The spindle and kinetochore-associated (Ska) complex enhances binding of the anaphase-promoting complex/cyclosome (APC/C) to chromosomes and promotes mitotic exit.
The spindle and kinetochore-associated (Ska) complex enhances binding of the anaphase-promoting complex/cyclosome (APC/C) to chromosomes and promotes mitotic exit.
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DOI：
10.1091/mbc.e13-07-0421
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发表时间：
2014-03
影响因子：
3.3
通讯作者：
Gorbsky GJ
中科院分区：
文献类型：
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作者：
Sivakumar S;Daum JR;Tipton AR;Rankin S;Gorbsky GJ
Ska 耗尽的细胞在中期停滞。染色体相关的 APC/C 显示出高泛素化活性。 Ska 复合体有助于将 APC/C 定位在染色体上。 Ska 复合体强制定位到动粒增强了 APC/C 定位到染色体并促进 APC/C 活性。纺锤体和着丝粒相关 (Ska) 蛋白复合物是及时发生后期所需的异源三聚体复合物。小干扰 RNA 介导的 Ska 耗竭后出现的主要表型是短暂的排列缺陷，随后是中期停滞，最终导致内聚疲劳。我们发现耗尽 Ska3 的细胞在中期停滞，仅部分降解细胞周期蛋白 B1 和 securin。在用微管药物抑制的细胞中，当纺锤体检查点因检查点激酶 Mps1 的抑制而沉默，或当细胞因 Cdk1 失活而被迫退出检查点沉默下游的有丝分裂时，Ska3 耗尽的细胞表现出较慢的有丝分裂退出。这些结果表明，Ska 复合体除了在促进动粒-微管附着和染色体排列方面发挥作用外，还具有促进后期开始的功能。我们发现 Ska3 和微管都促进后期促进复合物/环体 (APC/C) 的染色体关联。染色体结合的 APC/C 显示出比细胞质 APC/C 明显更强的泛素化活性。 Ska 复合体强制定位于着丝粒，不依赖于微管，导致 APC/C 在染色体上的积累增加，并在诱导有丝分裂退出期间加速细胞周期蛋白 B1 的降解。我们提出 Ska-微管-着丝粒关联促进 APC/C 定位到染色体，从而增强后期的开始和有丝分裂的退出。
Cells depleted of Ska arrest at metaphase. Chromosome-associated APC/C shows high ubiquitylation activity. Ska complex helps to localize APC/C on chromosomes. Forced localization of Ska complex to kinetochores enhances APC/C localization to chromosomes and promotes APC/C activity. The spindle and kinetochore–associated (Ska) protein complex is a heterotrimeric complex required for timely anaphase onset. The major phenotypes seen after small interfering RNA–mediated depletion of Ska are transient alignment defects followed by metaphase arrest that ultimately results in cohesion fatigue. We find that cells depleted of Ska3 arrest at metaphase with only partial degradation of cyclin B1 and securin. In cells arrested with microtubule drugs, Ska3-depleted cells exhibit slower mitotic exit when the spindle checkpoint is silenced by inhibition of the checkpoint kinase, Mps1, or when cells are forced to exit mitosis downstream of checkpoint silencing by inactivation of Cdk1. These results suggest that in addition to a role in fostering kinetochore–microtubule attachment and chromosome alignment, the Ska complex has functions in promoting anaphase onset. We find that both Ska3 and microtubules promote chromosome association of the anaphase-promoting complex/cyclosome (APC/C). Chromosome-bound APC/C shows significantly stronger ubiquitylation activity than cytoplasmic APC/C. Forced localization of Ska complex to kinetochores, independent of microtubules, results in enhanced accumulation of APC/C on chromosomes and accelerated cyclin B1 degradation during induced mitotic exit. We propose that a Ska-microtubule-kinetochore association promotes APC/C localization to chromosomes, thereby enhancing anaphase onset and mitotic exit.