Abstract
The inflammasome is a signalling platform leading to caspase-1 activation. Caspase-1 causes pyroptosis, a necrotic-like cell death. AIM2 is an inflammasome sensor for cytosolic DNA. The adaptor molecule ASC mediates AIM2-dependent caspase-1 activation. To date, no function besides caspase-1 activation has been ascribed to the AIM2/ASC complex. Here, by comparing the effect of gene inactivation at different levels of the inflammasome pathway, we uncovered a novel cell death pathway activated in an AIM2/ASC-dependent manner. Francisella tularensis, the agent of tularaemia, triggers AIM2/ASC-dependent caspase-3-mediated apoptosis in caspase-1-deficient macrophages. We further show that AIM2 engagement leads to ASC-dependent, caspase-1-independent activation of caspase-8 and caspase-9 and that caspase-1-independent death is reverted upon caspase-8 inhibition. Caspase-8 interacts with ASC and active caspase-8 specifically colocalizes with the AIM2/ASC speck thus identifying the AIM2/ASC complex as a novel caspase-8 activation platform. Furthermore, we demonstrate that caspase-1-independent apoptosis requires the activation of caspase-9 and of the intrinsic pathway in a typical type II cell manner. Finally, we identify the AIM2/ASC-dependent caspase-1-independent pathway as an innate immune mechanism able to restrict bacterial replication in vitro and control IFN-γ levels in vivo in Casp1KO mice. This work underscores the crosstalk between inflammasome components and the apoptotic machinery and highlights the versatility of the pathway, which can switch from pyroptosis to apoptosis.
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Abbreviations
- BMM:
-
bone marrow-derived macrophages
- BMDC:
-
bone marrow-derived dendritic cells
- EtDi:
-
ethidium homodimer
- LDH:
-
lactate dehydrogenase
- F. novicida :
-
Francisella tularensis subspecies novicida
- FPI:
-
Francisella pathogenicity island
- PI:
-
post-infection
- MEEBO:
-
mouse exonic evidence based oligonucleotide
- PRR:
-
pattern recognition receptors
- TSB:
-
tryptic soy broth
- TUNEL:
-
terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling
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Acknowledgements
We thank V Dixit, E Mocarsky, J Upton and W Kaiser; L Genestier and T Defrance; N Bonnefoy-Bérard for ASCKO, RIP3Casp8DKO, Myd88KO and TLR2KO mice, respectively. We thank D Monack, P Broz and K Belhocine for AIM2KO macrophages, B Py, J Yuan, S Mariathasan, and U Hasan for antibodies, R Tsien, S Yamada, S Méresse for plasmids. We thank R Vance and G Nolan for providing plasmids, cell lines and advice for retroviral transduction of primary macrophages, MC Michallet and S Djebali for purification of B and T cells, S Salcedo for protocols and advice on BMDC and Y Jamilloux for critical reading of the manuscript. We acknowledge the contribution of the PBES (P Contard, D Gallouche and S Blanc), PLATIM (C Chamot, C Lionnet), Cellulothèque (I Grosjean), flow cytometry (T Andrieu) platforms of SFR Biosciences Gerland-Lyon Sud (UMS344/US8). This work was supported by a Marie Curie reintegration grant (no.PIRG07-GA-2010-268399) and by a FINOVI Young investigator grant (http://www.finovi.org/en:start).
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Pierini, R., Juruj, C., Perret, M. et al. AIM2/ASC triggers caspase-8-dependent apoptosis in Francisella-infected caspase-1-deficient macrophages. Cell Death Differ 19, 1709–1721 (2012). https://doi.org/10.1038/cdd.2012.51
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DOI: https://doi.org/10.1038/cdd.2012.51
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