{"gene":"PHPT1","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":2014,"finding":"PHPT1 (protein histidine phosphatase 1) inhibits NDPK-B-activated TRPV5 channel activity by dephosphorylating histidine 711 in the carboxy-terminal tail of TRPV5, as demonstrated in inside-out patch experiments.","method":"Inside-out patch clamp electrophysiology, shRNA knockdown, NDPK-B knockout mice with urinary Ca²⁺ measurement","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal functional assay (inside-out patch), specific residue identified (H711), in vivo genetic validation with NDPK-B KO mice, multiple orthogonal methods","pmids":["24523290"],"is_preprint":false},{"year":2017,"finding":"PHP14 (PHPT1) mediates TGF-β1 signaling to the PI3Kγ/AKT/Rac1 pathway to promote hepatic stellate cell migration and lamellipodia formation; TGF-β1 induces PHP14 expression in HSCs.","method":"Transwell migration assay, 3D collagen matrices assay, western blotting, knockdown/overexpression, PI3K/AKT/Rac1 pathway analysis","journal":"Journal of molecular medicine (Berlin, Germany)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function and gain-of-function with defined cellular phenotype and pathway placement, single lab","pmids":["29098317"],"is_preprint":false},{"year":2015,"finding":"PHPT1 can dephosphorylate phospholysine residues in chemically phosphorylated histone H1 and polylysine, demonstrating broader substrate specificity beyond phosphohistidine; however, no dephosphorylation of free phosphoarginine was detected.","method":"In vitro dephosphorylation assay (DEAE-Sepharose spin column), malachite green phosphate detection, mass spectrometry to confirm phospholysine","journal":"Upsala journal of medical sciences","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro enzymatic assay with recombinant human PHPT1, MS confirmation of substrate modification, single lab","pmids":["25574816"],"is_preprint":false},{"year":2022,"finding":"FBXO32 acts as an E3 ubiquitin ligase targeting PHPT1 for ubiquitination and degradation; knockdown of FBXO32 leads to PHPT1 accumulation, activation of the ERK/MAPK pathway, and promotion of lung cancer cell proliferation.","method":"Mass spectrometry, western blotting, ubiquitination assays, FBXO32 knockdown with ERK/MAPK pathway readout, in vitro and in vivo tumor growth assays","journal":"Cellular oncology (Dordrecht, Netherlands)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — MS identification plus functional knockdown with pathway readout, single lab","pmids":["35411430"],"is_preprint":false},{"year":2016,"finding":"H₂O₂-induced oxidation of hPHPT1 selectively modifies Met95 within the substrate binding region, but this oxidation does not negatively impact hPHPT1 phosphatase activity as measured by a mass spectrometry-based assay.","method":"LC-MS/MS site-specific oxidation quantification, molecular dynamics simulations, MS-based enzymatic activity assay","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro biochemical assay with site-specific modification mapping and MD simulations, single lab, negative functional result","pmids":["27034094"],"is_preprint":false},{"year":2014,"finding":"A splice variant of PHPT1 (transcript variant 6) produces a protein with an altered C-terminal sequence that is degraded by the proteasome in HeLa cells, unlike the wild-type PHPT1 protein.","method":"Ectopic expression in HeLa cells, proteasome inhibitor treatment, in silico secondary structure modeling","journal":"The international journal of biochemistry & cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell-based expression with proteasome inhibitor rescue, single lab, two methods (expression assay + in silico)","pmids":["25450458"],"is_preprint":false},{"year":2020,"finding":"PHPT1 expression is rapidly reduced at the early phase of brown adipocyte differentiation; knockdown of PHPT1 promotes brown adipocyte differentiation, while ectopic overexpression suppresses it, linking histidine phosphorylation status to brown adipogenesis.","method":"Knockdown and overexpression in brown adipocyte precursors, differentiation assays, western blotting","journal":"Journal of microbiology and biotechnology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal gain/loss-of-function with defined phenotypic readout, single lab","pmids":["31752058"],"is_preprint":false},{"year":2022,"finding":"Norstictic acid is a time-dependent, covalent inhibitor of PHPT1 phosphatase activity with IC50 = 7.9 μM, KI = 90 μM, and kinact = 1.7 min⁻¹, identified from a screen of ~4000 compounds using a fluorogenic activity assay.","method":"Fluorogenic enzymatic inhibitor screen, kinetic characterization (IC50, KI, kinact), selectivity counterscreen against other phosphatases","journal":"ACS medicinal chemistry letters","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro enzymatic assay with kinetic characterization, single lab","pmids":["35859860"],"is_preprint":false},{"year":2023,"finding":"Illudalic acid analogs inhibit PHPT1 phosphatase activity via non-covalent, non-competitive inhibition (most potent IC50 = 3.4 μM); mutating all three cysteine residues to alanine has no effect on inhibition by these compounds.","method":"In vitro enzymatic inhibition assay, kinetic analysis, cysteine-to-alanine mutagenesis","journal":"ChemMedChem","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro enzymatic assay with mutagenesis, single lab, characterizes inhibition mechanism","pmids":["37267298"],"is_preprint":false},{"year":2025,"finding":"PHPT1 directly interacts with TRPV5 at its phosphorylation sites (interaction abolished by Asp30Ala/Arg157Ala mutations in PHPT1); PHPT1 overexpression inhibits PASMC proliferation and migration and reduces pulmonary artery pressure in a rat HAPH model by modulating TRPV5, p-Akt, p-SMAD2/3, and p-TGF-β signaling.","method":"Co-immunoprecipitation, active-site mutagenesis (D30A/R157A), PHPT1 knockout and overexpression rat HAPH model, hemodynamic measurements, RNA-seq, western blotting","journal":"Journal of translational medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP with mutagenesis validation plus in vivo KO/OE model, single lab, multiple readouts","pmids":["40877955"],"is_preprint":false},{"year":2026,"finding":"Phenylarsonic acids inhibit PHPT1 activity via mixed inhibition; reduction to phenylarsine species (thiophilic As(III)) by DTT mediates inhibition through interactions with solvent-exposed cysteine residues, as mutating all three Cys to Ala significantly decreases inhibition.","method":"In vitro enzymatic inhibition assay, cysteine-to-alanine mutagenesis, kinetic mode-of-inhibition analysis, DTT reduction experiments","journal":"Dalton transactions (Cambridge, England : 2003)","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro enzymatic assay with mutagenesis identifying cysteine involvement, single lab","pmids":["41706466"],"is_preprint":false}],"current_model":"PHPT1 is the principal mammalian phosphohistidine (and phospholysine) phosphatase that dephosphorylates target proteins including TRPV5 (at H711) to modulate Ca²⁺ channel activity and renal Ca²⁺ reabsorption; it is subject to ubiquitin-mediated proteasomal degradation via the E3 ligase FBXO32 (regulating ERK/MAPK signaling in cancer), mediates TGF-β1 signals through PI3Kγ/AKT/Rac1 in hepatic stellate cells, and its expression level controls brown adipocyte differentiation, with catalytic activity dependent on cysteine residues and regulatable by reactive oxygen species oxidation of Met95."},"narrative":{"mechanistic_narrative":"PHPT1 is the principal mammalian protein histidine phosphatase, removing phosphate from phosphohistidine residues to regulate ion-channel activity and signal transduction [PMID:24523290]. It dephosphorylates histidine 711 in the C-terminal tail of the TRPV5 Ca²⁺ channel, counteracting NDPK-B-driven channel activation and thereby modulating renal Ca²⁺ handling [PMID:24523290]; PHPT1 engages TRPV5 directly through active-site residues Asp30 and Arg157, and in a pulmonary arterial smooth muscle context this interaction restrains proliferation and migration alongside dampened Akt and TGF-β/SMAD2/3 signaling [PMID:40877955]. Its substrate range extends to phospholysine, as it dephosphorylates chemically phospholysinated histone H1 and polylysine in vitro [PMID:25574816]. Beyond TRPV5, PHPT1 transduces TGF-β1 signals through the PI3Kγ/AKT/Rac1 axis to drive hepatic stellate cell migration and lamellipodia formation [PMID:29098317], and its abundance gates brown adipocyte differentiation, where PHPT1 is downregulated early in differentiation and acts as a brake on adipogenesis [PMID:31752058]. PHPT1 protein levels are controlled post-translationally: the E3 ubiquitin ligase FBXO32 targets PHPT1 for ubiquitination and degradation, and loss of FBXO32 stabilizes PHPT1, activates ERK/MAPK signaling, and promotes lung cancer proliferation [PMID:35411430]. Its catalytic activity is tractable to small-molecule inhibition, with covalent (norstictic acid), non-competitive (illudalic acid analogs), and cysteine-dependent (phenylarsonic acid) inhibitors characterized in vitro [PMID:35859860, PMID:37267298, PMID:41706466].","teleology":[{"year":2014,"claim":"Establishing a direct physiological substrate answered whether PHPT1 acts on phosphohistidine in a specific channel and to what end, placing it as a negative regulator of TRPV5-mediated Ca²⁺ transport.","evidence":"Inside-out patch clamp with shRNA knockdown and NDPK-B knockout mice measuring urinary Ca²⁺","pmids":["24523290"],"confidence":"High","gaps":["Does not resolve PHPT1 subcellular localization at the channel","Stoichiometry and kinetics of H711 dephosphorylation not quantified"]},{"year":2014,"claim":"Identification of a proteasome-degraded splice variant raised the question of how PHPT1 protein levels are set, hinting at post-translational control of the active enzyme pool.","evidence":"Ectopic expression of transcript variant 6 in HeLa cells with proteasome inhibitor rescue and in silico modeling","pmids":["25450458"],"confidence":"Medium","gaps":["Endogenous expression and function of the variant unknown","E3 ligase responsible not identified in this study"]},{"year":2015,"claim":"Testing whether PHPT1 acts beyond phosphohistidine showed it can also remove phosphate from phospholysine, broadening its biochemical substrate class while excluding free phosphoarginine.","evidence":"In vitro dephosphorylation of chemically phospholysinated histone H1 and polylysine with malachite green and MS confirmation","pmids":["25574816"],"confidence":"Medium","gaps":["No physiological phospholysine substrate identified","Catalytic mechanism on phospholysine vs phosphohistidine not compared"]},{"year":2016,"claim":"Probing redox sensitivity addressed whether oxidative stress regulates PHPT1, finding Met95 in the substrate-binding region is selectively oxidized but without negative impact on activity.","evidence":"LC-MS/MS site-specific oxidation mapping, molecular dynamics, and MS-based activity assay after H₂O₂ treatment","pmids":["27034094"],"confidence":"Medium","gaps":["Functional consequence of Met95 oxidation in cells unresolved","Whether other residues mediate redox regulation not addressed"]},{"year":2017,"claim":"Linking PHPT1 to TGF-β1 signaling answered whether it participates in motility pathways, placing it upstream of PI3Kγ/AKT/Rac1 to drive hepatic stellate cell migration.","evidence":"Transwell and 3D collagen migration assays with knockdown/overexpression and pathway western blotting","pmids":["29098317"],"confidence":"Medium","gaps":["Direct phosphohistidine substrate in this pathway not identified","Mechanistic link between phosphatase activity and PI3Kγ activation unresolved"]},{"year":2020,"claim":"Reciprocal manipulation in brown adipocyte precursors established that PHPT1 abundance gates differentiation, connecting histidine phosphorylation status to adipogenic fate.","evidence":"Knockdown and overexpression in brown adipocyte precursors with differentiation assays and western blotting","pmids":["31752058"],"confidence":"Medium","gaps":["Relevant phosphohistidine substrate in adipogenesis unknown","Transcriptional program downstream of PHPT1 not mapped"]},{"year":2022,"claim":"Identifying FBXO32 as the E3 ligase resolved how PHPT1 protein levels are controlled and tied that control to ERK/MAPK-driven cancer proliferation.","evidence":"Mass spectrometry, ubiquitination assays, FBXO32 knockdown with ERK/MAPK readout, and in vitro/in vivo lung tumor growth","pmids":["35411430"],"confidence":"Medium","gaps":["Ubiquitination site on PHPT1 not mapped","Whether degradation is regulated by upstream signals unknown"]},{"year":2022,"claim":"Characterizing norstictic acid demonstrated PHPT1 is a druggable enzyme, providing the first kinetically defined covalent inhibitor.","evidence":"Fluorogenic inhibitor screen of ~4000 compounds with IC50/KI/kinact kinetics and phosphatase selectivity counterscreen","pmids":["35859860"],"confidence":"Medium","gaps":["Covalent adduct site on PHPT1 not defined","Cellular target engagement not demonstrated"]},{"year":2023,"claim":"Illudalic acid analogs defined a non-covalent, non-competitive inhibition mode independent of cysteine residues, distinguishing distinct inhibitor chemotypes for PHPT1.","evidence":"In vitro enzymatic inhibition with kinetic analysis and cysteine-to-alanine mutagenesis","pmids":["37267298"],"confidence":"Medium","gaps":["Binding site of the analogs not structurally resolved","Cellular activity not tested"]},{"year":2025,"claim":"Mapping a direct PHPT1–TRPV5 interaction via active-site residues and testing it in a disease model established PHPT1 as a protective regulator in hypoxic pulmonary hypertension.","evidence":"Co-IP with D30A/R157A active-site mutagenesis plus PHPT1 knockout/overexpression rat HAPH model with hemodynamics, RNA-seq, and western blotting","pmids":["40877955"],"confidence":"Medium","gaps":["Causal phosphohistidine substrate driving TGF-β/SMAD changes not pinned down","Single lab; reciprocal validation in human tissue lacking"]},{"year":2026,"claim":"Phenylarsonic acids revealed a cysteine-dependent inhibition route, showing solvent-exposed cysteines can be exploited for PHPT1 inhibition after reduction to thiophilic As(III).","evidence":"In vitro enzymatic inhibition with kinetic mode analysis, cysteine-to-alanine mutagenesis, and DTT reduction experiments","pmids":["41706466"],"confidence":"Medium","gaps":["Selectivity over other cysteine-containing phosphatases not established","No cellular or in vivo validation"]},{"year":null,"claim":"It remains unknown which physiological phosphohistidine substrates underlie PHPT1's roles in TGF-β signaling, adipogenesis, and cancer, and whether a unified structural mechanism connects its catalytic action across these contexts.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No high-resolution structure of PHPT1 bound to a physiological substrate","Substrate repertoire beyond TRPV5 and in vitro phospholysine targets uncharacterized","Tissue-specific regulation of PHPT1 abundance and activity incompletely defined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,2,9]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,2,7]}],"localization":[],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,9]},{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[0]}],"complexes":[],"partners":["TRPV5","FBXO32"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9NRX4","full_name":"14 kDa phosphohistidine phosphatase","aliases":["Phosphohistidine phosphatase 1","PHPT1","Protein histidine phosphatase","PHP","Protein janus-A homolog"],"length_aa":125,"mass_kda":13.8,"function":"Exhibits phosphohistidine phosphatase activity","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q9NRX4/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PHPT1","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"SAR1B","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/PHPT1","total_profiled":1310},"omim":[{"mim_id":"610167","title":"PHOSPHOHISTIDINE PHOSPHATASE 1; PHPT1","url":"https://www.omim.org/entry/610167"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Cytosol","reliability":"Approved"},{"location":"Nucleoplasm","reliability":"Additional"},{"location":"Nuclear bodies","reliability":"Additional"},{"location":"Plasma membrane","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PHPT1"},"hgnc":{"alias_symbol":["PHP14","HSPC141","CGI-202","DKFZp564M173","bA216L13.10"],"prev_symbol":[]},"alphafold":{"accession":"Q9NRX4","domains":[{"cath_id":"3.50.20.20","chopping":"11-29_39-120","consensus_level":"high","plddt":95.3307,"start":11,"end":120}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NRX4","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NRX4-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NRX4-F1-predicted_aligned_error_v6.png","plddt_mean":90.81},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PHPT1","jax_strain_url":"https://www.jax.org/strain/search?query=PHPT1"},"sequence":{"accession":"Q9NRX4","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9NRX4.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9NRX4/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NRX4"}},"corpus_meta":[{"pmid":"24523290","id":"PMC_24523290","title":"Regulation of the epithelial Ca²⁺ channel TRPV5 by reversible histidine phosphorylation mediated by NDPK-B and PHPT1.","date":"2014","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/24523290","citation_count":63,"is_preprint":false},{"pmid":"19380421","id":"PMC_19380421","title":"Ethylene regulates phosphorus remobilization and expression of a phosphate transporter (PhPT1) during petunia corolla senescence.","date":"2009","source":"Journal of experimental botany","url":"https://pubmed.ncbi.nlm.nih.gov/19380421","citation_count":33,"is_preprint":false},{"pmid":"29098317","id":"PMC_29098317","title":"PHP14 regulates hepatic stellate cells migration in liver fibrosis via mediating TGF-β1 signaling to PI3Kγ/AKT/Rac1 pathway.","date":"2017","source":"Journal of molecular medicine (Berlin, Germany)","url":"https://pubmed.ncbi.nlm.nih.gov/29098317","citation_count":24,"is_preprint":false},{"pmid":"25574816","id":"PMC_25574816","title":"Phosphohistidine phosphatase 1 (PHPT1) also dephosphorylates phospholysine of chemically phosphorylated histone H1 and polylysine.","date":"2015","source":"Upsala journal of medical sciences","url":"https://pubmed.ncbi.nlm.nih.gov/25574816","citation_count":22,"is_preprint":false},{"pmid":"35411430","id":"PMC_35411430","title":"FBXO32 targets PHPT1 for ubiquitination to regulate the growth of EGFR mutant lung cancer.","date":"2022","source":"Cellular oncology (Dordrecht, Netherlands)","url":"https://pubmed.ncbi.nlm.nih.gov/35411430","citation_count":20,"is_preprint":false},{"pmid":"27034094","id":"PMC_27034094","title":"Structural and activity characterization of human PHPT1 after oxidative modification.","date":"2016","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/27034094","citation_count":15,"is_preprint":false},{"pmid":"19396692","id":"PMC_19396692","title":"Immunohistochemical localization of phosphohistidine phosphatase PHPT1 in mouse and human tissues.","date":"2009","source":"Upsala journal of medical sciences","url":"https://pubmed.ncbi.nlm.nih.gov/19396692","citation_count":14,"is_preprint":false},{"pmid":"31752058","id":"PMC_31752058","title":"Roles of Protein Histidine Phosphatase 1 (PHPT1) in Brown Adipocyte Differentiation.","date":"2020","source":"Journal of microbiology and biotechnology","url":"https://pubmed.ncbi.nlm.nih.gov/31752058","citation_count":5,"is_preprint":false},{"pmid":"35859860","id":"PMC_35859860","title":"Inhibitor Screen Identifies Covalent Inhibitors of the Protein Histidine Phosphatase PHPT1.","date":"2022","source":"ACS medicinal chemistry letters","url":"https://pubmed.ncbi.nlm.nih.gov/35859860","citation_count":5,"is_preprint":false},{"pmid":"25450458","id":"PMC_25450458","title":"A splice variant of the human phosphohistidine phosphatase 1 (PHPT1) is degraded by the proteasome.","date":"2014","source":"The international journal of biochemistry & cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/25450458","citation_count":5,"is_preprint":false},{"pmid":"37267298","id":"PMC_37267298","title":"Derivatives of the Fungal Natural Product Illudalic Acid Inhibit the Activity of Protein Histidine Phosphatase PHPT1.","date":"2023","source":"ChemMedChem","url":"https://pubmed.ncbi.nlm.nih.gov/37267298","citation_count":2,"is_preprint":false},{"pmid":"19636872","id":"PMC_19636872","title":"(1)H, (13)C, and (15)N resonance assignments of human phosphohistidine phosphatase 1 (PHPT1).","date":"2007","source":"Biomolecular NMR assignments","url":"https://pubmed.ncbi.nlm.nih.gov/19636872","citation_count":2,"is_preprint":false},{"pmid":"40877955","id":"PMC_40877955","title":"PHPT1 acts as an inhibitor in high-altitude pulmonary hypertension via negative TRPV5 signaling regulation.","date":"2025","source":"Journal of translational medicine","url":"https://pubmed.ncbi.nlm.nih.gov/40877955","citation_count":0,"is_preprint":false},{"pmid":"41706466","id":"PMC_41706466","title":"Inhibition of PHPT1 by phenylarsonic acids.","date":"2026","source":"Dalton transactions (Cambridge, England : 2003)","url":"https://pubmed.ncbi.nlm.nih.gov/41706466","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":8733,"output_tokens":2638,"usd":0.032884,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9878,"output_tokens":3566,"usd":0.06927,"stage2_stop_reason":"end_turn"},"total_usd":0.102154,"stage1_batch_id":"msgbatch_01CNoDbkChHEkgrJnL7BwtGJ","stage2_batch_id":"msgbatch_016Y4x9E9Wg5VQDANj9quSQD","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2014,\n      \"finding\": \"PHPT1 (protein histidine phosphatase 1) inhibits NDPK-B-activated TRPV5 channel activity by dephosphorylating histidine 711 in the carboxy-terminal tail of TRPV5, as demonstrated in inside-out patch experiments.\",\n      \"method\": \"Inside-out patch clamp electrophysiology, shRNA knockdown, NDPK-B knockout mice with urinary Ca²⁺ measurement\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal functional assay (inside-out patch), specific residue identified (H711), in vivo genetic validation with NDPK-B KO mice, multiple orthogonal methods\",\n      \"pmids\": [\"24523290\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PHP14 (PHPT1) mediates TGF-β1 signaling to the PI3Kγ/AKT/Rac1 pathway to promote hepatic stellate cell migration and lamellipodia formation; TGF-β1 induces PHP14 expression in HSCs.\",\n      \"method\": \"Transwell migration assay, 3D collagen matrices assay, western blotting, knockdown/overexpression, PI3K/AKT/Rac1 pathway analysis\",\n      \"journal\": \"Journal of molecular medicine (Berlin, Germany)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function and gain-of-function with defined cellular phenotype and pathway placement, single lab\",\n      \"pmids\": [\"29098317\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"PHPT1 can dephosphorylate phospholysine residues in chemically phosphorylated histone H1 and polylysine, demonstrating broader substrate specificity beyond phosphohistidine; however, no dephosphorylation of free phosphoarginine was detected.\",\n      \"method\": \"In vitro dephosphorylation assay (DEAE-Sepharose spin column), malachite green phosphate detection, mass spectrometry to confirm phospholysine\",\n      \"journal\": \"Upsala journal of medical sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzymatic assay with recombinant human PHPT1, MS confirmation of substrate modification, single lab\",\n      \"pmids\": [\"25574816\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"FBXO32 acts as an E3 ubiquitin ligase targeting PHPT1 for ubiquitination and degradation; knockdown of FBXO32 leads to PHPT1 accumulation, activation of the ERK/MAPK pathway, and promotion of lung cancer cell proliferation.\",\n      \"method\": \"Mass spectrometry, western blotting, ubiquitination assays, FBXO32 knockdown with ERK/MAPK pathway readout, in vitro and in vivo tumor growth assays\",\n      \"journal\": \"Cellular oncology (Dordrecht, Netherlands)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — MS identification plus functional knockdown with pathway readout, single lab\",\n      \"pmids\": [\"35411430\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"H₂O₂-induced oxidation of hPHPT1 selectively modifies Met95 within the substrate binding region, but this oxidation does not negatively impact hPHPT1 phosphatase activity as measured by a mass spectrometry-based assay.\",\n      \"method\": \"LC-MS/MS site-specific oxidation quantification, molecular dynamics simulations, MS-based enzymatic activity assay\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro biochemical assay with site-specific modification mapping and MD simulations, single lab, negative functional result\",\n      \"pmids\": [\"27034094\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"A splice variant of PHPT1 (transcript variant 6) produces a protein with an altered C-terminal sequence that is degraded by the proteasome in HeLa cells, unlike the wild-type PHPT1 protein.\",\n      \"method\": \"Ectopic expression in HeLa cells, proteasome inhibitor treatment, in silico secondary structure modeling\",\n      \"journal\": \"The international journal of biochemistry & cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell-based expression with proteasome inhibitor rescue, single lab, two methods (expression assay + in silico)\",\n      \"pmids\": [\"25450458\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PHPT1 expression is rapidly reduced at the early phase of brown adipocyte differentiation; knockdown of PHPT1 promotes brown adipocyte differentiation, while ectopic overexpression suppresses it, linking histidine phosphorylation status to brown adipogenesis.\",\n      \"method\": \"Knockdown and overexpression in brown adipocyte precursors, differentiation assays, western blotting\",\n      \"journal\": \"Journal of microbiology and biotechnology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal gain/loss-of-function with defined phenotypic readout, single lab\",\n      \"pmids\": [\"31752058\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Norstictic acid is a time-dependent, covalent inhibitor of PHPT1 phosphatase activity with IC50 = 7.9 μM, KI = 90 μM, and kinact = 1.7 min⁻¹, identified from a screen of ~4000 compounds using a fluorogenic activity assay.\",\n      \"method\": \"Fluorogenic enzymatic inhibitor screen, kinetic characterization (IC50, KI, kinact), selectivity counterscreen against other phosphatases\",\n      \"journal\": \"ACS medicinal chemistry letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzymatic assay with kinetic characterization, single lab\",\n      \"pmids\": [\"35859860\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Illudalic acid analogs inhibit PHPT1 phosphatase activity via non-covalent, non-competitive inhibition (most potent IC50 = 3.4 μM); mutating all three cysteine residues to alanine has no effect on inhibition by these compounds.\",\n      \"method\": \"In vitro enzymatic inhibition assay, kinetic analysis, cysteine-to-alanine mutagenesis\",\n      \"journal\": \"ChemMedChem\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzymatic assay with mutagenesis, single lab, characterizes inhibition mechanism\",\n      \"pmids\": [\"37267298\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PHPT1 directly interacts with TRPV5 at its phosphorylation sites (interaction abolished by Asp30Ala/Arg157Ala mutations in PHPT1); PHPT1 overexpression inhibits PASMC proliferation and migration and reduces pulmonary artery pressure in a rat HAPH model by modulating TRPV5, p-Akt, p-SMAD2/3, and p-TGF-β signaling.\",\n      \"method\": \"Co-immunoprecipitation, active-site mutagenesis (D30A/R157A), PHPT1 knockout and overexpression rat HAPH model, hemodynamic measurements, RNA-seq, western blotting\",\n      \"journal\": \"Journal of translational medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP with mutagenesis validation plus in vivo KO/OE model, single lab, multiple readouts\",\n      \"pmids\": [\"40877955\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Phenylarsonic acids inhibit PHPT1 activity via mixed inhibition; reduction to phenylarsine species (thiophilic As(III)) by DTT mediates inhibition through interactions with solvent-exposed cysteine residues, as mutating all three Cys to Ala significantly decreases inhibition.\",\n      \"method\": \"In vitro enzymatic inhibition assay, cysteine-to-alanine mutagenesis, kinetic mode-of-inhibition analysis, DTT reduction experiments\",\n      \"journal\": \"Dalton transactions (Cambridge, England : 2003)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzymatic assay with mutagenesis identifying cysteine involvement, single lab\",\n      \"pmids\": [\"41706466\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PHPT1 is the principal mammalian phosphohistidine (and phospholysine) phosphatase that dephosphorylates target proteins including TRPV5 (at H711) to modulate Ca²⁺ channel activity and renal Ca²⁺ reabsorption; it is subject to ubiquitin-mediated proteasomal degradation via the E3 ligase FBXO32 (regulating ERK/MAPK signaling in cancer), mediates TGF-β1 signals through PI3Kγ/AKT/Rac1 in hepatic stellate cells, and its expression level controls brown adipocyte differentiation, with catalytic activity dependent on cysteine residues and regulatable by reactive oxygen species oxidation of Met95.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PHPT1 is the principal mammalian protein histidine phosphatase, removing phosphate from phosphohistidine residues to regulate ion-channel activity and signal transduction [#0]. It dephosphorylates histidine 711 in the C-terminal tail of the TRPV5 Ca²⁺ channel, counteracting NDPK-B-driven channel activation and thereby modulating renal Ca²⁺ handling [#0]; PHPT1 engages TRPV5 directly through active-site residues Asp30 and Arg157, and in a pulmonary arterial smooth muscle context this interaction restrains proliferation and migration alongside dampened Akt and TGF-β/SMAD2/3 signaling [#9]. Its substrate range extends to phospholysine, as it dephosphorylates chemically phospholysinated histone H1 and polylysine in vitro [#2]. Beyond TRPV5, PHPT1 transduces TGF-β1 signals through the PI3Kγ/AKT/Rac1 axis to drive hepatic stellate cell migration and lamellipodia formation [#1], and its abundance gates brown adipocyte differentiation, where PHPT1 is downregulated early in differentiation and acts as a brake on adipogenesis [#6]. PHPT1 protein levels are controlled post-translationally: the E3 ubiquitin ligase FBXO32 targets PHPT1 for ubiquitination and degradation, and loss of FBXO32 stabilizes PHPT1, activates ERK/MAPK signaling, and promotes lung cancer proliferation [#3]. Its catalytic activity is tractable to small-molecule inhibition, with covalent (norstictic acid), non-competitive (illudalic acid analogs), and cysteine-dependent (phenylarsonic acid) inhibitors characterized in vitro [#7, #8, #10].\",\n  \"teleology\": [\n    {\n      \"year\": 2014,\n      \"claim\": \"Establishing a direct physiological substrate answered whether PHPT1 acts on phosphohistidine in a specific channel and to what end, placing it as a negative regulator of TRPV5-mediated Ca²⁺ transport.\",\n      \"evidence\": \"Inside-out patch clamp with shRNA knockdown and NDPK-B knockout mice measuring urinary Ca²⁺\",\n      \"pmids\": [\"24523290\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not resolve PHPT1 subcellular localization at the channel\", \"Stoichiometry and kinetics of H711 dephosphorylation not quantified\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identification of a proteasome-degraded splice variant raised the question of how PHPT1 protein levels are set, hinting at post-translational control of the active enzyme pool.\",\n      \"evidence\": \"Ectopic expression of transcript variant 6 in HeLa cells with proteasome inhibitor rescue and in silico modeling\",\n      \"pmids\": [\"25450458\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Endogenous expression and function of the variant unknown\", \"E3 ligase responsible not identified in this study\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Testing whether PHPT1 acts beyond phosphohistidine showed it can also remove phosphate from phospholysine, broadening its biochemical substrate class while excluding free phosphoarginine.\",\n      \"evidence\": \"In vitro dephosphorylation of chemically phospholysinated histone H1 and polylysine with malachite green and MS confirmation\",\n      \"pmids\": [\"25574816\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No physiological phospholysine substrate identified\", \"Catalytic mechanism on phospholysine vs phosphohistidine not compared\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Probing redox sensitivity addressed whether oxidative stress regulates PHPT1, finding Met95 in the substrate-binding region is selectively oxidized but without negative impact on activity.\",\n      \"evidence\": \"LC-MS/MS site-specific oxidation mapping, molecular dynamics, and MS-based activity assay after H₂O₂ treatment\",\n      \"pmids\": [\"27034094\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of Met95 oxidation in cells unresolved\", \"Whether other residues mediate redox regulation not addressed\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Linking PHPT1 to TGF-β1 signaling answered whether it participates in motility pathways, placing it upstream of PI3Kγ/AKT/Rac1 to drive hepatic stellate cell migration.\",\n      \"evidence\": \"Transwell and 3D collagen migration assays with knockdown/overexpression and pathway western blotting\",\n      \"pmids\": [\"29098317\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct phosphohistidine substrate in this pathway not identified\", \"Mechanistic link between phosphatase activity and PI3Kγ activation unresolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Reciprocal manipulation in brown adipocyte precursors established that PHPT1 abundance gates differentiation, connecting histidine phosphorylation status to adipogenic fate.\",\n      \"evidence\": \"Knockdown and overexpression in brown adipocyte precursors with differentiation assays and western blotting\",\n      \"pmids\": [\"31752058\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relevant phosphohistidine substrate in adipogenesis unknown\", \"Transcriptional program downstream of PHPT1 not mapped\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identifying FBXO32 as the E3 ligase resolved how PHPT1 protein levels are controlled and tied that control to ERK/MAPK-driven cancer proliferation.\",\n      \"evidence\": \"Mass spectrometry, ubiquitination assays, FBXO32 knockdown with ERK/MAPK readout, and in vitro/in vivo lung tumor growth\",\n      \"pmids\": [\"35411430\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ubiquitination site on PHPT1 not mapped\", \"Whether degradation is regulated by upstream signals unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Characterizing norstictic acid demonstrated PHPT1 is a druggable enzyme, providing the first kinetically defined covalent inhibitor.\",\n      \"evidence\": \"Fluorogenic inhibitor screen of ~4000 compounds with IC50/KI/kinact kinetics and phosphatase selectivity counterscreen\",\n      \"pmids\": [\"35859860\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Covalent adduct site on PHPT1 not defined\", \"Cellular target engagement not demonstrated\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Illudalic acid analogs defined a non-covalent, non-competitive inhibition mode independent of cysteine residues, distinguishing distinct inhibitor chemotypes for PHPT1.\",\n      \"evidence\": \"In vitro enzymatic inhibition with kinetic analysis and cysteine-to-alanine mutagenesis\",\n      \"pmids\": [\"37267298\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Binding site of the analogs not structurally resolved\", \"Cellular activity not tested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Mapping a direct PHPT1–TRPV5 interaction via active-site residues and testing it in a disease model established PHPT1 as a protective regulator in hypoxic pulmonary hypertension.\",\n      \"evidence\": \"Co-IP with D30A/R157A active-site mutagenesis plus PHPT1 knockout/overexpression rat HAPH model with hemodynamics, RNA-seq, and western blotting\",\n      \"pmids\": [\"40877955\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal phosphohistidine substrate driving TGF-β/SMAD changes not pinned down\", \"Single lab; reciprocal validation in human tissue lacking\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Phenylarsonic acids revealed a cysteine-dependent inhibition route, showing solvent-exposed cysteines can be exploited for PHPT1 inhibition after reduction to thiophilic As(III).\",\n      \"evidence\": \"In vitro enzymatic inhibition with kinetic mode analysis, cysteine-to-alanine mutagenesis, and DTT reduction experiments\",\n      \"pmids\": [\"41706466\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Selectivity over other cysteine-containing phosphatases not established\", \"No cellular or in vivo validation\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unknown which physiological phosphohistidine substrates underlie PHPT1's roles in TGF-β signaling, adipogenesis, and cancer, and whether a unified structural mechanism connects its catalytic action across these contexts.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No high-resolution structure of PHPT1 bound to a physiological substrate\", \"Substrate repertoire beyond TRPV5 and in vitro phospholysine targets uncharacterized\", \"Tissue-specific regulation of PHPT1 abundance and activity incompletely defined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 2, 9]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 2, 7]}\n    ],\n    \"localization\": [],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 9]},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"TRPV5\", \"FBXO32\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"faith_supported":6,"faith_total":6,"faith_pct":100.0}}