Chemopreventive effects of the dietary histone deacetylase inhibitor tributyrin alone or in combination with vitamin A during the promotion phase of rat hepatocarcinogenesis.

The chemopreventive effects of tributyrin (TB) and vitamin A (VA), alone or in combination, were investigated during the promotion phase of rat hepatocarcinogenesis. Compared to diethylnitrosamine control rats, TB and TB+VA-treated rats, but not VA-treated rats, presented a lower incidence and mean number of hepatocyte nodules and a smaller size of persistent preneoplastic lesions (pPNLs). In addition, TB and TB+VA-treated rats exhibited a higher apoptotic body index in pPNL and remodeling PNL, whereas VA-treated rats presented only a higher apoptotic body index in remodeling PNL. None of the treatments inhibited cell proliferation in PNL. TB and TB+VA-treated rats, but not VA-treated rats, exhibited higher levels of H3K9 acetylation and p21 protein expression. TB and VA-treated rats exhibited increased hepatic concentrations of butyric acid and retinoids, respectively. Compared to normal rats, diethylnitrosamine control animals exhibited lower retinyl palmitate hepatic concentrations. All groups had similar expression levels and exhibited similar unmethylated CRBP-I promoter region in microdissected pPNL, indicating that epigenetic silencing of this gene was not involved in alteration of retinol metabolism in early hepatocarcinogenesis. Data support the effectiveness of TB as a dietary histone deacetylase inhibitor during the promotion phase of hepatocarcinogenesis, which should be considered for chemoprevention combination strategies.

ADAM23 negatively modulates alpha(v)beta(3) integrin activation during metastasis.

The ADAM23 gene is frequently silenced in different types of tumors, and, in breast tumors, silencing is correlated with tumor progression, suggesting that it might be associated with the acquisition of a metastatic phenotype. ADAM23 exerts its function mainly through the disintegrin domain, because its metalloprotease domain is inactive. Analysis of ADAM23 binding to integrins has revealed a specific interaction with alpha(v)beta(3) integrin mediated by the disintegrin domain. Altered expression of alpha(v)beta(3) integrin has been observed in different types of tumors, and expression of this integrin in the activated form has been shown to promote metastasis formation. Here, we investigated the possibility that interaction between ADAM23 and alpha(v)beta(3) integrin might negatively modulate alpha(v)beta(3) activation during metastatic progression. ADAM23 expression was knocked down using short hairpin RNA in the MDA-MB-435 cell line, which has been extensively used as a model for alpha(v)beta(3) integrin activation. Ablation of ADAM23 enhanced alpha(v)beta(3) integrin activation by at least 2- to 4-fold and ADAM23 knockdown cells showed enhanced migration and adhesion to classic alpha(v)beta(3) integrin ligands. Ablation of ADAM23 expression also enhanced pulmonary tumor cell arrest in immunodeficient mice. To complement our findings with clinical evidence, we showed that silencing of ADAM23 gene by DNA promoter hypermethylation in a collection of 94 primary breast tumors was significantly associated with lower distant metastases-free and disease-specific survivals and was an independent prognostic factor for poor disease outcome. Our results strongly support a functional role of ADAM23 during metastatic progression by negatively modulating alpha(v)beta(3) integrin activation.

SATR-1 hypomethylation is a common and early event in breast cancer.

Genome stability and normal gene expression are maintained by a fixed and predetermined DNA methylation pattern, which becomes abnormal in malignant cells. Hypomethylation of satellite DNA sequences is frequently found in tumors and has been associated with an increased frequency of DNA rearrangements and chromosome instability. In this work, we used methylation-sensitive arbitrarily primed polymerase chain reaction (MSAP-PCR) to identify differentially methylated DNA fragments in normal and tumor breast samples. We identified a novel differentially methylated fragment located on chromosome 5 with high similarity to a SATR-1 satellite sequence. This fragment was found to be hypomethylated in 63% of breast tumor cell lines and in 86% of breast tumors relative to normal breast tissue. We found that normal tissue adjacent to breast tumors displayed a variable decrease in methylation and that the decrease observed for most of these adjacent samples was higher than observed for normal breast tissue derived from reduction mammoplasty. The methylation decrease was, however, significantly higher in tumor samples than in adjacent tissue (chi2= 154, 1 df, P < 10(-4)), suggesting that SATR-1 hypomethylation frequently occurs in the early stages of tumor development. Our results highlight the importance of global DNA hypomethylation as a contributing factor in breast tumorigenesis.