A Direct Intersection between p53 and Transforming Growth Factor β Pathways Targets Chromatin Modification and Transcription Repression of the α-Fetoprotein Gene

Abstract

ABSTRACT We purified the oncoprotein SnoN and found that it functions as a corepressor of the tumor suppressor p53 in the regulation of the hepatic α -fetoprotein ( AFP ) tumor marker gene. p53 promotes SnoN and histone deacetylase interaction at an overlapping Smad binding, p53 regulatory element (SBE/p53RE) in AFP . Comparison of wild-type and p53-null mouse liver tissue by using chromatin immunoprecipitation (ChIP) reveals that the absence of p53 protein correlates with the disappearance of SnoN at the SBE/p53RE and loss of AFP developmental repression. Treatment of AFP -expressing hepatoma cells with transforming growth factor-β1 (TGF-β1) induced SnoN transcription and Smad2 activation, concomitant with AFP repression. ChIP assays show that TGF-β1 stimulates p53, Smad4, P-Smad2 binding, and histone H3K9 deacetylation and methylation, at the SBE/p53RE. Depletion, by small interfering RNA, of SnoN and/or p53 in hepatoma cells disrupted repression of AFP transcription. These findings support a model of cooperativity between p53 and TGF-β effectors in chromatin modification and transcription repression of an oncodevelopmental tumor marker gene.