Biology subjects

Tzur, A.

Publications and source records attributed to Tzur, A..

3 recordsLinked to original sources

bioRxiv2025

Cdk1 and PP2A constitute a molecular switch controlling orderly degradation of atypical E2Fs

Dynamic oscillations in the phosphorylation and ubiquitination of key proliferative regulators are defining features of the eukaryotic cell cycle. Resetting the cell cycle at the mitosis-to-G1 transition requires activation of the E3 ubiquitin ligase Anaphase-Promoting Complex/Cyclosome (APC/C), which ensures cell cycle irreversibility by targeting dozens of substrates for degradation, safeguarding genome integrity. However, the overall coupling of substrate phosphorylation with target recognition and degradation by the APC/C remains relatively unexplored. As a paradigm for further defining these rules, we focused on E2F7 and E2F8 - atypical E2F-family proteins that coordinate cell cycle gene expression by restraining the pro-proliferative transcriptional activity of E2F1. Leveraging complementary cell and cell-free systems, we demonstrate that flexible domains in the amino-termini of E2F7 and E2F8 contain APC/C recognition motifs adjacent to critical Thr residues, whose phosphorylation by Cdk1 is rate limiting for degradation. The removal of this phosphorylation by PP2A phosphatase serves as a molecular switch, coupling the degradation of E2F7 and E2F8 to the G1 phase, coinciding with the rise of E2F1. Collectively, these findings highlight a critical role for Cdk1-PP2A signaling in controlling the orderly degradation of APC/C substrates, ensuring precisely timed assembly of the transcriptional infrastructure that coordinates cell cycle commitment and progression.

cell biology↗

bioRxiv2021

Protein degradation analysis by affinity microfluidics

Protein degradation mediated by the ubiquitin-proteasome pathway regulates signaling events in all eukaryotic cells, with implications in pathological conditions such as cancer and neurodegenerative diseases. Detection of protein degradation is an elementary need in basic and translational research. In vitro degradation assays, in particular, have been instrumental in the understanding of how cell proliferation and other fundamental cellular processes are regulated. These assays are direct, quantitative and highly informative but also laborious, typically relying on low-throughput polyacrylamide gel-electrophoresis followed by autoradiography or immunoblotting. We present protein degradation on chip (pDOC), a MITOMI-based integrated microfluidic device for discovery and analysis of ubiquitin-mediated proteolysis. The platform accommodates microchambers on which protein degradation is assayed quickly and simultaneously in physiologically relevant environments, using minute amount of reagents. Essentially, pDOC provides a multiplexed, sensitive and colorimetric alternative to the conventional degradation assays, with relevance to biomedical and translational research.

bioengineering↗

bioRxiv2019

Cell cycle oscillators underlying orderly proteolysis of E2F8

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.

cell biology↗