Profiling and characterising differential deubiquitylase activity during the cell cycle (360G-Wellcome-096567_Z_11_Z)

A family of around eighty deubiquitylases (DUBs) can reverse the effects of ubiquitylation to stabilise proteins, or regulate their activity and localisation. Whilst phosphorylation, dephosphorylation and ubiquitylation play well-established roles in cell cycle progression, our understanding of the role for deubiquitylation is less developed. In a preliminary screen using immunoblotting for tagged ubiquitin activity probes we identified changes in the activity of specific DUBs between mitotic and interphase cell extracts, including USP7 which was highly active during interphase, but inactivated at mitosis. The key goals of this studentship are to: 1. Systematically profile changes in enzymatic activity for the family of DUBsduring key transitions of the cell cycle using pull-down of tagged ubiquitin activity probes coupled with mass spectrometry. 2. Elucidate the mechanism by which cell cycle-dependent DUB activity is regulated. For USP7, and other key cell cycle-regulated DUBs we identify, we will investigate cyclical changes in their phosphorylation status, cellular localisation, and protein interactions. 3. Provide mechanistic insight into the role of these DUBs during the cell cycle. We will establish whether appropriate USP7 regulation is crucial to the deubiquitylation of key substrates, or to normal cell cycle progression using expression of non-regulated mutants.