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Increased expression of tryptophan and tyrosine tRNAs elevates stop codon readthrough of reporter systems in human cell lines.

ABSTRACT: Regulation of translation via stop codon readthrough (SC-RT) expands not only tissue-specific but also viral proteomes in humans and, therefore, represents an important subject of study. Understanding this mechanism and all involved players is critical also from a point of view of prospective medical therapies of hereditary diseases caused by a premature termination codon. tRNAs were considered for a long time to be just passive players delivering amino acid residues according to the genetic code to ribosomes without any active regulatory roles. In contrast, our recent yeast work identified several endogenous tRNAs implicated in the regulation of SC-RT. Swiftly emerging studies of human tRNA-ome also advocate that tRNAs have unprecedented regulatory potential. Here, we developed a universal U6 promotor-based system expressing various human endogenous tRNA iso-decoders to study consequences of their increased dosage on SC-RT employing various reporter systems in vivo. This system combined with siRNA-mediated downregulations of selected aminoacyl-tRNA synthetases demonstrated that changing levels of human tryptophan and tyrosine tRNAs do modulate efficiency of SC-RT. Overall, our results suggest that tissue-to-tissue specific levels of selected near-cognate tRNAs may have a vital potential to fine-tune the final landscape of the human proteome, as well as that of its viral pathogens.

SUBMITTER: Beznoskova P

PROVIDER: S-EPMC8136774 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Accurate protein synthesis is a tightly controlled biological process with multiple quality control steps safeguarded by aminoacyl-transfer RNA (tRNA) synthetases and the ribosome. Reduced translational accuracy leads to various physiological changes in both prokaryotes and eukaryotes. Termination of translation is signaled by stop codons and catalyzed by release factors. Occasionally, stop codons can be suppressed by near-cognate aminoacyl-tRNAs, resulting in protein variants with extended C termini. We have recently shown that stop-codon readthrough is heterogeneous among single bacterial cells. However, little is known about how environmental factors affect the level and heterogeneity of stop-codon readthrough. In this study, we have combined dual-fluorescence reporters, mass spectrometry, mathematical modeling, and single-cell approaches to demonstrate that a metabolic stress caused by excess carbon substantially increases both the level and heterogeneity of stop-codon readthrough. Excess carbon leads to accumulation of acid metabolites, which lower the pH and the activity of release factors to promote readthrough. Furthermore, our time-lapse microscopy experiments show that single cells with high readthrough levels are more adapted to severe acid stress conditions and are more sensitive to an aminoglycoside antibiotic. Our work thus reveals a metabolic stress that promotes translational heterogeneity and phenotypic diversity.

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