Mitotic Kinases That Build a Dynein-Binding Platform on Kinetochores

Mitosis is a series of intricate and complex events that take place during each cell cycle. Regulation of mitosis is especially important at the kinetochore, the protein-rich area between the chromosome arms. Kinetochores are required for several aspects of mitosis, including initial interactions between chromosomes and microtubules (MTs), chromosome movement, and activities associated with the spindle assembly checkpoint (SAC). Cytoplasmic dynein plays a role in one or more of these kinetochore functions; however, the specific contributions of dynein remain under investigation. Recent work has suggested a linked between cytoplasmic dynein regulation and kinetochore kinases Aurora B and MPS-1. Aurora B is an essential mitotic kinase that regulates several aspects of the spindle assembly checkpoint (SAC). Because of this known function, we investigated the role Aurora B activity plays in recruitment of dynein to the kinetochore. Our study determined that Aurora B activity works upstream of the fibrous corona and is required for the proper recruitment of dynein to the kinetochore through regulation of dynein-binding platform assembly. Specifically, Aurora B activity regulates the interaction between Zwint-1 and ZW10 through direct phosphorylation of Zwint-1. Further work revealed that phosphorylation and dephosphorylation of Zwint-1are necessary for accurate significantly impact mitotic progression. Zwint-1 phosphorylation is required during prometaphase for proper assembly of the kinetochore and coordinated Zwint-1 dephoshorylation is required for entrance into anaphase and SAC silencing. Previous work has determined that Aurora B and MPS-1 have overlapping regulatory roles in kinetochore-based mechanisms that may be due to evolutionary redundancy. It was determined that Aurora B and MPS-1 inhibition give similar assembly defects in the dynein-binding platform; however these defects arise from different mechanisms. This study demonstrated that MPS-1 and Aurora B do not have substrate redundancy and that MPS-1 directly phosphorylates Zwilch in the RZZ complex, whereas Aurora B directly phosphorylates Zwint-1. Overall, these findings provide a better understanding of proper kinetochore assembly and regulation of the SAC by phosphorylation.