{"gene":"PTPA","run_date":"2026-06-10T06:43:36","timeline":{"discoveries":[{"year":1994,"finding":"PTPA (phosphotyrosyl phosphatase activator) stimulates the tyrosyl phosphatase activity of protein phosphatase 2A (PP2A) in an ATP- and Mg2+-requiring reaction. Recombinant bacterially expressed PTPA protein is soluble and active, confirming it is sufficient for this activating function.","method":"Biochemical activity assay with recombinant protein; molecular cloning and expression","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct in vitro enzymatic activity assay with recombinant protein, foundational paper replicated by multiple subsequent studies","pmids":["8195217"],"is_preprint":false},{"year":2013,"finding":"Crystal structure of PP2A catalytic subunit bound to PTPA and ATPγS reveals that PTPA makes broad contacts with structural elements surrounding the PP2A active site and the adenine moiety of ATP. PTPA-binding stabilizes the protein fold of apo-PP2A required for activation and orients ATP phosphoryl groups to bind directly to the PP2A active site, allowing ATP to modulate metal-binding preferences and utilize the PP2A active site for ATP hydrolysis. In vitro, ATP selectively enhances binding of endogenous catalytic metal ions requiring ATP hydrolysis, which is crucial for acquisition of pSer/Thr-specific phosphatase activity. Both PP2A- and ATP-binding are required for PTPA function in cell proliferation and survival.","method":"Crystal structure (X-ray crystallography); in vitro phosphatase activity assay; mutagenesis; cell proliferation/survival assays","journal":"Cell research","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure combined with in vitro reconstitution, mutagenesis, and functional cell-based validation in a single rigorous study","pmids":["24100351"],"is_preprint":false},{"year":2014,"finding":"PTPA interacts with the invariant C-terminal tail of the PP2A catalytic subunit at an additional interaction site. Phosphorylation of Tyr307 on PP2A-C or carboxymethylation of Leu309 abrogates or diminishes binding of the C-terminal tail to PTPA, whereas phosphorylation of Thr304 has no consequence on this interaction.","method":"Structural studies (NMR/X-ray); binding assays with posttranslationally modified C-terminal tail peptides","journal":"Biological chemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — structural and biochemical binding data from a single lab with multiple PTM conditions tested","pmids":["25003389"],"is_preprint":false},{"year":2005,"finding":"Yeast PTPA homologues Ypa1 and Ypa2 physically interact directly with the catalytic subunits of specific PP2A-like phosphatases: Ypa1 with Pph3, Sit4, and Ppg1; Ypa2 with Pph21 and Pph22. Interaction is independent of other regulatory subunits. Ypa1 and Ypa2 can reactivate inactive PP2A-methyl esterase complexes (except Pph22-Yme). The interaction of Ypa2 with PP2A is promoted by the presence of Ypa1, suggesting a cooperative role.","method":"Yeast two-hybrid; direct binding assays; phosphatase reactivation assays","journal":"The Biochemical journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding and functional activation assays in yeast, multiple interactors tested, single lab","pmids":["15447631"],"is_preprint":false},{"year":1998,"finding":"Yeast PTPA homologue yPtpa1p participates in the repair of oxidative DNA damage induced by 4-NQO and UVA. Deletion of yPTPA1 causes hypersensitivity to 4-NQO and UVA, a spontaneous mutator phenotype, and a defect in recovery of high molecular weight DNA following 4-NQO exposure, demonstrating a role in DNA repair via activation of a phosphatase.","method":"Yeast genetics (targeted gene deletion); mutagen sensitivity assays; DNA repair (high molecular weight DNA recovery)","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean genetic deletion with defined phenotypic readouts, multiple orthogonal assays, single lab","pmids":["9705277"],"is_preprint":false},{"year":2019,"finding":"UBE3A ubiquitinates PTPA, targeting it for degradation. Loss of maternal Ube3a increases PTPA levels, promotes PP2A holoenzyme assembly, and elevates PP2A activity. Reducing PTPA levels in vivo in Ube3am-/p+ mice restores defects in dendritic spine maturation. Pharmacological inhibition of PP2A activity alleviates reduction in excitatory synaptic transmission and motor impairment in these mice.","method":"Stable-isotope labeling of amino acids in mammals (SILAC); ubiquitination assays; mouse genetics (Ube3a maternal knockout); in vivo PTPA knockdown; PP2A activity assay; electrophysiology; behavioral assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods including SILAC proteomics, ubiquitination assays, in vivo mouse model, and functional rescue experiments","pmids":["31160454"],"is_preprint":false},{"year":2017,"finding":"Haploinsufficiency of PPP2R4 (encoding PTPA) promotes cancer development. Cancer-associated PTPA mutants show decreased ability to bind the PP2A catalytic subunit or activate PP2A. In Ppp2r4 gene-trapped mice, total PP2A activity and methylation are reduced, selectively affecting specific PP2A holoenzymes. Both Ppp2r4gt/gt and Ppp2r4+/gt mice show higher rates of spontaneous tumors with increased c-Myc phosphorylation and increased Wnt or Hedgehog signaling.","method":"Mouse genetics (gene-trap); PP2A activity assay; PP2A binding and activation assays with cancer-associated mutants; tumor incidence analysis; phosphorylation assays","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo mouse genetic model combined with biochemical validation of mutant function, multiple cancer types analyzed, multiple orthogonal methods","pmids":["29046336"],"is_preprint":false},{"year":2013,"finding":"PTPA activates PP2A by reducing inhibitory phosphorylation of PP2A catalytic subunit at Tyr307 (P-PP2AC). Overexpression of PTPA decreased P-PP2AC levels and activated PP2A, while knockdown increased P-PP2AC and inhibited PP2A. PTPA upregulates protein tyrosine phosphatase 1B (PTP1B) at protein and mRNA levels, and simultaneous knockdown of PTP1B abolishes PTPA-induced PP2A activation, indicating PTPA acts through PTP1B to dephosphorylate PP2AC-Tyr307.","method":"Overexpression/knockdown in cells; PP2A activity assay; Western blot for P-PP2AC; PTP1B knockdown epistasis","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis experiment placing PTPA upstream of PTP1B→PP2AC-pTyr307, multiple orthogonal approaches, single lab","pmids":["23428800"],"is_preprint":false},{"year":2007,"finding":"Transient overexpression of PTPA leads to caspase 3-dependent apoptosis in mammalian cells, with hallmarks including chromatin condensation, membrane blebbing, annexin V staining, dephosphorylation of Bad, and caspase-3 cleavage. This proapoptotic effect is not prevented by the PP2A inhibitor okadaic acid, indicating PTPA mediates apoptosis independently of PP2A.","method":"Transient overexpression; apoptosis assays (annexin V, caspase-3 cleavage, chromatin condensation); pharmacological inhibition with okadaic acid","journal":"Apoptosis : an international journal on programmed cell death","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — multiple apoptosis readouts with pharmacological epistasis showing PP2A-independence, single lab","pmids":["17333320"],"is_preprint":false},{"year":2023,"finding":"Homozygous missense variants in PTPA (p.Ala171Asp and p.Met298Arg) cause early-onset parkinsonism with intellectual disability. Both variants are associated with decreased PTPA RNA stability and decreased PTPA protein levels; p.Ala171Asp additionally shows decreased protein stability. Expression of both variants is associated with decreased PP2A complex levels and impaired PP2A phosphatase activation. Knock-down of PTPA ortholog in Drosophila neurons induces age-dependent locomotion impairment fully reversed by L-DOPA treatment.","method":"Overexpression studies in cultured cells; PP2A activity assay; PP2A complex assembly assay; Drosophila knockdown with climbing test and L-DOPA rescue","journal":"Brain : a journal of neurology","confidence":"High","confidence_rationale":"Tier 2 / Strong — functional studies in both mammalian cells and Drosophila model with pharmacological rescue, multiple orthogonal methods across two labs/families","pmids":["36073231"],"is_preprint":false},{"year":2023,"finding":"PTPA loss (identified by CRISPR-Cas12a genome-wide screen) elevates fetal globin (HBG1/HBG2) levels while preserving erythroid differentiation. Phenotypic rescue experiments revealed that PTPA silences HBG1/2 expression primarily by regulating BCL11A expression, placing PTPA upstream of BCL11A in the fetal hemoglobin silencing pathway.","method":"CRISPR-Cas12a genome-wide screen; domain-focused CRISPR-Cas9 screen; phenotypic rescue experiments in erythroid cells","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genome-wide screen with epistasis rescue placing PTPA upstream of BCL11A, single study","pmids":["41525452"],"is_preprint":false},{"year":2025,"finding":"PTPA localizes predominantly to the Golgi apparatus in osteoblasts, closely overlapping with the Golgi marker Giantin. Disruption of Golgi structure by Brefeldin A causes PTPA to disperse into the cytoplasm. PTPA overexpression inhibits osteoblast differentiation by downregulating key transcriptional regulators.","method":"Immunofluorescence co-localization with Golgi marker; Brefeldin A treatment; PTPA overexpression with differentiation assays","journal":"Biochemical and biophysical research communications","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single localization method, functional overexpression without mechanistic depth","pmids":["39827549"],"is_preprint":false},{"year":2021,"finding":"PPP2R4 (PTPA) depletion in A549 lung cancer cells increases anchorage-independent growth and xenograft growth, and accelerates KrasG12D-induced lung tumorigenesis in Ppp2r4 gene-trapped mice. PPP2R4 depletion induces resistance to MEK inhibitor selumetinib but sensitizes cells to mTOR inhibitor temsirolimus, establishing PTPA as a modifier of kinase inhibitor response in KRAS-mutant lung adenocarcinoma.","method":"PPP2R4 depletion in cell lines; anchorage-independent growth assay; xenograft; mouse genetics (gene-trap with KrasG12D); kinase inhibitor screen","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo mouse model plus in vitro functional assays, single lab, multiple orthogonal readouts","pmids":["34216687"],"is_preprint":false},{"year":1995,"finding":"The human PTPA gene is a single-copy gene located at chromosomal region 9q34, composed of 10 exons and 9 introns spanning ~60 kb. The promoter lacks a TATA box, is GC-rich, and contains Sp1 sites. Transfection with PTPA promoter-luciferase construct confirmed promoter activity in a cell-line-dependent manner.","method":"Fluorescence in situ hybridization (FISH); genomic cloning and sequencing; luciferase reporter transfection","journal":"Genomics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct FISH localization and functional promoter assay, single lab","pmids":["8530035"],"is_preprint":false},{"year":2026,"finding":"PTPA restoration in PTPA-low mesothelioma cells increases PP2A catalytic subunit expression and activity (methylation) without favoring specific PP2A holoenzymes. PTPA restoration activates oncogene-induced senescence (OIS) via PP2A-dependent dephosphorylation of Kinase Suppressor of Ras 1 (KSR1), activating p53 signaling and NF-κB. PTPA restoration also sensitizes MPM cells to carboplatin.","method":"PTPA re-expression in PTPA-low cells; PP2A activity/methylation assays; RNAseq/GSEA; SA-β-galactosidase senescence assay; SASP/NF-κB measurements; MEK inhibitor (Trametinib) epistasis; carboplatin sensitivity assays","journal":"Cellular oncology (Dordrecht, Netherlands)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods in a single study, epistasis with MEK inhibitor placing PTPA upstream of Ras/KSR1/senescence pathway, single lab","pmids":["42258127"],"is_preprint":false},{"year":2025,"finding":"Knockout of PPP2R4 in KELLY neuroblastoma cells, along with reduced methylation of PP2A catalytic subunit (mePPP2CA), increases AURKA protein levels, indicating that the PP2A pathway (activated by PTPA) regulates AURKA abundance post-translationally.","method":"CRISPR knockout of PPP2R4; Western blot for AURKA protein; PP2A methylation assay","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single preprint, single lab, limited mechanistic follow-up beyond protein level change","pmids":["bio_10.1101_2025.07.29.665837"],"is_preprint":true}],"current_model":"PTPA (PPP2R4/PR53) is an ATP-dependent activation chaperone for PP2A: it binds the PP2A catalytic subunit, stabilizes its apo-fold, positions ATP for hydrolysis at the PP2A active site to drive metal ion loading, and thereby converts inactive apo-PP2A into an active Ser/Thr phosphatase; additionally, PTPA reduces inhibitory Tyr307 phosphorylation on PP2A-C via upregulation of PTP1B, is itself ubiquitinated and degraded by UBE3A (linking it to Angelman syndrome and synaptic function), and harbors loss-of-function variants that impair PP2A activation and cause autosomal recessive early-onset parkinsonism with intellectual disability, while haploinsufficiency of PTPA is a recurrent tumor-suppressive mechanism in human cancers."},"narrative":{"mechanistic_narrative":"PTPA (PPP2R4/PR53) is an ATP- and Mg2+-dependent activation chaperone for protein phosphatase 2A (PP2A) that converts inactive apo-PP2A into a catalytically competent Ser/Thr phosphatase [PMID:8195217, PMID:24100351]. Structurally, PTPA makes broad contacts with elements surrounding the PP2A active site and engages the adenine moiety of ATP, stabilizing the apo-PP2A fold and orienting ATP phosphoryl groups within the PP2A active site so that ATP hydrolysis drives selective loading of catalytic metal ions required for acquisition of pSer/Thr phosphatase activity; both PP2A- and ATP-binding are essential for PTPA's role in cell proliferation and survival [PMID:24100351]. PTPA also docks on the invariant C-terminal tail of the PP2A catalytic subunit, an interaction abrogated by Tyr307 phosphorylation or Leu309 carboxymethylation [PMID:25003389], and it lowers inhibitory Tyr307 phosphorylation by upregulating the tyrosine phosphatase PTP1B [PMID:23428800]. This activation function is conserved: yeast orthologs bind and reactivate PP2A-family catalytic subunits and contribute to oxidative DNA damage repair [PMID:15447631, PMID:9705277]. PTPA protein levels are controlled by UBE3A-mediated ubiquitination and degradation, linking PTPA to dendritic spine maturation, excitatory synaptic transmission, and motor function through PP2A holoenzyme assembly [PMID:31160454]. Homozygous loss-of-function PTPA variants that destabilize the protein and impair PP2A activation cause autosomal recessive early-onset parkinsonism with intellectual disability [PMID:36073231], and PTPA haploinsufficiency is a recurrent tumor-suppressive lesion: loss reduces PP2A activity and promotes c-Myc phosphorylation, Wnt/Hedgehog signaling, KRAS-driven tumorigenesis, and altered kinase-inhibitor sensitivity, while restoration activates PP2A-dependent senescence [PMID:29046336, PMID:34216687, PMID:42258127].","teleology":[{"year":1994,"claim":"Established PTPA as a discrete factor that stimulates PP2A phosphatase activity, defining the protein's core biochemical function.","evidence":"Biochemical activity assay with recombinant bacterially expressed PTPA requiring ATP and Mg2+","pmids":["8195217"],"confidence":"High","gaps":["Molecular mechanism of activation not resolved","Did not distinguish chaperone vs catalytic role"]},{"year":1995,"claim":"Located and structured the human PTPA gene, providing genomic context for later variant and expression studies.","evidence":"FISH mapping to 9q34, genomic sequencing, and promoter-luciferase reporter assays","pmids":["8530035"],"confidence":"Medium","gaps":["No functional regulators of the promoter identified","Tissue-specific expression control unresolved"]},{"year":1998,"claim":"Connected PTPA function to a cellular phenotype, showing the yeast ortholog supports oxidative DNA damage repair via phosphatase activation.","evidence":"Yeast yPTPA1 deletion with mutagen sensitivity and DNA recovery assays","pmids":["9705277"],"confidence":"Medium","gaps":["Specific phosphatase substrate in repair pathway not defined","Direct relevance to human PTPA untested"]},{"year":2005,"claim":"Demonstrated direct, regulatory-subunit-independent binding of PTPA orthologs to multiple PP2A-family catalytic subunits and cooperative reactivation, generalizing PTPA's chaperone role across PP2A-like phosphatases.","evidence":"Yeast two-hybrid, direct binding, and phosphatase reactivation assays","pmids":["15447631"],"confidence":"Medium","gaps":["Structural basis of selectivity unknown","Cooperativity mechanism between Ypa1 and Ypa2 undefined"]},{"year":2007,"claim":"Identified a PP2A-independent proapoptotic activity of PTPA, raising the possibility of moonlighting functions.","evidence":"Transient overexpression with apoptosis readouts and okadaic acid epistasis showing PP2A-independence","pmids":["17333320"],"confidence":"Medium","gaps":["Effector pathway for PP2A-independent apoptosis not identified","Overexpression artifact not excluded"]},{"year":2013,"claim":"Resolved the structural and chemical mechanism of activation, showing PTPA stabilizes apo-PP2A and uses ATP hydrolysis at the PP2A active site to drive catalytic metal loading.","evidence":"X-ray crystal structure of PP2A-C bound to PTPA and ATPγS with in vitro reconstitution, mutagenesis, and cell-based validation","pmids":["24100351"],"confidence":"High","gaps":["In vivo ordering of metal loading vs holoenzyme assembly unresolved","Identity of native metal ions in cells not established"]},{"year":2013,"claim":"Defined a second, PTP1B-dependent route by which PTPA activates PP2A through removal of inhibitory Tyr307 phosphorylation.","evidence":"Overexpression/knockdown, PP2A activity assays, and PTP1B knockdown epistasis in cells","pmids":["23428800"],"confidence":"Medium","gaps":["Mechanism by which PTPA upregulates PTP1B transcript unknown","Single lab without reciprocal validation"]},{"year":2014,"claim":"Mapped a PTM-sensitive second interaction site on the PP2A C-terminal tail, linking PP2A modification status to PTPA engagement.","evidence":"Structural and peptide-binding assays with post-translationally modified C-terminal tail peptides","pmids":["25003389"],"confidence":"Medium","gaps":["Functional consequence of tail binding for activation kinetics untested","Single-lab structural data"]},{"year":2017,"claim":"Established PTPA as a haploinsufficient tumor suppressor whose loss reduces PP2A activity and drives oncogenic signaling.","evidence":"Ppp2r4 gene-trap mice, PP2A activity/methylation assays, and biochemical analysis of cancer-associated PTPA mutants","pmids":["29046336"],"confidence":"High","gaps":["Which specific PP2A holoenzymes mediate tumor suppression not fully resolved","Direct PP2A substrates downstream of c-Myc/Wnt/Hedgehog not enumerated"]},{"year":2019,"claim":"Identified UBE3A-mediated degradation of PTPA as a control point coupling PTPA abundance to PP2A holoenzyme assembly and synaptic function.","evidence":"SILAC proteomics, ubiquitination assays, Ube3a maternal-knockout mice with in vivo PTPA knockdown, electrophysiology, and behavior","pmids":["31160454"],"confidence":"High","gaps":["Ubiquitination site(s) on PTPA not mapped","Whether PP2A-independent PTPA functions contribute to synaptic phenotype untested"]},{"year":2021,"claim":"Extended PTPA's tumor-suppressor role to KRAS-mutant lung adenocarcinoma and showed it modifies kinase-inhibitor sensitivity.","evidence":"PPP2R4 depletion in A549, xenografts, KrasG12D gene-trap mice, and kinase inhibitor screening","pmids":["34216687"],"confidence":"Medium","gaps":["Mechanism linking PTPA loss to MEK vs mTOR inhibitor response undefined","Single lab"]},{"year":2023,"claim":"Tied PTPA loss-of-function variants directly to human early-onset parkinsonism with intellectual disability through impaired PP2A activation.","evidence":"Patient variants in cultured cells with PP2A activity/assembly assays and Drosophila knockdown with L-DOPA rescue","pmids":["36073231"],"confidence":"High","gaps":["Neuronal PP2A substrates underlying parkinsonism not identified","Cell-type specificity of vulnerability unresolved"]},{"year":2023,"claim":"Placed PTPA upstream of BCL11A in fetal hemoglobin silencing, revealing a role in erythroid gene regulation.","evidence":"Genome-wide CRISPR-Cas12a screen and phenotypic rescue in erythroid cells","pmids":["41525452"],"confidence":"Medium","gaps":["Whether HBG silencing depends on PP2A activation untested","Mechanism linking PTPA to BCL11A expression unknown"]},{"year":2026,"claim":"Showed PTPA restoration triggers PP2A-dependent oncogene-induced senescence via KSR1 dephosphorylation, defining a reversible tumor-suppressive program.","evidence":"PTPA re-expression in mesothelioma cells with PP2A activity assays, RNAseq, senescence/SASP readouts, MEK inhibitor epistasis, and carboplatin sensitivity","pmids":["42258127"],"confidence":"Medium","gaps":["Direct demonstration of KSR1 as a PP2A substrate incomplete","Single lal/single cancer model"]},{"year":null,"claim":"How PTPA's distinct activities — chaperone-mediated PP2A activation, PP2A-independent functions, and substrate-specific holoenzyme outcomes — are coordinated across tissues and disease states remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model linking PP2A-dependent and PP2A-independent PTPA roles","Direct PP2A substrates in neurons, cancer, and erythroid cells largely uncatalogued","Endogenous regulation of PTPA abundance beyond UBE3A undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,1,3]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,1,7]},{"term_id":"GO:0140657","term_label":"ATP-dependent activity","supporting_discovery_ids":[0,1]},{"term_id":"GO:0044183","term_label":"protein folding chaperone","supporting_discovery_ids":[1,3]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[11]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[6,12,14]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[6,9,12]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[1,5]}],"complexes":[],"partners":["PPP2CA","UBE3A","PTP1B"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P18433","full_name":"Receptor-type tyrosine-protein phosphatase alpha","aliases":[],"length_aa":802,"mass_kda":90.7,"function":"Tyrosine protein phosphatase which is involved in integrin-mediated focal adhesion formation (By similarity). Following integrin engagement, specifically recruits BCAR3, BCAR1 and CRK to focal adhesions thereby promoting SRC-mediated phosphorylation of BRAC1 and the subsequent activation of PAK and small GTPase RAC1 and CDC42 (By similarity)","subcellular_location":"Cell membrane; Cell junction, focal adhesion","url":"https://www.uniprot.org/uniprotkb/P18433/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/PTPA","classification":"Common Essential","n_dependent_lines":1002,"n_total_lines":1208,"dependency_fraction":0.8294701986754967},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PTPA","total_profiled":1310},"omim":[{"mim_id":"620482","title":"PARKINSON DISEASE 25, AUTOSOMAL RECESSIVE EARLY-ONSET, WITH IMPAIRED INTELLECTUAL DEVELOPMENT; PARK25","url":"https://www.omim.org/entry/620482"},{"mim_id":"600756","title":"PROTEIN PHOSPHATASE 2 PHOSPHATASE ACTIVATOR; PTPA","url":"https://www.omim.org/entry/600756"},{"mim_id":"600174","title":"PHOSPHATIDYLINOSITOL TRANSFER PROTEIN, ALPHA; PITPNA","url":"https://www.omim.org/entry/600174"},{"mim_id":"176884","title":"PROTEIN-TYROSINE PHOSPHATASE, RECEPTOR-TYPE, ALPHA; PTPRA","url":"https://www.omim.org/entry/176884"},{"mim_id":"168600","title":"PARKINSON DISEASE, LATE-ONSET; PD","url":"https://www.omim.org/entry/168600"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nucleoplasm","reliability":"Enhanced"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PTPA"},"hgnc":{"alias_symbol":["PR53"],"prev_symbol":["PPP2R4"]},"alphafold":{"accession":"P18433","domains":[{"cath_id":"3.90.190.10","chopping":"222-505","consensus_level":"medium","plddt":96.0738,"start":222,"end":505},{"cath_id":"3.90.190.10","chopping":"534-796","consensus_level":"medium","plddt":95.8502,"start":534,"end":796}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P18433","model_url":"https://alphafold.ebi.ac.uk/files/AF-P18433-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P18433-F1-predicted_aligned_error_v6.png","plddt_mean":81.5},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PTPA","jax_strain_url":"https://www.jax.org/strain/search?query=PTPA"},"sequence":{"accession":"P18433","fasta_url":"https://rest.uniprot.org/uniprotkb/P18433.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P18433/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P18433"}},"corpus_meta":[{"pmid":"22087003","id":"PMC_22087003","title":"Mycobacterium 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pathway","date":"2025-08-01","source":"bioRxiv","url":"https://doi.org/10.1101/2025.07.29.665837","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":22965,"output_tokens":4471,"usd":0.06798,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":12546,"output_tokens":4235,"usd":0.084303,"stage2_stop_reason":"end_turn"},"total_usd":0.152283,"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\": 1994,\n      \"finding\": \"PTPA (phosphotyrosyl phosphatase activator) stimulates the tyrosyl phosphatase activity of protein phosphatase 2A (PP2A) in an ATP- and Mg2+-requiring reaction. Recombinant bacterially expressed PTPA protein is soluble and active, confirming it is sufficient for this activating function.\",\n      \"method\": \"Biochemical activity assay with recombinant protein; molecular cloning and expression\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct in vitro enzymatic activity assay with recombinant protein, foundational paper replicated by multiple subsequent studies\",\n      \"pmids\": [\"8195217\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Crystal structure of PP2A catalytic subunit bound to PTPA and ATPγS reveals that PTPA makes broad contacts with structural elements surrounding the PP2A active site and the adenine moiety of ATP. PTPA-binding stabilizes the protein fold of apo-PP2A required for activation and orients ATP phosphoryl groups to bind directly to the PP2A active site, allowing ATP to modulate metal-binding preferences and utilize the PP2A active site for ATP hydrolysis. In vitro, ATP selectively enhances binding of endogenous catalytic metal ions requiring ATP hydrolysis, which is crucial for acquisition of pSer/Thr-specific phosphatase activity. Both PP2A- and ATP-binding are required for PTPA function in cell proliferation and survival.\",\n      \"method\": \"Crystal structure (X-ray crystallography); in vitro phosphatase activity assay; mutagenesis; cell proliferation/survival assays\",\n      \"journal\": \"Cell research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure combined with in vitro reconstitution, mutagenesis, and functional cell-based validation in a single rigorous study\",\n      \"pmids\": [\"24100351\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PTPA interacts with the invariant C-terminal tail of the PP2A catalytic subunit at an additional interaction site. Phosphorylation of Tyr307 on PP2A-C or carboxymethylation of Leu309 abrogates or diminishes binding of the C-terminal tail to PTPA, whereas phosphorylation of Thr304 has no consequence on this interaction.\",\n      \"method\": \"Structural studies (NMR/X-ray); binding assays with posttranslationally modified C-terminal tail peptides\",\n      \"journal\": \"Biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — structural and biochemical binding data from a single lab with multiple PTM conditions tested\",\n      \"pmids\": [\"25003389\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Yeast PTPA homologues Ypa1 and Ypa2 physically interact directly with the catalytic subunits of specific PP2A-like phosphatases: Ypa1 with Pph3, Sit4, and Ppg1; Ypa2 with Pph21 and Pph22. Interaction is independent of other regulatory subunits. Ypa1 and Ypa2 can reactivate inactive PP2A-methyl esterase complexes (except Pph22-Yme). The interaction of Ypa2 with PP2A is promoted by the presence of Ypa1, suggesting a cooperative role.\",\n      \"method\": \"Yeast two-hybrid; direct binding assays; phosphatase reactivation assays\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding and functional activation assays in yeast, multiple interactors tested, single lab\",\n      \"pmids\": [\"15447631\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Yeast PTPA homologue yPtpa1p participates in the repair of oxidative DNA damage induced by 4-NQO and UVA. Deletion of yPTPA1 causes hypersensitivity to 4-NQO and UVA, a spontaneous mutator phenotype, and a defect in recovery of high molecular weight DNA following 4-NQO exposure, demonstrating a role in DNA repair via activation of a phosphatase.\",\n      \"method\": \"Yeast genetics (targeted gene deletion); mutagen sensitivity assays; DNA repair (high molecular weight DNA recovery)\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean genetic deletion with defined phenotypic readouts, multiple orthogonal assays, single lab\",\n      \"pmids\": [\"9705277\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"UBE3A ubiquitinates PTPA, targeting it for degradation. Loss of maternal Ube3a increases PTPA levels, promotes PP2A holoenzyme assembly, and elevates PP2A activity. Reducing PTPA levels in vivo in Ube3am-/p+ mice restores defects in dendritic spine maturation. Pharmacological inhibition of PP2A activity alleviates reduction in excitatory synaptic transmission and motor impairment in these mice.\",\n      \"method\": \"Stable-isotope labeling of amino acids in mammals (SILAC); ubiquitination assays; mouse genetics (Ube3a maternal knockout); in vivo PTPA knockdown; PP2A activity assay; electrophysiology; behavioral assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods including SILAC proteomics, ubiquitination assays, in vivo mouse model, and functional rescue experiments\",\n      \"pmids\": [\"31160454\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Haploinsufficiency of PPP2R4 (encoding PTPA) promotes cancer development. Cancer-associated PTPA mutants show decreased ability to bind the PP2A catalytic subunit or activate PP2A. In Ppp2r4 gene-trapped mice, total PP2A activity and methylation are reduced, selectively affecting specific PP2A holoenzymes. Both Ppp2r4gt/gt and Ppp2r4+/gt mice show higher rates of spontaneous tumors with increased c-Myc phosphorylation and increased Wnt or Hedgehog signaling.\",\n      \"method\": \"Mouse genetics (gene-trap); PP2A activity assay; PP2A binding and activation assays with cancer-associated mutants; tumor incidence analysis; phosphorylation assays\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo mouse genetic model combined with biochemical validation of mutant function, multiple cancer types analyzed, multiple orthogonal methods\",\n      \"pmids\": [\"29046336\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PTPA activates PP2A by reducing inhibitory phosphorylation of PP2A catalytic subunit at Tyr307 (P-PP2AC). Overexpression of PTPA decreased P-PP2AC levels and activated PP2A, while knockdown increased P-PP2AC and inhibited PP2A. PTPA upregulates protein tyrosine phosphatase 1B (PTP1B) at protein and mRNA levels, and simultaneous knockdown of PTP1B abolishes PTPA-induced PP2A activation, indicating PTPA acts through PTP1B to dephosphorylate PP2AC-Tyr307.\",\n      \"method\": \"Overexpression/knockdown in cells; PP2A activity assay; Western blot for P-PP2AC; PTP1B knockdown epistasis\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis experiment placing PTPA upstream of PTP1B→PP2AC-pTyr307, multiple orthogonal approaches, single lab\",\n      \"pmids\": [\"23428800\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Transient overexpression of PTPA leads to caspase 3-dependent apoptosis in mammalian cells, with hallmarks including chromatin condensation, membrane blebbing, annexin V staining, dephosphorylation of Bad, and caspase-3 cleavage. This proapoptotic effect is not prevented by the PP2A inhibitor okadaic acid, indicating PTPA mediates apoptosis independently of PP2A.\",\n      \"method\": \"Transient overexpression; apoptosis assays (annexin V, caspase-3 cleavage, chromatin condensation); pharmacological inhibition with okadaic acid\",\n      \"journal\": \"Apoptosis : an international journal on programmed cell death\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — multiple apoptosis readouts with pharmacological epistasis showing PP2A-independence, single lab\",\n      \"pmids\": [\"17333320\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Homozygous missense variants in PTPA (p.Ala171Asp and p.Met298Arg) cause early-onset parkinsonism with intellectual disability. Both variants are associated with decreased PTPA RNA stability and decreased PTPA protein levels; p.Ala171Asp additionally shows decreased protein stability. Expression of both variants is associated with decreased PP2A complex levels and impaired PP2A phosphatase activation. Knock-down of PTPA ortholog in Drosophila neurons induces age-dependent locomotion impairment fully reversed by L-DOPA treatment.\",\n      \"method\": \"Overexpression studies in cultured cells; PP2A activity assay; PP2A complex assembly assay; Drosophila knockdown with climbing test and L-DOPA rescue\",\n      \"journal\": \"Brain : a journal of neurology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — functional studies in both mammalian cells and Drosophila model with pharmacological rescue, multiple orthogonal methods across two labs/families\",\n      \"pmids\": [\"36073231\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PTPA loss (identified by CRISPR-Cas12a genome-wide screen) elevates fetal globin (HBG1/HBG2) levels while preserving erythroid differentiation. Phenotypic rescue experiments revealed that PTPA silences HBG1/2 expression primarily by regulating BCL11A expression, placing PTPA upstream of BCL11A in the fetal hemoglobin silencing pathway.\",\n      \"method\": \"CRISPR-Cas12a genome-wide screen; domain-focused CRISPR-Cas9 screen; phenotypic rescue experiments in erythroid cells\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genome-wide screen with epistasis rescue placing PTPA upstream of BCL11A, single study\",\n      \"pmids\": [\"41525452\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PTPA localizes predominantly to the Golgi apparatus in osteoblasts, closely overlapping with the Golgi marker Giantin. Disruption of Golgi structure by Brefeldin A causes PTPA to disperse into the cytoplasm. PTPA overexpression inhibits osteoblast differentiation by downregulating key transcriptional regulators.\",\n      \"method\": \"Immunofluorescence co-localization with Golgi marker; Brefeldin A treatment; PTPA overexpression with differentiation assays\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single localization method, functional overexpression without mechanistic depth\",\n      \"pmids\": [\"39827549\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PPP2R4 (PTPA) depletion in A549 lung cancer cells increases anchorage-independent growth and xenograft growth, and accelerates KrasG12D-induced lung tumorigenesis in Ppp2r4 gene-trapped mice. PPP2R4 depletion induces resistance to MEK inhibitor selumetinib but sensitizes cells to mTOR inhibitor temsirolimus, establishing PTPA as a modifier of kinase inhibitor response in KRAS-mutant lung adenocarcinoma.\",\n      \"method\": \"PPP2R4 depletion in cell lines; anchorage-independent growth assay; xenograft; mouse genetics (gene-trap with KrasG12D); kinase inhibitor screen\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo mouse model plus in vitro functional assays, single lab, multiple orthogonal readouts\",\n      \"pmids\": [\"34216687\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"The human PTPA gene is a single-copy gene located at chromosomal region 9q34, composed of 10 exons and 9 introns spanning ~60 kb. The promoter lacks a TATA box, is GC-rich, and contains Sp1 sites. Transfection with PTPA promoter-luciferase construct confirmed promoter activity in a cell-line-dependent manner.\",\n      \"method\": \"Fluorescence in situ hybridization (FISH); genomic cloning and sequencing; luciferase reporter transfection\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct FISH localization and functional promoter assay, single lab\",\n      \"pmids\": [\"8530035\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"PTPA restoration in PTPA-low mesothelioma cells increases PP2A catalytic subunit expression and activity (methylation) without favoring specific PP2A holoenzymes. PTPA restoration activates oncogene-induced senescence (OIS) via PP2A-dependent dephosphorylation of Kinase Suppressor of Ras 1 (KSR1), activating p53 signaling and NF-κB. PTPA restoration also sensitizes MPM cells to carboplatin.\",\n      \"method\": \"PTPA re-expression in PTPA-low cells; PP2A activity/methylation assays; RNAseq/GSEA; SA-β-galactosidase senescence assay; SASP/NF-κB measurements; MEK inhibitor (Trametinib) epistasis; carboplatin sensitivity assays\",\n      \"journal\": \"Cellular oncology (Dordrecht, Netherlands)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods in a single study, epistasis with MEK inhibitor placing PTPA upstream of Ras/KSR1/senescence pathway, single lab\",\n      \"pmids\": [\"42258127\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Knockout of PPP2R4 in KELLY neuroblastoma cells, along with reduced methylation of PP2A catalytic subunit (mePPP2CA), increases AURKA protein levels, indicating that the PP2A pathway (activated by PTPA) regulates AURKA abundance post-translationally.\",\n      \"method\": \"CRISPR knockout of PPP2R4; Western blot for AURKA protein; PP2A methylation assay\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single preprint, single lab, limited mechanistic follow-up beyond protein level change\",\n      \"pmids\": [\"bio_10.1101_2025.07.29.665837\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"PTPA (PPP2R4/PR53) is an ATP-dependent activation chaperone for PP2A: it binds the PP2A catalytic subunit, stabilizes its apo-fold, positions ATP for hydrolysis at the PP2A active site to drive metal ion loading, and thereby converts inactive apo-PP2A into an active Ser/Thr phosphatase; additionally, PTPA reduces inhibitory Tyr307 phosphorylation on PP2A-C via upregulation of PTP1B, is itself ubiquitinated and degraded by UBE3A (linking it to Angelman syndrome and synaptic function), and harbors loss-of-function variants that impair PP2A activation and cause autosomal recessive early-onset parkinsonism with intellectual disability, while haploinsufficiency of PTPA is a recurrent tumor-suppressive mechanism in human cancers.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PTPA (PPP2R4/PR53) is an ATP- and Mg2+-dependent activation chaperone for protein phosphatase 2A (PP2A) that converts inactive apo-PP2A into a catalytically competent Ser/Thr phosphatase [#0, #1]. Structurally, PTPA makes broad contacts with elements surrounding the PP2A active site and engages the adenine moiety of ATP, stabilizing the apo-PP2A fold and orienting ATP phosphoryl groups within the PP2A active site so that ATP hydrolysis drives selective loading of catalytic metal ions required for acquisition of pSer/Thr phosphatase activity; both PP2A- and ATP-binding are essential for PTPA's role in cell proliferation and survival [#1]. PTPA also docks on the invariant C-terminal tail of the PP2A catalytic subunit, an interaction abrogated by Tyr307 phosphorylation or Leu309 carboxymethylation [#2], and it lowers inhibitory Tyr307 phosphorylation by upregulating the tyrosine phosphatase PTP1B [#7]. This activation function is conserved: yeast orthologs bind and reactivate PP2A-family catalytic subunits and contribute to oxidative DNA damage repair [#3, #4]. PTPA protein levels are controlled by UBE3A-mediated ubiquitination and degradation, linking PTPA to dendritic spine maturation, excitatory synaptic transmission, and motor function through PP2A holoenzyme assembly [#5]. Homozygous loss-of-function PTPA variants that destabilize the protein and impair PP2A activation cause autosomal recessive early-onset parkinsonism with intellectual disability [#9], and PTPA haploinsufficiency is a recurrent tumor-suppressive lesion: loss reduces PP2A activity and promotes c-Myc phosphorylation, Wnt/Hedgehog signaling, KRAS-driven tumorigenesis, and altered kinase-inhibitor sensitivity, while restoration activates PP2A-dependent senescence [#6, #12, #14].\",\n  \"teleology\": [\n    {\n      \"year\": 1994,\n      \"claim\": \"Established PTPA as a discrete factor that stimulates PP2A phosphatase activity, defining the protein's core biochemical function.\",\n      \"evidence\": \"Biochemical activity assay with recombinant bacterially expressed PTPA requiring ATP and Mg2+\",\n      \"pmids\": [\"8195217\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of activation not resolved\", \"Did not distinguish chaperone vs catalytic role\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Located and structured the human PTPA gene, providing genomic context for later variant and expression studies.\",\n      \"evidence\": \"FISH mapping to 9q34, genomic sequencing, and promoter-luciferase reporter assays\",\n      \"pmids\": [\"8530035\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional regulators of the promoter identified\", \"Tissue-specific expression control unresolved\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Connected PTPA function to a cellular phenotype, showing the yeast ortholog supports oxidative DNA damage repair via phosphatase activation.\",\n      \"evidence\": \"Yeast yPTPA1 deletion with mutagen sensitivity and DNA recovery assays\",\n      \"pmids\": [\"9705277\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific phosphatase substrate in repair pathway not defined\", \"Direct relevance to human PTPA untested\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Demonstrated direct, regulatory-subunit-independent binding of PTPA orthologs to multiple PP2A-family catalytic subunits and cooperative reactivation, generalizing PTPA's chaperone role across PP2A-like phosphatases.\",\n      \"evidence\": \"Yeast two-hybrid, direct binding, and phosphatase reactivation assays\",\n      \"pmids\": [\"15447631\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis of selectivity unknown\", \"Cooperativity mechanism between Ypa1 and Ypa2 undefined\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Identified a PP2A-independent proapoptotic activity of PTPA, raising the possibility of moonlighting functions.\",\n      \"evidence\": \"Transient overexpression with apoptosis readouts and okadaic acid epistasis showing PP2A-independence\",\n      \"pmids\": [\"17333320\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Effector pathway for PP2A-independent apoptosis not identified\", \"Overexpression artifact not excluded\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Resolved the structural and chemical mechanism of activation, showing PTPA stabilizes apo-PP2A and uses ATP hydrolysis at the PP2A active site to drive catalytic metal loading.\",\n      \"evidence\": \"X-ray crystal structure of PP2A-C bound to PTPA and ATPγS with in vitro reconstitution, mutagenesis, and cell-based validation\",\n      \"pmids\": [\"24100351\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo ordering of metal loading vs holoenzyme assembly unresolved\", \"Identity of native metal ions in cells not established\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Defined a second, PTP1B-dependent route by which PTPA activates PP2A through removal of inhibitory Tyr307 phosphorylation.\",\n      \"evidence\": \"Overexpression/knockdown, PP2A activity assays, and PTP1B knockdown epistasis in cells\",\n      \"pmids\": [\"23428800\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which PTPA upregulates PTP1B transcript unknown\", \"Single lab without reciprocal validation\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Mapped a PTM-sensitive second interaction site on the PP2A C-terminal tail, linking PP2A modification status to PTPA engagement.\",\n      \"evidence\": \"Structural and peptide-binding assays with post-translationally modified C-terminal tail peptides\",\n      \"pmids\": [\"25003389\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of tail binding for activation kinetics untested\", \"Single-lab structural data\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Established PTPA as a haploinsufficient tumor suppressor whose loss reduces PP2A activity and drives oncogenic signaling.\",\n      \"evidence\": \"Ppp2r4 gene-trap mice, PP2A activity/methylation assays, and biochemical analysis of cancer-associated PTPA mutants\",\n      \"pmids\": [\"29046336\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which specific PP2A holoenzymes mediate tumor suppression not fully resolved\", \"Direct PP2A substrates downstream of c-Myc/Wnt/Hedgehog not enumerated\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identified UBE3A-mediated degradation of PTPA as a control point coupling PTPA abundance to PP2A holoenzyme assembly and synaptic function.\",\n      \"evidence\": \"SILAC proteomics, ubiquitination assays, Ube3a maternal-knockout mice with in vivo PTPA knockdown, electrophysiology, and behavior\",\n      \"pmids\": [\"31160454\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Ubiquitination site(s) on PTPA not mapped\", \"Whether PP2A-independent PTPA functions contribute to synaptic phenotype untested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Extended PTPA's tumor-suppressor role to KRAS-mutant lung adenocarcinoma and showed it modifies kinase-inhibitor sensitivity.\",\n      \"evidence\": \"PPP2R4 depletion in A549, xenografts, KrasG12D gene-trap mice, and kinase inhibitor screening\",\n      \"pmids\": [\"34216687\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking PTPA loss to MEK vs mTOR inhibitor response undefined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Tied PTPA loss-of-function variants directly to human early-onset parkinsonism with intellectual disability through impaired PP2A activation.\",\n      \"evidence\": \"Patient variants in cultured cells with PP2A activity/assembly assays and Drosophila knockdown with L-DOPA rescue\",\n      \"pmids\": [\"36073231\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Neuronal PP2A substrates underlying parkinsonism not identified\", \"Cell-type specificity of vulnerability unresolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Placed PTPA upstream of BCL11A in fetal hemoglobin silencing, revealing a role in erythroid gene regulation.\",\n      \"evidence\": \"Genome-wide CRISPR-Cas12a screen and phenotypic rescue in erythroid cells\",\n      \"pmids\": [\"41525452\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether HBG silencing depends on PP2A activation untested\", \"Mechanism linking PTPA to BCL11A expression unknown\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Showed PTPA restoration triggers PP2A-dependent oncogene-induced senescence via KSR1 dephosphorylation, defining a reversible tumor-suppressive program.\",\n      \"evidence\": \"PTPA re-expression in mesothelioma cells with PP2A activity assays, RNAseq, senescence/SASP readouts, MEK inhibitor epistasis, and carboplatin sensitivity\",\n      \"pmids\": [\"42258127\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct demonstration of KSR1 as a PP2A substrate incomplete\", \"Single lal/single cancer model\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How PTPA's distinct activities — chaperone-mediated PP2A activation, PP2A-independent functions, and substrate-specific holoenzyme outcomes — are coordinated across tissues and disease states remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model linking PP2A-dependent and PP2A-independent PTPA roles\", \"Direct PP2A substrates in neurons, cancer, and erythroid cells largely uncatalogued\", \"Endogenous regulation of PTPA abundance beyond UBE3A undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 3]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 7]},\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"GO:0044183\", \"supporting_discovery_ids\": [1, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [11]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [6, 12, 14]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [6, 9, 12]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [1, 5]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"PPP2CA\", \"UBE3A\", \"PTP1B\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}