Specific adaptors regulate the activation of initiator caspases; for example, FADD and Apaf-1 engage caspases 8 and 9, respectively1. The adaptors ASC, Ipaf and RIP2 have each been proposed to regulate caspase-1 (also called interleukin (IL)-1 converting enzyme), which is activated within the ‘inflammasome’, a complex comprising several adaptors2. Here we show the impact of ASC-, Ipaf- or RIP2-deficiency on inflammasome function. ASC was essential for extracellular ATP-driven activation of caspase-1 in toll-like receptor (TLR)-stimulated macrophages. Accordingly, ASC-deficient macrophages exhibited defective maturation of IL-1β and IL-18, and ASC-null mice were resistant to lipopolysaccharide-induced endotoxic shock. Furthermore, activation of caspase-1 in response to an intracellular pathogen (Salmonella typhimurium) was abrogated severely in ASC-null macrophages. Unexpectedly, Ipaf-deficient macrophages activated caspase-1 in response to TLR plus ATP stimulation but not S. typhimurium. Caspase-1 activation was not compromised by loss of RIP2. These data show that whereas ASC is key to caspase-1 activation within the inflammasome, Ipaf provides a special conduit to the inflammasome for signals triggered by intracellular pathogens. Notably, cell death triggered by stimuli that engage caspase-1 was ablated in macrophages lacking either ASC or Ipaf, suggesting a coupling between the inflammatory and cell death pathways.
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We thank D. Dornan and other members of the Dixit laboratory for discussions, E. Humke for help with illustrations, and K. O'Rourke, D. Wadley, Z. Gu, C. Olsson, M. Bauer, L. Tom, J. Kloss, M. Fuentes, M. Osborn, C. Tan, J. Hongo, T. Wong and A. Chuntharapai for technical assistance.
The authors declare that they have no competing financial interests.
Targeted disruption of the murine asc gene. (PDF 397 kb)
LPS stimulation is not necessary for caspase-1 activation by S. typhimurium. (PDF 336 kb)
Association of ASC and caspase-1 was not detected in macrophage cell lysates. (PDF 767 kb)
Both TLR stimulation and extracellular ATP are required for caspase-1 activation and IL-1β release by macrophages. (PDF 870 kb)
Defective secretion of IL-1β by asc-/- macrophages is due to defective maturation of pro-IL-1β rather than impaired release of mature IL-1β. (PDF 684 kb)
ASC-deficient mice challenged with LPS and ATP produce less IL-α, IL-1β and IL-18 than their wild-type counterparts. (PDF 214 kb)
ASC is dispensable for normal LPS- and TNF-induced IKK and ERK activation. (PDF 775 kb)
RIP2 is dispensable for caspase-1 activation. (PDF 503 kb)
Generation of Ipaf-deficient mice. (PDF 279 kb)
Expression of ASC and Ipaf is not effected in Ipaf-null macrophages and ASC-null macrophages, respectively. (PDF 943 kb)
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Mariathasan, S., Newton, K., Monack, D. et al. Differential activation of the inflammasome by caspase-1 adaptors ASC and Ipaf. Nature 430, 213–218 (2004). https://doi.org/10.1038/nature02664
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