Abstract 2489: A functional genomics approach to determine mutant p53 gain-of-function mechanisms and phenotypes in tumorigenesis

Two of the most common events in human tumors are mutation of the tumor suppressor gene TP53 and development of aneuploidy. In addition to losing their wild-type (WT) tumor-suppressive function, mutant p53 proteins are proposed to acquire gain-of-function (GOF) activity, leading to novel oncogenic phenotypes. Mechanistic understanding of mutant p53 GOF activities is complicated by the diversity and context-specific nature of reported GOF phenotypes. The study of mutant p53 GOF activities is especially challenging because mutations in p53 are positively correlated with the development of aneuploidy, which can increase heterogeneity through diverse chromosomal alterations and itself contributes to tumorigenesis. To study mutant p53 GOF mechanisms and phenotypes, we used CRISPR/Cas9-mediated genome editing and developed two isogenic epithelial cell line models (one non-transformed and one tumor-derived) that express the most frequently occurring p53 missense mutations (R175H and R273H), are deficient for functional p53 protein (null), or retain the wild-type (WT) protein. In these engineered models, endogenous p53 expression is regulated by the native p53 promoter, thus providing a controlled system for rigorous functional experimentation across different p53 states. Additionally, the use of clonally-derived cell lines originating from the same near diploid parental genetic background allows for assessment of the genomic alterations and resulting molecular heterogeneity following mutation of TP53. Through genomic, transcriptomic, and cellular based assays we have validated our cell line models and found that missense mutant and p53 null cells display loss of p53 function. Through functional genomics analyses comparing isogenic epithelial cells, which initially differed only by the TP53 genotype, we have evaluated the relationship between mutant p53 and aneuploidy and assessed whether our clonal cell lines display several previously reported mutant p53 GOF phenotypes such as altered gene expression, proliferation, metabolism, drug sensitivity, and migration. Further, using lentiviral mediated knockdown of p53 protein we evaluated the dependency of these phenotypes on expression of mutant p53 protein. Finally, data from The Cancer Genome Atlas (TCGA) was used for the analysis of manifestations of clinical mutant p53 GOF phenotypes. The dissection of mutant p53 GOF phenotypes will improve the current understanding of the role of mutant p53 in tumorigenesis. The results generated from these studies have the potential for clinical translation in major types of human cancer that have high-frequency p53 mutation. Citation Format: Lindsay N. Redman-Rivera, Timothy M. Shaver, Hailing Jin, Johanna M. Schafer, Quanhu Sheng, Rachel A. Hongo, Kathryn E. Beckermann, Brian D. Lehmann, Ferrin C. Wheeler, Jennifer A. Pietenpol. A functional genomics approach to determine mutant p53 gain-of-function mechanisms and phenotypes in tumorigenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2489.