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Sci Rep. 2018 Feb 28;8(1):3788. doi: 10.1038/s41598-018-21998-3.

ASC- and caspase-8-dependent apoptotic pathway diverges from the NLRC4 inflammasome in macrophages.

Author information

1
Department of Physiological Chemistry, Genentech Inc., South San Francisco, California, USA.
2
Department of Bioinformatics, Genentech Inc., South San Francisco, California, USA.
3
Department of Molecular Biology, Genentech Inc., South San Francisco, California, USA.
4
Department of Pathology, Genentech Inc., South San Francisco, California, USA.
5
Department of Physiological Chemistry, Genentech Inc., South San Francisco, California, USA. kayagaki.nobuhiko@gene.com.

Abstract

The NLRC4 inflammasome recognizes bacterial flagellin and components of the type III secretion apparatus. NLRC4 stimulation leads to caspase-1 activation followed by a rapid lytic cell death known as pyroptosis. NLRC4 is linked to pathogen-free auto-inflammatory diseases, suggesting a role for NLRC4 in sterile inflammation. Here, we show that NLRC4 activates an alternative cell death program morphologically similar to apoptosis in caspase-1-deficient BMDMs. By performing an unbiased genome-wide CRISPR/Cas9 screen with subsequent validation studies in gene-targeted mice, we highlight a critical role for caspase-8 and ASC adaptor in an alternative apoptotic pathway downstream of NLRC4. Furthermore, caspase-1 catalytically dead knock-in (Casp1 C284A KI) BMDMs genetically segregate pyroptosis and apoptosis, and confirm that caspase-1 does not functionally compete with ASC for NLRC4 interactions. We show that NLRC4/caspase-8-mediated apoptotic cells eventually undergo plasma cell membrane damage in vitro, suggesting that this pathway can lead to secondary necrosis. Unexpectedly, we found that DFNA5/GSDME, a member of the pore-forming gasdermin family, is dispensable for the secondary necrosis that follows NLRC4-mediated apoptosis in macrophages. Together, our data confirm the existence of an alternative caspase-8 activation pathway diverging from the NLRC4 inflammasome in primary macrophages.

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