{"gene":"PTPRCAP","run_date":"2026-06-10T06:43:36","timeline":{"discoveries":[{"year":1994,"finding":"CD45-AP (PTPRCAP) was purified by virtue of its specific association with CD45, and in vitro translated CD45-AP bound specifically to CD45. CD45-AP is a leukocyte-specific ~30 kDa phosphorylated protein with no consensus tyrosine phosphorylation sites, proposed to act as an adapter molecule for CD45-mediated signal transduction.","method":"Protein purification, in vitro translation/binding assay, cDNA cloning","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro binding reconstitution combined with biochemical purification and molecular cloning; foundational paper replicated by subsequent studies","pmids":["8300558"],"is_preprint":false},{"year":1995,"finding":"The transmembrane segment of CD45-AP binds to the transmembrane portion of CD45. CD45-AP localizes to particulate (membrane) fractions of lymphocytes along with CD45, is resistant to extracellular proteolysis, and adopts an orientation in which only a short N-terminal segment is extracellular while the bulk of the protein is cytoplasmic.","method":"Deletion/chimeric mutant binding analysis, cell fractionation, protease protection assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — domain mapping with deletion/chimeric constructs plus orthogonal fractionation and protease protection experiments in a single rigorous study","pmids":["7673147"],"is_preprint":false},{"year":1997,"finding":"CD45-AP exists in two distinct protein forms differing by 12 N-terminal amino acids; both forms bind CD45 equally but use different mechanisms for ER membrane translocation. CD45-AP protein stability is reduced in the absence of CD45 (shorter half-life in CD45-negative cells). CD45-AP expression is restricted to T, B, and pre-B cells but absent from plasma cells and monocyte/macrophage lineage cells.","method":"Northern hybridization, Western blotting, pulse-chase/half-life analysis, cell-type expression survey","journal":"European journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal biochemical methods in a single lab study; replicates and extends the binding specificity established earlier","pmids":["9045908"],"is_preprint":false},{"year":1996,"finding":"The human PTPRCAP gene maps to chromosome 11q13.1–q13.3 and the mouse Ptprcap gene maps to chromosome 19B centromeric region. Both genes span ~3 kb, consist of two exons separated by a 1.2-kb intron, and lack TATA boxes but have consensus initiator sequences.","method":"Fluorescence in situ hybridization (FISH), multilocus cross Southern hybridization, genomic sequencing","journal":"Genomics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two independent groups (Bruyns et al. and Takai et al.) used FISH and genetic crosses, providing convergent chromosomal localization","pmids":["8954783","8975722"],"is_preprint":false},{"year":1998,"finding":"CD45-AP-null mice show reduced T and B lymphocyte proliferation in response to antigen receptor stimulation, impaired mixed leukocyte reaction, and reduced cytotoxic T lymphocyte function. Crucially, the interaction between CD45 and Lck is significantly reduced in CD45-AP-null T cells, indicating that CD45-AP directly or indirectly mediates the CD45–Lck interaction.","method":"CD45-AP knockout mice, co-immunoprecipitation, proliferation assays, MLR, CTL assay","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean knockout mouse model with multiple orthogonal functional readouts plus Co-IP demonstrating disrupted CD45–Lck interaction; independently partially replicated","pmids":["9607926"],"is_preprint":false},{"year":1999,"finding":"In T cells, CD45-AP is part of a multimolecular complex that includes CD45, TCR, CD4/CD8 coreceptors, and p56(lck). The association of CD45-AP with p56(lck) can occur independently of other lymphoid-specific components, indicating it is direct. Structure-function analysis showed that an acidic segment in the cytoplasmic region of CD45-AP mediates binding to the kinase domain of p56(lck), and this interaction is proportional to the degree of catalytic activation of Lck.","method":"Co-immunoprecipitation, structure-function/deletion analysis with recombinant proteins, binding assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — domain mapping with deletion constructs identifying specific binding surfaces, combined with co-IP in multiple cell contexts; consistent with independent data from Motoya et al. 1999","pmids":["10318863"],"is_preprint":false},{"year":1999,"finding":"Endogenous CD45-AP co-immunoprecipitates with Lck and ZAP-70 (but not Fyn or Csk) after TCR stimulation in both CD45-positive and CD45-negative T cells, and recombinant CD45-AP binds directly and selectively to recombinant Lck and ZAP-70. CD45 also co-immunoprecipitates with Lck and ZAP-70 after TCR stimulation only in CD45-positive cells.","method":"Endogenous co-immunoprecipitation, recombinant protein binding assays, TCR stimulation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — reciprocal co-IP of endogenous proteins plus direct recombinant protein binding assays confirming selectivity; consistent with Veillette et al. 1999","pmids":["9880514"],"is_preprint":false},{"year":1999,"finding":"LPAP (CD45-AP/PTPRCAP)-deficient mice show reduced CD45 surface expression on T and B lymphocytes but no significant alteration in CD45–Lck complex assembly or polyclonal T-cell responses; lymph nodes show increased cellularity, suggesting a role in restraining lymphocyte expansion rather than potentiating immune responses.","method":"Gene knockout (exon 2 disruption), immunofluorescence, co-immunoprecipitation, T-cell proliferation assay","journal":"European journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KO mouse with multiple readouts; this study contradicts some findings of Matsuda et al. 1998 regarding CD45–Lck interaction, so confidence is moderated by conflicting results","pmids":["10602004"],"is_preprint":false},{"year":2004,"finding":"CD45-AP inhibits CD45 dimer formation: T cells from CD45-AP-null mice or a CD45-AP-null T-cell line (ALST-1) display much higher levels of CD45 dimers than wild-type cells; transfection of CD45-AP into ALST-1 cells reduces CD45 dimerization proportional to the amount of CD45-AP expressed. Consistent with a model where dimers are inactive, CD45 phosphatase activity (measured in microsomal fractions) is significantly lower in CD45-AP-negative cells than in CD45-AP-positive cells.","method":"CD45-AP knockout T cells, CD45-AP-null T-cell line (ALST-1), transfection, CD45 dimer assay, microsomal PTP activity assay","journal":"Blood","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — enzymatic activity assay combined with CD45 dimerization measurement across null and reconstituted cells using multiple independent systems","pmids":["14715639"],"is_preprint":false},{"year":2007,"finding":"In CD4+ T cells from CD45-AP-deficient mice, co-immunoprecipitation of CD45 with the CD3/TCR complex and with Lck is significantly reduced compared to wild-type, correlating with decreased proliferative response, reduced IL-2 production, and reduced calcium flux specifically upon low-potency (but not high-avidity) peptide stimulation. This indicates CD45-AP promotes or stabilizes CD45 association with its substrates and lowers the threshold of T-cell activation.","method":"CD45-AP knockout mice, co-immunoprecipitation, proliferation assay, IL-2 ELISA, calcium flux measurement, altered peptide ligand stimulation","journal":"Immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO mice with multiple orthogonal functional readouts plus mechanistic co-IP data; consistent with prior knockout and interaction studies","pmids":["17428310"],"is_preprint":false},{"year":2015,"finding":"CD45-AP (PTPRCAP) expression is downregulated specifically in marginal zone (MZ) B cells compared to other splenic B-cell subsets. CD45-AP mutant mice have reduced transitional and increased mature MZ and follicular B cells, suggesting CD45-AP prevents premature entry of transitional B cells into the mature B-cell pool or controls their survival and proliferation.","method":"RNA-seq of sorted B-cell subsets, gene-deleted and overexpressing transgenic mice, B-cell subset quantification","journal":"Frontiers in immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO and transgenic mice with defined B-cell subset phenotypic readout; single lab, functional consequence established but molecular mechanism not fully resolved","pmids":["25717326"],"is_preprint":false},{"year":2025,"finding":"Overexpression of PTPRCAP in lung adenocarcinoma cell lines (A549, H1299) suppresses proliferation, migration, and invasion, and increases apoptosis. Mechanistically, PTPRCAP overexpression elevates pro-apoptotic Bax and cleaved caspase-3 while reducing anti-apoptotic Bcl-2. In vivo xenograft experiments confirm that PTPRCAP overexpression inhibits tumor growth.","method":"Plasmid overexpression in LUAD cell lines, CCK-8 proliferation assay, scratch/Transwell migration assay, Annexin V apoptosis assay, Western blot for Bax/Bcl-2/cleaved caspase-3, nude mouse xenografts","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal functional assays (in vitro + in vivo) in a single lab; Western blot identifies apoptosis pathway components modulated by PTPRCAP","pmids":["41411247"],"is_preprint":false},{"year":2025,"finding":"miR-582-3p directly binds the 3'-UTR of PTPRCAP (validated by dual-luciferase reporter assay) and suppresses PTPRCAP expression in LUAD cells. PTPRCAP overexpression inhibits Wnt/β-catenin signaling (reduced β-catenin and p-GSK3β; restored GSK3β), and rescue experiments show PTPRCAP restoration counteracts miR-582-3p-mediated oncogenic phenotypes, placing PTPRCAP downstream of miR-582-3p and upstream of Wnt/β-catenin in LUAD.","method":"Dual-luciferase reporter assay, bioinformatics (TargetScan8.0), RT-qPCR, Western blot for Wnt pathway components, functional rescue experiments in LUAD cell lines","journal":"Frontiers in oncology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — dual-luciferase validates direct miRNA-3'UTR interaction; rescue experiments provide epistasis; single lab, limited to cancer cell lines with no prior replication","pmids":["41064095"],"is_preprint":false}],"current_model":"PTPRCAP (CD45-AP) is a leukocyte-specific type I transmembrane adapter protein whose transmembrane domain directly docks onto the transmembrane segment of the tyrosine phosphatase CD45, stabilizing CD45 as a monomer (active form) and thereby up-regulating its phosphatase activity; in its cytoplasmic acidic domain, PTPRCAP binds directly and selectively to the kinase domains of Lck and ZAP-70 in a TCR-stimulation-dependent manner, assembling a multimolecular complex that includes CD45, TCR/CD3, CD4/CD8, and p56(lck), which promotes dephosphorylation of Lck's inhibitory tyrosine and lowers the threshold for antigen receptor signaling; loss of PTPRCAP in mice disrupts CD45–Lck co-association, reduces lymphocyte proliferation and cytotoxic responses, perturbs B-cell developmental subset transitions, and in non-immune (lung adenocarcinoma) contexts PTPRCAP acts as a tumor suppressor by promoting apoptosis through the Bax/caspase-3/Bcl-2 axis and by inhibiting Wnt/β-catenin signaling, the latter being regulated upstream by miR-582-3p targeting of the PTPRCAP 3'-UTR."},"narrative":{"mechanistic_narrative":"PTPRCAP (CD45-AP/LPAP) is a leukocyte-restricted type I transmembrane adapter protein that regulates the receptor tyrosine phosphatase CD45 and proximal antigen-receptor signaling in lymphocytes [PMID:8300558, PMID:9607926]. It was originally purified by its specific physical association with CD45, and reconstituted in vitro binding confirmed the interaction is direct [PMID:8300558]; domain mapping established that the transmembrane segment of PTPRCAP docks onto the transmembrane portion of CD45, with the bulk of the adapter oriented in the cytoplasm [PMID:7673147]. By opposing CD45 dimer formation, PTPRCAP stabilizes the active monomeric phosphatase and elevates CD45 catalytic activity, since CD45-AP-null cells accumulate inactive CD45 dimers and show reduced phosphatase activity [PMID:14715639]. Through an acidic segment in its cytoplasmic region, PTPRCAP binds directly and selectively to the kinase domains of Lck and ZAP-70 in a TCR-stimulation-dependent manner, the Lck interaction scaling with Lck catalytic activation, thereby assembling a multimolecular complex containing CD45, TCR/CD3, CD4/CD8 coreceptors, and p56(lck) [PMID:10318863, PMID:9880514]. Functionally, loss of PTPRCAP in mice reduces antigen-receptor-driven T and B cell proliferation and cytotoxic responses, weakens CD45 association with the TCR/CD3 complex and Lck, and lowers the threshold for T-cell activation under low-potency ligand stimulation [PMID:9607926, PMID:17428310]; it also restrains transitional B-cell maturation into the marginal-zone and follicular pools [PMID:25717326]. Beyond the immune system, PTPRCAP behaves as a tumor suppressor in lung adenocarcinoma, where its overexpression promotes apoptosis via increased Bax and cleaved caspase-3 with reduced Bcl-2 and inhibits Wnt/β-catenin signaling, and where it is suppressed by miR-582-3p binding to its 3'-UTR [PMID:41411247, PMID:41064095].","teleology":[{"year":1994,"claim":"Established that a leukocyte-specific ~30 kDa protein physically associates with CD45, defining PTPRCAP as a candidate CD45 adapter.","evidence":"Protein purification by CD45 association, in vitro translation/binding, and cDNA cloning","pmids":["8300558"],"confidence":"High","gaps":["Did not localize the binding interface","No functional consequence of the interaction established"]},{"year":1995,"claim":"Mapped the CD45 docking interface to the transmembrane segments and defined PTPRCAP's membrane topology, explaining how it engages CD45 within the membrane.","evidence":"Deletion/chimeric mutant binding analysis, cell fractionation, protease protection in lymphocytes","pmids":["7673147"],"confidence":"High","gaps":["Did not address effect on CD45 enzymatic activity","Cytoplasmic functional partners unidentified"]},{"year":1997,"claim":"Showed PTPRCAP exists in two N-terminal variant forms, that its stability depends on CD45, and that expression is confined to T, B, and pre-B cells, refining its cellular distribution.","evidence":"Northern blot, Western blot, pulse-chase half-life analysis, cell-type expression survey","pmids":["9045908"],"confidence":"Medium","gaps":["Functional difference between the two isoforms unresolved","Mechanism of CD45-dependent stabilization unknown"]},{"year":1996,"claim":"Defined the human and mouse gene structure and chromosomal location, providing the genomic foundation for the locus.","evidence":"FISH, multilocus cross Southern hybridization, genomic sequencing in two independent groups","pmids":["8954783","8975722"],"confidence":"Medium","gaps":["No regulatory element function characterized","Does not address protein function"]},{"year":1998,"claim":"Demonstrated in vivo that PTPRCAP supports antigen-receptor responses and is required for efficient CD45–Lck association, linking the adapter to functional immune signaling.","evidence":"CD45-AP knockout mice with co-IP, proliferation, MLR, and CTL assays","pmids":["9607926"],"confidence":"High","gaps":["Whether the CD45–Lck effect is direct or indirect not resolved","Molecular basis of impaired proliferation undefined"]},{"year":1999,"claim":"Identified the cytoplasmic acidic segment as a direct, activity-dependent binding site for the Lck and ZAP-70 kinase domains and placed PTPRCAP within a CD45/TCR/coreceptor/Lck complex.","evidence":"Co-IP in multiple cell contexts, structure-function deletion analysis, recombinant protein binding, TCR stimulation","pmids":["10318863","9880514"],"confidence":"High","gaps":["Selectivity over Fyn/Csk mechanistically unexplained","Stoichiometry of the multimolecular complex unknown"]},{"year":1999,"claim":"Provided a contrasting knockout phenotype in which CD45 surface expression was reduced but CD45–Lck assembly and polyclonal responses were intact, complicating the model of PTPRCAP as a pure positive regulator.","evidence":"Exon 2 disruption KO, immunofluorescence, co-IP, T-cell proliferation assay","pmids":["10602004"],"confidence":"Medium","gaps":["Conflicts with the CD45–Lck disruption reported in other KO lines","Mechanism of reduced CD45 surface expression not defined"]},{"year":2004,"claim":"Resolved how PTPRCAP regulates CD45 activity by showing it suppresses inactive CD45 dimer formation and thereby raises phosphatase activity.","evidence":"KO T cells and a CD45-AP-null T-cell line (ALST-1) with reconstitution, CD45 dimer assay, microsomal PTP activity assay","pmids":["14715639"],"confidence":"High","gaps":["Structural basis for monomer stabilization unknown","Link between dimer suppression and downstream signaling outputs not directly traced"]},{"year":2007,"claim":"Showed PTPRCAP stabilizes CD45 association with the TCR/CD3 complex and Lck and lowers the activation threshold for weak-affinity ligands, sharpening its role in signal sensitivity.","evidence":"KO mice with co-IP, proliferation, IL-2 ELISA, calcium flux, altered peptide ligand stimulation","pmids":["17428310"],"confidence":"High","gaps":["Why only low-potency ligand responses are affected unexplained","Quantitative contribution to substrate recruitment unknown"]},{"year":2015,"claim":"Extended PTPRCAP function to B-cell development, showing it controls transitional-to-mature B-cell subset transitions.","evidence":"RNA-seq of sorted B-cell subsets with gene-deleted and overexpressing transgenic mice","pmids":["25717326"],"confidence":"Medium","gaps":["Molecular mechanism of subset control not resolved","Whether effect depends on CD45 phosphatase regulation untested"]},{"year":2025,"claim":"Identified a non-immune tumor-suppressor role in lung adenocarcinoma via apoptosis induction and Wnt/β-catenin inhibition, with miR-582-3p as an upstream repressor of PTPRCAP.","evidence":"Overexpression in LUAD lines, CCK-8/migration/apoptosis assays, Western blot for Bax/Bcl-2/caspase-3 and Wnt components, xenografts, dual-luciferase reporter, rescue experiments","pmids":["41411247","41064095"],"confidence":"Medium","gaps":["Whether tumor suppression involves CD45/Lck or is phosphatase-independent unknown","Single-lab cancer cell line data without independent replication","Direct molecular link between PTPRCAP and Wnt/β-catenin not established"]},{"year":null,"claim":"How PTPRCAP mechanistically connects its membrane CD45-regulatory function to the cytoplasmic Wnt/apoptosis effects observed in epithelial tumors remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of the CD45–PTPRCAP transmembrane complex","Conflicting KO phenotypes on CD45–Lck not reconciled","Mechanism bridging immune and tumor-suppressor roles unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,5,6]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[8]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[1,5]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[4,5,9]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[6,9]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[11]}],"complexes":["CD45–TCR/CD3–CD4/CD8–Lck signaling complex"],"partners":["PTPRC","LCK","ZAP70"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q14761","full_name":"Protein tyrosine phosphatase receptor type C-associated protein","aliases":["CD45-associated protein","CD45-AP","Lymphocyte phosphatase-associated phosphoprotein"],"length_aa":206,"mass_kda":21.2,"function":"","subcellular_location":"Membrane","url":"https://www.uniprot.org/uniprotkb/Q14761/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PTPRCAP","classification":"Not Classified","n_dependent_lines":3,"n_total_lines":1208,"dependency_fraction":0.0024834437086092716},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PTPRCAP","total_profiled":1310},"omim":[{"mim_id":"601577","title":"PROTEIN-TYROSINE PHOSPHATASE, RECEPTOR-TYPE, C POLYPEPTIDE-ASSOCIATED PROTEIN; PTPRCAP","url":"https://www.omim.org/entry/601577"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"}],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"intestine","ntpm":112.6},{"tissue":"lymphoid tissue","ntpm":253.8}],"url":"https://www.proteinatlas.org/search/PTPRCAP"},"hgnc":{"alias_symbol":["LPAP","CD45-AP"],"prev_symbol":[]},"alphafold":{"accession":"Q14761","domains":[{"cath_id":"-","chopping":"67-100","consensus_level":"medium","plddt":62.3429,"start":67,"end":100},{"cath_id":"1.20.5","chopping":"33-66","consensus_level":"medium","plddt":82.0094,"start":33,"end":66}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q14761","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q14761-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q14761-F1-predicted_aligned_error_v6.png","plddt_mean":57.69},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PTPRCAP","jax_strain_url":"https://www.jax.org/strain/search?query=PTPRCAP"},"sequence":{"accession":"Q14761","fasta_url":"https://rest.uniprot.org/uniprotkb/Q14761.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q14761/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q14761"}},"corpus_meta":[{"pmid":"9429890","id":"PMC_9429890","title":"The 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biology","url":"https://pubmed.ncbi.nlm.nih.gov/41796190","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":14361,"output_tokens":3719,"usd":0.049434,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":11495,"output_tokens":3717,"usd":0.0752,"stage2_stop_reason":"end_turn"},"total_usd":0.124634,"stage1_batch_id":"msgbatch_01CNoDbkChHEkgrJnL7BwtGJ","stage2_batch_id":"msgbatch_016Y4x9E9Wg5VQDANj9quSQD","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1994,\n      \"finding\": \"CD45-AP (PTPRCAP) was purified by virtue of its specific association with CD45, and in vitro translated CD45-AP bound specifically to CD45. CD45-AP is a leukocyte-specific ~30 kDa phosphorylated protein with no consensus tyrosine phosphorylation sites, proposed to act as an adapter molecule for CD45-mediated signal transduction.\",\n      \"method\": \"Protein purification, in vitro translation/binding assay, cDNA cloning\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro binding reconstitution combined with biochemical purification and molecular cloning; foundational paper replicated by subsequent studies\",\n      \"pmids\": [\"8300558\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"The transmembrane segment of CD45-AP binds to the transmembrane portion of CD45. CD45-AP localizes to particulate (membrane) fractions of lymphocytes along with CD45, is resistant to extracellular proteolysis, and adopts an orientation in which only a short N-terminal segment is extracellular while the bulk of the protein is cytoplasmic.\",\n      \"method\": \"Deletion/chimeric mutant binding analysis, cell fractionation, protease protection assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — domain mapping with deletion/chimeric constructs plus orthogonal fractionation and protease protection experiments in a single rigorous study\",\n      \"pmids\": [\"7673147\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"CD45-AP exists in two distinct protein forms differing by 12 N-terminal amino acids; both forms bind CD45 equally but use different mechanisms for ER membrane translocation. CD45-AP protein stability is reduced in the absence of CD45 (shorter half-life in CD45-negative cells). CD45-AP expression is restricted to T, B, and pre-B cells but absent from plasma cells and monocyte/macrophage lineage cells.\",\n      \"method\": \"Northern hybridization, Western blotting, pulse-chase/half-life analysis, cell-type expression survey\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal biochemical methods in a single lab study; replicates and extends the binding specificity established earlier\",\n      \"pmids\": [\"9045908\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"The human PTPRCAP gene maps to chromosome 11q13.1–q13.3 and the mouse Ptprcap gene maps to chromosome 19B centromeric region. Both genes span ~3 kb, consist of two exons separated by a 1.2-kb intron, and lack TATA boxes but have consensus initiator sequences.\",\n      \"method\": \"Fluorescence in situ hybridization (FISH), multilocus cross Southern hybridization, genomic sequencing\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two independent groups (Bruyns et al. and Takai et al.) used FISH and genetic crosses, providing convergent chromosomal localization\",\n      \"pmids\": [\"8954783\", \"8975722\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"CD45-AP-null mice show reduced T and B lymphocyte proliferation in response to antigen receptor stimulation, impaired mixed leukocyte reaction, and reduced cytotoxic T lymphocyte function. Crucially, the interaction between CD45 and Lck is significantly reduced in CD45-AP-null T cells, indicating that CD45-AP directly or indirectly mediates the CD45–Lck interaction.\",\n      \"method\": \"CD45-AP knockout mice, co-immunoprecipitation, proliferation assays, MLR, CTL assay\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean knockout mouse model with multiple orthogonal functional readouts plus Co-IP demonstrating disrupted CD45–Lck interaction; independently partially replicated\",\n      \"pmids\": [\"9607926\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"In T cells, CD45-AP is part of a multimolecular complex that includes CD45, TCR, CD4/CD8 coreceptors, and p56(lck). The association of CD45-AP with p56(lck) can occur independently of other lymphoid-specific components, indicating it is direct. Structure-function analysis showed that an acidic segment in the cytoplasmic region of CD45-AP mediates binding to the kinase domain of p56(lck), and this interaction is proportional to the degree of catalytic activation of Lck.\",\n      \"method\": \"Co-immunoprecipitation, structure-function/deletion analysis with recombinant proteins, binding assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — domain mapping with deletion constructs identifying specific binding surfaces, combined with co-IP in multiple cell contexts; consistent with independent data from Motoya et al. 1999\",\n      \"pmids\": [\"10318863\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Endogenous CD45-AP co-immunoprecipitates with Lck and ZAP-70 (but not Fyn or Csk) after TCR stimulation in both CD45-positive and CD45-negative T cells, and recombinant CD45-AP binds directly and selectively to recombinant Lck and ZAP-70. CD45 also co-immunoprecipitates with Lck and ZAP-70 after TCR stimulation only in CD45-positive cells.\",\n      \"method\": \"Endogenous co-immunoprecipitation, recombinant protein binding assays, TCR stimulation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — reciprocal co-IP of endogenous proteins plus direct recombinant protein binding assays confirming selectivity; consistent with Veillette et al. 1999\",\n      \"pmids\": [\"9880514\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"LPAP (CD45-AP/PTPRCAP)-deficient mice show reduced CD45 surface expression on T and B lymphocytes but no significant alteration in CD45–Lck complex assembly or polyclonal T-cell responses; lymph nodes show increased cellularity, suggesting a role in restraining lymphocyte expansion rather than potentiating immune responses.\",\n      \"method\": \"Gene knockout (exon 2 disruption), immunofluorescence, co-immunoprecipitation, T-cell proliferation assay\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KO mouse with multiple readouts; this study contradicts some findings of Matsuda et al. 1998 regarding CD45–Lck interaction, so confidence is moderated by conflicting results\",\n      \"pmids\": [\"10602004\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"CD45-AP inhibits CD45 dimer formation: T cells from CD45-AP-null mice or a CD45-AP-null T-cell line (ALST-1) display much higher levels of CD45 dimers than wild-type cells; transfection of CD45-AP into ALST-1 cells reduces CD45 dimerization proportional to the amount of CD45-AP expressed. Consistent with a model where dimers are inactive, CD45 phosphatase activity (measured in microsomal fractions) is significantly lower in CD45-AP-negative cells than in CD45-AP-positive cells.\",\n      \"method\": \"CD45-AP knockout T cells, CD45-AP-null T-cell line (ALST-1), transfection, CD45 dimer assay, microsomal PTP activity assay\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — enzymatic activity assay combined with CD45 dimerization measurement across null and reconstituted cells using multiple independent systems\",\n      \"pmids\": [\"14715639\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"In CD4+ T cells from CD45-AP-deficient mice, co-immunoprecipitation of CD45 with the CD3/TCR complex and with Lck is significantly reduced compared to wild-type, correlating with decreased proliferative response, reduced IL-2 production, and reduced calcium flux specifically upon low-potency (but not high-avidity) peptide stimulation. This indicates CD45-AP promotes or stabilizes CD45 association with its substrates and lowers the threshold of T-cell activation.\",\n      \"method\": \"CD45-AP knockout mice, co-immunoprecipitation, proliferation assay, IL-2 ELISA, calcium flux measurement, altered peptide ligand stimulation\",\n      \"journal\": \"Immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO mice with multiple orthogonal functional readouts plus mechanistic co-IP data; consistent with prior knockout and interaction studies\",\n      \"pmids\": [\"17428310\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"CD45-AP (PTPRCAP) expression is downregulated specifically in marginal zone (MZ) B cells compared to other splenic B-cell subsets. CD45-AP mutant mice have reduced transitional and increased mature MZ and follicular B cells, suggesting CD45-AP prevents premature entry of transitional B cells into the mature B-cell pool or controls their survival and proliferation.\",\n      \"method\": \"RNA-seq of sorted B-cell subsets, gene-deleted and overexpressing transgenic mice, B-cell subset quantification\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO and transgenic mice with defined B-cell subset phenotypic readout; single lab, functional consequence established but molecular mechanism not fully resolved\",\n      \"pmids\": [\"25717326\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Overexpression of PTPRCAP in lung adenocarcinoma cell lines (A549, H1299) suppresses proliferation, migration, and invasion, and increases apoptosis. Mechanistically, PTPRCAP overexpression elevates pro-apoptotic Bax and cleaved caspase-3 while reducing anti-apoptotic Bcl-2. In vivo xenograft experiments confirm that PTPRCAP overexpression inhibits tumor growth.\",\n      \"method\": \"Plasmid overexpression in LUAD cell lines, CCK-8 proliferation assay, scratch/Transwell migration assay, Annexin V apoptosis assay, Western blot for Bax/Bcl-2/cleaved caspase-3, nude mouse xenografts\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal functional assays (in vitro + in vivo) in a single lab; Western blot identifies apoptosis pathway components modulated by PTPRCAP\",\n      \"pmids\": [\"41411247\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"miR-582-3p directly binds the 3'-UTR of PTPRCAP (validated by dual-luciferase reporter assay) and suppresses PTPRCAP expression in LUAD cells. PTPRCAP overexpression inhibits Wnt/β-catenin signaling (reduced β-catenin and p-GSK3β; restored GSK3β), and rescue experiments show PTPRCAP restoration counteracts miR-582-3p-mediated oncogenic phenotypes, placing PTPRCAP downstream of miR-582-3p and upstream of Wnt/β-catenin in LUAD.\",\n      \"method\": \"Dual-luciferase reporter assay, bioinformatics (TargetScan8.0), RT-qPCR, Western blot for Wnt pathway components, functional rescue experiments in LUAD cell lines\",\n      \"journal\": \"Frontiers in oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — dual-luciferase validates direct miRNA-3'UTR interaction; rescue experiments provide epistasis; single lab, limited to cancer cell lines with no prior replication\",\n      \"pmids\": [\"41064095\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PTPRCAP (CD45-AP) is a leukocyte-specific type I transmembrane adapter protein whose transmembrane domain directly docks onto the transmembrane segment of the tyrosine phosphatase CD45, stabilizing CD45 as a monomer (active form) and thereby up-regulating its phosphatase activity; in its cytoplasmic acidic domain, PTPRCAP binds directly and selectively to the kinase domains of Lck and ZAP-70 in a TCR-stimulation-dependent manner, assembling a multimolecular complex that includes CD45, TCR/CD3, CD4/CD8, and p56(lck), which promotes dephosphorylation of Lck's inhibitory tyrosine and lowers the threshold for antigen receptor signaling; loss of PTPRCAP in mice disrupts CD45–Lck co-association, reduces lymphocyte proliferation and cytotoxic responses, perturbs B-cell developmental subset transitions, and in non-immune (lung adenocarcinoma) contexts PTPRCAP acts as a tumor suppressor by promoting apoptosis through the Bax/caspase-3/Bcl-2 axis and by inhibiting Wnt/β-catenin signaling, the latter being regulated upstream by miR-582-3p targeting of the PTPRCAP 3'-UTR.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PTPRCAP (CD45-AP/LPAP) is a leukocyte-restricted type I transmembrane adapter protein that regulates the receptor tyrosine phosphatase CD45 and proximal antigen-receptor signaling in lymphocytes [#0, #4]. It was originally purified by its specific physical association with CD45, and reconstituted in vitro binding confirmed the interaction is direct [#0]; domain mapping established that the transmembrane segment of PTPRCAP docks onto the transmembrane portion of CD45, with the bulk of the adapter oriented in the cytoplasm [#1]. By opposing CD45 dimer formation, PTPRCAP stabilizes the active monomeric phosphatase and elevates CD45 catalytic activity, since CD45-AP-null cells accumulate inactive CD45 dimers and show reduced phosphatase activity [#8]. Through an acidic segment in its cytoplasmic region, PTPRCAP binds directly and selectively to the kinase domains of Lck and ZAP-70 in a TCR-stimulation-dependent manner, the Lck interaction scaling with Lck catalytic activation, thereby assembling a multimolecular complex containing CD45, TCR/CD3, CD4/CD8 coreceptors, and p56(lck) [#5, #6]. Functionally, loss of PTPRCAP in mice reduces antigen-receptor-driven T and B cell proliferation and cytotoxic responses, weakens CD45 association with the TCR/CD3 complex and Lck, and lowers the threshold for T-cell activation under low-potency ligand stimulation [#4, #9]; it also restrains transitional B-cell maturation into the marginal-zone and follicular pools [#10]. Beyond the immune system, PTPRCAP behaves as a tumor suppressor in lung adenocarcinoma, where its overexpression promotes apoptosis via increased Bax and cleaved caspase-3 with reduced Bcl-2 and inhibits Wnt/\\u03b2-catenin signaling, and where it is suppressed by miR-582-3p binding to its 3'-UTR [#11, #12].\",\n  \"teleology\": [\n    {\n      \"year\": 1994,\n      \"claim\": \"Established that a leukocyte-specific ~30 kDa protein physically associates with CD45, defining PTPRCAP as a candidate CD45 adapter.\",\n      \"evidence\": \"Protein purification by CD45 association, in vitro translation/binding, and cDNA cloning\",\n      \"pmids\": [\"8300558\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not localize the binding interface\", \"No functional consequence of the interaction established\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Mapped the CD45 docking interface to the transmembrane segments and defined PTPRCAP's membrane topology, explaining how it engages CD45 within the membrane.\",\n      \"evidence\": \"Deletion/chimeric mutant binding analysis, cell fractionation, protease protection in lymphocytes\",\n      \"pmids\": [\"7673147\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not address effect on CD45 enzymatic activity\", \"Cytoplasmic functional partners unidentified\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Showed PTPRCAP exists in two N-terminal variant forms, that its stability depends on CD45, and that expression is confined to T, B, and pre-B cells, refining its cellular distribution.\",\n      \"evidence\": \"Northern blot, Western blot, pulse-chase half-life analysis, cell-type expression survey\",\n      \"pmids\": [\"9045908\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional difference between the two isoforms unresolved\", \"Mechanism of CD45-dependent stabilization unknown\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Defined the human and mouse gene structure and chromosomal location, providing the genomic foundation for the locus.\",\n      \"evidence\": \"FISH, multilocus cross Southern hybridization, genomic sequencing in two independent groups\",\n      \"pmids\": [\"8954783\", \"8975722\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No regulatory element function characterized\", \"Does not address protein function\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Demonstrated in vivo that PTPRCAP supports antigen-receptor responses and is required for efficient CD45\\u2013Lck association, linking the adapter to functional immune signaling.\",\n      \"evidence\": \"CD45-AP knockout mice with co-IP, proliferation, MLR, and CTL assays\",\n      \"pmids\": [\"9607926\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the CD45\\u2013Lck effect is direct or indirect not resolved\", \"Molecular basis of impaired proliferation undefined\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Identified the cytoplasmic acidic segment as a direct, activity-dependent binding site for the Lck and ZAP-70 kinase domains and placed PTPRCAP within a CD45/TCR/coreceptor/Lck complex.\",\n      \"evidence\": \"Co-IP in multiple cell contexts, structure-function deletion analysis, recombinant protein binding, TCR stimulation\",\n      \"pmids\": [\"10318863\", \"9880514\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Selectivity over Fyn/Csk mechanistically unexplained\", \"Stoichiometry of the multimolecular complex unknown\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Provided a contrasting knockout phenotype in which CD45 surface expression was reduced but CD45\\u2013Lck assembly and polyclonal responses were intact, complicating the model of PTPRCAP as a pure positive regulator.\",\n      \"evidence\": \"Exon 2 disruption KO, immunofluorescence, co-IP, T-cell proliferation assay\",\n      \"pmids\": [\"10602004\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Conflicts with the CD45\\u2013Lck disruption reported in other KO lines\", \"Mechanism of reduced CD45 surface expression not defined\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Resolved how PTPRCAP regulates CD45 activity by showing it suppresses inactive CD45 dimer formation and thereby raises phosphatase activity.\",\n      \"evidence\": \"KO T cells and a CD45-AP-null T-cell line (ALST-1) with reconstitution, CD45 dimer assay, microsomal PTP activity assay\",\n      \"pmids\": [\"14715639\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for monomer stabilization unknown\", \"Link between dimer suppression and downstream signaling outputs not directly traced\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Showed PTPRCAP stabilizes CD45 association with the TCR/CD3 complex and Lck and lowers the activation threshold for weak-affinity ligands, sharpening its role in signal sensitivity.\",\n      \"evidence\": \"KO mice with co-IP, proliferation, IL-2 ELISA, calcium flux, altered peptide ligand stimulation\",\n      \"pmids\": [\"17428310\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Why only low-potency ligand responses are affected unexplained\", \"Quantitative contribution to substrate recruitment unknown\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Extended PTPRCAP function to B-cell development, showing it controls transitional-to-mature B-cell subset transitions.\",\n      \"evidence\": \"RNA-seq of sorted B-cell subsets with gene-deleted and overexpressing transgenic mice\",\n      \"pmids\": [\"25717326\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular mechanism of subset control not resolved\", \"Whether effect depends on CD45 phosphatase regulation untested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identified a non-immune tumor-suppressor role in lung adenocarcinoma via apoptosis induction and Wnt/\\u03b2-catenin inhibition, with miR-582-3p as an upstream repressor of PTPRCAP.\",\n      \"evidence\": \"Overexpression in LUAD lines, CCK-8/migration/apoptosis assays, Western blot for Bax/Bcl-2/caspase-3 and Wnt components, xenografts, dual-luciferase reporter, rescue experiments\",\n      \"pmids\": [\"41411247\", \"41064095\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether tumor suppression involves CD45/Lck or is phosphatase-independent unknown\", \"Single-lab cancer cell line data without independent replication\", \"Direct molecular link between PTPRCAP and Wnt/\\u03b2-catenin not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How PTPRCAP mechanistically connects its membrane CD45-regulatory function to the cytoplasmic Wnt/apoptosis effects observed in epithelial tumors remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of the CD45\\u2013PTPRCAP transmembrane complex\", \"Conflicting KO phenotypes on CD45\\u2013Lck not reconciled\", \"Mechanism bridging immune and tumor-suppressor roles unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 5, 6]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [8]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [1, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [4, 5, 9]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [6, 9]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [11]}\n    ],\n    \"complexes\": [\"CD45\\u2013TCR/CD3\\u2013CD4/CD8\\u2013Lck signaling complex\"],\n    \"partners\": [\"PTPRC\", \"LCK\", \"ZAP70\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"faith_supported":6,"faith_total":6,"faith_pct":100.0}}