NLRP3 recruitment by NLRC4 during Salmonella infection.

NLRC4 and NLRP3, of the NOD-like receptor (NLR) family of intracellular proteins, are expressed in innate immune cells and are thought to nucleate distinct inflammasome complexes that promote caspase-1 activation, secretion of the proinflammatory cytokines IL-1β and IL-18, and a form of cell death termed pyroptosis. We show that NLRP3 associates with NLRC4 in macrophages infected with Salmonella typhimurium or transfected with flagellin. The significance of the interaction between the NLRC4 NACHT domain and NLRP3 was revealed when Nlrc4(S533A/S533A) bone marrow-derived macrophages (BMDMs) expressing phosphorylation site mutant NLRC4 S533A had only a mild defect in caspase-1 activation when compared with NLRC4-deficient BMDMs. NLRC4 S533A activated caspase-1 by recruiting NLRP3 and its adaptor protein ASC. Thus, Nlrc4(S533A/S533A) Nlrp3(-/-) BMDMs more closely resembled Nlrc4(-/-) BMDMs in their response to S. typhimurium or flagellin. The interplay between NLRP3 and NLRC4 reveals an unexpected overlap between what had been considered distinct inflammasome scaffolds.

Qu Y ，Misaghi S ，Newton K ，Maltzman A ，Izrael-Tomasevic A ，Arnott D ，Dixit VM ... -  《-》

Bacterial Outer Membrane Vesicle-Mediated Cytosolic Delivery of Flagellin Triggers Host NLRC4 Canonical Inflammasome Signaling.

Bacteria-released components can modulate host innate immune response in the absence of direct host cell-bacteria interaction. In particular, bacteria-derived outer membrane vesicles (OMVs) were recently shown to activate host caspase-11-mediated non-canonical inflammasome pathway via deliverance of OMV-bound lipopolysaccharide. However, further precise understanding of innate immune-modulation by bacterial OMVs remains elusive. Here, we present evidence that flagellated bacteria-released OMVs can trigger NLRC4 canonical inflammasome activation via flagellin delivery to the cytoplasm of host cells. Salmonella typhimurium-derived OMVs caused a robust NLRC4-mediated caspase-1 activation and interleukin-1β secretion in macrophages in an endocytosis-dependent, but guanylate-binding protein-independent manner. Notably, OMV-associated flagellin is crucial for Salmonella OMV-induced inflammasome response. Flagellated Pseudomonas aeruginosa-released OMVs consistently promoted robust NLRC4 inflammasome activation, while non-flagellated Escherichia coli-released OMVs induced NLRC4-independent non-canonical inflammasome activation leading to NLRP3-mediated interleukin-1β secretion. Flagellin-deficient Salmonella OMVs caused a weak interleukin-1β production in a NLRP3-dependent manner. These findings indicate that Salmonella OMV triggers NLRC4 inflammasome activation via OMV-associated flagellin in addition to a mild induction of non-canonical inflammasome signaling via OMV-bound lipopolysaccharide. Intriguingly, flagellated Salmonella-derived OMVs induced more rapid inflammasome response than flagellin-deficient Salmonella OMV and non-flagellated Escherichia coli-derived OMVs. Supporting these in vitro results, Nlrc4-deficient mice showed significantly reduced interleukin-1β production after intraperitoneal challenge with Salmonella-released OMVs. Taken together, our results here propose that NLRC4 inflammasome machinery is a rapid sensor of bacterial OMV-bound flagellin as a host defense mechanism against bacterial pathogen infection.

Yang J ，Hwang I ，Lee E ，Shin SJ ，Lee EJ ，Rhee JH ，Yu JW ... -  《Frontiers in Immunology》

Modifying bacterial flagellin to evade Nod-like Receptor CARD 4 recognition enhances protective immunity against Salmonella.

Tourlomousis P ，Wright JA ，Bittante AS ，Hopkins LJ ，Webster SJ ，Bryant OJ ，Mastroeni P ，Maskell DJ ，Bryant CE ... -  《Nature Microbiology》

HUWE1 mediates inflammasome activation and promotes host defense against bacterial infection.

Guo Y ，Li L ，Xu T ，Guo X ，Wang C ，Li Y ，Yang Y ，Yang D ，Sun B ，Zhao X ，Shao G ，Qi X ... -  《-》

Redundant roles for inflammasome receptors NLRP3 and NLRC4 in host defense against Salmonella.

Broz P ，Newton K ，Lamkanfi M ，Mariathasan S ，Dixit VM ，Monack DM ... -  《-》