The rRNA m6A methyltransferase METTL5 is involved in pluripotency and developmental programs

Comprehensive review on lipid metabolism and RNA methylation: Biological mechanisms, perspectives and challenges

Adipose tissue plays a crucial role in maintaining energy balance, regulating hormones, and promoting metabolic health. To address disorders related to obesity and develop effective therapies, it is essential to have a deep understanding of adipose tissue biology. In recent years, RNA methylation has emerged as a significant epigenetic modification involved in various cellular functions and metabolic pathways. Particularly in the realm of adipogenesis and lipid metabolism, extensive research is ongoing to uncover the mechanisms and functional importance of RNA methylation. Increasing evidence suggests that RNA methylation plays a regulatory role in adipocyte development, metabolism, and lipid utilization across different organs. This comprehensive review aims to provide an overview of common RNA methylation modifications, their occurrences, and regulatory mechanisms, focusing specifically on their intricate connections to fat metabolism. Additionally, we discuss the research methodologies used in studying RNA methylation and highlight relevant databases that can aid researchers in this rapidly advancing field.

Exploring the role of ribosomal RNA modifications in cancer

Recent advances have highlighted the significant roles of post-transcriptional modifications in rRNA in various cancers. Evidence suggests that dysregulation of rRNA modifications acts as a common denominator in cancer development, with alterations in these modifications conferring competitive advantages to cancer cells. Specifically, rRNA modifications modulate protein synthesis and favor the specialized translation of oncogenic programs, thereby contributing to the formation of a protumorigenic proteome in cancer cells. These findings reveal a novel regulatory layer mediated by changes in the deposition of rRNA chemical modifications. Moreover, inhibition of these modifications in vitro and in preclinical studies demonstrates potential therapeutic applications. The recurrence of altered rRNA modification patterns across different types of cancer underscores their importance in cancer progression, proposing them as potential biomarkers and novel therapeutic targets. This review will highlight the latest insights into how post-transcriptional rRNA modifications contribute to cancer progression and summarize the main developments and ongoing challenges in this research area.

Decoding the ribosome's hidden language: rRNA modifications as key players in cancer dynamics and targeted therapies

Ribosomal RNA (rRNA) modifications, essential components of ribosome structure and function, significantly impact cellular proteomics and cancer biology. These chemical modifications transcend structural roles, critically shaping ribosome functionality and influencing cellular protein profiles. In this review, the mechanisms by which rRNA modifications regulate both rRNA functions and broader cellular physiological processes are critically discussed. Importantly, by altering the translational output, rRNA modifications can shift the cellular equilibrium towards oncogenesis, thus playing a key role in cancer development and progression. Moreover, a special focus is placed on the functions of mitochondrial rRNA modifications and their aberrant expression in cancer, an area with profound implications yet largely uncharted. Dysregulation in these modifications can lead to metabolic dysfunction and apoptosis resistance, hallmark traits of cancer cells. Furthermore, the current challenges and future perspectives in targeting rRNA modifications are highlighted as a therapeutic approach for cancer treatment. In conclusion, rRNA modifications represent a frontier in cancer research, offering novel insights and therapeutic possibilities. Understanding and harnessing these modifications can pave the way for breakthroughs in cancer treatment, potentially transforming the approach to combating this complex disease.

CYP19A1 Expression Is Controlled by mRNA Stability of the Upstream Transcription Factor AP-2γ in Placental JEG3 Cells

CYP19A1 encodes aromatase, which converts testosterone to estrogen, and is induced during placental maturation. To elucidate the molecular mechanism underlying this function, histone methylation was analyzed using the placental cytotrophoblast cell line, JEG3. Treatment of JEG3 cells with 3-deazaneplanocin A, an inhibitor of several methyltransferases, resulted in increased CYP19A1 expression, accompanied by removal of the repressive mark H3K27me3 from the CYP19A1 promoter. However, this increase was not observed in cells treated with GSK126, another specific inhibitor for H3K27me3 methylation. Expression of TFAP2C, which encodes AP-2γ, a transcription factor that regulates CYP19A1, was also elevated on 3-deazaneplanocin A treatment. Interestingly, TFAP2C messenger RNA (mRNA) was readily degraded in JEG3 cells but protected from degradation in the presence of 3-deazaneplanocin A. TFAP2C mRNA contained N6-methyladenosines, which were reduced on drug treatment. These observations indicate that the TFAP2C mRNA undergoes adenosine methylation and rapid degradation, whereas 3-deazaneplanocin A suppresses methylation, resulting in an increase in AP-2γ levels. We conclude that the increase in AP-2γ expression via stabilization of the TFAP2C mRNA is likely to underlie the increased CYP19A1 expression.

Profiling the role of m6A effectors in the regulation of pluripotent reprogramming

The N6-methyladenosine (m6A) RNA modification plays essential roles in multiple biological processes, including stem cell fate determination. To explore the role of the m6A modification in pluripotent reprogramming, we used RNA-seq to map m6A effectors in human iPSCs, fibroblasts, and H9 ESCs, as well as in mouse ESCs and fibroblasts. By integrating the human and mouse RNA-seq data, we found that 19 m6A effectors were significantly upregulated in reprogramming. Notably, IGF2BPs, particularly IGF2BP1, were among the most upregulated genes in pluripotent cells, while YTHDF3 had high levels of expression in fibroblasts. Using quantitative PCR and Western blot, we validated the pluripotency-associated elevation of IGF2BPs. Knockdown of IGF2BP1 induced the downregulation of stemness genes and exit from pluripotency. Proteome analysis of cells collected at both the beginning and terminal states of the reprogramming process revealed that the IGF2BP1 protein was positively correlated with stemness markers SOX2 and OCT4. The eCLIP-seq target analysis showed that IGF2BP1 interacted with the coding sequence (CDS) and 3'UTR regions of the SOX2 transcripts, in agreement with the location of m6A modifications. This study identifies IGF2BP1 as a vital pluripotency-associated m6A effector, providing new insight into the interplay between m6A epigenetic modifications and pluripotent reprogramming.

The m6A methyltransferase METTL5 promotes neutrophil extracellular trap network release to regulate hepatocellular carcinoma progression

BACKGROUND

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors worldwide, it has a poor prognosis due to its highly invasive and metastatic nature. Consequently, identifying effective prognostic markers and potential therapeutic targets has been extensively investigated. METTL5, an 18S rRNA methyltransferase, is abnormally high in HCC. But its biological function and prognostic significance in HCC remain largely unelucidated. This study aimed to investigate the role of METTL5 in HCC progression, and elucidate its possible molecular mechanisms in HCC via transcriptome sequencing, providing new insights for identifying new HCC prognostic markers and therapeutic targets.

METHODS

The METTL5 expression in HCC and paracancerous tissues was analyzed using HCC immunohistochemical microarrays and bioinformatic retrieval methods to correlate METTL5 with clinicopathological features and survival prognosis. We constructed a METTL5 knockdown hepatocellular carcinoma cell line model and an animal model to determine the effect of METTL5 on hepatocellular carcinoma progression. Subsequently, RNA sequencing was performed to analyze the molecular mechanism of METTL5 in HCC based on the sequencing results, and relevant experiments were performed to verify it.

RESULTS

We found that METTL5 expression was elevated in hepatocellular carcinoma tissues and correlated with poor patient prognosis, and in the analysis of clinicopathological features showed a correlation with TNM staging. In hepatocellular carcinoma cell lines with knockdown of METTL5, the malignant biological behavior was significantly reduced both in vitro and in vivo. Based on the sequencing results as well as the results of GO functional enrichment analysis and KEGG pathway enrichment analysis, we found that METTL5 could promote the generation and release of neutrophil extracellular capture network (NETs) and might further accelerate the progression of HCC.

CONCLUSION

The m6A methyltransferase METTL5 is overexpressed in hepatocellular carcinoma (HCC) and correlates with poor prognosis. METTL5 accelerates malignant progression of HCC by promoting generation and release of the neutrophil extracellular traps (NETs) network, providing new insights for clinical biomarkers and immunotherapeutic targets in HCC prognosis.

RNA modifications in cellular metabolism: implications for metabolism-targeted therapy and immunotherapy

Cellular metabolism is an intricate network satisfying bioenergetic and biosynthesis requirements of cells. Relevant studies have been constantly making inroads in our understanding of pathophysiology, and inspiring development of therapeutics. As a crucial component of epigenetics at post-transcription level, RNA modification significantly determines RNA fates, further affecting various biological processes and cellular phenotypes. To be noted, immunometabolism defines the metabolic alterations occur on immune cells in different stages and immunological contexts. In this review, we characterize the distribution features, modifying mechanisms and biological functions of 8 RNA modifications, including N6-methyladenosine (m6A), N6,2'-O-dimethyladenosine (m6Am), N1-methyladenosine (m1A), 5-methylcytosine (m5C), N4-acetylcytosine (ac4C), N7-methylguanosine (m7G), Pseudouridine (Ψ), adenosine-to-inosine (A-to-I) editing, which are relatively the most studied types. Then regulatory roles of these RNA modification on metabolism in diverse health and disease contexts are comprehensively described, categorized as glucose, lipid, amino acid, and mitochondrial metabolism. And we highlight the regulation of RNA modifications on immunometabolism, further influencing immune responses. Above all, we provide a thorough discussion about clinical implications of RNA modification in metabolism-targeted therapy and immunotherapy, progression of RNA modification-targeted agents, and its potential in RNA-targeted therapeutics. Eventually, we give legitimate perspectives for future researches in this field from methodological requirements, mechanistic insights, to therapeutic applications.

N6-methylation in the development, diagnosis, and treatment of gastric cancer

Gastric cancer (GC) ranks third among cancers in terms of mortality rate worldwide. A clear understanding of the mechanisms underlying the genesis and progression of GC will contribute to clinical decision making. N6-methyladenosine (m6A) is the most abundant among diverse mRNA modification types and regulates multiple facets of RNA metabolism. In recent years, emerging studies have shown that m6A modifications are involved in gastric carcinoma tumorigenesis and progression and can potentially be valuable new prospects for diagnosis and prognosis. This article reviews the recent progress regarding m6A in GC.

Emerging roles of biological m6A proteins in regulating virus infection: A review

N6-methyladenosine (m6A) is the most prevalent chemical modifications of intracellular RNA, which recently emerging as a multifaceted effector of viral genomic RNA. As a dynamic process, three groups of biological proteins control the levels of m6A modification in eukaryocyte, designed as m6A writers, erasers, and readers. The m6A writers comprising of methyltransferases complex initiate the modification process. On the contrary, the m6A erasers ALKBH5 or FTO abolish the modification through three-step demethylation: m6A to N6-hydroxymethyl adenosine (hm6A), then hm6A to N6-methyladenosine (f6A), and finally f6A to adenosine. The known m6A readers include the YTH family and the hnRNP family. As m6A modification regulates RNA nuclear exportation, stability, and translation, m6A proteins commonly participate in virus infection by regulating viral genomic RNA synthesis. Moreover, m6A proteins establish molecular linkages between virus genome/viral encode proteins and host cells proteins via their multifunctional roles in cellular RNA metabolism. The m6A writers and erasers directly impact interferon expression and macrophage innate immune responses, facilitating them to act as anti-/pro-viral factors. The m6A readers enable to alter cell metabolism and stress granules (SGs) production to regulate virus-host interactions. Here, the latest progress of m6A proteins in regulating viral infection is reviewed. Demonstrating the roles of m6A proteins will enhance the understanding of epigenetic regulation of virus infection and stimulate the development of novel antiviral strategies.

METTL5-mediated 18S rRNA m6A modification promotes oncogenic mRNA translation and intrahepatic cholangiocarcinoma progression

Intrahepatic cholangiocarcinoma (ICC) is a deadly cancer with rapid tumor progression. While hyperactive mRNA translation caused by mis-regulated mRNA or tRNA modifications promotes ICC development, the role of rRNA modifications remains elusive. Here, we found that 18S rRNA m6A modification and its methyltransferase METTL5 were aberrantly upregulated in ICC and associated with poorer survival (log rank test, p < 0.05). We further revealed the critical role of METTL5-mediated 18S rRNA m6A modification in regulation of ICC cell growth and metastasis using loss- and gain-of function assays in vitro and in vivo. The oncogenic function of METTL5 is corroborated using liver-specific knockout and overexpression ICC mouse models. Mechanistically, METTL5 depletion impairs 18S rRNA m6A modification that hampers ribosome synthesis and inhibits translation of G-quadruplex-containing mRNAs that are enriched in the transforming growth factor (TGF)-β pathway. Our study uncovers the important role of METTL5-mediated 18S rRNA m6A modification in ICC and unravels the mechanism of rRNA m6A modification-mediated oncogenic mRNA translation control.

RNA modification in cardiovascular disease: implications for therapeutic interventions

Cardiovascular disease (CVD) is the leading cause of death in the world, with a high incidence and a youth-oriented tendency. RNA modification is ubiquitous and indispensable in cell, maintaining cell homeostasis and function by dynamically regulating gene expression. Accumulating evidence has revealed the role of aberrant gene expression in CVD caused by dysregulated RNA modification. In this review, we focus on nine common RNA modifications: N6-methyladenosine (m6A), N1-methyladenosine (m1A), 5-methylcytosine (m5C), N7-methylguanosine (m7G), N4-acetylcytosine (ac4C), pseudouridine (Ψ), uridylation, adenosine-to-inosine (A-to-I) RNA editing, and modifications of U34 on tRNA wobble. We summarize the key regulators of RNA modification and their effects on gene expression, such as RNA splicing, maturation, transport, stability, and translation. Then, based on the classification of CVD, the mechanisms by which the disease occurs and progresses through RNA modifications are discussed. Potential therapeutic strategies, such as gene therapy, are reviewed based on these mechanisms. Herein, some of the CVD (such as stroke and peripheral vascular disease) are not included due to the limited availability of literature. Finally, the prospective applications and challenges of RNA modification in CVD are discussed for the purpose of facilitating clinical translation. Moreover, we look forward to more studies exploring the mechanisms and roles of RNA modification in CVD in the future, as there are substantial uncultivated areas to be explored.

Crosstalk Between m6A RNA Methylation and miRNA Biogenesis in Cancer: An Unholy Nexus

N6-methyladenosine (m6A) is one of the most prevalent internal reversible chemical modification of RNAs in eukaryotes, which has attracted widespread attention recently owing to its regulatory roles in a plethora of normal developmental processes and human diseases like cancer. Deposition of the m6A mark on RNAs is mediated by the dynamic interplay between m6A regulatory proteins such as m6A RNA methyltransferases (m6A writers), m6A RNA demethylases (m6A erasers) and m6A RNA binding proteins (m6A readers). m6A regulators are ectopically expressed in various cancer types, often leading to aberrant expression of tumor-suppressor and oncogenic mRNAs either directly or indirectly via regulating the biogenesis of non-coding RNAs like miRNAs. miRNAs are tiny regulators of gene expression, which often impact various hallmarks of cancer and thus influence tumorigenesis. It is becoming increasingly clear that m6A RNA modification impacts biogenesis and function of miRNAs, and recent studies have interestingly, uncovered many miRNAs whose biogenesis and function are regulated by m6A writers, erasers and readers. In this review, we discuss various mechanisms by which m6A RNA methylation regulates miRNA biogenesis, the functional crosstalk between m6A RNA methylation and miRNAs and how it modulates various aspects of tumorigenesis. The potential of m6A RNA methylation regulated miRNAs as biomarkers and novel therapeutic targets to treat various cancers is also addressed.

Ghost authors revealed: The structure and function of human N6 -methyladenosine RNA methyltransferases

Despite the discovery of modified nucleic acids nearly 75 years ago, their biological functions are still being elucidated. N6 -methyladenosine (m6 A) is the most abundant modification in eukaryotic messenger RNA (mRNA) and has also been detected in non-coding RNAs, including long non-coding RNA, ribosomal RNA, and small nuclear RNA. In general, m6 A marks can alter RNA secondary structure and initiate unique RNA-protein interactions that can alter splicing, mRNA turnover, and translation, just to name a few. Although m6 A marks in human RNAs have been known to exist since 1974, the structures and functions of methyltransferases responsible for writing m6 A marks have been established only recently. Thus far, there are four confirmed human methyltransferases that catalyze the transfer of a methyl group from S-adenosylmethionine (SAM) to the N6 position of adenosine, producing m6 A: methyltransferase-like protein (METTL) 3/METTL14 complex, METTL16, METTL5, and zinc-finger CCHC-domain-containing protein 4. Though the methyltransferases have unique RNA targets, all human m6 A RNA methyltransferases contain a Rossmann fold with a conserved SAM-binding pocket, suggesting that they utilize a similar catalytic mechanism for methyl transfer. For each of the human m6 A RNA methyltransferases, we present the biological functions and links to human disease, RNA targets, catalytic and kinetic mechanisms, and macromolecular structures. We also discuss m6 A marks in human viruses and parasites, assigning m6 A marks in the transcriptome to specific methyltransferases, small molecules targeting m6 A methyltransferases, and the enzymes responsible for hypermodified m6 A marks and their biological functions in humans. Understanding m6 A methyltransferases is a critical steppingstone toward establishing the m6 A epitranscriptome and more broadly the RNome. This article is categorized under: RNA Interactions with Proteins and Other Molecules > Protein-RNA Recognition RNA Interactions with Proteins and Other Molecules > RNA-Protein Complexes RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications.

The landscape of implantation and placentation: deciphering the function of dynamic RNA methylation at the maternal-fetal interface

The maternal-fetal interface is defined as the interface between maternal tissue and sections of the fetus in close contact. RNA methylation modifications are the most frequent kind of RNA alterations. It is effective throughout both normal and pathological implantation and placentation during pregnancy. By influencing early embryo development, embryo implantation, endometrium receptivity, immune microenvironment, as well as some implantation and placentation-related disorders like miscarriage and preeclampsia, it is essential for the establishment of the maternal-fetal interface. Our review focuses on the role of dynamic RNA methylation at the maternal-fetal interface, which has received little attention thus far. It has given the mechanistic underpinnings for both normal and abnormal implantation and placentation and could eventually provide an entirely novel approach to treating related complications.

Methylation across the central dogma in health and diseases: new therapeutic strategies

The proper transfer of genetic information from DNA to RNA to protein is essential for cell-fate control, development, and health. Methylation of DNA, RNAs, histones, and non-histone proteins is a reversible post-synthesis modification that finetunes gene expression and function in diverse physiological processes. Aberrant methylation caused by genetic mutations or environmental stimuli promotes various diseases and accelerates aging, necessitating the development of therapies to correct the disease-driver methylation imbalance. In this Review, we summarize the operating system of methylation across the central dogma, which includes writers, erasers, readers, and reader-independent outputs. We then discuss how dysregulation of the system contributes to neurological disorders, cancer, and aging. Current small-molecule compounds that target the modifiers show modest success in certain cancers. The methylome-wide action and lack of specificity lead to undesirable biological effects and cytotoxicity, limiting their therapeutic application, especially for diseases with a monogenic cause or different directions of methylation changes. Emerging tools capable of site-specific methylation manipulation hold great promise to solve this dilemma. With the refinement of delivery vehicles, these new tools are well positioned to advance the basic research and clinical translation of the methylation field.

RNA modification: mechanisms and therapeutic targets

RNA modifications are dynamic and reversible chemical modifications on substrate RNA that are regulated by specific modifying enzymes. They play important roles in the regulation of many biological processes in various diseases, such as the development of cancer and other diseases. With the help of advanced sequencing technologies, the role of RNA modifications has caught increasing attention in human diseases in scientific research. In this review, we briefly summarized the basic mechanisms of several common RNA modifications, including m6A, m5C, m1A, m7G, Ψ, A-to-I editing and ac4C. Importantly, we discussed their potential functions in human diseases, including cancer, neurological disorders, cardiovascular diseases, metabolic diseases, genetic and developmental diseases, as well as immune disorders. Through the "writing-erasing-reading" mechanisms, RNA modifications regulate the stability, translation, and localization of pivotal disease-related mRNAs to manipulate disease development. Moreover, we also highlighted in this review all currently available RNA-modifier-targeting small molecular inhibitors or activators, most of which are designed against m6A-related enzymes, such as METTL3, FTO and ALKBH5. This review provides clues for potential clinical therapy as well as future study directions in the RNA modification field. More in-depth studies on RNA modifications, their roles in human diseases and further development of their inhibitors or activators are needed for a thorough understanding of epitranscriptomics as well as diagnosis, treatment, and prognosis of human diseases.

N 2-methylguanosine modifications on human tRNAs and snRNA U6 are important for cell proliferation, protein translation and pre-mRNA splicing

Modified nucleotides in non-coding RNAs, such as tRNAs and snRNAs, represent an important layer of gene expression regulation through their ability to fine-tune mRNA maturation and translation. Dysregulation of such modifications and the enzymes installing them have been linked to various human pathologies including neurodevelopmental disorders and cancers. Several methyltransferases (MTases) are regulated allosterically by human TRMT112 (Trm112 in Saccharomyces cerevisiae), but the interactome of this regulator and targets of its interacting MTases remain incompletely characterized. Here, we have investigated the interaction network of human TRMT112 in intact cells and identify three poorly characterized putative MTases (TRMT11, THUMPD3 and THUMPD2) as direct partners. We demonstrate that these three proteins are active N2-methylguanosine (m2G) MTases and that TRMT11 and THUMPD3 methylate positions 10 and 6 of tRNAs, respectively. For THUMPD2, we discovered that it directly associates with the U6 snRNA, a core component of the catalytic spliceosome, and is required for the formation of m2G, the last 'orphan' modification in U6 snRNA. Furthermore, our data reveal the combined importance of TRMT11 and THUMPD3 for optimal protein synthesis and cell proliferation as well as a role for THUMPD2 in fine-tuning pre-mRNA splicing.

Methyltransferase-like proteins in cancer biology and potential therapeutic targeting

RNA modification has recently become a significant process of gene regulation, and the methyltransferase-like (METTL) family of proteins plays a critical role in RNA modification, methylating various types of RNAs, including mRNA, tRNA, microRNA, rRNA, and mitochondrial RNAs. METTL proteins consist of a unique seven-beta-strand domain, which binds to the methyl donor SAM to catalyze methyl transfer. The most typical family member METTL3/METTL14 forms a methyltransferase complex involved in N6-methyladenosine (m6A) modification of RNA, regulating tumor proliferation, metastasis and invasion, immunotherapy resistance, and metabolic reprogramming of tumor cells. METTL1, METTL4, METTL5, and METTL16 have also been recently identified to have some regulatory ability in tumorigenesis, and the rest of the METTL family members rely on their methyltransferase activity for methylation of different nucleotides, proteins, and small molecules, which regulate translation and affect processes such as cell differentiation and development. Herein, we summarize the literature on METTLs in the last three years to elucidate their roles in human cancers and provide a theoretical basis for their future use as potential therapeutic targets.

m6A modification and its role in neural development and neurological diseases

N6-methyladenosine (m6A) methylation, the most prevalent post-transcriptional modification in eukaryotes, represents a highly dynamic and reversible process that is regulated by m6A methyltransferases, m6A demethylases and RNA-binding proteins during RNA metabolism, which affects RNA function. Notably, m6A modification is significantly enriched in the brain and exerts regulatory roles in neurogenesis and neurodevelopment through various mechanisms, further influencing the occurrence and progression of neurological disorders. This study systematically summarizes and discusses the latest findings on common m6A regulators, examining their expression, function and mechanisms in neurodevelopment and neurological diseases. Additionally, we explore the potential of m6A modification in diagnosing and treating neurological disorders, aiming to provide new insights into the molecular mechanisms and potential therapeutic strategies for neurological disorders.

Connecting the Dots: N6-Methyladenosine (m6 A) Modification in Spermatogenesis

N6-methyladenosine (m6 A) is the most common RNA modification found in eukaryotes and is involved in multiple biological processes, including neuronal development, tumorigenesis, and gametogenesis. It is well known that methylation-modifying enzymes (classified into writers, erasers, and readers) mediate catalysis, clearance, and recognition of m6 A. Recent studies suggest that these genes may be associated with spermatogenesis. Numerous studies have revealed the m6 A role during spermatogenesis. However, the expression patterns and relationships of these m6 A enzymes during various stages of spermatogenesis remain unknown. In this review, it is aimed to provide an overview of m6 A enzyme functions and elucidate their potential mechanisms and regulatory relationships at a specific phase during spermatogenesis, providing new insights into the m6 A modification underlying the spermatogenesis process.

Coordination of RNA modifications in the brain and beyond

Gene expression regulation is a critical process throughout the body, especially in the nervous system. One mechanism by which biological systems regulate gene expression is via enzyme-mediated RNA modifications, also known as epitranscriptomic regulation. RNA modifications, which have been found on nearly all RNA species across all domains of life, are chemically diverse covalent modifications of RNA nucleotides and represent a robust and rapid mechanism for the regulation of gene expression. Although numerous studies have been conducted regarding the impact that single modifications in single RNA molecules have on gene expression, emerging evidence highlights potential crosstalk between and coordination of modifications across RNA species. These potential coordination axes of RNA modifications have emerged as a new direction in the field of epitranscriptomic research. In this review, we will highlight several examples of gene regulation via RNA modification in the nervous system, followed by a summary of the current state of the field of RNA modification coordination axes. In doing so, we aim to inspire the field to gain a deeper understanding of the roles of RNA modifications and coordination of these modifications in the nervous system.

m6A-ELISA, a simple method for quantifying N6-methyladenosine from mRNA populations

N6-methyladenosine (m6A) is a widely studied and abundant RNA modification. The m6A mark regulates the fate of RNAs in various ways, which in turn drives changes in cell physiology, development, and disease pathology. Over the last decade, numerous methods have been developed to map and quantify m6A sites genome-wide through deep sequencing. Alternatively, m6A levels can be quantified from a population of RNAs using techniques such as liquid chromatography-mass spectrometry or thin layer chromatography. However, many methods for quantifying m6A levels involve extensive protocols and specialized data analysis, and often only a few samples can be handled in a single experiment. Here, we developed a simple method for determining relative m6A levels in mRNA populations from various sources based on an enzyme-linked immunosorbent-based assay (m6A-ELISA). We have optimized various steps of m6A-ELISA, such as sample preparation and the background signal resulting from the primary antibody. We validated the method using mRNA populations from budding yeast and mouse embryonic stem cells. The full protocol takes less than a day, requiring only 25 ng of mRNA. The m6A-ELISA protocol is quick, cost-effective, and scalable, making it a valuable tool for determining relative m6A levels in samples from various sources that could be adapted to detect other mRNA modifications.

Functions of N6-methyladenosine in cancer metabolism: from mechanism to targeted therapy

N6-methyladenosine (m6A) is the most abundant modification of eukaryotic mRNA and is involved in almost every stage of RNA metabolism. The m6A modification on RNA has been demonstrated to be a regulator of the occurrence and development of a substantial number of diseases, especially cancers. Increasing evidence has shown that metabolic reprogramming is a hallmark of cancer and is crucial for maintaining the homeostasis of malignant tumors. Cancer cells rely on altered metabolic pathways to support their growth, proliferation, invasion and metastasis in an extreme microenvironment. m6A regulates metabolic pathways mainly by either directly acting on metabolic enzymes and transporters or indirectly influencing metabolism-related molecules. This review discusses the functions of the m6A modification on RNAs, its role in cancer cell metabolic pathways, the possible underlying mechanisms of its effects and the implication of this modification in cancer therapy.

Ribosome biogenesis and function in development and disease

Although differential transcription drives the development of multicellular organisms, the ultimate readout of a protein-coding gene is ribosome-dependent mRNA translation. Ribosomes were once thought of as uniform molecular machines, but emerging evidence indicates that the complexity and diversity of ribosome biogenesis and function should be given a fresh look in the context of development. This Review begins with a discussion of different developmental disorders that have been linked with perturbations in ribosome production and function. We then highlight recent studies that reveal how different cells and tissues exhibit variable levels of ribosome production and protein synthesis, and how changes in protein synthesis capacity can influence specific cell fate decisions. We finish by touching upon ribosome heterogeneity in stress responses and development. These discussions highlight the importance of considering both ribosome levels and functional specialization in the context of development and disease.

METTL5 stabilizes c-Myc by facilitating USP5 translation to reprogram glucose metabolism and promote hepatocellular carcinoma progression

BACKGROUND

Hepatocellular carcinoma (HCC) is one of the most prevalent cancers in the world, with a high likelihood of metastasis and a dismal prognosis. The reprogramming of glucose metabolism is critical in the development of HCC. The Warburg effect has recently been confirmed to occur in a variety of cancers, including HCC. However, little is known about the molecular biological mechanisms underlying the Warburg effect in HCC cells. In this study, we sought to better understand how methyltransferase 5, N6-adenosine (METTL5) controls the development of HCC and the Warburg effect.

METHODS

In the current study, quantitative real-time polymerase chain reaction and Western blotting were used to detect the expression of METTL5 in HCC tissues and cell lines. Several different cell models and animal models were established to determine the role of METTL5 in glucose metabolism reprogramming and the underlying molecular mechanism of HCC. Glutathione-S-transferase pulldown, coimmunoprecipitation, RNA sequencing, non-targeted metabolomics, polysome profiling, and luciferase reporter assays were performed to investigate the molecular mechanisms of METTL5 in HCC cells.

RESULTS

We discovered that METTL5 drove glucose metabolic reprogramming to promote the proliferation and metastasis of HCC. Mechanistically, upregulation of METTL5 promoted c-Myc stability and thus activated its downstream glycolytic genes lactate dehydrogenase A (LDHA), enolase 1 (ENO1), triosephosphate isomerase 1 (TPI1), solute carrier family 2 member 1 (SLC2A1), and pyruvate kinase M2 (PKM2). The c-Box and ubiquitin binding domain (UBA) regions of ubiquitin specific peptidase 5 (USP5) binded to c-Myc protein and inhibited K48-linked polyubiquitination of c-Myc. Further study revealed that METTL5 controled the USP5 translation process, which in turn regulated the ubiquitination of c-Myc. Furthermore, we identified cAMP responsive element binding protein 1 (CREB1)/P300 as a critical transcriptional regulator of METTL5 that promoted the transcription of METTL5 in HCC. In patient-derived tumor xenograft (PDX) models, adenovirus-mediated knockout of METTL5 had a good antitumor effect and prolonged the survival of PDX-bearing mice.

CONCLUSIONS

These findings point to a novel mechanism by which CREB1/P300-METTL5-USP5-c-Myc controls abnormal glucose metabolism and promotes tumor growth, suggesting that METTL5 is a potential therapeutic target and prognostic biomarker for HCC.

Biological roles of adenine methylation in RNA

N6-Methyladenosine (m6A) is one of the most abundant modifications of the epitranscriptome and is found in cellular RNAs across all kingdoms of life. Advances in detection and mapping methods have improved our understanding of the effects of m6A on mRNA fate and ribosomal RNA function, and have uncovered novel functional roles in virtually every species of RNA. In this Review, we explore the latest studies revealing roles for m6A-modified RNAs in chromatin architecture, transcriptional regulation and genome stability. We also summarize m6A functions in biological processes such as stem-cell renewal and differentiation, brain function, immunity and cancer progression.

N6-methyladenosine modification in 18S rRNA promotes tumorigenesis and chemoresistance via HSF4b/HSP90B1/mutant p53 axis

Aberrant N⁶-methyladenosine (m⁶A) modification on mRNA is correlated with cancer progression. However, the role of m⁶A on ribosomal RNA (rRNA) in cancer remains poorly understood. Our current study reveals that METTL5/TRMT112 and their mediated m⁶A modification at the 18S rRNA 1832 site (m⁶A₁₈₃₂) are elevated in nasopharyngeal carcinoma (NPC) and promote oncogenic transformation in vitro and in vivo. Moreover, loss of catalytic activity of METTL5 abolishes its oncogenic functions. Mechanistically, m⁶A₁₈₃₂ 18S rRNA modification facilitates the assembly of 80S ribosome via bridging the RPL24-18S rRNA interaction, therefore promoting the translation of mRNAs with 5' terminal oligopyrimidine (5' TOP) motifs. Further mechanistic analysis reveals that METTL5 enhances HSF4b translation to activate the transcription of HSP90B1, which binds with oncogenic mutant p53 (mutp53) protein and prevents it from undergoing ubiquitination-dependent degradation, therefore facilitating NPC tumorigenesis and chemoresistance. Overall, our findings uncover an innovative mechanism underlying rRNA epigenetic modification in regulating mRNA translation and the mutp53 pathway in cancer.

RNA m6A methylation across the transcriptome

Since the early days of foundational studies of nucleic acids, many chemical moieties have been discovered to decorate RNA and DNA in diverse organisms. In mammalian cells, one of these chemical modifications, N6-methyl adenosine (m6A), is unique in a way that it is highly abundant not only on RNA polymerase II (RNAPII) transcribed, protein-coding transcripts but also on non-coding RNAs, such as ribosomal RNAs and snRNAs, mediated by distinct, evolutionarily conserved enzymes. Here, we review RNA m6A modification in the light of the recent appreciation of nuclear roles for m6A in regulating chromatin states and gene expression, as well as the recent discoveries of the evolutionarily conserved methyltransferases, which catalyze methylation of adenosine on diverse sets of RNAs. Considering that the substrates of these enzymes are involved in many important biological processes, this modification warrants further research to understand the molecular mechanisms and functions of m6A in health and disease.

rDNA Transcription in Developmental Diseases and Stem Cells

As the first and rate-limiting step in ribosome biogenesis, rDNA transcription undergoes significant dynamic changes during cell pluripotency alteration. Over the past decades, rDNA activity has demonstrated dynamic changes, but most people view it as passive compliance with cellular needs. The evidence for rDNA transcriptional activity determining stem cell pluripotency is growing as research advances, resulting in the arrest of embryonic development and impairment of stem cell lines stemness by rDNA transcription inhibition. The exact mechanism by which rDNA activation influences pluripotency remains unknown. The first objective of this opinion article is to describe rDNA changes in the pathological and physiological course of life, including developmental diseases, tumor genesis, and stem cell differentiation. After that, we propose three hypotheses regarding rDNA regulation of pluripotency: 1) Specialized ribosomes synthesized from rDNA variant, 2) Nucleolar stress induced by the drop of rDNA transcription, 3) Interchromosomal interactions between rDNA and other genes. The pluripotency regulatory center is expected to focus strongly on rDNA. A small molecule inhibitor of rDNA is used to treat tumors caused by abnormal pluripotency activation. By understanding how rDNA regulates pluripotency, we hope to treat developmental diseases and safely apply somatic cell reprogramming in clinical settings.

METTLing in Stem Cell and Cancer Biology

The methyltransferase-like (METTL) family is a diverse group of methyltransferases that can methylate nucleotides, proteins, and small molecules. Despite this diverse array of substrates, they all share a characteristic seven-beta-strand catalytic domain, and recent evidence suggests many also share an important role in stem cell biology. The most well characterized family members METTL3 and METTL14 dimerize to form an N6-methyladenosine (m6A) RNA methyltransferase with established roles in cancer progression. However, new mouse models indicate that METTL3/METTL14 are also important for embryonic stem cell (ESC) development and postnatal hematopoietic and neural stem cell self-renewal and differentiation. METTL1, METTL5, METTL6, METTL8, and METTL17 also have recently identified roles in ESC pluripotency and differentiation, while METTL11A/11B, METTL4, METTL7A, and METTL22 have been shown to play roles in neural, mesenchymal, bone, and hematopoietic stem cell development, respectively. Additionally, a variety of other METTL family members are translational regulators, a role that could place them as important players in the transition from stem cell quiescence to differentiation. Here we will summarize what is known about the role of METTL proteins in stem cell differentiation and highlight the connection between their growing importance in development and their established roles in oncogenesis.

The novel m6A writer METTL5 as prognostic biomarker probably associating with the regulation of immune microenvironment in kidney cancer

Nowadays, among all urinary system cancers, the mortality of kidney cancer (KC) has risen to the first, and the incidence has been keeping on the third. Many recent studies have demonstrated that m6A modification regulated by the methyltransferases (writers) is closely related to the tumorigenesis of multiple cancers. In our previous study, we found that the methyltransferase METTL5 had a stronger association with the hazard ratio of KC more than most tumors, indicating its special function in carcinogenesis of KC. Until now, the expression, functions and mechanism of METTL5 in KC are still unclear. In this study, we analyzed the mRNA expression of METTL5 using the data sets from public databases, and revealed that the METTL5 expression was significantly up-regulated in tumor tissues of kidney renal clear cell carcinoma (KIRC) and kidney renal papillary cell carcinoma (KIRP) compared to normal tissues. Also, the METTL5 expression was correlated with the tumor stage and grade, indicating the potential involvement of METTL5 in tumor progression. Additionally, the higher expression of METTL5 predicted poorer prognosis of KIRC and KIRP patients. Subsequently, we revealed that the functions of METTL5 in KIRC might be related to immune modulation, because its co-expressed gene were enriched in immune-relevant pathways including Th17 cell differentiation, Th1 and Th2 cell differentiation, and phosphatidylinositol 3-kinase activity. Next, we disclosed that the METTL5 expression was correlated to the microenvironment score and immune score of KIRC and KIRP, and associated with the infiltration ratios of 25 types of immune cells. Besides, we demonstrated a wide difference of the METTL5's effect on the survival of patients with high and low immune infiltration, further suggesting METTL5 might affect tumor development via modulating the immune microenvironment. The findings of our study provide a novel potential prognostic biomarker and immune drug target for KC.

The Role of the m6A RNA Methyltransferase METTL16 in Gene Expression and SAM Homeostasis

The RNA methylation of adenosine at the N6-position (m⁶A) has attracted significant attention because of its abundance and dynamic nature. It accounts for more than 80% of all RNA modifications present in bacteria and eukaryotes and regulates crucial aspects of RNA biology and gene expression in numerous biological processes. The majority of m⁶A found in mammals is deposited by a multicomponent complex formed between methyltransferase-like (METTL) proteins METTL3 and METTL14. In the last few years, the list of m⁶A writers has grown, resulting in an expansion of our understanding of the importance of m⁶A and the methylation machinery. The characterization of the less familiar family member METTL16 has uncovered a new function of the m⁶A methylation apparatus, namely the fine-tuning of the cellular levels of the major methyl donor S-adenosylmethionine (SAM). METTL16 achieves this by adjusting the levels of the enzyme that synthesizes SAM in direct response to fluctuations in the SAM availability. This review summarizes recent progress made in understanding how METTL16 can sense and relay metabolic information and considers the wider implications. A brief survey highlights similarities and differences between METTL16 and the better-known METTL3/14 complex, followed by a discussion of the target specificity, modes of action and potential roles of METTL16.

RNA modifications in cardiovascular health and disease

RNA is not always a faithful copy of DNA. Advances in tools enabling the interrogation of the exact RNA sequence have permitted revision of how genetic information is transferred. We now know that RNA is a dynamic molecule, amenable to chemical modifications of its four canonical nucleotides by dedicated RNA-binding enzymes. The ever-expanding catalogue of identified RNA modifications in mammals has led to a burst of studies in the past 5 years that have explored the biological relevance of the RNA modifications, also known as epitranscriptome. These studies concluded that chemical modification of RNA nucleotides alters several properties of RNA molecules including sequence, secondary structure, RNA-protein interaction, localization and processing. Importantly, a plethora of cellular functions during development, homeostasis and disease are controlled by RNA modification enzymes. Understanding the regulatory interface between a single-nucleotide modification and cellular function will pave the way towards the development of novel diagnostic, prognostic and therapeutic tools for the management of diseases, including cardiovascular disease. In this Review, we use two well-studied and abundant RNA modifications - adenosine-to-inosine RNA editing and N⁶-methyladenosine RNA methylation - as examples on which to base the discussion about the current knowledge on installation or removal of RNA modifications, their effect on biological processes related to cardiovascular health and disease, and the potential for development and application of epitranscriptome-based prognostic, diagnostic and therapeutic tools for cardiovascular disease.

N6-methyladenosine Modification of Noncoding RNAs: Mechanisms and Clinical Applications in Cancer

N6-methyladenosine (m6A) modification remains the most pivotal epigenetic modification on RNA. As we know, m6A not only affects physiological processes but is also involved in carcinoma. Noncoding RNAs play an indispensable role in the occurrence and development of carcinoma. However, a large amount of research is focused on mRNA currently. Insufficient research has been done on the relationship between noncoding RNA (ncRNA) methylation and cancer. Therefore, this review aims to introduce the theoretical knowledge of m6A modification in noncoding RNA, discuss its function in tumorigenesis and progression, and ultimately summarize its potential clinical applications.

RNA m6 A methylation in cancer

N⁶ -methyladenosine (m⁶ A) is one of the most abundant internal modifications in eukaryotic messenger RNAs (mRNAs) and non-coding RNAs (ncRNAs). It is a reversible and dynamic RNA modification that has been observed in both internal coding segments and untranslated regions. Studies indicate that m⁶ A modifications play important roles in translation, RNA splicing, export, degradation and ncRNA processing control. In this review, we focus on the profiles and biological functions of RNA m⁶ A methylation on both mRNAs and ncRNAs. The dynamic modification of m⁶ A and its potential roles in cancer development are discussed. Moreover, we discuss the possibility of m⁶ A modifications serving as potential biomarkers for cancer diagnosis and targets for therapy.

Inhibition of METTL5 improves preimplantation development of mouse somatic cell nuclear transfer embryos

In brief

Several factors affect the reprogramming efficiency of nuclear transfer embryos. This study shows that inhibiting 18S rRNA m6A methyltransferase METTL5 during nuclear transfer can improve the developmental rate of nuclear transfer embryos.

Abstract

N6-methyladenosine (m6A) is one of the most important epigenetic modifications in eukaryotic RNAs, which regulates development and diseases. It is identified by several proteins. Methyltransferase-like 5 (METTL5), an enzyme that methylates 18S rRNA m6A, controls the translation of proteins and regulates pluripotency in embryonic stem cells. However, the functions of METTL5 in embryonic development have not been explored. Here, we found that Mettl5 was upregulated in somatic cell nuclear transfer (SCNT) embryos compared with normal fertilized embryos. Therefore, we hypothesized that METTL5 knockdown during the early stage of SCNT would improve the developmental rate of SCNT embryos. Notably, injection of Mettl5 siRNA (si-Mettl5) into enucleated oocytes during nuclear transfer increased the rate of development and the number of cells in blastocysts. Moreover, inhibition of METTL5 reduced the activity of phosphorylated ribosomal protein S6, decreased the levels of the repressive histone modification H3K27me3 and increased the expression of activating histone modifications H3K27ac and H3K4me3 and mRNA levels of some 2-cell-specific genes. These results expand our understanding of the role of METTL5 in early embryonic development and provide a novel idea for improving the efficiency of nuclear transfer cloning.

Exploring the epitranscriptome by native RNA sequencing

Chemical RNA modifications, collectively referred to as the "epitranscriptome," are essential players in fine-tuning gene expression. Our ability to analyze RNA modifications has improved rapidly in recent years, largely due to the advent of high-throughput sequencing methodologies, which typically consist of coupling modification-specific reagents, such as antibodies or enzymes, to next-generation sequencing. Recently, it also became possible to map RNA modifications directly by sequencing native RNAs using nanopore technologies, which has been applied for the detection of a number of RNA modifications, such as N6-methyladenosine (m⁶A), pseudouridine (Ψ), and inosine (I). However, the signal modulations caused by most RNA modifications are yet to be determined. A global effort is needed to determine the signatures of the full range of RNA modifications to avoid the technical biases that have so far limited our understanding of the epitranscriptome.

The epitranscriptome in ageing and stress resistance: A systematic review

Modifications of RNA, collectively called the "epitranscriptome", might provide novel biomarkers and innovative targets for interventions in geroscience but are just beginning to be studied in the context of ageing and stress resistance. RNA modifications modulate gene expression by affecting translation initiation and speed, miRNA binding, RNA stability, and RNA degradation. Nonetheless, the precise underlying molecular mechanisms and physiological consequences of most alterations of the epitranscriptome are still only poorly understood. We here systematically review different types of modifications of rRNA, tRNA and mRNA, the methodology to analyze them, current challenges in the field, and human disease associations. Furthermore, we compiled evidence for a connection between individual enzymes, which install RNA modifications, and lifespan in yeast, worm and fly. We also included resistance to different stressors and competitive fitness as search criteria for genes potentially relevant to ageing. Promising candidates identified by this approach include RCM1/NSUN5, RRP8, and F33A8.4/ZCCHC4 that introduce base methylations in rRNA, the methyltransferases DNMT2 and TRM9/ALKBH8, as well as factors involved in the thiolation or A to I editing in tRNA, and finally the m⁶A machinery for mRNA.

The emerging importance of METTL5-mediated ribosomal RNA methylation

The study of the epitranscriptome has thus far focused largely on mRNA methylation. Recent human genetics studies suggest that methylation of ribosomal RNA also contributes to brain development and cognition. In particular, the m⁶A modification at the A-1832 position of the 18S rRNA is installed by METTL5. Mutations or deletions of Mettl5 in humans and mice, respectively, cause abnormal translation and gene expression that in turn mediates stem cell behaviors such as differentiation. In this review, we provide an overview of the current knowledge of the methyltransferase METTL5, as well as the molecular biology surrounding m⁶A on rRNA and how it regulates cell behavior.

N6-methyladenosine modification: A potential regulatory mechanism in spinal cord injury

N6-methyladenosine (m6A), an essential post-transcriptional modification in eukaryotes, is closely related to the development of pathological processes in neurological diseases. Notably, spinal cord injury (SCI) is a serious traumatic disease of the central nervous system, with a complex pathological mechanism which is still not completely understood. Recent studies have found that m6A modification levels are changed after SCI, and m6A-related regulators are involved in the changes of the local spinal cord microenvironment after injury. However, research on the role of m6A modification in SCI is still in the early stages. This review discusses the latest progress in the dynamic regulation of m6A modification, including methyltransferases (“writers”), demethylases (“erasers”) and m6A -binding proteins (“readers”). And then analyses the pathological mechanism relationship between m6A and the microenvironment after SCI. The biological processes involved included cell death, axon regeneration, and scar formation, which provides new insight for future research on the role of m6A modification in SCI and the clinical transformation of strategies for promoting recovery of spinal cord function.

RNA modifications: importance in immune cell biology and related diseases

RNA modifications have become hot topics recently. By influencing RNA processes, including generation, transportation, function, and metabolization, they act as critical regulators of cell biology. The immune cell abnormality in human diseases is also a research focus and progressing rapidly these years. Studies have demonstrated that RNA modifications participate in the multiple biological processes of immune cells, including development, differentiation, activation, migration, and polarization, thereby modulating the immune responses and are involved in some immune related diseases. In this review, we present existing knowledge of the biological functions and underlying mechanisms of RNA modifications, including N⁶-methyladenosine (m⁶A), 5-methylcytosine (m⁵C), N¹-methyladenosine (m¹A), N⁷-methylguanosine (m⁷G), N⁴-acetylcytosine (ac⁴C), pseudouridine (Ψ), uridylation, and adenosine-to-inosine (A-to-I) RNA editing, and summarize their critical roles in immune cell biology. Via regulating the biological processes of immune cells, RNA modifications can participate in the pathogenesis of immune related diseases, such as cancers, infection, inflammatory and autoimmune diseases. We further highlight the challenges and future directions based on the existing knowledge. All in all, this review will provide helpful knowledge as well as novel ideas for the researchers in this area.

Primary specification of blastocyst trophectoderm by scRNA-seq: New insights into embryo implantation

Mechanisms of implantation such as determination of the attachment pole, fetal-maternal communication, and underlying causes of implantation failure are largely unexplored. Here, we performed single-cell RNA sequencing on peri-implantation embryos from both humans and mice to explore trophectoderm (TE) development and embryo-endometrium cross-talk. We found that the transcriptomes of polar and mural TE diverged after embryos hatched from the zona pellucida in both species, with polar TE being more mature than mural TE. The implantation poles show similarities in cell cycle activities, as well as in expression of genes critical for implantation and placentation. Embryos that either fail to attach in vitro or fail to implant in vivo show abnormalities in pathways related to energy production, protein metabolism, and 18S ribosomal RNA m⁶A methylation. These findings uncover the gene expression characteristics of humans and mice TE differentiation during the peri-implantation period and provide new insights into embryo implantation.

The Potential Role of m6A in the Regulation of TBI-Induced BGA Dysfunction

The brain–gut axis (BGA) is an important bidirectional communication pathway for the development, progress and interaction of many diseases between the brain and gut, but the mechanisms remain unclear, especially the post-transcriptional regulation of BGA after traumatic brain injury (TBI). RNA methylation is one of the most important modifications in post-transcriptional regulation. N6-methyladenosine (m⁶A), as the most abundant post-transcriptional modification of mRNA in eukaryotes, has recently been identified and characterized in both the brain and gut. The purpose of this review is to describe the pathophysiological changes in BGA after TBI, and then investigate the post-transcriptional bidirectional regulation mechanisms of TBI-induced BGA dysfunction. Here, we mainly focus on the characteristics of m⁶A RNA methylation in the post-TBI BGA, highlight the possible regulatory mechanisms of m⁶A modification in TBI-induced BGA dysfunction, and finally discuss the outcome of considering m⁶A as a therapeutic target to improve the recovery of the brain and gut dysfunction caused by TBI.

N6-methyladenosine (m6A) in 18S rRNA promotes fatty acid metabolism and oncogenic transformation

Aberrant RNA modifications lead to dysregulated gene expression and cancer progression. Ribosomal RNA (rRNA) accounts for more than 80% of a cell's total RNA, but the functions and molecular mechanisms underlying rRNA modifications in cancers are poorly understood. Here, we show that the 18S rRNA N⁶-methyladenosine (m⁶A) methyltransferase complex METTL5-TRMT112 is upregulated in various cancer types and correlated with poor prognosis. In addition, we demonstrate the critical functions of METTL5 in promoting hepatocellular carcinoma (HCC) tumorigenesis in vitro and in mouse models. Mechanistically, depletion of METTL5-mediated 18S rRNA m⁶A modification results in impaired 80S ribosome assembly and decreased translation of mRNAs involved in fatty acid metabolism. We further reveal that ACSL4 mediates the function of METTL5 on fatty acid metabolism and HCC progression, and targeting ACSL4 and METTL5 synergistically inhibits HCC tumorigenesis in vivo. Our study uncovers mechanistic insights underlying mRNA translation control and HCC tumorigenesis through lipid metabolism remodeling and provides a molecular basis for the development of therapeutic strategies for HCC treatment.

The role of N6-methyladenosine-modified non-coding RNAs in the pathological process of human cancer

Non-coding RNAs (ncRNAs) account for the majority of the widespread transcripts of mammalian genomes. They rarely encode proteins and peptides, but their regulatory role is crucial in numerous physiological and pathological processes. The m6A (N6-methyladenosine) modification is one of the most common internal RNA modifications in eukaryotes and is associated with all aspects of RNA metabolism. Accumulating researches have indicated a close association between m6A modification and ncRNAs, and suggested m6A-modified ncRNAs played a crucial role in tumor progression. The correlation between m6A modification and ncRNAs offers a novel perspective for investigating the potential mechanisms of cancer pathological processes, which suggests that both m6A modification and ncRNAs are critical prognostic markers and therapeutic targets in numerous malignancies. In the present report, we summarized the interaction between m6A modification and ncRNA, emphasizing how their interaction regulates pathological processes in cancer.

The emerging roles of N6-methyladenosine (m6A)-modified long non-coding RNAs in human cancers

N⁶-methyladenosine (m⁶A) epitranscriptional modifications widely exist in RNA, which play critical roles in RNA metabolism and biogenesis processes. Long non-coding RNAs (lncRNAs) are class of non-coding RNAs longer than 200 nucleotides without protein-coding ability. LncRNAs participate in a large number of vital biological progressions. With the great improvement of molecular biology, m⁶A and lncRNAs are attracting more attention from researchers and scholars. In this review, we overview the current status of m⁶A and lncRNAs based on the latest research, and propose some viewpoints for future research perspectives.

The Role of N6-Methyladenosine in the Promotion of Hepatoblastoma: A Critical Review

Simple Summary

Hepatoblastoma is the most common malignant pediatric tumor of the liver. Unlike hepatocellular carcinoma (HCC) which has been associated with hepatitis B virus infection or cirrhosis, the etiology of hepatoblastoma remains vague. Genetic syndromes, including familial adenomatous polyposis (FAP), Beckwith-Wiedemann syndrome (BWS), and trisomy 18 syndrome, have been associated with hepatoblastoma. BWS is an overgrowth syndrome which exhibits an alteration of genomic imprinting on chromosome 11p15.5. N⁶-Methyladenosine (M⁶A) is an RNA modification with rampant involvement in the metabolism of cells and malignant diseases. It has been observed to impact the development of various cancers via its governance of gene expression. Here, we explore the role of m⁶A and its genetic associates in promoting HB, and the impact this may have on our future management of the disease.

Abstract

Hepatoblastoma (HB) is a rare primary malignancy of the developing fetal liver. Its course is profoundly influenced by genetics, in the context of sporadic mutation or genetic syndromes. Conventionally, subtypes of HB are histologically determined based on the tissue type that is recapitulated by the tumor and the direction of its differentiation. This classification is being reevaluated based on advances on molecular pathology. The therapeutic approach comprises surgical intervention, chemotherapy (in a neoadjuvant or post-operative capacity), and in some cases, liver transplantation. Although diagnostic modalities and treatment options are evolving, some patients experience complications, including relapse, metastatic spread, and suboptimal response to chemotherapy. As yet, there is no consistent framework with which such outcomes can be predicted. N⁶-methyladenosine (m⁶A) is an RNA modification with rampant involvement in the normal processing of cell metabolism and neoplasia. It has been observed to impact the development of a variety of cancers via its governance of gene expression. M⁶A-associated genes appear prominently in HB. Literature data seem to underscore the role of m⁶A in promotion and clinical course of HB. Illuminating the pathogenetic mechanisms that drive HB are promising additions to the understanding of the clinically aggressive tumor behavior, given its potential to predict disease course and response to therapy. Implicated genes may also act as targets to facilitate the evolving personalized cancer therapy. Here, we explore the role of m⁶A and its genetic associates in the promotion of HB, and the impact this may have on the management of this neoplastic disease.

The Emerging Role of N6-Methyladenosine RNA Methylation as Regulators in Cancer Therapy and Drug Resistance

N6-methyladenosine (m⁶A) RNA methylation has been considered the most prevalent, abundant, and conserved internal transcriptional modification throughout the eukaryotic mRNAs. Typically, m⁶A RNA methylation is catalyzed by the RNA methyltransferases (writers), is removed by its demethylases (erasers), and interacts with m⁶A-binding proteins (readers). Accumulating evidence shows that abnormal changes in the m⁶A levels of these regulators are increasingly associated with human tumorigenesis and drug resistance. However, the molecular mechanisms underlying m⁶A RNA methylation in tumor occurrence and development have not been comprehensively clarified. We reviewed the recent findings on biological regulation of m⁶A RNA methylation and summarized its potential therapeutic strategies in various human cancers.

N6-Methyladenosine RNA Modification: A Potential Regulator of Stem Cell Proliferation and Differentiation

Stem cell transplantation (SCT) holds great promise for overcoming diseases by regenerating damaged cells, tissues and organs. The potential for self-renewal and differentiation is the key to SCT. RNA methylation, a dynamic and reversible epigenetic modification, is able to regulate the ability of stem cells to differentiate and regenerate. N⁶-methyladenosine (m⁶A) is the richest form of RNA methylation in eukaryotes and is regulated by three classes of proteins: methyltransferase complexes, demethylase complexes and m⁶A binding proteins. Through the coordination of these proteins, RNA methylation precisely modulates the expression of important target genes by affecting mRNA stability, translation, selective splicing, processing and microRNA maturation. In this review, we summarize the most recent findings on the regulation of m⁶A modification in embryonic stem cells, induced pluripotent stem cells and adult stem cells, hoping to provide new insights into improving SCT technology.