The Chromosomal Passenger Complex and its interaction partners: Ingredients for succesful chromosome segregation

Aurora B is the enzymatic moiety of the CPC, that further consists of INCENP, Survivin and Borealin. Together this protein complex plays an essential role in chromosome bi-orientation during mitosis in several ways. It promotes a dynamic KT-MT interface in early mitosis supporting the correction of erroneous attachments. It contributes to the mitotic checkpoint, not only indirectly by the destabilization of incorrect attachments but also directly by promoting the recruitment of Mps1 to kinetochores in early mitosis. In addition, it helps to remove the bulk of cohesin from the chromosomal arms but it also contributes to the maintenance of centromeric cohesion. In addition to early mitosis, the CPC also executes functions during anaphase that contribute to the completion of cytoplasmic division. The complexity and multitude of functions of the CPC are considered to be, in part, directed via the distinct interaction partners of the CPC. We therefore aimed to identify novel interaction partners of the CPC, to further examine the regulation and function of the CPC during mitosis. To do so, we performed large-scale immunoprecipitation experiments coupled to mass spectrometry analysis. In this thesis, we describe the identification of known (Sgo1, HP1, and Mklp2) and potential novel (SIRT1, Protein Phosphatase 6) interaction partners and discuss the potential consequence of the interactions found. We also describe an additional role for Sgo1, one of the already known interaction partners, on regulation of Aurora B activity. Besides Sgo1 aiding in the localization of the CPC to the centromere, and vice versa, we show that Protein Phosphatase 2A (PP2A), which is recruited to Sgo1, can counteract Aurora B activity, therefore balancing the activity of Aurora B. To gain a better molecular understanding of the interaction between Sgo1 and the CPC we used both biochemical and cellular methods to delineate the interaction between Sgo1 and the CPC. In the screens performed, we consistently identified Aurora A as an interaction partner of INCENP and a potential function for Aurora A interacting with INCENP is described. In the end, we summarize and further discuss the results described in this thesis in relation to the literature that is currently available.