S-phase-dependent p50/NF-кB1 phosphorylation in response to ATR and replication stress acts to maintain genomic stability

The apical damage kinase, ATR, is activated by replication stress (RS) both in response to DNA damage and during normal S-phase. Loss of function studies indicates that ATR acts to stabilize replication forks, block cell cycle progression and promote replication restart. Although checkpoint failure and replication fork collapse can result in cell death, no direct cytotoxic pathway downstream of ATR has previously been described. Here, we show that ATR directly reduces survival by inducing phosphorylation of the p50 (NF-κB1, p105) subunit of NF-кB and moreover, that this response is necessary for genome maintenance independent of checkpoint activity. Cell free and in vivo studies demonstrate that RS induces phosphorylation of p50 in an ATR-dependent but DNA damage-independent manner that acts to modulate NF-кB activity without affecting p50/p65 nuclear translocation. This response, evident in human and murine cells, occurs not only in response to exogenous RS but also during the unperturbed S-phase. Functi...