Pseudomonas aeruginosa pilin activates the inflammasome.
IL-1β is produced from inactive pro-IL-1β by activation of caspase-1 brought about by a multi-subunit protein platform called the inflammasome. Many bacteria can trigger inflammasome activity through flagellin activation of the host protein NLRC4. However, strains of the common human pathogen Pseudomonas aeruginosa lacking flagellin can still activate the inflammasome. We set out to identify what non-flagellin components could produce this activation. Using mass spectroscopy, we identified an inflammasome-activating factor from P. aeruginosa as pilin, the major component of the type IV bacterial pilus. Purified pilin introduced into mouse macrophages by liposomal delivery activated caspase-1 and led to secretion of mature IL-1β, as did recombinant pilin purified from Escherichia coli. This was dependent on caspase-1 but not on the host inflammasome proteins NLRC4, NLRP3 or ASC. Mutants of P. aeruginosa strain PA103 lacking pilin did not activate the inflammasome following infection of macrophages with live bacteria. Type III secretion remained intact in the absence of pili, showing this was not due to a lack of effector delivery. Our observations show pilin is a novel activator of the inflammasome in addition to flagellin and the recently described PrgJ protein family, the basal body rod component of the type III apparatus.
Institute of Infection, Immunity and Inflammation, College of Medicine, Veterinary and Life Sciences, University of Glasgow, UK.
Cecilia S Lindestam
CS
Arlehamn
Tom J
TJ
Evans
D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D015153:Blotting, Western; D053468:CARD Signaling Adaptor Proteins; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D020170:Caspase 1 / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D004926:Escherichia coli / Q000378:metabolism; D036781:Fimbriae Proteins / Q000235:genetics / Q000276:immunology* / Q000378:metabolism*; D005408:Flagellin / Q000235:genetics; D058847:Inflammasomes / Q000276:immunology* / Q000378:metabolism; D053583:Interleukin-1beta / Q000378:metabolism; D008264:Macrophages / Q000276:immunology*; D013058:Mass Spectrometry; D051379:Mice; D008810:Mice, Inbred C57BL; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; D011550:Pseudomonas aeruginosa / Q000235:genetics / Q000276:immunology*
D051017:Apoptosis Regulatory Proteins; D053468:CARD Signaling Adaptor Proteins; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D003598:Cytoskeletal Proteins; D058847:Inflammasomes; D053583:Interleukin-1beta; C512299:Ipaf protein, mouse; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; C492716:Nlrp3 protein, mouse; C498534:Pycard protein, mouse; D005408:Flagellin; D036781:Fimbriae Proteins; D020170:Caspase 1