Affinage

IVL

Involucrin · UniProt P07476

Round 2 corrected
Length
585 aa
Mass
68.5 kDa
Annotated
2026-04-28
44 papers in source corpus 13 papers cited in narrative 13 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

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).

Mechanistic history

Synthesis pass · year-by-year structured walk · 11 steps
  1. 1979 High

    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

    PMID:42494

    Open questions at the time
    • Specific cross-linking residues not yet identified
    • Identity of other cross-linked partner proteins unknown
    • In vivo relevance not yet demonstrated
  2. 1986 High

    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

    PMID:2873896

    Open questions at the time
    • Which specific glutamine residues are preferentially reactive was unknown
    • Functional significance of repeat number variation not established
  3. 1988 High

    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

    PMID:2461365

    Open questions at the time
    • Structural basis for conformational masking of internal glutamines unknown
    • Whether Gln496 preference holds in the context of the assembled CE not established
  4. 1993 Medium

    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

    PMID:8276421

    Open questions at the time
    • Shared regulatory elements controlling co-expression not identified
    • Functional interdependence among clustered genes not demonstrated experimentally
  5. 1995 High

    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

    PMID:7759510

    Open questions at the time
    • Upstream kinase cascade linking PKC to AP1 not yet mapped
    • Contribution of other transcription factor families (Sp1, C/EBP) not fully delineated
  6. 1997 High

    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

    PMID:8999895 PMID:9115270

    Open questions at the time
    • Temporal order of cross-linking events in vivo not resolved
    • Relative stoichiometry of different cross-link types unknown
  7. 1998 High

    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

    PMID:9651377

    Open questions at the time
    • Enzymatic mechanism catalyzing ester bond formation between IVL and ceramides not identified
    • Specific serine/threonine residues serving as ester attachment sites not mapped
  8. 2001 High

    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

    PMID:11443109

    Open questions at the time
    • 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
  9. 2004 Medium

    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

    PMID:15191537

    Open questions at the time
    • Direct biochemical demonstration of p38δ–ERK1/2 complex formation on the IVL promoter lacking
    • Calcium-sensing mechanism upstream of PKCδ not defined
  10. 2007 Medium

    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

    PMID:18166499

    Open questions at the time
    • 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
  11. 2018 Medium

    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

    PMID:29866992

    Open questions at the time
    • Direct AHR binding to the IVL promoter not demonstrated by ChIP
    • Identity of AHR-responsive element(s) in IVL promoter unknown

Open questions

Synthesis pass · forward-looking unresolved questions
  • 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.
  • 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

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005198 structural molecule activity 4
Localization
GO:0005886 plasma membrane 2 GO:0005829 cytosol 1
Pathway
GO:0005886 plasma membrane 1
Partners
CST1DSPLORSPRR1ASPRR1BTGM1TGM5

Evidence

Reading pass · 13 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1979 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. Protein purification (gel filtration, DEAE-cellulose, hydroxyapatite chromatography), transglutaminase incorporation assay with labeled amines, indirect immunofluorescence, calcium ionophore and detergent treatments Cell High 42494
1986 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. Gene cloning, DNA sequencing, sequence analysis of repeat structure and evolutionary relationships Cell High 2873896
1988 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. Tryptic peptide mapping, cyanogen bromide fragmentation, transglutaminase labeling assay with glycine ethyl ester as cosubstrate, peptide sequencing The Journal of biological chemistry High 2461365
1993 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. Physical mapping by pulsed-field gel electrophoresis and YAC analysis Genomics Medium 8276421
1995 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. 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 The Journal of biological chemistry High 7759510
1997 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. Saponification of cornified envelopes, immunogold electron microscopy, proteolytic digestion (methanol/KOH treatment), amino acid sequencing of cross-linked peptides The Journal of biological chemistry High 8999895
1997 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. Sequential proteolytic digestion (CNBr, trypsin, proteinase K) of purified CE fragments, peptide purification and sequencing The Journal of biological chemistry High 9115270
1998 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. Partial saponification of isolated foreskin epidermal CEs, limited proteolysis, biochemical and mass spectrometric characterization of lipopeptides, amino acid sequencing The Journal of biological chemistry High 9651377
2001 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. Recombinant expression of TGase5 splice variants in keratinocyte and baculovirus systems, kinetic assays, in vitro cross-linking experiments with CE substrates, immunolocalization The Journal of biological chemistry High 11443109
2004 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). Review synthesizing reporter gene assays, kinase inhibitors, dominant-negative constructs, and transcription factor binding studies from multiple experiments The Journal of investigative dermatology Medium 15191537
2007 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. Primary keratinocyte cultures treated with IL-4/IL-13, RT-PCR and protein expression analysis, STAT-6 transgenic mouse skin biopsies with immunohistochemistry Clinical immunology Medium 18166499
2018 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. Keratinocyte cell culture with RCE treatment, AHR inhibitor and OVOL1 knockdown experiments, RT-PCR and Western blot for IVL/FLG/LOR expression International journal of molecular sciences Medium 29866992
2025 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. UPLC-MS/MS characterization of iridoids, proteomics, molecular docking, molecular dynamics, HaCaT cell culture with AHR pathway validation, 3D epidermal models, Western blot Molecules Medium 41011656

Source papers

Stage 0 corpus · 44 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2002 Generation and initial analysis of more than 15,000 full-length human and mouse cDNA sequences. Proceedings of the National Academy of Sciences of the United States of America 1479 12477932
2015 The BioPlex Network: A Systematic Exploration of the Human Interactome. Cell 1118 26186194
2017 Architecture of the human interactome defines protein communities and disease networks. Nature 1085 28514442
1979 Presence in human epidermal cells of a soluble protein precursor of the cross-linked envelope: activation of the cross-linking by calcium ions. Cell 794 42494
2021 Dual proteome-scale networks reveal cell-specific remodeling of the human interactome. Cell 705 33961781
2004 The status, quality, and expansion of the NIH full-length cDNA project: the Mammalian Gene Collection (MGC). Genome research 438 15489334
2007 Loricrin and involucrin expression is down-regulated by Th2 cytokines through STAT-6. Clinical immunology (Orlando, Fla.) 416 18166499
1986 Structure and evolution of the human involucrin gene. Cell 407 2873896
2020 Regulation of Filaggrin, Loricrin, and Involucrin by IL-4, IL-13, IL-17A, IL-22, AHR, and NRF2: Pathogenic Implications in Atopic Dermatitis. International journal of molecular sciences 300 32751111
2010 Coordinate interaction between IL-13 and epithelial differentiation cluster genes in eosinophilic esophagitis. Journal of immunology (Baltimore, Md. : 1950) 240 20208004
2009 Proteomic analysis of human parotid gland exosomes by multidimensional protein identification technology (MudPIT). Journal of proteome research 237 19199708
2008 Retrospective analysis of intravascular large B-cell lymphoma treated with rituximab-containing chemotherapy as reported by the IVL study group in Japan. Journal of clinical oncology : official journal of the American Society of Clinical Oncology 217 18506023
2016 An organelle-specific protein landscape identifies novel diseases and molecular mechanisms. Nature communications 211 27173435
1997 S100A11, S100A10, annexin I, desmosomal proteins, small proline-rich proteins, plasminogen activator inhibitor-2, and involucrin are components of the cornified envelope of cultured human epidermal keratinocytes. The Journal of biological chemistry 198 9115270
1997 Direct evidence that involucrin is a major early isopeptide cross-linked component of the keratinocyte cornified cell envelope. The Journal of biological chemistry 188 8999895
1995 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. The Journal of biological chemistry 179 7759510
1998 Ceramides are bound to structural proteins of the human foreskin epidermal cornified cell envelope. The Journal of biological chemistry 169 9651377
2014 E-cadherin interactome complexity and robustness resolved by quantitative proteomics. Science signaling 162 25468996
1993 Physical mapping of a functional cluster of epidermal differentiation genes on chromosome 1q21. Genomics 136 8276421
2008 Effects of extracellular calcium on the growth-differentiation switch in immortalized keratinocyte HaCaT cells compared with normal human keratinocytes. Experimental dermatology 130 18637039
2004 Regulation of involucrin gene expression. The Journal of investigative dermatology 122 15191537
2009 Comparison between human fetal and adult skin. Archives of dermatological research 116 19701759
2002 Crucial role of fibroblasts in regulating epidermal morphogenesis. Cell and tissue research 112 12397374
2018 Histone Interaction Landscapes Visualized by Crosslinking Mass Spectrometry in Intact Cell Nuclei. Molecular & cellular proteomics : MCP 101 30021884
2010 Genome-wide YFP fluorescence complementation screen identifies new regulators for telomere signaling in human cells. Molecular & cellular proteomics : MCP 93 21044950
2001 Transglutaminase 5 cross-links loricrin, involucrin, and small proline-rich proteins in vitro. The Journal of biological chemistry 87 11443109
2020 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. The Lancet. Oncology 81 32171071
2014 Human-chromatin-related protein interactions identify a demethylase complex required for chromosome segregation. Cell reports 80 24981860
2014 hnRNPA1 couples nuclear export and translation of specific mRNAs downstream of FGF-2/S6K2 signalling. Nucleic acids research 78 25324306
1988 The glutamine residues reactive in transglutaminase-catalyzed cross-linking of involucrin. The Journal of biological chemistry 77 2461365
2006 Expression and regulation of cornified envelope proteins in human corneal epithelium. Investigative ophthalmology & visual science 75 16639001
2018 A protein-protein interaction map of the TNF-induced NF-κB signal transduction pathway. Scientific data 74 30561431
2018 Upregulation of FLG, LOR, and IVL Expression by Rhodiola crenulata Root Extract via Aryl Hydrocarbon Receptor: Differential Involvement of OVOL1. International journal of molecular sciences 47 29866992
2017 Complete Genome Sequence of Systemically Disseminated Sequence Type 8 Staphylococcal Cassette Chromosome mec Type IVl Community-Acquired Methicillin-Resistant Staphylococcus aureus. Genome announcements 13 28860242
2025 Rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisolone combined with high-dose methotrexate plus intrathecal chemotherapy for newly diagnosed intravascular large B-cell lymphoma (PRIMEUR-IVL): long-term results of a multicentre, single-arm, phase 2 trial. EClinicalMedicine 6 39968389
2022 Assignment of IVL-Methyl side chain of the ligand-free monomeric human MALT1 paracaspase-IgL3 domain in solution. Biomolecular NMR assignments 5 36094731
2022 1H, 13C and 15N resonance assignment of backbone and IVL-methyl side chain of the S135A mutant NS3pro/NS2B protein of Dengue II virus reveals unique secondary structure features in solution. Biomolecular NMR assignments 4 35149939
2010 Cutaneous angiogenesis in patient with intravascular lymphoma (IVL): A case report. Dermatology online journal 3 20804679
1996 Physical mapping of a centromere-proximal region of chromosome IV-L defines the placement of genes USO1, MBP1, PSA1 and SLC1. Yeast (Chichester, England) 2 8701613
2020 1H, 13C, 15N backbone and IVL methyl group resonance assignment of the fungal β-glucosidase from Trichoderma reesei. Biomolecular NMR assignments 1 32562251
2026 Hedera helix-derived α-hederin (IVL-11) demonstrates both ex vivo and in vivo flukicidal activities against Fasciola hepatica. Biomedicine & pharmacotherapy = Biomedecine & pharmacotherapie 0 41689997
2025 Stentless Intravascular Lithotripsy (IVL) for the Paravisceral Coral Reef Aorta: A Case Report. Cureus 0 40851875
2025 Gardeniae Fructus Enhances Skin Barrier Function via AHR-Mediated FLG/LOR/IVL Expression. Molecules (Basel, Switzerland) 0 41011656
1993 [Immunochemical analysis of Escherichia coli expression products of I3 and A2 genes of vaccinia virus strain L-IVL genome]. Molekuliarnaia biologiia 0 8487760