Induction of a pro-apoptotic ATM-NF-κB pathway and its repression by ATR in response to replication stress

The transcription factor NF-kappa B has critical functions in biologic responses to genotoxic stimuli. Activation of NF-kappa B in response to DNA double strand break (DSB) inducers can be mediated by ATM (ataxia telangiectasia mutated)-dependent phosphorylation of NEMO (NF-kappa B essential modulator). Here, we show that the replication stress inducers hydroxyurea (HU) and aphidicolin also activate this ATM-dependent signalling pathway. We further show that ATR (ATM- and Rad3-related) interacts with NEMO but surprisingly does not cause NEMO phosphorylation. Consequently, ATR represses NF-kappa B activation induced by replication stress. Reduction or increase of ATR expression by RNA interference or overexpression increased or reduced ATM-NEMO association and NF-kappa B activation induced by HU. Apoptosis gene expression and chromatin immunoprecipitation analyses indicated that HU and the DSB inducer etoposide caused complex patterns of NF-kappa B-dependent pro- and antiapoptotic gene expression with the overall outcome for the former being pro- apoptotic, whereas the latter antiapoptotic. Thus, replication stress and DSB inducers activate NF-kappa B through a conserved pathway with opposite biologic outcomes, and ATR antagonizes ATM function at least in part by competing for NEMO association.