Disrupted Control of Origin Activation Promotes Genomic Instability Upon Loss of the Pole4 and Trp53 Tumour Suppressors

The maintenance of genome stability relies on the coordinated control of origin activation and replication fork progression. How the interplay between these processes impacts human genetic disease and cancer remains incompletely characterized. Here we show that mouse cells lacking Pole4 and featuring Pole instability exhibit impaired genome-wide activation of DNA replication origins. Lack of POLE4 leads to proteasome-dependent Pole degradation prior to CMG (CDC45/MCM2-7/GINS) helicase formation and origin activation. Strikingly, Trp53 ablation in primary Pole4 knock-out cells rescued Pole levels and origin activation and reduced DNA damage levels in a transcription-dependent manner. Transcriptome analysis of primary Pole4/Trp53 double knock out cells revealed that the TRP53/CDKN1A/E2F axis maintains an appropriate level of replication factors during unchallenged S-phase. Loss of this control mechanism deregulates origin activation, perturbs genome-wide replication fork progression and induces fork stalling and DNA damage. While our data support an impaired origin activation model for a group of genetic diseases affecting CMG formation, we additionally propose that loss of the TRP53/CDKN1A/E2F axis induces inappropriate origin activation and deregulates genome wide fork progression. This phenomenon has broad implications for genetic instability and therapeutic targeting in cancer.