Editing and Chemical Modifications on Non-Coding RNAs in Cancer: A New Tale with Clinical Significance

RNA modifications in long non-coding RNAs and their implications in cancer biology

Long non-coding RNAs (lncRNAs) represent the most diverse class of RNAs in cells and play crucial roles in maintaining cellular functions. RNA modifications, being a significant factor in regulating RNA biology, have been found to be extensively present in lncRNAs and exert regulatory effects on their behavior and biological functions. Most common types of RNA modifications in lncRNAs include N6-methyladenosine (m6A), 5-methylcytosine (m5C), and N1-methyladenosine (m1A). In this review, we summarize the major RNA modification types associated with lncRNAs, the regulatory roles of each modification, and the implications of modified lncRNAs in tumorigenesis and development. By examining these aspects, we aim to provide insights into the role of RNA modifications in lncRNAs and their potential impact on cancer biology.

RBPs: an RNA editor's choice

RNA-binding proteins (RBPs) play a key role in gene expression and post-transcriptional RNA regulation. As integral components of ribonucleoprotein complexes, RBPs are susceptible to genomic and RNA Editing derived amino acid substitutions, impacting functional interactions. This article explores the prevalent RNA Editing of RBPs, unravelling the complex interplay between RBPs and RNA Editing events. Emphasis is placed on their influence on single amino acid variants (SAAVs) and implications for disease development. The role of Proteogenomics in identifying SAAVs is briefly discussed, offering insights into the RBP landscape. RNA Editing within RBPs emerges as a promising target for precision medicine, reshaping our understanding of genetic and epigenetic variations in health and disease.

The Function and Mechanism of Long Noncoding RNAs in Adipogenic Differentiation

Adipocytes are crucial for maintaining energy balance. Adipocyte differentiation involves distinct stages, including the orientation stage, clone amplification stage, clone amplification termination stage, and terminal differentiation stage. Understanding the regulatory mechanisms governing adipogenic differentiation is essential for comprehending the physiological processes and identifying potential biomarkers and therapeutic targets for metabolic diseases, ultimately improving glucose and fat metabolism. Adipogenic differentiation is influenced not only by key factors such as hormones, the peroxisome proliferator-activated receptor (PPAR) family, and the CCATT enhancer-binding protein (C/EBP) family but also by noncoding RNA, including microRNA (miRNA), long noncoding RNA (lncRNA), and circular RNA (circRNA). Among these, lncRNA has been identified as a significant regulator in adipogenic differentiation. Research has demonstrated various ways in which lncRNAs contribute to the molecular mechanisms of adipogenic differentiation. Throughout the adipogenesis process, lncRNAs modulate adipocyte differentiation and development by influencing relevant signaling pathways and transcription factors. This review provides a brief overview of the function and mechanism of lncRNAs in adipogenic differentiation.

An overview of challenges associated with exosomal miRNA isolation toward liquid biopsy-based ovarian cancer detection

As one of the deadliest gynaecological cancers, ovarian cancer has been on the list. With lesser-known symptoms and lack of an accurate detection method, it is still difficult to catch it early. In terms of both the diagnosis and outlook for cancer, liquid biopsy has come a long way with significant advancements. Exosomes, extracellular components commonly shed by cancerous cells, are nucleic acid-rich particles floating in almost all body fluids and hold enormous promise, leading to minimallyinvasive molecular diagnostics. They have been shown as potential biomarkers in liquid biopsy, being implicated in tumour growth and metastasis. In order to address the drawbacks of ovarian cancer tumor heterogeneity, a liquid biopsy-based approach is being investigated by detecting cell-free nucleic acids, particularly non-coding RNAs, having the advantage of being less invasive and more prominent in nature. microRNAs are known to actively contribute to cancer development and their existence inside exosomes has also been made quite apparent which can be leveraged to diagnose and treat the disease. Extraction of miRNAs and exosomes is an arduous execution, and while other approaches have been investigated, none have produced results that are as encouraging due to limits in time commitment, yield, and, most significantly, damage to the exosomal structure resulting discrepancies in miRNA-based expression profiling for disease diagnosis. We have briefly outlined and reviewed the difficulties with exosome isolation techniques and the need for their standardization. The several widely used procedures and their drawbacks in terms of the exosomal purity they may produce have also been outlined.

5-methylcytosine-mediated upregulation of circular RNA 0102913 augments malignant properties of colorectal cancer cells through a microRNA-571/Rac family small GTPase 2 axis

Circular RNAs (circRNAs) are a class of stable non-coding RNAs that have emerged as key regulators in human diseases including cancer. This study investigates the role of circRNA_0102913 (circ_0102913) in malignant behavior of colorectal cancer (CRC) cells and the underpinning mechanisms. By analyzing CRC-related GSE197991, GSE159669, and GSE223001 datasets, we obtained circ_0102913 as an aberrantly upregulated circRNA in CRC. Increased circ_0102913 expression was detected in CRC tissues and cells. By querying multiple bioinformatics systems (circBank, Circular RNA Interactome, TargetScan, miRDIP, miRwalk, and miRDB), we identified microRNA-571 (miR-571) as a target of circ_0102913 and Rac family small GTPase 2 (RAC2) mRNA as a target of miR-571. Biotinylated-RNA pull-down and/or luciferase assays showed that circ_0102913 bound to miR-571 to restore the expression of RAC2 mRNA. Circ_0102913 silencing or miR-571 overexpression repressed proliferation, migration and invasion, and in vivo tumorigenesis abilities of CRC cells. However, the malignant properties of cells were restored by RAC2 overexpression. The increased circ_0102913 expression in CRC cells was attributed to increased 5-methylcytosine (m5C) modification levels. Silencing of NOP2/Sun RNA methyltransferase 5 reduced the m5C level and therefore reduced stability and expression of circ_0102913 expression in CRC cells. In conclusion, this study demonstrates that m5C-mediated upregulation of circ_0102913 augments malignant properties of CRC cells through a miR-571/RAC2 axis.

RNA methylation-related inhibitors: Biological basis and therapeutic potential for cancer therapy

RNA methylation is widespread in nature. Abnormal expression of proteins associated with RNA methylation is strongly associated with a number of human diseases including cancer. Increasing evidence suggests that targeting RNA methylation holds promise for cancer treatment. This review specifically describes several common RNA modifications, such as the relatively well-studied N6-methyladenosine, as well as 5-methylcytosine and pseudouridine (Ψ). The regulatory factors involved in these modifications and their roles in RNA are also comprehensively discussed. We summarise the diverse regulatory functions of these modifications across different types of RNAs. Furthermore, we elucidate the structural characteristics of these modifications along with the development of specific inhibitors targeting them. Additionally, recent advancements in small molecule inhibitors targeting RNA modifications are presented to underscore their immense potential and clinical significance in enhancing therapeutic efficacy against cancer. KEY POINTS: In this paper, several important types of RNA modifications and their related regulatory factors are systematically summarised. Several regulatory factors related to RNA modification types were associated with cancer progression, and their relationships with cancer cell migration, invasion, drug resistance and immune environment were summarised. In this paper, the inhibitors targeting different regulators that have been proposed in recent studies are summarised in detail, which is of great significance for the development of RNA modification regulators and cancer treatment in the future.

Epitranscriptomic modifications in mesenchymal stem cell differentiation: advances, mechanistic insights, and beyond

RNA modifications, known as the "epitranscriptome", represent a key layer of regulation that influences a wide array of biological processes in mesenchymal stem cells (MSCs). These modifications, catalyzed by specific enzymes, often termed "writers", "readers", and "erasers", can dynamically alter the MSCs' transcriptomic landscape, thereby modulating cell differentiation, proliferation, and responses to environmental cues. These enzymes include members of the classes METTL, IGF2BP, WTAP, YTHD, FTO, NAT, and others. Many of these RNA-modifying agents are active during MSC lineage differentiation. This review provides a comprehensive overview of the current understanding of different RNA modifications in MSCs, their roles in regulating stem cell behavior, and their implications in MSC-based therapies. It delves into how RNA modifications impact MSC biology, the functional significance of individual modifications, and the complex interplay among these modifications. We further discuss how these intricate regulatory mechanisms contribute to the functional diversity of MSCs, and how they might be harnessed for therapeutic applications. The review also highlights current challenges and potential future directions in the study of RNA modifications in MSCs, emphasizing the need for innovative tools to precisely map these modifications and decipher their context-specific effects. Collectively, this work paves the way for a deeper understanding of the role of the epitranscriptome in MSC biology, potentially advancing therapeutic strategies in regenerative medicine and MSC-based therapies.

Identification of m5C-related lncRNAs signature to predict prognosis and therapeutic responses in esophageal squamous cell carcinoma patients

Esophageal squamous cell carcinoma (ESCC) has a dismal prognosis because of atypical early symptoms and heterogeneous therapeutic responses. 5-methylcytosine (m5C) modification plays an important role in the onset and development of many tumors and is widespread in long non-coding RNA (lncRNA) transcripts. However, the functions of m5C and lncRNAs in ESCC have not been completely elucidated. Herein, this study aimed to explore the role of m5C-related lncRNAs in ESCC. The RNA-seq transcriptome profiles and clinical information were downloaded from the TCGA-ESCC database. Pearson analysis was used to identify m5C-related lncRNAs. Then we established the m5C-related lncRNAs prognostic signature (m5C-LPS) using univariate Cox and least absolute shrinkage and selection operator (LASSO) regression analysis. Then, the prognostic value of m5C-LPS was evaluated internally and externally using the TCGA-ESCC and GSE53622 databases through multiple methods. We also detected the expression of these lncRNAs in ESCC cell lines and patient tissues. Fluorescence in situ hybridization (FISH) was used to detect the prognostic value of specific lncRNA. In addition, clinical parameters, immune status, genomic variants, oncogenic pathways, enrichment pathways, and therapeutic response features associated with m5C-LPS were explored using bioinformatics methods. We constructed and validated a prognostic signature based on 9 m5C-related lncRNAs (AC002091.2, AC009275.1, CAHM, LINC02057.1, AC0006329.1, AC037459.3, AC064807.1, ATP2B1-AS1, and UBAC2-AS1). The quantitative real-time polymerase chain reaction (qRT-PCR) revealed that most lncRNAs were upregulated in ESCC cell lines and patient tissues. And AC002091.2 was validated to have significant prognostic value in ESCC patients. A composite nomogram was generated to facilitate clinical practice by integrating this signature with the N stage. Besides, patients in the low-risk group were characterized by good clinical outcomes, favorable immune status, and low oncogenic alteration. Function enrichment analysis indicated that the risk score was associated with mRNA splicing, ncRNA processing, and DNA damage repair response. At the same time, we found significant differences in the responses to chemoradiotherapy between the two groups, proving the value of m5C-LPS in treatment decision-making in ESCC. This study established a novel prognostic signature based on 9 m5C-related lncRNAs, which is a promising biomarker for predicting clinical outcomes and therapeutic response in ESCC.

Non-Coding RNAs: Foes or Friends for Targeting Tumor Microenvironment

Non-coding RNAs (ncRNAs) are a group of molecules critical for cell development and growth regulation. They are key regulators of important cellular pathways in the tumor microenvironment. To analyze ncRNAs in the tumor microenvironment, the use of RNA sequencing technology has revolutionized the field. The advancement of this technique has broadened our understanding of the molecular biology of cancer, presenting abundant possibilities for the exploration of novel biomarkers for cancer treatment. In this review, we will summarize recent achievements in understanding the complex role of ncRNA in the tumor microenvironment, we will report the latest studies on the tumor microenvironment using RNA sequencing, and we will discuss the potential use of ncRNAs as therapeutics for the treatment of cancer.

M1A and m7G modification-related genes are potential biomarkers for survival prognosis and for deciphering the tumor immune microenvironment in esophageal squamous cell carcinoma

BACKGROUND

Esophageal squamous cell carcinoma (ESCC) is the most common esophageal malignancy, and RNA methylation has been reported to be involved in the tumorigenesis of ESCC. However, no study has explored methylation modifications in m¹A and m⁷G as prognostic markers for survival prediction in ESCC.

METHODS

Public gene-expression data and clinical annotation of 254 patients obtained from The Cancer Genome Atlas and the Gene Expression Omnibus databases were analyzed to identify potential consensus clusters of m¹A and m⁷G modification-related genes. The RNA-seq of 20 patients in Sun Yat-Sen University Cancer Center was used as the validation set. Following screening for relevant differentially expressed genes (DEGs) and enrichment pathways were elucidated. DEGs were used to construct risk models using the randomForest algorithm, and the prognostic role of the models was assessed by applying Kaplan-Meier analysis. Extent of immune cell infiltration, drug resistance, and response to cancer treatment among different clusters and risk groups were also evaluated.

RESULTS

Consensus clustering analysis based on m¹A and m⁷G modification patterns revealed three potential clusters. In total, 212 RNA methylation-related DEGs were identified. The methylation-associated signature consisting of 6 genes was then constructed to calculate methylation-related score (MRScore) and patients were dived into MRScore-high and MRScore-low groups. This signature has satisfied prognostic value for survival of ESCC (AUC = 0.66, 0.67, 0.64 for 2-, 3-, 4- year OS), and has satisfied performance in the validation SYSUCC cohort (AUC = 0.66 for 2- and 3-year OS). Significant correlation between m¹A and m⁷G modification-related genes and immune cell infiltration, and drug resistance was also observed.

CONCLUSIONS

Transcriptomic prognostic signatures based on m¹A and m⁷G modification-related genes are closely associated with immune cell infiltration in ESCC patients and have important correlations with the therapeutic sensitivity of multiple chemotherapeutic agents.

Circ_0000182 promotes cholesterol synthesis and proliferation of stomach adenocarcinoma cells by targeting miR-579-3p/SQLE axis

BACKGROUND

Circular RNAs (circRNAs) or cholesterol metabolism have been demonstrated to participate in stomach adenocarcinoma (STAD) progression. However, the relationship between circRNAs and cholesterol metabolism in STAD and its underlined mechanism remain unclear.

METHODS

RNA and protein expression levels were detected by qRT-PCR and Western blot. Cell proliferation was assessed by CCK-8, EdU incorporation and colony formation assays. Total cholesterol (TC) and free cholesterol (FC) levels were measured by the corresponding kits. The relationships between circ_0000182 and miR-579-3p or squalene epoxidase (SQLE) mRNA were investigated by bioinformatics analysis, RNA-RNA pull-down, luciferase reporter and RIP assays.

RESULTS

We found that circ_0000182 expression was significantly up-regulated in both STAD tissues and cell lines, and high circ_0000182 expression was correlated with increased tumor size. Circ_0000182 promoted cell proliferation and cholesterol synthesis of STAD cells. Accordingly, cell proliferation, cholesterol synthesis and SQLE expression were significantly inhibited by circ_0000182 knockdown in STAD cells, and these effects were partly reversed by miR-579-3p inhibition or SQLE over-expression. Furthermore, we identified that circ_0000182 acted as a competing endogenous RNA (ceRNA) by sponging miR-579-3p, thereby facilitating SQLE expression, cholesterol synthesis and cell proliferation.

CONCLUSION

Circ_0000182 promotes cholesterol synthesis and proliferation of STAD cells by enhancing SQLE expression via sponging miR-579-3p.

Epigenetic reprogramming in cancer: From diagnosis to treatment

Disruption of the epigenetic program of gene expression is a hallmark of cancer that initiates and propagates tumorigenesis. Altered DNA methylation, histone modifications and ncRNAs expression are a feature of cancer cells. The dynamic epigenetic changes during oncogenic transformation are related to tumor heterogeneity, unlimited self-renewal and multi-lineage differentiation. This stem cell-like state or the aberrant reprogramming of cancer stem cells is the major challenge in treatment and drug resistance. Given the reversible nature of epigenetic modifications, the ability to restore the cancer epigenome through the inhibition of the epigenetic modifiers is a promising therapy for cancer treatment, either as a monotherapy or in combination with other anticancer therapies, including immunotherapies. Herein, we highlighted the main epigenetic alterations, their potential as a biomarker for early diagnosis and the epigenetic therapies approved for cancer treatment.

ADAR1-dependent miR-3144-3p editing simultaneously induces MSI2 expression and suppresses SLC38A4 expression in liver cancer

Aberrant adenosine-to-inosine (A-to-I) RNA editing, catalyzed by adenosine deaminase acting on double-stranded RNA (ADAR), has been implicated in various cancers, but the mechanisms by which microRNA (miRNA) editing contributes to cancer development are largely unknown. Our multistage hepatocellular carcinogenesis transcriptome data analyses, together with publicly available data, indicated that ADAR1 was the most profoundly dysregulated gene among RNA-editing enzyme family members in liver cancer. Targeted inactivation of ADAR1 inhibited the in vitro tumorigenesis of liver cancer cells. An integrative computational analyses of RNA-edited hotspots and the known editing frequency of miRNAs suggested that the miRNA miR-3144-3p was edited by ADAR1 during liver cancer progression. Specifically, ADAR1 promoted A-to-I editing of canonical miR-3144-3p to replace the adenosine at Position 3 in the seed region with a guanine (ED_miR-3144-3p(3_A < G)) in liver cancer cells. We then demonstrated that Musashi RNA-binding protein 2 (MSI2) was a specific target of miR-3144-3p and that MSI2 overexpression was due to excessive ADAR1-dependent over-editing of canonical miR-3144-3p in liver cancer. In addition, target prediction analyses and validation experiments identified solute carrier family 38 member 4 (SLC38A4) as a specific gene target of ED_miR-3144-3p(3_A < G). The ectopic expression of both ADAR1 and the ED_miR-3144-3p(3_A < G) mimic enhanced mitotic activities, and ADAR1 suppressed SLC38A4 expression in liver cancer cells. Treatments with mouse-specific ADAR1-, MSI2-siRNA-, or SLC38A4-expressing plasmids suppressed tumorigenesis and tumor growth in a mouse model of spontaneous liver cancer. Our findings suggest that the aberrant regulation of ADAR1 augments oncogenic MSI2 effects by excessively editing canonical miR-3144-3p and that the resultant ED_miR-3144-3p(3_A < G) simultaneously suppresses tumor suppressor SLC38A4 expression, contributing to hepatocellular carcinogenesis.

N6-methyladenosine (m6A) RNA modification in the pathophysiology of heart failure: a narrative review

Background and Objective

Heart failure is the end-stage of various cardiovascular diseases. Recent progress in molecular biology has facilitated the understanding of the mechanisms of heart failure development at the molecular level. N6-adenosine methylation (m6A) is a post-transcriptional modification of RNA. Recent research work reported that m6A regulates gene expression and subsequently affects the activation of cell signaling pathways related to heart failure. Moreover, m6A regulators like methyltransferase-like 3 (METTL3) were reported to participate in myocardium hypertrophy. However, the current research work related to the role of m6A participating in the occurrence of heart failure is rare in some aspects like immune cell infiltration and diabetic heart diseases. Thus, it is reasonable to review the current achievements and provide further study orientation.

Methods

We searched related literature using the keywords: m6A AND heart failure in PubMed, Web of Science and Medline. The language was confined to English. The published year of searched literature ranged from 2012 to 2022. The searched results were put into Endnote software for management. Two authors investigated the searching terms and reviewed the full text of selected terms.

Key Content and Findings

m6A and its regulators are involved in the metabolism of various types of RNAs. m6A modification can regulate various types of cell signaling pathways related to the heart failure via interaction with m6A regulators. m6A and its regulators broadly participate in the myocardium fibrosis, myocardium hypertrophy, myocardial cell apoptosis, and ischemic reperfusion injury. Specifically, m6A participates in the cell apoptosis via regulation of autophagy flux. However, the current research work does not have enough evidence to prove that m6A regulator played its specific effect on the target transcript via regulating the m6A level.

Conclusions

m6A and its regulators participates in the progression of heart failure via modifying the RNA level. Future investigation of m6A should focus on the interaction between the m6A regulators and targeted transcript. Besides, the regulation role of m6A in immune cell infiltration and diabetic heart diseases should also be focused.

Epitranscriptome: Review of Top 25 Most-Studied RNA Modifications

The alphabet of building blocks for RNA molecules is much larger than the standard four nucleotides. The diversity is achieved by the post-transcriptional biochemical modification of these nucleotides into distinct chemical entities that are structurally and functionally different from their unmodified counterparts. Some of these modifications are constituent and critical for RNA functions, while others serve as dynamic markings to regulate the fate of specific RNA molecules. Together, these modifications form the epitranscriptome, an essential layer of cellular biochemistry. As of the time of writing this review, more than 300 distinct RNA modifications from all three life domains have been identified. However, only a few of the most well-established modifications are included in most reviews on this topic. To provide a complete overview of the current state of research on the epitranscriptome, we analyzed the extent of the available information for all known RNA modifications. We selected 25 modifications to describe in detail. Summarizing our findings, we describe the current status of research on most RNA modifications and identify further developments in this field.

Tumor-Suppressive and Oncogenic Roles of microRNA-149-5p in Human Cancers

Malignant tumors are always a critical threat to human health, with complex pathogenesis, numerous causative factors, and poor prognosis. The features of cancers, such as gene mutations, epigenetic alterations, and the activation and inhibition of signaling pathways in the organism, play important roles in tumorigenesis and prognosis. MicroRNA (miRNA) enables the control of various molecular mechanisms and plays a variety of roles in human cancers, such as radiation sensitivity and tumor immunity, through the regulation of target genes. MiR-149-5p participates in the process and is closely related to lipogenesis, the migration of vascular endothelial cells, and the expression of stem-cell-related proteins. In recent years, its role in cancer has dramatically increased. In this review, we summarize the regular physiological roles of miRNAs, specifically miR-149-5p, in the organism and discuss the tumor-suppressive or oncogenic roles of miR-149-5p in different human cancers with respect to signaling pathways involved in regulation. Possible clinical applications of miR-149-5p in future targeted therapies and prognosis improvement in oncology are suggested.

Mechanisms Controlling MicroRNA Expression in Tumor

MicroRNAs (miRNAs) are widely present in many organisms and regulate the expression of genes in various biological processes such as cell differentiation, metabolism, and development. Numerous studies have shown that miRNAs are abnormally expressed in tumor tissues and are closely associated with tumorigenesis. MiRNA-based cancer gene therapy has consistently shown promising anti-tumor effects and is recognized as a new field in cancer treatment. So far, some clinical trials involving the treatment of malignancies have been carried out; however, studies of miRNA-based cancer gene therapy are still proceeding slowly. Therefore, furthering our understanding of the regulatory mechanisms of miRNA can bring substantial benefits to the development of miRNA-based gene therapy or other combination therapies and the clinical outcome of patients with cancer. Recent studies have revealed that the aberrant expression of miRNA in tumors is associated with promoter sequence mutation, epigenetic alteration, aberrant RNA modification, etc., showing the complexity of aberrant expression mechanisms of miRNA in tumors. In this paper, we systematically summarized the regulation mechanisms of miRNA expression in tumors, with the aim of providing assistance in the subsequent elucidation of the role of miRNA in tumorigenesis and the development of new strategies for tumor prevention and treatment.

Comprehensive Analysis of Gene Signatures of m6ARNA Methylation Regulators in Lung Adenocarcinoma and Development of a Risk Scoring System

The recent application of targeted immunotherapy has greatly improved the clinical outcomes of patients with lung adenocarcinoma (LUAD), but drug resistance continues to emerge, and to evaluate and to improve patient prognosis are arduous. The diagnostic and prognostic value of N6-methyladenosine (M6A) in LUAD has attracted increasing attention. We systematically studied correlations among important M6A methylation regulators, tumor mutational burden (TMB), and immune infiltration in clinical and sequencing data from the LUAD cohort of the cancer genome map (TCGA). The molecular subtype clusters 1 and 2 were identified by the consensus clustering of 16 M6A regulatory factors. Clinical prognosis, M6A regulatory factor expression, TMB, pathway enrichment, and immune cell infiltration significantly differed between clusters 1 and 2. Compared with other clinical traits, a prognostic risk score system constructed using the M6A regulatory factors HNRNPA2B1 and HNRNPC can serve as an independent prognostic method for LUAD, with higher predictive sensitivity and specificity. Risk scores were significantly higher for cluster 2 than 1, which was consistent with the trend towards a better prognosis in cluster 1. Overall, our findings revealed an important role of M6A methylation regulators in LUAD, and our risk scoring system involving these regulators might help to screen groups at high risk for LUAD and provide important theoretical bioinformatic support for evaluating the prognosis of such patients.

ADAR1-Mediated RNA Editing and Its Role in Cancer

It is well known that the stability of RNA, the interaction between RNA and protein, and the correct translation of protein are significant forces that drive the transition from normal cell to malignant tumor. Adenosine deaminase acting on RNA 1 (ADAR1) is an RNA editing enzyme that catalyzes the deamination of adenosine to inosine (A-to-I), which is one dynamic modification that in a combinatorial manner can give rise to a very diverse transcriptome. ADAR1-mediated RNA editing is essential for survival in mammals and its dysregulation results in aberrant editing of its substrates that may affect the phenotypic changes in cancer. This overediting phenomenon occurs in many cancers, such as liver, lung, breast, and esophageal cancers, and promotes tumor progression in most cases. In addition to its editing role, ADAR1 can also play an editing-independent role, although current research on this mechanism is relatively shallowly explored in tumors. In this review, we summarize the nature of ADAR1, mechanisms of ADAR1 editing-dependent and editing-independent and implications for tumorigenesis and prognosis, and pay special attention to effects of ADAR1 on cancers by regulating non-coding RNA formation and function.

Circ_0000705 facilitates proline metabolism of esophageal squamous cell carcinoma cells by targeting miR-621/PYCR1 axis

CircRNAs have been found to play crucial roles in the metabolism and progression of cancers, but their roles and mechanisms in esophageal squamous cell carcinoma (ESCC) have not been fully elucidated. This work is aimed to explore the role and mechanism of hsa_circ_0000705 (circ_0000705) in ESCC. Circ_0000705 expression was up-regulated in ESCC tissues and cell lines, and high circ_0000705 expression was correlated with poor survival. Circ_0000705 facilitated cell proliferation, invasion, migration and proline metabolism of ESCC cells. The inhibitory effects of circ_0000705 knockdown on cell invasion, migration and proline metabolism were partly rescued by miR-621 inhibition or PYCR1 over-expression. Furthermore, circ_0000705 expression is negatively correlated with miR-621 expression, and positively correlated with PYCR1 in ESCC tissues. Mechanistically, circ_0000705 acted as a ceRNA by sponging miR-621, thereby facilitating PYCR1 expression in ESCC cells. In conclusion, circ_0000705 promoted proline metabolism and malignant progression of ESCC by regulating the miR‑621/PYCR1 axis.

Role of main RNA modifications in cancer: N6-methyladenosine, 5-methylcytosine, and pseudouridine

Cancer is one of the major diseases threatening human life and health worldwide. Epigenetic modification refers to heritable changes in the genetic material without any changes in the nucleic acid sequence and results in heritable phenotypic changes. Epigenetic modifications regulate many biological processes, such as growth, aging, and various diseases, including cancer. With the advancement of next-generation sequencing technology, the role of RNA modifications in cancer progression has become increasingly prominent and is a hot spot in scientific research. This review studied several common RNA modifications, such as N⁶-methyladenosine, 5-methylcytosine, and pseudouridine. The deposition and roles of these modifications in coding and noncoding RNAs are summarized in detail. Based on the RNA modification background, this review summarized the expression, function, and underlying molecular mechanism of these modifications and their regulators in cancer and further discussed the role of some existing small-molecule inhibitors. More in-depth studies on RNA modification and cancer are needed to broaden the understanding of epigenetics and cancer diagnosis, treatment, and prognosis.

Epitranscriptomic modifications in acute myeloid leukemia: m6A and 2'-O-methylation as targets for novel therapeutic strategies

Modifications of RNA commonly occur in all species. Multiple enzymes are involved as writers, erasers and readers of these modifications. Many RNA modifications or the respective enzymes are associated with human disease and especially cancer. Currently, the mechanisms how RNA modifications impact on a large number of intracellular processes are emerging and knowledge about the pathogenetic role of RNA modifications increases. In Acute Myeloid Leukemia (AML), the N6-methyladenosine (m6A) modification has emerged as an important modulator of leukemogenesis. The writer proteins METTL3 and METTL14 are both involved in AML pathogenesis and might be suitable therapeutic targets. Recently, close links between 2'-O-methylation (2'-O-me) of ribosomal RNA and leukemogenesis were discovered. The AML1-ETO oncofusion protein which specifically occurs in a subset of AML was found to depend on induction of snoRNAs and 2'-O-me for leukemogenesis. Also, NPM1, an important tumor suppressor in AML, was associated with altered snoRNAs and 2'-O-me. These findings point toward novel pathogenetic mechanisms and potential therapeutic interventions. The current knowledge and the implications are the topic of this review.

Up-to-date on the evidence linking miRNA-related epitranscriptomic modifications and disease settings. Can these modifications affect cross-kingdom regulation?

The field of epitranscriptomics is rapidly developing. Several modifications (e.g. methylations) have been identified for different RNA types. Current evidence shows that chemical RNA modifications can influence the whole molecule's secondary structure, translatability, functionality, stability, and degradation, and some are dynamically and reversibly modulated. miRNAs, in particular, are not only post-transcriptional modulators of gene expression but are themselves submitted to regulatory mechanisms. Understanding how these modifications are regulated and the resulting pathological consequences when dysregulation occurs is essential for the development of new therapeutic targets. In humans and other mammals, dietary components have been shown to affect miRNA expression and may also induce chemical modifications in miRNAs. The identification of chemical modifications in miRNAs (endogenous and exogenous) that can impact host gene expression opens up an alternative way to select new specific therapeutic targets.Hence, the aim of this review is to briefly address how RNA epitranscriptomic modifications can affect miRNA biogenesis and to summarize the existing evidence showing the connection between the (de)regulation of these processes and disease settings. In addition, we hypothesize on the potential effect certain chemical modifications could have on the potential cross-kingdom journey of dietary plant miRNAs.

Classical and noncanonical functions of miRNAs in cancers

Alterations in microRNAs (miRNAs) expression are causative in the initiation and progression of human cancers. The molecular events responsible for the widespread differential expression of miRNAs in malignancy are exemplified by their location in cancer-associated genomic regions, epigenetic mechanisms, transcriptional dysregulation, chemical modifications and editing, and alterations in miRNA biogenesis proteins. The classical miRNA function is synonymous with post-transcriptional repression of target protein genes. However, several studies have reported miRNAs functioning outside this paradigm and some of these novel modes of regulation of gene expression have been implicated in cancers. Here, we summarize key aspects of miRNA involvement in cancer, with a special focus on these lesser-studied mechanisms of action.

Advances in RNA Epigenetic Modifications in Hepatocellular Carcinoma and Potential Targeted Intervention Strategies

The current interventions for hepatocellular carcinoma (HCC) are not satisfactory, and more precise targets and promising strategies need to be explored. Recent research has demonstrated the non-negligible roles of RNA epigenetic modifications such as N6-methyladenosine (m6A) and 5-methylcytosine (m5C) in various cancers, including HCC. However, the specific targeting mechanisms are not well elucidated. In this review, we focus on the occurrence and detailed physiopathological roles of multiple RNA modifications on diverse RNAs closely related to the HCC process. In particular, we highlight fresh insights into the impact mechanisms of these posttranscriptional modifications on the whole progression of HCC. Furthermore, we analyzed the possibilities and significance of these modifications and regulators as potential therapeutic targets in HCC treatment, which provides the foundation for exploring targeted intervention strategies. This review will propel the identification of promising therapeutic targets and novel strategies that can be translated into clinical applications for HCC treatment.

Effect, Mechanism, and Applications of Coding/Non-coding RNA m6A Modification in Tumor Microenvironment

The tumor microenvironment (TME), which includes immune cells, fibroblasts, and other components, is the site of tumor cell growth and metastasis and significantly impacts tumor development. Among them, N6-methyladenosine RNA modifications (m6A RNA modifications) are the most abundant internal modifications in coding and non-coding RNAs, which can significantly influence the cancer process and have potential as biomarkers and potential therapeutic targets for tumor therapy. This manuscript reviews the role of m6A RNA modifications in TME and their application in tumor therapy. To some extent, an in-depth understanding of the relationship between TME and m6A RNA modifications will provide new approaches and ideas for future cancer therapy.

Circ-SFMBT2 drives the malignant phenotypes of esophageal cancer by the miR-107-dependent regulation of SLC1A5

Background

Increasing studies focused on the regulatory roles of circular RNAs (circRNAs) in diverse cancers. This study was to evaluate the function and mechanism of circRNA Scm-like with four malignant brain tumor domains 2 (circ-SFMBT2) in esophageal cancer (EC).

Methods

The circ-SFMBT2, microRNA-107 (miR-107) and solute-linked carrier family A1 member 5 (SLC1A5) levels were analyzed by quantitative real-time polymerase chain reaction (qRT-PCR). Cell proliferation was evaluated by 3-(4, 5-dimethylthiazol-2-y1)-2, 5-diphenyl tetrazolium bromide (MTT) assay, colony formation assay and EdU assay. Cell apoptosis and invasion were detected by flow cytometry and transwell assay. Glutamine metabolism was assessed by the corresponding kits for glutamine consumption, α-ketoglutarate production and glutamate production. Western blot was used for protein quantification. The binding analysis was performed using dual-luciferase reporter assay, RNA immunoprecipitation (RIP) and pull-down assays. The functional research of circ-SFMBT2 in vivo was performed by xenograft tumor assay. Exosomes were identified by morphological observation and protein detection.

Results

Circ-SFMBT2 was overexpressed in EC samples and cells. Circ-SFMBT2 downregulation inhibited EC cell proliferation, invasion and glutamine metabolism. Circ-SFMBT2 targeted miR-107 and the regulation of circ-SFMBT2 was achieved by sponging miR-107. SLC1A5 was a target of miR-107, and it worked as an oncogene in EC cells. MiR-107 retarded the EC progression by downregulating SLC1A5. Circ-SFMBT2 could affect the SLC1A5 expression by targeting miR-107. Circ-SFMBT2 regulated EC progression in vivo by miR-107/SLC1A5 axis. Circ-SFMBT2 was transferred by exosomes in EC cells.

Conclusion

These results suggested that circ-SFMBT2 upregulated the SLC1A5 expression to promote the malignant development of EC by serving as a miR-107 sponge.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-02156-8.

N1-methyladenosine profiling of long non-coding RNA in colorectal cancer

N1-methyladenosine (m1A), is a unique methyl group that confers post-transcriptional modification of gene expression, and plays important roles in various human diseases. However, the abundance of this modification and its effects on long non-coding RNAs (lncRNAs) in human colorectal cancer (CRC) remain unclear. In this study, methylated RNA immunoprecipitation sequencing was performed in three pairs of human CRC and nontumorous tissues to identify m1A peaks and its correlation with differential alterations of lncRNA expression in CRC. Gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) enrichment pathway analyses were applied to predict the potential roles of m1A on gene expression. We found that CRC and adjacent tissues had a noticeable difference in m1A distribution. Notably, HGGAGRA and WGGANGA were recognized as the most significantly enriched motifs, respectively. Co-analysis of methylation and RNA sequencing demonstrated downregulated lncRNAs along with m1A modification in CRC. GO and KEGG pathway analyses revealed that the unique distribution of m1A sites in lncRNAs had a significant correlation with CRC signaling pathways. In conclusion, our results delineated the distribution pattern of m1A methylation on lncRNAs, and provided potential roles of this modification in different pathways and tumor progression of CRC.

Long Non-Coding RNA Epigenetics

Long noncoding RNAs exceeding a length of 200 nucleotides play an important role in ensuring cell functions and proper organism development by interacting with cellular compounds such as miRNA, mRNA, DNA and proteins. However, there is an additional level of lncRNA regulation, called lncRNA epigenetics, in gene expression control. In this review, we describe the most common modified nucleosides found in lncRNA, 6-methyladenosine, 5-methylcytidine, pseudouridine and inosine. The biosynthetic pathways of these nucleosides modified by the writer, eraser and reader enzymes are important to understanding these processes. The characteristics of the individual methylases, pseudouridine synthases and adenine-inosine editing enzymes and the methods of lncRNA epigenetics for the detection of modified nucleosides, as well as the advantages and disadvantages of these methods, are discussed in detail. The final sections are devoted to the role of modifications in the most abundant lncRNAs and their functions in pathogenic processes.

Isolation of Cell-Free miRNA from Biological Fluids: Influencing Factors and Methods

A vast wealth of recent research has seen attempts of using microRNA (miRNA) found in biological fluids in clinical research and medicine. One of the reasons behind this trend is the apparent their high stability of cell-free miRNA conferred by small size and packaging in supramolecular complexes. However, researchers in both basic and clinical settings often face the problem of selecting adequate methods to extract appropriate quality miRNA preparations for use in specific downstream analysis pipelines. This review outlines the variety of different methods of miRNA isolation from biofluids and examines the key determinants of their efficiency, including, but not limited to, the structural properties of miRNA and factors defining their stability in the extracellular environment.