N(6)-Methyladenosine Methyltransferases and Demethylases: New Regulators of Stem Cell Pluripotency and Differentiation

Integrative analyses of N6-methyladenosine-associated single-nucleotide polymorphisms (m6A-SNPs) identify tumor suppressor gene AK9 in lung cancer

N6 -methyladenosine (m6 A) modification has been identified as one of the most important epigenetic regulation mechanisms in the development of human cancers. However, the association between m6 A-associated single-nucleotide polymorphisms (m6 A-SNPs) and lung cancer risk remains largely unknown. Here, we identified m6 A-SNPs and examined the association of these m6 A-SNPs with lung cancer risk in 13,793 lung cancer cases and 14,027 controls. In silico functional annotation was used to identify causal m6 A-SNPs and target genes. Furthermore, methylated RNA immunoprecipitation and quantitative real-time polymerase chain reaction (MeRIP-qPCR) assay was performed to assess the m6 A modification level of different genotypes of the causal SNP. In vitro assays were performed to validate the potential role of the target gene in lung cancer. A total of 8794 m6 A-SNPs were detected, among which 397 SNPs in nine susceptibility loci were associated with lung cancer risk, including six novel loci. Bioinformatics analyses indicated that rs1321328 in 6q21 was located around the m6 A modification site of AK9 and significantly reduced AK9 expression (β = -0.15, p = 2.78 × 10-8 ). Moreover, AK9 was significantly downregulated in lung cancer tissues than that in adjacent normal tissues of samples from the Cancer Genome Atlas and Nanjing Lung Cancer Cohort. MeRIP-qPCR assay suggested that C allele of rs1321328 could significantly decrease the m6 A modification level of AK9 compared with G allele. In vitro assays verified the tumor-suppressing role of AK9 in lung cancer. These findings shed light on the pathogenic mechanism of lung cancer susceptibility loci linked with m6 A modification.

The N6-methyladenosine:mechanisms, diagnostic value, immunotherapy prospec-ts and challenges in gastric cancer

The N6-methyladenosine(m⁶A) RNA modification is important in post-transcriptional regulation of RNA and are regulated reversibly by methyltransferases (writers), demethylases (erasers) and m⁶A recognition proteins (readers). Changes in the structure and function of key RNAs contribute to the development of diseases, particularly tumors. Many abnormal expressions of molecules related to m⁶A RNA methylation modification are discovered in gastric cancer(GC), which changes the methylation level and stability of target genes after transcription, and then regulates related metabolic pathways, affecting the occurrence and progression of GC. Therefore, an in-depth study of m⁶A RNA modification in GC is conducive to the development of new tumor therapies and the achieve of individualized treatment. At present, both basic and clinical studies indicate that m⁶A plays a complex and contentious role in GC. In this paper, we not only review the roles and mechanisms of m⁶A modified related proteins, but also discuss the value of m⁶A modulators in the clinical applications and current challenges of GC, aiming to provide research clues for the early diagnosis and explore the feasibility of m⁶A related proteins as specific targets for GC immunotherapy.

Advances in research of m6A methylation in hepatocellular carcinoma

RNA modification plays a vital role in many biological processes, and its abnormalities are associated with the progression of cancer. "N6-methyladenine (m⁶A) modification is the most prevalent and important RNA modification that plays a key role in almost all important biological processes. m⁶A methylation is a dynamic reversible process mediated by methyltransferases (m⁶A writers), demethylases (m⁶A erasers), and m⁶A recognition protein (m⁶A readers). In this paper, we review the m⁶A methylation modification and its associated regulatory proteins, with an emphasis on the role of m⁶A methylation in the development of liver cancer.

Discovery of Small Molecules that Activate RNA Methylation through Cooperative Binding to the METTL3-14-WTAP Complex Active Site

Chemical modifications of RNA provide an additional, epitranscriptomic, level of control over cellular functions. N-6-methylated adenosines (m6As) are found in several types of RNA, and their amounts are regulated by methyltransferases and demethylases. One of the most important enzymes catalyzing generation of m6A on mRNA is the trimer N-6-methyltransferase METTL3-14-WTAP complex. Its activity has been linked to such critical biological processes as cell differentiation, proliferation, and death. We used in silico-based discovery to identify small-molecule ligands that bind to METTL3-14-WTAP and determined experimentally their binding affinity and kinetics, as well as their effect on enzymatic function. We show that these ligands serve as activators of the METTL3-14-WTAP complex.

Characterization of METTL16 as a cytoplasmic RNA binding protein

mRNA modification by N6-methyladenosine (m6A) is involved in many post-transcriptional regulation processes including mRNA stability, splicing and promotion of translation. Accordingly, the recently identified mRNA methylation complex containing METTL3, METTL14, and WTAP has been the subject of intense study. However, METTL16 (METT10D) has also been identified as an RNA m6A methyltransferase that can methylate both coding and noncoding RNAs, but its biological role remains unclear. While global studies have identified many potential RNA targets of METTL16, only a handful, including the long noncoding RNA MALAT1, the snRNA U6, as well as the mRNA MAT2A have been verified and/or studied to any great extent. In this study we identified/verified METTL16 targets by immunoprecipitation of both endogenous as well as exogenous FLAG-tagged protein. Interestingly, exogenously overexpressed METTL16 differed from the endogenous protein in its relative affinity for RNA targets which prompted us to investigate METTL16's localization within the cell. Surprisingly, biochemical fractionation revealed that a majority of METTL16 protein resides in the cytoplasm of a number of cells. Furthermore, siRNA knockdown of METTL16 resulted in expression changes of a few mRNA targets suggesting that METTL16 may play a role in regulating gene expression. Thus, while METTL16 has been reported to be a nuclear protein, our findings suggest that METTL16 is also a cytoplasmic methyltransferase that may alter its RNA binding preferences depending on its cellular localization. Future studies will seek to confirm differences between cytoplasmic and nuclear RNA targets in addition to exploring the physiological role of METTL16 through long-term knockdown.

It's complicated… m6A-dependent regulation of gene expression in cancer

Cellular function relies on multiple pathways that are coordinated to ensure the proper execution of gene expression networks. Failure to coordinate the multiple programs active in the cell can have catastrophic consequences and lead to diseases such as cancer. At the post-transcriptional level, RNA modifications play important roles in the regulation of gene expression. N6-methyladenosine (m⁶A) is the most abundant internal messenger RNA (mRNA) modification and has gained increasing interest in the last few years as a dynamic regulator of RNA metabolism. Modifications regulate all stages of the RNA life cycle, from transcription to decay. Recent studies have pointed to the role of RNA methylation in cancer initiation and progression, and aberrant modification has served as a biomarker of early-stage diagnosis in several cancers. Here, we review the regulation of m⁶A, disruptions to methylation-dependent pathways that influence carcinogenesis, and potential avenues for m⁶A-related therapeutic strategies.

Above the Epitranscriptome: RNA Modifications and Stem Cell Identity

Sequence databases and transcriptome-wide mapping have revealed different reversible and dynamic chemical modifications of the nitrogen bases of RNA molecules. Modifications occur in coding RNAs and noncoding-RNAs post-transcriptionally and they can influence the RNA structure, metabolism, and function. The result is the expansion of the variety of the transcriptome. In fact, depending on the type of modification, RNA molecules enter into a specific program exerting the role of the player or/and the target in biological and pathological processes. Many research groups are exploring the role of RNA modifications (alias epitranscriptome) in cell proliferation, survival, and in more specialized activities. More recently, the role of RNA modifications has been also explored in stem cell biology. Our understanding in this context is still in its infancy. Available evidence addresses the role of RNA modifications in self-renewal, commitment, and differentiation processes of stem cells. In this review, we will focus on five epitranscriptomic marks: N6-methyladenosine, N1-methyladenosine, 5-methylcytosine, Pseudouridine (Ψ) and Adenosine-to-Inosine editing. We will provide insights into the function and the distribution of these chemical modifications in coding RNAs and noncoding-RNAs. Mainly, we will emphasize the role of epitranscriptomic mechanisms in the biology of naïve, primed, embryonic, adult, and cancer stem cells.

Mesenchymal Stem Cell-Based Immunomodulation: Properties and Clinical Application

Mesenchymal stem cells (MSCs) are multipotent stem cells characterized by self-renewal, production of clonal cell populations, and multilineage differentiation. They exist in nearly all tissues and play a significant role in tissue repair and regeneration. Additionally, MSCs possess wide immunoregulatory properties via interaction with immune cells in both innate and adaptive immune systems, leading to immunosuppression of various effector functions. Numerous bioactive molecules secreted by MSCs, particularly cytokines, growth factors, and chemokines, exert autocrine/paracrine effects that modulate the physiological processes of MSCs. These invaluable virtues of MSCs provide new insight into potential treatments for tissue damage and inflammation. In particular, their extensive immunosuppressive properties are being explored for promising therapeutic application in immune disorders. Recently, clinical trials for MSC-mediated therapies have rapidly developed for immune-related diseases following reports from preclinical studies declaring their therapeutic safety and efficacy. Though immunotherapy of MSCs remains controversial, these clinical trials pave the way for their widespread therapeutic application in immune-based diseases. In this review, we will summarize and update the latest research findings and clinical trials on MSC-based immunomodulation.

DNA N6-methyladenine demethylase ALKBH1 enhances osteogenic differentiation of human MSCs

ALKBH1 was recently discovered as a demethylase for DNA N⁶-methyladenine (N6-mA), a new epigenetic modification, and interacts with the core transcriptional pluripotency network of embryonic stem cells. However, the role of ALKBH1 and DNA N6-mA in regulating osteogenic differentiation is largely unknown. In this study, we demonstrated that the expression of ALKBH1 in human mesenchymal stem cells (MSCs) was upregulated during osteogenic induction. Knockdown of ALKBH1 increased the genomic DNA N6-mA levels and significantly reduced the expression of osteogenic-related genes, alkaline phosphatase activity, and mineralization. ALKBH1-depleted MSCs also exhibited a restricted capacity for bone formation in vivo. By contrast, the ectopic overexpression of ALKBH1 enhanced osteoblastic differentiation. Mechanically, we found that the depletion of ALKBH1 resulted in the accumulation of N6-mA on the promoter region of ATF4, which subsequently silenced ATF4 transcription. In addition, restoring the expression of ATP by adenovirus-mediated transduction successfully rescued osteogenic differentiation. Taken together, our results demonstrate that ALKBH1 is indispensable for the osteogenic differentiation of MSCs and indicate that DNA N6-mA modifications area new mechanism for the epigenetic regulation of stem cell differentiation.