caa a22 4500 528787209 20190923032428.0 cr unu---uuuuu 180924e20100830xx s 000 0 eng 10.3929/ethz-b-000022234 doi 10.1371/journal.pone.0012477 doi (ETHRESEARCH)oai:www.research-collection.ethz.ch:20.500.11850/22234 In Macrophages, Caspase-1 Activation by SopE and the Type III Secretion System-1 of S. Typhimurium Can Proceed in the Absence of Flagellin [Elektronische Daten] [Claudia Hoffmann, Marlies Galle, Sabrina Dilling, Rina Käppeli, Andreas J. Müller, Pascal Songhet, Rudi Beyaert, Wolf-Dietrich; id_orcid 0000-0002-9892-6420 Hardt] PLoS ONE Open access ethresearch The innate immune system is of vital importance for protection against infectious pathogens. Inflammasome mediated caspase-1 activation and subsequent release of pro-inflammatory cytokines like IL-1β and IL-18 is an important arm of the innate immune system. Salmonella enterica subspecies 1 serovar Typhimurium (S. Typhimurium, SL1344) is an enteropathogenic bacterium causing diarrheal diseases. Different reports have shown that in macrophages, S. Typhimurium may activate caspase-1 by at least three different types of stimuli: flagellin, the type III secretion system 1 (T1) and the T1 effector protein SopE. However, the relative importance and interdependence of the different factors in caspase-1 activation is still a matter of debate. Here, we have analyzed their relative contributions to caspase-1 activation in LPS-pretreated RAW264.7 macrophages. Using flagellar mutants (fliGHI, flgK) and centrifugation to mediate pathogen-host cell contact, we show that flagellins account for a small part of the caspase-1 activation in RAW264.7 cells. In addition, functional flagella are of key importance for motility and host cell attachment which is a prerequisite for mediating caspase-1 activation via these three stimuli. Using site directed mutants lacking several T1 effector proteins and flagellin expression, we found that SopE elicits caspase-1 activation even when flagellins are absent. In contrast, disruption of essential genes of the T1 protein injection system (invG, sipB) completely abolished caspase-1 activation. However, a robust level of caspase-1 activation is retained by the T1 system (or unidentified T1 effectors) in the absence of flagellin and SopE. T1-mediated inflammasome activation is in line with recent work by others and suggests that the T1 system itself may represent the basic caspase-1 activating stimulus in RAW264.7 macrophages which is further enhanced independently by SopE and/or flagellin. Creative Commons Attribution 3.0 Unported http://creativecommons.org/licenses/by/3.0 ethresearch Hoffmann Claudia joint author Galle Marlies joint author Dilling Sabrina joint author Käppeli Rina joint author Müller Andreas J. joint author Songhet Pascal joint author Beyaert Rudi joint author Hardt Wolf-Dietrich; id_orcid 0000-0002-9892-6420 joint author PLoS ONE Lawrence, KS, USA : PLoS 5 (8), p. e12477 1932-6203 http://hdl.handle.net/20.500.11850/22234 text/html WWW-Backlink auf das Repository (Open access) 1 Journal Article ethresearch ETHRESEARCH 856 40 http://hdl.handle.net/20.500.11850/22234 text/html WWW-Backlink auf das Repository (Open access) ETHRESEARCH 700 1- Hoffmann Claudia joint author ETHRESEARCH 700 1- Galle Marlies joint author ETHRESEARCH 700 1- Dilling Sabrina joint author ETHRESEARCH 700 1- Käppeli Rina joint author ETHRESEARCH 700 1- Müller Andreas J. joint author ETHRESEARCH 700 1- Songhet Pascal joint author ETHRESEARCH 700 1- Beyaert Rudi joint author ETHRESEARCH 700 1- Hardt Wolf-Dietrich; id_orcid 0000-0002-9892-6420 joint author ETHRESEARCH 773 0- PLoS ONE Lawrence, KS, USA : PLoS 5 (8), p. e12477 1932-6203 BK010053 XK010053 XK010000 ETHRESEARCH ETHRESEARCH ETHRESEARCH Journal Article Open access