3’-END HOMEOSTASIS OF DNA REPLICATION FORKS IN HEALTH AND DISEASE

My postdoctoral work addressed a long-standing question: how the DNA damage checkpoint prevents cell lethality by preventing irreversible DNA replication fork collapse. I demonstrated that the checkpoint maintains “3’-end homeostasis” at replication forks by preventing excess origin firing and restraining fork progression. This ensures that the number of DNA 3’-ends generated during replication remains below a critical threshold, avoiding depletion of protective factors that simultaneously drive processive DNA synthesis and shield 3’-ends at forks from enzymatic attacks that could lead to irreversible collapse. Moreover, I have identified key enzymes specifically responsible for replication fork collapse. I propose that 3’-end homeostasis at forks -characterised by the dynamic regulation of the number and accessibility of 3’ ends- is a critical factor influencing the fate of replication forks, determining whether they undergo DNA synthesis, DNA repair/fork remodelling, or collapse. This proposal aims to investigate mechanisms of 3’-end homeostasis, leading to replication fork stabilisation in healthy cells, or to fork collapse and cancer when deregulated. This work is directly relevant to understanding how tumour cell death or resistance arise from excessive origin activation in cancer, for example in response to ATR inhibitors, or upon overexpression of oncogenes such as C-MYC, or CYCLIN-E.