Molecular Dissection Of PLK1-Aurora B Kinase Crosstalk Underlying Cellular Dynamics In Mitosis

Cell cycle is a complicated and delicate process with huge protein network, it works properly so that genetic material can be distributed to daughter cells accurately. Any errors during mitosis can lead to aneuploidy and genetic instability, therefore cell death or cancer. So it is of great importance to make sure how cellular dynamics and plasticity are regulated and orchestrated during the process. With the use of bio-sensor and small molecules, I explored the molecular delineation of accurate chromosome congress and segregation.The kinetochore is a super-molecular complex assembled at each centromere in eukaryotes. It provides a chromosomal attachment point for the mitotic spindle, linking the chromosome to the microtubules and functions in initiating, controlling and monitoring the movements of chromosomes during mitosis. The kinetochore of animal cells contains two functional domains; that is, the inner kinetochore, which is tightly and persistently associated with centromeric DNA sequences throughout the cell cycle and the outer kinetochore which is composed of many dynamic protein complexes that interact with microtubules only during mitosis.During prophase Aurora B regulates global events such as changes to mitotic chromatin, whereas in prometaphase each mitotic chromosome is autonomously controlled by Aurora B activity to generate spindle checkpoint signals and correct kinetochore-microtubule attachments. Chromosomal passengers are a group of evolutionarily conserved proteins orchestrating chromosome segregation and cytokinesis. This protein complex containing Aurora B, survivin, INCENP and borealin, is relocated from the kinetochore to the central spindle upon anaphase onset. Perturbation of their function results in defects in metaphase chromosome alignment, chromosome segregation and cytokinesis. The current working model argues that survivin is responsible for docking Aurora B to the centromere whereas its precise role in Aurora B activation has been unclear. It has been recently proposed that Aurora B substrates can inhibit kinase activation, and this is relieved by phosphorylation of these substrates by PLK1. However, it was unclear whether and how PLK1 and Aurora B cooperate in centromere during mitosis.Duing mitosis, chromosome congress and segregation are regulated by kinetochore-microtubule attachment, in which kinase and protease signal cascade play criticle role. As the key kinases, PLK1 and Aurora B interact with each other in many ways to support the process. However it’s not clear how they affect each other, how their feed-back loop work. Using a fluorescence resonance energy transfer based sensor, we monitored PLK1 kinase activity during mitosis, and demonstrated Aurora B maintain PLK1 kinase activity on kinetochores through phosphorylation of PLK1 T210.Therefore demonstrated the interaction between Aurora B and PLK1 during mitosis.In conclusion, we identified a novel regulatory mechanism underlying Aurora B kinase priming by PLK1 phosphorylation. Our biochemical characterization demonstrates that survivin is a substrate of PLK1 in mitosis, which is critical for orchestrating Aurora B activity at the centromere and accurate chromosome segregation. We also demonstrate the interaction, regulation and dynamic plasticity between PLK1 and Aurora B, shed light on the mechanism of PLK1-Aurora B regulation in mitosis.