Cytoskeleton-Associated Protein 2 is Required for the Maintenance of Chromosomal Stability by Tethering Spindle Microtubules to their Poles
Open AccessCytoskeleton-Associated Protein 2 is Required for the Maintenance of Chromosomal Stability by Tethering Spindle Microtubules to their PolesErrors in chromosome segregation lead to aneuploidy. Integrity of the microtubule spindle apparatus and intact cell division checkpoints are essential to ensure the fidelity of chromosome distribution into daughter cells. Cytoskeleton-associated protein 2, CKAP2, is a microtubule-associated protein that colocalizes with spindle poles and aids in microtubule stabilization, but the exact function and mechanism of its action are poorly understood. In the present study, RNA interference was utilized to determine the extent to which the expression of CKAP2 plays a role in chromosome segregation in colorectal cancer cells. CKAP2-depleted cells showed a significant increase of multi-polar mitoses and other spindle pole aberrations. Notably, when interrogated for microtubule nucleation capacity, CKAP2-depleted cells showed a very unusual phenotype as early as two minutes after release from mitotic block, consisting of dispersal of newly polymerized microtubule filaments through the entire chromatin region. Nevertheless, spindle poles were formed after one hour of mitotic release, suggesting that centrosome-mediated nucleation remained dominant. Kinetochore-driven microtubule nucleation was not implicated, as there was no colocalization of nascent microtubule filaments with Hec1. Interestingly, there was no effect on the localization of nuclear mitotic apparatus (NuMA) protein in CKAP2-depleted cells. Finally, we showed that suppression of CKAP2 results in a higher incidence of merotelic attachments, anaphase lagging, and chromosomal instability. In conclusion, CKAP2 is involved in tethering the microtubule-minus ends to the spindle pole in early mitosis. Delays in this process may alter the mitotic spindle tension, ultimately promoting merotelic kinetochore-microtubule attachments that result in chromosome lagging and increased chromosomal instability.
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