The spindle protein CKAP2 regulates microtubule dynamics and ensures faithful chromosome segregation

Abstract

AbstractRegulation of microtubule dynamics by microtubule-associated proteins (MAPs) is essential for mitotic spindle assembly and chromosome segregation. Altered microtubule dynamics, particularly increased microtubule growth rates, were found to be a contributing factor for the development of chromosomal instability, which potentiates tumorigenesis. The MAP XMAP215/CKAP5 is the only known microtubule growth factor, and whether other MAPs regulate microtubule growth in cells is unclear. Our recentin vitroreconstitution experiments have demonstrated that Cytoskeleton-Associated Protein 2 (CKAP2) increases microtubule nucleation and growth rates, and here we find that CKAP2 is also an essential microtubule growth factor in cells. By applying CRISPR-Cas9 knock-in and knock-out as well as microtubule plus-end tracking live cell imaging, we show that CKAP2 is a mitotic spindle protein that ensures faithful chromosome segregation by regulating microtubule growth. Live cell imaging of endogenously-labelled CKAP2 showed that it localizes to the spindle during mitosis, and rapidly shifts its localization to the chromatin upon mitotic exit before being degraded. Cells lacking CKAP2 display reduced microtubule growth rates and an increased proportion of chromosome segregation errors and aneuploidy that may be a result of an accumulation of kinetochore-microtubule mis-attachments. Microtubule growth rates and chromosome segregation fidelity can be rescued upon CKAP2 expression in knock-out cells, revealing a direct link between CKAP2 expression and microtubule dynamics. Our results unveil a role of CKAP2 in regulating microtubule growth in cells and provide a mechanistic explanation for the oncogenic potential of CKAP2 misregulation.Significance statementCell division is accomplished by the assembly of a mitotic spindle composed of microtubules that segregate the chromosomes. Cells with altered microtubule dynamics frequently mis-segregate chromosomes and develop aneuploidy, which contributes to cancer development. However, how microtubule dynamics are regulated in cells is not entirely understood. Here, using CRISPR-Cas9 genome editing and live cell imaging, we find that the microtubule-associated protein CKAP2 tightly regulates microtubule growth and ensures the proper segregation of chromosomes. Cells lacking CKAP2 develop errors in chromosome segregation and aneuploidy due to a substantial decline in microtubule growth rates. The essential role of CKAP2 in the regulation of microtubule growth provides an explanation for the oncogenic potential of CKAP2 misregulation.ClassificationBiological Sciences – Cell Biology