Coordinated regulation of Citron kinase by CDK1 and Aurora B regulates midbody formation and stability

Many cell division events are regulated by protein phosphorylation, which can result from cross-talk mechanisms among mitotic kinases and phosphatases that have yet to be fully elucidated. Here, we report the characterization of a novel cross talk mechanism by which CDK1 and Aurora B (AURKB) kinases regulate the distribution and interactions of Citron kinase (CIT-K). We show that CDK1 and AURKB phosphorylate two distinct serine residues, S440 and S699, located adjacent to or within the coiled coil domain of CIT-K. S440 and S699 temporal phosphorylation profiles reflect the activity of the kinases responsible for their phosphorylation. Functional analyses using phospho mutants indicate that S699 phosphorylation is important for CIT-K localization and successful cytokinesis, while perturbing S440 phosphorylation leads to abnormal midbody formation and accumulation of post-mitotic midbody remnants (MBRs). Furthermore, we found that phosphorylation at either residue reduces the ability of CIT-K to interact with its midbody partners AURKB, KIF14 and KIF23/MKLP1. Together, our findings indicate that coordinated phosphorylation of CIT-K by CDK1 and AURKB regulates midbody formation and MBR stability by controlling the association of CIT-K with its midbody partners. They expand our understanding of the molecular mechanisms that regulate abscission and can lead to further insights into the role of MBRs in post-mitotic events.