Differential activation of the inflammasome by caspase-1 adaptors ASC and Ipaf

Abstract

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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Figure 1: ASC is essential for S. typhimurium-induced caspase-1 activation.
Figure 2: ASC deficiency impairs maturation of IL-1β and IL-18 in response to TLR agonists and extracellular ATP.
Figure 3: Ipaf is essential for caspase-1 activation in response to S. typhimurium.
Figure 4: ASC- and Ipaf-deficient macrophages are resistant to cell death induced by S. typhimurium infection.

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Acknowledgements

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.

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Correspondence to Vishva M. Dixit.

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Supplementary information

Supplementary Figure 1

Targeted disruption of the murine asc gene. (PDF 397 kb)

Supplementary Figure 2

LPS stimulation is not necessary for caspase-1 activation by S. typhimurium. (PDF 336 kb)

Supplementary Figure 3

Association of ASC and caspase-1 was not detected in macrophage cell lysates. (PDF 767 kb)

Supplementary Figure 4

Both TLR stimulation and extracellular ATP are required for caspase-1 activation and IL-1β release by macrophages. (PDF 870 kb)

Supplementary Figure 5

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)

Supplementary Figure 6

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)

Supplementary Figure 7

ASC is dispensable for normal LPS- and TNF-induced IKK and ERK activation. (PDF 775 kb)

Supplementary Figure 8

RIP2 is dispensable for caspase-1 activation. (PDF 503 kb)

Supplementary Figure 9

Generation of Ipaf-deficient mice. (PDF 279 kb)

Supplementary Figure 10

Expression of ASC and Ipaf is not effected in Ipaf-null macrophages and ASC-null macrophages, respectively. (PDF 943 kb)

Supplementary Figure Legends and References (DOC 44 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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