{"gene":"NLRP1","run_date":"2026-04-29T11:37:57","timeline":{"discoveries":[{"year":2019,"finding":"NLRP1B activation by anthrax lethal toxin cleavage proceeds through proteasome-mediated degradation of the N-terminal fragment, liberating a C-terminal fragment that potently activates caspase-1; proteasomal degradation is both necessary and sufficient for NLRP1B activation. The Shigella E3 ubiquitin ligase IpaH7.8 independently induces NLRP1B degradation and activation by the same mechanism ('functional degradation').","method":"In vitro assays, proteasome inhibitor experiments, IpaH7.8 E3 ligase identification, cell-based functional assays","journal":"Science","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal methods, mechanistic model validated with two independent pathogen effectors in one study","pmids":["30872533"],"is_preprint":false},{"year":2020,"finding":"Human NLRP1 is a direct sensor for double-stranded RNA; its leucine-rich repeat (LRR) domain binds dsRNA, which causes the NACHT domain to gain ATPase activity, triggering inflammasome activation. Semliki Forest virus replication and associated dsRNA formation is required and sufficient to engage human NLRP1.","method":"Biochemical dsRNA-binding assays, ATPase activity assays, viral infection studies in keratinocytes, deletion/domain analysis","journal":"Science","confidence":"High","confidence_rationale":"Tier 1–2 — biochemical reconstitution of binding and enzymatic activity with domain-level mechanistic detail","pmids":["33243852"],"is_preprint":false},{"year":2020,"finding":"Enteroviral 3C proteases directly cleave human NLRP1 at a single site (between Glu130 and Gly131), triggering N-glycine-mediated degradation of the autoinhibitory N-terminal fragment via the cullin–ZER1/ZYG11B E3 ligase complex, which liberates the activating C-terminal fragment and drives NLRP1 inflammasome assembly in airway epithelial cells.","method":"Protease cleavage assays, site-directed mutagenesis, ubiquitin ligase identification, primary airway epithelial cell infection with live HRV","journal":"Science","confidence":"High","confidence_rationale":"Tier 1–2 — direct cleavage site mapped, degradation pathway identified with multiple orthogonal approaches","pmids":["33093214"],"is_preprint":false},{"year":2021,"finding":"Cryo-EM structures of the human NLRP1–DPP9 complex (alone and with Val-boroPro) reveal a ternary complex containing DPP9, full-length NLRP1, and the NLRP1 C-terminal fragment (NLRP1 CT). DPP9 sequesters the NLRP1 CT; the N-terminus of NLRP1 CT inserts into the DPP9 active site. Full-length NLRP1 is required for NLRP1 CT binding to DPP9. VbP disrupts this interaction and accelerates N-terminal fragment degradation to induce inflammasome activation.","method":"Cryo-EM structure determination, co-immunoprecipitation, cell-based functional assays, autoproteolysis-deficient NLRP1 rescue experiments","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — atomic-resolution cryo-EM with functional validation and mutagenesis","pmids":["33731932"],"is_preprint":false},{"year":2021,"finding":"Structural and biochemical studies of rat NLRP1–DPP9 reveal a 2:1 complex containing autoinhibited full-length NLRP1 and one active UPA-CARD fragment; the ZU5 domain is required both for autoinhibition and complex assembly. Complex formation prevents UPA-mediated oligomerization of UPA-CARD and strengthens ZU5-mediated NLRP1 autoinhibition. Both DPP9 enzymatic activity and NLRP1 binding are required for DPP9-mediated suppression in human cells.","method":"Cryo-EM structure, biochemical reconstitution, structure-guided mutagenesis, cell-based inflammasome activation assays","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — two independent cryo-EM/structural studies (same issue) with orthogonal biochemical and functional validation","pmids":["33731929"],"is_preprint":false},{"year":2021,"finding":"Cryo-EM structures of NLRP1-CT and CARD8-CT assemblies show that respective CARD domains form central helical filaments surrounded by oligomerized UPA subdomains. The UPA lowers the threshold for CARD filament formation and signalling. NLRP1-CARD filament subunits dimerize with additional exterior CARDs, distinguishing NLRP1 from other known CARD filaments. An ASCCARD–caspase-1CARD octamer structure indicates ASC uses opposing surfaces for NLRP1 vs. caspase-1 recruitment.","method":"Cryo-EM structure determination, biochemical filament assays, cell-based ASC speck formation assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 — high-resolution cryo-EM with functional cellular validation","pmids":["33420033"],"is_preprint":false},{"year":2021,"finding":"Cryo-EM structures of human NLRP1 and CARD8 FIINDUPA-CARD assemblies show that NLRP1 forms a two-layered filament with an inner CARD core and outer FIINDUPA ring. NLRP1-CARD filaments alone are sufficient to drive ASC speck formation; FIINDUPA oligomers greatly enhance this. Unique structural features of NLRP1-CARD and CARD8-CARD enable selective discrimination between ASC and pro-caspase-1.","method":"Cryo-EM (3.7 Å), recombinant protein reconstitution, cell-based ASC speck formation assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 — cryo-EM plus biochemical reconstitution with cellular functional validation","pmids":["33420028"],"is_preprint":false},{"year":2022,"finding":"The ribotoxic stress response (RSR) activates human NLRP1 via MAP3K20/ZAKα kinase-driven direct hyperphosphorylation of a human-specific disordered linker region (NLRP1DR); downstream p38 also phosphorylates this region. Mutation of a single ZAKα phosphorylation site abrogates UVB- and ribotoxin-driven pyroptosis in keratinocytes. Fusing NLRP1DR to CARD8 confers NLRP1-like RSR sensing.","method":"Kinase assays, phosphoproteomic analysis, domain mutagenesis, keratinocyte functional assays, chimeric protein experiments","journal":"Science","confidence":"High","confidence_rationale":"Tier 1–2 — direct kinase–substrate relationship identified with mutagenesis and chimeric-protein rescue","pmids":["35857590"],"is_preprint":false},{"year":2022,"finding":"p38 kinase directly phosphorylates NLRP1 at serine 107 in the linker region, triggered by diverse signals including ribotoxic stress (ZAKα-dependent) and alphavirus infection (ZAKα and potentially other MAP3Ks). Phosphorylation is followed by ubiquitination of NLRP1 PYD, N-terminal degradation, and NLRP1 UPA-CARD inflammasome nucleation. Activation by nanobody-mediated ubiquitination, viral proteases, or DPP9 inhibition is p38-independent.","method":"Kinase assays, phospho-site mutagenesis, ubiquitination assays, viral infection experiments, pathway inhibitor studies","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 1–2 — direct phosphorylation demonstrated with site-specific mutagenesis and multiple activation paradigms tested","pmids":["36315050"],"is_preprint":false},{"year":2022,"finding":"Human NLRP1 senses SARS-CoV-2 infection in lung epithelial cells via cleavage at Q333 by multiple coronavirus 3CL proteases, triggering inflammasome assembly and cell death. 3CL proteases also inactivate Gasdermin D; consequently, caspase-3 and GSDME promote alternative pyroptosis.","method":"Protease cleavage assays, primary lung epithelial cell infection, NLRP1 knockout experiments, plasma biomarker analysis from COVID-19 patients","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 — direct cleavage site mapped with multiple orthogonal methods and patient validation","pmids":["35594856"],"is_preprint":false},{"year":2021,"finding":"Diverse viral proteases from picornaviruses cleave human NLRP1 within a rapidly evolving 'tripwire' region in a host-specific and virus-specific manner, leading to NLRP1 inflammasome activation. Host mimicry of viral polyprotein cleavage sites is an evolutionary strategy to activate innate immunity.","method":"Protease cleavage assays, cell-based inflammasome activation assays, evolutionary analysis of tripwire sequences","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 — multiple viral proteases tested, cleavage sites identified, functional activation confirmed","pmids":["33410748"],"is_preprint":false},{"year":2018,"finding":"DPP9 (dipeptidyl peptidase 9) is an endogenous inhibitor of human NLRP1 that binds to the FIIND domain of NLRP1. DPP9 represses NLRP1 inflammasome via both its scaffolding (FIIND-binding) function and its catalytic (peptidase) activity, which act synergistically. A patient-derived germline missense mutation in NLRP1 FIIND abrogates DPP9 binding and causes inflammasome hyperactivation in autoinflammatory disease.","method":"Proteomics screen, co-immunoprecipitation, CRISPR/Cas9 knockout, small-molecule DPP8/9 inhibitors, primary human cell assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods including proteomics, genetic knockout, pharmacological inhibition, and disease mutation","pmids":["30291141"],"is_preprint":false},{"year":2019,"finding":"DPP8/9 inhibitors activate all functional rodent NLRP1 alleles, indicating DPP8/9 inhibition induces a signal detected by all NLRP1 proteins regardless of allelic variation. The sensitivity pattern of NLRP1 alleles to DPP8/9 inhibition closely parallels sensitivity to Toxoplasma gondii, suggesting DPP8/9 inhibition phenocopies a key T. gondii activity.","method":"Cell-based pyroptosis assays across multiple rodent NLRP1 alleles, DPP8/9 inhibitor treatment, T. gondii infection comparison","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 — multiple alleles tested but indirect mechanistic link to T. gondii","pmids":["31383852"],"is_preprint":false},{"year":2015,"finding":"NLRP1 inflammasome functions in non-hematopoietic (colon epithelial) cells to attenuate colitis and colitis-associated tumorigenesis; Nlrp1b-/- mice show increased disease correlated with reduced IL-1β and IL-18. Bone marrow reconstitution experiments established the epithelial cell compartment as the relevant site of NLRP1 function.","method":"Nlrp1b knockout mouse colitis and cancer models, bone marrow reconstitution, cytokine measurements","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 — clean knockout mouse with defined phenotype and bone marrow reconstitution to place pathway","pmids":["25725098"],"is_preprint":false},{"year":2014,"finding":"Rat NLRP1 controls macrophage susceptibility to Toxoplasma gondii-induced pyroptosis and parasite replication. Knockdown of Nlrp1 in pyroptosis-sensitive macrophages increased parasite replication; reciprocally, overexpression of the NLRP1 variant from sensitive macrophages in resistant macrophages sensitized them to pyroptosis.","method":"siRNA knockdown, overexpression in resistant macrophages, Toxoplasma infection assays, IL-1β/IL-18 processing measurements","journal":"PLoS pathogens","confidence":"Medium","confidence_rationale":"Tier 2 — reciprocal gain/loss-of-function with defined cellular phenotype","pmids":["24626226"],"is_preprint":false},{"year":2015,"finding":"ATF4 transcription factor directly binds the NLRP1 promoter during ER stress and drives NLRP1 expression. Both IRE1α and PERK (but not ATF6) pathways modulate NLRP1 gene expression during ER stress.","method":"Mutagenesis, chromatin immunoprecipitation, CRISPR-Cas9 genome editing, reporter assays","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 1–2 — ChIP and mutagenesis identify direct ATF4-NLRP1 promoter interaction; pathway placement by genetic editing","pmids":["26086088"],"is_preprint":false},{"year":2022,"finding":"KSHV ORF45 protein activates human NLRP1 inflammasome through a non-protease mechanism by binding to the Linker1 region (between PYD and NACHT domains). At steady state, interaction between Linker1 and the UPA subdomain maintains NLRP1 in an auto-inhibitory conformation independent of DPP9. ORF45 displaces UPA from the Linker1-UPA complex, releasing the NLRP1 C-terminal domain for inflammasome assembly.","method":"Co-immunoprecipitation, domain deletion/mutagenesis, cell-based inflammasome activation assays, primate ortholog comparison","journal":"Nature immunology","confidence":"Medium","confidence_rationale":"Tier 2 — reciprocal binding experiments and domain-level mechanism identified with multiple cell-based readouts","pmids":["35618833"],"is_preprint":false},{"year":2023,"finding":"Diphtheria toxin (DT) triggers ZAKα-driven ribotoxic stress response (RSR) and NLRP1 inflammasome activation in primary human keratinocytes. This requires iron-mediated DT production in bacteria, diphthamide synthesis in host cells, and ZAKα/p38-driven NLRP1 phosphorylation. NLRP1 deletion abrogates IL-1β and IL-18 secretion; ZAKα inhibition is more protective than caspase-1 inhibition in a 3D skin model.","method":"Primary keratinocyte infection, gene knockout/deletion, pharmacologic kinase inhibitors, 3D skin model, cytokine assays","journal":"The Journal of experimental medicine","confidence":"Medium","confidence_rationale":"Tier 2 — mechanistic dissection in primary cells with genetic and pharmacological validation","pmids":["37642997"],"is_preprint":false},{"year":2024,"finding":"Nigericin activates the human NLRP1 inflammasome by depleting cytosolic potassium ions, which inhibits ribosome elongation and activates the RSR sensor kinase ZAKα, p38, JNK, and NLRP1 linker domain hyperphosphorylation. Extracellular K+ supplementation, ZAKα knockout, or ZAKα/p38 inhibitors block nigericin-induced NLRP1 pyroptosis in keratinocytes. Electroneutrality of ion movement is essential for RSR activation.","method":"Ion supplementation experiments, ZAKα knockout, kinase inhibitors, NLRP1 phosphorylation assays, ionophore panel screen","journal":"Proceedings of the National Academy of Sciences","confidence":"Medium","confidence_rationale":"Tier 2 — mechanistic connection between K+ efflux, ribosomal stress, and NLRP1 phosphorylation established with genetic and pharmacological tools","pmids":["38175865"],"is_preprint":false},{"year":2023,"finding":"The dsDNA mimetic poly(dA:dT) activates NLRP1 in human keratinocytes (where AIM2 is absent) through a pathway requiring oxidative nucleic acid damage and cellular stress that activates MAP3 kinases including ZAKα, which converge on p38 to activate NLRP1. RNA intermediates from poly(dA:dT) transcription are insufficient; the response is independent of AIM2, cGAS-STING, and NLRP3.","method":"Genetic knockouts (NLRP1, AIM2, ZAKα), pathway inhibitors, poly(dA:dT) transfection in keratinocytes, caspase-1 activation assays","journal":"Proceedings of the National Academy of Sciences","confidence":"Medium","confidence_rationale":"Tier 2 — genetic epistasis places poly(dA:dT) → oxidative stress → ZAKα → p38 → NLRP1 pathway","pmids":["36693106"],"is_preprint":false},{"year":2023,"finding":"Several agents that interfere with protein folding (aminopeptidase inhibitors, chaperone inhibitors, unfolded protein response inducers) accelerate N-terminal fragment degradation of NLRP1 but alone do not trigger inflammasome assembly because released CT fragments are sequestered by DPP9. DPP9-binding ligands must co-occur to disrupt CT–DPP9 complexes and allow CT oligomerization into inflammasomes.","method":"Cell-based inflammasome assays, protein folding stress inducers, DPP9 inhibitor combinations, biochemical fractionation","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 — two-signal requirement model established with multiple pharmacological combinations","pmids":["36649711"],"is_preprint":false},{"year":2013,"finding":"NLRP1 haplotypes carrying L155H and M1184V substitutions increase basal and TLR-stimulated IL-1β processing (1.8-fold basal increase) without altering NLRP1 RNA or protein levels, indicating that altered NLRP1 polypeptide function (not expression) drives inflammasome hyperactivation in autoimmune disease-associated haplotypes.","method":"Ex vivo monocyte IL-1β assays from haplotype-stratified donors, TLR agonist stimulation, protein/RNA quantification","journal":"Proceedings of the National Academy of Sciences","confidence":"Medium","confidence_rationale":"Tier 2 — functional consequence of specific coding variants established in primary human cells with longitudinal replication","pmids":["23382179"],"is_preprint":false},{"year":2017,"finding":"Rare loss-of-function variants in the N-terminal pyrin domain of NLRP1 confirm that the PYD domain is autoinhibitory; its loss causes familial autoinflammatory skin disease and requires NLRP1 autolytic cleavage within the FIIND domain for activation. Autolytic cleavage generates a C-terminal CARD-containing fragment that forms an ASC-dependent inflammasome, and under some conditions caspase-1 can be directly engaged without processing.","method":"Genetic variant analysis, functional domain mutagenesis, caspase-1 processing assays, ASC speck formation assays","journal":"Journal of molecular biology","confidence":"Medium","confidence_rationale":"Tier 2 — genetic and functional dissection of autoinhibitory PYD and FIIND domains","pmids":["28733143"],"is_preprint":false}],"current_model":"NLRP1 is an innate immune sensor that undergoes autoproteolysis within its FIIND domain to generate non-covalently associated N-terminal (autoinhibitory) and C-terminal (activating UPA-CARD) fragments; diverse pathogen-encoded enzymatic activities (anthrax lethal toxin, enteroviral/coronavirus 3C proteases, Shigella IpaH7.8 E3 ligase) trigger proteasomal degradation of the N-terminal fragment via a 'functional degradation' mechanism, while non-enzymatic activators such as dsRNA (sensed via the LRR domain), the ribotoxic stress response (via ZAKα/p38-mediated hyperphosphorylation of the linker region), and KSHV ORF45 (by displacing the Linker1–UPA autoinhibitory interaction) also liberate the C-terminal fragment; the endogenous inhibitor DPP9 sequesters the free C-terminal fragment in a ternary complex with full-length NLRP1, and DPP8/9 inhibitors or protein-folding stress disrupt this checkpoint to allow C-terminal fragment oligomerization into a CARD filament that recruits ASC and activates caspase-1, driving IL-1β/IL-18 maturation and pyroptosis."},"narrative":{"teleology":[{"year":2013,"claim":"Establishing that coding variants in NLRP1 alter inflammasome output at the protein level resolved whether disease-associated haplotypes act through expression or functional changes, setting the stage for domain-level mechanistic dissection.","evidence":"Ex vivo monocyte IL-1β assays from haplotype-stratified donors showing L155H/M1184V increase caspase-1 processing without altering NLRP1 levels","pmids":["23382179"],"confidence":"Medium","gaps":["Precise structural mechanism by which L155H or M1184V alter inflammasome threshold was not defined","Whether these variants affect DPP9 binding or autoproteolysis was not tested"]},{"year":2014,"claim":"Demonstrating that allelic variants of rat NLRP1 control macrophage pyroptosis and Toxoplasma replication established NLRP1 as a cell-autonomous anti-parasitic effector, though the direct activating signal remained unknown.","evidence":"Reciprocal siRNA knockdown and overexpression of NLRP1 alleles in rat macrophages during T. gondii infection","pmids":["24626226"],"confidence":"Medium","gaps":["Direct parasite-derived signal sensed by NLRP1 not identified","Whether functional degradation mechanism applies to Toxoplasma activation was not tested"]},{"year":2015,"claim":"Identifying NLRP1 function in non-hematopoietic epithelial cells during colitis established that NLRP1 acts as a tissue-resident inflammasome sensor beyond macrophages, while ATF4-mediated transcriptional upregulation during ER stress linked NLRP1 expression to cellular stress pathways.","evidence":"Nlrp1b knockout mice with bone marrow reconstitution in colitis models; ChIP and reporter assays identifying ATF4 binding to NLRP1 promoter","pmids":["25725098","26086088"],"confidence":"Medium","gaps":["Whether ER stress-driven NLRP1 expression leads to functional inflammasome activation in vivo was not established","Downstream epithelial signaling consequences beyond IL-1β/IL-18 were not characterized"]},{"year":2017,"claim":"Genetic and functional analysis of familial autoinflammatory mutations revealed that the PYD is autoinhibitory and that FIIND autoproteolysis is required for activation, establishing the two-fragment architecture as central to NLRP1 signaling.","evidence":"Disease-associated PYD loss-of-function variants with FIIND mutagenesis and ASC speck/caspase-1 processing assays","pmids":["28733143"],"confidence":"Medium","gaps":["How PYD physically restrains the C-terminal fragment was not structurally resolved","Whether DPP9 checkpoint was intact in these disease mutants was unknown"]},{"year":2018,"claim":"Discovery that DPP9 binds the FIIND domain and represses NLRP1 through both scaffolding and catalytic functions identified a dedicated endogenous checkpoint, and a patient mutation disrupting this interaction explained a Mendelian autoinflammatory phenotype.","evidence":"Proteomics screen, co-IP, CRISPR knockout of DPP9, and DPP8/9 inhibitor studies in primary human cells","pmids":["30291141"],"confidence":"High","gaps":["Structural basis of DPP9–FIIND interaction was unknown","Catalytic substrate of DPP9 relevant to NLRP1 repression was not identified"]},{"year":2019,"claim":"The 'functional degradation' model was established: anthrax lethal toxin cleavage and Shigella IpaH7.8-mediated ubiquitination independently trigger proteasomal destruction of the N-terminal fragment, liberating the C-terminal fragment for caspase-1 activation—unifying two pathogen effectors under one mechanism.","evidence":"Proteasome inhibitor experiments, IpaH7.8 identification, and cell-based assays with two independent pathogen effectors","pmids":["30872533"],"confidence":"High","gaps":["Whether functional degradation applied to human NLRP1 (vs. mouse NLRP1B) was not shown in this study","Identity of the E3 ligase for lethal toxin-cleaved fragment was not determined"]},{"year":2020,"claim":"Two key activating inputs for human NLRP1 were identified: enteroviral 3C protease cleavage at Glu130-Gly131 leading to N-end rule degradation via cullin–ZER1/ZYG11B, and direct dsRNA binding by the LRR domain triggering NACHT ATPase activity—revealing that human NLRP1 integrates both protease cleavage and nucleic acid sensing.","evidence":"Protease cleavage mapping with site-directed mutagenesis and E3 ligase identification in airway cells; biochemical dsRNA-binding and ATPase assays with viral infection in keratinocytes","pmids":["33093214","33243852"],"confidence":"High","gaps":["Whether dsRNA sensing and protease cleavage pathways converge on the same downstream degradation mechanism was not resolved","Structural basis for dsRNA recognition by the LRR was not determined"]},{"year":2021,"claim":"Cryo-EM structures of human and rat NLRP1–DPP9 ternary complexes revealed that DPP9 sequesters the freed C-terminal fragment by threading its N-terminus into the DPP9 active site, with full-length NLRP1 required as an adaptor, explaining how DPP8/9 inhibitors derepress the inflammasome; concurrent structures of UPA-CARD filaments showed a unique two-layered architecture where UPA oligomerization lowers the threshold for CARD filament nucleation and ASC recruitment.","evidence":"Cryo-EM at atomic resolution (human and rat complexes, NLRP1-CT/CARD8-CT filaments), reconstitution, mutagenesis, and ASC speck assays","pmids":["33731932","33731929","33420033","33420028"],"confidence":"High","gaps":["The DPP9 catalytic substrate relevant to NLRP1 repression remains unidentified","Structural transition from autoinhibited full-length to active oligomeric state was not captured"]},{"year":2021,"claim":"Systematic testing of diverse picornavirus proteases demonstrated that a rapidly evolving 'tripwire' region in human NLRP1 mimics viral polyprotein cleavage sites, establishing evolutionary host–pathogen co-adaptation as a design principle of NLRP1 sensing.","evidence":"Panel of viral 3C protease cleavage assays, evolutionary sequence analysis, and cell-based inflammasome activation","pmids":["33410748"],"confidence":"High","gaps":["Whether tripwire evolution imposes fitness costs or trade-offs was not addressed","Structural basis for cleavage site accessibility in full-length NLRP1 was not resolved"]},{"year":2022,"claim":"A non-protease, non-degradative activation pathway was defined: the ribotoxic stress response via ZAKα/p38 directly hyperphosphorylates a human-specific disordered linker region in NLRP1, and separately, KSHV ORF45 displaces the Linker1–UPA autoinhibitory interaction, revealing two DPP9-independent activation mechanisms.","evidence":"Kinase assays, phosphosite mutagenesis, chimeric proteins, domain mapping of ORF45–Linker1 interaction, and keratinocyte functional assays; SARS-CoV-2 3CL protease cleavage at Q333 mapped in lung epithelial cells","pmids":["35857590","36315050","35618833","35594856"],"confidence":"High","gaps":["How phosphorylation of the disordered linker mechanistically destabilizes the N-terminal fragment is unclear","Whether Linker1–UPA autoinhibition and DPP9-mediated sequestration cooperate quantitatively in vivo is undefined"]},{"year":2023,"claim":"The convergence of multiple stress signals—diphtheria toxin ribotoxicity, poly(dA:dT)-induced oxidative damage, and K+-efflux-driven ribosome stalling—on the ZAKα/p38→NLRP1 phosphorylation axis established the RSR as a general upstream integrator of NLRP1 activation, while a two-signal model showed that protein-folding stress accelerates NT degradation but DPP9 disruption is additionally required for CT release and inflammasome formation.","evidence":"Primary keratinocyte infections, ZAKα knockouts, K+ supplementation, pharmacological kinase/DPP9 inhibitor combinations, biochemical fractionation","pmids":["37642997","36693106","36649711","38175865"],"confidence":"Medium","gaps":["Whether the two-signal model (NT degradation + DPP9 displacement) applies to all activation stimuli has not been tested","The quantitative phosphorylation threshold for activation is not defined","How ion flux connects mechanistically to ribosomal collision/ZAKα activation at the molecular level is incomplete"]},{"year":null,"claim":"Key unresolved questions include the identity of the endogenous DPP9 catalytic substrate(s) that contribute to NLRP1 repression, the structural basis for dsRNA recognition by the LRR domain, how linker phosphorylation mechanistically destabilizes the N-terminal fragment, and whether NLRP1 directly senses Toxoplasma gondii or responds indirectly via host stress.","evidence":"","pmids":[],"confidence":"Low","gaps":["DPP9 catalytic substrate identity unknown","No structure of NLRP1 LRR–dsRNA complex","Direct Toxoplasma-derived NLRP1 agonist not identified","Full-length autoinhibited NLRP1 structure not yet determined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140299","term_label":"molecular sensor activity","supporting_discovery_ids":[0,1,2,7,9,10]},{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[1]},{"term_id":"GO:0140657","term_label":"ATP-dependent activity","supporting_discovery_ids":[1]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[3,4,22]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,3,5]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,1,2,5,7,9,13]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[0,2,9,14]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[7,8,18,19]}],"complexes":["NLRP1 inflammasome","NLRP1–DPP9 ternary complex"],"partners":["DPP9","ASC","CASP1","ZAK","MAPK14","IPAH7.8","ZYG11B"],"other_free_text":[]},"mechanistic_narrative":"NLRP1 is an inflammasome-forming innate immune sensor that detects diverse pathogen-associated enzymatic activities and cellular stress signals to activate caspase-1-driven pyroptosis and IL-1β/IL-18 maturation, functioning prominently in epithelial barrier tissues such as skin and airway. Autoproteolysis within the FIIND domain generates non-covalently associated N-terminal (autoinhibitory) and C-terminal (UPA-CARD, activating) fragments; pathogen proteases (enteroviral 3C, coronavirus 3CL, anthrax lethal toxin) and the Shigella E3 ligase IpaH7.8 trigger proteasomal degradation of the N-terminal fragment via a 'functional degradation' mechanism, while the ribotoxic stress response acts through ZAKα/p38-mediated hyperphosphorylation of a human-specific disordered linker to achieve the same outcome [PMID:30872533, PMID:33093214, PMID:35857590, PMID:35594856]. The endogenous inhibitor DPP9 sequesters the freed C-terminal fragment in a ternary complex with full-length NLRP1, and a separate Linker1–UPA autoinhibitory interaction provides DPP9-independent repression; disruption of either checkpoint—by DPP8/9 inhibitors, protein-folding stress, or the KSHV ORF45 protein—liberates the C-terminal fragment, which oligomerizes into a UPA-scaffolded CARD filament that nucleates ASC specks and activates caspase-1 [PMID:33731932, PMID:33731929, PMID:33420033, PMID:35618833, PMID:36649711]. Germline gain-of-function mutations in NLRP1 that disrupt PYD-mediated autoinhibition or DPP9 binding cause familial autoinflammatory skin disease [PMID:28733143, PMID:30291141]."},"prefetch_data":{"uniprot":{"accession":"Q9C000","full_name":"NACHT, LRR and PYD domains-containing protein 1","aliases":["Caspase recruitment domain-containing protein 7","Death effector filament-forming ced-4-like apoptosis protein","Nucleotide-binding domain and caspase recruitment domain"],"length_aa":1473,"mass_kda":165.9,"function":"Acts as the sensor component of the NLRP1 inflammasome, which mediates inflammasome activation in response to various pathogen-associated signals, leading to subsequent pyroptosis (PubMed:12191486, PubMed:17349957, PubMed:22665479, PubMed:27662089, PubMed:31484767, PubMed:33093214, PubMed:33410748, PubMed:33731929, PubMed:33731932, PubMed:35857590). Inflammasomes are supramolecular complexes that assemble in the cytosol in response to pathogens and other damage-associated signals and play critical roles in innate immunity and inflammation (PubMed:12191486, PubMed:17349957, PubMed:22665479). Acts as a recognition receptor (PRR): recognizes specific pathogens and other damage-associated signals, such as cleavage by some human enteroviruses and rhinoviruses, double-stranded RNA, UV-B irradiation, or Val-boroPro inhibitor, and mediates the formation of the inflammasome polymeric complex composed of NLRP1, CASP1 and PYCARD/ASC (PubMed:12191486, PubMed:17349957, PubMed:22665479, PubMed:25562666, PubMed:30096351, PubMed:30291141, PubMed:33093214, PubMed:33243852, PubMed:33410748, PubMed:35857590). In response to pathogen-associated signals, the N-terminal part of NLRP1 is degraded by the proteasome, releasing the cleaved C-terminal part of the protein (NACHT, LRR and PYD domains-containing protein 1, C-terminus), which polymerizes and associates with PYCARD/ASC to initiate the formation of the inflammasome complex: the NLRP1 inflammasome recruits pro-caspase-1 (proCASP1) and promotes caspase-1 (CASP1) activation, which subsequently cleaves and activates inflammatory cytokines IL1B and IL18 and gasdermin-D (GSDMD), leading to pyroptosis (PubMed:12191486, PubMed:17349957, PubMed:22665479, PubMed:32051255, PubMed:33093214). In the absence of GSDMD expression, the NLRP1 inflammasome is able to recruit and activate CASP8, leading to activation of gasdermin-E (GSDME) (PubMed:33852854, PubMed:35594856). Activation of NLRP1 inflammasome is also required for HMGB1 secretion; the active cytokines and HMGB1 stimulate inflammatory responses (PubMed:22801494). Binds ATP and shows ATPase activity (PubMed:11113115, PubMed:15212762, PubMed:33243852). Plays an important role in antiviral immunity and inflammation in the human airway epithelium (PubMed:33093214). Specifically recognizes a number of pathogen-associated signals: upon infection by human rhinoviruses 14 and 16 (HRV-14 and HRV-16), NLRP1 is cleaved and activated which triggers NLRP1-dependent inflammasome activation and IL18 secretion (PubMed:33093214). Positive-strand RNA viruses, such as Semliki forest virus and long dsRNA activate the NLRP1 inflammasome, triggering IL1B release in a NLRP1-dependent fashion (PubMed:33243852). Acts as a direct sensor for long dsRNA and thus RNA virus infection (PubMed:33243852). May also be activated by muramyl dipeptide (MDP), a fragment of bacterial peptidoglycan, in a NOD2-dependent manner (PubMed:18511561). The NLRP1 inflammasome is also activated in response to UV-B irradiation causing ribosome collisions: ribosome collisions cause phosphorylation and activation of NLRP1 in a MAP3K20-dependent manner, leading to pyroptosis (PubMed:35857590) Constitutes the precursor of the NLRP1 inflammasome, which mediates autoproteolytic processing within the FIIND domain to generate the N-terminal and C-terminal parts, which are associated non-covalently in absence of pathogens and other damage-associated signals Regulatory part that prevents formation of the NLRP1 inflammasome: in absence of pathogens and other damage-associated signals, interacts with the C-terminal part of NLRP1 (NACHT, LRR and PYD domains-containing protein 1, C-terminus), preventing activation of the NLRP1 inflammasome (PubMed:33093214). In response to pathogen-associated signals, this part is ubiquitinated and degraded by the proteasome, releasing the cleaved C-terminal part of the protein, which polymerizes and forms the NLRP1 inflammasome (PubMed:33093214) Constitutes the active part of the NLRP1 inflammasome (PubMed:33093214, PubMed:33731929, PubMed:33731932). In absence of pathogens and other damage-associated signals, interacts with the N-terminal part of NLRP1 (NACHT, LRR and PYD domains-containing protein 1, N-terminus), preventing activation of the NLRP1 inflammasome (PubMed:33093214). In response to pathogen-associated signals, the N-terminal part of NLRP1 is degraded by the proteasome, releasing this form, which polymerizes and associates with PYCARD/ASC to form of the NLRP1 inflammasome complex: the NLRP1 inflammasome complex then directly recruits pro-caspase-1 (proCASP1) and promotes caspase-1 (CASP1) activation, leading to gasdermin-D (GSDMD) cleavage and subsequent pyroptosis (PubMed:33093214) It is unclear whether is involved in inflammasome formation. It is not cleaved within the FIIND domain, does not assemble into specks, nor promote IL1B release (PubMed:22665479). 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NLRP1 Inflammasome Activation in Patients with Atopic Dermatitis.","date":"2023","source":"The Journal of investigative dermatology","url":"https://pubmed.ncbi.nlm.nih.gov/36736455","citation_count":22,"is_preprint":false},{"pmid":"37673864","id":"PMC_37673864","title":"A pathogen-induced putative NAC transcription factor mediates leaf rust resistance in barley.","date":"2023","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/37673864","citation_count":21,"is_preprint":false},{"pmid":"35216304","id":"PMC_35216304","title":"HuNAC20 and HuNAC25, Two Novel NAC Genes from Pitaya, Confer Cold Tolerance in Transgenic Arabidopsis.","date":"2022","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/35216304","citation_count":21,"is_preprint":false},{"pmid":"26847865","id":"PMC_26847865","title":"Evaluation of in vitro storage characteristics of cold stored platelet concentrates with N acetylcysteine (NAC).","date":"2016","source":"Transfusion and apheresis science : official journal of the World Apheresis Association : official journal of the European Society for Haemapheresis","url":"https://pubmed.ncbi.nlm.nih.gov/26847865","citation_count":20,"is_preprint":false},{"pmid":"37055801","id":"PMC_37055801","title":"Inhibition of NLRP1 inflammasome improves autophagy dysfunction and Aβ disposition in APP/PS1 mice.","date":"2023","source":"Behavioral and brain functions : BBF","url":"https://pubmed.ncbi.nlm.nih.gov/37055801","citation_count":20,"is_preprint":false},{"pmid":"37546258","id":"PMC_37546258","title":"Jasmonic acid regulates lignin deposition in poplar through JAZ5-MYB/NAC interaction.","date":"2023","source":"Frontiers in plant science","url":"https://pubmed.ncbi.nlm.nih.gov/37546258","citation_count":20,"is_preprint":false},{"pmid":"39557108","id":"PMC_39557108","title":"Eriocitrin ameliorates hepatic fibrosis and inflammation: The involvement of PPARα-mediated NLRP1/NLRC4 inflammasome signaling cascades.","date":"2024","source":"Journal of ethnopharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/39557108","citation_count":20,"is_preprint":false},{"pmid":"32276737","id":"PMC_32276737","title":"Inflammasome activation by NLRP1 and NLRC4 in patients with coronary stenosis.","date":"2020","source":"Immunobiology","url":"https://pubmed.ncbi.nlm.nih.gov/32276737","citation_count":20,"is_preprint":false},{"pmid":"32899791","id":"PMC_32899791","title":"Inflammasome Sensor NLRP1 Confers Acquired Drug Resistance to Temozolomide in Human Melanoma.","date":"2020","source":"Cancers","url":"https://pubmed.ncbi.nlm.nih.gov/32899791","citation_count":20,"is_preprint":false},{"pmid":"38365003","id":"PMC_38365003","title":"Advances in membrane-tethered NAC transcription factors in plants.","date":"2024","source":"Plant science : an international journal of experimental plant biology","url":"https://pubmed.ncbi.nlm.nih.gov/38365003","citation_count":19,"is_preprint":false},{"pmid":"37311351","id":"PMC_37311351","title":"Tripping the wire: sensing of viral protease activity by CARD8 and NLRP1 inflammasomes.","date":"2023","source":"Current opinion in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/37311351","citation_count":19,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":49576,"output_tokens":6105,"usd":0.120151},"stage2":{"model":"claude-opus-4-6","input_tokens":9799,"output_tokens":3672,"usd":0.211193},"total_usd":0.331344,"stage1_batch_id":"msgbatch_012ZiiCUBfB62NCTQd4Bk1Jo","stage2_batch_id":"msgbatch_01Xuqq9aUHoQouS7UVGZNStZ","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2019,\n      \"finding\": \"NLRP1B activation by anthrax lethal toxin cleavage proceeds through proteasome-mediated degradation of the N-terminal fragment, liberating a C-terminal fragment that potently activates caspase-1; proteasomal degradation is both necessary and sufficient for NLRP1B activation. The Shigella E3 ubiquitin ligase IpaH7.8 independently induces NLRP1B degradation and activation by the same mechanism ('functional degradation').\",\n      \"method\": \"In vitro assays, proteasome inhibitor experiments, IpaH7.8 E3 ligase identification, cell-based functional assays\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods, mechanistic model validated with two independent pathogen effectors in one study\",\n      \"pmids\": [\"30872533\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Human NLRP1 is a direct sensor for double-stranded RNA; its leucine-rich repeat (LRR) domain binds dsRNA, which causes the NACHT domain to gain ATPase activity, triggering inflammasome activation. Semliki Forest virus replication and associated dsRNA formation is required and sufficient to engage human NLRP1.\",\n      \"method\": \"Biochemical dsRNA-binding assays, ATPase activity assays, viral infection studies in keratinocytes, deletion/domain analysis\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — biochemical reconstitution of binding and enzymatic activity with domain-level mechanistic detail\",\n      \"pmids\": [\"33243852\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Enteroviral 3C proteases directly cleave human NLRP1 at a single site (between Glu130 and Gly131), triggering N-glycine-mediated degradation of the autoinhibitory N-terminal fragment via the cullin–ZER1/ZYG11B E3 ligase complex, which liberates the activating C-terminal fragment and drives NLRP1 inflammasome assembly in airway epithelial cells.\",\n      \"method\": \"Protease cleavage assays, site-directed mutagenesis, ubiquitin ligase identification, primary airway epithelial cell infection with live HRV\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct cleavage site mapped, degradation pathway identified with multiple orthogonal approaches\",\n      \"pmids\": [\"33093214\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Cryo-EM structures of the human NLRP1–DPP9 complex (alone and with Val-boroPro) reveal a ternary complex containing DPP9, full-length NLRP1, and the NLRP1 C-terminal fragment (NLRP1 CT). DPP9 sequesters the NLRP1 CT; the N-terminus of NLRP1 CT inserts into the DPP9 active site. Full-length NLRP1 is required for NLRP1 CT binding to DPP9. VbP disrupts this interaction and accelerates N-terminal fragment degradation to induce inflammasome activation.\",\n      \"method\": \"Cryo-EM structure determination, co-immunoprecipitation, cell-based functional assays, autoproteolysis-deficient NLRP1 rescue experiments\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — atomic-resolution cryo-EM with functional validation and mutagenesis\",\n      \"pmids\": [\"33731932\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Structural and biochemical studies of rat NLRP1–DPP9 reveal a 2:1 complex containing autoinhibited full-length NLRP1 and one active UPA-CARD fragment; the ZU5 domain is required both for autoinhibition and complex assembly. Complex formation prevents UPA-mediated oligomerization of UPA-CARD and strengthens ZU5-mediated NLRP1 autoinhibition. Both DPP9 enzymatic activity and NLRP1 binding are required for DPP9-mediated suppression in human cells.\",\n      \"method\": \"Cryo-EM structure, biochemical reconstitution, structure-guided mutagenesis, cell-based inflammasome activation assays\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — two independent cryo-EM/structural studies (same issue) with orthogonal biochemical and functional validation\",\n      \"pmids\": [\"33731929\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Cryo-EM structures of NLRP1-CT and CARD8-CT assemblies show that respective CARD domains form central helical filaments surrounded by oligomerized UPA subdomains. The UPA lowers the threshold for CARD filament formation and signalling. NLRP1-CARD filament subunits dimerize with additional exterior CARDs, distinguishing NLRP1 from other known CARD filaments. An ASCCARD–caspase-1CARD octamer structure indicates ASC uses opposing surfaces for NLRP1 vs. caspase-1 recruitment.\",\n      \"method\": \"Cryo-EM structure determination, biochemical filament assays, cell-based ASC speck formation assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution cryo-EM with functional cellular validation\",\n      \"pmids\": [\"33420033\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Cryo-EM structures of human NLRP1 and CARD8 FIINDUPA-CARD assemblies show that NLRP1 forms a two-layered filament with an inner CARD core and outer FIINDUPA ring. NLRP1-CARD filaments alone are sufficient to drive ASC speck formation; FIINDUPA oligomers greatly enhance this. Unique structural features of NLRP1-CARD and CARD8-CARD enable selective discrimination between ASC and pro-caspase-1.\",\n      \"method\": \"Cryo-EM (3.7 Å), recombinant protein reconstitution, cell-based ASC speck formation assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM plus biochemical reconstitution with cellular functional validation\",\n      \"pmids\": [\"33420028\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The ribotoxic stress response (RSR) activates human NLRP1 via MAP3K20/ZAKα kinase-driven direct hyperphosphorylation of a human-specific disordered linker region (NLRP1DR); downstream p38 also phosphorylates this region. Mutation of a single ZAKα phosphorylation site abrogates UVB- and ribotoxin-driven pyroptosis in keratinocytes. Fusing NLRP1DR to CARD8 confers NLRP1-like RSR sensing.\",\n      \"method\": \"Kinase assays, phosphoproteomic analysis, domain mutagenesis, keratinocyte functional assays, chimeric protein experiments\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct kinase–substrate relationship identified with mutagenesis and chimeric-protein rescue\",\n      \"pmids\": [\"35857590\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"p38 kinase directly phosphorylates NLRP1 at serine 107 in the linker region, triggered by diverse signals including ribotoxic stress (ZAKα-dependent) and alphavirus infection (ZAKα and potentially other MAP3Ks). Phosphorylation is followed by ubiquitination of NLRP1 PYD, N-terminal degradation, and NLRP1 UPA-CARD inflammasome nucleation. Activation by nanobody-mediated ubiquitination, viral proteases, or DPP9 inhibition is p38-independent.\",\n      \"method\": \"Kinase assays, phospho-site mutagenesis, ubiquitination assays, viral infection experiments, pathway inhibitor studies\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct phosphorylation demonstrated with site-specific mutagenesis and multiple activation paradigms tested\",\n      \"pmids\": [\"36315050\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Human NLRP1 senses SARS-CoV-2 infection in lung epithelial cells via cleavage at Q333 by multiple coronavirus 3CL proteases, triggering inflammasome assembly and cell death. 3CL proteases also inactivate Gasdermin D; consequently, caspase-3 and GSDME promote alternative pyroptosis.\",\n      \"method\": \"Protease cleavage assays, primary lung epithelial cell infection, NLRP1 knockout experiments, plasma biomarker analysis from COVID-19 patients\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct cleavage site mapped with multiple orthogonal methods and patient validation\",\n      \"pmids\": [\"35594856\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Diverse viral proteases from picornaviruses cleave human NLRP1 within a rapidly evolving 'tripwire' region in a host-specific and virus-specific manner, leading to NLRP1 inflammasome activation. Host mimicry of viral polyprotein cleavage sites is an evolutionary strategy to activate innate immunity.\",\n      \"method\": \"Protease cleavage assays, cell-based inflammasome activation assays, evolutionary analysis of tripwire sequences\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple viral proteases tested, cleavage sites identified, functional activation confirmed\",\n      \"pmids\": [\"33410748\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"DPP9 (dipeptidyl peptidase 9) is an endogenous inhibitor of human NLRP1 that binds to the FIIND domain of NLRP1. DPP9 represses NLRP1 inflammasome via both its scaffolding (FIIND-binding) function and its catalytic (peptidase) activity, which act synergistically. A patient-derived germline missense mutation in NLRP1 FIIND abrogates DPP9 binding and causes inflammasome hyperactivation in autoinflammatory disease.\",\n      \"method\": \"Proteomics screen, co-immunoprecipitation, CRISPR/Cas9 knockout, small-molecule DPP8/9 inhibitors, primary human cell assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods including proteomics, genetic knockout, pharmacological inhibition, and disease mutation\",\n      \"pmids\": [\"30291141\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"DPP8/9 inhibitors activate all functional rodent NLRP1 alleles, indicating DPP8/9 inhibition induces a signal detected by all NLRP1 proteins regardless of allelic variation. The sensitivity pattern of NLRP1 alleles to DPP8/9 inhibition closely parallels sensitivity to Toxoplasma gondii, suggesting DPP8/9 inhibition phenocopies a key T. gondii activity.\",\n      \"method\": \"Cell-based pyroptosis assays across multiple rodent NLRP1 alleles, DPP8/9 inhibitor treatment, T. gondii infection comparison\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple alleles tested but indirect mechanistic link to T. gondii\",\n      \"pmids\": [\"31383852\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"NLRP1 inflammasome functions in non-hematopoietic (colon epithelial) cells to attenuate colitis and colitis-associated tumorigenesis; Nlrp1b-/- mice show increased disease correlated with reduced IL-1β and IL-18. Bone marrow reconstitution experiments established the epithelial cell compartment as the relevant site of NLRP1 function.\",\n      \"method\": \"Nlrp1b knockout mouse colitis and cancer models, bone marrow reconstitution, cytokine measurements\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean knockout mouse with defined phenotype and bone marrow reconstitution to place pathway\",\n      \"pmids\": [\"25725098\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Rat NLRP1 controls macrophage susceptibility to Toxoplasma gondii-induced pyroptosis and parasite replication. Knockdown of Nlrp1 in pyroptosis-sensitive macrophages increased parasite replication; reciprocally, overexpression of the NLRP1 variant from sensitive macrophages in resistant macrophages sensitized them to pyroptosis.\",\n      \"method\": \"siRNA knockdown, overexpression in resistant macrophages, Toxoplasma infection assays, IL-1β/IL-18 processing measurements\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal gain/loss-of-function with defined cellular phenotype\",\n      \"pmids\": [\"24626226\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"ATF4 transcription factor directly binds the NLRP1 promoter during ER stress and drives NLRP1 expression. Both IRE1α and PERK (but not ATF6) pathways modulate NLRP1 gene expression during ER stress.\",\n      \"method\": \"Mutagenesis, chromatin immunoprecipitation, CRISPR-Cas9 genome editing, reporter assays\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — ChIP and mutagenesis identify direct ATF4-NLRP1 promoter interaction; pathway placement by genetic editing\",\n      \"pmids\": [\"26086088\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"KSHV ORF45 protein activates human NLRP1 inflammasome through a non-protease mechanism by binding to the Linker1 region (between PYD and NACHT domains). At steady state, interaction between Linker1 and the UPA subdomain maintains NLRP1 in an auto-inhibitory conformation independent of DPP9. ORF45 displaces UPA from the Linker1-UPA complex, releasing the NLRP1 C-terminal domain for inflammasome assembly.\",\n      \"method\": \"Co-immunoprecipitation, domain deletion/mutagenesis, cell-based inflammasome activation assays, primate ortholog comparison\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal binding experiments and domain-level mechanism identified with multiple cell-based readouts\",\n      \"pmids\": [\"35618833\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Diphtheria toxin (DT) triggers ZAKα-driven ribotoxic stress response (RSR) and NLRP1 inflammasome activation in primary human keratinocytes. This requires iron-mediated DT production in bacteria, diphthamide synthesis in host cells, and ZAKα/p38-driven NLRP1 phosphorylation. NLRP1 deletion abrogates IL-1β and IL-18 secretion; ZAKα inhibition is more protective than caspase-1 inhibition in a 3D skin model.\",\n      \"method\": \"Primary keratinocyte infection, gene knockout/deletion, pharmacologic kinase inhibitors, 3D skin model, cytokine assays\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic dissection in primary cells with genetic and pharmacological validation\",\n      \"pmids\": [\"37642997\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Nigericin activates the human NLRP1 inflammasome by depleting cytosolic potassium ions, which inhibits ribosome elongation and activates the RSR sensor kinase ZAKα, p38, JNK, and NLRP1 linker domain hyperphosphorylation. Extracellular K+ supplementation, ZAKα knockout, or ZAKα/p38 inhibitors block nigericin-induced NLRP1 pyroptosis in keratinocytes. Electroneutrality of ion movement is essential for RSR activation.\",\n      \"method\": \"Ion supplementation experiments, ZAKα knockout, kinase inhibitors, NLRP1 phosphorylation assays, ionophore panel screen\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic connection between K+ efflux, ribosomal stress, and NLRP1 phosphorylation established with genetic and pharmacological tools\",\n      \"pmids\": [\"38175865\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"The dsDNA mimetic poly(dA:dT) activates NLRP1 in human keratinocytes (where AIM2 is absent) through a pathway requiring oxidative nucleic acid damage and cellular stress that activates MAP3 kinases including ZAKα, which converge on p38 to activate NLRP1. RNA intermediates from poly(dA:dT) transcription are insufficient; the response is independent of AIM2, cGAS-STING, and NLRP3.\",\n      \"method\": \"Genetic knockouts (NLRP1, AIM2, ZAKα), pathway inhibitors, poly(dA:dT) transfection in keratinocytes, caspase-1 activation assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis places poly(dA:dT) → oxidative stress → ZAKα → p38 → NLRP1 pathway\",\n      \"pmids\": [\"36693106\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Several agents that interfere with protein folding (aminopeptidase inhibitors, chaperone inhibitors, unfolded protein response inducers) accelerate N-terminal fragment degradation of NLRP1 but alone do not trigger inflammasome assembly because released CT fragments are sequestered by DPP9. DPP9-binding ligands must co-occur to disrupt CT–DPP9 complexes and allow CT oligomerization into inflammasomes.\",\n      \"method\": \"Cell-based inflammasome assays, protein folding stress inducers, DPP9 inhibitor combinations, biochemical fractionation\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — two-signal requirement model established with multiple pharmacological combinations\",\n      \"pmids\": [\"36649711\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"NLRP1 haplotypes carrying L155H and M1184V substitutions increase basal and TLR-stimulated IL-1β processing (1.8-fold basal increase) without altering NLRP1 RNA or protein levels, indicating that altered NLRP1 polypeptide function (not expression) drives inflammasome hyperactivation in autoimmune disease-associated haplotypes.\",\n      \"method\": \"Ex vivo monocyte IL-1β assays from haplotype-stratified donors, TLR agonist stimulation, protein/RNA quantification\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional consequence of specific coding variants established in primary human cells with longitudinal replication\",\n      \"pmids\": [\"23382179\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Rare loss-of-function variants in the N-terminal pyrin domain of NLRP1 confirm that the PYD domain is autoinhibitory; its loss causes familial autoinflammatory skin disease and requires NLRP1 autolytic cleavage within the FIIND domain for activation. Autolytic cleavage generates a C-terminal CARD-containing fragment that forms an ASC-dependent inflammasome, and under some conditions caspase-1 can be directly engaged without processing.\",\n      \"method\": \"Genetic variant analysis, functional domain mutagenesis, caspase-1 processing assays, ASC speck formation assays\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic and functional dissection of autoinhibitory PYD and FIIND domains\",\n      \"pmids\": [\"28733143\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"NLRP1 is an innate immune sensor that undergoes autoproteolysis within its FIIND domain to generate non-covalently associated N-terminal (autoinhibitory) and C-terminal (activating UPA-CARD) fragments; diverse pathogen-encoded enzymatic activities (anthrax lethal toxin, enteroviral/coronavirus 3C proteases, Shigella IpaH7.8 E3 ligase) trigger proteasomal degradation of the N-terminal fragment via a 'functional degradation' mechanism, while non-enzymatic activators such as dsRNA (sensed via the LRR domain), the ribotoxic stress response (via ZAKα/p38-mediated hyperphosphorylation of the linker region), and KSHV ORF45 (by displacing the Linker1–UPA autoinhibitory interaction) also liberate the C-terminal fragment; the endogenous inhibitor DPP9 sequesters the free C-terminal fragment in a ternary complex with full-length NLRP1, and DPP8/9 inhibitors or protein-folding stress disrupt this checkpoint to allow C-terminal fragment oligomerization into a CARD filament that recruits ASC and activates caspase-1, driving IL-1β/IL-18 maturation and pyroptosis.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"NLRP1 is an inflammasome-forming innate immune sensor that detects diverse pathogen-associated enzymatic activities and cellular stress signals to activate caspase-1-driven pyroptosis and IL-1β/IL-18 maturation, functioning prominently in epithelial barrier tissues such as skin and airway. Autoproteolysis within the FIIND domain generates non-covalently associated N-terminal (autoinhibitory) and C-terminal (UPA-CARD, activating) fragments; pathogen proteases (enteroviral 3C, coronavirus 3CL, anthrax lethal toxin) and the Shigella E3 ligase IpaH7.8 trigger proteasomal degradation of the N-terminal fragment via a 'functional degradation' mechanism, while the ribotoxic stress response acts through ZAKα/p38-mediated hyperphosphorylation of a human-specific disordered linker to achieve the same outcome [PMID:30872533, PMID:33093214, PMID:35857590, PMID:35594856]. The endogenous inhibitor DPP9 sequesters the freed C-terminal fragment in a ternary complex with full-length NLRP1, and a separate Linker1–UPA autoinhibitory interaction provides DPP9-independent repression; disruption of either checkpoint—by DPP8/9 inhibitors, protein-folding stress, or the KSHV ORF45 protein—liberates the C-terminal fragment, which oligomerizes into a UPA-scaffolded CARD filament that nucleates ASC specks and activates caspase-1 [PMID:33731932, PMID:33731929, PMID:33420033, PMID:35618833, PMID:36649711]. Germline gain-of-function mutations in NLRP1 that disrupt PYD-mediated autoinhibition or DPP9 binding cause familial autoinflammatory skin disease [PMID:28733143, PMID:30291141].\",\n  \"teleology\": [\n    {\n      \"year\": 2013,\n      \"claim\": \"Establishing that coding variants in NLRP1 alter inflammasome output at the protein level resolved whether disease-associated haplotypes act through expression or functional changes, setting the stage for domain-level mechanistic dissection.\",\n      \"evidence\": \"Ex vivo monocyte IL-1β assays from haplotype-stratified donors showing L155H/M1184V increase caspase-1 processing without altering NLRP1 levels\",\n      \"pmids\": [\"23382179\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Precise structural mechanism by which L155H or M1184V alter inflammasome threshold was not defined\", \"Whether these variants affect DPP9 binding or autoproteolysis was not tested\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Demonstrating that allelic variants of rat NLRP1 control macrophage pyroptosis and Toxoplasma replication established NLRP1 as a cell-autonomous anti-parasitic effector, though the direct activating signal remained unknown.\",\n      \"evidence\": \"Reciprocal siRNA knockdown and overexpression of NLRP1 alleles in rat macrophages during T. gondii infection\",\n      \"pmids\": [\"24626226\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct parasite-derived signal sensed by NLRP1 not identified\", \"Whether functional degradation mechanism applies to Toxoplasma activation was not tested\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identifying NLRP1 function in non-hematopoietic epithelial cells during colitis established that NLRP1 acts as a tissue-resident inflammasome sensor beyond macrophages, while ATF4-mediated transcriptional upregulation during ER stress linked NLRP1 expression to cellular stress pathways.\",\n      \"evidence\": \"Nlrp1b knockout mice with bone marrow reconstitution in colitis models; ChIP and reporter assays identifying ATF4 binding to NLRP1 promoter\",\n      \"pmids\": [\"25725098\", \"26086088\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether ER stress-driven NLRP1 expression leads to functional inflammasome activation in vivo was not established\", \"Downstream epithelial signaling consequences beyond IL-1β/IL-18 were not characterized\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Genetic and functional analysis of familial autoinflammatory mutations revealed that the PYD is autoinhibitory and that FIIND autoproteolysis is required for activation, establishing the two-fragment architecture as central to NLRP1 signaling.\",\n      \"evidence\": \"Disease-associated PYD loss-of-function variants with FIIND mutagenesis and ASC speck/caspase-1 processing assays\",\n      \"pmids\": [\"28733143\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How PYD physically restrains the C-terminal fragment was not structurally resolved\", \"Whether DPP9 checkpoint was intact in these disease mutants was unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Discovery that DPP9 binds the FIIND domain and represses NLRP1 through both scaffolding and catalytic functions identified a dedicated endogenous checkpoint, and a patient mutation disrupting this interaction explained a Mendelian autoinflammatory phenotype.\",\n      \"evidence\": \"Proteomics screen, co-IP, CRISPR knockout of DPP9, and DPP8/9 inhibitor studies in primary human cells\",\n      \"pmids\": [\"30291141\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of DPP9–FIIND interaction was unknown\", \"Catalytic substrate of DPP9 relevant to NLRP1 repression was not identified\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"The 'functional degradation' model was established: anthrax lethal toxin cleavage and Shigella IpaH7.8-mediated ubiquitination independently trigger proteasomal destruction of the N-terminal fragment, liberating the C-terminal fragment for caspase-1 activation—unifying two pathogen effectors under one mechanism.\",\n      \"evidence\": \"Proteasome inhibitor experiments, IpaH7.8 identification, and cell-based assays with two independent pathogen effectors\",\n      \"pmids\": [\"30872533\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether functional degradation applied to human NLRP1 (vs. mouse NLRP1B) was not shown in this study\", \"Identity of the E3 ligase for lethal toxin-cleaved fragment was not determined\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Two key activating inputs for human NLRP1 were identified: enteroviral 3C protease cleavage at Glu130-Gly131 leading to N-end rule degradation via cullin–ZER1/ZYG11B, and direct dsRNA binding by the LRR domain triggering NACHT ATPase activity—revealing that human NLRP1 integrates both protease cleavage and nucleic acid sensing.\",\n      \"evidence\": \"Protease cleavage mapping with site-directed mutagenesis and E3 ligase identification in airway cells; biochemical dsRNA-binding and ATPase assays with viral infection in keratinocytes\",\n      \"pmids\": [\"33093214\", \"33243852\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether dsRNA sensing and protease cleavage pathways converge on the same downstream degradation mechanism was not resolved\", \"Structural basis for dsRNA recognition by the LRR was not determined\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Cryo-EM structures of human and rat NLRP1–DPP9 ternary complexes revealed that DPP9 sequesters the freed C-terminal fragment by threading its N-terminus into the DPP9 active site, with full-length NLRP1 required as an adaptor, explaining how DPP8/9 inhibitors derepress the inflammasome; concurrent structures of UPA-CARD filaments showed a unique two-layered architecture where UPA oligomerization lowers the threshold for CARD filament nucleation and ASC recruitment.\",\n      \"evidence\": \"Cryo-EM at atomic resolution (human and rat complexes, NLRP1-CT/CARD8-CT filaments), reconstitution, mutagenesis, and ASC speck assays\",\n      \"pmids\": [\"33731932\", \"33731929\", \"33420033\", \"33420028\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The DPP9 catalytic substrate relevant to NLRP1 repression remains unidentified\", \"Structural transition from autoinhibited full-length to active oligomeric state was not captured\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Systematic testing of diverse picornavirus proteases demonstrated that a rapidly evolving 'tripwire' region in human NLRP1 mimics viral polyprotein cleavage sites, establishing evolutionary host–pathogen co-adaptation as a design principle of NLRP1 sensing.\",\n      \"evidence\": \"Panel of viral 3C protease cleavage assays, evolutionary sequence analysis, and cell-based inflammasome activation\",\n      \"pmids\": [\"33410748\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether tripwire evolution imposes fitness costs or trade-offs was not addressed\", \"Structural basis for cleavage site accessibility in full-length NLRP1 was not resolved\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"A non-protease, non-degradative activation pathway was defined: the ribotoxic stress response via ZAKα/p38 directly hyperphosphorylates a human-specific disordered linker region in NLRP1, and separately, KSHV ORF45 displaces the Linker1–UPA autoinhibitory interaction, revealing two DPP9-independent activation mechanisms.\",\n      \"evidence\": \"Kinase assays, phosphosite mutagenesis, chimeric proteins, domain mapping of ORF45–Linker1 interaction, and keratinocyte functional assays; SARS-CoV-2 3CL protease cleavage at Q333 mapped in lung epithelial cells\",\n      \"pmids\": [\"35857590\", \"36315050\", \"35618833\", \"35594856\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How phosphorylation of the disordered linker mechanistically destabilizes the N-terminal fragment is unclear\", \"Whether Linker1–UPA autoinhibition and DPP9-mediated sequestration cooperate quantitatively in vivo is undefined\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"The convergence of multiple stress signals—diphtheria toxin ribotoxicity, poly(dA:dT)-induced oxidative damage, and K+-efflux-driven ribosome stalling—on the ZAKα/p38→NLRP1 phosphorylation axis established the RSR as a general upstream integrator of NLRP1 activation, while a two-signal model showed that protein-folding stress accelerates NT degradation but DPP9 disruption is additionally required for CT release and inflammasome formation.\",\n      \"evidence\": \"Primary keratinocyte infections, ZAKα knockouts, K+ supplementation, pharmacological kinase/DPP9 inhibitor combinations, biochemical fractionation\",\n      \"pmids\": [\"37642997\", \"36693106\", \"36649711\", \"38175865\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether the two-signal model (NT degradation + DPP9 displacement) applies to all activation stimuli has not been tested\", \"The quantitative phosphorylation threshold for activation is not defined\", \"How ion flux connects mechanistically to ribosomal collision/ZAKα activation at the molecular level is incomplete\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the identity of the endogenous DPP9 catalytic substrate(s) that contribute to NLRP1 repression, the structural basis for dsRNA recognition by the LRR domain, how linker phosphorylation mechanistically destabilizes the N-terminal fragment, and whether NLRP1 directly senses Toxoplasma gondii or responds indirectly via host stress.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"DPP9 catalytic substrate identity unknown\", \"No structure of NLRP1 LRR–dsRNA complex\", \"Direct Toxoplasma-derived NLRP1 agonist not identified\", \"Full-length autoinhibited NLRP1 structure not yet determined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140299\", \"supporting_discovery_ids\": [0, 1, 2, 7, 9, 10]},\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [3, 4, 22]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 3, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 1, 2, 5, 7, 9, 13]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [0, 2, 9, 14]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [7, 8, 18, 19]}\n    ],\n    \"complexes\": [\n      \"NLRP1 inflammasome\",\n      \"NLRP1–DPP9 ternary complex\"\n    ],\n    \"partners\": [\n      \"DPP9\",\n      \"ASC\",\n      \"CASP1\",\n      \"ZAK\",\n      \"MAPK14\",\n      \"IpaH7.8\",\n      \"ZYG11B\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}