DNA Damage Sensor ATM-CHK2 Boosts Antioxidant Defense by Activating Nrf2

Oxidative stress is a central driver of aging and age-related diseases, and cells rely on the transcription factor Nrf2 to coordinate antioxidant gene expression. While Nrf2 has long been known to be regulated by the E3 ligase adaptor Keap1, the upstream signaling events that translate ROS signals into Nrf2 activation have remained poorly understood. This study identifies a direct, previously unknown pathway: ROS activate the DNA damage response (DDR) kinase CHK2, which in turn stabilizes and activates Nrf2.

The researchers employed a combination of cell-based assays, biochemical analyses, phosphoproteomic mapping, co-immunoprecipitation, and in vivo mouse models to dissect the mechanism. They demonstrated that ROS generated by hydrogen peroxide or the model oxidant tert-butyl hydroperoxide activate ATM, which phosphorylates and activates CHK2. Active CHK2 then acts through two complementary routes to enhance Nrf2 function.

In the first route, CHK2 phosphorylates the autophagy adaptor protein p62 (SQSTM1) at serine-349. This phosphorylation event dramatically increases p62's affinity for Keap1, effectively sequestering Keap1 away from Nrf2. Since Keap1 normally bridges Nrf2 to the Cullin3-based E3 ubiquitin ligase complex for proteasomal degradation, disrupting Keap1-Nrf2 interaction allows Nrf2 protein to accumulate. In the second route, CHK2 directly phosphorylates Nrf2 itself at serine-566 and serine-577, modifications that enhance its transcriptional activity independently of protein stabilization.

In vivo validation used Chk2−/− mice subjected to renal ischemia/reperfusion (I/R) injury, an established model of ROS-dependent organ damage. Compared to wild-type mice, Chk2-null mice showed markedly impaired Nrf2 target gene expression (including HO-1, NQO1, and GCLM), elevated oxidative damage markers, and more severe histological kidney injury. These findings confirm that the CHK2-Nrf2 axis is physiologically required for tissue protection against oxidative stress.

This study reframes the DDR not only as a genome guardian but as a broader stress-sensing system that actively mobilizes antioxidant defenses. The ATM-CHK2-Nrf2 axis provides a mechanistic explanation for why DNA damage and oxidative stress responses are so frequently co-activated, and suggests that DDR kinase activity is part of the normal cellular antioxidant program. These findings have implications for aging biology, ischemia-reperfusion injury, cancer, and any context where oxidative stress and genome integrity intersect.