Kinetochore stretching-mediated rapid silencing of the spindle-assembly checkpoint required for failsafe chromosome segregation.

The spindle-assembly checkpoint facilitates mitotic fidelity by delaying anaphase onset in response to microtubule vacancy at kinetochores. Following microtubule attachment, kinetochores receive microtubule-derived force, which causes kinetochores to undergo repetitive cycles of deformation; this phenomenon is referred to as kinetochore stretching. The nature of the forces and the relevance relating this deformation are not well understood. Here, we show that kinetochore stretching occurs within a framework of single end-on attached kinetochores, irrespective of microtubule poleward pulling force. An experimental method to conditionally interfere with the stretching allowed us to determine that kinetochore stretching comprises an essential process of checkpoint silencing by promoting PP1 phosphatase recruitment after the establishment of end-on attachments and removal of the majority of checkpoint-activating kinase Mps1 from kinetochores. Remarkably, we found that a lower frequency of kinetochore stretching largely correlates with a prolonged metaphase in cancer cell lines with chromosomal instability. Perturbation of kinetochore stretching and checkpoint silencing in chromosomally stable cells produced anaphase bridges, which can be alleviated by reducing chromosome-loaded cohesin. These observations indicate that kinetochore stretching-mediated checkpoint silencing provides an unanticipated etiology underlying chromosomal instability and underscores the importance of a rapid metaphase-to-anaphase transition in sustaining mitotic fidelity. [Display omitted] • Intra-kinetochore stretching occurs within a framework of single kinetochores • Kinetochore stretching is an essential process for checkpoint silencing • Kinetochore stretching promotes PP1 recruitment at end-on attached kinetochores • Defective kinetochore stretching and checkpoint silencing are widespread in cancers Uchida et al. show that kinetochore stretching, repetitive cycles of extension and recoiling, depends on the dynamic nature of microtubule tips, instead of the poleward-pulling force. By silencing the mitotic checkpoint, kinetochore stretching promotes a speedy transition from metaphase to anaphase and thereby fail-safe chromosome segregation. [ABSTRACT FROM AUTHOR]