CHIP-mediated Ubiquitin Modification And Lysosome-dependent Degradation Regulates ZBP1 Levels And Programmed Cell Necrosis

Inflammation and cell death are two important mechanisms which play important roles in eliminating invading pathogens by the host and maintaining biological homeostasis.As an innate immune sensor,ZBP1 can sense viral nucleic acid and trigger apoptosis and necroptosis.Upon IAV infection,ZBP1 recognizes IAV genomic RNA and activates RIPK3 to induce apoptosis and necroptosis and inhibit virus replication.ZBP1 also sen ses MCMV infection and interacts with RIPK3 to induce RHIMdependent n ecroptosis which is inhibited by the viral RHIM protein M45.In addition,after IAV infection,ZBP1 can also regulate the activation of NLRP3 inflammasome and the secretion of proinflammatory cytokines.Currently,there are few studies on the mechanism that regulates ZBP1 protein level.Previous study has shown that CHIP controls necroptosis through ubiquitination and lysosome-dependent degradation of RIPK3.As a key up.stream protein of RIPK3,ZBP1 often forms a complex with RIPK3 and regulates downstream signaling pathways.An important question is that does ZBP1 also be regulated by CHIP?Here we demonstrated that the protein stability of ZBP1 is regulated by CHIP.CHIP degrades ZBP1 and shortens the half-life of ZBP1 protein.Our results showed that CHIP degrades ZBP1 through the lysosome-dependent ubiquitination.ZBP1,RIPK3,and CHIP protein can form a complex.The interaction of CHIP and ZBP1 depends on the RHIM domain of ZBP1.CHIP reduces the interaction of ZBP1 and RIPK3,thereby negatively regulating the downstream pathways of ZBPI and inhibiting necroptosis induced by ZBP1 and RIPK3,and also inhibiting the signal transduction pathway mediated by ZBP1,including the activation of NF-κB and the production of IFN-β.After IAV infection,ZBP1 senses viral ribonucleoprotein(vRNP)complexes to induce ubiquitination of ZBP1 and trigger cell death.However,it has not been clarified how the ubiquitination of ZBP1 occurs upon IAV infection.Which proteins is involved in the regulation of ZBP1?Is it the CHIP protein?In the future further study is needed.In conclusion,we discovered that the E3 ligase protein CHIP regulates the level of ZBP1 protein,which shed new light on the understanding of the innate immune response regulated by ZBP1.