{"gene":"KRT5","run_date":"2026-04-28T18:30:27","timeline":{"discoveries":[{"year":1992,"finding":"KRT5 (keratin 5) was mapped to human chromosome 12q near D12S14 by PCR analysis of somatic cell hybrids and multicolor fluorescence in situ hybridization, establishing it as the candidate gene for epidermolysis bullosa simplex linked to that locus.","method":"PCR analysis of somatic cell hybrids; multicolor fluorescence in situ hybridization (FISH)","journal":"Genomics","confidence":"High","confidence_rationale":"Tier 1 — direct physical mapping with two orthogonal methods","pmids":["1377166"],"is_preprint":false},{"year":1997,"finding":"KRT5 encodes a type II keratin that, together with KRT14, constitutes the primary structural component of 10-nm intermediate filaments in mitotic epidermal basal cells; single missense mutations in the rod domain (e.g., E477K in the conserved KLLEGE motif at the helix boundary) disrupt the keratin intermediate filament cytoskeleton, causing epidermolysis bullosa simplex.","method":"Direct sequencing of KRT5 exons amplified from leukocyte genomic DNA; genotype-phenotype correlation","journal":"The Journal of investigative dermatology","confidence":"High","confidence_rationale":"Tier 1/2 — replicated across multiple independent cohorts, mutation-phenotype correlation established","pmids":["9036937"],"is_preprint":false},{"year":1999,"finding":"The P24L (P25L) substitution in the KRT5 gene (71C→T transition in the non-helical head domain) is the causative mutation for epidermolysis bullosa simplex with mottled pigmentation (EBS-MP), confirmed by mutation analysis in affected family members and sporadic patients.","method":"KRT5 gene mutation analysis; clinical correlation in families","journal":"American journal of medical genetics","confidence":"Medium","confidence_rationale":"Tier 2 — replicated in multiple families, single mutation identified","pmids":["10494094"],"is_preprint":false},{"year":2006,"finding":"Mutations affecting the highly conserved helix boundary motifs (helix initiation and termination peptides) of the rod domain of KRT5 (and KRT14) cause the most severe EBS phenotype (Dowling-Meara), while mutations elsewhere produce milder forms, demonstrating that the rod domain helix boundaries are structurally critical for keratin intermediate filament assembly.","method":"Sequence analysis of entire coding sequences of KRT5 and KRT14 in EBS patients; genotype-phenotype correlation","journal":"Human mutation","confidence":"High","confidence_rationale":"Tier 2 — replicated across multiple independent large cohorts with consistent genotype-phenotype correlation","pmids":["16786515","21375516","20199538"],"is_preprint":false},{"year":2009,"finding":"Immortalized keratinocytes carrying a KRT5 V186L mutation form cytoplasmic keratin filament aggregates upon heat-shock stress, and this aggregation (a measure of cytoskeletal disruption) is significantly reduced by pretreatment with the chemical chaperone trimethylamine N-oxide (TMAO), demonstrating that TMAO stabilizes the mutant KRT5 protein against thermal stress.","method":"Immortalized cell lines from EBS patients (HPV16 E6E7 transduction); heat-shock assay; assessment of keratin aggregate formation with and without TMAO","journal":"Journal of dermatological science","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro functional assay with chemical chaperone intervention in patient-derived cell lines","pmids":["19157792"],"is_preprint":false},{"year":2010,"finding":"Different KRT5 missense mutations (I183M, E475G, V186L) confer mutation-specific degrees of cellular fragility in primary keratinocytes upon heat stress, and TMAO dose-dependently reduces keratin aggregate formation and cell loss in all three mutant lines, establishing a genotype-dependent cytoskeletal vulnerability mechanism.","method":"Primary EBS keratinocyte cultures; heat-stress assay; TMAO treatment; keratin aggregate quantification","journal":"The British journal of dermatology","confidence":"Medium","confidence_rationale":"Tier 2 — primary patient cells, quantitative functional assay, dose-response with TMAO","pmids":["20128788"],"is_preprint":false},{"year":2010,"finding":"KRT5 frameshift/insertion mutations (c.418dupA) in the Dowling-Degos disease/Galli-Galli disease spectrum demonstrate that loss-of-function mutations in KRT5 cause reticular hyperpigmentation phenotypes, and that Galli-Galli disease (with acantholysis) shares identical KRT5 mutations with Dowling-Degos disease, establishing them as variants of the same disorder.","method":"Systematic KRT5 sequencing; histopathological re-evaluation; genotype-phenotype correlation","journal":"The British journal of dermatology","confidence":"Medium","confidence_rationale":"Tier 2 — systematic mutation screening with histopathological validation","pmids":["20222933"],"is_preprint":false},{"year":2014,"finding":"Pre-existing p63+/KRT5+ distal airway stem cells (DASCp63/Krt5) undergo proliferative expansion after influenza-induced lung damage, assemble into nascent alveoli, and differentiate into type I and type II pneumocytes as well as bronchiolar secretory cells after transplantation; selective in vivo ablation of these cells prevents lung regeneration and leads to pre-fibrotic lesions.","method":"Lineage tracing; in vivo selective ablation; single-cell pedigree transplantation; live imaging; organoid culture; H1N1 mouse model","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1/2 — multiple orthogonal methods including ablation, transplantation, and clonal analysis in vivo","pmids":["25383540"],"is_preprint":false},{"year":2014,"finding":"In basal-like breast epithelial cells, KRT5 expression is regulated by an anticorrelated TGFBR3-JUND circuit: TGFBR3 and JUND are connected through four negative-feedback loops, and their dynamic toggling controls KRT5 expression in ECM-attached cells during 3D culture; ECM detachment rewires the circuit via RPS6 dephosphorylation and juxtacrine tenascin C.","method":"Single-cell gene expression profiling; 3D organotypic culture; siRNA knockdown; circuit modelling; in vivo intraductal transplantation","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods; in vitro and in vivo validation of regulatory circuit","pmids":["24658685"],"is_preprint":false},{"year":2019,"finding":"Biallelic homozygous missense variants of KRT5 in human patients cause autosomal recessive EBS with generalized phenotype; a homozygous null (KRT5 'knock-out') mutation results in complete absence of KRT5 RNA and protein and is perinatally lethal, demonstrating that KRT5 is essential for basal keratinocyte integrity and survival.","method":"Whole exome sequencing; NGS panel; immunofluorescence microscopy; expression profiling; ultrastructural analysis","journal":"Matrix biology","confidence":"High","confidence_rationale":"Tier 1/2 — human KO with protein/RNA absence confirmed, multiple methods","pmids":["31302245"],"is_preprint":false},{"year":2019,"finding":"FoxM1 transcription factor directly binds a consensus AP-2 cis element in KRT5 (and KRT7) regulatory regions and activates their transcription; KRT5 and KRT7 loss-of-function inhibits migration but not proliferation of SK-OV-3 ovarian cancer cells, placing KRT5 downstream of FoxM1 in a migration-promoting pathway.","method":"ChIP-seq; RNA-seq; qPCR; Western blot; KRT5 knockdown; wound healing/migration assay","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP-seq binding + RNA-seq + functional KD migration assay","pmids":["32659254"],"is_preprint":false},{"year":2019,"finding":"Krt5+/Krt15+ foregut basal progenitor cells are the cell of origin for gastric acid stress-induced tumors, and tumor formation from these cells is dependent on Cyclooxygenase-2 (COX-2) activity, as demonstrated in genetically engineered mouse models.","method":"Genetically engineered mouse models; lineage tracing; COX-2-dependent tumor formation assay","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo lineage tracing with genetic epistasis showing COX-2 dependence","pmids":["31110179"],"is_preprint":false},{"year":2021,"finding":"Human alveolar type 2 cells (hAEC2s), but not murine AEC2s, transdifferentiate into KRT5+ basal cells in response to fibrotic mesenchymal signaling (TGF-β1 and anti-BMP signaling) through alveolar-basal intermediates, demonstrating that aberrant mesenchymal signals drive hAEC2-to-KRT5+ basal cell lineage conversion in IPF.","method":"Organoid co-cultures; single-cell RNA-seq trajectory analysis; TGF-β1/BMP pathway manipulation; in vivo xenograft; histologic analysis of IPF tissue","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 1/2 — multiple orthogonal in vitro and in vivo methods demonstrating mechanistic lineage conversion","pmids":["34969962"],"is_preprint":false},{"year":2021,"finding":"A KRT5 homozygous missense mutation (c.1474T>C) causes structural alteration of keratin 5 and collapse of keratin intermediate filaments without a quantitative change in protein level; the KRT5 mutation inhibits MAPK signaling, leading to upregulation of the desmosomal protein DSG1 (desmoglein 1), and EGFR phosphorylation inhibition in vitro similarly upregulates DSG1, placing KRT5 upstream of MAPK-EGFR-DSG1 signaling.","method":"Biochemical experiments (structural analysis); immunofluorescence; Western blot; in vitro EGFR inhibitor treatment; patient skin biopsy analysis","journal":"Frontiers in genetics","confidence":"Medium","confidence_rationale":"Tier 2 — patient mutation functional characterization with pathway analysis and in vitro validation","pmids":["34912369"],"is_preprint":false},{"year":2023,"finding":"TRIM29 E3 ubiquitin ligase directly interacts with KRT5 (confirmed by co-immunoprecipitation) and promotes its ubiquitination, reducing KRT5 protein stability; TRIM29 knockdown decreases KRT5 ubiquitination, enhances KRT5 protein stability and expression, and inhibits colon cancer cell proliferation, which is reversed by KRT5 knockdown.","method":"Co-immunoprecipitation; cycloheximide chase (protein stability assay); Western blot; qRT-PCR; CCK-8/colony formation/EDU proliferation assays","journal":"Open life sciences","confidence":"Medium","confidence_rationale":"Tier 2/3 — Co-IP confirmed interaction, cycloheximide chase for stability, functional rescue experiment","pmids":["37671092"],"is_preprint":false},{"year":2023,"finding":"Downregulation of KRT5 in keratinocytes (via CRISPR/Cas9 or shRNA) decreases expression of Notch ligands in keratinocytes and Notch1 intracellular domain in melanocytes, reducing melanogenesis markers TYR and Fascin1; activation of Notch signaling reverses these effects, establishing that KRT5 in keratinocytes regulates melanocyte melanogenesis through paracrine Notch signaling.","method":"CRISPR/Cas9 site-directed mutation; lentivirus-mediated shRNA; co-culture system; Western blot; Notch inhibitor/activator treatment; immunohistochemistry of DDD patient lesions","journal":"Experimental dermatology","confidence":"Medium","confidence_rationale":"Tier 2 — two independent loss-of-function models, pathway rescue, patient tissue validation","pmids":["36809573"],"is_preprint":false},{"year":2023,"finding":"KRT5+ basal cell migratory behavior and expression of extracellular matrix remodeling genes are modulated by ECM composition and organization; SPARC (secreted by IPF lung fibroblasts and identified by mass spectrometry-based proteomics) restricts KRT5+ cell migration in vitro, revealing a mechanism by which altered ECM in IPF directly controls KRT5+ cell activity.","method":"In vitro migration assays on defined ECM substrates; mass spectrometry-based proteomics of fibroblast-secreted ECM; SPARC overexpression; primary human KRT5+ cell culture","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 — proteomics identified ECM component, functional migration assay with SPARC overexpression","pmids":["37758700"],"is_preprint":false},{"year":2017,"finding":"Retinoic acid (RA) signaling directly in salivary gland epithelium represses Krt5 and Krt14 expression; inhibition of RA signaling upregulates Krt5/Krt14 independently of stem cell markers (Kit), demonstrated by isolating epithelial explants from other tissues.","method":"Mouse embryonic salivary gland epithelial explant culture; RA signaling inhibition; qPCR for Krt5/Krt14 expression; Kit expression analysis","journal":"Developmental dynamics","confidence":"Medium","confidence_rationale":"Tier 2 — isolated epithelial explants demonstrate direct RA regulation of Krt5","pmids":["27884045"],"is_preprint":false},{"year":2020,"finding":"Trp53 mutation specifically in Krt5-expressing basal urothelial cells facilitates more efficient tumorigenesis of muscle-invasive bladder cancer with squamous differentiation compared to Trp53 mutation in Upk2-expressing cells, establishing that Krt5+ basal cells are a preferred cell of origin for the basal-squamous subtype of bladder cancer.","method":"Lineage tracing in genetically engineered mouse model; BBN chemical carcinogenesis; morphological and genetic characterization of tumors","journal":"The American journal of pathology","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo lineage-tracing genetic epistasis with specific cell-type Trp53 mutation","pmids":["32339497"],"is_preprint":false},{"year":2025,"finding":"p63 regulates the Krt8-to-Krt5 transition during ameloblast (AmG) cell differentiation in the enamel organ, paralleling its function in skin; this regulation involves chromatin landscape remodeling at Krt5 loci, with shared transcription factor usage (p63 and AP-2 family members) between skin and enamel organ development.","method":"Single-cell RNA sequencing; trajectory reconstruction; comparative transcriptome analysis; chromatin accessibility (ATAC-seq); comparative motif discovery; p63 knockout mouse model","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 — scRNA-seq with chromatin accessibility and motif analysis, preprint","pmids":["39990386"],"is_preprint":true}],"current_model":"KRT5 encodes keratin 5, a type II intermediate filament protein that obligately heterodimerizes with KRT14 to form the primary 10-nm cytoskeletal filament network of basal keratinocytes; mutations in its conserved rod-domain helix boundary motifs disrupt filament assembly causing mechanobullous disease (EBS), while KRT5 also functions in epithelial stem cell identity (p63+/KRT5+ lung and urothelial basal cells serving as tissue-regenerative progenitors), is transcriptionally regulated downstream of p63, FoxM1, retinoic acid, and TGF-β/BMP signaling, undergoes TRIM29-mediated ubiquitination controlling its protein stability, and participates in paracrine Notch signaling between keratinocytes and melanocytes to regulate pigmentation."},"narrative":{"teleology":[{"year":1992,"claim":"Identifying the chromosomal locus of KRT5 established it as the candidate gene for the EBS locus on 12q, enabling subsequent mutation hunting in mechanobullous disease.","evidence":"PCR analysis of somatic cell hybrids and multicolor FISH mapping KRT5 to chromosome 12q","pmids":["1377166"],"confidence":"High","gaps":["No causative mutations yet identified","Functional consequence of KRT5 disruption not demonstrated"]},{"year":1997,"claim":"Direct sequencing of KRT5 in EBS patients demonstrated that single missense mutations in the rod domain (e.g., E477K in the KLLEGE helix-boundary motif) disrupt intermediate filament formation, establishing the molecular basis of EBS and the structural criticality of helix boundary motifs.","evidence":"Direct sequencing of KRT5 exons from patient genomic DNA with genotype–phenotype correlation across multiple cohorts","pmids":["9036937"],"confidence":"High","gaps":["No in vitro reconstitution of mutant filament assembly","Mechanism of aggregate formation under stress not yet characterized"]},{"year":1999,"claim":"Identification of the P24L head-domain mutation as the cause of EBS with mottled pigmentation extended the KRT5 disease spectrum beyond purely mechanical fragility to include pigmentary phenotypes.","evidence":"KRT5 gene mutation analysis in affected families and sporadic patients","pmids":["10494094"],"confidence":"Medium","gaps":["Mechanism linking a head-domain KRT5 mutation to pigmentation abnormality unknown","Only a single recurrent mutation identified"]},{"year":2006,"claim":"Systematic genotype–phenotype mapping across large EBS cohorts established that helix initiation and termination peptides of the KRT5 rod domain are the structural determinants of filament assembly, with mutations at these sites causing the most severe (Dowling-Meara) phenotype.","evidence":"Complete KRT5/KRT14 coding sequence analysis in EBS patient cohorts with phenotype stratification","pmids":["16786515","21375516","20199538"],"confidence":"High","gaps":["No atomic-resolution structural model of the KRT5/KRT14 heterodimer","Mechanism by which specific mutations differentially weaken filaments not resolved"]},{"year":2010,"claim":"Functional cell-based assays demonstrated that different KRT5 missense mutations confer mutation-specific degrees of cytoskeletal vulnerability to heat stress, and that the chemical chaperone TMAO can partially rescue mutant filament aggregation, providing proof-of-concept for pharmacological intervention.","evidence":"Heat-shock assays in primary and immortalized EBS keratinocytes with TMAO dose-response quantification of keratin aggregate formation","pmids":["19157792","20128788"],"confidence":"Medium","gaps":["TMAO mechanism of action on keratin folding not defined","No in vivo therapeutic validation","Applicability across all mutation classes untested"]},{"year":2010,"claim":"KRT5 loss-of-function frameshift mutations were shown to cause Dowling-Degos/Galli-Galli disease, unifying these as a single disorder and extending KRT5's disease repertoire to reticular pigmentation syndromes.","evidence":"Systematic KRT5 sequencing with histopathological re-evaluation","pmids":["20222933"],"confidence":"Medium","gaps":["Mechanism linking KRT5 haploinsufficiency to aberrant pigmentation not identified","Cell-type-specific consequences of KRT5 loss in melanocyte–keratinocyte interaction unknown"]},{"year":2014,"claim":"Lineage tracing and selective ablation in vivo established that p63+/KRT5+ distal airway stem cells are the regenerative progenitors that reconstitute alveolar epithelium after influenza injury, repositioning KRT5 as a marker and functional component of adult lung stem cells.","evidence":"Lineage tracing, in vivo ablation, single-cell transplantation, and organoid culture in H1N1 mouse model","pmids":["25383540"],"confidence":"High","gaps":["Whether KRT5 protein is functionally required for progenitor behavior or is merely a marker","Origin of KRT5+ progenitors in distal airways not fully resolved"]},{"year":2014,"claim":"Single-cell profiling revealed that KRT5 expression in basal-like breast epithelial cells is controlled by an anticorrelated TGFBR3–JUND regulatory circuit modulated by ECM attachment, revealing upstream signaling logic governing KRT5 in epithelial identity.","evidence":"Single-cell gene expression profiling, 3D culture, siRNA knockdown, circuit modeling, and in vivo intraductal transplantation","pmids":["24658685"],"confidence":"High","gaps":["Whether this circuit operates in non-mammary KRT5+ epithelia untested","Direct transcription factor binding at KRT5 locus not demonstrated in this study"]},{"year":2017,"claim":"Retinoic acid signaling was shown to directly repress KRT5 transcription in epithelial explants independently of stem cell markers, identifying RA as a negative regulator of the KRT5 basal cell program.","evidence":"Mouse embryonic salivary gland epithelial explant culture with RA signaling inhibition and qPCR","pmids":["27884045"],"confidence":"Medium","gaps":["Direct RA receptor binding at KRT5 regulatory elements not demonstrated","Generalizability to other epithelial tissues not tested"]},{"year":2019,"claim":"A human homozygous KRT5 null mutation resulting in complete absence of protein was shown to be perinatally lethal, definitively establishing KRT5 as essential for basal keratinocyte survival, while biallelic missense variants cause autosomal recessive EBS.","evidence":"Whole exome sequencing, NGS panel, immunofluorescence, and ultrastructural analysis in human patients","pmids":["31302245"],"confidence":"High","gaps":["Molecular mechanism of lethality (pure structural failure vs. signaling disruption) not dissected","No rescue experiment performed"]},{"year":2019,"claim":"ChIP-seq demonstrated that FoxM1 directly binds KRT5 regulatory regions to activate transcription, and KRT5 knockdown inhibited cancer cell migration without affecting proliferation, placing KRT5 as a FoxM1-driven effector of cell motility.","evidence":"ChIP-seq, RNA-seq, qPCR, Western blot, KRT5 knockdown, and wound healing assay in SK-OV-3 cells","pmids":["32659254"],"confidence":"Medium","gaps":["Mechanism by which KRT5 promotes migration not defined","Tested in a single ovarian cancer cell line"]},{"year":2020,"claim":"In vivo lineage tracing established that Krt5+ basal urothelial cells are a preferred cell of origin for basal-squamous bladder cancer, with Trp53 loss in these cells driving more efficient muscle-invasive tumorigenesis than in luminal cells.","evidence":"Lineage tracing in genetically engineered mouse model with BBN chemical carcinogenesis","pmids":["32339497"],"confidence":"Medium","gaps":["Whether KRT5 functionally contributes to tumorigenesis or marks the susceptible population","Applicability to human bladder cancer subtypes not directly tested"]},{"year":2021,"claim":"Human alveolar type 2 cells were shown to undergo TGF-β1/anti-BMP-driven transdifferentiation into KRT5+ basal cells through alveolar-basal intermediates, establishing a disease-relevant lineage conversion mechanism in idiopathic pulmonary fibrosis.","evidence":"Organoid co-cultures, single-cell RNA-seq trajectory analysis, TGF-β/BMP manipulation, in vivo xenograft, and IPF tissue analysis","pmids":["34969962"],"confidence":"High","gaps":["Whether preventing KRT5+ conversion would ameliorate fibrosis not tested","Signals directing KRT5+ cells to pathological vs. regenerative fates not distinguished"]},{"year":2021,"claim":"A homozygous KRT5 missense mutation was shown to collapse keratin filaments and inhibit MAPK signaling, leading to DSG1 upregulation, revealing that KRT5 structural integrity feeds into MAPK-EGFR signaling and desmosomal protein expression.","evidence":"Biochemical structural analysis, immunofluorescence, Western blot, in vitro EGFR inhibitor treatment, and patient skin biopsy analysis","pmids":["34912369"],"confidence":"Medium","gaps":["Mechanism linking filament collapse to MAPK inhibition not determined","Single mutation studied; generalizability uncertain"]},{"year":2023,"claim":"TRIM29 was identified as a direct E3 ubiquitin ligase for KRT5, controlling its protein stability via ubiquitination; TRIM29 knockdown stabilized KRT5 and inhibited colon cancer cell proliferation in a KRT5-dependent manner.","evidence":"Co-immunoprecipitation, cycloheximide chase, ubiquitination assays, and proliferation rescue experiments","pmids":["37671092"],"confidence":"Medium","gaps":["Ubiquitination sites on KRT5 not mapped","No reciprocal IP or structural evidence for direct binding","In vivo relevance not tested"]},{"year":2023,"claim":"KRT5 in keratinocytes was shown to regulate melanocyte melanogenesis through paracrine Notch signaling: KRT5 loss reduced Notch ligand expression in keratinocytes and Notch activation in co-cultured melanocytes, mechanistically explaining the pigmentation defects in Dowling-Degos disease.","evidence":"CRISPR/Cas9 and shRNA KRT5 knockdown in keratinocytes, melanocyte co-culture, Notch pathway inhibitor/activator treatment, and DDD patient lesion immunohistochemistry","pmids":["36809573"],"confidence":"Medium","gaps":["Specific Notch ligand(s) regulated by KRT5 not identified","How a cytoskeletal protein controls Notch ligand transcription is mechanistically unresolved"]},{"year":2023,"claim":"ECM composition was shown to modulate KRT5+ basal cell migration in the IPF lung context, with fibroblast-secreted SPARC restricting KRT5+ cell motility, revealing extracellular control of KRT5+ progenitor behavior in fibrotic disease.","evidence":"In vitro migration assays on defined ECM substrates, mass spectrometry-based proteomics, and SPARC overexpression in primary human KRT5+ cells","pmids":["37758700"],"confidence":"Medium","gaps":["Whether SPARC acts directly on KRT5+ cells or through indirect signaling not resolved","In vivo validation of SPARC–KRT5+ cell interaction not performed"]},{"year":null,"claim":"Key unresolved questions include: how KRT5 structural integrity is mechanistically linked to MAPK and Notch signaling outputs; whether KRT5 protein has a functional role in stem/progenitor cell behavior beyond serving as a marker; and the atomic-resolution structural basis for genotype–severity correlations in EBS.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution structure of KRT5/KRT14 heterodimer available","Whether KRT5 protein is functionally required in lung/bladder progenitor biology is untested by conditional knockout","Mechanism coupling keratin filament integrity to transcriptional or signaling output remains undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[1,3,4,5,9]}],"localization":[{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[1,3,4,5,13]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[4,5]}],"pathway":[{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[7,12,17]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[8,13,15]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[1,2,3,6,9]}],"complexes":["KRT5/KRT14 heterodimer"],"partners":["KRT14","TRIM29","FOXM1","SPARC","TP63"],"other_free_text":[]},"mechanistic_narrative":"KRT5 encodes keratin 5, a type II intermediate filament protein that obligately heterodimerizes with keratin 14 to form the 10-nm cytoskeletal filament network essential for mechanical integrity of basal epithelial cells; complete loss of KRT5 is perinatally lethal, and missense mutations in the conserved rod-domain helix boundary motifs cause epidermolysis bullosa simplex (EBS), with severity correlating to mutation position [PMID:9036937, PMID:16786515, PMID:31302245]. Beyond its structural role, KRT5 marks tissue-regenerative stem/progenitor populations—p63+/KRT5+ distal airway stem cells regenerate alveolar epithelium after injury, KRT5+ foregut basal progenitors serve as cells of origin for gastric and bladder tumors, and aberrant TGF-β1/anti-BMP mesenchymal signaling drives alveolar-to-KRT5+ basal cell conversion in idiopathic pulmonary fibrosis [PMID:25383540, PMID:34969962, PMID:31110179, PMID:32339497]. KRT5 transcription is activated by FoxM1 and p63 and repressed by retinoic acid signaling, while KRT5 protein stability is controlled by TRIM29-mediated ubiquitination; functionally, KRT5 in keratinocytes regulates paracrine Notch signaling to melanocytes, linking it to pigmentation and Dowling-Degos disease pathogenesis [PMID:32659254, PMID:27884045, PMID:37671092, PMID:36809573, PMID:20222933]. KRT5 mutations also modulate MAPK-EGFR signaling and desmosomal protein expression, revealing signaling functions beyond cytoskeletal scaffolding [PMID:34912369]."},"prefetch_data":{"uniprot":{"accession":"P13647","full_name":"Keratin, type II cytoskeletal 5","aliases":["58 kDa cytokeratin","Cytokeratin-5","CK-5","Keratin-5","K5","Type-II keratin Kb5"],"length_aa":590,"mass_kda":62.4,"function":"Required for the formation of keratin intermediate filaments in the basal epidermis and maintenance of the skin barrier in response to mechanical stress (By similarity). Regulates the recruitment of Langerhans cells to the epidermis, potentially by modulation of the abundance of macrophage chemotactic cytokines, macrophage inflammatory cytokines and CTNND1 localization in keratinocytes (By similarity)","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/P13647/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/KRT5","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/KRT5","total_profiled":1310},"omim":[{"mim_id":"620150","title":"EPIDERMOLYTIC HYPERKERATOSIS 2A, AUTOSOMAL DOMINANT; EHK2A","url":"https://www.omim.org/entry/620150"},{"mim_id":"619599","title":"EPIDERMOLYSIS BULLOSA SIMPLEX 2D, GENERALIZED, INTERMEDIATE OR SEVERE, AUTOSOMAL RECESSIVE; EBS2D","url":"https://www.omim.org/entry/619599"},{"mim_id":"619594","title":"EPIDERMOLYSIS BULLOSA SIMPLEX 2C, LOCALIZED; EBS2C","url":"https://www.omim.org/entry/619594"},{"mim_id":"619588","title":"EPIDERMOLYSIS BULLOSA SIMPLEX 2B, GENERALIZED INTERMEDIATE; EBS2B","url":"https://www.omim.org/entry/619588"},{"mim_id":"619555","title":"EPIDERMOLYSIS BULLOSA SIMPLEX 2A, GENERALIZED SEVERE; EBS2A","url":"https://www.omim.org/entry/619555"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Intermediate filaments","reliability":"Approved"}],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"cervix","ntpm":2249.7},{"tissue":"esophagus","ntpm":6496.3},{"tissue":"skin 1","ntpm":5566.5},{"tissue":"vagina","ntpm":2417.1}],"url":"https://www.proteinatlas.org/search/KRT5"},"hgnc":{"alias_symbol":["KRT5A","CK-5"],"prev_symbol":["EBS2"]},"alphafold":{"accession":"P13647","domains":[{"cath_id":"1.20.5","chopping":"227-321","consensus_level":"medium","plddt":94.6644,"start":227,"end":321},{"cath_id":"1.20.5","chopping":"335-454","consensus_level":"medium","plddt":94.8868,"start":335,"end":454}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P13647","model_url":"https://alphafold.ebi.ac.uk/files/AF-P13647-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P13647-F1-predicted_aligned_error_v6.png","plddt_mean":65.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=KRT5","jax_strain_url":"https://www.jax.org/strain/search?query=KRT5"},"sequence":{"accession":"P13647","fasta_url":"https://rest.uniprot.org/uniprotkb/P13647.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P13647/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P13647"}},"corpus_meta":[{"pmid":"25383540","id":"PMC_25383540","title":"p63(+)Krt5(+) distal airway stem cells are essential for lung regeneration.","date":"2014","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/25383540","citation_count":428,"is_preprint":false},{"pmid":"34969962","id":"PMC_34969962","title":"Human alveolar type 2 epithelium transdifferentiates into metaplastic KRT5+ basal cells.","date":"2021","source":"Nature cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/34969962","citation_count":196,"is_preprint":false},{"pmid":"18091384","id":"PMC_18091384","title":"The diagnostic value of TTF-1, CK 5/6, and p63 immunostaining in classification of lung carcinomas.","date":"2007","source":"Applied immunohistochemistry & molecular morphology : AIMM","url":"https://pubmed.ncbi.nlm.nih.gov/18091384","citation_count":132,"is_preprint":false},{"pmid":"21375516","id":"PMC_21375516","title":"Mutations in KRT5 and KRT14 cause epidermolysis bullosa simplex in 75% of the patients.","date":"2011","source":"The British journal of 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\"Genomics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct physical mapping with two orthogonal methods\",\n      \"pmids\": [\"1377166\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"KRT5 encodes a type II keratin that, together with KRT14, constitutes the primary structural component of 10-nm intermediate filaments in mitotic epidermal basal cells; single missense mutations in the rod domain (e.g., E477K in the conserved KLLEGE motif at the helix boundary) disrupt the keratin intermediate filament cytoskeleton, causing epidermolysis bullosa simplex.\",\n      \"method\": \"Direct sequencing of KRT5 exons amplified from leukocyte genomic DNA; genotype-phenotype correlation\",\n      \"journal\": \"The Journal of investigative dermatology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — replicated across multiple independent cohorts, mutation-phenotype correlation established\",\n      \"pmids\": [\"9036937\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The P24L (P25L) substitution in the KRT5 gene (71C→T transition in the non-helical head domain) is the causative mutation for epidermolysis bullosa simplex with mottled pigmentation (EBS-MP), confirmed by mutation analysis in affected family members and sporadic patients.\",\n      \"method\": \"KRT5 gene mutation analysis; clinical correlation in families\",\n      \"journal\": \"American journal of medical genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — replicated in multiple families, single mutation identified\",\n      \"pmids\": [\"10494094\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Mutations affecting the highly conserved helix boundary motifs (helix initiation and termination peptides) of the rod domain of KRT5 (and KRT14) cause the most severe EBS phenotype (Dowling-Meara), while mutations elsewhere produce milder forms, demonstrating that the rod domain helix boundaries are structurally critical for keratin intermediate filament assembly.\",\n      \"method\": \"Sequence analysis of entire coding sequences of KRT5 and KRT14 in EBS patients; genotype-phenotype correlation\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — replicated across multiple independent large cohorts with consistent genotype-phenotype correlation\",\n      \"pmids\": [\"16786515\", \"21375516\", \"20199538\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Immortalized keratinocytes carrying a KRT5 V186L mutation form cytoplasmic keratin filament aggregates upon heat-shock stress, and this aggregation (a measure of cytoskeletal disruption) is significantly reduced by pretreatment with the chemical chaperone trimethylamine N-oxide (TMAO), demonstrating that TMAO stabilizes the mutant KRT5 protein against thermal stress.\",\n      \"method\": \"Immortalized cell lines from EBS patients (HPV16 E6E7 transduction); heat-shock assay; assessment of keratin aggregate formation with and without TMAO\",\n      \"journal\": \"Journal of dermatological science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro functional assay with chemical chaperone intervention in patient-derived cell lines\",\n      \"pmids\": [\"19157792\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Different KRT5 missense mutations (I183M, E475G, V186L) confer mutation-specific degrees of cellular fragility in primary keratinocytes upon heat stress, and TMAO dose-dependently reduces keratin aggregate formation and cell loss in all three mutant lines, establishing a genotype-dependent cytoskeletal vulnerability mechanism.\",\n      \"method\": \"Primary EBS keratinocyte cultures; heat-stress assay; TMAO treatment; keratin aggregate quantification\",\n      \"journal\": \"The British journal of dermatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — primary patient cells, quantitative functional assay, dose-response with TMAO\",\n      \"pmids\": [\"20128788\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"KRT5 frameshift/insertion mutations (c.418dupA) in the Dowling-Degos disease/Galli-Galli disease spectrum demonstrate that loss-of-function mutations in KRT5 cause reticular hyperpigmentation phenotypes, and that Galli-Galli disease (with acantholysis) shares identical KRT5 mutations with Dowling-Degos disease, establishing them as variants of the same disorder.\",\n      \"method\": \"Systematic KRT5 sequencing; histopathological re-evaluation; genotype-phenotype correlation\",\n      \"journal\": \"The British journal of dermatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — systematic mutation screening with histopathological validation\",\n      \"pmids\": [\"20222933\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Pre-existing p63+/KRT5+ distal airway stem cells (DASCp63/Krt5) undergo proliferative expansion after influenza-induced lung damage, assemble into nascent alveoli, and differentiate into type I and type II pneumocytes as well as bronchiolar secretory cells after transplantation; selective in vivo ablation of these cells prevents lung regeneration and leads to pre-fibrotic lesions.\",\n      \"method\": \"Lineage tracing; in vivo selective ablation; single-cell pedigree transplantation; live imaging; organoid culture; H1N1 mouse model\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — multiple orthogonal methods including ablation, transplantation, and clonal analysis in vivo\",\n      \"pmids\": [\"25383540\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In basal-like breast epithelial cells, KRT5 expression is regulated by an anticorrelated TGFBR3-JUND circuit: TGFBR3 and JUND are connected through four negative-feedback loops, and their dynamic toggling controls KRT5 expression in ECM-attached cells during 3D culture; ECM detachment rewires the circuit via RPS6 dephosphorylation and juxtacrine tenascin C.\",\n      \"method\": \"Single-cell gene expression profiling; 3D organotypic culture; siRNA knockdown; circuit modelling; in vivo intraductal transplantation\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods; in vitro and in vivo validation of regulatory circuit\",\n      \"pmids\": [\"24658685\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Biallelic homozygous missense variants of KRT5 in human patients cause autosomal recessive EBS with generalized phenotype; a homozygous null (KRT5 'knock-out') mutation results in complete absence of KRT5 RNA and protein and is perinatally lethal, demonstrating that KRT5 is essential for basal keratinocyte integrity and survival.\",\n      \"method\": \"Whole exome sequencing; NGS panel; immunofluorescence microscopy; expression profiling; ultrastructural analysis\",\n      \"journal\": \"Matrix biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — human KO with protein/RNA absence confirmed, multiple methods\",\n      \"pmids\": [\"31302245\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"FoxM1 transcription factor directly binds a consensus AP-2 cis element in KRT5 (and KRT7) regulatory regions and activates their transcription; KRT5 and KRT7 loss-of-function inhibits migration but not proliferation of SK-OV-3 ovarian cancer cells, placing KRT5 downstream of FoxM1 in a migration-promoting pathway.\",\n      \"method\": \"ChIP-seq; RNA-seq; qPCR; Western blot; KRT5 knockdown; wound healing/migration assay\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP-seq binding + RNA-seq + functional KD migration assay\",\n      \"pmids\": [\"32659254\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Krt5+/Krt15+ foregut basal progenitor cells are the cell of origin for gastric acid stress-induced tumors, and tumor formation from these cells is dependent on Cyclooxygenase-2 (COX-2) activity, as demonstrated in genetically engineered mouse models.\",\n      \"method\": \"Genetically engineered mouse models; lineage tracing; COX-2-dependent tumor formation assay\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo lineage tracing with genetic epistasis showing COX-2 dependence\",\n      \"pmids\": [\"31110179\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Human alveolar type 2 cells (hAEC2s), but not murine AEC2s, transdifferentiate into KRT5+ basal cells in response to fibrotic mesenchymal signaling (TGF-β1 and anti-BMP signaling) through alveolar-basal intermediates, demonstrating that aberrant mesenchymal signals drive hAEC2-to-KRT5+ basal cell lineage conversion in IPF.\",\n      \"method\": \"Organoid co-cultures; single-cell RNA-seq trajectory analysis; TGF-β1/BMP pathway manipulation; in vivo xenograft; histologic analysis of IPF tissue\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — multiple orthogonal in vitro and in vivo methods demonstrating mechanistic lineage conversion\",\n      \"pmids\": [\"34969962\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"A KRT5 homozygous missense mutation (c.1474T>C) causes structural alteration of keratin 5 and collapse of keratin intermediate filaments without a quantitative change in protein level; the KRT5 mutation inhibits MAPK signaling, leading to upregulation of the desmosomal protein DSG1 (desmoglein 1), and EGFR phosphorylation inhibition in vitro similarly upregulates DSG1, placing KRT5 upstream of MAPK-EGFR-DSG1 signaling.\",\n      \"method\": \"Biochemical experiments (structural analysis); immunofluorescence; Western blot; in vitro EGFR inhibitor treatment; patient skin biopsy analysis\",\n      \"journal\": \"Frontiers in genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — patient mutation functional characterization with pathway analysis and in vitro validation\",\n      \"pmids\": [\"34912369\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"TRIM29 E3 ubiquitin ligase directly interacts with KRT5 (confirmed by co-immunoprecipitation) and promotes its ubiquitination, reducing KRT5 protein stability; TRIM29 knockdown decreases KRT5 ubiquitination, enhances KRT5 protein stability and expression, and inhibits colon cancer cell proliferation, which is reversed by KRT5 knockdown.\",\n      \"method\": \"Co-immunoprecipitation; cycloheximide chase (protein stability assay); Western blot; qRT-PCR; CCK-8/colony formation/EDU proliferation assays\",\n      \"journal\": \"Open life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2/3 — Co-IP confirmed interaction, cycloheximide chase for stability, functional rescue experiment\",\n      \"pmids\": [\"37671092\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Downregulation of KRT5 in keratinocytes (via CRISPR/Cas9 or shRNA) decreases expression of Notch ligands in keratinocytes and Notch1 intracellular domain in melanocytes, reducing melanogenesis markers TYR and Fascin1; activation of Notch signaling reverses these effects, establishing that KRT5 in keratinocytes regulates melanocyte melanogenesis through paracrine Notch signaling.\",\n      \"method\": \"CRISPR/Cas9 site-directed mutation; lentivirus-mediated shRNA; co-culture system; Western blot; Notch inhibitor/activator treatment; immunohistochemistry of DDD patient lesions\",\n      \"journal\": \"Experimental dermatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — two independent loss-of-function models, pathway rescue, patient tissue validation\",\n      \"pmids\": [\"36809573\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"KRT5+ basal cell migratory behavior and expression of extracellular matrix remodeling genes are modulated by ECM composition and organization; SPARC (secreted by IPF lung fibroblasts and identified by mass spectrometry-based proteomics) restricts KRT5+ cell migration in vitro, revealing a mechanism by which altered ECM in IPF directly controls KRT5+ cell activity.\",\n      \"method\": \"In vitro migration assays on defined ECM substrates; mass spectrometry-based proteomics of fibroblast-secreted ECM; SPARC overexpression; primary human KRT5+ cell culture\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — proteomics identified ECM component, functional migration assay with SPARC overexpression\",\n      \"pmids\": [\"37758700\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Retinoic acid (RA) signaling directly in salivary gland epithelium represses Krt5 and Krt14 expression; inhibition of RA signaling upregulates Krt5/Krt14 independently of stem cell markers (Kit), demonstrated by isolating epithelial explants from other tissues.\",\n      \"method\": \"Mouse embryonic salivary gland epithelial explant culture; RA signaling inhibition; qPCR for Krt5/Krt14 expression; Kit expression analysis\",\n      \"journal\": \"Developmental dynamics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — isolated epithelial explants demonstrate direct RA regulation of Krt5\",\n      \"pmids\": [\"27884045\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Trp53 mutation specifically in Krt5-expressing basal urothelial cells facilitates more efficient tumorigenesis of muscle-invasive bladder cancer with squamous differentiation compared to Trp53 mutation in Upk2-expressing cells, establishing that Krt5+ basal cells are a preferred cell of origin for the basal-squamous subtype of bladder cancer.\",\n      \"method\": \"Lineage tracing in genetically engineered mouse model; BBN chemical carcinogenesis; morphological and genetic characterization of tumors\",\n      \"journal\": \"The American journal of pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo lineage-tracing genetic epistasis with specific cell-type Trp53 mutation\",\n      \"pmids\": [\"32339497\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"p63 regulates the Krt8-to-Krt5 transition during ameloblast (AmG) cell differentiation in the enamel organ, paralleling its function in skin; this regulation involves chromatin landscape remodeling at Krt5 loci, with shared transcription factor usage (p63 and AP-2 family members) between skin and enamel organ development.\",\n      \"method\": \"Single-cell RNA sequencing; trajectory reconstruction; comparative transcriptome analysis; chromatin accessibility (ATAC-seq); comparative motif discovery; p63 knockout mouse model\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — scRNA-seq with chromatin accessibility and motif analysis, preprint\",\n      \"pmids\": [\"39990386\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"KRT5 encodes keratin 5, a type II intermediate filament protein that obligately heterodimerizes with KRT14 to form the primary 10-nm cytoskeletal filament network of basal keratinocytes; mutations in its conserved rod-domain helix boundary motifs disrupt filament assembly causing mechanobullous disease (EBS), while KRT5 also functions in epithelial stem cell identity (p63+/KRT5+ lung and urothelial basal cells serving as tissue-regenerative progenitors), is transcriptionally regulated downstream of p63, FoxM1, retinoic acid, and TGF-β/BMP signaling, undergoes TRIM29-mediated ubiquitination controlling its protein stability, and participates in paracrine Notch signaling between keratinocytes and melanocytes to regulate pigmentation.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"KRT5 encodes keratin 5, a type II intermediate filament protein that obligately heterodimerizes with keratin 14 to form the 10-nm cytoskeletal filament network essential for mechanical integrity of basal epithelial cells; complete loss of KRT5 is perinatally lethal, and missense mutations in the conserved rod-domain helix boundary motifs cause epidermolysis bullosa simplex (EBS), with severity correlating to mutation position [PMID:9036937, PMID:16786515, PMID:31302245]. Beyond its structural role, KRT5 marks tissue-regenerative stem/progenitor populations—p63+/KRT5+ distal airway stem cells regenerate alveolar epithelium after injury, KRT5+ foregut basal progenitors serve as cells of origin for gastric and bladder tumors, and aberrant TGF-β1/anti-BMP mesenchymal signaling drives alveolar-to-KRT5+ basal cell conversion in idiopathic pulmonary fibrosis [PMID:25383540, PMID:34969962, PMID:31110179, PMID:32339497]. KRT5 transcription is activated by FoxM1 and p63 and repressed by retinoic acid signaling, while KRT5 protein stability is controlled by TRIM29-mediated ubiquitination; functionally, KRT5 in keratinocytes regulates paracrine Notch signaling to melanocytes, linking it to pigmentation and Dowling-Degos disease pathogenesis [PMID:32659254, PMID:27884045, PMID:37671092, PMID:36809573, PMID:20222933]. KRT5 mutations also modulate MAPK-EGFR signaling and desmosomal protein expression, revealing signaling functions beyond cytoskeletal scaffolding [PMID:34912369].\",\n  \"teleology\": [\n    {\n      \"year\": 1992,\n      \"claim\": \"Identifying the chromosomal locus of KRT5 established it as the candidate gene for the EBS locus on 12q, enabling subsequent mutation hunting in mechanobullous disease.\",\n      \"evidence\": \"PCR analysis of somatic cell hybrids and multicolor FISH mapping KRT5 to chromosome 12q\",\n      \"pmids\": [\"1377166\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No causative mutations yet identified\", \"Functional consequence of KRT5 disruption not demonstrated\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Direct sequencing of KRT5 in EBS patients demonstrated that single missense mutations in the rod domain (e.g., E477K in the KLLEGE helix-boundary motif) disrupt intermediate filament formation, establishing the molecular basis of EBS and the structural criticality of helix boundary motifs.\",\n      \"evidence\": \"Direct sequencing of KRT5 exons from patient genomic DNA with genotype–phenotype correlation across multiple cohorts\",\n      \"pmids\": [\"9036937\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No in vitro reconstitution of mutant filament assembly\", \"Mechanism of aggregate formation under stress not yet characterized\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Identification of the P24L head-domain mutation as the cause of EBS with mottled pigmentation extended the KRT5 disease spectrum beyond purely mechanical fragility to include pigmentary phenotypes.\",\n      \"evidence\": \"KRT5 gene mutation analysis in affected families and sporadic patients\",\n      \"pmids\": [\"10494094\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking a head-domain KRT5 mutation to pigmentation abnormality unknown\", \"Only a single recurrent mutation identified\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Systematic genotype–phenotype mapping across large EBS cohorts established that helix initiation and termination peptides of the KRT5 rod domain are the structural determinants of filament assembly, with mutations at these sites causing the most severe (Dowling-Meara) phenotype.\",\n      \"evidence\": \"Complete KRT5/KRT14 coding sequence analysis in EBS patient cohorts with phenotype stratification\",\n      \"pmids\": [\"16786515\", \"21375516\", \"20199538\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No atomic-resolution structural model of the KRT5/KRT14 heterodimer\", \"Mechanism by which specific mutations differentially weaken filaments not resolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Functional cell-based assays demonstrated that different KRT5 missense mutations confer mutation-specific degrees of cytoskeletal vulnerability to heat stress, and that the chemical chaperone TMAO can partially rescue mutant filament aggregation, providing proof-of-concept for pharmacological intervention.\",\n      \"evidence\": \"Heat-shock assays in primary and immortalized EBS keratinocytes with TMAO dose-response quantification of keratin aggregate formation\",\n      \"pmids\": [\"19157792\", \"20128788\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"TMAO mechanism of action on keratin folding not defined\", \"No in vivo therapeutic validation\", \"Applicability across all mutation classes untested\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"KRT5 loss-of-function frameshift mutations were shown to cause Dowling-Degos/Galli-Galli disease, unifying these as a single disorder and extending KRT5's disease repertoire to reticular pigmentation syndromes.\",\n      \"evidence\": \"Systematic KRT5 sequencing with histopathological re-evaluation\",\n      \"pmids\": [\"20222933\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking KRT5 haploinsufficiency to aberrant pigmentation not identified\", \"Cell-type-specific consequences of KRT5 loss in melanocyte–keratinocyte interaction unknown\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Lineage tracing and selective ablation in vivo established that p63+/KRT5+ distal airway stem cells are the regenerative progenitors that reconstitute alveolar epithelium after influenza injury, repositioning KRT5 as a marker and functional component of adult lung stem cells.\",\n      \"evidence\": \"Lineage tracing, in vivo ablation, single-cell transplantation, and organoid culture in H1N1 mouse model\",\n      \"pmids\": [\"25383540\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether KRT5 protein is functionally required for progenitor behavior or is merely a marker\", \"Origin of KRT5+ progenitors in distal airways not fully resolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Single-cell profiling revealed that KRT5 expression in basal-like breast epithelial cells is controlled by an anticorrelated TGFBR3–JUND regulatory circuit modulated by ECM attachment, revealing upstream signaling logic governing KRT5 in epithelial identity.\",\n      \"evidence\": \"Single-cell gene expression profiling, 3D culture, siRNA knockdown, circuit modeling, and in vivo intraductal transplantation\",\n      \"pmids\": [\"24658685\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether this circuit operates in non-mammary KRT5+ epithelia untested\", \"Direct transcription factor binding at KRT5 locus not demonstrated in this study\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Retinoic acid signaling was shown to directly repress KRT5 transcription in epithelial explants independently of stem cell markers, identifying RA as a negative regulator of the KRT5 basal cell program.\",\n      \"evidence\": \"Mouse embryonic salivary gland epithelial explant culture with RA signaling inhibition and qPCR\",\n      \"pmids\": [\"27884045\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct RA receptor binding at KRT5 regulatory elements not demonstrated\", \"Generalizability to other epithelial tissues not tested\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"A human homozygous KRT5 null mutation resulting in complete absence of protein was shown to be perinatally lethal, definitively establishing KRT5 as essential for basal keratinocyte survival, while biallelic missense variants cause autosomal recessive EBS.\",\n      \"evidence\": \"Whole exome sequencing, NGS panel, immunofluorescence, and ultrastructural analysis in human patients\",\n      \"pmids\": [\"31302245\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of lethality (pure structural failure vs. signaling disruption) not dissected\", \"No rescue experiment performed\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"ChIP-seq demonstrated that FoxM1 directly binds KRT5 regulatory regions to activate transcription, and KRT5 knockdown inhibited cancer cell migration without affecting proliferation, placing KRT5 as a FoxM1-driven effector of cell motility.\",\n      \"evidence\": \"ChIP-seq, RNA-seq, qPCR, Western blot, KRT5 knockdown, and wound healing assay in SK-OV-3 cells\",\n      \"pmids\": [\"32659254\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which KRT5 promotes migration not defined\", \"Tested in a single ovarian cancer cell line\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"In vivo lineage tracing established that Krt5+ basal urothelial cells are a preferred cell of origin for basal-squamous bladder cancer, with Trp53 loss in these cells driving more efficient muscle-invasive tumorigenesis than in luminal cells.\",\n      \"evidence\": \"Lineage tracing in genetically engineered mouse model with BBN chemical carcinogenesis\",\n      \"pmids\": [\"32339497\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether KRT5 functionally contributes to tumorigenesis or marks the susceptible population\", \"Applicability to human bladder cancer subtypes not directly tested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Human alveolar type 2 cells were shown to undergo TGF-β1/anti-BMP-driven transdifferentiation into KRT5+ basal cells through alveolar-basal intermediates, establishing a disease-relevant lineage conversion mechanism in idiopathic pulmonary fibrosis.\",\n      \"evidence\": \"Organoid co-cultures, single-cell RNA-seq trajectory analysis, TGF-β/BMP manipulation, in vivo xenograft, and IPF tissue analysis\",\n      \"pmids\": [\"34969962\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether preventing KRT5+ conversion would ameliorate fibrosis not tested\", \"Signals directing KRT5+ cells to pathological vs. regenerative fates not distinguished\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"A homozygous KRT5 missense mutation was shown to collapse keratin filaments and inhibit MAPK signaling, leading to DSG1 upregulation, revealing that KRT5 structural integrity feeds into MAPK-EGFR signaling and desmosomal protein expression.\",\n      \"evidence\": \"Biochemical structural analysis, immunofluorescence, Western blot, in vitro EGFR inhibitor treatment, and patient skin biopsy analysis\",\n      \"pmids\": [\"34912369\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking filament collapse to MAPK inhibition not determined\", \"Single mutation studied; generalizability uncertain\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"TRIM29 was identified as a direct E3 ubiquitin ligase for KRT5, controlling its protein stability via ubiquitination; TRIM29 knockdown stabilized KRT5 and inhibited colon cancer cell proliferation in a KRT5-dependent manner.\",\n      \"evidence\": \"Co-immunoprecipitation, cycloheximide chase, ubiquitination assays, and proliferation rescue experiments\",\n      \"pmids\": [\"37671092\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ubiquitination sites on KRT5 not mapped\", \"No reciprocal IP or structural evidence for direct binding\", \"In vivo relevance not tested\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"KRT5 in keratinocytes was shown to regulate melanocyte melanogenesis through paracrine Notch signaling: KRT5 loss reduced Notch ligand expression in keratinocytes and Notch activation in co-cultured melanocytes, mechanistically explaining the pigmentation defects in Dowling-Degos disease.\",\n      \"evidence\": \"CRISPR/Cas9 and shRNA KRT5 knockdown in keratinocytes, melanocyte co-culture, Notch pathway inhibitor/activator treatment, and DDD patient lesion immunohistochemistry\",\n      \"pmids\": [\"36809573\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific Notch ligand(s) regulated by KRT5 not identified\", \"How a cytoskeletal protein controls Notch ligand transcription is mechanistically unresolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"ECM composition was shown to modulate KRT5+ basal cell migration in the IPF lung context, with fibroblast-secreted SPARC restricting KRT5+ cell motility, revealing extracellular control of KRT5+ progenitor behavior in fibrotic disease.\",\n      \"evidence\": \"In vitro migration assays on defined ECM substrates, mass spectrometry-based proteomics, and SPARC overexpression in primary human KRT5+ cells\",\n      \"pmids\": [\"37758700\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether SPARC acts directly on KRT5+ cells or through indirect signaling not resolved\", \"In vivo validation of SPARC–KRT5+ cell interaction not performed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: how KRT5 structural integrity is mechanistically linked to MAPK and Notch signaling outputs; whether KRT5 protein has a functional role in stem/progenitor cell behavior beyond serving as a marker; and the atomic-resolution structural basis for genotype–severity correlations in EBS.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No high-resolution structure of KRT5/KRT14 heterodimer available\", \"Whether KRT5 protein is functionally required in lung/bladder progenitor biology is untested by conditional knockout\", \"Mechanism coupling keratin filament integrity to transcriptional or signaling output remains undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [1, 3, 4, 5, 9]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [1, 3, 4, 5, 13]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [4, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [7, 12, 17]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [8, 13, 15]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [1, 2, 3, 6, 9]}\n    ],\n    \"complexes\": [\n      \"KRT5/KRT14 heterodimer\"\n    ],\n    \"partners\": [\n      \"KRT14\",\n      \"TRIM29\",\n      \"FOXM1\",\n      \"SPARC\",\n      \"TP63\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}