Abstract 1212: Mutant p53 stabilizes and protects the transcription factor ETS2 from proteasomal degradation by the ubiquitin ligase COP1/DET1

Abstract

Abstract Genetic mutations of the tumor suppressor gene TP53 contribute to a great majority of human cancers. One mechanism by which mutant TP53 (mtp53) acts is through the interaction with other transcription factors, which can either enhance or repress the transcription of their target genes. Mtp53 preferentially interacts with ETS2, an ETS transcription factor, and increases its stability. This results in an increase of the expression of ETS target genes that are associated with the transition of normal cells into tumor cells. Previous studies have shown that the ubiquitin-proteasomal pathway regulates ETS2 stability. To study the mechanism of ETS2 ubiquitin-mediated degradation, we used siRNA to knockdown ubiquitin ligases known to interact with ETS2. A significant increase in ETS2 stability was observed when the ubiquitin ligase COP1 and its binding partner DET1 were knocked down. We find that ectopically expressed COP1/DET1 leads to ETS2 ubiquitination and degradation, and that a COP1 without an intact RING domain fails to degrade ETS2. Mutation of COP1 putative binding sites in ETS2 also prevented its degradation. Given that mtp53 interacts with ETS2, we assessed mtp53's role in ETS2 stability by conducting ubiquitination assays. Our data showed that mtp53 prevents COP1/DET1 from ubiquitinating ETS2, thus preventing it from being degraded. We are currently studying the mechanism of COP1/DET1 binding to ETS2 and how mtp53 interferes with this process, thus rescuing ETS2. We surmise that mtp53 disrupts the binding of COP1/DET1 to ETS2, leading to its stabilization. Through this mechanism, mtp53 can alter the balance of ETS proteins in normal cells, which results in an increased ETS2 transcriptional program that drives cancer cells to be more invasive and metastatic. Citation Format: Zunamys I. Carrero, Madhusudhan Kollareddy, Krishna M. Chauhan, Gopalakrishnan Ramakrishnan, Luis A. Martinez. Mutant p53 stabilizes and protects the transcription factor ETS2 from proteasomal degradation by the ubiquitin ligase COP1/DET1. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1212. doi:10.1158/1538-7445.AM2015-1212