Mitochondrial translation requires folate-dependent tRNA methylation

Abstract

Folates enable the activation and transfer of one-carbon units for biosynthesis of purines, thymidine and methionine1–3. Antifolates are important immunosuppressive4 and anticancer agents5. In proliferating lymphocytes6 and human cancers7,8, folate enzymes localizing to the mitochondria are particularly strongly upregulated. This in part reflects the need for mitochondria to generate one-carbon units and export them to the cytosol for anabolic metabolism2,9. The full range of uses of folate-bound one-carbon units in the mitochondrial compartment itself, however, has not been thoroughly explored. Here we show that loss of catalytic activity of the mitochondrial folate enzyme serine hydroxymethyltransferase 2 (SHMT2), but not other folate enzymes, leads to defective oxidative phosphorylation due to impaired mitochondrial translation. We find that SHMT2, presumably by generating mitochondrial 5,10-methylenetetrahydrofolate, provides methyl donors for producing the taurinomethyluridine base at the wobble position of select mitochondrial tRNAs. Mitochondrial ribosome profiling reveals that SHMT2 knockout cells, due to lack of this modified base, suffer from defective translation with preferential mitochondrial ribosome stalling at certain lysine (AAG) and leucine (UUG) codons. This results in impaired respiratory chain enzyme expression. Stalling at these specific codons also occurs in certain mitochondrial inborn errors of metabolism. Disrupting whole-cell folate metabolism, by folate deficiency or antifolate therapy, also impairs the respiratory chain. In summary, mammalian mitochondria use folate-bound one-carbon units to methylate tRNA, and this modification is required for respiratory chain translation and thus oxidative phosphorylation.

The complexity of the serine glycine one-carbon pathway in cancer

“…SHMT2 deficiency or MTFMT mutations impair the formylation of the initiating methionine tRNA (formyl-Met-tRNA), affecting the translation of mitochondrial-coded proteins, such as COX1, and simultaneously reducing oxidative phosphorylation in human cell lines (Minton et al, 2018;Tucker et al, 2011). Additionally, SHMT2-generated 5,10-methylene-THF reportedly contributes to the formation of the taurinomethyluridine base of other specific tRNAs, such as lysine and leucine (Morscher et al, 2018). Thus, tRNA modification by different one-carbon pools in the mitochondria is required for adequate protein translation of oxidative phosphorylation complexes and is probably the cause of specific several inborn errors of mitochondrial metabolism.…”

Mitochondrial One-Carbon Pathway Supports Cytosolic Folate Integrity in Cancer Cells

“…Blocking folate recycling effectively ablates folate-dependent processes that require rapid turnovers in the respective compartment. Hence, deletion of SHMT2 , MTHFD2 , or MTHFD1L in cell lines results in a similar glycine-requiring growth phenotype (Ducker et al, 2016), although mitochondrial protein translation, for which the demand for 1C is quantitatively small, is affected differentially (Minton et al, 2018; Morscher et al, 2018). …”

Proteome overabundance enables respiration but limitation onsets carbon overflow

“…For example, the THF cycle has been demonstrated for developing bioprocesses in S. cerevisiae (Gonzalez de la Cruz et al, 2019). Also, the both C1 metabolism and aspartate biosynthesis are potential anticancer targets as rapidly proliferating mammalian cells can rely upon these metabolites for respiration (Koseki et al, 2018;Meiser et al, 2016;Morscher et al, 2018;Sullivan et al, 2015).…”