Biology subjects

Chui, A. J.

Publications and source records attributed to Chui, A. J..

3 recordsLinked to original sources

bioRxiv2022

Cytosolic peptide accumulation activates the NLRP1 and CARD8 inflammasomes

NLRP1 and CARD8 are related sensors that form inflammasomes, but the danger signals that they detect are not fully established. These proteins undergo autoproteolysis, generating repressive N-terminal (NT) and inflammatory C-terminal (CT) fragments. The proteasome- mediated degradation of the NT releases the CT from autoinhibition, but the CT is then sequestered in a complex with the full-length sensor and DPP9. Here, we show that cytosolic peptide accumulation activates these inflammasomes. We found that a diverse array of peptides accelerates NT degradation, and those with N-terminal XP sequences also destabilize the ternary complexes. Peptides interfere with many biological processes, including protein folding. We show that unrelated agents that disrupt protein folding also induce NT degradation, but do not cause inflammasome activation because DPP9 sequesters the CT fragments in the absence of XP peptides. Overall, these results indicate that NLRP1 and CARD8 detect protein misfolding that is associated with peptide accumulation.

immunology↗

bioRxiv2022

A ubiquitin-independent proteasome pathway controls the CARD8 inflammasome

CARD8 is a pattern-recognition receptor that forms a caspase-1-activating inflammasome. CARD8 undergoes autoproteolysis, generating an N-terminal (NT) fragment with a disordered region and a ZU5 domain and a C-terminal (CT) fragment with UPA and CARD domains. DPP8 and DPP9 (DPP8/9) inhibitors, including Val-boroPro (VbP), accelerate the degradation of the NT fragment via a poorly characterized proteasome-mediated pathway, thereby releasing the inflammatory CT fragment from autoinhibition. Here, we show that the core 20S proteasome, which degrades disordered and misfolded proteins independent of ubiquitin, controls CARD8 activation. In unstressed cells, the 20S proteasome degrades just the NT disordered region, leaving behind the folded ZU5, UPA, and CARD domains to act as an inhibitor of inflammasome assembly. In VbP-stressed cells, the 20S proteasome degrades the entire NT fragment, perhaps due to ZU5 domain unfolding, freeing the CT fragment from autoinhibition. Overall, this work shows that CARD8 NTs susceptibility to 20S proteasome-mediated degradation controls inflammasome activation.

immunology↗

bioRxiv2018

N-terminal degradation activates the Nlrp1b inflammasome

Intracellular pathogens and danger signals trigger the formation of inflammasomes, which activate inflammatory caspases and induce pyroptotic cell death. The anthrax lethal factor metalloprotease and small molecule DPP8/9 inhibitors both activate the Nlrp1b inflammasome, but the molecular mechanism of Nlrp1b activation is not known. Here, we used genome-wide CRISPR/Cas9 knockout screens to identify genes required for Nlrp1b-mediated pyroptosis, and discovered that lethal factor induces cell death via the N-end rule proteasomal degradation pathway. Lethal factor directly cleaves Nlrp1b, which induces the N-end rule-mediated degradation of the Nlrp1b N-terminus and thereby frees the Nlrp1b C-terminus to activate caspase-1. DPP8/9 inhibitors also induce proteasomal degradation of the Nlrp1b N-terminus, but, in contrast, not through the N-end rule pathway. Overall, these data reveal that N-terminal degradation is the common mechanism for activation of this innate immune sensor protein.\n\nOne Sentence SummaryProteasome-mediated degradation of the Nlrp1b N-terminus releases the Nlrp1b C-terminus to activate caspase-1 and induce pyroptotic cell death.

immunology↗