The roles and regulation of ubiquitin/ubiquitin-like protein conjugation pathways in responses to oxidative stress in Schizosaccharomyces pombe

Abstract

Ubiquitin and ubiquitin-like proteins (Ubls) are conjugated to proteins to regulate activity, stability, localisation or function. Ubiquitin/Ubl conjugation pathways are highly conserved in eukaryotes, and usually involve activating enzymes (E1s) and conjugating enzymes (E2s) specific for each ubiquitin/Ubl. Many studies have suggested that ubiquitin/Ubl conjugation pathways are important for oxidative stress resistance. However, there is much to learn regarding the roles of these pathways in oxidative stress responses. Additionally, limited studies in mammalian cells and yeast have indicated that certain E1s and E2s are redox-regulated, although how this relates to stress resistance is largely unclear, and these regulatory mechanisms have never been shown to be conserved in eukaryotes. Here, the roles and regulation of ubiquitin/Ubl conjugation pathways in responses to oxidative stress are investigated in Schizosaccharomyces pombe. Firstly, while our previous research has shown that the budding yeast E2, Cdc34, is redox-regulated, it was unclear whether ubiquitination is redox-regulated in other organisms. Results presented here show that the fission yeast Cdc34 homologue, Ubc15, is redox-regulated, suggesting that redox regulation of specific ubiquitination events may be conserved. Furthermore, Ubc15 is important for resistance to oxidative stress in S. pombe. Secondly, the Ubl Urm1 is found to be important for resistance to a range of stress conditions in S. pombe, as in S. cerevisiae, thus demonstrating for the first time that urmylation has conserved roles in stress resistance in eukaryotes. Additionally, urmylation controls the activation of a conserved mitogen-activated protein kinase during exposure to H2O2. Finally, although autophagic Ubl conjugation is not important for oxidative stress responses in S. pombe, these investigations have identified an E2 with roles in oxidative stress responses and cell cycle control. Taken together, these findings advance the study of the roles of ubiquitin/Ubl conjugation pathways in responses to oxidative stress, and offer exciting prospects for future investigations.