The mitotic spindle protein CKAP2 potently increases formation and stability of microtubules.

Thomas S Mcalear,Susanne Bechstedt

doi:10.7554/elife.72202

Abstract

Cells increase microtubule dynamics to make large rearrangements to their microtubule cytoskeleton during cell division. Changes in microtubule dynamics are essential for the formation and function of the mitotic spindle, and misregulation can lead to aneuploidy and cancer. Using in vitro reconstitution assays we show that the mitotic spindle protein Cytoskeleton-Associated Protein 2 (CKAP2) has a strong effect on nucleation of microtubules by lowering the critical tubulin concentration 100-fold. CKAP2 increases the apparent rate constant ka of microtubule growth by 50-fold and increases microtubule growth rates. In addition, CKAP2 strongly suppresses catastrophes. Our results identify CKAP2 as the most potent microtubule growth factor to date. These finding help explain CKAP2's role as an important spindle protein, proliferation marker, and oncogene.

Highlights

During mitosis, cells build mitotic spindles to faithfully segregate their chromosomes.Assembling mitotic spindles requires a complete rearrangement of the microtubule cytoskeleton, which is driven by the concerted action of microtubule-associated proteins (MAPs) and motor proteins (Kapoor, 2017)
The primary amino acid sequence of Cytoskeleton-Associated Protein 2 (CKAP2) is poorly conserved compared to other MAPs like
Like TPX2, CKAP2 is predicted to be highly intrinsically disordered in solution, and both proteins are significantly enriched in lysines (CKAP2 ~10%, TPX2 ~13%), likely to facilitate interactions with the negatively charged C-terminal tails of tubulin

Summary

Introduction

Cells build mitotic spindles to faithfully segregate their chromosomes. Assembling mitotic spindles requires a complete rearrangement of the microtubule cytoskeleton, which is driven by the concerted action of microtubule-associated proteins (MAPs) and motor proteins (Kapoor, 2017). Microtubule turnover increases significantly in mitosis resulting from increased microtubule nucleation (Piehl et al, 2004) in combination with shorter microtubule lifetimes (Saxton et al, 1984). How exactly microtubule nucleation and growth in mitotic spindles is controlled and if all the major assembly factors have been identified remains an open question. XMAP215/chTOG and TPX2 have been implicated as two major factors in nucleation (Roostalu et al, 2015). XMAP215/chTOG family members are the only protein shown to speed up microtubule growth by more than a factor of 3 in in vitro assays (Brouhard et al, 2008)

Methods

Results

Conclusion