{"gene":"EXPH5","run_date":"2026-04-28T17:46:03","timeline":{"discoveries":[{"year":2009,"finding":"EXPH5 (Slac2-b/exophilin-5) functions as a Rab27b effector in the exosome secretion pathway; silencing EXPH5 inhibited exosome secretion and phenocopied Rab27b silencing, including redistribution of multivesicular endosomes (MVEs) toward the perinuclear region, establishing EXPH5's role in MVE docking at the plasma membrane.","method":"RNAi screen in HeLa cells, RNA interference knockdown with phenotypic readout (exosome secretion quantification, MVE localization by imaging)","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 2 — large-scale RNAi screen with multiple orthogonal readouts, highly cited foundational study replicated across labs","pmids":["19966785"],"is_preprint":false},{"year":2004,"finding":"Slac2-b (EXPH5) binds specifically to GTP-bound Rab27A/B (but not other Rabs) through its Slp homology domain (SHD), forming a complex on secretory granules in vivo; disruption of the Rab27B–Slac2-b interaction by introducing recombinant SHD or blocking antibodies strongly inhibited stimulated exocytosis in parotid acinar cells.","method":"Subcellular fractionation, co-immunoprecipitation, immunohistochemistry, permeabilized cell secretion assay with recombinant domain competition and blocking antibodies","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP, subcellular fractionation, and functional rescue/inhibition with multiple orthogonal methods in a single study","pmids":["15039459"],"is_preprint":false},{"year":2006,"finding":"The Slp homology domain (SHD) of Slac2-b (EXPH5) was used as a pull-down tool to quantify GTP-bound Rab27 in platelets, confirming Slac2-b binds specifically to GTP-Rab27; Rab27 in unstimulated platelets is predominantly GTP-bound and undergoes GTP hydrolysis upon granule secretion, with Slac2-b binding used as functional readout.","method":"Pull-down assay using recombinant Slac2-b SHD domain, thin-layer chromatography of nucleotides from immunoprecipitated Rab27, permeabilized platelet secretion assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — biochemical pull-down with functional context, but EXPH5 itself is used as a tool/effector rather than the primary subject","pmids":["16880209"],"is_preprint":false},{"year":2012,"finding":"Loss-of-function mutations in EXPH5 cause inherited skin fragility (epidermolysis bullosa simplex) associated with disruption of keratinocyte adhesion in the lower epidermis, increased perinuclear vesicles, and cytoskeletal disruption (keratin intermediate filaments); Slac2-b colocalizes with Rab27B and β4 integrin at early adhesion initiation sites in spreading keratinocytes, establishing its role in keratinocyte biology.","method":"Whole-exome sequencing, shRNA knockdown in normal keratinocytes, immunofluorescence colocalization, transmission electron microscopy, keratinocyte adhesion assay","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (genetics, knockdown, imaging, adhesion assay) establishing functional role in keratinocytes","pmids":["23176819"],"is_preprint":false},{"year":2020,"finding":"Slac2-b (EXPH5) regulates keratinocyte cell–matrix adhesion and migration by coordinating trafficking of CD63+ extracellular vesicles to the plasma membrane; loss of Slac2-b causes perinuclear accumulation of CD63+ vesicles, reduces Rab27a protein expression, reduces secretion of extracellular vesicles containing extracellular matrix proteins, and impairs focal adhesion dynamics as revealed by live imaging.","method":"Primary keratinocytes from EXPH5-mutant patients, shRNA knockdown, live cell imaging of CD63+ vesicle trafficking, extracellular vesicle isolation and proteomics, focal adhesion dynamics analysis","journal":"The Journal of investigative dermatology","confidence":"High","confidence_rationale":"Tier 2 — patient-derived cells plus knockdown, multiple orthogonal readouts including live imaging and vesicle proteomics","pmids":["32890627"],"is_preprint":false},{"year":2024,"finding":"EXPH5 is a substrate of ATM kinase phosphorylation; phosphoproteomic analysis identified EXPH5 as among the most strongly downregulated ATM/ATR substrate phosphopeptides upon ATM depletion, implicating EXPH5 in ATM-regulated protein secretion and endosome dynamics.","method":"Global proteome and phosphoproteomics (ATM/ATR substrate profiling) in human neuroblastoma cells with ATM depletion","journal":"Neurobiology of disease","confidence":"Medium","confidence_rationale":"Tier 2 — phosphoproteomic mass spectrometry, but functional validation of the specific EXPH5 phosphorylation event was not performed","pmids":["39615799"],"is_preprint":false}],"current_model":"EXPH5 (Slac2-b/exophilin-5) functions as a Rab27B effector protein that binds GTP-Rab27 via its Slp homology domain to regulate intracellular vesicle/MVE trafficking to the plasma membrane, thereby controlling exosome/extracellular vesicle secretion, keratinocyte cell–matrix adhesion (through focal adhesion dynamics and ECM-containing vesicle secretion), and secretory granule exocytosis; loss of EXPH5 disrupts keratin cytoskeleton and causes inherited skin fragility (epidermolysis bullosa simplex), and EXPH5 is additionally a phosphorylation substrate of ATM kinase."},"narrative":{"teleology":[{"year":2004,"claim":"Establishing EXPH5 as a GTP-Rab27-specific effector answered how Rab27 couples to downstream vesicle trafficking machinery: Slac2-b binds GTP-Rab27A/B via its SHD and this interaction is required for stimulated exocytosis in secretory acinar cells.","evidence":"Co-immunoprecipitation, subcellular fractionation, and permeabilized cell secretion assay with recombinant SHD competition and blocking antibodies in parotid acinar cells","pmids":["15039459"],"confidence":"High","gaps":["The downstream effector mechanism linking Rab27–EXPH5 binding to vesicle fusion was not identified","Whether EXPH5 functions in non-secretory cell types was unknown"]},{"year":2006,"claim":"Demonstrating that the Slac2-b SHD quantitatively captures GTP-Rab27 in platelets confirmed the generality of the EXPH5–Rab27 interaction across secretory cell types and revealed that resting Rab27 is predominantly GTP-loaded.","evidence":"Recombinant SHD pull-down assay and thin-layer chromatography of Rab27-bound nucleotides in permeabilized platelets","pmids":["16880209"],"confidence":"Medium","gaps":["EXPH5 was used as a biochemical tool rather than the primary subject; its endogenous role in platelets was not tested","No direct assessment of EXPH5 loss-of-function in platelet granule secretion"]},{"year":2009,"claim":"Placing EXPH5 in the exosome secretion pathway resolved the question of which Rab27b effector mediates MVE docking at the plasma membrane: silencing EXPH5 phenocopied Rab27b loss, causing perinuclear MVE accumulation and reduced exosome release.","evidence":"RNAi screen in HeLa cells with exosome secretion quantification and MVE localization imaging","pmids":["19966785"],"confidence":"High","gaps":["The molecular mechanism by which EXPH5 tethers MVEs to the plasma membrane was not determined","Whether EXPH5 acts alone or requires additional tethering/SNARE factors was unresolved"]},{"year":2012,"claim":"Discovery that EXPH5 loss-of-function mutations cause epidermolysis bullosa simplex established the gene's non-redundant role in keratinocyte adhesion and linked its vesicle-trafficking function to human disease and cytoskeletal integrity.","evidence":"Whole-exome sequencing in patients, shRNA knockdown in keratinocytes, electron microscopy, immunofluorescence colocalization of Slac2-b with Rab27B and β4 integrin, and adhesion assays","pmids":["23176819"],"confidence":"High","gaps":["How EXPH5 loss disrupts keratin intermediate filament organization was not mechanistically explained","Whether the skin fragility reflects defective integrin trafficking, ECM secretion, or both was unclear"]},{"year":2020,"claim":"Demonstrating that EXPH5 controls CD63+ vesicle trafficking to deliver ECM cargo and regulate focal adhesion dynamics resolved the cellular mechanism underlying the adhesion defect in EXPH5-deficient keratinocytes.","evidence":"Patient-derived primary keratinocytes and shRNA knockdown with live imaging of CD63+ vesicles, extracellular vesicle proteomics, and focal adhesion dynamics analysis","pmids":["32890627"],"confidence":"High","gaps":["The specific cargo receptor or sorting signal directing ECM proteins into EXPH5-dependent vesicles is unknown","Whether EXPH5 directly interacts with focal adhesion components or acts indirectly through vesicle delivery was not resolved"]},{"year":2024,"claim":"Identification of EXPH5 as an ATM kinase substrate raised the possibility that DNA damage signaling modulates EXPH5-dependent vesicle trafficking, though the functional significance of this phosphorylation was not tested.","evidence":"Global phosphoproteomics with ATM/ATR substrate profiling in ATM-depleted human neuroblastoma cells","pmids":["39615799"],"confidence":"Medium","gaps":["No functional validation of the specific EXPH5 phosphorylation event was performed","The phosphorylation site(s) on EXPH5 and their effect on Rab27 binding or vesicle trafficking are unknown","Whether ATM-dependent phosphorylation of EXPH5 is relevant in keratinocytes or other physiological contexts is untested"]},{"year":null,"claim":"Major unresolved questions include the structural basis of EXPH5–Rab27 interaction, the identity of downstream tethering/fusion partners at the plasma membrane, how EXPH5 loss leads to keratin cytoskeleton disruption, and whether ATM-mediated phosphorylation of EXPH5 is functionally significant.","evidence":"","pmids":[],"confidence":"Low","gaps":["No crystal structure or cryo-EM structure of EXPH5 or its complexes exists","The plasma membrane tethering or SNARE partners that cooperate with EXPH5 for vesicle fusion are unidentified","The mechanism connecting EXPH5 vesicle trafficking to keratin intermediate filament organization is unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,1,4]}],"localization":[{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[0,3,4]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,3]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,1,4]},{"term_id":"R-HSA-1500931","term_label":"Cell-Cell communication","supporting_discovery_ids":[3,4]}],"complexes":[],"partners":["RAB27B","RAB27A"],"other_free_text":[]},"mechanistic_narrative":"EXPH5 (Slac2-b/exophilin-5) is a Rab27 effector that couples intracellular vesicle trafficking to exocytosis and cell adhesion. It binds specifically to GTP-bound Rab27A/B through its Slp homology domain (SHD) on secretory granules, and disruption of this interaction inhibits regulated exocytosis in secretory cells [PMID:15039459]. EXPH5 mediates docking of multivesicular endosomes (MVEs) at the plasma membrane to promote exosome secretion, as its silencing causes perinuclear MVE redistribution and reduced exosome release [PMID:19966785]. In keratinocytes, EXPH5 coordinates trafficking of CD63+ extracellular vesicles containing extracellular matrix proteins to control focal adhesion dynamics and cell–matrix adhesion, and loss-of-function mutations in EXPH5 cause inherited epidermolysis bullosa simplex with keratin cytoskeleton disruption and skin fragility [PMID:23176819, PMID:32890627]."},"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":2134,"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":57,"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":42,"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":35,"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":27,"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":13168,"output_tokens":1746,"usd":0.032847},"stage2":{"model":"claude-opus-4-6","input_tokens":4993,"output_tokens":2044,"usd":0.114098},"total_usd":0.146945,"stage1_batch_id":"msgbatch_0118RScg3WGaGkaZRtWZbtce","stage2_batch_id":"msgbatch_01Cpfzvtbj42aqp5oYZ5Te2s","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2009,\n      \"finding\": \"EXPH5 (Slac2-b/exophilin-5) functions as a Rab27b effector in the exosome secretion pathway; silencing EXPH5 inhibited exosome secretion and phenocopied Rab27b silencing, including redistribution of multivesicular endosomes (MVEs) toward the perinuclear region, establishing EXPH5's role in MVE docking at the plasma membrane.\",\n      \"method\": \"RNAi screen in HeLa cells, RNA interference knockdown with phenotypic readout (exosome secretion quantification, MVE localization by imaging)\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — large-scale RNAi screen with multiple orthogonal readouts, highly cited foundational study replicated across labs\",\n      \"pmids\": [\"19966785\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Slac2-b (EXPH5) binds specifically to GTP-bound Rab27A/B (but not other Rabs) through its Slp homology domain (SHD), forming a complex on secretory granules in vivo; disruption of the Rab27B–Slac2-b interaction by introducing recombinant SHD or blocking antibodies strongly inhibited stimulated exocytosis in parotid acinar cells.\",\n      \"method\": \"Subcellular fractionation, co-immunoprecipitation, immunohistochemistry, permeabilized cell secretion assay with recombinant domain competition and blocking antibodies\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP, subcellular fractionation, and functional rescue/inhibition with multiple orthogonal methods in a single study\",\n      \"pmids\": [\"15039459\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"The Slp homology domain (SHD) of Slac2-b (EXPH5) was used as a pull-down tool to quantify GTP-bound Rab27 in platelets, confirming Slac2-b binds specifically to GTP-Rab27; Rab27 in unstimulated platelets is predominantly GTP-bound and undergoes GTP hydrolysis upon granule secretion, with Slac2-b binding used as functional readout.\",\n      \"method\": \"Pull-down assay using recombinant Slac2-b SHD domain, thin-layer chromatography of nucleotides from immunoprecipitated Rab27, permeabilized platelet secretion assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — biochemical pull-down with functional context, but EXPH5 itself is used as a tool/effector rather than the primary subject\",\n      \"pmids\": [\"16880209\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Loss-of-function mutations in EXPH5 cause inherited skin fragility (epidermolysis bullosa simplex) associated with disruption of keratinocyte adhesion in the lower epidermis, increased perinuclear vesicles, and cytoskeletal disruption (keratin intermediate filaments); Slac2-b colocalizes with Rab27B and β4 integrin at early adhesion initiation sites in spreading keratinocytes, establishing its role in keratinocyte biology.\",\n      \"method\": \"Whole-exome sequencing, shRNA knockdown in normal keratinocytes, immunofluorescence colocalization, transmission electron microscopy, keratinocyte adhesion assay\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (genetics, knockdown, imaging, adhesion assay) establishing functional role in keratinocytes\",\n      \"pmids\": [\"23176819\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Slac2-b (EXPH5) regulates keratinocyte cell–matrix adhesion and migration by coordinating trafficking of CD63+ extracellular vesicles to the plasma membrane; loss of Slac2-b causes perinuclear accumulation of CD63+ vesicles, reduces Rab27a protein expression, reduces secretion of extracellular vesicles containing extracellular matrix proteins, and impairs focal adhesion dynamics as revealed by live imaging.\",\n      \"method\": \"Primary keratinocytes from EXPH5-mutant patients, shRNA knockdown, live cell imaging of CD63+ vesicle trafficking, extracellular vesicle isolation and proteomics, focal adhesion dynamics analysis\",\n      \"journal\": \"The Journal of investigative dermatology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — patient-derived cells plus knockdown, multiple orthogonal readouts including live imaging and vesicle proteomics\",\n      \"pmids\": [\"32890627\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"EXPH5 is a substrate of ATM kinase phosphorylation; phosphoproteomic analysis identified EXPH5 as among the most strongly downregulated ATM/ATR substrate phosphopeptides upon ATM depletion, implicating EXPH5 in ATM-regulated protein secretion and endosome dynamics.\",\n      \"method\": \"Global proteome and phosphoproteomics (ATM/ATR substrate profiling) in human neuroblastoma cells with ATM depletion\",\n      \"journal\": \"Neurobiology of disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — phosphoproteomic mass spectrometry, but functional validation of the specific EXPH5 phosphorylation event was not performed\",\n      \"pmids\": [\"39615799\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"EXPH5 (Slac2-b/exophilin-5) functions as a Rab27B effector protein that binds GTP-Rab27 via its Slp homology domain to regulate intracellular vesicle/MVE trafficking to the plasma membrane, thereby controlling exosome/extracellular vesicle secretion, keratinocyte cell–matrix adhesion (through focal adhesion dynamics and ECM-containing vesicle secretion), and secretory granule exocytosis; loss of EXPH5 disrupts keratin cytoskeleton and causes inherited skin fragility (epidermolysis bullosa simplex), and EXPH5 is additionally a phosphorylation substrate of ATM kinase.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"EXPH5 (Slac2-b/exophilin-5) is a Rab27 effector that couples intracellular vesicle trafficking to exocytosis and cell adhesion. It binds specifically to GTP-bound Rab27A/B through its Slp homology domain (SHD) on secretory granules, and disruption of this interaction inhibits regulated exocytosis in secretory cells [PMID:15039459]. EXPH5 mediates docking of multivesicular endosomes (MVEs) at the plasma membrane to promote exosome secretion, as its silencing causes perinuclear MVE redistribution and reduced exosome release [PMID:19966785]. In keratinocytes, EXPH5 coordinates trafficking of CD63+ extracellular vesicles containing extracellular matrix proteins to control focal adhesion dynamics and cell–matrix adhesion, and loss-of-function mutations in EXPH5 cause inherited epidermolysis bullosa simplex with keratin cytoskeleton disruption and skin fragility [PMID:23176819, PMID:32890627].\",\n  \"teleology\": [\n    {\n      \"year\": 2004,\n      \"claim\": \"Establishing EXPH5 as a GTP-Rab27-specific effector answered how Rab27 couples to downstream vesicle trafficking machinery: Slac2-b binds GTP-Rab27A/B via its SHD and this interaction is required for stimulated exocytosis in secretory acinar cells.\",\n      \"evidence\": \"Co-immunoprecipitation, subcellular fractionation, and permeabilized cell secretion assay with recombinant SHD competition and blocking antibodies in parotid acinar cells\",\n      \"pmids\": [\"15039459\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"The downstream effector mechanism linking Rab27–EXPH5 binding to vesicle fusion was not identified\",\n        \"Whether EXPH5 functions in non-secretory cell types was unknown\"\n      ]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Demonstrating that the Slac2-b SHD quantitatively captures GTP-Rab27 in platelets confirmed the generality of the EXPH5–Rab27 interaction across secretory cell types and revealed that resting Rab27 is predominantly GTP-loaded.\",\n      \"evidence\": \"Recombinant SHD pull-down assay and thin-layer chromatography of Rab27-bound nucleotides in permeabilized platelets\",\n      \"pmids\": [\"16880209\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"EXPH5 was used as a biochemical tool rather than the primary subject; its endogenous role in platelets was not tested\",\n        \"No direct assessment of EXPH5 loss-of-function in platelet granule secretion\"\n      ]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Placing EXPH5 in the exosome secretion pathway resolved the question of which Rab27b effector mediates MVE docking at the plasma membrane: silencing EXPH5 phenocopied Rab27b loss, causing perinuclear MVE accumulation and reduced exosome release.\",\n      \"evidence\": \"RNAi screen in HeLa cells with exosome secretion quantification and MVE localization imaging\",\n      \"pmids\": [\"19966785\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"The molecular mechanism by which EXPH5 tethers MVEs to the plasma membrane was not determined\",\n        \"Whether EXPH5 acts alone or requires additional tethering/SNARE factors was unresolved\"\n      ]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Discovery that EXPH5 loss-of-function mutations cause epidermolysis bullosa simplex established the gene's non-redundant role in keratinocyte adhesion and linked its vesicle-trafficking function to human disease and cytoskeletal integrity.\",\n      \"evidence\": \"Whole-exome sequencing in patients, shRNA knockdown in keratinocytes, electron microscopy, immunofluorescence colocalization of Slac2-b with Rab27B and β4 integrin, and adhesion assays\",\n      \"pmids\": [\"23176819\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"How EXPH5 loss disrupts keratin intermediate filament organization was not mechanistically explained\",\n        \"Whether the skin fragility reflects defective integrin trafficking, ECM secretion, or both was unclear\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Demonstrating that EXPH5 controls CD63+ vesicle trafficking to deliver ECM cargo and regulate focal adhesion dynamics resolved the cellular mechanism underlying the adhesion defect in EXPH5-deficient keratinocytes.\",\n      \"evidence\": \"Patient-derived primary keratinocytes and shRNA knockdown with live imaging of CD63+ vesicles, extracellular vesicle proteomics, and focal adhesion dynamics analysis\",\n      \"pmids\": [\"32890627\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"The specific cargo receptor or sorting signal directing ECM proteins into EXPH5-dependent vesicles is unknown\",\n        \"Whether EXPH5 directly interacts with focal adhesion components or acts indirectly through vesicle delivery was not resolved\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identification of EXPH5 as an ATM kinase substrate raised the possibility that DNA damage signaling modulates EXPH5-dependent vesicle trafficking, though the functional significance of this phosphorylation was not tested.\",\n      \"evidence\": \"Global phosphoproteomics with ATM/ATR substrate profiling in ATM-depleted human neuroblastoma cells\",\n      \"pmids\": [\"39615799\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No functional validation of the specific EXPH5 phosphorylation event was performed\",\n        \"The phosphorylation site(s) on EXPH5 and their effect on Rab27 binding or vesicle trafficking are unknown\",\n        \"Whether ATM-dependent phosphorylation of EXPH5 is relevant in keratinocytes or other physiological contexts is untested\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Major unresolved questions include the structural basis of EXPH5–Rab27 interaction, the identity of downstream tethering/fusion partners at the plasma membrane, how EXPH5 loss leads to keratin cytoskeleton disruption, and whether ATM-mediated phosphorylation of EXPH5 is functionally significant.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No crystal structure or cryo-EM structure of EXPH5 or its complexes exists\",\n        \"The plasma membrane tethering or SNARE partners that cooperate with EXPH5 for vesicle fusion are unidentified\",\n        \"The mechanism connecting EXPH5 vesicle trafficking to keratin intermediate filament organization is unknown\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 1, 4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [0, 3, 4]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 1, 4]},\n      {\"term_id\": \"R-HSA-1500931\", \"supporting_discovery_ids\": [3, 4]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"RAB27B\",\n      \"RAB27A\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}