Abstract 1993: Interaction between histone demethylase and deacetylase may mediate activity of HDAC inhibitors in human breast cancer cells

Abstract

Abstract Histone acetylation and methylation are two important epigenetic entities that interact with each other in chromatin remodeling and gene transcription regulation. It has been shown that abnormal activities of histone lysine deacetylases (HDACs) and histone lysine demethylases (KDMs) are associated with aberrant gene expression in cancer development. However, the precise molecular mechanisms underlying the crosstalk between HDACs and KDMs are still elusive. In this study, we showed that exposure of human breast cancer MDA-MB-231 and MDA-MB-468 cells to inhibitors against the zinc cofactor dependent class I or II HDACs, but not NAD+ dependent class III HDAC, led to significant increases of global di or mono-methylation of histone 3 lysine 4 (H3K4me2/me1) which are specific substrates of histone lysine-specific demethylase 1 (LSD1) and key positive chromatin marks promoting transcriptional activation. HDAC inhibitors did not affect in vitro demethylation activity of recombinant LSD1 and did not alter the nuclear presence of the LSD-CoREST-HDAC1/2 complex, indicating the inhibition of LSD1 activity in breast cancer cells by specific HDAC inhibitors likely occurs through disrupting the functional interaction between LSD1 and HDACs rather than direct competition with enzymatic substrate at the active site of LSD1 or suppression of LSD1 protein levels. Inhibition of LSD1 activity by its inhibitor, pargyline, or RNAi in MDA-MB-231 cells caused an increase in acetylation of H3K9 (AcH3K9), suggesting that LSD1 is an important regulator of HDAC activity in breast cancer. Chromatin immunoprecipitation (ChIP) demonstrated that LSD1/HDAC repressive complex is recruited to the promoter of one candidate target gene, estrogen receptor alpha (ERα), in ER negative breast cancer cells and the reactivation of silenced ERα by HDAC inhibitor is associated with increased H3K4me2, acetylH3K9 and acetylH4K16 at ERα promoter. In addition, combined treatment with HDAC inhibitors and the LSD1 inhibitor, pargyline, resulted in enhanced levels of H3K4me2 and AcH3K9, and synergistic growth inhibition of MDA-MB-231 cells. These data suggest a crosstalk between the histone demethylase, LSD1, and histone deacetylases as a novel regulatory mechanism in mediating activity of HDAC inhibitors and may help in designing combinations that could have significant clinical translation in breast cancer therapy. 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 1993. doi:10.1158/1538-7445.AM2011-1993