title: Loss of XIAP facilitates switch to TNFα-induced necroptosis in mouse neutrophils.
abstract: Neutrophils are essential players in the first-line defense against invading bacteria and fungi. Besides its antiapoptotic role, the inhibitor of apoptosis protein (IAP) family member X-linked IAP (XIAP) has been shown to regulate innate immune signaling. Whereas the role of XIAP in innate signaling pathways is derived mostly from work in macrophages and dendritic cells, it is not known if and how XIAP contributes to these pathways in neutrophils. Here we show that in response to bacterial lipopolysaccharides (LPS), mouse neutrophils secreted considerable amounts of tumor necrosis factor-α (TNFα) and interleukin-1β (IL-1β) and, in accordance with earlier reports, XIAP prevented LPS-induced hypersecretion of IL-1β also in neutrophils. Interestingly, and in contrast to macrophages or dendritic cells, Xiap-deficient neutrophils were insensitive to LPS-induced cell death. However, combined loss of function of XIAP and cIAP1/-2 resulted in rapid neutrophil cell death in response to LPS. This cell death occurred by classical apoptosis initiated by a TNFα- and RIPK1-dependent, but RIPK3- and MLKL-independent, pathway. Inhibition of caspases under the same experimental conditions caused a shift to RIPK3-dependent cell death. Accordingly, we demonstrate that treatment of neutrophils with high concentrations of TNFα induced apoptotic cell death, which was fully blockable by pancaspase inhibition in wild-type neutrophils. However, in the absence of XIAP, caspase inhibition resulted in a shift from apoptosis to RIPK3- and MLKL-dependent necroptosis. Loss of XIAP further sensitized granulocyte-macrophage colony-stimulating factor (GM-CSF)-primed neutrophils to TNFα-induced killing. These data suggest that XIAP antagonizes the switch from TNFα-induced apoptosis to necroptosis in mouse neutrophils. Moreover, our data may implicate an important role of neutrophils in the development of hyperinflammation and disease progression of patients diagnosed with X-linked lymphoproliferative syndrome type 2, which are deficient in XIAP.
authors.affiliation: Institute of Pharmacology, University of Bern, Bern, Switzerland.
authors.forename: Simone
authors.initials: S
authors.lastname: Wicki
authors.affiliation: Institute of Pharmacology, University of Bern, Bern, Switzerland.
authors.forename: Ursina
authors.initials: U
authors.lastname: Gurzeler
authors.affiliation: Institute of Experimental Immunology, University of Zurich, Zurich, Switzerland.
authors.forename: W
authors.initials: W
authors.lastname: Wei-Lynn Wong
authors.affiliation: III. Medizinische Klinik, Klinikum rechts der Isar, Technische Universität München, Munich, Germany.
authors.forename: Philipp J
authors.identifier: 0000-0003-2454-0362
authors.initials: PJ
authors.lastname: Jost
authors.affiliation: Institute of Pharmacology, University of Bern, Bern, Switzerland.
authors.forename: Daniel
authors.initials: D
authors.lastname: Bachmann
authors.affiliation: Institute of Pharmacology, University of Bern, Bern, Switzerland.
authors.forename: Thomas
authors.identifier: 0000-0001-9906-874X
authors.initials: T
authors.lastname: Kaufmann
mesh_terms: D000590:Amino Acid Chloromethyl Ketones; D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D053583:Interleukin-1beta / Q000378:metabolism; D008070:Lipopolysaccharides; D008810:Mice, Inbred C57BL; D024101:Mitochondrial Proteins / Q000494:pharmacology; D009336:Necrosis; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism*; D011804:Quinolines; D053422:Receptor-Interacting Protein Serine-Threonine Kinases / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D051636:X-Linked Inhibitor of Apoptosis Protein / Q000172:deficiency* / Q000378:metabolism
chemical_list: D000590:Amino Acid Chloromethyl Ketones; D053583:Interleukin-1beta; D008070:Lipopolysaccharides; D024101:Mitochondrial Proteins; D011804:Quinolines; D014409:Tumor Necrosis Factor-alpha; D051636:X-Linked Inhibitor of Apoptosis Protein; C468548:quinoline-val-asp(OMe)-CH2-OPH; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D053422:Receptor-Interacting Protein Serine-Threonine Kinases