TRK-fused gene (TFG) regulates ULK1 stability via TRAF3-mediated ubiquitination and protects macrophages from LPS-induced pyroptosis

TRK-fused gene (TFG) is known to be involved in protein secretion and plays essential roles in an antiviral innate immune response. However, its function in LPS-induced inflammation and pyroptotic cell death is still unknown. Here, we reported that TFG promotes the stabilization of Unc-51 like autophagy activating kinase (ULK1) and participates in LPS plus nigericin (Ng) induced pyroptotic cell death. Our results showed that TFG-deficient THP-1 macrophages exhibit higher mitochondrial ROS production. LPS/Ng stimulation triggers a much higher level of ROS and induces pyroptotic cell death. ULK1 undergoes a rapid turnover in TFG-deficient THP-1 cells. TFG forms complex with an E3 ligase, tumor necrosis factor receptor-associated factor 3 (TRAF3), and stabilizes ULK1 via disturbing ULK1-TRAF3 interaction. Knockdown of TFG facilitates the interaction of ULK1 with TRAF3 and subsequent K48-linked ULK1 ubiquitination and proteasome degradation. Rescue of ULK1 expression blocks LPS/Ng-induced cell death in TFG-deficient THP-1 macrophages. Taken together, TFG plays an essential role in LPS/Ng-induced pyroptotic cell death via regulating K48-linked ULK1 ubiquitination in macrophages.