Abstract 5000: Epigenetic de-silencing of Glutathione s-transferase pi by tumor suppressive maspin

Abstract

Abstract Abstract: Loss of expression of the GST pi isoform due to DNA hypermethylation-mediated epigenetic silencing is one of the most common molecular events in precancerous and cancerous lesions of human prostate. Our previous studies demonstrated that tumor suppressive maspin, an endogenous inhibitor of histone deacetylase 1, could up-regulated GST activity and reduced reactive oxygen species (ROS) generation in response to oxidative stress treatment. We confirmed that maspin restored GST pi expression in maspin transfected prostate cancer cell line DU145. Conversely, maspin knocking down by siRNA in PC3 cells led to reduced GST pi expression. We further investigated the possibility that the epigenetic regulation by DNA-methylation and histone deacetylation were coupled dynamic processes that HDAC inhibition by maspin alone was sufficient to reverse the DNA-methylation silencing effects. Using methylation-specific polymerase chain reaction (M-PCR), DNA demethylation in GST pi promoter was detected only in maspin-expressing cells. Chromatin immunoprecipitation (ChIP) assay showed that a significant higher level of acetylated histone 3 was associated with the GST pi promoter DNA complex. In the same DNA complex from maspin transfected cells, less DNA methylation transferase (DNMT1) and methyl-CpG-binding domain (MBD2/3) proteins were detected as compared to that from the mock control cells. It was noted that in DU145-derived transfected cells, maspin simultaneously restored GST pi expression and sensitized tumor cells to drug-induced apoptosis, while overexprssion of GST pi alone in LNCaP prostate cancer cells conferred resistance to oxidative stress in cell death, HIF-1α induction, and phosphorylation of histone 2A.X. These data suggest that, as an epithelial-specific HDAC1 inhibitor, maspin may function to maintain the epithelial tissue homeostasis through balancing the GST pi-dependent detoxification and HDAC1 inhibition-dependent apoptosis sensitivity. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5000.