{"gene":"DPP8","run_date":"2026-06-09T23:54:42","timeline":{"discoveries":[{"year":2000,"finding":"DPP8 is a cytoplasmic, non-glycosylated, monomeric (~100 kDa) serine dipeptidyl aminopeptidase with post-proline cleavage activity, hydrolyzing DPPIV substrates Ala-Pro, Arg-Pro, and Gly-Pro, with a neutral pH optimum consistent with non-lysosomal localization. It lacks a transmembrane domain.","method":"Recombinant expression in COS-7 cells, Western blot, confocal microscopy, enzymatic activity assay with chromogenic substrates","journal":"European journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro enzymatic assay with defined substrates, direct subcellular localization by confocal microscopy and fractionation, multiple orthogonal methods in a single study","pmids":["11012666"],"is_preprint":false},{"year":2004,"finding":"Purified recombinant DPP8 expressed in Sf9 insect cells is enzymatically active, cleaving post-proline peptide bonds with kcat similar to DPP-IV, and shows substrate preference at both the P1 and P2 sites.","method":"Baculovirus expression in Sf9 cells, protein purification to homogeneity, kinetic assay with chromogenic substrates (H-Gly-Pro-pNA and others)","journal":"Protein expression and purification","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstituted in vitro enzymatic activity with purified protein and multiple substrates, kinetic constants determined","pmids":["15039077"],"is_preprint":false},{"year":2006,"finding":"DPP8 is predominantly dimeric in purified form and in cell extracts, as shown by analytical ultracentrifugation and native gel electrophoresis. Four conserved C-terminal loop residues (Phe822, Val833, Tyr844, His859) are required for optimal enzymatic activity but not for dimerization, indicating dimerization alone is insufficient for activity. These mutations decrease kcat and dramatically increase Km independent of substrate. DPP8 shows strict substrate selectivity for hydrophobic or basic residues at the P2 site, unlike DPP-IV.","method":"Analytical ultracentrifugation, native gel electrophoresis, site-directed mutagenesis, enzyme kinetics","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstitution with mutagenesis, multiple orthogonal methods (AUC + native gel + kinetics), detailed mechanistic dissection of dimer interface and substrate specificity","pmids":["17040910"],"is_preprint":false},{"year":2006,"finding":"DPP8 overexpression impairs cell migration on collagen I and wound healing on collagen I and fibronectin. These effects on cell survival, adhesion, and wound healing are independent of DPP8's catalytic serine, indicating an extraenzymatic mechanism.","method":"Overexpression of GFP-fusion proteins, cell migration (transwell), wound healing assay, catalytic serine mutant","journal":"The FEBS journal","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — overexpression with defined phenotypic readouts and catalytic mutant controls, single lab, no endogenous loss-of-function","pmids":["16704418"],"is_preprint":false},{"year":2006,"finding":"DPP8 overexpression enhances induced apoptosis. This effect is independent of the catalytic serine, indicating an extraenzymatic pro-apoptotic function.","method":"Overexpression of GFP-fusion proteins, apoptosis assay, catalytic serine mutant","journal":"The FEBS journal","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — overexpression with apoptosis readout and catalytic mutant, single lab","pmids":["16704418"],"is_preprint":false},{"year":2010,"finding":"Hydrophilic residues lining the S1/S2 substrate pockets of DPP8 (D772, Y315, H434, D435) contribute to both catalysis and dimer stabilization. Mutations at these positions reduce catalytic activity and affect dimerization, and homology modeling places D772, H434, and D435 at the junction between the alpha-beta hydrolase and beta-propeller domains.","method":"Site-directed mutagenesis, substrate kinetics, size-exclusion chromatography, homology modeling","journal":"Biological chemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — mutagenesis with kinetics and SEC, single lab, no independent replication","pmids":["20536396"],"is_preprint":false},{"year":2016,"finding":"Inhibition of DPP8 and DPP9 (but not DPP4 or other post-proline cleaving proteases alone) by Val-boroPro triggers pyroptosis in monocytes and macrophages via activation of pro-caspase-1 independently of the inflammasome adaptor ASC. Activated pro-caspase-1 does not efficiently process itself or IL-1β but cleaves and activates gasdermin D. Mice lacking caspase-1 do not show immune stimulation after Val-boroPro treatment.","method":"Selective inhibitors, caspase-1 knockout mice, genetic rescue experiments, cell death assays (LDH, PI staining), immunoblot for gasdermin D cleavage","journal":"Nature chemical biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (pharmacological inhibition + genetic KO + mechanistic dissection), replicated across cell types and species","pmids":["27820798"],"is_preprint":false},{"year":2018,"finding":"Inhibition of DPP8 and DPP9 in mouse myeloid cells activates the inflammasome sensor Nlrp1b, which in turn activates pro-caspase-1 to mediate pyroptosis. DPP8/9 thus serve as an intracellular checkpoint restraining Nlrp1b and innate immune activation.","method":"Genetic epistasis (Nlrp1b knockout/overexpression), selective inhibitors, cell death assays, caspase-1 activation assays","journal":"Cell chemical biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis with Nlrp1b KO, pharmacological inhibition, multiple cell types, mechanistic pathway placement","pmids":["29396289"],"is_preprint":false},{"year":2018,"finding":"In human myeloid cells, DPP8/9 inhibitor-induced pyroptosis is mediated by CARD8 (not NLRP1b), which activates pro-caspase-1 to induce cell death. This identifies CARD8 as an activator in human cells responding to DPP8/9 inhibition.","method":"CARD8 knockdown/knockout, pro-caspase-1 inhibitors, cell death assays in human AML cell lines and primary AML samples","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO/KD of CARD8 with defined pyroptotic phenotype, validated in multiple human cell lines and primary samples","pmids":["29967349"],"is_preprint":false},{"year":2019,"finding":"DPP8/9 inhibitors activate all functional rodent NLRP1 alleles, indicating that DPP8/9 inhibition generates a signal sensed universally by NLRP1 proteins regardless of allelic variation. NLRP1 allele sensitivities to DPP8/9 inhibition and Toxoplasma gondii infection are strikingly similar, suggesting DPP8/9 inhibition phenocopies a T. gondii activity.","method":"Overexpression of diverse NLRP1 alleles, selective DPP8/9 inhibitors, pyroptosis assays, comparison with T. gondii infection","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple alleles tested in defined genetic system, pharmacological and biological comparator, single lab","pmids":["31383852"],"is_preprint":false},{"year":2020,"finding":"DPP8/9 inhibitors activate pyroptosis in resting human and rodent CD4+ and CD8+ T lymphocytes via CARD8. Activated human T cells, despite expressing CARD8 and required proteins, are completely resistant to DPP8/9 inhibitors, revealing a cell-state-dependent checkpoint.","method":"CARD8 knockdown, selective DPP8/9 inhibitors, cell death assays in resting vs. activated T cells","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic knockdown with defined phenotype across multiple cell types and states, single lab","pmids":["32796818"],"is_preprint":false},{"year":2023,"finding":"DPP8 and DPP9 are not required to cleave the vast majority of proline-containing peptides generated by the proteasome in cell lysates, indicating a much more limited substrate scope than previously suggested by pseudopeptide reporter studies.","method":"Peptide degradation assays in cell lysates with DPP8/9 inhibitors or knockout, broad peptide array","journal":"Israel journal of chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — systematic biochemical screen in cell lysates with inhibitors and genetic tools, negative finding with mechanistic implication, single lab","pmids":["37982048"],"is_preprint":false},{"year":2025,"finding":"DPP8 and DPP9 process the N-terminus of cytosolic adenylate kinase 2 (AK2), exposing an IAP-binding motif (IBM) that enables IAP E3 ligase-mediated proteasomal degradation of AK2. N-terminal acetylation by NatA blocks this IAP interaction and stabilizes cytosolic AK2. A genome-wide in silico screen identified 129 potential substrates with IBMs that could be unmasked by DPP8/9 processing; EIF2A was experimentally validated as one such substrate.","method":"Co-immunoprecipitation, N-terminal processing assays, IBM mutagenesis, NatA knockdown, genome-wide in silico screen with experimental validation of EIF2A","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 1 / Moderate — biochemical reconstitution of processing, binding partner identification (IAPs), mutagenesis of IBM, multiple orthogonal methods, two substrates validated experimentally","pmids":["40312560"],"is_preprint":false},{"year":2025,"finding":"A genetically encoded fluorescent sensor (DiPAK) based on AK2 processing by DPP8/9 enables real-time monitoring of DPP8/9 activity in living cells. Using this sensor, LPS-induced primary B-cell activation was found to depend on DPP8/9, as absence of DPP8/9 activity results in apoptotic (not pyroptotic) cell death; DPP8/9 activity increases during B-cell maturation.","method":"Ratiometric fluorescent sensor in live cells, DPP9 overexpression/knockout, LPS stimulation, B-cell maturation assays","journal":"Life science alliance","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — novel sensor validated by genetic perturbation, direct functional consequence demonstrated in primary B cells, single lab","pmids":["40355159"],"is_preprint":false},{"year":2021,"finding":"DPP8 and DPP9 promote TGF-β1/Smad signaling-dependent epithelial-to-mesenchymal transition (EMT) and tubulointerstitial fibrosis. siRNA knockdown of DPP8 or DPP9 in TGF-β1-treated HK-2 cells decreases EMT- and ECM-related proteins, an effect reversible by lentiviral DPP8 re-expression.","method":"siRNA knockdown, lentiviral rescue, DPP8/9 inhibitor TC-E5007, UUO mouse model, HK-2 cell EMT assays, immunoblot for Smad signaling","journal":"Pharmacological research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function with rescue, pathway placement via Smad signaling, in vivo and in vitro corroboration, single lab","pmids":["33932609"],"is_preprint":false},{"year":2024,"finding":"DPP8 promotes TGF-β1-induced ECM deposition in human mesangial cells via Smad2/3 and Akt phosphorylation. siRNA silencing of DPP8 inhibits TGF-β1-induced collagen III, collagen IV, fibronectin, and MMP2 expression, as well as phosphorylation of Smad2, Smad3, and Akt.","method":"siRNA knockdown, TGF-β1 stimulation, immunoblot for Smad and Akt phosphorylation, ECM protein expression in human mesangial cells","journal":"Toxicology letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic loss-of-function with defined signaling readouts, single lab, corroborated by parallel DPP9 findings","pmids":["38458339"],"is_preprint":false},{"year":2026,"finding":"MST1 knockdown modulates DPP8 protein expression, thereby regulating the NLRP1/Caspase-1/GSDMD-N signaling axis to inhibit microglial pyroptosis in an Alzheimer's disease mouse model, positioning DPP8 downstream of MST1 in this neuroinflammatory pathway.","method":"MST1 knockdown in 5xFAD mice, immunoblot for DPP8 and downstream NLRP1/caspase-1/GSDMD-N, behavioral assays","journal":"Journal of neuroinflammation","confidence":"Low","confidence_rationale":"Tier 3 / Weak — indirect placement of DPP8 downstream of MST1 by knockdown, no direct DPP8 manipulation, single study","pmids":["41689046"],"is_preprint":false}],"current_model":"DPP8 is an intracellular cytoplasmic serine dipeptidyl aminopeptidase that cleaves N-terminal Xaa-Pro dipeptides from substrates (including AK2 and EIF2A), exposing neo-N-termini that can unmask IAP-binding motifs to trigger proteasomal degradation; its inhibition relieves a checkpoint that restrains the NLRP1 and CARD8 inflammasomes, triggering gasdermin D-dependent pyroptosis via caspase-1 in a cell-type-specific manner, while also promoting TGF-β1/Smad-dependent fibrotic signaling and possessing extraenzymatic roles in cell adhesion, migration, and apoptosis independent of its catalytic activity."},"narrative":{"mechanistic_narrative":"DPP8 is an intracellular, non-glycosylated serine dipeptidyl aminopeptidase that cleaves N-terminal Xaa-Pro dipeptides from cytosolic substrates at neutral pH, distinguishing it from lysosomal and membrane-anchored post-proline peptidases [PMID:11012666, PMID:15039077]. It is enzymatically active with kinetics comparable to DPP-IV but imposes strict selectivity for hydrophobic or basic residues at the P2 site; its activity depends on conserved C-terminal loop residues and on residues lining the S1/S2 pockets that also contribute to dimerization, though dimerization alone is insufficient for catalysis [PMID:17040910, PMID:20536396]. A defining cellular role is as an N-terminal processing enzyme that exposes IAP-binding motifs on substrates such as adenylate kinase 2 (AK2) and EIF2A, licensing IAP E3 ligase-mediated proteasomal degradation, a fate counteracted by NatA-mediated N-terminal acetylation [PMID:40312560]. Functionally, DPP8 (with DPP9) acts as an intracellular checkpoint restraining inflammasome activation: its pharmacological inhibition triggers gasdermin D-dependent pyroptosis through pro-caspase-1, sensed by Nlrp1b in mouse myeloid cells and by CARD8 in human myeloid cells and T lymphocytes in a cell-state-dependent manner [PMID:27820798, PMID:29396289, PMID:29967349, PMID:32796818]. DPP8 additionally promotes TGF-β1/Smad-dependent epithelial-to-mesenchymal transition and fibrotic extracellular-matrix deposition [PMID:33932609, PMID:38458339], and carries catalysis-independent functions in cell migration, adhesion, and apoptosis [PMID:16704418].","teleology":[{"year":2000,"claim":"Establishing that DPP8 was a genuine post-proline-cleaving peptidase distinct in localization from the known DPP-IV answered whether a cytoplasmic enzyme could perform Xaa-Pro dipeptidase chemistry outside the lysosomal/membrane compartment.","evidence":"Recombinant expression in COS-7 cells with confocal localization and chromogenic substrate assays","pmids":["11012666"],"confidence":"High","gaps":["No physiological substrate identified at this stage","Quaternary structure and active-site architecture undefined"]},{"year":2004,"claim":"Purification to homogeneity and kinetic characterization established that DPP8 is intrinsically catalytically competent with DPP-IV-like turnover, settling whether activity required cellular cofactors.","evidence":"Baculovirus expression in Sf9 cells, purification, kinetic assays with multiple chromogenic substrates","pmids":["15039077"],"confidence":"High","gaps":["Natural substrates remained unknown","Did not address oligomeric state requirements"]},{"year":2006,"claim":"Structural and mutational dissection defined DPP8 as a dimer with a distinct P2 substrate preference and showed that specific C-terminal loop and pocket residues govern catalysis independently of dimer assembly, refining how the enzyme achieves selectivity.","evidence":"Analytical ultracentrifugation, native gels, site-directed mutagenesis, and enzyme kinetics; homology modeling","pmids":["17040910","20536396"],"confidence":"High","gaps":["No experimental crystal structure","Substrate selectivity inferred from synthetic peptides, not endogenous targets"]},{"year":2006,"claim":"Overexpression with catalytic-serine mutants revealed that DPP8 modulates cell migration, adhesion, wound healing, and apoptosis through a mechanism independent of its peptidase activity, introducing extraenzymatic roles.","evidence":"GFP-fusion overexpression with transwell/wound-healing and apoptosis assays plus catalytic mutant controls","pmids":["16704418"],"confidence":"Medium","gaps":["No endogenous loss-of-function validation","Molecular partners mediating the non-catalytic effects unidentified","Single lab"]},{"year":2016,"claim":"Demonstrating that DPP8/9 inhibition triggers ASC-independent, caspase-1- and gasdermin D-dependent pyroptosis defined these enzymes as suppressors of an inflammatory cell-death pathway.","evidence":"Selective inhibitors, caspase-1 knockout mice, gasdermin D cleavage immunoblots, cell-death assays","pmids":["27820798"],"confidence":"High","gaps":["The upstream sensor was not yet identified","Endogenous substrate linking DPP8/9 activity to the checkpoint unknown"]},{"year":2018,"claim":"Genetic epistasis identified the sensors downstream of DPP8/9 inhibition, with Nlrp1b operating in mouse myeloid cells and CARD8 in human myeloid cells, establishing species-specific inflammasome wiring of the checkpoint.","evidence":"Nlrp1b and CARD8 knockout/knockdown with selective inhibitors and caspase-1 activation assays in mouse and human cells including primary AML","pmids":["29396289","29967349"],"confidence":"High","gaps":["Biochemical signal generated by DPP8/9 inhibition that activates the sensors not defined","Did not resolve why sensitivity differs across cell types"]},{"year":2019,"claim":"Showing that all functional rodent NLRP1 alleles respond to DPP8/9 inhibition, mirroring Toxoplasma gondii sensitivity, indicated a universal NLRP1-sensed signal and a possible pathogen-mimicking mechanism.","evidence":"Overexpression of diverse NLRP1 alleles with inhibitors and comparison to T. gondii infection","pmids":["31383852"],"confidence":"Medium","gaps":["Molecular identity of the shared signal unresolved","Single lab"]},{"year":2020,"claim":"Extending the checkpoint to lymphocytes revealed that DPP8/9 inhibition drives CARD8-dependent pyroptosis in resting but not activated T cells, establishing a cell-state-dependent control of the pathway.","evidence":"CARD8 knockdown and selective inhibitors in resting versus activated human and rodent T cells","pmids":["32796818"],"confidence":"Medium","gaps":["Mechanism conferring resistance in activated T cells unknown","Single lab"]},{"year":2021,"claim":"Systematic peptide-degradation profiling demonstrated that DPP8/9 do not process most proline-containing proteasomal peptides, narrowing the enzymes' substrate scope from earlier reporter-based assumptions.","evidence":"Broad peptide degradation assays in cell lysates with inhibitors and knockout","pmids":["37982048"],"confidence":"Medium","gaps":["Negative result; did not pinpoint the bona fide physiological substrates","Lysate context may not reflect intact-cell processing"]},{"year":2025,"claim":"Identifying AK2 and EIF2A as DPP8/9 substrates whose N-terminal processing unmasks IAP-binding motifs for proteasomal degradation provided the first defined endogenous substrate mechanism, linking peptidase activity to regulated protein turnover and a degron logic counteracted by NatA acetylation.","evidence":"Co-IP, N-terminal processing and IBM mutagenesis, NatA knockdown, genome-wide in silico screen with EIF2A validation; live-cell DiPAK sensor linking DPP8/9 activity to B-cell activation","pmids":["40312560","40355159"],"confidence":"High","gaps":["Only two of 129 candidate substrates experimentally validated","Link between substrate processing and the NLRP1/CARD8 checkpoint not directly established"]},{"year":2021,"claim":"Loss-of-function with rescue placed DPP8 as a positive regulator of TGF-β1/Smad and Akt signaling driving EMT and fibrotic ECM deposition, broadening its physiological role beyond immunity.","evidence":"siRNA knockdown with lentiviral rescue, DPP8/9 inhibitor, UUO mouse model, and Smad/Akt immunoblots in HK-2 and mesangial cells","pmids":["33932609","38458339"],"confidence":"Medium","gaps":["Whether the fibrotic effect requires catalytic activity not resolved","Direct DPP8 substrate in the TGF-β1 pathway unknown"]},{"year":2026,"claim":"Positioning DPP8 downstream of MST1 in microglial NLRP1/caspase-1/GSDMD pyroptosis extended the checkpoint to a neuroinflammatory disease context.","evidence":"MST1 knockdown in 5xFAD mice with downstream immunoblots and behavioral assays","pmids":["41689046"],"confidence":"Low","gaps":["DPP8 placement is indirect with no direct DPP8 manipulation","How MST1 controls DPP8 expression undefined","Single study"]},{"year":null,"claim":"It remains unknown which endogenous substrate(s) processed by DPP8/9 generate the signal sensed by NLRP1/CARD8, and how catalytic versus extraenzymatic activities are partitioned across immunity, fibrosis, and migration.","evidence":"","pmids":[],"confidence":"Low","gaps":["No direct biochemical link between identified substrates (AK2/EIF2A) and inflammasome activation","Extraenzymatic partners undefined","No experimental high-resolution structure of human DPP8"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,1,2,12]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,1,2]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,12]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[6,7,8,10]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[6,7,8]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[12]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[14,15]}],"complexes":[],"partners":["DPP9","AK2","EIF2A"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q6V1X1","full_name":"Dipeptidyl peptidase 8","aliases":["Dipeptidyl peptidase IV-related protein 1","DPRP-1","Dipeptidyl peptidase VIII","DPP VIII","Prolyl dipeptidase DPP8"],"length_aa":898,"mass_kda":103.4,"function":"Dipeptidyl peptidase that cleaves off N-terminal dipeptides from proteins having a Pro or Ala residue at position 2 (PubMed:11012666, PubMed:12534281, PubMed:12662155, PubMed:15039077, PubMed:15664838, PubMed:20536396, PubMed:29382749). Acts as a key inhibitor of caspase-1-dependent monocyte and macrophage pyroptosis in resting cells by preventing activation of NLRP1 and CARD8 (PubMed:27820798, PubMed:29967349, PubMed:32796818). Sequesters the cleaved C-terminal part of NLRP1 and CARD8, which respectively constitute the active part of the NLRP1 and CARD8 inflammasomes, in a ternary complex, thereby preventing their oligomerization and activation (PubMed:33731929, PubMed:33731932, PubMed:34019797). The dipeptidyl peptidase activity is required to suppress NLRP1 and CARD8; however, neither NLRP1 nor CARD8 are bona fide substrates of DPP8, suggesting the existence of substrate(s) required for NLRP1 and CARD8 inhibition (By similarity)","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q6V1X1/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/DPP8","classification":"Not Classified","n_dependent_lines":3,"n_total_lines":1208,"dependency_fraction":0.0024834437086092716},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/DPP8","total_profiled":1310},"omim":[{"mim_id":"608258","title":"DIPEPTIDYL PEPTIDASE IX; DPP9","url":"https://www.omim.org/entry/608258"},{"mim_id":"606819","title":"DIPEPTIDYL PEPTIDASE VIII; DPP8","url":"https://www.omim.org/entry/606819"},{"mim_id":"606636","title":"NLR FAMILY, PYRIN DOMAIN-CONTAINING 1; NLRP1","url":"https://www.omim.org/entry/606636"},{"mim_id":"600185","title":"BRCA2 DNA REPAIR-ASSOCIATED PROTEIN; BRCA2","url":"https://www.omim.org/entry/600185"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Cytosol","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/DPP8"},"hgnc":{"alias_symbol":["DP8","DPRP1","MSTP141","FLJ14920","FLJ20283","MGC26191"],"prev_symbol":[]},"alphafold":{"accession":"Q6V1X1","domains":[{"cath_id":"3.40.50.1820","chopping":"48-73_646-895","consensus_level":"high","plddt":94.9247,"start":48,"end":895},{"cath_id":"2.40.128","chopping":"528-624","consensus_level":"medium","plddt":93.7055,"start":528,"end":624}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6V1X1","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q6V1X1-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q6V1X1-F1-predicted_aligned_error_v6.png","plddt_mean":90.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=DPP8","jax_strain_url":"https://www.jax.org/strain/search?query=DPP8"},"sequence":{"accession":"Q6V1X1","fasta_url":"https://rest.uniprot.org/uniprotkb/Q6V1X1.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q6V1X1/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6V1X1"}},"corpus_meta":[{"pmid":"29967349","id":"PMC_29967349","title":"DPP8/DPP9 inhibitor-induced pyroptosis for treatment of acute myeloid leukemia.","date":"2018","source":"Nature medicine","url":"https://pubmed.ncbi.nlm.nih.gov/29967349","citation_count":304,"is_preprint":false},{"pmid":"27820798","id":"PMC_27820798","title":"DPP8 and DPP9 inhibition induces pro-caspase-1-dependent monocyte and macrophage pyroptosis.","date":"2016","source":"Nature chemical biology","url":"https://pubmed.ncbi.nlm.nih.gov/27820798","citation_count":243,"is_preprint":false},{"pmid":"11012666","id":"PMC_11012666","title":"Cloning, expression and chromosomal localization of a novel human dipeptidyl peptidase (DPP) IV homolog, DPP8.","date":"2000","source":"European journal of biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/11012666","citation_count":242,"is_preprint":false},{"pmid":"29396289","id":"PMC_29396289","title":"Inhibition of Dpp8/9 Activates the Nlrp1b Inflammasome.","date":"2018","source":"Cell chemical biology","url":"https://pubmed.ncbi.nlm.nih.gov/29396289","citation_count":163,"is_preprint":false},{"pmid":"32796818","id":"PMC_32796818","title":"DPP8/9 inhibitors activate the CARD8 inflammasome in resting lymphocytes.","date":"2020","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/32796818","citation_count":90,"is_preprint":false},{"pmid":"17967935","id":"PMC_17967935","title":"Regulation of expression and function of dipeptidyl peptidase 4 (DP4), DP8/9, and DP10 in allergic responses of the lung in rats.","date":"2007","source":"The journal of histochemistry and cytochemistry : official journal of the Histochemistry Society","url":"https://pubmed.ncbi.nlm.nih.gov/17967935","citation_count":82,"is_preprint":false},{"pmid":"31383852","id":"PMC_31383852","title":"DPP8/9 inhibitors are universal activators of functional NLRP1 alleles.","date":"2019","source":"Cell death & 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chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/17040910","citation_count":34,"is_preprint":false},{"pmid":"31792328","id":"PMC_31792328","title":"DPP8 is a novel therapeutic target for multiple myeloma.","date":"2019","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/31792328","citation_count":29,"is_preprint":false},{"pmid":"26454447","id":"PMC_26454447","title":"The Dipeptidyl Peptidases 4, 8, and 9 in Mouse Monocytes and Macrophages: DPP8/9 Inhibition Attenuates M1 Macrophage Activation in Mice.","date":"2016","source":"Inflammation","url":"https://pubmed.ncbi.nlm.nih.gov/26454447","citation_count":29,"is_preprint":false},{"pmid":"15039077","id":"PMC_15039077","title":"Purification and characterization of human prolyl dipeptidase DPP8 in Sf9 insect cells.","date":"2004","source":"Protein expression and purification","url":"https://pubmed.ncbi.nlm.nih.gov/15039077","citation_count":28,"is_preprint":false},{"pmid":"23850796","id":"PMC_23850796","title":"DPP8 and DPP9 expression in cynomolgus monkey and Sprague Dawley rat tissues.","date":"2013","source":"Regulatory peptides","url":"https://pubmed.ncbi.nlm.nih.gov/23850796","citation_count":16,"is_preprint":false},{"pmid":"33932609","id":"PMC_33932609","title":"Profibrotic mechanisms of DPP8 and DPP9 highly expressed in the proximal renal tubule epithelial cells.","date":"2021","source":"Pharmacological research","url":"https://pubmed.ncbi.nlm.nih.gov/33932609","citation_count":15,"is_preprint":false},{"pmid":"30467600","id":"PMC_30467600","title":"Expression and clinical role of the dipeptidyl peptidases DPP8 and DPP9 in ovarian carcinoma.","date":"2018","source":"Virchows Archiv : an international journal of pathology","url":"https://pubmed.ncbi.nlm.nih.gov/30467600","citation_count":14,"is_preprint":false},{"pmid":"16110352","id":"PMC_16110352","title":"Expression of a novel dipeptidyl peptidase 8 (DPP8) transcript variant, DPP8-v3, in human testis.","date":"2005","source":"Asian journal of andrology","url":"https://pubmed.ncbi.nlm.nih.gov/16110352","citation_count":11,"is_preprint":false},{"pmid":"20536396","id":"PMC_20536396","title":"Hydrophilic residues surrounding the S1 and S2 pockets contribute to dimerisation and catalysis in human dipeptidyl peptidase 8 (DP8).","date":"2010","source":"Biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/20536396","citation_count":11,"is_preprint":false},{"pmid":"26579375","id":"PMC_26579375","title":"Establishment of a selective evaluation method for DPP4 inhibitors based on recombinant human DPP8 and DPP9 proteins.","date":"2014","source":"Acta pharmaceutica Sinica. B","url":"https://pubmed.ncbi.nlm.nih.gov/26579375","citation_count":10,"is_preprint":false},{"pmid":"7790083","id":"PMC_7790083","title":"Monoclonal antibodies against Haemophilus lipopolysaccharides: clone DP8 specific for Haemophilus ducreyi and clone DH24 binding to lacto-N-neotetraose.","date":"1995","source":"Infection and immunity","url":"https://pubmed.ncbi.nlm.nih.gov/7790083","citation_count":8,"is_preprint":false},{"pmid":"37048172","id":"PMC_37048172","title":"DPP8 Selective Inhibitor Tominostat as a Novel and Broad-Spectrum Anticancer Agent against Hematological Malignancies.","date":"2023","source":"Cells","url":"https://pubmed.ncbi.nlm.nih.gov/37048172","citation_count":7,"is_preprint":false},{"pmid":"38458339","id":"PMC_38458339","title":"DPP8/9 inhibition attenuates the TGF-β1-induced excessive deposition of extracellular matrix (ECM) in human mesangial cells via Smad and Akt signaling pathways.","date":"2024","source":"Toxicology letters","url":"https://pubmed.ncbi.nlm.nih.gov/38458339","citation_count":7,"is_preprint":false},{"pmid":"40312560","id":"PMC_40312560","title":"DPP8/9 processing of human AK2 unmasks an IAP binding motif.","date":"2025","source":"EMBO reports","url":"https://pubmed.ncbi.nlm.nih.gov/40312560","citation_count":4,"is_preprint":false},{"pmid":"37230592","id":"PMC_37230592","title":"The amino-dipeptidyl peptidases DPP8 and DPP9: Purification and enzymatic assays.","date":"2023","source":"Methods in enzymology","url":"https://pubmed.ncbi.nlm.nih.gov/37230592","citation_count":3,"is_preprint":false},{"pmid":"40665400","id":"PMC_40665400","title":"DPP8 and DPP9 promote tubular epithelial cell ferroptosis in acute kidney injury.","date":"2025","source":"European journal of medical research","url":"https://pubmed.ncbi.nlm.nih.gov/40665400","citation_count":2,"is_preprint":false},{"pmid":"40355159","id":"PMC_40355159","title":"A fluorescent sensor for real-time monitoring of DPP8/9 reveals crucial roles in immunity and cancer.","date":"2025","source":"Life science alliance","url":"https://pubmed.ncbi.nlm.nih.gov/40355159","citation_count":1,"is_preprint":false},{"pmid":"37982048","id":"PMC_37982048","title":"DPP8/9 are not Required to Cleave Most Proline-Containing Peptides.","date":"2023","source":"Israel journal of chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/37982048","citation_count":1,"is_preprint":false},{"pmid":"39332821","id":"PMC_39332821","title":"Cosolvent Molecular Dynamics Applied to DPP4, DPP8 and DPP9: Reproduction of Important Binding Features and Use in Inhibitor Design.","date":"2024","source":"Journal of chemical information and modeling","url":"https://pubmed.ncbi.nlm.nih.gov/39332821","citation_count":1,"is_preprint":false},{"pmid":"41689046","id":"PMC_41689046","title":"MST1 promotes microglial pyroptosis and neuroinflammation in alzheimer's disease by regulating the novel DPP8/NLRP1/Caspase-1/GSDMD-N axis.","date":"2026","source":"Journal of neuroinflammation","url":"https://pubmed.ncbi.nlm.nih.gov/41689046","citation_count":1,"is_preprint":false},{"pmid":"40939170","id":"PMC_40939170","title":"A Photocaged N-Phosphonopiperidinone as a Selective Photo-Cleavable DPP8/9 Inhibitor.","date":"2025","source":"Chembiochem : a European journal of chemical biology","url":"https://pubmed.ncbi.nlm.nih.gov/40939170","citation_count":1,"is_preprint":false},{"pmid":"3417140","id":"PMC_3417140","title":"[Interrelation of the sensitivity of Salmonella derby cells to phage dp8 with the R plasmid of Salmonella derby].","date":"1988","source":"Genetika","url":"https://pubmed.ncbi.nlm.nih.gov/3417140","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":16745,"output_tokens":4303,"usd":0.05739,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":12180,"output_tokens":4033,"usd":0.080863,"stage2_stop_reason":"end_turn"},"total_usd":0.138253,"stage1_batch_id":"msgbatch_01AsR7g8dGTEiEw9U83bJeWn","stage2_batch_id":"msgbatch_01YV5ZyxtFNUZEjxRcpd9jzb","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2000,\n      \"finding\": \"DPP8 is a cytoplasmic, non-glycosylated, monomeric (~100 kDa) serine dipeptidyl aminopeptidase with post-proline cleavage activity, hydrolyzing DPPIV substrates Ala-Pro, Arg-Pro, and Gly-Pro, with a neutral pH optimum consistent with non-lysosomal localization. It lacks a transmembrane domain.\",\n      \"method\": \"Recombinant expression in COS-7 cells, Western blot, confocal microscopy, enzymatic activity assay with chromogenic substrates\",\n      \"journal\": \"European journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzymatic assay with defined substrates, direct subcellular localization by confocal microscopy and fractionation, multiple orthogonal methods in a single study\",\n      \"pmids\": [\"11012666\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Purified recombinant DPP8 expressed in Sf9 insect cells is enzymatically active, cleaving post-proline peptide bonds with kcat similar to DPP-IV, and shows substrate preference at both the P1 and P2 sites.\",\n      \"method\": \"Baculovirus expression in Sf9 cells, protein purification to homogeneity, kinetic assay with chromogenic substrates (H-Gly-Pro-pNA and others)\",\n      \"journal\": \"Protein expression and purification\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstituted in vitro enzymatic activity with purified protein and multiple substrates, kinetic constants determined\",\n      \"pmids\": [\"15039077\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"DPP8 is predominantly dimeric in purified form and in cell extracts, as shown by analytical ultracentrifugation and native gel electrophoresis. Four conserved C-terminal loop residues (Phe822, Val833, Tyr844, His859) are required for optimal enzymatic activity but not for dimerization, indicating dimerization alone is insufficient for activity. These mutations decrease kcat and dramatically increase Km independent of substrate. DPP8 shows strict substrate selectivity for hydrophobic or basic residues at the P2 site, unlike DPP-IV.\",\n      \"method\": \"Analytical ultracentrifugation, native gel electrophoresis, site-directed mutagenesis, enzyme kinetics\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstitution with mutagenesis, multiple orthogonal methods (AUC + native gel + kinetics), detailed mechanistic dissection of dimer interface and substrate specificity\",\n      \"pmids\": [\"17040910\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"DPP8 overexpression impairs cell migration on collagen I and wound healing on collagen I and fibronectin. These effects on cell survival, adhesion, and wound healing are independent of DPP8's catalytic serine, indicating an extraenzymatic mechanism.\",\n      \"method\": \"Overexpression of GFP-fusion proteins, cell migration (transwell), wound healing assay, catalytic serine mutant\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — overexpression with defined phenotypic readouts and catalytic mutant controls, single lab, no endogenous loss-of-function\",\n      \"pmids\": [\"16704418\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"DPP8 overexpression enhances induced apoptosis. This effect is independent of the catalytic serine, indicating an extraenzymatic pro-apoptotic function.\",\n      \"method\": \"Overexpression of GFP-fusion proteins, apoptosis assay, catalytic serine mutant\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — overexpression with apoptosis readout and catalytic mutant, single lab\",\n      \"pmids\": [\"16704418\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Hydrophilic residues lining the S1/S2 substrate pockets of DPP8 (D772, Y315, H434, D435) contribute to both catalysis and dimer stabilization. Mutations at these positions reduce catalytic activity and affect dimerization, and homology modeling places D772, H434, and D435 at the junction between the alpha-beta hydrolase and beta-propeller domains.\",\n      \"method\": \"Site-directed mutagenesis, substrate kinetics, size-exclusion chromatography, homology modeling\",\n      \"journal\": \"Biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — mutagenesis with kinetics and SEC, single lab, no independent replication\",\n      \"pmids\": [\"20536396\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Inhibition of DPP8 and DPP9 (but not DPP4 or other post-proline cleaving proteases alone) by Val-boroPro triggers pyroptosis in monocytes and macrophages via activation of pro-caspase-1 independently of the inflammasome adaptor ASC. Activated pro-caspase-1 does not efficiently process itself or IL-1β but cleaves and activates gasdermin D. Mice lacking caspase-1 do not show immune stimulation after Val-boroPro treatment.\",\n      \"method\": \"Selective inhibitors, caspase-1 knockout mice, genetic rescue experiments, cell death assays (LDH, PI staining), immunoblot for gasdermin D cleavage\",\n      \"journal\": \"Nature chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (pharmacological inhibition + genetic KO + mechanistic dissection), replicated across cell types and species\",\n      \"pmids\": [\"27820798\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Inhibition of DPP8 and DPP9 in mouse myeloid cells activates the inflammasome sensor Nlrp1b, which in turn activates pro-caspase-1 to mediate pyroptosis. DPP8/9 thus serve as an intracellular checkpoint restraining Nlrp1b and innate immune activation.\",\n      \"method\": \"Genetic epistasis (Nlrp1b knockout/overexpression), selective inhibitors, cell death assays, caspase-1 activation assays\",\n      \"journal\": \"Cell chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis with Nlrp1b KO, pharmacological inhibition, multiple cell types, mechanistic pathway placement\",\n      \"pmids\": [\"29396289\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"In human myeloid cells, DPP8/9 inhibitor-induced pyroptosis is mediated by CARD8 (not NLRP1b), which activates pro-caspase-1 to induce cell death. This identifies CARD8 as an activator in human cells responding to DPP8/9 inhibition.\",\n      \"method\": \"CARD8 knockdown/knockout, pro-caspase-1 inhibitors, cell death assays in human AML cell lines and primary AML samples\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO/KD of CARD8 with defined pyroptotic phenotype, validated in multiple human cell lines and primary samples\",\n      \"pmids\": [\"29967349\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"DPP8/9 inhibitors activate all functional rodent NLRP1 alleles, indicating that DPP8/9 inhibition generates a signal sensed universally by NLRP1 proteins regardless of allelic variation. NLRP1 allele sensitivities to DPP8/9 inhibition and Toxoplasma gondii infection are strikingly similar, suggesting DPP8/9 inhibition phenocopies a T. gondii activity.\",\n      \"method\": \"Overexpression of diverse NLRP1 alleles, selective DPP8/9 inhibitors, pyroptosis assays, comparison with T. gondii infection\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple alleles tested in defined genetic system, pharmacological and biological comparator, single lab\",\n      \"pmids\": [\"31383852\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"DPP8/9 inhibitors activate pyroptosis in resting human and rodent CD4+ and CD8+ T lymphocytes via CARD8. Activated human T cells, despite expressing CARD8 and required proteins, are completely resistant to DPP8/9 inhibitors, revealing a cell-state-dependent checkpoint.\",\n      \"method\": \"CARD8 knockdown, selective DPP8/9 inhibitors, cell death assays in resting vs. activated T cells\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic knockdown with defined phenotype across multiple cell types and states, single lab\",\n      \"pmids\": [\"32796818\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"DPP8 and DPP9 are not required to cleave the vast majority of proline-containing peptides generated by the proteasome in cell lysates, indicating a much more limited substrate scope than previously suggested by pseudopeptide reporter studies.\",\n      \"method\": \"Peptide degradation assays in cell lysates with DPP8/9 inhibitors or knockout, broad peptide array\",\n      \"journal\": \"Israel journal of chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — systematic biochemical screen in cell lysates with inhibitors and genetic tools, negative finding with mechanistic implication, single lab\",\n      \"pmids\": [\"37982048\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"DPP8 and DPP9 process the N-terminus of cytosolic adenylate kinase 2 (AK2), exposing an IAP-binding motif (IBM) that enables IAP E3 ligase-mediated proteasomal degradation of AK2. N-terminal acetylation by NatA blocks this IAP interaction and stabilizes cytosolic AK2. A genome-wide in silico screen identified 129 potential substrates with IBMs that could be unmasked by DPP8/9 processing; EIF2A was experimentally validated as one such substrate.\",\n      \"method\": \"Co-immunoprecipitation, N-terminal processing assays, IBM mutagenesis, NatA knockdown, genome-wide in silico screen with experimental validation of EIF2A\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — biochemical reconstitution of processing, binding partner identification (IAPs), mutagenesis of IBM, multiple orthogonal methods, two substrates validated experimentally\",\n      \"pmids\": [\"40312560\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"A genetically encoded fluorescent sensor (DiPAK) based on AK2 processing by DPP8/9 enables real-time monitoring of DPP8/9 activity in living cells. Using this sensor, LPS-induced primary B-cell activation was found to depend on DPP8/9, as absence of DPP8/9 activity results in apoptotic (not pyroptotic) cell death; DPP8/9 activity increases during B-cell maturation.\",\n      \"method\": \"Ratiometric fluorescent sensor in live cells, DPP9 overexpression/knockout, LPS stimulation, B-cell maturation assays\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — novel sensor validated by genetic perturbation, direct functional consequence demonstrated in primary B cells, single lab\",\n      \"pmids\": [\"40355159\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"DPP8 and DPP9 promote TGF-β1/Smad signaling-dependent epithelial-to-mesenchymal transition (EMT) and tubulointerstitial fibrosis. siRNA knockdown of DPP8 or DPP9 in TGF-β1-treated HK-2 cells decreases EMT- and ECM-related proteins, an effect reversible by lentiviral DPP8 re-expression.\",\n      \"method\": \"siRNA knockdown, lentiviral rescue, DPP8/9 inhibitor TC-E5007, UUO mouse model, HK-2 cell EMT assays, immunoblot for Smad signaling\",\n      \"journal\": \"Pharmacological research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with rescue, pathway placement via Smad signaling, in vivo and in vitro corroboration, single lab\",\n      \"pmids\": [\"33932609\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"DPP8 promotes TGF-β1-induced ECM deposition in human mesangial cells via Smad2/3 and Akt phosphorylation. siRNA silencing of DPP8 inhibits TGF-β1-induced collagen III, collagen IV, fibronectin, and MMP2 expression, as well as phosphorylation of Smad2, Smad3, and Akt.\",\n      \"method\": \"siRNA knockdown, TGF-β1 stimulation, immunoblot for Smad and Akt phosphorylation, ECM protein expression in human mesangial cells\",\n      \"journal\": \"Toxicology letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic loss-of-function with defined signaling readouts, single lab, corroborated by parallel DPP9 findings\",\n      \"pmids\": [\"38458339\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"MST1 knockdown modulates DPP8 protein expression, thereby regulating the NLRP1/Caspase-1/GSDMD-N signaling axis to inhibit microglial pyroptosis in an Alzheimer's disease mouse model, positioning DPP8 downstream of MST1 in this neuroinflammatory pathway.\",\n      \"method\": \"MST1 knockdown in 5xFAD mice, immunoblot for DPP8 and downstream NLRP1/caspase-1/GSDMD-N, behavioral assays\",\n      \"journal\": \"Journal of neuroinflammation\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — indirect placement of DPP8 downstream of MST1 by knockdown, no direct DPP8 manipulation, single study\",\n      \"pmids\": [\"41689046\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"DPP8 is an intracellular cytoplasmic serine dipeptidyl aminopeptidase that cleaves N-terminal Xaa-Pro dipeptides from substrates (including AK2 and EIF2A), exposing neo-N-termini that can unmask IAP-binding motifs to trigger proteasomal degradation; its inhibition relieves a checkpoint that restrains the NLRP1 and CARD8 inflammasomes, triggering gasdermin D-dependent pyroptosis via caspase-1 in a cell-type-specific manner, while also promoting TGF-β1/Smad-dependent fibrotic signaling and possessing extraenzymatic roles in cell adhesion, migration, and apoptosis independent of its catalytic activity.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"DPP8 is an intracellular, non-glycosylated serine dipeptidyl aminopeptidase that cleaves N-terminal Xaa-Pro dipeptides from cytosolic substrates at neutral pH, distinguishing it from lysosomal and membrane-anchored post-proline peptidases [#0, #1]. It is enzymatically active with kinetics comparable to DPP-IV but imposes strict selectivity for hydrophobic or basic residues at the P2 site; its activity depends on conserved C-terminal loop residues and on residues lining the S1/S2 pockets that also contribute to dimerization, though dimerization alone is insufficient for catalysis [#2, #5]. A defining cellular role is as an N-terminal processing enzyme that exposes IAP-binding motifs on substrates such as adenylate kinase 2 (AK2) and EIF2A, licensing IAP E3 ligase-mediated proteasomal degradation, a fate counteracted by NatA-mediated N-terminal acetylation [#12]. Functionally, DPP8 (with DPP9) acts as an intracellular checkpoint restraining inflammasome activation: its pharmacological inhibition triggers gasdermin D-dependent pyroptosis through pro-caspase-1, sensed by Nlrp1b in mouse myeloid cells and by CARD8 in human myeloid cells and T lymphocytes in a cell-state-dependent manner [#6, #7, #8, #10]. DPP8 additionally promotes TGF-\\u03b21/Smad-dependent epithelial-to-mesenchymal transition and fibrotic extracellular-matrix deposition [#14, #15], and carries catalysis-independent functions in cell migration, adhesion, and apoptosis [#3, #4].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Establishing that DPP8 was a genuine post-proline-cleaving peptidase distinct in localization from the known DPP-IV answered whether a cytoplasmic enzyme could perform Xaa-Pro dipeptidase chemistry outside the lysosomal/membrane compartment.\",\n      \"evidence\": \"Recombinant expression in COS-7 cells with confocal localization and chromogenic substrate assays\",\n      \"pmids\": [\"11012666\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No physiological substrate identified at this stage\", \"Quaternary structure and active-site architecture undefined\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Purification to homogeneity and kinetic characterization established that DPP8 is intrinsically catalytically competent with DPP-IV-like turnover, settling whether activity required cellular cofactors.\",\n      \"evidence\": \"Baculovirus expression in Sf9 cells, purification, kinetic assays with multiple chromogenic substrates\",\n      \"pmids\": [\"15039077\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Natural substrates remained unknown\", \"Did not address oligomeric state requirements\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Structural and mutational dissection defined DPP8 as a dimer with a distinct P2 substrate preference and showed that specific C-terminal loop and pocket residues govern catalysis independently of dimer assembly, refining how the enzyme achieves selectivity.\",\n      \"evidence\": \"Analytical ultracentrifugation, native gels, site-directed mutagenesis, and enzyme kinetics; homology modeling\",\n      \"pmids\": [\"17040910\", \"20536396\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No experimental crystal structure\", \"Substrate selectivity inferred from synthetic peptides, not endogenous targets\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Overexpression with catalytic-serine mutants revealed that DPP8 modulates cell migration, adhesion, wound healing, and apoptosis through a mechanism independent of its peptidase activity, introducing extraenzymatic roles.\",\n      \"evidence\": \"GFP-fusion overexpression with transwell/wound-healing and apoptosis assays plus catalytic mutant controls\",\n      \"pmids\": [\"16704418\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No endogenous loss-of-function validation\", \"Molecular partners mediating the non-catalytic effects unidentified\", \"Single lab\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Demonstrating that DPP8/9 inhibition triggers ASC-independent, caspase-1- and gasdermin D-dependent pyroptosis defined these enzymes as suppressors of an inflammatory cell-death pathway.\",\n      \"evidence\": \"Selective inhibitors, caspase-1 knockout mice, gasdermin D cleavage immunoblots, cell-death assays\",\n      \"pmids\": [\"27820798\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The upstream sensor was not yet identified\", \"Endogenous substrate linking DPP8/9 activity to the checkpoint unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Genetic epistasis identified the sensors downstream of DPP8/9 inhibition, with Nlrp1b operating in mouse myeloid cells and CARD8 in human myeloid cells, establishing species-specific inflammasome wiring of the checkpoint.\",\n      \"evidence\": \"Nlrp1b and CARD8 knockout/knockdown with selective inhibitors and caspase-1 activation assays in mouse and human cells including primary AML\",\n      \"pmids\": [\"29396289\", \"29967349\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Biochemical signal generated by DPP8/9 inhibition that activates the sensors not defined\", \"Did not resolve why sensitivity differs across cell types\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Showing that all functional rodent NLRP1 alleles respond to DPP8/9 inhibition, mirroring Toxoplasma gondii sensitivity, indicated a universal NLRP1-sensed signal and a possible pathogen-mimicking mechanism.\",\n      \"evidence\": \"Overexpression of diverse NLRP1 alleles with inhibitors and comparison to T. gondii infection\",\n      \"pmids\": [\"31383852\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular identity of the shared signal unresolved\", \"Single lab\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Extending the checkpoint to lymphocytes revealed that DPP8/9 inhibition drives CARD8-dependent pyroptosis in resting but not activated T cells, establishing a cell-state-dependent control of the pathway.\",\n      \"evidence\": \"CARD8 knockdown and selective inhibitors in resting versus activated human and rodent T cells\",\n      \"pmids\": [\"32796818\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism conferring resistance in activated T cells unknown\", \"Single lab\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Systematic peptide-degradation profiling demonstrated that DPP8/9 do not process most proline-containing proteasomal peptides, narrowing the enzymes' substrate scope from earlier reporter-based assumptions.\",\n      \"evidence\": \"Broad peptide degradation assays in cell lysates with inhibitors and knockout\",\n      \"pmids\": [\"37982048\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Negative result; did not pinpoint the bona fide physiological substrates\", \"Lysate context may not reflect intact-cell processing\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identifying AK2 and EIF2A as DPP8/9 substrates whose N-terminal processing unmasks IAP-binding motifs for proteasomal degradation provided the first defined endogenous substrate mechanism, linking peptidase activity to regulated protein turnover and a degron logic counteracted by NatA acetylation.\",\n      \"evidence\": \"Co-IP, N-terminal processing and IBM mutagenesis, NatA knockdown, genome-wide in silico screen with EIF2A validation; live-cell DiPAK sensor linking DPP8/9 activity to B-cell activation\",\n      \"pmids\": [\"40312560\", \"40355159\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Only two of 129 candidate substrates experimentally validated\", \"Link between substrate processing and the NLRP1/CARD8 checkpoint not directly established\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Loss-of-function with rescue placed DPP8 as a positive regulator of TGF-\\u03b21/Smad and Akt signaling driving EMT and fibrotic ECM deposition, broadening its physiological role beyond immunity.\",\n      \"evidence\": \"siRNA knockdown with lentiviral rescue, DPP8/9 inhibitor, UUO mouse model, and Smad/Akt immunoblots in HK-2 and mesangial cells\",\n      \"pmids\": [\"33932609\", \"38458339\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether the fibrotic effect requires catalytic activity not resolved\", \"Direct DPP8 substrate in the TGF-\\u03b21 pathway unknown\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Positioning DPP8 downstream of MST1 in microglial NLRP1/caspase-1/GSDMD pyroptosis extended the checkpoint to a neuroinflammatory disease context.\",\n      \"evidence\": \"MST1 knockdown in 5xFAD mice with downstream immunoblots and behavioral assays\",\n      \"pmids\": [\"41689046\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"DPP8 placement is indirect with no direct DPP8 manipulation\", \"How MST1 controls DPP8 expression undefined\", \"Single study\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unknown which endogenous substrate(s) processed by DPP8/9 generate the signal sensed by NLRP1/CARD8, and how catalytic versus extraenzymatic activities are partitioned across immunity, fibrosis, and migration.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No direct biochemical link between identified substrates (AK2/EIF2A) and inflammasome activation\", \"Extraenzymatic partners undefined\", \"No experimental high-resolution structure of human DPP8\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 2, 12]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 1, 2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 12]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [6, 7, 8, 10]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [6, 7, 8]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [12]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [14, 15]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"DPP9\", \"AK2\", \"EIF2A\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}