| During mitosis, the duplicated genome is irreversibly distributed over two newly formed cells. A multisubunit assemby -the Anaphase Promoting Complex or Cyclosome (APC/C)- ubiquitinates key regulatory proteins at highly defined mitotic time points. Poly-ubiquitination targets these APC/C substrates for rapid proteolysis by the 26S proteasome. Sequential degradation of APC/C substrates such as Cyclin A, Cyclin B1 and Securin orchestrates cell division with segregation of sister chromatids, essential to guarantee genomic integrity. The question remains how the APC/C recognizes a critical substrate at the right time. To address this important issue, I established an innovative, combinatorial approach of gene silencing, biochemistry and live cell imaging. Hereby, we identified a role for APC/C phosphorylation in controlling Cyclin A destruction. Furthermore, we discovered that APC3 coordinates Cyclin B1 and Securin destruction in metaphase. Our results show that individual subunits, phosphorylation events as well as the intracellular localization of APC/C-complexes contribute to substrate selection. My aim is to build a comprehensive model of how the APC/C coordinates cell division in human cells. I will focus on two central objectives: ? to reveal the contribution of individual subunits -and their regulatory domains- to specific APC/C activity; ? to identify critical determinants of substrate selection by the APC/C. In particular, we will determine complex formation between the APC/C and its substrates, and uncover spatio-temporal dynamics of the APC/C in live cells. This project will lead to the discovery and understanding of fundamental mechanisms by which the APC/C targets its substrates and coordinates cell division. It will also yield important insight into how the APC/C responds to cell cycle checkpoints. Finally, a molecular model of APC/C activity could create new opportunities to design anti-cancer drugs. |
