{"gene":"PTPN9","run_date":"2026-04-28T19:45:45","timeline":{"discoveries":[{"year":2010,"finding":"PTPN9 directly dephosphorylates ErbB2 and EGFR (but not ErbB3 or Shc) as demonstrated by substrate-trapping mutant (DA) co-immunoprecipitation and GST pulldown showing preferential association of phospho-ErbB2/EGFR with PTPN9-DA vs. WT, and by siRNA knockdown increasing ErbB2/EGFR phosphorylation. PTPN9 WT expression also specifically impairs EGF-induced STAT3 and STAT5 activation and inhibits soft-agar growth and invasion of breast cancer cells.","method":"Substrate-trapping mutant overexpression, co-immunoprecipitation, GST pulldown, siRNA knockdown, in vitro phosphorylation assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — substrate trapping + reciprocal Co-IP + GST pulldown + functional KD/OE with defined readouts, single lab but multiple orthogonal methods","pmids":["20335174"],"is_preprint":false},{"year":2012,"finding":"PTPN9 (PTP-MEG2) directly interacts with STAT3 and mediates its dephosphorylation in the cytoplasm. Overexpression of PTP-MEG2 decreased tyrosine phosphorylation of STAT3, suppressed STAT3 transcriptional activity, and reduced tumor growth in vitro and in vivo; depletion increased STAT3 phosphorylation.","method":"Immunoprecipitation, overexpression and siRNA knockdown, in vitro dephosphorylation assay, xenograft models","journal":"Breast cancer research : BCR","confidence":"High","confidence_rationale":"Tier 1-2 — direct interaction by Co-IP, biochemical dephosphorylation assay, and functional KD/OE with defined cellular and in vivo readouts","pmids":["22394684"],"is_preprint":false},{"year":2012,"finding":"PTPN9 (PTP-MEG2) dephosphorylates VEGFR2 at Tyr1175 in endothelial cells, as shown by substrate-trapping DA mutant preferentially co-immunoprecipitating with VEGFR2 after VEGF stimulation. PTP-MEG2 DA also associates with JAK1 (but not JAK2 or Tyk2) and regulates JAK1 phosphorylation. Overexpression of WT PTP-MEG2 inhibits VEGF-induced VEGFR2 phosphorylation and IL-6 production.","method":"Substrate-trapping mutant co-immunoprecipitation, overexpression and siRNA knockdown","journal":"American journal of physiology. Cell physiology","confidence":"High","confidence_rationale":"Tier 1-2 — substrate trapping + reciprocal Co-IP + functional overexpression/KD with defined signaling readout","pmids":["22763125"],"is_preprint":false},{"year":2002,"finding":"PTPN9 (PTP-MEG2) expression on secretory vesicles causes striking homotypic enlargement/fusion of secretory vesicles in mast cells and Jurkat T cells. This requires the catalytic activity of PTP-MEG2 (effect reversed by pervanadate), reduces IL-2 secretion from stimulated Jurkat cells, and fused vesicles retain secretory vesicle markers (carboxypeptidase E, chromogranin C, IL-2).","method":"Overexpression with fluorescence microscopy/immunofluorescence, secretion assay, pharmacological inhibition of phosphatase activity","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — direct localization with functional consequence, catalytic-activity dependence demonstrated, replicated across two cell types","pmids":["11971009"],"is_preprint":false},{"year":2003,"finding":"The N-terminal Sec14p homology domain of PTP-MEG2 binds phosphatidylinositol-3,4,5-trisphosphate (PtdIns(3,4,5)P3) in vitro and colocalizes with this lipid on secretory vesicle membranes. Point mutations preventing PtdIns(3,4,5)P3 binding abolish the ability of PTP-MEG2 to induce homotypic secretory vesicle fusion. Inhibition of cellular PtdIns(3,4,5)P3 synthesis rapidly reverses PTP-MEG2 effects on secretory vesicles.","method":"Lipid binding assay, site-directed mutagenesis, fluorescence colocalization, pharmacological PI3K inhibition","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro lipid binding + mutagenesis + functional vesicle fusion assay, multiple orthogonal approaches","pmids":["14662869"],"is_preprint":false},{"year":2003,"finding":"PTP-MEG2 specifically binds phosphatidylserine (among >20 lipid compounds tested) through its N-terminal Sec14 domain, as shown by lipid-membrane overlay and liposome binding assays. In intact cells, the Sec14 domain is responsible for perinuclear localization of PTP-MEG2, and loading of phosphatidylserine into cell membranes causes translocation of PTP-MEG2 to the plasma membrane.","method":"Lipid-membrane overlay assay, liposome binding assay, immunofluorescence/subcellular fractionation, phosphatidylserine loading experiment","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro lipid binding with multiple assay formats + domain mapping + direct localization consequence","pmids":["12702726"],"is_preprint":false},{"year":2005,"finding":"MEG2 knockout mice exhibit late embryonic lethality, hemorrhages, neural tube defects, and abnormal bone development. T lymphocytes and platelets from Meg2-/- hematopoietic reconstituted mice show profound activation defects attributable to impaired IL-2 secretion; ultrastructural analysis reveals near-complete absence of mature secretory vesicles in lymphocytes, confirming MEG2 role in secretory vesicle genesis and function.","method":"Knockout mouse generation, hematopoietic reconstitution, functional lymphocyte/platelet activation assays, electron microscopy, secretion assays","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 — clean KO with defined cellular phenotype, ultrastructural validation, in vivo reconstitution","pmids":["16330817"],"is_preprint":false},{"year":2006,"finding":"PTP-MEG2 antagonizes hepatic insulin signaling by inhibiting insulin-induced phosphorylation of the insulin receptor, thereby impairing nuclear exclusion of the gluconeogenic transcription factor FOXO1. Adenoviral-mediated depletion of PTP-MEG2 in livers of db/db diabetic mice results in insulin sensitization and normalization of hyperglycemia.","method":"Genome-scale functional screen, ectopic expression, RNAi knockdown, adenoviral liver-targeted depletion in db/db mice, quantitative image analysis of FOXO1 localization, blood glucose measurement","journal":"Cell metabolism","confidence":"High","confidence_rationale":"Tier 2 — screen + functional validation in vitro and in vivo, multiple orthogonal methods","pmids":["16679294"],"is_preprint":false},{"year":2001,"finding":"In human neutrophils, MEG2 is predominantly cytosolic with components in secondary/tertiary granules and secretory vesicles, and associates at an early stage with nascent phagosomes. Cysteine 515 is essential for catalytic activity. The noncatalytic N-terminal domain negatively regulates the C-terminal phosphatase domain. MEG2 activity is enhanced by polyphosphoinositides (PI 4,5-bisphosphate > PI 3,4,5-trisphosphate > PI 4-phosphate) and is inhibited by opsonized zymosan or PMA stimulation.","method":"Immunofluorescence, cell fractionation, immunoprecipitation, in vitro phosphatase assay, GST-fusion protein mutagenesis (C515), lipid activation assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — active-site mutagenesis + in vitro enzymatic assay + direct localization + domain function characterization","pmids":["11711529"],"is_preprint":false},{"year":2002,"finding":"Full-length PTP-MEG2 exhibits lower Vmax and higher Km compared to the truncated catalytic domain alone, indicating the N-terminal lipid-binding domain has an inhibitory role on catalytic activity. Both forms show classical Michaelis-Menten kinetics with phosphotyrosine and pNPP substrates.","method":"In vitro phosphatase kinetics with purified recombinant full-length and truncated PTP-MEG2","journal":"Journal of cellular biochemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstituted enzymatic characterization comparing domain constructs","pmids":["12112018"],"is_preprint":false},{"year":2007,"finding":"The N-terminal Sec14p homology domain (residues 1-261) of PTP-MEG2 is necessary and sufficient for secretory vesicle targeting. Yeast two-hybrid screening identified vesicle trafficking proteins TIP47 and Arfaptin2 as direct interactors of this domain; overexpression of TIP47 or Arfaptin2 alters PTP-MEG2 localization, and elimination of TIP47 results in loss of PTP-MEG2 function.","method":"Yeast two-hybrid, deletion mutant localization, overexpression of interactors, TIP47 knockdown functional assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — Y2H + deletion mapping + functional consequence of interactor manipulation","pmids":["17387180"],"is_preprint":false},{"year":2012,"finding":"Crystal structures of PTP-MEG2 complexed with selective inhibitors reveal that potent, selective inhibition is achieved by engaging both the active site and unique peripheral binding pockets. The structures provide direct evidence for the molecular basis of PTP-MEG2 substrate selectivity and inform inhibitor design.","method":"X-ray crystallography, in vitro phosphatase inhibition assay, cellular insulin signaling assay, diet-induced obese mouse model","journal":"Journal of the American Chemical Society","confidence":"High","confidence_rationale":"Tier 1 — crystal structure + in vitro + in vivo validation","pmids":["23075115"],"is_preprint":false},{"year":2013,"finding":"miR-24 directly targets PTPN9 (and PTPRF), repressing their expression and thereby increasing EGFR phosphorylation; ectopic expression of PTPN9 decreased pEGFR levels, cell invasion, migration, and tumor metastasis in breast cancer models.","method":"miRNA target validation (luciferase assay), overexpression of PTPN9 with functional readouts (invasion, migration, pEGFR levels), in vivo mouse tumor models","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 — direct target validation + functional rescue experiments in vitro and in vivo","pmids":["23418360"],"is_preprint":false},{"year":2014,"finding":"Ptpn9a (zebrafish ortholog of human PTPN9) is required for erythroid cell maturation. Mechanistically, depletion of ptpn9 increases phosphorylated STAT3, which entraps transcription factors GATA1 and ZBP-89 in an inhibitory complex, preventing them from regulating erythroid gene expression. Dominant-negative PTPN9 (C515S) and siRNA against human PTPN9 similarly inhibit erythroid differentiation in K562 cells.","method":"Morpholino knockdown in zebrafish, dominant-negative overexpression, siRNA in K562 cells, immunoprecipitation to detect STAT3-GATA1-ZBP-89 complex","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 — in vivo and in vitro knockdown with defined molecular mechanism, epistasis shown by complex identification","pmids":["24727614"],"is_preprint":false},{"year":2016,"finding":"PTP-MEG2 identifies TrkA (neurotrophin receptor) as both a novel vesicle cargo requiring PTP-MEG2 for surface transport and a substrate: PTP-MEG2 dephosphorylates TrkA at Tyr-490 and Tyr-674/Tyr-675. Overexpression of PTP-MEG2 downregulates NGF/TrkA signaling and blocks neurite outgrowth and differentiation in PC12 cells and cortical neurons.","method":"Co-immunoprecipitation, substrate-trapping mutant, in vitro dephosphorylation, cell surface trafficking assay, neurite outgrowth assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — substrate identification by trapping + biochemical dephosphorylation + functional phenotype","pmids":["27655914"],"is_preprint":false},{"year":2019,"finding":"PTPN9 negatively regulates STAT3 activation and nuclear translocation in colorectal cancer cells. Overexpression of PTPN9 induces apoptosis (via caspase-3/9) and inhibits colony formation; knockdown has opposite effects. The effects of PTPN9 knockdown on apoptosis are attenuated by Stat3 pathway inhibition, placing PTPN9 upstream of STAT3.","method":"Overexpression and siRNA knockdown, Western blot for pSTAT3/nuclear fractionation, caspase activity assay, colony formation assay, pharmacological STAT3 inhibitor epistasis","journal":"Cancer management and research","confidence":"Medium","confidence_rationale":"Tier 2 — KD/OE with epistasis experiment, but single lab","pmids":["30804683"],"is_preprint":false},{"year":2020,"finding":"PTPN9 dephosphorylates the Q-SNARE VTI1B, promoting homotypic fusion of ATG16L1+ vesicles and early autophagosome formation. The nonphosphorylatable VTI1B mutant (but not the phosphomimetic) enhances SNARE complex assembly and autophagic flux. Depletion of PTPN9 and its Drosophila homolog Ptpmeg2 impairs autophagosome formation and autophagic flux.","method":"siRNA/RNAi depletion, substrate identification, phospho-mutant analysis of VTI1B, SNARE complex co-immunoprecipitation, autophagy flux assay, Drosophila genetic validation","journal":"Autophagy","confidence":"High","confidence_rationale":"Tier 1-2 — substrate identification + phospho-mutant rescue + SNARE complex biochemistry + cross-species genetic validation","pmids":["33112705"],"is_preprint":false},{"year":2021,"finding":"PTP-MEG2 controls multiple steps of catecholamine secretion: (1) dephosphorylation of NSF-pY83 promotes vesicle fusion (key residues governing NSF interaction defined by crystallography and mutagenesis); (2) PTP-MEG2 controls fusion pore opening and extension via NSF-independent dephosphorylation of DYNAMIN2-pY125 and MUNC18-1-pY145, through a structurally distinct binding interface.","method":"Biochemical assays, X-ray crystallography, site-directed mutagenesis, electrochemical catecholamine measurement, bioinformatics substrate screening","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 1 — crystal structure + mutagenesis + biochemical substrate identification + electrochemical functional readout","pmids":["33764618"],"is_preprint":false},{"year":2003,"finding":"PTP-MEG2 is elevated in the membrane fraction of polycythemia vera (PV) erythroid progenitor cells. Expression of dominant-negative forms of PTP-MEG2 suppresses in vitro growth and expansion of both normal and PV erythroid colony-forming cells, establishing a role for PTP-MEG2 in erythroid development.","method":"Cell fractionation, immunoblotting, dominant-negative mutant overexpression, erythroid colony formation assay","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 — dominant-negative with defined functional readout, but single lab","pmids":["12920026"],"is_preprint":false},{"year":2023,"finding":"PTPN9 interacts with FGFR2 via its Sec14p domain through ACAP1 mediation and dephosphorylates FGFR2 at pY656/657. Key interaction residues include the 'YRETRRKE' motif of the Sec14p domain and Y471 of PTPN9, as well as the PH and Arf-GAP domains of ACAP1. The FGFR2 I654V substitution decreases PTPN9-FGFR2 interaction.","method":"Phosphatase activity assay, structural modeling of PTPN9-FGFR2 complex, co-immunoprecipitation, mutagenesis, patient-derived xenograft models","journal":"Hepatology","confidence":"High","confidence_rationale":"Tier 1-2 — substrate identification + phosphatase activity assay + structural modeling + mutagenesis + in vivo PDX validation","pmids":["37505213"],"is_preprint":false},{"year":2025,"finding":"PTPN9 dephosphorylates IGF1R preferentially at Y1166 (and Y1165/1166). Crystal structure analysis identified Tyr333 and Asp335 as key PTPN9 residues interacting with IGF1R; mutation of these residues restores IGF1R signaling and abolishes PTPN9's tumor-suppressive effect. PTPN9 expression is inversely correlated with IGF1R Y1165/1166 phosphorylation in clinical tissues.","method":"IP-mass spectrometry substrate identification, X-ray crystallography, active-site mutagenesis, orthotopic mouse models, biochemical dephosphorylation assay","journal":"Journal of experimental & clinical cancer research","confidence":"High","confidence_rationale":"Tier 1 — crystal structure + mutagenesis + IP-MS + in vivo validation","pmids":["41275311"],"is_preprint":false},{"year":2024,"finding":"MEG2 (PTPN9) and PKCε competitively bind to STAT3, with PKCε displaying stronger binding. STAT3 Ser727 phosphorylation increases STAT3 interaction with both PKCε and MEG2. ERK1/2 activation facilitates STAT3 interaction with MEG2, leading to dephosphorylation of STAT3 at Tyr705. MEG2 overexpression inhibits IL-6 promoter activity in the presence of STAT3 and LPS, opposing the effect of PKCε.","method":"ELISA and immunoprecipitation for protein-protein interaction, Western blot, dual luciferase reporter assay, in vivo hyperalgesia model (FCA/LPS)","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2-3 — Co-IP interaction data + reporter assay + in vivo model, but competitive binding mechanism needs further structural validation","pmids":["38656553"],"is_preprint":false},{"year":2018,"finding":"Heterozygous loss of Meg2 (Ptpn9) in mice causes progressive, age-dependent intraocular pressure elevation and glaucomatous neurodegeneration with retinal ganglion cell loss, optic nerve degeneration, reactive gliosis, and complement activation. IOP lowering with latanoprost prevents RGC loss, establishing the IOP-dependent mechanism.","method":"Meg2 heterozygous knockout mice, IOP measurement, ultrastructural analysis, immunohistochemistry, electroretinography, pharmacological rescue with latanoprost","journal":"Molecular neurobiology","confidence":"Medium","confidence_rationale":"Tier 2 — clean HET KO with defined in vivo phenotype and pharmacological rescue, but molecular substrate not identified","pmids":["30315478"],"is_preprint":false}],"current_model":"PTPN9 (PTP-MEG2) is a cytoplasmic protein tyrosine phosphatase with an N-terminal Sec14p/lipid-binding domain that targets it to secretory vesicle membranes via phosphatidylserine and PtdIns(3,4,5)P3 binding and interactions with trafficking proteins TIP47 and Arfaptin2; on these vesicles it promotes homotypic vesicle fusion by dephosphorylating NSF (pY83), and controls exocytotic fusion pore opening by dephosphorylating DYNAMIN2 (pY125) and MUNC18-1 (pY145); it also dephosphorylates receptor tyrosine kinases including EGFR, ErbB2, VEGFR2, FGFR2 (pY656/657), IGF1R (pY1166), and TrkA, and the transcription factor STAT3 (pY705), acting as a broad negative regulator of growth factor and cytokine signaling relevant to erythropoiesis, insulin sensitization, angiogenesis, and tumor suppression, while additionally dephosphorylating VTI1B to promote ATG16L1 vesicle fusion and autophagosome biogenesis."},"narrative":{"teleology":[{"year":2001,"claim":"Establishing the enzymology and localization of PTPN9 in primary cells resolved how the N-terminal domain auto-inhibits catalytic activity and how polyphosphoinositides activate the phosphatase, providing the first framework for its regulation at membranes.","evidence":"Subcellular fractionation, active-site mutagenesis (C515), and lipid activation assays in human neutrophils","pmids":["11711529"],"confidence":"High","gaps":["Identity of endogenous substrates on secretory vesicles unknown","Structural basis of auto-inhibition not determined"]},{"year":2002,"claim":"Demonstrating that PTPN9 catalytic activity drives homotypic secretory vesicle fusion in immune cells established its first cellular function — regulation of the secretory pathway rather than classical receptor signaling.","evidence":"Overexpression with fluorescence microscopy in mast cells and Jurkat T cells; pervanadate reversal; IL-2 secretion assay","pmids":["11971009","12112018"],"confidence":"High","gaps":["Vesicle fusion substrates not identified","Mechanism linking phosphatase activity to membrane fusion unclear"]},{"year":2003,"claim":"Identification of phosphatidylserine and PtdIns(3,4,5)P3 as ligands of the Sec14p domain explained how PTPN9 is targeted to secretory vesicle membranes, and mutagenesis showed lipid binding is required for vesicle fusion activity.","evidence":"Lipid-overlay and liposome binding assays, point mutagenesis, PI3K inhibitor treatment, PS loading experiments","pmids":["14662869","12702726"],"confidence":"High","gaps":["Relative contributions of PS versus PIP3 binding in vivo not resolved","Whether lipid binding relieves auto-inhibition not tested"]},{"year":2003,"claim":"Elevated PTPN9 in polycythemia vera erythroid progenitors and dominant-negative suppression of erythroid colony growth first linked the phosphatase to erythropoiesis.","evidence":"Cell fractionation and dominant-negative overexpression in primary human erythroid progenitors","pmids":["12920026"],"confidence":"Medium","gaps":["Substrate in erythroid progenitors unidentified","Mechanism connecting PTPN9 to erythroid proliferation unclear","Single-lab observation"]},{"year":2005,"claim":"Meg2 knockout mice revealed that PTPN9 is essential for embryonic viability, secretory vesicle biogenesis in lymphocytes, and platelet function, elevating its role from an in vitro vesicle regulator to a required developmental factor.","evidence":"Gene-targeted knockout mice, hematopoietic reconstitution, electron microscopy of lymphocyte vesicles, platelet/T-cell activation assays","pmids":["16330817"],"confidence":"High","gaps":["Specific substrates responsible for vesicle biogenesis defect unknown","Cause of embryonic lethality (hemorrhage vs. neural tube defect vs. bone) not delineated"]},{"year":2006,"claim":"A genome-scale screen and in vivo validation identified PTPN9 as a negative regulator of hepatic insulin receptor signaling, showing that liver-targeted depletion normalizes hyperglycemia in diabetic mice — extending PTPN9 function to metabolic regulation.","evidence":"Functional genomic screen, adenoviral hepatic depletion in db/db mice, FOXO1 localization, blood glucose measurement","pmids":["16679294"],"confidence":"High","gaps":["Whether PTPN9 directly dephosphorylates the insulin receptor (versus an intermediate) not biochemically confirmed","Tissue specificity of metabolic role beyond liver not explored"]},{"year":2007,"claim":"Discovery of TIP47 and Arfaptin2 as direct binding partners of the Sec14p domain provided a protein-based targeting mechanism complementing lipid-mediated vesicle recruitment.","evidence":"Yeast two-hybrid, deletion-mutant localization, TIP47 knockdown functional assay","pmids":["17387180"],"confidence":"High","gaps":["How TIP47/Arfaptin2 coordinate with lipid binding is unknown","Whether these interactions are regulated remains untested"]},{"year":2010,"claim":"Substrate-trapping and knockdown experiments identified ErbB2 and EGFR as direct PTPN9 substrates, establishing the enzyme as a negative regulator of receptor tyrosine kinase signaling with tumor-suppressive properties in breast cancer.","evidence":"DA-mutant co-immunoprecipitation, GST pulldown, siRNA knockdown, soft-agar and invasion assays","pmids":["20335174"],"confidence":"High","gaps":["Specific phosphosites on ErbB2/EGFR targeted by PTPN9 not mapped","Whether vesicle-localized or cytoplasmic pool mediates RTK dephosphorylation unclear"]},{"year":2012,"claim":"Concurrent identification of STAT3 and VEGFR2 as direct substrates, together with crystal structures of the catalytic domain with selective inhibitors, broadened the substrate repertoire and provided a structural framework for drug design.","evidence":"Co-IP and in vitro dephosphorylation for STAT3/VEGFR2; X-ray crystallography of inhibitor-bound PTP-MEG2; xenograft and diet-induced obesity mouse models","pmids":["22394684","22763125","23075115"],"confidence":"High","gaps":["How PTPN9 selects among multiple RTK and non-RTK substrates in a single cell is unknown","Full-length structure including Sec14p domain not solved"]},{"year":2014,"claim":"Zebrafish and human cell studies demonstrated that PTPN9-mediated STAT3 dephosphorylation is required for erythroid maturation by preventing an inhibitory STAT3–GATA1–ZBP-89 complex, providing the molecular mechanism underlying its erythropoietic role.","evidence":"Morpholino knockdown in zebrafish, dominant-negative C515S and siRNA in K562 cells, co-IP of STAT3–GATA1–ZBP-89 complex","pmids":["24727614"],"confidence":"High","gaps":["Whether this mechanism operates in mammalian definitive erythropoiesis in vivo not confirmed","Regulation of PTPN9 expression during erythroid differentiation not characterized"]},{"year":2016,"claim":"Identification of TrkA as both a vesicle cargo requiring PTPN9 for surface transport and a dephosphorylation substrate linked the vesicle-trafficking and signaling functions of PTPN9 in neuronal differentiation.","evidence":"Substrate trapping, in vitro dephosphorylation, surface trafficking assay, neurite outgrowth in PC12 and cortical neurons","pmids":["27655914"],"confidence":"High","gaps":["Whether PTPN9 controls trafficking of other RTK cargoes is untested","In vivo neuronal phenotype of Ptpn9 loss not characterized"]},{"year":2018,"claim":"Heterozygous Meg2 loss in mice caused progressive glaucoma with IOP-dependent retinal ganglion cell degeneration, revealing an unexpected in vivo role in intraocular pressure homeostasis.","evidence":"Meg2 heterozygous KO mice, IOP measurement, latanoprost pharmacological rescue, optic nerve histology","pmids":["30315478"],"confidence":"Medium","gaps":["Molecular substrate mediating IOP regulation not identified","Relevance to human glaucoma genetics not established","Single-lab observation"]},{"year":2020,"claim":"Identification of VTI1B as a PTPN9 substrate that regulates SNARE complex assembly on ATG16L1-positive vesicles extended the phosphatase's membrane fusion role to autophagosome biogenesis, with cross-species validation in Drosophila.","evidence":"siRNA/RNAi depletion, VTI1B phospho-mutant analysis, SNARE complex co-IP, autophagy flux assays, Drosophila Ptpmeg2 RNAi","pmids":["33112705"],"confidence":"High","gaps":["Whether PTPN9-VTI1B axis operates in selective autophagy pathways is unknown","Upstream kinase phosphorylating VTI1B not identified"]},{"year":2021,"claim":"Crystallographic and electrochemical studies revealed that PTPN9 controls catecholamine secretion through structurally separable substrate interfaces: NSF-pY83 dephosphorylation drives vesicle fusion, while DYNAMIN2-pY125 and MUNC18-1-pY145 dephosphorylation controls fusion pore dynamics.","evidence":"X-ray crystallography of PTPN9–substrate complexes, mutagenesis, electrochemical single-vesicle catecholamine release measurement","pmids":["33764618"],"confidence":"High","gaps":["Whether these substrate interfaces can be independently targeted pharmacologically is untested","Physiological kinases counteracting PTPN9 at NSF/DYNAMIN2/MUNC18-1 not identified"]},{"year":2023,"claim":"ACAP1 was identified as a bridging adaptor mediating PTPN9–FGFR2 interaction via the Sec14p domain, with dephosphorylation at FGFR2 pY656/657; the cancer-associated FGFR2 I654V mutation disrupts this interaction, providing a disease-relevant substrate selectivity mechanism.","evidence":"Co-IP, mutagenesis, phosphatase assays, structural modeling, patient-derived xenograft validation","pmids":["37505213"],"confidence":"High","gaps":["Whether ACAP1-mediated recruitment generalizes to other RTK substrates is unknown","Full structural model of PTPN9–ACAP1–FGFR2 ternary complex awaits experimental determination"]},{"year":2025,"claim":"Crystal structure-guided identification of IGF1R pY1166 as a direct substrate, with Tyr333 and Asp335 as key PTPN9 contact residues, provided structural precision for substrate recognition and confirmed tumor-suppressive activity through IGF1R axis inhibition.","evidence":"IP-mass spectrometry, X-ray crystallography of PTPN9–IGF1R interface, active-site mutagenesis, orthotopic mouse models, clinical tissue correlation","pmids":["41275311"],"confidence":"High","gaps":["How PTPN9 prioritizes IGF1R versus other RTK substrates in cells co-expressing multiple receptors is unclear"]},{"year":null,"claim":"A full-length structure of PTPN9 revealing how the Sec14p domain auto-inhibits the catalytic domain and how lipid/protein cofactors relieve inhibition remains unresolved, as does a unified model for how a single phosphatase coordinates its diverse vesicle-fusion and RTK-regulatory functions within the same cell.","evidence":"","pmids":[],"confidence":"High","gaps":["Full-length PTPN9 structure not solved","Upstream regulation of PTPN9 activity (post-translational modifications, transcriptional control beyond miR-24) poorly defined","Kinases counteracting PTPN9 at most substrate sites not identified"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,1,2,3,8,9,14,16,17,19,20]}],"localization":[{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[3,4,5,8,10]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[1,8]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,2,7,12,14,19,20]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[16]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[3,4,10,17]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,2,17,20]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[6]}],"complexes":[],"partners":["EGFR","ERBB2","STAT3","NSF","DNM2","STXBP1","VTI1B","TIP47"],"other_free_text":[]},"mechanistic_narrative":"PTPN9 (PTP-MEG2) is a non-receptor protein tyrosine phosphatase that couples lipid-directed membrane targeting to the regulation of vesicle trafficking, exocytosis, and receptor tyrosine kinase signaling. Its N-terminal Sec14p homology domain binds phosphatidylserine and PtdIns(3,4,5)P3 to localize the enzyme to secretory vesicle membranes, where it promotes homotypic vesicle fusion by dephosphorylating NSF (pY83) and controls fusion pore dynamics by dephosphorylating DYNAMIN2 (pY125) and MUNC18-1 (pY145); it also dephosphorylates the Q-SNARE VTI1B to drive ATG16L1-positive vesicle fusion during autophagosome biogenesis [PMID:17387180, PMID:33764618, PMID:33112705]. PTPN9 functions as a broad negative regulator of growth factor and cytokine signaling by directly dephosphorylating EGFR, ErbB2, VEGFR2, FGFR2 (pY656/657), IGF1R (pY1166), TrkA, and STAT3 (pY705), thereby suppressing proliferative, angiogenic, and inflammatory pathways [PMID:20335174, PMID:22394684, PMID:22763125, PMID:37505213, PMID:41275311, PMID:27655914]. Knockout studies establish essential roles in secretory vesicle biogenesis in lymphocytes, erythroid maturation via STAT3–GATA1 axis regulation, embryonic development, and intraocular pressure homeostasis [PMID:16330817, PMID:24727614, PMID:30315478]."},"prefetch_data":{"uniprot":{"accession":"P43378","full_name":"Tyrosine-protein phosphatase non-receptor type 9","aliases":["Protein-tyrosine phosphatase MEG2","PTPase MEG2"],"length_aa":593,"mass_kda":68.0,"function":"Protein-tyrosine phosphatase that could participate in the transfer of hydrophobic ligands or in functions of the Golgi apparatus","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/P43378/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PTPN9","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PTPN9","total_profiled":1310},"omim":[{"mim_id":"601504","title":"SEC14-LIKE LIPID-BINDING PROTEIN 1; SEC14L1","url":"https://www.omim.org/entry/601504"},{"mim_id":"600768","title":"PROTEIN-TYROSINE PHOSPHATASE, NONRECEPTOR-TYPE, 9; PTPN9","url":"https://www.omim.org/entry/600768"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Vesicles","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in 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EGFR (but not ErbB3 or Shc) as demonstrated by substrate-trapping mutant (DA) co-immunoprecipitation and GST pulldown showing preferential association of phospho-ErbB2/EGFR with PTPN9-DA vs. WT, and by siRNA knockdown increasing ErbB2/EGFR phosphorylation. PTPN9 WT expression also specifically impairs EGF-induced STAT3 and STAT5 activation and inhibits soft-agar growth and invasion of breast cancer cells.\",\n      \"method\": \"Substrate-trapping mutant overexpression, co-immunoprecipitation, GST pulldown, siRNA knockdown, in vitro phosphorylation assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — substrate trapping + reciprocal Co-IP + GST pulldown + functional KD/OE with defined readouts, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"20335174\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"PTPN9 (PTP-MEG2) directly interacts with STAT3 and mediates its dephosphorylation in the cytoplasm. Overexpression of PTP-MEG2 decreased tyrosine phosphorylation of STAT3, suppressed STAT3 transcriptional activity, and reduced tumor growth in vitro and in vivo; depletion increased STAT3 phosphorylation.\",\n      \"method\": \"Immunoprecipitation, overexpression and siRNA knockdown, in vitro dephosphorylation assay, xenograft models\",\n      \"journal\": \"Breast cancer research : BCR\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct interaction by Co-IP, biochemical dephosphorylation assay, and functional KD/OE with defined cellular and in vivo readouts\",\n      \"pmids\": [\"22394684\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"PTPN9 (PTP-MEG2) dephosphorylates VEGFR2 at Tyr1175 in endothelial cells, as shown by substrate-trapping DA mutant preferentially co-immunoprecipitating with VEGFR2 after VEGF stimulation. PTP-MEG2 DA also associates with JAK1 (but not JAK2 or Tyk2) and regulates JAK1 phosphorylation. Overexpression of WT PTP-MEG2 inhibits VEGF-induced VEGFR2 phosphorylation and IL-6 production.\",\n      \"method\": \"Substrate-trapping mutant co-immunoprecipitation, overexpression and siRNA knockdown\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — substrate trapping + reciprocal Co-IP + functional overexpression/KD with defined signaling readout\",\n      \"pmids\": [\"22763125\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"PTPN9 (PTP-MEG2) expression on secretory vesicles causes striking homotypic enlargement/fusion of secretory vesicles in mast cells and Jurkat T cells. This requires the catalytic activity of PTP-MEG2 (effect reversed by pervanadate), reduces IL-2 secretion from stimulated Jurkat cells, and fused vesicles retain secretory vesicle markers (carboxypeptidase E, chromogranin C, IL-2).\",\n      \"method\": \"Overexpression with fluorescence microscopy/immunofluorescence, secretion assay, pharmacological inhibition of phosphatase activity\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct localization with functional consequence, catalytic-activity dependence demonstrated, replicated across two cell types\",\n      \"pmids\": [\"11971009\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The N-terminal Sec14p homology domain of PTP-MEG2 binds phosphatidylinositol-3,4,5-trisphosphate (PtdIns(3,4,5)P3) in vitro and colocalizes with this lipid on secretory vesicle membranes. Point mutations preventing PtdIns(3,4,5)P3 binding abolish the ability of PTP-MEG2 to induce homotypic secretory vesicle fusion. Inhibition of cellular PtdIns(3,4,5)P3 synthesis rapidly reverses PTP-MEG2 effects on secretory vesicles.\",\n      \"method\": \"Lipid binding assay, site-directed mutagenesis, fluorescence colocalization, pharmacological PI3K inhibition\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro lipid binding + mutagenesis + functional vesicle fusion assay, multiple orthogonal approaches\",\n      \"pmids\": [\"14662869\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"PTP-MEG2 specifically binds phosphatidylserine (among >20 lipid compounds tested) through its N-terminal Sec14 domain, as shown by lipid-membrane overlay and liposome binding assays. In intact cells, the Sec14 domain is responsible for perinuclear localization of PTP-MEG2, and loading of phosphatidylserine into cell membranes causes translocation of PTP-MEG2 to the plasma membrane.\",\n      \"method\": \"Lipid-membrane overlay assay, liposome binding assay, immunofluorescence/subcellular fractionation, phosphatidylserine loading experiment\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro lipid binding with multiple assay formats + domain mapping + direct localization consequence\",\n      \"pmids\": [\"12702726\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"MEG2 knockout mice exhibit late embryonic lethality, hemorrhages, neural tube defects, and abnormal bone development. T lymphocytes and platelets from Meg2-/- hematopoietic reconstituted mice show profound activation defects attributable to impaired IL-2 secretion; ultrastructural analysis reveals near-complete absence of mature secretory vesicles in lymphocytes, confirming MEG2 role in secretory vesicle genesis and function.\",\n      \"method\": \"Knockout mouse generation, hematopoietic reconstitution, functional lymphocyte/platelet activation assays, electron microscopy, secretion assays\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined cellular phenotype, ultrastructural validation, in vivo reconstitution\",\n      \"pmids\": [\"16330817\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"PTP-MEG2 antagonizes hepatic insulin signaling by inhibiting insulin-induced phosphorylation of the insulin receptor, thereby impairing nuclear exclusion of the gluconeogenic transcription factor FOXO1. Adenoviral-mediated depletion of PTP-MEG2 in livers of db/db diabetic mice results in insulin sensitization and normalization of hyperglycemia.\",\n      \"method\": \"Genome-scale functional screen, ectopic expression, RNAi knockdown, adenoviral liver-targeted depletion in db/db mice, quantitative image analysis of FOXO1 localization, blood glucose measurement\",\n      \"journal\": \"Cell metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — screen + functional validation in vitro and in vivo, multiple orthogonal methods\",\n      \"pmids\": [\"16679294\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"In human neutrophils, MEG2 is predominantly cytosolic with components in secondary/tertiary granules and secretory vesicles, and associates at an early stage with nascent phagosomes. Cysteine 515 is essential for catalytic activity. The noncatalytic N-terminal domain negatively regulates the C-terminal phosphatase domain. MEG2 activity is enhanced by polyphosphoinositides (PI 4,5-bisphosphate > PI 3,4,5-trisphosphate > PI 4-phosphate) and is inhibited by opsonized zymosan or PMA stimulation.\",\n      \"method\": \"Immunofluorescence, cell fractionation, immunoprecipitation, in vitro phosphatase assay, GST-fusion protein mutagenesis (C515), lipid activation assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — active-site mutagenesis + in vitro enzymatic assay + direct localization + domain function characterization\",\n      \"pmids\": [\"11711529\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Full-length PTP-MEG2 exhibits lower Vmax and higher Km compared to the truncated catalytic domain alone, indicating the N-terminal lipid-binding domain has an inhibitory role on catalytic activity. Both forms show classical Michaelis-Menten kinetics with phosphotyrosine and pNPP substrates.\",\n      \"method\": \"In vitro phosphatase kinetics with purified recombinant full-length and truncated PTP-MEG2\",\n      \"journal\": \"Journal of cellular biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted enzymatic characterization comparing domain constructs\",\n      \"pmids\": [\"12112018\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The N-terminal Sec14p homology domain (residues 1-261) of PTP-MEG2 is necessary and sufficient for secretory vesicle targeting. Yeast two-hybrid screening identified vesicle trafficking proteins TIP47 and Arfaptin2 as direct interactors of this domain; overexpression of TIP47 or Arfaptin2 alters PTP-MEG2 localization, and elimination of TIP47 results in loss of PTP-MEG2 function.\",\n      \"method\": \"Yeast two-hybrid, deletion mutant localization, overexpression of interactors, TIP47 knockdown functional assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — Y2H + deletion mapping + functional consequence of interactor manipulation\",\n      \"pmids\": [\"17387180\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Crystal structures of PTP-MEG2 complexed with selective inhibitors reveal that potent, selective inhibition is achieved by engaging both the active site and unique peripheral binding pockets. The structures provide direct evidence for the molecular basis of PTP-MEG2 substrate selectivity and inform inhibitor design.\",\n      \"method\": \"X-ray crystallography, in vitro phosphatase inhibition assay, cellular insulin signaling assay, diet-induced obese mouse model\",\n      \"journal\": \"Journal of the American Chemical Society\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure + in vitro + in vivo validation\",\n      \"pmids\": [\"23075115\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"miR-24 directly targets PTPN9 (and PTPRF), repressing their expression and thereby increasing EGFR phosphorylation; ectopic expression of PTPN9 decreased pEGFR levels, cell invasion, migration, and tumor metastasis in breast cancer models.\",\n      \"method\": \"miRNA target validation (luciferase assay), overexpression of PTPN9 with functional readouts (invasion, migration, pEGFR levels), in vivo mouse tumor models\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct target validation + functional rescue experiments in vitro and in vivo\",\n      \"pmids\": [\"23418360\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Ptpn9a (zebrafish ortholog of human PTPN9) is required for erythroid cell maturation. Mechanistically, depletion of ptpn9 increases phosphorylated STAT3, which entraps transcription factors GATA1 and ZBP-89 in an inhibitory complex, preventing them from regulating erythroid gene expression. Dominant-negative PTPN9 (C515S) and siRNA against human PTPN9 similarly inhibit erythroid differentiation in K562 cells.\",\n      \"method\": \"Morpholino knockdown in zebrafish, dominant-negative overexpression, siRNA in K562 cells, immunoprecipitation to detect STAT3-GATA1-ZBP-89 complex\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo and in vitro knockdown with defined molecular mechanism, epistasis shown by complex identification\",\n      \"pmids\": [\"24727614\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"PTP-MEG2 identifies TrkA (neurotrophin receptor) as both a novel vesicle cargo requiring PTP-MEG2 for surface transport and a substrate: PTP-MEG2 dephosphorylates TrkA at Tyr-490 and Tyr-674/Tyr-675. Overexpression of PTP-MEG2 downregulates NGF/TrkA signaling and blocks neurite outgrowth and differentiation in PC12 cells and cortical neurons.\",\n      \"method\": \"Co-immunoprecipitation, substrate-trapping mutant, in vitro dephosphorylation, cell surface trafficking assay, neurite outgrowth assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — substrate identification by trapping + biochemical dephosphorylation + functional phenotype\",\n      \"pmids\": [\"27655914\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PTPN9 negatively regulates STAT3 activation and nuclear translocation in colorectal cancer cells. Overexpression of PTPN9 induces apoptosis (via caspase-3/9) and inhibits colony formation; knockdown has opposite effects. The effects of PTPN9 knockdown on apoptosis are attenuated by Stat3 pathway inhibition, placing PTPN9 upstream of STAT3.\",\n      \"method\": \"Overexpression and siRNA knockdown, Western blot for pSTAT3/nuclear fractionation, caspase activity assay, colony formation assay, pharmacological STAT3 inhibitor epistasis\",\n      \"journal\": \"Cancer management and research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KD/OE with epistasis experiment, but single lab\",\n      \"pmids\": [\"30804683\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PTPN9 dephosphorylates the Q-SNARE VTI1B, promoting homotypic fusion of ATG16L1+ vesicles and early autophagosome formation. The nonphosphorylatable VTI1B mutant (but not the phosphomimetic) enhances SNARE complex assembly and autophagic flux. Depletion of PTPN9 and its Drosophila homolog Ptpmeg2 impairs autophagosome formation and autophagic flux.\",\n      \"method\": \"siRNA/RNAi depletion, substrate identification, phospho-mutant analysis of VTI1B, SNARE complex co-immunoprecipitation, autophagy flux assay, Drosophila genetic validation\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — substrate identification + phospho-mutant rescue + SNARE complex biochemistry + cross-species genetic validation\",\n      \"pmids\": [\"33112705\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PTP-MEG2 controls multiple steps of catecholamine secretion: (1) dephosphorylation of NSF-pY83 promotes vesicle fusion (key residues governing NSF interaction defined by crystallography and mutagenesis); (2) PTP-MEG2 controls fusion pore opening and extension via NSF-independent dephosphorylation of DYNAMIN2-pY125 and MUNC18-1-pY145, through a structurally distinct binding interface.\",\n      \"method\": \"Biochemical assays, X-ray crystallography, site-directed mutagenesis, electrochemical catecholamine measurement, bioinformatics substrate screening\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure + mutagenesis + biochemical substrate identification + electrochemical functional readout\",\n      \"pmids\": [\"33764618\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"PTP-MEG2 is elevated in the membrane fraction of polycythemia vera (PV) erythroid progenitor cells. Expression of dominant-negative forms of PTP-MEG2 suppresses in vitro growth and expansion of both normal and PV erythroid colony-forming cells, establishing a role for PTP-MEG2 in erythroid development.\",\n      \"method\": \"Cell fractionation, immunoblotting, dominant-negative mutant overexpression, erythroid colony formation assay\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — dominant-negative with defined functional readout, but single lab\",\n      \"pmids\": [\"12920026\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PTPN9 interacts with FGFR2 via its Sec14p domain through ACAP1 mediation and dephosphorylates FGFR2 at pY656/657. Key interaction residues include the 'YRETRRKE' motif of the Sec14p domain and Y471 of PTPN9, as well as the PH and Arf-GAP domains of ACAP1. The FGFR2 I654V substitution decreases PTPN9-FGFR2 interaction.\",\n      \"method\": \"Phosphatase activity assay, structural modeling of PTPN9-FGFR2 complex, co-immunoprecipitation, mutagenesis, patient-derived xenograft models\",\n      \"journal\": \"Hepatology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — substrate identification + phosphatase activity assay + structural modeling + mutagenesis + in vivo PDX validation\",\n      \"pmids\": [\"37505213\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PTPN9 dephosphorylates IGF1R preferentially at Y1166 (and Y1165/1166). Crystal structure analysis identified Tyr333 and Asp335 as key PTPN9 residues interacting with IGF1R; mutation of these residues restores IGF1R signaling and abolishes PTPN9's tumor-suppressive effect. PTPN9 expression is inversely correlated with IGF1R Y1165/1166 phosphorylation in clinical tissues.\",\n      \"method\": \"IP-mass spectrometry substrate identification, X-ray crystallography, active-site mutagenesis, orthotopic mouse models, biochemical dephosphorylation assay\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure + mutagenesis + IP-MS + in vivo validation\",\n      \"pmids\": [\"41275311\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"MEG2 (PTPN9) and PKCε competitively bind to STAT3, with PKCε displaying stronger binding. STAT3 Ser727 phosphorylation increases STAT3 interaction with both PKCε and MEG2. ERK1/2 activation facilitates STAT3 interaction with MEG2, leading to dephosphorylation of STAT3 at Tyr705. MEG2 overexpression inhibits IL-6 promoter activity in the presence of STAT3 and LPS, opposing the effect of PKCε.\",\n      \"method\": \"ELISA and immunoprecipitation for protein-protein interaction, Western blot, dual luciferase reporter assay, in vivo hyperalgesia model (FCA/LPS)\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — Co-IP interaction data + reporter assay + in vivo model, but competitive binding mechanism needs further structural validation\",\n      \"pmids\": [\"38656553\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Heterozygous loss of Meg2 (Ptpn9) in mice causes progressive, age-dependent intraocular pressure elevation and glaucomatous neurodegeneration with retinal ganglion cell loss, optic nerve degeneration, reactive gliosis, and complement activation. IOP lowering with latanoprost prevents RGC loss, establishing the IOP-dependent mechanism.\",\n      \"method\": \"Meg2 heterozygous knockout mice, IOP measurement, ultrastructural analysis, immunohistochemistry, electroretinography, pharmacological rescue with latanoprost\",\n      \"journal\": \"Molecular neurobiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean HET KO with defined in vivo phenotype and pharmacological rescue, but molecular substrate not identified\",\n      \"pmids\": [\"30315478\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PTPN9 (PTP-MEG2) is a cytoplasmic protein tyrosine phosphatase with an N-terminal Sec14p/lipid-binding domain that targets it to secretory vesicle membranes via phosphatidylserine and PtdIns(3,4,5)P3 binding and interactions with trafficking proteins TIP47 and Arfaptin2; on these vesicles it promotes homotypic vesicle fusion by dephosphorylating NSF (pY83), and controls exocytotic fusion pore opening by dephosphorylating DYNAMIN2 (pY125) and MUNC18-1 (pY145); it also dephosphorylates receptor tyrosine kinases including EGFR, ErbB2, VEGFR2, FGFR2 (pY656/657), IGF1R (pY1166), and TrkA, and the transcription factor STAT3 (pY705), acting as a broad negative regulator of growth factor and cytokine signaling relevant to erythropoiesis, insulin sensitization, angiogenesis, and tumor suppression, while additionally dephosphorylating VTI1B to promote ATG16L1 vesicle fusion and autophagosome biogenesis.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"PTPN9 (PTP-MEG2) is a non-receptor protein tyrosine phosphatase that couples lipid-directed membrane targeting to the regulation of vesicle trafficking, exocytosis, and receptor tyrosine kinase signaling. Its N-terminal Sec14p homology domain binds phosphatidylserine and PtdIns(3,4,5)P3 to localize the enzyme to secretory vesicle membranes, where it promotes homotypic vesicle fusion by dephosphorylating NSF (pY83) and controls fusion pore dynamics by dephosphorylating DYNAMIN2 (pY125) and MUNC18-1 (pY145); it also dephosphorylates the Q-SNARE VTI1B to drive ATG16L1-positive vesicle fusion during autophagosome biogenesis [PMID:17387180, PMID:33764618, PMID:33112705]. PTPN9 functions as a broad negative regulator of growth factor and cytokine signaling by directly dephosphorylating EGFR, ErbB2, VEGFR2, FGFR2 (pY656/657), IGF1R (pY1166), TrkA, and STAT3 (pY705), thereby suppressing proliferative, angiogenic, and inflammatory pathways [PMID:20335174, PMID:22394684, PMID:22763125, PMID:37505213, PMID:41275311, PMID:27655914]. Knockout studies establish essential roles in secretory vesicle biogenesis in lymphocytes, erythroid maturation via STAT3–GATA1 axis regulation, embryonic development, and intraocular pressure homeostasis [PMID:16330817, PMID:24727614, PMID:30315478].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Establishing the enzymology and localization of PTPN9 in primary cells resolved how the N-terminal domain auto-inhibits catalytic activity and how polyphosphoinositides activate the phosphatase, providing the first framework for its regulation at membranes.\",\n      \"evidence\": \"Subcellular fractionation, active-site mutagenesis (C515), and lipid activation assays in human neutrophils\",\n      \"pmids\": [\"11711529\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of endogenous substrates on secretory vesicles unknown\", \"Structural basis of auto-inhibition not determined\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Demonstrating that PTPN9 catalytic activity drives homotypic secretory vesicle fusion in immune cells established its first cellular function — regulation of the secretory pathway rather than classical receptor signaling.\",\n      \"evidence\": \"Overexpression with fluorescence microscopy in mast cells and Jurkat T cells; pervanadate reversal; IL-2 secretion assay\",\n      \"pmids\": [\"11971009\", \"12112018\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Vesicle fusion substrates not identified\", \"Mechanism linking phosphatase activity to membrane fusion unclear\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Identification of phosphatidylserine and PtdIns(3,4,5)P3 as ligands of the Sec14p domain explained how PTPN9 is targeted to secretory vesicle membranes, and mutagenesis showed lipid binding is required for vesicle fusion activity.\",\n      \"evidence\": \"Lipid-overlay and liposome binding assays, point mutagenesis, PI3K inhibitor treatment, PS loading experiments\",\n      \"pmids\": [\"14662869\", \"12702726\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contributions of PS versus PIP3 binding in vivo not resolved\", \"Whether lipid binding relieves auto-inhibition not tested\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Elevated PTPN9 in polycythemia vera erythroid progenitors and dominant-negative suppression of erythroid colony growth first linked the phosphatase to erythropoiesis.\",\n      \"evidence\": \"Cell fractionation and dominant-negative overexpression in primary human erythroid progenitors\",\n      \"pmids\": [\"12920026\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Substrate in erythroid progenitors unidentified\", \"Mechanism connecting PTPN9 to erythroid proliferation unclear\", \"Single-lab observation\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Meg2 knockout mice revealed that PTPN9 is essential for embryonic viability, secretory vesicle biogenesis in lymphocytes, and platelet function, elevating its role from an in vitro vesicle regulator to a required developmental factor.\",\n      \"evidence\": \"Gene-targeted knockout mice, hematopoietic reconstitution, electron microscopy of lymphocyte vesicles, platelet/T-cell activation assays\",\n      \"pmids\": [\"16330817\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific substrates responsible for vesicle biogenesis defect unknown\", \"Cause of embryonic lethality (hemorrhage vs. neural tube defect vs. bone) not delineated\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"A genome-scale screen and in vivo validation identified PTPN9 as a negative regulator of hepatic insulin receptor signaling, showing that liver-targeted depletion normalizes hyperglycemia in diabetic mice — extending PTPN9 function to metabolic regulation.\",\n      \"evidence\": \"Functional genomic screen, adenoviral hepatic depletion in db/db mice, FOXO1 localization, blood glucose measurement\",\n      \"pmids\": [\"16679294\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PTPN9 directly dephosphorylates the insulin receptor (versus an intermediate) not biochemically confirmed\", \"Tissue specificity of metabolic role beyond liver not explored\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Discovery of TIP47 and Arfaptin2 as direct binding partners of the Sec14p domain provided a protein-based targeting mechanism complementing lipid-mediated vesicle recruitment.\",\n      \"evidence\": \"Yeast two-hybrid, deletion-mutant localization, TIP47 knockdown functional assay\",\n      \"pmids\": [\"17387180\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How TIP47/Arfaptin2 coordinate with lipid binding is unknown\", \"Whether these interactions are regulated remains untested\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Substrate-trapping and knockdown experiments identified ErbB2 and EGFR as direct PTPN9 substrates, establishing the enzyme as a negative regulator of receptor tyrosine kinase signaling with tumor-suppressive properties in breast cancer.\",\n      \"evidence\": \"DA-mutant co-immunoprecipitation, GST pulldown, siRNA knockdown, soft-agar and invasion assays\",\n      \"pmids\": [\"20335174\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific phosphosites on ErbB2/EGFR targeted by PTPN9 not mapped\", \"Whether vesicle-localized or cytoplasmic pool mediates RTK dephosphorylation unclear\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Concurrent identification of STAT3 and VEGFR2 as direct substrates, together with crystal structures of the catalytic domain with selective inhibitors, broadened the substrate repertoire and provided a structural framework for drug design.\",\n      \"evidence\": \"Co-IP and in vitro dephosphorylation for STAT3/VEGFR2; X-ray crystallography of inhibitor-bound PTP-MEG2; xenograft and diet-induced obesity mouse models\",\n      \"pmids\": [\"22394684\", \"22763125\", \"23075115\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How PTPN9 selects among multiple RTK and non-RTK substrates in a single cell is unknown\", \"Full-length structure including Sec14p domain not solved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Zebrafish and human cell studies demonstrated that PTPN9-mediated STAT3 dephosphorylation is required for erythroid maturation by preventing an inhibitory STAT3–GATA1–ZBP-89 complex, providing the molecular mechanism underlying its erythropoietic role.\",\n      \"evidence\": \"Morpholino knockdown in zebrafish, dominant-negative C515S and siRNA in K562 cells, co-IP of STAT3–GATA1–ZBP-89 complex\",\n      \"pmids\": [\"24727614\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether this mechanism operates in mammalian definitive erythropoiesis in vivo not confirmed\", \"Regulation of PTPN9 expression during erythroid differentiation not characterized\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Identification of TrkA as both a vesicle cargo requiring PTPN9 for surface transport and a dephosphorylation substrate linked the vesicle-trafficking and signaling functions of PTPN9 in neuronal differentiation.\",\n      \"evidence\": \"Substrate trapping, in vitro dephosphorylation, surface trafficking assay, neurite outgrowth in PC12 and cortical neurons\",\n      \"pmids\": [\"27655914\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PTPN9 controls trafficking of other RTK cargoes is untested\", \"In vivo neuronal phenotype of Ptpn9 loss not characterized\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Heterozygous Meg2 loss in mice caused progressive glaucoma with IOP-dependent retinal ganglion cell degeneration, revealing an unexpected in vivo role in intraocular pressure homeostasis.\",\n      \"evidence\": \"Meg2 heterozygous KO mice, IOP measurement, latanoprost pharmacological rescue, optic nerve histology\",\n      \"pmids\": [\"30315478\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular substrate mediating IOP regulation not identified\", \"Relevance to human glaucoma genetics not established\", \"Single-lab observation\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identification of VTI1B as a PTPN9 substrate that regulates SNARE complex assembly on ATG16L1-positive vesicles extended the phosphatase's membrane fusion role to autophagosome biogenesis, with cross-species validation in Drosophila.\",\n      \"evidence\": \"siRNA/RNAi depletion, VTI1B phospho-mutant analysis, SNARE complex co-IP, autophagy flux assays, Drosophila Ptpmeg2 RNAi\",\n      \"pmids\": [\"33112705\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PTPN9-VTI1B axis operates in selective autophagy pathways is unknown\", \"Upstream kinase phosphorylating VTI1B not identified\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Crystallographic and electrochemical studies revealed that PTPN9 controls catecholamine secretion through structurally separable substrate interfaces: NSF-pY83 dephosphorylation drives vesicle fusion, while DYNAMIN2-pY125 and MUNC18-1-pY145 dephosphorylation controls fusion pore dynamics.\",\n      \"evidence\": \"X-ray crystallography of PTPN9–substrate complexes, mutagenesis, electrochemical single-vesicle catecholamine release measurement\",\n      \"pmids\": [\"33764618\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether these substrate interfaces can be independently targeted pharmacologically is untested\", \"Physiological kinases counteracting PTPN9 at NSF/DYNAMIN2/MUNC18-1 not identified\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"ACAP1 was identified as a bridging adaptor mediating PTPN9–FGFR2 interaction via the Sec14p domain, with dephosphorylation at FGFR2 pY656/657; the cancer-associated FGFR2 I654V mutation disrupts this interaction, providing a disease-relevant substrate selectivity mechanism.\",\n      \"evidence\": \"Co-IP, mutagenesis, phosphatase assays, structural modeling, patient-derived xenograft validation\",\n      \"pmids\": [\"37505213\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether ACAP1-mediated recruitment generalizes to other RTK substrates is unknown\", \"Full structural model of PTPN9–ACAP1–FGFR2 ternary complex awaits experimental determination\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Crystal structure-guided identification of IGF1R pY1166 as a direct substrate, with Tyr333 and Asp335 as key PTPN9 contact residues, provided structural precision for substrate recognition and confirmed tumor-suppressive activity through IGF1R axis inhibition.\",\n      \"evidence\": \"IP-mass spectrometry, X-ray crystallography of PTPN9–IGF1R interface, active-site mutagenesis, orthotopic mouse models, clinical tissue correlation\",\n      \"pmids\": [\"41275311\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How PTPN9 prioritizes IGF1R versus other RTK substrates in cells co-expressing multiple receptors is unclear\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A full-length structure of PTPN9 revealing how the Sec14p domain auto-inhibits the catalytic domain and how lipid/protein cofactors relieve inhibition remains unresolved, as does a unified model for how a single phosphatase coordinates its diverse vesicle-fusion and RTK-regulatory functions within the same cell.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length PTPN9 structure not solved\", \"Upstream regulation of PTPN9 activity (post-translational modifications, transcriptional control beyond miR-24) poorly defined\", \"Kinases counteracting PTPN9 at most substrate sites not identified\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 2, 3, 8, 9, 14, 16, 17, 19, 20]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [3, 4, 5, 8, 10]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [1, 8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0005773\", \"supporting_discovery_ids\": []},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 2, 7, 12, 14, 19, 20]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [16]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [3, 4, 10, 17]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 2, 17, 20]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"EGFR\",\n      \"ERBB2\",\n      \"STAT3\",\n      \"NSF\",\n      \"DNM2\",\n      \"STXBP1\",\n      \"VTI1B\",\n      \"TIP47\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}