Functional interplay between MDM2, p63/p73 and mutant p53.

M H Stindt,S Kehrloesser,R L Ludwig,V Dötsch,P A J Muller,K H Vousden

doi:10.1038/onc.2014.359

Abstract

Many cancers express mutant p53 proteins that have lost wild-type tumor suppressor activity and, in many cases, have acquired oncogenic functions that can contribute to tumor progression. These activities of mutant p53 reflect interactions with several other proteins, including the p53 family members p63 and p73. Mutations in p53 that affect protein conformation (such as R175H) show strong binding to p63 and p73, whereas p53 mutants that only mildly affect the conformation (such as R273H) bind less well. A previously described aggregation domain of mutant p53 is not required for p63 or p73 binding; indeed, mutations within this region lead to the acquisition of a mutant p53 phenotype—including a conformational shift, p63/p73 binding and the ability to promote invasion. The activity of wild-type p53 is regulated by an interaction with MDM2 and we have investigated the potential role of MDM2 in the mutant p53/p63/p73 interactions. Both mutant p53 and p73 bind MDM2 well, whereas p63 binds much more weakly. We found that MDM2 can inhibit p63 binding to p53R175H but enhances the weaker p53R273H/p73 interaction. These effects on the interactions are reflected in an ability of MDM2 to relieve the inhibition of p63 by p53R175H, but enhance the inhibition of p73 activity by p53R175H and R273H. We propose a model in which MDM2 competes with p63 for binding to p53R175H to restore p63 activity, but forms a trimeric complex with p73 and p53R273H to more strongly inhibit p73 function.

Highlights

P53 is an important tumor suppressor protein that functions as a transcription factor, binding DNA sequences in the promoters of a large number of target genes that mediate responses such as cell cycle arrest, senescence and apoptosis.[1] p53 is altered in the majority of human cancers, frequently resulting in the expression of mutant p53 proteins with single amino-acid substitutions in the DNA-binding domain (DBD).[2]
Many of the mutant p53 proteins have been shown to acquire a gain of function that can contribute to all stages of tumorigenesis, including the ability to promote invasion and metastasis.[4,5]
P63 and p73 can form heterotetramers through the oligomerization domain, this region of p53 is unable to interact with p63 or p73.15,16 cancerassociated point mutations within the DBD of p53 can both change the conformation of the p53 protein and allow the interaction of mutant p53 with p63 and p73.17–21 This interaction of mutant p53 with p63/p73 can inhibit the transcriptional activity of p63/p73 and promote invasion.[22,23,24]

Summary

Introduction

P53 is an important tumor suppressor protein that functions as a transcription factor, binding DNA sequences in the promoters of a large number of target genes that mediate responses such as cell cycle arrest, senescence and apoptosis.[1] p53 is altered in the majority of human cancers, frequently resulting in the expression of mutant p53 proteins with single amino-acid substitutions in the DNA-binding domain (DBD).[2]. A p53 protein carrying only the I254R mutation promoted invasion in this assay as efficiently as a series of tumor-derived p53 mutants that have previously been shown to acquire this gain of function (Figure 2f) and was able to inhibit TAp63α transcriptional activity (Supplementary Figure 1E).

Results

Conclusion