E3 ubiquitin-protein ligase TRIM32
positive regulation of autophagosome assembly
ATM-CHK2-TRIM32 axis regulates ATG7 ubiquitination to initiate autophagy under oxidative stress.
Oxidative stress-induced autophagy helps to prevent cellular damage and to maintain homeostasis. However, the regulatory pathway that initiates autophagy remains unclear. We previously showed that reactive oxygen species (ROS) function as signaling molecules to activate the ATM-CHK2 pathway and promote autophagy. Here, we find that the E3 ubiquitin ligase TRIM32 functions downstream of ATM-CHK2 to regulate ATG7 ubiquitination. Under metabolic stress, ROS induce ATM phosphorylation at S1981, which in turn phosphorylates CHK2 at T68. We show that CHK2 binds and phosphorylates TRIM32 at the S55 site, which then mediates K63-linked ubiquitination of ATG7 at the K45 site to initiate autophagy. In addition, Chk2<sup>-/-</sup> mice show an aggravated infarction phenotype and reduced phosphorylation of TRIM32 and ubiquitination of ATG7 in a stroke model. We propose a molecular mechanism for autophagy initiation by ROS via the ATM-CHK2-TRIM32-ATG7 axis to maintain intracellular homeostasis and to protect cells exposed to pathological conditions from stress-induced tissue damage.