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

Publication Type	Academic Article
Authors	Hsiao J, Neugroschl A, Chui A, Taabazuing C, Griswold A, Wang Q, Huang H, Orth-He E, Ball D, Hiotis G, Bachovchin D
Journal	J Biol Chem
Volume	298
Issue	7
Pagination	102032
Date Published	05/14/2022
ISSN	1083-351X
Keywords	CARD Signaling Adaptor Proteins, Inflammasomes, Proteasome Endopeptidase Complex
Abstract	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 8 and dipeptidyl peptidase 9 inhibitors, including Val-boroPro, 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 Val-boroPro-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.
DOI	10.1016/j.jbc.2022.102032
PubMed ID	35580636
PubMed Central ID	PMC9213247