title: Lipopolysaccharide Primes the NALP3 Inflammasome by Inhibiting Its Ubiquitination and Degradation Mediated by the SCFFBXL2 E3 Ligase.
abstract: The inflammasome is a multiprotein complex that augments the proinflammatory response by increasing the generation and cellular release of key cytokines. Specifically, the NALP3 inflammasome requires two-step signaling, priming and activation, to be functional to release the proinflammatory cytokines IL-1β and IL-18. The priming process, through unknown mechanisms, increases the protein levels of NALP3 and pro-IL-1β in cells. Here we show that LPS increases the NALP3 protein lifespan without significantly altering steady-state mRNA in human cells. LPS exposure reduces the ubiquitin-mediated proteasomal processing of NALP3 by inducing levels of an E3 ligase component, FBXO3, which targets FBXL2. The latter is an endogenous mediator of NALP3 degradation. FBXL2 recognizes Trp-73 within NALP3 for interaction and targets Lys-689 within NALP3 for ubiquitin ligation and degradation. A unique small molecule inhibitor of FBXO3 restores FBXL2 levels, resulting in decreased NALP3 protein levels in cells and, thereby, reducing the release of IL-1β and IL-18 in human inflammatory cells after NALP3 activation. Our findings uncover NALP3 as a molecular target for FBXL2 and suggest that therapeutic targeting of the inflammasome may serve as a platform for preclinical intervention.
authors.affiliation: Department of Medicine, Acute Lung Injury Center of Excellence, University of Pittsburgh, Pittsburgh, Pennsylvania 15213.
authors.forename: SeungHye
authors.initials: S
authors.lastname: Han
authors.affiliation: Department of Medicine, Acute Lung Injury Center of Excellence, University of Pittsburgh, Pittsburgh, Pennsylvania 15213.
authors.forename: Travis B
authors.initials: TB
authors.lastname: Lear
authors.affiliation: Department of Medicine, Acute Lung Injury Center of Excellence, University of Pittsburgh, Pittsburgh, Pennsylvania 15213.
authors.forename: Jacob A
authors.initials: JA
authors.lastname: Jerome
authors.affiliation: Department of Medicine, Acute Lung Injury Center of Excellence, University of Pittsburgh, Pittsburgh, Pennsylvania 15213.
authors.forename: Shristi
authors.initials: S
authors.lastname: Rajbhandari
authors.affiliation: Department of Medicine, Acute Lung Injury Center of Excellence, University of Pittsburgh, Pittsburgh, Pennsylvania 15213.
authors.forename: Courtney A
authors.initials: CA
authors.lastname: Snavely
authors.affiliation: Department of Medicine, Acute Lung Injury Center of Excellence, University of Pittsburgh, Pittsburgh, Pennsylvania 15213.
authors.forename: Dexter L
authors.initials: DL
authors.lastname: Gulick
authors.affiliation: Department of Medicine, Acute Lung Injury Center of Excellence, University of Pittsburgh, Pittsburgh, Pennsylvania 15213.
authors.forename: Kevin F
authors.initials: KF
authors.lastname: Gibson
authors.affiliation: Department of Medicine, Acute Lung Injury Center of Excellence, University of Pittsburgh, Pittsburgh, Pennsylvania 15213.
authors.forename: Chunbin
authors.initials: C
authors.lastname: Zou
authors.affiliation: Department of Medicine, Acute Lung Injury Center of Excellence, University of Pittsburgh, Pittsburgh, Pennsylvania 15213.
authors.forename: Bill B
authors.initials: BB
authors.lastname: Chen
authors.affiliation: Department of Medicine, Acute Lung Injury Center of Excellence, University of Pittsburgh, Pittsburgh, Pennsylvania 15213; Department of Cell Biology, Physiology, and Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania 15213; Medical Specialty Service Line, Veterans Affairs Pittsburgh Healthcare System, Pittsburgh, Pennsylvania 15240. Electronic address: mallampallirk@upmc.edu.
authors.forename: Rama K
authors.initials: RK
authors.lastname: Mallampalli
mesh_terms: D002352:Carrier Proteins / Q000276:immunology* / Q000378:metabolism; D002460:Cell Line; D044783:F-Box Proteins / Q000276:immunology* / Q000378:metabolism; D006801:Humans; D007113:Immunity, Innate; D058847:Inflammasomes / Q000276:immunology* / Q000378:metabolism; D020382:Interleukin-18 / Q000276:immunology; D053583:Interleukin-1beta / Q000276:immunology; D008070:Lipopolysaccharides / Q000276:immunology*; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; D059748:Proteolysis; D044843:SKP Cullin F-Box Protein Ligases / Q000276:immunology / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000276:immunology* / Q000378:metabolism; D054875:Ubiquitination
chemical_list: D002352:Carrier Proteins; D044783:F-Box Proteins; D058847:Inflammasomes; D020382:Interleukin-18; D053583:Interleukin-1beta; D008070:Lipopolysaccharides; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; D044843:SKP Cullin F-Box Protein Ligases; D044767:Ubiquitin-Protein Ligases; C122028:FBXL2 protein, human; C533903:FBXO3 protein, human; C453881:NLRP3 protein, human
keywords: IL-1; NALP3; cytokine induction; inflammasome; inflammation; innate immunity