The mechanism of NLRP3 inflammasome initiation: Trimerization but not dimerization of the NLRP3 pyrin domain induces robust activation of IL-1β

• Published in: Biochemical and biophysical research communications 2017-02, Vol.483 (2), p.823-828
• Main Authors: Sušjan, Petra, Roškar, Samo, Hafner-Bratkovič, Iva
• Format: Article
• Language: English
• Subjects: Animals; Caspase 1 - metabolism; Cell Line; Enzyme Activation; Inflammasome; Inflammasomes - immunology; Inflammasomes - metabolism; Interleukin-1beta - metabolism; Mice; NLR Family, Pyrin Domain-Containing 3 Protein - chemistry; NLR Family, Pyrin Domain-Containing 3 Protein - genetics; NLR Family, Pyrin Domain-Containing 3 Protein - metabolism; NLRP3; Oligomerization; Protein Domains; Protein Multimerization; Pyrin; Pyrin - chemistry; Recombinant Fusion Proteins - chemistry; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - metabolism
• ISSN: 0006-291X; 1090-2104
• DOI: 10.1016/j.bbrc.2017.01.008

NLRP3 inflammasome is a multiprotein platform for the activation of caspase-1. Despite the increasing number of reports linking NLRP3 inflammasome to a variety of diseases, the mechanism behind the NLRP3 activation remains elusive, especially in terms of the early stages which are critical to the NLRP3 inflammasome assembly. In the present study we aimed to determine the minimal oligomerization state required for the NLRP3 inflammasome activation. For this purpose, NLRP3 pyrin domain (NLRP3PYD) was fused to various dimerization and trimerization domains. The constructs were expressed under the inducible promoter in mouse macrophages lacking endogenous NLRP3. Dimerization of the NLRP3PYD either in parallel or in antiparallel orientation was insufficient for the inflammasome activation. Trimerization of the NLRP3PYD with the foldon domain, however, induced pyroptosis and robust IL-1β maturation, which was caspase-1 dependent. Interestingly, foldon-induced constitutive activation is resistant to inhibition with NLRP3-specific inhibitor MCC950 and does not lead to ASC speck formation. Although we cannot exclude that wild-type NLRP3 forms higher oligomer species similar to NLRP1 or NLRC4, our results clearly demonstrate that efficient IL-1β response can be achieved by the induced trimerization of the NLRP3PYD domain. •Dimerization of NLRP3 pyrin domain does not lead to IL-1β activation.•Trimerization of NLRP3 pyrin domain with foldon induces robust IL-1β activation.•Trimerization induced IL-1β activation depends on caspase-1.•Activation of trimeric NLRP3 pyrin domain proceeds in the absence of ASC specks.