{"gene":"ITIH4","run_date":"2026-06-10T01:55:23","timeline":{"discoveries":[{"year":2021,"finding":"ITIH4 functions as a protease inhibitor by a novel bait mechanism: proteases cleave ITIH4 within a protease-susceptible region, enabling ITIH4 to form a noncovalent, inhibitory complex with the executing protease that depends on the ITIH4 von Willebrand factor A domain. ITIH4 inhibits MASP-1, MASP-2, and plasma kallikrein by sterically preventing larger protein substrates from accessing their active sites while leaving the active site accessible to small substrates.","method":"In vitro protease inhibition assays, domain mutagenesis (vWFA domain dependence), substrate competition assays, biochemical reconstitution of inhibitory complex","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution of inhibitory complex, active-site mechanism defined, domain mutagenesis, multiple orthogonal assays in single rigorous study","pmids":["33523981"],"is_preprint":false},{"year":1999,"finding":"ITIH4 expression in hepatocytes is specifically up-regulated by IL-6 (but not by IL-1β or TNF-α), establishing it as a type II acute-phase protein. This was demonstrated by dose-response IL-6 treatment of HepG2 cells showing increased ITIH4 mRNA and 35S-labeled secreted protein.","method":"Northern blot / RT-PCR for mRNA, 35S metabolic labeling of secreted protein, dose-response cytokine treatment of HepG2 cells","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — replicated across multiple labs (human HepG2, porcine hepatocytes, mouse models) with orthogonal mRNA and protein methods","pmids":["10486281","10712621","33348064"],"is_preprint":false},{"year":2000,"finding":"ITIH4 (IHRP) binds actin and inhibits actin polymerization, and also suppresses phagocytic activity of polymorphonuclear (PMN) cells, suggesting it functions as an anti-inflammatory protein by neutralizing actin released from damaged cells and by binding cell-surface actin on PMN cells.","method":"In vitro actin polymerization assay, phagocytosis assay with PMN cells in presence of purified IHRP","journal":"Inflammation research","confidence":"Medium","confidence_rationale":"Tier 1–2 / Weak — in vitro biochemical assays with purified protein, single lab, no mutagenesis or structural validation","pmids":["10939621"],"is_preprint":false},{"year":1995,"finding":"ITIH4 (IHRP) is encoded by a 2,977 bp cDNA in human liver encoding 930 amino acids including a 28-residue signal peptide. The N-terminal ~600 residues show homology to ITI heavy chains while the C-terminal ~300 residues show homology to ATP-dependent proteases. The protein is cleaved into 85- and 35-kDa fragments at a proline-rich region (Arg-Arg-Leu site) when plasma is incubated at 37°C. Expression is liver-restricted.","method":"cDNA cloning, amino acid sequencing of proteolytic fragments, Northern blot of human tissues, SDS-PAGE of cleavage products","journal":"Journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct cDNA cloning with sequence determination, in vitro cleavage characterization, replicated by multiple subsequent studies","pmids":["7775381"],"is_preprint":false},{"year":1996,"finding":"The ITIH4 (ITIHL1) gene spans 15 kb, is composed of 24 exons, maps to chromosome 3p21→p14, and contains hepatocyte nuclear factor binding sites (LF-A1, HNF-5, NF-IL6, C/EBP) in the 5'-flanking region that likely confer liver-specific transcription. Two major transcription initiation sites were identified with no typical TATA box.","method":"Genomic cloning of three overlapping clones, exon-intron mapping, fluorescence in situ hybridization (FISH), promoter element identification by sequence analysis","journal":"Journal of biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct gene structure determination by genomic cloning, FISH mapping, promoter analysis by sequence; functional promoter validation not performed experimentally","pmids":["8797089","7587397"],"is_preprint":false},{"year":1998,"finding":"Rat and human ITIH4 differ substantially in their proline-rich region (PRR): rat PRR contains 6 repeats of Gly-X-Pro collagen-like motifs absent in human. Human ITIH4 also produces two alternative splice variants of the PRR. Rat ITIH4 mRNA is up-regulated by acute systemic inflammation, whereas neither human ITIH4 mRNA variant is up-regulated in human liver under the same conditions.","method":"cDNA cloning, sequence comparison of rat vs human H4P, RT-PCR splice variant analysis, Northern blot of inflamed vs control tissue","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct comparative cDNA and mRNA analysis, two species, orthogonal methods but single lab","pmids":["9480842"],"is_preprint":false},{"year":1998,"finding":"Mouse itih-4 encodes a 942 amino acid protein containing two EF-hand (helix-loop-helix) calcium-binding motifs, is expressed prominently in embryonic liver (as early as E9) and is developmentally regulated, suggesting a role as a scaffolding/extracellular matrix regulatory protein in early liver development.","method":"Subtraction hybridization of embryonic liver cDNA, full-length cDNA sequencing, RT-PCR across developmental stages and tissues","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct cDNA characterization with developmental expression profiling, single lab, no functional mutagenesis of EF-hand motifs","pmids":["9602042"],"is_preprint":false},{"year":2002,"finding":"Itih-4 expression in liver is induced by IL-6 in hepatocyte explant cultures and peaks in a bimodal manner (at 30 min and 12 hr) after partial hepatectomy, correlating with immediate-early gene expression and suggesting Itih-4 contributes to entry of quiescent hepatocytes into the cell cycle. A GST-fusion Itih-4 protein showed no detectable binding to calcium or hyaluronic acid, indicating posttranslational modifications may be required for these proposed interactions.","method":"IL-6 treatment of liver explant cultures, immunohistochemistry at developmental stages, partial hepatectomy model, GST-fusion protein binding assay for calcium and hyaluronic acid","journal":"Developmental dynamics","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — direct localization and expression in functional contexts (hepatectomy, IL-6 treatment), negative binding result explicitly reported, single lab","pmids":["11803570"],"is_preprint":false},{"year":2023,"finding":"Phosphoglycerate kinase 1 (PGK1) was identified as a binding partner of ITI-H4. PGK1 increases ITI-H4 expression levels and blocks KLKB1 (kallikrein B1)-mediated cleavage of ITI-H4. PGK1 also inhibits pro-inflammatory JAK2/STAT3 signaling.","method":"Immunoprecipitation of ITIH4-associated proteins from cell lysates, MALDI-TOF/MS identification of binding partners, Western blot validation of PGK1 interaction and effect on ITIH4 cleavage","journal":"Biomedicine & pharmacotherapy","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — single Co-IP/pulldown with MS identification, functional cleavage assay, single lab with two orthogonal methods","pmids":["36841032"],"is_preprint":false},{"year":2020,"finding":"IL-6-mediated induction of ITIH4 in HepG2 cells operates through the JAK/STAT signaling pathway, as demonstrated by significant reduction of ITIH4 protein and mRNA levels upon JAK/STAT inhibitor treatment before IL-6 or LPS stimulation.","method":"JAK/STAT inhibitor pretreatment, Western blot, real-time PCR, immunohistochemistry in mouse liver and HepG2 cell model","journal":"Cytokine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological pathway dissection with JAK/STAT inhibitor, multiple readouts (protein + mRNA), single lab","pmids":["33348064"],"is_preprint":false},{"year":2024,"finding":"ITIH4 regulates vascular smooth muscle cell (VSMC) stiffness: ITIH4 overexpression increases VSMC stiffness and acetylated α-tubulin while inhibiting ERK1/2 and JNK (but not p38 MAPK). Thrombin downregulates ITIH4, and ITIH4 partially reverses thrombin-induced changes in acetylated α-tubulin and VSMC stiffness through JNK and ERK signaling.","method":"ITIH4 expression vector and siRNA transfection in VSMCs, atomic force microscopy for cell stiffness, Western blot for signaling molecules, ERK inhibitor (PD98059) and JNK inhibitor (SP600125) treatment","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain-of-function and loss-of-function with pharmacological pathway dissection, single lab, multiple orthogonal methods","pmids":["39069151"],"is_preprint":false},{"year":2025,"finding":"ITIH4 deficiency in airway epithelial cells exacerbates oxidative-stress-induced apoptosis, while ITIH4 overexpression inhibits it. Mechanistically, ITIH4 attenuates JNK activation and prevents β-catenin decrease upon oxidative stress. Acute hydrogen peroxide exposure causes rapid ITIH4 protein degradation with no effect at the transcriptional level.","method":"ITIH4 overexpression in primary COPD small airway epithelial cells and normal cells, siRNA knockdown, human apoptosis antibody array, Western blot, clinical cohort ITIH4 measurements","journal":"The European respiratory journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain- and loss-of-function with defined apoptotic and signaling readouts, apoptosis array, single lab","pmids":["40404214"],"is_preprint":false},{"year":2024,"finding":"ITIH4 interacts with CXCR4 in rheumatoid arthritis fibroblast-like synoviocytes (RA-FLS): siRNA-mediated knockdown of ITIH4 led to significant downregulation of CXCR4 protein expression. In a CIA rat model, ITIH4 knockdown inhibited arthritis progression, decreased cellular infiltration, cytokine production, and pannus formation. The ITIH4-CXCR4 interaction was linked to PI3K/Akt signaling modulation of apoptosis and inflammation.","method":"siRNA knockdown in RA-FLS, Western blot validation, in vivo CIA rat model, molecular dynamics simulation of ITIH4-CXCR4 interaction","journal":"Rheumatology (Oxford, England)","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — siRNA knockdown with cellular and in vivo phenotypic readouts plus computational interaction modelling, single lab","pmids":["40608509"],"is_preprint":false},{"year":2024,"finding":"ITIH4 is cleaved in hereditary angioedema (HAE) patients with C1 inhibitor deficiency (types 1 and 2), indicating ongoing enzymatic activity in the plasma of HAE patients. HAE patients have significantly lower intact ITIH4 levels compared to controls, and immediate cleavage of added recombinant ITIH4 was observed in serum lacking endogenous intact ITIH4, demonstrating a compensatory protease inhibitor role for ITIH4 in HAE-associated proteolytic pathways.","method":"Specific immunoassays for intact vs. total ITIH4, Western blot of cleavage products, recombinant ITIH4 addition to patient serum, clinical cohort of 80 HAE patients vs. 100 controls","journal":"The Journal of allergy and clinical immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical reconstitution experiment (rITIH4 cleavage in patient serum), orthogonal immunoassay and Western blot, validated cohort, single lab","pmids":["38657796"],"is_preprint":false},{"year":2026,"finding":"In macrophages, full-length ITIH4 increases under pro-inflammatory conditions due to decreased cleavage. 4-Octyl itaconate promotes synthesis and secretion of full-length ITIH4. ITIH4 overexpression in macrophages attenuates pro-inflammatory responses via the NF-κB signaling pathway, and macrophages with ITIH4 overexpression activate cAMP signaling to enhance viability and tight junction integrity of colonic epithelial cells.","method":"Quantitative proteomics (mass spectrometry) of BMDMs, ITIH4 overexpression and knockdown in Raw264.7 and THP-1 cells, RNA-seq, Western blot, qRT-PCR, CCK8 viability assay, scratch wound healing assay","journal":"Inflammation research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain- and loss-of-function with RNA-seq pathway analysis and multiple orthogonal validation methods, single lab","pmids":["41998424"],"is_preprint":false},{"year":2025,"finding":"ITIH4 knockdown in A549 cells increases MP-induced apoptosis and pro-inflammatory cytokine release, while overexpression of NLRP3 reverses the protective effects of ITIH4 knockdown. This places ITIH4 upstream of NLRP3 inflammasome activation in the context of Mycoplasma pneumoniae-induced lung epithelial cell inflammation.","method":"Lentiviral ITIH4 knockdown in A549 cells, NLRP3 reactivation rescue experiment, flow cytometry for apoptosis, ELISA for cytokines, Western blot for inflammasome proteins","journal":"Allergologia et immunopathologia","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis experiment (NLRP3 reactivation rescues ITIH4-knockdown phenotype), multiple readouts, single lab","pmids":["40682224"],"is_preprint":false},{"year":2025,"finding":"Recombinant ITIH4 (rITIH4) attenuates acute lung injury in mice exposed to Fe-containing particulate matter by modulating the Hippo pathway in type II alveolar epithelial cells (AECII): rITIH4 restored Cdh1, Pdpn, Wwtr1, and Yap1 in AECII, increased α-catenin and p-YAP, and modulated pTAZ/TAZ and LC3BII/I ratios.","method":"Intratracheal DEP/FeCl3 instillation mouse model, intranasal rITIH4 treatment, single-cell RNA sequencing, single-cell ICP-MS for Fe, immunofluorescence, BALF cytokine measurement","journal":"Respiratory research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo gain-of-function with rITIH4, scRNA-seq pathway identification, multiple orthogonal readouts, single lab","pmids":["40437524"],"is_preprint":false},{"year":2026,"finding":"ITIH4 regulates YAP/TAZ-mediated apoptosis in type II alveolar epithelial cells: ITIH4 knockdown decreases YAP and TAZ while increasing p-YAP and SIRT1; ITIH4 overexpression increases p-TAZ/TAZ and SIRT1 and decreases ATM and caspase-3. rITIH4 treatment of LPS-injured mice restored ITIH4 in SPC+ cells, reduced caspase-3, and transiently elevated YAP in damaged lung regions, indicating spatiotemporal Hippo pathway regulation during lung repair.","method":"ITIH4 knockdown and overexpression in A549 cells, rITIH4 treatment in LPS-ARDS mouse model, Western blot for Hippo pathway components, immunofluorescence in SPC+ cells, H&E with K-means clustering","journal":"Pharmaceutical research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain- and loss-of-function with defined mechanistic pathway readouts, in vivo validation, single lab","pmids":["41735691"],"is_preprint":false},{"year":2025,"finding":"ITIH4 administration in an OVA-induced asthma mouse model significantly reduced Th2 cytokines (IL-4, IL-5, IL-13), IgE, and eosinophils/lymphocytes in BALF, modulated lung and gut microbiome composition (enriching Gram-positive taxa, depleting Helicobacteraceae), altered short-chain fatty acids, and proteomic analysis of intestinal tissue revealed dose-dependent granzyme A signaling activation and suppression of metabolic/solute transport pathways.","method":"Mouse OVA asthma model, lung function measurement, BALF cytokine ELISA, 16S rRNA microbiome profiling, GC-MS for SCFAs, intestinal tissue proteomics","journal":"Molecular medicine","confidence":"Low","confidence_rationale":"Tier 3 / Weak — in vivo phenotypic rescue with rITIH4 but downstream molecular mechanism linking ITIH4 directly to identified pathways not established mechanistically, single lab","pmids":["40410722"],"is_preprint":false}],"current_model":"ITIH4 is a liver-derived, IL-6-inducible (via JAK/STAT) type II acute-phase plasma glycoprotein that acts as a protease inhibitor through a novel bait mechanism: proteases cleave ITIH4 within a susceptible region, inducing formation of a noncovalent inhibitory complex dependent on ITIH4's von Willebrand factor A domain, which sterically blocks large substrates from protease active sites while leaving small substrates accessible—thereby inhibiting MASP-1, MASP-2, and plasma kallikrein; the protein also binds actin to inhibit polymerization and PMN phagocytosis, interacts with PGK1 (which blocks its kallikrein-mediated cleavage), associates with CXCR4 to modulate PI3K/Akt signaling, regulates VSMC stiffness through ERK/JNK pathways, and controls epithelial and macrophage inflammatory responses via NF-κB and Hippo/YAP-TAZ signaling."},"narrative":{"mechanistic_narrative":"ITIH4 is a liver-restricted, IL-6-inducible type II acute-phase plasma glycoprotein that acts as a protease inhibitor and modulator of inflammatory signaling [PMID:10486281, PMID:10712621, PMID:33348064, PMID:7775381]. Its inhibitory activity follows a bait mechanism: proteases cleave ITIH4 within a susceptible proline-rich region (an Arg-Arg-Leu site yielding 85- and 35-kDa fragments), inducing a noncovalent inhibitory complex dependent on the ITIH4 von Willebrand factor A domain that sterically excludes large protein substrates from the protease active site while leaving small substrates accessible, thereby inhibiting MASP-1, MASP-2, and plasma kallikrein [PMID:33523981, PMID:7775381]. Hepatic expression is driven specifically by IL-6 through the JAK/STAT pathway, not by IL-1β or TNF-α, and the gene carries liver-specific transcription factor binding sites in its promoter [PMID:10486281, PMID:10712621, PMID:33348064, PMID:8797089, PMID:7587397]. ITIH4 cleavage tracks ongoing proteolytic activity in vivo, as intact ITIH4 is depleted and recombinant ITIH4 is rapidly cleaved in serum from hereditary angioedema patients with C1 inhibitor deficiency, consistent with a compensatory inhibitory role in plasma protease cascades [PMID:38657796]. Beyond protease inhibition, ITIH4 binds actin to inhibit polymerization and suppress PMN phagocytosis [PMID:10939621], and acts as an anti-inflammatory and cytoprotective factor in epithelial, macrophage, and smooth muscle contexts—restraining oxidative-stress and pathogen-induced apoptosis and cytokine release via JNK, NF-κB, NLRP3, and Hippo/YAP-TAZ signaling [PMID:39069151, PMID:40404214, PMID:41998424, PMID:40682224, PMID:41735691]. PGK1 binds ITIH4 and blocks kallikrein-mediated cleavage, stabilizing the intact protein [PMID:36841032].","teleology":[{"year":1995,"claim":"Established the molecular identity of ITIH4, defining its domain architecture and the proteolytic cleavage behavior that would later prove central to its function.","evidence":"cDNA cloning, peptide sequencing of plasma cleavage fragments, and tissue Northern blot","pmids":["7775381"],"confidence":"High","gaps":["The protease responsible for physiological cleavage was not identified","Functional consequence of cleavage was unknown at this stage"]},{"year":1996,"claim":"Resolved the gene structure and identified liver-specific promoter elements, explaining the hepatic restriction of ITIH4 expression.","evidence":"Genomic cloning, exon-intron mapping, FISH to 3p21-p14, and promoter sequence analysis","pmids":["8797089","7587397"],"confidence":"Medium","gaps":["Promoter elements identified by sequence only; functional transcription assays not performed"]},{"year":1998,"claim":"Cross-species comparison revealed divergence in the proline-rich region and showed acute-phase regulation differs between rat and human, while mouse work tied ITIH4 to embryonic liver development.","evidence":"Comparative cDNA/mRNA analysis (rat vs human), splice variant RT-PCR, and developmental expression profiling in mouse","pmids":["9480842","9602042"],"confidence":"Medium","gaps":["Functional significance of the proline-rich repeats and predicted EF-hand motifs not tested","Species differences in inflammatory induction not mechanistically explained"]},{"year":1999,"claim":"Defined ITIH4 as a type II acute-phase protein by showing its hepatic induction is specific to IL-6.","evidence":"Dose-response IL-6 treatment of HepG2 cells with mRNA and 35S-labeled protein readouts","pmids":["10486281","10712621","33348064"],"confidence":"High","gaps":["Signaling pathway downstream of IL-6 not yet defined"]},{"year":2000,"claim":"Provided the first functional activity for ITIH4 beyond an acute-phase marker—actin binding and suppression of PMN phagocytosis—framing it as anti-inflammatory.","evidence":"In vitro actin polymerization and phagocytosis assays with purified IHRP","pmids":["10939621"],"confidence":"Medium","gaps":["No mutagenesis or structural mapping of the actin-binding interface","In vivo relevance not established"]},{"year":2002,"claim":"Connected ITIH4 induction to liver regeneration and tested predicted ligand interactions, finding the unmodified protein does not bind calcium or hyaluronic acid.","evidence":"IL-6-treated liver explants, partial hepatectomy time course, and GST-fusion binding assays","pmids":["11803570"],"confidence":"Medium","gaps":["Whether posttranslational modification enables calcium/HA binding untested","Causal role in hepatocyte cell-cycle entry not demonstrated"]},{"year":2020,"claim":"Identified JAK/STAT as the signaling route for IL-6-driven ITIH4 induction, completing the regulatory pathway upstream of the protein.","evidence":"JAK/STAT inhibitor pretreatment before IL-6/LPS in HepG2 and mouse liver, with protein and mRNA readouts","pmids":["33348064"],"confidence":"Medium","gaps":["Specific STAT factor and direct promoter binding not defined"]},{"year":2021,"claim":"Established the central mechanism: ITIH4 is a substrate-cleavage-activated, vWFA-domain-dependent steric protease inhibitor of MASP-1, MASP-2, and plasma kallikrein.","evidence":"In vitro protease inhibition, domain mutagenesis, substrate competition assays, and reconstitution of the noncovalent inhibitory complex","pmids":["33523981"],"confidence":"High","gaps":["Full structural model of the inhibitory complex not resolved","In vivo contribution to complement/kallikrein control not quantified"]},{"year":2023,"claim":"Identified PGK1 as an ITIH4 binding partner that stabilizes intact ITIH4 by blocking kallikrein-mediated cleavage.","evidence":"Co-IP with MALDI-TOF/MS identification and Western blot cleavage assays","pmids":["36841032"],"confidence":"Medium","gaps":["Single Co-IP without reciprocal structural validation","Mechanism by which PGK1 blocks cleavage unresolved"]},{"year":2024,"claim":"Extended ITIH4 function to tissue and disease contexts—VSMC stiffness via ERK/JNK, CXCR4-linked PI3K/Akt signaling in arthritis, and in vivo evidence of compensatory protease inhibition in hereditary angioedema.","evidence":"Gain/loss-of-function with pharmacological pathway dissection in VSMCs, siRNA and CIA rat model for CXCR4, and immunoassay/Western/recombinant-protein cleavage in HAE patient serum","pmids":["39069151","40608509","38657796"],"confidence":"Medium","gaps":["Whether ITIH4-CXCR4 is a direct physical interaction beyond computational modeling untested","Mechanism linking ITIH4 to cytoskeletal acetylation not defined"]},{"year":2025,"claim":"Defined ITIH4 as a cytoprotective, anti-inflammatory factor in epithelial and lung-injury models, acting through JNK/β-catenin, NLRP3, and Hippo/YAP-TAZ signaling.","evidence":"Gain/loss-of-function in airway epithelial and A549 cells, NLRP3 rescue epistasis, and rITIH4 treatment in particulate-matter and OVA-asthma mouse models with scRNA-seq","pmids":["40404214","40682224","40437524","40410722"],"confidence":"Medium","gaps":["Direct molecular link between ITIH4 and these pathways not established (mostly correlative)","Receptor mediating extracellular rITIH4 effects unknown"]},{"year":2026,"claim":"Showed that full-length ITIH4 accumulates under pro-inflammatory conditions and acts cell-non-autonomously, dampening macrophage NF-κB responses and supporting epithelial barrier integrity, and dynamically tuning Hippo signaling during lung repair.","evidence":"Quantitative proteomics of BMDMs, ITIH4 overexpression/knockdown in macrophage lines with RNA-seq, and Hippo pathway readouts in A549 and LPS-ARDS mice","pmids":["41998424","41735691"],"confidence":"Medium","gaps":["Mechanism coupling intracellular/secreted ITIH4 to NF-κB and Hippo not defined","Whether protease-inhibition and signaling functions are mechanistically linked unknown"]},{"year":null,"claim":"How ITIH4's defined plasma protease-inhibitor mechanism relates to its diverse intracellular and cell-non-autonomous signaling roles (NF-κB, Hippo/YAP-TAZ, NLRP3, CXCR4/PI3K-Akt) remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No receptor identified for extracellular ITIH4 signaling effects","Unclear whether cleaved versus intact ITIH4 drives the signaling phenotypes","No structural model unifying the bait mechanism with the signaling functions"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,13]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[2]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[1,3,13]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,13,14]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[1,9,11]}],"complexes":[],"partners":["PGK1","KLKB1","CXCR4","ACTB"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q14624","full_name":"Inter-alpha-trypsin inhibitor heavy chain H4","aliases":["Inter-alpha-trypsin inhibitor family heavy chain-related protein","IHRP","Plasma kallikrein sensitive glycoprotein 120","Gp120","PK-120"],"length_aa":930,"mass_kda":103.4,"function":"Type II acute-phase protein (APP) involved in inflammatory responses to trauma. May also play a role in liver development or regeneration","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/Q14624/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ITIH4","classification":"Not Classified","n_dependent_lines":7,"n_total_lines":1208,"dependency_fraction":0.005794701986754967},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/ITIH4","total_profiled":1310},"omim":[{"mim_id":"600564","title":"INTER-ALPHA-TRYPSIN INHIBITOR, HEAVY CHAIN 4; ITIH4","url":"https://www.omim.org/entry/600564"},{"mim_id":"147270","title":"INTER-ALPHA-TRYPSIN INHIBITOR, HEAVY CHAIN 1; ITIH1","url":"https://www.omim.org/entry/147270"},{"mim_id":"146650","title":"INTER-ALPHA-TRYPSIN INHIBITOR, HEAVY CHAIN 3; ITIH3","url":"https://www.omim.org/entry/146650"},{"mim_id":"143890","title":"HYPERCHOLESTEROLEMIA, FAMILIAL, 1; FHCL1","url":"https://www.omim.org/entry/143890"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Vesicles","reliability":"Approved"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"liver","ntpm":1743.0}],"url":"https://www.proteinatlas.org/search/ITIH4"},"hgnc":{"alias_symbol":["IHRP","H4P"],"prev_symbol":["ITIHL1"]},"alphafold":{"accession":"Q14624","domains":[{"cath_id":"2.60.40,2.60.40","chopping":"34-246_588-596_603-607","consensus_level":"medium","plddt":88.0988,"start":34,"end":607},{"cath_id":"-","chopping":"251-269_469-575","consensus_level":"medium","plddt":91.9771,"start":251,"end":575},{"cath_id":"3.40.50.410","chopping":"274-459","consensus_level":"high","plddt":95.1775,"start":274,"end":459},{"cath_id":"-","chopping":"735-930","consensus_level":"high","plddt":84.2565,"start":735,"end":930}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q14624","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q14624-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q14624-F1-predicted_aligned_error_v6.png","plddt_mean":80.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ITIH4","jax_strain_url":"https://www.jax.org/strain/search?query=ITIH4"},"sequence":{"accession":"Q14624","fasta_url":"https://rest.uniprot.org/uniprotkb/Q14624.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q14624/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q14624"}},"corpus_meta":[{"pmid":"10486281","id":"PMC_10486281","title":"ITIH4 serum concentration increases during acute-phase processes in human patients and is up-regulated by interleukin-6 in hepatocarcinoma HepG2 cells.","date":"1999","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/10486281","citation_count":93,"is_preprint":false},{"pmid":"15213118","id":"PMC_15213118","title":"ITIH4 (inter-alpha-trypsin inhibitor heavy chain 4) is a new acute-phase protein isolated from cattle during experimental infection.","date":"2004","source":"Infection and immunity","url":"https://pubmed.ncbi.nlm.nih.gov/15213118","citation_count":68,"is_preprint":false},{"pmid":"10712621","id":"PMC_10712621","title":"Pig MAP/ITIH4 and haptoglobin are interleukin-6-dependent acute-phase plasma proteins in porcine primary cultured hepatocytes.","date":"2000","source":"European journal of biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/10712621","citation_count":60,"is_preprint":false},{"pmid":"7775381","id":"PMC_7775381","title":"Cloning and characterization of cDNA for inter-alpha-trypsin inhibitor family heavy chain-related protein (IHRP), a novel human plasma glycoprotein.","date":"1995","source":"Journal of biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/7775381","citation_count":53,"is_preprint":false},{"pmid":"33523981","id":"PMC_33523981","title":"ITIH4 acts as a protease inhibitor by a novel inhibitory mechanism.","date":"2021","source":"Science advances","url":"https://pubmed.ncbi.nlm.nih.gov/33523981","citation_count":51,"is_preprint":false},{"pmid":"11803570","id":"PMC_11803570","title":"Itih-4, a serine protease inhibitor regulated in interleukin-6-dependent liver formation: role in liver development and regeneration.","date":"2002","source":"Developmental dynamics : an official publication of the American Association of Anatomists","url":"https://pubmed.ncbi.nlm.nih.gov/11803570","citation_count":51,"is_preprint":false},{"pmid":"31557619","id":"PMC_31557619","title":"Long Non-coding RNA ITIH4-AS1 Accelerates the Proliferation and Metastasis of Colorectal Cancer by Activating JAK/STAT3 Signaling.","date":"2019","source":"Molecular therapy. Nucleic acids","url":"https://pubmed.ncbi.nlm.nih.gov/31557619","citation_count":47,"is_preprint":false},{"pmid":"33348064","id":"PMC_33348064","title":"ITIH4, as an inflammation biomarker, mainly increases in bacterial bloodstream infection.","date":"2020","source":"Cytokine","url":"https://pubmed.ncbi.nlm.nih.gov/33348064","citation_count":44,"is_preprint":false},{"pmid":"31238892","id":"PMC_31238892","title":"Elevated levels of circulating ITIH4 are associated with hepatocellular carcinoma with nonalcoholic fatty liver disease: from pig model to human study.","date":"2019","source":"BMC cancer","url":"https://pubmed.ncbi.nlm.nih.gov/31238892","citation_count":40,"is_preprint":false},{"pmid":"10939621","id":"PMC_10939621","title":"The novel acute phase protein, IHRP, inhibits actin polymerization and phagocytosis of polymorphonuclear cells.","date":"2000","source":"Inflammation research : official journal of the European Histamine Research Society ... 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ITIH4 inhibits MASP-1, MASP-2, and plasma kallikrein by sterically preventing larger protein substrates from accessing their active sites while leaving the active site accessible to small substrates.\",\n      \"method\": \"In vitro protease inhibition assays, domain mutagenesis (vWFA domain dependence), substrate competition assays, biochemical reconstitution of inhibitory complex\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution of inhibitory complex, active-site mechanism defined, domain mutagenesis, multiple orthogonal assays in single rigorous study\",\n      \"pmids\": [\"33523981\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"ITIH4 expression in hepatocytes is specifically up-regulated by IL-6 (but not by IL-1β or TNF-α), establishing it as a type II acute-phase protein. This was demonstrated by dose-response IL-6 treatment of HepG2 cells showing increased ITIH4 mRNA and 35S-labeled secreted protein.\",\n      \"method\": \"Northern blot / RT-PCR for mRNA, 35S metabolic labeling of secreted protein, dose-response cytokine treatment of HepG2 cells\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — replicated across multiple labs (human HepG2, porcine hepatocytes, mouse models) with orthogonal mRNA and protein methods\",\n      \"pmids\": [\"10486281\", \"10712621\", \"33348064\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"ITIH4 (IHRP) binds actin and inhibits actin polymerization, and also suppresses phagocytic activity of polymorphonuclear (PMN) cells, suggesting it functions as an anti-inflammatory protein by neutralizing actin released from damaged cells and by binding cell-surface actin on PMN cells.\",\n      \"method\": \"In vitro actin polymerization assay, phagocytosis assay with PMN cells in presence of purified IHRP\",\n      \"journal\": \"Inflammation research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Weak — in vitro biochemical assays with purified protein, single lab, no mutagenesis or structural validation\",\n      \"pmids\": [\"10939621\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"ITIH4 (IHRP) is encoded by a 2,977 bp cDNA in human liver encoding 930 amino acids including a 28-residue signal peptide. The N-terminal ~600 residues show homology to ITI heavy chains while the C-terminal ~300 residues show homology to ATP-dependent proteases. The protein is cleaved into 85- and 35-kDa fragments at a proline-rich region (Arg-Arg-Leu site) when plasma is incubated at 37°C. Expression is liver-restricted.\",\n      \"method\": \"cDNA cloning, amino acid sequencing of proteolytic fragments, Northern blot of human tissues, SDS-PAGE of cleavage products\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct cDNA cloning with sequence determination, in vitro cleavage characterization, replicated by multiple subsequent studies\",\n      \"pmids\": [\"7775381\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"The ITIH4 (ITIHL1) gene spans 15 kb, is composed of 24 exons, maps to chromosome 3p21→p14, and contains hepatocyte nuclear factor binding sites (LF-A1, HNF-5, NF-IL6, C/EBP) in the 5'-flanking region that likely confer liver-specific transcription. Two major transcription initiation sites were identified with no typical TATA box.\",\n      \"method\": \"Genomic cloning of three overlapping clones, exon-intron mapping, fluorescence in situ hybridization (FISH), promoter element identification by sequence analysis\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct gene structure determination by genomic cloning, FISH mapping, promoter analysis by sequence; functional promoter validation not performed experimentally\",\n      \"pmids\": [\"8797089\", \"7587397\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Rat and human ITIH4 differ substantially in their proline-rich region (PRR): rat PRR contains 6 repeats of Gly-X-Pro collagen-like motifs absent in human. Human ITIH4 also produces two alternative splice variants of the PRR. Rat ITIH4 mRNA is up-regulated by acute systemic inflammation, whereas neither human ITIH4 mRNA variant is up-regulated in human liver under the same conditions.\",\n      \"method\": \"cDNA cloning, sequence comparison of rat vs human H4P, RT-PCR splice variant analysis, Northern blot of inflamed vs control tissue\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct comparative cDNA and mRNA analysis, two species, orthogonal methods but single lab\",\n      \"pmids\": [\"9480842\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Mouse itih-4 encodes a 942 amino acid protein containing two EF-hand (helix-loop-helix) calcium-binding motifs, is expressed prominently in embryonic liver (as early as E9) and is developmentally regulated, suggesting a role as a scaffolding/extracellular matrix regulatory protein in early liver development.\",\n      \"method\": \"Subtraction hybridization of embryonic liver cDNA, full-length cDNA sequencing, RT-PCR across developmental stages and tissues\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct cDNA characterization with developmental expression profiling, single lab, no functional mutagenesis of EF-hand motifs\",\n      \"pmids\": [\"9602042\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Itih-4 expression in liver is induced by IL-6 in hepatocyte explant cultures and peaks in a bimodal manner (at 30 min and 12 hr) after partial hepatectomy, correlating with immediate-early gene expression and suggesting Itih-4 contributes to entry of quiescent hepatocytes into the cell cycle. A GST-fusion Itih-4 protein showed no detectable binding to calcium or hyaluronic acid, indicating posttranslational modifications may be required for these proposed interactions.\",\n      \"method\": \"IL-6 treatment of liver explant cultures, immunohistochemistry at developmental stages, partial hepatectomy model, GST-fusion protein binding assay for calcium and hyaluronic acid\",\n      \"journal\": \"Developmental dynamics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — direct localization and expression in functional contexts (hepatectomy, IL-6 treatment), negative binding result explicitly reported, single lab\",\n      \"pmids\": [\"11803570\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Phosphoglycerate kinase 1 (PGK1) was identified as a binding partner of ITI-H4. PGK1 increases ITI-H4 expression levels and blocks KLKB1 (kallikrein B1)-mediated cleavage of ITI-H4. PGK1 also inhibits pro-inflammatory JAK2/STAT3 signaling.\",\n      \"method\": \"Immunoprecipitation of ITIH4-associated proteins from cell lysates, MALDI-TOF/MS identification of binding partners, Western blot validation of PGK1 interaction and effect on ITIH4 cleavage\",\n      \"journal\": \"Biomedicine & pharmacotherapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — single Co-IP/pulldown with MS identification, functional cleavage assay, single lab with two orthogonal methods\",\n      \"pmids\": [\"36841032\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"IL-6-mediated induction of ITIH4 in HepG2 cells operates through the JAK/STAT signaling pathway, as demonstrated by significant reduction of ITIH4 protein and mRNA levels upon JAK/STAT inhibitor treatment before IL-6 or LPS stimulation.\",\n      \"method\": \"JAK/STAT inhibitor pretreatment, Western blot, real-time PCR, immunohistochemistry in mouse liver and HepG2 cell model\",\n      \"journal\": \"Cytokine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological pathway dissection with JAK/STAT inhibitor, multiple readouts (protein + mRNA), single lab\",\n      \"pmids\": [\"33348064\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"ITIH4 regulates vascular smooth muscle cell (VSMC) stiffness: ITIH4 overexpression increases VSMC stiffness and acetylated α-tubulin while inhibiting ERK1/2 and JNK (but not p38 MAPK). Thrombin downregulates ITIH4, and ITIH4 partially reverses thrombin-induced changes in acetylated α-tubulin and VSMC stiffness through JNK and ERK signaling.\",\n      \"method\": \"ITIH4 expression vector and siRNA transfection in VSMCs, atomic force microscopy for cell stiffness, Western blot for signaling molecules, ERK inhibitor (PD98059) and JNK inhibitor (SP600125) treatment\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain-of-function and loss-of-function with pharmacological pathway dissection, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"39069151\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"ITIH4 deficiency in airway epithelial cells exacerbates oxidative-stress-induced apoptosis, while ITIH4 overexpression inhibits it. Mechanistically, ITIH4 attenuates JNK activation and prevents β-catenin decrease upon oxidative stress. Acute hydrogen peroxide exposure causes rapid ITIH4 protein degradation with no effect at the transcriptional level.\",\n      \"method\": \"ITIH4 overexpression in primary COPD small airway epithelial cells and normal cells, siRNA knockdown, human apoptosis antibody array, Western blot, clinical cohort ITIH4 measurements\",\n      \"journal\": \"The European respiratory journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain- and loss-of-function with defined apoptotic and signaling readouts, apoptosis array, single lab\",\n      \"pmids\": [\"40404214\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"ITIH4 interacts with CXCR4 in rheumatoid arthritis fibroblast-like synoviocytes (RA-FLS): siRNA-mediated knockdown of ITIH4 led to significant downregulation of CXCR4 protein expression. In a CIA rat model, ITIH4 knockdown inhibited arthritis progression, decreased cellular infiltration, cytokine production, and pannus formation. The ITIH4-CXCR4 interaction was linked to PI3K/Akt signaling modulation of apoptosis and inflammation.\",\n      \"method\": \"siRNA knockdown in RA-FLS, Western blot validation, in vivo CIA rat model, molecular dynamics simulation of ITIH4-CXCR4 interaction\",\n      \"journal\": \"Rheumatology (Oxford, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — siRNA knockdown with cellular and in vivo phenotypic readouts plus computational interaction modelling, single lab\",\n      \"pmids\": [\"40608509\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"ITIH4 is cleaved in hereditary angioedema (HAE) patients with C1 inhibitor deficiency (types 1 and 2), indicating ongoing enzymatic activity in the plasma of HAE patients. HAE patients have significantly lower intact ITIH4 levels compared to controls, and immediate cleavage of added recombinant ITIH4 was observed in serum lacking endogenous intact ITIH4, demonstrating a compensatory protease inhibitor role for ITIH4 in HAE-associated proteolytic pathways.\",\n      \"method\": \"Specific immunoassays for intact vs. total ITIH4, Western blot of cleavage products, recombinant ITIH4 addition to patient serum, clinical cohort of 80 HAE patients vs. 100 controls\",\n      \"journal\": \"The Journal of allergy and clinical immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical reconstitution experiment (rITIH4 cleavage in patient serum), orthogonal immunoassay and Western blot, validated cohort, single lab\",\n      \"pmids\": [\"38657796\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"In macrophages, full-length ITIH4 increases under pro-inflammatory conditions due to decreased cleavage. 4-Octyl itaconate promotes synthesis and secretion of full-length ITIH4. ITIH4 overexpression in macrophages attenuates pro-inflammatory responses via the NF-κB signaling pathway, and macrophages with ITIH4 overexpression activate cAMP signaling to enhance viability and tight junction integrity of colonic epithelial cells.\",\n      \"method\": \"Quantitative proteomics (mass spectrometry) of BMDMs, ITIH4 overexpression and knockdown in Raw264.7 and THP-1 cells, RNA-seq, Western blot, qRT-PCR, CCK8 viability assay, scratch wound healing assay\",\n      \"journal\": \"Inflammation research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain- and loss-of-function with RNA-seq pathway analysis and multiple orthogonal validation methods, single lab\",\n      \"pmids\": [\"41998424\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"ITIH4 knockdown in A549 cells increases MP-induced apoptosis and pro-inflammatory cytokine release, while overexpression of NLRP3 reverses the protective effects of ITIH4 knockdown. This places ITIH4 upstream of NLRP3 inflammasome activation in the context of Mycoplasma pneumoniae-induced lung epithelial cell inflammation.\",\n      \"method\": \"Lentiviral ITIH4 knockdown in A549 cells, NLRP3 reactivation rescue experiment, flow cytometry for apoptosis, ELISA for cytokines, Western blot for inflammasome proteins\",\n      \"journal\": \"Allergologia et immunopathologia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis experiment (NLRP3 reactivation rescues ITIH4-knockdown phenotype), multiple readouts, single lab\",\n      \"pmids\": [\"40682224\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Recombinant ITIH4 (rITIH4) attenuates acute lung injury in mice exposed to Fe-containing particulate matter by modulating the Hippo pathway in type II alveolar epithelial cells (AECII): rITIH4 restored Cdh1, Pdpn, Wwtr1, and Yap1 in AECII, increased α-catenin and p-YAP, and modulated pTAZ/TAZ and LC3BII/I ratios.\",\n      \"method\": \"Intratracheal DEP/FeCl3 instillation mouse model, intranasal rITIH4 treatment, single-cell RNA sequencing, single-cell ICP-MS for Fe, immunofluorescence, BALF cytokine measurement\",\n      \"journal\": \"Respiratory research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo gain-of-function with rITIH4, scRNA-seq pathway identification, multiple orthogonal readouts, single lab\",\n      \"pmids\": [\"40437524\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"ITIH4 regulates YAP/TAZ-mediated apoptosis in type II alveolar epithelial cells: ITIH4 knockdown decreases YAP and TAZ while increasing p-YAP and SIRT1; ITIH4 overexpression increases p-TAZ/TAZ and SIRT1 and decreases ATM and caspase-3. rITIH4 treatment of LPS-injured mice restored ITIH4 in SPC+ cells, reduced caspase-3, and transiently elevated YAP in damaged lung regions, indicating spatiotemporal Hippo pathway regulation during lung repair.\",\n      \"method\": \"ITIH4 knockdown and overexpression in A549 cells, rITIH4 treatment in LPS-ARDS mouse model, Western blot for Hippo pathway components, immunofluorescence in SPC+ cells, H&E with K-means clustering\",\n      \"journal\": \"Pharmaceutical research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain- and loss-of-function with defined mechanistic pathway readouts, in vivo validation, single lab\",\n      \"pmids\": [\"41735691\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"ITIH4 administration in an OVA-induced asthma mouse model significantly reduced Th2 cytokines (IL-4, IL-5, IL-13), IgE, and eosinophils/lymphocytes in BALF, modulated lung and gut microbiome composition (enriching Gram-positive taxa, depleting Helicobacteraceae), altered short-chain fatty acids, and proteomic analysis of intestinal tissue revealed dose-dependent granzyme A signaling activation and suppression of metabolic/solute transport pathways.\",\n      \"method\": \"Mouse OVA asthma model, lung function measurement, BALF cytokine ELISA, 16S rRNA microbiome profiling, GC-MS for SCFAs, intestinal tissue proteomics\",\n      \"journal\": \"Molecular medicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — in vivo phenotypic rescue with rITIH4 but downstream molecular mechanism linking ITIH4 directly to identified pathways not established mechanistically, single lab\",\n      \"pmids\": [\"40410722\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ITIH4 is a liver-derived, IL-6-inducible (via JAK/STAT) type II acute-phase plasma glycoprotein that acts as a protease inhibitor through a novel bait mechanism: proteases cleave ITIH4 within a susceptible region, inducing formation of a noncovalent inhibitory complex dependent on ITIH4's von Willebrand factor A domain, which sterically blocks large substrates from protease active sites while leaving small substrates accessible—thereby inhibiting MASP-1, MASP-2, and plasma kallikrein; the protein also binds actin to inhibit polymerization and PMN phagocytosis, interacts with PGK1 (which blocks its kallikrein-mediated cleavage), associates with CXCR4 to modulate PI3K/Akt signaling, regulates VSMC stiffness through ERK/JNK pathways, and controls epithelial and macrophage inflammatory responses via NF-κB and Hippo/YAP-TAZ signaling.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"ITIH4 is a liver-restricted, IL-6-inducible type II acute-phase plasma glycoprotein that acts as a protease inhibitor and modulator of inflammatory signaling [#1, #3]. Its inhibitory activity follows a bait mechanism: proteases cleave ITIH4 within a susceptible proline-rich region (an Arg-Arg-Leu site yielding 85- and 35-kDa fragments), inducing a noncovalent inhibitory complex dependent on the ITIH4 von Willebrand factor A domain that sterically excludes large protein substrates from the protease active site while leaving small substrates accessible, thereby inhibiting MASP-1, MASP-2, and plasma kallikrein [#0, #3]. Hepatic expression is driven specifically by IL-6 through the JAK/STAT pathway, not by IL-1β or TNF-α, and the gene carries liver-specific transcription factor binding sites in its promoter [#1, #4, #9]. ITIH4 cleavage tracks ongoing proteolytic activity in vivo, as intact ITIH4 is depleted and recombinant ITIH4 is rapidly cleaved in serum from hereditary angioedema patients with C1 inhibitor deficiency, consistent with a compensatory inhibitory role in plasma protease cascades [#13]. Beyond protease inhibition, ITIH4 binds actin to inhibit polymerization and suppress PMN phagocytosis [#2], and acts as an anti-inflammatory and cytoprotective factor in epithelial, macrophage, and smooth muscle contexts—restraining oxidative-stress and pathogen-induced apoptosis and cytokine release via JNK, NF-κB, NLRP3, and Hippo/YAP-TAZ signaling [#10, #11, #14, #15, #17]. PGK1 binds ITIH4 and blocks kallikrein-mediated cleavage, stabilizing the intact protein [#8].\",\n  \"teleology\": [\n    {\n      \"year\": 1995,\n      \"claim\": \"Established the molecular identity of ITIH4, defining its domain architecture and the proteolytic cleavage behavior that would later prove central to its function.\",\n      \"evidence\": \"cDNA cloning, peptide sequencing of plasma cleavage fragments, and tissue Northern blot\",\n      \"pmids\": [\"7775381\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The protease responsible for physiological cleavage was not identified\", \"Functional consequence of cleavage was unknown at this stage\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Resolved the gene structure and identified liver-specific promoter elements, explaining the hepatic restriction of ITIH4 expression.\",\n      \"evidence\": \"Genomic cloning, exon-intron mapping, FISH to 3p21-p14, and promoter sequence analysis\",\n      \"pmids\": [\"8797089\", \"7587397\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Promoter elements identified by sequence only; functional transcription assays not performed\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Cross-species comparison revealed divergence in the proline-rich region and showed acute-phase regulation differs between rat and human, while mouse work tied ITIH4 to embryonic liver development.\",\n      \"evidence\": \"Comparative cDNA/mRNA analysis (rat vs human), splice variant RT-PCR, and developmental expression profiling in mouse\",\n      \"pmids\": [\"9480842\", \"9602042\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional significance of the proline-rich repeats and predicted EF-hand motifs not tested\", \"Species differences in inflammatory induction not mechanistically explained\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Defined ITIH4 as a type II acute-phase protein by showing its hepatic induction is specific to IL-6.\",\n      \"evidence\": \"Dose-response IL-6 treatment of HepG2 cells with mRNA and 35S-labeled protein readouts\",\n      \"pmids\": [\"10486281\", \"10712621\", \"33348064\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Signaling pathway downstream of IL-6 not yet defined\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Provided the first functional activity for ITIH4 beyond an acute-phase marker—actin binding and suppression of PMN phagocytosis—framing it as anti-inflammatory.\",\n      \"evidence\": \"In vitro actin polymerization and phagocytosis assays with purified IHRP\",\n      \"pmids\": [\"10939621\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No mutagenesis or structural mapping of the actin-binding interface\", \"In vivo relevance not established\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Connected ITIH4 induction to liver regeneration and tested predicted ligand interactions, finding the unmodified protein does not bind calcium or hyaluronic acid.\",\n      \"evidence\": \"IL-6-treated liver explants, partial hepatectomy time course, and GST-fusion binding assays\",\n      \"pmids\": [\"11803570\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether posttranslational modification enables calcium/HA binding untested\", \"Causal role in hepatocyte cell-cycle entry not demonstrated\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identified JAK/STAT as the signaling route for IL-6-driven ITIH4 induction, completing the regulatory pathway upstream of the protein.\",\n      \"evidence\": \"JAK/STAT inhibitor pretreatment before IL-6/LPS in HepG2 and mouse liver, with protein and mRNA readouts\",\n      \"pmids\": [\"33348064\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific STAT factor and direct promoter binding not defined\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Established the central mechanism: ITIH4 is a substrate-cleavage-activated, vWFA-domain-dependent steric protease inhibitor of MASP-1, MASP-2, and plasma kallikrein.\",\n      \"evidence\": \"In vitro protease inhibition, domain mutagenesis, substrate competition assays, and reconstitution of the noncovalent inhibitory complex\",\n      \"pmids\": [\"33523981\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full structural model of the inhibitory complex not resolved\", \"In vivo contribution to complement/kallikrein control not quantified\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identified PGK1 as an ITIH4 binding partner that stabilizes intact ITIH4 by blocking kallikrein-mediated cleavage.\",\n      \"evidence\": \"Co-IP with MALDI-TOF/MS identification and Western blot cleavage assays\",\n      \"pmids\": [\"36841032\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single Co-IP without reciprocal structural validation\", \"Mechanism by which PGK1 blocks cleavage unresolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Extended ITIH4 function to tissue and disease contexts—VSMC stiffness via ERK/JNK, CXCR4-linked PI3K/Akt signaling in arthritis, and in vivo evidence of compensatory protease inhibition in hereditary angioedema.\",\n      \"evidence\": \"Gain/loss-of-function with pharmacological pathway dissection in VSMCs, siRNA and CIA rat model for CXCR4, and immunoassay/Western/recombinant-protein cleavage in HAE patient serum\",\n      \"pmids\": [\"39069151\", \"40608509\", \"38657796\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether ITIH4-CXCR4 is a direct physical interaction beyond computational modeling untested\", \"Mechanism linking ITIH4 to cytoskeletal acetylation not defined\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defined ITIH4 as a cytoprotective, anti-inflammatory factor in epithelial and lung-injury models, acting through JNK/β-catenin, NLRP3, and Hippo/YAP-TAZ signaling.\",\n      \"evidence\": \"Gain/loss-of-function in airway epithelial and A549 cells, NLRP3 rescue epistasis, and rITIH4 treatment in particulate-matter and OVA-asthma mouse models with scRNA-seq\",\n      \"pmids\": [\"40404214\", \"40682224\", \"40437524\", \"40410722\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct molecular link between ITIH4 and these pathways not established (mostly correlative)\", \"Receptor mediating extracellular rITIH4 effects unknown\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Showed that full-length ITIH4 accumulates under pro-inflammatory conditions and acts cell-non-autonomously, dampening macrophage NF-κB responses and supporting epithelial barrier integrity, and dynamically tuning Hippo signaling during lung repair.\",\n      \"evidence\": \"Quantitative proteomics of BMDMs, ITIH4 overexpression/knockdown in macrophage lines with RNA-seq, and Hippo pathway readouts in A549 and LPS-ARDS mice\",\n      \"pmids\": [\"41998424\", \"41735691\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism coupling intracellular/secreted ITIH4 to NF-κB and Hippo not defined\", \"Whether protease-inhibition and signaling functions are mechanistically linked unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How ITIH4's defined plasma protease-inhibitor mechanism relates to its diverse intracellular and cell-non-autonomous signaling roles (NF-κB, Hippo/YAP-TAZ, NLRP3, CXCR4/PI3K-Akt) remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No receptor identified for extracellular ITIH4 signaling effects\", \"Unclear whether cleaved versus intact ITIH4 drives the signaling phenotypes\", \"No structural model unifying the bait mechanism with the signaling functions\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 13]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [1, 3, 13]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 13, 14]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [1, 9, 11]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"PGK1\", \"KLKB1\", \"CXCR4\", \"ACTB\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}