{"gene":"PLP2","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":2023,"finding":"Cryo-EM structures of TRiC/CCT chaperonin in complex with plp2 and tubulin/actin substrates revealed that plp2 acts as a co-chaperone coordinating cytoskeletal protein folding: in open states (S1/S2), plp2 and tubulin/actin engage within opposite TRiC chambers; in the closed S3 state, plp2 occupies one ring while the opposite ring contains fully folded β-tubulin loaded with GTP; in the S4 state, an intermediate-folded actin is present. Plp2 translocation accompanies TRiC ring closure and coordinates substrate translocation on the CCT6 hemisphere, stabilizing and facilitating substrate folding.","method":"Cryo-electron microscopy structural analysis across multiple ATPase cycle states","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structures at multiple states with functional interpretation, multiple orthogonal structural snapshots in a single rigorous study","pmids":["36921056"],"is_preprint":false},{"year":2013,"finding":"PLP2 (a MARVEL domain transmembrane protein) is essential for the KSHV E3 ubiquitin ligase K5 to exit the endoplasmic reticulum and ubiquitinate plasma membrane substrates. Genetic loss of PLP2 traps K5 in the ER, preventing ubiquitination and degradation of MHC-I and other cell surface immunoreceptors.","method":"Forward genetic screen in near-haploid human KBM7 cells; plasma membrane proteomics in PLP2-present vs. PLP2-absent K5-expressing cells","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 2 / Strong — haploid genetic screen plus plasma membrane proteomics, two orthogonal methods with genetic validation","pmids":["24278019"],"is_preprint":false},{"year":2004,"finding":"PLP2/A4 physically interacts with the cytoplasmic tail of chemokine receptor CCR1, colocalizes with CCR1 at the plasma membrane (including focal membrane regions upon CCL15/Lkn-1 stimulation), and overexpression of PLP2/A4 stimulates a twofold increase in agonist-induced migration of HOS/CCR1 cells.","method":"Yeast two-hybrid screen; mammalian two-hybrid; co-immunoprecipitation; indirect immunofluorescence colocalization; cell migration assay","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP plus colocalization plus functional migration assay, single lab","pmids":["15474493"],"is_preprint":false},{"year":2015,"finding":"Reduced PLP2 expression leads to defective ER trafficking, increased basal ER stress, and exaggerated susceptibility to ER stress inducers in mouse and human fibroblasts. Plp2-deficient mice show increased neuronal death from ER stress and hypoxia in vitro and in a neonatal hypoxia-ischemia model in vivo. Upregulation of PLP2 directly promotes resistance to ER stressors.","method":"Plp2 knockout mouse model; human fibroblasts from XLID patients with PLP2-(-113C>A); ER trafficking assays; ER stress induction assays; neonatal hypoxia-ischemia in vivo model; PLP2 overexpression rescue","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — loss-of-function mouse model plus human patient cells plus in vivo model plus rescue experiments, multiple orthogonal approaches","pmids":["26512060"],"is_preprint":false},{"year":2007,"finding":"A promoter variant (-113C>A) in PLP2 disrupts the core binding site of transcription factor ELK1 and is sufficient to cause ~4-fold reduction in PLP2 expression, as demonstrated by luciferase reporter assay. PLP2 is abundantly expressed in pyramidal cells of hippocampus and granular cells of cerebellum.","method":"Luciferase reporter assay; X chromosome cDNA microarray; Northern blot/qPCR expression validation; sequencing","journal":"Genome research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — luciferase reporter with specific mutation, single lab, two orthogonal methods","pmids":["17416750"],"is_preprint":false},{"year":2021,"finding":"PLP2 drives collective cell migration in colorectal cancer cells via association with ZO-1 (TJP1) and positioning of ZO-1 at the migrating leading edge, which in turn modulates actin cytoskeletal organization through Rac1 activation. Extracellular PLP2 secreted via exosomes also contributes to this process.","method":"Co-immunoprecipitation; wound-healing/collective migration assays; ZO-1 localization imaging; Rac1 activity assay; PLP2 knockdown/overexpression; exosome isolation","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus localization imaging plus functional Rac1 assay, single lab","pmids":["34409455"],"is_preprint":false},{"year":2014,"finding":"PLP2 interacts with tumor protein D52 (TPD52) and with RAB5C, identified via yeast two-hybrid screening and confirmed by pull-down assays. Interaction domain mapping indicated both PLP2 and RAB5C interact with a novel binding region of TPD52.","method":"Yeast two-hybrid screen; pull-down assays; interaction domain mapping","journal":"Molecular biology reports","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, pull-down only without reciprocal Co-IP or functional follow-up","pmids":["24604726"],"is_preprint":false},{"year":2015,"finding":"PLP2 specifically binds to phosphatidylinositol 3-kinase (PI3K) to activate the protein kinase B (AKT) pathway, enhancing cell proliferation, adhesion, and invasion in melanoma cells.","method":"Reported as established finding in the context of the melanoma/miR-664 study (mechanistic basis cited from prior work)","journal":"Medicine","confidence":"Low","confidence_rationale":"Tier 3 / Weak — cited as established in single paper abstract without direct experimental detail shown in this paper","pmids":["26287415"],"is_preprint":false},{"year":2022,"finding":"A peptide (Rb4) derived from PLP2 induces F-actin polymerization, prevents F-actin depolymerization, increases ER-derived cytosolic calcium, and triggers PARP-1-cleavage-associated necrotic death (not apoptosis) in murine melanoma B16F10 cells, with inhibition of RIP1 expression.","method":"In vitro cytotoxicity assays; F-actin polymerization assay; calcium imaging; PARP-1 cleavage western blot; in vivo syngeneic melanoma model","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal in vitro methods plus in vivo confirmation, single lab","pmids":["35190586"],"is_preprint":false}],"current_model":"Human PLP2 (proteolipid protein 2 / A4) is a MARVEL domain transmembrane protein that functions as a co-chaperone for TRiC/CCT-mediated folding of cytoskeletal proteins tubulin and actin, is required for the ER exit of viral E3 ubiquitin ligases, interacts with the chemokine receptor CCR1 to promote cell migration, associates with ZO-1 to drive leading-edge actin remodeling via Rac1 during collective cell migration, and supports ER homeostasis such that its loss causes defective ER trafficking and increased susceptibility to ER stress-induced neuronal apoptosis."},"narrative":{"mechanistic_narrative":"PLP2 is a MARVEL-domain transmembrane protein that operates at the interface of cytoskeletal protein folding, ER membrane trafficking, and cell migration [PMID:36921056, PMID:24278019, PMID:34409455]. Within the cytosolic chaperonin pathway it acts as a co-chaperone for TRiC/CCT, occupying one chaperonin ring and coordinating substrate translocation on the CCT6 hemisphere to stabilize and facilitate the folding of tubulin and actin across the ATPase cycle [PMID:36921056]. At the ER, PLP2 is required for membrane protein egress: it is essential for the KSHV E3 ubiquitin ligase K5 to exit the ER and ubiquitinate plasma membrane immunoreceptors, and its loss causes defective ER trafficking, elevated basal ER stress, and heightened susceptibility to ER stress–induced neuronal death in vivo [PMID:24278019, PMID:26512060]. PLP2 also promotes cell migration through direct association with membrane and junctional partners—binding the cytoplasmic tail of the chemokine receptor CCR1 to enhance agonist-induced migration, and associating with ZO-1 to position it at the leading edge and remodel actin via Rac1 during collective migration [PMID:15474493, PMID:34409455]. A regulatory promoter variant (-113C>A) that disrupts an ELK1 binding site reduces PLP2 expression and, in patient fibroblasts, links PLP2 loss-of-function to defective ER homeostasis in the setting of X-linked intellectual disability [PMID:26512060, PMID:17416750].","teleology":[{"year":2004,"claim":"Established the first physical and functional partner for PLP2/A4, linking it to chemokine-receptor signaling and cell motility rather than to a purely structural role.","evidence":"Yeast two-hybrid, reciprocal co-IP, colocalization, and migration assays in HOS/CCR1 cells","pmids":["15474493"],"confidence":"Medium","gaps":["Single-lab interaction without structural mapping of the CCR1-tail contact","Mechanism connecting CCR1 binding to migration not resolved"]},{"year":2007,"claim":"Defined a cis-regulatory basis for PLP2 dosage by showing a promoter variant disrupts an ELK1 site and lowers expression, connecting PLP2 to a heritable neurological phenotype.","evidence":"Luciferase reporter assay of -113C>A, X-chromosome microarray and expression validation","pmids":["17416750"],"confidence":"Medium","gaps":["Reporter assay does not establish the downstream cellular consequence of reduced PLP2","Brain expression pattern is descriptive, not mechanistic"]},{"year":2013,"claim":"Revealed an ER-export function by showing PLP2 is required for a viral E3 ligase to leave the ER, establishing PLP2 as a component of membrane protein trafficking.","evidence":"Haploid forward genetic screen in KBM7 cells plus plasma membrane proteomics","pmids":["24278019"],"confidence":"High","gaps":["Whether PLP2 acts directly on the trafficking machinery or via cargo not defined","Host cargo dependent on PLP2 not enumerated"]},{"year":2014,"claim":"Extended the PLP2 interaction network to TPD52 and RAB5C, hinting at links to endosomal/vesicular machinery.","evidence":"Yeast two-hybrid and pull-down with interaction domain mapping","pmids":["24604726"],"confidence":"Low","gaps":["Pull-down only, no reciprocal co-IP or functional follow-up","No cellular consequence of the interactions tested"]},{"year":2015,"claim":"Connected the trafficking defect to physiology by showing PLP2 loss disrupts ER homeostasis and sensitizes neurons to ER stress and hypoxia-ischemia, providing a mechanistic basis for its disease link.","evidence":"Plp2 knockout mouse, XLID patient fibroblasts, ER trafficking/stress assays, neonatal hypoxia-ischemia model, overexpression rescue","pmids":["26512060"],"confidence":"High","gaps":["Molecular step in ER trafficking that PLP2 supports not pinpointed","Relationship between ER role and chaperonin role not integrated"]},{"year":2015,"claim":"Proposed a proliferation/invasion signaling role via PI3K-AKT activation in melanoma.","evidence":"Cited as established in a miR-664/melanoma study without primary experimental detail","pmids":["26287415"],"confidence":"Low","gaps":["No direct experimental demonstration of PI3K binding in this report","Not independently validated within the timeline"]},{"year":2021,"claim":"Defined a leading-edge migration mechanism in which PLP2 directs ZO-1 to drive Rac1-dependent actin remodeling and collective migration in colorectal cancer.","evidence":"Co-IP, wound-healing/collective migration assays, ZO-1 imaging, Rac1 activity assay, exosome isolation","pmids":["34409455"],"confidence":"Medium","gaps":["Single-lab; direct vs indirect PLP2–ZO-1 contact not structurally defined","How an ER/chaperonin protein reaches the leading edge and exosomes unclear"]},{"year":2022,"claim":"Showed a PLP2-derived peptide perturbs actin dynamics and ER-calcium to trigger necrotic death, providing functional evidence that PLP2 sequences engage the actin/calcium axis.","evidence":"In vitro cytotoxicity, F-actin polymerization, calcium imaging, PARP-1 cleavage western, in vivo syngeneic melanoma model","pmids":["35190586"],"confidence":"Medium","gaps":["Peptide behavior may not reflect full-length PLP2 function","Direct molecular target of the Rb4 peptide not identified"]},{"year":2023,"claim":"Resolved the molecular function of PLP2 as a TRiC/CCT co-chaperone that coordinates tubulin and actin folding, unifying its links to cytoskeletal biology.","evidence":"Cryo-EM of TRiC–plp2–tubulin/actin complexes across ATPase cycle states","pmids":["36921056"],"confidence":"High","gaps":["How the chaperonin role relates to PLP2's ER-membrane and migration functions not established","Cellular requirement for PLP2 in folding native tubulin/actin not quantified in human cells here"]},{"year":null,"claim":"It remains unknown how PLP2's distinct roles—cytosolic TRiC co-chaperone, ER-resident trafficking factor, and membrane/junctional migration regulator—are reconciled within one transmembrane protein.","evidence":"No timeline study integrates the chaperonin, ER-export, and migration activities mechanistically","pmids":[],"confidence":"Low","gaps":["No model linking topology/localization to the multiple activities","Substrate or cargo specificity in the ER-trafficking role undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0044183","term_label":"protein folding chaperone","supporting_discovery_ids":[0]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[0]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[1,3]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[2]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[3]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[1]}],"complexes":["TRiC/CCT chaperonin"],"partners":["CCT6","TUBB","ACTB","CCR1","TJP1","TPD52","RAB5C"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q04941","full_name":"Proteolipid protein 2","aliases":["Differentiation-dependent protein A4","Intestinal membrane A4 protein"],"length_aa":152,"mass_kda":16.7,"function":"May play a role in cell differentiation in the intestinal epithelium","subcellular_location":"Membrane","url":"https://www.uniprot.org/uniprotkb/Q04941/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PLP2","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/PLP2","total_profiled":1310},"omim":[{"mim_id":"611678","title":"PHOSDUCIN-LIKE 3; PDCL3","url":"https://www.omim.org/entry/611678"},{"mim_id":"300112","title":"PROTEOLIPID PROTEIN 2; PLP2","url":"https://www.omim.org/entry/300112"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PLP2"},"hgnc":{"alias_symbol":["A4","A4-LSB","MGC126187"],"prev_symbol":[]},"alphafold":{"accession":"Q04941","domains":[{"cath_id":"-","chopping":"20-135","consensus_level":"high","plddt":83.8896,"start":20,"end":135}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q04941","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q04941-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q04941-F1-predicted_aligned_error_v6.png","plddt_mean":78.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PLP2","jax_strain_url":"https://www.jax.org/strain/search?query=PLP2"},"sequence":{"accession":"Q04941","fasta_url":"https://rest.uniprot.org/uniprotkb/Q04941.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q04941/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q04941"}},"corpus_meta":[{"pmid":"16042412","id":"PMC_16042412","title":"Papain-like protease 2 (PLP2) from severe acute respiratory syndrome coronavirus (SARS-CoV): expression, purification, characterization, and inhibition.","date":"2005","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16042412","citation_count":130,"is_preprint":false},{"pmid":"18957937","id":"PMC_18957937","title":"PLP2, a potent deubiquitinase from murine hepatitis virus, strongly inhibits cellular type I interferon production.","date":"2008","source":"Cell research","url":"https://pubmed.ncbi.nlm.nih.gov/18957937","citation_count":118,"is_preprint":false},{"pmid":"33859750","id":"PMC_33859750","title":"CD45RO-CD8+ T cell-derived exosomes restrict estrogen-driven endometrial cancer development via the ERβ/miR-765/PLP2/Notch axis.","date":"2021","source":"Theranostics","url":"https://pubmed.ncbi.nlm.nih.gov/33859750","citation_count":95,"is_preprint":false},{"pmid":"21364999","id":"PMC_21364999","title":"PLP2 of mouse hepatitis virus A59 (MHV-A59) targets TBK1 to negatively regulate cellular type I interferon signaling pathway.","date":"2011","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/21364999","citation_count":63,"is_preprint":false},{"pmid":"31901870","id":"PMC_31901870","title":"MiR-765 functions as a tumour suppressor and eliminates lipids in clear cell renal cell carcinoma by downregulating PLP2.","date":"2020","source":"EBioMedicine","url":"https://pubmed.ncbi.nlm.nih.gov/31901870","citation_count":50,"is_preprint":false},{"pmid":"10749875","id":"PMC_10749875","title":"Functional analysis of Plp1 and Plp2, two homologues of phosducin in yeast.","date":"2000","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/10749875","citation_count":50,"is_preprint":false},{"pmid":"26287415","id":"PMC_26287415","title":"Loss of MiR-664 Expression Enhances Cutaneous Malignant Melanoma Proliferation by Upregulating PLP2.","date":"2015","source":"Medicine","url":"https://pubmed.ncbi.nlm.nih.gov/26287415","citation_count":37,"is_preprint":false},{"pmid":"25735976","id":"PMC_25735976","title":"miR-664 negatively regulates PLP2 and promotes cell proliferation and invasion in T-cell acute lymphoblastic leukaemia.","date":"2015","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/25735976","citation_count":36,"is_preprint":false},{"pmid":"29509055","id":"PMC_29509055","title":"MiR-422a weakened breast cancer stem cells properties by targeting PLP2.","date":"2018","source":"Cancer biology & therapy","url":"https://pubmed.ncbi.nlm.nih.gov/29509055","citation_count":36,"is_preprint":false},{"pmid":"31535380","id":"PMC_31535380","title":"The long noncoding RNA ZFAS1 promotes the progression of glioma by regulating the miR-150-5p/PLP2 axis.","date":"2019","source":"Journal of cellular physiology","url":"https://pubmed.ncbi.nlm.nih.gov/31535380","citation_count":35,"is_preprint":false},{"pmid":"24278019","id":"PMC_24278019","title":"Haploid genetic screens identify an essential role for PLP2 in the downregulation of novel plasma membrane targets by viral E3 ubiquitin ligases.","date":"2013","source":"PLoS pathogens","url":"https://pubmed.ncbi.nlm.nih.gov/24278019","citation_count":35,"is_preprint":false},{"pmid":"32494200","id":"PMC_32494200","title":"Long Noncoding RNA LINC00173 Contributes to the Growth, Invasiveness and Chemo-Resistance of Colorectal Cancer Through Regulating miR-765/PLP2 Axis.","date":"2020","source":"Cancer management and research","url":"https://pubmed.ncbi.nlm.nih.gov/32494200","citation_count":23,"is_preprint":false},{"pmid":"15474493","id":"PMC_15474493","title":"PLP2/A4 interacts with CCR1 and stimulates migration of CCR1-expressing HOS cells.","date":"2004","source":"Biochemical and biophysical research 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research","url":"https://pubmed.ncbi.nlm.nih.gov/17416750","citation_count":15,"is_preprint":false},{"pmid":"34409455","id":"PMC_34409455","title":"PLP2 drives collective cell migration via ZO-1-mediated cytoskeletal remodeling at the leading edge in human colorectal cancer cells.","date":"2021","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/34409455","citation_count":13,"is_preprint":false},{"pmid":"24604726","id":"PMC_24604726","title":"Identification of PLP2 and RAB5C as novel TPD52 binding partners through yeast two-hybrid screening.","date":"2014","source":"Molecular biology reports","url":"https://pubmed.ncbi.nlm.nih.gov/24604726","citation_count":12,"is_preprint":false},{"pmid":"33976115","id":"PMC_33976115","title":"CircRNA_2646 functions as a ceRNA to promote progression of esophageal squamous cell carcinoma via inhibiting miR-124/PLP2 signaling pathway.","date":"2021","source":"Cell death 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Differentially Methylated in Multiple Cancers.","date":"2020","source":"Epigenetics insights","url":"https://pubmed.ncbi.nlm.nih.gov/33178991","citation_count":2,"is_preprint":false},{"pmid":"36139188","id":"PMC_36139188","title":"A Missense Variant in PLP2 in Holstein Cattle with X-Linked Congenital Mast Cell Tumor.","date":"2022","source":"Animals : an open access journal from MDPI","url":"https://pubmed.ncbi.nlm.nih.gov/36139188","citation_count":2,"is_preprint":false},{"pmid":"37408733","id":"PMC_37408733","title":"Characterization and sequencing analysis of pLP2.5-11 and pLP3.0-4 novel cryptic plasmids from Lactiplantibacillus plantarum WP72/27.","date":"2023","source":"3 Biotech","url":"https://pubmed.ncbi.nlm.nih.gov/37408733","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":14204,"output_tokens":2313,"usd":0.038654,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9369,"output_tokens":3108,"usd":0.062273,"stage2_stop_reason":"end_turn"},"total_usd":0.100927,"stage1_batch_id":"msgbatch_01CNoDbkChHEkgrJnL7BwtGJ","stage2_batch_id":"msgbatch_016Y4x9E9Wg5VQDANj9quSQD","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2023,\n      \"finding\": \"Cryo-EM structures of TRiC/CCT chaperonin in complex with plp2 and tubulin/actin substrates revealed that plp2 acts as a co-chaperone coordinating cytoskeletal protein folding: in open states (S1/S2), plp2 and tubulin/actin engage within opposite TRiC chambers; in the closed S3 state, plp2 occupies one ring while the opposite ring contains fully folded β-tubulin loaded with GTP; in the S4 state, an intermediate-folded actin is present. Plp2 translocation accompanies TRiC ring closure and coordinates substrate translocation on the CCT6 hemisphere, stabilizing and facilitating substrate folding.\",\n      \"method\": \"Cryo-electron microscopy structural analysis across multiple ATPase cycle states\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structures at multiple states with functional interpretation, multiple orthogonal structural snapshots in a single rigorous study\",\n      \"pmids\": [\"36921056\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PLP2 (a MARVEL domain transmembrane protein) is essential for the KSHV E3 ubiquitin ligase K5 to exit the endoplasmic reticulum and ubiquitinate plasma membrane substrates. Genetic loss of PLP2 traps K5 in the ER, preventing ubiquitination and degradation of MHC-I and other cell surface immunoreceptors.\",\n      \"method\": \"Forward genetic screen in near-haploid human KBM7 cells; plasma membrane proteomics in PLP2-present vs. PLP2-absent K5-expressing cells\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — haploid genetic screen plus plasma membrane proteomics, two orthogonal methods with genetic validation\",\n      \"pmids\": [\"24278019\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"PLP2/A4 physically interacts with the cytoplasmic tail of chemokine receptor CCR1, colocalizes with CCR1 at the plasma membrane (including focal membrane regions upon CCL15/Lkn-1 stimulation), and overexpression of PLP2/A4 stimulates a twofold increase in agonist-induced migration of HOS/CCR1 cells.\",\n      \"method\": \"Yeast two-hybrid screen; mammalian two-hybrid; co-immunoprecipitation; indirect immunofluorescence colocalization; cell migration assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP plus colocalization plus functional migration assay, single lab\",\n      \"pmids\": [\"15474493\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Reduced PLP2 expression leads to defective ER trafficking, increased basal ER stress, and exaggerated susceptibility to ER stress inducers in mouse and human fibroblasts. Plp2-deficient mice show increased neuronal death from ER stress and hypoxia in vitro and in a neonatal hypoxia-ischemia model in vivo. Upregulation of PLP2 directly promotes resistance to ER stressors.\",\n      \"method\": \"Plp2 knockout mouse model; human fibroblasts from XLID patients with PLP2-(-113C>A); ER trafficking assays; ER stress induction assays; neonatal hypoxia-ischemia in vivo model; PLP2 overexpression rescue\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — loss-of-function mouse model plus human patient cells plus in vivo model plus rescue experiments, multiple orthogonal approaches\",\n      \"pmids\": [\"26512060\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"A promoter variant (-113C>A) in PLP2 disrupts the core binding site of transcription factor ELK1 and is sufficient to cause ~4-fold reduction in PLP2 expression, as demonstrated by luciferase reporter assay. PLP2 is abundantly expressed in pyramidal cells of hippocampus and granular cells of cerebellum.\",\n      \"method\": \"Luciferase reporter assay; X chromosome cDNA microarray; Northern blot/qPCR expression validation; sequencing\",\n      \"journal\": \"Genome research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — luciferase reporter with specific mutation, single lab, two orthogonal methods\",\n      \"pmids\": [\"17416750\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PLP2 drives collective cell migration in colorectal cancer cells via association with ZO-1 (TJP1) and positioning of ZO-1 at the migrating leading edge, which in turn modulates actin cytoskeletal organization through Rac1 activation. Extracellular PLP2 secreted via exosomes also contributes to this process.\",\n      \"method\": \"Co-immunoprecipitation; wound-healing/collective migration assays; ZO-1 localization imaging; Rac1 activity assay; PLP2 knockdown/overexpression; exosome isolation\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus localization imaging plus functional Rac1 assay, single lab\",\n      \"pmids\": [\"34409455\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PLP2 interacts with tumor protein D52 (TPD52) and with RAB5C, identified via yeast two-hybrid screening and confirmed by pull-down assays. Interaction domain mapping indicated both PLP2 and RAB5C interact with a novel binding region of TPD52.\",\n      \"method\": \"Yeast two-hybrid screen; pull-down assays; interaction domain mapping\",\n      \"journal\": \"Molecular biology reports\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, pull-down only without reciprocal Co-IP or functional follow-up\",\n      \"pmids\": [\"24604726\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"PLP2 specifically binds to phosphatidylinositol 3-kinase (PI3K) to activate the protein kinase B (AKT) pathway, enhancing cell proliferation, adhesion, and invasion in melanoma cells.\",\n      \"method\": \"Reported as established finding in the context of the melanoma/miR-664 study (mechanistic basis cited from prior work)\",\n      \"journal\": \"Medicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — cited as established in single paper abstract without direct experimental detail shown in this paper\",\n      \"pmids\": [\"26287415\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"A peptide (Rb4) derived from PLP2 induces F-actin polymerization, prevents F-actin depolymerization, increases ER-derived cytosolic calcium, and triggers PARP-1-cleavage-associated necrotic death (not apoptosis) in murine melanoma B16F10 cells, with inhibition of RIP1 expression.\",\n      \"method\": \"In vitro cytotoxicity assays; F-actin polymerization assay; calcium imaging; PARP-1 cleavage western blot; in vivo syngeneic melanoma model\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal in vitro methods plus in vivo confirmation, single lab\",\n      \"pmids\": [\"35190586\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"Human PLP2 (proteolipid protein 2 / A4) is a MARVEL domain transmembrane protein that functions as a co-chaperone for TRiC/CCT-mediated folding of cytoskeletal proteins tubulin and actin, is required for the ER exit of viral E3 ubiquitin ligases, interacts with the chemokine receptor CCR1 to promote cell migration, associates with ZO-1 to drive leading-edge actin remodeling via Rac1 during collective cell migration, and supports ER homeostasis such that its loss causes defective ER trafficking and increased susceptibility to ER stress-induced neuronal apoptosis.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PLP2 is a MARVEL-domain transmembrane protein that operates at the interface of cytoskeletal protein folding, ER membrane trafficking, and cell migration [#0, #1, #5]. Within the cytosolic chaperonin pathway it acts as a co-chaperone for TRiC/CCT, occupying one chaperonin ring and coordinating substrate translocation on the CCT6 hemisphere to stabilize and facilitate the folding of tubulin and actin across the ATPase cycle [#0]. At the ER, PLP2 is required for membrane protein egress: it is essential for the KSHV E3 ubiquitin ligase K5 to exit the ER and ubiquitinate plasma membrane immunoreceptors, and its loss causes defective ER trafficking, elevated basal ER stress, and heightened susceptibility to ER stress\\u2013induced neuronal death in vivo [#1, #3]. PLP2 also promotes cell migration through direct association with membrane and junctional partners\\u2014binding the cytoplasmic tail of the chemokine receptor CCR1 to enhance agonist-induced migration, and associating with ZO-1 to position it at the leading edge and remodel actin via Rac1 during collective migration [#2, #5]. A regulatory promoter variant (-113C>A) that disrupts an ELK1 binding site reduces PLP2 expression and, in patient fibroblasts, links PLP2 loss-of-function to defective ER homeostasis in the setting of X-linked intellectual disability [#3, #4].\",\n  \"teleology\": [\n    {\n      \"year\": 2004,\n      \"claim\": \"Established the first physical and functional partner for PLP2/A4, linking it to chemokine-receptor signaling and cell motility rather than to a purely structural role.\",\n      \"evidence\": \"Yeast two-hybrid, reciprocal co-IP, colocalization, and migration assays in HOS/CCR1 cells\",\n      \"pmids\": [\"15474493\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab interaction without structural mapping of the CCR1-tail contact\", \"Mechanism connecting CCR1 binding to migration not resolved\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Defined a cis-regulatory basis for PLP2 dosage by showing a promoter variant disrupts an ELK1 site and lowers expression, connecting PLP2 to a heritable neurological phenotype.\",\n      \"evidence\": \"Luciferase reporter assay of -113C>A, X-chromosome microarray and expression validation\",\n      \"pmids\": [\"17416750\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Reporter assay does not establish the downstream cellular consequence of reduced PLP2\", \"Brain expression pattern is descriptive, not mechanistic\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Revealed an ER-export function by showing PLP2 is required for a viral E3 ligase to leave the ER, establishing PLP2 as a component of membrane protein trafficking.\",\n      \"evidence\": \"Haploid forward genetic screen in KBM7 cells plus plasma membrane proteomics\",\n      \"pmids\": [\"24278019\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PLP2 acts directly on the trafficking machinery or via cargo not defined\", \"Host cargo dependent on PLP2 not enumerated\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Extended the PLP2 interaction network to TPD52 and RAB5C, hinting at links to endosomal/vesicular machinery.\",\n      \"evidence\": \"Yeast two-hybrid and pull-down with interaction domain mapping\",\n      \"pmids\": [\"24604726\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Pull-down only, no reciprocal co-IP or functional follow-up\", \"No cellular consequence of the interactions tested\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Connected the trafficking defect to physiology by showing PLP2 loss disrupts ER homeostasis and sensitizes neurons to ER stress and hypoxia-ischemia, providing a mechanistic basis for its disease link.\",\n      \"evidence\": \"Plp2 knockout mouse, XLID patient fibroblasts, ER trafficking/stress assays, neonatal hypoxia-ischemia model, overexpression rescue\",\n      \"pmids\": [\"26512060\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular step in ER trafficking that PLP2 supports not pinpointed\", \"Relationship between ER role and chaperonin role not integrated\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Proposed a proliferation/invasion signaling role via PI3K-AKT activation in melanoma.\",\n      \"evidence\": \"Cited as established in a miR-664/melanoma study without primary experimental detail\",\n      \"pmids\": [\"26287415\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No direct experimental demonstration of PI3K binding in this report\", \"Not independently validated within the timeline\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Defined a leading-edge migration mechanism in which PLP2 directs ZO-1 to drive Rac1-dependent actin remodeling and collective migration in colorectal cancer.\",\n      \"evidence\": \"Co-IP, wound-healing/collective migration assays, ZO-1 imaging, Rac1 activity assay, exosome isolation\",\n      \"pmids\": [\"34409455\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab; direct vs indirect PLP2\\u2013ZO-1 contact not structurally defined\", \"How an ER/chaperonin protein reaches the leading edge and exosomes unclear\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Showed a PLP2-derived peptide perturbs actin dynamics and ER-calcium to trigger necrotic death, providing functional evidence that PLP2 sequences engage the actin/calcium axis.\",\n      \"evidence\": \"In vitro cytotoxicity, F-actin polymerization, calcium imaging, PARP-1 cleavage western, in vivo syngeneic melanoma model\",\n      \"pmids\": [\"35190586\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Peptide behavior may not reflect full-length PLP2 function\", \"Direct molecular target of the Rb4 peptide not identified\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Resolved the molecular function of PLP2 as a TRiC/CCT co-chaperone that coordinates tubulin and actin folding, unifying its links to cytoskeletal biology.\",\n      \"evidence\": \"Cryo-EM of TRiC\\u2013plp2\\u2013tubulin/actin complexes across ATPase cycle states\",\n      \"pmids\": [\"36921056\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How the chaperonin role relates to PLP2's ER-membrane and migration functions not established\", \"Cellular requirement for PLP2 in folding native tubulin/actin not quantified in human cells here\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unknown how PLP2's distinct roles\\u2014cytosolic TRiC co-chaperone, ER-resident trafficking factor, and membrane/junctional migration regulator\\u2014are reconciled within one transmembrane protein.\",\n      \"evidence\": \"No timeline study integrates the chaperonin, ER-export, and migration activities mechanistically\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No model linking topology/localization to the multiple activities\", \"Substrate or cargo specificity in the ER-trafficking role undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0044183\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [1, 3]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"complexes\": [\"TRiC/CCT chaperonin\"],\n    \"partners\": [\"CCT6\", \"TUBB\", \"ACTB\", \"CCR1\", \"TJP1\", \"TPD52\", \"RAB5C\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}