{"gene":"SLC15A3","run_date":"2026-06-10T07:46:32","timeline":{"discoveries":[{"year":2024,"finding":"Cryo-EM structure of apo SLC15A3 reveals that each protomer adopts an outward-facing conformation, establishing the structural basis for substrate recognition of free histidine and certain dipeptides transported from the endolysosomal lumen to the cytosol.","method":"Cryo-electron microscopy (cryo-EM) structure determination","journal":"Structure (London, England : 1993)","confidence":"High","confidence_rationale":"Tier 1 / Moderate — cryo-EM structure with functional context, single lab but direct structural determination with conformational state assignment","pmids":["39719710"],"is_preprint":false},{"year":2014,"finding":"PhT2 (SLC15A3) localizes to the lysosomal membrane, as confirmed by co-localization with lysosome-associated membrane protein 1 (LAMP1) in transfected HEK293 cells using dual-labeling immunofluorescence and confocal laser scanning microscopy.","method":"Dual-labeling immunofluorescence and confocal laser scanning microscopy in transfected HEK293 cells","journal":"Molecular pharmaceutics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization experiment with LAMP1 co-localization, replicated in later papers; single lab","pmids":["24754256"],"is_preprint":false},{"year":2014,"finding":"SLC15A3 (PhT2) mRNA expression is upregulated by LPS via the NF-κB signaling pathway; this upregulation is suppressed by pyrrolidine dithiocarbamate, a specific NF-κB inhibitor, in THP-1 macrophage cells and in mouse spleen during acute inflammation.","method":"LPS-induced inflammatory cell model with NF-κB inhibitor treatment; mRNA expression analysis","journal":"Molecular pharmaceutics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological inhibition of NF-κB pathway with in vitro and in vivo confirmation, single lab","pmids":["24754256"],"is_preprint":false},{"year":2018,"finding":"SLC15A3 is regulated by TLR2, TLR4, TLR7, and TLR9 ligands in macrophages via activation of NF-κB, MAPK, and IRF3 signaling pathways; reporter gene assay identified NF-κB binding sites in the SLC15A3 promoter responsible for this regulation.","method":"Reporter gene assay; pharmacological pathway inhibition; mRNA and protein expression analysis in macrophages","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reporter gene assay with multiple TLR ligands and pathway inhibitors, single lab, two orthogonal methods","pmids":["29991810"],"is_preprint":false},{"year":2018,"finding":"Knockdown or overexpression of SLC15A3 in macrophages modulates TLR4-triggered expression of proinflammatory cytokines, establishing a functional role for SLC15A3 in TLR4-mediated inflammatory responses.","method":"Knockdown and overexpression studies in macrophages with cytokine expression readout","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function and gain-of-function with defined cellular phenotype, single lab","pmids":["29991810"],"is_preprint":false},{"year":2018,"finding":"SLC15A3 interacts with MAVS and STING, and potentiates MAVS- and STING-mediated type I and type III interferon production in response to HSV-1 infection; overexpression inhibits HSV-1 replication while silencing enhances it.","method":"Co-immunoprecipitation (interaction with MAVS and STING); overexpression and siRNA knockdown in 293T cells with viral replication and IFN production readouts","journal":"Journal of immunology research","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — single Co-IP for interactions, but complemented by gain-of-function and loss-of-function with defined phenotypic readouts across multiple cell types","pmids":["30069489"],"is_preprint":false},{"year":2019,"finding":"Human PHT2 (SLC15A3) transports histidine and dipeptides with proton coupling; transport activity is maximal at extracellular pH 5.5, with a high affinity for d3-L-histidine (Km ~67 μM) and lower affinity for Gly-Sar (Km ~428 μM); valacyclovir, Gly-Gly-Gly, and cefadroxil are substrates, whereas 5-aminolevulinic acid and captopril are not.","method":"In vitro transport assay in MDCK cells stably expressing hPHT2 membrane-targeted mutants; competitive inhibition and Km determination","journal":"Journal of pharmaceutical sciences","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro functional transport assay with Km determination, substrate profiling, and pH-dependence; single lab with multiple orthogonal substrate measurements","pmids":["31254495"],"is_preprint":false},{"year":2019,"finding":"SLC15A3 (PHT2) mediates uptake of carnosine (β-alanyl-L-histidine) in glioblastoma cells; siRNA-mediated knockdown of PHT2 significantly reduced carnosine uptake, and competitive inhibition with L-histidine (an inhibitor of PHT1/2) also reduced uptake.","method":"siRNA knockdown; competitive inhibition; HPLC-MS quantification of carnosine uptake in glioblastoma cell lines","journal":"Amino acids","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown combined with competitive inhibition and quantitative MS measurement, single lab","pmids":["31073693"],"is_preprint":false},{"year":2024,"finding":"SLC15A3 interacts with the scaffold protein p62 to regulate p62 expression and phosphorylation, thereby modulating the p62-NRF2 antioxidant stress pathway and reactive oxygen species (ROS) production in macrophages; SLC15A3 deficiency in mice protected against bleomycin- or radiation-induced pulmonary fibrosis by reducing macrophage oxidative stress.","method":"Co-immunoprecipitation (SLC15A3–p62 interaction); SLC15A3 knockout mice model; ROS measurement; western blot for p62 phosphorylation and NRF2 pathway","journal":"Cell death and differentiation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP for interaction combined with KO mouse model and pathway analysis, single lab","pmids":["38374230"],"is_preprint":false},{"year":2024,"finding":"SLC15A3 transcription is directly activated by both p65 (NF-κB subunit) and HIF1α, which bind to the SLC15A3 promoter; luciferase reporter assay showed that inhibiting p65 or silencing HIF1α reduced SLC15A3 transcriptional activity in LPS/OGD-induced BV2 cells, and direct promoter binding was confirmed in NIH 3T3 cells.","method":"Luciferase reporter assay; siRNA knockdown; pharmacological inhibition (BAY 11-7082); chromatin binding assay in NIH 3T3 cells","journal":"Molecular neurobiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — luciferase reporter with multiple complementary approaches (siRNA, pharmacological inhibition, direct binding), single lab","pmids":["38717559"],"is_preprint":false},{"year":2025,"finding":"METTL3/ALKBH5-mediated m6A RNA modification targets SLC15A3 to regulate macrophage M1 polarization; SLC15A3 enhances TASL recruitment to augment IRF5 signaling via a mechanism parallel to the SLC15A4-TASL-IRF5 axis; conditional knockout of Mettl3 in macrophages inhibited M1 polarization and alleviated psoriasis-like symptoms, while Alkbh5 knockout exacerbated them.","method":"Conditional knockout mouse models (Mettl3, Alkbh5); in vivo and in vitro polarization assays; epistasis linking m6A modification → SLC15A3 → TASL–IRF5","journal":"Advanced science (Weinheim, Baden-Wurttemberg, Germany)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional KO in vivo combined with in vitro mechanistic pathway, single lab","pmids":["40679079"],"is_preprint":false}],"current_model":"SLC15A3 is a proton-coupled transporter localized to the lysosomal membrane that moves free histidine, dipeptides (e.g., carnosine), and certain peptidomimetics from the lysosomal lumen to the cytosol (maximal activity at pH 5.5, high affinity for histidine); its expression is transcriptionally upregulated by multiple TLR ligands and by LPS through NF-κB, MAPK, IRF3, p65, and HIF1α, and post-transcriptionally regulated by METTL3/ALKBH5-mediated m6A modification; once induced, SLC15A3 promotes innate immune signaling by interacting with MAVS and STING to potentiate type I/III interferon responses and by enhancing TASL recruitment to augment IRF5-driven M1 macrophage polarization, and it also modulates macrophage oxidative stress by interacting with the scaffold protein p62 to regulate the p62-NRF2-ROS antioxidant pathway."},"narrative":{"mechanistic_narrative":"SLC15A3 is a proton-coupled, lysosomal-membrane peptide/histidine transporter that doubles as a signaling scaffold in innate immune macrophages [PMID:24754256, PMID:31254495, PMID:30069489]. It resides in the lysosomal membrane, co-localizing with LAMP1 [PMID:24754256], and a cryo-EM structure captures each protomer in an outward-facing state poised for substrate recognition [PMID:39719710]. Functionally it transports free L-histidine with high affinity (Km ~67 μM) and dipeptides/peptidomimetics including Gly-Sar, valacyclovir, cefadroxil, and carnosine in a proton-coupled manner maximal at pH 5.5 [PMID:31254495, PMID:31073693]. SLC15A3 expression is strongly induced during inflammation: multiple TLR ligands (TLR2/4/7/9) drive transcription through NF-κB, MAPK, and IRF3, with NF-κB (p65) and HIF1α binding directly to the promoter, and m6A RNA modification by METTL3/ALKBH5 adds post-transcriptional control [PMID:24754256, PMID:29991810, PMID:38717559, PMID:40679079]. Once induced, SLC15A3 acts as a positive regulator of antiviral and inflammatory signaling: it interacts with MAVS and STING to potentiate type I/III interferon responses and restrict HSV-1 replication [PMID:30069489], enhances TASL recruitment to augment IRF5-driven M1 macrophage polarization [PMID:40679079], and binds the scaffold protein p62 to modulate the p62–NRF2 antioxidant/ROS axis, with its loss protecting mice from bleomycin- or radiation-induced pulmonary fibrosis [PMID:38374230].","teleology":[{"year":2014,"claim":"Established where SLC15A3 acts and that its expression is inflammation-responsive, framing it as an endolysosomal protein engaged during innate immunity.","evidence":"LAMP1 co-localization by confocal microscopy in HEK293 cells, and NF-κB-inhibitor-sensitive LPS induction in THP-1 macrophages and mouse spleen","pmids":["24754256"],"confidence":"Medium","gaps":["Did not define transported substrates or transport mechanism","Single-cell-type localization without endogenous protein imaging"]},{"year":2018,"claim":"Showed SLC15A3 is a broadly TLR-inducible gene with a functional role in shaping macrophage inflammatory output, moving it from passive transporter to immune effector.","evidence":"Reporter gene assays mapping NF-κB promoter sites, pathway inhibition, and knockdown/overexpression cytokine readouts in macrophages","pmids":["29991810"],"confidence":"Medium","gaps":["Mechanistic link between transport activity and cytokine modulation not resolved","Relative contributions of NF-κB vs MAPK vs IRF3 not dissected"]},{"year":2018,"claim":"Identified SLC15A3 as a scaffold for antiviral adaptors, demonstrating a signaling role beyond transport.","evidence":"Co-IP showing MAVS and STING interaction plus overexpression/knockdown effects on IFN production and HSV-1 replication in 293T cells","pmids":["30069489"],"confidence":"Medium","gaps":["Single Co-IP without reciprocal or endogenous validation","Whether transport activity is required for IFN potentiation untested"]},{"year":2019,"claim":"Defined the biochemical identity of SLC15A3 as a proton-coupled histidine/peptide transporter with a quantitative substrate profile.","evidence":"In vitro transport assays in MDCK cells with membrane-targeted hPHT2, Km determination and substrate/non-substrate profiling; carnosine uptake by knockdown and competitive inhibition in glioblastoma cells","pmids":["31254495","31073693"],"confidence":"High","gaps":["Physiological substrate flux at the native lysosomal membrane not measured","Link between substrate transport and immune signaling not established"]},{"year":2024,"claim":"Provided the structural basis for substrate recognition by capturing the transporter's conformational state.","evidence":"Cryo-EM structure of apo SLC15A3 showing outward-facing protomers","pmids":["39719710"],"confidence":"High","gaps":["Substrate-bound and inward-facing states not resolved","Structural elements coupling transport to protein-protein interactions undefined"]},{"year":2024,"claim":"Connected SLC15A3 to redox control via the p62–NRF2 axis and demonstrated a disease-relevant phenotype in vivo.","evidence":"Co-IP of SLC15A3–p62, SLC15A3 knockout mice, ROS measurement, and western blot of p62/NRF2 in fibrosis models","pmids":["38374230"],"confidence":"Medium","gaps":["Single Co-IP for the p62 interaction","How transporter activity feeds into p62 phosphorylation not mechanistically resolved"]},{"year":2024,"claim":"Identified the transcription factors directly driving SLC15A3 induction, refining the upstream regulatory logic.","evidence":"Luciferase reporter, siRNA, pharmacological inhibition, and chromatin binding for p65 and HIF1α in LPS/OGD-induced BV2 and NIH 3T3 cells","pmids":["38717559"],"confidence":"Medium","gaps":["Cooperativity or hierarchy between p65 and HIF1α unresolved","Generalizability beyond microglial/fibroblast contexts untested"]},{"year":2025,"claim":"Placed SLC15A3 in a TASL–IRF5 macrophage polarization axis under m6A post-transcriptional control, linking RNA modification to inflammatory cell fate.","evidence":"Conditional Mettl3/Alkbh5 knockout mice, polarization assays, and epistasis linking m6A → SLC15A3 → TASL–IRF5 in psoriasis models","pmids":["40679079"],"confidence":"Medium","gaps":["Direct SLC15A3–TASL physical interaction not shown by structure or reciprocal Co-IP","Whether transport function is needed for TASL recruitment unknown"]},{"year":null,"claim":"How SLC15A3's transport activity is mechanistically coupled to its scaffolding of MAVS/STING, TASL, and p62 remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No experiment separates transport-dead mutants from signaling competence","No structure of SLC15A3 bound to any signaling partner","Endogenous stoichiometry of these interactions in primary macrophages unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[6,7]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[5,8]}],"localization":[{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[1,0]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[3,4,5,10]}],"complexes":[],"partners":["MAVS","STING1","P62/SQSTM1","TASL/CXORF21"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8IY34","full_name":"Solute carrier family 15 member 3","aliases":["Osteoclast transporter","Peptide transporter 3","Peptide/histidine transporter 2","hPHT2"],"length_aa":581,"mass_kda":63.6,"function":"Proton-coupled amino-acid transporter that transports free histidine and certain di- and tripeptides, and is involved in innate immune response (PubMed:39719710). Preferably binds to short peptides with a basic residue at the first position and a hydrophobic residue at the second position (PubMed:39719710). Also able to transport carnosine (PubMed:31073693, PubMed:31254495). Involved in the detection of microbial pathogens by toll-like receptors (TLRs) and NOD-like receptors (NLRs), probably by mediating transport of bacterial peptidoglycans across the endolysosomal membrane: catalyzes the transport of certain bacterial peptidoglycans, such as muramyl dipeptide (MDP), the NOD2 ligand (By similarity)","subcellular_location":"Lysosome membrane; Endosome membrane","url":"https://www.uniprot.org/uniprotkb/Q8IY34/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SLC15A3","classification":"Not Classified","n_dependent_lines":10,"n_total_lines":1208,"dependency_fraction":0.008278145695364239},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SLC15A3","total_profiled":1310},"omim":[{"mim_id":"615806","title":"SOLUTE CARRIER FAMILY 15 (OLIGOPEPTIDE TRANSPORTER), MEMBER 4; SLC15A4","url":"https://www.omim.org/entry/615806"},{"mim_id":"610408","title":"SOLUTE CARRIER FAMILY 15 (OLIGOPEPTIDE TRANSPORTER), MEMBER 3; SLC15A3","url":"https://www.omim.org/entry/610408"},{"mim_id":"605956","title":"NUCLEOTIDE-BINDING OLIGOMERIZATION DOMAIN PROTEIN 2; NOD2","url":"https://www.omim.org/entry/605956"},{"mim_id":"603455","title":"RECEPTOR-INTERACTING SERINE/THREONINE KINASE 2; RIPK2","url":"https://www.omim.org/entry/603455"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Vesicles","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/SLC15A3"},"hgnc":{"alias_symbol":["PHT2","hPTR3"],"prev_symbol":[]},"alphafold":{"accession":"Q8IY34","domains":[{"cath_id":"1.20.1250.20","chopping":"26-133_156-259","consensus_level":"medium","plddt":90.9225,"start":26,"end":259},{"cath_id":"1.20.1250.20","chopping":"264-277_305-351_371-569","consensus_level":"medium","plddt":88.2961,"start":264,"end":569}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8IY34","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8IY34-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8IY34-F1-predicted_aligned_error_v6.png","plddt_mean":80.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SLC15A3","jax_strain_url":"https://www.jax.org/strain/search?query=SLC15A3"},"sequence":{"accession":"Q8IY34","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8IY34.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8IY34/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8IY34"}},"corpus_meta":[{"pmid":"29991810","id":"PMC_29991810","title":"Regulation and biological role of the peptide/histidine transporter SLC15A3 in Toll-like receptor-mediated inflammatory responses in macrophage.","date":"2018","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/29991810","citation_count":50,"is_preprint":false},{"pmid":"38374230","id":"PMC_38374230","title":"SLC15A3 plays a crucial role in pulmonary fibrosis by regulating macrophage oxidative stress.","date":"2024","source":"Cell death and differentiation","url":"https://pubmed.ncbi.nlm.nih.gov/38374230","citation_count":31,"is_preprint":false},{"pmid":"31073693","id":"PMC_31073693","title":"The proton-coupled oligopeptide transporters PEPT2, PHT1 and PHT2 mediate the uptake of carnosine in glioblastoma cells.","date":"2019","source":"Amino acids","url":"https://pubmed.ncbi.nlm.nih.gov/31073693","citation_count":28,"is_preprint":false},{"pmid":"30069489","id":"PMC_30069489","title":"The Solute Carrier Transporter SLC15A3 Participates in Antiviral Innate Immune Responses against Herpes Simplex Virus-1.","date":"2018","source":"Journal of immunology research","url":"https://pubmed.ncbi.nlm.nih.gov/30069489","citation_count":24,"is_preprint":false},{"pmid":"37156803","id":"PMC_37156803","title":"Antibacterial activity of vB_AbaM_PhT2 phage hydrophobic amino acid fusion endolysin, combined with colistin against Acinetobacter baumannii.","date":"2023","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/37156803","citation_count":24,"is_preprint":false},{"pmid":"24754256","id":"PMC_24754256","title":"Expression and regulation of the proton-coupled oligopeptide transporter PhT2 by LPS in macrophages and mouse spleen.","date":"2014","source":"Molecular pharmaceutics","url":"https://pubmed.ncbi.nlm.nih.gov/24754256","citation_count":22,"is_preprint":false},{"pmid":"31254495","id":"PMC_31254495","title":"Substrate Transport Properties of the Human Peptide/Histidine Transporter PHT2 in Transfected MDCK Cells.","date":"2019","source":"Journal of pharmaceutical sciences","url":"https://pubmed.ncbi.nlm.nih.gov/31254495","citation_count":6,"is_preprint":false},{"pmid":"40679079","id":"PMC_40679079","title":"METTL3/ALKBH5-Mediated N6-Methyladenosine Modification Drives Macrophage M1 Polarization via the SLC15A3-TASL-IRF5 Signaling Axis in Psoriasis.","date":"2025","source":"Advanced science (Weinheim, Baden-Wurttemberg, Germany)","url":"https://pubmed.ncbi.nlm.nih.gov/40679079","citation_count":5,"is_preprint":false},{"pmid":"38717559","id":"PMC_38717559","title":"SLC15A3 is transcriptionally regulated by HIF1α and p65 to worsen neuroinflammation in experimental ischemic stroke.","date":"2024","source":"Molecular neurobiology","url":"https://pubmed.ncbi.nlm.nih.gov/38717559","citation_count":5,"is_preprint":false},{"pmid":"38253252","id":"PMC_38253252","title":"Preventing severe hypoglycemia in adults with type 2 diabetes (PHT2): Design, delivery and evaluation framework for a randomized controlled trial.","date":"2024","source":"Contemporary clinical trials","url":"https://pubmed.ncbi.nlm.nih.gov/38253252","citation_count":1,"is_preprint":false},{"pmid":"39719710","id":"PMC_39719710","title":"The structures of the peptide transporters SLC15A3 and SLC15A4 reveal the recognition mechanisms for substrate and TASL.","date":"2024","source":"Structure (London, England : 1993)","url":"https://pubmed.ncbi.nlm.nih.gov/39719710","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7745,"output_tokens":2828,"usd":0.032828,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10105,"output_tokens":2850,"usd":0.060887,"stage2_stop_reason":"end_turn"},"total_usd":0.093715,"stage1_batch_id":"msgbatch_013LWZZT6MWaqB9qyTSeQBmU","stage2_batch_id":"msgbatch_0194ZzQaTGNpruoNJBbEMbt3","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2024,\n      \"finding\": \"Cryo-EM structure of apo SLC15A3 reveals that each protomer adopts an outward-facing conformation, establishing the structural basis for substrate recognition of free histidine and certain dipeptides transported from the endolysosomal lumen to the cytosol.\",\n      \"method\": \"Cryo-electron microscopy (cryo-EM) structure determination\",\n      \"journal\": \"Structure (London, England : 1993)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — cryo-EM structure with functional context, single lab but direct structural determination with conformational state assignment\",\n      \"pmids\": [\"39719710\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PhT2 (SLC15A3) localizes to the lysosomal membrane, as confirmed by co-localization with lysosome-associated membrane protein 1 (LAMP1) in transfected HEK293 cells using dual-labeling immunofluorescence and confocal laser scanning microscopy.\",\n      \"method\": \"Dual-labeling immunofluorescence and confocal laser scanning microscopy in transfected HEK293 cells\",\n      \"journal\": \"Molecular pharmaceutics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization experiment with LAMP1 co-localization, replicated in later papers; single lab\",\n      \"pmids\": [\"24754256\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"SLC15A3 (PhT2) mRNA expression is upregulated by LPS via the NF-κB signaling pathway; this upregulation is suppressed by pyrrolidine dithiocarbamate, a specific NF-κB inhibitor, in THP-1 macrophage cells and in mouse spleen during acute inflammation.\",\n      \"method\": \"LPS-induced inflammatory cell model with NF-κB inhibitor treatment; mRNA expression analysis\",\n      \"journal\": \"Molecular pharmaceutics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological inhibition of NF-κB pathway with in vitro and in vivo confirmation, single lab\",\n      \"pmids\": [\"24754256\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SLC15A3 is regulated by TLR2, TLR4, TLR7, and TLR9 ligands in macrophages via activation of NF-κB, MAPK, and IRF3 signaling pathways; reporter gene assay identified NF-κB binding sites in the SLC15A3 promoter responsible for this regulation.\",\n      \"method\": \"Reporter gene assay; pharmacological pathway inhibition; mRNA and protein expression analysis in macrophages\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reporter gene assay with multiple TLR ligands and pathway inhibitors, single lab, two orthogonal methods\",\n      \"pmids\": [\"29991810\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Knockdown or overexpression of SLC15A3 in macrophages modulates TLR4-triggered expression of proinflammatory cytokines, establishing a functional role for SLC15A3 in TLR4-mediated inflammatory responses.\",\n      \"method\": \"Knockdown and overexpression studies in macrophages with cytokine expression readout\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function and gain-of-function with defined cellular phenotype, single lab\",\n      \"pmids\": [\"29991810\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SLC15A3 interacts with MAVS and STING, and potentiates MAVS- and STING-mediated type I and type III interferon production in response to HSV-1 infection; overexpression inhibits HSV-1 replication while silencing enhances it.\",\n      \"method\": \"Co-immunoprecipitation (interaction with MAVS and STING); overexpression and siRNA knockdown in 293T cells with viral replication and IFN production readouts\",\n      \"journal\": \"Journal of immunology research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — single Co-IP for interactions, but complemented by gain-of-function and loss-of-function with defined phenotypic readouts across multiple cell types\",\n      \"pmids\": [\"30069489\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Human PHT2 (SLC15A3) transports histidine and dipeptides with proton coupling; transport activity is maximal at extracellular pH 5.5, with a high affinity for d3-L-histidine (Km ~67 μM) and lower affinity for Gly-Sar (Km ~428 μM); valacyclovir, Gly-Gly-Gly, and cefadroxil are substrates, whereas 5-aminolevulinic acid and captopril are not.\",\n      \"method\": \"In vitro transport assay in MDCK cells stably expressing hPHT2 membrane-targeted mutants; competitive inhibition and Km determination\",\n      \"journal\": \"Journal of pharmaceutical sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro functional transport assay with Km determination, substrate profiling, and pH-dependence; single lab with multiple orthogonal substrate measurements\",\n      \"pmids\": [\"31254495\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SLC15A3 (PHT2) mediates uptake of carnosine (β-alanyl-L-histidine) in glioblastoma cells; siRNA-mediated knockdown of PHT2 significantly reduced carnosine uptake, and competitive inhibition with L-histidine (an inhibitor of PHT1/2) also reduced uptake.\",\n      \"method\": \"siRNA knockdown; competitive inhibition; HPLC-MS quantification of carnosine uptake in glioblastoma cell lines\",\n      \"journal\": \"Amino acids\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown combined with competitive inhibition and quantitative MS measurement, single lab\",\n      \"pmids\": [\"31073693\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SLC15A3 interacts with the scaffold protein p62 to regulate p62 expression and phosphorylation, thereby modulating the p62-NRF2 antioxidant stress pathway and reactive oxygen species (ROS) production in macrophages; SLC15A3 deficiency in mice protected against bleomycin- or radiation-induced pulmonary fibrosis by reducing macrophage oxidative stress.\",\n      \"method\": \"Co-immunoprecipitation (SLC15A3–p62 interaction); SLC15A3 knockout mice model; ROS measurement; western blot for p62 phosphorylation and NRF2 pathway\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP for interaction combined with KO mouse model and pathway analysis, single lab\",\n      \"pmids\": [\"38374230\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SLC15A3 transcription is directly activated by both p65 (NF-κB subunit) and HIF1α, which bind to the SLC15A3 promoter; luciferase reporter assay showed that inhibiting p65 or silencing HIF1α reduced SLC15A3 transcriptional activity in LPS/OGD-induced BV2 cells, and direct promoter binding was confirmed in NIH 3T3 cells.\",\n      \"method\": \"Luciferase reporter assay; siRNA knockdown; pharmacological inhibition (BAY 11-7082); chromatin binding assay in NIH 3T3 cells\",\n      \"journal\": \"Molecular neurobiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — luciferase reporter with multiple complementary approaches (siRNA, pharmacological inhibition, direct binding), single lab\",\n      \"pmids\": [\"38717559\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"METTL3/ALKBH5-mediated m6A RNA modification targets SLC15A3 to regulate macrophage M1 polarization; SLC15A3 enhances TASL recruitment to augment IRF5 signaling via a mechanism parallel to the SLC15A4-TASL-IRF5 axis; conditional knockout of Mettl3 in macrophages inhibited M1 polarization and alleviated psoriasis-like symptoms, while Alkbh5 knockout exacerbated them.\",\n      \"method\": \"Conditional knockout mouse models (Mettl3, Alkbh5); in vivo and in vitro polarization assays; epistasis linking m6A modification → SLC15A3 → TASL–IRF5\",\n      \"journal\": \"Advanced science (Weinheim, Baden-Wurttemberg, Germany)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO in vivo combined with in vitro mechanistic pathway, single lab\",\n      \"pmids\": [\"40679079\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SLC15A3 is a proton-coupled transporter localized to the lysosomal membrane that moves free histidine, dipeptides (e.g., carnosine), and certain peptidomimetics from the lysosomal lumen to the cytosol (maximal activity at pH 5.5, high affinity for histidine); its expression is transcriptionally upregulated by multiple TLR ligands and by LPS through NF-κB, MAPK, IRF3, p65, and HIF1α, and post-transcriptionally regulated by METTL3/ALKBH5-mediated m6A modification; once induced, SLC15A3 promotes innate immune signaling by interacting with MAVS and STING to potentiate type I/III interferon responses and by enhancing TASL recruitment to augment IRF5-driven M1 macrophage polarization, and it also modulates macrophage oxidative stress by interacting with the scaffold protein p62 to regulate the p62-NRF2-ROS antioxidant pathway.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SLC15A3 is a proton-coupled, lysosomal-membrane peptide/histidine transporter that doubles as a signaling scaffold in innate immune macrophages [#1, #6, #5]. It resides in the lysosomal membrane, co-localizing with LAMP1 [#1], and a cryo-EM structure captures each protomer in an outward-facing state poised for substrate recognition [#0]. Functionally it transports free L-histidine with high affinity (Km ~67 \\u03bcM) and dipeptides/peptidomimetics including Gly-Sar, valacyclovir, cefadroxil, and carnosine in a proton-coupled manner maximal at pH 5.5 [#6, #7]. SLC15A3 expression is strongly induced during inflammation: multiple TLR ligands (TLR2/4/7/9) drive transcription through NF-\\u03baB, MAPK, and IRF3, with NF-\\u03baB (p65) and HIF1\\u03b1 binding directly to the promoter, and m6A RNA modification by METTL3/ALKBH5 adds post-transcriptional control [#2, #3, #9, #10]. Once induced, SLC15A3 acts as a positive regulator of antiviral and inflammatory signaling: it interacts with MAVS and STING to potentiate type I/III interferon responses and restrict HSV-1 replication [#5], enhances TASL recruitment to augment IRF5-driven M1 macrophage polarization [#10], and binds the scaffold protein p62 to modulate the p62\\u2013NRF2 antioxidant/ROS axis, with its loss protecting mice from bleomycin- or radiation-induced pulmonary fibrosis [#8].\",\n  \"teleology\": [\n    {\n      \"year\": 2014,\n      \"claim\": \"Established where SLC15A3 acts and that its expression is inflammation-responsive, framing it as an endolysosomal protein engaged during innate immunity.\",\n      \"evidence\": \"LAMP1 co-localization by confocal microscopy in HEK293 cells, and NF-\\u03baB-inhibitor-sensitive LPS induction in THP-1 macrophages and mouse spleen\",\n      \"pmids\": [\"24754256\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not define transported substrates or transport mechanism\", \"Single-cell-type localization without endogenous protein imaging\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Showed SLC15A3 is a broadly TLR-inducible gene with a functional role in shaping macrophage inflammatory output, moving it from passive transporter to immune effector.\",\n      \"evidence\": \"Reporter gene assays mapping NF-\\u03baB promoter sites, pathway inhibition, and knockdown/overexpression cytokine readouts in macrophages\",\n      \"pmids\": [\"29991810\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanistic link between transport activity and cytokine modulation not resolved\", \"Relative contributions of NF-\\u03baB vs MAPK vs IRF3 not dissected\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identified SLC15A3 as a scaffold for antiviral adaptors, demonstrating a signaling role beyond transport.\",\n      \"evidence\": \"Co-IP showing MAVS and STING interaction plus overexpression/knockdown effects on IFN production and HSV-1 replication in 293T cells\",\n      \"pmids\": [\"30069489\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single Co-IP without reciprocal or endogenous validation\", \"Whether transport activity is required for IFN potentiation untested\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Defined the biochemical identity of SLC15A3 as a proton-coupled histidine/peptide transporter with a quantitative substrate profile.\",\n      \"evidence\": \"In vitro transport assays in MDCK cells with membrane-targeted hPHT2, Km determination and substrate/non-substrate profiling; carnosine uptake by knockdown and competitive inhibition in glioblastoma cells\",\n      \"pmids\": [\"31254495\", \"31073693\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological substrate flux at the native lysosomal membrane not measured\", \"Link between substrate transport and immune signaling not established\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Provided the structural basis for substrate recognition by capturing the transporter's conformational state.\",\n      \"evidence\": \"Cryo-EM structure of apo SLC15A3 showing outward-facing protomers\",\n      \"pmids\": [\"39719710\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Substrate-bound and inward-facing states not resolved\", \"Structural elements coupling transport to protein-protein interactions undefined\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Connected SLC15A3 to redox control via the p62\\u2013NRF2 axis and demonstrated a disease-relevant phenotype in vivo.\",\n      \"evidence\": \"Co-IP of SLC15A3\\u2013p62, SLC15A3 knockout mice, ROS measurement, and western blot of p62/NRF2 in fibrosis models\",\n      \"pmids\": [\"38374230\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single Co-IP for the p62 interaction\", \"How transporter activity feeds into p62 phosphorylation not mechanistically resolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identified the transcription factors directly driving SLC15A3 induction, refining the upstream regulatory logic.\",\n      \"evidence\": \"Luciferase reporter, siRNA, pharmacological inhibition, and chromatin binding for p65 and HIF1\\u03b1 in LPS/OGD-induced BV2 and NIH 3T3 cells\",\n      \"pmids\": [\"38717559\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Cooperativity or hierarchy between p65 and HIF1\\u03b1 unresolved\", \"Generalizability beyond microglial/fibroblast contexts untested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Placed SLC15A3 in a TASL\\u2013IRF5 macrophage polarization axis under m6A post-transcriptional control, linking RNA modification to inflammatory cell fate.\",\n      \"evidence\": \"Conditional Mettl3/Alkbh5 knockout mice, polarization assays, and epistasis linking m6A \\u2192 SLC15A3 \\u2192 TASL\\u2013IRF5 in psoriasis models\",\n      \"pmids\": [\"40679079\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct SLC15A3\\u2013TASL physical interaction not shown by structure or reciprocal Co-IP\", \"Whether transport function is needed for TASL recruitment unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How SLC15A3's transport activity is mechanistically coupled to its scaffolding of MAVS/STING, TASL, and p62 remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No experiment separates transport-dead mutants from signaling competence\", \"No structure of SLC15A3 bound to any signaling partner\", \"Endogenous stoichiometry of these interactions in primary macrophages unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [6, 7]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [5, 8]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [1, 0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [3, 4, 5, 10]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"MAVS\", \"STING1\", \"p62/SQSTM1\", \"TASL/CXorf21\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}