Abstract 2365: Mechanisms of mutant p53 targeting to the genome

Abstract

Abstract Mutations in genes often result in tumor formation, especially when these mutations occur in tumor suppressors. TP53 is a tumor suppressor that is frequently mutated in cancer, with mutations in this gene occurring in nearly 50% of all cancer cases. Once mutated, p53 loses its tumor suppressive function while simultaneously gaining oncogenic function. One of the functions that mutant p53 loses is the ability to directly bind to chromatin, however, it has been reported that mutant p53 can still affect the transcriptome of cancer cells via interactions with other transcription factors. One of these interacting partners is ETS2. ETS2 belongs to the ETS transcription factor family, which has 28 family members. This family is characterized by their affinity for an ETS binding site (EBS). EBS’s are present in 50% of all mutant p53 occupied promoters. Other ETS family members have also been linked to mutant p53 but these interactions have either been deemed as weak (ETS1) or have yet to be identified as direct (ERG). To determine which ETS proteins interact with mutant p53 I conducted affinity pull-down assays using purified ETS proteins and purified mutants of p53. My data shows that several ETS proteins interact with mutant p53 better than ETS2. I then sought to determine which residues are important for this interaction through truncation studies in which I used purified truncations of ETS proteins and purified mutants of p53. I found that ERG, one protein that strongly interacted with mutant p53, had two interaction interfaces. This may explain why the interaction is strong. My next step was to determine which ETS proteins are responsible for the targeting of mutant p53 to the genome. To address the requirement for ETS to recruit mutant p53 to chromatin I performed chromatin immunoprecipitation sequencing studies in the presence or absence of different ETS factors to determine differences in mutant p53 binding. For these studies I knocked down ETS2 or ERG prior to performing p53 ChIP-Seq to determine differences in p53 binding to chromatin under these conditions. My analyses of these data indicate that each of the conditions resulted in different p53 binding patterns in the ChIP-Seq and that there is a requirement for ETS in mutant p53 binding.My studies have demonstrated that ETS proteins interact with mutant p53 and that this interaction seems to be required for mutant p53 binding to the genome. My future work will test phenotypes related to ETS/mutant p53 interactions. Ultimately, if ETS/mutant p53 interactions are deemed important for oncogenic function, these will be attractive targets for future drug development. Citation Format: Stephanie Metcalf, Stevie Morris, Peter Hollenhorst. Mechanisms of mutant p53 targeting to the genome [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2365.