Microtubule poleward flux as a target for modifying chromosome segregation errors

Abstract

Cancer cells often display errors in chromosome segregation, some of which result from improper chromosome alignment at the spindle midplane. Chromosome alignment is facilitated by different rates of microtubule poleward flux between sister kinetochore fibers. However, the role of the poleward flux in supporting mitotic fidelity remains unknown. Here, we introduce the hypothesis that the finely tuned poleward flux safeguards against lagging chromosomes and micronuclei at mitotic exit by promoting chromosome alignment in metaphase. We used human untransformed RPE-1 cells depleted of KIF18A/kinesin-8 as a system with reduced mitotic fidelity, which we rescued by three mechanistically independent treatments, comprising low-dose taxol or co-depletion of the spindle proteins HAUS8 or NuMA. The rescue of mitotic errors was due to shortening of the excessively long overlaps of antiparallel microtubules, serving as a platform for motor proteins that drive the flux, which in turn slowed down the overly fast flux and improved chromosome alignment. In contrast to the prevailing view, the rescue was not accompanied by reduction of overall microtubules growth rates. Speckle microscopy revealed that the improved chromosome alignment in the rescue treatments was associated with slower growth and flux of kinetochore microtubules. In a similar manner, a low-dose taxol treatment rescued mitotic errors in a high-grade serous ovarian carcinoma cell line OVKATE. Collectively, our results highlight the potential of targeting microtubule poleward flux to modify chromosome instability and provide insight into the mechanism through which low doses of taxol rescue mitotic errors in cancer cells.

Microtubule pivoting driven by spindle elongation rescues polar chromosomes to ensure faithful mitosis

“…The pivoting model predicts that cancer cells with poor spindle elongation should have more polar chromosomes, which may be rescued by increasing spindle elongation. To rescue such mitotic errors, we searched the literature for candidate cell lines that show frequent unaligned chromosomes and short spindles (Supplementary Figure 7A) (Barretina et al, 2012; Bird and Hyman, 2008; Cerami et al, 2012; de Bruijn et al, 2023; Gao et al, 2013; Ghandi et al, 2019; Gomes et al, 2022; Klaasen et al, 2022; Kletter et al, 2021; Reinhold et al, 2012; Risteski et al, 2024; Tamura et al, 2020; Tucker et al, 2023). The ovarian carcinoma cell line OVSAHO was identified as the most promising candidate (Figure 7A and Supplementary Figure 7A).…”