N-Methyladenosine Modulates Nonsense-Mediated mRNA Decay in Human Glioblastoma.

The N-methyladenosine (mA) modification influences various mRNA metabolic events and tumorigenesis, however, its functions in nonsense-mediated mRNA decay (NMD) and whether NMD detects induced carcinogenesis pathways remain undefined. Here, we showed that the mA methyltransferase METTL3 sustained its oncogenic role by modulating NMD of splicing factors and alternative splicing isoform switches in glioblastoma (GBM). Methylated RNA immunoprecipitation-seq (MeRIP-seq) analyses showed that mA modification peaks were enriched at metabolic pathway-related transcripts in glioma stem cells (GSC) compared with neural progenitor cells. In addition, the clinical aggressiveness of malignant gliomas was associated with elevated expression of METTL3. Furthermore, silencing or overexpressing dominant-negative mutant METTL3 suppressed the growth and self-renewal of GSCs. Integrated transcriptome and MeRIP-seq analyses revealed that downregulating the expression of METTL3 decreased mA modification levels of serine- and arginine-rich splicing factors (), which led to YTHDC1-dependent NMD of transcripts and decreased SRSF protein expression. Reduced expression of SRSFs led to larger changes in alternative splicing isoform switches. Importantly, the phenotypes mediated by METTL3 deficiency could be rescued by downregulating or isoforms. Overall, these results establish a novel function of mA in modulating NMD and uncover the mechanism by which METTL3 promotes GBM tumor growth and progression. SIGNIFICANCE: These findings establish the oncogenic role of mA writer METTL3 in glioblastoma stem cells.