A ubiquitin-independent proteasome pathway controls activation of the CARD8 inflammasome.

TitleA ubiquitin-independent proteasome pathway controls activation of the CARD8 inflammasome.
Publication TypeJournal Article
Year of Publication2022
AuthorsHsiao JC, Neugroschl AR, Chui AJ, Taabuzing CY, Griswold AR, Wang Q, Huang H-C, Orth-He EL, Ball DP, Hiotis G, Bachovchin DA
JournalJ Biol Chem
Date Published2022 May 14

CARD8 is a pattern-recognition receptor that forms a caspase-1-activating inflammasome. CARD8 undergoes constitutive 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. Dipeptidyl peptidase (DPP) 8 and DPP9 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 modification, controls activation of the CARD8 inflammasome. In unstressed cells, we discovered that 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. However, in VbP-stressed cells, we show the 20S proteasome degrades the entire NT fragment, perhaps due to ZU5 domain unfolding, freeing the CT fragment from autoinhibition. Taken together, these results show that the susceptibility of the CARD8 NT domain to 20S proteasome-mediated degradation controls inflammasome activation.

Alternate JournalJ Biol Chem
PubMed ID35580636

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