Context specific ubiquitin modification of ribosomes regulates translation under oxidative stress

Abstract

Cellular exposure to oxidative stress is known to activate several translational control pathways through ribosome ubiquitination. Two such pathways, Redox-control of translation by ubiquitin (RTU) and Ribosome-associated quality control (RQC), modify the ribosome with K63-linked polyubiquitination, but result in two different ribosome fates. RTU responds to peroxide stress exposure by inducing a burst or ribosome polyubiquitination and subsequent pause of translational elongation. Alternatively, RQC leads to ubiquitination of already stalled ribosomes and mediates their clearance through subunit dissociation. Understanding how site-specific ribosome ubiquitination induces translation regulation is difficult due to the simultaneous occurrence of these distinct translational control pathways. Here we develop a targeted proteomics approach to quantify site-specific ubiquitin modification across the ribosome in steady state and stress conditions. We found several sites to be differentially ubiquitinated due to stress, including sites known to be targeted by the RQC. The results indicate that the RTU and RQC target distinct ribosome subpopulations within the cell, and differentially contribute to the cellular stress response in an oxidative stressor-specific manner. These findings significantly contribute to the dissection of the complex coordination of translation in response to stress and shed light on the integration of important quality control pathways during cellular response to stress