An intermediate Rb-E2F activity state safeguards proliferation commitment

• 成果类型: Article
• 署名作者: Konagaya, Yumi; Rosenthal, David; Ratnayeke, Nalin; Fan, Yilin; Meyer, Tobias
• 署名单位: Cornell University; Weill Cornell Medicine; Stanford University; RIKEN; Harvard University; Harvard University Medical Affiliates; Massachusetts General Hospital; Harvard University; Harvard University Medical Affiliates; Massachusetts General Hospital; Harvard University; Harvard Medical School
• 刊物名称: Nature
• ISSN/ISSBN: 0028-4493
• DOI: 10.1038/s41586-024-07554-2
• 发表日期: 2024-07-11
• 关键词: retinoblastoma protein; cell-cycle; histone deacetylase; multiple mechanisms; fluorescent protein; activation domain; e2f; phosphorylation; transcription; rb

摘要

Tissue repair, immune defence and cancer progression rely on a vital cellular decision between quiescence and proliferation1,2. Mammalian cells proliferate by triggering a positive feedback mechanism3,4. The transcription factor E2F activates cyclin-dependent kinase 2 (CDK2), which in turn phosphorylates and inactivates the E2F inhibitor protein retinoblastoma (Rb). This action further increases E2F activity to express genes needed for proliferation. Given that positive feedback can inadvertently amplify small signals, understanding how cells keep this positive feedback in check remains a puzzle. Here we measured E2F and CDK2 signal changes in single cells and found that the positive feedback mechanism engages only late in G1 phase. Cells spend variable and often extended times in a reversible state of intermediate E2F activity before committing to proliferate. This intermediate E2F activity is proportional to the amount of phosphorylation of a conserved T373 residue in Rb that is mediated by CDK2 or CDK4/CDK6. Such T373-phosphorylated Rb remains bound on chromatin but dissociates from it once Rb is hyperphosphorylated at many sites, which fully activates E2F. The preferential initial phosphorylation of T373 can be explained by its relatively slower rate of dephosphorylation. Together, our study identifies a primed state of intermediate E2F activation whereby cells sense external and internal signals and decide whether to reverse and exit to quiescence or trigger the positive feedback mechanism that initiates cell proliferation. Cells actively sense external and internal signals to stay quiescent or proliferate, and this trigger relies on being in a reversible primed G1 state of partial retinoblastoma inactivation and E2F activation.