NuSAP modulates the dynamics of kinetochore microtubules by attenuating MCAK depolymerisation activity.

Chenyu Li,Yih-Cherng Liou,Stella Ying Sun,Ee Sin Chen,Fan Ye,Qiaoyun Yang,Yajun Zhang

doi:10.1038/srep18773

Abstract

Nucleolar and spindle-associated protein (NuSAP) is a microtubule-associated protein that functions as a microtubule stabiliser. Depletion of NuSAP leads to severe mitotic defects, however the mechanism by which NuSAP regulates mitosis remains elusive. In this study, we identify the microtubule depolymeriser, mitotic centromere-associated kinesin (MCAK), as a novel binding partner of NuSAP. We show that NuSAP regulates the dynamics and depolymerisation activity of MCAK. Phosphorylation of MCAK by Aurora B kinase, a component of the chromosomal passenger complex, significantly enhances the interaction of NuSAP with MCAK and modulates the effects of NuSAP on the depolymerisation activity of MCAK. Our results reveal an underlying mechanism by which NuSAP controls kinetochore microtubule dynamics spatially and temporally by modulating the depolymerisation function of MCAK in an Aurora B kinase-dependent manner. Hence, this study provides new insights into the function of NuSAP in spindle formation during mitosis.

Highlights

Kinetochore microtubules directly connect to kinetochores on sister chromatids to generate proper tension and ensure error-free chromosome separation[1,2]
The half-lives (T1/2) of spindle microtubules in Nucleolar and spindle-associated protein (NuSAP)- and NuSAP233–441-overexpressing cells were 67.46 ± 6.32 sec and 92.49 ± 9.32 sec, respectively, considerably longer than those of the control (44.06 ± 4.93 sec) and NuSAP1–233-transfected cells (40.73 ± 6.56 sec) (Fig. 1A,B). These results suggest that NuSAP functions as a microtubule stabiliser through its C-terminal microtubule-binding domain by decreasing microtubule turnover rate
Since the dynamics of Mitotic centromere-associated kinesin (MCAK) localisation are essential for its depolymerisation activity, we investigated the effect of NuSAP on MCAK dynamics by FRAP (Fluorescence Recovery After Photobleaching) assay

Summary

Introduction

Kinetochore microtubules directly connect to kinetochores on sister chromatids to generate proper tension and ensure error-free chromosome separation[1,2]. The dynamics of kinetochore microtubules are tightly controlled by microtubule-associated proteins, motor proteins, and mitotic kinases to precisely align chromosomes at the metaphase plate[3,4,5,6,7]. Aurora B, which is concentrated between sister chromatids from prometaphase to metaphase[31,32], corrects imprecise attachment of kinetochore microtubules and regulates kinetochore microtubule dynamics to ensure accurate chromosome alignment[33,34]. It remains unclear whether additional regulators of MCAK exist during mitosis. Our study provides new insights into the pivotal role of NuSAP in maintaining the fidelity of chromosome segregation during mitosis

Methods

Results

Conclusion