P53 deficiency triggers hypertranscription, inducing nucleotide insufficiency causing replication stress, and genomic instability

P53 prevents DNA damage by inducing repair processes, cell cycle arrest or apoptosis. P53 loss leads to replication stress and genomic instability, yet the mechanisms underlying these effects and their contribution to catastrophic genomic events such as chromothripsis remain poorly understood. Using patient-derived fibroblasts with germline p53 variants, that spontaneously undergo chromothripsis, and p53-downregulated fibroblasts, we discovered that p53 loss leads to aberrant transcriptional upregulation, increasing nucleotide consumption while simultaneously decreasing nucleotide biosynthesis. This imbalance in production and consumption results in insufficient nucleotide pools, leading to replication stress and genomic instability, which are rescued by nucleoside supplementation or transcription normalization. The replication stress triggers telomere dysfunction, micronuclei formation, and ultimately chromothripsis. Emerging dominant chromothriptic clones exhibit normal DNA replication, telomere stabilization, and ecDNA, highlighting critical features for clonal selection. Hence, p53 coordinates transcription and nucleotide pools, crucial for maintaining genomic stability and preventing early cancer development.