DNA-contact mutant p53 displaces BRCA2 from chromatin and drives R-loop-associated genome instability

Mutations in the tumor suppressor p53 are among the most frequent events in human cancers. Mutant p53 acquires oncogenic activities beyond the loss of tumor suppressive function. However, how different mutation subtypes differ in their contributions to tumorigenesis remains incompletely understood. Through pan-cancer TCGA analysis, we find that patients with p53 DNA contact mutations exhibit worse clinical outcomes than those carrying conformational mutations. Mechanistically, we demonstrate that the DNA contact mutation p53-R273H forms aberrant condensates that sequester BRCA2 and displace it from chromatin, leading to R-loop accumulation and genomic instability. We further identify the DEAD-box helicase DDX3X as a critical factor required for BRCA2-dependent R-loop resolution. Pharmacological inhibition of DDX3X with RK-33 synergizes with the PARP inhibitor Olaparib, enhancing therapeutic efficacy in p53 DNA contact mutant cancer cells. Our study establishes a pathogenic axis through which the clinically aggressive p53 DNA contact mutations drive genomic instability by dislodging BRCA2 from chromatin and disrupting R-loop homeostasis. These findings suggest a potential therapeutic avenue for treating cancers harboring high-risk p53 DNA contact mutations.