P53 induces distinct epigenetic states at its direct target promoters

Lukas Vrba,Damian J Junk,Petr Novak,Bernard W Futscher

doi:10.1186/1471-2164-9-486

Abstract

BackgroundThe tumor suppressor protein p53 is a transcription factor that is mutated in many cancers. Regulation of gene expression by binding of wild-type p53 to its target sites is accompanied by changes in epigenetic marks like histone acetylation. We studied DNA binding and epigenetic changes induced by wild-type and mutant p53 in non-malignant hTERT-immortalized human mammary epithelial cells overexpressing either wild-type p53 or one of four p53 mutants (R175H, R249S, R273H and R280K) on a wild-type p53 background.ResultsUsing chromatin immunoprecipitation coupled to a 13,000 human promoter microarray, we found that wild-type p53 bound 197 promoters on the microarray including known and novel p53 targets. Of these p53 targets only 20% showed a concomitant increase in histone acetylation, which was linked to increased gene expression, while 80% of targets showed no changes in histone acetylation. We did not observe any decreases in histone acetylation in genes directly bound by wild-type p53. DNA binding in samples expressing mutant p53 was reduced over 95% relative to wild-type p53 and very few changes in histone acetylation and no changes in DNA methylation were observed in mutant p53 expressing samples.ConclusionWe conclude that wild-type p53 induces transcription of target genes by binding to DNA and differential induction of histone acetylation at target promoters. Several new wild-type p53 target genes, including DGKZ, FBXO22 and GDF9, were found. DNA binding of wild-type p53 is highly compromised if mutant p53 is present due to interaction of both p53 forms resulting in no direct effect on epigenetic marks.

Highlights

The tumor suppressor protein p53 is a transcription factor that is mutated in many cancers
The p53 mutants R175H, R249S, R273H and R280K were stably overexpressed in hTERTimmortalized human mammary epithelial cells (HME1) cells containing endogenous wt p53 to analyze the effect that mt p53 had on wt p53's function as a transcription factor
Wt p53 when overexpressed from adenoviral vector in HME1 cells bound 197 promoters of the human gene promoter microarray. p53 binding resulted in statistically significant increases in histone acetylation of either histone H3 or histone H4 or both for 40 of these promoters

Summary

Introduction

The tumor suppressor protein p53 is a transcription factor that is mutated in many cancers. Regulation of gene expression by binding of wild-type p53 to its target sites is accompanied by changes in epigenetic marks like histone acetylation. The wild-type (wt) p53 protein acts as a transcription factor that responds to a variety of stress stimuli that pose a threat to normal cells. Binding of wt p53 results in the recruitment of the co-activator p300/CBP and subsequent acetylation of promoter associated histones H3 and H4 [1,2,6,7,8]. Binding of this activation complex and increased histone acetylation was linked to increased expression of these genes. Chromatin immunoprecipitation studies have shown binding of wt p53 to the promoter regions of some (page number not for citation purposes)

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