Potapova Tamara A, Daum John R, Pittman Bradley D, Hudson Joanna R, Jones Tara N, Satinover David L, Stukenberg P Todd, Gorbsky Gary J
Program in Molecular, Cell and Developmental Biology, Oklahoma Medical Research Foundation, 825 NE 13th Street, Oklahoma City, Oklahoma 73104, USA.
Nature. 2006 Apr 13;440(7086):954-8. doi: 10.1038/nature04652.
A guiding hypothesis for cell-cycle regulation asserts that regulated proteolysis constrains the directionality of certain cell-cycle transitions. Here we test this hypothesis for mitotic exit, which is regulated by degradation of the cyclin-dependent kinase 1 (Cdk1) activator, cyclin B. Application of chemical Cdk1 inhibitors to cells in mitosis induces cytokinesis and other normal aspects of mitotic exit, including cyclin B degradation. However, chromatid segregation fails, resulting in entrapment of chromatin in the midbody. If cyclin B degradation is blocked with a proteasome inhibitor or by expression of non-degradable cyclin B, Cdk inhibitors will nonetheless induce mitotic exit and cytokinesis. However, if after mitotic exit, the Cdk1 inhibitor is washed free from cells in which cyclin B degradation is blocked, the cells can revert back to M phase. This reversal is characterized by chromosome recondensation, nuclear envelope breakdown, assembly of microtubules into a mitotic spindle, and in most cases, dissolution of the midbody, reopening of the cleavage furrow, and realignment of chromosomes at the metaphase plate. These findings demonstrate that proteasome-dependent degradation of cyclin B provides directionality for the M phase to G1 transition.
细胞周期调控的一个指导性假说认为，受调控的蛋白水解作用限制了某些细胞周期转换的方向性。在此，我们针对有丝分裂退出过程对这一假说进行验证，有丝分裂退出过程由细胞周期蛋白依赖性激酶1（Cdk1）激活剂细胞周期蛋白B的降解所调控。向处于有丝分裂期的细胞中应用化学Cdk1抑制剂可诱导胞质分裂以及有丝分裂退出的其他正常过程，包括细胞周期蛋白B的降解。然而，染色单体分离失败，导致染色质被困在中体中。如果用蛋白酶体抑制剂或通过表达不可降解的细胞周期蛋白B来阻断细胞周期蛋白B的降解，Cdk抑制剂仍会诱导有丝分裂退出和胞质分裂。但是，如果在有丝分裂退出后，将Cdk1抑制剂从细胞周期蛋白B降解被阻断的细胞中冲洗掉，这些细胞会恢复到M期。这种逆转的特征是染色体重新凝聚、核膜破裂、微管组装成有丝分裂纺锤体，并且在大多数情况下，中体溶解、分裂沟重新开放以及染色体在中期板重新排列。这些发现表明，细胞周期蛋白B的蛋白酶体依赖性降解为从M期到G1期的转换提供了方向性。
