Hagting Anja, Den Elzen Nicole, Vodermaier Hartmut C, Waizenegger Irene C, Peters Jan-Michael, Pines Jonathon
Wellcome/Cancer Research UK Institute, Cambridge CB2 1QR, United Kingdom.
J Cell Biol. 2002 Jun 24;157(7):1125-37. doi: 10.1083/jcb.200111001. Epub 2002 Jun 17.
Progress through mitosis is controlled by the sequential destruction of key regulators including the mitotic cyclins and securin, an inhibitor of anaphase whose destruction is required for sister chromatid separation. Here we have used live cell imaging to determine the exact time when human securin is degraded in mitosis. We show that the timing of securin destruction is set by the spindle checkpoint; securin destruction begins at metaphase once the checkpoint is satisfied. Furthermore, reimposing the checkpoint rapidly inactivates securin destruction. Thus, securin and cyclin B1 destruction have very similar properties. Moreover, we find that both cyclin B1 and securin have to be degraded before sister chromatids can separate. A mutant form of securin that lacks its destruction box (D-box) is still degraded in mitosis, but now this is in anaphase. This destruction requires a KEN box in the NH2 terminus of securin and may indicate the time in mitosis when ubiquitination switches from APCCdc20 to APCCdh1. Lastly, a D-box mutant of securin that cannot be degraded in metaphase inhibits sister chromatid separation, generating a cut phenotype where one cell can inherit both copies of the genome. Thus, defects in securin destruction alter chromosome segregation and may be relevant to the development of aneuploidy in cancer.
有丝分裂的进程由关键调节因子的顺序性降解所控制，这些调节因子包括有丝分裂周期蛋白和分离酶抑制蛋白，后者是后期的一种抑制剂，其降解是姐妹染色单体分离所必需的。在这里，我们利用活细胞成像技术来确定人类分离酶抑制蛋白在有丝分裂中降解的确切时间。我们发现，分离酶抑制蛋白的降解时间由纺锤体检查点设定；一旦检查点得到满足，分离酶抑制蛋白在中期开始降解。此外，迅速重新施加检查点会使分离酶抑制蛋白的降解失活。因此，分离酶抑制蛋白和周期蛋白B1的降解具有非常相似的特性。此外，我们发现，在姐妹染色单体能够分离之前，周期蛋白B1和分离酶抑制蛋白都必须被降解。一种缺乏其破坏框（D-box）的分离酶抑制蛋白突变体在有丝分裂中仍会被降解，但现在是在后期。这种降解需要分离酶抑制蛋白NH2末端的一个KEN框，这可能表明有丝分裂中泛素化从后期促进复合物/细胞周期蛋白依赖性激酶20（APCCdc20）转换为后期促进复合物/细胞周期蛋白依赖性激酶1（APCCdh1）的时间。最后，一种在中期不能被降解的分离酶抑制蛋白D-box突变体抑制姐妹染色单体分离，产生一种切割表型，即一个细胞可以继承基因组的两个拷贝。因此，分离酶抑制蛋白降解的缺陷会改变染色体分离，可能与癌症中非整倍体的发生有关。
