Abstract 3035: Bridging the gap: Exploring the roles of ETS- coactivator interactions in promoting prostate cancer
Authors: Mills Kaitlyn M. , Downing Nicholas , Metcalf Stephanie , Hollenhorst Peter 
Published: March 2024

Abstract
The ETS family of transcription factors is comprised of 28 members that all share a common C- terminal DNA-binding domain. ETS play essential roles in developmental processes, such as stem cell maintenance, blood vessel formation, and cellular fate. While absent in the normal prostate, four members of the ETS family become expressed in prostate tumors: ETV1, ETV4, ETV5 and ERG. Our lab has previously classified these proteins as oncogenic ETS for their ability to promote cellular migration in normal prostate epithelial RWPE1 cells. Transcription factors may need to interact with additional proteins to serve oncogenic roles. My research explores the interactions between 1) ETV1 and EWS, as well as 2) ERG and p53. Our lab has established that ETV1, ETV4 and ETV5 form essential interactions with EWS, a transcriptional coactivator that promotes ETS activity. In prostate tumors, chromosomal rearrangements result in the N-terminal truncations of ETV1, ETV4 and ETV5. I hypothesize that the EWS interaction domain is retained and that these truncated ETVs will remain oncogenic. Pulldown assays using purified full-length and truncated ETV1 suggests EWS interacts with both N-terminal and C-terminal portions ETV1. I am attempting to express truncated ETV1, ETV4 and ETV5 in RWPE1 cells. Upon stable expression, I will evaluate their interactions with EWS and their ability to promote migration in vitro. To identify putative proteins that bridge EWS to ETV1, immunoprecipitation mass spectrometry will be used. Mutations in p53, a tumor suppressor protein, promote oncogenesis and occur in nearly half of all cancer cases. We hypothesize that mutant p53 interacts with ETS to promote its recruitment to new genomic sites. Previous studies demonstrate that mutant p53 binds ETS2 at a higher affinity than wildtype p53 and we have expanded this list of interacting ETS to include ERG. We seek to explore whether ERG and mutant p53 cooperate to promote oncogenic phenotypes. I successfully cloned wildtype p53, mutant p53 (R248W) and double-mutant p53 (R248W, T81A) into a retroviral backbone. I then transduced RWPE1-Vector and RWPE1-ERG expressing cells to express these constructs. Although additional replicates are needed, it appears that mutant p53 promotes colony formation in both cell types relative to wildtype p53. I plan to validate these observations and generate an appropriate negative control cell line before extending into a mouse model. Through the continuation of this work, I will provide critical insight into the molecular mechanisms by which a subset of ETS factors achieve oncogenic function. We address the contributions of DNA-binding specificity and coactivator interactions in promoting the phenotypes associated with prostate cancer.
Citation Format: Kaitlyn M. Mills, Nicholas Downing, Stephanie Metcalf, Peter Hollenhorst. Bridging the gap: Exploring the roles of ETS- coactivator interactions in promoting prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3035.