Abstract 4795: The epigenetic regulation of HPP1 expression in colon cancer

Abstract

Abstract Background: Tumors often are associated with aberrant epigenetic gene silencing. HPP1, a tumor suppressor gene, is epigenetically silenced by promoter methylation in a number of tumor types including colon cancer however, the contribution of histone acetylation is not clear. Moreover, c-myc interaction with the HPP1 promoter is thought to suppress expression. The purpose of this study is to examine the interplay between c-myc, DNA methylation and histone acetylation in the epigenetic regulation of HPP1 expression. Methods: The HPP1-negative cell line, HCT-116, was treated with the DNA methylation inhibitor 5-aza-2’-deoxycitidine (5-aza-DC) and/or HDAC inhibitors, including sodium butyrate (SB), Vorinostat (SAHA), trichostatin A (TSA), and valproic acid (VPA). Knockdowns of c-Myc and HDAC-3 were performed using siRNA. Protein and mRNA expression of HPP1 were determined by Western Blot and RT-PCR respectively. HPP1 promoter methylation was assessed by real-time methylation-specific PCR. Furthermore, Chromatin immunoprecipitation (ChIP) experiments were used to demonstrate the binding of c-Myc to the HPP1 promoter. Results: 5-aza-DC (0.4uM) as well as the HDAC inhibitors, SB (5mM), TSA (200nM), SAHA (5uM) and VPA (2mM), increased the expression of HPP1 in HCT-116 cells. The treatment of 5-aza-DC in combination with individual HDAC inhibitors resulted in a synergistic effect on increasing HPP1 expression as detected by both RT-PCR and Western blotting. We found that SAHA reduced the expression of HDAC-3 and c-Myc. Concordantly, knockdown of c-Myc and HDAC-3 by siRNA significantly enhanced HPP1 expression. We have also confirmed that c-Myc binds to the HPP1 promoter and its knockdown results in a reduction of HPP1 promoter methylation. Conclusions: These results indicate that c-Myc- and HDAC-3-associated promoter methylation and histone deacetylation contribute to HPP1 epigenetic silencing. Colon cancer cells treated with DNA methylation and HDAC inhibitors can re-express the cancer suppressor gene HPP1. This study supports the conept that 5-aza-DC and HDAC inhibitors represent potentially promising classes of anticancer drugs for the future treatment of colon cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4795. doi:10.1158/1538-7445.AM2011-4795