Gain-of-function p53^R175H blocks apoptosis in a precursor model of ovarian high-grade serous carcinoma

Ovarian high-grade serous carcinoma (HGSC) is a highly lethal malignancy for which early detection is a challenge and treatment of late-stage disease is ineffective. HGSC initiation involves exfoliation of fallopian tube epithelial (FTE) cells which form multicellular clusters called spheroids that colonize and invade the ovary. HGSC contains universal mutation of the tumour suppressor gene TP53. However, not all TP53 mutations are the same, as specific p53 missense mutants contain gain-of-function (GOF) properties that drive tumour formation. Additionally, the role of GOF p53 in spheroid-mediated spread is poorly understood. In this study, we developed and characterized an in vitro model of HGSC based on mutation of TP53 in mouse oviductal epithelial cells (OVE). We discovered increased bulk spheroid survival and increased anchorage-independent growth in OVE cells expressing the missense mutant p53^R175H compared to OVE parental and Trp53ko cells. Transcriptomic analysis on spheroids identified decreased apoptosis signaling due to p53^R175H. Further assessment of the apoptosis pathway demonstrated decreased expression of intrinsic and extrinsic apoptosis signaling molecules due to Trp53 deletion and p53^R175H, but Caspase-3 activation was only decreased in spheroids with p53^R175H. These results highlight this model as a useful tool for discovering early HGSC transformation mechanisms and uncover a potential anti-apoptosis GOF mechanism of p53^R175H.