N6-methyladenosine-modified CircRNA-SORE sustains sorafenib resistance in hepatocellular carcinoma by regulating β-catenin signaling

Unraveling the crosstalk: circRNAs and the wnt signaling pathway in cancers of the digestive system

Circular RNA (circRNA) is a unique type of noncoding RNA molecule characterized by its closed-loop structure. Functionally versatile, circRNAs play pivotal roles in gene expression regulation, protein activity modulation, and participation in cell signaling processes. In the context of cancers of the digestive system, the Wnt signaling pathway holds particular significance. Anomalous activation of the Wnt pathway serves as a primary catalyst for the development of colorectal cancer. Extensive research underscores the notable participation of circRNAs associated with the Wnt pathway in the progression of digestive system tumors. These circRNAs exhibit pronounced dysregulation across esophageal cancer, gastric cancer, liver cancer, colorectal cancer, pancreatic cancer, and cholangiocarcinoma. Furthermore, the altered expression of circRNAs linked to the Wnt pathway correlates with prognostic factors in digestive system tumors. Additionally, circRNAs related to the Wnt pathway showcase potential as diagnostic, therapeutic, and prognostic markers within the realm of digestive system tumors. This comprehensive review outlines the interplay between circRNAs and the Wnt signaling pathway in cancers of the digestive system. It seeks to provide a comprehensive perspective on their association while delving into ongoing research that explores the clinical applications of circRNAs associated with the Wnt pathway.

Recent advances in the reciprocal regulation of m6A modification with non-coding RNAs and its therapeutic application in acute myeloid leukemia

N6-methyladenosine (m6A) is one of the most common modifications of RNA in eukaryotic cells and is involved in mRNA metabolism, including stability, translation, maturation, splicing, and export. m6A also participates in the modification of multiple types of non-coding RNAs, such as microRNAs, long non-coding RNAs, and circular RNAs, thereby affecting their metabolism and functions. Increasing evidence has revealed that m6A regulators, such as writers, erasers, and readers, perform m6A-dependent modification of ncRNAs, thus affecting cancer progression. Moreover, ncRNAs modulate m6A regulators to affect cancer development and progression. In this review, we summarize recent advances in understanding m6A modification and ncRNAs and provide insights into the interaction between m6A modification and ncRNAs in cancer. We also discuss the potential clinical applications of the mechanisms underlying the interplay between m6A modifications and ncRNAs in acute myeloid leukemia (AML). Therefore, clarifying the mutual regulation between m6A modifications and ncRNAs is of great significance to identify novel therapeutic targets for AML and has great clinical application prospects.

A new strategy for overcoming drug resistance in liver cancer: Epigenetic regulation

Drug resistance in hepatocellular carcinoma has posed significant obstacles to effective treatment. Recent evidence indicates that, in addition to traditional gene mutations, epigenetic recoding plays a crucial role in HCC drug resistance. Unlike irreversible gene mutations, epigenetic changes are reversible, offering a promising avenue for preventing and overcoming drug resistance in liver cancer. This review focuses on various epigenetic modifications relevant to drug resistance in HCC and their underlying mechanisms. Additionally, we introduce current clinical epigenetic drugs and clinical trials of these drugs as regulators of drug resistance in other solid tumors. Although there is no clinical study to prevent the occurrence of drug resistance in liver cancer, the development of liquid biopsy and other technologies has provided a bridge to achieve this goal.

A prognostic four-gene signature and a therapeutic strategy for hepatocellular carcinoma: Construction and analysis of a circRNA-mediated competing endogenous RNA network

BACKGROUND

Hepatocellular carcinoma (HCC) has a poor long-term prognosis. The competition of circular RNAs (circRNAs) with endogenous RNA is a novel tool for predicting HCC prognosis. Based on the alterations of circRNA regulatory networks, the analysis of gene modules related to HCC is feasible.

METHODS

Multiple expression datasets and RNA element targeting prediction tools were used to construct a circRNA-microRNA-mRNA network in HCC. Gene function, pathway, and protein interaction analyses were performed for the differentially expressed genes (DEGs) in this regulatory network. In the protein-protein interaction network, hub genes were identified and subjected to regression analysis, producing an optimized four-gene signature for prognostic risk stratification in HCC patients. Anti-HCC drugs were excavated by assessing the DEGs between the low- and high-risk groups. A circRNA-microRNA-hub gene subnetwork was constructed, in which three hallmark genes, KIF4A, CCNA2, and PBK, were subjected to functional enrichment analysis.

RESULTS

A four-gene signature (KIF4A, CCNA2, PBK, and ZWINT) that effectively estimated the overall survival and aided in prognostic risk assessment in the The Cancer Genome Atlas (TCGA) cohort and International Cancer Genome Consortium (ICGC) cohort was developed. CDK inhibitors, PI3K inhibitors, HDAC inhibitors, and EGFR inhibitors were predicted as four potential mechanisms of drug action (MOA) in high-risk HCC patients. Subsequent analysis has revealed that PBK, CCNA2, and KIF4A play a crucial role in regulating the tumor microenvironment by promoting immune cell invasion, regulating microsatellite instability (MSI), and exerting an impact on HCC progression.

CONCLUSIONS

The present study highlights the role of the circRNA-related regulatory network, identifies a four-gene prognostic signature and biomarkers, and further identifies novel therapy for HCC.

Unraveling the cross-talk between N6-methyladenosine modification and non-coding RNAs in breast cancer: Mechanisms and clinical implications

In recent years, breast cancer (BC) has surpassed lung cancer as the most common malignant tumor worldwide and remains the leading cause of cancer death in women. The etiology of BC usually involves dysregulation of epigenetic mechanisms and aberrant expression of certain non-coding RNAs (ncRNAs). N6-methyladenosine (m6A), the most prevalent RNA modification in eukaryotes, widely exists in ncRNAs to affect its biosynthesis and function, and is an important regulator of tumor-related signaling pathways. Interestingly, ncRNAs can also regulate or target m6A modification, playing a key role in cancer progression. However, the m6A-ncRNAs regulatory network in BC has not been fully elucidated, especially the regulation of m6A modification by ncRNAs. Therefore, in this review, we comprehensively summarize the interaction mechanisms and biological significance of m6A modifications and ncRNAs in BC. Meanwhile, we also focused on the clinical application value of m6A modification in BC diagnosis and prognosis, intending to explore new biomarkers and potential therapeutic targets.

CircDCAF8 promotes the progression of hepatocellular carcinoma through miR-217/NAP1L1 Axis, and induces angiogenesis and regorafenib resistance via exosome-mediated transfer

BACKGROUND

Circular RNAs (circRNAs), which are a new type of single-stranded circular RNA, have significant involvement in progression of many diseases, including tumors. Currently, multiple circRNAs have been identified in hepatocellular carcinoma (HCC). Our study aims to investigate the function and mechanism of circDCAF8 in HCC.

METHODS

The expression of circDCAF8 (hsa_circ_0014879) in HCC and para-carcinoma tissue samples was determined using quantitative real-time polymerase chain reaction (qRT-PCR). The biological function of circDCAF8 in HCC was confirmed by experiments conducted both in vitro and in vivo. And the relationship between circDCAF8, miR-217 and NAP1L1 was predicted by database and verified using qRT-PCR, RNA-binding protein immunoprecipitation (RIP) and dual-luciferase reporter assays. Exosomes isolated from HCC cells were utilized to assess the connection of exosomal circDCAF8 with HCC angiogenesis and regorafenib resistance.

RESULTS

CircDCAF8 is upregulated in HCC tissues and cell lines, and is linked to an unfavourable prognosis for HCC patients. Functionally, circDCAF8 was proved to facilitate proliferation, migration, invasion and Epithelial-Mesenchymal Transformation (EMT) in HCC cells. Animal examinations also validated the tumor-promoting characteristics of circDCAF8 on HCC. Besides, exosomal circDCAF8 promoted angiogenesis in HUVECs. Mechanistically, circDCAF8 interacted with miR-217 and NAP1L1 was a downstream protein of miR-217. CircDCAF8 promoted NAP1L1 expression by sponging miR-217. In addition, exosomes may transfer circDCAF8 from regorafenib-resistant HCC cells to sensitive cells, where it would confer a resistant phenotype.

CONCLUSION

CircDCAF8 facilitates HCC proliferation and metastasis via the miR-217/NAP1L1 axis. Meanwhile, circDCAF8 can promote angiogenesis and drive resistance to regorafenib, making it a viable therapeutic target for HCC patients.

RNA modifications in the progression of liver diseases: from fatty liver to cancer

Non-alcoholic fatty liver disease (NAFLD) has emerged as a prominent global health concern associated with high risk of metabolic syndrome, and has impacted a substantial segment of the population. The disease spectrum ranges from simple fatty liver to non-alcoholic steatohepatitis (NASH), which can progress to cirrhosis and hepatocellular carcinoma (HCC) and is increasingly becoming a prevalent indication for liver transplantation. The existing therapeutic options for NAFLD, NASH, and HCC are limited, underscoring the urgent need for innovative treatment strategies. Insights into gene expression, particularly RNA modifications such as N6 methyladenosine (m6A), hold promising avenues for interventions. These modifications play integral roles in RNA metabolism and cellular functions, encompassing the entire NAFLD-NASH-HCC progression. This review will encompass recent insights on diverse RNA modifications, including m6A, pseudouridine (ψ), N1-methyladenosine (m1A), and 5-methylcytidine (m5C) across various RNA species. It will uncover their significance in crucial aspects such as steatosis, inflammation, fibrosis, and tumorigenesis. Furthermore, prospective research directions and therapeutic implications will be explored, advancing our comprehensive understanding of the intricate interconnected nature of these pathological conditions.

Exploring non-coding RNA mechanisms in hepatocellular carcinoma: implications for therapy and prognosis

Hepatocellular carcinoma (HCC) is a significant contributor to cancer-related deaths in the world. The development and progression of HCC are closely correlated with the abnormal regulation of non-coding RNAs (ncRNAs), such as microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs). Important biological pathways in cancer biology, such as cell proliferation, death, and metastasis, are impacted by these ncRNAs, which modulate gene expression. The abnormal expression of non-coding RNAs in HCC raises the possibility that they could be applied as new biomarkers for diagnosis, prognosis, and treatment targets. Furthermore, by controlling the expression of cancer-related genes, miRNAs can function as either tumor suppressors or oncogenes. On the other hand, lncRNAs play a role in the advancement of cancer by interacting with other molecules within the cell, which, in turn, affects processes such as chromatin remodeling, transcription, and post-transcriptional processes. The importance of ncRNA-driven regulatory systems in HCC is being highlighted by current research, which sheds light on tumor behavior and therapy response. This research highlights the great potential of ncRNAs to improve patient outcomes in this difficult disease landscape by augmenting the present methods of HCC care through the use of precision medicine approaches.

Crosstalk between m6A modification and non-coding RNAs in HCC

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related deaths worldwide, with high morbidity and occurrence. Although various therapeutic approaches have been rapidly developed in recent years, the underlying molecular mechanisms in the pathogenesis of HCC remain enigmatic. The N6-methyladenosine (m6A) RNA modification is believed to regulate RNA metabolism and further gene expression. This process is intricately regulated by multiple regulators, such as methylases and demethylases. Non-coding RNAs (ncRNAs) are involved in the regulation of the epigenetic modification, mRNA transcription and other biological processes, exhibiting crucial roles in tumor occurrence and development. The m6A-ncRNA interaction has been implicated in the malignant phenotypes of HCC and plays an important role in drug resistance. This review summarizes the effect of m6A-ncRNA crosstalk on HCC progression and their clinical implications as prognostic markers and therapeutic targets in this disease.

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.

Targeting non-coding RNAs and N6-methyladenosine modification in hepatocellular carcinoma

Hepatocellular carcinoma (HCC), the most common form of primary liver cancers, accounts for a significant portion of cancer-related death globally. However, the molecular mechanisms driving the onset and progression of HCC are still not fully understood. Emerging evidence has indicated that non-protein-coding regions of genomes could give rise to transcripts, termed non-coding RNA (ncRNA), forming novel functional driving force for aberrant cellular activity. Over the past decades, overwhelming evidence has denoted involvement of a complex array of molecular function of ncRNAs at different stages of HCC tumorigenesis and progression. In this context, several pre-clinical studies have highlighted the potentials of ncRNAs as novel therapeutic modalities in the management of human HCC. Moreover, N6-methyladenosine (m6A) modification, the most prevalent form of internal mRNA modifications in mammalian cells, is essential for the governance of biological processes within cells. Dysregulation of m6A in ncRNAs has been implicated in human carcinogenesis, including HCC. In this review, we will discuss dysregulation of several hallmark ncRNAs (miRNAs, lncRNAs, and circRNAs) in HCC and address the latest advances for their involvement in the onset and progression of HCC. We also focus on dysregulation of m6A modification and various m6A regulators in the etiology of HCC. In the end, we discussed the contemporary preclinical and clinical application of ncRNA-based and m6A-targeted therapies in HCC.

RNA modification-mediated mRNA translation regulation in liver cancer: mechanisms and clinical perspectives

Malignant liver cancer is characterized by rapid tumour progression and a high mortality rate, whereas the molecular mechanisms underlying liver cancer initiation and progression are still poorly understood. The dynamic and reversible RNA modifications have crucial functions in gene expression regulation by modulating RNA processing and mRNA translation. Emerging evidence has revealed that alterations in RNA modifications facilitate the selective translation of oncogenic transcripts and promote the diverse tumorigenic processes of liver cancer. In this Review, we first highlight the current progress on the functions and mechanisms underlying RNA modifications in the regulation of mRNA translation and then summarize the exciting discoveries on aberrant RNA modification-mediated mRNA translation in the regulation of tumour initiation, metastasis, metabolism, tumour microenvironment, and drug and radiotherapy resistance in liver cancer. Finally, we discuss the diagnostic and therapeutic potentials of targeting RNA modifications and mRNA translation for the clinical management of liver cancer.

N6-methyladenosine (m6A) modification in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the deadliest cancers of human, the tumor-related death of which ranks third among the common malignances. N6-methyladenosine (m6A) methylation, the most abundant internal modification of RNA in mammals, participates in the metabolism of mRNA and interrelates with ncRNAs. In this paper, we overviewed the complex function of m6A regulators in HCC, including regulating the tumorigenesis, progression, prognosis, stemness, metabolic reprogramming, autophagy, ferroptosis, drug resistance and tumor immune microenvironment (TIME). Furthermore, we elucidated the interplay between m6A modification and non-coding RNAs (ncRNAs), including microRNAs (miRNAs), long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs). Finally, we summarized the potential of m6A regulators as diagnostic biomarkers. What's more, we reviewed the inhibitors targeting m6A enzymes as promising therapeutic targets of HCC. We aimed to help understand the function of m6A methylation in HCC systematically and comprehensively so that more effective strategies for HCC treatment will be developed.

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.

METTL3 promotes osteogenic differentiation of human umbilical cord mesenchymal stem cells by up-regulating m6A modification of circCTTN

BACKGROUND

Human umbilical cord mesenchymal stem cells (hUCMSCs) are promising seed cells in bone tissue engineering. circRNA and N6-methyladenosine (m6A) RNA methylation play important roles in osteogenic differentiation. Here, we investigated the potential relevance of a critical circRNA, hsa_circ_0003376 (circCTTN), and methyltransferase-like 3 (METTL3) in osteogenic differentiation of hUCMSCs.

METHODS

Expression of circCTTN after hUCMSC osteogenic induction was detected by qRT-PCR. Three databases (RMBase v2.0, BERMP, and SRAMP) were used to predict m6A sites of circCTTN. RNA was enriched by methylated RNA immunoprecipitation (MeRIP), followed by quantitative real-time polymerase chain reaction to detect m6A level of circCTTN after METTL3 overexpression and osteogenic induction. RNA pull-down, Western blotting, and protein mass spectrometry were performed to investigate the potential mechanisms by which METTL3 promoted m6A modification of circCTTN. Bioinformatic analyses based on database (STRING) search and co-immunoprecipitation were used to analyze the proteins that interacted with METTL3.

RESULTS

Overexpression of METTL3 promoted osteogenic differentiation of hUCMSCs and increased m6A level of circCTTN. Two potential m6A modification sites of circCTTN were predicted. No direct interaction between METTL3 and circCTTN was observed. Thirty-one proteins were pulled down by probes specific for circCTTN, including NOP2, and two m6A reading proteins, EIF3A and SND1. Bioinformatics analysis and co-immunoprecipitation showed that METTL3 interacted with EIF3A indirectly through NOP2.

CONCLUSIONS

METTL3 promotes the osteogenic differentiation of hUCMSCs by increasing the m6A level of circCTTN. However, METTL3 does not bind directly to circCTTN. METTL3 interacts with circCTTN indirectly through NOP2 and EIF3A.

Lopinavir enhances anoikis by remodeling autophagy in a circRNA-dependent manner

Macroautophagy/autophagy-mediated anoikis resistance is crucial for tumor metastasis. As a key autophagy-related protein, ATG4B has been demonstrated to be a prospective anti-tumor target. However, the existing ATG4B inhibitors are still far from clinical application, especially for tumor metastasis. In this study, we identified a novel circRNA, circSPECC1, that interacted with ATG4B. CircSPECC1 facilitated liquid-liquid phase separation of ATG4B, which boosted the ubiquitination and degradation of ATG4B in gastric cancer (GC) cells. Thus, pharmacological addition of circSPECC1 may serve as an innovative approach to suppress autophagy by targeting ATG4B. Specifically, the circSPECC1 underwent significant m6A modification in GC cells and was subsequently recognized and suppressed by the m6A reader protein ELAVL1/HuR. The activation of the ELAVL1-circSPECC1-ATG4B pathway was demonstrated to mediate anoikis resistance in GC cells. Moreover, we also verified that the above pathway was closely related to metastasis in tissues from GC patients. Furthermore, we determined that the FDA-approved compound lopinavir efficiently enhanced anoikis and prevented metastasis by eliminating repression of ELAVL1 on circSPECC1. In summary, this study provides novel insights into ATG4B-mediated autophagy and introduces a viable clinical inhibitor of autophagy, which may be beneficial for the treatment of GC with metastasis.

The dual roles of circRNAs in Wnt/β-Catenin signaling and cancer progression

Cancer, a complex pathophysiological condition, arises from the abnormal proliferation and survival of cells due to genetic mutations. Dysregulation of cell cycle control, apoptosis, and genomic stability contribute to uncontrolled growth and metastasis. Tumor heterogeneity, microenvironmental influences, and immune evasion further complicate cancer dynamics. The intricate interplay between circular RNAs (circRNAs) and the Wnt/β-Catenin signalling pathway has emerged as a pivotal axis in the landscape of cancer biology. The Wnt/β-Catenin pathway, a critical regulator of cell fate and proliferation, is frequently dysregulated in various cancers. CircRNAs, a class of non-coding RNAs with closed-loop structures, have garnered increasing attention for their diverse regulatory functions. This review systematically explores the intricate crosstalk between circRNAs and the Wnt/β-Catenin pathway, shedding light on their collective impact on cancer initiation and progression. The review explores the diverse mechanisms through which circRNAs modulate the Wnt/β-Catenin pathway, including sponging microRNAs, interacting with RNA-binding proteins, and influencing the expression of key components in the pathway. Furthermore, the review highlights specific circRNAs implicated in various cancer types, elucidating their roles as either oncogenic or tumour-suppressive players in the context of Wnt/β-Catenin signaling. The intricate regulatory networks formed by circRNAs in conjunction with the Wnt/β-Catenin pathway are discussed, providing insights into potential therapeutic targets and diagnostic biomarkers. This comprehensive review delves into the multifaceted roles of circRNAs in orchestrating tumorigenesis through their regulatory influence on the Wnt/β-Catenin pathway.

Non-coding RNA-Mediated N6-Methyladenosine (m6A) deposition: A pivotal regulator of cancer, impacting key signaling pathways in carcinogenesis and therapy response

The emergence of RNA modifications has recently been considered as critical post-transcriptional regulations which governed gene expression. N6-methyladenosine (m6A) modification is the most abundant type of RNA modification which is mediated by three distinct classes of proteins called m6A writers, readers, and erasers. Accumulating evidence has been made in understanding the role of m6A modification of non-coding RNAs (ncRNAs) in cancer. Importantly, aberrant expression of ncRNAs and m6A regulators has been elucidated in various cancers. As the key role of ncRNAs in regulation of cancer hallmarks is well accepted now, it could be accepted that m6A modification of ncRNAs could affect cancer progression. The present review intended to discuss the latest knowledge and importance of m6A epigenetic regulation of ncRNAs including mircoRNAs, long non-coding RNAs, and circular RNAs, and their interaction in the context of cancer. Moreover, the current insight into the underlying mechanisms of therapy resistance and also immune response and escape mediated by m6A regulators and ncRNAs are discussed.

CREB3L4 promotes hepatocellular carcinoma progression and decreases sorafenib chemosensitivity by promoting RHEB-mTORC1 signaling pathway

This study was designed to explore the roles of CREB3L4 in the pathogenesis and drug resistance of hepatocellular carcinoma (HCC). The proliferation of HCC lines was determined in the presence of CREB3L4 over-expression and silencing. Chromatin immunoprecipitation (ChIP) assay and dual-luciferase reporter assay were performed to screen the potential target of CREB3L4 on mTORC1. Xenografted tumor model was established to define the regulatory effects of CREB3L4 in the tumorigenesis. Then we evaluated the roles of CREB3L4 in chemosensitivity to sorafenib treatment. CREB3L4 significantly induced the HCC cell proliferation by modulating the activation of mTROC1-S6K1 signaling pathway via binding with RHEB promoter. Moreover, CREB3L4 dramatically inhibited the chemosensitivity to sorafenib treatment via up-regulating RHEB-mTORC1 signaling. CREB3L4 promoted HCC progression and decreased its chemosensitivity to sorafenib through up-regulating RHEB-mTORC1 signaling pathway, indicating a potential treatment strategy for HCC through targeting CREB3L4.

Noncoding RNAs in Hepatocellular Carcinoma: Potential Applications in Combined Therapeutic Strategies and Promising Candidates of Treatment Response

The incidence of hepatocellular carcinoma (HCC) is increasing, and 40% of patients are diagnosed at advanced stages. Over the past 5 years, the number of clinically available treatments has dramatically increased for HCC, making patient management particularly complex. Immune checkpoint inhibitors (ICIs) have improved the overall survival of patients, showing a durable treatment benefit over time and a different response pattern with respect to tyrosine kinase inhibitors (TKIs). Although there is improved survival in responder cases, a sizeable group of patients are primary progressors or are ineligible for immunotherapy. Indeed, patients with nonviral etiologies, such as nonalcoholic steatohepatitis (NASH), and alterations in specific driver genes might be less responsive to immunotherapy. Therefore, improving the comprehension of mechanisms of drug resistance and identifying biomarkers that are informative of the best treatment approach are required actions to improve patient survival. Abundant evidence indicates that noncoding RNAs (ncRNAs) are pivotal players in cancer. Molecular mechanisms through which ncRNAs exert their effects in cancer progression and drug resistance have been widely investigated. Nevertheless, there are no studies summarizing the synergistic effect between ncRNA-based strategies and TKIs or ICIs in the preclinical setting. This review aims to provide up-to-date information regarding the possible use of ncRNAs as therapeutic targets in association with molecular-targeted agents and immunotherapies and as predictive tools for the selection of optimized treatment options in advanced HCCs.

IGF2BP2-m6A-circMMP9 axis recruits ETS1 to promote TRIM59 transcription in laryngeal squamous cell carcinoma

Laryngeal squamous cell carcinoma (LSCC) is a common malignancy of the head and neck. Recently, circular RNA (circRNA) has been studied extensively in multisystem diseases. However, there are few research on biological functions and molecular mechanisms of circRNAs in LSCC. CircRNA array was used to detect the differentially expressed circRNAs. Kaplan-Meier and cox regression analysis were used to identify survival based on circMMP9. The qRT-PCR, RNase R treatment, sanger sequencing and in situ hybridization were used to verify circMMP9 expression, characteristics and localization in LSCC tissues and cells. Functionally, colony formation, MTS, transwell and in vivo assays were proceeded to detect the biological function of circMMP9 in LSCC progression. The RNA-seq was conducted to identify the molecular targets of circMMP9. Mechanically, MeRIP, RNA Immunoprecipitation (RIP), RNA pulldown, Chromatin immunoprecipitation (ChIP) and dual-luciferase reporter assays were carried on to verify the regulatory mechanism of circMMP9. CircMMP9 was discovered upregulated in LSCC tissues and cells, and high level of circMMP9 was associated with poor prognosis, low degree of pathological grading, high TNM stage and lymph node metastasis of LSCC. CircMMP9 knockdown prevented LSCC progression both in vitro and in vivo, whereas, circMMP9 overexpression had the opposite effect. CircMMP9 was stabilized by IGF2BP2 in m6A-dependent manner. TRIM59 was identified as downstream target of circMMP9. CircMMP9 recruited ETS1 to stimulate TRIM59 transcription. Moreover, TRIM59 accelerated LSCC progression via activating the PI3K/AKT signal pathway. Our findings offered a unique regulatory mechanism for circMMP9 in LSCC, as well as a novel proof that circMMP9 may be utilize as a diagnostic marker and therapeutic target for LSCC patients.

Research progress and perspectives of noncoding RNAs in adrenocortical carcinoma: A review

Adrenocortical carcinoma (ACC) is a rare and highly aggressive endocrine malignancy. Although surgery can cure localized disease, but the majority of patients experience recurrence of ACC. The 5-year survival rate of patients with metastatic ACC is <15%, and the prognosis is poor. Therefore, it is urgent to explore the potential diagnostic markers and therapeutic targets for ACC. Recently, it has been proved that non-coding RNA (ncRNAs) is widely involved in pathological and physiological processes, including tumorigenesis and development. Aberrantly expressed ncRNAs have been found to be involved in the pathogenesis of ACC. Here, we summarized the expression patterns and the molecular mechanism of the involvement of microRNAs (miRNAs), long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs) in ACC development. To explore the clinical value of ncRNAs as noninvasive biomarkers of ACC, we also displayed the relationship between the expression level of ncRNAs and the diagnosis and prognosis of patients with ACC.

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.

m6A-Atlas v2.0: updated resources for unraveling the N6-methyladenosine (m6A) epitranscriptome among multiple species

N 6-Methyladenosine (m6A) is one of the most abundant internal chemical modifications on eukaryote mRNA and is involved in numerous essential molecular functions and biological processes. To facilitate the study of this important post-transcriptional modification, we present here m6A-Atlas v2.0, an updated version of m6A-Atlas. It was expanded to include a total of 797 091 reliable m6A sites from 13 high-resolution technologies and two single-cell m6A profiles. Additionally, three methods (exomePeaks2, MACS2 and TRESS) were used to identify >16 million m6A enrichment peaks from 2712 MeRIP-seq experiments covering 651 conditions in 42 species. Quality control results of MeRIP-seq samples were also provided to help users to select reliable peaks. We also estimated the condition-specific quantitative m6A profiles (i.e. differential methylation) under 172 experimental conditions for 19 species. Further, to provide insights into potential functional circuitry, the m6A epitranscriptomics were annotated with various genomic features, interactions with RNA-binding proteins and microRNA, potentially linked splicing events and single nucleotide polymorphisms. The collected m6A sites and their functional annotations can be freely queried and downloaded via a user-friendly graphical interface at: http://rnamd.org/m6a.

Mechanisms of immune checkpoint inhibitors: insights into the regulation of circular RNAS involved in cancer hallmarks

Current treatment strategies for cancer, especially advanced cancer, are limited and unsatisfactory. One of the most substantial advances in cancer therapy, in the last decades, was the discovery of a new layer of immunotherapy approach, immune checkpoint inhibitors (ICIs), which can specifically activate immune cells by targeting immune checkpoints. Immune checkpoints are a type of immunosuppressive molecules expressed on immune cells, which can regulate the degree of immune activation and avoid autoimmune responses. ICIs, such as anti-PD-1/PD-L1 drugs, has shown inspiring efficacy and broad applicability across various cancers. Unfortunately, not all cancer patients benefit remarkably from ICIs, and the overall response rates to ICIs remain relatively low for most cancer types. Moreover, the primary and acquired resistance to ICIs pose serious challenges to the clinical application of cancer immunotherapy. Thus, a deeper understanding of the molecular biological properties and regulatory mechanisms of immune checkpoints is urgently needed to improve clinical options for current therapies. Recently, circular RNAs (circRNAs) have attracted increasing attention, not only due to their involvement in various aspects of cancer hallmarks, but also for their impact on immune checkpoints in shaping the tumor immune microenvironment. In this review, we systematically summarize the current status of immune checkpoints in cancer and the existing regulatory roles of circRNAs on immune checkpoints. Meanwhile, we also aim to settle the issue in an evidence-oriented manner that circRNAs involved in cancer hallmarks regulate the effects and resistance of ICIs by targeting immune checkpoints.

Circular RNA-circPan3 attenuates cardiac hypertrophy via miR-320-3p/HSP20 axis

BACKGROUND

Circular RNAs are enriched in cardiac tissue and play important roles in the pathogenesis of heart diseases. In this study, we aimed to investigate the regulatory mechanism of a conserved heart-enriched circRNA, circPan3, in cardiac hypertrophy.

METHODS

Cardiac hypertrophy was induced by isoproterenol. The progression of cardiomyocyte hypertrophy was assessed by sarcomere organization staining, cell surface area measurement, and expression levels of cardiac hypertrophy markers. RNA interactions were detected by RNA pull-down assays, and methylated RNA immunoprecipitation was used to detect m6A level.

RESULTS

The expression of circPan3 was downregulated in an isoproterenol-induced cardiac hypertrophy model. Forced expression of circPan3 attenuated cardiomyocyte hypertrophy, while inhibition of circPan3 aggravated cardiomyocyte hypertrophy. Mechanistically, circPan3 was an endogenous sponge of miR-320-3p without affecting miR-320-3p levels. It elevated the expression of HSP20 by endogenously interacting with miR-320-3p. In addition, circPan3 was N6-methylated. Stimulation by isoproterenol downregulated the m6A eraser ALKBH5, resulting in N6-methylation and destabilization of circPan3.

CONCLUSIONS

Our research is the first to report that circPan3 has an antihypertrophic effect in cardiomyocytes and revealed a novel circPan3-modulated signalling pathway involved in cardiac hypertrophy. CircPan3 inhibits cardiac hypertrophy by targeting the miR-320-3p/HSP20 axis and is regulated by ALKBH5-mediated N6-methylation. This pathway could provide potential therapeutic targets for cardiac hypertrophy.

METTL3/YTHDC1-medicated m6A modification of circRNA3634 regulates the proliferation and differentiation of antler chondrocytes by miR-124486-5-MAPK1 axis

BACKGROUND

The deer antler, a remarkable mammalian appendage, has a growth rate surpassing that of any other known osseous organ. Emerging evidence indicates that circRNA and MAPK1 play critical roles in chondrocytes. Thus, exploration of their functions in antler chondrocytes will help us to understand the mechanism regulating the rapid antler growth.

METHODS

qRT-PCR, western blot, and immunohistochemistry were used to assess the expression of mRNAs and proteins. CCK-8, EdU, Cell migration, ALP activity detection, and ALP staining examined the effects of MAPK1 in antler chondrocytes. FISH, RIP, and luciferase assays were performed to evaluate the interactions among circRNA3634/MAPK1 and miR-124486-5. RIP and RAP assays proved the binding interaction between circRNA3634 and RBPs. Me-RIP was used to determine the m6A methylation modification of circRNA3634.

RESULTS

This study revealed high MAPK1 expression in antler cartilage tissue. Overexpression of MAPK1 promoted the proliferation, migration, and differentiation of antler chondrocytes and increased the expression of MAPK3, RAF1, MEK1, RUNX2, and SOX9. The silencing of MAPK1 had the opposite effect. CircRNA3634 was found to act as a molecular sponge for miR-124486-5, leading to increased MAPK1 expression and enhanced proliferation and migration of antler chondrocytes through competitive miR-124486-5 binding. We discovered that METTL3 mediates m6A modification near the splicing site of circRNA3634 and is involved in the proliferation and differentiation of antler chondrocytes. The m6A reader YTHDC1 facilitated the nuclear export of circRNA3634 in an m6A-dependent manner. Our results indicate that m6A-modified circRNA3634 promotes the proliferation of antler chondrocytes by targeting MAPK1 and show that the nuclear export of circRNA3634 is related to the expression of YTHDC1, suggesting that circRNA3634 could represent a critical regeneration marker for the antler.

CONCLUSIONS

Our results revealed a novel m6A-modified circRNA3634 promoted the proliferation and differentiation of antler chondrocytes by regulating MAPK1. The nuclear export of circRNA3634 was related to the expression of YTHDC1.

New insight into circRNAs: characterization, strategies, and biomedical applications

Circular RNAs (circRNAs) are a class of covalently closed, endogenous ncRNAs. Most circRNAs are derived from exonic or intronic sequences by precursor RNA back-splicing. Advanced high-throughput RNA sequencing and experimental technologies have enabled the extensive identification and characterization of circRNAs, such as novel types of biogenesis, tissue-specific and cell-specific expression patterns, epigenetic regulation, translation potential, localization and metabolism. Increasing evidence has revealed that circRNAs participate in diverse cellular processes, and their dysregulation is involved in the pathogenesis of various diseases, particularly cancer. In this review, we systematically discuss the characterization of circRNAs, databases, challenges for circRNA discovery, new insight into strategies used in circRNA studies and biomedical applications. Although recent studies have advanced the understanding of circRNAs, advanced knowledge and approaches for circRNA annotation, functional characterization and biomedical applications are continuously needed to provide new insights into circRNAs. The emergence of circRNA-based protein translation strategy will be a promising direction in the field of biomedicine.

N6 -methyladenosine-modified circSTX6 promotes hepatocellular carcinoma progression by regulating the HNRNPD/ATF3 axis and encoding a 144 amino acid polypeptide

BACKGROUND

Circular RNAs (circRNAs) play a significant role in the initiation and progression of various cancers, including hepatocellular carcinoma (HCC). Circular syntaxin 6 (circSTX6, also known as hsa_circ_0007905) has been identified as a microRNA (miRNA) sponge in pancreatic adenocarcinoma. However, its full range of functions in terms of protein scaffold and translation remain largely unexplored in the context of HCC.

METHODS

The expression of circSTX6 and its encoded protein was examined in HCC tumour tissues. N6 -methyladenosine (m6 A) on circSTX6 was verified and quantified by methylated RNA immunoprecipitation (Me-RIP), RIP and dual luciferase reporter assays. The biological functions of circSTX6 and its encoded protein in HCC were clarified by in vitro and in vivo experiments. Mechanistically, the interaction between circSTX6 and heterogeneous nuclear ribonucleoprotein D (HNRNPD) was investigated by RNA pull-down, RIP and fluorescence in situ hybridization (FISH)/IF. The regulatory effects of circSTX6 and HNRNPD on activating transcription factor 3 (ATF3) mRNA were determined by mRNA stability and RIP assays. Furthermore, the presence of circSTX6-encoded protein was verified by mass spectrometry.

RESULTS

CircSTX6 and its encoded 144 amino acid polypeptide, circSTX6-144aa, were highly expressed in HCC tumour tissues and served as independent risk factors for overall survival in HCC patients. The expression of circSTX6 was regulated by METTL14 in an m6 A-dependent manner. Functionally, circSTX6 accelerated HCC proliferation and tumourigenicity and reinforced tumour metastasis in vitro and in vivo. Mechanistically, circSTX6 acted as a sponge for HNRNPD protein, facilitating its binding to ATF3 mRNA, consequently promoting ATF3 mRNA decay. Meanwhile, circSTX6-144aa promoted HCC proliferation, migration and invasion independent of circSTX6 itself.

CONCLUSION

Collectively, our study reveals that m6 A-modified circSTX6 drives malignancy in HCC through the HNRNPD/ATF3 axis, while its encoded circSTX6-144aa contributes to HCC progression independent of circSTX6. CirSTX6 and its encoded protein hold promise as potential biomarkers and therapeutic targets in HCC.

N6 -methyladenosine-modified circFUT8 competitively interacts with YTHDF2 and miR-186-5p to stabilize FUT8 mRNA to promote malignant progression in lung adenocarcinoma

BACKGROUND

Lung cancer is the leading cause of cancer related to mortality worldwide, and the main pathological type is lung adenocarcinoma (LUAD). Circular RNAs (circRNAs) have been reported to be modified by N6 -methyladenosine (m6A), which is involved in the progression of diverse tumors. However, the crosstalk between circRNAs and m6A modification has not been well elucidated in LUAD.

METHODS

MeRIP-seq and YTHDF2-RIP-seq datasets were explored to identify candidate circRNAs modified by YTHDF2. Dual-luciferase reporter assay, RIP, and rescue assays were performed to explore the relationship between circFUT8 and its parent mRNA of FUT8. In vitro and in vivo experiments were utilized to uncover the function of circFUT8.

RESULTS

In this study, we identified a novel m6A-modified circFUT8, derived from exon 3 of FUT8, which was elevated in tumor tissues compared with adjacent noncancerous tissues. The m6A reader YTHDF2 recognized and destabilized circFUT8 in an m6A-dependent manner. YTHDF2 also combined with the line form of FUT8 (mFUT8), and circFUT8 competitively interacted with YTHDF2, blunting its binding to mFUT8, to stabilize the mRNA level of FUT8. Additionally, circFUT8 sponged miR-186-5p to elevate the expression of mFUT8. Finally, we revealed that circFUT8 promoted the malignant progression of LUAD dependent on the oncogenic function of FUT8.

CONCLUSIONS

These findings identified a novel m6A-modified circFUT8 recognized and destabilized by YTHDF2, which competitively interacted with YTHDF2 and miR-186-5p to stabilize FUT8 mRNA to promote malignant progression in LUAD.

hsa_circ_0129047 Upregulates LYVE1 to Inhibit Hepatocellular Carcinoma Progression by Sponging miR-492

Compelling evidence indicates the regulatory role of circular RNAs in cancers, including hepatocellular carcinoma (HCC). Our study aimed to elucidate the regulatory function of circ_0129047 in HCC progression. A reverse transcription-quantitative polymeric chain reaction was conducted to detect the expression of circ_0129047, lymphatic vessel endothelial hyaluronan receptor-1 (LYVE1), and miR-492 in HCC tissues and cells. The characteristics of circ_0129047 were determined by evaluating the nuclear and cytoplasmic fractions and by RNase R digestion assays. The cell counting kit-8 assay, scratch wound, and transwell invasion assays were used to examine the effects of circ_0129047 overexpression, miR-492 mimic, and LYVE1 overexpression on the proliferation, migration, and invasion abilities of HCC cells in vitro. A mouse xenograft model was also established. The relationship between miR-492 and circ_0129047 or LYVE1 was clarified using luciferase reporter and Argonaute-2 RNA immunoprecipitation assays. We found that circ_0129047 and LYVE1 were poorly expressed in HCC tissues and cells, whereas miR-492 was upregulated. Overexpression of circ_0129047 inhibits HCC cell proliferation, migration, and invasion and delays in vivo tumor growth. Furthermore, circ_0129047 sponged miR-492, and 3'UTR LYVE1 was a direct target of miR-492. Additionally, LYVE1 overexpression reduced the oncogenic activity of the miR-492 mimic, whereas the miR-492 mimic abolished the antimigratory, antiproliferative, and anti-invasive effects of circ_0129047 overexpression in HCC cells. These data suggest that circ_0129047 exerts a tumor-suppressive role in HCC by sponging miR-492 away from LYVE1 and that the circ_0129047/miR-492/LYVE1 axis may be a promising target for HCC treatment.

CircRNAs: A Promising Star for Treatment and Prognosis in Oral Squamous Cell Carcinoma

CircRNAs are a class of endogenous long non-coding RNAs with a single-stranded circular structure. Most circRNAs are relatively stable, highly conserved, and specifically expressed in tissue during the cell and developmental stages. Many circRNAs have been discovered in OSCC. OSCC is one of the most severe and frequent forms of head and neck cancer today, with a poor prognosis and low overall survival rate. Due to its prevalence, OSCC is a global health concern, characterized by genetic and epigenomic changes. However, the mechanism remains vague. With the advancement of biotechnology, a large number of circRNAs have been discovered in mammalian cells. CircRNAs are dysregulated in OSCC tissues and thus associated with the clinicopathological characteristics and prognosis of OSCC patients. Research studies have demonstrated that circRNAs can serve as biomarkers for OSCC diagnosis and treatment. Here, we summarized the properties, functions, and biogenesis of circRNAs, focusing on the progress of current research on circRNAs in OSCC.

M6A transcriptome-wide map of circRNAs identified in the testis of normal and AZ-treated Xenopus laevis

BACKGROUND

Evidence showed that N6-methyladenosine (m6A) is strongly associated with male germline development. However, the role of m6A methylation on circRNAs in amphibians remains unknown. In this study, we conducted m6A sequencing analysis to explore the m6A transcriptome-wide profile of circRNAs in testis tissues of Xenopus laevis (X. laevis) with and without treatment with 100 µg/L atrazine (AZ).

RESULTS

The analysis showed that m6A modification of circRNAs enriched in sense overlapping in testes of X. laevis. We identified the differential m6A modification sites within circRNAs in testes of AZ-exposed X. laevis and compared that with animals from control group. The results showed that a total of 1507 methylated m6A sites was induced by AZ (760 up-methylated and 747 down-methylated). The cross-analysis exhibited a negative correlation of differentially methylated m6A peaks and circRNAs expression level. The Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that 20 key pathways may be involved in the mechanism of testis damage of AZ-exposed X. laevis.

CONCLUSIONS

These findings indicated that differentially m6A-methylated circRNAs may play important roles in abnormal testis development of AZ-exposed X. laevis. This study is the first report about a map of m6A modification of circRNAs in male X. laevis and provides a basis for further studying on the function and mechanism of m6A methylation of circRNAs in the testis development of amphibian.

N6-methyladenosine-modified circIRF2, identified by YTHDF2, suppresses liver fibrosis via facilitating FOXO3 nuclear translocation

Circular RNA (circRNA) has been implicated in liver fibrosis and modulated by multiple elusive molecular mechanisms, while the effects of N6-methyladenosine (m6A) modification on circRNA are still elusive. Herein, we identify circIRF2 from our circRNA sequencing data, which decreased in liver fibrogenesis stage and restored in resolution stage, indicating that dysregulated circIRF2 may be closely associated with liver fibrosis. Gain/loss-of-function analysis was performed to evaluate the effects of circIRF2 on liver fibrosis at both the fibrogenesis and resolution in vivo. Ectopic expression of circIRF2 attenuated liver fibrogenesis and HSCs activation at the fibrogenesis stage, whereas downregulation of circIRF2 impaired mouse liver injury repair and inflammation resolution. Mechanistically, YTHDF2 recognized m6A-modified circIRF2 and diminished circIRF2 stability, partly accounting for the decreased circIRF2 in liver fibrosis. Microarray was applied to investigate miRNAs regulated by circIRF2, our data elucidate cytoplasmic circIRF2 may directly harbor miR-29b-1-5p and competitively relieve its inhibitory effect on FOXO3, inducing FOXO3 nuclear translocation and accumulation. Clinically, circIRF2 downregulation was prevalent in liver fibrosis patients compared with healthy individuals. In summary, our findings offer a novel insight into m6A modification-mediated regulation of circRNA and suggest that circIRF2 may be an exploitable prognostic marker and/or therapeutic target for liver fibrosis.

Circular RNA in cholangiocarcinoma: A systematic review and bibliometric analysis

BACKGROUND

Cholangiocarcinoma (CCA) is a common primary liver malignancy with a poor prognosis. Many studies have demonstrated the involvement of circular RNAs (circRNAs) in tumorigenesis and progression.

METHODS

Four online databases (PubMed, Web of Science, Embase, and Scopus) were searched on May 04, 2023, for original papers regarding CCA and circRNAs. Bibliometric analysis of included studies was performed on R Studio and GraphPad Prism.

RESULTS

Thirty studies were included in the systematic review and bibliometric analysis. The systematic review showed that circRNAs were involved in CCA proliferation, invasion, metastasis, chemotherapy resistance, and other biological processes and were related to the prognosis of patients and many clinicopathological features. Exosomal circRNAs provide a new idea for the early diagnosis of CCA. The bibliometric analysis showed a significant upward trend in the number of studies on CCA and circRNAs. The 30 included papers had 201 authors and were published in 22 English journals. The first paper was published in 2018, and the second paper was the most cited (148 citations).

CONCLUSION

This systematic review and bibliometric analysis demonstrates that circRNAs in CCA have not been studied enough. CircRNAs play an important role in the occurrence and progression of CCA. They may become new targets for the diagnosis, treatment, and prognostic monitoring of CCA.

cDCBLD2 mediates sorafenib resistance in hepatocellular carcinoma by sponging miR-345-5p binding to the TOP2A coding sequence

Sorafenib is a first-line chemotherapy drug for treating advanced hepatocellular carcinoma (HCC). However, its therapeutic effect has been seriously affected by the emergence of sorafenib resistance in HCC patients. The underlying mechanism of sorafenib resistance is unclear. Here, we report a circular RNA, cDCBLD2, which plays an important role in sorafenib resistance in HCC. We found that cDCBLD2 was upregulated in sorafenib-resistant (SR) HCC cells, and knocking down cDCBLD2 expression could significantly increase sorafenib-related cytotoxicity. Further evidence showed that cDCBLD2 can bind to microRNA (miR)-345-5p through a competing endogenous RNA mechanism, increase type IIA topoisomerase (TOP2A) mRNA stability through a miRNA sponge mechanism, and reduce the effects of sorafenib treatment on HCC by inhibiting apoptosis. Our findings also suggest that miR-345-5p can negatively regulate TOP2A levels by binding to the coding sequence region of its mRNA. Additionally, targeting cDCBLD2 by injecting a specific small interfering RNA (siRNA) could significantly overcome sorafenib resistance in a patient-derived xenograft (PDX) mouse model of HCC. Taken together, our study provides a proof-of-concept for a potential strategy to overcome sorafenib resistance in HCC patients by targeting cDCBLD2 or TOP2A.

ATRA sensitized the response of hepatocellular carcinoma to Sorafenib by downregulation of p21-activated kinase 1

BACKGROUND

Sorafenib resistance greatly reduces the efficacy of treatments in advanced hepatocellular carcinoma (HCC) patients, but the underlying mechanisms are not thoroughly understood. All-trans retinoic acid (ATRA), an anti-leukaemia agent, has attracted considerable attention due to its role in sensitizing cells to other anticancer treatments. We aimed to investigate the combined effect of ATRA and Sorafenib on HCC and the underlying mechanisms.

METHODS

CCK-8, cell sphere formation, trans-well migration, and wound-healing assays were used to analyse the biological behaviours of HCC cells in vitro. Western blotting and qRT-PCR analysis were conducted to measure the expression of p21 activated kinase 1 (PAK1) and phospho-p21 activated kinase 1 (pPAK1). Xenograft models were established to confirm the synergistic effects of ATRA and Sorafenib in vivo. TUNEL assays and immunohistochemistry were utilized to determine apoptosis, proliferation, PAK1 and pPAK1 levels in tumour tissues.

RESULTS

We observed that PAK1 was overexpressed in HCC, and its expression was negatively correlated with the survival of patients. PAK1 promoted the proliferation, self-renewal and epithelial-mesenchymal transition of HCC cells. Correlation analysis indicated that the IC50 of Sorafenib was positively correlated with the level of pPAK1 in HCC cell lines. ATRA inhibited the progression of HCC and sensitized HCC response to Sorafenib by downregulation of PAK1, as shown by the calculated coefficient of drug interaction and the data obtained from xenograft models.

CONCLUSIONS

Our findings indicated that instead of treatment with Sorafenib alone, the combination of ATRA and Sorafenib provides a more effective treatment for HCC patients. Video Abstract.

A spotlight on the interplay between Wnt/β-catenin signaling and circular RNAs in hepatocellular carcinoma progression

Hepatocellular carcinoma (HCC) is one of the deadliest cancers due to multifocal development and distant metastasis resulting from late diagnosis. Consequently, new approaches to HCC diagnosis and treatment are required to reduce mortality rates. A large body of evidence suggests that non-coding RNAs (ncRNAs) are important in cancer initiation and progression. Cancer cells release many of these ncRNAs into the blood or urine, enabling their use as a diagnostic tool. Circular RNAs (CircRNAs) are as a members of the ncRNAs that regulate cancer cell expansion, migration, metastasis, and chemoresistance through different mechanisms such as the Wnt/β-catenin Signaling pathway. The Wnt/β-catenin pathway plays prominent roles in several biological processes including organogenesis, stem cell regeneration, and cell survival. Aberrant signaling of both pathways mentioned above could affect the progression and metastasis of many cancers, including HCC. Based on several studies investigated in the current review, circRNAs have an effect on HCC formation and progression by sponging miRNAs and RNA-binding proteins (RBPs) and regulating the Wnt/β-catenin signaling pathway. Therefore, circRNAs/miRNAs or RBPs/Wnt/β-catenin signaling pathway could be considered promising prognostic and therapeutic targets in HCC.

Crosstalk between m6A and coding/non-coding RNA in cancer and detection methods of m6A modification residues

N6-methyladenosine (m6A) is one of the most common and well-known internal RNA modifications that occur on mRNAs or ncRNAs. It affects various aspects of RNA metabolism, including splicing, stability, translocation, and translation. An abundance of evidence demonstrates that m6A plays a crucial role in various pathological and biological processes, especially in tumorigenesis and tumor progression. In this article, we introduce the potential functions of m6A regulators, including "writers" that install m6A marks, "erasers" that demethylate m6A, and "readers" that determine the fate of m6A-modified targets. We have conducted a review on the molecular functions of m6A, focusing on both coding and noncoding RNAs. Additionally, we have compiled an overview of the effects noncoding RNAs have on m6A regulators and explored the dual roles of m6A in the development and advancement of cancer. Our review also includes a detailed summary of the most advanced databases for m6A, state-of-the-art experimental and sequencing detection methods, and machine learning-based computational predictors for identifying m6A sites.

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 in colorectal cancer: potential biomarkers and therapeutic targets

Globally, colorectal cancer (CRC) is the third most prevalent cancer and the second leading cause of cancer-related deaths. Circular RNAs (circRNAs) are single-stranded RNA with covalently closed-loop structures and are highly stable, conserved, and abundantly expressed in various organs and tissues. Recent research found abnormal circRNA expression in CRC patients' blood/serum, cells, CRC tissues, and exosomes. Furthermore, mounting data demonstrated that circRNAs are crucial to the development of CRC. CircRNAs have been shown to exert biological functions by acting as microRNA sponges, RNA-binding protein sponges, regulators of gene splicing and transcription, and protein/peptide translators. These characteristics make circRNAs potential markers for CRC diagnosis and prognosis, potential therapeutic targets, and circRNA-based therapies. However, further studies are still necessary to improve the understanding of the roles and biological mechanisms of circRNAs in the development of CRC. In this review, up-to-date research on the role of circRNAs in CRC was examined, focusing on their potential application in CRC diagnosis and targeted therapy, which would advance the knowledge of the functions of circRNAs in the development and progression of CRC.

The role of m6A methylation in therapy resistance in cancer

Cancer therapy resistance is the main cause of cancer treatment failure. The mechanism of therapy resistance is a hot topic in epigenetics. As one of the most common RNA modifications, N6-methyladenosine (m6A) is involved in various processes of RNA metabolism, such as stability, splicing, transcription, translation, and degradation. A large number of studies have shown that m6A RNA methylation regulates the proliferation and invasion of cancer cells, but the role of m6A in cancer therapy resistance is unclear. In this review, we summarized the research progress related to the role of m6A in regulating therapy resistance in cancers.

Modifications of noncoding RNAs in cancer and their therapeutic implications

In the last 50 years, over 150 various chemical modifications on RNA molecules, including mRNAs, rRNAs, tRNAs, and other noncoding RNAs (ncRNAs), have been identified and characterized. These RNA modifications regulate RNA biogenesis and biological functions and are widely involved in various physiological processes and diseases, including cancer. In recent decades, broad interest has arisen in the epigenetic modification of ncRNAs due to the increased knowledge of the critical roles of ncRNAs in cancer. In this review, we summarize the various modifications of ncRNAs and highlight their roles in cancer initiation and progression. In particular, we discuss the potential of RNA modifications as novel biomarkers and therapeutic targets in cancer.

Insights into N6-methyladenosine (m6A) modification of noncoding RNA in tumor microenvironment

N6-methyladenosine (m6A) is the most abundant RNA modification in eukaryotes, and it participates in the regulation of pathophysiological processes in various diseases, including malignant tumors, by regulating the expression and function of both coding and non-coding RNAs (ncRNAs). More and more studies demonstrated that m6A modification regulates the production, stability, and degradation of ncRNAs and that ncRNAs also regulate the expression of m6A-related proteins. Tumor microenvironment (TME) refers to the internal and external environment of tumor cells, which is composed of numerous tumor stromal cells, immune cells, immune factors, and inflammatory factors that are closely related to tumors occurrence and development. Recent studies have suggested that crosstalk between m6A modifications and ncRNAs plays an important role in the biological regulation of TME. In this review, we summarized and analyzed the effects of m6A modification-associated ncRNAs on TME from various perspectives, including tumor proliferation, angiogenesis, invasion and metastasis, and immune escape. Herein, we showed that m6A-related ncRNAs can not only be expected to become detection markers of tumor tissue samples, but can also be wrapped into exosomes and secreted into body fluids, thus exhibiting potential as markers for liquid biopsy. This review provides a deeper understanding of the relationship between m6A-related ncRNAs and TME, which is of great significance to the development of a new strategy for precise tumor therapy.

Non-coding RNA-based therapeutics in cancer therapy: An emphasis on Wnt/β-catenin control

Non-coding RNA transcripts are RNA molecules that have mainly regulatory functions and they do not encode proteins. microRNAs (miRNAs), lncRNAs and circRNAs are major types of this family and these epigenetic factors participate in disease pathogenesis, especially cancer that their abnormal expression may lead to cancer progression. miRNAs and lncRNAs possess a linear structure, whereas circRNAs possess ring structures and high stability. Wnt/β-catenin is an important factor in cancer with oncogenic function and it can increase growth, invasion and therapy resistance in tumors. Wnt upregulation occurs upon transfer of β-catenin to nucleus. Interaction of ncRNAs with Wnt/β-catenin signaling can determine tumorigenesis. Wnt upregulation is observed in cancers and miRNAs are able to bind to 3'-UTR of Wnt to reduce its level. LncRNAs can directly/indirectly regulate Wnt and in indirect manner, lncRNAs sponge miRNAs. CircRNAs are new emerging regulators of Wnt and by its stimulation, they increase tumor progression. CircRNA/miRNA axis can affect Wnt and carcinogenesis. Overall, interaction of ncRNAs with Wnt can determine proliferation rate, migration ability and therapy response of cancers. Furthermore, ncRNA/Wnt/β-catenin axis can be utilized as biomarker in cancer and for prognostic applications in patients.

Circ_RBM23 knockdown suppresses chemoresistance, proliferation, migration and invasion of sorafenib-resistant HCC cells through miR-338-3p/RAB1B axis

BACKGROUND

Circular RNA RNA-binding motif protein 23 (circ_RBM23; ID: hsa_circ_0000524) is a novel regulator in hepatocellular carcinoma (HCC). Herein, we planned to investigate its role in sorafenib resistance in HCC.

METHOD

Levels of circ_RBM23, microRNA (miR)-338-3p, Ras-related GTPase-trafficking protein (RAB1B), Snail and E-cadherin were detected by real-time quantitative PCR and western blotting. Sorafenib resistant (SR) HCC cells (Huh7/SR and SK-HEP-1/SR) were established by acquisition of sorafenib resistance, and cell functions were measured by MTT assay, Edu assay, colony formation assay, apoptosis assay, transwell assay, and in vivo xenograft formation assay. Crosslink between miR-338-3p and circ_RBM23 or RAB1B was confirmed by bioinformatics analysis and dual-luciferase reporter assay.

RESULTS

Circ_RBM23 upregulation was discovered in the tissues of SR patients and SR cells, which was accompanied with miR-338-3p downregulation and RAB1B upregulation. The 50% inhibitory concentration (IC₅₀) of sorafenib in SR cells was greatly suppressed by interfering circ_RBM23 or reinforcing miR-338-3p, allied with this was the inhibition of EdU-positive cell rate, colony formation and migration/invasion abilities under sorafenib treatment, as well as the enhancement of apoptotic rate. Moreover, circ_RBM23 inhibition delayed tumor growth of Huh7/SR cells under sorfanib treatment in vivo.

CONCLUSION

Circ_RBM23 promoted chemoresistance, malignant proliferation, migration and invasion of SR HCC cells by modulating miR-338-3p/RAB1B axis.

Exosomal circCLIP1 regulates PM2.5-induced airway obstruction via targeting SEPT10 in vitro

Fine particulate matter (PM_2.5) exposure correlates with airway obstruction, but the mechanism remains to be fully elucidated. We aim to investigate the role of exosomal circular RNAs (circRNAs)-mediated communication between airway epithelial cells and airway smooth muscle cells in PM_2.5-induced airway obstruction. RNA sequencing revealed that acute PM_2.5 exposure altered the expression profiles of 2904 exosomal circRNAs. Among them, exosomal hsa_circ_0029069 (spliced from CLIP1, thus termed circCLIP1 hereafter) with a loop structure was upregulated by PM_2.5 exposure and mainly encapsulated in exosomes. Then, the biological functions and the underlying mechanisms were explored by Western blot, RNA immunoprecipitation and RNA pull-down, etc. Phenotypically, exosomal circCLIP1 entered recipient cells, inducing mucus secretion in recipient HBE cells and contractility of sensitive HBSMCs. Mechanistically, circCLIP1 was upregulated by METTL3-mediated N⁶-methyladenine (m⁶A) modification in PM_2.5-treated producer HBE cells and exosomes, then enhancing the expression of SEPT10 in recipient HBE cells and sensitive HBSMCs. Our study revealed that exosomal circCLIP1 played a critical role in PM_2.5-induced airway obstruction and provided a new potential biomarker for the assessment of PM_2.5-related adverse effects.

Exosome-derived circCCAR1 promotes CD8 + T-cell dysfunction and anti-PD1 resistance in hepatocellular carcinoma

BACKGROUND

Circular RNAs (circRNAs) can be encapsulated into exosomes to participate in intercellular communication, affecting the malignant progression of a variety of tumors. Dysfunction of CD8 + T cells is the main factor in immune escape from hepatocellular carcinoma (HCC). Nevertheless, the effect of exosome-derived circRNAs on CD8 + T-cell dysfunction needs further exploration.

METHODS

The effect of circCCAR1 on the tumorigenesis and metastasis of HCC was assessed by in vitro and in vivo functional experiments. The function of circCCAR1 in CD8 + T-cell dysfunction was measured by enzyme-linked immunosorbent assay (ELISA), western blotting and flow cytometry. Chromatin immunoprecipitation, biotinylated RNA pull-down, RNA immunoprecipitation, and MS2 pull-down assays were used to the exploration of mechanism. A mouse model with reconstituted human immune system components (huNSG mice) was constructed to explore the role of exosomal circCCAR1 in the resistance to anti-PD1 therapy in HCC.

RESULTS

Increased circCCAR1 levels existed in tumor tissues and exosomes in the plasma of HCC patients, in the culture supernatant and HCC cells. CircCCAR1 accelerated the growth and metastasis of HCC in vitro and in vivo. E1A binding protein p300 (EP300) and eukaryotic translation initiation factor 4A3 (EIF4A3) promoted the biogenesis of circCCAR1, and Wilms tumor 1-associated protein (WTAP)-mediated m6A modification enhanced circCCAR1 stability by binding insulin-like growth factor 2 mRNA-binding protein 3 (IGF2BP3). CircCCAR1 acted as a sponge for miR-127-5p to upregulate its target WTAP and a feedback loop comprising circCCAR1/miR-127-5p/WTAP axis was formed. CircCCAR1 is secreted by HCC cells in a heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNPA2B1)-dependent manner. Exosomal circCCAR1 was taken in by CD8 + T cells and caused dysfunction of CD8 + T cells by stabilizing the PD-1 protein. CircCCAR1 promoted resistance to anti-PD1 immunotherapy. Furthermore, increased cell division cycle and apoptosis regulator 1 (CCAR1) induced by EP300 promoted the binding of CCAR1 and β-catenin protein, which further enhanced the transcription of PD-L1.

CONCLUSIONS

The circCCAR1/miR-127-5p/WTAP feedback loop enhances the growth and metastasis of HCC. Exosomal circCCAR1 released by HCC cells contributes to immunosuppression by facilitating CD8 + T-cell dysfunction in HCC. CircCCAR1 induces resistance to anti-PD1 immunotherapy, providing a potential therapeutic strategy for HCC patients.

The critical role of circular RNAs in drug resistance in gastrointestinal cancers

Nowadays, drug resistance (DR) in gastrointestinal (GI) cancers, as the main reason for cancer-related mortality worldwide, has become a serious problem in the management of patients. Several mechanisms have been proposed for resistance to anticancer drugs, including altered transport and metabolism of drugs, mutation of drug targets, altered DNA repair system, inhibited apoptosis and autophagy, cancer stem cells, tumor heterogeneity, and epithelial-mesenchymal transition. Compelling evidence has revealed that genetic and epigenetic factors are strongly linked to DR. Non-coding RNA (ncRNA) interferences are the most crucial epigenetic alterations explored so far, and among these ncRNAs, circular RNAs (circRNAs) are the most emerging members known to have unique properties. Due to the absence of 5' and 3' ends in these novel RNAs, the two ends are covalently bonded together and are generated from pre-mRNA in a process known as back-splicing, which makes them more stable than other RNAs. As far as the unique structure and function of circRNAs is concerned, they are implicated in proliferation, migration, invasion, angiogenesis, metastasis, and DR. A clear understanding of the molecular mechanisms responsible for circRNAs-mediated DR in the GI cancers will open a new window to the management of GI cancers. Hence, in the present review, we will describe briefly the biogenesis, multiple features, and different biological functions of circRNAs. Then, we will summarize current mechanisms of DR, and finally, discuss molecular mechanisms through which circRNAs regulate DR development in esophageal cancer, pancreatic cancer, gastric cancer, colorectal cancer, and hepatocellular carcinoma.

The significance of N6-methyladenosine-modified non-coding RNAs in different disorders

N6-methyladenosine (m6A) is the most widespread endogenous modification affecting the expression of eukaryotic mRNA transcripts. Recent studies have shown that the m6A marks within non-coding RNAs can affect their functions and expression in a manner similar to that of mRNA-coding genes. Since non-coding RNAs are involved in the pathophysiology of several disorders, identification of the role of m6A marks in the regulation of expression of non-coding RNAs can open a new era for identifying underlying mechanisms of several disorders and designing novel therapeutic modalities for a variety of disorders, particularly cancers. Moreover, a number of non-coding RNAs can affect m6A levels. In the current review, we discuss the impacts of m6A marks on the expression of non-coding RNAs in the context of different disorders, such as bone, gastrointestinal, neurologic, renal, pulmonary, hepatic and other disorders.