title: Critical role for Ipaf in Pseudomonas aeruginosa-induced caspase-1 activation.
abstract: Pseudomonas aeruginosa is an opportunistic Gram-negative human pathogen that is responsible for a broad range of infections in individuals with a variety of predisposing conditions. After infection, P. aeruginosa induces a marked inflammatory response in the host. However the mechanisms involved in bacterium recognition and induction of immune responses are poorly understood. Here we report that the Nod-like receptor family member Ipaf is required for optimal bacterial clearance in an in vivo model of P. aeruginosa lung infection. Further analysis showed that bacterial flagellin was essential for caspase-1 and IL-1beta and this activity depended on Ipaf and the adaptor ASC but not TLR5. Notably, P. aeruginosa induced macrophage cell death and this event relied on flagellin and Ipaf but not on ASC. Analysis of Pseudomonas mutants revealed that different amino acid residues of flagellin were critical for sensing by Ipaf and TLR5. Finally, activation of caspase-1 and IL-1beta secretion by P. aeruginosa required a functional type III secretion system, but not the effector molecules ExoS, ExoT and ExoY. These results provide new insight into the interaction of P. aeruginosa with host macrophages and suggest that distinct regions of flagellin are sensed by Ipaf and TLR5.
authors.affiliation: Department of Pathology and Comprehensive Cancer Center, The University of Michigan Medical School, Ann Arbor, MI 48109, USA.
authors.forename: Luigi
authors.initials: L
authors.lastname: Franchi
authors.forename: Joshua
authors.initials: J
authors.lastname: Stoolman
authors.forename: Thirumala-Devi
authors.initials: TD
authors.lastname: Kanneganti
authors.forename: Amrisha
authors.initials: A
authors.lastname: Verma
authors.forename: Reuben
authors.initials: R
authors.lastname: Ramphal
authors.forename: Gabriel
authors.initials: G
authors.lastname: Núñez
mesh_terms: D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism*; D053468:CARD Signaling Adaptor Proteins; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D020170:Caspase 1 / Q000378:metabolism*; D003598:Cytoskeletal Proteins / Q000378:metabolism; D004789:Enzyme Activation / Q000276:immunology*; D005408:Flagellin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015151:Immunoblotting; D053583:Interleukin-1beta / Q000378:metabolism; D016676:Macrophages, Alveolar / Q000276:immunology*; D051379:Mice; D018345:Mice, Knockout; D011552:Pseudomonas Infections / Q000276:immunology* / Q000378:metabolism; D011550:Pseudomonas aeruginosa; D051198:Toll-Like Receptor 5 / Q000378:metabolism
chemical_list: D051017:Apoptosis Regulatory Proteins; D053468:CARD Signaling Adaptor Proteins; D002135:Calcium-Binding Proteins; D003598:Cytoskeletal Proteins; D053583:Interleukin-1beta; C512299:Ipaf protein, mouse; C498534:Pycard protein, mouse; D051198:Toll-Like Receptor 5; D005408:Flagellin; D020170:Caspase 1