Faculty of Life Sciences and Institute of Nanotechnology and Advanced Materials, Bar-llan University, Ramat-Gan 5290002, Israel.
Department of Pharmacology, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599.
Mol Biol Cell. 2020 Apr 1;31(8):725-740. doi: 10.1091/mbc.E19-12-0725. Epub 2020 Jan 29.
E2F8 is a transcriptional repressor that antagonizes E2F1 at the crossroads of the cell cycle, apoptosis, and cancer. Previously, we discovered that E2F8 is a direct target of the APC/C ubiquitin ligase. Nevertheless, it remains unknown how E2F8 is dynamically controlled throughout the entirety of the cell cycle. Here, using newly developed human cell-free systems that recapitulate distinct inter-mitotic and G1 phases and a continuous transition from prometaphase to G1, we reveal an interlocking dephosphorylation switch coordinating E2F8 degradation with mitotic exit and the activation of APC/C. Further, we uncover differential proteolysis rates for E2F8 at different points within G1 phase, accounting for its accumulation in late G1 while APC/C is still active. Finally, we demonstrate that the F-box protein Cyclin F regulates E2F8 in G2-phase. Altogether, our data define E2F8 regulation throughout the cell cycle, illuminating an extensive coordination between phosphorylation, ubiquitination and transcription in mammalian cell cycle.
E2F8 是一种转录抑制因子，在细胞周期、细胞凋亡和癌症的交汇点上拮抗 E2F1。此前，我们发现 E2F8 是 APC/C 泛素连接酶的直接靶标。然而，E2F8 如何在整个细胞周期中被动态控制仍然未知。在这里，我们使用新开发的人类无细胞系统，重现了不同的有丝分裂和 G1 期以及从前期到 G1 期的连续过渡，揭示了一个连锁去磷酸化开关，协调 E2F8 的降解与有丝分裂退出和 APC/C 的激活。此外，我们发现 E2F8 在 G1 期的不同点有不同的蛋白水解速率，这解释了为什么在 APC/C 仍然活跃时，E2F8 在 G1 晚期积累。最后，我们证明了 F 盒蛋白 Cyclin F 在 G2 期调节 E2F8。总的来说，我们的数据定义了 E2F8 在整个细胞周期中的调节，阐明了哺乳动物细胞周期中磷酸化、泛素化和转录之间的广泛协调。
