs (circRNAs) are a new class of endogenous long non-coding RNAs characterized by covalently closed loops. Because they do not have a 5' cap structure and a 3' poly(A) tail, circRNAs have higher stability, abundance, and evolutionary conservation than linear RNAs. CircRNAs are expressed in a tissue- or developmental stage-specific manner. These features produce various potential biological functions of circRNAs, such as acting as sponges of microRNAs (miRNAs; circRNAs bind to miRNAs to eliminate the inhibitory effect of miRNAs on their target genes and play a role of competing endogenous RNAs) or forming RNA protein complexes through RNA binding proteins, participating in the regulation of protein functions. In recent years, more and more studies have shown that circRNAs play a vital role in the occurrence and development of digestive system tumors. At the same time, their enormous potential as a biomarker and therapeutic target is also evolving. In this review, we summarize the latest research progress of circRNAs in digestive system malignancies.

Emerging Role of Circular RNAs in Cancer

Circular RNAs (circRNAs), which are generated mainly from back-splicing of exons in precursor mRNAs (pre-mRNAs), are a novel class of endogenous covalently closed RNA molecules. Their functions as microRNA sponges, protein scaffolds, and modulators of transcription and splicing, as well as occasional templates for polypeptide production, are beginning to be recognized, though the investigation of circRNAs is in its infancy. circRNAs play critical roles in diverse cellular processes. Aberrant expression of circRNAs in malignancies sustains cellular growth and proliferation, promotes cellular invasiveness, and circumvents cellular senescence and death, suggesting their potential for exploitation as clinical biomarkers and therapeutic targets. In this review, we highlight recent progress in research on circRNAs in cancer, emphasizing the molecular mechanisms and potential clinical value of circRNAs.

Circular RNA hsa_circ_0008285 inhibits colorectal cancer cell proliferation and migration via the miR-382-5p/PTEN axis

Abundant evidence has showed that circular RNA (circRNA) plays an important role in cancer. Nonetheless, little is known about the roles and mechanisms of specific circRNAs in different cancer types. Hsa_circ_0008285 (circ_0008285), derived from the coding gene chromodomain y-like protein (CDYL), is upregulated in hepatocellular carcinoma and mantle cell lymphoma. However, we previously found, by analyzing two independent high-throughput sequencing datasets, that it was reduced in colon cancer. In this study, we explored the function and mechanism of circ_0008285 in the progression of colorectal cancer (CRC). First, the downregulated expression of circ_0008285 in CRC tissues and cell lines was confirmed using RT-qPCR analysis. In addition, the expression level of circ_0008285 was inversely correlated with tumor size, lymphatic metastasis, and tumor-node-metastasis (TNM) stage through clinicopathological parameter analysis. Functionally, knockdown of circ_0008285 promoted CRC cell proliferation and migration in vitro. Mechanistically, by using RNA-sequencing, bioinformatics analysis, dual-luciferase reporter assay, and western blotting, we determined that circ_0008285 suppressed the PI3K/AKT pathway via the miR-382-5p/PTEN axis. In conclusion, our data demonstrate a tumor suppressor role for circ_0008285 in CRC and suggest circ_0008285 as a potential target for CRC treatment.

The circular RNA circMAST1 promotes hepatocellular carcinoma cell proliferation and migration by sponging miR-1299 and regulating CTNND1 expression

Circular RNAs (circRNAs) are a class of non-coding RNAs with a loop structure; however, their functions remain largely unknown. Growing evidence suggests that circRNAs play a pivotal role in the progression of malignant diseases. However, the expression profiles and function of circRNAs in hepatocellular carcinoma (HCC) remain unclear. We investigated the expression of microtubule-associated serine/threonine kinase 1 (MAST1) circRNA (circMAST1) in HCC and healthy tissues using bioinformatics, quantitative real-time PCR (qRT-PCR), and fluorescence in situ hybridization. Luciferase reporter assays were performed to assess the interaction between circMAST1 and miR-1299. Proliferation assays, colony formation assays, flow cytometry, transwell assays, and western blotting were also performed. A mouse xenograft model was also used to determine the effect of circMAST1 on HCC growth in vivo. CircMAST1 was upregulated in HCC tissues and cell lines; silencing via small interfering RNA inhibited migration, invasion, and proliferation of HCC cell lines in vitro as well as tumor growth in vivo. Furthermore, the expression of circMAST1 was positively correlated with catenin delta-1 (CTNND1) and negatively correlated with microRNA (miR)-1299 in HCC clinical samples. Importantly, circMAST1 sponged miR-1299 to stabilize the expression of CTNND1 and promoted tumorigenic features in HCC cell lines. We found that circMAST1 may serve as a novel biomarker for HCC. Moreover, circMAST1 elicits HCC progression by sponging miRNA-1299 and stabilizing CTNND1. Our data provide potential options for therapeutic targets in patients with HCC.

circNFIB1 inhibits lymphangiogenesis and lymphatic metastasis via the miR-486-5p/PIK3R1/VEGF-C axis in pancreatic cancer

BACKGROUND

Patients with lymph node (LN)-positive pancreatic ductal adenocarcinoma (PDAC) have extremely poor survival rates. Circular RNAs (circRNAs), a newly discovered type of endogenous noncoding RNAs, have been proposed to mediate the progression of diverse types of tumors. However, the role and underlying regulatory mechanisms of circRNAs in the LN metastasis of PDAC remain unknown.

METHODS

Next-generation sequencing was used to identify differentially expressed circRNAs between PDAC and normal adjacent tissues. In vitro and in vivo experiments were conducted to evaluate the functional role of circNFIB1. RNA pulldown and luciferase assays were performed to examine the binding of circNFIB1 and miR-486-5p.

RESULTS

In the present study, we identified that a novel circRNA (circNFIB1, hsa_circ_0086375) was downregulated in PDAC and negatively associated with LN metastasis in PDAC patients. Functionally, circNFIB1 knockdown promoted lymphangiogenesis and LN metastasis of PDAC both in vitro and in vivo. Mechanistically, circNFIB1 functioned as a sponge of miR-486-5p, and partially reversed the effect of miR-486-5p. Moreover, circNFIB1 attenuated the oncogenic effect of miR-486-5p and consequently upregulated PIK3R1 expression, which further downregulated VEGF-C expression through inhibition of the PI3K/Akt pathway, and ultimately suppressed lymphangiogenesis and LN metastasis in PDAC.

CONCLUSIONS

Our findings provide novel insight into the underlying mechanism of circRNA-mediated LN metastasis of PDAC and suggest that circNFIB1 may serve as a potential therapeutic target for LN metastasis in PDAC.

Circ-camk4 involved in cerebral ischemia/reperfusion induced neuronal injury

Stroke and subsequent cerebral ischemia/reperfusion (I/R) injury is a frequently occurring disease that can have serious consequences in the absence of timely intervention. Circular RNAs (circRNAs) in association with microRNAs (miRNAs) and RNA-binding proteins (RBPs) can influence gene expression. However, whether circRNAs have a role in cerebral I/R injury pathogenesis, especially soon after onset, is unclear. In this study, we used the SD rat middle cerebral artery occlusion (MCAO) model of stroke to examine the role of circRNAs in cerebral I/R injury. We used high-throughput sequencing (HTS) to compare the expression levels of circRNAs in cerebral cortex tissue from MCAO rats during the occlusion-reperfusion latency period 3 hours after I/R injury with those in control cerebral cortices. Our sequencing results revealed that expression levels of 44 circRNAs were significantly altered after I/R, with 16 and 28 circRNAs showing significant up- and down-regulation, respectively, relative to levels in control cortex. We extended these results in vitro in primary cultured neuron cells exposed to oxygen-glucose deprivation/reperfusion (OGD/R) using qRT-PCR to show that levels of circ-camk4 were increased in OGD/R neurons relative to control neurons. Bioinformatics analyses predicted that several miRNAs could be associated with circ-camk4 and this prediction was confirmed in a RNA pull-down assay. KEGG analysis to predict pathways that involve circ-camk4 included the glutamatergic synapse pathway, MAPK signaling pathway, and apoptosis signaling pathways, all of which are known to be involved in brain injury after I/R. Our results also demonstrate that levels of the human homolog to circ-camk4 (hsa-circ-camk4) are elevated in SH-SY5Y cells exposed to OGD/R treatment. Overexpression of hsa-circ-camk4 in SH-SY5Y cells significantly increased the rate of cell death after OGD/R, suggesting that circ-camk4 may play a key role in progression of cerebral I/R injury.

Circular RNA circ-CDYL sponges miR-1180 to elevate yes-associated protein in multiple myeloma

IMPACT STATEMENT

Multiple myeloma (MM) is an extremely complex and heterogeneous disease, and its pathogenesis is poorly understood. Here, we described an important MM-related circular RNA (circRNA), circ-CDYL. It was remarkably increased in both MM cells and plasma. Depletion of circ-CDYL evidently stunted MM growth. Circ-CDYL could absorb miR-1180 and alleviated the repression of miR-1180 on YAP, leading to increased YAP expression, ultimately triggering MM uncontrolled growth. Therefore, our findings advance the understanding of MM pathogenesis, and also raise the possibility of considering circ-CDYL as a potential therapeutic intervention for MM.

Diagnostic and prognostic value of circular RNAs in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the sixth most common malignant tumour, which has posed a heavy health and financial burden worldwide. Due to limited symptoms at the early stage and the limitation in current biomarkers, HCC patients are usually diagnosed at the advanced stage with a pessimistic overall survival rate. Circular RNAs (circRNAs) are a subclass of single‐stranded RNAs characterized by a covalently closed loop structure without 3’‐ or 5’‐end. With advances in high‐throughput sequencing technology and bioinformatics, accumulating studies have demonstrated the promotor or suppressor roles of circRNAs in the carcinogenesis, progression, and metastasis of HCC. Moreover, circRNAs are characteristic of higher abundance, stability and conservation compared with linear RNAs. Therefore, circRNAs have emerged as one of the most promising diagnostic and prognostic biomarkers for HCC with reliable accuracy, sensitivity and specificity. In this review, we briefly introduce the characteristics of circRNAs and summarize the roles of circRNAs in the biological procedures of HCC. Furthermore, we provide an overview on the potential diagnostic and prognostic value of circRNAs as biomarkers for patients with HCC. Finally, we discuss future perspectives of circRNAs in cancer research.

Circular RNAs and their participation in stemness of cancer

Circular RNAs (circRNA) are covalently closed single-stranded RNA molecules that act as important regulators of gene expression through different mechanisms. Meanwhile, cancer stem cells (CSCs) are a small subpopulation of cells, with properties similar to normal stem cells that arise during the development of cancer and support tumor growth, induce resistance to therapy, and are responsible for metastatic spread. Since the elimination of CSCs is an important goal of cancer treatment, the circRNAs that participate in regulating gene expression and signaling pathways linked to CSCs have aroused attention in recent years, especially because it has been suggested that these molecules may function as therapeutic targets and/or clinical biomarkers. Thus, the proposal of this work is to enumerate a series of circRNAs that have been shown to play a relevant role in CSCs and explain in detail the molecular regulatory mechanisms that they establish to perform that function.

Autophagy-associated circRNA circCDYL augments autophagy and promotes breast cancer progression

BACKGROUND

Although both circular RNAs (circRNAs) and autophagy are associated with the function of breast cancer (BC), whether circRNAs regulate BC progression via autophagy remains unknown. In this study, we aim to explore the regulatory mechanisms and the clinical significance of autophagy-associated circRNAs in BC.

METHODS

Autophagy associated circRNAs were screened by circRNAs deep sequencing and validated by qRT-PCR in BC tissues with high- and low- autophagic level. The biological function of autophagy associated circRNAs were assessed by plate colony formation, cell viability, transwells, flow cytometry and orthotopic animal models. For mechanistic study, RNA immunoprecipitation, circRNAs pull-down, Dual luciferase report assay, Western Blot, Immunofluorescence and Immunohistochemical staining were performed.

RESULTS

An autophagy associated circRNA circCDYL was elevated by 3.2 folds in BC tissues as compared with the adjacent non-cancerous tissues, and circCDYL promoted autophagic level in BC cells via the miR-1275-ATG7/ULK1 axis; Moreover, circCDYL enhanced the malignant progression of BC cells in vitro and in vivo. Clinically, increased circCDYL in the tumor tissues and serum of BC patients was associated with higher tumor burden, shorter survival and poorer clinical response to therapy.

CONCLUSIONS

circCDYL promotes BC progression via the miR-1275-ATG7/ULK1-autophagic axis and circCDYL could act as a potential prognostic and predictive molecule for breast cancer patients.

Potential diagnostic and therapeutic value of circular RNAs in cardiovascular diseases

Cardiovascular diseases (CVDs) have imposed a massive health and financial burden worldwide with high mortality and morbidity. However, the diagnostic value of current biomarkers might be impaired by a wide variety of noncardiac causes. Moreover, cardiovascular outcomes, survival, and prognosis of patients with CVDs remain poor despite advances in treatment. Therefore, novel diagnostic and therapeutic strategies are urgently required for timely identification of possible heart diseases in the early stage, which might effectively contribute to reducing the CVDs-caused morbidity and mortality. Circular RNA (circRNA) was initially identified as aberrant byproducts or abnormally spliced transcripts. However, with advances in bioinformatics and high-throughput sequencing technology, circRNAs has become an essential topic on a wide range of biological functions and emerged as novel players in diagnostic and therapeutic strategies for CVDs. In this article, we briefly introduce the biogenesis and functions of circRNAs. Moreover, we describe the roles of circRNAs in multiple CVDs, including atherosclerosis, coronary artery disease, myocardial infarction, as well as cardiomyopathy. In addition, we provide an overview on the current challenges and directions for further application.

Exosomal circRNA-100338 promotes hepatocellular carcinoma metastasis via enhancing invasiveness and angiogenesis

Background

Exosomes play crucial roles in regulating the crosstalk between normal and cancer cells in the tumor microenvironment, and in regulating cancer proliferation, migration and invasion through their cargo molecules.

Methods

We analyzed the pro-invasiveness of exosomal circRNA-100,338 in HCC using the transwell invasion assay. The co-culture of human umbilical vein endothelial cells (HUVEC) and exosomes derived from HCC cell lines were used to evaluate the impact of HCC derived exosomes on HUVEC. Nude mice models were used to validate the findings in vitro. Clinically, quantitative RT-PCR was used to quantify the expression of serum exosomal circRNA-100,338 in HCC patients at both pre-surgery within one week and post-surgery within three weeks.

Results

We aim to investigate the pro-invasive role of exosomal circRNA-100,338 in HCC metastasis. We for the first time demonstrated that circRNA-100,338 was highly expressed in both highly metastatic HCC cells and their secreted exosomes. The transwell invasion assay showed that the overexpression or knockdown of exosomal circRNA-100,338 significantly enhanced or reduced the invasive abilities of HCC cells. Subsequently, in vitro and in vivo assays showed that exosomal circRNA-100,338 affected the cell proliferation, angiogenesis, permeability, and vasculogenic mimicry (VM) formation ability of human umbilical vein endothelial cells (HUVEC), and tumor metastasis. Furthermore, we also observed that the persistent high expression of exosomal circRNA-100,338 in serum of HCC patients who underwent curative hepatectomy may be a risk indicator of pulmonary metastasis and poor survival.

Conclusions

Our findings indicated that metastatic ability of HCC cells could be enhanced by transferring exosomal circRNA-100,338 to recipient HUVECs, which could affect proangiogenic activity by regulating angiogenesis.

M6A-mediated upregulation of LINC00958 increases lipogenesis and acts as a nanotherapeutic target in hepatocellular carcinoma

BACKGROUND

Long non-coding RNAs (lncRNAs) possess significant regulatory functions in multiple biological and pathological processes, especially in cancer. Dysregulated lncRNAs in hepatocellular carcinoma (HCC) and their therapeutic applications remain unclear.

METHODS

Differentially expressed lncRNA profile in HCC was constructed using TCGA data. LINC00958 expression level was examined in HCC cell lines and tissues. Univariate and multivariate analyses were performed to demonstrate the prognostic value of LINC00958. Loss-of-function and gain-of-function experiments were used to assess the effects of LINC00958 on cell proliferation, motility, and lipogenesis. Patient-derived xenograft model was established for in vivo experiments. RNA immunoprecipitation, dual luciferase reporter, biotin-labeled miRNA pull-down, fluorescence in situ hybridization, and RNA sequencing assays were performed to elucidate the underlying molecular mechanisms. We developed a PLGA-based nanoplatform encapsulating LINC00958 siRNA and evaluated its superiority for systemic administration.

RESULTS

We identified a lipogenesis-related lncRNA, LINC00958, whose expression was upregulated in HCC cell lines and tissues. High LINC00958 level independently predicted poor overall survival. Functional assays showed that LINC00958 aggravated HCC malignant phenotypes in vitro and in vivo. Mechanistically, LINC00958 sponged miR-3619-5p to upregulate hepatoma-derived growth factor (HDGF) expression, thereby facilitating HCC lipogenesis and progression. METTL3-mediated N⁶-methyladenosine modification led to LINC00958 upregulation through stabilizing its RNA transcript. A PLGA-based nanoplatform loaded with si-LINC00958 was developed for HCC systemic administration. This novel drug delivery system was controlled release, tumor targeting, safe, and presented satisfactory antitumor efficacy.

CONCLUSIONS

Our results delineate the clinical significance of LINC00958 in HCC and the regulatory mechanisms involved in HCC lipogenesis and progression, providing a novel prognostic indicator and promising nanotherapeutic target.