CYLD Proteolysis Protects Macrophages from TNF-Mediated Auto-necroptosis Induced by LPS and Licensed by Type I IFN

• TLR4 activates CASPASE-8 to remove CYLD and disable the TNF necroptosis pathway
• Autocrine TNF induces necroptosis in a cell-autonomous manner
• Priming of macrophages by type I IFN is needed for necroptosis induced by LPS or TNF
• Type I IFN primes expression of TNFR2 and MLKL, which are needed to induce necroptosis

SummaryTumor necrosis factor (TNF) induces necroptosis, a RIPK3/MLKL-dependent form of inflammatory cell death. In response to infection by Gram-negative bacteria, multiple receptors on macrophages, including TLR4, TNF, and type I IFN receptors, are concurrently activated, but it is unclear how they crosstalk to regulate necroptosis. We report that TLR4 activates CASPASE-8 to cleave and remove the deubiquitinase cylindromatosis (CYLD) in a TRIF- and RIPK1-dependent manner to disable necroptosis in macrophages. Inhibiting CASPASE-8 leads to CYLD-dependent necroptosis caused by the TNF produced in response to TLR4 ligation. While lipopolysaccharides (LPS)-induced necroptosis was abrogated in Tnf−/− macrophages, a soluble TNF antagonist was not able to do so in Tnf+/+ macrophages, indicating that necroptosis occurs in a cell-autonomous manner. Surprisingly, TNF-mediated auto-necroptosis of macrophages requires type I IFN, which primes the expression of key necroptosis-signaling molecules, including TNFR2 and MLKL. Thus, the TNF necroptosis pathway is regulated by both negative and positive crosstalk.

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