{"gene":"TRAPPC4","run_date":"2026-04-28T21:42:59","timeline":{"discoveries":[{"year":2021,"finding":"TRAPPC4 interacts with PD-L1 in recycling endosomes, acting as a scaffold between PD-L1 and RAB11, and promotes RAB11-mediated recycling of PD-L1 back to the tumor cell surface; TRAPPC4 depletion significantly reduces PD-L1 surface expression.","method":"Co-immunoprecipitation, live-cell imaging of recycling endosomes, knockdown/overexpression with PD-L1 surface expression readout, in vivo tumor models","journal":"Nature Communications","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, subcellular localization with functional consequence, in vivo validation; moderate-to-strong evidence from multiple methods in one study","pmids":["34518538"],"is_preprint":false},{"year":2020,"finding":"TRAPPC4, as the orthologue of yeast Trs23, is a core subunit essential for guanine nucleotide exchange factor (GEF) activity toward Rab1 GTPase within TRAPP complexes; pathogenic reduction of TRAPPC4 causes defects in TRAPP complex assembly/stability, delayed Golgi entry and exit of cargo (VSVG-GFP-ts045), and impaired autophagy/autophagic flux in patient fibroblasts; wild-type TRAPPC4 re-expression rescues these trafficking defects.","method":"Native PAGE, size exclusion chromatography, VSVG-GFP-ts045 trafficking assay, lentiviral rescue, autophagy flux assays, yeast trs23 temperature-sensitive mutant complementation","journal":"Brain","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal biochemical and cell-biological assays with rescue experiment and yeast model validation in a single rigorous study","pmids":["31794024"],"is_preprint":false},{"year":2011,"finding":"TRAPPC4 physically interacts with ERK2 and promotes ERK1/2 phosphorylation and nuclear translocation; TRAPPC4 depletion reduces nuclear pERK1/2 and suppresses colorectal cancer cell proliferation while promoting apoptosis, whereas TRAPPC4 overexpression enhances nuclear pERK1/2 and cell viability.","method":"Yeast two-hybrid screen, Co-IP, GST pull-down, TRAPPC4 knockdown/overexpression with pERK1/2 subcellular fractionation and cell viability/apoptosis assays","journal":"PloS One","confidence":"Medium","confidence_rationale":"Tier 2–3 — interaction confirmed by three methods (Y2H, Co-IP, GST pull-down) with functional cellular readout; single lab","pmids":["21826244"],"is_preprint":false},{"year":2013,"finding":"TRAPPC4-ERK2 interaction regulates G0/G1 cell cycle arrest, p21 upregulation, cyclin B1 downregulation, and EGF-stimulated pERK2 nuclear translocation in colorectal cancer cells; TRAPPC4 overexpression rescues ERK2-knockdown-induced G0/G1 arrest, and TRAPPC4 modulates xenograft tumor growth in vivo by controlling pERK2 levels in nucleus and cytoplasm.","method":"siRNA knockdown, overexpression, cell cycle FACS analysis, immunohistochemistry, in vivo xenograft models with pERK2 subcellular fractionation","journal":"Molecular Carcinogenesis","confidence":"Medium","confidence_rationale":"Tier 2 — epistasis/rescue experiment (TRAPPC4 OE rescues ERK2 KD) with in vivo validation; single lab","pmids":["23625650"],"is_preprint":false},{"year":2023,"finding":"Acetylation of PD-L1 protein increases its interaction with TRAPPC4 and promotes PD-L1 recycling to the cell surface; HDAC inhibitor VPA-induced acetylation of PD-L1 enhances TRAPPC4–PD-L1 interaction and surface PD-L1 levels in pancreatic cancer cells.","method":"Co-immunoprecipitation, flow cytometry for surface PD-L1, HDAC inhibitor (VPA) and BRD4 inhibitor (JQ-1) pharmacological intervention","journal":"Discover Oncology","confidence":"Medium","confidence_rationale":"Tier 3 — Co-IP with pharmacological perturbation; single lab, single method for the interaction claim","pmids":["37603071"],"is_preprint":false},{"year":2026,"finding":"TRAPPC4 promotes ferroptosis resistance in HNSCC by decreasing chromatin accessibility at a distal regulatory element upstream of TRIM55, thereby limiting FOS-dependent transcription of TRIM55; reduced TRIM55 prevents ubiquitination and degradation of GPX4, stabilizing GPX4 and conferring ferroptosis resistance. TRAPPC4-binding compound pitavastatin calcium promotes TRAPPC4 degradation and synergizes with RSL3 to induce ferroptosis.","method":"Genome-wide CRISPR-Cas9 knockout screen, ATAC-seq (chromatin accessibility), transcriptomics, ubiquitination assay, patient-derived organoids, CDX/PDX models, Trappc4-conditional knockout mice, structure-based virtual screening, in vivo metastasis models","journal":"Cancer Research","confidence":"High","confidence_rationale":"Tier 1–2 — CRISPR screen plus multiple orthogonal mechanistic assays (ATAC-seq, ubiquitination, structural docking, conditional KO mice, organoids) in one comprehensive study","pmids":["41974002"],"is_preprint":false}],"current_model":"TRAPPC4 is a core TRAPP complex subunit with GEF activity toward Rab1 that regulates ER-to-Golgi vesicular trafficking and autophagy; it additionally acts as a scaffold in recycling endosomes linking PD-L1 to RAB11-mediated recycling to the cell surface, interacts with ERK2 to promote nuclear pERK1/2 signaling, and suppresses FOS-dependent TRIM55 transcription to stabilize GPX4 and confer ferroptosis resistance."},"narrative":{"teleology":[{"year":2011,"claim":"Identifying TRAPPC4 as a physical interactor of ERK2 that promotes nuclear pERK1/2 established a previously unknown link between a vesicular trafficking subunit and MAPK signaling in cancer cell proliferation.","evidence":"Yeast two-hybrid, Co-IP, and GST pull-down with knockdown/overexpression and subcellular fractionation in colorectal cancer cells","pmids":["21826244"],"confidence":"Medium","gaps":["Interaction confirmed in a single lab; independent replication needed","Mechanism by which TRAPPC4 promotes ERK2 nuclear translocation is unresolved","Whether this function is independent of TRAPP complex membership is unknown"]},{"year":2013,"claim":"Demonstrating that TRAPPC4 overexpression rescues ERK2-knockdown-induced G0/G1 arrest and modulates xenograft growth via nuclear pERK2 levels established an epistatic relationship between TRAPPC4 and ERK2 in cell cycle control.","evidence":"siRNA epistasis/rescue, FACS cell cycle analysis, and in vivo xenograft models in colorectal cancer cells","pmids":["23625650"],"confidence":"Medium","gaps":["Single-lab study without independent validation","Direct biochemical mechanism of TRAPPC4 on ERK2 phosphorylation remains unknown","Relevance beyond colorectal cancer is unaddressed"]},{"year":2020,"claim":"Establishing TRAPPC4 as the core TRAPP subunit required for Rab1 GEF activity, TRAPP complex stability, ER-to-Golgi trafficking, and autophagy defined its fundamental cell-biological function and linked its loss to a neurodevelopmental disease.","evidence":"Native PAGE, size exclusion chromatography, VSVG-GFP trafficking assay, lentiviral rescue, autophagy flux assays, and yeast trs23 complementation in patient fibroblasts","pmids":["31794024"],"confidence":"High","gaps":["Structural basis for how TRAPPC4 contributes to GEF catalysis is not resolved","Whether TRAPP II and TRAPP III complexes are differentially affected is unclear","Full phenotypic spectrum of TRAPPC4 deficiency in humans remains incomplete"]},{"year":2021,"claim":"Showing that TRAPPC4 scaffolds PD-L1 with RAB11 in recycling endosomes to drive PD-L1 surface recycling revealed a non-canonical trafficking role with direct implications for tumor immune evasion.","evidence":"Reciprocal Co-IP, live-cell imaging of recycling endosomes, knockdown/overexpression with surface PD-L1 readout, and in vivo tumor models","pmids":["34518538"],"confidence":"High","gaps":["Whether TRAPPC4-mediated recycling extends to other immune checkpoint molecules is unknown","The structural basis of the TRAPPC4–PD-L1 interaction is unresolved","Contribution of TRAPP complex versus monomeric TRAPPC4 to this recycling function is unclear"]},{"year":2023,"claim":"Demonstrating that PD-L1 acetylation enhances its interaction with TRAPPC4 and surface expression linked post-translational modification of cargo to TRAPPC4-dependent recycling.","evidence":"Co-IP and flow cytometry with HDAC inhibitor (VPA) treatment in pancreatic cancer cells","pmids":["37603071"],"confidence":"Medium","gaps":["Single Co-IP method for the acetylation-dependent interaction change","Specific acetylation sites on PD-L1 mediating enhanced TRAPPC4 binding are not mapped","In vivo validation of acetylation-dependent recycling is lacking"]},{"year":2026,"claim":"A CRISPR screen and multi-omic dissection revealed that TRAPPC4 confers ferroptosis resistance by closing chromatin at a TRIM55 regulatory element, reducing FOS-dependent TRIM55 transcription, and thereby preventing GPX4 ubiquitination and degradation — a mechanism entirely distinct from its trafficking roles.","evidence":"Genome-wide CRISPR screen, ATAC-seq, transcriptomics, ubiquitination assay, patient-derived organoids, CDX/PDX models, conditional knockout mice, and structure-based virtual screening in HNSCC","pmids":["41974002"],"confidence":"High","gaps":["Mechanism by which TRAPPC4 modulates chromatin accessibility at the TRIM55 locus is not defined","Whether this chromatin-regulatory function operates in tissues beyond HNSCC is unknown","How TRAPPC4 integrates its trafficking and chromatin/ferroptosis functions remains unaddressed"]},{"year":null,"claim":"How TRAPPC4 coordinates its canonical TRAPP-dependent trafficking role with its non-canonical functions in ERK signaling, PD-L1 recycling, and chromatin-level ferroptosis regulation — and whether these represent context-dependent or concurrent activities — remains an open question.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structural model of TRAPPC4 within TRAPP II or TRAPP III at high resolution","Whether monomeric TRAPPC4 acts independently of the TRAPP complex in signaling and chromatin contexts is untested","Comprehensive interactome mapping beyond individual partner studies is lacking"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,4]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[2,3]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[5]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[1]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[0]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[0,1]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,1,4]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[1]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2,3]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[5]}],"complexes":["TRAPP complex"],"partners":["RAB11","ERK2","PD-L1","GPX4","TRIM55","RAB1"],"other_free_text":[]},"mechanistic_narrative":"TRAPPC4 is a core subunit of the TRAPP complex that functions as a guanine nucleotide exchange factor (GEF) for Rab1 GTPase, essential for ER-to-Golgi vesicular trafficking and autophagic flux; pathogenic loss of TRAPPC4 disrupts TRAPP complex assembly, delays cargo transport, and impairs autophagy [PMID:31794024]. Beyond its canonical trafficking role, TRAPPC4 acts as a scaffold in recycling endosomes linking PD-L1 to RAB11, promoting RAB11-mediated recycling of PD-L1 to the tumor cell surface, with acetylation of PD-L1 enhancing this interaction [PMID:34518538, PMID:37603071]. TRAPPC4 physically interacts with ERK2 and promotes ERK1/2 phosphorylation and nuclear translocation, regulating cell cycle progression and proliferation in colorectal cancer cells [PMID:21826244, PMID:23625650]. TRAPPC4 also confers ferroptosis resistance by suppressing FOS-dependent TRIM55 transcription via chromatin accessibility changes, thereby preventing TRIM55-mediated ubiquitination and degradation of GPX4 [PMID:41974002]."},"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":59,"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":"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":"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":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":7021,"output_tokens":1756,"usd":0.023702},"stage2":{"model":"claude-opus-4-6","input_tokens":5000,"output_tokens":2220,"usd":0.12075},"total_usd":0.144452,"stage1_batch_id":"msgbatch_01RPbVc9PDH9zQmYK5Hs6srm","stage2_batch_id":"msgbatch_01JVbVLzeKN2yVrsGp3zC8aM","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, and promotes RAB11-mediated recycling of PD-L1 back to the tumor cell surface; TRAPPC4 depletion significantly reduces PD-L1 surface expression.\",\n      \"method\": \"Co-immunoprecipitation, live-cell imaging of recycling endosomes, knockdown/overexpression with PD-L1 surface expression readout, in vivo tumor models\",\n      \"journal\": \"Nature Communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, subcellular localization with functional consequence, in vivo validation; moderate-to-strong evidence from multiple methods in one study\",\n      \"pmids\": [\"34518538\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"TRAPPC4, as the orthologue of yeast Trs23, is a core subunit essential for guanine nucleotide exchange factor (GEF) activity toward Rab1 GTPase within TRAPP complexes; pathogenic reduction of TRAPPC4 causes defects in TRAPP complex assembly/stability, delayed Golgi entry and exit of cargo (VSVG-GFP-ts045), and impaired autophagy/autophagic flux in patient fibroblasts; wild-type TRAPPC4 re-expression rescues these trafficking defects.\",\n      \"method\": \"Native PAGE, size exclusion chromatography, VSVG-GFP-ts045 trafficking assay, lentiviral rescue, autophagy flux assays, yeast trs23 temperature-sensitive mutant complementation\",\n      \"journal\": \"Brain\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal biochemical and cell-biological assays with rescue experiment and yeast model validation in a single rigorous study\",\n      \"pmids\": [\"31794024\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"TRAPPC4 physically interacts with ERK2 and promotes ERK1/2 phosphorylation and nuclear translocation; TRAPPC4 depletion reduces nuclear pERK1/2 and suppresses colorectal cancer cell proliferation while promoting apoptosis, whereas TRAPPC4 overexpression enhances nuclear pERK1/2 and cell viability.\",\n      \"method\": \"Yeast two-hybrid screen, Co-IP, GST pull-down, TRAPPC4 knockdown/overexpression with pERK1/2 subcellular fractionation and cell viability/apoptosis assays\",\n      \"journal\": \"PloS One\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — interaction confirmed by three methods (Y2H, Co-IP, GST pull-down) with functional cellular readout; single lab\",\n      \"pmids\": [\"21826244\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"TRAPPC4-ERK2 interaction regulates G0/G1 cell cycle arrest, p21 upregulation, cyclin B1 downregulation, and EGF-stimulated pERK2 nuclear translocation in colorectal cancer cells; TRAPPC4 overexpression rescues ERK2-knockdown-induced G0/G1 arrest, and TRAPPC4 modulates xenograft tumor growth in vivo by controlling pERK2 levels in nucleus and cytoplasm.\",\n      \"method\": \"siRNA knockdown, overexpression, cell cycle FACS analysis, immunohistochemistry, in vivo xenograft models with pERK2 subcellular fractionation\",\n      \"journal\": \"Molecular Carcinogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — epistasis/rescue experiment (TRAPPC4 OE rescues ERK2 KD) with in vivo validation; single lab\",\n      \"pmids\": [\"23625650\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Acetylation of PD-L1 protein increases its interaction with TRAPPC4 and promotes PD-L1 recycling to the cell surface; HDAC inhibitor VPA-induced acetylation of PD-L1 enhances TRAPPC4–PD-L1 interaction and surface PD-L1 levels in pancreatic cancer cells.\",\n      \"method\": \"Co-immunoprecipitation, flow cytometry for surface PD-L1, HDAC inhibitor (VPA) and BRD4 inhibitor (JQ-1) pharmacological intervention\",\n      \"journal\": \"Discover Oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — Co-IP with pharmacological perturbation; single lab, single method for the interaction claim\",\n      \"pmids\": [\"37603071\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"TRAPPC4 promotes ferroptosis resistance in HNSCC by decreasing chromatin accessibility at a distal regulatory element upstream of TRIM55, thereby limiting FOS-dependent transcription of TRIM55; reduced TRIM55 prevents ubiquitination and degradation of GPX4, stabilizing GPX4 and conferring ferroptosis resistance. TRAPPC4-binding compound pitavastatin calcium promotes TRAPPC4 degradation and synergizes with RSL3 to induce ferroptosis.\",\n      \"method\": \"Genome-wide CRISPR-Cas9 knockout screen, ATAC-seq (chromatin accessibility), transcriptomics, ubiquitination assay, patient-derived organoids, CDX/PDX models, Trappc4-conditional knockout mice, structure-based virtual screening, in vivo metastasis models\",\n      \"journal\": \"Cancer Research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — CRISPR screen plus multiple orthogonal mechanistic assays (ATAC-seq, ubiquitination, structural docking, conditional KO mice, organoids) in one comprehensive study\",\n      \"pmids\": [\"41974002\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TRAPPC4 is a core TRAPP complex subunit with GEF activity toward Rab1 that regulates ER-to-Golgi vesicular trafficking and autophagy; it additionally acts as a scaffold in recycling endosomes linking PD-L1 to RAB11-mediated recycling to the cell surface, interacts with ERK2 to promote nuclear pERK1/2 signaling, and suppresses FOS-dependent TRIM55 transcription to stabilize GPX4 and confer ferroptosis resistance.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"TRAPPC4 is a core subunit of the TRAPP complex that functions as a guanine nucleotide exchange factor (GEF) for Rab1 GTPase, essential for ER-to-Golgi vesicular trafficking and autophagic flux; pathogenic loss of TRAPPC4 disrupts TRAPP complex assembly, delays cargo transport, and impairs autophagy [PMID:31794024]. Beyond its canonical trafficking role, TRAPPC4 acts as a scaffold in recycling endosomes linking PD-L1 to RAB11, promoting RAB11-mediated recycling of PD-L1 to the tumor cell surface, with acetylation of PD-L1 enhancing this interaction [PMID:34518538, PMID:37603071]. TRAPPC4 physically interacts with ERK2 and promotes ERK1/2 phosphorylation and nuclear translocation, regulating cell cycle progression and proliferation in colorectal cancer cells [PMID:21826244, PMID:23625650]. TRAPPC4 also confers ferroptosis resistance by suppressing FOS-dependent TRIM55 transcription via chromatin accessibility changes, thereby preventing TRIM55-mediated ubiquitination and degradation of GPX4 [PMID:41974002].\",\n  \"teleology\": [\n    {\n      \"year\": 2011,\n      \"claim\": \"Identifying TRAPPC4 as a physical interactor of ERK2 that promotes nuclear pERK1/2 established a previously unknown link between a vesicular trafficking subunit and MAPK signaling in cancer cell proliferation.\",\n      \"evidence\": \"Yeast two-hybrid, Co-IP, and GST pull-down with knockdown/overexpression and subcellular fractionation in colorectal cancer cells\",\n      \"pmids\": [\"21826244\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Interaction confirmed in a single lab; independent replication needed\",\n        \"Mechanism by which TRAPPC4 promotes ERK2 nuclear translocation is unresolved\",\n        \"Whether this function is independent of TRAPP complex membership is unknown\"\n      ]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Demonstrating that TRAPPC4 overexpression rescues ERK2-knockdown-induced G0/G1 arrest and modulates xenograft growth via nuclear pERK2 levels established an epistatic relationship between TRAPPC4 and ERK2 in cell cycle control.\",\n      \"evidence\": \"siRNA epistasis/rescue, FACS cell cycle analysis, and in vivo xenograft models in colorectal cancer cells\",\n      \"pmids\": [\"23625650\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single-lab study without independent validation\",\n        \"Direct biochemical mechanism of TRAPPC4 on ERK2 phosphorylation remains unknown\",\n        \"Relevance beyond colorectal cancer is unaddressed\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Establishing TRAPPC4 as the core TRAPP subunit required for Rab1 GEF activity, TRAPP complex stability, ER-to-Golgi trafficking, and autophagy defined its fundamental cell-biological function and linked its loss to a neurodevelopmental disease.\",\n      \"evidence\": \"Native PAGE, size exclusion chromatography, VSVG-GFP trafficking assay, lentiviral rescue, autophagy flux assays, and yeast trs23 complementation in patient fibroblasts\",\n      \"pmids\": [\"31794024\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis for how TRAPPC4 contributes to GEF catalysis is not resolved\",\n        \"Whether TRAPP II and TRAPP III complexes are differentially affected is unclear\",\n        \"Full phenotypic spectrum of TRAPPC4 deficiency in humans remains incomplete\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showing that TRAPPC4 scaffolds PD-L1 with RAB11 in recycling endosomes to drive PD-L1 surface recycling revealed a non-canonical trafficking role with direct implications for tumor immune evasion.\",\n      \"evidence\": \"Reciprocal Co-IP, live-cell imaging of recycling endosomes, knockdown/overexpression with surface PD-L1 readout, and in vivo tumor models\",\n      \"pmids\": [\"34518538\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether TRAPPC4-mediated recycling extends to other immune checkpoint molecules is unknown\",\n        \"The structural basis of the TRAPPC4–PD-L1 interaction is unresolved\",\n        \"Contribution of TRAPP complex versus monomeric TRAPPC4 to this recycling function is unclear\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Demonstrating that PD-L1 acetylation enhances its interaction with TRAPPC4 and surface expression linked post-translational modification of cargo to TRAPPC4-dependent recycling.\",\n      \"evidence\": \"Co-IP and flow cytometry with HDAC inhibitor (VPA) treatment in pancreatic cancer cells\",\n      \"pmids\": [\"37603071\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single Co-IP method for the acetylation-dependent interaction change\",\n        \"Specific acetylation sites on PD-L1 mediating enhanced TRAPPC4 binding are not mapped\",\n        \"In vivo validation of acetylation-dependent recycling is lacking\"\n      ]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"A CRISPR screen and multi-omic dissection revealed that TRAPPC4 confers ferroptosis resistance by closing chromatin at a TRIM55 regulatory element, reducing FOS-dependent TRIM55 transcription, and thereby preventing GPX4 ubiquitination and degradation — a mechanism entirely distinct from its trafficking roles.\",\n      \"evidence\": \"Genome-wide CRISPR screen, ATAC-seq, transcriptomics, ubiquitination assay, patient-derived organoids, CDX/PDX models, conditional knockout mice, and structure-based virtual screening in HNSCC\",\n      \"pmids\": [\"41974002\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Mechanism by which TRAPPC4 modulates chromatin accessibility at the TRIM55 locus is not defined\",\n        \"Whether this chromatin-regulatory function operates in tissues beyond HNSCC is unknown\",\n        \"How TRAPPC4 integrates its trafficking and chromatin/ferroptosis functions remains unaddressed\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How TRAPPC4 coordinates its canonical TRAPP-dependent trafficking role with its non-canonical functions in ERK signaling, PD-L1 recycling, and chromatin-level ferroptosis regulation — and whether these represent context-dependent or concurrent activities — remains an open question.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No structural model of TRAPPC4 within TRAPP II or TRAPP III at high resolution\",\n        \"Whether monomeric TRAPPC4 acts independently of the TRAPP complex in signaling and chromatin contexts is untested\",\n        \"Comprehensive interactome mapping beyond individual partner studies is lacking\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 4]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [2, 3]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 1, 4]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 3]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"complexes\": [\"TRAPP complex\"],\n    \"partners\": [\"RAB11\", \"ERK2\", \"PD-L1\", \"GPX4\", \"TRIM55\", \"RAB1\"],\n    \"other_free_text\": []\n  }\n}\n```"}