A pre-DNA-damage response specific to non-blocking/ low endogenous replication stress

Using primary human fibroblasts, we discovered a cellular response specific to endogenous low-level replication stress that does not arrest DNA synthesis and cell cycle progression. This stress response induces the production of ROS by the NADPH oxidases DUOX1 and DUOX2, under the control of NF-kB and PARP1. Replication stress-induced ROS (RIR) act as second messengers for an adaptive response through the activation of the FOXO1 detoxifying pathway, which prevents the accumulation of the pre-mutagenic 8-oxoG DNA lesions in the genome. Therefore to address the consequences of this response on mutagenesis, we treated cells with the pro-mutagen H2O2 with or without pre-treatment with low HU doses that induces the cell response specific to low doses. Both HU and H2O2 are individually mutagenic, but their association did not result in additive mutagenesis, consistent with a protective effect of HU pre-treatment against exogenous H2O2 exposure.