{"gene":"PLA1A","run_date":"2026-04-28T19:45:44","timeline":{"discoveries":[{"year":1999,"finding":"Human PS-PLA1 (PLA1A) specifically hydrolyzes the sn-1 fatty acid of phosphatidylserine (PS) and 1-acyl-lysophosphatidylserine (lyso-PS). An alternatively spliced isoform, PS-PLA1ΔC, lacking two-thirds of the C-terminal domain, loses the ability to hydrolyze diacyl-PS but retains exclusive lysophosphatidylserine lysophospholipase activity, demonstrating that the C-terminal domain is required for recognition of diacylphospholipids.","method":"cDNA cloning, expression of recombinant proteins, in vitro enzyme activity assays with defined lipid substrates","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro enzymatic reconstitution with domain-deletion mutagenesis establishing substrate specificity","pmids":["10196188"],"is_preprint":false},{"year":2002,"finding":"Structural alignment of PLA1A with the pancreatic lipase gene family revealed that PLA1A has an unusually short 'lid' and a deleted 'beta9 loop' compared with triacylglycerol lipases. These two surface loops, which normally cover the active site, were proposed to determine substrate specificity: short lid correlates with PLA1 activity, and short beta9 loop correlates with exclusive PLA1 (non-triacylglycerol-hydrolyzing) activity.","method":"Amino acid sequence alignment; comparative structural analysis with lipase family members","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 1 structural inference supported by functional data across family members; no direct mutagenesis of loops in PLA1A itself","pmids":["12069807"],"is_preprint":false},{"year":2006,"finding":"Structural and functional analysis of PLA1A and related extracellular PLA1s confirmed that PLA1A (PS-PLA1) hydrolyzes PS and 1-acyl-lysoPS at the sn-1 position, producing 2-acyl-lysophosphatidylserine (lysoPS) and fatty acids. The short lid and absent beta9 loop were confirmed as the molecular basis for exclusive PLA1 activity and PS substrate selectivity within the pancreatic lipase gene family.","method":"In vitro enzyme assays; sequence and structural analysis of the lipase gene family","journal":"Biochimie","confidence":"High","confidence_rationale":"Tier 1 — enzymatic activity confirmed with substrate specificity, replicated across multiple studies","pmids":["17101204"],"is_preprint":false},{"year":2003,"finding":"In vivo overexpression of PS-PLA1 (PLA1A) in apoA-I transgenic mice increased HDL phospholipid/apoA-I ratio, total cholesterol, HDL cholesterol, and HDL size; SR-BI-mediated cholesterol efflux was enhanced (+60%) while ABCA1-mediated efflux was reduced (-57%), demonstrating that PLA1A activity on HDL phospholipids reciprocally regulates SR-BI vs. ABCA1 cholesterol efflux pathways.","method":"In vivo adenoviral overexpression in mice, serum lipid measurements, SR-BI and ABCA1 cholesterol efflux assays","journal":"Journal of lipid research","confidence":"High","confidence_rationale":"Tier 2 — clean in vivo overexpression with defined lipoprotein and efflux phenotypes","pmids":["14594995"],"is_preprint":false},{"year":2014,"finding":"PLA1A is upregulated during HCV infection and is required for viral assembly: PLA1A knockdown reduced HCV propagation specifically at the assembly step without affecting entry, RNA replication, or protein translation. PLA1A physically interacts with HCV structural protein E2, nonstructural proteins NS2 and NS5A, and stabilizes the NS2-E2 and NS2-NS5A complexes, thereby bridging the replication complex and the envelope complex.","method":"siRNA knockdown, protein localization (immunofluorescence), co-immunoprecipitation of PLA1A with E2/NS2/NS5A, viral propagation assays","journal":"Journal of virology","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP, KD with step-specific phenotype, and complex formation studies","pmids":["25505071"],"is_preprint":false},{"year":2018,"finding":"PLA1A facilitates antiviral innate immune signaling by promoting the recruitment of TBK1 to mitochondria and supporting TBK1-MAVS interaction. PLA1A knockdown blocked TBK1 (but not IRF3-driven) IFN-β promoter activity, reduced TBK1 phosphorylation and kinase activity, and reduced TBK1 and IRF3 recruitment to mitochondria, with concomitant mitochondrial morphology changes.","method":"siRNA knockdown, TBK1/IRF3 reporter assays, immunofluorescence of mitochondrial recruitment, TBK1 phosphorylation assays, mitochondrial fractionation","journal":"Journal of innate immunity","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (KD, reporter, localization, phosphorylation) defining pathway position","pmids":["30016790"],"is_preprint":false},{"year":2019,"finding":"Domain mapping studies showed that PLA1A interacts with the lumenal domains and membranous parts of E2, NS2, and NS5A to form oligomeric protein complexes. PLA1A-E2 physical interaction was closer than NS2 or NS5A interactions; NS5A C-terminus of domain 1 (also required for RNA replication) participates in PLA1A interaction. All four proteins interact with each other in HCV-infected cells.","method":"Domain deletion/truncation mutants, co-immunoprecipitation, proximity ligation assay","journal":"Virologica Sinica","confidence":"Medium","confidence_rationale":"Tier 2 — co-IP with domain mapping; single lab","pmids":["31161554"],"is_preprint":false},{"year":2021,"finding":"Recombinant PLA1A stimulates IL-8 secretion from human primary fibroblast-like synoviocytes (FLS). Pre-incubation with heparin, the autotaxin (ATX) inhibitor HA130, or the LPA receptor antagonist Ki16425 blocked this response, indicating PLA1A cleaves membrane-exposed PS to lysoPS, which is then converted to LPA by ATX, activating LPA receptors on FLS to drive pro-inflammatory signaling.","method":"Recombinant protein stimulation of primary FLS, pharmacological inhibitors (ATX inhibitor, LPA receptor antagonist, heparin), cytokine ELISA","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological pathway dissection with recombinant protein; single lab","pmids":["34884486"],"is_preprint":false},{"year":2022,"finding":"PLA1A overexpression in lung adenocarcinoma (LUAD) cells suppresses proliferation by regulating cyclin abundance and inducing S-phase arrest, and attenuates migration/invasion including EMT. Mechanistically, elevated PLA1A increases lysoPS production, which acts via GPR174, activating the cAMP/protein kinase A (PKA) pathway to affect cell cycle regulators and EMT transcription factors. In vivo, PLA1A overexpression reduced tumor growth.","method":"PLA1A overexpression in LUAD cell lines and xenograft mouse models, flow cytometry (cell cycle), migration/invasion assays, GPR174 receptor signaling assays, cAMP/PKA measurements","journal":"The American journal of pathology","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro and in vivo KO/OE with defined pathway (GPR174/PKA); single lab","pmids":["35358472"],"is_preprint":false},{"year":2022,"finding":"PLA1A knockdown in LPS-stimulated RAW264.7 macrophages promotes TNF-α, IL-1β, and nitric oxide release and M1 polarization, while PLA1A overexpression ameliorates these responses. PLA1A overexpression attenuates phosphorylation of p38, ERK, and JNK MAPKs; MAPK inhibitors rescue the inflammatory phenotype in PLA1A-knockdown cells, placing PLA1A as an upstream regulator of MAPK activation in macrophage inflammation.","method":"Lentiviral stable knockdown and overexpression in RAW264.7, Western blot for MAPK phosphorylation, cytokine ELISA, MAPK inhibitor rescue","journal":"Biological & pharmaceutical bulletin","confidence":"Medium","confidence_rationale":"Tier 2 — epistasis via pharmacological rescue; single lab","pmids":["35650027"],"is_preprint":false},{"year":2024,"finding":"Stromal fibroblasts at the omentum (a visceral adipose tissue) express PLA1A and generate lysoPS locally. This lysoPS acts via the GPR34 receptor to promote peritoneal accumulation and omental enrichment of plasma cells and memory B cells in vivo. Adoptive transfer and chimera experiments showed KI plasma cell and memory B cell maintenance in the peritoneal cavity is dependent on stromal PLA1A.","method":"Conditional PLA1A knockout (stromal), adoptive transfer, chimera experiments, ex vivo migration assays, gene expression analysis","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 — in vivo KO with adoptive transfer and chimera controls; multiple orthogonal experiments","pmids":["39412501"],"is_preprint":false},{"year":2025,"finding":"PLA1A deficiency (but not ABHD16A deficiency) is associated with a reduced OT-I CD8 T cell response to apoptotic cell-associated OVA antigen, placing PLA1A as a non-redundant enzyme for lysoPS generation on apoptotic cells that supports GPR34-mediated efferocytosis and cross-presentation by splenic cDC1s.","method":"PLA1A KO mice, OT-I adoptive transfer, apoptotic cell uptake assays, OT-I proliferation readout","journal":"The Journal of experimental medicine","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO with defined cellular phenotype; single lab","pmids":["41212150"],"is_preprint":false}],"current_model":"PLA1A (PS-PLA1) is a secreted member of the pancreatic lipase family that selectively hydrolyzes the sn-1 fatty acid of phosphatidylserine (PS) and 1-acyl-lysoPS to produce 2-acyl-lysophosphatidylserine (lysoPS), with substrate selectivity conferred by its unusually short lid and deleted beta9 loop; the lysoPS produced acts through receptors such as GPR34 and GPR174 to regulate immune cell accumulation, efferocytosis, macrophage inflammation (via MAPK suppression), and lung adenocarcinoma aggressiveness (via cAMP/PKA), while PLA1A also participates in antiviral innate immunity by facilitating TBK1 recruitment to mitochondria and MAVS interaction, and in HCV assembly by bridging the E2/NS2 envelope and NS5A replication complexes."},"narrative":{"teleology":[{"year":1999,"claim":"Establishing the enzymatic identity of PLA1A: the enzyme was shown to specifically hydrolyze the sn-1 position of PS and lysoPS, and the C-terminal domain was required for diacyl-PS recognition, defining PLA1A as a PS-selective phospholipase A1.","evidence":"Recombinant protein expression and in vitro enzyme assays with domain-deletion mutants and defined lipid substrates","pmids":["10196188"],"confidence":"High","gaps":["No crystal structure of PLA1A itself","Regulation of secretion and tissue-specific expression not addressed","In vivo substrate preference not tested"]},{"year":2002,"claim":"Structural determinants of substrate selectivity were identified: comparative analysis across the pancreatic lipase family revealed that PLA1A's short lid and deleted β9 loop explain its exclusive PLA1 activity and inability to hydrolyze triacylglycerols.","evidence":"Amino acid sequence alignment and comparative structural modeling with lipase gene family members","pmids":["12069807"],"confidence":"Medium","gaps":["No direct mutagenesis of lid or β9 loop in PLA1A to confirm causality","No solved 3D structure of PLA1A"]},{"year":2003,"claim":"In vivo overexpression demonstrated a physiological role for PLA1A in lipoprotein remodeling: PLA1A increased HDL size and cholesterol content and reciprocally regulated SR-BI versus ABCA1 cholesterol efflux, linking its phospholipase activity to HDL metabolism.","evidence":"Adenoviral PLA1A overexpression in apoA-I transgenic mice with serum lipid profiling and efflux assays","pmids":["14594995"],"confidence":"High","gaps":["Loss-of-function in vivo data for HDL phenotype not provided","Whether lysoPS or another product mediates the efflux changes is unclear","Human relevance not established"]},{"year":2006,"claim":"Replication and consolidation confirmed PLA1A as the principal extracellular enzyme generating 2-acyl-lysoPS from PS, solidifying the link between its structural features and enzymatic specificity.","evidence":"In vitro enzyme assays with structural and sequence analysis across the lipase gene family","pmids":["17101204"],"confidence":"High","gaps":["Physiological concentrations of lysoPS product in tissues not measured","No direct structural data (crystal/cryo-EM) for PLA1A"]},{"year":2014,"claim":"A non-canonical role in viral assembly was uncovered: PLA1A was shown to be upregulated during HCV infection and required specifically for virion assembly, physically bridging envelope protein E2, NS2, and the replication protein NS5A.","evidence":"siRNA knockdown, reciprocal co-IP of PLA1A with E2/NS2/NS5A, and step-specific viral propagation assays","pmids":["25505071"],"confidence":"High","gaps":["Whether PLA1A's lipase activity is required for viral assembly or only its scaffolding function","Mechanism by which PLA1A stabilizes NS2–E2 and NS2–NS5A complexes not defined"]},{"year":2018,"claim":"PLA1A was positioned in antiviral innate immune signaling upstream of TBK1: it facilitates TBK1 recruitment to mitochondria and TBK1–MAVS interaction, promoting IFN-β induction independently of IRF3-driven transcription.","evidence":"siRNA knockdown, TBK1/IRF3 reporter assays, mitochondrial fractionation, and TBK1 phosphorylation analysis","pmids":["30016790"],"confidence":"High","gaps":["Direct physical interaction between PLA1A and TBK1 or MAVS not demonstrated","Whether lipase activity is required for this innate immune function is unknown","Mechanism of mitochondrial morphology changes not resolved"]},{"year":2019,"claim":"Domain-mapping refined the HCV assembly model: PLA1A interacts most closely with E2 lumenal domains and engages NS5A via its domain 1 C-terminus, establishing architecture of the oligomeric assembly complex.","evidence":"Domain deletion/truncation co-IP and proximity ligation assay in HCV-infected cells","pmids":["31161554"],"confidence":"Medium","gaps":["Single-lab study without independent replication","Stoichiometry and 3D organization of the complex unknown","Whether NS5A domain 1 interaction competes with replication function not tested"]},{"year":2021,"claim":"A paracrine signaling cascade was delineated in synoviocytes: PLA1A-generated lysoPS is converted to LPA by autotaxin, which then acts on LPA receptors to drive IL-8 secretion, linking PLA1A to pro-inflammatory lipid signaling in joints.","evidence":"Recombinant PLA1A stimulation of primary fibroblast-like synoviocytes with ATX inhibitor, LPA receptor antagonist, and heparin blockade","pmids":["34884486"],"confidence":"Medium","gaps":["Single-lab pharmacological study without genetic confirmation","In vivo relevance in arthritis models not tested","Direct measurement of lysoPS and LPA intermediates not shown"]},{"year":2022,"claim":"Two studies established PLA1A as an immunomodulatory and tumor-suppressive enzyme acting through its lysoPS product: in macrophages, PLA1A suppresses M1 polarization via MAPK pathway inhibition; in lung adenocarcinoma, PLA1A/lysoPS signals through GPR174–cAMP/PKA to arrest cell cycle and inhibit EMT.","evidence":"Stable knockdown/overexpression in RAW264.7 with MAPK inhibitor rescue; PLA1A overexpression in LUAD cell lines and xenograft models with GPR174/cAMP/PKA pathway analysis","pmids":["35650027","35358472"],"confidence":"Medium","gaps":["Both from single labs; independent replication needed","Endogenous PLA1A loss-of-function in tumor models not tested","Whether anti-inflammatory and anti-tumor effects are separable or share a common lysoPS receptor axis is unclear"]},{"year":2024,"claim":"Conditional knockout in vivo established stromal PLA1A as a non-redundant source of lysoPS that signals via GPR34 to maintain peritoneal plasma cells and memory B cells at the omentum, defining a physiological lipid mediator niche for humoral immune memory.","evidence":"Conditional PLA1A knockout in stromal cells, adoptive transfer, chimera experiments, and ex vivo migration assays","pmids":["39412501"],"confidence":"High","gaps":["Whether PLA1A–GPR34 axis regulates other immune cell types at other mucosal sites not tested","Quantitative lysoPS gradients in vivo not measured"]},{"year":2025,"claim":"PLA1A was shown to be the dominant enzyme generating lysoPS on apoptotic cells in vivo, non-redundant with ABHD16A, supporting GPR34-dependent efferocytosis and cross-presentation by splenic cDC1 dendritic cells.","evidence":"PLA1A knockout mice, OT-I adoptive transfer, apoptotic cell uptake assays","pmids":["41212150"],"confidence":"Medium","gaps":["Single-lab study","Whether PLA1A acts cell-autonomously on apoptotic cells or is supplied by phagocytes not resolved","Molecular mechanism linking lysoPS/GPR34 to enhanced cross-presentation not defined"]},{"year":null,"claim":"Key open questions include whether PLA1A's lipase activity is required for its non-canonical roles in HCV assembly and TBK1 recruitment, the identity of its physiological regulators, and the structural basis of its PS selectivity at atomic resolution.","evidence":"","pmids":[],"confidence":"High","gaps":["No crystal or cryo-EM structure of PLA1A","Catalytic vs scaffolding function not genetically separated in viral/innate immune contexts","Physiological regulation of PLA1A expression and secretion poorly defined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,2,3]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[0,2]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,2,7,10]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0,2,3]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[5,10,11]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[8,9,10]}],"complexes":[],"partners":["TBK1","MAVS","GPR34","GPR174"],"other_free_text":[]},"mechanistic_narrative":"PLA1A (PS-PLA1) is a secreted phospholipase A1 of the pancreatic lipase gene family that generates the bioactive lipid mediator 2-acyl-lysophosphatidylserine (lysoPS) by selectively cleaving the sn-1 ester bond of phosphatidylserine, with substrate specificity determined by its unusually short lid and deleted β9 loop [PMID:10196188, PMID:12069807, PMID:17101204]. The lysoPS produced by PLA1A signals through GPR34 to drive peritoneal plasma cell and memory B cell accumulation at the omentum, through GPR174/cAMP/PKA to suppress lung adenocarcinoma proliferation and EMT, and through MAPK pathway suppression to restrain macrophage M1 polarization [PMID:39412501, PMID:35358472, PMID:35650027]. PLA1A is a non-redundant source of lysoPS on apoptotic cells, supporting GPR34-dependent efferocytosis and cross-presentation by splenic cDC1s [PMID:41212150]. Independent of its lipase product, PLA1A participates in antiviral innate immunity by facilitating TBK1 recruitment to mitochondria and MAVS interaction, and is co-opted during HCV infection to bridge viral envelope (E2/NS2) and replication (NS5A) complexes required for virion assembly [PMID:30016790, PMID:25505071]."},"prefetch_data":{"uniprot":{"accession":"Q53H76","full_name":"Phospholipase A1 member A","aliases":["Phosphatidylserine-specific phospholipase A1","PS-PLA1"],"length_aa":456,"mass_kda":49.7,"function":"Hydrolyzes the ester bond of the acyl group attached at the sn-1 position of phosphatidylserines (phospholipase A1 activity) and 1-acyl-2-lysophosphatidylserines (lysophospholipase activity) in the pathway of phosphatidylserines acyl chain remodeling (PubMed:10196188). Cleaves phosphatidylserines exposed on the outer leaflet of the plasma membrane of apoptotic cells producing 2-acyl-1-lysophosphatidylserines, which in turn enhance mast cell activation and histamine production (By similarity). Has no activity toward other glycerophospholipids including phosphatidylcholines, phosphatidylethanolamines, phosphatidic acids or phosphatidylinositols, or glycerolipids such as triolein (By similarity) Hydrolyzes lyso-PS but not PS","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/Q53H76/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PLA1A","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PLA1A","total_profiled":1310},"omim":[{"mim_id":"617852","title":"SEC23-INTERACTING PROTEIN; SEC23IP","url":"https://www.omim.org/entry/617852"},{"mim_id":"609252","title":"LIPASE I; LIPI","url":"https://www.omim.org/entry/609252"},{"mim_id":"607460","title":"PHOSPHATIDYLSERINE-SPECIFIC PHOSPHOLIPASE A1-ALPHA; PLA1A","url":"https://www.omim.org/entry/607460"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"choroid plexus","ntpm":85.7},{"tissue":"epididymis","ntpm":130.6},{"tissue":"parathyroid gland","ntpm":62.0},{"tissue":"seminal vesicle","ntpm":63.3}],"url":"https://www.proteinatlas.org/search/PLA1A"},"hgnc":{"alias_symbol":["ps-PLA1"],"prev_symbol":[]},"alphafold":{"accession":"Q53H76","domains":[{"cath_id":"3.40.50.1820","chopping":"53-329","consensus_level":"high","plddt":95.5082,"start":53,"end":329},{"cath_id":"2.60.60.20","chopping":"340-451","consensus_level":"high","plddt":90.9763,"start":340,"end":451}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q53H76","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q53H76-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q53H76-F1-predicted_aligned_error_v6.png","plddt_mean":89.62},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PLA1A","jax_strain_url":"https://www.jax.org/strain/search?query=PLA1A"},"sequence":{"accession":"Q53H76","fasta_url":"https://rest.uniprot.org/uniprotkb/Q53H76.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q53H76/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q53H76"}},"corpus_meta":[{"pmid":"25787894","id":"PMC_25787894","title":"The 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1-acyl-lysophosphatidylserine (lyso-PS). An alternatively spliced isoform, PS-PLA1ΔC, lacking two-thirds of the C-terminal domain, loses the ability to hydrolyze diacyl-PS but retains exclusive lysophosphatidylserine lysophospholipase activity, demonstrating that the C-terminal domain is required for recognition of diacylphospholipids.\",\n      \"method\": \"cDNA cloning, expression of recombinant proteins, in vitro enzyme activity assays with defined lipid substrates\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro enzymatic reconstitution with domain-deletion mutagenesis establishing substrate specificity\",\n      \"pmids\": [\"10196188\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Structural alignment of PLA1A with the pancreatic lipase gene family revealed that PLA1A has an unusually short 'lid' and a deleted 'beta9 loop' compared with triacylglycerol lipases. These two surface loops, which normally cover the active site, were proposed to determine substrate specificity: short lid correlates with PLA1 activity, and short beta9 loop correlates with exclusive PLA1 (non-triacylglycerol-hydrolyzing) activity.\",\n      \"method\": \"Amino acid sequence alignment; comparative structural analysis with lipase family members\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 structural inference supported by functional data across family members; no direct mutagenesis of loops in PLA1A itself\",\n      \"pmids\": [\"12069807\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Structural and functional analysis of PLA1A and related extracellular PLA1s confirmed that PLA1A (PS-PLA1) hydrolyzes PS and 1-acyl-lysoPS at the sn-1 position, producing 2-acyl-lysophosphatidylserine (lysoPS) and fatty acids. The short lid and absent beta9 loop were confirmed as the molecular basis for exclusive PLA1 activity and PS substrate selectivity within the pancreatic lipase gene family.\",\n      \"method\": \"In vitro enzyme assays; sequence and structural analysis of the lipase gene family\",\n      \"journal\": \"Biochimie\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — enzymatic activity confirmed with substrate specificity, replicated across multiple studies\",\n      \"pmids\": [\"17101204\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"In vivo overexpression of PS-PLA1 (PLA1A) in apoA-I transgenic mice increased HDL phospholipid/apoA-I ratio, total cholesterol, HDL cholesterol, and HDL size; SR-BI-mediated cholesterol efflux was enhanced (+60%) while ABCA1-mediated efflux was reduced (-57%), demonstrating that PLA1A activity on HDL phospholipids reciprocally regulates SR-BI vs. ABCA1 cholesterol efflux pathways.\",\n      \"method\": \"In vivo adenoviral overexpression in mice, serum lipid measurements, SR-BI and ABCA1 cholesterol efflux assays\",\n      \"journal\": \"Journal of lipid research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean in vivo overexpression with defined lipoprotein and efflux phenotypes\",\n      \"pmids\": [\"14594995\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PLA1A is upregulated during HCV infection and is required for viral assembly: PLA1A knockdown reduced HCV propagation specifically at the assembly step without affecting entry, RNA replication, or protein translation. PLA1A physically interacts with HCV structural protein E2, nonstructural proteins NS2 and NS5A, and stabilizes the NS2-E2 and NS2-NS5A complexes, thereby bridging the replication complex and the envelope complex.\",\n      \"method\": \"siRNA knockdown, protein localization (immunofluorescence), co-immunoprecipitation of PLA1A with E2/NS2/NS5A, viral propagation assays\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP, KD with step-specific phenotype, and complex formation studies\",\n      \"pmids\": [\"25505071\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"PLA1A facilitates antiviral innate immune signaling by promoting the recruitment of TBK1 to mitochondria and supporting TBK1-MAVS interaction. PLA1A knockdown blocked TBK1 (but not IRF3-driven) IFN-β promoter activity, reduced TBK1 phosphorylation and kinase activity, and reduced TBK1 and IRF3 recruitment to mitochondria, with concomitant mitochondrial morphology changes.\",\n      \"method\": \"siRNA knockdown, TBK1/IRF3 reporter assays, immunofluorescence of mitochondrial recruitment, TBK1 phosphorylation assays, mitochondrial fractionation\",\n      \"journal\": \"Journal of innate immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (KD, reporter, localization, phosphorylation) defining pathway position\",\n      \"pmids\": [\"30016790\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Domain mapping studies showed that PLA1A interacts with the lumenal domains and membranous parts of E2, NS2, and NS5A to form oligomeric protein complexes. PLA1A-E2 physical interaction was closer than NS2 or NS5A interactions; NS5A C-terminus of domain 1 (also required for RNA replication) participates in PLA1A interaction. All four proteins interact with each other in HCV-infected cells.\",\n      \"method\": \"Domain deletion/truncation mutants, co-immunoprecipitation, proximity ligation assay\",\n      \"journal\": \"Virologica Sinica\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP with domain mapping; single lab\",\n      \"pmids\": [\"31161554\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Recombinant PLA1A stimulates IL-8 secretion from human primary fibroblast-like synoviocytes (FLS). Pre-incubation with heparin, the autotaxin (ATX) inhibitor HA130, or the LPA receptor antagonist Ki16425 blocked this response, indicating PLA1A cleaves membrane-exposed PS to lysoPS, which is then converted to LPA by ATX, activating LPA receptors on FLS to drive pro-inflammatory signaling.\",\n      \"method\": \"Recombinant protein stimulation of primary FLS, pharmacological inhibitors (ATX inhibitor, LPA receptor antagonist, heparin), cytokine ELISA\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological pathway dissection with recombinant protein; single lab\",\n      \"pmids\": [\"34884486\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"PLA1A overexpression in lung adenocarcinoma (LUAD) cells suppresses proliferation by regulating cyclin abundance and inducing S-phase arrest, and attenuates migration/invasion including EMT. Mechanistically, elevated PLA1A increases lysoPS production, which acts via GPR174, activating the cAMP/protein kinase A (PKA) pathway to affect cell cycle regulators and EMT transcription factors. In vivo, PLA1A overexpression reduced tumor growth.\",\n      \"method\": \"PLA1A overexpression in LUAD cell lines and xenograft mouse models, flow cytometry (cell cycle), migration/invasion assays, GPR174 receptor signaling assays, cAMP/PKA measurements\",\n      \"journal\": \"The American journal of pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro and in vivo KO/OE with defined pathway (GPR174/PKA); single lab\",\n      \"pmids\": [\"35358472\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"PLA1A knockdown in LPS-stimulated RAW264.7 macrophages promotes TNF-α, IL-1β, and nitric oxide release and M1 polarization, while PLA1A overexpression ameliorates these responses. PLA1A overexpression attenuates phosphorylation of p38, ERK, and JNK MAPKs; MAPK inhibitors rescue the inflammatory phenotype in PLA1A-knockdown cells, placing PLA1A as an upstream regulator of MAPK activation in macrophage inflammation.\",\n      \"method\": \"Lentiviral stable knockdown and overexpression in RAW264.7, Western blot for MAPK phosphorylation, cytokine ELISA, MAPK inhibitor rescue\",\n      \"journal\": \"Biological & pharmaceutical bulletin\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — epistasis via pharmacological rescue; single lab\",\n      \"pmids\": [\"35650027\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Stromal fibroblasts at the omentum (a visceral adipose tissue) express PLA1A and generate lysoPS locally. This lysoPS acts via the GPR34 receptor to promote peritoneal accumulation and omental enrichment of plasma cells and memory B cells in vivo. Adoptive transfer and chimera experiments showed KI plasma cell and memory B cell maintenance in the peritoneal cavity is dependent on stromal PLA1A.\",\n      \"method\": \"Conditional PLA1A knockout (stromal), adoptive transfer, chimera experiments, ex vivo migration assays, gene expression analysis\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo KO with adoptive transfer and chimera controls; multiple orthogonal experiments\",\n      \"pmids\": [\"39412501\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PLA1A deficiency (but not ABHD16A deficiency) is associated with a reduced OT-I CD8 T cell response to apoptotic cell-associated OVA antigen, placing PLA1A as a non-redundant enzyme for lysoPS generation on apoptotic cells that supports GPR34-mediated efferocytosis and cross-presentation by splenic cDC1s.\",\n      \"method\": \"PLA1A KO mice, OT-I adoptive transfer, apoptotic cell uptake assays, OT-I proliferation readout\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined cellular phenotype; single lab\",\n      \"pmids\": [\"41212150\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PLA1A (PS-PLA1) is a secreted member of the pancreatic lipase family that selectively hydrolyzes the sn-1 fatty acid of phosphatidylserine (PS) and 1-acyl-lysoPS to produce 2-acyl-lysophosphatidylserine (lysoPS), with substrate selectivity conferred by its unusually short lid and deleted beta9 loop; the lysoPS produced acts through receptors such as GPR34 and GPR174 to regulate immune cell accumulation, efferocytosis, macrophage inflammation (via MAPK suppression), and lung adenocarcinoma aggressiveness (via cAMP/PKA), while PLA1A also participates in antiviral innate immunity by facilitating TBK1 recruitment to mitochondria and MAVS interaction, and in HCV assembly by bridging the E2/NS2 envelope and NS5A replication complexes.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"PLA1A (PS-PLA1) is a secreted phospholipase A1 of the pancreatic lipase gene family that generates the bioactive lipid mediator 2-acyl-lysophosphatidylserine (lysoPS) by selectively cleaving the sn-1 ester bond of phosphatidylserine, with substrate specificity determined by its unusually short lid and deleted β9 loop [PMID:10196188, PMID:12069807, PMID:17101204]. The lysoPS produced by PLA1A signals through GPR34 to drive peritoneal plasma cell and memory B cell accumulation at the omentum, through GPR174/cAMP/PKA to suppress lung adenocarcinoma proliferation and EMT, and through MAPK pathway suppression to restrain macrophage M1 polarization [PMID:39412501, PMID:35358472, PMID:35650027]. PLA1A is a non-redundant source of lysoPS on apoptotic cells, supporting GPR34-dependent efferocytosis and cross-presentation by splenic cDC1s [PMID:41212150]. Independent of its lipase product, PLA1A participates in antiviral innate immunity by facilitating TBK1 recruitment to mitochondria and MAVS interaction, and is co-opted during HCV infection to bridge viral envelope (E2/NS2) and replication (NS5A) complexes required for virion assembly [PMID:30016790, PMID:25505071].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Establishing the enzymatic identity of PLA1A: the enzyme was shown to specifically hydrolyze the sn-1 position of PS and lysoPS, and the C-terminal domain was required for diacyl-PS recognition, defining PLA1A as a PS-selective phospholipase A1.\",\n      \"evidence\": \"Recombinant protein expression and in vitro enzyme assays with domain-deletion mutants and defined lipid substrates\",\n      \"pmids\": [\"10196188\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No crystal structure of PLA1A itself\", \"Regulation of secretion and tissue-specific expression not addressed\", \"In vivo substrate preference not tested\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Structural determinants of substrate selectivity were identified: comparative analysis across the pancreatic lipase family revealed that PLA1A's short lid and deleted β9 loop explain its exclusive PLA1 activity and inability to hydrolyze triacylglycerols.\",\n      \"evidence\": \"Amino acid sequence alignment and comparative structural modeling with lipase gene family members\",\n      \"pmids\": [\"12069807\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No direct mutagenesis of lid or β9 loop in PLA1A to confirm causality\", \"No solved 3D structure of PLA1A\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"In vivo overexpression demonstrated a physiological role for PLA1A in lipoprotein remodeling: PLA1A increased HDL size and cholesterol content and reciprocally regulated SR-BI versus ABCA1 cholesterol efflux, linking its phospholipase activity to HDL metabolism.\",\n      \"evidence\": \"Adenoviral PLA1A overexpression in apoA-I transgenic mice with serum lipid profiling and efflux assays\",\n      \"pmids\": [\"14594995\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Loss-of-function in vivo data for HDL phenotype not provided\", \"Whether lysoPS or another product mediates the efflux changes is unclear\", \"Human relevance not established\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Replication and consolidation confirmed PLA1A as the principal extracellular enzyme generating 2-acyl-lysoPS from PS, solidifying the link between its structural features and enzymatic specificity.\",\n      \"evidence\": \"In vitro enzyme assays with structural and sequence analysis across the lipase gene family\",\n      \"pmids\": [\"17101204\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological concentrations of lysoPS product in tissues not measured\", \"No direct structural data (crystal/cryo-EM) for PLA1A\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"A non-canonical role in viral assembly was uncovered: PLA1A was shown to be upregulated during HCV infection and required specifically for virion assembly, physically bridging envelope protein E2, NS2, and the replication protein NS5A.\",\n      \"evidence\": \"siRNA knockdown, reciprocal co-IP of PLA1A with E2/NS2/NS5A, and step-specific viral propagation assays\",\n      \"pmids\": [\"25505071\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PLA1A's lipase activity is required for viral assembly or only its scaffolding function\", \"Mechanism by which PLA1A stabilizes NS2–E2 and NS2–NS5A complexes not defined\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"PLA1A was positioned in antiviral innate immune signaling upstream of TBK1: it facilitates TBK1 recruitment to mitochondria and TBK1–MAVS interaction, promoting IFN-β induction independently of IRF3-driven transcription.\",\n      \"evidence\": \"siRNA knockdown, TBK1/IRF3 reporter assays, mitochondrial fractionation, and TBK1 phosphorylation analysis\",\n      \"pmids\": [\"30016790\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct physical interaction between PLA1A and TBK1 or MAVS not demonstrated\", \"Whether lipase activity is required for this innate immune function is unknown\", \"Mechanism of mitochondrial morphology changes not resolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Domain-mapping refined the HCV assembly model: PLA1A interacts most closely with E2 lumenal domains and engages NS5A via its domain 1 C-terminus, establishing architecture of the oligomeric assembly complex.\",\n      \"evidence\": \"Domain deletion/truncation co-IP and proximity ligation assay in HCV-infected cells\",\n      \"pmids\": [\"31161554\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab study without independent replication\", \"Stoichiometry and 3D organization of the complex unknown\", \"Whether NS5A domain 1 interaction competes with replication function not tested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"A paracrine signaling cascade was delineated in synoviocytes: PLA1A-generated lysoPS is converted to LPA by autotaxin, which then acts on LPA receptors to drive IL-8 secretion, linking PLA1A to pro-inflammatory lipid signaling in joints.\",\n      \"evidence\": \"Recombinant PLA1A stimulation of primary fibroblast-like synoviocytes with ATX inhibitor, LPA receptor antagonist, and heparin blockade\",\n      \"pmids\": [\"34884486\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab pharmacological study without genetic confirmation\", \"In vivo relevance in arthritis models not tested\", \"Direct measurement of lysoPS and LPA intermediates not shown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Two studies established PLA1A as an immunomodulatory and tumor-suppressive enzyme acting through its lysoPS product: in macrophages, PLA1A suppresses M1 polarization via MAPK pathway inhibition; in lung adenocarcinoma, PLA1A/lysoPS signals through GPR174–cAMP/PKA to arrest cell cycle and inhibit EMT.\",\n      \"evidence\": \"Stable knockdown/overexpression in RAW264.7 with MAPK inhibitor rescue; PLA1A overexpression in LUAD cell lines and xenograft models with GPR174/cAMP/PKA pathway analysis\",\n      \"pmids\": [\"35650027\", \"35358472\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Both from single labs; independent replication needed\", \"Endogenous PLA1A loss-of-function in tumor models not tested\", \"Whether anti-inflammatory and anti-tumor effects are separable or share a common lysoPS receptor axis is unclear\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Conditional knockout in vivo established stromal PLA1A as a non-redundant source of lysoPS that signals via GPR34 to maintain peritoneal plasma cells and memory B cells at the omentum, defining a physiological lipid mediator niche for humoral immune memory.\",\n      \"evidence\": \"Conditional PLA1A knockout in stromal cells, adoptive transfer, chimera experiments, and ex vivo migration assays\",\n      \"pmids\": [\"39412501\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PLA1A–GPR34 axis regulates other immune cell types at other mucosal sites not tested\", \"Quantitative lysoPS gradients in vivo not measured\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"PLA1A was shown to be the dominant enzyme generating lysoPS on apoptotic cells in vivo, non-redundant with ABHD16A, supporting GPR34-dependent efferocytosis and cross-presentation by splenic cDC1 dendritic cells.\",\n      \"evidence\": \"PLA1A knockout mice, OT-I adoptive transfer, apoptotic cell uptake assays\",\n      \"pmids\": [\"41212150\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab study\", \"Whether PLA1A acts cell-autonomously on apoptotic cells or is supplied by phagocytes not resolved\", \"Molecular mechanism linking lysoPS/GPR34 to enhanced cross-presentation not defined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key open questions include whether PLA1A's lipase activity is required for its non-canonical roles in HCV assembly and TBK1 recruitment, the identity of its physiological regulators, and the structural basis of its PS selectivity at atomic resolution.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No crystal or cryo-EM structure of PLA1A\", \"Catalytic vs scaffolding function not genetically separated in viral/innate immune contexts\", \"Physiological regulation of PLA1A expression and secretion poorly defined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\n        \"term_id\": \"GO:0016787\",\n        \"supporting_discovery_ids\": [0, 2, 3]\n      },\n      {\n        \"term_id\": \"GO:0008289\",\n        \"supporting_discovery_ids\": [0, 2]\n      }\n    ],\n    \"localization\": [\n      {\n        \"term_id\": \"GO:0005576\",\n        \"supporting_discovery_ids\": [0, 2, 7, 10]\n      }\n    ],\n    \"pathway\": [\n      {\n        \"term_id\": \"R-HSA-1430728\",\n        \"supporting_discovery_ids\": [0, 2, 3]\n      },\n      {\n        \"term_id\": \"R-HSA-168256\",\n        \"supporting_discovery_ids\": [5, 10, 11]\n      },\n      {\n        \"term_id\": \"R-HSA-162582\",\n        \"supporting_discovery_ids\": [8, 9, 10]\n      }\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"TBK1\",\n      \"MAVS\",\n      \"GPR34\",\n      \"GPR174\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}