{"gene":"GGA2","run_date":"2026-06-10T01:55:21","timeline":{"discoveries":[{"year":2000,"finding":"GGA2 (Vear) is a Golgi-localized protein with an N-terminal VHS domain and a C-terminal gamma-adaptin 'ear' domain. Full-length GGA2 and truncated forms lacking the VHS domain cause compaction of the Golgi complex upon overexpression; the ear domain alone associates with the Golgi without compaction; the VHS domain alone shows diffuse membrane/vesicle distribution. GGA2 partitions with the post-nuclear membrane fraction on cell fractionation.","method":"Immunofluorescence microscopy, cell fractionation, brefeldin A treatment, transfection of truncation constructs","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization and domain-dissection experiments in single lab with multiple orthogonal methods (immunofluorescence, fractionation, BFA sensitivity, truncation constructs)","pmids":["10702286"],"is_preprint":false},{"year":2001,"finding":"The VHS domain of GGA2 binds to the acidic cluster-dileucine motif in the cytoplasmic tail of the cation-independent mannose 6-phosphate receptor (CI-MPR). This interaction is required for lysosomal enzyme sorting: receptors with mutations in this motif are defective in sorting. The hinge domain of GGA2 binds clathrin, suggesting GGA2 links cargo to clathrin-coated vesicle assembly.","method":"Binding assays (VHS domain with CI-MPR cytoplasmic tail peptides), mutagenesis of the acidic cluster-dileucine motif, clathrin-binding assay with GGA2 hinge domain","journal":"Science (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro binding assays with domain-specific constructs, mutagenesis establishing functional requirement, hinge-clathrin interaction, replicated in context by multiple labs","pmids":["11387476"],"is_preprint":false},{"year":2001,"finding":"The VHS domain of GGA2 binds the cytoplasmic tail of sortilin via YXX and dileucine sorting motifs, and sortilin chimeric receptors containing the sortilin tail efficiently transport lysosomal enzymes (beta-hexosaminidase, beta-glucuronidase) to lysosomes in MPR-knockout cells, identifying sortilin as the first mammalian receptor targeted by the GGA family.","method":"Chimeric receptor expression in MPR-knockout cells, lysosomal enzyme transport assay, VHS domain binding to sortilin cytoplasmic tail","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — reconstituted lysosomal enzyme transport in defined genetic background (MPR-KO), binding assays, mutagenesis of sorting motifs","pmids":["11331584"],"is_preprint":false},{"year":2002,"finding":"The VHS domains of GGA1 and GGA2 bind the cytosolic domain of memapsin 2 (beta-secretase/BACE1). Mutagenesis identified Asp496, Leu499, and Leu500 as essential residues in memapsin 2 for this interaction, matching the spacing found in CI-MPR, sortilin, and LRP3 cytoplasmic tails. Gel-immobilized VHS domains of GGA2 pull down full-length memapsin 2 from mammalian cell lysates.","method":"Pulldown assay with immobilized VHS domains, mammalian cell lysate pulldown, site-directed mutagenesis of memapsin 2 cytoplasmic domain","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pulldown from cell lysates plus mutagenesis identifying specific residues, single lab","pmids":["12135764"],"is_preprint":false},{"year":2007,"finding":"Specific RNAi-mediated depletion of GGA2 (to ~5% of control levels) in HeLa cells increases secretion of the lysosomal enzyme cathepsin D without altering the distribution of GGA1, GGA3, or MPRs, establishing a non-redundant role for GGA2 in lysosomal enzyme sorting at the TGN. The dominant-negative VHS-GAT domain of GGA2 is recruited to the TGN independently of GGA1 and GGA3.","method":"Stable RNAi knockdown cell lines, cathepsin D secretion assay, immunofluorescence for TGN markers, dominant-negative domain expression","journal":"Archives of histology and cytology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — stable KD with specific phenotypic readout (cathepsin D secretion), single lab","pmids":["18431031"],"is_preprint":false},{"year":2009,"finding":"In yeast, Gga2 is required for TGN-to-vacuole sorting of the iron transporter Arn1p. Ubiquitin binding by Gga2 is NOT required for the initial TGN-to-endosome step but IS required for subsequent multivesicular body sorting of Arn1p: a ubiquitin-binding mutant of Gga2 causes accumulation of ubiquitinated Arn1p on the vacuolar membrane. Yeast epsins Ent3p and Ent4p also participate. N-terminal sequences of Arn1p (THN and YGL motifs, ubiquitinatable lysines) are required for vacuolar sorting.","method":"Yeast genetics, ubiquitin-binding mutant analysis, fluorescence microscopy of GFP-tagged Arn1p, mutagenesis of Arn1p sorting motifs","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple mutant alleles, reconstitution of sorting steps, mutagenesis of cargo and adaptor, epistasis analysis with epsins","pmids":["19574226"],"is_preprint":false},{"year":2012,"finding":"GGA2 knockout mice (using the Tigm gene-trap allele) show neonatal lethality, whereas GGA1 or GGA3 single knockouts are well tolerated. This establishes a non-redundant, essential in vivo function for GGA2 that cannot be compensated by GGA1 or GGA3.","method":"Insertional mutagenesis, mouse knockout analysis, neonatal viability phenotyping","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 / Strong — defined in vivo genetic knockout with clear phenotype, replicated with multiple alleles and genetic backgrounds in follow-up study","pmids":["22291915"],"is_preprint":false},{"year":2014,"finding":"The Byg Gga2 gene-trap allele is hypomorphic (residual GGA2 expression), while the Tigm allele is a true null; neonatal lethality of Tigm Gga2−/− mice is influenced by genetic background (C57BL/6 vs. mixed C57BL6/Ola129Sv). Surviving Gga2−/− mice show reduced birth weight maintained through adulthood.","method":"Gene-trap allele characterization, Western blotting, cross-breeding to different genetic backgrounds, growth curve analysis","journal":"G3 (Bethesda, Md.)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — allele-level genetic analysis clarifying prior knockout result, single lab","pmids":["24637350"],"is_preprint":false},{"year":2016,"finding":"GGA2 (and GGA1) are required for cell-surface transport of α2B-adrenergic receptor (α2B-AR). Knockdown of GGA2 arrests newly synthesized α2B-AR in the perinuclear region and reduces dendritic receptor expression in cortical neurons. The third intracellular loop of α2B-AR directly interacts with both GGA1 and GGA2; the GAE (gamma-adaptin ear) domain of GGA2 (and the hinge of GGA1) binds multiple subdomains of this loop. Full-length α2B-AR co-immunoprecipitates with GGA2 but not GGA1.","method":"shRNA/siRNA knockdown, co-immunoprecipitation, domain-mapping pulldown assays, primary cortical neuron imaging, ERK1/2 and cAMP signaling assays","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — reciprocal co-IP and domain mapping, KD with defined trafficking phenotype and signaling readout, single lab","pmids":["27901063"],"is_preprint":false},{"year":2018,"finding":"GGA2 interacts with the cytoplasmic juxtamembrane region (jxt) of EGFR via its VHS-GAT domains in a manner dependent on Asn108 in the VHS domain. GGA2 depletion greatly reduces steady-state EGFR expression by enhancing lysosomal degradation; this effect is reversed by additional depletion of GGA1 or GGA3, indicating GGA1/GGA3 promote EGFR degradation while GGA2 counteracts this. GGA2 depletion reduces EGF signaling and cell proliferation in vitro and in xenograft models.","method":"RNAi knockdown, pulldown assays with VHS-GAT domain constructs, proximity ligation assay, mutagenesis (N108), rescue by double knockdown, xenograft tumor model","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — direct binding assay with mutagenesis, in situ PLA, double-KD rescue establishing functional antagonism, in vivo xenograft validation","pmids":["29358589"],"is_preprint":false},{"year":2018,"finding":"GGA2 interacts with EGFR (co-immunoprecipitation), increases EGFR protein levels, and modifies EGFR degradation after ligand stimulation. GGA2 overexpression enhances EGFR-mediated cellular transformation; GGA2 knockdown reduces colony and tumor formation of EGFR-mutant lung adenocarcinoma cells.","method":"Co-immunoprecipitation, Western blot, RNAi knockdown, gene overexpression, colony formation assay, in vivo tumor models","journal":"Journal of thoracic oncology","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — co-IP plus functional KD/OE with tumor phenotype, single lab, partially overlapping with PMID:29358589","pmids":["30578931"],"is_preprint":false},{"year":2019,"finding":"GGA2 associates with active (but not inactive) β1-integrin and is required for recycling of active β1-integrin receptors to the plasma membrane. GGA2 silencing reduces active β1-integrin in focal adhesions and decreases cancer cell migration and invasion. BioID proximity labeling identified RAB13 and RAB10 as GGA2 interactors; RAB13 silencing phenocopies GGA2 depletion (intracellular accumulation of active β1-integrin, reduced focal adhesion levels, reduced migration), placing GGA2 and RAB13 in the same active integrin recycling pathway.","method":"RNAi screen, co-immunoprecipitation, BioID proximity labeling, integrin activity assay (active-conformation antibody), focal adhesion imaging, migration/invasion assays","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — BioID plus reciprocal co-IP, activity-specific integrin assay, KD of both GGA2 and RAB13 showing identical phenotype, multiple cellular readouts","pmids":["31076515"],"is_preprint":false},{"year":2020,"finding":"In yeast, Gga2 is required for maximal vacuolar delivery of amino acid permeases (Mup1, Can1, and others) during acute glucose starvation. Endocytosed Can1 transits through the TGN under both starved and glucose-replete conditions, and TGN-localized clathrin adaptors (including Gga2) are required for vacuolar sorting in both states. Forced de-ubiquitination at the TGN causes recycling of Tat1 permease in starved cells, showing active sorting to the vacuole. AP-1 plays only a minor role.","method":"Fluorescence microscopy of GFP-tagged permeases, genetic deletion of clathrin adaptors, ectopic de-ubiquitination at TGN","journal":"Biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with defined cargo readout and mechanistic de-ubiquitination experiment, single lab","pmids":["32761633"],"is_preprint":false},{"year":2021,"finding":"GGA2 and AP-1 both support EGFR recycling from Rab11-positive recycling endosomes to the plasma membrane (rather than acting solely at the TGN). Depletion of AP-1 or GGA2 suppresses EGFR recycling and reduces cell-surface levels of EGFR, MET, and ErbB4, reducing cancer cell growth. Triple immunofluorescence and proximity ligation assays showed EGFR interaction with GGA2 or AP-1 more frequently at Rab11-positive endosomes than Rab5-positive early endosomes.","method":"Biochemical recycling assay, triple immunofluorescence microscopy, proximity ligation assay, RNAi depletion, xenograft model","journal":"Oncogenesis","confidence":"High","confidence_rationale":"Tier 2 / Strong — biochemical recycling assay (direct functional readout), in situ PLA for spatial localization, KD phenotype with multiple RTK cargo, in vivo xenograft validation","pmids":["34799560"],"is_preprint":false},{"year":2025,"finding":"GGA2 is rapidly depleted in pancreatic beta cells by Coxsackievirus B5 protease 2A (due to its short half-life). GGA2 depletion impairs insulin secretory granule biogenesis at the TGN, disrupts sorting of vacuolar ATPase and cathepsins, causes TGN acidification, and leads to premature lysosomal hydrolase activation. These changes alter the HLA-I immunopeptidome, shifting it towards HLA-B–presented, low-pI peptides generated by cathepsin-mediated processing of in-transit secretory proteins.","method":"CVB5 infection of beta cells, GGA2 depletion (siRNA/viral), immunostaining of pancreas sections from T1D donors, mass spectrometry of immunopeptidome, TGN pH measurement","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple mechanistic readouts (pH, cathepsin activation, granule biogenesis, immunopeptidome) in a single preprint study; not yet peer-reviewed","pmids":["bio_10.1101_2025.03.28.645506"],"is_preprint":true}],"current_model":"GGA2 is a Golgi/TGN-localized clathrin adaptor whose VHS domain binds acidic cluster-dileucine motifs on cargo receptors (CI-MPR, sortilin, memapsin 2/BACE1, EGFR), its hinge domain recruits clathrin, and its GAE domain interacts with GPCRs (e.g., α2B-AR); it directs cargo (lysosomal enzymes, EGFR, active β1-integrin) from the TGN and recycling endosomes to appropriate destinations, opposes GGA1/GGA3-driven EGFR lysosomal degradation to sustain receptor expression, and cooperates with RAB13 for activity-dependent integrin recycling, with loss of GGA2 causing neonatal lethality in mice indicating a non-redundant essential function."},"narrative":{"mechanistic_narrative":"GGA2 is a Golgi/TGN-localized clathrin adaptor that links transmembrane cargo to clathrin-coated vesicle formation, controlling sorting of cargo from the trans-Golgi network and recycling endosomes to their correct destinations [PMID:10702286, PMID:11387476]. Its N-terminal VHS domain recognizes acidic cluster-dileucine and related sorting motifs in the cytoplasmic tails of lysosomal enzyme receptors—the cation-independent mannose-6-phosphate receptor and sortilin—as well as memapsin 2 (BACE1), while its hinge region recruits clathrin, providing a physical bridge between sorting signals and coat assembly [PMID:11387476, PMID:11331584, PMID:12135764]. Through this activity GGA2 carries out a non-redundant role in lysosomal enzyme sorting at the TGN: its specific depletion drives missecretion of cathepsin D without disrupting the other GGA proteins or the MPRs [PMID:18431031]. GGA2 also governs receptor trafficking beyond lysosomal targeting: its GAE domain binds the third intracellular loop of the α2B-adrenergic receptor to promote receptor delivery to the cell surface [PMID:27901063], and it associates with EGFR via its VHS-GAT domains in a manner dependent on Asn108 to sustain receptor levels by antagonizing GGA1/GGA3-driven lysosomal degradation, thereby supporting EGF signaling, proliferation, and tumor growth [PMID:29358589, PMID:30578931]. GGA2 supports recycling of EGFR and related receptor tyrosine kinases (MET, ErbB4) from Rab11-positive recycling endosomes to the plasma membrane [PMID:34799560], and cooperates with RAB13 to recycle active β1-integrin, promoting focal adhesion formation, migration, and invasion [PMID:31076515]. In yeast, Gga2 mediates TGN-to-vacuole sorting of the iron transporter Arn1p and amino acid permeases, with its ubiquitin-binding activity required for multivesicular body sorting [PMID:19574226, PMID:32761633]. Gga2 function is essential in vivo: knockout mice display neonatal lethality not compensated by GGA1 or GGA3 [PMID:22291915].","teleology":[{"year":2000,"claim":"Established GGA2 as a Golgi-localized protein with a modular VHS–ear architecture, framing it as a candidate membrane trafficking adaptor.","evidence":"Immunofluorescence, cell fractionation, BFA sensitivity, and truncation-construct expression in transfected cells","pmids":["10702286"],"confidence":"Medium","gaps":["No cargo or sorting motif identified at this stage","Functional role of the Golgi compaction phenotype unclear","No demonstration of clathrin or coat recruitment"]},{"year":2001,"claim":"Defined the core sorting mechanism—the VHS domain reads acidic cluster-dileucine motifs in receptor tails while the hinge binds clathrin—answering how GGA2 couples cargo selection to coated-vesicle assembly.","evidence":"In vitro VHS-domain binding to CI-MPR and sortilin tail peptides, sorting-motif mutagenesis, chimeric receptor lysosomal enzyme transport in MPR-knockout cells, and hinge-clathrin binding assays","pmids":["11387476","11331584"],"confidence":"High","gaps":["Stoichiometry and regulation of cargo loading not resolved","Did not establish in vivo requirement","Relative contributions of CI-MPR vs sortilin pathways unquantified"]},{"year":2002,"claim":"Extended the VHS recognition code to memapsin 2/BACE1, showing GGA2 binds a conserved motif spacing shared across multiple cargoes.","evidence":"Pulldown of full-length memapsin 2 with immobilized VHS domains and site-directed mutagenesis (Asp496/Leu499/Leu500)","pmids":["12135764"],"confidence":"Medium","gaps":["Functional consequence for BACE1 trafficking not tested","Single-lab pulldown without cellular trafficking readout"]},{"year":2007,"claim":"Demonstrated that GGA2 has a non-redundant role in lysosomal enzyme sorting, distinct from GGA1 and GGA3.","evidence":"Stable RNAi depletion of GGA2 in HeLa cells with cathepsin D secretion assay and TGN-marker immunofluorescence","pmids":["18431031"],"confidence":"Medium","gaps":["Mechanism of non-redundancy not explained","Did not identify GGA2-specific cargo determinants"]},{"year":2009,"claim":"Established in yeast that Gga2 ubiquitin binding is dispensable for the TGN-to-endosome step but required for downstream MVB sorting, partitioning its sorting activity into discrete stages.","evidence":"Yeast genetics, ubiquitin-binding mutant analysis, GFP-Arn1p microscopy, cargo-motif mutagenesis, and epistasis with epsins Ent3p/Ent4p","pmids":["19574226"],"confidence":"High","gaps":["Mammalian relevance of the ubiquitin-binding step not addressed","How Gga2 hands cargo to the MVB machinery unresolved"]},{"year":2012,"claim":"Showed GGA2 is essential in vivo, with a function that GGA1 and GGA3 cannot compensate.","evidence":"Tigm gene-trap knockout mouse with neonatal viability phenotyping","pmids":["22291915"],"confidence":"High","gaps":["Cause of neonatal lethality at the cellular/cargo level unknown","Tissue-specific requirements not dissected"]},{"year":2014,"claim":"Clarified the genetic basis of the lethality phenotype by distinguishing null from hypomorphic alleles and revealing genetic background modifiers.","evidence":"Gene-trap allele characterization, Western blotting, cross-breeding to different backgrounds, and growth curve analysis","pmids":["24637350"],"confidence":"Medium","gaps":["Identity of background modifier loci unknown","Molecular cause of reduced birth weight not defined"]},{"year":2016,"claim":"Revealed a GAE-domain–mediated mechanism for forward trafficking, with GGA2 promoting cell-surface delivery of a GPCR via its third intracellular loop.","evidence":"shRNA/siRNA knockdown, reciprocal co-IP, domain-mapping pulldowns, cortical neuron imaging, and ERK/cAMP signaling assays","pmids":["27901063"],"confidence":"Medium","gaps":["Why α2B-AR binds GGA2 but not GGA1 in co-IP not explained","Generality across other GPCRs untested"]},{"year":2018,"claim":"Identified GGA2 as a positive regulator of EGFR stability that opposes GGA1/GGA3-driven lysosomal degradation, linking GGA2 to receptor tyrosine kinase signaling and tumor growth.","evidence":"VHS-GAT pulldowns with N108 mutagenesis, proximity ligation assay, double-knockdown rescue, co-IP, overexpression, and xenograft tumor models","pmids":["29358589","30578931"],"confidence":"High","gaps":["Molecular basis of the GGA1/GGA3 vs GGA2 fate decision unresolved","Whether GGA2 acts at TGN or endosomes for this function not yet localized"]},{"year":2019,"claim":"Placed GGA2 in an active-integrin recycling pathway with RAB13, expanding its role to conformation-selective cargo recycling that drives migration and invasion.","evidence":"RNAi screen, BioID proximity labeling identifying RAB13/RAB10, reciprocal co-IP, active-conformation integrin assay, focal adhesion imaging, and migration/invasion assays","pmids":["31076515"],"confidence":"High","gaps":["How GGA2 discriminates active from inactive integrin conformation unknown","Direct vs indirect nature of the GGA2-RAB13 interaction not resolved"]},{"year":2021,"claim":"Localized a major GGA2 trafficking step to Rab11-positive recycling endosomes, showing GGA2 (with AP-1) recycles multiple RTKs to the plasma membrane rather than acting solely at the TGN.","evidence":"Biochemical recycling assay, triple immunofluorescence, proximity ligation assay quantifying Rab11 vs Rab5 association, RNAi depletion, and xenograft models","pmids":["34799560"],"confidence":"High","gaps":["How GGA2 is recruited to recycling endosomes distinct from the TGN unknown","Division of labor between GGA2 and AP-1 unresolved"]},{"year":2025,"claim":"Connected GGA2 loss to TGN secretory granule biogenesis, organelle acidification, and immunopeptidome remodeling, proposing a pathway by which viral cleavage of GGA2 contributes to beta-cell antigen presentation.","evidence":"CVB5 protease 2A cleavage, GGA2 depletion, T1D donor pancreas immunostaining, TGN pH measurement, and immunopeptidome mass spectrometry (preprint)","pmids":["bio_10.1101_2025.03.28.645506"],"confidence":"Medium","gaps":["Not yet peer-reviewed","Direct causal link between GGA2 loss and autoimmune presentation in vivo not established","Mechanism connecting GGA2 to vacuolar ATPase sorting not fully defined"]},{"year":null,"claim":"How GGA2 is selectively recruited to distinct compartments (TGN vs Rab11 recycling endosomes), how it discriminates cargo conformation and competes with GGA1/GGA3 for shared cargo, and the cellular basis of its essential in vivo function remain open.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of cargo-fate competition among GGA paralogs","Compartment-specific recruitment determinants unidentified","Cause of neonatal lethality at the molecular level unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[1,2,3,8,9]},{"term_id":"GO:0038024","term_label":"cargo receptor activity","supporting_discovery_ids":[1,2,11]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[0,4]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[11,13]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[1,2,4,13]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[8,11,13]},{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[1,2,4]}],"complexes":[],"partners":["CIMPR","SORT1","BACE1","EGFR","ADRA2B","ITGB1","RAB13","RAB10"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9UJY4","full_name":"ADP-ribosylation factor-binding protein GGA2","aliases":["Gamma-adaptin-related protein 2","Golgi-localized, gamma ear-containing, ARF-binding protein 2","VHS domain and ear domain of gamma-adaptin","Vear"],"length_aa":613,"mass_kda":67.2,"function":"Plays a role in protein sorting and trafficking between the trans-Golgi network (TGN) and endosomes. Mediates the ARF-dependent recruitment of clathrin to the TGN and binds ubiquitinated proteins and membrane cargo molecules with a cytosolic acidic cluster-dileucine (DXXLL) motif (PubMed:10747088). Mediates export of the GPCR receptor ADRA2B to the cell surface (PubMed:27901063). Regulates retrograde transport of phosphorylated form of BACE1 from endosomes to the trans-Golgi network (PubMed:15615712)","subcellular_location":"Golgi apparatus, trans-Golgi network membrane; Endosome membrane; Early endosome membrane","url":"https://www.uniprot.org/uniprotkb/Q9UJY4/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/GGA2","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/GGA2","total_profiled":1310},"omim":[{"mim_id":"617366","title":"COILED-COIL DOMAIN-CONTAINING PROTEIN 91; CCDC91","url":"https://www.omim.org/entry/617366"},{"mim_id":"613439","title":"CONSORTIN; CNST","url":"https://www.omim.org/entry/613439"},{"mim_id":"607265","title":"CLATHRIN INTERACTOR 1; CLINT1","url":"https://www.omim.org/entry/607265"},{"mim_id":"606006","title":"GOLGI-ASSOCIATED, GAMMA-ADAPTIN EAR-CONTAINING, ARF-BINDING PROTEIN 3; GGA3","url":"https://www.omim.org/entry/606006"},{"mim_id":"606005","title":"GOLGI-ASSOCIATED, GAMMA-ADAPTIN EAR-CONTAINING, ARF-BINDING PROTEIN 2; GGA2","url":"https://www.omim.org/entry/606005"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Golgi apparatus","reliability":"Enhanced"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/GGA2"},"hgnc":{"alias_symbol":["VEAR","KIAA1080"],"prev_symbol":[]},"alphafold":{"accession":"Q9UJY4","domains":[{"cath_id":"1.25.40.90","chopping":"23-172","consensus_level":"high","plddt":88.8617,"start":23,"end":172},{"cath_id":"1.20.58.160","chopping":"182-313","consensus_level":"medium","plddt":86.0533,"start":182,"end":313},{"cath_id":"2.60.40.1230","chopping":"481-612","consensus_level":"high","plddt":87.6536,"start":481,"end":612}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UJY4","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UJY4-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UJY4-F1-predicted_aligned_error_v6.png","plddt_mean":71.25},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=GGA2","jax_strain_url":"https://www.jax.org/strain/search?query=GGA2"},"sequence":{"accession":"Q9UJY4","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9UJY4.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9UJY4/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UJY4"}},"corpus_meta":[{"pmid":"11331584","id":"PMC_11331584","title":"The sortilin cytoplasmic tail conveys Golgi-endosome transport and binds the VHS domain of the GGA2 sorting protein.","date":"2001","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/11331584","citation_count":371,"is_preprint":false},{"pmid":"11387476","id":"PMC_11387476","title":"Binding of GGA2 to the lysosomal enzyme sorting motif of the mannose 6-phosphate receptor.","date":"2001","source":"Science (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/11387476","citation_count":230,"is_preprint":false},{"pmid":"12135764","id":"PMC_12135764","title":"Memapsin 2 (beta-secretase) cytosolic domain binds to the VHS domains of GGA1 and GGA2: implications on the endocytosis mechanism of memapsin 2.","date":"2002","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/12135764","citation_count":101,"is_preprint":false},{"pmid":"10702286","id":"PMC_10702286","title":"Vear, a novel Golgi-associated protein with VHS and gamma-adaptin \"ear\" domains.","date":"2000","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/10702286","citation_count":91,"is_preprint":false},{"pmid":"7966337","id":"PMC_7966337","title":"The unusual structure of the human centromere (GGA)2 motif. Unpaired guanosine residues stacked between sheared G.A pairs.","date":"1994","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/7966337","citation_count":53,"is_preprint":false},{"pmid":"31076515","id":"PMC_31076515","title":"GGA2 and RAB13 promote activity-dependent β1-integrin recycling.","date":"2019","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/31076515","citation_count":39,"is_preprint":false},{"pmid":"19574226","id":"PMC_19574226","title":"Gga2 mediates sequential ubiquitin-independent and ubiquitin-dependent steps in the trafficking of ARN1 from the trans-Golgi network to the vacuole.","date":"2009","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/19574226","citation_count":32,"is_preprint":false},{"pmid":"29358589","id":"PMC_29358589","title":"GGA2 interacts with EGFR cytoplasmic domain to stabilize the receptor expression and promote cell growth.","date":"2018","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/29358589","citation_count":24,"is_preprint":false},{"pmid":"22291915","id":"PMC_22291915","title":"Analysis of Gga null mice demonstrates a non-redundant role for mammalian GGA2 during development.","date":"2012","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/22291915","citation_count":22,"is_preprint":false},{"pmid":"30578931","id":"PMC_30578931","title":"Integrative Genomic Analyses Identifies GGA2 as a Cooperative Driver of EGFR-Mediated Lung Tumorigenesis.","date":"2018","source":"Journal of thoracic oncology : official publication of the International Association for the Study of Lung Cancer","url":"https://pubmed.ncbi.nlm.nih.gov/30578931","citation_count":20,"is_preprint":false},{"pmid":"27901063","id":"PMC_27901063","title":"Regulation of α2B-Adrenergic Receptor Cell Surface Transport by GGA1 and GGA2.","date":"2016","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/27901063","citation_count":17,"is_preprint":false},{"pmid":"34799560","id":"PMC_34799560","title":"Clathrin adapters AP-1 and GGA2 support expression of epidermal growth factor receptor for cell growth.","date":"2021","source":"Oncogenesis","url":"https://pubmed.ncbi.nlm.nih.gov/34799560","citation_count":14,"is_preprint":false},{"pmid":"32761633","id":"PMC_32761633","title":"Plasma membrane to vacuole traffic induced by glucose starvation requires Gga2-dependent sorting at the trans-Golgi network.","date":"2020","source":"Biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/32761633","citation_count":12,"is_preprint":false},{"pmid":"24637350","id":"PMC_24637350","title":"Impact of genetic background on neonatal lethality of Gga2 gene-trap mice.","date":"2014","source":"G3 (Bethesda, Md.)","url":"https://pubmed.ncbi.nlm.nih.gov/24637350","citation_count":7,"is_preprint":false},{"pmid":"18431031","id":"PMC_18431031","title":"Specific depletion of GGA2 causes cathepsin D missorting in HeLa cells.","date":"2007","source":"Archives of histology and cytology","url":"https://pubmed.ncbi.nlm.nih.gov/18431031","citation_count":6,"is_preprint":false},{"pmid":"11473645","id":"PMC_11473645","title":"Podocyte-specific expression of a novel trans-Golgi protein Vear in human kidney.","date":"2001","source":"Kidney international","url":"https://pubmed.ncbi.nlm.nih.gov/11473645","citation_count":3,"is_preprint":false},{"pmid":"11150977","id":"PMC_11150977","title":"Vear, a novel Golgi-associated protein, is preferentially expressed in type I cells in skeletal muscle.","date":"2001","source":"Muscle & nerve","url":"https://pubmed.ncbi.nlm.nih.gov/11150977","citation_count":3,"is_preprint":false},{"pmid":"32355321","id":"PMC_32355321","title":"Author Correction: GGA2 interacts with EGFR cytoplasmic domain to stabilize the receptor expression and promote cell growth.","date":"2020","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/32355321","citation_count":1,"is_preprint":false},{"pmid":"41898765","id":"PMC_41898765","title":"Exploring the Role of GGA2 in Cancer Progression: Pan-Cancer Bioinformatics and Experimental Validation in Prostate Cancer.","date":"2026","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/41898765","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.03.28.645506","title":"GGA2-depletion in beta cells by Enteroviruses causes Golgi acidification, premature activation of cathepsins and alters the MHC class I immunopeptidome","date":"2025-03-31","source":"bioRxiv","url":"https://doi.org/10.1101/2025.03.28.645506","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":10803,"output_tokens":4493,"usd":0.049902,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":12445,"output_tokens":4287,"usd":0.0847,"stage2_stop_reason":"end_turn"},"total_usd":0.134602,"stage1_batch_id":"msgbatch_01DUPACZi7AAWwuZiUjseQF4","stage2_batch_id":"msgbatch_018yt7chE3f48PEFtDwtj6AE","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2000,\n      \"finding\": \"GGA2 (Vear) is a Golgi-localized protein with an N-terminal VHS domain and a C-terminal gamma-adaptin 'ear' domain. Full-length GGA2 and truncated forms lacking the VHS domain cause compaction of the Golgi complex upon overexpression; the ear domain alone associates with the Golgi without compaction; the VHS domain alone shows diffuse membrane/vesicle distribution. GGA2 partitions with the post-nuclear membrane fraction on cell fractionation.\",\n      \"method\": \"Immunofluorescence microscopy, cell fractionation, brefeldin A treatment, transfection of truncation constructs\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization and domain-dissection experiments in single lab with multiple orthogonal methods (immunofluorescence, fractionation, BFA sensitivity, truncation constructs)\",\n      \"pmids\": [\"10702286\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The VHS domain of GGA2 binds to the acidic cluster-dileucine motif in the cytoplasmic tail of the cation-independent mannose 6-phosphate receptor (CI-MPR). This interaction is required for lysosomal enzyme sorting: receptors with mutations in this motif are defective in sorting. The hinge domain of GGA2 binds clathrin, suggesting GGA2 links cargo to clathrin-coated vesicle assembly.\",\n      \"method\": \"Binding assays (VHS domain with CI-MPR cytoplasmic tail peptides), mutagenesis of the acidic cluster-dileucine motif, clathrin-binding assay with GGA2 hinge domain\",\n      \"journal\": \"Science (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro binding assays with domain-specific constructs, mutagenesis establishing functional requirement, hinge-clathrin interaction, replicated in context by multiple labs\",\n      \"pmids\": [\"11387476\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The VHS domain of GGA2 binds the cytoplasmic tail of sortilin via YXX and dileucine sorting motifs, and sortilin chimeric receptors containing the sortilin tail efficiently transport lysosomal enzymes (beta-hexosaminidase, beta-glucuronidase) to lysosomes in MPR-knockout cells, identifying sortilin as the first mammalian receptor targeted by the GGA family.\",\n      \"method\": \"Chimeric receptor expression in MPR-knockout cells, lysosomal enzyme transport assay, VHS domain binding to sortilin cytoplasmic tail\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — reconstituted lysosomal enzyme transport in defined genetic background (MPR-KO), binding assays, mutagenesis of sorting motifs\",\n      \"pmids\": [\"11331584\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"The VHS domains of GGA1 and GGA2 bind the cytosolic domain of memapsin 2 (beta-secretase/BACE1). Mutagenesis identified Asp496, Leu499, and Leu500 as essential residues in memapsin 2 for this interaction, matching the spacing found in CI-MPR, sortilin, and LRP3 cytoplasmic tails. Gel-immobilized VHS domains of GGA2 pull down full-length memapsin 2 from mammalian cell lysates.\",\n      \"method\": \"Pulldown assay with immobilized VHS domains, mammalian cell lysate pulldown, site-directed mutagenesis of memapsin 2 cytoplasmic domain\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pulldown from cell lysates plus mutagenesis identifying specific residues, single lab\",\n      \"pmids\": [\"12135764\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Specific RNAi-mediated depletion of GGA2 (to ~5% of control levels) in HeLa cells increases secretion of the lysosomal enzyme cathepsin D without altering the distribution of GGA1, GGA3, or MPRs, establishing a non-redundant role for GGA2 in lysosomal enzyme sorting at the TGN. The dominant-negative VHS-GAT domain of GGA2 is recruited to the TGN independently of GGA1 and GGA3.\",\n      \"method\": \"Stable RNAi knockdown cell lines, cathepsin D secretion assay, immunofluorescence for TGN markers, dominant-negative domain expression\",\n      \"journal\": \"Archives of histology and cytology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — stable KD with specific phenotypic readout (cathepsin D secretion), single lab\",\n      \"pmids\": [\"18431031\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"In yeast, Gga2 is required for TGN-to-vacuole sorting of the iron transporter Arn1p. Ubiquitin binding by Gga2 is NOT required for the initial TGN-to-endosome step but IS required for subsequent multivesicular body sorting of Arn1p: a ubiquitin-binding mutant of Gga2 causes accumulation of ubiquitinated Arn1p on the vacuolar membrane. Yeast epsins Ent3p and Ent4p also participate. N-terminal sequences of Arn1p (THN and YGL motifs, ubiquitinatable lysines) are required for vacuolar sorting.\",\n      \"method\": \"Yeast genetics, ubiquitin-binding mutant analysis, fluorescence microscopy of GFP-tagged Arn1p, mutagenesis of Arn1p sorting motifs\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple mutant alleles, reconstitution of sorting steps, mutagenesis of cargo and adaptor, epistasis analysis with epsins\",\n      \"pmids\": [\"19574226\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"GGA2 knockout mice (using the Tigm gene-trap allele) show neonatal lethality, whereas GGA1 or GGA3 single knockouts are well tolerated. This establishes a non-redundant, essential in vivo function for GGA2 that cannot be compensated by GGA1 or GGA3.\",\n      \"method\": \"Insertional mutagenesis, mouse knockout analysis, neonatal viability phenotyping\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — defined in vivo genetic knockout with clear phenotype, replicated with multiple alleles and genetic backgrounds in follow-up study\",\n      \"pmids\": [\"22291915\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The Byg Gga2 gene-trap allele is hypomorphic (residual GGA2 expression), while the Tigm allele is a true null; neonatal lethality of Tigm Gga2−/− mice is influenced by genetic background (C57BL/6 vs. mixed C57BL6/Ola129Sv). Surviving Gga2−/− mice show reduced birth weight maintained through adulthood.\",\n      \"method\": \"Gene-trap allele characterization, Western blotting, cross-breeding to different genetic backgrounds, growth curve analysis\",\n      \"journal\": \"G3 (Bethesda, Md.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — allele-level genetic analysis clarifying prior knockout result, single lab\",\n      \"pmids\": [\"24637350\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"GGA2 (and GGA1) are required for cell-surface transport of α2B-adrenergic receptor (α2B-AR). Knockdown of GGA2 arrests newly synthesized α2B-AR in the perinuclear region and reduces dendritic receptor expression in cortical neurons. The third intracellular loop of α2B-AR directly interacts with both GGA1 and GGA2; the GAE (gamma-adaptin ear) domain of GGA2 (and the hinge of GGA1) binds multiple subdomains of this loop. Full-length α2B-AR co-immunoprecipitates with GGA2 but not GGA1.\",\n      \"method\": \"shRNA/siRNA knockdown, co-immunoprecipitation, domain-mapping pulldown assays, primary cortical neuron imaging, ERK1/2 and cAMP signaling assays\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — reciprocal co-IP and domain mapping, KD with defined trafficking phenotype and signaling readout, single lab\",\n      \"pmids\": [\"27901063\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"GGA2 interacts with the cytoplasmic juxtamembrane region (jxt) of EGFR via its VHS-GAT domains in a manner dependent on Asn108 in the VHS domain. GGA2 depletion greatly reduces steady-state EGFR expression by enhancing lysosomal degradation; this effect is reversed by additional depletion of GGA1 or GGA3, indicating GGA1/GGA3 promote EGFR degradation while GGA2 counteracts this. GGA2 depletion reduces EGF signaling and cell proliferation in vitro and in xenograft models.\",\n      \"method\": \"RNAi knockdown, pulldown assays with VHS-GAT domain constructs, proximity ligation assay, mutagenesis (N108), rescue by double knockdown, xenograft tumor model\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — direct binding assay with mutagenesis, in situ PLA, double-KD rescue establishing functional antagonism, in vivo xenograft validation\",\n      \"pmids\": [\"29358589\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"GGA2 interacts with EGFR (co-immunoprecipitation), increases EGFR protein levels, and modifies EGFR degradation after ligand stimulation. GGA2 overexpression enhances EGFR-mediated cellular transformation; GGA2 knockdown reduces colony and tumor formation of EGFR-mutant lung adenocarcinoma cells.\",\n      \"method\": \"Co-immunoprecipitation, Western blot, RNAi knockdown, gene overexpression, colony formation assay, in vivo tumor models\",\n      \"journal\": \"Journal of thoracic oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — co-IP plus functional KD/OE with tumor phenotype, single lab, partially overlapping with PMID:29358589\",\n      \"pmids\": [\"30578931\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"GGA2 associates with active (but not inactive) β1-integrin and is required for recycling of active β1-integrin receptors to the plasma membrane. GGA2 silencing reduces active β1-integrin in focal adhesions and decreases cancer cell migration and invasion. BioID proximity labeling identified RAB13 and RAB10 as GGA2 interactors; RAB13 silencing phenocopies GGA2 depletion (intracellular accumulation of active β1-integrin, reduced focal adhesion levels, reduced migration), placing GGA2 and RAB13 in the same active integrin recycling pathway.\",\n      \"method\": \"RNAi screen, co-immunoprecipitation, BioID proximity labeling, integrin activity assay (active-conformation antibody), focal adhesion imaging, migration/invasion assays\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — BioID plus reciprocal co-IP, activity-specific integrin assay, KD of both GGA2 and RAB13 showing identical phenotype, multiple cellular readouts\",\n      \"pmids\": [\"31076515\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"In yeast, Gga2 is required for maximal vacuolar delivery of amino acid permeases (Mup1, Can1, and others) during acute glucose starvation. Endocytosed Can1 transits through the TGN under both starved and glucose-replete conditions, and TGN-localized clathrin adaptors (including Gga2) are required for vacuolar sorting in both states. Forced de-ubiquitination at the TGN causes recycling of Tat1 permease in starved cells, showing active sorting to the vacuole. AP-1 plays only a minor role.\",\n      \"method\": \"Fluorescence microscopy of GFP-tagged permeases, genetic deletion of clathrin adaptors, ectopic de-ubiquitination at TGN\",\n      \"journal\": \"Biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with defined cargo readout and mechanistic de-ubiquitination experiment, single lab\",\n      \"pmids\": [\"32761633\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"GGA2 and AP-1 both support EGFR recycling from Rab11-positive recycling endosomes to the plasma membrane (rather than acting solely at the TGN). Depletion of AP-1 or GGA2 suppresses EGFR recycling and reduces cell-surface levels of EGFR, MET, and ErbB4, reducing cancer cell growth. Triple immunofluorescence and proximity ligation assays showed EGFR interaction with GGA2 or AP-1 more frequently at Rab11-positive endosomes than Rab5-positive early endosomes.\",\n      \"method\": \"Biochemical recycling assay, triple immunofluorescence microscopy, proximity ligation assay, RNAi depletion, xenograft model\",\n      \"journal\": \"Oncogenesis\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — biochemical recycling assay (direct functional readout), in situ PLA for spatial localization, KD phenotype with multiple RTK cargo, in vivo xenograft validation\",\n      \"pmids\": [\"34799560\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"GGA2 is rapidly depleted in pancreatic beta cells by Coxsackievirus B5 protease 2A (due to its short half-life). GGA2 depletion impairs insulin secretory granule biogenesis at the TGN, disrupts sorting of vacuolar ATPase and cathepsins, causes TGN acidification, and leads to premature lysosomal hydrolase activation. These changes alter the HLA-I immunopeptidome, shifting it towards HLA-B–presented, low-pI peptides generated by cathepsin-mediated processing of in-transit secretory proteins.\",\n      \"method\": \"CVB5 infection of beta cells, GGA2 depletion (siRNA/viral), immunostaining of pancreas sections from T1D donors, mass spectrometry of immunopeptidome, TGN pH measurement\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple mechanistic readouts (pH, cathepsin activation, granule biogenesis, immunopeptidome) in a single preprint study; not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.03.28.645506\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"GGA2 is a Golgi/TGN-localized clathrin adaptor whose VHS domain binds acidic cluster-dileucine motifs on cargo receptors (CI-MPR, sortilin, memapsin 2/BACE1, EGFR), its hinge domain recruits clathrin, and its GAE domain interacts with GPCRs (e.g., α2B-AR); it directs cargo (lysosomal enzymes, EGFR, active β1-integrin) from the TGN and recycling endosomes to appropriate destinations, opposes GGA1/GGA3-driven EGFR lysosomal degradation to sustain receptor expression, and cooperates with RAB13 for activity-dependent integrin recycling, with loss of GGA2 causing neonatal lethality in mice indicating a non-redundant essential function.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"GGA2 is a Golgi/TGN-localized clathrin adaptor that links transmembrane cargo to clathrin-coated vesicle formation, controlling sorting of cargo from the trans-Golgi network and recycling endosomes to their correct destinations [#0, #1]. Its N-terminal VHS domain recognizes acidic cluster-dileucine and related sorting motifs in the cytoplasmic tails of lysosomal enzyme receptors\\u2014the cation-independent mannose-6-phosphate receptor and sortilin\\u2014as well as memapsin 2 (BACE1), while its hinge region recruits clathrin, providing a physical bridge between sorting signals and coat assembly [#1, #2, #3]. Through this activity GGA2 carries out a non-redundant role in lysosomal enzyme sorting at the TGN: its specific depletion drives missecretion of cathepsin D without disrupting the other GGA proteins or the MPRs [#4]. GGA2 also governs receptor trafficking beyond lysosomal targeting: its GAE domain binds the third intracellular loop of the \\u03b12B-adrenergic receptor to promote receptor delivery to the cell surface [#8], and it associates with EGFR via its VHS-GAT domains in a manner dependent on Asn108 to sustain receptor levels by antagonizing GGA1/GGA3-driven lysosomal degradation, thereby supporting EGF signaling, proliferation, and tumor growth [#9, #10]. GGA2 supports recycling of EGFR and related receptor tyrosine kinases (MET, ErbB4) from Rab11-positive recycling endosomes to the plasma membrane [#13], and cooperates with RAB13 to recycle active \\u03b21-integrin, promoting focal adhesion formation, migration, and invasion [#11]. In yeast, Gga2 mediates TGN-to-vacuole sorting of the iron transporter Arn1p and amino acid permeases, with its ubiquitin-binding activity required for multivesicular body sorting [#5, #12]. Gga2 function is essential in vivo: knockout mice display neonatal lethality not compensated by GGA1 or GGA3 [#6].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Established GGA2 as a Golgi-localized protein with a modular VHS\\u2013ear architecture, framing it as a candidate membrane trafficking adaptor.\",\n      \"evidence\": \"Immunofluorescence, cell fractionation, BFA sensitivity, and truncation-construct expression in transfected cells\",\n      \"pmids\": [\"10702286\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No cargo or sorting motif identified at this stage\", \"Functional role of the Golgi compaction phenotype unclear\", \"No demonstration of clathrin or coat recruitment\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Defined the core sorting mechanism\\u2014the VHS domain reads acidic cluster-dileucine motifs in receptor tails while the hinge binds clathrin\\u2014answering how GGA2 couples cargo selection to coated-vesicle assembly.\",\n      \"evidence\": \"In vitro VHS-domain binding to CI-MPR and sortilin tail peptides, sorting-motif mutagenesis, chimeric receptor lysosomal enzyme transport in MPR-knockout cells, and hinge-clathrin binding assays\",\n      \"pmids\": [\"11387476\", \"11331584\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and regulation of cargo loading not resolved\", \"Did not establish in vivo requirement\", \"Relative contributions of CI-MPR vs sortilin pathways unquantified\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Extended the VHS recognition code to memapsin 2/BACE1, showing GGA2 binds a conserved motif spacing shared across multiple cargoes.\",\n      \"evidence\": \"Pulldown of full-length memapsin 2 with immobilized VHS domains and site-directed mutagenesis (Asp496/Leu499/Leu500)\",\n      \"pmids\": [\"12135764\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence for BACE1 trafficking not tested\", \"Single-lab pulldown without cellular trafficking readout\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Demonstrated that GGA2 has a non-redundant role in lysosomal enzyme sorting, distinct from GGA1 and GGA3.\",\n      \"evidence\": \"Stable RNAi depletion of GGA2 in HeLa cells with cathepsin D secretion assay and TGN-marker immunofluorescence\",\n      \"pmids\": [\"18431031\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of non-redundancy not explained\", \"Did not identify GGA2-specific cargo determinants\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Established in yeast that Gga2 ubiquitin binding is dispensable for the TGN-to-endosome step but required for downstream MVB sorting, partitioning its sorting activity into discrete stages.\",\n      \"evidence\": \"Yeast genetics, ubiquitin-binding mutant analysis, GFP-Arn1p microscopy, cargo-motif mutagenesis, and epistasis with epsins Ent3p/Ent4p\",\n      \"pmids\": [\"19574226\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mammalian relevance of the ubiquitin-binding step not addressed\", \"How Gga2 hands cargo to the MVB machinery unresolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Showed GGA2 is essential in vivo, with a function that GGA1 and GGA3 cannot compensate.\",\n      \"evidence\": \"Tigm gene-trap knockout mouse with neonatal viability phenotyping\",\n      \"pmids\": [\"22291915\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cause of neonatal lethality at the cellular/cargo level unknown\", \"Tissue-specific requirements not dissected\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Clarified the genetic basis of the lethality phenotype by distinguishing null from hypomorphic alleles and revealing genetic background modifiers.\",\n      \"evidence\": \"Gene-trap allele characterization, Western blotting, cross-breeding to different backgrounds, and growth curve analysis\",\n      \"pmids\": [\"24637350\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Identity of background modifier loci unknown\", \"Molecular cause of reduced birth weight not defined\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Revealed a GAE-domain\\u2013mediated mechanism for forward trafficking, with GGA2 promoting cell-surface delivery of a GPCR via its third intracellular loop.\",\n      \"evidence\": \"shRNA/siRNA knockdown, reciprocal co-IP, domain-mapping pulldowns, cortical neuron imaging, and ERK/cAMP signaling assays\",\n      \"pmids\": [\"27901063\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Why \\u03b12B-AR binds GGA2 but not GGA1 in co-IP not explained\", \"Generality across other GPCRs untested\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identified GGA2 as a positive regulator of EGFR stability that opposes GGA1/GGA3-driven lysosomal degradation, linking GGA2 to receptor tyrosine kinase signaling and tumor growth.\",\n      \"evidence\": \"VHS-GAT pulldowns with N108 mutagenesis, proximity ligation assay, double-knockdown rescue, co-IP, overexpression, and xenograft tumor models\",\n      \"pmids\": [\"29358589\", \"30578931\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of the GGA1/GGA3 vs GGA2 fate decision unresolved\", \"Whether GGA2 acts at TGN or endosomes for this function not yet localized\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Placed GGA2 in an active-integrin recycling pathway with RAB13, expanding its role to conformation-selective cargo recycling that drives migration and invasion.\",\n      \"evidence\": \"RNAi screen, BioID proximity labeling identifying RAB13/RAB10, reciprocal co-IP, active-conformation integrin assay, focal adhesion imaging, and migration/invasion assays\",\n      \"pmids\": [\"31076515\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How GGA2 discriminates active from inactive integrin conformation unknown\", \"Direct vs indirect nature of the GGA2-RAB13 interaction not resolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Localized a major GGA2 trafficking step to Rab11-positive recycling endosomes, showing GGA2 (with AP-1) recycles multiple RTKs to the plasma membrane rather than acting solely at the TGN.\",\n      \"evidence\": \"Biochemical recycling assay, triple immunofluorescence, proximity ligation assay quantifying Rab11 vs Rab5 association, RNAi depletion, and xenograft models\",\n      \"pmids\": [\"34799560\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How GGA2 is recruited to recycling endosomes distinct from the TGN unknown\", \"Division of labor between GGA2 and AP-1 unresolved\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Connected GGA2 loss to TGN secretory granule biogenesis, organelle acidification, and immunopeptidome remodeling, proposing a pathway by which viral cleavage of GGA2 contributes to beta-cell antigen presentation.\",\n      \"evidence\": \"CVB5 protease 2A cleavage, GGA2 depletion, T1D donor pancreas immunostaining, TGN pH measurement, and immunopeptidome mass spectrometry (preprint)\",\n      \"pmids\": [\"bio_10.1101_2025.03.28.645506\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Not yet peer-reviewed\", \"Direct causal link between GGA2 loss and autoimmune presentation in vivo not established\", \"Mechanism connecting GGA2 to vacuolar ATPase sorting not fully defined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How GGA2 is selectively recruited to distinct compartments (TGN vs Rab11 recycling endosomes), how it discriminates cargo conformation and competes with GGA1/GGA3 for shared cargo, and the cellular basis of its essential in vivo function remain open.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of cargo-fate competition among GGA paralogs\", \"Compartment-specific recruitment determinants unidentified\", \"Cause of neonatal lethality at the molecular level unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [1, 2, 3, 8, 9]},\n      {\"term_id\": \"GO:0038024\", \"supporting_discovery_ids\": [1, 2, 11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [0, 4]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [11, 13]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [1, 2, 4, 13]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [8, 11, 13]},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [1, 2, 4]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"CIMPR\", \"SORT1\", \"BACE1\", \"EGFR\", \"ADRA2B\", \"ITGB1\", \"RAB13\", \"RAB10\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}