{"gene":"C8G","run_date":"2026-06-09T22:02:45","timeline":{"discoveries":[{"year":1989,"finding":"C8G (gamma subunit of complement C8) is encoded by a separate gene located on chromosome 9q, distinct from C8A and C8B which are on chromosome 1p. The alpha-gamma subunit forms a disulfide-linked dimer, while the beta chain is non-covalently associated.","method":"Somatic cell hybrid panel analysis with cDNA probes for each subunit; genomic DNA digest probing","journal":"Genomics","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct chromosomal assignment using somatic cell hybrids with subunit-specific cDNA probes, replicated by genomic restriction mapping","pmids":["2613233"],"is_preprint":false},{"year":1995,"finding":"C8G is classified as a member of the lipocalin superfamily, a family of proteins that bind small hydrophobic ligands. The gamma chain is not related to any other complement protein but shares lipocalin structural features.","method":"Sequence homology analysis and chromosomal mapping; gene family classification","journal":"Annals of human genetics","confidence":"Medium","confidence_rationale":"Tier 3 / Strong — sequence-based classification replicated across multiple mapping and evolutionary studies","pmids":["8865989","7829063"],"is_preprint":false},{"year":1995,"finding":"IL-6 induces upregulation of C8 alpha-gamma and beta subunit biosynthesis in HepG2 hepatoma cells, characterizing C8 as a positive acute-phase protein. Evidence for post-transcriptional regulation of the C8 beta subunit was also obtained. No autoregulatory IL-6 or IL-6 receptor induction was detected.","method":"Immunoprecipitation and SDS-PAGE of biosynthetically labeled subunits in HepG2 cells treated with IL-6; mRNA analysis","journal":"Experimental and clinical immunogenetics","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct protein-level measurement by immunoprecipitation/SDS-PAGE in a single lab using relevant cell model","pmids":["7710765"],"is_preprint":false},{"year":2021,"finding":"C8G inhibits neuroinflammation and glial hyperactivation by interacting with sphingosine-1-phosphate receptor 2 (S1PR2), antagonizing the pro-inflammatory action of S1P in microglia. C8G is mainly expressed in brain astrocytes, and astrocyte-derived C8G interacts with S1PR2 to exert its anti-inflammatory effect.","method":"Recombinant C8G protein administration and shRNA-mediated knockdown in acute and chronic Alzheimer's disease mouse models; identification of S1PR2 as C8G interaction partner; pharmacological manipulation of S1PR2","journal":"Brain : a journal of neurology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal interaction identification combined with gain-of-function (recombinant protein) and loss-of-function (shRNA knockdown) experiments in multiple in vivo and in vitro models with defined phenotypic readouts","pmids":["33382892"],"is_preprint":false},{"year":2021,"finding":"C8G is localized to perivascular astrocytes in the brain, while its receptor S1PR2 is expressed in endothelial cells. C8G protects blood-brain barrier (BBB) integrity by antagonizing S1PR2-mediated inflammatory activation of endothelial cells; shRNA knockdown of C8G enhanced BBB permeability and neutrophil infiltration, while recombinant C8G preserved endothelial integrity in vitro.","method":"Immunohistochemical localization; intracerebroventricular recombinant protein administration; shRNA knockdown; in vitro BBB model; pharmacological S1PR2 agonists/antagonists","journal":"Frontiers in physiology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — direct localization experiment tied to functional consequence, combined with gain- and loss-of-function approaches in both in vivo and in vitro models in a single lab","pmids":["34149451"],"is_preprint":false},{"year":2024,"finding":"Hepatic expression of C8G is positively regulated by the nuclear receptor HNF4α. HNF4α binds to C8G gene regulatory regions and transactivates C8G expression; C8G expression is markedly decreased in liver-specific Hnf4a-null mice and human hepatoma cell lines with HNF4α suppression, and is induced upon forced HNF4α expression.","method":"Liver-specific Hnf4a-null mouse models (constitutive and tamoxifen-inducible); HNF4α knockdown in human hepatoma cell lines; forced HNF4α expression in immortalized hepatocytes; transactivation assays with HNF4α binding sites","journal":"In vitro cellular & developmental biology. Animal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — transactivation assays with binding site analysis plus multiple in vivo knockout models and in vitro gain/loss-of-function in a single study","pmids":["39285151"],"is_preprint":false},{"year":2024,"finding":"C8G (as part of the C8 heterotrimer with C8A) is a component of the C5b-9 membrane attack complex. Effective urate-lowering therapy in gout patients led to decreased serum C8A and C8G levels, and febuxostat inhibited complement activation pathway proteins in cultured bone marrow macrophages.","method":"Unbiased serum proteomics at baseline and 48 weeks of urate-lowering therapy in two independent cohorts; proteomics of cultured XOI-treated murine bone marrow macrophages","journal":"Research square","confidence":"Low","confidence_rationale":"Tier 3 / Weak — proteomics observation in clinical cohorts and cell culture; no direct mechanistic experiment on C8G itself; preprint","pmids":["38766125"],"is_preprint":true}],"current_model":"C8G encodes the gamma chain of complement component C8, a lipocalin-family protein that forms a disulfide-linked dimer with the alpha chain and participates in membrane attack complex assembly; beyond its classical complement role, astrocyte-expressed C8G acts as a neuroinflammation inhibitor by binding and antagonizing sphingosine-1-phosphate receptor 2 (S1PR2) on microglia and endothelial cells, thereby suppressing glial activation and protecting blood-brain barrier integrity, with its hepatic expression transcriptionally regulated by HNF4α."},"narrative":{"mechanistic_narrative":"C8G encodes the gamma chain of complement component C8, a lipocalin-superfamily protein that forms a disulfide-linked dimer with the alpha chain and participates in assembly of the C5b-9 membrane attack complex [PMID:2613233, PMID:8865989, PMID:7829063]. The gene resides on chromosome 9q, distinct from the C8A and C8B genes [PMID:2613233], and unlike other complement proteins its sequence places it in the lipocalin family of small hydrophobic-ligand binders [PMID:8865989, PMID:7829063]. Hepatic C8 synthesis is induced by IL-6 as a positive acute-phase response [PMID:7710765], and basal hepatic C8G transcription is driven by the nuclear receptor HNF4α, which binds C8G regulatory regions and transactivates its expression [PMID:39285151]. Beyond this classical complement role, astrocyte-expressed C8G functions as a neuroinflammation inhibitor: it binds and antagonizes sphingosine-1-phosphate receptor 2 (S1PR2), suppressing S1P-driven microglial hyperactivation in Alzheimer's disease models [PMID:33382892] and, from perivascular astrocytes, protecting blood-brain barrier integrity by blocking S1PR2-mediated inflammatory activation of endothelial cells [PMID:34149451].","teleology":[{"year":1989,"claim":"Establishing that C8G is encoded by a gene separate from C8A and C8B clarified the genetic architecture of the trimeric C8 complement protein and the covalent organization of its subunits.","evidence":"Somatic cell hybrid panel analysis with subunit-specific cDNA probes and genomic restriction mapping","pmids":["2613233"],"confidence":"High","gaps":["Does not define the functional contribution of the gamma chain to membrane attack complex activity","No structural basis for the alpha-gamma disulfide linkage"]},{"year":1995,"claim":"Classifying the gamma chain as a lipocalin rather than a complement-related protein revealed an unexpected evolutionary origin and predicted a hydrophobic-ligand-binding fold distinct from its complement partners.","evidence":"Sequence homology analysis, chromosomal mapping, and gene-family classification","pmids":["8865989","7829063"],"confidence":"Medium","gaps":["No identified physiological hydrophobic ligand","Functional significance of the lipocalin fold within C8 unresolved"]},{"year":1995,"claim":"Demonstrating IL-6 induction of C8 subunit biosynthesis placed C8 within the hepatic acute-phase response and identified subunit-specific regulatory modes.","evidence":"Immunoprecipitation/SDS-PAGE of biosynthetically labeled subunits and mRNA analysis in IL-6-treated HepG2 cells","pmids":["7710765"],"confidence":"Medium","gaps":["Transcription factors mediating IL-6 induction not defined","Performed in a single hepatoma cell model"]},{"year":2021,"claim":"Identifying S1PR2 as a C8G interaction partner revealed a non-complement signaling function in which C8G acts as an endogenous receptor antagonist to restrain neuroinflammation.","evidence":"Recombinant protein gain-of-function and shRNA loss-of-function in acute and chronic Alzheimer's mouse models, with S1PR2 pharmacological manipulation","pmids":["33382892"],"confidence":"High","gaps":["Binding interface and stoichiometry of the C8G–S1PR2 interaction not resolved","Relationship between the lipocalin ligand-binding capacity and S1PR2 antagonism unknown"]},{"year":2021,"claim":"Localizing C8G to perivascular astrocytes and S1PR2 to endothelial cells extended the anti-inflammatory role to blood-brain barrier protection.","evidence":"Immunohistochemistry, intracerebroventricular recombinant protein, shRNA knockdown, in vitro BBB model, and S1PR2 agonists/antagonists","pmids":["34149451"],"confidence":"High","gaps":["Whether astrocyte-derived C8G acts on the same endothelial S1PR2 pool in vivo not directly shown","Contribution of complement-derived versus locally secreted C8G unclear"]},{"year":2024,"claim":"Identifying HNF4α as a transcriptional activator of C8G defined an upstream regulator of its hepatic expression.","evidence":"Liver-specific Hnf4a-null mice, HNF4α knockdown and forced expression in hepatoma/hepatocyte lines, and transactivation assays with binding-site analysis","pmids":["39285151"],"confidence":"High","gaps":["Whether HNF4α regulates astrocyte/brain C8G expression not addressed","Interplay with IL-6-driven acute-phase induction not examined"]},{"year":2024,"claim":"Correlating serum C8G with urate-lowering therapy linked C8G complement function to gout-associated inflammation, but only as an observational association.","evidence":"Unbiased serum proteomics in two cohorts and proteomics of XOI-treated murine bone marrow macrophages (preprint)","pmids":["38766125"],"confidence":"Low","gaps":["No direct mechanistic experiment on C8G itself","Causality between C8G levels and gout inflammation not established","Preprint, not peer-reviewed"]},{"year":null,"claim":"How the lipocalin ligand-binding pocket of C8G relates mechanistically to both its membrane attack complex role and its S1PR2 antagonism remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structure of the C8G–S1PR2 complex","No identified endogenous hydrophobic ligand","Unknown whether complement and neuroinflammatory functions share a molecular determinant"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[3,4]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[1]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[4,6]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,6]}],"complexes":["C5b-9 membrane attack complex","C8 (alpha-gamma-beta) heterotrimer"],"partners":["C8A","S1PR2","HNF4A"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P07360","full_name":"Complement component C8 gamma chain","aliases":[],"length_aa":202,"mass_kda":22.3,"function":"Component of the membrane attack complex (MAC), a multiprotein complex activated by the complement cascade, which inserts into a target cell membrane and forms a pore, leading to target cell membrane rupture and cell lysis (PubMed:26841837, PubMed:27052168, PubMed:30552328). The MAC is initiated by proteolytic cleavage of C5 into complement C5b in response to the classical, alternative, lectin and GZMK complement pathways (PubMed:30552328, PubMed:39914456, PubMed:39814882). The complement pathways consist in a cascade of proteins that leads to phagocytosis and breakdown of pathogens and signaling that strengthens the adaptive immune system (PubMed:30552328). C8G, together with C8A and C8B, inserts into the target membrane, but does not form pores by itself (PubMed:30552328). During MAC assembly, associates with C5b, C6 and C7 to form the C5b8 intermediate complex that inserts into the target membrane and traverses the bilayer increasing membrane rigidity (PubMed:30552328, PubMed:6833260)","subcellular_location":"Secreted; Target cell membrane","url":"https://www.uniprot.org/uniprotkb/P07360/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/C8G","classification":"Not Classified","n_dependent_lines":14,"n_total_lines":1208,"dependency_fraction":0.011589403973509934},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/C8G","total_profiled":1310},"omim":[{"mim_id":"613790","title":"COMPLEMENT COMPONENT 8 DEFICIENCY, TYPE I; C8D1","url":"https://www.omim.org/entry/613790"},{"mim_id":"613789","title":"COMPLEMENT COMPONENT 8 DEFICIENCY, TYPE II; C8D2","url":"https://www.omim.org/entry/613789"},{"mim_id":"120960","title":"COMPLEMENT COMPONENT 8, BETA SUBUNIT; C8B","url":"https://www.omim.org/entry/120960"},{"mim_id":"120950","title":"COMPLEMENT COMPONENT 8, ALPHA SUBUNIT; C8A","url":"https://www.omim.org/entry/120950"},{"mim_id":"120930","title":"COMPLEMENT COMPONENT 8, GAMMA SUBUNIT; C8G","url":"https://www.omim.org/entry/120930"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"liver","ntpm":522.4}],"url":"https://www.proteinatlas.org/search/C8G"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"P07360","domains":[{"cath_id":"2.40.128.20","chopping":"36-199","consensus_level":"high","plddt":95.5774,"start":36,"end":199}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P07360","model_url":"https://alphafold.ebi.ac.uk/files/AF-P07360-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P07360-F1-predicted_aligned_error_v6.png","plddt_mean":89.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=C8G","jax_strain_url":"https://www.jax.org/strain/search?query=C8G"},"sequence":{"accession":"P07360","fasta_url":"https://rest.uniprot.org/uniprotkb/P07360.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P07360/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P07360"}},"corpus_meta":[{"pmid":"7829063","id":"PMC_7829063","title":"Comparative mapping of lipocalin genes in human and mouse: the four genes for complement C8 gamma chain, prostaglandin-D-synthase, oncogene-24p3, and progestagen-associated endometrial protein map to HSA9 and MMU2.","date":"1994","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/7829063","citation_count":54,"is_preprint":false},{"pmid":"20167877","id":"PMC_20167877","title":"Serum proteomic analysis of diet-induced steatohepatitis and metabolic syndrome in the Ossabaw miniature swine.","date":"2010","source":"American journal of physiology. 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The alpha-gamma subunit forms a disulfide-linked dimer, while the beta chain is non-covalently associated.\",\n      \"method\": \"Somatic cell hybrid panel analysis with cDNA probes for each subunit; genomic DNA digest probing\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct chromosomal assignment using somatic cell hybrids with subunit-specific cDNA probes, replicated by genomic restriction mapping\",\n      \"pmids\": [\"2613233\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"C8G is classified as a member of the lipocalin superfamily, a family of proteins that bind small hydrophobic ligands. The gamma chain is not related to any other complement protein but shares lipocalin structural features.\",\n      \"method\": \"Sequence homology analysis and chromosomal mapping; gene family classification\",\n      \"journal\": \"Annals of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Strong — sequence-based classification replicated across multiple mapping and evolutionary studies\",\n      \"pmids\": [\"8865989\", \"7829063\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"IL-6 induces upregulation of C8 alpha-gamma and beta subunit biosynthesis in HepG2 hepatoma cells, characterizing C8 as a positive acute-phase protein. Evidence for post-transcriptional regulation of the C8 beta subunit was also obtained. No autoregulatory IL-6 or IL-6 receptor induction was detected.\",\n      \"method\": \"Immunoprecipitation and SDS-PAGE of biosynthetically labeled subunits in HepG2 cells treated with IL-6; mRNA analysis\",\n      \"journal\": \"Experimental and clinical immunogenetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct protein-level measurement by immunoprecipitation/SDS-PAGE in a single lab using relevant cell model\",\n      \"pmids\": [\"7710765\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"C8G inhibits neuroinflammation and glial hyperactivation by interacting with sphingosine-1-phosphate receptor 2 (S1PR2), antagonizing the pro-inflammatory action of S1P in microglia. C8G is mainly expressed in brain astrocytes, and astrocyte-derived C8G interacts with S1PR2 to exert its anti-inflammatory effect.\",\n      \"method\": \"Recombinant C8G protein administration and shRNA-mediated knockdown in acute and chronic Alzheimer's disease mouse models; identification of S1PR2 as C8G interaction partner; pharmacological manipulation of S1PR2\",\n      \"journal\": \"Brain : a journal of neurology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal interaction identification combined with gain-of-function (recombinant protein) and loss-of-function (shRNA knockdown) experiments in multiple in vivo and in vitro models with defined phenotypic readouts\",\n      \"pmids\": [\"33382892\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"C8G is localized to perivascular astrocytes in the brain, while its receptor S1PR2 is expressed in endothelial cells. C8G protects blood-brain barrier (BBB) integrity by antagonizing S1PR2-mediated inflammatory activation of endothelial cells; shRNA knockdown of C8G enhanced BBB permeability and neutrophil infiltration, while recombinant C8G preserved endothelial integrity in vitro.\",\n      \"method\": \"Immunohistochemical localization; intracerebroventricular recombinant protein administration; shRNA knockdown; in vitro BBB model; pharmacological S1PR2 agonists/antagonists\",\n      \"journal\": \"Frontiers in physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization experiment tied to functional consequence, combined with gain- and loss-of-function approaches in both in vivo and in vitro models in a single lab\",\n      \"pmids\": [\"34149451\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Hepatic expression of C8G is positively regulated by the nuclear receptor HNF4α. HNF4α binds to C8G gene regulatory regions and transactivates C8G expression; C8G expression is markedly decreased in liver-specific Hnf4a-null mice and human hepatoma cell lines with HNF4α suppression, and is induced upon forced HNF4α expression.\",\n      \"method\": \"Liver-specific Hnf4a-null mouse models (constitutive and tamoxifen-inducible); HNF4α knockdown in human hepatoma cell lines; forced HNF4α expression in immortalized hepatocytes; transactivation assays with HNF4α binding sites\",\n      \"journal\": \"In vitro cellular & developmental biology. Animal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — transactivation assays with binding site analysis plus multiple in vivo knockout models and in vitro gain/loss-of-function in a single study\",\n      \"pmids\": [\"39285151\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"C8G (as part of the C8 heterotrimer with C8A) is a component of the C5b-9 membrane attack complex. Effective urate-lowering therapy in gout patients led to decreased serum C8A and C8G levels, and febuxostat inhibited complement activation pathway proteins in cultured bone marrow macrophages.\",\n      \"method\": \"Unbiased serum proteomics at baseline and 48 weeks of urate-lowering therapy in two independent cohorts; proteomics of cultured XOI-treated murine bone marrow macrophages\",\n      \"journal\": \"Research square\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — proteomics observation in clinical cohorts and cell culture; no direct mechanistic experiment on C8G itself; preprint\",\n      \"pmids\": [\"38766125\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"C8G encodes the gamma chain of complement component C8, a lipocalin-family protein that forms a disulfide-linked dimer with the alpha chain and participates in membrane attack complex assembly; beyond its classical complement role, astrocyte-expressed C8G acts as a neuroinflammation inhibitor by binding and antagonizing sphingosine-1-phosphate receptor 2 (S1PR2) on microglia and endothelial cells, thereby suppressing glial activation and protecting blood-brain barrier integrity, with its hepatic expression transcriptionally regulated by HNF4α.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"C8G encodes the gamma chain of complement component C8, a lipocalin-superfamily protein that forms a disulfide-linked dimer with the alpha chain and participates in assembly of the C5b-9 membrane attack complex [#0, #1]. The gene resides on chromosome 9q, distinct from the C8A and C8B genes [#0], and unlike other complement proteins its sequence places it in the lipocalin family of small hydrophobic-ligand binders [#1]. Hepatic C8 synthesis is induced by IL-6 as a positive acute-phase response [#2], and basal hepatic C8G transcription is driven by the nuclear receptor HNF4\\u03b1, which binds C8G regulatory regions and transactivates its expression [#5]. Beyond this classical complement role, astrocyte-expressed C8G functions as a neuroinflammation inhibitor: it binds and antagonizes sphingosine-1-phosphate receptor 2 (S1PR2), suppressing S1P-driven microglial hyperactivation in Alzheimer's disease models [#3] and, from perivascular astrocytes, protecting blood-brain barrier integrity by blocking S1PR2-mediated inflammatory activation of endothelial cells [#4].\",\n  \"teleology\": [\n    {\n      \"year\": 1989,\n      \"claim\": \"Establishing that C8G is encoded by a gene separate from C8A and C8B clarified the genetic architecture of the trimeric C8 complement protein and the covalent organization of its subunits.\",\n      \"evidence\": \"Somatic cell hybrid panel analysis with subunit-specific cDNA probes and genomic restriction mapping\",\n      \"pmids\": [\"2613233\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not define the functional contribution of the gamma chain to membrane attack complex activity\", \"No structural basis for the alpha-gamma disulfide linkage\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Classifying the gamma chain as a lipocalin rather than a complement-related protein revealed an unexpected evolutionary origin and predicted a hydrophobic-ligand-binding fold distinct from its complement partners.\",\n      \"evidence\": \"Sequence homology analysis, chromosomal mapping, and gene-family classification\",\n      \"pmids\": [\"8865989\", \"7829063\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No identified physiological hydrophobic ligand\", \"Functional significance of the lipocalin fold within C8 unresolved\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Demonstrating IL-6 induction of C8 subunit biosynthesis placed C8 within the hepatic acute-phase response and identified subunit-specific regulatory modes.\",\n      \"evidence\": \"Immunoprecipitation/SDS-PAGE of biosynthetically labeled subunits and mRNA analysis in IL-6-treated HepG2 cells\",\n      \"pmids\": [\"7710765\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Transcription factors mediating IL-6 induction not defined\", \"Performed in a single hepatoma cell model\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identifying S1PR2 as a C8G interaction partner revealed a non-complement signaling function in which C8G acts as an endogenous receptor antagonist to restrain neuroinflammation.\",\n      \"evidence\": \"Recombinant protein gain-of-function and shRNA loss-of-function in acute and chronic Alzheimer's mouse models, with S1PR2 pharmacological manipulation\",\n      \"pmids\": [\"33382892\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Binding interface and stoichiometry of the C8G\\u2013S1PR2 interaction not resolved\", \"Relationship between the lipocalin ligand-binding capacity and S1PR2 antagonism unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Localizing C8G to perivascular astrocytes and S1PR2 to endothelial cells extended the anti-inflammatory role to blood-brain barrier protection.\",\n      \"evidence\": \"Immunohistochemistry, intracerebroventricular recombinant protein, shRNA knockdown, in vitro BBB model, and S1PR2 agonists/antagonists\",\n      \"pmids\": [\"34149451\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether astrocyte-derived C8G acts on the same endothelial S1PR2 pool in vivo not directly shown\", \"Contribution of complement-derived versus locally secreted C8G unclear\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identifying HNF4\\u03b1 as a transcriptional activator of C8G defined an upstream regulator of its hepatic expression.\",\n      \"evidence\": \"Liver-specific Hnf4a-null mice, HNF4\\u03b1 knockdown and forced expression in hepatoma/hepatocyte lines, and transactivation assays with binding-site analysis\",\n      \"pmids\": [\"39285151\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether HNF4\\u03b1 regulates astrocyte/brain C8G expression not addressed\", \"Interplay with IL-6-driven acute-phase induction not examined\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Correlating serum C8G with urate-lowering therapy linked C8G complement function to gout-associated inflammation, but only as an observational association.\",\n      \"evidence\": \"Unbiased serum proteomics in two cohorts and proteomics of XOI-treated murine bone marrow macrophages (preprint)\",\n      \"pmids\": [\"38766125\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No direct mechanistic experiment on C8G itself\", \"Causality between C8G levels and gout inflammation not established\", \"Preprint, not peer-reviewed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the lipocalin ligand-binding pocket of C8G relates mechanistically to both its membrane attack complex role and its S1PR2 antagonism remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structure of the C8G\\u2013S1PR2 complex\", \"No identified endogenous hydrophobic ligand\", \"Unknown whether complement and neuroinflammatory functions share a molecular determinant\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [3, 4]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [4, 6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 6]}\n    ],\n    \"complexes\": [\"C5b-9 membrane attack complex\", \"C8 (alpha-gamma-beta) heterotrimer\"],\n    \"partners\": [\"C8A\", \"S1PR2\", \"HNF4A\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":4,"faith_total":4,"faith_pct":100.0}}