Cell cycle oscillators underlying orderly proteolysis of E2F8 revealed by ‘static’ and ‘dynamic’ cell-free systems

E2F8 is a transcriptional repressor that antagonizes the canonical cell cycle transcription factor E2F1. Despite the importance of this atypical E2F
family member in cell cycle, apoptosis and cancer, we lack a complete description of the mechanisms that control its dynamics. To address this question,
we developed a complementary set of static and dynamic cell-free systems of human origin, which recapitulate inter-mitotic and G1 phases, and a full
transition from pro-metaphase to G1. This revealed an interlocking molecular switch controlling E2F8 degradation at mitotic exit, involving
dephosphorylation of Cdk1 sites in E2F8 and the activation of APC/CCdh1, but not APC/CCdc20. Further, we revealed a differential stability of E2F8, accounting for its accumulation in late G1 while APC/CCdh1 is still active and suggesting a key role for APC/C in controlling G1-S transcription. Finally, we identified SCF-Cyclin F as the ubiquitin ligase controlling E2F8 in G2-phase. Altogether, our data provide new insights into the regulation of E2F8 throughout the cell cycle, illuminating an extensive coordination between phosphorylation, ubiquitination and transcription in promoting orderly cell cycle progression.