The canonical NF-κB pathway differentially protects normal and human tumor cells from ROS-induced DNA damage

DNA damage responses (DDR) invoke senescence or apoptosis depending on stimulus intensity and the degree of activation of the p53-p21(Cip/Waf1) axis: but the functional impact of NF-kappa B signaling on these different outcomes in normal vs. human cancer cells remains poorly understood. We investigated the NF-kappa B-dependent effects and mechanism underlying reactive oxygen species (ROS)-mediated DDR outcomes of normal human lung fibroblasts (HDFs) and A549 human lung cancer epithelial cells. To activate DDR, ROS accumulation was induced by different doses of H2O2. The effect of ROS induction caused a G2 or G2-M phase cell cycle arrest of both human cell types. However, ROS-mediated DDR eventually culminated in different end points with HDFs undergoing premature senescence and A549 cancer cells succumbing to apoptosis. NF-kappa B p65/RelA nuclear translocation and Ser536 phosphorylation were induced in response to H2O2-mediated ROS accumulation. Importantly, blocking the activities of canonical NF-kappa B subunits with an I kappa B alpha super-repressor or suppressing canonical NF-kappa B signaling by IKK beta knock-down accelerated HDF premature senescence by up-regulating the p53-p21(Cip/Waf1) axis: but inhibiting the canonical NF-kappa B pathway exacerbated H2O2-induced A549 cell apoptosis. HDF premature aging occurred in conjunction with gamma-H2AX chromatin deposition, senescence-associated heterochromatic foci and beta-galactosidase staining. p53 knock-down abrogated H2O2-induced premature senescence of vector control- and I kappa B alpha SR-expressing HDFs functionally linking canonical NF-kappa B-dependent control of p53 levels to ROS-induced HDF senescence. We conclude that IKK beta-driven canonical NF-kappa B signaling has different functional roles for the outcome of ROS responses in the contexts of normal vs. human tumor cells by respectively protecting them against DDR-dependent premature senescence and apoptosis. (C) 2012 Elsevier Inc. All rights reserved.