p53 Targets Chromatin Structure Alteration to Repress α-Fetoprotein Gene Expression

Abstract

Many of the functions ascribed to p53 tumor suppressor protein are mediated through transcription regulation. We have shown that p53 represses hepatic-specific ␣-fetoprotein (AFP) gene expression by direct interaction with a composite HNF-3/p53 DNA binding element. Using solid-phase, chromatin-assembled AFP DNA templates and analysis of chromatin structure and transcription in vitro, we find that p53 binds DNA and alters chromatin structure at the AFP core promoter to regulate transcription. Chromatin assembled in the presence of hepatoma extracts is activated for AFP transcription with an open, accessible core promoter structure. Distal (؊850) binding of p53 during chromatin assembly, but not post-assembly, reverses transcription activation concomitant with promoter inaccessibility to restriction enzyme digestion. Inhibition of histone deacetylase activity by trichostatin-A (TSA) addition, prior to and during chromatin assembly, activated chromatin transcription in parallel with increased core promoter accessibility. Chromatin immunoprecipitation analyses showed increased H3 and H4 acetylated histones at the core promoter in the presence of TSA, while histone acetylation remained unchanged at the site of distal p53 binding. Our data reveal that p53 targets chromatin structure alteration at the core promoter, independently of effects on histone acetylation, to establish repressed AFP gene expression.

MicroRNA122 is a key regulator of α-fetoprotein expression and influences the aggressiveness of hepatocellular carcinoma

“…In contrast, overexpression of p110 CUX1 was able to accelerate S phase entry and to stimulate proliferation, migration and invasion 35,48 . Moreover, CUX1 was shown to promote genomic instability following cytokinesis failure 30 Regulation of AFP gene expression is a complex process mediated by a number of transcriptional activators and repressors that bind the AFP gene 7,8 . ZBTB20 was recently identified as a potent repressor of AFP transcription in knockout mouse studies 9 .…”

“…7), we assessed p53 activity using reporter constructs. However, no changes in p53 activity were detected in miR122-silenced cells (Fig.…”

Plakoglobin is a new target gene of histone deacetylase in human fibrosarcoma HT1080 cells

“…Examination of the sequence of the plakoglobin distal promoter on the web (http://www.generegulation.com) revealed that several potential binding factors capable of interacting with HDAC are present. They include retinoic acid receptors (Lin et al, 1998), Sp1 (Sowa et al, 1997), and HNF-3 (Ogden et al, 2001). Identification of the specific factors regulating plakoglobin repression will provide clues for elucidating the molecular mechanisms controlling its expression in certain tumors.…”

Embryonic development of the liver†

“…Still, FoxA has been shown to relieve p53-mediated transcriptional repression of the ␣-fetoprotein gene in vitro. [50][51][52] Also, it is yet to be determined whether, prior to formation of the ventral endoderm, the regulatory elements of hepatic genes are indeed in a compacted state and whether specific mechanisms exist to generate such a state during embryogenesis.…”