Oral Presentation Lowy Cancer Symposium 2015

Global Phosphoproteomic Mapping Reveals How Phosphatases Control Mitotic Exit And Maintain Genome Stability (#4)

Rachael McCloy 1 , Benjamin L Parker 2 , Samuel Rogers 1 , Rima Chaudhuri 2 , Velimir Gayevskiy 1 , Nolan J Hoffman 2 , Naveid Ali , Roger Daly 3 , David E James 2 , Thierry Lorca 4 , Anna Castro 4 , Andrew Burgess 1
  1. Kinghorn Cancer Center, Garvan Institute of Medical Research, Darlinghurst, NSW, Australia
  2. The Charles Perkins Centre, School of Molecular Bioscience and Sydney Medical School, The University of Sydney, Sydney, NSW, Australia
  3. Department of Biochemistry and Molecular Biology, School of Biomedical Sciences , Monash University, Melbourne, VIC, Australia
  4. Centre de Recherche de Biochimie Macromoléculaire, CNRS, Montpellier, FRANCE

Entry into mitosis is driven by the coordinated phosphorylation of thousands of proteins. For the cell to complete mitosis and divide into two identical daughter cells it must regulate dephosphorylation of these proteins in a highly ordered, temporal manner. We have shown that disruption of this order causes significant and catastrophic mitotic defects leading to aneuploidy [1,2], a hallmark of genomic instability and cancer. Currently we do not know which phosphatase/s control mitotic exit or the substrates that they regulate. To answers these questions, we performed a large unbiased, global analysis to map the very first dephosphorylation events that occur as cells exit mitosis. Using this method we identified and quantified the modification of >16,000 phosphosites on sites on >3,300 unique proteins during early mitotic exit, providing up to 8 fold greater resolution than previous studies. Only a small fraction (~10%) of phosphorylation sites were dephosphorylated during early mitotic exit and these occurred on proteins involved in critical early exit events, including organization of the mitotic spindle, the spindle assembly checkpoint, and reformation of the nuclear envelope. Surprisingly this enrichment was observed across all kinase consensus motifs, indicating that it is independent of the upstream phosphorylating kinase. Therefore dephosphorylation of these sites is likely determined by the specificity of phosphatase/s rather than the activity of kinase/s. Dephosphorylation was significantly affected by the amino acids at and surrounding the phosphorylation site, with several unique evolutionarily conserved amino acids correlating strongly with phosphorylation status. These data provide a potential mechanism for the specificity of phosphatases, and how they co-ordinate the ordered events of mitotic exit. In summary, our results provide a global overview of the phosphorylation changes that occur during the very first stages of mitotic exit, providing novel mechanistic insight into how phosphatase/s specifically regulate this critical transition, which could have significant implications on our understanding of how aberrant mitotic divisions drive genomic instability and cancer development.

  1. McCloy, R. A. et al. Partial inhibition of Cdk1 in G2 phase overrides the SAC and decouples mitotic events. Cell Cycle 13, 1400–1412 (2014).
  2. Burgess, A. et al. Loss of human Greatwall results in G2 arrest and multiple mitotic defects due to deregulation of the cyclin B-Cdc2/PP2A balance. PNAS 107, 12564–12569 (2010).