Exosomal export of activated CASPASE-8 is linked to the prevention of TNF-induced cytotoxicity

Tumor Necrosis Factor (TNF) is a key pro-inflammatory cytokine whose sensing by TNFR1 triggers gene activation or cell death induction. While TNF cytotoxicity can be beneficial during infections by supporting effective immune responses, its chronic or excessive induction is harmful and promotes inflammatory pathologies. Protective brakes, known as cell death checkpoints, normally repress TNF cytotoxicity and therefore constitute crucial safeguards against these diseases. Death by TNF mainly proceeds upon inactivation of a checkpoint by microbial effector proteins or pathological mutations. We previously identified lysosomal turnover of TNFR1 Complex II by TAX1BP1-mediated selective macro-autophagy as a brake on TNF cytotoxicity. Here, we propose an alternative mechanism that prevents TNF-induced RIPK1 kinase-independent apoptosis. We found that inhibiting the ESCRT machinery, HSC70 or TAX1BP1 interferes with the TNF-dependent targeting of activated CASPASE-8 into endosomal intralumenal vesicles (ILVs) and is associated with apoptosis induction. Furthermore, we identified TAX1BP1 and TNFR1 Complex II components as TNF-induced cargoes of extracellular vesicles, suggesting that exosomal release of TNFR1 Complex II serves as a parallel detoxification pathway to lysosomal turnover. Finally, we show that Salmonella Typhimurium and Mycobacterium tuberculosis effector proteins activate TNF cytotoxicity by inhibiting components of the ESCRT machinery involved in this detoxification process.