{"gene":"EXPH5","run_date":"2026-06-09T23:54:43","timeline":{"discoveries":[{"year":2009,"finding":"Slac2-b (EXPH5) silencing inhibited exosome secretion in HeLa cells and phenocopied Rab27b silencing, placing Slac2-b as a Rab27b effector in the MVE docking/exosome secretion pathway.","method":"RNAi knockdown with exosome secretion assay; epistasis with Rab27b silencing","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — RNAi knockdown with functional secretion readout, replicated in context of epistasis screen, published in high-quality journal with multiple orthogonal validations","pmids":["19966785"],"is_preprint":false},{"year":2004,"finding":"The Slp homology domain of Slac2-b specifically binds Rab27A/B but not other Rabs; introduction of this recombinant domain into permeabilized parotid acinar cells strongly inhibited isoproterenol-stimulated amylase release, demonstrating that Slac2-b participates in Rab27B-mediated secretory granule exocytosis.","method":"Recombinant domain competition assay in streptolysin O-permeabilized cells; immunoprecipitation; subcellular fractionation","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vitro binding domain specificity assay combined with functional inhibition in permeabilized cells and Co-IP, multiple orthogonal methods in one study","pmids":["15039459"],"is_preprint":false},{"year":2006,"finding":"The Slp homology domain of Slac2-b (GTP-Rab27-binding domain) was used as a pull-down tool to quantify GTP-bound Rab27 in platelets, demonstrating that Rab27 is maintained in the GTP-bound form in resting platelets and undergoes GTP hydrolysis upon dense granule secretion; this established Slac2-b's SHD as a functional GTP-Rab27 sensor.","method":"Pull-down assay using Slac2-b SHD to capture GTP-Rab27; thin-layer chromatography of nucleotides; permeabilized platelet secretion assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional pull-down with biochemical readout and secretion assay, single lab, two orthogonal methods","pmids":["16880209"],"is_preprint":false},{"year":2012,"finding":"Loss-of-function frameshift mutation in EXPH5 (p.Pro1929Leufs*8) causes inherited skin fragility with disruption of keratinocyte adhesion in the lower epidermis and increased perinuclear vesicles; shRNA knockdown of Slac2-b in normal keratinocytes recapitulated cytoskeletal disruption (keratin intermediate filaments) and decreased adhesion; Slac2-b co-localizes with Rab27B and β4 integrin at early adhesion initiation sites in spreading keratinocytes.","method":"Whole-exome sequencing; shRNA knockdown; immunofluorescence co-localization; skin biopsy analysis; immunostaining","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — loss-of-function human genetics combined with shRNA knockdown phenocopy and co-localization, multiple orthogonal methods across patient-derived and normal cells","pmids":["23176819"],"is_preprint":false},{"year":2020,"finding":"Slac2-b (EXPH5) coordinates extracellular vesicle secretion to regulate keratinocyte adhesion and migration: EXPH5-mutant and Slac2-b-deficient keratinocytes showed reduced CD63+ vesicle trafficking to the plasma membrane, reduced secretion of extracellular vesicles containing extracellular matrix proteins, reduced Rab27a protein expression, and defective focal adhesion dynamics; live imaging linked CD63+ vesicle trafficking to focal adhesion turnover.","method":"Live-cell imaging; shRNA knockdown; extracellular vesicle secretion assay; focal adhesion dynamics analysis; patient-derived keratinocytes","journal":"The Journal of investigative dermatology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (live imaging, vesicle secretion assay, patient-derived cells, knockdown) with defined cellular phenotypes, single lab","pmids":["32890627"],"is_preprint":false},{"year":2024,"finding":"EXPH5 was identified as an ATM/ATR substrate by phosphoproteomics in human neuroblastoma cells; stronger downregulation of EXPH5 phosphopeptides after ATM depletion was documented, placing EXPH5 in an ATM-regulated secretory pathway.","method":"Global proteome and phosphoproteomics (ATM/ATR substrate profiling) in ATM-depleted neuroblastoma cells","journal":"Neurobiology of disease","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — phosphoproteomic mass spectrometry is a rigorous method, but EXPH5 is one of many hits and functional validation specific to EXPH5 was not reported; single lab, single method for this gene","pmids":["39615799"],"is_preprint":false}],"current_model":"EXPH5/Slac2-b is a Rab27B effector protein whose Slp homology domain selectively binds GTP-Rab27A/B; it functions in MVE docking and exosome/extracellular vesicle secretion, and in keratinocytes it coordinates CD63+ vesicle trafficking to the plasma membrane to regulate focal adhesion dynamics, cytoskeletal integrity (keratin filaments), and cell–matrix adhesion, with loss-of-function causing inherited skin fragility."},"narrative":{"mechanistic_narrative":"EXPH5 (Slac2-b) is a Rab27 effector that couples GTP-bound Rab27A/B to membrane vesicle docking and regulated secretion across multiple cell types [PMID:19966785, PMID:15039459]. Its Slp homology domain binds GTP-Rab27A/B with selectivity over other Rabs, and this domain functions both as a structural determinant of secretory granule exocytosis and as a sensor for the activated, GTP-loaded state of Rab27 [PMID:15039459, PMID:16880209]. As a Rab27b effector, EXPH5 acts in the multivesicular endosome docking and exosome/extracellular vesicle secretion pathway, where its depletion phenocopies loss of Rab27b [PMID:19966785]. In keratinocytes, EXPH5 directs trafficking of CD63+ vesicles to the plasma membrane and the secretion of extracellular vesicles carrying matrix proteins, thereby coupling vesicle delivery to focal adhesion turnover, keratin intermediate filament integrity, and cell–matrix adhesion; its loss reduces Rab27a expression and disrupts focal adhesion dynamics [PMID:23176819, PMID:32890627]. A loss-of-function frameshift mutation in EXPH5 causes inherited skin fragility, with impaired keratinocyte adhesion in the lower epidermis [PMID:23176819]. EXPH5 has additionally been recovered as an ATM-regulated phosphoprotein, linking it to a DNA-damage-responsive secretory axis [PMID:39615799].","teleology":[{"year":2004,"claim":"Establishing that Slac2-b is a bona fide Rab27 effector required showing its domain both binds the GTPase selectively and is functionally required for secretion, which this work demonstrated.","evidence":"Recombinant Slp homology domain binding specificity, Co-IP, and competition in streptolysin O-permeabilized parotid acinar cells with amylase release readout","pmids":["15039459"],"confidence":"High","gaps":["Did not resolve EXPH5 domain architecture beyond the SHD","Mechanism of how SHD binding drives granule docking not defined"]},{"year":2006,"claim":"The question of whether the SHD could report Rab27 activation state was addressed by repurposing it as a GTP-Rab27 capture reagent, establishing it as a functional sensor of activated Rab27.","evidence":"Pull-down with Slac2-b SHD coupled to nucleotide thin-layer chromatography and permeabilized platelet dense granule secretion assay","pmids":["16880209"],"confidence":"Medium","gaps":["Used SHD as a tool rather than testing endogenous EXPH5 function in platelets","Single lab"]},{"year":2009,"claim":"Whether EXPH5 contributes to exosome biogenesis was answered by placing it epistatically downstream of Rab27b in the MVE docking/exosome secretion pathway.","evidence":"RNAi knockdown in HeLa cells with exosome secretion assay and epistasis against Rab27b silencing","pmids":["19966785"],"confidence":"High","gaps":["Molecular step EXPH5 controls within MVE docking not pinpointed","Cargo selectivity of EXPH5-dependent exosomes not defined"]},{"year":2012,"claim":"The physiological consequence of EXPH5 loss in humans was established by linking a frameshift mutation to inherited skin fragility and connecting EXPH5 to keratinocyte adhesion and cytoskeletal integrity.","evidence":"Whole-exome sequencing of patients, shRNA knockdown phenocopy in normal keratinocytes, and immunofluorescence co-localization with Rab27B and β4 integrin","pmids":["23176819"],"confidence":"High","gaps":["Mechanism connecting vesicle trafficking to keratin filament disruption not resolved","Relationship between perinuclear vesicle accumulation and adhesion loss unclear"]},{"year":2020,"claim":"How EXPH5-dependent vesicle trafficking governs adhesion was clarified by linking CD63+ vesicle delivery and extracellular vesicle secretion of matrix proteins to focal adhesion dynamics.","evidence":"Live-cell imaging, shRNA knockdown, EV secretion assays, and focal adhesion dynamics in patient-derived and normal keratinocytes","pmids":["32890627"],"confidence":"High","gaps":["Identity of the matrix cargo that drives adhesion not fully defined","Causal link between reduced Rab27a expression and EXPH5 loss not mechanistically explained"]},{"year":2024,"claim":"An unexpected regulatory input was revealed by recovering EXPH5 as an ATM-responsive phosphoprotein, suggesting its secretory function is coupled to DNA-damage signaling.","evidence":"Global proteome and phosphoproteomics profiling of ATM/ATR substrates in ATM-depleted neuroblastoma cells","pmids":["39615799"],"confidence":"Medium","gaps":["EXPH5 was one of many hits without gene-specific functional validation","Phosphosite function and effect on Rab27 binding unknown"]},{"year":null,"claim":"How EXPH5 phosphorylation, Rab27 binding, and cargo selection are integrated to control which vesicles dock and secrete in different cell types remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of the EXPH5–Rab27 complex in the timeline","Regulatory phosphorylation not functionally linked to secretion","Tissue-specific cargo determinants undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140299","term_label":"molecular sensor activity","supporting_discovery_ids":[1,2]},{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[0,1]}],"localization":[{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[3,4]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[4]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,4]},{"term_id":"R-HSA-1474244","term_label":"Extracellular matrix organization","supporting_discovery_ids":[4]}],"complexes":[],"partners":["RAB27B","RAB27A","ITGB4","CD63"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8NEV8","full_name":"Exophilin-5","aliases":["Synaptotagmin-like protein homolog lacking C2 domains b","SlaC2-b","Slp homolog lacking C2 domains b"],"length_aa":1989,"mass_kda":222.5,"function":"May act as Rab effector protein and play a role in vesicle trafficking","subcellular_location":"","url":"https://www.uniprot.org/uniprotkb/Q8NEV8/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/EXPH5","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":[{"gene":"HSPA4","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/EXPH5","total_profiled":1310},"omim":[{"mim_id":"615028","title":"EPIDERMOLYSIS BULLOSA SIMPLEX 4, LOCALIZED OR GENERALIZED INTERMEDIATE, AUTOSOMAL RECESSIVE; EBS4","url":"https://www.omim.org/entry/615028"},{"mim_id":"612878","title":"EXOPHILIN 5; EXPH5","url":"https://www.omim.org/entry/612878"},{"mim_id":"131760","title":"EPIDERMOLYSIS BULLOSA SIMPLEX 1A, GENERALIZED SEVERE; EBS1A","url":"https://www.omim.org/entry/131760"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"brain","ntpm":15.1},{"tissue":"skin 1","ntpm":24.4}],"url":"https://www.proteinatlas.org/search/EXPH5"},"hgnc":{"alias_symbol":["SLAC2-B"],"prev_symbol":[]},"alphafold":{"accession":"Q8NEV8","domains":[{"cath_id":"-","chopping":"48-78","consensus_level":"medium","plddt":73.6281,"start":48,"end":78},{"cath_id":"1.20.5","chopping":"13-46","consensus_level":"medium","plddt":89.3794,"start":13,"end":46}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8NEV8","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8NEV8-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8NEV8-F1-predicted_aligned_error_v6.png","plddt_mean":36.12},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=EXPH5","jax_strain_url":"https://www.jax.org/strain/search?query=EXPH5"},"sequence":{"accession":"Q8NEV8","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8NEV8.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8NEV8/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8NEV8"}},"corpus_meta":[{"pmid":"19966785","id":"PMC_19966785","title":"Rab27a and Rab27b control different steps of the exosome secretion pathway.","date":"2009","source":"Nature cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/19966785","citation_count":2160,"is_preprint":false},{"pmid":"15039459","id":"PMC_15039459","title":"The small GTPase Rab27B regulates amylase release from rat parotid acinar cells.","date":"2004","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/15039459","citation_count":94,"is_preprint":false},{"pmid":"23176819","id":"PMC_23176819","title":"Germline Mutation in EXPH5 Implicates the Rab27B Effector Protein Slac2-b in Inherited Skin Fragility.","date":"2012","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/23176819","citation_count":58,"is_preprint":false},{"pmid":"16880209","id":"PMC_16880209","title":"Constitutive GDP/GTP exchange and secretion-dependent GTP hydrolysis activity for Rab27 in platelets.","date":"2006","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16880209","citation_count":49,"is_preprint":false},{"pmid":"27902686","id":"PMC_27902686","title":"Genomic Characterization of Metformin Hepatic Response.","date":"2016","source":"PLoS genetics","url":"https://pubmed.ncbi.nlm.nih.gov/27902686","citation_count":44,"is_preprint":false},{"pmid":"26719633","id":"PMC_26719633","title":"Recently Identified Forms of Epidermolysis Bullosa.","date":"2015","source":"Annals of dermatology","url":"https://pubmed.ncbi.nlm.nih.gov/26719633","citation_count":36,"is_preprint":false},{"pmid":"30016581","id":"PMC_30016581","title":"Next generation sequencing identifies double homozygous mutations in two distinct genes (EXPH5 and COL17A1) in a patient with concomitant simplex and junctional epidermolysis bullosa.","date":"2018","source":"Human mutation","url":"https://pubmed.ncbi.nlm.nih.gov/30016581","citation_count":28,"is_preprint":false},{"pmid":"36746116","id":"PMC_36746116","title":"Revealing EXPH5 as a potential diagnostic gene biomarker of the late stage of COPD based on machine learning analysis.","date":"2023","source":"Computers in biology and medicine","url":"https://pubmed.ncbi.nlm.nih.gov/36746116","citation_count":21,"is_preprint":false},{"pmid":"27384765","id":"PMC_27384765","title":"Association of Epidermolysis Bullosa Simplex With Mottled Pigmentation and EXPH5 Mutations.","date":"2016","source":"JAMA dermatology","url":"https://pubmed.ncbi.nlm.nih.gov/27384765","citation_count":18,"is_preprint":false},{"pmid":"36658473","id":"PMC_36658473","title":"Selection signatures for local and regional adaptation in Chinese Mongolian horse breeds reveal candidate genes for hoof health.","date":"2023","source":"BMC genomics","url":"https://pubmed.ncbi.nlm.nih.gov/36658473","citation_count":16,"is_preprint":false},{"pmid":"32890627","id":"PMC_32890627","title":"Slac2-b Coordinates Extracellular Vesicle Secretion to Regulate Keratinocyte Adhesion and Migration.","date":"2020","source":"The Journal of investigative dermatology","url":"https://pubmed.ncbi.nlm.nih.gov/32890627","citation_count":11,"is_preprint":false},{"pmid":"35504439","id":"PMC_35504439","title":"Pathomechanisms of epidermolysis bullosa: Beyond structural proteins.","date":"2022","source":"Matrix biology : journal of the International Society for Matrix Biology","url":"https://pubmed.ncbi.nlm.nih.gov/35504439","citation_count":11,"is_preprint":false},{"pmid":"24443915","id":"PMC_24443915","title":"Mutations in EXPH5 result in autosomal recessive inherited skin fragility.","date":"2014","source":"The British journal of dermatology","url":"https://pubmed.ncbi.nlm.nih.gov/24443915","citation_count":10,"is_preprint":false},{"pmid":"25576648","id":"PMC_25576648","title":"Dissecting the mechanism of colorectal tumorigenesis based on RNA-sequencing data.","date":"2015","source":"Experimental and molecular pathology","url":"https://pubmed.ncbi.nlm.nih.gov/25576648","citation_count":9,"is_preprint":false},{"pmid":"27730671","id":"PMC_27730671","title":"A novel homozygous deletion in EXPH5 causes a skin fragility phenotype.","date":"2016","source":"Clinical and experimental dermatology","url":"https://pubmed.ncbi.nlm.nih.gov/27730671","citation_count":7,"is_preprint":false},{"pmid":"32425970","id":"PMC_32425970","title":"Exome Sequencing Analysis Identifies Rare Variants in ATM and RPL8 That Are Associated With Shorter Telomere Length.","date":"2020","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/32425970","citation_count":6,"is_preprint":false},{"pmid":"37611365","id":"PMC_37611365","title":"A human identification system for hair shaft using RNA polymorphism.","date":"2023","source":"Forensic science international. Genetics","url":"https://pubmed.ncbi.nlm.nih.gov/37611365","citation_count":5,"is_preprint":false},{"pmid":"39615799","id":"PMC_39615799","title":"The ataxia-telangiectasia disease protein ATM controls vesicular protein secretion via CHGA and microtubule dynamics via CRMP5.","date":"2024","source":"Neurobiology of disease","url":"https://pubmed.ncbi.nlm.nih.gov/39615799","citation_count":4,"is_preprint":false},{"pmid":"40595076","id":"PMC_40595076","title":"Predictive effect and clinical diagnosis significance of exosome-related genes for nonalcoholic fatty liver disease-related hepatocellular carcinoma.","date":"2025","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/40595076","citation_count":3,"is_preprint":false},{"pmid":"38902479","id":"PMC_38902479","title":"Rare variants analyses suggest novel cleft genes in the African population.","date":"2024","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/38902479","citation_count":3,"is_preprint":false},{"pmid":"35960249","id":"PMC_35960249","title":"Potential di-genic contribution to guttate leukoderma as the predominant feature of epidermolysis bullosa simplex.","date":"2022","source":"Experimental dermatology","url":"https://pubmed.ncbi.nlm.nih.gov/35960249","citation_count":2,"is_preprint":false},{"pmid":"39125467","id":"PMC_39125467","title":"Identification of Pathogenic Pathways for Recurrence of Focal Segmental Glomerulosclerosis after Kidney Transplantation.","date":"2024","source":"Diagnostics (Basel, Switzerland)","url":"https://pubmed.ncbi.nlm.nih.gov/39125467","citation_count":1,"is_preprint":false},{"pmid":"38464065","id":"PMC_38464065","title":"Rare Variants Analyses Suggest Novel Cleft Genes in the African Population.","date":"2024","source":"Research square","url":"https://pubmed.ncbi.nlm.nih.gov/38464065","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":13928,"output_tokens":1679,"usd":0.033485,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8445,"output_tokens":2444,"usd":0.051663,"stage2_stop_reason":"end_turn"},"total_usd":0.085148,"stage1_batch_id":"msgbatch_01AsR7g8dGTEiEw9U83bJeWn","stage2_batch_id":"msgbatch_01YV5ZyxtFNUZEjxRcpd9jzb","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2009,\n      \"finding\": \"Slac2-b (EXPH5) silencing inhibited exosome secretion in HeLa cells and phenocopied Rab27b silencing, placing Slac2-b as a Rab27b effector in the MVE docking/exosome secretion pathway.\",\n      \"method\": \"RNAi knockdown with exosome secretion assay; epistasis with Rab27b silencing\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — RNAi knockdown with functional secretion readout, replicated in context of epistasis screen, published in high-quality journal with multiple orthogonal validations\",\n      \"pmids\": [\"19966785\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The Slp homology domain of Slac2-b specifically binds Rab27A/B but not other Rabs; introduction of this recombinant domain into permeabilized parotid acinar cells strongly inhibited isoproterenol-stimulated amylase release, demonstrating that Slac2-b participates in Rab27B-mediated secretory granule exocytosis.\",\n      \"method\": \"Recombinant domain competition assay in streptolysin O-permeabilized cells; immunoprecipitation; subcellular fractionation\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro binding domain specificity assay combined with functional inhibition in permeabilized cells and Co-IP, multiple orthogonal methods in one study\",\n      \"pmids\": [\"15039459\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"The Slp homology domain of Slac2-b (GTP-Rab27-binding domain) was used as a pull-down tool to quantify GTP-bound Rab27 in platelets, demonstrating that Rab27 is maintained in the GTP-bound form in resting platelets and undergoes GTP hydrolysis upon dense granule secretion; this established Slac2-b's SHD as a functional GTP-Rab27 sensor.\",\n      \"method\": \"Pull-down assay using Slac2-b SHD to capture GTP-Rab27; thin-layer chromatography of nucleotides; permeabilized platelet secretion assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional pull-down with biochemical readout and secretion assay, single lab, two orthogonal methods\",\n      \"pmids\": [\"16880209\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Loss-of-function frameshift mutation in EXPH5 (p.Pro1929Leufs*8) causes inherited skin fragility with disruption of keratinocyte adhesion in the lower epidermis and increased perinuclear vesicles; shRNA knockdown of Slac2-b in normal keratinocytes recapitulated cytoskeletal disruption (keratin intermediate filaments) and decreased adhesion; Slac2-b co-localizes with Rab27B and β4 integrin at early adhesion initiation sites in spreading keratinocytes.\",\n      \"method\": \"Whole-exome sequencing; shRNA knockdown; immunofluorescence co-localization; skin biopsy analysis; immunostaining\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — loss-of-function human genetics combined with shRNA knockdown phenocopy and co-localization, multiple orthogonal methods across patient-derived and normal cells\",\n      \"pmids\": [\"23176819\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Slac2-b (EXPH5) coordinates extracellular vesicle secretion to regulate keratinocyte adhesion and migration: EXPH5-mutant and Slac2-b-deficient keratinocytes showed reduced CD63+ vesicle trafficking to the plasma membrane, reduced secretion of extracellular vesicles containing extracellular matrix proteins, reduced Rab27a protein expression, and defective focal adhesion dynamics; live imaging linked CD63+ vesicle trafficking to focal adhesion turnover.\",\n      \"method\": \"Live-cell imaging; shRNA knockdown; extracellular vesicle secretion assay; focal adhesion dynamics analysis; patient-derived keratinocytes\",\n      \"journal\": \"The Journal of investigative dermatology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (live imaging, vesicle secretion assay, patient-derived cells, knockdown) with defined cellular phenotypes, single lab\",\n      \"pmids\": [\"32890627\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"EXPH5 was identified as an ATM/ATR substrate by phosphoproteomics in human neuroblastoma cells; stronger downregulation of EXPH5 phosphopeptides after ATM depletion was documented, placing EXPH5 in an ATM-regulated secretory pathway.\",\n      \"method\": \"Global proteome and phosphoproteomics (ATM/ATR substrate profiling) in ATM-depleted neuroblastoma cells\",\n      \"journal\": \"Neurobiology of disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — phosphoproteomic mass spectrometry is a rigorous method, but EXPH5 is one of many hits and functional validation specific to EXPH5 was not reported; single lab, single method for this gene\",\n      \"pmids\": [\"39615799\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"EXPH5/Slac2-b is a Rab27B effector protein whose Slp homology domain selectively binds GTP-Rab27A/B; it functions in MVE docking and exosome/extracellular vesicle secretion, and in keratinocytes it coordinates CD63+ vesicle trafficking to the plasma membrane to regulate focal adhesion dynamics, cytoskeletal integrity (keratin filaments), and cell–matrix adhesion, with loss-of-function causing inherited skin fragility.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"EXPH5 (Slac2-b) is a Rab27 effector that couples GTP-bound Rab27A/B to membrane vesicle docking and regulated secretion across multiple cell types [#0, #1]. Its Slp homology domain binds GTP-Rab27A/B with selectivity over other Rabs, and this domain functions both as a structural determinant of secretory granule exocytosis and as a sensor for the activated, GTP-loaded state of Rab27 [#1, #2]. As a Rab27b effector, EXPH5 acts in the multivesicular endosome docking and exosome/extracellular vesicle secretion pathway, where its depletion phenocopies loss of Rab27b [#0]. In keratinocytes, EXPH5 directs trafficking of CD63+ vesicles to the plasma membrane and the secretion of extracellular vesicles carrying matrix proteins, thereby coupling vesicle delivery to focal adhesion turnover, keratin intermediate filament integrity, and cell\\u2013matrix adhesion; its loss reduces Rab27a expression and disrupts focal adhesion dynamics [#3, #4]. A loss-of-function frameshift mutation in EXPH5 causes inherited skin fragility, with impaired keratinocyte adhesion in the lower epidermis [#3]. EXPH5 has additionally been recovered as an ATM-regulated phosphoprotein, linking it to a DNA-damage-responsive secretory axis [#5].\"\n  ,\n  \"teleology\": [\n    {\n      \"year\": 2004,\n      \"claim\": \"Establishing that Slac2-b is a bona fide Rab27 effector required showing its domain both binds the GTPase selectively and is functionally required for secretion, which this work demonstrated.\",\n      \"evidence\": \"Recombinant Slp homology domain binding specificity, Co-IP, and competition in streptolysin O-permeabilized parotid acinar cells with amylase release readout\",\n      \"pmids\": [\"15039459\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve EXPH5 domain architecture beyond the SHD\", \"Mechanism of how SHD binding drives granule docking not defined\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"The question of whether the SHD could report Rab27 activation state was addressed by repurposing it as a GTP-Rab27 capture reagent, establishing it as a functional sensor of activated Rab27.\",\n      \"evidence\": \"Pull-down with Slac2-b SHD coupled to nucleotide thin-layer chromatography and permeabilized platelet dense granule secretion assay\",\n      \"pmids\": [\"16880209\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Used SHD as a tool rather than testing endogenous EXPH5 function in platelets\", \"Single lab\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Whether EXPH5 contributes to exosome biogenesis was answered by placing it epistatically downstream of Rab27b in the MVE docking/exosome secretion pathway.\",\n      \"evidence\": \"RNAi knockdown in HeLa cells with exosome secretion assay and epistasis against Rab27b silencing\",\n      \"pmids\": [\"19966785\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular step EXPH5 controls within MVE docking not pinpointed\", \"Cargo selectivity of EXPH5-dependent exosomes not defined\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"The physiological consequence of EXPH5 loss in humans was established by linking a frameshift mutation to inherited skin fragility and connecting EXPH5 to keratinocyte adhesion and cytoskeletal integrity.\",\n      \"evidence\": \"Whole-exome sequencing of patients, shRNA knockdown phenocopy in normal keratinocytes, and immunofluorescence co-localization with Rab27B and \\u03b24 integrin\",\n      \"pmids\": [\"23176819\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism connecting vesicle trafficking to keratin filament disruption not resolved\", \"Relationship between perinuclear vesicle accumulation and adhesion loss unclear\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"How EXPH5-dependent vesicle trafficking governs adhesion was clarified by linking CD63+ vesicle delivery and extracellular vesicle secretion of matrix proteins to focal adhesion dynamics.\",\n      \"evidence\": \"Live-cell imaging, shRNA knockdown, EV secretion assays, and focal adhesion dynamics in patient-derived and normal keratinocytes\",\n      \"pmids\": [\"32890627\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the matrix cargo that drives adhesion not fully defined\", \"Causal link between reduced Rab27a expression and EXPH5 loss not mechanistically explained\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"An unexpected regulatory input was revealed by recovering EXPH5 as an ATM-responsive phosphoprotein, suggesting its secretory function is coupled to DNA-damage signaling.\",\n      \"evidence\": \"Global proteome and phosphoproteomics profiling of ATM/ATR substrates in ATM-depleted neuroblastoma cells\",\n      \"pmids\": [\"39615799\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"EXPH5 was one of many hits without gene-specific functional validation\", \"Phosphosite function and effect on Rab27 binding unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How EXPH5 phosphorylation, Rab27 binding, and cargo selection are integrated to control which vesicles dock and secrete in different cell types remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of the EXPH5\\u2013Rab27 complex in the timeline\", \"Regulatory phosphorylation not functionally linked to secretion\", \"Tissue-specific cargo determinants undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140299\", \"supporting_discovery_ids\": [1, 2]},\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [3, 4]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 4]},\n      {\"term_id\": \"R-HSA-1474244\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"RAB27B\", \"RAB27A\", \"ITGB4\", \"CD63\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}