LKB1 reduces ROS-mediated cell damage via activation of p38

Liver kinase B1 (LKB1, also known as serine/threonine kinase 11, STK11) is a tumor suppressor mutated in Peutz-Jeghers syndrome and in a variety of sporadic cancers. Herein, we demonstrate that LKB1 controls the levels of intracellular reactive oxygen species (ROS) and protects the genome from oxidative damage. Cells lacking LKB1 exhibit markedly increased intracellular ROS levels, excessive oxidation of DNA, increased mutation rates and accumulation of DNA damage, which are effectively prevented by ectopic expression of LKB1 and by incubation with antioxidant N-acetylcysteine. The role of LKB1 in suppressing ROS is independent of AMP-activated protein kinase, a canonical substrate of LKB1. Instead, under the elevated ROS, LKB1 binds to and maintains the activity of the cdc42-PAK1 (p21-activated kinase 1) complex, which triggers the activation of p38 and its downstream signaling targets, such as ATF-2, thereby enhancing the activity of superoxide dismutase-2 and catalase, two antioxidant enzymes that protect the cells from ROS accumulation, DNA damage and loss of viability. Our results provide a new paradigm for a non-canonical tumor suppressor function of LKB1 and highlight the importance of targeting ROS signaling as a potential therapeutic strategy for cancer cells lacking LKB1.