Successful infection by enteric bacterial pathogens depends on the ability of the bacteria to colonize the gut, replicate in host tissues and disseminate to other hosts. Pathogens such as Salmonella, Shigella and enteropathogenic and enterohaemorrhagic (EPEC and EHEC, respectively) Escherichia coli use a type III secretion system (T3SS) to deliver virulence effector proteins into host cells during infection that promote colonization and interfere with antimicrobial host responses1,2,3. Here we report that the T3SS effector NleB1 from EPEC binds to host cell death-domain-containing proteins and thereby inhibits death receptor signalling. Protein interaction studies identified FADD, TRADD and RIPK1 as binding partners of NleB1. NleB1 expressed ectopically or injected by the bacterial T3SS prevented Fas ligand or TNF-induced formation of the canonical death-inducing signalling complex (DISC) and proteolytic activation of caspase-8, an essential step in death-receptor-induced apoptosis. This inhibition depended on the N-acetylglucosamine transferase activity of NleB1, which specifically modified Arg 117 in the death domain of FADD. The importance of the death receptor apoptotic pathway to host defence was demonstrated using mice deficient in the FAS signalling pathway, which showed delayed clearance of the EPEC-like mouse pathogen Citrobacter rodentium and reversion to virulence of an nleB mutant. The activity of NleB suggests that EPEC and other attaching and effacing pathogens antagonize death-receptor-induced apoptosis of infected cells, thereby blocking a major antimicrobial host response.
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We gratefully acknowledge P. Bouillet for the gift of Bid−/− mice and T. Cumming for assistance with animal work. This work was supported by the Australian National Health and Medical Research Council (Program Grant no.606788 to E.L.H., Project Grants no.637332, no.1009145 to A.S., no.1009145 to L.O.R., Australia Fellowship to A.S.), the Wellcome Trust to G.F., the Juvenile Diabetes Foundation; the Leukaemia and the Lymphoma Society (New York; SCOR grant no.7413) to A.S. E.L.H was supported by an Australian Research Council Future Fellowship. J.S.P., M.K., T.W., C.G. and P.R. were supported by Australian Postgraduate Awards. This work was made possible through Victorian State Government Operational Infrastructure Support and Australian Government NHMRC IRIISS.
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Operational Experience of an Open-Access, Subscription-Based Mass Spectrometry and Proteomics Facility
Journal of The American Society for Mass Spectrometry (2018)