{"doi":"10.1016/j.jbc.2022.102032","title":"A ubiquitin-independent proteasome pathway controls activation of the CARD8 inflammasome","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. 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. Several intracellular danger-associated signals induce the assembly of multiprotein complexes called inflammasomes (1Broz P. Dixit V.M. Inflammasomes: mechanism of assembly, regulation and signalling.Nat. Rev. Immunol. 2016; 16: 407-420Crossref PubMed Scopus (2091) Google Scholar, 2Rathinam V.A. Fitzgerald K.A. Inflammasome complexes: emerging mechanisms and effector functions.Cell. 2016; 165: 792-800Abstract Full Text Full Text PDF PubMed Scopus (683) Google Scholar). The typical process of inflammasome formation involves a pattern recognition receptor (PRR) protein detecting a specific danger signal, self-oligomerizing, and then recruiting (directly or indirectly via the adapter protein ASC) the cysteine protease caspase-1 (CASP1). CASP1 undergoes proximity-induced autoproteolysis on this platform, generating an active enzyme that cleaves and activates gasdermin D (GSDMD) and, in most cases, interleukin-1β (IL-1β) and IL-18. The N-terminal fragment of cleaved GSDMD (GSDMDp30) forms pores in the cell membrane, releasing the activated cytokines and triggering pyroptotic cell death. CARD8 is a human PRR that forms an inflammasome (3Johnson D.C. Taabazuing C.Y. Okondo M.C. Chui A.J. Rao S.D. Brown F.C. et al.DPP8/DPP9 inhibitor-induced pyroptosis for treatment of acute myeloid leukemia.Nat. Med. 2018; 24: 1151-1156Crossref PubMed Scopus (218) Google Scholar). CARD8 has an N-terminal unstructured region consisting of ∼160 amino acids followed by a function-to-find domain and a caspase act","journal":"Journal of Biological Chemistry","year":2022,"id":252593,"datarank":0.47670807455219194,"base_score":3.1780538303479458,"endowment":3.1780538303479458,"self_citation_contribution":0.47670807455219194,"citation_network_contribution":0.0,"self_endowment_contribution":0.47670807455219194,"citer_contribution":0.0,"corpus_percentile":null,"corpus_rank":null,"citation_count":23,"citer_count":0,"citers_with_citation_signal":0,"citers_with_endowment":0,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.9481,"is_data_producer":false,"deposit_databanks":null,"is_oa":true,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2022-01-01","fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":897785,"name":"Atara R. Neugroschl","orcid":null,"position":1,"is_corresponding":false},{"id":324256,"name":"Ashley J. Chui","orcid":"0000-0003-0037-5761","position":2,"is_corresponding":false},{"id":260796,"name":"Cornelius Y. Taabazuing","orcid":"0000-0003-2361-5457","position":3,"is_corresponding":false},{"id":260797,"name":"Andrew R. Griswold","orcid":"0000-0003-2957-2355","position":4,"is_corresponding":false},{"id":308912,"name":"Qinghui Wang","orcid":"0000-0002-1223-8193","position":5,"is_corresponding":false},{"id":274276,"name":"Hsin‐Che Huang","orcid":"0000-0001-8677-7803","position":6,"is_corresponding":false},{"id":260798,"name":"Elizabeth L. Orth-He","orcid":"0000-0002-8180-1330","position":7,"is_corresponding":false},{"id":260795,"name":"Daniel P. Ball","orcid":"0000-0003-0693-7614","position":8,"is_corresponding":false},{"id":737902,"name":"Giorgos Hiotis","orcid":null,"position":9,"is_corresponding":false},{"id":260803,"name":"Daniel A. Bachovchin","orcid":"0000-0001-8210-1662","position":10,"is_corresponding":false},{"id":324258,"name":"Jeffrey C. Hsiao","orcid":"0000-0002-4363-9467","position":0,"is_corresponding":true}],"reference_count":29,"raw_metadata":{"citation_network_status":"fetched"},"created_at":"2026-07-19T00:24:50.819822Z","pmid":"35580636","pmcid":null,"fwci":null,"citation_percentile":null,"influential_citations":0,"oa_status":null,"license":null,"views":0,"total_file_size_bytes":0,"version_count":0,"fair_f":null,"fair_a":null,"fair_i":null,"fair_r":null,"fair_zscore":null,"fair_rationale":null,"fair_model":null,"fair_agent_version":null,"fair_fulltext_source":null,"fair_has_llm":null,"fair_computed_at":null,"clinical_trials":[],"software_tools":[],"db_accessions":[],"linked_datasets":[],"topics":[]}