Hein Jamin B, Garvanska Dimitriya H, Nasa Isha, Kettenbach Arminja N, Nilsson Jakob
Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Science, Copenhagen, Denmark.
Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth College, Hanover, NH.
J Cell Biol. 2021 May 3;220(5). doi: 10.1083/jcb.202012081.
Tight regulation of the APC/C-Cdc20 ubiquitin ligase that targets cyclin B1 for degradation is important for mitotic fidelity. The spindle assembly checkpoint (SAC) inhibits Cdc20 through the mitotic checkpoint complex (MCC). In addition, phosphorylation of Cdc20 by cyclin B1-Cdk1 independently inhibits APC/C-Cdc20 activation. This creates a conundrum for how Cdc20 is activated before cyclin B1 degradation. Here, we show that the MCC component BubR1 harbors both Cdc20 inhibition and activation activities, allowing for cross-talk between the two Cdc20 inhibition pathways. Specifically, BubR1 acts as a substrate specifier for PP2A-B56 to enable efficient Cdc20 dephosphorylation in the MCC. A mutant Cdc20 mimicking the dephosphorylated state escapes a mitotic checkpoint arrest, arguing that restricting Cdc20 dephosphorylation to the MCC is important. Collectively, our work reveals how Cdc20 can be dephosphorylated in the presence of cyclin B1-Cdk1 activity without causing premature anaphase onset.
对靶向细胞周期蛋白B1进行降解的后期促进复合物/细胞分裂周期蛋白20（APC/C-Cdc20）泛素连接酶进行严格调控，对于有丝分裂的保真度至关重要。纺锤体组装检查点（SAC）通过有丝分裂检查点复合物（MCC）抑制Cdc20。此外，细胞周期蛋白B1 - Cdk1对Cdc20的磷酸化独立抑制APC/C-Cdc20的激活。这就产生了一个难题，即在细胞周期蛋白B1降解之前，Cdc20是如何被激活的。在这里，我们表明MCC组分BubR1兼具Cdc20抑制和激活活性，使得两条Cdc20抑制途径之间能够相互作用。具体而言，BubR1作为蛋白磷酸酶2A - B56（PP2A-B56）的底物特异性识别因子，从而在MCC中实现有效的Cdc20去磷酸化。模拟去磷酸化状态的突变型Cdc20能逃避有丝分裂检查点阻滞，这表明将Cdc20去磷酸化限制在MCC中很重要。总体而言，我们的研究揭示了在细胞周期蛋白B1 - Cdk1活性存在的情况下，Cdc20如何去磷酸化而不导致过早进入后期。
