TRAF3 promotes ROS production and pyroptosis by targeting ULK1 ubiquitination in macrophages

Abstract

oxygen species; TLR, toll-like receptor; TRAF3, tumor necrosis factor receptorassociated factor 3; ULK1, Unc-51 like autophagy activating kinase 1. AbstractDisrupted mitochondrial function and reactive oxygen species (ROS) generation cause cellular damage and oxidative stress-induced macrophage inflammatory cell death. It remains unclear how mitochondrial dysfunction relates to inflammasome activation and pyroptotic cell death. In this study, we demonstrated that tumor necrosis factor receptor-associated factor 3 (TRAF3) regulates mitochondrial ROS production and promotes TLR agonist LPS plus nigericin (LPS/Ng)-induced inflammasome and pyroptosis in mouse primary macrophages and human monocyte THP-1 cells. Co-IP assays confirmed that TRAF3 forms a complex with TRAF2 and cIAP1 and mediates ubiquitin and degradation of Unc-51 like autophagy activating kinase 1 (ULK1). Moreover, knockdown of ULK1 in THP-1 cells significantly promoted LPS/Ng-induced inflammasome by activating caspase 1 and mature IL-1β. Apoptosis inducing factor (AIF) translocation from mitochondrial to nuclear was observed in ULK1-deficient THP-1 cells under LPS/Ng stimulation, which mediates LPS/Ng-induced cell death in ULK1 deficient macrophages. In conclusion, this study identified a novel role of TRAF3 in regulation of ULK1 ubiquitination and inflammasome signaling and provided molecular mechanisms by which ubiquitination of ULK1 controls mitochondrial ROS production, inflammasome activity, and AIF-dependent pyroptosis. K E Y W O R D S cell death, inflammasome, macrophages, mitochondrial, reactive oxygen species | 7145 SHEN Et al.

High resistance to Toxoplasma gondii infection in inducible nitric oxide synthase knockout rats

“…ROS production in macrophages is always related to inflammasome activation, which may directly cause cellular damage, oxidative stress, and pyroptotic processes ( Shen et al, 2020 ; Wang et al., 2019b ). Pyroptosis in pathogen restriction is a critical innate immune response to prevent intracellular infection ( Boucher et al., 2015 ).…”

Autophagy, Pyroptosis, and Ferroptosis: New Regulatory Mechanisms for Atherosclerosis

“…In addition, as a mitochondrial outer membrane protein that directly interacted with LC3, NIX was found to promote the degradation and removal of excess mitochondria and ROS by regulating autophagy, thus inhibiting ox-LDL-induced pyroptosis of macrophages in atherosclerosis ( Peng et al, 2020 ). However, tumor necrosis factor receptor-associated factor 3 (TRAF3) has been reported to form a complex with TRAF2 and cIAP1 and mediate ubiquitin and degradation of ULK1, in which mitochondrial ROS production and pyroptosis were promoted ( Shen et al, 2020 ). Therefore, ROS-activated autophagic machinery may represent a negative feedback mechanism that limits ROS-regulated caspase-1 activation through removing ROS-damaged organelles and proteins.…”

ULK1 Signaling in the Liver: Autophagy Dependent and Independent Actions

“…Anti-inflammatory action of autophagy in liver macrophages, such as Kupffer cells, involves limiting inflammasome activation and release of interleukin 1 beta (IL-1β) cytokine (Lodder et al, 2015) associated with liver fibrosis. A recent study demonstrates that loss of ULK1 mediated autophagy in macrophages leads to increased inflammasome activation and pyroptosis (Shen et al, 2020). Interestingly, a non-autophagic contribution of ULK1 in repressing innate immune response is via phosphorylation of STING (Konno et al, 2013).…”