Inefficient degradation of cyclin B1 re-activates the spindle checkpoint right after sister chromatid disjunction
Inefficient degradation of cyclin B1 re-activates the spindle checkpoint right after sister chromatid disjunction
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DOI：
10.4161/cc.29336
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发表时间：
2014-08-01
期刊：
影响因子：
4.3
通讯作者：
Wolthuis, Rob M. F.
中科院分区：
文献类型：
--
作者：
Clijsters, Linda;van Zon, Wouter;Wolthuis, Rob M. F.
姐妹染色单体分离会使着丝点突然失去张力，这在原理上可以在后期重新激活纺锤体检查点。这种所谓的“后期问题”可能是通过细胞周期蛋白B1-Cdk1的及时失活来避免的，这可能会阻止纺锤体张力传感的Aurora B激酶在后期失去张力时破坏着丝点-微管相互作用的稳定性。然而，究竟如何阻止纺锤体检查点重新激活仍然不清楚。在这里，我们研究了不同程度的细胞周期蛋白B1稳定如何影响中期和后期纺锤体检查点。表达cyclin B1强稳定（R42A）突变体的细胞正常降解APC/C-Cdc20底物，表明检查点释放不受cyclin B1- cdk1高活性的抑制。然而，在APC/C-Cdc20活性的初始波之后，纺锤体检查点在具有未粘聚姐妹染色单体的细胞中返回。细胞周期蛋白B1的赖氨酸突变体的表达仅被轻微低效地降解，允许正常的中期到后期转变。然而，引人注目的是，在后期发作后10-15分钟，纺锤体检查点在未降解细胞周期蛋白B1突变体的细胞中返回。当细胞周期蛋白B1停留在后期时，细胞质分裂停止，从分离的姐妹染色单体向纺锤体中间区的转移被阻断。这种后期阻滞需要极光B和Mps1的活动。总之，我们的研究结果表明，完全去除细胞周期蛋白B1对于防止姐妹染色单体分离后纺锤体检查点的返回是必不可少的。推测，后期APC/C-Cdc20活性的增加有助于保持细胞周期蛋白B1的低水平。
Sister chromatid separation creates a sudden loss of tension on kinetochores, which could, in principle, re-activate the spindle checkpoint in anaphase. This so-called "anaphase problem" is probably avoided by timely inactivation of cyclin B1-Cdk1, which may prevent the spindle tension sensing Aurora B kinase from destabilizing kinetochore-microtubule interactions as they lose tension in anaphase. However, exactly how spindle checkpoint re-activation is prevented remains unclear.Here, we investigated how different degrees of cyclin B1 stabilization affected the spindle checkpoint in metaphase and anaphase. Cells expressing a strongly stabilized (R42A) mutant of cyclin B1 degraded APC/C-Cdc20 substrates normally, showing that checkpoint release was not inhibited by high cyclin B1-Cdk1 activity. However, after this initial wave of APC/C-Cdc20 activity, the spindle checkpoint returned in cells with uncohesed sister chromatids. Expression of a lysine mutant of cyclin B1 that is degraded only slightly inefficiently allowed a normal metaphase-to-anaphase transition. Strikingly, however, the spindle checkpoint returned in cells that had not degraded the cyclin B1 mutant 10-15 min after anaphase onset. When cyclin B1 remained in late anaphase, cytokinesis stalled, and translocation of INCENP from separated sister chromatids to the spindle midzone was blocked. This late anaphase arrest required the activity of Aurora B and Mps1. In conclusion, our results reveal that complete removal of cyclin B1 is essential to prevent the return of the spindle checkpoint following sister chromatid disjunction. Speculatively, increasing activity of APC/C-Cdc20 in late anaphase helps to keep cyclin B1 levels low.