{"gene":"PTPN21","run_date":"2026-06-10T06:43:36","timeline":{"discoveries":[{"year":2019,"finding":"PTPN21 FERM domain binds the tail region of KIF1C kinesin-3, relieving autoinhibition caused by interaction between KIF1C motor domain's microtubule-binding surface and its stalk. This increases KIF1C landing rate onto microtubules and activates processive, plus-end directed transport of dense core vesicles and integrins.","method":"In vitro reconstitution with purified full-length KIF1C and PTPN21 FERM domain, microtubule landing rate assays, rescue of integrin trafficking in KIF1C-depleted cells, stimulation of dense core vesicle transport in primary hippocampal neurons","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with purified proteins, multiple orthogonal assays (landing rate, vesicle transport, cell trafficking rescue), functional domain mapping","pmids":["31217419"],"is_preprint":false},{"year":2008,"finding":"PTPD1 (PTPN21) forms a stable complex with actin, Src tyrosine kinase, and FAK at adhesion plaques via distinct molecular modules. Both PTPD1 catalytic activity and its FERM domain are required for EGF-induced FAK autophosphorylation, ERK1/2 signaling, and cell migration.","method":"Co-immunoprecipitation, shRNA-mediated silencing, overexpression of catalytically dead mutant (C1108S) and FERM-deleted mutant (Δ1-325), cell scattering/migration assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP demonstrating complex, domain-mutant dissection, functional readouts in two orthogonal assays (phosphorylation, migration), single lab","pmids":["18223254"],"is_preprint":false},{"year":2010,"finding":"PTPD1 (PTPN21) is recruited to endocytic vesicles containing EGFR during EGF stimulation through interaction with the endosomal kinesin KIF16B, and this endosomal localization of PTPD1 is required for EGF receptor stability and downstream ERK signaling.","method":"Co-immunoprecipitation with KIF16B, siRNA silencing of PTPD1, receptor degradation assays, ERK signaling readouts","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — single lab, Co-IP with KIF16B and functional silencing experiments, single study","pmids":["20923765"],"is_preprint":false},{"year":2014,"finding":"PTPD1 (PTPN21) FERM domain mediates localization to the plasma membrane, where it forms pre-existing signaling complexes with EGFR. Transient co-localization at EGF stimulation sites promotes spatial propagation of EGFR phosphorylated species; interference with PTPD1 expression decreases peripheral EGFR phosphorylation.","method":"Live-cell imaging, FRAP, FERM-domain deletion/mutation, EGFR phosphorylation assays, siRNA knockdown","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — live imaging with functional domain dissection, multiple readouts, single lab","pmids":["25062045"],"is_preprint":false},{"year":2019,"finding":"Ptpn21 dephosphorylates Septin1 at Tyr246 in hematopoietic stem cells (HSCs). Loss of Ptpn21 elevates Septin1 phosphorylation, impairing cytoskeletal remodeling, decreasing cell stiffness, increasing deformability, and causing HSC egress from the bone marrow niche with decreased quiescence and reconstitution capacity.","method":"Ptpn21 knockout mouse model, atomic force microscopy for cell stiffness, phospho-specific detection of Septin1 Tyr246, cell egress and reconstitution assays","journal":"Cell stem cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with defined substrate (Septin1 pTyr246), biophysical measurements, and functional stem cell reconstitution assays in a rigorous study","pmids":["30880025"],"is_preprint":false},{"year":2015,"finding":"PTPN21 dephosphorylates ErbB4, leading to upregulation of downstream ErbB4 signaling. Phosphatase-dead PTPN21 (C1108S) or kinase-dead ErbB4 (K751R) abolish this effect. PTPN21 activates Elk-1, which drives NRG3 expression via a novel Elk-1 binding motif upstream of the NRG3 initiation codon, promoting cortical neuronal survival and neuritic elongation.","method":"Biotinylated receptor tracking, immunoprecipitation, phosphatase-dead and kinase-dead mutant analysis, Elk-1 reporter assays, cortical neuron survival and neurite length measurements","journal":"The international journal of biochemistry & cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods including receptor tracking, IP, and mutant analysis in single lab","pmids":["25681686"],"is_preprint":false},{"year":2017,"finding":"PTPN21 directly dephosphorylates phospho-IKKβ at Ser177/181 in TNF-α-stimulated keratinocytes. This dephosphorylation stabilizes IκBα and inhibits NF-κB activity, thereby suppressing ICAM-1 expression. Catalytically inactive PTPN21 (C1108S) fails to inhibit ICAM-1 expression.","method":"Overexpression and C1108S phosphatase-dead mutant, Western blot for p-IKKβ, IκBα, and NF-κB targets, ICAM-1 expression assays","journal":"BMB reports","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct substrate dephosphorylation with mutant validation, single lab, single study","pmids":["29065968"],"is_preprint":false},{"year":2020,"finding":"The Drosophila ortholog of PTPN21 (Pez) acts downstream of damage-induced H2O2 and operates via its FERM domain together with the SFK Src42A and damage receptor Draper to drive macrophage migration to wounds. This role is conserved in vertebrates: PTPN21 crispant zebrafish larvae show failure of leukocyte recruitment to wounds.","method":"Proteomics, live imaging, Drosophila genetics, CRISPR crispant zebrafish, epistasis analysis with H2O2 pathway","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis in Drosophila, live imaging, conservation validated in zebrafish crispants, multiple orthogonal methods","pmids":["33296680"],"is_preprint":false},{"year":2021,"finding":"HPV18 E7 conserved region 3 (CR3) forms a 2:2 complex with the PTP domain of PTPN21 with a dissociation constant of ~5 nM. Unlike PTPN14, PTPN21 is not subjected to proteasomal degradation in HPV18-positive cells. Knockdown of PTPN21 retards migration/invasion of HeLa cells and HPV18 E7-expressing keratinocytes.","method":"Biochemical binding assays (Kd determination), complex stoichiometry analysis, proteasomal degradation assays, siRNA knockdown with migration/invasion assays","journal":"Molecules and cells","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — quantitative binding characterization with Kd, functional knockdown validation, single lab","pmids":["33431714"],"is_preprint":false},{"year":2024,"finding":"Crystal structures of individual PTPN21 FERM and PTP domains and their complex reveal that the FERM domain directly contacts the PTP domain, sterically blocking its active site and autoinhibiting the weakly active PTP. Disruption of FERM-PTP interaction enhances ERK activation. The HPV18 E7 oncoprotein binds the PTP domain at the same interface as the FERM domain, suggesting displacement of autoinhibition as E7's mechanism of action on PTPN21.","method":"X-ray crystallography of FERM, PTP, and FERM-PTP complex; biochemical phosphatase activity assays; mutagenesis of FERM-PTP interface; ERK activation assays","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structures combined with biochemical validation and mutagenesis in a single rigorous study","pmids":["38416831"],"is_preprint":false},{"year":1995,"finding":"PTP-RL10 (PTPN21) encodes a cytoplasmic-type protein tyrosine phosphatase with an amino-terminal domain homologous to cytoskeletal proteins 4.1 and ezrin (FERM-like), and no membrane-spanning region, establishing its domain architecture as a non-receptor cytosolic PTP.","method":"PCR-based cloning, cDNA sequencing, Northern blotting of regenerating mouse liver","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — initial cloning and domain architecture determination replicated by subsequent studies confirming FERM-PTP architecture","pmids":["7838537"],"is_preprint":false},{"year":2017,"finding":"PTPN21 activates the ERK1/2 signaling pathway to upregulate CDK5 expression, protecting PC12 neuronal cells from oxygen-glucose deprivation-induced apoptosis. Inhibition of ERK1/2 with PD98059 or CDK5 siRNA abolishes the pro-survival effect of PTPN21 overexpression.","method":"siRNA knockdown and overexpression in PC12 cells, ERK1/2 inhibitor PD98059, caspase-3 activity assay, Western blot, cell viability assays","journal":"European journal of pharmacology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, no direct substrate identification, pathway placement by inhibitor only","pmids":["28843827"],"is_preprint":false},{"year":2024,"finding":"PTPN21 overexpression in ALL cells promotes proliferation and cell cycle progression under EGF stimulation via activation of Src tyrosine kinase and MAPK pathways; MAPK pathway inhibitors abolish this pro-proliferative effect.","method":"Lentiviral overexpression, Western blot for Src and MAPK pathway phosphorylation, MAPK inhibitor treatment, proliferation and cell cycle assays","journal":"Hematology (Amsterdam, Netherlands)","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, pathway placement only by inhibitor, no direct substrate identification","pmids":["38785187"],"is_preprint":false},{"year":2025,"finding":"PTPN21 inhibits chemotherapy-induced apoptosis in ALL cells by suppressing the GADD45A and JNK signaling pathways, thereby reversing G2/M cell cycle arrest. Restoration of GADD45A reverses the anti-apoptotic effect of PTPN21.","method":"PTPN21 knockdown/overexpression, GADD45A rescue experiments, JNK pathway analysis, apoptosis assays with vincristine and daunorubicin","journal":"PloS one","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, pathway placement by rescue experiment without direct substrate identification","pmids":["40305474"],"is_preprint":false}],"current_model":"PTPN21 is a FERM domain-containing non-receptor protein tyrosine phosphatase whose FERM domain mediates interaction with KIF1C kinesin to relieve its autoinhibition and activate cargo transport, localizes the enzyme to actin filaments, adhesion plaques, and the plasma membrane to potentiate Src-FAK-EGFR signaling and cell migration, and whose intramolecular FERM-PTP interaction autoinhibits its weak phosphatase activity; identified substrates include ErbB4, IKKβ, Septin1 (Tyr246), and FAK, placing PTPN21 at the intersection of cytoskeletal organization, intracellular transport activation, inflammatory signaling, and hematopoietic stem cell niche retention."},"narrative":{"mechanistic_narrative":"PTPN21 is a non-receptor cytosolic protein tyrosine phosphatase built from an N-terminal FERM domain and a C-terminal PTP domain, an architecture that places it at the intersection of cytoskeletal organization, intracellular transport, and receptor tyrosine kinase signaling [PMID:7838537]. Its phosphatase activity is intrinsically weak and held in check by an intramolecular autoinhibitory interaction in which the FERM domain directly contacts and sterically occludes the PTP active site; disrupting this interface enhances ERK activation [PMID:38416831]. The FERM domain is the principal targeting and effector module: it binds the tail of the kinesin-3 motor KIF1C to relieve its motor-domain autoinhibition, increasing microtubule landing rate and activating processive plus-end transport of dense core vesicles and integrins [PMID:31217419], and it localizes PTPN21 to the plasma membrane and adhesion plaques where the enzyme assembles with actin, Src, and FAK to drive EGF-induced FAK autophosphorylation, ERK signaling, and cell migration in a manner requiring both catalytic activity and the FERM domain [PMID:18223254, PMID:25062045]. PTPN21 acts on defined substrates to control distinct outputs: it dephosphorylates Septin1 at Tyr246 to support cytoskeletal stiffness and retention of hematopoietic stem cells in the bone marrow niche [PMID:30880025], dephosphorylates ErbB4 to potentiate downstream Elk-1/NRG3 signaling in cortical neurons [PMID:25681686], and dephosphorylates IKKβ at Ser177/181 to stabilize IκBα and suppress NF-κB-driven ICAM-1 expression [PMID:29065968]. The FERM-dependent migratory function is conserved, with the Drosophila ortholog Pez acting with Src42A and the Draper receptor downstream of wound-induced H2O2 to drive macrophage recruitment, a role retained in zebrafish leukocyte recruitment [PMID:33296680]. The HPV18 E7 oncoprotein binds the PTP domain at the same interface used by the FERM domain, displacing autoinhibition and engaging PTPN21 to promote cell migration and invasion [PMID:33431714, PMID:38416831].","teleology":[{"year":1995,"claim":"Established the founding domain architecture, defining PTPN21 as a cytosolic non-receptor PTP carrying an N-terminal FERM-like (band 4.1/ezrin homology) region.","evidence":"PCR cloning, cDNA sequencing, and Northern blotting of regenerating mouse liver","pmids":["7838537"],"confidence":"Medium","gaps":["No functional role assigned to either domain","No substrate identified","No subcellular localization determined"]},{"year":2008,"claim":"Showed PTPN21 is not a free-standing enzyme but a scaffolded one, assembling with actin, Src, and FAK at adhesion plaques where both its catalytic activity and FERM domain are required for EGF-driven FAK phosphorylation and migration.","evidence":"Reciprocal Co-IP, shRNA silencing, catalytic-dead (C1108S) and FERM-deleted mutant dissection, migration assays","pmids":["18223254"],"confidence":"High","gaps":["Direct substrate within the Src-FAK module not pinned down","Single lab","Mechanism of FERM-mediated complex assembly not resolved structurally"]},{"year":2010,"claim":"Linked PTPN21 to receptor trafficking by placing it on EGFR-containing endosomes via the kinesin KIF16B, connecting its localization to EGFR stability and ERK output.","evidence":"Co-IP with KIF16B, siRNA silencing, receptor degradation and ERK readouts","pmids":["20923765"],"confidence":"Medium","gaps":["Single Co-IP-based interaction without structural mapping","Phosphatase substrate on the endosome not identified","Single study"]},{"year":2014,"claim":"Refined the membrane localization mechanism, showing the FERM domain targets PTPN21 to pre-existing EGFR signaling complexes at the plasma membrane to propagate peripheral EGFR phosphorylation.","evidence":"Live-cell imaging, FRAP, FERM-domain deletion/mutation, EGFR phosphorylation assays, siRNA knockdown","pmids":["25062045"],"confidence":"Medium","gaps":["Direct molecular contacts of FERM with the membrane/EGFR complex not defined","Single lab","Catalytic contribution at the membrane not separated from scaffolding"]},{"year":2015,"claim":"Identified ErbB4 as a direct substrate and connected dephosphorylation to a transcriptional program (Elk-1/NRG3) governing cortical neuronal survival and neurite outgrowth.","evidence":"Receptor tracking, IP, phosphatase-dead and kinase-dead mutants, Elk-1 reporter, neuron survival/neurite assays","pmids":["25681686"],"confidence":"Medium","gaps":["Phospho-site on ErbB4 not mapped","Single lab","In vivo relevance in brain not tested genetically"]},{"year":2017,"claim":"Extended substrate repertoire into inflammatory signaling by showing PTPN21 dephosphorylates IKKβ at Ser177/181 to suppress NF-κB and ICAM-1.","evidence":"Overexpression and C1108S mutant, Western blot for p-IKKβ/IκBα/NF-κB targets, ICAM-1 assays in keratinocytes","pmids":["29065968"],"confidence":"Medium","gaps":["Note: IKKβ substrate sites are Ser, atypical for a tyrosine phosphatase, unresolved here","Single lab and study","Direct in vitro dephosphorylation not shown"]},{"year":2019,"claim":"Established a high-confidence physiological substrate-phenotype axis: Ptpn21 dephosphorylates Septin1 Tyr246 to maintain HSC stiffness, quiescence, and niche retention.","evidence":"Ptpn21 knockout mice, atomic force microscopy, phospho-specific Septin1 Tyr246 detection, egress and reconstitution assays","pmids":["30880025"],"confidence":"High","gaps":["Whether Septin1 is dephosphorylated directly versus indirectly not fully resolved","Role of FERM/autoinhibition in this context untested"]},{"year":2019,"claim":"Defined a non-catalytic transport-activating function: the FERM domain binds KIF1C to relieve motor autoinhibition and switch on processive cargo transport.","evidence":"In vitro reconstitution with purified KIF1C and PTPN21 FERM, landing-rate assays, integrin trafficking rescue, neuronal vesicle transport","pmids":["31217419"],"confidence":"High","gaps":["Whether full-length PTPN21 (with autoinhibition) engages KIF1C identically not addressed","Coupling of transport activation to phosphatase activity unknown"]},{"year":2020,"claim":"Demonstrated evolutionary conservation of a FERM-dependent migratory role, placing PTPN21/Pez downstream of wound H2O2 with Src and the Draper receptor to drive immune cell recruitment.","evidence":"Drosophila genetics/epistasis, proteomics, live imaging, CRISPR crispant zebrafish","pmids":["33296680"],"confidence":"High","gaps":["Catalytic substrate in this pathway not identified","Human leukocyte relevance inferred from zebrafish"]},{"year":2024,"claim":"Provided the structural basis for regulation, showing FERM-PTP intramolecular contact autoinhibits the weak phosphatase and that HPV18 E7 binds the PTP at the FERM interface to displace autoinhibition.","evidence":"X-ray crystallography of FERM, PTP, and complex; phosphatase assays; interface mutagenesis; ERK activation; Kd determination of E7 binding","pmids":["38416831","33431714"],"confidence":"High","gaps":["How physiological FERM ligands (KIF1C, membrane) relieve autoinhibition not structurally shown","Conformational dynamics in cells not visualized"]},{"year":2024,"claim":"Associated PTPN21 with leukemia cell proliferation and chemoresistance through Src/MAPK and GADD45A/JNK pathways.","evidence":"Lentiviral overexpression/knockdown in ALL cells, pathway inhibitors, GADD45A rescue, proliferation/apoptosis assays","pmids":["38785187","40305474"],"confidence":"Low","gaps":["Pathway placement by inhibitor/rescue only, no direct substrate identified","Single lab per study","Causal direction of GADD45A/JNK regulation not mechanistically resolved"]},{"year":null,"claim":"How physiological FERM-domain ligands relieve intramolecular autoinhibition to switch on phosphatase activity at specific subcellular sites, and how transport-activating versus catalytic functions are coordinated, remain unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No structure of full-length PTPN21 bound to a physiological FERM ligand","Unclear whether catalytic and KIF1C-activating activities operate simultaneously","Substrate selection rules across tissues not defined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[4,5,6,9]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[9,10]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[1,0]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[1,3]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[10]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[3,1]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[1,4]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[2]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[0]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,3,5]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[0,2]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[6,7]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0]}],"complexes":["PTPD1-actin-Src-FAK adhesion plaque complex"],"partners":["KIF1C","SRC","FAK","KIF16B","EGFR","ERBB4","IKKB","SEPTIN1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q16825","full_name":"Tyrosine-protein phosphatase non-receptor type 21","aliases":["Protein-tyrosine phosphatase D1"],"length_aa":1174,"mass_kda":133.3,"function":"","subcellular_location":"Cytoplasm, cytoskeleton","url":"https://www.uniprot.org/uniprotkb/Q16825/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PTPN21","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PTPN21","total_profiled":1310},"omim":[{"mim_id":"603619","title":"FIZZY AND CELL DIVISION CYCLE 20-RELATED PROTEIN 1; FZR1","url":"https://www.omim.org/entry/603619"},{"mim_id":"603271","title":"PROTEIN-TYROSINE PHOSPHATASE, NONRECEPTOR-TYPE, 21; PTPN21","url":"https://www.omim.org/entry/603271"},{"mim_id":"176803","title":"PROSTAGLANDIN D2 SYNTHASE, BRAIN; PTGDS","url":"https://www.omim.org/entry/176803"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Cytosol","reliability":"Approved"},{"location":"Golgi apparatus","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PTPN21"},"hgnc":{"alias_symbol":["PTPD1","PTPRL10"],"prev_symbol":[]},"alphafold":{"accession":"Q16825","domains":[{"cath_id":"1.20.80.10","chopping":"23-213","consensus_level":"medium","plddt":91.2732,"start":23,"end":213},{"cath_id":"2.30.29.30","chopping":"221-308","consensus_level":"high","plddt":89.0848,"start":221,"end":308},{"cath_id":"3.90.190.10","chopping":"912-1154","consensus_level":"high","plddt":93.4601,"start":912,"end":1154}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q16825","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q16825-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q16825-F1-predicted_aligned_error_v6.png","plddt_mean":62.97},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PTPN21","jax_strain_url":"https://www.jax.org/strain/search?query=PTPN21"},"sequence":{"accession":"Q16825","fasta_url":"https://rest.uniprot.org/uniprotkb/Q16825.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q16825/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q16825"}},"corpus_meta":[{"pmid":"31217419","id":"PMC_31217419","title":"PTPN21 and Hook3 relieve KIF1C autoinhibition and activate intracellular transport.","date":"2019","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/31217419","citation_count":57,"is_preprint":false},{"pmid":"18223254","id":"PMC_18223254","title":"Protein-tyrosine phosphatase PTPD1 regulates focal adhesion kinase autophosphorylation and cell migration.","date":"2008","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/18223254","citation_count":55,"is_preprint":false},{"pmid":"30880025","id":"PMC_30880025","title":"Ptpn21 Controls Hematopoietic Stem Cell Homeostasis and Biomechanics.","date":"2019","source":"Cell stem cell","url":"https://pubmed.ncbi.nlm.nih.gov/30880025","citation_count":49,"is_preprint":false},{"pmid":"20923765","id":"PMC_20923765","title":"PTPD1 supports receptor stability and mitogenic signaling in bladder cancer cells.","date":"2010","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/20923765","citation_count":44,"is_preprint":false},{"pmid":"7838537","id":"PMC_7838537","title":"Enhanced expression of multiple protein tyrosine phosphatases in the regenerating mouse liver: isolation of PTP-RL10, a novel cytoplasmic-type phosphatase with sequence homology to cytoskeletal protein 4.1.","date":"1995","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/7838537","citation_count":30,"is_preprint":false},{"pmid":"25062045","id":"PMC_25062045","title":"Dynamic recruitment of protein tyrosine phosphatase PTPD1 to EGF stimulation sites potentiates EGFR activation.","date":"2014","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/25062045","citation_count":21,"is_preprint":false},{"pmid":"25681686","id":"PMC_25681686","title":"PTPN21 exerts pro-neuronal survival and neuritic elongation via ErbB4/NRG3 signaling.","date":"2015","source":"The international journal of biochemistry & cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/25681686","citation_count":20,"is_preprint":false},{"pmid":"28843827","id":"PMC_28843827","title":"PTPN21 protects PC12 cell against oxygen-glucose deprivation by activating cdk5 through ERK1/2 signaling pathway.","date":"2017","source":"European journal of pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/28843827","citation_count":15,"is_preprint":false},{"pmid":"33431714","id":"PMC_33431714","title":"Molecular Analysis of the Interaction between Human PTPN21 and the Oncoprotein E7 from Human Papillomavirus Genotype 18.","date":"2021","source":"Molecules and cells","url":"https://pubmed.ncbi.nlm.nih.gov/33431714","citation_count":12,"is_preprint":false},{"pmid":"35907586","id":"PMC_35907586","title":"Inhibition of PTPN21 has antitumor effects in glioma by restraining the EGFR/PI3K/AKT pathway.","date":"2022","source":"Toxicology and applied pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/35907586","citation_count":9,"is_preprint":false},{"pmid":"29065968","id":"PMC_29065968","title":"Protein tyrosine phosphatase PTPN21 acts as a negative regulator of ICAM-1 by dephosphorylating IKKβ in TNF-α-stimulated human keratinocytes.","date":"2017","source":"BMB reports","url":"https://pubmed.ncbi.nlm.nih.gov/29065968","citation_count":9,"is_preprint":false},{"pmid":"33296680","id":"PMC_33296680","title":"PTPN21/Pez Is a Novel and Evolutionarily Conserved Key Regulator of Inflammation In Vivo.","date":"2020","source":"Current biology : CB","url":"https://pubmed.ncbi.nlm.nih.gov/33296680","citation_count":8,"is_preprint":false},{"pmid":"38416831","id":"PMC_38416831","title":"Structural analysis of PTPN21 reveals a dominant-negative effect of the FERM domain on its phosphatase activity.","date":"2024","source":"Science 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endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/16918960","citation_count":4,"is_preprint":false},{"pmid":"10585123","id":"PMC_10585123","title":"Expression of protein tyrosine phosphatase PTP-RL10 and its isoform in the mouse testis.","date":"1999","source":"International journal of urology : official journal of the Japanese Urological Association","url":"https://pubmed.ncbi.nlm.nih.gov/10585123","citation_count":4,"is_preprint":false},{"pmid":"39633451","id":"PMC_39633451","title":"Loss of PTPN21 disrupted mitochondrial metabolic homeostasis and aggravated experimental pulmonary fibrosis.","date":"2024","source":"Respiratory research","url":"https://pubmed.ncbi.nlm.nih.gov/39633451","citation_count":2,"is_preprint":false},{"pmid":"38785187","id":"PMC_38785187","title":"Overexpression of PTPN21 promotes proliferation of EGF-stimulated acute lymphoblastic leukemia cells via the MAPK signaling pathways.","date":"2024","source":"Hematology (Amsterdam, Netherlands)","url":"https://pubmed.ncbi.nlm.nih.gov/38785187","citation_count":2,"is_preprint":false},{"pmid":"40305474","id":"PMC_40305474","title":"PTPN21 inhibits cell apoptosis of acute lymphoblastic leukemia induced by chemotherapeutic agents via GADD45A and JNK signaling pathway.","date":"2025","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/40305474","citation_count":1,"is_preprint":false},{"pmid":"31406157","id":"PMC_31406157","title":"Targeted sequencing of linkage region in Dominican families implicates PRIMA1 and the SPATA7-PTPN21-ZC3H14-EML5-TTC8 locus in carotid-intima media thickness and atherosclerotic events.","date":"2019","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/31406157","citation_count":1,"is_preprint":false},{"pmid":"41047545","id":"PMC_41047545","title":"Development of Novel PTPN2/1 Inhibitors for the Treatment of Melanoma.","date":"2025","source":"Journal of medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/41047545","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":13214,"output_tokens":3645,"usd":0.047158,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":11222,"output_tokens":4280,"usd":0.081555,"stage2_stop_reason":"end_turn"},"total_usd":0.128713,"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\": 2019,\n      \"finding\": \"PTPN21 FERM domain binds the tail region of KIF1C kinesin-3, relieving autoinhibition caused by interaction between KIF1C motor domain's microtubule-binding surface and its stalk. This increases KIF1C landing rate onto microtubules and activates processive, plus-end directed transport of dense core vesicles and integrins.\",\n      \"method\": \"In vitro reconstitution with purified full-length KIF1C and PTPN21 FERM domain, microtubule landing rate assays, rescue of integrin trafficking in KIF1C-depleted cells, stimulation of dense core vesicle transport in primary hippocampal neurons\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with purified proteins, multiple orthogonal assays (landing rate, vesicle transport, cell trafficking rescue), functional domain mapping\",\n      \"pmids\": [\"31217419\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"PTPD1 (PTPN21) forms a stable complex with actin, Src tyrosine kinase, and FAK at adhesion plaques via distinct molecular modules. Both PTPD1 catalytic activity and its FERM domain are required for EGF-induced FAK autophosphorylation, ERK1/2 signaling, and cell migration.\",\n      \"method\": \"Co-immunoprecipitation, shRNA-mediated silencing, overexpression of catalytically dead mutant (C1108S) and FERM-deleted mutant (Δ1-325), cell scattering/migration assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP demonstrating complex, domain-mutant dissection, functional readouts in two orthogonal assays (phosphorylation, migration), single lab\",\n      \"pmids\": [\"18223254\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PTPD1 (PTPN21) is recruited to endocytic vesicles containing EGFR during EGF stimulation through interaction with the endosomal kinesin KIF16B, and this endosomal localization of PTPD1 is required for EGF receptor stability and downstream ERK signaling.\",\n      \"method\": \"Co-immunoprecipitation with KIF16B, siRNA silencing of PTPD1, receptor degradation assays, ERK signaling readouts\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — single lab, Co-IP with KIF16B and functional silencing experiments, single study\",\n      \"pmids\": [\"20923765\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PTPD1 (PTPN21) FERM domain mediates localization to the plasma membrane, where it forms pre-existing signaling complexes with EGFR. Transient co-localization at EGF stimulation sites promotes spatial propagation of EGFR phosphorylated species; interference with PTPD1 expression decreases peripheral EGFR phosphorylation.\",\n      \"method\": \"Live-cell imaging, FRAP, FERM-domain deletion/mutation, EGFR phosphorylation assays, siRNA knockdown\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — live imaging with functional domain dissection, multiple readouts, single lab\",\n      \"pmids\": [\"25062045\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Ptpn21 dephosphorylates Septin1 at Tyr246 in hematopoietic stem cells (HSCs). Loss of Ptpn21 elevates Septin1 phosphorylation, impairing cytoskeletal remodeling, decreasing cell stiffness, increasing deformability, and causing HSC egress from the bone marrow niche with decreased quiescence and reconstitution capacity.\",\n      \"method\": \"Ptpn21 knockout mouse model, atomic force microscopy for cell stiffness, phospho-specific detection of Septin1 Tyr246, cell egress and reconstitution assays\",\n      \"journal\": \"Cell stem cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with defined substrate (Septin1 pTyr246), biophysical measurements, and functional stem cell reconstitution assays in a rigorous study\",\n      \"pmids\": [\"30880025\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"PTPN21 dephosphorylates ErbB4, leading to upregulation of downstream ErbB4 signaling. Phosphatase-dead PTPN21 (C1108S) or kinase-dead ErbB4 (K751R) abolish this effect. PTPN21 activates Elk-1, which drives NRG3 expression via a novel Elk-1 binding motif upstream of the NRG3 initiation codon, promoting cortical neuronal survival and neuritic elongation.\",\n      \"method\": \"Biotinylated receptor tracking, immunoprecipitation, phosphatase-dead and kinase-dead mutant analysis, Elk-1 reporter assays, cortical neuron survival and neurite length measurements\",\n      \"journal\": \"The international journal of biochemistry & cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods including receptor tracking, IP, and mutant analysis in single lab\",\n      \"pmids\": [\"25681686\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PTPN21 directly dephosphorylates phospho-IKKβ at Ser177/181 in TNF-α-stimulated keratinocytes. This dephosphorylation stabilizes IκBα and inhibits NF-κB activity, thereby suppressing ICAM-1 expression. Catalytically inactive PTPN21 (C1108S) fails to inhibit ICAM-1 expression.\",\n      \"method\": \"Overexpression and C1108S phosphatase-dead mutant, Western blot for p-IKKβ, IκBα, and NF-κB targets, ICAM-1 expression assays\",\n      \"journal\": \"BMB reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct substrate dephosphorylation with mutant validation, single lab, single study\",\n      \"pmids\": [\"29065968\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"The Drosophila ortholog of PTPN21 (Pez) acts downstream of damage-induced H2O2 and operates via its FERM domain together with the SFK Src42A and damage receptor Draper to drive macrophage migration to wounds. This role is conserved in vertebrates: PTPN21 crispant zebrafish larvae show failure of leukocyte recruitment to wounds.\",\n      \"method\": \"Proteomics, live imaging, Drosophila genetics, CRISPR crispant zebrafish, epistasis analysis with H2O2 pathway\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis in Drosophila, live imaging, conservation validated in zebrafish crispants, multiple orthogonal methods\",\n      \"pmids\": [\"33296680\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"HPV18 E7 conserved region 3 (CR3) forms a 2:2 complex with the PTP domain of PTPN21 with a dissociation constant of ~5 nM. Unlike PTPN14, PTPN21 is not subjected to proteasomal degradation in HPV18-positive cells. Knockdown of PTPN21 retards migration/invasion of HeLa cells and HPV18 E7-expressing keratinocytes.\",\n      \"method\": \"Biochemical binding assays (Kd determination), complex stoichiometry analysis, proteasomal degradation assays, siRNA knockdown with migration/invasion assays\",\n      \"journal\": \"Molecules and cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — quantitative binding characterization with Kd, functional knockdown validation, single lab\",\n      \"pmids\": [\"33431714\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Crystal structures of individual PTPN21 FERM and PTP domains and their complex reveal that the FERM domain directly contacts the PTP domain, sterically blocking its active site and autoinhibiting the weakly active PTP. Disruption of FERM-PTP interaction enhances ERK activation. The HPV18 E7 oncoprotein binds the PTP domain at the same interface as the FERM domain, suggesting displacement of autoinhibition as E7's mechanism of action on PTPN21.\",\n      \"method\": \"X-ray crystallography of FERM, PTP, and FERM-PTP complex; biochemical phosphatase activity assays; mutagenesis of FERM-PTP interface; ERK activation assays\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structures combined with biochemical validation and mutagenesis in a single rigorous study\",\n      \"pmids\": [\"38416831\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"PTP-RL10 (PTPN21) encodes a cytoplasmic-type protein tyrosine phosphatase with an amino-terminal domain homologous to cytoskeletal proteins 4.1 and ezrin (FERM-like), and no membrane-spanning region, establishing its domain architecture as a non-receptor cytosolic PTP.\",\n      \"method\": \"PCR-based cloning, cDNA sequencing, Northern blotting of regenerating mouse liver\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — initial cloning and domain architecture determination replicated by subsequent studies confirming FERM-PTP architecture\",\n      \"pmids\": [\"7838537\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PTPN21 activates the ERK1/2 signaling pathway to upregulate CDK5 expression, protecting PC12 neuronal cells from oxygen-glucose deprivation-induced apoptosis. Inhibition of ERK1/2 with PD98059 or CDK5 siRNA abolishes the pro-survival effect of PTPN21 overexpression.\",\n      \"method\": \"siRNA knockdown and overexpression in PC12 cells, ERK1/2 inhibitor PD98059, caspase-3 activity assay, Western blot, cell viability assays\",\n      \"journal\": \"European journal of pharmacology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, no direct substrate identification, pathway placement by inhibitor only\",\n      \"pmids\": [\"28843827\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PTPN21 overexpression in ALL cells promotes proliferation and cell cycle progression under EGF stimulation via activation of Src tyrosine kinase and MAPK pathways; MAPK pathway inhibitors abolish this pro-proliferative effect.\",\n      \"method\": \"Lentiviral overexpression, Western blot for Src and MAPK pathway phosphorylation, MAPK inhibitor treatment, proliferation and cell cycle assays\",\n      \"journal\": \"Hematology (Amsterdam, Netherlands)\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, pathway placement only by inhibitor, no direct substrate identification\",\n      \"pmids\": [\"38785187\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PTPN21 inhibits chemotherapy-induced apoptosis in ALL cells by suppressing the GADD45A and JNK signaling pathways, thereby reversing G2/M cell cycle arrest. Restoration of GADD45A reverses the anti-apoptotic effect of PTPN21.\",\n      \"method\": \"PTPN21 knockdown/overexpression, GADD45A rescue experiments, JNK pathway analysis, apoptosis assays with vincristine and daunorubicin\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, pathway placement by rescue experiment without direct substrate identification\",\n      \"pmids\": [\"40305474\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PTPN21 is a FERM domain-containing non-receptor protein tyrosine phosphatase whose FERM domain mediates interaction with KIF1C kinesin to relieve its autoinhibition and activate cargo transport, localizes the enzyme to actin filaments, adhesion plaques, and the plasma membrane to potentiate Src-FAK-EGFR signaling and cell migration, and whose intramolecular FERM-PTP interaction autoinhibits its weak phosphatase activity; identified substrates include ErbB4, IKKβ, Septin1 (Tyr246), and FAK, placing PTPN21 at the intersection of cytoskeletal organization, intracellular transport activation, inflammatory signaling, and hematopoietic stem cell niche retention.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PTPN21 is a non-receptor cytosolic protein tyrosine phosphatase built from an N-terminal FERM domain and a C-terminal PTP domain, an architecture that places it at the intersection of cytoskeletal organization, intracellular transport, and receptor tyrosine kinase signaling [#10]. Its phosphatase activity is intrinsically weak and held in check by an intramolecular autoinhibitory interaction in which the FERM domain directly contacts and sterically occludes the PTP active site; disrupting this interface enhances ERK activation [#9]. The FERM domain is the principal targeting and effector module: it binds the tail of the kinesin-3 motor KIF1C to relieve its motor-domain autoinhibition, increasing microtubule landing rate and activating processive plus-end transport of dense core vesicles and integrins [#0], and it localizes PTPN21 to the plasma membrane and adhesion plaques where the enzyme assembles with actin, Src, and FAK to drive EGF-induced FAK autophosphorylation, ERK signaling, and cell migration in a manner requiring both catalytic activity and the FERM domain [#1, #3]. PTPN21 acts on defined substrates to control distinct outputs: it dephosphorylates Septin1 at Tyr246 to support cytoskeletal stiffness and retention of hematopoietic stem cells in the bone marrow niche [#4], dephosphorylates ErbB4 to potentiate downstream Elk-1/NRG3 signaling in cortical neurons [#5], and dephosphorylates IKK\\u03b2 at Ser177/181 to stabilize I\\u03baB\\u03b1 and suppress NF-\\u03baB-driven ICAM-1 expression [#6]. The FERM-dependent migratory function is conserved, with the Drosophila ortholog Pez acting with Src42A and the Draper receptor downstream of wound-induced H2O2 to drive macrophage recruitment, a role retained in zebrafish leukocyte recruitment [#7]. The HPV18 E7 oncoprotein binds the PTP domain at the same interface used by the FERM domain, displacing autoinhibition and engaging PTPN21 to promote cell migration and invasion [#8, #9].\"\n,\n  \"teleology\": [\n    {\n      \"year\": 1995,\n      \"claim\": \"Established the founding domain architecture, defining PTPN21 as a cytosolic non-receptor PTP carrying an N-terminal FERM-like (band 4.1/ezrin homology) region.\",\n      \"evidence\": \"PCR cloning, cDNA sequencing, and Northern blotting of regenerating mouse liver\",\n      \"pmids\": [\"7838537\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional role assigned to either domain\", \"No substrate identified\", \"No subcellular localization determined\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Showed PTPN21 is not a free-standing enzyme but a scaffolded one, assembling with actin, Src, and FAK at adhesion plaques where both its catalytic activity and FERM domain are required for EGF-driven FAK phosphorylation and migration.\",\n      \"evidence\": \"Reciprocal Co-IP, shRNA silencing, catalytic-dead (C1108S) and FERM-deleted mutant dissection, migration assays\",\n      \"pmids\": [\"18223254\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct substrate within the Src-FAK module not pinned down\", \"Single lab\", \"Mechanism of FERM-mediated complex assembly not resolved structurally\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Linked PTPN21 to receptor trafficking by placing it on EGFR-containing endosomes via the kinesin KIF16B, connecting its localization to EGFR stability and ERK output.\",\n      \"evidence\": \"Co-IP with KIF16B, siRNA silencing, receptor degradation and ERK readouts\",\n      \"pmids\": [\"20923765\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single Co-IP-based interaction without structural mapping\", \"Phosphatase substrate on the endosome not identified\", \"Single study\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Refined the membrane localization mechanism, showing the FERM domain targets PTPN21 to pre-existing EGFR signaling complexes at the plasma membrane to propagate peripheral EGFR phosphorylation.\",\n      \"evidence\": \"Live-cell imaging, FRAP, FERM-domain deletion/mutation, EGFR phosphorylation assays, siRNA knockdown\",\n      \"pmids\": [\"25062045\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct molecular contacts of FERM with the membrane/EGFR complex not defined\", \"Single lab\", \"Catalytic contribution at the membrane not separated from scaffolding\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identified ErbB4 as a direct substrate and connected dephosphorylation to a transcriptional program (Elk-1/NRG3) governing cortical neuronal survival and neurite outgrowth.\",\n      \"evidence\": \"Receptor tracking, IP, phosphatase-dead and kinase-dead mutants, Elk-1 reporter, neuron survival/neurite assays\",\n      \"pmids\": [\"25681686\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Phospho-site on ErbB4 not mapped\", \"Single lab\", \"In vivo relevance in brain not tested genetically\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Extended substrate repertoire into inflammatory signaling by showing PTPN21 dephosphorylates IKK\\u03b2 at Ser177/181 to suppress NF-\\u03baB and ICAM-1.\",\n      \"evidence\": \"Overexpression and C1108S mutant, Western blot for p-IKK\\u03b2/I\\u03baB\\u03b1/NF-\\u03baB targets, ICAM-1 assays in keratinocytes\",\n      \"pmids\": [\"29065968\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Note: IKK\\u03b2 substrate sites are Ser, atypical for a tyrosine phosphatase, unresolved here\", \"Single lab and study\", \"Direct in vitro dephosphorylation not shown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Established a high-confidence physiological substrate-phenotype axis: Ptpn21 dephosphorylates Septin1 Tyr246 to maintain HSC stiffness, quiescence, and niche retention.\",\n      \"evidence\": \"Ptpn21 knockout mice, atomic force microscopy, phospho-specific Septin1 Tyr246 detection, egress and reconstitution assays\",\n      \"pmids\": [\"30880025\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Septin1 is dephosphorylated directly versus indirectly not fully resolved\", \"Role of FERM/autoinhibition in this context untested\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Defined a non-catalytic transport-activating function: the FERM domain binds KIF1C to relieve motor autoinhibition and switch on processive cargo transport.\",\n      \"evidence\": \"In vitro reconstitution with purified KIF1C and PTPN21 FERM, landing-rate assays, integrin trafficking rescue, neuronal vesicle transport\",\n      \"pmids\": [\"31217419\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether full-length PTPN21 (with autoinhibition) engages KIF1C identically not addressed\", \"Coupling of transport activation to phosphatase activity unknown\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Demonstrated evolutionary conservation of a FERM-dependent migratory role, placing PTPN21/Pez downstream of wound H2O2 with Src and the Draper receptor to drive immune cell recruitment.\",\n      \"evidence\": \"Drosophila genetics/epistasis, proteomics, live imaging, CRISPR crispant zebrafish\",\n      \"pmids\": [\"33296680\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Catalytic substrate in this pathway not identified\", \"Human leukocyte relevance inferred from zebrafish\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Provided the structural basis for regulation, showing FERM-PTP intramolecular contact autoinhibits the weak phosphatase and that HPV18 E7 binds the PTP at the FERM interface to displace autoinhibition.\",\n      \"evidence\": \"X-ray crystallography of FERM, PTP, and complex; phosphatase assays; interface mutagenesis; ERK activation; Kd determination of E7 binding\",\n      \"pmids\": [\"38416831\", \"33431714\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How physiological FERM ligands (KIF1C, membrane) relieve autoinhibition not structurally shown\", \"Conformational dynamics in cells not visualized\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Associated PTPN21 with leukemia cell proliferation and chemoresistance through Src/MAPK and GADD45A/JNK pathways.\",\n      \"evidence\": \"Lentiviral overexpression/knockdown in ALL cells, pathway inhibitors, GADD45A rescue, proliferation/apoptosis assays\",\n      \"pmids\": [\"38785187\", \"40305474\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Pathway placement by inhibitor/rescue only, no direct substrate identified\", \"Single lab per study\", \"Causal direction of GADD45A/JNK regulation not mechanistically resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How physiological FERM-domain ligands relieve intramolecular autoinhibition to switch on phosphatase activity at specific subcellular sites, and how transport-activating versus catalytic functions are coordinated, remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structure of full-length PTPN21 bound to a physiological FERM ligand\", \"Unclear whether catalytic and KIF1C-activating activities operate simultaneously\", \"Substrate selection rules across tissues not defined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [4, 5, 6, 9]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [9, 10]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [1, 0]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [1, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [10]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [3, 1]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [1, 4]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 3, 5]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [6, 7]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"complexes\": [\n      \"PTPD1-actin-Src-FAK adhesion plaque complex\"\n    ],\n    \"partners\": [\n      \"KIF1C\",\n      \"Src\",\n      \"FAK\",\n      \"KIF16B\",\n      \"EGFR\",\n      \"ErbB4\",\n      \"IKKB\",\n      \"Septin1\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"faith_supported":6,"faith_total":6,"faith_pct":100.0}}