Abstract 3652: HDAC inhibitors activate NF-κB in human leukemia cells through an ATM/NEMO-dependent DNA Damage-related pathway

Abstract

Abstract The ability of HDAC inhibitors (HDACIs) to induce sustained activation of NF-κB (p65/RelA) has been attributed to reversible RelA acetylation (Chen et al., Science 293:1653-7, 2001), a phenomenon that diminishes HDACI antineoplastic activity (Dai et al., Mol Cell Biol. 25:5429-44, 2005). However, the process by which HDACIs initially activate NF-κB has yet to be elucidated. To address this question, mechanisms underlying HDAC inhibitor (HDACI)-mediated NF-κB activation were investigated in human myeloid leukemia cells. Exposure of U937 and other leukemia cells to the pan-HDACI LBH-589 induced reactive oxygen species (ROS) and p65/RelA activation, the NF-κB-dependent induction of Mn-SOD2 mRNA and protein accompanied by ROS elimination, and sequential induction of XRCC1 (single strand) followed by γ-H2A. X (double strand) DNA breaks. LBH-589 lethality was significantly attenuated by siRNA knockdown of the chromatin-linked DNA damage protein histone H1.2. U937 IκBα super-repressor cells lacking serine 32 and 36 IκBα phosphorylation sites displayed diminished HDACI-mediated NF-κB activation/Mn-SOD2 induction, accompanied by enhanced ROS accumulation, DNA damage, and apoptosis. In contrast, TRAF2 siRNA knockdown blocked TNFα- but not HDACI-mediated NF-κB activation and lethality. The Mn-SOD2 mimetic TBAP prevented HDACI-induced NF-κB activation and nuclear localization, while dramatically attenuating DNA damage and apoptosis. Notably, LBH-589 exposure activated ATM (on serine 1981) and increased its association with NEMO, events comprising a recently described “inside-out” nuclear NF-κB activation pathway (Wu et al., Science 311:1110-1, 2006). Notably, siRNA NEMO or ATM knockdown blocked HDACI-mediated NF-κB nuclear translocation/activation, diminished MnSOD2 induction, and potentiated oxidative injury, DNA damage and cell death. Similarly, SUMOylation-site mutant NEMO (K277A and/or K309A) cells exposed to LBH-589 displayed diminished association of ATM with NEMO, reduced NEMO and p65/RelA nuclear localization/activation, and MnSOD2 down-regulation. These events were accompanied by increased ROS production, γ-H2A. X formation, and enhanced lethality. Collectively, these findings indicate that in human leukemia cells, HDACIs activate the cytoprotective NF-κB pathway through an ATM/NEMO-dependent process involving the induction of ROS and DNA damage. They also raise the possibility that blocking NF-κB activation via the atypical DNA damage-related ATM/NEMO nuclear pathway has the potential to enhance HDACI antileukemic activity. 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 3652.