{"gene":"TRAPPC4","run_date":"2026-06-10T10:51:55","timeline":{"discoveries":[{"year":2021,"finding":"TRAPPC4 interacts with PD-L1 in recycling endosomes, acting as a scaffold between PD-L1 and RAB11, thereby promoting RAB11-mediated recycling of PD-L1 back to the tumor cell surface. TRAPPC4 depletion significantly reduces PD-L1 surface expression in vitro and in vivo.","method":"Co-immunoprecipitation, subcellular fractionation/localization, knockdown/overexpression with PD-L1 surface expression readout, in vivo tumor models","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP establishing scaffold interaction, subcellular localization in recycling endosomes, functional rescue by overexpression, validated in vivo","pmids":["34518538"],"is_preprint":false},{"year":2023,"finding":"Acetylation of PD-L1 protein increases its interaction with TRAPPC4, leading to enhanced surface localization of PD-L1 on pancreatic cancer cells.","method":"HDAC inhibitor (VPA) treatment, Co-immunoprecipitation of acetylated PD-L1 with TRAPPC4, flow cytometry for surface PD-L1","journal":"Discover oncology","confidence":"Medium","confidence_rationale":"Tier 3 / Weak — single lab, single Co-IP under pharmacological perturbation, no direct mutagenesis of acetylation sites to confirm causality","pmids":["37603071"],"is_preprint":false},{"year":2011,"finding":"TRAPPC4 physically interacts with ERK2 (identified by yeast two-hybrid and confirmed by Co-IP and GST pull-down). TRAPPC4 depletion decreases activated ERK1/2 specifically in the nucleus, while overexpression promotes nuclear accumulation of phospho-ERK1/2 and increases cell viability; TRAPPC4 knockdown induces apoptosis in colorectal cancer cells.","method":"Yeast two-hybrid, Co-immunoprecipitation, GST pull-down, subcellular fractionation, knockdown/overexpression with proliferation and apoptosis readouts","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — interaction confirmed by three orthogonal methods (Y2H, Co-IP, GST pull-down), functional consequence with localization readout, single lab","pmids":["21826244"],"is_preprint":false},{"year":2013,"finding":"TRAPPC4 regulates ERK2 activation and nuclear translocation of phospho-ERK2 in colorectal cancer cells; silencing TRAPPC4 causes G0/G1 arrest with upregulation of p21 and downregulation of cyclin B1, while overexpression rescues ERK2-silencing-induced cell cycle effects. EGF stimulation upregulates both TRAPPC4 and pERK2 and induces pERK2 nuclear translocation.","method":"siRNA knockdown, overexpression, immunohistochemistry, cell cycle analysis, xenograft tumor models","journal":"Molecular carcinogenesis","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo xenograft plus in vitro cell cycle and signaling assays; replicates and extends prior TRAPPC4-ERK2 interaction finding; single lab","pmids":["23625650"],"is_preprint":false},{"year":2020,"finding":"TRAPPC4, like its yeast Trs23 orthologue, is a core TRAPP complex subunit required for guanine nucleotide exchange factor (GEF) activity toward Rab1 GTPase. A splice variant (c.454+3A>G) reduces full-length TRAPPC4 protein and disrupts TRAPP complex assembly/stability, causing delayed ER-to-Golgi and intra-Golgi trafficking (VSVG-GFP-ts045 assay), basal autophagy defects, and delayed autophagic flux in patient fibroblasts. Lentiviral re-expression of wild-type TRAPPC4 restored trafficking. Yeast trs23 temperature-sensitive variants phenocopy autophagy and secretory defects.","method":"Native PAGE and size exclusion chromatography (TRAPP complex assembly), VSVG-GFP-ts045 trafficking assay, autophagy flux assay, lentiviral complementation, yeast genetic model","journal":"Brain : a journal of neurology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal assays (complex assembly, trafficking reconstitution, autophagy flux, genetic complementation in patient cells and yeast), mechanistic rescue experiment included","pmids":["31794024"],"is_preprint":false},{"year":2026,"finding":"TRAPPC4 promotes GPX4 protein stability by decreasing chromatin accessibility at a distal regulatory element upstream of TRIM55, thereby limiting FOS-dependent TRIM55 transcription. Reduced TRIM55 diminishes TRIM55-mediated ubiquitination and degradation of GPX4, resulting in GPX4 stabilization and ferroptosis resistance. Structure-based screening identified pitavastatin calcium as a TRAPPC4-binding compound that promotes TRAPPC4 degradation and synergizes with the ferroptosis inducer RSL3.","method":"Genome-wide CRISPR-Cas9 knockout screen, patient-derived organoids, xenografts, conditional knockout mice, ATAC-seq (chromatin accessibility), ubiquitination assay, structure-based virtual screening, drug synergy experiments","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — genome-wide unbiased screen plus mechanistic dissection across multiple orthogonal models (cell lines, organoids, CDX, PDX, conditional KO mice) with ATAC-seq and ubiquitination assays","pmids":["41974002"],"is_preprint":false}],"current_model":"TRAPPC4 is a core TRAPP complex subunit that provides GEF activity for Rab1, mediates ER-to-Golgi vesicular trafficking and autophagosome maturation, scaffolds PD-L1 with RAB11 in recycling endosomes to recycle PD-L1 to the cell surface, interacts with and modulates nuclear localization of phospho-ERK1/2 to regulate cell proliferation and apoptosis, and suppresses TRIM55-mediated ubiquitination/degradation of GPX4 to confer ferroptosis resistance."},"narrative":{"mechanistic_narrative":"TRAPPC4 is a core subunit of the multimeric TRAPP complex that drives intracellular membrane trafficking and is co-opted in cancer to control immune evasion, proliferation, and ferroptosis resistance [PMID:31794024, PMID:34518538]. As a TRAPP subunit it is required for guanine nucleotide exchange activity toward the Rab1 GTPase, and its loss disrupts TRAPP complex assembly/stability, delaying ER-to-Golgi and intra-Golgi trafficking and impairing basal autophagy and autophagic flux; a splice variant (c.454+3A>G) reduces full-length protein and causes these defects, which are reversed by wild-type re-expression [PMID:31794024]. In tumor cells TRAPPC4 acts as a scaffold linking PD-L1 to RAB11 in recycling endosomes, promoting RAB11-mediated recycling of PD-L1 to the cell surface, an interaction enhanced by PD-L1 acetylation [PMID:34518538, PMID:37603071]. Independently, TRAPPC4 binds ERK2 and governs the nuclear accumulation of phospho-ERK1/2, thereby promoting cell-cycle progression and viability while its depletion induces G0/G1 arrest, p21 upregulation, and apoptosis in colorectal cancer cells [PMID:21826244, PMID:23625650]. TRAPPC4 also confers ferroptosis resistance by reducing chromatin accessibility at a regulatory element upstream of TRIM55, limiting FOS-dependent TRIM55 transcription and thereby suppressing TRIM55-mediated ubiquitination and degradation of GPX4 [PMID:41974002].","teleology":[{"year":2011,"claim":"Established that TRAPPC4 is not solely a trafficking factor but physically engages the MAPK pathway, defining a route by which it influences proliferation and survival.","evidence":"Yeast two-hybrid, Co-IP, and GST pull-down for ERK2 binding with subcellular fractionation and knockdown/overexpression in colorectal cancer cells","pmids":["21826244"],"confidence":"Medium","gaps":["Direct binding region/interface on TRAPPC4 not mapped","Mechanism by which TRAPPC4 controls nuclear pERK localization unresolved","Single lab"]},{"year":2013,"claim":"Connected the TRAPPC4-ERK2 axis to defined cell-cycle control, showing TRAPPC4 is required for EGF-driven pERK2 nuclear translocation and proliferation in vivo.","evidence":"siRNA/overexpression, cell cycle analysis, IHC, and xenograft models with EGF stimulation","pmids":["23625650"],"confidence":"Medium","gaps":["Does not establish whether trafficking role and ERK role are mechanistically coupled","Single lab"]},{"year":2020,"claim":"Defined the conserved core mechanism: TRAPPC4 is a TRAPP subunit required for Rab1 GEF activity and complex stability, linking its loss to secretory and autophagy defects in human disease.","evidence":"Native PAGE/SEC complex assembly, VSVG-GFP-ts045 trafficking assay, autophagy flux, lentiviral complementation in patient fibroblasts, and yeast trs23 genetic model","pmids":["31794024"],"confidence":"High","gaps":["Structural detail of how TRAPPC4 contributes to GEF catalysis not resolved","Specific neurological disease entity not detailed here"]},{"year":2021,"claim":"Revealed a cancer-specific membrane-trafficking role: TRAPPC4 scaffolds PD-L1 to RAB11 for recycling-endosome return to the surface, implicating it in tumor immune evasion.","evidence":"Reciprocal Co-IP, subcellular fractionation, knockdown/overexpression with PD-L1 surface readout, and in vivo tumor models","pmids":["34518538"],"confidence":"High","gaps":["Binding interface between TRAPPC4 and PD-L1 not mapped","Relationship to core TRAPP/Rab1 function unclear"]},{"year":2023,"claim":"Extended the recycling model by showing PD-L1 acetylation increases its TRAPPC4 association and surface localization in pancreatic cancer.","evidence":"HDAC inhibitor (VPA) treatment, Co-IP of acetylated PD-L1 with TRAPPC4, and flow cytometry for surface PD-L1","pmids":["37603071"],"confidence":"Medium","gaps":["No mutagenesis of acetylation sites to confirm causality","Single Co-IP under pharmacological perturbation","Single lab"]},{"year":2026,"claim":"Identified a transcription/chromatin-linked function whereby TRAPPC4 limits TRIM55 expression to stabilize GPX4 and confer ferroptosis resistance, and nominated a druggable handle.","evidence":"Genome-wide CRISPR knockout screen, ATAC-seq, ubiquitination assays, organoids/CDX/PDX and conditional KO mice, plus structure-based screening identifying pitavastatin calcium","pmids":["41974002"],"confidence":"High","gaps":["Mechanism by which a trafficking subunit modulates chromatin accessibility unexplained","Direct DNA/chromatin association of TRAPPC4 not demonstrated"]},{"year":null,"claim":"How TRAPPC4's conserved TRAPP/Rab1 trafficking function mechanistically relates to its distinct roles in ERK nuclear signaling, PD-L1 recycling, and TRIM55/GPX4-mediated ferroptosis resistance remains unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No unifying model connecting the trafficking, signaling, and chromatin roles","Structural basis of non-TRAPP interactions undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[4]}],"localization":[{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[0]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[4]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,4]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[4]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[5]}],"complexes":["TRAPP complex"],"partners":["PD-L1","RAB11","ERK2","RAB1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9Y296","full_name":"Trafficking protein particle complex subunit 4","aliases":["Hematopoietic stem/progenitor cell protein 172","Synbindin","TRS23 homolog"],"length_aa":219,"mass_kda":24.3,"function":"Core component of the TRAPP complexes which has a function of guanine nucleotide exchange factor activity for Rab1 GTPase (Probable). Plays a role in vesicular transport from endoplasmic reticulum to Golgi and autophagy (PubMed:31794024). May play a role in dendrite postsynaptic membrane trafficking (By similarity)","subcellular_location":"Postsynaptic cell membrane; Golgi apparatus membrane; Endoplasmic reticulum; Vesicle","url":"https://www.uniprot.org/uniprotkb/Q9Y296/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/TRAPPC4","classification":"Common Essential","n_dependent_lines":1170,"n_total_lines":1208,"dependency_fraction":0.9685430463576159},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"TRAPPC1","stoichiometry":10.0},{"gene":"TRAPPC2","stoichiometry":10.0},{"gene":"MIS12","stoichiometry":4.0},{"gene":"ACTR2","stoichiometry":0.2},{"gene":"ARL3","stoichiometry":0.2},{"gene":"ARL6IP6","stoichiometry":0.2},{"gene":"ARL8A","stoichiometry":0.2},{"gene":"ARL8B","stoichiometry":0.2},{"gene":"KRAS","stoichiometry":0.2},{"gene":"TRAPPC11","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/TRAPPC4","total_profiled":1310},"omim":[{"mim_id":"618741","title":"NEURODEVELOPMENTAL DISORDER WITH EPILEPSY, SPASTICITY, AND BRAIN ATROPHY; NEDESBA","url":"https://www.omim.org/entry/618741"},{"mim_id":"614781","title":"TECTONIN BETA-PROPELLER REPEAT-CONTAINING 1; TECPR1","url":"https://www.omim.org/entry/614781"},{"mim_id":"610971","title":"TRAFFICKING PROTEIN PARTICLE COMPLEX, SUBUNIT 4; TRAPPC4","url":"https://www.omim.org/entry/610971"},{"mim_id":"168600","title":"PARKINSON DISEASE, LATE-ONSET; PD","url":"https://www.omim.org/entry/168600"},{"mim_id":"142460","title":"SYNDECAN 2; SDC2","url":"https://www.omim.org/entry/142460"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/TRAPPC4"},"hgnc":{"alias_symbol":["TRS23","SBDN","PTD009"],"prev_symbol":[]},"alphafold":{"accession":"Q9Y296","domains":[{"cath_id":"3.30.450.70","chopping":"2-22_103-212","consensus_level":"high","plddt":92.5155,"start":2,"end":212},{"cath_id":"2.30.42.40","chopping":"26-98","consensus_level":"high","plddt":92.2348,"start":26,"end":98}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y296","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y296-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y296-F1-predicted_aligned_error_v6.png","plddt_mean":90.62},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=TRAPPC4","jax_strain_url":"https://www.jax.org/strain/search?query=TRAPPC4"},"sequence":{"accession":"Q9Y296","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9Y296.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9Y296/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y296"}},"corpus_meta":[{"pmid":"34518538","id":"PMC_34518538","title":"TRAPPC4 regulates the intracellular trafficking of PD-L1 and antitumor immunity.","date":"2021","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/34518538","citation_count":64,"is_preprint":false},{"pmid":"31794024","id":"PMC_31794024","title":"Deficiencies in vesicular transport mediated by TRAPPC4 are associated with severe syndromic intellectual disability.","date":"2020","source":"Brain : a journal of neurology","url":"https://pubmed.ncbi.nlm.nih.gov/31794024","citation_count":38,"is_preprint":false},{"pmid":"21826244","id":"PMC_21826244","title":"TRAPPC4-ERK2 interaction activates ERK1/2, modulates its nuclear localization and regulates proliferation and apoptosis of colorectal cancer cells.","date":"2011","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/21826244","citation_count":31,"is_preprint":false},{"pmid":"23625650","id":"PMC_23625650","title":"The role of ERK2 in colorectal carcinogenesis is partly regulated by TRAPPC4.","date":"2013","source":"Molecular carcinogenesis","url":"https://pubmed.ncbi.nlm.nih.gov/23625650","citation_count":16,"is_preprint":false},{"pmid":"32901138","id":"PMC_32901138","title":"A relatively common homozygous TRAPPC4 splicing variant is associated with an early-infantile neurodegenerative syndrome.","date":"2020","source":"European journal of human genetics : EJHG","url":"https://pubmed.ncbi.nlm.nih.gov/32901138","citation_count":15,"is_preprint":false},{"pmid":"37603071","id":"PMC_37603071","title":"Acetylation increases expression, interaction with TRAPPC4 and surface localization of PD-L1.","date":"2023","source":"Discover oncology","url":"https://pubmed.ncbi.nlm.nih.gov/37603071","citation_count":7,"is_preprint":false},{"pmid":"41974002","id":"PMC_41974002","title":"TRAPPC4 Promotes GPX4 Stability to Drive Ferroptosis Resistance and Tumor Progression in Head and Neck Squamous Cell Carcinoma.","date":"2026","source":"Cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/41974002","citation_count":0,"is_preprint":false},{"pmid":"40173375","id":"PMC_40173375","title":"Child Neurology: TRAPPC4-Related Neurodevelopmental Disorder.","date":"2025","source":"Neurology","url":"https://pubmed.ncbi.nlm.nih.gov/40173375","citation_count":0,"is_preprint":false},{"pmid":"39787667","id":"PMC_39787667","title":"Generation and heterozygous repair of human iPSC lines from two individuals with the neurodevelopmental disorder, TRAPPC4 deficiency.","date":"2024","source":"Stem cell research","url":"https://pubmed.ncbi.nlm.nih.gov/39787667","citation_count":0,"is_preprint":false},{"pmid":"39818540","id":"PMC_39818540","title":"Identification of TRAPPC4 as a Key Autoantigen in Immune-Related Pancytopenia: Epitope Characterization and Immune Activation Mechanisms.","date":"2025","source":"Turkish journal of haematology : official journal of Turkish Society of Haematology","url":"https://pubmed.ncbi.nlm.nih.gov/39818540","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.01.02.25319880","title":"Integrating GWAS and Transcriptomic Data Using PrediXcan and Multimodal Deep Learning Reveals Genetic Basis and Drug Repositioning Opportunities for Alzheimer’s Disease","date":"2025-01-02","source":"bioRxiv","url":"https://doi.org/10.1101/2025.01.02.25319880","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7786,"output_tokens":1814,"usd":0.025284,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8729,"output_tokens":2572,"usd":0.053972,"stage2_stop_reason":"end_turn"},"total_usd":0.079256,"stage1_batch_id":"msgbatch_017qqVz33Ga63SCDwzb35XPb","stage2_batch_id":"msgbatch_01Scr2Ei9x4HJMiRGxwrmvLK","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2021,\n      \"finding\": \"TRAPPC4 interacts with PD-L1 in recycling endosomes, acting as a scaffold between PD-L1 and RAB11, thereby promoting RAB11-mediated recycling of PD-L1 back to the tumor cell surface. TRAPPC4 depletion significantly reduces PD-L1 surface expression in vitro and in vivo.\",\n      \"method\": \"Co-immunoprecipitation, subcellular fractionation/localization, knockdown/overexpression with PD-L1 surface expression readout, in vivo tumor models\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP establishing scaffold interaction, subcellular localization in recycling endosomes, functional rescue by overexpression, validated in vivo\",\n      \"pmids\": [\"34518538\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Acetylation of PD-L1 protein increases its interaction with TRAPPC4, leading to enhanced surface localization of PD-L1 on pancreatic cancer cells.\",\n      \"method\": \"HDAC inhibitor (VPA) treatment, Co-immunoprecipitation of acetylated PD-L1 with TRAPPC4, flow cytometry for surface PD-L1\",\n      \"journal\": \"Discover oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single Co-IP under pharmacological perturbation, no direct mutagenesis of acetylation sites to confirm causality\",\n      \"pmids\": [\"37603071\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"TRAPPC4 physically interacts with ERK2 (identified by yeast two-hybrid and confirmed by Co-IP and GST pull-down). TRAPPC4 depletion decreases activated ERK1/2 specifically in the nucleus, while overexpression promotes nuclear accumulation of phospho-ERK1/2 and increases cell viability; TRAPPC4 knockdown induces apoptosis in colorectal cancer cells.\",\n      \"method\": \"Yeast two-hybrid, Co-immunoprecipitation, GST pull-down, subcellular fractionation, knockdown/overexpression with proliferation and apoptosis readouts\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — interaction confirmed by three orthogonal methods (Y2H, Co-IP, GST pull-down), functional consequence with localization readout, single lab\",\n      \"pmids\": [\"21826244\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"TRAPPC4 regulates ERK2 activation and nuclear translocation of phospho-ERK2 in colorectal cancer cells; silencing TRAPPC4 causes G0/G1 arrest with upregulation of p21 and downregulation of cyclin B1, while overexpression rescues ERK2-silencing-induced cell cycle effects. EGF stimulation upregulates both TRAPPC4 and pERK2 and induces pERK2 nuclear translocation.\",\n      \"method\": \"siRNA knockdown, overexpression, immunohistochemistry, cell cycle analysis, xenograft tumor models\",\n      \"journal\": \"Molecular carcinogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo xenograft plus in vitro cell cycle and signaling assays; replicates and extends prior TRAPPC4-ERK2 interaction finding; single lab\",\n      \"pmids\": [\"23625650\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"TRAPPC4, like its yeast Trs23 orthologue, is a core TRAPP complex subunit required for guanine nucleotide exchange factor (GEF) activity toward Rab1 GTPase. A splice variant (c.454+3A>G) reduces full-length TRAPPC4 protein and disrupts TRAPP complex assembly/stability, causing delayed ER-to-Golgi and intra-Golgi trafficking (VSVG-GFP-ts045 assay), basal autophagy defects, and delayed autophagic flux in patient fibroblasts. Lentiviral re-expression of wild-type TRAPPC4 restored trafficking. Yeast trs23 temperature-sensitive variants phenocopy autophagy and secretory defects.\",\n      \"method\": \"Native PAGE and size exclusion chromatography (TRAPP complex assembly), VSVG-GFP-ts045 trafficking assay, autophagy flux assay, lentiviral complementation, yeast genetic model\",\n      \"journal\": \"Brain : a journal of neurology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal assays (complex assembly, trafficking reconstitution, autophagy flux, genetic complementation in patient cells and yeast), mechanistic rescue experiment included\",\n      \"pmids\": [\"31794024\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"TRAPPC4 promotes GPX4 protein stability by decreasing chromatin accessibility at a distal regulatory element upstream of TRIM55, thereby limiting FOS-dependent TRIM55 transcription. Reduced TRIM55 diminishes TRIM55-mediated ubiquitination and degradation of GPX4, resulting in GPX4 stabilization and ferroptosis resistance. Structure-based screening identified pitavastatin calcium as a TRAPPC4-binding compound that promotes TRAPPC4 degradation and synergizes with the ferroptosis inducer RSL3.\",\n      \"method\": \"Genome-wide CRISPR-Cas9 knockout screen, patient-derived organoids, xenografts, conditional knockout mice, ATAC-seq (chromatin accessibility), ubiquitination assay, structure-based virtual screening, drug synergy experiments\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — genome-wide unbiased screen plus mechanistic dissection across multiple orthogonal models (cell lines, organoids, CDX, PDX, conditional KO mice) with ATAC-seq and ubiquitination assays\",\n      \"pmids\": [\"41974002\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TRAPPC4 is a core TRAPP complex subunit that provides GEF activity for Rab1, mediates ER-to-Golgi vesicular trafficking and autophagosome maturation, scaffolds PD-L1 with RAB11 in recycling endosomes to recycle PD-L1 to the cell surface, interacts with and modulates nuclear localization of phospho-ERK1/2 to regulate cell proliferation and apoptosis, and suppresses TRIM55-mediated ubiquitination/degradation of GPX4 to confer ferroptosis resistance.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"TRAPPC4 is a core subunit of the multimeric TRAPP complex that drives intracellular membrane trafficking and is co-opted in cancer to control immune evasion, proliferation, and ferroptosis resistance [#4, #0]. As a TRAPP subunit it is required for guanine nucleotide exchange activity toward the Rab1 GTPase, and its loss disrupts TRAPP complex assembly/stability, delaying ER-to-Golgi and intra-Golgi trafficking and impairing basal autophagy and autophagic flux; a splice variant (c.454+3A>G) reduces full-length protein and causes these defects, which are reversed by wild-type re-expression [#4]. In tumor cells TRAPPC4 acts as a scaffold linking PD-L1 to RAB11 in recycling endosomes, promoting RAB11-mediated recycling of PD-L1 to the cell surface, an interaction enhanced by PD-L1 acetylation [#0, #1]. Independently, TRAPPC4 binds ERK2 and governs the nuclear accumulation of phospho-ERK1/2, thereby promoting cell-cycle progression and viability while its depletion induces G0/G1 arrest, p21 upregulation, and apoptosis in colorectal cancer cells [#2, #3]. TRAPPC4 also confers ferroptosis resistance by reducing chromatin accessibility at a regulatory element upstream of TRIM55, limiting FOS-dependent TRIM55 transcription and thereby suppressing TRIM55-mediated ubiquitination and degradation of GPX4 [#5].\",\n  \"teleology\": [\n    {\n      \"year\": 2011,\n      \"claim\": \"Established that TRAPPC4 is not solely a trafficking factor but physically engages the MAPK pathway, defining a route by which it influences proliferation and survival.\",\n      \"evidence\": \"Yeast two-hybrid, Co-IP, and GST pull-down for ERK2 binding with subcellular fractionation and knockdown/overexpression in colorectal cancer cells\",\n      \"pmids\": [\"21826244\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct binding region/interface on TRAPPC4 not mapped\", \"Mechanism by which TRAPPC4 controls nuclear pERK localization unresolved\", \"Single lab\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Connected the TRAPPC4-ERK2 axis to defined cell-cycle control, showing TRAPPC4 is required for EGF-driven pERK2 nuclear translocation and proliferation in vivo.\",\n      \"evidence\": \"siRNA/overexpression, cell cycle analysis, IHC, and xenograft models with EGF stimulation\",\n      \"pmids\": [\"23625650\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Does not establish whether trafficking role and ERK role are mechanistically coupled\", \"Single lab\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Defined the conserved core mechanism: TRAPPC4 is a TRAPP subunit required for Rab1 GEF activity and complex stability, linking its loss to secretory and autophagy defects in human disease.\",\n      \"evidence\": \"Native PAGE/SEC complex assembly, VSVG-GFP-ts045 trafficking assay, autophagy flux, lentiviral complementation in patient fibroblasts, and yeast trs23 genetic model\",\n      \"pmids\": [\"31794024\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural detail of how TRAPPC4 contributes to GEF catalysis not resolved\", \"Specific neurological disease entity not detailed here\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Revealed a cancer-specific membrane-trafficking role: TRAPPC4 scaffolds PD-L1 to RAB11 for recycling-endosome return to the surface, implicating it in tumor immune evasion.\",\n      \"evidence\": \"Reciprocal Co-IP, subcellular fractionation, knockdown/overexpression with PD-L1 surface readout, and in vivo tumor models\",\n      \"pmids\": [\"34518538\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Binding interface between TRAPPC4 and PD-L1 not mapped\", \"Relationship to core TRAPP/Rab1 function unclear\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Extended the recycling model by showing PD-L1 acetylation increases its TRAPPC4 association and surface localization in pancreatic cancer.\",\n      \"evidence\": \"HDAC inhibitor (VPA) treatment, Co-IP of acetylated PD-L1 with TRAPPC4, and flow cytometry for surface PD-L1\",\n      \"pmids\": [\"37603071\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No mutagenesis of acetylation sites to confirm causality\", \"Single Co-IP under pharmacological perturbation\", \"Single lab\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Identified a transcription/chromatin-linked function whereby TRAPPC4 limits TRIM55 expression to stabilize GPX4 and confer ferroptosis resistance, and nominated a druggable handle.\",\n      \"evidence\": \"Genome-wide CRISPR knockout screen, ATAC-seq, ubiquitination assays, organoids/CDX/PDX and conditional KO mice, plus structure-based screening identifying pitavastatin calcium\",\n      \"pmids\": [\"41974002\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which a trafficking subunit modulates chromatin accessibility unexplained\", \"Direct DNA/chromatin association of TRAPPC4 not demonstrated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How TRAPPC4's conserved TRAPP/Rab1 trafficking function mechanistically relates to its distinct roles in ERK nuclear signaling, PD-L1 recycling, and TRIM55/GPX4-mediated ferroptosis resistance remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No unifying model connecting the trafficking, signaling, and chromatin roles\", \"Structural basis of non-TRAPP interactions undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 4]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"complexes\": [\"TRAPP complex\"],\n    \"partners\": [\"PD-L1\", \"RAB11\", \"ERK2\", \"Rab1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":4,"faith_total":5,"faith_pct":80.0}}