ATM-associated signalling triggers the unfolded protein response and cell death in response to stress

Endoplasmic reticulum (ER) stress can be caused by perturbations in ER function resulting from the accumulation of unfolded/misfolded proteins in the ER lumen. Accumulating unfolded proteins trigger unfolded protein responses (UPRs) through activating three transmembrane sensors on the ER: IRE1 alpha, PERK, and ATF6. The orchestrated action of these molecules upregulates genes encoding proteins involved in the downregulation of protein synthesis and acceleration of protein secretion. Ineffectiveness of these fail-safe mechanisms may lead to apoptosis. However, the molecular mechanisms upstream of the UPR are not fully understood. Here we show participation of ataxia telangiectasia mutated (ATM) in stress-induced apoptosis. Cytoplasmic ATM serves as a platform on which protein phosphatase 2A-dependent dephosphorylation of AKT activates glycogen synthase kinase 3 beta, thereby downregulating nascent polypeptide-associated complex alpha subunit and gamma -taxilin, triggering UPRs and leading to mitochondria-dependent apoptosis. These results suggest an ATM/AKT-dependent cell death pathway triggered by various forms of stress. Hotokezaka et al. identify a role for ataxia telangiectasia mutated (ATM) in stress-induced signalling responses. They show that ATM-associated protein phosphatase 2A mediates dephosphorylation of AKT which triggers the unfolded protein response leading to mitochondria-dependent apoptosis in response to various forms of stress.