Genome safeguarding during mitosis

Safeguarding the genome during mitosis is essential for the accurate transmission of genetic information. While canonical DNA repair pathways are active during interphase, their suppression in mitosis prevents errors that could disrupt chromosome segregation. Cells thus rely on specialized, non-canonical, mechanisms to manage DNA damage during mitosis. Persistent DNA lesions, such as those from replication stress or checkpoint bypass, can cause chromosomal instability, a hallmark of cancer that drives tumor heterogeneity and drug resistance.
This thesis investigates the origins of mitotic DNA damage and the cellular mechanisms that mitigate their consequences. Amplification of proto-oncogenes like CCNE1, encoding Cyclin E1, intensifies replication stress, leading to DNA lesions that persist into mitosis. Using cell line models and fluorescence microscopy, we demonstrate that Cyclin E1-amplified cells rely on a RAD52-mediated mitosis-specific pathway to address these challenges, revealing potential therapeutic vulnerabilities. In addition, we identified RAD52 and FANCA as key mitotic DNA damage response factors using proteomic analysis, uncovering centromere-stabilizing mechanisms and mitosis-specific repair pathways essential for genome integrity.
By integrating findings from genomically unstable cancer models and proteomics-based approaches, this work provides a comprehensive view of how cells manage mitotic DNA damage to maintain chromosomal stability. These insights clarify the relationship between DNA damage responses and cancer progression and highlight new opportunities to target mitotic vulnerabilities for cancer therapy. Overall, this study emphasizes the vital role of genome safeguarding during mitosis in ensuring cellular fidelity and preventing disease.