title: Caspase-8 as an Effector and Regulator of NLRP3 Inflammasome Signaling.
abstract: We recently described the induction of noncanonical IL-1β processing via caspase-8 recruited to ripoptosome signaling platforms in myeloid leukocytes. Here, we demonstrate that activated NLRP3·ASC inflammasomes recruit caspase-8 to drive IL-1β processing in murine bone marrow-derived dendritic cells (BMDC) independent of caspase-1 and -11. Sustained stimulation (>2 h) of LPS-primed caspase-1-deficient (Casp1/11(-/-)) BMDC with the canonical NLRP3 inflammasome agonist nigericin results in release of bioactive IL-1β in conjunction with robust caspase-8 activation. This IL-1β processing and caspase-8 activation do not proceed in Nlrp3(-/-) or Asc(-/-) BMDC and are suppressed by pharmacological inhibition of caspase-8, indicating that caspase-8 can act as a direct IL-1β-converting enzyme during NLRP3 inflammasome activation. In contrast to the rapid caspase-1-mediated death of wild type (WT) BMDC via NLRP3-dependent pyroptosis, nigericin-stimulated Casp1/11(-/-) BMDC exhibit markedly delayed cell death via NLRP3-dependent apoptosis. Biochemical analyses of WT and Casp1/11(-/-) BMDC indicated that caspase-8 is proteolytically processed within detergent-insoluble ASC-enriched protein complexes prior to extracellular export during nigericin treatment. Although nigericin-stimulated caspase-1 activation and activity are only modestly attenuated in caspase-8-deficient (Casp8(-/-)Rip3(-/-)) BMDC, these cells do not exhibit the rapid loss of viability of WT cells. These results support a contribution of caspase-8 to both IL-1β production and regulated death signaling via NLRP3 inflammasomes. In the absence of caspase-1, NLRP3 inflammasomes directly utilize caspase-8 as both a pro-apoptotic initiator and major IL-1β-converting protease. In the presence of caspase-1, caspase-8 acts as a positive modulator of the NLRP3-dependent caspase-1 signaling cascades that drive both IL-1β production and pyroptotic death.
authors.affiliation: Pathology, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106.
authors.forename: Christina
authors.initials: C
authors.lastname: Antonopoulos
authors.affiliation: Pathology, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106.
authors.forename: Hana M
authors.initials: HM
authors.lastname: Russo
authors.affiliation: From the Departments of Physiology and Biophysics and.
authors.forename: Caroline
authors.initials: C
authors.lastname: El Sanadi
authors.affiliation: Pathology, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106, the Department of Immunology, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, Ohio 44195, and.
authors.forename: Bradley N
authors.initials: BN
authors.lastname: Martin
authors.affiliation: the Department of Immunology, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, Ohio 44195, and.
authors.forename: Xiaoxia
authors.initials: X
authors.lastname: Li
authors.affiliation: the Department of Microbiology and Immunology, Emory Vaccine Center, Emory University School of Medicine, Atlanta, Georgia 30322.
authors.forename: William J
authors.initials: WJ
authors.lastname: Kaiser
authors.affiliation: the Department of Microbiology and Immunology, Emory Vaccine Center, Emory University School of Medicine, Atlanta, Georgia 30322.
authors.forename: Edward S
authors.initials: ES
authors.lastname: Mocarski
authors.affiliation: Pathology, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106, From the Departments of Physiology and Biophysics and george.dubyak@case.edu.
authors.forename: George R
authors.initials: GR
authors.lastname: Dubyak
mesh_terms: D000818:Animals; D017209:Apoptosis; D002352:Carrier Proteins / Q000378:metabolism*; D020170:Caspase 1 / Q000378:metabolism; D053181:Caspase 8 / Q000378:metabolism*; D058847:Inflammasomes / Q000187:drug effects / Q000378:metabolism*; D053583:Interleukin-1beta / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; D009550:Nigericin / Q000494:pharmacology; D015398:Signal Transduction
chemical_list: D002352:Carrier Proteins; D058847:Inflammasomes; D053583:Interleukin-1beta; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; C492716:Nlrp3 protein, mouse; D053181:Caspase 8; D020170:Caspase 1; D009550:Nigericin
keywords: apoptosis; caspase 1 (CASP1); caspase 8; dendritic cell; inflammasome; inflammation; interleukin 1 (IL-1); pyroptosis