Phosphorylation at Threonine 288 by Cell Cycle Checkpoint Kinase 2 (CHK2) Controls Human Monopolar Spindle 1 (Mps1) Kinetochore Localization

Background: hMps1 and CHK2 are both required to safeguard the mitotic checkpoint, and yet the relationship between the two proteins is unclear. Results: hMps1 Thr-288 mutation causes misaligned chromosomes and polyploidy as a result of defective kinetochore localization. Conclusion: Phosphorylation of hMps1 Thr-288 by CHK2 facilitates kinetochore localization of hMps1. Significance: The study provides insights on the involvement of CHK2 in SAC through hMps1. Human Mps1 (hMps1) is a mitotic checkpoint kinase responsible for sensing the unattached and tensionless kinetochore. Despite its importance in safeguarding proper chromosome segregation, how hMps1 is recruited to the kinetochore remains incompletely understood. Here, we demonstrate that phosphorylation at Thr-288 by the cell cycle checkpoint kinase CHK2 is involved in this process. We discovered that the phosphorylation-deficient T288A mutant has an impaired ability to localize to the kinetochore and cannot reestablish the mitotic checkpoint in hMps1-depleted cells. In support, we found that nocodazole induced hMps1 phosphorylation at the previously identified CHK2 site Thr-288 and that this could be detected at the kinetochore in a CHK2-dependent manner. Mechanistically, phosphorylation at Thr-288 promoted the interaction with the KMN (KNL1-Mis12-Ndc80 network) protein HEC1. Forced kinetochore localization corrected the defects associated with the T288A mutant. Our results provide evidence of a newly identified hMps1 phosphorylation site that is involved in the mitotic checkpoint and that CHK2 contributes to chromosomal stability through hMps1.