Human cells adapt to translational errors by modulating protein synthesis rate and protein turnover.

Deregulation of tRNAs, aminoacyl-tRNA synthetases (aaRS) or tRNA modifying enzymes, increase the level of protein synthesis errors (PSE) and are associated with several diseases, but the cause-effect mechanisms of these pathologies remain elusive. To clarify the role of PSE in human biology, we have engineered a HEK293 cell line to overexpress a wild type (Wt) tRNA(Ser) and two tRNA(Ser) mutants that misincorporate serine at non-cognate codon sites. Then, we followed long-term adaptation to PSE of such recombinant cells by analysing cell viability, protein synthesis rate and activation of protein quality control mechanisms (PQC). Engineered cells showed higher level of misfolded and aggregated proteins; activated the ubiquitin-proteasome system (UPS) and the unfolded protein response (UPR), indicative of proteotoxic stress. Adaptation to PSE involved increased protein turnover, UPR up-regulation and altered protein synthesis rate. Gene expression analysis showed that engineered cells presented recurrent alterations in the endoplasmic reticulum, cell adhesion and calcium homeostasis. Herein, we unveil new phenotypic consequences of protein synthesis errors in human cells and identify the protein quality control processes that are necessary for long-term adaptation to PSE and proteotoxic stress. Our data provide important insight on how chronic proteotoxic stress may cause disease and highlight potential biological pathways that support the association of PSE with disease.