Poster Presentation Lorne Infection and Immunity 2013

Never say die: NleB antagonises death receptor signaling during bacterial gut infection (#148)

Jaclyn S Pearson 1 , Michelle Kelly 1 , Patrice Riedmaier 1 , Keith S Robinson 2 , Gad Frankel 2 , Elizabeth L Hartland 1
  1. Microbiology & Immunology, University of Melbourne, Parkville, VIC, Australia
  2. Centre for Molecular Microbiology and Infection, Imperial College, London, United Kingdom

Enteropathogenic E. coli (EPEC) is an attaching an effacing (A/E) pathogen that adheres intimately to the apical surface of host enterocytes and causes acute gastroenteritis in humans. EPEC utilises a type III secretion system (T3SS) to deliver multiple effector proteins directly into host cells where they subvert various cellular processes including, apoptosis and inflammatory signaling. In this study, we found that the T3SS effector, NleB interrupted host extrinsic apoptotic signaling via the death receptors, TNFR1 and FAS. NleB expressed ectopically or delivered by the T3SS bound to the death domain (DD) proteins FADD, RIPK1 and TRADD in a DD dependent manner thereby preventing FasL and TNF-induced caspase-8 activation and cell death. Furthermore, NleB inhibited the formation of the death inducing signaling complex (DISC) during EPEC infection. Previously, we and other research groups showed that a subset of T3SS effectors inhibit NF-κB activation and suppress production of the pro-inflammatory cytokine IL-8 during EPEC infection. Although NleB binds to NF- κB signaling adaptors RIPK1 and TRADD, the effector had no impact on suppression of IL-8 production by EPEC suggesting its main function in the TNF pathway was to inhibit apoptosis. Overall, this study revealed a new virulence mechanism in bacterial infection, where a T3SS effector binds to DD containing proteins and thereby inhibits death receptor mediated apoptosis. NleB represents a family of T3SS effectors from A/E pathogens and Salmonella that may target a range of host DD proteins to disrupt anti-microbial signaling during infection, thereby promoting bacterial dissemination.