Ribosome Footprinting (RiboSeq) analysis of mRNA translation in HEK293T WT and METTL2A/2B/6 knockout cells
Ontology highlight
ABSTRACT: The ‘epitranscriptome’ includes a diversity of RNA modifications that influence gene expression. N3-methylcytidine (m3C) mainly occurs in the anticodon loop (position C32) of certain tRNAs yet its role is poorly understood. Here, using HAC-Seq, we report comprehensive METTL2A/B-, METTL6-, and METTL2A/B/6-dependent m3C profiles in human cells. METTL2A/B modifies most tRNA-Arginine and tRNA-Threonine members, whereas METTL6 modifies the tRNA-Serine family. However, decreased m3C32 on tRNA-Ser-GCT isodecoders was only observed with combined METTL2A/B/6 deletion. Ribo-Seq revealed altered translation of genes related to cell cycle and DNA repair pathways in METTL2A/2B/6-deficient cells, and these mRNAs are enriched in AGU codons that require tRNA-Ser-GCT for translation. These results, supported by reporter assays, help explain the observed slowed proliferation, altered cell cycle, and increased Cisplatin-sensitivity phenotypes of METTL2A/B/6-deficient cells. Thus, we define METTL2A/B/6-dependent methylomes and uncover a particular requirement of m3C tRNA modification for Serine codon-biased mRNA translation of cell cycle, and DNA repair genes.
Project description:The ‘epitranscriptome’ includes a diversity of RNA modifications that influence gene expression. N3-methylcytidine (m3C) mainly occurs in the anticodon loop (position C32) of certain tRNAs yet its role is poorly understood. Here, using HAC-Seq, we report comprehensive METTL2A/B-, METTL6-, and METTL2A/B/6-dependent m3C profiles in human cells. METTL2A/B modifies most tRNA-Arginine and tRNA-Threonine members, whereas METTL6 modifies the tRNA-Serine family. However, decreased m3C32 on tRNA-Ser-GCT isodecoders was only observed with combined METTL2A/B/6 deletion. Ribo-Seq revealed altered translation of genes related to cell cycle and DNA repair pathways in METTL2A/2B/6-deficient cells, and these mRNAs are enriched in AGU codons that require tRNA-Ser-GCT for translation. These results, supported by reporter assays, help explain the observed slowed proliferation, altered cell cycle, and increased Cisplatin-sensitivity phenotypes of METTL2A/B/6-deficient cells. Thus, we define METTL2A/B/6-dependent methylomes and uncover a particular requirement of m3C tRNA modification for Serine codon-biased mRNA translation of cell cycle, and DNA repair genes.
Project description:Here, we identified METTL6 as a bona fide tRNA methyltransferase, catalysing the formation of 3-methylcytidine (m3C) at C32 of specific serine tRNA isoacceptors. Accordingly, deletion of METTL6 in mouse stem cells results in changes in ribosome occupancy and RNA levels, as well as a spontaneous loss of pluripotency
Project description:A subset of eukaryotic tRNAs is methylated in the anticodon loop to form the 3-methylcytosine (m3C) modification. In mammals, the number of tRNAs containing m3C has expanded to include mitochondrial (mt) tRNA-Ser-UGA and mt-tRNA-Thr-UGU. Whereas the enzymes catalyzing m3C formation in nuclear-encoded cytoplasmic tRNAs have been identified, the proteins responsible for m3C modification in mt-tRNAs are unknown. Here, we show that m3C formation in human mt-tRNAs is dependent upon the Methyltransferase-Like 8 (METTL8) enzyme. We find that METTL8 is a mitochondria-associated protein that interacts with mitochondrial seryl-tRNA synthetase along with mt-tRNAs containing m3C. Human cells deficient in METTL8 exhibit loss of m3C modification in mt-tRNAs but not nuclear-encoded tRNAs. Consistent with the mitochondrial import of METTL8, the formation of m3C in METTL8-deficient cells can be rescued by re-expression of wildtype METTL8 but not by a METTL8 variant lacking the N-terminal mitochondrial localization signal. Notably, METTL8-deficiency in human cells causes alterations in the native migration pattern of mt-tRNA-Ser-UGA suggesting a role for m3C in tRNA folding. Altogether, these findings demonstrate that METTL8 is required for m3C formation in mitochondrial tRNAs and uncover a potential role for m3C modification in mitochondrial tRNA structure.
Project description:Editing of mischarged tRNAs by cytoplasmic aminoacyl-tRNA synthetases (aaRSs) is of high significance for protein homeostasis, whose impairment causes neurodegeneration. However, whether mitochondrial translation needs fidelity and the significance of proofreading (editing) by mitochondrial aaRSs are long-term mysteries. Here, we showed that NIH-3T3 cell line critically depend on the editing of mitochondrial threonyl-tRNA synthetase (Tars2) editing, the disruption of which accumulated Ser-tRNAThr and generated a large abundance of Thr-to-Ser misincorporated peptides. Such infidelity impaired mitochondrial translation and oxidative phosphorylation, causing oxidative stress and cell cycle arrest at G0/G1 phase. ROS removal by N-acetylcysteine relieved abnormal cell proliferation.
Project description:We report a m3C-specific high-throughput sequencing techinque, Hydrazine-Aniline Cleavage sequencing (HAC-seq) to profile the m3C methylome at single-nucleotide resolution. We apply HAC-seq to analyze ribosomal RNA-depleted total RNA from MCF7 cells. We find that tRNA are the predominant m3C-modified RNA species. We find no evidence of m3C-modification of mRNA or other non-coding RNAs at comparable levels to tRNA in MCF7 cells.
Project description:3-Methylcytidine (m3C), a prevalent modification of tRNAs, was recently identified in eukaryotic mRNAs. However, its precise distribution and formation mechanisms in mRNAs remain elusive. Here we develop a novel approach, m3C immunoprecipitation and sequencing (m3C-IP-seq), utilizing antibody enrichment to profile the m3C methylome at single-nucleotide resolution. m3C-IP-seq captures 12 m3C modification sites in cytoplasmic tRNA isoacceptors and 2 in mitochondrial tRNA isoacceptors. Moreover, m3C-IP-seq permits the comprehensive profiling of m3C sites in mRNAs and lncRNAs, with their presence reliant on a nuclear isoform of METTL8. A significant proportion of m3C sites is concentrated in the 3’ untranslated region (3’ UTR) of mRNAs. Additionally, m3C methylation is dynamic and responds to hypoxia. Functionally, m3C formation in the 3’ UTR is associated with mRNA degradation. Collectively, our data demonstrate the widespread presence of m3C modification in the human transcriptome and provide a resource for functional studies of m3C-mediated RNA metabolism.
Project description:Mitochondria contain a specific translation machinery for the synthesis of respiratory chain components encoded on the mitochondrial genome. Mitochondrial tRNAs (mt-tRNAs) are also generated from the mitochondrial genome and, similar to their cytoplasmic counterparts, are modified at various positions. Here, we find that the RNA methyltransferase METTL8, is a mitochondrial protein that facilitates m3C methylation at position C32 of mt-tRNASer(UCN) and mt-tRNAThr. METTL8 knock out cells show reduced and over expressing cells enhanced respiratory chain activity. In pancreatic cancer, METTL8 levels are high, which correlates with patient survival. Indeed, METTL8 up regulation stimulates respiratory chain activity in these cells. Ribosome occupancy analysis using ribosome profiling revealed ribosome stalling on mt-tRNASer(UCN) and mt-tRNAThr codons and mass spectrometry analysis of native ribosomal subcomplexes unraveled reduced respiratory chain incorporation of the mitochondria encoded proteins ND6 and ND1. A well-balanced translation of mt-tRNASer(UCN) and mt-tRNAThr codons through METTL8-mediated C32 methylation might therefore provide optimal respiratory chain compositions and function.
Project description:Modified nucleotides in tRNAs are important determinants of folding, structure and function. Here, we identify METTL8 as a mitochondrial matrix protein and active RNA methyltransferase responsible for installing m3C32 in the human mitochondrial (mt-)tRNAThr and mt-tRNASer(UCN). METTL8 crosslinks to the anticodon stem loop (ASL) of many mt-tRNAs in cells, raising the question of how methylation target specificity is achieved. Dissection of mt-tRNA recognition elements revealed U34G35 and t6A37/(ms2)i6A37, present concomitantly only in the ASLs of the two substrate mt-tRNAs, as key determinations for METTL8-mediated methylation of C32. Several lines of evidence demonstrate the influence of U34, G35, and the m3C32 and t6A37/(ms2)i6A37 modifications in mt-tRNAThr/Ser(UCN) on the structure of these mt-tRNAs. Although mt-tRNAThr/Ser(UCN) lacking METTL8-mediated m3C32 are efficiently aminoacylated and associate with mitochondrial ribosomes, mitochondrial translation is mildly impaired by lack of METTL8. Together these results define the cellular targets of METTL8 and shed new light on the role of m3C32 within mt-tRNAs.
Project description:Modified nucleotides in tRNAs are important determinants of folding, structure and function. Here, we identify METTL8 as a mitochondrial matrix protein and active RNA methyltransferase responsible for installing m3C32 in the human mitochondrial (mt-)tRNAThr and mt-tRNASer(UCN). METTL8 crosslinks to the anticodon stem loop (ASL) of many mt-tRNAs in cells, raising the question of how methylation target specificity is achieved. Dissection of mt-tRNA recognition elements revealed U34G35 and t6A37/(ms2)i6A37, present concomitantly only in the ASLs of the two substrate mt-tRNAs, as key determinations for METTL8-mediated methylation of C32. Several lines of evidence demonstrate the influence of U34, G35, and the m3C32 and t6A37/(ms2)i6A37 modifications in mt-tRNAThr/Ser(UCN) on the structure of these mt-tRNAs. Although mt-tRNAThr/Ser(UCN) lacking METTL8-mediated m3C32 are efficiently aminoacylated and associate with mitochondrial ribosomes, mitochondrial translation is mildly impaired by lack of METTL8. Together these results define the cellular targets of METTL8 and shed new light on the role of m3C32 within mt-tRNAs.
Project description:The number of tRNA isodecoder genes has increased dramatically in mammals, but the specific molecular and physiological reasons for this expansion remain elusive. To address this fundamental question we used CRISPR editing to knockout the seven-membered phenylalanine tRNA gene family in mice, both individually and combinatorially. Using ATAC-seq, RNA-seq and proteomics we observed distinct molecular consequences of individual tRNA deletions. We show that tRNA-Phe-1-1 is required for neuronal function and its loss is partially compensated by increased expression of other tRNAs but results in mistranslation. In contrast, the other tRNA-Phe isodecoders compensate for the loss of each of the remaining six tRNA-Phe genes. In the tRNA-Phe gene family, the expression of at least four tRNA-Phe isodecoders is required for embryonic development and survival. The loss of tRNA-Phe-1-1 and any other three tRNA-Phe genes causes embryonic lethality indicating that tRNA-Phe-1-1 is most important for development and survival. Our results reveal that the multi-copy configuration of tRNA isodecoder genes is required to buffer translation and viability in mammals.