{"gene":"ATP6V0A2","run_date":"2026-06-09T22:02:44","timeline":{"discoveries":[{"year":2005,"finding":"Human TJ6 (ATP6V0A2) encodes a membrane protein with six predicted transmembrane-spanning regions; overexpression in HEK 293 cells increased H+ uptake into intracellular organelles in a bafilomycin-sensitive manner, establishing it as a functional vacuolar ATPase (V-ATPase) proton pump regulatory subunit (a2 subunit). The protein also contains a putative ITAM sequence (residues 452–466), but it was a poor substrate for tyrosine-phosphorylating enzymes, suggesting the ITAM is non-functional in PTK-mediated signaling.","method":"Overexpression in HEK 293 cells with H+ uptake assay, bafilomycin inhibition, Northern blot, immunolocalization, sequence analysis","journal":"International immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional H+ uptake assay with pharmacological inhibition in cell overexpression system, single lab, multiple methods","pmids":["16113235"],"is_preprint":false},{"year":2009,"finding":"Loss-of-function mutations in ATP6V0A2 (via siRNA knockdown or patient ARCL2 cells) result in distended Golgi cisternae, accumulation of abnormal lysosomes and multivesicular bodies, impaired secretion and intracellular retention of tropoelastin (TE) in the Golgi, reduced extracellular deposition of mature elastin, and increased apoptosis of elastogenic cells. Fibrillin-1 microfibril assembly and secreted lysyl oxidase activity were unaffected.","method":"siRNA knockdown, pulse-chase secretion assays, immunostaining, insoluble elastin assays, TUNEL staining, electron microscopy of patient fibroblasts","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (siRNA, pulse-chase, immunostaining, TUNEL) in both patient cells and knockdown cells, single lab but highly rigorous","pmids":["19321599"],"is_preprint":false},{"year":2012,"finding":"ATP6V0A2 localizes to the Golgi apparatus; loss of ATP6V0A2 protein in patient dermal fibroblasts or ATP6V0A2-deficient HeLa cells delays brefeldin A-induced Golgi collapse, implicating ATP6V0A2 in membrane fusion/Golgi dynamics. Patient fibroblasts also displayed elevated TGF-β signaling and increased TGF-β1 secretion. This Golgi collapse delay was not observed in cells deficient for ARCL-associated proteins GORAB or PYCR1, placing ATP6V0A2 in a distinct pathway.","method":"Immunostaining (localization to Golgi), brefeldin A-induced Golgi collapse assay in patient fibroblasts and ATP6V0A2-deficient HeLa cells, genetic epistasis with GORAB/PYCR1-deficient cells, TGF-β ELISA and signaling assays","journal":"Human genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal cell-type controls, epistasis with GORAB/PYCR1, multiple orthogonal methods including functional Golgi collapse assay and signaling readouts","pmids":["22773132"],"is_preprint":false},{"year":2015,"finding":"Reduced ATP6V0A2 expression in senescent human diploid fibroblasts (TIG-1) causes Golgi dispersal and altered glycosylation patterns (detected by FITC-lectin staining and glycoblotting). siRNA-mediated reduction of ATP6V0A2 in young TIG-1 cells recapitulated the glycosylation changes seen in senescent cells, establishing ATP6V0A2 as a mediator of Golgi-dependent glycosylation maintenance and a regulator of cellular senescence.","method":"Differential proteomic analysis, siRNA knockdown, FITC-lectin staining, glycoblotting, immunostaining for Golgi structure","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown with multiple readouts (Golgi morphology, glycosylation profiling), single lab","pmids":["26611489"],"is_preprint":false},{"year":2018,"finding":"The disease-causing missense mutation a2P405L (causing cutis laxa) renders the ATP6V0A2 protein unstable (shown by cycloheximide chase), degraded through both proteasomal and lysosomal pathways, and causes defective Golgi trafficking. The protein remains fully N-glycosylated. Co-immunoprecipitation showed no significant change in its association with the V0 assembly factor VMA21 (unlike a4R449H). This places P405L-induced instability at the level of post-ER Golgi trafficking failure.","method":"Cycloheximide chase assay, endoglycosidase treatment, immunofluorescence, co-immunoprecipitation, transient expression in HEK 293 cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — multiple orthogonal biochemical methods (CHX chase, endoglycosidase, Co-IP, IF) in a single rigorous study with mutagenesis","pmids":["29311258"],"is_preprint":false},{"year":2018,"finding":"ATP6V0A2 is required for acrosomal acidification in sperm; lower expression of ATP6V0A2 was found in asthenozoospermic males by 2D-DIGE/mass spectrometry and confirmed by western blot and ELISA, and is proposed to be responsible for acrosomal de-acidification and reduced sperm motility.","method":"2D-DIGE, mass spectrometry, western blot, ELISA, qRT-PCR in patient vs. control sperm proteomes","journal":"Life sciences","confidence":"Low","confidence_rationale":"Tier 3 / Weak — proteomic correlation with no functional manipulation of ATP6V0A2 itself; mechanism is inferred rather than directly tested","pmids":["30550884"],"is_preprint":false},{"year":2024,"finding":"ATP6V0A2 is required for lysosomal acidification in cardiomyocytes; epirubicin downregulates ATP6V0A2, disrupts lysosomal acidification, and triggers ferroptosis. Overexpression of ATP6V0A2 restored lysosomal acidification, reduced oxidative stress and lipid peroxidation accumulation, and protected cardiomyocytes from ferroptosis-driven epirubicin-induced cardiotoxicity both in vitro and in vivo.","method":"Microarray screening, qRT-PCR, immunoblotting, ATP6V0A2 overexpression in primary cardiomyocytes and mouse hearts, lysosomal acidification assay, ferroptosis inhibitor (Ferrostatin-1) rescue, in vivo mouse model","journal":"Cell death discovery","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain-of-function overexpression with multiple functional readouts (lysosomal pH, lipid peroxidation, ferroptosis markers) in vitro and in vivo, single lab","pmids":["39048556"],"is_preprint":false},{"year":2018,"finding":"ATP6V0A2 mutations increase pH in secretory vesicles, thereby impairing glycosyltransferase activity and organelle trafficking. A novel frameshift mutation (c.2085_2088del) in ATP6V0A2 was identified in patients with bleeding diathesis and defective wound healing, expanding the known functional consequences of ATP6V0A2 loss beyond glycosylation and elastic fiber defects to include platelet abnormalities.","method":"Linkage analysis, exome sequencing, electron microscopy of patient fibroblasts and epidermal basal cells, clinical and histological analysis","journal":"Turkish journal of haematology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — descriptive pathological/genetic study with no direct functional manipulation of ATP6V0A2; mechanism inferred from known biology","pmids":["30474613"],"is_preprint":false},{"year":2024,"finding":"A non-canonical splicing-site variant (c.117+5G>T) in ATP6V0A2 was shown by minigene assay to disrupt pre-mRNA splicing, establishing that splicing integrity is required for normal ATP6V0A2 function.","method":"Whole-exome sequencing, Sanger sequencing, bioinformatics analysis, minigene splicing assay","journal":"Molecular biology reports","confidence":"Low","confidence_rationale":"Tier 3 / Weak — minigene assay demonstrates splicing defect but does not directly probe protein function; single case report","pmids":["38598037"],"is_preprint":false}],"current_model":"ATP6V0A2 encodes the a2 subunit of the vacuolar H+-ATPase (V-ATPase), a membrane protein with six transmembrane domains that drives proton translocation into intracellular organelles (Golgi, lysosomes, secretory vesicles) in a bafilomycin-sensitive manner; it is required for Golgi structural integrity and membrane fusion, luminal acidification of Golgi compartments and lysosomes, proper N- and O-linked glycosylation by maintaining the pH optima for glycosyltransferases, and secretion of tropoelastin/elastin, with loss-of-function causing Golgi distension, lysosomal dysfunction, tropoelastin aggregation, impaired elastin deposition, increased apoptosis, and ferroptosis in cardiomyocytes."},"narrative":{"mechanistic_narrative":"ATP6V0A2 encodes the a2 subunit of the vacuolar H+-ATPase, a six-transmembrane membrane protein that drives bafilomycin-sensitive proton translocation into intracellular organelles and localizes to the Golgi apparatus [PMID:16113235, PMID:22773132]. Through this acidifying activity it maintains Golgi structural integrity and membrane dynamics: loss of function distends Golgi cisternae, produces abnormal lysosomes and multivesicular bodies, and delays brefeldin A-induced Golgi collapse, while impairing secretion of tropoelastin and extracellular deposition of mature elastin and increasing apoptosis of elastogenic cells [PMID:19321599, PMID:22773132]. By sustaining luminal pH, ATP6V0A2 supports Golgi-dependent glycosylation, and its reduction in senescent fibroblasts reproduces senescence-associated glycosylation changes [PMID:26611489]. The disease-causing P405L missense mutation destabilizes the protein and disrupts post-ER Golgi trafficking without affecting its association with the V0 assembly factor VMA21 [PMID:29311258]. Beyond the Golgi, ATP6V0A2 maintains lysosomal acidification in cardiomyocytes, where its loss triggers ferroptosis and its re-expression restores lysosomal pH and protects against oxidative cardiotoxicity [PMID:39048556]. Loss-of-function mutations in ATP6V0A2 cause autosomal recessive cutis laxa type 2 [PMID:19321599, PMID:29311258].","teleology":[{"year":2005,"claim":"Established that ATP6V0A2 is a functional proton pump subunit rather than merely a membrane protein of unknown role, by showing its overexpression increases organellar H+ uptake.","evidence":"Overexpression in HEK 293 cells with H+ uptake assay and bafilomycin inhibition, plus sequence/topology analysis","pmids":["16113235"],"confidence":"Medium","gaps":["Endogenous proton-pumping role not tested by loss-of-function","Functional relevance of the putative ITAM left unresolved","No native organellar localization shown in this study"]},{"year":2009,"claim":"Connected ATP6V0A2 loss to a defined cellular phenotype, showing it is required for Golgi/lysosome integrity and for tropoelastin secretion and elastin deposition.","evidence":"siRNA knockdown, pulse-chase secretion assays, immunostaining, insoluble elastin assays, TUNEL, and electron microscopy of patient fibroblasts","pmids":["19321599"],"confidence":"High","gaps":["Did not establish how luminal pH controls tropoelastin trafficking mechanistically","Specificity for tropoelastin over other secreted cargo only partially addressed"]},{"year":2012,"claim":"Localized ATP6V0A2 to the Golgi and implicated it in Golgi membrane dynamics distinct from other cutis laxa genes, while linking its loss to elevated TGF-beta signaling.","evidence":"Immunostaining, brefeldin A-induced Golgi collapse assay, genetic epistasis with GORAB/PYCR1-deficient cells, and TGF-beta signaling assays","pmids":["22773132"],"confidence":"High","gaps":["Molecular basis of the membrane-fusion/Golgi-dynamics defect not defined","Causal link between TGF-beta elevation and disease phenotype not established"]},{"year":2015,"claim":"Tied ATP6V0A2 to maintenance of Golgi-dependent glycosylation and cellular senescence, showing its reduction recapitulates senescence-associated glycosylation changes.","evidence":"Differential proteomics, siRNA knockdown, FITC-lectin staining, glycoblotting, and Golgi immunostaining in human diploid fibroblasts","pmids":["26611489"],"confidence":"Medium","gaps":["Which glycosyltransferases are pH-affected not identified","Causal role in driving senescence versus correlation not fully separated"]},{"year":2018,"claim":"Defined the molecular consequence of a disease mutation, showing P405L destabilizes the protein and blocks post-ER Golgi trafficking without altering VMA21 binding.","evidence":"Cycloheximide chase, endoglycosidase treatment, immunofluorescence, and co-immunoprecipitation in HEK 293 cells","pmids":["29311258"],"confidence":"High","gaps":["Why instability manifests at Golgi trafficking rather than ER not mechanistically resolved","Generalizability to other missense alleles untested"]},{"year":2018,"claim":"Extended the phenotypic spectrum of ATP6V0A2 loss to platelet/bleeding and acrosomal acidification defects, though mechanism was inferred from genetics/proteomics rather than functional manipulation.","evidence":"Exome/linkage analysis with patient EM (bleeding diathesis); 2D-DIGE/MS proteomic correlation in asthenozoospermic sperm","pmids":["30474613","30550884"],"confidence":"Low","gaps":["No direct functional manipulation of ATP6V0A2 in these tissues","Causal versus correlative role in platelet and sperm phenotypes unresolved"]},{"year":2024,"claim":"Demonstrated a protective role for ATP6V0A2 in lysosomal acidification, showing its re-expression rescues lysosomal pH and blocks ferroptosis in drug-injured cardiomyocytes.","evidence":"Microarray, immunoblotting, ATP6V0A2 overexpression with lysosomal acidification and lipid peroxidation assays, ferroptosis inhibitor rescue, in vitro and in vivo mouse model","pmids":["39048556"],"confidence":"Medium","gaps":["Mechanistic link between lysosomal pH and ferroptosis pathway not fully delineated","Whether endogenous loss alone is sufficient to drive cardiac ferroptosis not isolated"]},{"year":null,"claim":"How ATP6V0A2-dependent luminal acidification is mechanistically coupled to specific glycosyltransferase activities, membrane fusion machinery, and cargo selectivity across distinct tissues remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of the a2-containing V-ATPase complex in the timeline","Tissue-specific cargo and pH-sensitive effector enzymes not enumerated","Direct molecular partners beyond VMA21 association not characterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0]},{"term_id":"GO:0140657","term_label":"ATP-dependent activity","supporting_discovery_ids":[0]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[1,2,3]},{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[1,6]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[1,2]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[3]}],"complexes":["V-ATPase"],"partners":["VMA21"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9Y487","full_name":"V-type proton ATPase 116 kDa subunit a 2","aliases":["Lysosomal H(+)-transporting ATPase V0 subunit a 2","TJ6","Vacuolar proton translocating ATPase 116 kDa subunit a isoform 2"],"length_aa":856,"mass_kda":98.1,"function":"Subunit of the V0 complex of vacuolar(H+)-ATPase (V-ATPase), a multisubunit enzyme composed of a peripheral complex (V1) that hydrolyzes ATP and a membrane integral complex (V0) that translocates protons (By similarity). V-ATPase is responsible for acidifying and maintaining the pH of intracellular compartments and in some cell types, is targeted to the plasma membrane, where it is responsible for acidifying the extracellular environment (By similarity). Essential component of the endosomal pH-sensing machinery (PubMed:16415858). May play a role in maintaining the Golgi functions, such as glycosylation maturation, by controlling the Golgi pH (PubMed:18157129). In aerobic conditions, involved in intracellular iron homeostasis, thus triggering the activity of Fe(2+) prolyl hydroxylase (PHD) enzymes, and leading to HIF1A hydroxylation and subsequent proteasomal degradation (PubMed:28296633)","subcellular_location":"Cell membrane; Endosome membrane","url":"https://www.uniprot.org/uniprotkb/Q9Y487/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ATP6V0A2","classification":"Not Classified","n_dependent_lines":42,"n_total_lines":1208,"dependency_fraction":0.0347682119205298},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000185344","cell_line_id":"CID001642","localizations":[{"compartment":"golgi","grade":3},{"compartment":"er","grade":2}],"interactors":[{"gene":"ATP6AP1","stoichiometry":10.0},{"gene":"ATP6AP2","stoichiometry":10.0},{"gene":"VMA21","stoichiometry":10.0},{"gene":"ATP6V1F","stoichiometry":10.0},{"gene":"ATP6V0D1","stoichiometry":10.0},{"gene":"TMEM199","stoichiometry":10.0},{"gene":"CCDC115","stoichiometry":0.2},{"gene":"ATP6V0C","stoichiometry":0.2},{"gene":"ATP6V1B2","stoichiometry":0.2},{"gene":"CANX","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID001642","total_profiled":1310},"omim":[{"mim_id":"617627","title":"SMALL REGULATORY POLYPEPTIDE OF AMINO ACID RESPONSE; SPAAR","url":"https://www.omim.org/entry/617627"},{"mim_id":"611716","title":"ATPase, H+ TRANSPORTING, LYSOSOMAL, V0 SUBUNIT A2; ATP6V0A2","url":"https://www.omim.org/entry/611716"},{"mim_id":"278250","title":"WRINKLY SKIN SYNDROME; WSS","url":"https://www.omim.org/entry/278250"},{"mim_id":"231070","title":"GERODERMA OSTEODYSPLASTICUM; GO","url":"https://www.omim.org/entry/231070"},{"mim_id":"219200","title":"CUTIS LAXA, AUTOSOMAL RECESSIVE, TYPE IIA; ARCL2A","url":"https://www.omim.org/entry/219200"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Plasma membrane","reliability":"Supported"},{"location":"Connecting piece","reliability":"Supported"},{"location":"Mid piece","reliability":"Supported"},{"location":"Vesicles","reliability":"Additional"},{"location":"Focal adhesion sites","reliability":"Additional"},{"location":"Principal piece","reliability":"Additional"},{"location":"End piece","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/ATP6V0A2"},"hgnc":{"alias_symbol":["TJ6","a2","TJ6s","TJ6M","ATP6a2","J6B7","ATP6N1D","Vph1","Stv1","a2V","RTF"],"prev_symbol":[]},"alphafold":{"accession":"Q9Y487","domains":[{"cath_id":"3.30.70.120","chopping":"2-41_316-370","consensus_level":"medium","plddt":87.1824,"start":2,"end":370},{"cath_id":"3.30.70.2750","chopping":"116-143_171-280","consensus_level":"medium","plddt":84.8246,"start":116,"end":280},{"cath_id":"1.20.58","chopping":"548-678_728-732","consensus_level":"medium","plddt":86.8317,"start":548,"end":732}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y487","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y487-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y487-F1-predicted_aligned_error_v6.png","plddt_mean":81.56},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ATP6V0A2","jax_strain_url":"https://www.jax.org/strain/search?query=ATP6V0A2"},"sequence":{"accession":"Q9Y487","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9Y487.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9Y487/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y487"}},"corpus_meta":[{"pmid":"19321599","id":"PMC_19321599","title":"Loss-of-function mutations in ATP6V0A2 impair vesicular trafficking, tropoelastin secretion and cell survival.","date":"2009","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/19321599","citation_count":111,"is_preprint":false},{"pmid":"22773132","id":"PMC_22773132","title":"Further characterization of ATP6V0A2-related autosomal recessive cutis laxa.","date":"2012","source":"Human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/22773132","citation_count":63,"is_preprint":false},{"pmid":"33714158","id":"PMC_33714158","title":"Mechanisms of Enterobacter bugandensis TJ6 immobilization of heavy metals and inhibition of Cd and Pb uptake by wheat based on metabolomics and proteomics.","date":"2021","source":"Chemosphere","url":"https://pubmed.ncbi.nlm.nih.gov/33714158","citation_count":42,"is_preprint":false},{"pmid":"8579758","id":"PMC_8579758","title":"Reciprocal alteration in circulating TJ6+ CD19+ and TJ6+ CD56+ leukocytes in early pregnancy predicts success or miscarriage.","date":"1995","source":"American journal of reproductive immunology (New York, N.Y. : 1989)","url":"https://pubmed.ncbi.nlm.nih.gov/8579758","citation_count":32,"is_preprint":false},{"pmid":"7513260","id":"PMC_7513260","title":"Expression of a membrane form of the pregnancy-associated protein TJ6 on lymphocytes.","date":"1994","source":"Cellular immunology","url":"https://pubmed.ncbi.nlm.nih.gov/7513260","citation_count":32,"is_preprint":false},{"pmid":"26611489","id":"PMC_26611489","title":"Impaired ATP6V0A2 expression contributes to Golgi dispersion and glycosylation changes in senescent cells.","date":"2015","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/26611489","citation_count":27,"is_preprint":false},{"pmid":"29311258","id":"PMC_29311258","title":"Molecular mechanisms of cutis laxa- and distal renal tubular acidosis-causing mutations in V-ATPase a subunits, ATP6V0A2 and ATP6V0A4.","date":"2018","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/29311258","citation_count":24,"is_preprint":false},{"pmid":"8739450","id":"PMC_8739450","title":"TJ6: the pregnancy-associated cytokine.","date":"1996","source":"American journal of reproductive immunology (New York, N.Y. : 1989)","url":"https://pubmed.ncbi.nlm.nih.gov/8739450","citation_count":19,"is_preprint":false},{"pmid":"7619235","id":"PMC_7619235","title":"Purification and characterization of a pregnancy-associated protein: TJ6s.","date":"1995","source":"American journal of reproductive immunology (New York, N.Y. : 1989)","url":"https://pubmed.ncbi.nlm.nih.gov/7619235","citation_count":19,"is_preprint":false},{"pmid":"30550884","id":"PMC_30550884","title":"Proteomic analyses reveal lower expression of TEX40 and ATP6V0A2 proteins related to calcium ion entry and acrosomal acidification in asthenozoospermic males.","date":"2018","source":"Life sciences","url":"https://pubmed.ncbi.nlm.nih.gov/30550884","citation_count":17,"is_preprint":false},{"pmid":"30474613","id":"PMC_30474613","title":"A Novel ATP6V0A2 Mutation Causing Recessive Cutis Laxa with Unusual Manifestations of Bleeding Diathesis and Defective Wound Healing.","date":"2018","source":"Turkish journal of haematology : official journal of Turkish Society of Haematology","url":"https://pubmed.ncbi.nlm.nih.gov/30474613","citation_count":11,"is_preprint":false},{"pmid":"27896089","id":"PMC_27896089","title":"ATP6V0A2 mutations present in two Mexican Mestizo children with an autosomal recessive cutis laxa syndrome type IIA.","date":"2014","source":"Molecular genetics and metabolism reports","url":"https://pubmed.ncbi.nlm.nih.gov/27896089","citation_count":11,"is_preprint":false},{"pmid":"16113235","id":"PMC_16113235","title":"Cloning, expression and functional characterization of the putative regeneration and tolerance factor (RTF/TJ6) as a functional vacuolar ATPase proton pump regulatory subunit with a conserved sequence of immunoreceptor tyrosine-based activation motif.","date":"2005","source":"International immunology","url":"https://pubmed.ncbi.nlm.nih.gov/16113235","citation_count":9,"is_preprint":false},{"pmid":"39048556","id":"PMC_39048556","title":"Epirubicin induces cardiotoxicity through disrupting ATP6V0A2-dependent lysosomal acidification and triggering ferroptosis in cardiomyocytes.","date":"2024","source":"Cell death discovery","url":"https://pubmed.ncbi.nlm.nih.gov/39048556","citation_count":8,"is_preprint":false},{"pmid":"9325490","id":"PMC_9325490","title":"Expression of TJ6 during pregnancy.","date":"1997","source":"American journal of reproductive immunology (New York, N.Y. : 1989)","url":"https://pubmed.ncbi.nlm.nih.gov/9325490","citation_count":7,"is_preprint":false},{"pmid":"8920165","id":"PMC_8920165","title":"Expression of membrane form of the pregnancy associated protein TJ6 on decidual lymphocytes in the first trimester of pregnancy.","date":"1996","source":"Journal of reproductive immunology","url":"https://pubmed.ncbi.nlm.nih.gov/8920165","citation_count":6,"is_preprint":false},{"pmid":"36520350","id":"PMC_36520350","title":"A novel deletion mutation in the ATP6V0A2 gene in an Iranian patient affected by autosomal recessive cutis laxa.","date":"2022","source":"Irish journal of medical science","url":"https://pubmed.ncbi.nlm.nih.gov/36520350","citation_count":4,"is_preprint":false},{"pmid":"37119015","id":"PMC_37119015","title":"Two novel homozygous variants of ATP6V0A2 and ALDH18A1 lead to autosomal recessive cutis laxa type 2 and 3 in two Pakistani families.","date":"2023","source":"The journal of gene medicine","url":"https://pubmed.ncbi.nlm.nih.gov/37119015","citation_count":1,"is_preprint":false},{"pmid":"38598037","id":"PMC_38598037","title":"Identification of a novel intronic variant of ATP6V0A2 in a Han-Chinese family with cutis laxa.","date":"2024","source":"Molecular biology 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and a Novel Frameshift Variant.","date":"2026","source":"American journal of medical genetics. Part A","url":"https://pubmed.ncbi.nlm.nih.gov/41732832","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":13640,"output_tokens":2719,"usd":0.040852,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9971,"output_tokens":2937,"usd":0.06164,"stage2_stop_reason":"end_turn"},"total_usd":0.102492,"stage1_batch_id":"msgbatch_0179Z2pxRYBsXi2xADneafRw","stage2_batch_id":"msgbatch_01LaY9ZaVdgjWArcZo9eqQE5","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2005,\n      \"finding\": \"Human TJ6 (ATP6V0A2) encodes a membrane protein with six predicted transmembrane-spanning regions; overexpression in HEK 293 cells increased H+ uptake into intracellular organelles in a bafilomycin-sensitive manner, establishing it as a functional vacuolar ATPase (V-ATPase) proton pump regulatory subunit (a2 subunit). The protein also contains a putative ITAM sequence (residues 452–466), but it was a poor substrate for tyrosine-phosphorylating enzymes, suggesting the ITAM is non-functional in PTK-mediated signaling.\",\n      \"method\": \"Overexpression in HEK 293 cells with H+ uptake assay, bafilomycin inhibition, Northern blot, immunolocalization, sequence analysis\",\n      \"journal\": \"International immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional H+ uptake assay with pharmacological inhibition in cell overexpression system, single lab, multiple methods\",\n      \"pmids\": [\"16113235\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Loss-of-function mutations in ATP6V0A2 (via siRNA knockdown or patient ARCL2 cells) result in distended Golgi cisternae, accumulation of abnormal lysosomes and multivesicular bodies, impaired secretion and intracellular retention of tropoelastin (TE) in the Golgi, reduced extracellular deposition of mature elastin, and increased apoptosis of elastogenic cells. Fibrillin-1 microfibril assembly and secreted lysyl oxidase activity were unaffected.\",\n      \"method\": \"siRNA knockdown, pulse-chase secretion assays, immunostaining, insoluble elastin assays, TUNEL staining, electron microscopy of patient fibroblasts\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (siRNA, pulse-chase, immunostaining, TUNEL) in both patient cells and knockdown cells, single lab but highly rigorous\",\n      \"pmids\": [\"19321599\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"ATP6V0A2 localizes to the Golgi apparatus; loss of ATP6V0A2 protein in patient dermal fibroblasts or ATP6V0A2-deficient HeLa cells delays brefeldin A-induced Golgi collapse, implicating ATP6V0A2 in membrane fusion/Golgi dynamics. Patient fibroblasts also displayed elevated TGF-β signaling and increased TGF-β1 secretion. This Golgi collapse delay was not observed in cells deficient for ARCL-associated proteins GORAB or PYCR1, placing ATP6V0A2 in a distinct pathway.\",\n      \"method\": \"Immunostaining (localization to Golgi), brefeldin A-induced Golgi collapse assay in patient fibroblasts and ATP6V0A2-deficient HeLa cells, genetic epistasis with GORAB/PYCR1-deficient cells, TGF-β ELISA and signaling assays\",\n      \"journal\": \"Human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal cell-type controls, epistasis with GORAB/PYCR1, multiple orthogonal methods including functional Golgi collapse assay and signaling readouts\",\n      \"pmids\": [\"22773132\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Reduced ATP6V0A2 expression in senescent human diploid fibroblasts (TIG-1) causes Golgi dispersal and altered glycosylation patterns (detected by FITC-lectin staining and glycoblotting). siRNA-mediated reduction of ATP6V0A2 in young TIG-1 cells recapitulated the glycosylation changes seen in senescent cells, establishing ATP6V0A2 as a mediator of Golgi-dependent glycosylation maintenance and a regulator of cellular senescence.\",\n      \"method\": \"Differential proteomic analysis, siRNA knockdown, FITC-lectin staining, glycoblotting, immunostaining for Golgi structure\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown with multiple readouts (Golgi morphology, glycosylation profiling), single lab\",\n      \"pmids\": [\"26611489\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"The disease-causing missense mutation a2P405L (causing cutis laxa) renders the ATP6V0A2 protein unstable (shown by cycloheximide chase), degraded through both proteasomal and lysosomal pathways, and causes defective Golgi trafficking. The protein remains fully N-glycosylated. Co-immunoprecipitation showed no significant change in its association with the V0 assembly factor VMA21 (unlike a4R449H). This places P405L-induced instability at the level of post-ER Golgi trafficking failure.\",\n      \"method\": \"Cycloheximide chase assay, endoglycosidase treatment, immunofluorescence, co-immunoprecipitation, transient expression in HEK 293 cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — multiple orthogonal biochemical methods (CHX chase, endoglycosidase, Co-IP, IF) in a single rigorous study with mutagenesis\",\n      \"pmids\": [\"29311258\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"ATP6V0A2 is required for acrosomal acidification in sperm; lower expression of ATP6V0A2 was found in asthenozoospermic males by 2D-DIGE/mass spectrometry and confirmed by western blot and ELISA, and is proposed to be responsible for acrosomal de-acidification and reduced sperm motility.\",\n      \"method\": \"2D-DIGE, mass spectrometry, western blot, ELISA, qRT-PCR in patient vs. control sperm proteomes\",\n      \"journal\": \"Life sciences\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — proteomic correlation with no functional manipulation of ATP6V0A2 itself; mechanism is inferred rather than directly tested\",\n      \"pmids\": [\"30550884\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"ATP6V0A2 is required for lysosomal acidification in cardiomyocytes; epirubicin downregulates ATP6V0A2, disrupts lysosomal acidification, and triggers ferroptosis. Overexpression of ATP6V0A2 restored lysosomal acidification, reduced oxidative stress and lipid peroxidation accumulation, and protected cardiomyocytes from ferroptosis-driven epirubicin-induced cardiotoxicity both in vitro and in vivo.\",\n      \"method\": \"Microarray screening, qRT-PCR, immunoblotting, ATP6V0A2 overexpression in primary cardiomyocytes and mouse hearts, lysosomal acidification assay, ferroptosis inhibitor (Ferrostatin-1) rescue, in vivo mouse model\",\n      \"journal\": \"Cell death discovery\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain-of-function overexpression with multiple functional readouts (lysosomal pH, lipid peroxidation, ferroptosis markers) in vitro and in vivo, single lab\",\n      \"pmids\": [\"39048556\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"ATP6V0A2 mutations increase pH in secretory vesicles, thereby impairing glycosyltransferase activity and organelle trafficking. A novel frameshift mutation (c.2085_2088del) in ATP6V0A2 was identified in patients with bleeding diathesis and defective wound healing, expanding the known functional consequences of ATP6V0A2 loss beyond glycosylation and elastic fiber defects to include platelet abnormalities.\",\n      \"method\": \"Linkage analysis, exome sequencing, electron microscopy of patient fibroblasts and epidermal basal cells, clinical and histological analysis\",\n      \"journal\": \"Turkish journal of haematology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — descriptive pathological/genetic study with no direct functional manipulation of ATP6V0A2; mechanism inferred from known biology\",\n      \"pmids\": [\"30474613\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"A non-canonical splicing-site variant (c.117+5G>T) in ATP6V0A2 was shown by minigene assay to disrupt pre-mRNA splicing, establishing that splicing integrity is required for normal ATP6V0A2 function.\",\n      \"method\": \"Whole-exome sequencing, Sanger sequencing, bioinformatics analysis, minigene splicing assay\",\n      \"journal\": \"Molecular biology reports\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — minigene assay demonstrates splicing defect but does not directly probe protein function; single case report\",\n      \"pmids\": [\"38598037\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ATP6V0A2 encodes the a2 subunit of the vacuolar H+-ATPase (V-ATPase), a membrane protein with six transmembrane domains that drives proton translocation into intracellular organelles (Golgi, lysosomes, secretory vesicles) in a bafilomycin-sensitive manner; it is required for Golgi structural integrity and membrane fusion, luminal acidification of Golgi compartments and lysosomes, proper N- and O-linked glycosylation by maintaining the pH optima for glycosyltransferases, and secretion of tropoelastin/elastin, with loss-of-function causing Golgi distension, lysosomal dysfunction, tropoelastin aggregation, impaired elastin deposition, increased apoptosis, and ferroptosis in cardiomyocytes.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"ATP6V0A2 encodes the a2 subunit of the vacuolar H+-ATPase, a six-transmembrane membrane protein that drives bafilomycin-sensitive proton translocation into intracellular organelles and localizes to the Golgi apparatus [#0, #2]. Through this acidifying activity it maintains Golgi structural integrity and membrane dynamics: loss of function distends Golgi cisternae, produces abnormal lysosomes and multivesicular bodies, and delays brefeldin A-induced Golgi collapse, while impairing secretion of tropoelastin and extracellular deposition of mature elastin and increasing apoptosis of elastogenic cells [#1, #2]. By sustaining luminal pH, ATP6V0A2 supports Golgi-dependent glycosylation, and its reduction in senescent fibroblasts reproduces senescence-associated glycosylation changes [#3]. The disease-causing P405L missense mutation destabilizes the protein and disrupts post-ER Golgi trafficking without affecting its association with the V0 assembly factor VMA21 [#4]. Beyond the Golgi, ATP6V0A2 maintains lysosomal acidification in cardiomyocytes, where its loss triggers ferroptosis and its re-expression restores lysosomal pH and protects against oxidative cardiotoxicity [#6]. Loss-of-function mutations in ATP6V0A2 cause autosomal recessive cutis laxa type 2 [#1, #4].\",\n  \"teleology\": [\n    {\n      \"year\": 2005,\n      \"claim\": \"Established that ATP6V0A2 is a functional proton pump subunit rather than merely a membrane protein of unknown role, by showing its overexpression increases organellar H+ uptake.\",\n      \"evidence\": \"Overexpression in HEK 293 cells with H+ uptake assay and bafilomycin inhibition, plus sequence/topology analysis\",\n      \"pmids\": [\"16113235\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\n        \"Endogenous proton-pumping role not tested by loss-of-function\",\n        \"Functional relevance of the putative ITAM left unresolved\",\n        \"No native organellar localization shown in this study\"\n      ]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Connected ATP6V0A2 loss to a defined cellular phenotype, showing it is required for Golgi/lysosome integrity and for tropoelastin secretion and elastin deposition.\",\n      \"evidence\": \"siRNA knockdown, pulse-chase secretion assays, immunostaining, insoluble elastin assays, TUNEL, and electron microscopy of patient fibroblasts\",\n      \"pmids\": [\"19321599\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\n        \"Did not establish how luminal pH controls tropoelastin trafficking mechanistically\",\n        \"Specificity for tropoelastin over other secreted cargo only partially addressed\"\n      ]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Localized ATP6V0A2 to the Golgi and implicated it in Golgi membrane dynamics distinct from other cutis laxa genes, while linking its loss to elevated TGF-beta signaling.\",\n      \"evidence\": \"Immunostaining, brefeldin A-induced Golgi collapse assay, genetic epistasis with GORAB/PYCR1-deficient cells, and TGF-beta signaling assays\",\n      \"pmids\": [\"22773132\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\n        \"Molecular basis of the membrane-fusion/Golgi-dynamics defect not defined\",\n        \"Causal link between TGF-beta elevation and disease phenotype not established\"\n      ]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Tied ATP6V0A2 to maintenance of Golgi-dependent glycosylation and cellular senescence, showing its reduction recapitulates senescence-associated glycosylation changes.\",\n      \"evidence\": \"Differential proteomics, siRNA knockdown, FITC-lectin staining, glycoblotting, and Golgi immunostaining in human diploid fibroblasts\",\n      \"pmids\": [\"26611489\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\n        \"Which glycosyltransferases are pH-affected not identified\",\n        \"Causal role in driving senescence versus correlation not fully separated\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Defined the molecular consequence of a disease mutation, showing P405L destabilizes the protein and blocks post-ER Golgi trafficking without altering VMA21 binding.\",\n      \"evidence\": \"Cycloheximide chase, endoglycosidase treatment, immunofluorescence, and co-immunoprecipitation in HEK 293 cells\",\n      \"pmids\": [\"29311258\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\n        \"Why instability manifests at Golgi trafficking rather than ER not mechanistically resolved\",\n        \"Generalizability to other missense alleles untested\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Extended the phenotypic spectrum of ATP6V0A2 loss to platelet/bleeding and acrosomal acidification defects, though mechanism was inferred from genetics/proteomics rather than functional manipulation.\",\n      \"evidence\": \"Exome/linkage analysis with patient EM (bleeding diathesis); 2D-DIGE/MS proteomic correlation in asthenozoospermic sperm\",\n      \"pmids\": [\"30474613\", \"30550884\"],\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\n        \"No direct functional manipulation of ATP6V0A2 in these tissues\",\n        \"Causal versus correlative role in platelet and sperm phenotypes unresolved\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Demonstrated a protective role for ATP6V0A2 in lysosomal acidification, showing its re-expression rescues lysosomal pH and blocks ferroptosis in drug-injured cardiomyocytes.\",\n      \"evidence\": \"Microarray, immunoblotting, ATP6V0A2 overexpression with lysosomal acidification and lipid peroxidation assays, ferroptosis inhibitor rescue, in vitro and in vivo mouse model\",\n      \"pmids\": [\"39048556\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\n        \"Mechanistic link between lysosomal pH and ferroptosis pathway not fully delineated\",\n        \"Whether endogenous loss alone is sufficient to drive cardiac ferroptosis not isolated\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How ATP6V0A2-dependent luminal acidification is mechanistically coupled to specific glycosyltransferase activities, membrane fusion machinery, and cargo selectivity across distinct tissues remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\n        \"No structural model of the a2-containing V-ATPase complex in the timeline\",\n        \"Tissue-specific cargo and pH-sensitive effector enzymes not enumerated\",\n        \"Direct molecular partners beyond VMA21 association not characterized\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [1, 2, 3]},\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [1, 6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [1, 2]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"complexes\": [\"V-ATPase\"],\n    \"partners\": [\"VMA21\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":6,"faith_pct":83.33333333333333}}