Circular RNA circTRIM33-12 acts as the sponge of MicroRNA-191 to suppress hepatocellular carcinoma progression

Establishment of a circRNA-regulated E3 ubiquitin ligase signature and nomogram to predict immunotherapeutic efficacy and prognosis in hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is a common type of malignant tumor where the prognosis is dismal. Circular RNA (CircRNA) is a novel RNA that regulates downstream gene transcription and translation to influence the progression of HCC. However, the regulatory relationship that exists between E3 ligases, which is a class of post-translational modifying proteins, and circRNA remains unclear.

METHODS

Based on the E3 ubiquitin ligase in the competitive endogenous RNA (ceRNA) network, a circRNA-regulated E3 ubiquitin ligase signature (CRE3UL) was developed. A CRE3UL signature was created using the least absolute shrinkage and selection operator (Lasso) and Cox regression analysis and merged it with clinicopathologic characteristics to generate a nomogram for prognosis prediction. The pRRophetic algorithm was utilized and immunological checkpoints were analyzed to compare the responses of patients in the high-risk group (HRG) and low-risk group (LRG) to targeted therapy and immunotherapy. Finally, experimental research will further elucidate the relationship between E3 ubiquitin ligase signature and HCC.

RESULTS

HRG patients were found to have a worse prognosis than LRG patients. Furthermore, significant variations in prognosis were observed among different subgroups based on various clinical characteristics. The CRE3UL signature was identified as being an independent prognostic indicator. The nomogram that combined clinical characteristics and the CRE3UL signature was found to accurately predict the prognosis of HCC patients and demonstrated greater clinical utility than the current TNM staging approach. According to anticancer medication sensitivity predictions, the tumors of HRG patients were more responsive to gefitinib and nilotinib. From immune-checkpoint markers analysis, immunotherapy was identified as being more probable to assist those in the HRG.

CONCLUSIONS

We found a significant correlation between the CRE3UL signature and the tumor microenvironment, enabling precise prognosis prediction for HCC patients. Additionally, a nomogram was developed that performs well in predicting the overall survival (OS) of HCC patients. This provides valuable guidance for clinicians in devising specific personalized treatment strategies.

The role of circular RNAs in regulating resistance to cancer immunotherapy: mechanisms and implications

Cancer immunotherapy has rapidly transformed cancer treatment, yet resistance remains a significant hurdle, limiting its efficacy in many patients. Circular RNAs (circRNAs), a novel class of non-coding RNAs, have emerged as pivotal regulators of gene expression and cellular processes. Increasing evidence indicates their involvement in modulating resistance to cancer immunotherapy. Notably, certain circRNAs function as miRNA sponges or interact with proteins, influencing the expression of immune-related genes, including crucial immune checkpoint molecules. This, in turn, shapes the tumor microenvironment and significantly impacts the response to immunotherapy. In this comprehensive review, we explore the evolving role of circRNAs in orchestrating resistance to cancer immunotherapy, with a specific focus on their mechanisms in influencing immune checkpoint gene expression. Additionally, we underscore the potential of circRNAs as promising therapeutic targets to augment the effectiveness of cancer immunotherapy. Understanding the role of circRNAs in cancer immunotherapy resistance could contribute to the development of new therapeutic strategies to overcome resistance and improve patient outcomes.

Biological functions of circRNA in regulating the hallmarks of gastrointestinal cancer (Review)

Circular RNA (circRNA) was first observed in the cytoplasm of eukaryotic cells in 1979, but it was not characterized in detail until 2012, when high‑throughput sequencing technology was more advanced and available. Consequently, the mechanism of circRNA formation and its biological function have been progressively elucidated by researchers. circRNA is abundant in eukaryotic cells and exhibits a certain degree of organization, timing and disease‑specificity. Additionally, it is poorly degradable, meeting the characteristics of an ideal clinical biomarker. In the present review, the recent research progress of circRNAs in digestive tract malignant tumors was primarily discussed. This included the roles, biological functions and clinical significance of circRNA, providing references for its research value and clinical potential in gastrointestinal cancer.

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.

CircSNX6 promotes proliferation, metastasis, and angiogenesis in hepatocellular carcinoma via miR-383-5p/VEGFA signaling pathway

The role of circular RNA (circRNAs) in hepatocellular carcinoma (HCC) has been extensively studied. Previous research has highlighted the regulatory role of circSNX6 in HCC cells and tissues. However, the precise mechanism underlying HCC progression still requires comprehensive investigation. The study initially utilized quantitative reverse transcription-polymerase chain reaction (qRT-PCR) to assess circSNX6 expression levels in HCC cell lines and tissues. Subsequently, the stability of circRNA was evaluated through Ribonuclease R and actinomycin D treatment assays. The impact of circSNX6 knockdown on proliferation, migration, invasion, and angiogenesis abilities was determined using various assays including colony formation, Transwell culture system, tube formation assay, and cell counting kit (CCK)-8 assays. Additionally, RNA immunoprecipitation chip and dual-luciferase reporter assays were employed to investigate the interactions between circSNX6 and miR-383-5p. Finally, an HCC xenograft tumor model in mice was established to assess the in vivo expression of circSNX6 and its functional role in HCC. Our findings revealed an elevated circSNX6 expression in HCC tissues, which was correlated with poor patient prognosis. Knockdown of circSNX6 suppressed HCC cell growth, invasion, metastasis, and angiogenesis. The downregulation of miR-383-5p, a target of circSNX6, significantly attenuated the tumor-suppressive effects induced by circSNX6 knockdown. Moreover, circSNX6 was found to modulate VEGFA expression by targeting miR-383-5p. The inhibition of HCC cell proliferation by miR-383-5p could be partially reversed by overexpressing VEGFA. Silencing circSNX6 also suppressed tumor formation and the metastasis of HCC cells in a mouse model. In summary, our findings suggest that circSNX6 promotes cell proliferation, metastasis, and angiogenesis in HCC by regulating the miR-383-5p/VEGFA pathway.

CircGPC3 promotes hepatocellular carcinoma progression and metastasis by sponging miR-578 and regulating RAB7A/PSME3 expression

CircRNAs are a class of highly stable noncoding RNAs that play an important role in the progression of many diseases, especially cancer. In this study, high-throughput sequencing was used to screen for abnormally expressed circRNAs, and we found that circGPC3 was overexpressed in HCC tissues. However, the underlying mechanism of circGPC3 in the development and metastasis of hepatocellular carcinoma (HCC) remains unknown. In our study, we found that circGPC3 was significantly upregulated in HCC tissues and cells and that its overexpression was positively correlated with overall survival, TNM stage and lymph node metastasis. In vivo and in vitro experiments showed that circGPC3 knockdown repressed HCC cell migration, invasion and proliferation and promoted apoptosis. Mechanistically, circGPC3 promoted HCC proliferation and metastasis through the miR-578/RAB7A/PSME3 axis. Our results demonstrate that circGPC3 contributes to the progression of HCC and provides an intervention target for HCC.

Involvement of CircRNAs in regulating The "New Generation of Cancer Hallmarks": A Special Depiction on Hepatocellular Carcinoma

The concept of 'Hallmarks of Cancer' is an approach of reducing the enormous complexity of cancer to a set of guiding principles. As the underlying mechanism of cancer are portrayed, we find that we gain insight and additional aspects of the disease arise. The understanding of the tumor microenvironment (TME) brought a new dimension and led to the discovery of novel hallmarks such as senescent cells, non-mutational epigenetic reprogramming, polymorphic microbiomes and unlocked phenotypic plasticity. Circular RNAs (circRNAs) are single-stranded, covalently closed RNA molecules that are ubiquitous across all species. Recent studies on the circRNAs have highlighted their crucial function in regulating the formation of human malignancies through a range of biological processes. The primary goal of this review is to clarify the role of circRNAs in the most common form of liver cancer, hepatocellular carcinoma (HCC). This review also addressed the topic of how circRNAs affect HCC hallmarks, including the new generation hallmarks. Finally, the enormous applications that these rapidly expanding ncRNA molecules serve in the functional and molecular development of effective HCC diagnostic biomarkers and therapeutic targets.

TRIM5 as a promising diagnostic biomarker of hepatocellular carcinoma: integrated analysis and experimental validation

The TRIM family is associated with the membrane, and its involvement in the progression, growth, and development of various cancer types has been researched extensively. However, the role played by the TRIM5 gene within this family has yet to be explored to a great extent in terms of hepatocellular carcinoma (HCC). The data of patients relating to mRNA expression and the survival rate of individuals diagnosed with HCC were extracted from The Cancer Genome Atlas (TCGA) database. UALCAN was employed to examine the potential link between TRIM5 expression and clinicopathological characteristics. In addition, enrichment analysis of differentially expressed genes (DEGs) was conducted as a means of deciphering the function and mechanism of TRIM5 in HCC. The data in the TCGA and TIMER2.0 databases was utilized to explore the correlation between TRIM5 and immune infiltration in HCC. WGCNA was performed as a means of assessing TRIM5-related co-expressed genes. The "OncoPredict" R package was also used for investigating the association between TRIM5 and drug sensitivity. Finally, qRT-PCR, Western blotting (WB) and immunohistochemistry (IHC) were employed for exploring the differential expression of TRIM5 and its clinical relevance in HCC. According to the results that were obtained from the vitro experiments, mRNA and protein levels of TRIM5 demonstrated a significant upregulation in HCC tissues. It is notable that TRIM5 expression levels were found to have a strong association with the infiltration of diverse immune cells and displayed a positive correlation with several immune checkpoint inhibitors. The TRIM5 expression also displayed promising clinical prognostic value for HCC patients.

Circular RNAs as biomarkers and therapeutic targets for gastrointestinal cancers

Circular RNAs are a class of noncoding RNAs with covalently linked 5' and 3' ends that arise from backsplicing events. The absence of a 5' cap and a 3' poly(A) tail makes circular RNAs relatively more stable than their linear counterparts. They are evolutionary conserved and tissue-specific, and some show disease-specific expression patterns. Although their biological functions remain largely unknown, circular RNAs have been shown to play regulatory roles by acting as microRNA sponges, regulators of RNA-binding proteins, alternative splicing, and parental gene expression, and they could even encode proteins. Over the past few decades, circular RNAs have attracted wide attention in oncology owing to their implications in various tumors. Many circular RNAs have been characterized as key players in gastrointestinal cancers and influence cancer growth, progression, metastasis, and therapeutic resistance. Accumulating evidence reveals that their unique characteristics, coupled with their critical roles in tumorigenesis, make circular RNAs promising non-invasive clinical biomarkers for gastrointestinal cancers. In the present review, we summarized the biological roles of the emerging circular RNAs and their potential as biomarkers and therapeutic targets, which may help better understand their clinical significance in the management of gastrointestinal cancers.

Role of circular RNAs and gut microbiome in gastrointestinal cancers and therapeutic targets

Gastrointestinal cancers are a huge worldwide health concern, which includes a wide variety of digestive tract cancers. Circular RNAs (circRNAs), a kind of non-coding RNA (ncRNAs), are a family of single-stranded, covalently closed RNAs that have become recognized as crucial gene expression regulators, having an impact on several cellular functions in cancer biology. The gut microbiome, which consists of several different bacteria, actively contributes to the regulation of host immunity, inflammation, and metabolism. CircRNAs and the gut microbiome interact significantly to greatly affect the growth of GI cancer. Several studies focus on the complex functions of circRNAs and the gut microbiota in GI cancers, including esophageal cancer, colorectal cancer, gastric cancer, hepatocellular cancer, and pancreatic cancer. It also emphasizes how changed circRNA expression profiles and gut microbiota affect pathways connected to malignancy as well as how circRNAs affect hallmarks of gastrointestinal cancers. Furthermore, circRNAs and gut microbiota have been recommended as biological markers for therapeutic targets as well as diagnostic and prognostic purposes. Targeting circRNAs and the gut microbiota for the treatment of gastrointestinal cancers is also being continued to study. Despite significant initiatives, the connection between circRNAs and the gut microbiota and the emergence of gastrointestinal cancers remains poorly understood. In this study, we will go over the most recent studies to emphasize the key roles of circRNAs and gut microbiota in gastrointestinal cancer progression and therapeutic options. In order to create effective therapies and plan for the future gastrointestinal therapy, it is important to comprehend the functions and mechanisms of circRNAs and the gut microbiota.

Circular RNA circFCHO2(hsa_circ_0002490) promotes the proliferation of melanoma by directly binding to DND1

Circular RNAs (circRNAs) have been documented to play crucial roles in the biology of various cancers. However, their investigation in melanoma is still at an early stage, particularly as a broader mechanism beyond acting as miRNA sponges needs to be explored. We report here that circFCHO2(hsa_circ_0002490), a circRNA encompassing exons 19 and 20 of the FCHO2 gene, exhibited a consistent overexpression in melanoma tissues. Furthermore, elevated circFCHO2 levels demonstrated a positive correlation with the malignant phenotype and poor prognosis among the 158 melanoma patients studied. Besides, we observed that heightened levels of circFCHO2 promoted melanoma cell proliferation, migration, and invasion in vitro, along with contributing to tumor growth in vivo. Furthermore, we found differences in the secondary structure of circFCHO2 compared to most other circular RNA structures. It has fewer miRNA binding sites, while it has more RNA binding protein binding sites. We therefore speculate that circFCHO2 may have a function of interacting with RNA binding proteins. Mechanistically, it was confirmed by fluorescence in situ hybridization (FISH), RNA-pull down, RNA immunoprecipitation (RIP), and western blotting assays that circFCHO2 interacts with dead end protein homolog 1 (DND1) and reverses the inhibition of the PI3K/AKT signaling pathway by binding to DND1. Our findings reveal that circFCHO2 drives melanoma progression by regulating the PI3K/AKT signaling pathway through direct binding to DND1 and may serve as a potential diagnostic biomarker and therapeutic target for the treatment of melanoma.

Recent research progress of circular RNAs in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is an extremely heterogeneous malignant tumor with a high morbidity and mortality. Circular RNAs (circRNAs) are noncoding RNAs with high stability, organ/tissue/cell-specific expression and are conserved across species. Accumulating evidence suggested that circRNAs play crucial roles as microRNA sponges, protein sponges, scaffolds, recruiters and could even polypeptide encoders. Many studies have since revealed that circRNAs were aberrantly expressed in HCC and acted as crucial modulators of HCC carcinogenesis and progression. Furthermore, circRNAs have also been identified as potential diagnostic and prognostic biomarkers for HCC. In this review, we thoroughly outline and evaluate the function of circRNAs in HCC development, with an emphasis on the specific molecular pathways by which they participated in the formation and progression of HCC, and we address their potential for serving as clinical biomarkers in HCC.

Crosstalk Between circRNA and Tumor Microenvironment of Hepatocellular Carcinoma: Mechanism, Function and Applications

Hepatocellular carcinoma (HCC) is one of the most common aggressive tumors in the world. Despite the availability of various treatments, its prognosis remains poor due to the lack of specific diagnostic indicators and the high heterogeneity of HCC cases. CircRNAs are noncoding RNAs with stable and highly specific expression. Extensive research evidence suggests that circRNAs mediate the pathogenesis and progression of HCC through acting as miRNA sponges, protein modulators, and translation templates. Tumor microenvironment (TME) has become a hotspot of immune-related research in recent years due to its effects on metabolism, secretion and immunity of HCC. Accordingly, understanding the role played by circRNAs in TME is important for the study of HCC. This review will discuss the crosstalk between circRNAs and TME in HCC. In addition, we will discuss the current deficiencies and controversies in research on circRNAs and predict future research directions.

Non-coding RNA methylation modifications in hepatocellular carcinoma: interactions and potential implications

RNA methylation modification plays a crucial role as an epigenetic regulator in the oncogenesis of hepatocellular carcinoma (HCC). Numerous studies have investigated the molecular mechanisms underlying the methylation of protein-coding RNAs in the progression of HCC. Beyond their impact on mRNA, methylation modifications also influence the biological functions of non-coding RNAs (ncRNAs). Here, we present an advanced and comprehensive overview of the interplay between methylation modifications and ncRNAs in HCC, with a specific focus on their potential implications for the tumor immune microenvironment. Moreover, we summarize promising therapeutic targets for HCC based on methylation-related proteins. In the future, a more profound investigation is warranted to elucidate the effects of ncRNA methylation modifications on HCC pathogenesis and devise valuable intervention strategies. Video Abstract.

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.

Exploring the interplay between PARP1 and circRNA biogenesis and function

PARP1 (poly-ADP-ribose polymerase 1) is a multidomain protein with a flexible and self-folding structure that allows it to interact with a wide range of biomolecules, including nucleic acids and target proteins. PARP1 interacts with its target molecules either covalently via PARylation or non-covalently through its PAR moieties induced by auto-PARylation. These diverse interactions allow PARP1 to participate in complex regulatory circuits and cellular functions. Although the most studied PARP1-mediated functions are associated with DNA repair and cellular stress response, subsequent discoveries have revealed additional biological functions. Based on these findings, PARP1 is now recognized as a major modulator of gene expression. Several discoveries show that this multifunctional protein has been intimately connected to several steps of mRNA biogenesis, from transcription initiation to mRNA splicing, polyadenylation, export, and translation of mRNA to proteins. Nevertheless, our understanding of PARP1's involvement in the biogenesis of both coding and noncoding RNA, notably circular RNA (circRNA), remains restricted. In this review, we outline the possible roles of PARP1 in circRNA biogenesis. A full examination of the regulatory roles of PARP1 in nuclear processes with an emphasis on circRNA may reveal new avenues to control dysregulation implicated in the pathogenesis of several diseases such as neurodegenerative disorders and cancers. This article is categorized under: RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications Regulatory RNAs/RNAi/Riboswitches > Regulatory RNAs RNA Processing > Splicing Regulation/Alternative Splicing.

Deciphering roles of TRIMs as promising targets in hepatocellular carcinoma: current advances and future directions

Tripartite motif (TRIM) family is assigned to RING-finger-containing ligases harboring the largest number of proteins in E3 ubiquitin ligating enzymes. E3 ubiquitin ligases target the specific substrate for proteasomal degradation via the ubiquitin-proteasome system (UPS), which seems to be a more effective and direct strategy for tumor therapy. Recent advances have demonstrated that TRIM genes associate with the occurrence and progression of hepatocellular carcinoma (HCC). TRIMs trigger or inhibit multiple biological activities like proliferation, apoptosis, metastasis, ferroptosis and autophagy in HCC dependent on its highly conserved yet diverse structures. Remarkably, autophagy is another proteolytic pathway for intracellular protein degradation and TRIM proteins may help to delineate the interaction between the two proteolytic systems. In depth research on the precise molecular mechanisms of TRIM family will allow for targeting TRIM in HCC treatment. We also highlight several potential directions warranted further development associated with TRIM family to provide bright insight into its translational values in hepatocellular carcinoma.

circCBL and its host gene CBL collaboratively enhance the antiviral immunity and antibacterial immunity by targeting MITA in fish

IMPORTANCE

Increasing evidence indicates that circular RNAs exert crucial functions in regulating gene expression in mammals. However, the function of circRNAs in lower vertebrates still needs further exploration. Our research results demonstrated that circRNA, namely circCBL, is involved in modulating antiviral and antibacterial immune responses in lower vertebrates. In addition, our study also found that circCBL can serve as a competing endogenous RNA to facilitate MITA expression, thereby modulating MITA-mediated innate immunity. Further research has proved that the host gene CBL also promotes the expression of MITA, enhancing antiviral and antibacterial immune responses. Our study not only elucidated the underlying biological mechanism of the circRNA-miRNA-mRNA axis in the innate immune response of lower vertebrates but also unveiled the synergistic antibacterial and antiviral mechanisms between circRNA and its host gene in lower vertebrates.

The Circular RNA circFGFR4 Facilitates Resistance to Anti-PD-1 of Triple-Negative Breast Cancer by Targeting the miR-185-5p/CXCR4 Axis

Purpose

One of the most catastrophic malignant tumors is triple negative breast cancer (TNBC). It is characterized by rapid progression in the clinic. CircRNAs are abnormally expressed in almost all cancers and play important roles in tumor immune evasion. Nevertheless, the biological roles of the circular fibroblast growth factor receptor 4 RNA (circFGFR4) in TNBC remain unclear.

Methods

The expression of circFGFR4 in TNBC tissues and paired nontumor tissues was detected using quantitative real-time polymerase chain reaction (qRT-PCR). The role of circFGFR4 in TNBC immune evasion was estimated by analyzing clinical tissues. In vivo circRNA precipitation, RNA immunoprecipitation, and luciferase reporter assays were performed to explore interaction between circFGFR4 and miR-185-5p.

Results

Our results indicated that circFGFR4 was significantly overexpressed in TNBC tissues. Upregulated circFGFR4 expression was correlated with decreased CD8+ T cell infiltration in tumor tissues and resistance to anti-programmed cell death 1 (PD-1) immunotherapy in TNBC patients and mice bearing TNBC tumors. Forced circFGFR4 expression inhibited CD8+ T cell infiltration in tissue sections from TNCB tumor bearing mice. Mechanistically, circFGFR4 competitively sponged miR-185-5p and prevented miR-185-5p from decreasing the levels of C-X-C motif chemokine receptor 4 (CXCR4).

Conclusion

Ultimately, our results indicated that circFGFR4 plays an important role in immune evasion and anti-PD-1 immunotherapy resistance via regulates miR-185-5p/CXCR4 axis in TNBC, thus suggesting that circFGFR4 has significant potential as a biomarker for predicting sensitivity to anti-PD-1 immunotherapy and as an immunotherapeutic target for TNBC.

Circular RNAs in hepatocellular carcinoma: biogenesis, function, and pathology

Hepatocellular carcinoma (HCC) is one of the most common causes of cancer-related death worldwide. Both genetic and environmental factors through a multitude of underlying molecular mechanisms participate in the pathogenesis of HCC. Recently, numerous studies have shown that circular RNAs (circRNAs), an emerging class of non-coding RNAs characterized by the presence of covalent bonds linking 3' and 5' ends, play an important role in the initiation and progression of cancers, including HCC. In this review, we outline the current status of the field of circRNAs, with an emphasis on the functions and mechanisms of circRNAs in HCC and its microenvironment. We also summarize and discuss recent advances of circRNAs as biomarkers and therapeutic targets. These efforts are anticipated to throw new insights into future perspectives about circRNAs in basic, translational and clinical research, eventually advancing the diagnosis, prevention and treatment of HCC.

CircRNAs regulate the crosstalk between inflammation and tumorigenesis: The bilateral association and molecular mechanisms

Inflammation, a hallmark of cancer, has been associated with tumor progression, transition into malignant phenotype and efficacy of the chemotherapeutic agents in cancer. Chronic inflammation provides a favorable environment for tumorigenesis by inducing immunosuppression, whereas acute inflammation prompts tumor suppression by generating anti-tumor immune responses. Inflammatory factors derived from interstitial cells or tumor cells can stimulate cell proliferation and survival by modulating oncogenes and/or tumor suppressors. Recently, a new class of RNAs, i.e., circular RNAs (circRNAs), has been implicated in inflammatory diseases. Although there are reports on circRNAs imparting functions in inflammatory insults, whether these circularized transcripts hold the potential to regulate inflammation-induced cancer or tumor-related inflammation, and modulate the interactions between tumor microenvironment (TME) and the inflammatory stromal/immune cells, awaits further elucidation. Contextually, the current review describes the molecular association between inflammation and cancer, and spotlights the regulatory mechanisms by which circRNAs can moderate TME in response to inflammatory signals/triggers. We also present comprehensive information about the immune cell(s)-specific expression and functions of the circRNAs in TME, modulation of inflammatory signaling pathways to drive tumorigenesis, and their plausible roles in inflammasomes and tumor development. Moreover, the therapeutic potential of these circRNAs in harnessing inflammatory responses in cancer is also discussed.

Hsa_circ_0084003 modulates glycolysis and epithelial-mesenchymal transition in pancreatic ductal adenocarcinoma through targeting hsa-miR-143-3p/DNMT3A axis

Pancreatic ductal adenocarcinoma, one of the deadliest tumors of the digestive tract, is a difficult and invasive malignancy. Current treatment for pancreatic ductal adenocarcinoma mainly depends on surgery combined with radiotherapy and chemotherapy, which, however, often resulting in questionable curative effect. Therefore, new targeted therapies are needed in future treatment. We first interfered with hsa_circ_0084003 expression in pancreatic ductal adenocarcinoma cells, and further studied how hsa_circ_0084003 functioned in regulating pancreatic ductal adenocarcinoma cell aerobic glycolysis and epithelial-mesenchymal transition, and also evaluated the regulatingeffect of hsa_circ_0084003 on hsa-miR-143-3p and its target DNA methyltransferase 3A. Hsa_circ_0084003 knockdown could notably inhibit the aerobic glycolysis and epithelial-mesenchymal transition of pancreatic ductal adenocarcinoma cells. Mechanistically, hsa_circ_0084003 could regulate its downstream target DNA methyltransferase 3A by binding to hsa-miR-143-3p, and overexpression of hsa_circ_0084003 could reverse the anticarcinogenic effect of hsa-miR-143-3p on aerobic glycolysis and epithelial-mesenchymal transition in pancreatic ductal adenocarcinoma cells. Hsa_circ_0084003, as a carcinogenic circular RNA, regulated its downstream target DNA methyltransferase 3A to promote pancreatic ductal adenocarcinoma cell aerobic glycolysis and epithelial-mesenchymal transition through sponging hsa-miR-143-3p. Therefore, hsa_circ_0084003 could be studied as a possible therapeutic target regarding pancreatic ductal adenocarcinoma.

CircFOXK2 promotes hepatocellular carcinoma progression and leads to a poor clinical prognosis via regulating the Warburg effect

BACKGROUND

The Warburg effect is well-established to be essential for tumor progression and accounts for the poor clinical outcomes of hepatocellular carcinoma (HCC) patients. An increasing body of literature suggests that circular RNAs (circRNAs) are important regulators for HCC. However, few circRNAs involved in the Warburg effect of HCC have hitherto been investigated. Herein, we aimed to explore the contribution of circFOXK2 to glucose metabolism reprogramming in HCC.

METHODS

In the present study, different primers were designed to identify 14 circRNAs originating from the FOXK2 gene, and their differential expression between HCC and adjacent liver tissues was screened. Ultimately, circFOXK2 (hsa_circ_0000817) was selected for further research. Next, the clinical significance of circFOXK2 was evaluated. We then assessed the pro-oncogenic activity of circFOXK2 and its impact on the Warburg effect in both HCC cell lines and animal xenografts. Finally, the molecular mechanisms of how circFOXK2 regulates the Warburg effect of HCC were explored.

RESULTS

CircFOXK2 was aberrantly upregulated in HCC tissues and positively correlated with poor clinical outcomes in patients that underwent radical hepatectomy. Silencing of circFOXK2 significantly suppressed HCC progression both in vitro and in vivo. Mechanistically, circFOXK2 upregulated the expression of protein FOXK2-142aa to promote LDHA phosphorylation and led to mitochondrial fission by regulating the miR-484/Fis1 pathway, ultimately activating the Warburg effect in HCC.

CONCLUSIONS

CircFOXK2 is a prognostic biomarker of HCC that promotes the Warburg effect by promoting the expression of proteins and miRNA sponges that lead to tumor progression. Overall, circFOXK2 has huge prospects as a potential therapeutic target for patients with HCC.

Circ_0007429/miR-637/TRIM71/Ago2 axis participates in the regulation of proliferation, migration, invasion, apoptosis, and aerobic glycolysis of HCC

CircRNAs play an important role in the progression of hepatocellular carcinoma (HCC), however, the role of circ_0007429 in HCC remains unknown. Using bioinformatics tools, we selected circ_0007429 that was most highly expressed in HCC tissues and investigated its role in HCC progression. Immunohistochemistry, plasmid transfection, real-time quantitative PCR, and western blot analysis were used to identify the relationship between circ_0007429 and its potential target, miR-637, and TRIM71. The regulatory effect of circ_0007429 on miR-637/TRIM71/Ago2 signaling and its key role in HCC progression were studied in vitro. A nude mouse xenograft model was used to examine tumor growth in vivo. Circ_0007429 and TRIM71 expression were upregulated, while miR-637 expression was downregulated in HCC tissues and cells compared with their expression in control groups. Knockdown of circ_0007429 enhanced apoptosis in HCC cells, while impeded proliferation, migration, invasion, and aerobic glycolysis, which were reversed by miR-637 inhibitor. High levels of circ_0007429 correlated with a poor survival rate of HCC patients. Additionally, circ_0007429 interfering inhibited tumor growth in vivo. TRIM71 directly bound to miR-637 and inhibited Ago2 expression. Moreover, circ_0007429 promotes aerobic glycolysis in HCC cells through the miR/TRIM71/Ago2 axis. Circ_0007429 promotes HCC progression by promoting cell proliferation, migration, invasion, and aerobic glycolysis and by inhibiting cell apoptosis through the miR/TRIM71/Ago2 axis. These results provide molecular insights into the mechanism of HCC and suggest that circ_0007429 could be a therapeutic target for HCC.

CircRNA-104718 promotes glioma malignancy through regulation of miR-218-5p/HMGB1 signalling pathway

Increasing number of studies have proven that circular RNAs (circRNAs) play a major role in the biological processes of many different cancers, including glioma, especially as competitive molecular sponges of microRNAs (miRNAs). However, the clear molecular mechanism of the circRNA network in glioma is still not well understood. The expression level of circRNA-104718 and microRNA (miR)-218-5p in glioma tissues and cells were detected by quantitative real-time polymerase chain reaction (qRT-PCR). The target protein's expression level was assessed by western blotting. Bioinformatics systems were used to predict the possible microRNAs and target genes of circRNA-104718, after which dual-luciferase reporter assays were used to confirm the predicted interactions. The proliferation, invasion, migration and apoptosis of glioma cells were detected by CCK, EdU, transwell, wound-healing and flow cytometry assays. CircRNA-104718 was upregulated in human glioma tissues, and a higher level of circRNA-104718 indicated poorer outcomes in glioma patients. In contrast, in glioma tissues, miR-218-5p was downregulated. Knockdown of circRNA-104718 suppressed migration and invasion while boosting the apoptosis rate of glioma cells. In addition, the upregulation of miR-218-5p in glioma cells caused the same suppression. Mechanistically, circRNA-104718 inhibited the protein expression level of high mobility group box-1 (HMGB1) by acting as a molecular sponge for miR-218-5p. CircRNA-104718 is a suppressive factor in glioma cells and might represent a new target for the treatment of glioma patients. CircRNA-104718 modulates glioma cell proliferation through the miR-218-5p/HMGB1 signalling axis. CircRNA-104718 provides a possible mechanism for understanding the pathogenesis of glioma.

Circular RNA circPlce1 regulates innate immune response in miiuy croaker, Miichthys miiuy

In recent years, more and more researchers have devoted to the study of circular RNAs (circRNAs) in noncoding RNAs. As an important regulator in a variety of biological processes, circRNAs are relatively abundant in the study of mammals, while research in lower vertebrates is still lacking. In this study, we found a circRNA, circPlce1, related to innate immune response in Miichthys miiuy (miiuy croaker). The experimental results confirmed that circPlce1 could promote the production of antiviral genes and inflammatory response under the stimulation of poly (I: C) and LPS. We also confirmed that circPlce1 can promote NF-κB and IRF3 pathways through luciferase reporter assay experiment. In addition, we also found that circPlce1 can promote cell proliferation and improve cell viability. In conclusion, our results showed that circPlce1 plays an active role in regulating inflammatory response, cell proliferation and cell viability, providing a foundation for the study of the biological function of circRNAs in the innate immune response in teleost fish.

Insights into the role of long non-coding RNAs in DNA methylation mediated transcriptional regulation

DNA methylation is one of the most important epigenetic mechanisms that governing regulation of gene expression, aberrant DNA methylation patterns are strongly associated with human malignancies. Long non-coding RNAs (lncRNAs) have being discovered as a significant regulator on gene expression at the epigenetic level. Emerging evidences have indicated the intricate regulatory effects between lncRNAs and DNA methylation. On one hand, transcription of lncRNAs are controlled by the promoter methylation, which is similar to protein coding genes, on the other hand, lncRNA could interact with enzymes involved in DNA methylation to affect the methylation pattern of downstream genes, thus regulating their expression. In addition, circular RNAs (circRNAs) being an important class of noncoding RNA are also found to participate in this complex regulatory network. In this review, we summarize recent research progress on this crosstalk between lncRNA, circRNA, and DNA methylation as well as their potential functions in complex diseases including cancer. This work reveals a hidden layer for gene transcriptional regulation and enhances our understanding for epigenetics regarding detailed mechanisms on lncRNA regulatory function in human cancers.

A new acidic microenvironment related lncRNA signature predicts the prognosis of liver cancer patients

BACKGROUND

The acidic microenvironment (AME), like hypoxia, inflammation, or immunoreaction, is a hallmark of the tumor microenvironment (TME). This work aimed to develop a prediction signature dependent on AME-associated lncRNAs in order to predict the prognosis of LC individuals.

METHODS

We downloaded RNA-seq information and the corresponding clinical and predictive data from The Cancer Genome Atlas (TCGA) dataset and conducted univariate and multivariate Cox regression analyses to identify AME-associated lncRNAs for the construction of a prediction signature The Kaplan-Meier technique was utilized to determine the overall survival (OS) rate of the high (H)-risk and low (L)-risk groups. Using gene set enrichment analysis (GSEA) the functional variations between the H- and L-risk groups were investigated. The association between the prediction signature and immunological state was investigated using single-sample GSEA (ssGSEA). Additionally, the association between the predicted signature and the therapeutic response of LC individuals was evaluated. Lastly, quantitative reverse transcription polymerase chain reaction (qRT-PCR) was performed to verify the risk model.

RESULTS

We generated a signature comprised of seven AME-associated lncRNAs (LINC01116, AC002511.2, LINC00426, ARHGAP31-AS1, LINC01060, TMCC1-AS1, AC012065.1). The H-risk group had a worse prognosis than the L- risk group. The AME-associated lncRNA signature might determine the prognosis of individuals with LC independently. The AME-related lncRNA signature shows a greater predictive effectiveness than clinic-pathological factors, with an area under the receiver operating characteristic (ROC) curve of 0.806%. When participants were categorized based on several clinico-pathological characteristics, the OS of high-risk individuals was shorter compared to low-risk patients. GSEA demonstrated that the metabolism of different acids and the PPAR signaling pathway are closely associated with low-risk individuals. The prognostic signature was substantially associated with the immunological status of LC individuals, as determined by ssGSEA. High risk individuals were more sensitive to some immunotherapies (including anti-TNFSF4 anti-SIRPA, anti-CD276 and anti-TNFSF15) and some conventional chemotherapy drugs (including lapatinib and paclitaxel). Finally, the expression levels of the seven lncRNAs comprising the signature were tested by qRT-PCR.

CONCLUSIONS

A basis for the mechanism of AME-associated lncRNAs in LC is provided by the prediction signature, which also offers clinical therapeutic recommendations for LC individuals.

TRIM proteins in hepatocellular carcinoma

The tripartite motif (TRIM) protein family is a highly conserved group of E3 ligases with 77 members known in the human, most of which consist of a RING-finger domain, one or two B-box domains, and a coiled-coil domain. Generally, TRIM proteins function as E3 ligases to facilitate specific proteasomal degradation of target proteins. In addition, E3 ligase independent functions of TRIM protein were also reported. In hepatocellular carcinoma, expressions of TRIM proteins are both regulated by genetic and epigenetic mechanisms. TRIM proteins regulate multiple biological activities and signaling cascades. And TRIM proteins influence hallmarks of HCC. This review systematically demonstrates the versatile roles of TRIM proteins in HCC and helps us better understand the molecular mechanism of the development and progression of HCC.

CircSOD2 Contributes to Tumor Progression, Immune Evasion and Anti-PD-1 Resistance in Hepatocellular Carcinoma by Targeting miR-497-5p/ANXA11 Axis

Circular RNAs (circRNAs) can function as functional molecules in hepatocellular carcinoma (HCC). Herein, circRNA superoxide dismutase 2 (circSOD2) was researched in HCC progression and immune system. The real-time polymerase chain reaction (qRT-PCR) was used for quantification of circSOD2, microRNA-497-5p (miR-497-5p) and Annexin A11 (ANXA11). Cell assays were performed by 3-(4, 5-dimethylthiazol-2-y1)-2, 5-diphenyl tetrazolium bromide (MTT) and colony formation assays for proliferation, flow cytometry for apoptosis and cell cycle, wound healing assay for migration and transwell assay for migration/invasion. ANXA11 and metastatic protein levels were measured by western blot. Dual-luciferase reporter and RNA immunoprecipitation (RIP) assays were performed to analyze target binding. CD8⁺ T cell immunity was assessed by Immunohistochemistry (IHC) assay, and the effect of circSOD2 on programmed cell death 1 (PD-1) immune checkpoint inhibitors (anti-PD-1) therapy was evaluated by mice xenograft assay. CircSOD2 was upregulated in HCC tissues and cells. Knockdown of circSOD2 resulted in HCC cell growth inhibition, apoptosis promotion, cell cycle arrest and metastasis suppression. Mechanically, circSOD2 promoted HCC development by acting as a miR-497-5p sponge and miR-497-5p played a tumor-inhibitory role in HCC cells by targeting ANXA11. Moreover, circSOD2 induced upregulation of ANXA11 expression by interacting with miR-497-5p. Also, the promoting effects of circSOD2 on immune evasion and anti-PD-1 resistance were related to miR-497-5p/ANXA11 axis. This study elucidated the pivotal function of circSOD2 in HCC progression and immunosuppression by mediating miR-497-6p/ANXA11 axis. CircSOD2/miR-497-5p/ANXA11 axis was a novel view of circRNA research in HCC.

Circular Noncoding RNA hsa_circ_0003570 as a Prognostic Biomarker for Hepatocellular Carcinoma

Circular RNAs (circRNAs) are potential biomarkers owing to their stability, tissue specificity, and abundance. This study aimed to evaluate the clinical significance of hsa_circ_0003570 expression and to investigate its potential as a biomarker in hepatocellular carcinoma (HCC). We evaluated hsa_circ_0003570 expression in 121 HCC tissue samples, its association with clinicopathological characteristics, and overall and progression-free survival. Hsa_circ_0003570 expression was downregulated in HCC tissues. Low hsa_circ_0003570 expression was more common in tumors larger than 5 cm (odds ratio (OR), 6.369; 95% confidence interval (CI), 2.725−14.706; p < 0.001), vessel invasion (OR, 5.128; 95% CI, 2.288−11.494; p < 0.001); advanced tumor-node metastasis stage (III/IV; OR, 4.082; 95% CI, 1.866−8.929; p < 0.001); higher Barcelona Clinic Liver Cancer stage (B/C; OR, 3.215; 95% CI, 1.475−6.993; p = 0.003); and higher AFP (>200 ng/mL; OR, 2.475; 95% CI, 1.159−5.291; p = 0.018). High hsa_circ_0003570 expression was an independent prognostic factor for overall survival (hazard ratio (HR), 0.541; 95% confidence interval (CI), 0.327−0.894; p = 0.017) and progression-free survival (HR, 0.633; 95% CI, 0.402−0.997; p = 0.048). Hsa_circ_0003570 is a potential prognostic biomarker in patients with HCC, and further validation of hsa_circ_0003570 is needed.

Noncoding RNA-mediated molecular bases of chemotherapy resistance in hepatocellular carcinoma

Despite the significant progress in decreasing the occurrence and mortality of hepatocellular carcinoma (HCC), it remains a public health issue worldwide on the basis of its late presentation and tumor recurrence. To date, apart from surgical interventions, such as surgical resection, liver transplantation and locoregional ablation, current standard antitumor protocols include conventional cytotoxic chemotherapy. However, due to the high chemoresistance nature, most current therapeutic agents show dismal outcomes for this refractory malignancy, leading to disease relapse. Nevertheless, the molecular mechanisms involved in chemotherapy resistance remain systematically ambiguous. Herein, HCC is hierarchically characterized by the formation of primitive cancer stem cells (CSCs), progression of epithelial-mesenchymal transition (EMT), unbalanced autophagy, delivery of extracellular vesicles (EVs), escape of immune surveillance, disruption of ferroptosis, alteration of the tumor microenvironment and multidrug resistance-related signaling pathways that mediate the multiplicity and complexity of chemoresistance. Of note, anecdotal evidence has corroborated that noncoding RNAs (ncRNAs) extensively participate in the critical physiological processes mentioned above. Therefore, understanding the detailed regulatory bases that underlie ncRNA-mediated chemoresistance is expected to yield novel insights into HCC treatment. In the present review, a comprehensive summary of the latest progress in the investigation of chemotherapy resistance concerning ncRNAs will be elucidated to promote tailored individual treatment for HCC patients.

Hepatic stellate cell exosome-derived circWDR25 promotes the progression of hepatocellular carcinoma via the miRNA-4474-3P-ALOX-15 and EMT axes

Recently, the emerging role of circular RNAs (circRNAs) in tumor development and progression has been a topic of great interest. Nevertheless, the effects of hepatic stellate cell (HSC)-derived exosomes in hepatocellular carcinoma (HCC) remain unclear. Here, we aim to explore the potential effect of HSC exosome-derived circWDR25 on the aggressiveness of HCC. Firstly, a microarray analysis of circRNAs was performed to profile and identify the differentially expressed circRNAs derived from HSC exosomes activated by HCC cells. Subsequently, the roles of circWDR25 in HCC tumor growth and aggressiveness were confirmed through in vitro and in vivo functional experiments. Moreover, RNA pull-down, dual-luciferase reporter assays, and fluorescent in situ hybridization (FISH) were performed to determine interactions in the circWDR25-miR-4474-3p-ALOX15 loop. Immunohistochemical analysis was also performed on a microarray of HCC tissues and peritumoral tissues. We found that overexpressed peritumoral circWDR25 was associated with survival and recurrence in patients with HCC and promoted the progression of HCC cells both in vitro and in vivo. Mechanistically, both exogenous and HSC exosomal-derived circWDR25 regulated the expression of ALOX15 by sponging miR-4474-3p and ultimately inducing an epithelial-to-mesenchymal transition (EMT) in HCC cells. Moreover, exogenous and HSC exosomal-derived circWDR25 promoted the expression of CTLA-4 in HSCs and PD-L1 in HCC cells. In conclusion, circWDR25 facilitated HCC cell proliferation and invasion via the circWDR25/miR-4474-3p/ALOX15 and EMT axes and it promoted the expression of CTLA-4 in HSCs and PD-L1 in HCC cells, thus providing insights into the mechanism of tumor aggressiveness mediated by HSC-derived exosomal circWDR25.

Circular RNA: An emerging frontier in RNA therapeutic targets, RNA therapeutics, and mRNA vaccines

Circular RNAs (circRNA) is a class of natural (biogenic) or synthetic closed RNA without 5' or 3' ends. Meanwhile, their unique covalently-closed structures of circRNA prevent RNA degradation by exonucleases, thereby empowering them with high pharmaceutical stability and biostability relative to current standard-of-care linear mRNA. Natural circRNA can be non-coding RNAs as well as protein-coding RNA, the latter of which was recently discovered. The physiological functions of biogenic circRNAs, which largely remain elusive, include protein and gene sponges, cell activity modulators, and protein translation. The discovery that the circRNA levels can be correlated with some human diseases empowers circRNA with the potential as a novel type of disease biomarkers and a noncanonical class of therapeutic targets. Recently, synthetic circRNA have been engineered to explore their applications as a novel class of mRNA therapeutics and vaccines. In this review, we will discuss the current understanding of the biogenesis and physiological functions of natural circRNAs, the approaches to circRNA synthesis, and current research in the exploration of endogenous circRNAs as novel therapeutic targets and testing circRNAs as an emerging class of RNA therapeutics and vaccines.

CircGPR137B/miR-4739/FTO feedback loop suppresses tumorigenesis and metastasis of hepatocellular carcinoma

Background

Emerging evidence indicates that circular RNAs (circRNAs) and m⁶A RNA methylation participate in the pathogenesis and metastasis of multiple malignancies including hepatocellular carcinoma (HCC). However, it remains undocumented how circRNAs form a feedback loop with the m⁶A modification contributing to HCC.

Methods

A novel hsa_circ_0017114 (circGPR137B) was identified from three pairs of primary HCC and adjacent normal tissues by circRNA expression profiling. The association of circGPR137B and miR-4739 with clinicopathological parameters and prognosis in patients with HCC was analyzed by RT-qPCR, fluorescence in situ hybridization and TCGA cohorts. The role of circGPR137B in HCC was estimated in vitro and in vivo. RT-qPCR, western blot, m⁶A dot blot, RIP, MeRIP and dual-luciferase reporter assays were used to validate the reciprocal regulation of the feedback loop among circGPR137B, miR-4739 and m⁶A demethylase FTO. Meanwhile, the expression, function and prognosis of FTO in HCC were investigated by RT-qPCR, western blot, TCGA and rescue experiments.

Results

We identified a new dramatically downregulated circGPR137B in HCC tissues, and found that downregulation of circGPR137B or upregulation of miR-4739 was associated with poor prognosis in patients with HCC. Ectopic expression of circGPR137B strikingly repressed the proliferation, colony formation and invasion, whereas knockdown of circGPR137B harbored the opposite effects. Moreover, restored expression of circGPR137B inhibited tumor growth and lung metastasis in vivo. Further investigations showed that circGPR137B, co-localized with miR-4739 in the cytoplasm, acted as a sponge for miR-4739 to upregulate its target FTO, which mediated m⁶A demethylation of circGPR137B and promoted its expression. Thus, a feedback loop comprising circGPR137B/miR-4739/FTO axis was formed. FTO suppressed cell growth and indicated favorable survival in patients with HCC.

Conclusion

Our results demonstrate that circGPR137B inhibits HCC tumorigenesis and metastasis through the circGPR137B/miR-4739/FTO feedback loop. This positive feedback mechanism executed by functional coupling between a circRNA sponge and an m⁶A modification event suggests a model for epigenetics.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12943-022-01619-4.

CircKIF5B Promotes Hepatocellular Carcinoma Progression by Regulating the miR-192 Family/XIAP Axis

Background

The long-term prognosis of HCC (hepatocellular carcinoma) with metastasis remains extremely poor. CircRNAs are promising as critical biological markers in identifying disease mechanisms and developing new effective treatments. However, the role of the aberrant expression of circRNAs in HCC progression remains largely unknown.

Methods

CircKIF5B location was investigated by RNA fluorescence in situ hybridization (RNA-FISH). For circRNA determination, RNase R treatment and Real-Time Quantitative RT-PCR (qRT-PCR) were performed. Transwell chamber assays examined the chemotactic migration and invasion of liver cancer cells.

Results

This study identified the circRNA circKIF5B originating from exons 1, 2, and 3 of the KIF5B gene. Importantly, we found that circKIF5B circRNA, rather than KIF5B linear mRNA, was notably upregulated in liver cancer cell lines and tissues. Moreover, we found that silencing circKIF5B markedly reduced the proliferation, invasion, and metastasis of liver cancer cells by sponging the miR-192 family, thus decreasing the expression of X-linked inhibitor of apoptosis (XIAP).

Conclusion

Our data demonstrate that circKIF5B can regulate XIAP expression by sponging miR-192 and miR-215 competing for the ceRNA mechanism, indicating that circKIF5B may act as an essential upstream regulator and providing mechanistic evidence to support the view that circKIF5B/miR-192s/XIAP is a promising therapeutic target for treating liver cancer.

Circular RNA EPB41 expression predicts unfavorable prognoses in NSCLC by regulating miR-486-3p/eIF5A axis-mediated stemness

Dysregulation of circular RNAs (circRNAs) has recently been found to play an important role in the progression and development of cancers such as non-small cell lung cancer (NSCLC). Yet the functions of many circRNAs in NSCLC remain unclear. In this study, the circRNA expression profiles in NSCLC tumor tissues and adjacent non-tumorous tissues were detected by high-throughput sequencing. Bioinformatics analyses, the dual-luciferase reporter system, fluorescence in situ hybridization (FISH) and miRNA/mRNA high-throughput sequencing were used to identify circ-EPB41 and its downstream target. The subcutaneous tumor/caudal vein transfer mouse model was used for tumor growth and invasion analysis. The results show that the circ-EPB41 was upregulated in NSCLC tissues and cell lines. Increased circ-EPB41 expression in NSCLC was significantly correlated with malignant characteristics, and positive to post-surgical overall survival of NSCLC patients. Reduced circ-EPB41 expression in NSCLC decreased cell proliferation and invasion in both in vitro and in vivo experiments. The miRNA/mRNA high-throughput sequencing suggested that downregulation of circ-EPB41 promoted microRNA (miR)-486-3p and suppressed eukaryotic translation initiation factor 5A (eIF5A) expression. Luciferase reporter experiments confirmed that miR-486-3p/eIF5A were downstream targets of circ-EPB41. In addition, we also found that downregulation of circ-EPB41 suppressed self-renewal and decreased expression of stemness markers SOX2, OCT-4, Nanog and CD133 by sponging miR-486-3p to enhance eIF5A expression. Taken togeter, these data revealed the important role of circ-EPB41 in regulating NSCLC cell invasion and proliferation by modifying miR-486-3p/eIF5A axis-mediated stemness. We believe our study provides a novel perspective regarding the role of circRNAs in NSCLC progression.

Circular RNA as a Novel Biomarker and Therapeutic Target for HCC

Circular RNA (circRNA) is a kind of endogenous non-coding RNA (ncRNA), which is produced by the reverse splicing of precursor mRNA (pre mRNA). It is widely expressed in a variety of biological cells. Due to the special formation mode, circRNA does not have a 5′ terminal cap and 3′ poly (A) tail structure. Compared with linear RNA, circRNA is more stable to exonuclease and ribonuclease. In addition, circRNA is structurally conserved, has a stable sequence and is tissue-specific. With the development of high-throughput sequencing and bioinformatics technology, more and more circRNAs have been found. CircRNA plays an important pathophysiological role in the occurrence and development of alcoholic liver injury (ALI), hepatic fibrosis (HF), hepatocellular carcinoma (HCC), and other liver diseases. Our group has been committed to the research of liver disease diagnosis and treatment targets. We review the function and mechanism of circRNA in ALI, HF and HCC, expecting to provide new ideas for the diagnosis, treatment, and prognosis of liver diseases.

Circular RNAs in hepatocellular carcinoma: Recent advances

Circular RNAs (circRNAs) have covalently closed loop structures at both ends, exhibiting characteristics dissimilar to those of linear RNAs. Emerging evidence suggests that aberrantly expressed circRNAs play crucial roles in hepatocellular carcinoma (HCC) by affecting the proliferation, apoptosis and invasive capacity of HCC cells. Certain circRNAs may be used as biomarkers to diagnose and predict the prognosis of HCC. Therefore, circRNAs are expected to become novel biomarkers and therapeutic targets for HCC. Herein, we briefly review the characteristics and biological functions of circRNAs, focusing on their roles in HCC to provide new insights for the early diagnosis and targeted therapy of HCC.

Down-regulation of circPTTG1IP induces hepatocellular carcinoma development via miR-16-5p/RNF125/JAK1 axis

Circular RNAs are known to regulate the biological processes of hepatocellular carcinoma (HCC), and humans with Down syndrome are at low risk of developing solid tumors due to the amplification of several tumor suppressor genes on human chromosome 21 (HSA21). Here, we aimed to investigate the potential role of circRNAs originating from HSA21 in the progression of HCC. CircRNA-sequencing was performed to analyze differentially expressed circRNAs in 4 HCC and peritumor tissues, and circRNAs originating from HSA21 were further analyzed. Circ_0061984 (circPTTG1IP) was chosen for further study because it showed the lowest expression in HCC tissues, and qRT-PCR was used to confirm the expression of circPTTG1IP in HCC patient tissues. The biological function of circPTTG1IP was detected in HCC cells both in vivo and in vitro. Moreover, luciferase reporter assays, circRNA immunoprecipitation, and fluorescence in situ hybridization (FISH) were used to investigate the potential mechanism of circPTTG1IP. Finally, the possible mechanisms of filgotinib in circPTTG1IP-driven HCC were assessed. CircPTTG1IP expression was decreased in HCC compared to peritumoral tissues. Moreover, low circPTTG1IP expression was revealed to be associated with a poor prognosis of HCC patients. Elevation of circPTTG1IP was revealed to inhibit HCC development both in vitro and in vivo. Mechanistically, circPTTG1IP was shown to function as a competing endogenous RNA (ceRNA) of RNF125 by binding miR-16-5p to increase the level of the E3 ubiquitin ligase RNF125, which further ubiquitinated and degraded JAK1 protein. Finally, we demonstrated that administration of filgotinib, a JAK1 inhibitor, restricted HCC progression induced by low circPTTG1IP expression. Thus, we revealed that circPTTG1IP is a novel tumor suppresser circRNA in HCC and that a low circPTTG1IP level promotes HCC development via the miR-16-5p/RNF125/JAK1 axis. Patients with low circPTTG1IP may benefit from filgotinib treatment.

Low miR-10b-3p associated with sorafenib resistance in hepatocellular carcinoma

BACKGROUND

Sorafenib is one of the standard first-line therapies for advanced hepatocellular carcinoma (HCC). Unfortunately, there are currently no appropriate biomarkers to predict the clinical efficacy of sorafenib in HCC patients. MicroRNAs (miRNAs) have been studied for their biological functions and clinical applications in human cancers.

METHODS

In this study, we found that miR-10b-3p expression was suppressed in sorafenib-resistant HCC cell lines through miRNA microarray analysis.

RESULTS

Sorafenib-induced apoptosis in HCC cells was significantly enhanced by miR-10b-3p overexpression and partially abrogated by miR-10b-3p depletion. Among 45 patients who received sorafenib for advanced HCC, those with high miR-10b-3p levels, compared to those with low levels, exhibited significantly longer overall survival (OS) (median, 13.9 vs. 3.5 months, p = 0.021), suggesting that high serum miR-10b-3p level in patients treated with sorafenib for advanced HCC serves as a biomarker for predicting sorafenib efficacy. Furthermore, we confirmed that cyclin E1, a known promoter of sorafenib resistance reported by our previous study, is the downstream target for miR-10b-3p in HCC cells.

CONCLUSIONS

This study not only identified the molecular target for miR-10b-3p, but also provided evidence that circulating miR-10b-3p may be used as a biomarker for predicting sorafenib sensitivity in patients with HCC.

Hsa_circ_0006692 Promotes Lung Cancer Progression via miR-205-5p/CDK19 Axis

Circular RNA (CircRNA) is related to tumor development. Nevertheless, the regulation and function of hsa_circ_0006692 and its interactions with miR-205-5p and CDK19 in the development of non-small-cell lung cancer (NSCLC) were un-explored. The correlations of expression levels of hsa_circ_0006692 in NSCLC specimens and cells with pathological characteristics were studied. The interactions of hsa_circ_0006692 with miR-205-5p and CDK19 were assessed with real-time PCR, RNA-binding protein immunoprecipitation (RIP), luciferase reporter, RNA pull-down, and fluorescence in situ hybridization (FISH). The roles of hsa_circ_0006692 on cell growth, invasion, and migration in vitro and metastasis in vivo were evaluated. Hsa_circ_0006692 was over-expressed in 60 cases of NSCLC specimens and cells, which was positively correlated with TNM stage, tumor size, and invasion of the lung basal layer. The results of the in vitro and in vivo studies revealed that the over-expression of hsa_circ_0006692 facilitated NSCLC cell growth, migration, and invasion, cell cycle arrest at the S phase, and the activation of BCL-2, CCND1, and PCNA. The results of the dual-luciferase reporter assay, RNA immunoprecipitation, and pull-down assays indicated that hsa_circ_0006692 sponged miR-205-5p, which targeted CDK19 and facilitated the malignant behaviors of lung cancer cells. Hsa_circ_0006692 modulated EMT of lung cancer cells via the stimulation of CDH1, CDH2, VIMENTIN, and MMP7. This study revealed that hsa_circ_0006692 promoted NSCLC progression via enhancing cell growth, invasion, and metastasis through sponging mir-205-5p, up-regulating the downstream oncogene CDK19 and modulating EMT of lung cancer cells. The circ-0006692/mir-205-5p/CDK19 axis might serve as a prognosis biomarker and target for drugs aimed against NSCLC.

The Mechanism Underlying the ncRNA Dysregulation Pattern in Hepatocellular Carcinoma and Its Tumor Microenvironment

HCC is one of the most common malignant tumors and has an extremely poor prognosis. Accumulating studies have shown that noncoding RNA (ncRNA) plays an important role in hepatocellular carcinoma (HCC) development. However, the details of the related mechanisms remain unclear. The heterogeneity of the tumor microenvironment (TME) calls for ample research with deep molecular characterization, with the hope of developing novel biomarkers to improve prognosis, diagnosis and treatment. ncRNAs, particularly microRNAs (miRNAs), long noncoding RNAs (lncRNAs), and circular RNAs (circRNAs), have been found to be correlated with HCC neogenesis and progression. In this review, we summarized the aberrant epigenetic and genetic alterations caused by dysregulated ncRNAs and the functional mechanism of classical ncRNAs in the regulation of gene expression. In addition, we focused on the role of ncRNAs in the TME in the regulation of tumor cell proliferation, invasion, migration, immune cell infiltration and functional activation. This may provide a foundation for the development of promising potential prognostic/predictive biomarkers and novel therapies for HCC patients.

CircRNA VPRBP inhibits tumorigenicity of cervical cancer via miR-93-5p/FRMD6 axis

BACKGROUND

Cervical cancer is a malignant tumor that threatens the life and health of women. Circular RNA (circRNA) is a research hotspot in human diseases including cervical cancer. However, the research of circRNA viral protein R-binding protein (circ_VPRBP) in cervical cancer is blank.

METHODS

Real-time quantitative polymerase chain reaction (RT-qPCR) was used to detect the expression of target genes in cervical cancer tissues and cells. The expression of related proteins was detected by western blot. The localization of circ_VPRBP was detected by nuclear cytoplasmic separation, and the stability of circ_VPRBP was verified by actinomycin D. After transfection with oligonucleotides and/or plasmids, cell proliferation, migration, invasion and apoptosis were detected by 3-(4, 5-dimethylthiazol-2-yl) -2, 5-diphenyl-2-H-tetrazolium bromide (MTT), colony formation, 5-ethynyl-2'-deoxyuridine (EdU), transwell, or flow cytometry assays. Mechanistically, the interaction between microRNA-93-5p (miR-93-5p) and circ_VPRBP/FERM domain containing 6 (FRMD6) was verified by dual luciferase reporter assay. Animal experiment was conducted to investigate the role of circ_VPRBP in vivo.

RESULTS

Circ_VPRBP was down-regulated in cervical cancer tissues and cells, and overexpression of circ_VPRBP inhibited proliferation and promoted apoptosis of Caski and C33A cells. MiR-93-5p was a target of circ_VPRBP, and miR-93-5p mimic reversed the effect of circ_VPRBP on cell behavior. FRMD6 was a downstream target of miR-93-5p, and down-regulated FRMD6 reversed the cell viability, migration and invasion of cervical cancer cells inhibited by anti-miR-93-5p. Circ_VPRBP inhibited tumor growth by regulating miR-93-5p and FRMD6 in vivo.

CONCLUSION

Circ_VPRBP inhibited cell proliferation, migration and invasion and promoted cell apoptosis of cervical cancer cells by regulating miR-93-5p/FRMD6 axis.

The Role of NcRNAs to Regulate Immune Checkpoints in Cancer

At present, the incidence of cancer is becoming more and more common, but its treatment has always been a problem. Although a small number of cancers can be treated, the recurrence rates are generally high and cannot be completely cured. At present, conventional cancer therapies mainly include chemotherapy and radiotherapy, which are the first-line therapies for most cancer patients, but there are palliatives. Approaches to cancer treatment are not as fast as cancer development. The current cancer treatments have not been effective in stopping the development of cancer, and cancer treatment needs to be imported into new strategies. Non-coding RNAs (ncRNAs) is a hot research topic at present. NcRNAs, which include microRNAs (miRNAs), circular RNAs (circRNAs), and long non-coding RNAs (lncRNAs), participate in all aspects of cancer biology. They are involved in the progression of tumors into a new form, including B-cell lymphoma, glioma, or the parenchymal tumors such as gastric cancer and colon cancer, among others. NcRNAs target various immune checkpoints to affect tumor proliferation, differentiation, and development. This might represent a new strategy for cancer treatment.

Construction and Bioinformatics Analysis of circRNA-miRNA-mRNA Network in Acute Myocardial Infarction

Background: Acute myocardial infarction (AMI) is one of the main fatal diseases of cardiovascular diseases. Circular RNA (circRNA) is a non-coding RNA (ncRNA), which plays a role in cardiovascular disease as a competitive endogenous RNA (ceRNA). However, their role in AMI has not been fully clarified. This study aims to explore the mechanism of circRNA-related ceRNA network in AMI, and to identify the corresponding immune infiltration characteristics.

Materials and Methods: The circRNA (GSE160717), miRNA (GSE24548), and mRNA (GSE60993) microarray datasets of AMI were downloaded from the Gene Expression Omnibus (GEO) database. Differentially expressed circRNAs (DEcircRNAs), miRNAs (DEmiRNAs), and mRNAs (DEmRNAs) were identified by the “limma” package. After integrating the circRNA, miRNA and mRNA interaction, we constructed a circRNA-miRNA-mRNA network. The “clusterProfiler” package and String database were used for functional enrichment analysis and protein-protein interaction (PPI) analysis, respectively. After that, we constructed a circRNA-miRNA-hub gene network and validated the circRNAs and mRNAs using an independent dataset (GSE61144) as well as qRT-PCR. Finally, we used CIBERSORTx database to analyze the immune infiltration characteristics of AMI and the correlation between hub genes and immune cells.

Results: Using the “limma” package of the R, 83 DEcircRNAs, 54 DEmiRNAs, and 754 DEmRNAs were identified in the microarray datasets of AMI. Among 83 DEcircRNAs, there are 55 exonic DEcircRNAs. Then, a circRNA-miRNA-mRNA network consists of 21 DEcircRNAs, 11 DEmiRNAs, and 106 DEmRNAs were predicted by the database. After that, 10 hub genes from the PPI network were identified. Then, a new circRNA-miRNA-hub gene network consists of 14 DEcircRNAs, 7 DEmiRNAs, and 9 DEmRNAs was constructed. After that, three key circRNAs (hsa_circ_0009018, hsa_circ_0030569 and hsa_circ_0031017) and three hub genes (BCL6, PTGS2 and PTEN) were identified from the network by qRT-PCR. Finally, immune infiltration analysis showed that hub genes were significantly positively correlated with up-regulated immune cells (neutrophils, macrophages and plasma cells) in AMI.

Conclusion: Our study constructed a circRNA-related ceRNA networks in AMI, consists of hsa_circ_0031017/hsa-miR-142-5p/PTEN axis, hsa_circ_0030569/hsa-miR-545/PTGS2 axis and hsa_circ_0009018/hsa-miR-139-3p/BCL6 axis. These three hub genes were significantly positively correlated with up-regulated immune cells (neutrophils, macrophages and plasma cells) in AMI. It helps improve understanding of AMI mechanism and provides future potential therapeutic targets.

Ali M, Mesbah NM, Abo-Elmatty DM, Abdel-Hamed AR. Cyanidin-3-Glucoside Modulates hsa_circ_0001345/miRNA106b/ATG16L1 Axis Expression as a Potential Protective Mechanism against Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the most common form of malignancy in the liver. Autophagy was found to have a significant effect in controlling HCC. Anthocyanins, which are naturally occurring pigments in a variety of fruits and vegetables, have been thoroughly documented to be involved in a variety of bioactive activities and are widely employed for their antioxidant capabilities. Cyanidin-3-glucoside (C3G) extracted from Morus alba L. has promising antioxidant and anti-tumour activities. The current study aims to examine the protective action of C3G against hepatocellular carcinoma through the investigation of the autophagy protein ATG16L1 expression along with its related RNA molecules (hsa_circ_0001345 and miRNA106b) in Wistar rats. In vivo precancerous lesions (PCL) were induced using diethylnitrosamine (DEN) and acetamidofluorene (2-AAF). Rats were treated with C3G (10, 15, and 20 mg/kg; 4 times weekly) for 112 days (16 weeks). Liver function tests, alfa fetoprotein, ATG16L1 expression, hsa_circ_0001345, and miRNA106b differential expression were examined. Liver sections were examined by histological and immunohistochemical approaches. The current study’s findings indicated that C3G administration protects against the negative effects of DEN-2-AAF on liver functions and liver histopathological sections, which nominated C3G as a potential prophylactic agent against HCC.

Circ_0000854 regulates the progression of hepatocellular carcinoma through miR-1294 /IRGQ axis

BACKGROUND

Hepatocellular carcinoma (HCC) is a common cancer disease with the second highest mortality. Circular RNAs (circRNAs) have been shown to play key roles in many tumors, including HCC. However, the function of circ_0000854 in the progression of HCC has not been clarified.

METHODS

Quantitative real-time polymerase chain reaction (qRT-PCR) was used to detect the expression levels of circ_0000854, microRNA-1294 (miR-1294) and immunity related GTPase Q (IRGQ) in HCC cells and tissues. Western blot was used for protein expression analysis. Cell processes were detected by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium Bromide (MTT) assay, thymidine analog 5-ethynyl-2'-deoxyuridine (EdU) assay, transwell assay, flow cytometry, and wound healing assay. Mechanically, the interaction of miR-1294 with circ_0000854 or IRGQ was notarized by dual-luciferase reporter assay and RNA pull-down assay. The xenotransplantation model was established to study the role of circ_0000854 in vivo.

RESULTS

Circ_0000854 and IRGQ were highly expressed in HCC tissues and cells, while miR-1294 was downregulated. Silencing circ_0000854 suppressed HCC cell malignant behaviors, including proliferation, cell cycle progression, migration and invasion. Circ_0000854 exhibited sponge effect on miR-1294 and miR-1294 inhibition reversed function of circ_0000854 knockdown. In addition, miR-1294 targeted IRGQ and circ_0000854 sponged miR-1294 to upregulate IRGQ. Overexpression of IRGQ restored miR-1294-induced anti-tumor regulation in HCC cells. Animal experiments confirmed that silencing circ_0000854 inhibited tumor growth and metastasis of HCC via mediating miR-1294 and IRGQ levels in vivo.

CONCLUSION

Circ_0000854 accelerated HCC progression via the miR-1294/IRGQ axis, providing a novel regulatory mechanism for HCC pathogenesis.