Department of Biochemistry, The Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa 31096, Israel.
Proc Natl Acad Sci U S A. 2024 Sep 10;121(37):e2413089121. doi: 10.1073/pnas.2413089121. Epub 2024 Sep 4.
The ubiquitin ligase Anaphase-Promoting Complex/Cyclosome (APC/C) and its regulatory protein Cdc20 play important roles in the control of different stages of mitosis. APC/C associated with Cdc20 is active and promotes metaphase-anaphase transition by targeting for degradation inhibitors of anaphase initiation. Earlier in mitosis, premature action of APC/C is prevented by the mitotic checkpoint (or spindle assembly checkpoint) system, which ensures that anaphase is not initiated until all chromosomes are properly attached to the mitotic spindle. The active mitotic checkpoint system promotes the assembly of a Mitotic Checkpoint Complex (MCC), which binds to APC/C and inhibits its activity. The interaction of MCC with APC/C is strongly enhanced by Cdc20 bound to APC/C. While the association of Cdc20 with APC/C was known to be essential for both these stages of mitosis, it was not known how Cdc20 remains bound in spite of ongoing processes, phosphorylation and ubiquitylation, that stimulate its release from APC/C. We find that MCC strongly inhibits the release of Cdc20 from APC/C by the action of mitotic protein kinase Cdk1-cyclin B. This is not due to protection from phosphorylation of specific sites in Cdc20 that affect its interaction with APC/C. Rather, MCC stabilizes the binding to APC/C of partially phosphorylated forms of Cdc20. MCC also inhibits the autoubiquitylation of APC/C-bound Cdc20 and its ubiquitylation-promoted release from APC/C. We propose that these actions of MCC to maintain Cdc20 bound to APC/C in mitosis are essential for the control of mitosis during active mitotic checkpoint and in subsequent anaphase initiation.
泛素连接酶有丝分裂后期促进复合物/细胞周期蛋白（APC/C）及其调节蛋白 Cdc20 在控制有丝分裂的不同阶段中发挥重要作用。与 Cdc20 结合的 APC/C 是活跃的，通过靶向降解有丝分裂起始抑制剂来促进中期-后期转变。在有丝分裂早期，过早的 APC/C 作用被有丝分裂检查点（或纺锤体组装检查点）系统所阻止，该系统确保所有染色体都正确附着到有丝分裂纺锤体后才开始后期。活跃的有丝分裂检查点系统促进有丝分裂检查点复合物（MCC）的组装，该复合物与 APC/C 结合并抑制其活性。MCC 与 APC/C 的相互作用通过与 APC/C 结合的 Cdc20 强烈增强。虽然已知 Cdc20 与 APC/C 的结合对于有丝分裂的这两个阶段都是必不可少的，但不知道尽管存在刺激其从 APC/C 释放的进行中的过程、磷酸化和泛素化，Cdc20 如何仍然保持结合。我们发现，MCC 通过有丝分裂蛋白激酶 Cdk1-cyclin B 的作用强烈抑制 Cdc20 从 APC/C 的释放。这不是由于保护 Cdc20 中的特定磷酸化位点免受影响其与 APC/C 相互作用的磷酸化。相反，MCC 稳定了部分磷酸化形式的 Cdc20 与 APC/C 的结合。MCC 还抑制 APC/C 结合的 Cdc20 的自泛素化及其促进从 APC/C 的泛素化释放。我们提出，MCC 对维持 APC/C 结合的 Cdc20 在有丝分裂中的结合的这些作用对于有丝分裂检查点活跃期间和随后的后期起始期间的有丝分裂控制是必不可少的。
