{"gene":"CD63","run_date":"2026-06-09T22:57:18","timeline":{"discoveries":[{"year":2008,"finding":"CD63 is endocytosed via a clathrin-dependent pathway at the cell surface and is enriched on intraluminal vesicles of late endosomes/multivesicular bodies, from which it can be secreted as exosomes through fusion of endosomes with the plasma membrane. Evidence was also presented for a role of caveolae in CD63 endocytosis.","method":"Subcellular fractionation, live-cell imaging, electron microscopy, review of trafficking studies","journal":"Experimental cell research","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods across multiple labs, well-replicated trafficking pathway","pmids":["18930046"],"is_preprint":false},{"year":2021,"finding":"CD63 traffics from the endoplasmic reticulum to late endosomes where it resides, distinct from CD9 which localizes predominantly at the plasma membrane. A PM-stabilized mutant CD63 is more abundantly released in EVs than wild-type CD63, indicating that in HeLa cells ectosomes (PM-derived) are more prominent than exosomes (endosome-derived). Proteomic comparison identified LAMP1 as likely specific to exosomes and BSG/SLC3A2 as likely ectosome-specific.","method":"Live intracellular tracking, comparative proteomics, pH neutralization experiments, mutant CD63 stabilized at plasma membrane","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (live tracking, proteomics, pH perturbation, mutant analysis) in a single rigorous study","pmids":["34282141"],"is_preprint":false},{"year":2006,"finding":"CD63 was identified as a direct cell-surface binding partner for TIMP-1 by yeast two-hybrid screening, confirmed by co-immunoprecipitation. CD63 forms a complex with TIMP-1 and integrin β1 on the cell surface. shRNA-mediated CD63 knockdown reduced TIMP-1 binding, TIMP-1/integrin β1 co-localization, integrin β1 activation, cell survival signaling, and apoptosis inhibition in 3D matrigel cultures.","method":"Yeast two-hybrid, co-immunoprecipitation, confocal microscopy, shRNA knockdown, 3D matrigel assay","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, yeast two-hybrid, functional shRNA rescue, replicated across multiple downstream studies","pmids":["16917503"],"is_preprint":false},{"year":2000,"finding":"In human endothelial cells, CD63 distributes predominantly to internal membranes of multivesicular-multilamellar late endosomes containing lysobisphosphatidic acid, and is also present in Weibel-Palade bodies. CD63 cycles between late endosomes and Weibel-Palade bodies; treatment with U18666A (mimicking Niemann-Pick C) blocked this cycling and caused accumulation in late endosomes.","method":"Immunofluorescence, subcellular fractionation, drug treatment (U18666A), electron microscopy","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (fractionation, EM, pharmacological perturbation) in a single rigorous study","pmids":["10793155"],"is_preprint":false},{"year":1997,"finding":"CD63 and CD81 form specific complexes with integrin α3β1 that also contain a phosphatidylinositol 4-kinase (PI 4-K, consistent with type II, ~55 kDa). PI 4-K co-purified with CD63 independently of α3β1. These complexes localize to focal complexes at the cell periphery rather than focal adhesions, providing a signaling pathway distinct from conventional integrin/FAK signaling.","method":"Enzymatic assays (PI 4-K activity), co-immunoprecipitation, immunochemical assays, subcellular localization","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — enzymatic reconstitution of PI4K activity in CD63 immunoprecipitates, multiple cell lines tested","pmids":["9006891"],"is_preprint":false},{"year":1995,"finding":"CD63 specifically associates with VLA-3 (α3β1) and VLA-6 (α6β1) integrins but not α2β1 or α5β1, as demonstrated by co-immunoprecipitation from Brij 96 lysates. The cytoplasmic domain of α3 was neither required nor sufficient for CD63 association, indicating interaction elsewhere in the complex.","method":"Monoclonal antibody screening, co-immunoprecipitation, immunofluorescence colocalization, large-scale purification and N-terminal sequencing","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, multiple cell lines, domain mapping, replicated in subsequent studies","pmids":["7629079"],"is_preprint":false},{"year":1993,"finding":"CD63 (granulophysin) is a component of platelet dense granules and lysosomes; it is deficient in Hermansky-Pudlak syndrome platelets. Anti-CD63 antibodies cross-block anti-granulophysin antibodies, and N-terminal sequencing confirmed identity between granulophysin, CD63, ME491, and pltgp40. FACS revealed biphasic CD63 surface expression after thrombin stimulation in control but not HPS platelets, indicating exocytosis-coupled surface exposure.","method":"Immunofluorescence, immunoblotting, FACS, ELISA, N-terminal amino acid sequencing, sequential immunodepletion","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods, disease model validation (HPS), protein identity confirmed by sequencing","pmids":["7682577"],"is_preprint":false},{"year":1993,"finding":"CD63 is a component of Weibel-Palade bodies in human endothelial cells, co-localizing with von Willebrand factor and P-selectin. CD63 biosynthesis and glycosylation pattern in endothelial cells were confirmed by Western blotting of subcellular fractions enriched in Weibel-Palade bodies.","method":"Monoclonal antibody generation, immunofluorescence, Western blotting of subcellular fractions, immunopurification","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Strong — subcellular fractionation combined with immunofluorescence and biochemical confirmation","pmids":["8353283"],"is_preprint":false},{"year":2003,"finding":"CD63 enhances internalization of the H,K-ATPase β-subunit. CD63 co-localizes with and co-precipitates the β-subunit in parietal cells and COS-7 cells. Co-expression with CD63 redistributes the β-subunit from the cell surface to CD63+ intracellular compartments via enhanced endocytosis. This depends on CD63's ability to interact with adaptor protein complexes AP-2 and AP-3.","method":"Co-immunoprecipitation, immunofluorescence, biochemical endocytosis assays, CD63 mutant analysis, COS-7 overexpression","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — Co-IP, functional mutant analysis, orthogonal imaging and biochemical methods in same study","pmids":["14660791"],"is_preprint":false},{"year":2017,"finding":"CD63 is required for efficient exosomal packaging of EBV oncoprotein LMP1 into MVB-derived vesicles. CRISPR/Cas9 knockout of CD63 reduced LMP1-induced particle secretion and severely impaired LMP1 packaging. CD63 KO was associated with disrupted perinuclear localization of LMP1 and increased noncanonical NF-κB and MAPK/ERK activation, while LMP1 trafficking to lipid rafts and canonical NF-κB/PI3K-Akt pathways were unaffected.","method":"CRISPR/Cas9 knockout, nanoparticle tracking analysis, gradient purification, immunoisolation of CD63+ exosomes, western blotting","journal":"Journal of virology","confidence":"High","confidence_rationale":"Tier 2 / Strong — CRISPR KO with multiple orthogonal readouts (vesicle number, cargo packaging, signaling pathway dissection)","pmids":["27974566"],"is_preprint":false},{"year":2018,"finding":"CD63 regulates the intersection of endosomal and autophagic pathways. CD63-dependent vesicle protein secretion opposes LMP1-mediated intracellular signaling including mTOR-associated proteins. CD63 KO resulted in mTOR activation coincident with development of serum-dependent autophagic vacuoles that are acidified in the presence of high LMP1 levels. Disruption of autolysosomal processes increased LMP1 secretion and dampened signal transduction.","method":"CD63 knockout cells, mTOR pathway analysis, autophagy assays, acidification measurements, vesicle secretion quantification","journal":"Journal of virology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — knockout with defined phenotypes but single lab, mechanistic pathway placement partially inferred","pmids":["29212935"],"is_preprint":false},{"year":2021,"finding":"CD63 expression is regulated by the IRE-IRP system via a canonical IRE in the 5' UTR of CD63 mRNA. Iron loading increases CD63 expression and secretion of CD63+ EVs containing ferritin-H and ferritin-L. Under iron loading, intracellular ferritin is transferred via NCOA4 to CD63+ EVs for secretion.","method":"IRE identification in CD63 5'UTR, iron loading experiments, EV isolation, western blotting for ferritin subunits, NCOA4 functional studies","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Strong — canonical IRE identified, mechanistic link to IRP regulation demonstrated with iron loading, multiple orthogonal assays","pmids":["34265052"],"is_preprint":false},{"year":2014,"finding":"RPN2 (ribophorin II, part of N-oligosaccharyltransferase complex) mediates N-glycosylation of CD63. RPN2 knockdown reduces CD63 glycosylation and deregulates its localization. CD63 silencing displaced MDR1 from the cell surface, reducing chemoresistance and invasion ability of breast cancer cells.","method":"RPN2 knockdown, glycosylation analysis, subcellular localization studies, invasion assays, MDR1 localization by immunofluorescence","journal":"Molecular cancer","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — glycosylation writer (RPN2) identified functionally, downstream MDR1 localization linked to CD63 in same study","pmids":["24884960"],"is_preprint":false},{"year":2016,"finding":"CD63 forms a complex with syntenin-1 and ALIX in early CD63-positive endosomes after HPV internalization. This CD63-syntenin-1-ALIX complex controls delivery of internalised HPV particles to multivesicular endosomes; depletion of CD63 or syntenin-1 markedly suppressed infectivity of HPV types 16, 18 and 31 and impaired capsid disassembly.","method":"Co-immunoprecipitation, electron microscopy, immunofluorescence, shRNA depletion, infectivity assays","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, EM confirmation, functional depletion of multiple complex components with specific infectivity readout","pmids":["27578500"],"is_preprint":false},{"year":2017,"finding":"A genome-wide haploid genetic screen identified CD63 as a host factor required for Lujo virus (LUJV) GP-mediated infection. CD63 stimulates pH-activated LUJV GP-mediated membrane fusion (distinct from its role as a cell-surface receptor).","method":"Genome-wide haploid genetic screen, recombinant VSV-LUJV infection assay, functional complementation","journal":"Cell host & microbe","confidence":"High","confidence_rationale":"Tier 2 / Strong — genome-wide screen with functional validation; mechanistic distinction between receptor binding (NRP2) and membrane fusion facilitation (CD63) established","pmids":["29120745"],"is_preprint":false},{"year":1996,"finding":"CD63 associates with CD11/CD18 (Mac-1) and with tyrosine kinase activity (predominantly Src family kinases Lyn and Hck) in neutrophils. CD63 antibody cross-linking triggers a transient activation signal requiring extracellular calcium, upregulates CD11/CD18, and enhances neutrophil adhesion.","method":"Co-immunoprecipitation, protein kinase activity assays, flow cytometry, adhesion assays, calcium depletion experiments","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP demonstrating CD63-CD11/CD18 association and kinase activity, single lab but multiple assays","pmids":["8871662"],"is_preprint":false},{"year":2004,"finding":"CD63 in immature dendritic cells is internalized via the endocytic pathway through early endosomes, lysosomes, and MHC class II-enriched compartments (MIICs) within one hour of stimulation. CD63 is internalized during Saccharomyces cerevisiae phagocytosis and associates with dectin-1. CD63 was found to associate with integrins CD11b and CD18 by immunoprecipitation. CD63 antibodies enhanced DC migration and decreased surface expression of CD29, CD11b, CD18, and α5 integrins.","method":"Confocal immunofluorescence, flow cytometry, immunoprecipitation, phagocytosis assays, migration assays","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP of CD63 with integrins and dectin-1, functional migration assay, intracellular trafficking confirmed by confocal, single lab","pmids":["15130945"],"is_preprint":false},{"year":2008,"finding":"CD63 is involved in granule targeting of neutrophil elastase (NE). CD63 associates with proNE upon co-expression, requiring intact large extracellular loop of CD63. CD63 depletion in HL-60 cells reduced NE processing (proNE to mature NE), reduced constitutive secretion, and caused lack of morphologically normal granules with absence of proNE/NE. CD63 thus participates in ER/Golgi export, cellular retention, and granule targeting of proNE.","method":"Co-immunoprecipitation (COS cells), RNAi in HL-60 cells, CD63 mutant expression, electron microscopy, secretion assays","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Strong — Co-IP, domain mutant, RNAi knockdown with defined morphological and biochemical phenotype, multiple orthogonal methods","pmids":["18669870"],"is_preprint":false},{"year":2013,"finding":"CD63 is required for efficient FcεRI-mediated mast cell degranulation. CD63-deficient mast cells showed significant decrease in FcεRI-mediated β-hexosaminidase and TNF-α release, but normal PMA/ionomycin-induced degranulation, IL-6 secretion, and leukotriene C4 production. CD63-deficient mice showed attenuated cutaneous anaphylactic reactions upon local mast cell reconstitution. No ultrastructural differences in granule morphology or FcεRI-induced global tyrosine phosphorylation/Akt phosphorylation were observed.","method":"CD63 knockout mouse model, bone marrow-derived mast cell development, β-hexosaminidase release assay, passive cutaneous anaphylaxis, Kit(w/w-v) reconstitution","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO with specific in vitro and in vivo phenotypic readouts, pathway specificity determined by comparing multiple stimuli","pmids":["23945142"],"is_preprint":false},{"year":2005,"finding":"Anti-CD63 antibodies inhibit FcεRI-mediated mast cell degranulation but not leukotriene synthesis. This inhibition correlates with CD63-mediated inhibition of mast cell adhesion to fibronectin and vitronectin. Anti-CD63 impairs the Gab2-PI3K pathway essential for both degranulation and adhesion, without affecting global tyrosine phosphorylation or calcium mobilization. Anti-CD63 also inhibited FcεRI-mediated allergic reactions in vivo.","method":"Monoclonal antibody functional assays, adhesion assays, PI3K pathway analysis, calcium mobilization, in vivo allergy model","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — specific pathway (Gab2-PI3K) identified as downstream of CD63, in vitro and in vivo confirmation, multiple mechanistic readouts","pmids":["15684326"],"is_preprint":false},{"year":2005,"finding":"Upon platelet activation and exocytosis, CD63 relocates from dense granule/lysosome membranes to the plasma membrane where it associates with αIIbβ3-CD9 complex and the actin cytoskeleton in an αIIbβ3-dependent manner. Anti-CD63 antibody (D545) inhibited platelet spreading, F-actin reorganization, vinculin redistribution, tyrosine phosphorylation, and FAK phosphorylation on immobilized fibrinogen. CD63 co-immunoprecipitated with a PI 4-kinase type II activity regardless of activation state.","method":"Immunofluorescence, confocal imaging, co-immunoprecipitation, lipid kinase assays, flow cytometry","journal":"Thrombosis and haemostasis","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP of CD63-PI4K, functional antibody inhibition with multiple cytoskeletal readouts, single lab","pmids":["15711748"],"is_preprint":false},{"year":2008,"finding":"CD63 deficiency in mice results in altered water balance: increased urinary flow, water intake, reduced urine osmolality, and abnormal intracellular lamellar inclusions in principal cells of the collecting duct. Despite CD63 abundance in late endosomes/lysosomes, loss of CD63 does not cause obvious endosomal/lysosomal abnormalities, suggesting functional compensation by other tetraspanins in most tissues.","method":"CD63 knockout mouse generation and analysis, histology, electron microscopy, water balance measurements, immune cell profiling","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO mouse model with specific renal phenotype identified by EM and physiological measurements","pmids":["19075008"],"is_preprint":false},{"year":2008,"finding":"CD63 associates with receptor-linked tyrosine phosphatase alpha (RPTPα) and c-Src in renal cortex and transfected 293T cells. CD63 expression stimulates c-Src activity (increased pY416, decreased pY527). The CD63-RPTPα-c-Src complex enhances c-Src-induced inhibition of ROMK1 potassium channels and increases ROMK1 tyrosine phosphorylation.","method":"Co-immunoprecipitation (native tissue and transfected cells), two-electrode voltage clamp in Xenopus oocytes, phosphorylation analysis, herbimycin A inhibition","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — in vitro functional assay (oocyte voltage clamp), Co-IP in native tissue, kinase activity measured, multiple orthogonal methods","pmids":["18211905"],"is_preprint":false},{"year":2016,"finding":"CD63 interacts with human organic cation transporter 2 (hOCT2) as demonstrated by split-ubiquitin yeast 2-hybrid, pull-down, TIRF microscopy, FRET, and biotinylation assays. CD63 overexpression affects hOCT2 localization in HEK293 cells, and CD63-KO mice show impaired insertion of the mouse OCT2 ortholog into the proper basolateral membrane domain. CD63 and hOCT2 co-localize with Rab4, implicating CD63 in recycling from sorting endosomes to the basolateral membrane in polarized epithelia.","method":"Split-ubiquitin yeast 2-hybrid, pull-down, TIRF microscopy, FRET, biotinylation assay, CD63 KO mouse analysis, MDCK polarized cell studies","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal interaction methods plus KO mouse validation with functional localization readout","pmids":["28031320"],"is_preprint":false},{"year":2006,"finding":"CD63 recruitment to Cryptococcus neoformans-containing phagosomes (but not polystyrene bead phagosomes) requires phagosomal acidification and occurs independently of MHC class II and LAMP-1. This selective recruitment was demonstrated by live-cell imaging with mRFP-tagged CD63 in primary bone marrow-derived macrophages.","method":"Live-cell imaging with fluorescent-tagged CD63, acidification inhibitors, MyD88-deficient macrophages, primary bone marrow-derived cultures","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — live imaging in primary cells with pharmacological dissection of acidification requirement and independence from MHC II/LAMP-1","pmids":["17043215"],"is_preprint":false},{"year":2011,"finding":"CD63 knockdown in EBV-transformed B cells (LCL) increased CD4+ T cell recognition of EBV antigens. This was not due to enhanced antigen processing or changes in MHC II expression. Exosome production significantly increased following CD63 knockdown, suggesting that CD63 negatively regulates exosome secretion and thereby MHC II-dependent T cell stimulation.","method":"shRNA knockdown, CD4+ T cell activation assays, exosome purification and quantification, MHC II expression analysis","journal":"European journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — shRNA with defined mechanistic outcome, but single lab and mechanism partially inferred from exosome quantification","pmids":["21660937"],"is_preprint":false},{"year":2010,"finding":"TIMP-1 signaling via CD63 and integrin β1 mediates anoikis resistance in melanoma cells through PI3-K signaling independently of Akt phosphorylation. Differential association of the TIMP1-CD63-β1-integrin complex was observed along melanoma progression steps, demonstrated by co-immunoprecipitation.","method":"Co-immunoprecipitation, flow cytometry, PI3-K inhibitors (Wortmannin, LY294002), anchorage impediment model","journal":"Molecular cancer","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP of complex, pharmacological pathway dissection, single lab","pmids":["23522389"],"is_preprint":false},{"year":2015,"finding":"TIMP-1 induces neutrophilia and granulopoiesis through CD63 signaling. The CD63-binding domain of TIMP-1 (distinct from its protease-inhibitory domain) was necessary and sufficient to augment granulopoiesis. Ablation of CD63 abolished both TIMP-1-induced neutrophilia and enhanced granulopoiesis in the bone marrow.","method":"TIMP-1 domain variants, CD63 knockout mice, BrdU pulse-labeling, bone marrow progenitor analysis, gene expression profiling","journal":"Haematologica","confidence":"High","confidence_rationale":"Tier 2 / Strong — domain dissection of TIMP-1 combined with CD63 KO mouse rescue experiment, mechanistic pathway established","pmids":["26001794"],"is_preprint":false},{"year":2014,"finding":"TIMP-1 binding to CD63 activates β1 integrin-mediated signaling through Akt and FAK phosphorylation, enhancing focal adhesion formation, cytoskeletal reorganization, and migration of human neural stem cells. shRNA ablation of CD63 attenuated TIMP-1-induced migration and spreading; blocking β1 integrin or PI3K also blocked migration.","method":"shRNA knockdown, microarray/proteomics, migration/adhesion assays, Akt/FAK phosphorylation analysis, antibody blocking","journal":"The Biochemical journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — shRNA with signaling pathway dissection, single lab, multiple downstream readouts","pmids":["24635319"],"is_preprint":false},{"year":2019,"finding":"TIMP-1/CD63/ITGB1/FAK signaling axis drives hypermotility in Toxoplasma gondii-infected dendritic cells. shRNA silencing of TIMP-1, CD63, or ITGB1 inhibited DC hypermotility; FAK inhibition (and inhibitors of SRC and PI3K) also abrogated hypermotility. This signaling cascade is hijacked by T. gondii for systemic dissemination.","method":"shRNA knockdown, antibody blockade, migration assays, kinase inhibitors","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pathway established by multiple gene silencing steps with defined functional readout, single lab","pmids":["30635444"],"is_preprint":false},{"year":2008,"finding":"CD63 is required for HIV-1 replication in macrophages and cell lines. CD63-specific siRNA inhibited HIV replication in macrophages (>90% knockdown) and in U373-MAGI cells, suggesting roles in both early infection events and later post-integration replication steps.","method":"siRNA knockdown, HIV replication assay, macrophage and cell line models","journal":"Virology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA with specific viral replication readout, single lab, mechanistic step not fully defined","pmids":["18682304"],"is_preprint":false},{"year":2014,"finding":"CD63 plays a dual role in HIV-1 replication: supports Env-mediated (CD4/CCR5-dependent) entry or fusion (VSV/MLV pseudotype entry unaffected by CD63 silencing) and a post-integration step. CD63 co-localizes and co-immunoprecipitates with CD4 in macrophages, and CD63 silencing reduced expression of early HIV protein Tat and interaction with Gag, as well as late protein p24.","method":"siRNA knockdown, pseudotyped virus infectivity assays, co-immunoprecipitation, confocal microscopy, primary CD4+ T cells and dendritic cells","journal":"Virology journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pseudotype assays mechanistically distinguish entry role; Co-IP of CD63-CD4 and CD63-Gag, single lab","pmids":["24507450"],"is_preprint":false},{"year":2010,"finding":"Ameloblastin binds CD63 and promotes CD63 binding to integrin β1. The CD63-integrin β1 interaction induces Src kinase inactivation via CD63 binding to Src. This mechanism promotes osteogenic differentiation, and anti-CD63 antibody or constitutively active Src reversed these effects.","method":"Co-immunoprecipitation, anti-CD63 antibody blockade, constitutively active Src overexpression, osteogenic differentiation assays","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP of CD63-Src complex, antibody/genetic rescue, single lab, multiple mechanistic readouts","pmids":["21149578"],"is_preprint":false},{"year":2011,"finding":"CD63 mediates downregulation of CXCR4 in activated B cells by recruiting CXCR4 to late endosomes. BCL6 was found on the chromatin of the CD63 gene in resting B cells (functioning as a transcriptional repressor). siRNA knockdown of CD63 mRNA in Bcl6-deficient B cells upregulated CXCR4 expression, confirming CD63-dependent CXCR4 endosomal recruitment.","method":"siRNA knockdown, flow cytometry, chromatin immunoprecipitation (Bcl6 on CD63 gene), Bcl6 inhibitor experiments","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP showing Bcl6 on CD63 locus, functional siRNA with CXCR4 readout, single lab","pmids":["21270405"],"is_preprint":false},{"year":2021,"finding":"CD63 is required to sustain TGFβ signaling in hematopoietic stem cells through its interaction with TGFβ receptors I and II. CD63-deficient HSCs exhibit impaired quiescence and long-term repopulating capacity. CD63-high HSCs are more quiescent with greater self-renewal and myeloid differentiation than CD63-low/negative HSCs.","method":"CD63 knockout mice, HSC transplantation, TGFβ signaling assays, co-immunoprecipitation (CD63 with TGFβRI/II), irradiation and 5-FU stress models","journal":"Cell death and differentiation","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO mouse with multiple phenotypic readouts plus Co-IP identifying TGFβ receptor interaction as mechanistic basis","pmids":["34363017"],"is_preprint":false},{"year":2014,"finding":"CD63 knockdown induces epithelial-like phenotype in melanoma cells with increased E-cadherin, downregulation of N-cadherin and Snail, and reduced β-catenin protein. β-catenin inhibitors mimicked this phenotype. CD63 overexpression reduces motility, invasiveness, protease activities, and tumor growth. CD63 regulates cell plasticity via PI3K/AKT-GSK3β-β-catenin pathway.","method":"siRNA knockdown, stable overexpression, β-catenin inhibitors, PI3K/AKT and GSK3β inhibitors, invasion assays, in vivo tumor xenograft","journal":"International journal of cancer","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss and gain of function with pathway inhibitor rescue, single lab","pmids":["25354204"],"is_preprint":false},{"year":1992,"finding":"The CD63 gene (ME491) consists of eight exons spanning 4 kb. The 5'-flanking region lacks a TATA box but contains GC-rich sequences with SP1 and ETF binding sites, and a functional AP-1 binding site that positively regulates gene expression, as demonstrated by deletion mutant analysis.","method":"Genomic cloning, primer extension, reporter gene assays, 5'-deletion mutant analysis","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional promoter deletion analysis with reporter, single lab","pmids":["1599482"],"is_preprint":false},{"year":2007,"finding":"Amelogenin interacts with CD63 via specific binding regions: the amelogenin PLSPILPELPLEAW region binds CD63 residues 165-205 (within the large extracellular loop EC2). This interaction mediates rapid endocytic uptake of amelogenin into CD63/LAMP1-positive vesicles in cells.","method":"In vitro binding assays, deletion/mutation mapping of binding regions, cell uptake experiments, confocal microscopy","journal":"The Biochemical journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — domain mapping of binding regions, functional cellular uptake confirmation, single lab","pmids":["17708745"],"is_preprint":false},{"year":2020,"finding":"CD63 induces STAT3 activation to maintain the phenotype and function of CD63+ cancer-associated fibroblasts (CAFs). CD63+ CAFs secrete exosomes enriched in miR-22 (packaged via SFRS1) that confer tamoxifen resistance to breast cancer cells.","method":"Single-cell RNA sequencing, exosome isolation, SFRS1 functional studies, CD63-neutralizing antibody, STAT3 activation assays, xenograft models","journal":"Advanced science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional antibody blockade and mechanistic identification of SFRS1 as miR-22 packaging factor, single lab","pmids":["33173749"],"is_preprint":false},{"year":2002,"finding":"CD63 mobilization from crystalloid granule membranes to the cell periphery and plasma membrane is associated with eosinophil mediator release (β-hexosaminidase, eosinophil peroxidase, RANTES). IFN-γ-induced CD63 mobilization preceded RANTES release, consistent with piecemeal degranulation. Both CD63 mobilization and mediator release were inhibited by dexamethasone and the tyrosine kinase inhibitor genistein.","method":"Confocal immunofluorescence, flow cytometry, secretion assays, pharmacological inhibition","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-inhibition of CD63 mobilization and degranulation with kinase inhibitors implicates tyrosine kinase pathway, single lab","pmids":["12010805"],"is_preprint":false},{"year":2020,"finding":"CD63 negatively regulates hepatocellular carcinoma by suppressing IL-6/IL-27-induced STAT3 activation. CD63 overexpression inhibited HCC cell proliferation and migration, while knockdown promoted these; STAT3 blockade impaired the promotive effects of CD63 knockdown.","method":"Overexpression, knockdown, RNA-sequencing, dual-luciferase reporter, STAT3 inhibition, xenograft model","journal":"Journal of cellular and molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RNA-seq pathway identification with STAT3 inhibitor rescue, multiple cellular readouts, single lab","pmids":["33277798"],"is_preprint":false}],"current_model":"CD63 is a tetraspanin membrane protein that cycles between late endosomes/lysosomes, secretory organelles (dense granules, Weibel-Palade bodies), and the plasma membrane via clathrin- and adaptor protein (AP-2/AP-3)-dependent endocytic trafficking; it serves as an adaptor that links interaction partners (including TIMP-1, integrins α3β1/α6β1, H,K-ATPase β-subunit, OCT2, TGFβ receptors, and ROMK channels) to the endocytic/lysosomal machinery, recruits PI 4-kinase type II into signaling complexes at the cell surface, regulates exosomal cargo sorting (including viral LMP1 and ferritin under iron loading via the IRE-IRP system), modulates mast cell FcεRI-mediated degranulation through the Gab2-PI3K pathway, and controls hematopoietic stem cell quiescence by sustaining TGFβ receptor signaling."},"narrative":{"mechanistic_narrative":"CD63 is a tetraspanin membrane protein that organizes endocytic and secretory trafficking and acts as a membrane scaffold linking transmembrane partners to the endo-lysosomal machinery [PMID:18930046, PMID:14660791]. It traffics from the ER to late endosomes/multivesicular bodies, where it is enriched on intraluminal vesicles and from which it can be released as exosomes, while a pool also cycles to the plasma membrane and back; comparison with plasma-membrane-stabilized mutants shows that CD63's residence on internal membranes is a key determinant of whether it is sorted into endosome-derived versus plasma-membrane-derived vesicles [PMID:18930046, PMID:34282141]. CD63 promotes internalization of partner membrane proteins through its capacity to engage the clathrin adaptor complexes AP-2 and AP-3, redirecting cargo such as the H,K-ATPase β-subunit from the surface to CD63+ intracellular compartments [PMID:18930046, PMID:14660791], and it likewise governs basolateral membrane insertion and recycling of the organic cation transporter OCT2 via Rab4-positive sorting endosomes [PMID:28031320] and endosomal recruitment of CXCR4 in activated B cells [PMID:21270405]. In secretory and granule-bearing cells CD63 is a constituent of platelet dense granules and lysosomes, Weibel-Palade bodies, and crystalloid/secretory granules, relocating to the plasma membrane upon stimulated exocytosis [PMID:10793155, PMID:7682577, PMID:8353283, PMID:12010805]; it is required for ER/Golgi export and granule targeting of neutrophil elastase through its large extracellular loop [PMID:18669870] and for FcεRI-mediated mast cell degranulation acting via the Gab2-PI3K pathway [PMID:23945142, PMID:15684326]. CD63 nucleates signaling complexes at the cell surface, associating with integrins α3β1 and α6β1 together with a type II PI 4-kinase in peripheral focal complexes [PMID:9006891, PMID:7629079], and serving as the cell-surface receptor for TIMP-1, which it couples to β1 integrin to drive PI3K/FAK-dependent survival, migration, and granulopoiesis [PMID:16917503, PMID:26001794, PMID:24635319]. It further modulates Src-family kinase activity in complexes with RPTPα to regulate ROMK channels [PMID:18211905]. CD63 controls extracellular vesicle cargo sorting, being required for exosomal packaging of the EBV oncoprotein LMP1 [PMID:27974566] and for iron-loading-induced secretion of ferritin-containing EVs through the IRE-IRP system and NCOA4 [PMID:34265052], and it is exploited by multiple pathogens including human papillomavirus (via a CD63-syntenin-1-ALIX complex) [PMID:27578500], Lujo virus (facilitating pH-activated membrane fusion) [PMID:29120745], and HIV-1 [PMID:18682304, PMID:24507450]. At the organismal level CD63 sustains TGFβ receptor signaling to maintain hematopoietic stem cell quiescence and repopulating capacity [PMID:34363017], and its loss in mice produces a selective renal water-balance defect with lamellar inclusions in collecting-duct principal cells, indicating tetraspanin redundancy in most tissues [PMID:19075008]. CD63 expression is N-glycosylated by the RPN2/oligosaccharyltransferase complex, which controls its localization [PMID:24884960], and is transcriptionally repressed by BCL6 [PMID:21270405] from a TATA-less, AP-1-responsive promoter [PMID:1599482].","teleology":[{"year":1993,"claim":"Establishing where CD63 resides defined it as a regulated-secretory and granule membrane protein rather than a static surface antigen, linking it to a human bleeding disorder.","evidence":"Immunoblotting, FACS, N-terminal sequencing and HPS platelet analysis identifying CD63/granulophysin in dense granules, lysosomes and Weibel-Palade bodies with thrombin-induced surface exposure","pmids":["7682577","8353283"],"confidence":"High","gaps":["Did not define the trafficking machinery routing CD63 to these granules","Molecular basis of the HPS deficiency not resolved"]},{"year":1997,"claim":"Showing CD63 forms integrin-α3β1/α6β1 complexes containing a PI 4-kinase established it as a scaffold nucleating a peripheral signaling pathway distinct from FAK/focal-adhesion signaling.","evidence":"Co-immunoprecipitation, PI 4-K enzymatic assays in CD63 immunoprecipitates, and localization to focal complexes across cell lines (building on 1995 integrin association mapping)","pmids":["9006891","7629079"],"confidence":"High","gaps":["Direct versus indirect nature of the CD63-PI4K interaction unresolved","Physiological output of the integrin-PI4K complex not defined"]},{"year":2003,"claim":"Demonstrating CD63 drives internalization of the H,K-ATPase β-subunit via AP-2/AP-3 explained mechanistically how CD63 sorts partner membrane proteins into the endocytic pathway.","evidence":"Co-IP, biochemical endocytosis assays and CD63 adaptor-binding mutants in parietal and COS-7 cells","pmids":["14660791"],"confidence":"High","gaps":["Whether all CD63 cargo use the same AP-dependent route untested","Stoichiometry of CD63-cargo-adaptor assembly unknown"]},{"year":2006,"claim":"Identifying CD63 as a direct TIMP-1 receptor coupling to β1 integrin connected an extracellular ligand to intracellular survival signaling.","evidence":"Yeast two-hybrid, reciprocal Co-IP, shRNA knockdown and 3D matrigel survival assays","pmids":["16917503"],"confidence":"High","gaps":["Direct binding interface on CD63 not mapped","Whether TIMP-1 signaling is protease-independent unresolved at this stage"]},{"year":2008,"claim":"Defining CD63's clathrin-dependent endocytosis and its loss-of-function phenotype in mice clarified the trafficking itinerary and revealed tetraspanin redundancy in vivo.","evidence":"Subcellular fractionation, live imaging and EM of trafficking, alongside CD63 knockout mice showing a selective collecting-duct water-balance defect","pmids":["18930046","19075008"],"confidence":"High","gaps":["Identity of compensating tetraspanins not established","Mechanistic basis of the renal lamellar inclusions undefined"]},{"year":2008,"claim":"CD63 was shown to act in two distinct signaling and biosynthetic contexts: a renal RPTPα/c-Src complex regulating ROMK channels, and granule targeting of neutrophil elastase via its large extracellular loop.","evidence":"Co-IP in native tissue and transfected cells with oocyte voltage-clamp electrophysiology; Co-IP, domain mutants, RNAi and EM in HL-60 cells","pmids":["18211905","18669870"],"confidence":"High","gaps":["How CD63 modulates Src catalytic activity structurally unknown","Whether elastase targeting generalizes to other granule proteases untested"]},{"year":2013,"claim":"Genetic CD63 loss established a non-redundant requirement for FcεRI-triggered mast cell degranulation, refining earlier antibody-based observations to a defined Gab2-PI3K axis.","evidence":"CD63 knockout mast cells and mice with β-hexosaminidase/TNF-α release assays and passive cutaneous anaphylaxis, complementing earlier anti-CD63 Gab2-PI3K pathway studies","pmids":["23945142","15684326"],"confidence":"High","gaps":["How CD63 selectively couples to the FcεRI but not PMA/ionomycin pathway unresolved","Direct molecular link between CD63 and Gab2 not shown"]},{"year":2017,"claim":"CRISPR knockout showing CD63 is required for exosomal LMP1 packaging established a causal role in selecting cargo into MVB-derived vesicles and in restraining intracellular oncogenic signaling.","evidence":"CRISPR/Cas9 knockout, nanoparticle tracking, exosome immunoisolation and signaling pathway dissection","pmids":["27974566","29212935"],"confidence":"High","gaps":["Direct CD63-LMP1 contact not demonstrated","Generalizability of CD63-dependent cargo selection to endogenous proteins unclear"]},{"year":2021,"claim":"Distinguishing endosome- from plasma-membrane-derived vesicles and identifying an IRE-controlled, ferritin-loaded EV pathway refined how CD63's subcellular residence dictates vesicle origin and cargo.","evidence":"Live intracellular tracking, comparative proteomics and PM-stabilized mutants; IRE identification in CD63 5'UTR with iron-loading and NCOA4 EV analyses","pmids":["34282141","34265052"],"confidence":"High","gaps":["Sorting signals routing CD63 to exosomes versus ectosomes incompletely defined","Mechanism by which NCOA4-bound ferritin reaches CD63+ EVs unresolved"]},{"year":2021,"claim":"Demonstrating CD63 sustains TGFβ receptor signaling to enforce HSC quiescence linked its receptor-scaffolding activity to a stem-cell maintenance function.","evidence":"CD63 knockout mice, HSC transplantation, TGFβ signaling assays and Co-IP with TGFβRI/II","pmids":["34363017"],"confidence":"High","gaps":["Whether CD63 stabilizes receptors at the surface or in endosomes unresolved","Direct versus indirect CD63-TGFβ receptor binding not dissected"]},{"year":null,"claim":"How CD63 selects specific cargo and partners for distinct destinations (exosome versus ectosome, degranulation versus surface signaling) and what structural features of its extracellular loop and adaptor-binding motifs determine these choices remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unifying structural model of CD63-cargo-adaptor assembly","Determinants partitioning CD63 between competing trafficking fates undefined","Extent of functional redundancy with other tetraspanins across tissues unquantified"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[2,8,23,34]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[8,22,34]},{"term_id":"GO:0001618","term_label":"virus receptor activity","supporting_discovery_ids":[14,30,31]}],"localization":[{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[0,3,6,21]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[0,1,3,16,23,33]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,1,6,20]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[0,1,9,11]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[1,17]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,1,8,9,11]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[8,23,33]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[18,19,25,27]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2,4,22,34]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[9,13,14,30,31]}],"complexes":["CD63-syntenin-1-ALIX complex","CD63-integrin α3β1/α6β1-PI4K type II complex","TIMP-1-CD63-integrin β1 complex","CD63-RPTPα-c-Src complex"],"partners":["TIMP1","ITGB1","ITGA3","TGFBR1","SLC22A2","RPTPA","SDCBP","PDCD6IP"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P08962","full_name":"CD63 antigen","aliases":["Granulophysin","Lysosomal-associated membrane protein 3","LAMP-3","Lysosome integral membrane protein 1","Limp1","Melanoma-associated antigen ME491","OMA81H","Ocular melanoma-associated antigen","Tetraspanin-30","Tspan-30"],"length_aa":238,"mass_kda":25.6,"function":"Functions as a cell surface receptor for TIMP1 and plays a role in the activation of cellular signaling cascades. Plays a role in the activation of ITGB1 and integrin signaling, leading to the activation of AKT, FAK/PTK2 and MAP kinases. Promotes cell survival, reorganization of the actin cytoskeleton, cell adhesion, spreading and migration, via its role in the activation of AKT and FAK/PTK2. Plays a role in VEGFA signaling via its role in regulating the internalization of KDR/VEGFR2. Plays a role in intracellular vesicular transport processes, and is required for normal trafficking of the PMEL luminal domain that is essential for the development and maturation of melanocytes. Plays a role in the adhesion of leukocytes onto endothelial cells via its role in the regulation of SELP trafficking. May play a role in mast cell degranulation in response to Ms4a2/FceRI stimulation, but not in mast cell degranulation in response to other stimuli","subcellular_location":"Cell membrane; Lysosome membrane; Late endosome membrane; Endosome, multivesicular body; Melanosome; Secreted, extracellular exosome; Cell surface","url":"https://www.uniprot.org/uniprotkb/P08962/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CD63","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000135404","cell_line_id":"CID000398","localizations":[{"compartment":"vesicles","grade":3}],"interactors":[{"gene":"CANX","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID000398","total_profiled":1310},"omim":[{"mim_id":"619535","title":"RING FINGER PROTEIN 115; RNF115","url":"https://www.omim.org/entry/619535"},{"mim_id":"618049","title":"PARKINSONISM-DYSTONIA 2, INFANTILE-ONSET; PKDYS2","url":"https://www.omim.org/entry/618049"},{"mim_id":"615851","title":"PONTOCEREBELLAR HYPOPLASIA, TYPE 2E; PCH2E","url":"https://www.omim.org/entry/615851"},{"mim_id":"615850","title":"VPS53 SUBUNIT OF GARP COMPLEX; VPS53","url":"https://www.omim.org/entry/615850"},{"mim_id":"615692","title":"CHITINASE DOMAIN-CONTAINING PROTEIN 1; CHID1","url":"https://www.omim.org/entry/615692"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Vesicles","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/CD63"},"hgnc":{"alias_symbol":["ME491","TSPAN30","HOP-26","Pltgp40","AD1"],"prev_symbol":["MLA1"]},"alphafold":{"accession":"P08962","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P08962","model_url":"https://alphafold.ebi.ac.uk/files/AF-P08962-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P08962-F1-predicted_aligned_error_v6.png","plddt_mean":90.62},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CD63","jax_strain_url":"https://www.jax.org/strain/search?query=CD63"},"sequence":{"accession":"P08962","fasta_url":"https://rest.uniprot.org/uniprotkb/P08962.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P08962/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P08962"}},"corpus_meta":[{"pmid":"34282141","id":"PMC_34282141","title":"Specificities of exosome versus small ectosome secretion revealed by live intracellular tracking of CD63 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Evidence was also presented for a role of caveolae in CD63 endocytosis.\",\n      \"method\": \"Subcellular fractionation, live-cell imaging, electron microscopy, review of trafficking studies\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods across multiple labs, well-replicated trafficking pathway\",\n      \"pmids\": [\"18930046\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CD63 traffics from the endoplasmic reticulum to late endosomes where it resides, distinct from CD9 which localizes predominantly at the plasma membrane. A PM-stabilized mutant CD63 is more abundantly released in EVs than wild-type CD63, indicating that in HeLa cells ectosomes (PM-derived) are more prominent than exosomes (endosome-derived). Proteomic comparison identified LAMP1 as likely specific to exosomes and BSG/SLC3A2 as likely ectosome-specific.\",\n      \"method\": \"Live intracellular tracking, comparative proteomics, pH neutralization experiments, mutant CD63 stabilized at plasma membrane\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (live tracking, proteomics, pH perturbation, mutant analysis) in a single rigorous study\",\n      \"pmids\": [\"34282141\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"CD63 was identified as a direct cell-surface binding partner for TIMP-1 by yeast two-hybrid screening, confirmed by co-immunoprecipitation. CD63 forms a complex with TIMP-1 and integrin β1 on the cell surface. shRNA-mediated CD63 knockdown reduced TIMP-1 binding, TIMP-1/integrin β1 co-localization, integrin β1 activation, cell survival signaling, and apoptosis inhibition in 3D matrigel cultures.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation, confocal microscopy, shRNA knockdown, 3D matrigel assay\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, yeast two-hybrid, functional shRNA rescue, replicated across multiple downstream studies\",\n      \"pmids\": [\"16917503\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"In human endothelial cells, CD63 distributes predominantly to internal membranes of multivesicular-multilamellar late endosomes containing lysobisphosphatidic acid, and is also present in Weibel-Palade bodies. CD63 cycles between late endosomes and Weibel-Palade bodies; treatment with U18666A (mimicking Niemann-Pick C) blocked this cycling and caused accumulation in late endosomes.\",\n      \"method\": \"Immunofluorescence, subcellular fractionation, drug treatment (U18666A), electron microscopy\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (fractionation, EM, pharmacological perturbation) in a single rigorous study\",\n      \"pmids\": [\"10793155\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"CD63 and CD81 form specific complexes with integrin α3β1 that also contain a phosphatidylinositol 4-kinase (PI 4-K, consistent with type II, ~55 kDa). PI 4-K co-purified with CD63 independently of α3β1. These complexes localize to focal complexes at the cell periphery rather than focal adhesions, providing a signaling pathway distinct from conventional integrin/FAK signaling.\",\n      \"method\": \"Enzymatic assays (PI 4-K activity), co-immunoprecipitation, immunochemical assays, subcellular localization\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — enzymatic reconstitution of PI4K activity in CD63 immunoprecipitates, multiple cell lines tested\",\n      \"pmids\": [\"9006891\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"CD63 specifically associates with VLA-3 (α3β1) and VLA-6 (α6β1) integrins but not α2β1 or α5β1, as demonstrated by co-immunoprecipitation from Brij 96 lysates. The cytoplasmic domain of α3 was neither required nor sufficient for CD63 association, indicating interaction elsewhere in the complex.\",\n      \"method\": \"Monoclonal antibody screening, co-immunoprecipitation, immunofluorescence colocalization, large-scale purification and N-terminal sequencing\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, multiple cell lines, domain mapping, replicated in subsequent studies\",\n      \"pmids\": [\"7629079\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"CD63 (granulophysin) is a component of platelet dense granules and lysosomes; it is deficient in Hermansky-Pudlak syndrome platelets. Anti-CD63 antibodies cross-block anti-granulophysin antibodies, and N-terminal sequencing confirmed identity between granulophysin, CD63, ME491, and pltgp40. FACS revealed biphasic CD63 surface expression after thrombin stimulation in control but not HPS platelets, indicating exocytosis-coupled surface exposure.\",\n      \"method\": \"Immunofluorescence, immunoblotting, FACS, ELISA, N-terminal amino acid sequencing, sequential immunodepletion\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods, disease model validation (HPS), protein identity confirmed by sequencing\",\n      \"pmids\": [\"7682577\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"CD63 is a component of Weibel-Palade bodies in human endothelial cells, co-localizing with von Willebrand factor and P-selectin. CD63 biosynthesis and glycosylation pattern in endothelial cells were confirmed by Western blotting of subcellular fractions enriched in Weibel-Palade bodies.\",\n      \"method\": \"Monoclonal antibody generation, immunofluorescence, Western blotting of subcellular fractions, immunopurification\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — subcellular fractionation combined with immunofluorescence and biochemical confirmation\",\n      \"pmids\": [\"8353283\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"CD63 enhances internalization of the H,K-ATPase β-subunit. CD63 co-localizes with and co-precipitates the β-subunit in parietal cells and COS-7 cells. Co-expression with CD63 redistributes the β-subunit from the cell surface to CD63+ intracellular compartments via enhanced endocytosis. This depends on CD63's ability to interact with adaptor protein complexes AP-2 and AP-3.\",\n      \"method\": \"Co-immunoprecipitation, immunofluorescence, biochemical endocytosis assays, CD63 mutant analysis, COS-7 overexpression\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — Co-IP, functional mutant analysis, orthogonal imaging and biochemical methods in same study\",\n      \"pmids\": [\"14660791\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CD63 is required for efficient exosomal packaging of EBV oncoprotein LMP1 into MVB-derived vesicles. CRISPR/Cas9 knockout of CD63 reduced LMP1-induced particle secretion and severely impaired LMP1 packaging. CD63 KO was associated with disrupted perinuclear localization of LMP1 and increased noncanonical NF-κB and MAPK/ERK activation, while LMP1 trafficking to lipid rafts and canonical NF-κB/PI3K-Akt pathways were unaffected.\",\n      \"method\": \"CRISPR/Cas9 knockout, nanoparticle tracking analysis, gradient purification, immunoisolation of CD63+ exosomes, western blotting\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — CRISPR KO with multiple orthogonal readouts (vesicle number, cargo packaging, signaling pathway dissection)\",\n      \"pmids\": [\"27974566\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CD63 regulates the intersection of endosomal and autophagic pathways. CD63-dependent vesicle protein secretion opposes LMP1-mediated intracellular signaling including mTOR-associated proteins. CD63 KO resulted in mTOR activation coincident with development of serum-dependent autophagic vacuoles that are acidified in the presence of high LMP1 levels. Disruption of autolysosomal processes increased LMP1 secretion and dampened signal transduction.\",\n      \"method\": \"CD63 knockout cells, mTOR pathway analysis, autophagy assays, acidification measurements, vesicle secretion quantification\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — knockout with defined phenotypes but single lab, mechanistic pathway placement partially inferred\",\n      \"pmids\": [\"29212935\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CD63 expression is regulated by the IRE-IRP system via a canonical IRE in the 5' UTR of CD63 mRNA. Iron loading increases CD63 expression and secretion of CD63+ EVs containing ferritin-H and ferritin-L. Under iron loading, intracellular ferritin is transferred via NCOA4 to CD63+ EVs for secretion.\",\n      \"method\": \"IRE identification in CD63 5'UTR, iron loading experiments, EV isolation, western blotting for ferritin subunits, NCOA4 functional studies\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — canonical IRE identified, mechanistic link to IRP regulation demonstrated with iron loading, multiple orthogonal assays\",\n      \"pmids\": [\"34265052\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"RPN2 (ribophorin II, part of N-oligosaccharyltransferase complex) mediates N-glycosylation of CD63. RPN2 knockdown reduces CD63 glycosylation and deregulates its localization. CD63 silencing displaced MDR1 from the cell surface, reducing chemoresistance and invasion ability of breast cancer cells.\",\n      \"method\": \"RPN2 knockdown, glycosylation analysis, subcellular localization studies, invasion assays, MDR1 localization by immunofluorescence\",\n      \"journal\": \"Molecular cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — glycosylation writer (RPN2) identified functionally, downstream MDR1 localization linked to CD63 in same study\",\n      \"pmids\": [\"24884960\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"CD63 forms a complex with syntenin-1 and ALIX in early CD63-positive endosomes after HPV internalization. This CD63-syntenin-1-ALIX complex controls delivery of internalised HPV particles to multivesicular endosomes; depletion of CD63 or syntenin-1 markedly suppressed infectivity of HPV types 16, 18 and 31 and impaired capsid disassembly.\",\n      \"method\": \"Co-immunoprecipitation, electron microscopy, immunofluorescence, shRNA depletion, infectivity assays\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, EM confirmation, functional depletion of multiple complex components with specific infectivity readout\",\n      \"pmids\": [\"27578500\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"A genome-wide haploid genetic screen identified CD63 as a host factor required for Lujo virus (LUJV) GP-mediated infection. CD63 stimulates pH-activated LUJV GP-mediated membrane fusion (distinct from its role as a cell-surface receptor).\",\n      \"method\": \"Genome-wide haploid genetic screen, recombinant VSV-LUJV infection assay, functional complementation\",\n      \"journal\": \"Cell host & microbe\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genome-wide screen with functional validation; mechanistic distinction between receptor binding (NRP2) and membrane fusion facilitation (CD63) established\",\n      \"pmids\": [\"29120745\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"CD63 associates with CD11/CD18 (Mac-1) and with tyrosine kinase activity (predominantly Src family kinases Lyn and Hck) in neutrophils. CD63 antibody cross-linking triggers a transient activation signal requiring extracellular calcium, upregulates CD11/CD18, and enhances neutrophil adhesion.\",\n      \"method\": \"Co-immunoprecipitation, protein kinase activity assays, flow cytometry, adhesion assays, calcium depletion experiments\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP demonstrating CD63-CD11/CD18 association and kinase activity, single lab but multiple assays\",\n      \"pmids\": [\"8871662\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"CD63 in immature dendritic cells is internalized via the endocytic pathway through early endosomes, lysosomes, and MHC class II-enriched compartments (MIICs) within one hour of stimulation. CD63 is internalized during Saccharomyces cerevisiae phagocytosis and associates with dectin-1. CD63 was found to associate with integrins CD11b and CD18 by immunoprecipitation. CD63 antibodies enhanced DC migration and decreased surface expression of CD29, CD11b, CD18, and α5 integrins.\",\n      \"method\": \"Confocal immunofluorescence, flow cytometry, immunoprecipitation, phagocytosis assays, migration assays\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP of CD63 with integrins and dectin-1, functional migration assay, intracellular trafficking confirmed by confocal, single lab\",\n      \"pmids\": [\"15130945\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"CD63 is involved in granule targeting of neutrophil elastase (NE). CD63 associates with proNE upon co-expression, requiring intact large extracellular loop of CD63. CD63 depletion in HL-60 cells reduced NE processing (proNE to mature NE), reduced constitutive secretion, and caused lack of morphologically normal granules with absence of proNE/NE. CD63 thus participates in ER/Golgi export, cellular retention, and granule targeting of proNE.\",\n      \"method\": \"Co-immunoprecipitation (COS cells), RNAi in HL-60 cells, CD63 mutant expression, electron microscopy, secretion assays\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — Co-IP, domain mutant, RNAi knockdown with defined morphological and biochemical phenotype, multiple orthogonal methods\",\n      \"pmids\": [\"18669870\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"CD63 is required for efficient FcεRI-mediated mast cell degranulation. CD63-deficient mast cells showed significant decrease in FcεRI-mediated β-hexosaminidase and TNF-α release, but normal PMA/ionomycin-induced degranulation, IL-6 secretion, and leukotriene C4 production. CD63-deficient mice showed attenuated cutaneous anaphylactic reactions upon local mast cell reconstitution. No ultrastructural differences in granule morphology or FcεRI-induced global tyrosine phosphorylation/Akt phosphorylation were observed.\",\n      \"method\": \"CD63 knockout mouse model, bone marrow-derived mast cell development, β-hexosaminidase release assay, passive cutaneous anaphylaxis, Kit(w/w-v) reconstitution\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO with specific in vitro and in vivo phenotypic readouts, pathway specificity determined by comparing multiple stimuli\",\n      \"pmids\": [\"23945142\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Anti-CD63 antibodies inhibit FcεRI-mediated mast cell degranulation but not leukotriene synthesis. This inhibition correlates with CD63-mediated inhibition of mast cell adhesion to fibronectin and vitronectin. Anti-CD63 impairs the Gab2-PI3K pathway essential for both degranulation and adhesion, without affecting global tyrosine phosphorylation or calcium mobilization. Anti-CD63 also inhibited FcεRI-mediated allergic reactions in vivo.\",\n      \"method\": \"Monoclonal antibody functional assays, adhesion assays, PI3K pathway analysis, calcium mobilization, in vivo allergy model\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — specific pathway (Gab2-PI3K) identified as downstream of CD63, in vitro and in vivo confirmation, multiple mechanistic readouts\",\n      \"pmids\": [\"15684326\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Upon platelet activation and exocytosis, CD63 relocates from dense granule/lysosome membranes to the plasma membrane where it associates with αIIbβ3-CD9 complex and the actin cytoskeleton in an αIIbβ3-dependent manner. Anti-CD63 antibody (D545) inhibited platelet spreading, F-actin reorganization, vinculin redistribution, tyrosine phosphorylation, and FAK phosphorylation on immobilized fibrinogen. CD63 co-immunoprecipitated with a PI 4-kinase type II activity regardless of activation state.\",\n      \"method\": \"Immunofluorescence, confocal imaging, co-immunoprecipitation, lipid kinase assays, flow cytometry\",\n      \"journal\": \"Thrombosis and haemostasis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP of CD63-PI4K, functional antibody inhibition with multiple cytoskeletal readouts, single lab\",\n      \"pmids\": [\"15711748\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"CD63 deficiency in mice results in altered water balance: increased urinary flow, water intake, reduced urine osmolality, and abnormal intracellular lamellar inclusions in principal cells of the collecting duct. Despite CD63 abundance in late endosomes/lysosomes, loss of CD63 does not cause obvious endosomal/lysosomal abnormalities, suggesting functional compensation by other tetraspanins in most tissues.\",\n      \"method\": \"CD63 knockout mouse generation and analysis, histology, electron microscopy, water balance measurements, immune cell profiling\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO mouse model with specific renal phenotype identified by EM and physiological measurements\",\n      \"pmids\": [\"19075008\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"CD63 associates with receptor-linked tyrosine phosphatase alpha (RPTPα) and c-Src in renal cortex and transfected 293T cells. CD63 expression stimulates c-Src activity (increased pY416, decreased pY527). The CD63-RPTPα-c-Src complex enhances c-Src-induced inhibition of ROMK1 potassium channels and increases ROMK1 tyrosine phosphorylation.\",\n      \"method\": \"Co-immunoprecipitation (native tissue and transfected cells), two-electrode voltage clamp in Xenopus oocytes, phosphorylation analysis, herbimycin A inhibition\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — in vitro functional assay (oocyte voltage clamp), Co-IP in native tissue, kinase activity measured, multiple orthogonal methods\",\n      \"pmids\": [\"18211905\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"CD63 interacts with human organic cation transporter 2 (hOCT2) as demonstrated by split-ubiquitin yeast 2-hybrid, pull-down, TIRF microscopy, FRET, and biotinylation assays. CD63 overexpression affects hOCT2 localization in HEK293 cells, and CD63-KO mice show impaired insertion of the mouse OCT2 ortholog into the proper basolateral membrane domain. CD63 and hOCT2 co-localize with Rab4, implicating CD63 in recycling from sorting endosomes to the basolateral membrane in polarized epithelia.\",\n      \"method\": \"Split-ubiquitin yeast 2-hybrid, pull-down, TIRF microscopy, FRET, biotinylation assay, CD63 KO mouse analysis, MDCK polarized cell studies\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal interaction methods plus KO mouse validation with functional localization readout\",\n      \"pmids\": [\"28031320\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"CD63 recruitment to Cryptococcus neoformans-containing phagosomes (but not polystyrene bead phagosomes) requires phagosomal acidification and occurs independently of MHC class II and LAMP-1. This selective recruitment was demonstrated by live-cell imaging with mRFP-tagged CD63 in primary bone marrow-derived macrophages.\",\n      \"method\": \"Live-cell imaging with fluorescent-tagged CD63, acidification inhibitors, MyD88-deficient macrophages, primary bone marrow-derived cultures\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — live imaging in primary cells with pharmacological dissection of acidification requirement and independence from MHC II/LAMP-1\",\n      \"pmids\": [\"17043215\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"CD63 knockdown in EBV-transformed B cells (LCL) increased CD4+ T cell recognition of EBV antigens. This was not due to enhanced antigen processing or changes in MHC II expression. Exosome production significantly increased following CD63 knockdown, suggesting that CD63 negatively regulates exosome secretion and thereby MHC II-dependent T cell stimulation.\",\n      \"method\": \"shRNA knockdown, CD4+ T cell activation assays, exosome purification and quantification, MHC II expression analysis\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — shRNA with defined mechanistic outcome, but single lab and mechanism partially inferred from exosome quantification\",\n      \"pmids\": [\"21660937\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"TIMP-1 signaling via CD63 and integrin β1 mediates anoikis resistance in melanoma cells through PI3-K signaling independently of Akt phosphorylation. Differential association of the TIMP1-CD63-β1-integrin complex was observed along melanoma progression steps, demonstrated by co-immunoprecipitation.\",\n      \"method\": \"Co-immunoprecipitation, flow cytometry, PI3-K inhibitors (Wortmannin, LY294002), anchorage impediment model\",\n      \"journal\": \"Molecular cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP of complex, pharmacological pathway dissection, single lab\",\n      \"pmids\": [\"23522389\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"TIMP-1 induces neutrophilia and granulopoiesis through CD63 signaling. The CD63-binding domain of TIMP-1 (distinct from its protease-inhibitory domain) was necessary and sufficient to augment granulopoiesis. Ablation of CD63 abolished both TIMP-1-induced neutrophilia and enhanced granulopoiesis in the bone marrow.\",\n      \"method\": \"TIMP-1 domain variants, CD63 knockout mice, BrdU pulse-labeling, bone marrow progenitor analysis, gene expression profiling\",\n      \"journal\": \"Haematologica\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — domain dissection of TIMP-1 combined with CD63 KO mouse rescue experiment, mechanistic pathway established\",\n      \"pmids\": [\"26001794\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"TIMP-1 binding to CD63 activates β1 integrin-mediated signaling through Akt and FAK phosphorylation, enhancing focal adhesion formation, cytoskeletal reorganization, and migration of human neural stem cells. shRNA ablation of CD63 attenuated TIMP-1-induced migration and spreading; blocking β1 integrin or PI3K also blocked migration.\",\n      \"method\": \"shRNA knockdown, microarray/proteomics, migration/adhesion assays, Akt/FAK phosphorylation analysis, antibody blocking\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — shRNA with signaling pathway dissection, single lab, multiple downstream readouts\",\n      \"pmids\": [\"24635319\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"TIMP-1/CD63/ITGB1/FAK signaling axis drives hypermotility in Toxoplasma gondii-infected dendritic cells. shRNA silencing of TIMP-1, CD63, or ITGB1 inhibited DC hypermotility; FAK inhibition (and inhibitors of SRC and PI3K) also abrogated hypermotility. This signaling cascade is hijacked by T. gondii for systemic dissemination.\",\n      \"method\": \"shRNA knockdown, antibody blockade, migration assays, kinase inhibitors\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pathway established by multiple gene silencing steps with defined functional readout, single lab\",\n      \"pmids\": [\"30635444\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"CD63 is required for HIV-1 replication in macrophages and cell lines. CD63-specific siRNA inhibited HIV replication in macrophages (>90% knockdown) and in U373-MAGI cells, suggesting roles in both early infection events and later post-integration replication steps.\",\n      \"method\": \"siRNA knockdown, HIV replication assay, macrophage and cell line models\",\n      \"journal\": \"Virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA with specific viral replication readout, single lab, mechanistic step not fully defined\",\n      \"pmids\": [\"18682304\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"CD63 plays a dual role in HIV-1 replication: supports Env-mediated (CD4/CCR5-dependent) entry or fusion (VSV/MLV pseudotype entry unaffected by CD63 silencing) and a post-integration step. CD63 co-localizes and co-immunoprecipitates with CD4 in macrophages, and CD63 silencing reduced expression of early HIV protein Tat and interaction with Gag, as well as late protein p24.\",\n      \"method\": \"siRNA knockdown, pseudotyped virus infectivity assays, co-immunoprecipitation, confocal microscopy, primary CD4+ T cells and dendritic cells\",\n      \"journal\": \"Virology journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pseudotype assays mechanistically distinguish entry role; Co-IP of CD63-CD4 and CD63-Gag, single lab\",\n      \"pmids\": [\"24507450\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Ameloblastin binds CD63 and promotes CD63 binding to integrin β1. The CD63-integrin β1 interaction induces Src kinase inactivation via CD63 binding to Src. This mechanism promotes osteogenic differentiation, and anti-CD63 antibody or constitutively active Src reversed these effects.\",\n      \"method\": \"Co-immunoprecipitation, anti-CD63 antibody blockade, constitutively active Src overexpression, osteogenic differentiation assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP of CD63-Src complex, antibody/genetic rescue, single lab, multiple mechanistic readouts\",\n      \"pmids\": [\"21149578\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"CD63 mediates downregulation of CXCR4 in activated B cells by recruiting CXCR4 to late endosomes. BCL6 was found on the chromatin of the CD63 gene in resting B cells (functioning as a transcriptional repressor). siRNA knockdown of CD63 mRNA in Bcl6-deficient B cells upregulated CXCR4 expression, confirming CD63-dependent CXCR4 endosomal recruitment.\",\n      \"method\": \"siRNA knockdown, flow cytometry, chromatin immunoprecipitation (Bcl6 on CD63 gene), Bcl6 inhibitor experiments\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP showing Bcl6 on CD63 locus, functional siRNA with CXCR4 readout, single lab\",\n      \"pmids\": [\"21270405\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CD63 is required to sustain TGFβ signaling in hematopoietic stem cells through its interaction with TGFβ receptors I and II. CD63-deficient HSCs exhibit impaired quiescence and long-term repopulating capacity. CD63-high HSCs are more quiescent with greater self-renewal and myeloid differentiation than CD63-low/negative HSCs.\",\n      \"method\": \"CD63 knockout mice, HSC transplantation, TGFβ signaling assays, co-immunoprecipitation (CD63 with TGFβRI/II), irradiation and 5-FU stress models\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO mouse with multiple phenotypic readouts plus Co-IP identifying TGFβ receptor interaction as mechanistic basis\",\n      \"pmids\": [\"34363017\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"CD63 knockdown induces epithelial-like phenotype in melanoma cells with increased E-cadherin, downregulation of N-cadherin and Snail, and reduced β-catenin protein. β-catenin inhibitors mimicked this phenotype. CD63 overexpression reduces motility, invasiveness, protease activities, and tumor growth. CD63 regulates cell plasticity via PI3K/AKT-GSK3β-β-catenin pathway.\",\n      \"method\": \"siRNA knockdown, stable overexpression, β-catenin inhibitors, PI3K/AKT and GSK3β inhibitors, invasion assays, in vivo tumor xenograft\",\n      \"journal\": \"International journal of cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss and gain of function with pathway inhibitor rescue, single lab\",\n      \"pmids\": [\"25354204\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"The CD63 gene (ME491) consists of eight exons spanning 4 kb. The 5'-flanking region lacks a TATA box but contains GC-rich sequences with SP1 and ETF binding sites, and a functional AP-1 binding site that positively regulates gene expression, as demonstrated by deletion mutant analysis.\",\n      \"method\": \"Genomic cloning, primer extension, reporter gene assays, 5'-deletion mutant analysis\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional promoter deletion analysis with reporter, single lab\",\n      \"pmids\": [\"1599482\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Amelogenin interacts with CD63 via specific binding regions: the amelogenin PLSPILPELPLEAW region binds CD63 residues 165-205 (within the large extracellular loop EC2). This interaction mediates rapid endocytic uptake of amelogenin into CD63/LAMP1-positive vesicles in cells.\",\n      \"method\": \"In vitro binding assays, deletion/mutation mapping of binding regions, cell uptake experiments, confocal microscopy\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — domain mapping of binding regions, functional cellular uptake confirmation, single lab\",\n      \"pmids\": [\"17708745\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CD63 induces STAT3 activation to maintain the phenotype and function of CD63+ cancer-associated fibroblasts (CAFs). CD63+ CAFs secrete exosomes enriched in miR-22 (packaged via SFRS1) that confer tamoxifen resistance to breast cancer cells.\",\n      \"method\": \"Single-cell RNA sequencing, exosome isolation, SFRS1 functional studies, CD63-neutralizing antibody, STAT3 activation assays, xenograft models\",\n      \"journal\": \"Advanced science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional antibody blockade and mechanistic identification of SFRS1 as miR-22 packaging factor, single lab\",\n      \"pmids\": [\"33173749\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"CD63 mobilization from crystalloid granule membranes to the cell periphery and plasma membrane is associated with eosinophil mediator release (β-hexosaminidase, eosinophil peroxidase, RANTES). IFN-γ-induced CD63 mobilization preceded RANTES release, consistent with piecemeal degranulation. Both CD63 mobilization and mediator release were inhibited by dexamethasone and the tyrosine kinase inhibitor genistein.\",\n      \"method\": \"Confocal immunofluorescence, flow cytometry, secretion assays, pharmacological inhibition\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-inhibition of CD63 mobilization and degranulation with kinase inhibitors implicates tyrosine kinase pathway, single lab\",\n      \"pmids\": [\"12010805\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CD63 negatively regulates hepatocellular carcinoma by suppressing IL-6/IL-27-induced STAT3 activation. CD63 overexpression inhibited HCC cell proliferation and migration, while knockdown promoted these; STAT3 blockade impaired the promotive effects of CD63 knockdown.\",\n      \"method\": \"Overexpression, knockdown, RNA-sequencing, dual-luciferase reporter, STAT3 inhibition, xenograft model\",\n      \"journal\": \"Journal of cellular and molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RNA-seq pathway identification with STAT3 inhibitor rescue, multiple cellular readouts, single lab\",\n      \"pmids\": [\"33277798\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CD63 is a tetraspanin membrane protein that cycles between late endosomes/lysosomes, secretory organelles (dense granules, Weibel-Palade bodies), and the plasma membrane via clathrin- and adaptor protein (AP-2/AP-3)-dependent endocytic trafficking; it serves as an adaptor that links interaction partners (including TIMP-1, integrins α3β1/α6β1, H,K-ATPase β-subunit, OCT2, TGFβ receptors, and ROMK channels) to the endocytic/lysosomal machinery, recruits PI 4-kinase type II into signaling complexes at the cell surface, regulates exosomal cargo sorting (including viral LMP1 and ferritin under iron loading via the IRE-IRP system), modulates mast cell FcεRI-mediated degranulation through the Gab2-PI3K pathway, and controls hematopoietic stem cell quiescence by sustaining TGFβ receptor signaling.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CD63 is a tetraspanin membrane protein that organizes endocytic and secretory trafficking and acts as a membrane scaffold linking transmembrane partners to the endo-lysosomal machinery [#0, #8]. It traffics from the ER to late endosomes/multivesicular bodies, where it is enriched on intraluminal vesicles and from which it can be released as exosomes, while a pool also cycles to the plasma membrane and back; comparison with plasma-membrane-stabilized mutants shows that CD63's residence on internal membranes is a key determinant of whether it is sorted into endosome-derived versus plasma-membrane-derived vesicles [#0, #1]. CD63 promotes internalization of partner membrane proteins through its capacity to engage the clathrin adaptor complexes AP-2 and AP-3, redirecting cargo such as the H,K-ATPase β-subunit from the surface to CD63+ intracellular compartments [#0, #8], and it likewise governs basolateral membrane insertion and recycling of the organic cation transporter OCT2 via Rab4-positive sorting endosomes [#23] and endosomal recruitment of CXCR4 in activated B cells [#33]. In secretory and granule-bearing cells CD63 is a constituent of platelet dense granules and lysosomes, Weibel-Palade bodies, and crystalloid/secretory granules, relocating to the plasma membrane upon stimulated exocytosis [#3, #6, #7, #39]; it is required for ER/Golgi export and granule targeting of neutrophil elastase through its large extracellular loop [#17] and for FcεRI-mediated mast cell degranulation acting via the Gab2-PI3K pathway [#18, #19]. CD63 nucleates signaling complexes at the cell surface, associating with integrins α3β1 and α6β1 together with a type II PI 4-kinase in peripheral focal complexes [#4, #5], and serving as the cell-surface receptor for TIMP-1, which it couples to β1 integrin to drive PI3K/FAK-dependent survival, migration, and granulopoiesis [#2, #27, #28]. It further modulates Src-family kinase activity in complexes with RPTPα to regulate ROMK channels [#22]. CD63 controls extracellular vesicle cargo sorting, being required for exosomal packaging of the EBV oncoprotein LMP1 [#9] and for iron-loading-induced secretion of ferritin-containing EVs through the IRE-IRP system and NCOA4 [#11], and it is exploited by multiple pathogens including human papillomavirus (via a CD63-syntenin-1-ALIX complex) [#13], Lujo virus (facilitating pH-activated membrane fusion) [#14], and HIV-1 [#30, #31]. At the organismal level CD63 sustains TGFβ receptor signaling to maintain hematopoietic stem cell quiescence and repopulating capacity [#34], and its loss in mice produces a selective renal water-balance defect with lamellar inclusions in collecting-duct principal cells, indicating tetraspanin redundancy in most tissues [#21]. CD63 expression is N-glycosylated by the RPN2/oligosaccharyltransferase complex, which controls its localization [#12], and is transcriptionally repressed by BCL6 [#33] from a TATA-less, AP-1-responsive promoter [#36].\",\n  \"teleology\": [\n    {\n      \"year\": 1993,\n      \"claim\": \"Establishing where CD63 resides defined it as a regulated-secretory and granule membrane protein rather than a static surface antigen, linking it to a human bleeding disorder.\",\n      \"evidence\": \"Immunoblotting, FACS, N-terminal sequencing and HPS platelet analysis identifying CD63/granulophysin in dense granules, lysosomes and Weibel-Palade bodies with thrombin-induced surface exposure\",\n      \"pmids\": [\"7682577\", \"8353283\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the trafficking machinery routing CD63 to these granules\", \"Molecular basis of the HPS deficiency not resolved\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Showing CD63 forms integrin-α3β1/α6β1 complexes containing a PI 4-kinase established it as a scaffold nucleating a peripheral signaling pathway distinct from FAK/focal-adhesion signaling.\",\n      \"evidence\": \"Co-immunoprecipitation, PI 4-K enzymatic assays in CD63 immunoprecipitates, and localization to focal complexes across cell lines (building on 1995 integrin association mapping)\",\n      \"pmids\": [\"9006891\", \"7629079\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct versus indirect nature of the CD63-PI4K interaction unresolved\", \"Physiological output of the integrin-PI4K complex not defined\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Demonstrating CD63 drives internalization of the H,K-ATPase β-subunit via AP-2/AP-3 explained mechanistically how CD63 sorts partner membrane proteins into the endocytic pathway.\",\n      \"evidence\": \"Co-IP, biochemical endocytosis assays and CD63 adaptor-binding mutants in parietal and COS-7 cells\",\n      \"pmids\": [\"14660791\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether all CD63 cargo use the same AP-dependent route untested\", \"Stoichiometry of CD63-cargo-adaptor assembly unknown\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Identifying CD63 as a direct TIMP-1 receptor coupling to β1 integrin connected an extracellular ligand to intracellular survival signaling.\",\n      \"evidence\": \"Yeast two-hybrid, reciprocal Co-IP, shRNA knockdown and 3D matrigel survival assays\",\n      \"pmids\": [\"16917503\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct binding interface on CD63 not mapped\", \"Whether TIMP-1 signaling is protease-independent unresolved at this stage\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Defining CD63's clathrin-dependent endocytosis and its loss-of-function phenotype in mice clarified the trafficking itinerary and revealed tetraspanin redundancy in vivo.\",\n      \"evidence\": \"Subcellular fractionation, live imaging and EM of trafficking, alongside CD63 knockout mice showing a selective collecting-duct water-balance defect\",\n      \"pmids\": [\"18930046\", \"19075008\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of compensating tetraspanins not established\", \"Mechanistic basis of the renal lamellar inclusions undefined\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"CD63 was shown to act in two distinct signaling and biosynthetic contexts: a renal RPTPα/c-Src complex regulating ROMK channels, and granule targeting of neutrophil elastase via its large extracellular loop.\",\n      \"evidence\": \"Co-IP in native tissue and transfected cells with oocyte voltage-clamp electrophysiology; Co-IP, domain mutants, RNAi and EM in HL-60 cells\",\n      \"pmids\": [\"18211905\", \"18669870\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How CD63 modulates Src catalytic activity structurally unknown\", \"Whether elastase targeting generalizes to other granule proteases untested\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Genetic CD63 loss established a non-redundant requirement for FcεRI-triggered mast cell degranulation, refining earlier antibody-based observations to a defined Gab2-PI3K axis.\",\n      \"evidence\": \"CD63 knockout mast cells and mice with β-hexosaminidase/TNF-α release assays and passive cutaneous anaphylaxis, complementing earlier anti-CD63 Gab2-PI3K pathway studies\",\n      \"pmids\": [\"23945142\", \"15684326\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How CD63 selectively couples to the FcεRI but not PMA/ionomycin pathway unresolved\", \"Direct molecular link between CD63 and Gab2 not shown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"CRISPR knockout showing CD63 is required for exosomal LMP1 packaging established a causal role in selecting cargo into MVB-derived vesicles and in restraining intracellular oncogenic signaling.\",\n      \"evidence\": \"CRISPR/Cas9 knockout, nanoparticle tracking, exosome immunoisolation and signaling pathway dissection\",\n      \"pmids\": [\"27974566\", \"29212935\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct CD63-LMP1 contact not demonstrated\", \"Generalizability of CD63-dependent cargo selection to endogenous proteins unclear\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Distinguishing endosome- from plasma-membrane-derived vesicles and identifying an IRE-controlled, ferritin-loaded EV pathway refined how CD63's subcellular residence dictates vesicle origin and cargo.\",\n      \"evidence\": \"Live intracellular tracking, comparative proteomics and PM-stabilized mutants; IRE identification in CD63 5'UTR with iron-loading and NCOA4 EV analyses\",\n      \"pmids\": [\"34282141\", \"34265052\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Sorting signals routing CD63 to exosomes versus ectosomes incompletely defined\", \"Mechanism by which NCOA4-bound ferritin reaches CD63+ EVs unresolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Demonstrating CD63 sustains TGFβ receptor signaling to enforce HSC quiescence linked its receptor-scaffolding activity to a stem-cell maintenance function.\",\n      \"evidence\": \"CD63 knockout mice, HSC transplantation, TGFβ signaling assays and Co-IP with TGFβRI/II\",\n      \"pmids\": [\"34363017\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CD63 stabilizes receptors at the surface or in endosomes unresolved\", \"Direct versus indirect CD63-TGFβ receptor binding not dissected\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How CD63 selects specific cargo and partners for distinct destinations (exosome versus ectosome, degranulation versus surface signaling) and what structural features of its extracellular loop and adaptor-binding motifs determine these choices remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unifying structural model of CD63-cargo-adaptor assembly\", \"Determinants partitioning CD63 between competing trafficking fates undefined\", \"Extent of functional redundancy with other tetraspanins across tissues unquantified\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [2, 8, 23, 34]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [8, 22, 34]},\n      {\"term_id\": \"GO:0001618\", \"supporting_discovery_ids\": [14, 30, 31]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [0, 3, 6, 21]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [0, 1, 3, 16, 23, 33]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 1, 6, 20]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [0, 1, 9, 11]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [1, 17]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 1, 8, 9, 11]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [8, 23, 33]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [18, 19, 25, 27]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 4, 22, 34]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [9, 13, 14, 30, 31]}\n    ],\n    \"complexes\": [\n      \"CD63-syntenin-1-ALIX complex\",\n      \"CD63-integrin α3β1/α6β1-PI4K type II complex\",\n      \"TIMP-1-CD63-integrin β1 complex\",\n      \"CD63-RPTPα-c-Src complex\"\n    ],\n    \"partners\": [\n      \"TIMP1\",\n      \"ITGB1\",\n      \"ITGA3\",\n      \"TGFBR1\",\n      \"SLC22A2\",\n      \"RPTPA\",\n      \"SDCBP\",\n      \"PDCD6IP\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":9,"faith_pct":88.88888888888889}}