Mechanistic Study Of Kinases Mst1/2 Regulating Protein Stability Of Nrf2

Hippo signaling plays an important role in organ size regulation,tissue development,cell proliferation and tumor development.The Hippo signaling pathway also plays an important role in the immune system.It has been previously reported that patients who lack the key kinase Mst1/2 in Hippo signaling showed recurrent bacterial and viral infection and autoimmune manifestations.Previous studies have shown that when macrophages are infected by bacteria,they can activate Mst1/2 through TLR on the cell membrane.The activation of Mst1/2 can activate GDP-Rac to form GTP-Rac.The transformation of this process results in the release of TRAF6,which is originally combined with GDP-Rac,and the formation of complex with ECSIT on mitochondria and through the rearrangement of cytoskeleton,mitochondria are translocated to the phagocytes,producing reactive oxygen species(ROS)that help macrophages kill bacteria.However,macrophages lacking Mst1/2 were more likely to suffer oxidative damage,senescence and death than wild-type macrophages.These observeation suggested that Mstl/2 can not only promote the production of ROS,but also eliminate excessive ROS to protect macrophages.However,how Mstl/2 can eliminate the excess ROS in macrophages remains unknown.ROS,as a "double-edged sword" in macrophages,will lead to death of macrophages when it is produced too much.Therefore,there must be many mechanisms to clear too much ROS in macrophages.Nrf2,which regulates the expression of many antioxidant genes and protect cells from ROS damage,is a typical transcription factor that can reduce ROS level in macrophages.The protein level of Nrf2 in macrophages is mainly regulated by Keap1.Mstl/2 can phosphorylate three threonines and one serine of Keap1.When these four amino acids are mutated into alanine,Keapl can not form dimer and polymer.At the same time,we also detected that the binding of Keap1 and Nrf2 was weakened after mutation,and the ubiquitination level of Nrf2 was weakened,and the stability of Nrf2 protein in cells was increased,so as to promote the expression of more antioxidant genes to protect cells from oxidative damage.In conclusion,this project mainly describes that MST1/2 kinases can be activated in macrophages upon bacteria infection.Activated MST1/2 can not only promote the induction of ROS,but also clear the excess ROS through MST1/2-Keap1-Nrf2 signal pathway for maintainin redox homeostasis in macrophages.