Context-Dependent

Objectives: Mutant p53 (mutp53) proteins can exhibit oncogenic gain-of-function (GOF) activities that promote tumor progression; however, the mechanisms underlying context-dependent mutp53 GOF remain poorly understood. We investigated the functional interactions between Methods: Isogenic UM-SCC-1 HNSCC cell lines expressing mutp53 R175H or G245D, alone or in combination with constitutively active PIK3CA H1047R, were generated. Functional assays were performed to assess invasive growth in vitro and metastatic potential in vivo. Optical genome mapping was used to characterize genomic alterations across the engineered cell lines. Results: PI3K activation (PIK3CA H1047R) alone increased primary tumor growth in vivo but did not promote invasive growth in vitro or metastasis in vivo, whereas mutp53 G245D, but not mutp53 R175H, promoted invasive growth in vitro and metastasis in vivo in addition to enhancing primary tumor growth, indicating that primary tumor growth and invasion/metastasis are separable, context-dependent GOF phenotypes in this model. Genomic analyses revealed distinct patterns of alteration among the engineered models: mutp53 R175H and PI3K activation primarily induced chromosomal number variations, whereas mutp53 G245D drove qualitative genomic alterations, including chromosomal insertions, deletions, and translocations. These qualitative genomic changes strongly correlated with the observed GOF phenotypes. Conclusion: In this isogenic UM-SCC-1 HNSCC model, mutp53 GOF was highly context-dependent, varying between the two p53 mutations examined (R175H vs. G245D), and was linked to distinct patterns of genomic instability. In particular, mutp53 G245D-associated qualitative genomic alterations may underlie its oncogenic activity, suggesting that mutp53-driven genomic instability may represent one mechanism associated with context-dependent GOF phenotypes. Level of Evidence: 5.