N2-methylguanosine modifications on human tRNAs and snRNA U6 are important for colon cancer 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 transla-tion. Growing evidences support important roles of tRNA/snRNAs modifications and hence the enzymes that install them, in eukaryotic cell development and their dysregulation has been linked to various human pathologies including neurodevelopmental disorders and cancers. Human TRMT112 (Trm112 in Saccharomyces cerevisiae) functions as an allosteric regulator of several methyltransfer-ases (MTases) targeting molecules (tRNAs, rRNAs and proteins) involved in protein synthesis. Here, we have investigated the interaction network of human TRMT112 in intact cells and identify three poorly characterized putative MTases (TRMT11, THUMPD3 and THUMD2) as direct part-ners. 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. In contrast, we discovered that THUMPD2 directly associates with the U6 snRNA and is required for the for-mation of m2G in this core component of the catalytic spliceosome. Consistently, our data reveal the combined importance of TRMT11 and THUMPD3 for optimal protein synthesis and cancer cell proliferation as well as a role for THUMPD2 in fine-tuning pre-mRNA splicing.