Integrative analysis of m3C associated genes reveals METTL2A as a potential oncogene in breast Cancer.

RNA methylation modifications, especially m6A mRNA modification, are known to be extensively involved in tumor development. However, the relationship between N3-methylcytidine (m3C) related genes and tumorigenesis has rarely been studied. In this research, we found that m3C-related genes were expressed at different levels and affected patients' prognosis across multiple cancer types from The Cancer Genome Atlas and multi-omics levels. Importantly, methyltransferase-like proteins 2A (METTL2A) had a high amplification frequency (~ 7%) in patients with breast invasive carcinoma (BRCA), and its overexpression was an independent predictor of poor overall survival. Enrichment analysis of associated genes revealed that METTL2A may activate DNA synthesis and cell proliferation pathways in BRCA cells. Through drug sensitivity analysis, Trifluridine, PD407824, and Taselisib were shown to be effective drugs for METTL2A-positive BRCA patients. Overall, our research conducts a holistic view of the expression level and prognostic signature of m3C-related genes with multiple malignancies. Importantly, METTL2A has been intensely explored as a potential oncogene in BRCA, to aid the development of potential drug agents for precision therapy in breast cancer patients.

Three distinct 3-methylcytidine (m3C) methyltransferases modify tRNA and mRNA in mice and humans.

Chemical RNA modifications are central features of epitranscriptomics, highlighted by the discovery of modified ribonucleosides in mRNA and exemplified by the critical roles of RNA modifications in normal physiology and disease. Despite a resurgent interest in these modifications, the biochemistry of 3-methylcytidine (m3C) formation in mammalian RNAs is still poorly understood. However, the recent discovery of trm141 as the second gene responsible for m3C presence in RNA in fission yeast raises the possibility that multiple enzymes are involved in m3C formation in mammals as well. Here, we report the discovery and characterization of three distinct m3C-contributing enzymes in mice and humans. We found that methyltransferase-like (METTL) 2 and 6 contribute m3C in specific tRNAs and that METTL8 only contributes m3C to mRNA. MS analysis revealed that there is an ∼30-40% and ∼10-15% reduction, respectively, in METTL2 and -6 null-mutant cells, of m3C in total tRNA, and primer extension analysis located METTL2-modified m3C at position 32 of tRNAThr isoacceptors and tRNAArg(CCU) We also noted that METTL6 interacts with seryl-tRNA synthetase in an RNA-dependent manner, suggesting a role for METTL6 in modifying serine tRNA isoacceptors. METTL8, however, modified only mRNA, as determined by biochemical and genetic analyses in Mettl8 null-mutant mice and two human METTL8 mutant cell lines. Our findings provide the first evidence of the existence of m3C modification in mRNA, and the discovery of METTL8 as an mRNA m3C writer enzyme opens the door to future studies of other m3C epitranscriptomic reader and eraser functions.