The METTL3-m6A Epitranscriptome: Dynamic Regulator of Epithelial Development, Differentiation, and Cancer

METTL3 promotes non-small-cell lung cancer growth and metastasis by inhibiting FDX1 through copper death-associated pri-miR-21-5p maturation

Objective: We probed into the significance of METTL3 in the maturation process of pri-miR-21-5p. We specifically investigated its impact on the regulation of FDX1 and its involvement in the progression of non-small-cell lung cancer (NSCLC). Methods: The Cancer Genome Atlas (TCGA) identified NSCLC factors. Methylation-specific PCR (MSP), clonogenic tests and flow cytometry analyzed cells. Methylated RNA immunoprecipitation (Me-RIP) and dual-luciferase studied miR-21-5p/FDX1. Mice xenografts showed METTL3's tumorigenic effect. Results: METTL3, with high expression but low methylation in NSCLC, influenced cell behaviors. Its suppression reduced oncogenic properties. METTL3 enhanced miR-21-5p maturation, targeting FDX1 and boosting NSCLC tumorigenicity in mice. Conclusion: METTL3 may promote NSCLC development by facilitating pri-miR-21-5p maturation, upregulating miR-21-5p and targeting inhibition of FDX1.

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.

Mettl3-catalyzed m6A regulates histone modifier and modification expression in self-renewing somatic tissue

N6-methyladenosine (m6A) is the most abundant modification on messenger RNAs (mRNAs) and is catalyzed by methyltransferase-like protein 3 (Mettl3). To understand the role of m6A in a self-renewing somatic tissue, we deleted Mettl3 in epidermal progenitors in vivo. Mice lacking Mettl3 demonstrate marked features of dysfunctional development and self-renewal, including a loss of hair follicle morphogenesis and impaired cell adhesion and polarity associated with oral ulcerations. We show that Mettl3 promotes the m6A-mediated degradation of mRNAs encoding critical histone modifying enzymes. Depletion of Mettl3 results in the loss of m6A on these mRNAs and increases their expression and associated modifications, resulting in widespread gene expression abnormalities that mirror the gross phenotypic abnormalities. Collectively, these results have identified an additional layer of gene regulation within epithelial tissues, revealing an essential role for m6A in the regulation of chromatin modifiers, and underscoring a critical role for Mettl3-catalyzed m6A in proper epithelial development and self-renewal.

METTL3 Reduces Oxidative Stress-induced Apoptosis in Presbycusis by Regulating the N6-methyladenosine Level of SIRT1 mRNA

N6-methyl adenosine (m6A) modification is known to play a crucial role in various aging-related diseases. However, its involvement in presbycusis, a type of age-related hearing loss, is not yet clear. We examined the changes in oxidative stress levels in both plasma of presbycusis patients and mice. To determine the expression of m6A and its functional enzymes, we used liquid chromatography tandem-mass spectrometry (LC-MS/MS), enzyme-linked immunosorbent assay (ELISA), and RT-PCR to analyze the total RNA of presbycusis patients blood cells (n = 8). Additionally, we detected the expression of m6A functional enzymes in the cochlea of presbycusis mice using immunohistochemistry. We assessed the effects of m6A methyltransferase METTL3 on SIRT1 protein expression, reactive oxygen species (ROS) levels, and apoptosis in an oxidative stress model of organ of Corti 1 (OC1) cells. To observe the effect on SIRT1 protein expression, we interfered with the m6A recognition protein IGF2BP3 using siRNA. In both presbycusis patients and mice, there was an increased level of oxidative stress in plasma.There was a decrease in the expression of m6A, METTL3, and IGF2BP3 in presbycusis patients blood cells. The expression of METTL3 and IGF2BP3 was also reduced in the cochlea of presbycusis mice. In OC1 cells, METTL3 positively regulated SIRT1 protein levels, while reversely regulated the level of ROS and apoptosis. IGF2BP3 was found to be involved in the regulation of SIRT1 protein expression. In addition, METTL3 may play a protective role in oxidative stress-induced injury of OC1 cells, while both METTL3 and IGF2BP3 cooperatively regulate the level of m6A and the fate of SIRT1 mRNA in OC1 cells.

N6-methyladenosine functions and its role in skin cancer

N6-methyladenosine (m6A) methylation is the most abundant mammalian mRNA modification. m6A regulates RNA processing, splicing, nucleation, translation and stability by transferring, removing and recognizing m6A methylation sites, which are critical for cancer initiation, progression, metabolism and metastasis. m6A is involved in pathophysiological tumour development by altering m6A modification and expression levels in tumour oncogenes and suppressor genes. Skin cancers are by far the most common malignancies in humans, with well over a million cases diagnosed each year. Skin cancers are grouped into two main categories: melanoma and non-melanoma skin cancers (NMSC), based on cell origin and clinical behaviour. In this review, we summarize m6A methylation functions in different skin cancers, and discuss how m6A methylation is involved in disease development and progression. Moreover, we review potential prognostic biomarkers and molecular targets for early skin cancer diagnosis and treatment.

Integrative proteomics and m6A microarray analyses of the signatures induced by METTL3 reveals prognostically significant in gastric cancer by affecting cellular metabolism

METTL3-mediated RNA N6-methyladenosine (m6A) is the most prevalent modification that participates in tumor initiation and progression via governing the expression of their target genes in cancers. However, its role in tumor cell metabolism remains poorly characterized. In this study, m6A microarray and quantitative proteomics were employed to explore the potential effect and mechanism of METTL3 on the metabolism in GC cells. Our results showed that METTL3 induced significant alterations in the protein and m6A modification profile in GC cells. Gene Ontology (GO) enrichment indicated that down-regulated proteins were significantly enriched in intracellular mitochondrial oxidative phosphorylation (OXPHOS). Moreover, the protein-protein Interaction (PPI) network analysis found that these differentially expressed proteins were significantly associated with OXPHOS. A prognostic model was subsequently constructed based on the Cancer Genome Atlas (TCGA) and the Gene Expression Omnibus (GEO) databases, and the high-risk group exhibited a worse prognosis in GC patients. Meanwhile, Gene Set Enrichment Analysis (GSEA) demonstrated significant enrichment in the energy metabolism signaling pathway. Then, combined with the results of the m6A microarray analysis, the intersection molecules of DEPs and differential methylation genes (DMGs) were significantly correlated with the molecules of OXPHOS. Besides, there were significant differences in prognosis and GSEA enrichment between the two clusters of GC patients classified according to the consensus clustering algorithm. Finally, highly expressed and highly methylated molecules regulated by METTL3 were analyzed and three (AVEN, DAZAP2, DNAJB1) genes were identified to be significantly associated with poor prognosis in GC patients. These results signified that METTL3-regulated DEPs in GC cells were significantly associated with OXPHOS. After combined with m6A microarray analysis, the results suggested that these proteins might be implicated in cell energy metabolism through m6A modifications thus influencing the prognosis of GC patients. Overall, our study revealed that METTL3 is involved in cell metabolism through an m6A-dependent mechanism in GC cells, and indicated a potential biomarker for prognostic prediction in GC.

Role of N6-Methyladenosine Methylation Regulators in the Drug Therapy of Digestive System Tumours

Digestive system tumours, including stomach, colon, esophagus, liver and pancreatic tumours, are serious diseases affecting human health. Although surgical treatment and postoperative chemoradiotherapy effectively improve patient survival, current diagnostic and therapeutic strategies for digestive system tumours lack sensitivity and specificity. Moreover, the tumour's tolerance to drug therapy is enhanced owing to tumour cell heterogeneity. Thus, primary or acquired treatment resistance is currently the main hindrance to chemotherapy efficiency. N6-methyladenosine (m6A) has various biological functions in RNA modification. m6A modification, a key regulator of transcription expression, regulates RNA metabolism and biological processes through the interaction of m6A methyltransferase ("writers") and demethylase ("erasers") with the binding protein decoding m6A methylation ("readers"). Additionally, m6A modification regulates the occurrence and development of tumours and is a potential driving factor of tumour drug resistance. This review systematically summarises the regulatory mechanisms of m6A modification in the drug therapy of digestive system malignancies. Furthermore, it clarifies the related mechanisms and therapeutic prospects of m6A modification in the resistence of digestive system malignancies to drug therapy.

Downregulation of m6 A writer complex member METTL14 in bladder urothelial carcinoma suppresses tumor aggressiveness

N6-methyladenosine (m6 A) and its regulatory proteins have been associated with tumorigenesis in several cancer types. However, knowledge on the mechanistic network related to m6 A in bladder cancer (BlCa) is rather limited, requiring further investigation of its functional role. We aimed to uncover the biological role of m6 A and related proteins in BlCa and understand how this influences tumor aggressiveness. N6-adenosine-methyltransferase catalytic subunit (METTL3), N6-adenosine-methyltransferase noncatalytic subunit (METTL14), protein virilizer homolog (VIRMA), and RNA demethylase ALKBH5 (ALKBH5) had significantly lower expression levels in BlCa compared to that in normal urothelium. METTL14 knockdown led to disruption of the remaining methyltransferase complex and a decrease in m6 A abundance, as well as overall reduced tumor aggressiveness (decreased cell invasion and migration capacity and increased apoptosis). Furthermore, in vivo, METTL14 knockdown caused tumor size reduction. Collectively, we propose methyltransferase METTL14 as a key component for m6 A RNA deposit and that it is closely related to BlCa progression, playing an important role in tumor aggressiveness. These data contribute to a better understanding of the m6 A writer complex, which might constitute an appealing therapeutic target.

Current Advances in N6-Methyladenosine Methylation Modification During Bladder Cancer

N6-methyladenosine (m6A) is a dynamic, reversible post-transcriptional modification, and the most common internal modification of eukaryotic messenger RNA (mRNA). Considerable evidence now shows that m6A alters gene expression, thereby regulating cell self-renewal, differentiation, invasion, and apoptotic processes. M6A methylation disorders are directly related to abnormal RNA metabolism, which may lead to tumor formation. M6A methyltransferase is the dominant catalyst during m6A modification; it removes m6A demethylase, promotes recognition by m6A binding proteins, and regulates mRNA metabolic processes. Bladder cancer (BC) is a urinary system malignant tumor, with complex etiology and high incidence rates. A well-differentiated or moderately differentiated pathological type at initial diagnosis accounts for most patients with BC. For differentiated superficial bladder urothelial carcinoma, the prognosis is normally good after surgery. However, due to poor epithelial cell differentiation, BC urothelial cell proliferation and infiltration may lead to invasive or metastatic BC, which lowers the 5-years survival rate and significantly affects clinical treatments in elderly patients. Here, we review the latest progress in m6A RNA methylation research and investigate its regulation on BC occurrence and development.

Long intergenic non-protein coding RNA 1273 confers sorafenib resistance in hepatocellular carcinoma via regulation of methyltransferase 3

Hepatocellular carcinoma (HCC) is often diagnosed in patients with advanced disease who are ineligible for curative surgical therapies. Sorafenib is a first-line agent approved for the treatment of advanced HCC. However, the frequent resistance of HCC cells to sorafenib greatly reduces its efficacy. Herein, we describe a novel long non-coding RNA (lncRNA) conferring sorafenib resistance. Long intergenic non-protein coding RNA 1273 (LINC01273) was significantly overexpressed in human HCC and sorafenib-resistant tissues, linking it to poor overall and relapse-free survival. We established sorafenib-resistant Huh7 (Huh7-SR) and SMMC-7721 (SMMC-7721-SR) cells, and found that the knockdown of LINC01273 repressed the viability, colony formation, and DNA synthesis rate of Huh7-SR and SMMC-7721-SR cells. The level of N6-methyladenosine (m⁶A) in sorafenib-resistant HCC cells was significantly decreased, which was rescued by LINC01273 silencing. Mechanistically, LINC01273 complementarity bound to miR-600, served as a ‘reservoir’ increasing miR-600 stability, and facilitating miR-600 targeting methyltransferase 3 (METTL3), a m⁶A ‘writer’, resulting in reducing METTL3 level. In addition, LINC01273 was modified with m⁶A, METTL3 increased LINC01273 m⁶A modification, followed by LINC01273 decay in the presence of YTHDF2, a m⁶A ‘reader’. Our findings reveal the key role of LINC01273 in sorafenib-resistant HCC cells, and targeting of the newly identified LINC01273/miR-600/METTL3 feedback regulatory axis may be a promising effective intervention for HCC patients with sorafenib resistance.

Emerging Role of Epitranscriptomics in Diabetes Mellitus and Its Complications

Diabetes mellitus (DM) and its related complications are among the leading causes of disability and mortality worldwide. Substantial studies have explored epigenetic regulation that is involved in the modifications of DNA and proteins, but RNA modifications in diabetes are still poorly investigated. In recent years, posttranscriptional epigenetic modification of RNA (the so-called 'epitranscriptome') has emerged as an interesting field of research. Numerous modifications, mainly N⁶ -methyladenosine (m⁶A), have been identified in nearly all types of RNAs and have been demonstrated to have an indispensable effect in a variety of human diseases, such as cancer, obesity, and diabetes. Therefore, it is particularly important to understand the molecular basis of RNA modifications, which might provide a new perspective for the pathogenesis of diabetes mellitus and the discovery of new therapeutic targets. In this review, we aim to summarize the recent progress in the epitranscriptomics involved in diabetes and diabetes-related complications. We hope to provide some insights for enriching the understanding of the epitranscriptomic regulatory mechanisms of this disease as well as the development of novel therapeutic targets for future clinical benefit.