Regulation of the cell division cycle by ubiquitin and ubiquitin-like modifications in yeast

Abstract

The ability of a cell to regulate its cell cycle in response to external stimuli, such as oxidative stress, is important to maintain viability by preventing damage and allowing time for repair. However, the underlying sensing and signalling mechanisms behind cell cycle regulation in response to oxidative stress remain largely unclear. Ubiquitin and ubiquitin-like (Ubl) proteins are a family of highly conserved protein modifiers with a role in many cellular processes including cell cycle regulation. The use of catalytic cysteine residues in the conjugation pathways of ubiquitin and Ubls suggest a mechanism by which these modifiers can be redox-regulated. Thus the aim of this project was to investigate the regulation of the cell division cycle by ubiquitin and Ubls in response to two conditions previously observed to lead to G1 phase cell cycle arrest in S. cerevisiae, treatment with the oxidising agent diamide and glutathione depletion. We find that in response to diamide the ubiquitin E2, Cdc34 is particularly sensitive to oxidation compared to the other E2s examined. Oxidation of Cdc34 was shown to lead to an increase in the stability of the Cdc34 substrate Sic1, coincident with G1 phase arrest. We also find that the Rub1 Ubl modifier is essential for regulation of the cell cycle in response to diamide. Interestingly, we find that Rub1 is also required to prevent budding in response to glutathione depletion. Importantly, here we reveal that SIC1 is essential to maintain viability by preventing replication-induced DNA damage following glutathione depletion. Our studies demonstrate that G1 phase cell cycle arrest in response to diamide and glutathione depletion is multifaceted, involving many of the same proteins but that these proteins are regulated differently in response to the two conditions.