p53 targets chromatin structure alteration to repress alpha-fetoprotein gene expression

Many of the functions ascribed to p53 tumor suppressor protein are mediated through transcription regulation. We have shown that p53 represses hepatic -specific a-fetoprotein (A-FP) gene expression by direct interaction with a composite HNF-3/p53 DNA binding element. Using solid-phase, chromatin-asse mbled AFP DNA templates and analysis of chromatin structure and transcripti on in vitro, we find that p53 binds DNA and alters chromatin structure at t he AFP core promoter to regulate transcription. Chromatin assembled in the presence of hepatoma extracts is activated for AFP transcription with an op en, accessible core promoter structure. Distal (-850) binding of p53 during chromatin assembly, but not post-assembly, reverses transcription activati on concomitant with promoter inaccessibility to restriction enzyme digestio n. Inhibition of histone deacetylase activity by trichostatin-A (TSA) addit ion, prior to and during chromatin assembly, activated chromatin transcript ion in parallel with increased core promoter accessibility. Chromatin immun oprecipitation analyses showed increased H3 and H4 acetylated histones at t he core promoter in the presence of TSA, while histone acetylation remained unchanged at the site of distal p53 binding. Our data reveal that p53 targ ets chromatin structure alteration at the core promoter, independently of e ffects on histone acetylation, to establish repressed AFP gene expression.