Mutant p53 protects ETS2 from non-canonical COP1/DET1 dependent degradation.

Zunamys I Carrero,Krishna M Chauhan,Madhusudhan Kollareddy,Luis A Martinez,Gopalakrishnan Ramakrishnan

doi:10.18632/oncotarget.7275

Abstract

Mutations in the tumor suppressor gene TP53 contribute to the development of approximately half of all human cancers. One mechanism by which mutant p53 (mtp53) acts is through interaction with other transcription factors, which can either enhance or repress the transcription of their target genes. Mtp53 preferentially interacts with the erythroblastosis virus E26 oncogene homologue 2 (ETS2), an ETS transcription factor, and increases its protein stability. To study the mechanism underlying ETS2 degradation, we knocked down ubiquitin ligases known to interact with ETS2. We observed that knockdown of the constitutive photomorphogenesis protein 1 (COP1) and its binding partner De-etiolated 1 (DET1) significantly increased ETS2 stability, and conversely, their ectopic expression led to increased ETS2 ubiquitination and degradation. Surprisingly, we observed that DET1 binds to ETS2 independently of COP1, and we demonstrated that mutation of multiple sites required for ETS2 degradation abrogated the interaction between DET1 and ETS2. Furthermore, we demonstrate that mtp53 prevents the COP1/DET1 complex from ubiquitinating ETS2 and thereby marking it for destruction. Mechanistically, we show that mtp53 destabilizes DET1 and also disrupts the DET1/ETS2 complex thereby preventing ETS2 degradation. Our study reveals a hitherto unknown function in which DET1 mediates the interaction with the substrates of its cognate ubiquitin ligase complex and provides an explanation for the ability of mtp53 to protect ETS2.

Highlights

The majority of human cancers exhibit a loss of p53 function either as a result of mutations in the p53 gene (TP53) or due to dysfunctions in pathways that signal to p53 [1]
Previous studies have reported that ETS2 is a substrate of the anaphase promoting complex (APC)/C and SCF ubiquitin ligase complexes
Other studies have shown that the E3 ubiquitin ligase constitutive photomorphogenesis protein 1 (COP1) can bind to E26 transformationspecific (ETS) family members and in the presence of its binding partner, De-etiolated 1 (DET1), promote their degradation [10, 15]

Summary

Introduction

The majority of human cancers exhibit a loss of p53 function either as a result of mutations in the p53 gene (TP53) or due to dysfunctions in pathways that signal to p53 [1]. R273H), and conformational mutations can cause local (e.g. R249S and G245S) or global (e.g., R175H and R282W) conformational distortions [3] These changes provide multiple functions for mtp that can affect the genes that are transcribed by wild-type p53 and its interaction with other proteins (e.g. transcription factors). ChIP-on-chip and ChIP-seq analyses have shown that the predominant binding motif in mtp target genes is GGAAG, which corresponds to the consensusbinding site for the erythroblastosis E26 transformationspecific (ETS) family of transcription factors [4]. ETS2, an evolutionary conserved protooncogene and a downstream effector of the Ras/Raf/ MAPK pathway, regulates the number of genes with potentially important functions in cancers such as: tumor environment, which includes growth factors, adhesion molecules, extracellular proteases and anti-apoptotic genes [7]

Methods

Results

Conclusion