NOD-, LRR-, and pyrin domain-containing 3 (NLRP3) is a cytosolic innate immune sensor of cellular stress signals, triggered by infection and sterile inflammation. Upon detection of an activating stimulus, NLRP3 transitions from an inactive homo-oligomeric multimer into an active multimeric inflammasome, which promotes the helical oligomeric assembly of the adaptor molecule ASC. ASC oligomers provide a platform for caspase-1 activation, leading to the proteolytic cleavage and activation of proinflammatory cytokines in the IL-1 family and gasdermin D, which can induce a lytic form of cell death. Recent studies investigating both the cellular requirement for NLRP3 activation and the structure of NLRP3 have revealed the complex regulation of NLRP3 and the multiple steps involved in its activation. This review presents a perspective on the biochemical and cellular processes controlling the assembly of the NLRP3 inflammasome with particular emphasis on structural regulation and the role of organelles. We also highlight the latest research on metabolic control of this inflammatory pathway and discuss promising clinical targets for intervention.

Activity of the NLRP3 inflammasome, a critical mediator of inflammation, is controlled by accessory proteins, posttranslational modifications, cellular localization, and oligomerization. How these factors relate is unclear. We show that a well-established drug target, Bruton’s tyrosine kinase (BTK), affects several levels of NLRP3 regulation. BTK directly interacts with NLRP3 in immune cells and phosphorylates four conserved tyrosine residues upon inflammasome activation, in vitro and in vivo. Furthermore, BTK promotes NLRP3 relocalization, oligomerization, ASC polymerization, and full inflammasome assembly, probably by charge neutralization, upon modification of a polybasic linker known to direct NLRP3 Golgi association and inflammasome nucleation. As NLRP3 tyrosine modification by BTK also positively regulates IL-1β release, we propose BTK as a multifunctional positive regulator of NLRP3 regulation and BTK phosphorylation of NLRP3 as a novel and therapeutically tractable step in the control of inflammation.

Activity of the NLRP3 inflammasome, a critical mediator of inflammation (1), is controlled by accessory proteins (2, 3), post-translational modifications (4, 5), cellular localization (6, 7) and oligomerization (8). How these factors relate, is unclear. We show that the established drug target, Bruton’s Tyrosine Kinase (BTK) (2, 9), integrates several levels of NLRP3 regulation: BTK phosphorylation of four conserved tyrosine residues, by neutralizing the charge of a polybasic linker region, weakens the interaction of NLRP3 with Golgi phospholipids and may thus guide NLRP3 cytosolic localization. BTK activity also promotes NLRP3 oligomerization and subsequent formation of inflammasomes. As NLRP3 tyrosine modification ultimately also impacts on IL-1β release, we propose BTK-mediated, charge-switch-based NLRP3 regulation as a novel and therapeutically tractable step in the control of inflammation.One Sentence SummaryMulti-phosphorylation of NLRP3 by Bruton’s tyrosine kinase modulates NLRP3 cellular localization, inflammasome assembly, and IL-1β release.

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