{"gene":"IVL","run_date":"2026-04-28T18:06:54","timeline":{"discoveries":[{"year":1979,"finding":"Involucrin (IVL) was identified as a soluble cytosolic precursor protein (~92 kDa, pI ~4.5, ~46% Glu residues) in cultured epidermal keratinocytes that serves as a substrate for transglutaminase and becomes cross-linked into the cornified envelope beneath the plasma membrane upon calcium-dependent transglutaminase activation. The protein is first present in the cytoplasm of suprabasal keratinocytes, then concentrates at the cell periphery before cross-linking.","method":"Protein purification (gel filtration, DEAE-cellulose, hydroxyapatite chromatography), transglutaminase incorporation assay with labeled amines, indirect immunofluorescence, calcium ionophore and detergent treatments","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 — original purification with biochemical reconstitution and multiple orthogonal methods; foundational paper with 794 citations","pmids":["42494"],"is_preprint":false},{"year":1986,"finding":"The human involucrin gene was cloned and sequenced, revealing that the central coding region contains 39 tandem repeats of a 30-nucleotide sequence encoding 10 amino acids (including 3 glutamines and 2 glutamic acids). This repetitive structure arose by successive duplications of a simpler ancestral sequence, and the glutamine-rich repeats provide the transglutaminase substrate sites that enable IVL's function as a cornified envelope precursor.","method":"Gene cloning, DNA sequencing, sequence analysis of repeat structure and evolutionary relationships","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 — direct gene sequencing with structural analysis; highly cited foundational paper (407 citations)","pmids":["2873896"],"is_preprint":false},{"year":1988,"finding":"Among the many glutamine residues in involucrin, a single glutamine at residue 496 (located 89 residues from the C-terminal end) is the preferential reactive site for transglutaminase-catalyzed cross-linking in the intact protein. Additional glutamine residues throughout the molecule become reactive only when the intact protein is fragmented, indicating that the N-terminal and C-terminal ends suppress reactivity of internal glutamine residues in the native conformation.","method":"Tryptic peptide mapping, cyanogen bromide fragmentation, transglutaminase labeling assay with glycine ethyl ester as cosubstrate, peptide sequencing","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro enzymatic assay with mutagenic fragmentation and direct peptide sequencing identifying specific reactive residue","pmids":["2461365"],"is_preprint":false},{"year":1993,"finding":"The involucrin gene (IVL) is physically located on chromosome 1q21 within a ~2.05 Mb cluster of epidermal differentiation genes, in the order: calpactin I light chain — trichohyalin — profilaggrin — involucrin/small proline-rich protein — loricrin — calcyclin. This co-localization with functionally interdependent genes suggests shared regulatory elements controlling terminal differentiation.","method":"Physical mapping by pulsed-field gel electrophoresis and YAC analysis","journal":"Genomics","confidence":"Medium","confidence_rationale":"Tier 2 — direct physical mapping; establishes genomic context for co-regulation","pmids":["8276421"],"is_preprint":false},{"year":1995,"finding":"Transcription of the human involucrin gene is driven by two discrete AP1 binding sites in the promoter: a distal AP1-5 site and a proximal AP1-1 site. Simultaneous mutation of both sites reduces transcription by 80%. The transcription factors Fra-1, JunB, and JunD bind these sites. Both AP1 sites also mediate the phorbol ester (PKC)-dependent 5–11-fold increase in involucrin promoter activity, linking PKC signaling to involucrin induction during keratinocyte differentiation.","method":"Reporter gene assays in human keratinocytes, site-directed mutagenesis of AP1 sites, gel supershift assays identifying Fra-1/JunB/JunD binding, RT-PCR for involucrin mRNA","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 — reporter mutagenesis combined with gel supershift identifying specific transcription factors; replicated with multiple constructs","pmids":["7759510"],"is_preprint":false},{"year":1997,"finding":"Direct biochemical evidence confirmed that involucrin is a major early scaffold component of the keratinocyte cornified cell envelope (CE), cross-linked via transglutaminase-induced isopeptide bonds. Specific cross-linking sites were identified: Gln495/496 to desmoplakin, Gln288 to keratins, and Lys468/485/508 and Gln465/489 for interchain involucrin–involucrin cross-links. Involucrin cross-links to numerous other CE proteins including cystatin alpha, desmoplakin, elafin, keratins, small proline-rich proteins, and loricrin.","method":"Saponification of cornified envelopes, immunogold electron microscopy, proteolytic digestion (methanol/KOH treatment), amino acid sequencing of cross-linked peptides","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — direct isolation and sequencing of isopeptide cross-linked peptides from native CEs with identification of specific cross-linking residues","pmids":["8999895"],"is_preprint":false},{"year":1997,"finding":"Involucrin, S100A11, S100A10, annexin I, desmosomal proteins (desmoglein 3, desmocollin A/B, desmoplakin I, plakoglobin, plakophilin), small proline-rich proteins (SPR1A, SPR1B), plasminogen activator inhibitor-2, and envoplakin were all identified as isopeptide cross-linked components of the human keratinocyte cornified envelope by proteolytic release and peptide sequencing.","method":"Sequential proteolytic digestion (CNBr, trypsin, proteinase K) of purified CE fragments, peptide purification and sequencing","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — direct biochemical identification of CE components by peptide sequencing from native tissue","pmids":["9115270"],"is_preprint":false},{"year":1998,"finding":"Involucrin serves as a primary protein scaffold for covalent attachment of ceramides (via ester linkages) in the human epidermal cornified envelope, contributing to barrier function. Approximately 35% of recovered lipopeptides from CE saponification were derived from the glutamine-glutamate-rich ancestral regions of involucrin. Periplakin and envoplakin also serve as ceramide attachment substrates.","method":"Partial saponification of isolated foreskin epidermal CEs, limited proteolysis, biochemical and mass spectrometric characterization of lipopeptides, amino acid sequencing","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — direct mass spectrometry and sequencing identifying specific protein-lipid attachment sites in native tissue","pmids":["9651377"],"is_preprint":false},{"year":2001,"finding":"Transglutaminase 5 (TGase 5) efficiently cross-links involucrin, loricrin, and small proline-rich protein 3 (SPR3) in vitro, and is induced during early stages of keratinocyte differentiation. The full-length TGase 5 and the Delta11 splice variant are enzymatically active toward these CE substrates, while Delta3 and Delta3Delta11 variants have very low activity. TGase 5 co-localizes with vimentin in an intermediate filament-enriched fraction.","method":"Recombinant expression of TGase5 splice variants in keratinocyte and baculovirus systems, kinetic assays, in vitro cross-linking experiments with CE substrates, immunolocalization","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro enzymatic reconstitution with multiple substrates and splice variant analysis","pmids":["11443109"],"is_preprint":false},{"year":2004,"finding":"Involucrin gene expression is regulated by a signaling cascade involving novel PKC isoforms → Ras → MEKK1 → MEK3 → a p38δ–ERK1/2 complex, which in turn regulates AP1, Sp1, and C/EBP transcription factor binding to two discrete involucrin promoter regions (the distal regulatory region and the proximal regulatory region).","method":"Review synthesizing reporter gene assays, kinase inhibitors, dominant-negative constructs, and transcription factor binding studies from multiple experiments","journal":"The Journal of investigative dermatology","confidence":"Medium","confidence_rationale":"Tier 2 — synthesis of multiple epistasis and reporter assays establishing pathway from PKC to IVL promoter; review paper but based on primary experimental data","pmids":["15191537"],"is_preprint":false},{"year":2007,"finding":"The Th2 cytokines IL-4 and IL-13 significantly downregulate involucrin (IVL) and loricrin expression in human keratinocytes through a STAT-6-dependent mechanism. STAT-6 transgenic mouse skin is deficient in IVL and loricrin expression and production.","method":"Primary keratinocyte cultures treated with IL-4/IL-13, RT-PCR and protein expression analysis, STAT-6 transgenic mouse skin biopsies with immunohistochemistry","journal":"Clinical immunology","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro cytokine treatment with transgenic in vivo validation linking STAT-6 to IVL repression","pmids":["18166499"],"is_preprint":false},{"year":2018,"finding":"Rhodiola crenulata root extract (RCE) upregulates involucrin (IVL) expression in keratinocytes via the aryl hydrocarbon receptor (AHR) signaling pathway, but this upregulation is independent of the transcription factor OVOL1 (unlike FLG and LOR upregulation by RCE, which requires both AHR and OVOL1). This demonstrates that AHR differentially regulates IVL versus other barrier genes.","method":"Keratinocyte cell culture with RCE treatment, AHR inhibitor and OVOL1 knockdown experiments, RT-PCR and Western blot for IVL/FLG/LOR expression","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 — knockdown/inhibitor experiments distinguishing AHR-dependent, OVOL1-independent pathway for IVL regulation","pmids":["29866992"],"is_preprint":false},{"year":2025,"finding":"Gardeniae Fructus (GF) iridoids upregulate IVL (as well as FLG and LOR) mRNA and protein expression in HaCaT keratinocytes and 3D epidermal models through binding to and activating the aryl hydrocarbon receptor (AHR), as confirmed by proteomics, molecular docking, molecular dynamics simulation, and in vitro validation with AHR pathway inhibition.","method":"UPLC-MS/MS characterization of iridoids, proteomics, molecular docking, molecular dynamics, HaCaT cell culture with AHR pathway validation, 3D epidermal models, Western blot","journal":"Molecules","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods (proteomics, docking, in vitro validation) linking AHR activation to IVL upregulation","pmids":["41011656"],"is_preprint":false}],"current_model":"Involucrin (IVL) is a ~92 kDa glutamine/glutamate-rich cytosolic keratinocyte protein that functions as an early scaffold component of the cornified cell envelope: it is cross-linked by transglutaminases (notably TGase 1 and TGase 5) at specific glutamine residues (principally Gln496 in the intact protein) to itself and to numerous CE partners (desmoplakin, keratins, cystatin alpha, loricrin, small proline-rich proteins) via isopeptide bonds, and also serves as a primary covalent attachment site for ceramides via ester linkages, thereby contributing to epidermal barrier function; its transcription is driven by Fra-1/JunB/JunD binding to two AP1 sites in its promoter and is activated downstream of a PKCδ → Ras → MEKK1 → MEK3 → p38δ–ERK1/2 cascade, while being suppressed by Th2 cytokines (IL-4, IL-13) via STAT-6 and induced by aryl hydrocarbon receptor (AHR) activation in an OVOL1-independent manner."},"narrative":{"teleology":[{"year":1979,"claim":"The foundational question of what soluble precursor protein becomes the insoluble cornified envelope was answered by purifying involucrin from keratinocytes and showing it is a cytosolic transglutaminase substrate that concentrates at the cell periphery before calcium-dependent cross-linking.","evidence":"Protein purification with gel filtration/chromatography, transglutaminase incorporation assay, immunofluorescence, and calcium ionophore treatment in cultured human keratinocytes","pmids":["42494"],"confidence":"High","gaps":["Specific cross-linking residues not yet identified","Identity of other cross-linked partner proteins unknown","In vivo relevance not yet demonstrated"]},{"year":1986,"claim":"The structural basis for involucrin's transglutaminase reactivity was established by cloning the gene and revealing 39 tandem 10-amino-acid repeats rich in glutamine and glutamic acid, arising from successive duplication of an ancestral element.","evidence":"Gene cloning and complete DNA sequencing with evolutionary repeat analysis","pmids":["2873896"],"confidence":"High","gaps":["Which specific glutamine residues are preferentially reactive was unknown","Functional significance of repeat number variation not established"]},{"year":1988,"claim":"The question of whether all glutamine residues are equivalently reactive was resolved by demonstrating that Gln496, near the C-terminus, is the single preferential transglutaminase cross-linking site in the intact protein, with internal glutamines masked by the native conformation.","evidence":"Tryptic and CNBr fragmentation with transglutaminase labeling and peptide sequencing","pmids":["2461365"],"confidence":"High","gaps":["Structural basis for conformational masking of internal glutamines unknown","Whether Gln496 preference holds in the context of the assembled CE not established"]},{"year":1993,"claim":"IVL was physically mapped to chromosome 1q21 within the epidermal differentiation complex alongside loricrin, profilaggrin, and SPR genes, establishing the genomic context for coordinated regulation of CE genes.","evidence":"Pulsed-field gel electrophoresis and YAC-based physical mapping","pmids":["8276421"],"confidence":"Medium","gaps":["Shared regulatory elements controlling co-expression not identified","Functional interdependence among clustered genes not demonstrated experimentally"]},{"year":1995,"claim":"The transcriptional control of IVL was elucidated by identifying two AP1 sites in the promoter bound by Fra-1/JunB/JunD that are necessary for both basal transcription and PKC-dependent induction during differentiation.","evidence":"Reporter gene assays with site-directed mutagenesis and gel supershift assays in human keratinocytes","pmids":["7759510"],"confidence":"High","gaps":["Upstream kinase cascade linking PKC to AP1 not yet mapped","Contribution of other transcription factor families (Sp1, C/EBP) not fully delineated"]},{"year":1997,"claim":"The molecular architecture of involucrin within the assembled CE was resolved by identifying specific isopeptide cross-link sites to desmoplakin (Gln495/496), keratins (Gln288), and involucrin itself (Lys468/485/508, Gln465/489), establishing IVL as a central scaffold connecting diverse CE components.","evidence":"Saponification of native foreskin CEs, immunogold EM, proteolytic digestion, and amino acid sequencing of cross-linked peptides","pmids":["8999895","9115270"],"confidence":"High","gaps":["Temporal order of cross-linking events in vivo not resolved","Relative stoichiometry of different cross-link types unknown"]},{"year":1998,"claim":"Beyond protein cross-linking, involucrin was shown to serve as a primary covalent attachment scaffold for ceramides via ester linkages, directly linking the protein envelope to the lipid barrier and explaining how IVL contributes to the epidermal permeability barrier.","evidence":"Partial saponification of isolated epidermal CEs with mass spectrometric and amino acid sequence characterization of lipopeptides","pmids":["9651377"],"confidence":"High","gaps":["Enzymatic mechanism catalyzing ester bond formation between IVL and ceramides not identified","Specific serine/threonine residues serving as ester attachment sites not mapped"]},{"year":2001,"claim":"The identity of which transglutaminase isoforms cross-link IVL was expanded by demonstrating that TGase 5 efficiently cross-links involucrin in vitro, supplementing the known role of TGase 1 and indicating redundancy in CE assembly.","evidence":"Recombinant TGase5 splice variant expression with kinetic cross-linking assays using purified CE substrates","pmids":["11443109"],"confidence":"High","gaps":["Relative contributions of TGase 1 vs TGase 5 to IVL cross-linking in vivo not determined","Whether TGase 5 targets the same Gln496 site as TGase 1 not established"]},{"year":2004,"claim":"The full upstream signaling cascade driving IVL transcription was mapped as PKCδ→Ras→MEKK1→MEK3→p38δ–ERK1/2, converging on AP1/Sp1/C/EBP elements in two discrete promoter regions, integrating earlier AP1 findings into a complete pathway model.","evidence":"Synthesis of epistasis experiments using kinase inhibitors, dominant-negative constructs, and transcription factor binding studies","pmids":["15191537"],"confidence":"Medium","gaps":["Direct biochemical demonstration of p38δ–ERK1/2 complex formation on the IVL promoter lacking","Calcium-sensing mechanism upstream of PKCδ not defined"]},{"year":2007,"claim":"A negative regulatory axis was identified: Th2 cytokines IL-4 and IL-13 suppress IVL expression through STAT-6, providing a mechanistic link between atopic inflammation and impaired barrier gene expression.","evidence":"Keratinocyte culture with IL-4/IL-13 treatment and STAT-6 transgenic mouse skin analysis by immunohistochemistry","pmids":["18166499"],"confidence":"Medium","gaps":["Whether STAT-6 directly binds the IVL promoter or acts indirectly not resolved","Relevance to human atopic dermatitis barrier defects not confirmed by patient studies"]},{"year":2018,"claim":"AHR was identified as an additional transcriptional activator of IVL, and importantly, IVL's AHR-dependent induction was shown to be independent of OVOL1, distinguishing its regulation from FLG and LOR.","evidence":"Keratinocyte culture with AHR inhibitor and OVOL1 knockdown, RT-PCR and Western blot","pmids":["29866992"],"confidence":"Medium","gaps":["Direct AHR binding to the IVL promoter not demonstrated by ChIP","Identity of AHR-responsive element(s) in IVL promoter unknown"]},{"year":null,"claim":"Key unresolved questions include the structural basis for conformational masking of internal glutamine residues, the enzyme and mechanism responsible for ceramide ester bond formation to IVL, the relative in vivo contributions of TGase 1 versus TGase 5 to IVL cross-linking, and whether STAT-6 and AHR directly bind IVL promoter elements.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution structure of involucrin available","Ceramide-ester-forming enzyme unidentified","No in vivo genetic rescue or IVL-null phenotypic characterization in the timeline"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,5,6,7]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,5]}],"pathway":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0]}],"complexes":[],"partners":["TGM1","TGM5","DSP","LOR","SPRR1A","SPRR1B","CST1"],"other_free_text":[]},"mechanistic_narrative":"Involucrin (IVL) is a glutamine/glutamate-rich soluble cytosolic precursor protein of the keratinocyte cornified cell envelope (CE) that functions as an early structural scaffold cross-linked by transglutaminases during terminal epidermal differentiation [PMID:42494, PMID:8999895]. The protein contains 39 tandem 10-amino-acid repeats rich in glutamine residues that serve as transglutaminase substrate sites, with Gln496 acting as the preferential reactive residue in the intact native conformation; upon cross-linking, IVL forms isopeptide bonds with itself and numerous CE partners including desmoplakin, keratins, cystatin alpha, loricrin, and small proline-rich proteins, and additionally provides covalent ester-linked attachment sites for ceramides essential for epidermal barrier function [PMID:2873896, PMID:2461365, PMID:8999895, PMID:9651377]. IVL transcription is driven by Fra-1/JunB/JunD binding to two AP1 sites in its promoter downstream of a PKCδ→Ras→MEKK1→MEK3→p38δ–ERK1/2 cascade, is induced by aryl hydrocarbon receptor (AHR) activation independently of OVOL1, and is suppressed by Th2 cytokines IL-4/IL-13 via STAT-6 [PMID:7759510, PMID:15191537, PMID:29866992, PMID:18166499]."},"prefetch_data":{"uniprot":{"accession":"P07476","full_name":"Involucrin","aliases":[],"length_aa":585,"mass_kda":68.5,"function":"Part of the insoluble cornified cell envelope (CE) of stratified squamous epithelia","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/P07476/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/IVL","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/IVL","total_profiled":1310},"omim":[{"mim_id":"617211","title":"DERMOKINE; DMKN","url":"https://www.omim.org/entry/617211"},{"mim_id":"616363","title":"SMALL PROLINE-RICH PROTEIN 4; SPRR4","url":"https://www.omim.org/entry/616363"},{"mim_id":"613924","title":"LIPASE FAMILY, MEMBER N; LIPN","url":"https://www.omim.org/entry/613924"},{"mim_id":"611764","title":"CORNIFELIN; CNFN","url":"https://www.omim.org/entry/611764"},{"mim_id":"610378","title":"GLIS FAMILY ZINC FINGER PROTEIN 1; GLIS1","url":"https://www.omim.org/entry/610378"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Cytosol","reliability":"Supported"},{"location":"Nuclear bodies","reliability":"Additional"},{"location":"Centrosome","reliability":"Additional"}],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"cervix","ntpm":195.7},{"tissue":"esophagus","ntpm":294.3},{"tissue":"salivary gland","ntpm":84.6},{"tissue":"skin 1","ntpm":156.4},{"tissue":"vagina","ntpm":223.1}],"url":"https://www.proteinatlas.org/search/IVL"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"P07476","domains":[{"cath_id":"1.20.5","chopping":"81-150","consensus_level":"medium","plddt":78.1546,"start":81,"end":150},{"cath_id":"2.160.20","chopping":"196-297","consensus_level":"medium","plddt":60.047,"start":196,"end":297},{"cath_id":"1.20.5","chopping":"393-440","consensus_level":"medium","plddt":49.9821,"start":393,"end":440}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P07476","model_url":"https://alphafold.ebi.ac.uk/files/AF-P07476-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P07476-F1-predicted_aligned_error_v6.png","plddt_mean":49.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=IVL","jax_strain_url":"https://www.jax.org/strain/search?query=IVL"},"sequence":{"accession":"P07476","fasta_url":"https://rest.uniprot.org/uniprotkb/P07476.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P07476/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P07476"}},"corpus_meta":[{"pmid":"18506023","id":"PMC_18506023","title":"Retrospective analysis of intravascular large B-cell lymphoma treated with rituximab-containing chemotherapy as reported by the IVL study group in Japan.","date":"2008","source":"Journal of clinical oncology : official journal of the American Society of Clinical Oncology","url":"https://pubmed.ncbi.nlm.nih.gov/18506023","citation_count":217,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"32171071","id":"PMC_32171071","title":"Rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisolone combined with high-dose methotrexate plus intrathecal chemotherapy for newly diagnosed intravascular large B-cell lymphoma (PRIMEUR-IVL): a multicentre, single-arm, phase 2 trial.","date":"2020","source":"The Lancet. 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human epidermal keratinocytes.","date":"1997","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/9115270","citation_count":198,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"8999895","id":"PMC_8999895","title":"Direct evidence that involucrin is a major early isopeptide cross-linked component of the keratinocyte cornified cell envelope.","date":"1997","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/8999895","citation_count":188,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"7759510","id":"PMC_7759510","title":"Fos-related antigen (Fra-1), junB, and junD activate human involucrin promoter transcription by binding to proximal and distal AP1 sites to mediate phorbol ester effects on promoter activity.","date":"1995","source":"The Journal of biological 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research","url":"https://pubmed.ncbi.nlm.nih.gov/25324306","citation_count":78,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"2461365","id":"PMC_2461365","title":"The glutamine residues reactive in transglutaminase-catalyzed cross-linking of involucrin.","date":"1988","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/2461365","citation_count":77,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"16639001","id":"PMC_16639001","title":"Expression and regulation of cornified envelope proteins in human corneal epithelium.","date":"2006","source":"Investigative ophthalmology & visual science","url":"https://pubmed.ncbi.nlm.nih.gov/16639001","citation_count":75,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"30561431","id":"PMC_30561431","title":"A protein-protein interaction map of the TNF-induced NF-κB signal transduction pathway.","date":"2018","source":"Scientific data","url":"https://pubmed.ncbi.nlm.nih.gov/30561431","citation_count":74,"is_preprint":false,"source_track":"gene2pubmed"}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":10635,"output_tokens":774,"usd":0.021757},"stage2":{"model":"claude-opus-4-6","input_tokens":3948,"output_tokens":897,"usd":0.063247},"total_usd":0.419792,"stage1_batch_id":"msgbatch_01DzrsgVgYngY1hvM3DU1yF2","stage2_batch_id":"msgbatch_01KA9b7iRzKFdhoBUT7vCvSe","note":"batch pricing = 50% of standard","round2_stage1":{"model":"claude-sonnet-4-6","input_tokens":23957,"output_tokens":4557,"usd":0.070113},"round2_rules_fired":"R3","round2_stage2":{"model":"claude-opus-4-6","input_tokens":7310,"output_tokens":5596,"usd":0.264675}},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2018,\n      \"finding\": \"Involucrin (IVL) expression in keratinocytes is upregulated by Rhodiola crenulata root extract (RCE) via aryl hydrocarbon receptor (AHR) activation, but this upregulation is OVOL1-independent (in contrast to FLG and LOR which require both AHR and OVOL1).\",\n      \"method\": \"Cell-based assays with AHR inhibition/knockdown and OVOL1 knockdown in keratinocytes, measuring IVL mRNA/protein expression\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KD with defined molecular pathway, single lab with two orthogonal perturbations (AHR and OVOL1)\",\n      \"pmids\": [\"29866992\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"IVL expression is upregulated by Gardeniae Fructus iridoids via AHR activation, as demonstrated by AHR binding (molecular docking/MD) and subsequent upregulation of IVL mRNA and protein in HaCaT cells and 3D epidermal models.\",\n      \"method\": \"Proteomics, molecular docking, molecular dynamics simulation, validated by mRNA and protein expression in HaCaT cells and 3D epidermal models\",\n      \"journal\": \"Molecules (Basel, Switzerland)\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, primarily computational with limited functional validation of AHR-IVL axis\",\n      \"pmids\": [\"41011656\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"IVL+ differentiation-committed epidermal basal cells exhibit tumour resistance with long latency upon MAPK hyperactivation, in contrast to K14/K5+ stem-cell-like cells which are tumour-primed; SOX2 is necessary and sufficient to transform IVL+ cells by preventing delamination/differentiation and promoting stemness.\",\n      \"method\": \"Mouse genetic models with lineage-specific oncogene induction in IVL+ vs K14/K5+ cells; SOX2 gain- and loss-of-function experiments; transcriptomic analysis\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean cell-of-origin genetic model with loss- and gain-of-function, but preprint and single lab\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"Involucrin (IVL) is a keratinocyte differentiation marker whose expression is regulated transcriptionally downstream of aryl hydrocarbon receptor (AHR) activation in an OVOL1-independent manner, and IVL+ committed epidermal progenitor cells represent a tumour-resistant population whose transformation requires the pioneer factor SOX2.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll classify each paper first, then extract discoveries only from KEEP papers.\n\n**Classification:**\n\nRetrieved papers:\n- [1,2,5,8]: IVL = Intravascular Large B-cell Lymphoma → EXCLUDE (alias collision)\n- [3]: IVL = Involucrin (canonical protein) → KEEP\n- [4]: IVL = SCCmec type IVl (MRSA classification) → EXCLUDE (alias collision)\n- [6]: IVL-Methyl = NMR notation for Ile/Val/Leu methyls in MALT1 → EXCLUDE (alias collision)\n- [7]: IVL methyl = NMR notation in Dengue NS3pro → EXCLUDE (alias collision)\n- [9]: IV-L = chromosome IV left arm in yeast → EXCLUDE (alias collision)\n- [10]: IVL methyl = NMR notation for TrBgl2 → EXCLUDE (alias collision)\n- [11]: IVL = Involucrin (canonical protein) → KEEP\n- [12]: IVL = Intravascular Lithotripsy → EXCLUDE (alias collision)\n- [13]: IVL-11 = α-hederin compound name → EXCLUDE (alias collision)\n- [14]: L-IVP/L-IVL = vaccinia virus strain name → EXCLUDE (alias collision)\n- [15]: IVL = Intravascular Lithotripsy → EXCLUDE (preprint, alias collision)\n- [16]: GroES IVL = NMR/computational notation → EXCLUDE (alias collision)\n- [17]: IVL+ cells = Involucrin-expressing cells (canonical) → KEEP (mentions IVL+ as differentiation marker but no mechanistic discovery about IVL protein itself — will evaluate)\n- [18]: IVL = intervertebral ligament → EXCLUDE (alias collision)\n\nGene2pubmed papers:\n- [1,2]: MGC cDNA sequencing — no mechanism → low value but KEEP for context\n- [3,5]: BioPlex interactome — KEEP if IVL interactions found\n- [4]: Rice RH & Green H 1979 — IVL precursor protein, original discovery → KEEP\n- [6]: MGC cDNA → minimal mechanism\n- [7]: Loricrin/IVL downregulated by Th2/STAT-6 → KEEP\n- [8]: IVL gene structure → KEEP\n- [9]: IVL regulation by cytokines/AHR → KEEP\n- [10]: IL-13 and EDC genes → KEEP\n- [11]: Parotid exosomes, IVL detected → minimal mechanism\n- [12]: Organelle proteomics → minimal IVL mechanism\n- [13]: S100A11, IVL components of cornified envelope → KEEP\n- [14]: IVL cross-linked in CE, direct evidence → KEEP\n- [15]: AP1 sites in IVL promoter → KEEP\n- [16]: Ceramides bound to IVL → KEEP\n- [17]: E-cadherin interactome → IVL peripherally mentioned\n- [18]: EDC cluster mapping → KEEP (genomic context)\n- [19]: Calcium-induced differentiation, IVL marker → minimal mechanism\n- [20]: Regulation of IVL gene expression review → KEEP\n- [21,22]: IVL as differentiation marker → minimal mechanism\n- [25]: TGase5 cross-links IVL in vitro → KEEP\n- [28]: Glutamine residues reactive in TGase cross-linking of IVL → KEEP\n- [29]: IVL in corneal epithelium → KEEP (UVB regulation)\n- Others: general interactome studies where IVL may appear incidentally\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1979,\n      \"finding\": \"Involucrin (IVL) was identified as a soluble cytosolic precursor protein (~92 kDa, pI ~4.5, ~46% Glu residues) in cultured epidermal keratinocytes that serves as a substrate for transglutaminase and becomes cross-linked into the cornified envelope beneath the plasma membrane upon calcium-dependent transglutaminase activation. The protein is first present in the cytoplasm of suprabasal keratinocytes, then concentrates at the cell periphery before cross-linking.\",\n      \"method\": \"Protein purification (gel filtration, DEAE-cellulose, hydroxyapatite chromatography), transglutaminase incorporation assay with labeled amines, indirect immunofluorescence, calcium ionophore and detergent treatments\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — original purification with biochemical reconstitution and multiple orthogonal methods; foundational paper with 794 citations\",\n      \"pmids\": [\"42494\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"The human involucrin gene was cloned and sequenced, revealing that the central coding region contains 39 tandem repeats of a 30-nucleotide sequence encoding 10 amino acids (including 3 glutamines and 2 glutamic acids). This repetitive structure arose by successive duplications of a simpler ancestral sequence, and the glutamine-rich repeats provide the transglutaminase substrate sites that enable IVL's function as a cornified envelope precursor.\",\n      \"method\": \"Gene cloning, DNA sequencing, sequence analysis of repeat structure and evolutionary relationships\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct gene sequencing with structural analysis; highly cited foundational paper (407 citations)\",\n      \"pmids\": [\"2873896\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1988,\n      \"finding\": \"Among the many glutamine residues in involucrin, a single glutamine at residue 496 (located 89 residues from the C-terminal end) is the preferential reactive site for transglutaminase-catalyzed cross-linking in the intact protein. Additional glutamine residues throughout the molecule become reactive only when the intact protein is fragmented, indicating that the N-terminal and C-terminal ends suppress reactivity of internal glutamine residues in the native conformation.\",\n      \"method\": \"Tryptic peptide mapping, cyanogen bromide fragmentation, transglutaminase labeling assay with glycine ethyl ester as cosubstrate, peptide sequencing\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro enzymatic assay with mutagenic fragmentation and direct peptide sequencing identifying specific reactive residue\",\n      \"pmids\": [\"2461365\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"The involucrin gene (IVL) is physically located on chromosome 1q21 within a ~2.05 Mb cluster of epidermal differentiation genes, in the order: calpactin I light chain — trichohyalin — profilaggrin — involucrin/small proline-rich protein — loricrin — calcyclin. This co-localization with functionally interdependent genes suggests shared regulatory elements controlling terminal differentiation.\",\n      \"method\": \"Physical mapping by pulsed-field gel electrophoresis and YAC analysis\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct physical mapping; establishes genomic context for co-regulation\",\n      \"pmids\": [\"8276421\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Transcription of the human involucrin gene is driven by two discrete AP1 binding sites in the promoter: a distal AP1-5 site and a proximal AP1-1 site. Simultaneous mutation of both sites reduces transcription by 80%. The transcription factors Fra-1, JunB, and JunD bind these sites. Both AP1 sites also mediate the phorbol ester (PKC)-dependent 5–11-fold increase in involucrin promoter activity, linking PKC signaling to involucrin induction during keratinocyte differentiation.\",\n      \"method\": \"Reporter gene assays in human keratinocytes, site-directed mutagenesis of AP1 sites, gel supershift assays identifying Fra-1/JunB/JunD binding, RT-PCR for involucrin mRNA\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — reporter mutagenesis combined with gel supershift identifying specific transcription factors; replicated with multiple constructs\",\n      \"pmids\": [\"7759510\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Direct biochemical evidence confirmed that involucrin is a major early scaffold component of the keratinocyte cornified cell envelope (CE), cross-linked via transglutaminase-induced isopeptide bonds. Specific cross-linking sites were identified: Gln495/496 to desmoplakin, Gln288 to keratins, and Lys468/485/508 and Gln465/489 for interchain involucrin–involucrin cross-links. Involucrin cross-links to numerous other CE proteins including cystatin alpha, desmoplakin, elafin, keratins, small proline-rich proteins, and loricrin.\",\n      \"method\": \"Saponification of cornified envelopes, immunogold electron microscopy, proteolytic digestion (methanol/KOH treatment), amino acid sequencing of cross-linked peptides\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct isolation and sequencing of isopeptide cross-linked peptides from native CEs with identification of specific cross-linking residues\",\n      \"pmids\": [\"8999895\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Involucrin, S100A11, S100A10, annexin I, desmosomal proteins (desmoglein 3, desmocollin A/B, desmoplakin I, plakoglobin, plakophilin), small proline-rich proteins (SPR1A, SPR1B), plasminogen activator inhibitor-2, and envoplakin were all identified as isopeptide cross-linked components of the human keratinocyte cornified envelope by proteolytic release and peptide sequencing.\",\n      \"method\": \"Sequential proteolytic digestion (CNBr, trypsin, proteinase K) of purified CE fragments, peptide purification and sequencing\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct biochemical identification of CE components by peptide sequencing from native tissue\",\n      \"pmids\": [\"9115270\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Involucrin serves as a primary protein scaffold for covalent attachment of ceramides (via ester linkages) in the human epidermal cornified envelope, contributing to barrier function. Approximately 35% of recovered lipopeptides from CE saponification were derived from the glutamine-glutamate-rich ancestral regions of involucrin. Periplakin and envoplakin also serve as ceramide attachment substrates.\",\n      \"method\": \"Partial saponification of isolated foreskin epidermal CEs, limited proteolysis, biochemical and mass spectrometric characterization of lipopeptides, amino acid sequencing\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct mass spectrometry and sequencing identifying specific protein-lipid attachment sites in native tissue\",\n      \"pmids\": [\"9651377\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Transglutaminase 5 (TGase 5) efficiently cross-links involucrin, loricrin, and small proline-rich protein 3 (SPR3) in vitro, and is induced during early stages of keratinocyte differentiation. The full-length TGase 5 and the Delta11 splice variant are enzymatically active toward these CE substrates, while Delta3 and Delta3Delta11 variants have very low activity. TGase 5 co-localizes with vimentin in an intermediate filament-enriched fraction.\",\n      \"method\": \"Recombinant expression of TGase5 splice variants in keratinocyte and baculovirus systems, kinetic assays, in vitro cross-linking experiments with CE substrates, immunolocalization\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro enzymatic reconstitution with multiple substrates and splice variant analysis\",\n      \"pmids\": [\"11443109\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Involucrin gene expression is regulated by a signaling cascade involving novel PKC isoforms → Ras → MEKK1 → MEK3 → a p38δ–ERK1/2 complex, which in turn regulates AP1, Sp1, and C/EBP transcription factor binding to two discrete involucrin promoter regions (the distal regulatory region and the proximal regulatory region).\",\n      \"method\": \"Review synthesizing reporter gene assays, kinase inhibitors, dominant-negative constructs, and transcription factor binding studies from multiple experiments\",\n      \"journal\": \"The Journal of investigative dermatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — synthesis of multiple epistasis and reporter assays establishing pathway from PKC to IVL promoter; review paper but based on primary experimental data\",\n      \"pmids\": [\"15191537\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The Th2 cytokines IL-4 and IL-13 significantly downregulate involucrin (IVL) and loricrin expression in human keratinocytes through a STAT-6-dependent mechanism. STAT-6 transgenic mouse skin is deficient in IVL and loricrin expression and production.\",\n      \"method\": \"Primary keratinocyte cultures treated with IL-4/IL-13, RT-PCR and protein expression analysis, STAT-6 transgenic mouse skin biopsies with immunohistochemistry\",\n      \"journal\": \"Clinical immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro cytokine treatment with transgenic in vivo validation linking STAT-6 to IVL repression\",\n      \"pmids\": [\"18166499\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Rhodiola crenulata root extract (RCE) upregulates involucrin (IVL) expression in keratinocytes via the aryl hydrocarbon receptor (AHR) signaling pathway, but this upregulation is independent of the transcription factor OVOL1 (unlike FLG and LOR upregulation by RCE, which requires both AHR and OVOL1). This demonstrates that AHR differentially regulates IVL versus other barrier genes.\",\n      \"method\": \"Keratinocyte cell culture with RCE treatment, AHR inhibitor and OVOL1 knockdown experiments, RT-PCR and Western blot for IVL/FLG/LOR expression\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — knockdown/inhibitor experiments distinguishing AHR-dependent, OVOL1-independent pathway for IVL regulation\",\n      \"pmids\": [\"29866992\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Gardeniae Fructus (GF) iridoids upregulate IVL (as well as FLG and LOR) mRNA and protein expression in HaCaT keratinocytes and 3D epidermal models through binding to and activating the aryl hydrocarbon receptor (AHR), as confirmed by proteomics, molecular docking, molecular dynamics simulation, and in vitro validation with AHR pathway inhibition.\",\n      \"method\": \"UPLC-MS/MS characterization of iridoids, proteomics, molecular docking, molecular dynamics, HaCaT cell culture with AHR pathway validation, 3D epidermal models, Western blot\",\n      \"journal\": \"Molecules\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (proteomics, docking, in vitro validation) linking AHR activation to IVL upregulation\",\n      \"pmids\": [\"41011656\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"Involucrin (IVL) is a ~92 kDa glutamine/glutamate-rich cytosolic keratinocyte protein that functions as an early scaffold component of the cornified cell envelope: it is cross-linked by transglutaminases (notably TGase 1 and TGase 5) at specific glutamine residues (principally Gln496 in the intact protein) to itself and to numerous CE partners (desmoplakin, keratins, cystatin alpha, loricrin, small proline-rich proteins) via isopeptide bonds, and also serves as a primary covalent attachment site for ceramides via ester linkages, thereby contributing to epidermal barrier function; its transcription is driven by Fra-1/JunB/JunD binding to two AP1 sites in its promoter and is activated downstream of a PKCδ → Ras → MEKK1 → MEK3 → p38δ–ERK1/2 cascade, while being suppressed by Th2 cytokines (IL-4, IL-13) via STAT-6 and induced by aryl hydrocarbon receptor (AHR) activation in an OVOL1-independent manner.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"Involucrin (IVL) is a structural protein expressed in differentiating keratinocytes whose transcription is upregulated downstream of aryl hydrocarbon receptor (AHR) activation independently of the transcription factor OVOL1 [PMID:29866992]. IVL marks a population of differentiation-committed epidermal basal progenitor cells that are intrinsically resistant to oncogenic transformation by MAPK hyperactivation; the pioneer factor SOX2 is necessary and sufficient to override this tumour resistance by blocking delamination and restoring stemness.\",\n  \"teleology\": [\n    {\n      \"year\": 2018,\n      \"claim\": \"Establishing that IVL transcription is driven by AHR signaling but, unlike other barrier genes (FLG, LOR), does not require OVOL1 resolved how different differentiation markers are wired to distinct regulatory nodes within the same upstream pathway.\",\n      \"evidence\": \"AHR inhibition/knockdown and OVOL1 knockdown in human keratinocytes measuring IVL mRNA and protein\",\n      \"pmids\": [\"29866992\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct AHR binding to the IVL promoter has not been demonstrated by ChIP\",\n        \"Identity of transcription factors mediating AHR-dependent but OVOL1-independent IVL induction is unknown\",\n        \"Whether this regulatory logic operates in vivo in stratified epidermis is untested\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Demonstrating that IVL+ committed progenitors are tumour-resistant while K14/K5+ stem-like cells are tumour-primed identified differentiation commitment as a cell-intrinsic barrier to epidermal transformation, and showed SOX2 as the specific factor that overcomes this barrier.\",\n      \"evidence\": \"(preprint) Lineage-specific oncogene induction in IVL+ vs K14/K5+ mouse epidermal cells with SOX2 gain- and loss-of-function\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Preprint not yet peer-reviewed\",\n        \"Whether SOX2 directly represses IVL transcription or acts indirectly through a stemness program is unresolved\",\n        \"Relevance of IVL+ cell tumour resistance in human squamous cell carcinoma has not been validated\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The direct transcriptional regulators that bind the IVL promoter downstream of AHR, and the precise structural role of involucrin protein in cornified envelope assembly, remain incompletely defined at the mechanistic level in the current literature.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No cis-regulatory element mapping of the IVL locus downstream of AHR has been performed\",\n        \"Structural basis of involucrin cross-linking by transglutaminase is not resolved at atomic resolution\",\n        \"Functional consequence of IVL loss on barrier integrity and tumour susceptibility has not been tested genetically\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"pathway\": [],\n    \"complexes\": [],\n    \"partners\": [],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"Involucrin (IVL) is a glutamine/glutamate-rich soluble cytosolic precursor protein of the keratinocyte cornified cell envelope (CE) that functions as an early structural scaffold cross-linked by transglutaminases during terminal epidermal differentiation [PMID:42494, PMID:8999895]. The protein contains 39 tandem 10-amino-acid repeats rich in glutamine residues that serve as transglutaminase substrate sites, with Gln496 acting as the preferential reactive residue in the intact native conformation; upon cross-linking, IVL forms isopeptide bonds with itself and numerous CE partners including desmoplakin, keratins, cystatin alpha, loricrin, and small proline-rich proteins, and additionally provides covalent ester-linked attachment sites for ceramides essential for epidermal barrier function [PMID:2873896, PMID:2461365, PMID:8999895, PMID:9651377]. IVL transcription is driven by Fra-1/JunB/JunD binding to two AP1 sites in its promoter downstream of a PKCδ→Ras→MEKK1→MEK3→p38δ–ERK1/2 cascade, is induced by aryl hydrocarbon receptor (AHR) activation independently of OVOL1, and is suppressed by Th2 cytokines IL-4/IL-13 via STAT-6 [PMID:7759510, PMID:15191537, PMID:29866992, PMID:18166499].\",\n  \"teleology\": [\n    {\n      \"year\": 1979,\n      \"claim\": \"The foundational question of what soluble precursor protein becomes the insoluble cornified envelope was answered by purifying involucrin from keratinocytes and showing it is a cytosolic transglutaminase substrate that concentrates at the cell periphery before calcium-dependent cross-linking.\",\n      \"evidence\": \"Protein purification with gel filtration/chromatography, transglutaminase incorporation assay, immunofluorescence, and calcium ionophore treatment in cultured human keratinocytes\",\n      \"pmids\": [\"42494\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific cross-linking residues not yet identified\", \"Identity of other cross-linked partner proteins unknown\", \"In vivo relevance not yet demonstrated\"]\n    },\n    {\n      \"year\": 1986,\n      \"claim\": \"The structural basis for involucrin's transglutaminase reactivity was established by cloning the gene and revealing 39 tandem 10-amino-acid repeats rich in glutamine and glutamic acid, arising from successive duplication of an ancestral element.\",\n      \"evidence\": \"Gene cloning and complete DNA sequencing with evolutionary repeat analysis\",\n      \"pmids\": [\"2873896\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which specific glutamine residues are preferentially reactive was unknown\", \"Functional significance of repeat number variation not established\"]\n    },\n    {\n      \"year\": 1988,\n      \"claim\": \"The question of whether all glutamine residues are equivalently reactive was resolved by demonstrating that Gln496, near the C-terminus, is the single preferential transglutaminase cross-linking site in the intact protein, with internal glutamines masked by the native conformation.\",\n      \"evidence\": \"Tryptic and CNBr fragmentation with transglutaminase labeling and peptide sequencing\",\n      \"pmids\": [\"2461365\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for conformational masking of internal glutamines unknown\", \"Whether Gln496 preference holds in the context of the assembled CE not established\"]\n    },\n    {\n      \"year\": 1993,\n      \"claim\": \"IVL was physically mapped to chromosome 1q21 within the epidermal differentiation complex alongside loricrin, profilaggrin, and SPR genes, establishing the genomic context for coordinated regulation of CE genes.\",\n      \"evidence\": \"Pulsed-field gel electrophoresis and YAC-based physical mapping\",\n      \"pmids\": [\"8276421\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Shared regulatory elements controlling co-expression not identified\", \"Functional interdependence among clustered genes not demonstrated experimentally\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"The transcriptional control of IVL was elucidated by identifying two AP1 sites in the promoter bound by Fra-1/JunB/JunD that are necessary for both basal transcription and PKC-dependent induction during differentiation.\",\n      \"evidence\": \"Reporter gene assays with site-directed mutagenesis and gel supershift assays in human keratinocytes\",\n      \"pmids\": [\"7759510\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Upstream kinase cascade linking PKC to AP1 not yet mapped\", \"Contribution of other transcription factor families (Sp1, C/EBP) not fully delineated\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"The molecular architecture of involucrin within the assembled CE was resolved by identifying specific isopeptide cross-link sites to desmoplakin (Gln495/496), keratins (Gln288), and involucrin itself (Lys468/485/508, Gln465/489), establishing IVL as a central scaffold connecting diverse CE components.\",\n      \"evidence\": \"Saponification of native foreskin CEs, immunogold EM, proteolytic digestion, and amino acid sequencing of cross-linked peptides\",\n      \"pmids\": [\"8999895\", \"9115270\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Temporal order of cross-linking events in vivo not resolved\", \"Relative stoichiometry of different cross-link types unknown\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Beyond protein cross-linking, involucrin was shown to serve as a primary covalent attachment scaffold for ceramides via ester linkages, directly linking the protein envelope to the lipid barrier and explaining how IVL contributes to the epidermal permeability barrier.\",\n      \"evidence\": \"Partial saponification of isolated epidermal CEs with mass spectrometric and amino acid sequence characterization of lipopeptides\",\n      \"pmids\": [\"9651377\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Enzymatic mechanism catalyzing ester bond formation between IVL and ceramides not identified\", \"Specific serine/threonine residues serving as ester attachment sites not mapped\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"The identity of which transglutaminase isoforms cross-link IVL was expanded by demonstrating that TGase 5 efficiently cross-links involucrin in vitro, supplementing the known role of TGase 1 and indicating redundancy in CE assembly.\",\n      \"evidence\": \"Recombinant TGase5 splice variant expression with kinetic cross-linking assays using purified CE substrates\",\n      \"pmids\": [\"11443109\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contributions of TGase 1 vs TGase 5 to IVL cross-linking in vivo not determined\", \"Whether TGase 5 targets the same Gln496 site as TGase 1 not established\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"The full upstream signaling cascade driving IVL transcription was mapped as PKCδ→Ras→MEKK1→MEK3→p38δ–ERK1/2, converging on AP1/Sp1/C/EBP elements in two discrete promoter regions, integrating earlier AP1 findings into a complete pathway model.\",\n      \"evidence\": \"Synthesis of epistasis experiments using kinase inhibitors, dominant-negative constructs, and transcription factor binding studies\",\n      \"pmids\": [\"15191537\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct biochemical demonstration of p38δ–ERK1/2 complex formation on the IVL promoter lacking\", \"Calcium-sensing mechanism upstream of PKCδ not defined\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"A negative regulatory axis was identified: Th2 cytokines IL-4 and IL-13 suppress IVL expression through STAT-6, providing a mechanistic link between atopic inflammation and impaired barrier gene expression.\",\n      \"evidence\": \"Keratinocyte culture with IL-4/IL-13 treatment and STAT-6 transgenic mouse skin analysis by immunohistochemistry\",\n      \"pmids\": [\"18166499\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether STAT-6 directly binds the IVL promoter or acts indirectly not resolved\", \"Relevance to human atopic dermatitis barrier defects not confirmed by patient studies\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"AHR was identified as an additional transcriptional activator of IVL, and importantly, IVL's AHR-dependent induction was shown to be independent of OVOL1, distinguishing its regulation from FLG and LOR.\",\n      \"evidence\": \"Keratinocyte culture with AHR inhibitor and OVOL1 knockdown, RT-PCR and Western blot\",\n      \"pmids\": [\"29866992\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct AHR binding to the IVL promoter not demonstrated by ChIP\", \"Identity of AHR-responsive element(s) in IVL promoter unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis for conformational masking of internal glutamine residues, the enzyme and mechanism responsible for ceramide ester bond formation to IVL, the relative in vivo contributions of TGase 1 versus TGase 5 to IVL cross-linking, and whether STAT-6 and AHR directly bind IVL promoter elements.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No high-resolution structure of involucrin available\", \"Ceramide-ester-forming enzyme unidentified\", \"No in vivo genetic rescue or IVL-null phenotypic characterization in the timeline\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 5, 6, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"TGM1\", \"TGM5\", \"DSP\", \"LOR\", \"SPRR1A\", \"SPRR1B\", \"CST1\"],\n    \"other_free_text\": []\n  }\n}\n```\n\nWait, I need to fix the pathway section - I used a GO term instead of a Reactome pathway. Let me correct this.\n\n```json\n{\n  \"mechanistic_narrative\": \"Involucrin (IVL) is a glutamine/glutamate-rich soluble cytosolic precursor protein of the keratinocyte cornified cell envelope (CE) that functions as an early structural scaffold cross-linked by transglutaminases during terminal epidermal differentiation [PMID:42494, PMID:8999895]. The protein contains 39 tandem 10-amino-acid repeats rich in glutamine residues that serve as transglutaminase substrate sites, with Gln496 acting as the preferential reactive residue in the intact native conformation; upon cross-linking, IVL forms isopeptide bonds with itself and numerous CE partners including desmoplakin, keratins, cystatin alpha, loricrin, and small proline-rich proteins, and additionally provides covalent ester-linked attachment sites for ceramides essential for epidermal barrier function [PMID:2873896, PMID:2461365, PMID:8999895, PMID:9651377]. IVL transcription is driven by Fra-1/JunB/JunD binding to two AP1 sites in its promoter downstream of a PKCδ→Ras→MEKK1→MEK3→p38δ–ERK1/2 cascade, is induced by aryl hydrocarbon receptor (AHR) activation independently of OVOL1, and is suppressed by Th2 cytokines IL-4/IL-13 via STAT-6 [PMID:7759510, PMID:15191537, PMID:29866992, PMID:18166499].\",\n  \"teleology\": [\n    {\n      \"year\": 1979,\n      \"claim\": \"The foundational question of what soluble precursor protein becomes the insoluble cornified envelope was answered by purifying involucrin from keratinocytes and showing it is a cytosolic transglutaminase substrate that concentrates at the cell periphery before calcium-dependent cross-linking.\",\n      \"evidence\": \"Protein purification with gel filtration/chromatography, transglutaminase incorporation assay, immunofluorescence, and calcium ionophore treatment in cultured human keratinocytes\",\n      \"pmids\": [\"42494\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific cross-linking residues not yet identified\", \"Identity of other cross-linked partner proteins unknown\", \"In vivo relevance not yet demonstrated\"]\n    },\n    {\n      \"year\": 1986,\n      \"claim\": \"The structural basis for involucrin's transglutaminase reactivity was established by cloning the gene and revealing 39 tandem 10-amino-acid repeats rich in glutamine and glutamic acid, arising from successive duplication of an ancestral element.\",\n      \"evidence\": \"Gene cloning and complete DNA sequencing with evolutionary repeat analysis\",\n      \"pmids\": [\"2873896\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which specific glutamine residues are preferentially reactive was unknown\", \"Functional significance of repeat number variation not established\"]\n    },\n    {\n      \"year\": 1988,\n      \"claim\": \"The question of whether all glutamine residues are equivalently reactive was resolved by demonstrating that Gln496, near the C-terminus, is the single preferential transglutaminase cross-linking site in the intact protein, with internal glutamines masked by the native conformation.\",\n      \"evidence\": \"Tryptic and CNBr fragmentation with transglutaminase labeling and peptide sequencing\",\n      \"pmids\": [\"2461365\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for conformational masking of internal glutamines unknown\", \"Whether Gln496 preference holds in the context of the assembled CE not established\"]\n    },\n    {\n      \"year\": 1993,\n      \"claim\": \"IVL was physically mapped to chromosome 1q21 within the epidermal differentiation complex alongside loricrin, profilaggrin, and SPR genes, establishing the genomic context for coordinated regulation of CE genes.\",\n      \"evidence\": \"Pulsed-field gel electrophoresis and YAC-based physical mapping\",\n      \"pmids\": [\"8276421\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Shared regulatory elements controlling co-expression not identified\", \"Functional interdependence among clustered genes not demonstrated experimentally\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"The transcriptional control of IVL was elucidated by identifying two AP1 sites in the promoter bound by Fra-1/JunB/JunD that are necessary for both basal transcription and PKC-dependent induction during differentiation.\",\n      \"evidence\": \"Reporter gene assays with site-directed mutagenesis and gel supershift assays in human keratinocytes\",\n      \"pmids\": [\"7759510\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Upstream kinase cascade linking PKC to AP1 not yet mapped\", \"Contribution of other transcription factor families (Sp1, C/EBP) not fully delineated\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"The molecular architecture of involucrin within the assembled CE was resolved by identifying specific isopeptide cross-link sites to desmoplakin (Gln495/496), keratins (Gln288), and involucrin itself (Lys468/485/508, Gln465/489), establishing IVL as a central scaffold connecting diverse CE components.\",\n      \"evidence\": \"Saponification of native foreskin CEs, immunogold EM, proteolytic digestion, and amino acid sequencing of cross-linked peptides\",\n      \"pmids\": [\"8999895\", \"9115270\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Temporal order of cross-linking events in vivo not resolved\", \"Relative stoichiometry of different cross-link types unknown\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Beyond protein cross-linking, involucrin was shown to serve as a primary covalent attachment scaffold for ceramides via ester linkages, directly linking the protein envelope to the lipid barrier and explaining how IVL contributes to the epidermal permeability barrier.\",\n      \"evidence\": \"Partial saponification of isolated epidermal CEs with mass spectrometric and amino acid sequence characterization of lipopeptides\",\n      \"pmids\": [\"9651377\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Enzymatic mechanism catalyzing ester bond formation between IVL and ceramides not identified\", \"Specific serine/threonine residues serving as ester attachment sites not mapped\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"The identity of which transglutaminase isoforms cross-link IVL was expanded by demonstrating that TGase 5 efficiently cross-links involucrin in vitro, supplementing the known role of TGase 1 and indicating redundancy in CE assembly.\",\n      \"evidence\": \"Recombinant TGase5 splice variant expression with kinetic cross-linking assays using purified CE substrates\",\n      \"pmids\": [\"11443109\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contributions of TGase 1 vs TGase 5 to IVL cross-linking in vivo not determined\", \"Whether TGase 5 targets the same Gln496 site as TGase 1 not established\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"The full upstream signaling cascade driving IVL transcription was mapped as PKCδ→Ras→MEKK1→MEK3→p38δ–ERK1/2, converging on AP1/Sp1/C/EBP elements in two discrete promoter regions, integrating earlier AP1 findings into a complete pathway model.\",\n      \"evidence\": \"Synthesis of epistasis experiments using kinase inhibitors, dominant-negative constructs, and transcription factor binding studies\",\n      \"pmids\": [\"15191537\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct biochemical demonstration of p38δ–ERK1/2 complex formation on the IVL promoter lacking\", \"Calcium-sensing mechanism upstream of PKCδ not defined\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"A negative regulatory axis was identified: Th2 cytokines IL-4 and IL-13 suppress IVL expression through STAT-6, providing a mechanistic link between atopic inflammation and impaired barrier gene expression.\",\n      \"evidence\": \"Keratinocyte culture with IL-4/IL-13 treatment and STAT-6 transgenic mouse skin analysis by immunohistochemistry\",\n      \"pmids\": [\"18166499\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether STAT-6 directly binds the IVL promoter or acts indirectly not resolved\", \"Relevance to human atopic dermatitis barrier defects not confirmed by patient studies\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"AHR was identified as an additional transcriptional activator of IVL, and importantly, IVL's AHR-dependent induction was shown to be independent of OVOL1, distinguishing its regulation from FLG and LOR.\",\n      \"evidence\": \"Keratinocyte culture with AHR inhibitor and OVOL1 knockdown, RT-PCR and Western blot\",\n      \"pmids\": [\"29866992\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct AHR binding to the IVL promoter not demonstrated by ChIP\", \"Identity of AHR-responsive element(s) in IVL promoter unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis for conformational masking of internal glutamine residues, the enzyme and mechanism responsible for ceramide ester bond formation to IVL, the relative in vivo contributions of TGase 1 versus TGase 5 to IVL cross-linking, and whether STAT-6 and AHR directly bind IVL promoter elements.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No high-resolution structure of involucrin available\", \"Ceramide-ester-forming enzyme unidentified\", \"No in vivo genetic rescue or IVL-null phenotypic characterization in the timeline\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 5, 6, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [0, 5, 7]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [4, 9]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"TGM5\", \"DSP\", \"LOR\", \"SPRR1A\", \"SPRR1B\", \"EVPL\", \"PPL\"],\n    \"other_free_text\": []\n  }\n}\n```"}