{"gene":"PAG1","run_date":"2026-06-10T05:19:53","timeline":{"discoveries":[{"year":2000,"finding":"PAG (PAG1) is a transmembrane adaptor protein constitutively tyrosine-phosphorylated in resting T cells and lymphoid lines; it directly binds the tyrosine kinase Csk via its cytoplasmic tail, recruiting Csk to glycosphingolipid-enriched membrane microdomains (lipid rafts). Expression in COS cells recruits endogenous Csk, alters Src kinase activity, and impairs phosphorylation of Src-specific substrates. Overexpression in Jurkat cells downregulates TCR-mediated NFAT activation.","method":"Co-immunoprecipitation, COS-cell overexpression functional assay, Jurkat NFAT reporter assay, primary T cell biochemistry","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, functional overexpression assays in multiple cell systems, replicated across subsequent studies","pmids":["10790433"],"is_preprint":false},{"year":2003,"finding":"PAG-mediated inhibition of TCR signaling requires tyrosine phosphorylation of PAG and its association with Csk; the inhibitory effect is rescued by a constitutively activated Src-related kinase, confirming that PAG-associated Csk inactivates Src kinases. CD45 transmembrane phosphatase is implicated in PAG dephosphorylation following TCR stimulation, whereas PEP and SHP-1 are not required for this dephosphorylation.","method":"Wild-type and phosphorylation-defective PAG overexpression in primary mouse T cells, cell fractionation, analysis of CD45-, PEP-, and SHP-1-deficient mice","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal approaches including dominant-negative mutants, constitutively active kinase rescue, and genetically modified mice in a single study","pmids":["12612075"],"is_preprint":false},{"year":2001,"finding":"PAG interacts with EBP50 (NHERF) via a C-terminal PDZ-binding motif (TRL sequence of PAG) and the N-terminal PDZ domain(s) of EBP50; since EBP50 binds ERM-family proteins that connect to actin cytoskeleton, this interaction links membrane rafts to the actin cytoskeleton.","method":"Yeast two-hybrid screen, domain-mapping with PAG C-terminal truncations","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — yeast two-hybrid plus domain mapping, single lab, not confirmed by reciprocal Co-IP in mammalian cells in this study","pmids":["11684085"],"is_preprint":false},{"year":2007,"finding":"PAG is constitutively associated with FynT in unstimulated T cells via tyrosines other than Y314; FynT is required for PAG tyrosine phosphorylation and consequent Csk binding. Dissociation of the PAG-FynT complex precedes PAG dephosphorylation after TCR engagement. In anergic T cells, PAG-FynT association is increased. A PAG variant that binds FynT but not Csk enhances TCR-triggered calcium flux and promotes T-cell anergy in a FynT-dependent manner.","method":"Co-immunoprecipitation, PAG mutant overexpression, FynT-knockout mice, calcium flux assays, T-cell anergy assays","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, multiple PAG mutants, FynT-KO validation, functional readouts across orthogonal assays in one study","pmids":["17210649"],"is_preprint":false},{"year":2007,"finding":"In B-NHL rafts, PAG/Cbp is phosphorylated at Y317 and binds Lyn SH2 via pY299; together with auto-phosphorylated Lyn and phospho-STAT3 (linked via SH2 to Lyn C-terminal regulatory tyrosine), they form a constitutive raft-associated signalosome. Lyn inhibitors prevent Lyn and PAG phosphorylation, dissociate the signalosome, and induce cell death, implicating the PAG-Lyn complex in B-NHL survival.","method":"Biochemical fractionation, Co-IP, site-specific phospho-antibodies, Lyn kinase inhibitor treatment, cell viability assays","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, phosphosite-specific antibodies, inhibitor-based functional validation; single lab","pmids":["18070987"],"is_preprint":false},{"year":2007,"finding":"FynT interacts with PAG via a dual-domain docking mechanism: FynT SH2 domain binds PAG phosphotyrosines and FynT SH3 domain binds the first proline-rich region of PAG. SH3 engagement is required for efficient PAG phosphorylation initiation, while SH2 engagement renders FynT insensitive to Csk negative regulation. This dual-domain binding modulates FynT kinase activity, PAG phosphorylation, and recruitment of FynT and Csk in Jurkat and primary T cells.","method":"SPR binding assays, kinase activity assays, SH3/SH2 domain mutant overexpression in Jurkat cells and primary T cells, Co-IP","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — in vitro binding kinetics (SPR), mutagenesis of interaction domains, in-cell kinase assays, and functional TCR signaling readouts","pmids":["18056706"],"is_preprint":false},{"year":2005,"finding":"Protein tyrosine phosphatase alpha (PTPalpha) localizes in part to lipid rafts of thymocytes and regulates raft-associated Fyn activity; in PTPalpha-null thymocytes, Fyn is hyperactivated (increased phosphorylation of Y528 and Y417), which causes hyperphosphorylation of PAG/Cbp and enhanced association of PAG with Csk. PTPalpha is not the phosphatase responsible for PAG dephosphorylation after TCR stimulation.","method":"PTPalpha-knockout mouse thymocytes, kinase activity assays, phospho-specific antibodies, lipid raft fractionation","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — knockout mouse model, multiple biochemical readouts; single lab, and the PTPalpha negative result for PAG dephosphorylation is explicitly reported","pmids":["16339530"],"is_preprint":false},{"year":2008,"finding":"PAG regulates PDGF receptor (PDGFR) partitioning in caveolae and SFK mitogenic signaling through a Csk-independent mechanism. The N-terminal 97 aa of PAG (including extracellular/transmembrane domains, palmitoylation sites, and short cytoplasmic sequence) increase ganglioside GM1 levels at the cell surface via the ganglioside-specific sialidase Neu-3, thereby displacing PDGFR from caveolae.","method":"PAG truncation mutants, ganglioside GM1 quantification, PDGFR caveolae fractionation, Csk-deficient cell reconstitution, Neu-3 siRNA knockdown","journal":"The Journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple domain mutants and mechanistic dissection (Csk-independence confirmed, Neu-3 requirement shown); single lab","pmids":["18695048"],"is_preprint":false},{"year":2010,"finding":"PAG/Cbp (PAG1) suppresses anchorage-independent growth of c-Src-upregulated NSCLC cells by recruiting c-Src and Csk to lipid rafts, thereby reducing c-Src kinase activity. PAG1 re-expression attenuates tumor formation in nude mice, invasion in vitro, and metastasis in vivo; its expression is markedly downregulated in NSCLC cells.","method":"PAG1 ectopic expression in NSCLC cell lines, c-Src kinase assay, lipid raft fractionation, Co-IP, xenograft tumor model, in vitro invasion assay","journal":"Molecular cancer research : MCR","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical mechanism (Csk recruitment to rafts) plus in vivo xenograft validation; single lab","pmids":["21156787"],"is_preprint":false},{"year":2011,"finding":"PAG1/Cbp expression is downregulated in Src-transformed cells by epigenetic histone modifications (decreased H4 acetylation and increased H3K27 trimethylation at the cbp promoter) via the MAPK/PI3K pathway; HDAC inhibitors and HDAC1/2 siRNA knockdown restore PAG1 expression. DNA methylation of the cbp promoter CpG islands is not involved.","method":"MEK/PI3K inhibitors, HDAC inhibitor treatment, HDAC1/2 siRNA, ChIP for histone modifications, mRNA stability assay, promoter reporter assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP mechanistic evidence plus pharmacological and RNAi confirmation; single lab, multiple orthogonal methods","pmids":["21388951"],"is_preprint":false},{"year":2013,"finding":"Cbp/PAG is phosphorylated by Lyn at Y314 in developing cerebellar growth cones; ganglioside GD3 co-immunoprecipitates with Cbp/PAG and antibody crosslinking of GD3 or GD1b activates Lyn and induces Cbp/PAG tyrosine phosphorylation. Active Lyn and Y314-phosphorylated Cbp/PAG are concentrated in growth cone DRM raft fractions of developing cerebellum.","method":"Co-immunoprecipitation with anti-ganglioside antibody, sucrose density gradient fractionation, Lyn/Cbp overexpression in CHO cells, antibody-induced signaling assays","journal":"Journal of neurochemistry","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — Co-IP, ectopic expression kinase assay, antibody crosslinking; single lab","pmids":["23035659"],"is_preprint":false},{"year":2015,"finding":"A distal hypoxia response element (HRE) 82 kb upstream of PAG1 physically interacts with the PAG1 promoter in a HIF-independent constitutive chromatin loop (shown by 3C); HIF-1 directly binds this HRE to drive hypoxia-induced PAG1 expression. Ablation of the consensus HRE motif by TALEN gene editing abolishes hypoxic PAG1 induction without affecting general oxygen signaling.","method":"ChIP, chromosome conformation capture (3C), TALEN gene editing, luciferase reporter assays, RT-qPCR in multiple cell lines and mouse tissues","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — TALEN mutagenesis, 3C conformation capture, ChIP, and reporter assays provide multiple orthogonal mechanistic lines of evidence","pmids":["26007655"],"is_preprint":false},{"year":2016,"finding":"Genetic deletion of PAG enhances effector (but not naive) T cell activation and augments T cell-dependent autoimmunity and resistance to anergy in vivo. In PAG-deficient mice, Csk redistributes to alternative partners PTPN22 and Dok adaptors; combined PAG + PTPN22 or PAG + Dok deficiency further amplifies effector T cell responses, establishing epistatic cooperation.","method":"PAG-knockout mice, PTPN22- and Dok-deficient mice, double knockout combinations, T cell activation and autoimmunity assays, Co-IP for Csk partners","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo knockout genetic epistasis with multiple double-KO combinations and orthogonal functional readouts","pmids":["27926878"],"is_preprint":false},{"year":2014,"finding":"PAG-deficient bone marrow-derived mast cells exhibit impaired antigen-induced degranulation, calcium uptake, tyrosine phosphorylation of FcεRI subunits, Syk, and PLCγ, cytokine/chemokine production, and chemotaxis, indicating PAG acts as a positive regulator of FcεRI signaling. Conversely, PAG-deficient BMMCs show enhanced Kit receptor-induced degranulation, indicating PAG acts as a negative regulator of Kit signaling. LYN and FYN kinase activities are increased in non-activated PAG-KO cells, suggesting a negative regulatory loop.","method":"PAG-knockout and PAG-knockdown bone marrow-derived mast cells, degranulation assays, calcium flux, phospho-flow cytometry, cytokine ELISA, in vivo passive systemic anaphylaxis","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo KO model, multiple orthogonal signaling readouts, in vivo anaphylaxis validation; single lab with comprehensive phenotyping","pmids":["25246632"],"is_preprint":false},{"year":2021,"finding":"PAG is phosphorylated following PD-1 ligation in human T cells and mediates PD-1 inhibitory signaling; PAG knockdown prevents PD-1-mediated inhibition of cytokine secretion, cell adhesion, CD69 expression, and ERK phosphorylation, and enhances SRC527 phosphorylation. PAG overexpression rescues these effects. In vivo, PAG deficiency limits T cell presence in tumors and sensitizes tumors to PD-1 blockade.","method":"PAG knockdown/overexpression in primary T cells, PD-1 ligation experiments, phospho-protein assays, in vivo murine tumor models (MC38 and B16) with PAG deletion","journal":"Communications biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KD/OE with multiple functional readouts plus in vivo validation; single lab","pmids":["34083754"],"is_preprint":false},{"year":2010,"finding":"PAG participates in a supramolecular signaling complex consisting of PKA type I, Ezrin, EBP50, PAG, and Csk in effector T cell lipid rafts. This Ezrin-EBP50-PAG scaffold spatiotemporally controls cAMP immunomodulation through the PKA-Csk inhibitory pathway.","method":"Co-immunoprecipitation, lipid raft fractionation, complex component identification","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — Co-IP and fractionation demonstrating complex assembly; multiple independent labs had previously identified individual interactions","pmids":["20420835"],"is_preprint":false},{"year":2015,"finding":"Quantitative proteomics of tagged-PAG complexes in primary mouse CD4+ T cells reveals PAG has low tyrosine phosphorylation in resting cells that increases after stimulation (peaking at 2 min), contrary to prior biochemical studies showing constitutive phosphorylation in resting cells. PTPN22 and SHIP-1 dynamically associate with PAG following T cell activation, suggesting they cooperate with Csk to terminate T cell activation.","method":"Affinity-purification mass spectrometry (AP-MS) with knock-in tagged PAG, quantitative phosphoproteomics, primary thymocytes and CD4+ T cells","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — quantitative AP-MS with endogenous tag knock-in; single lab, contradicts earlier biochemical studies on phosphorylation timing","pmids":["26512138"],"is_preprint":false},{"year":2013,"finding":"PAG knockdown in primary human T cells enhances Src kinase activity and TCR proximal signaling, but rather than causing hyperproliferation, leads to unresponsiveness mediated by Fyn-dependent hyperphosphorylation of CTLA-4, which recruits Shp-1 phosphatase to lipid rafts. Co-suppression of CTLA-4 restores proliferation, identifying a CTLA-4-dependent fail-safe downstream of PAG loss.","method":"PAG siRNA knockdown in primary human T cells, CTLA-4 co-knockdown, Src kinase activity assay, CTLA-4 phosphorylation assay, lipid raft fractionation, proliferation assays","journal":"Cell communication and signaling : CCS","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RNAi + genetic epistasis (co-knockdown), multiple functional readouts; single lab","pmids":["23601194"],"is_preprint":false},{"year":2018,"finding":"PAG1 interacts with integrin β1 in lipid rafts of radioresistant laryngeal cancer cells; this interaction can be disrupted by methyl-β-cyclodextrin (lipid raft disruptor). PAG1-integrin β1 complex activates STAT3, and STAT3 activation is required for PAG1-mediated radioresistance; STAT3 inhibition sensitizes cells to radiation. Two binding sites in the PAG1 cytoplasmic domain (Pro216-Arg232 and Asn356-Gly377) mediate interaction with integrin β1.","method":"Proteomic Co-IP screen, immunofluorescence co-localization, MβCD disruption, peptide array mapping, integrin β1 siRNA knockdown, STAT3 inhibitor treatment, clonogenic survival assay","journal":"Journal of Cancer / Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — proteomic Co-IP plus domain mapping and functional rescue; single lab, multiple orthogonal methods","pmids":["30519312","29913153"],"is_preprint":false},{"year":2019,"finding":"PAG1 deficiency in mice leads to increased airway epithelial HMGB1 translocation/release, expanded ILC2s and monocyte-derived dendritic cells, and enhanced TH2-cell differentiation following allergen challenge, resulting in more severe type 2 airway inflammation. T cell adoptive transfer experiments show that the heightened TH2 differentiation is both T cell-intrinsic and T cell-extrinsic.","method":"Pag1-knockout mice, HDM allergen challenge, CD4+ T cell depletion, adoptive transfer of OVA-specific T cells, flow cytometry, cytokine measurements","journal":"Allergy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo KO model with adoptive transfer dissection; single lab, multiple orthogonal readouts","pmids":["31321783"],"is_preprint":false},{"year":2008,"finding":"A palmitoylation-deficient PAG mutant (lacking the CxxC palmitoylation motif) is expressed at the plasma membrane but outside GEM rafts; it still binds Fyn, EBP50, becomes tyrosine-phosphorylated, and recruits Csk, but unlike wild-type PAG does not block proximal TCR signaling. Instead, it depletes Csk from GEM fractions, enhancing CXCL12-induced T cell migration and Src kinase activity in rafts. This demonstrates that raft compartmentalization of PAG is essential for its inhibitory function on TCR signaling.","method":"PAG palmitoylation mutant overexpression, lipid raft fractionation, Co-IP, TCR signaling assays, PAG RNAi, migration assays","journal":"European journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — separation-of-function mutant plus RNAi validation with multiple functional readouts; single lab","pmids":["18085663"],"is_preprint":false}],"current_model":"PAG1 (PAG/Cbp) is a palmitoylated transmembrane adaptor protein constitutively resident in lipid rafts that acts as a critical negative regulator of Src-family kinase (SFK) signaling by serving as a membrane scaffold for Csk: FynT phosphorylates PAG1 on multiple tyrosines (most critically Y314/Y317), enabling Csk binding and consequent inhibitory phosphorylation of raft-associated SFKs including Lck; TCR stimulation triggers CD45-mediated PAG1 dephosphorylation and Csk release, permitting T cell activation. Raft localization (dependent on palmitoylation) is required for this inhibitory function. Beyond Csk, PAG1 assembles multi-protein complexes including FynT (via dual SH2/SH3 docking), EBP50/Ezrin (linking rafts to actin cytoskeleton), PKA/Csk (cAMP pathway scaffold), PTPN22 and Dok adaptors (cooperative Csk-independent inhibition in effector T cells), integrin β1 (activating STAT3 in cancer), and mediates PD-1 inhibitory signaling; in mast cells PAG1 can function as either positive (FcεRI) or negative (Kit) regulator depending on the receptor context, and its expression is subject to hypoxia-induced transcriptional regulation via a distal HRE and to epigenetic silencing via HDAC-dependent histone modifications in oncogenically transformed cells."},"narrative":{"mechanistic_narrative":"PAG1 (PAG/Cbp) is a palmitoylated transmembrane adaptor that resides constitutively in glycosphingolipid-enriched lipid rafts and functions as a central negative regulator of Src-family kinase signaling by recruiting the inhibitory kinase Csk to the membrane [PMID:10790433, PMID:12612075]. In resting T cells PAG1 is tyrosine-phosphorylated by raft-associated FynT, which docks through a dual SH2/SH3 mechanism—its SH3 domain engaging a PAG1 proline-rich region to initiate phosphorylation and its SH2 domain binding PAG1 phosphotyrosines to render FynT resistant to Csk—and this phosphorylation creates the binding site that anchors Csk to inactivate raft SFKs including Lck [PMID:17210649, PMID:18056706]. TCR engagement triggers CD45-mediated dephosphorylation of PAG1 and Csk release, relieving the brake and permitting T cell activation [PMID:12612075]. Localization within rafts, which depends on the palmitoylation (CxxC) motif, is strictly required for the inhibitory function: a non-palmitoylated mutant still binds Fyn and Csk but fails to suppress TCR signaling and instead depletes Csk from rafts [PMID:18085663]. Genetic loss of PAG1 selectively augments effector T cell activation and autoimmunity, with Csk redistributing to alternative scaffolds PTPN22 and Dok in epistatic cooperation [PMID:27926878, PMID:26512138]. PAG1 nucleates additional raft signalosomes, linking rafts to the actin cytoskeleton via an EBP50/Ezrin module and to cAMP control via a PKA-I/Ezrin/EBP50/PAG/Csk complex [PMID:11684085, PMID:20420835], and it transmits PD-1 inhibitory signaling in human T cells [PMID:34083754]. Beyond lymphocytes, PAG1 acts as a tumor suppressor by recruiting c-Src and Csk to rafts in lung cancer [PMID:21156787], is epigenetically silenced through HDAC-dependent histone modifications in Src-transformed cells [PMID:21388951], and is transcriptionally induced under hypoxia through a HIF-1-bound distal enhancer that loops to the promoter [PMID:26007655]. Its regulatory output is context-dependent, acting as a positive regulator of FcεRI but a negative regulator of Kit signaling in mast cells [PMID:25246632].","teleology":[{"year":2000,"claim":"Established PAG1 as the membrane anchor that recruits Csk to lipid rafts, answering how the cytosolic inhibitory kinase reaches raft-resident Src kinases.","evidence":"Co-IP, COS-cell overexpression, and Jurkat NFAT reporter assays in T cells","pmids":["10790433"],"confidence":"High","gaps":["Did not resolve which kinase phosphorylates PAG1 or which phosphatase reverses it","Specific Src substrates affected not enumerated"]},{"year":2003,"claim":"Demonstrated that PAG1 inhibition of TCR signaling requires its phosphorylation and Csk association, and identified CD45 as the phosphatase driving post-TCR PAG1 dephosphorylation.","evidence":"Phosphorylation-defective PAG mutants and constitutively active Src rescue in primary mouse T cells, plus CD45-, PEP-, SHP-1-deficient mice","pmids":["12612075"],"confidence":"High","gaps":["Mechanism of CD45 access/specificity to PAG1 not defined","Kinase responsible for PAG1 phosphorylation not yet identified here"]},{"year":2001,"claim":"Connected PAG1 rafts to the actin cytoskeleton by mapping a C-terminal PDZ-binding motif that engages EBP50/NHERF.","evidence":"Yeast two-hybrid screen with PAG C-terminal truncation domain mapping","pmids":["11684085"],"confidence":"Medium","gaps":["Not confirmed by reciprocal Co-IP in mammalian cells in this study","Functional consequence of raft-actin linkage not tested"]},{"year":2005,"claim":"Placed PAG1 phosphorylation downstream of raft Fyn activity by showing PTPalpha loss hyperactivates Fyn and hyperphosphorylates PAG1, while excluding PTPalpha as the TCR-responsive PAG1 phosphatase.","evidence":"PTPalpha-knockout thymocytes with kinase assays and raft fractionation","pmids":["16339530"],"confidence":"Medium","gaps":["Identity of the TCR-stimulation phosphatase still open in this study","Single lab"]},{"year":2007,"claim":"Defined the dual SH2/SH3 docking mechanism by which FynT binds and phosphorylates PAG1 and showed PAG1-FynT interactions can drive T-cell anergy independently of Csk binding.","evidence":"SPR binding kinetics, SH2/SH3 mutants, FynT-KO mice, Co-IP, and calcium/anergy assays","pmids":["18056706","17210649"],"confidence":"High","gaps":["Trigger for PAG1-FynT dissociation after TCR engagement not fully resolved","Structural basis of the dual-domain docking not solved"]},{"year":2007,"claim":"Extended PAG1 signalosome function to malignancy, showing a constitutive raft PAG-Lyn-STAT3 complex sustains B-NHL survival.","evidence":"Biochemical fractionation, phosphosite antibodies, Lyn inhibitor treatment, viability assays","pmids":["18070987"],"confidence":"Medium","gaps":["Single lab","Direct contribution of PAG1 versus Lyn to survival not genetically separated"]},{"year":2008,"claim":"Proved that raft compartmentalization, conferred by palmitoylation, is essential for PAG1's inhibitory function, separating membrane localization from Csk/Fyn binding.","evidence":"Palmitoylation-deficient (CxxC) mutant with raft fractionation, Co-IP, TCR/migration assays, RNAi","pmids":["18085663"],"confidence":"Medium","gaps":["Single lab","Quantitative raft-versus-non-raft Csk pool dynamics not measured in vivo"]},{"year":2008,"claim":"Revealed a Csk-independent PAG1 mechanism: an N-terminal segment raises surface GM1 via Neu-3 to displace PDGFR from caveolae and modulate mitogenic SFK signaling.","evidence":"PAG truncation mutants, GM1 quantification, caveolae fractionation, Csk-deficient reconstitution, Neu-3 siRNA","pmids":["18695048"],"confidence":"Medium","gaps":["Molecular link between PAG1 N-terminus and Neu-3 activity unresolved","Single lab"]},{"year":2010,"claim":"Defined PAG1 as a tumor suppressor in c-Src-driven lung cancer by recruiting c-Src and Csk to rafts and suppressing anchorage-independent growth and metastasis.","evidence":"PAG1 ectopic re-expression in NSCLC lines, c-Src kinase assay, raft fractionation, xenograft and invasion assays","pmids":["21156787"],"confidence":"Medium","gaps":["Cause of PAG1 downregulation in NSCLC not yet established here","Single lab"]},{"year":2010,"claim":"Identified a higher-order raft scaffold (PKA-I/Ezrin/EBP50/PAG/Csk) coupling cAMP signaling to the Csk inhibitory pathway in effector T cells.","evidence":"Co-IP and lipid raft fractionation defining complex composition","pmids":["20420835"],"confidence":"Medium","gaps":["Direct versus indirect connectivity among complex members not dissected","Single lab"]},{"year":2011,"claim":"Explained PAG1 loss in transformed cells as epigenetic silencing through MAPK/PI3K-driven HDAC-dependent histone modifications rather than DNA methylation.","evidence":"MEK/PI3K and HDAC inhibitors, HDAC1/2 siRNA, ChIP for histone marks, promoter reporter assays","pmids":["21388951"],"confidence":"Medium","gaps":["Direct HDAC1/2 recruitment mechanism to the promoter not shown","Single lab"]},{"year":2013,"claim":"Extended PAG1/Lyn raft signaling to neural development, showing ganglioside crosslinking activates Lyn to phosphorylate Cbp/PAG at Y314 in cerebellar growth cones.","evidence":"Anti-ganglioside Co-IP, density gradient fractionation, Lyn/Cbp ectopic expression and crosslinking assays","pmids":["23035659"],"confidence":"Medium","gaps":["Functional consequence for axon/growth-cone behavior not established","Single lab"]},{"year":2013,"claim":"Uncovered a CTLA-4-dependent fail-safe downstream of PAG loss, where Fyn-driven CTLA-4 hyperphosphorylation recruits Shp-1 and enforces T cell unresponsiveness despite elevated Src activity.","evidence":"PAG and CTLA-4 siRNA co-knockdown in primary human T cells, kinase and phosphorylation assays, proliferation readouts","pmids":["23601194"],"confidence":"Medium","gaps":["Whether this fail-safe operates in vivo not tested here","Single lab"]},{"year":2014,"claim":"Showed PAG1 has receptor-context-dependent polarity in mast cells—positive for FcεRI, negative for Kit—rather than a uniform inhibitory role.","evidence":"PAG-knockout/knockdown BMMCs, degranulation, calcium flux, phospho-flow, cytokine ELISA, in vivo anaphylaxis","pmids":["25246632"],"confidence":"High","gaps":["Molecular basis distinguishing FcεRI versus Kit outcomes not resolved","Single lab"]},{"year":2015,"claim":"Identified a HIF-1-bound distal HRE that loops constitutively to the PAG1 promoter to drive hypoxic induction, defining transcriptional control of PAG1.","evidence":"ChIP, 3C chromosome conformation capture, TALEN editing, luciferase reporters, RT-qPCR across cell lines and tissues","pmids":["26007655"],"confidence":"High","gaps":["Physiological role of hypoxic PAG1 induction not connected to signaling output","Loop-forming factors not identified"]},{"year":2015,"claim":"Quantitative endogenous-tag proteomics challenged the constitutive-phosphorylation model, showing low resting PAG1 phosphorylation that rises after stimulation and revealed dynamic recruitment of PTPN22 and SHIP-1.","evidence":"AP-MS with knock-in tagged PAG and quantitative phosphoproteomics in primary CD4+ T cells","pmids":["26512138"],"confidence":"Medium","gaps":["Reconciliation with earlier constitutive-phosphorylation biochemistry incomplete","Functional role of SHIP-1 association not tested"]},{"year":2016,"claim":"Genetic epistasis defined PAG1 as a selective brake on effector T cells whose loss redistributes Csk to PTPN22 and Dok adaptors in cooperative inhibition.","evidence":"PAG, PTPN22, and Dok single and double knockout mice with autoimmunity and Co-IP readouts","pmids":["27926878"],"confidence":"High","gaps":["Why effector but not naive T cells depend on PAG not mechanistically resolved","Stoichiometry of Csk redistribution not quantified"]},{"year":2018,"claim":"Linked PAG1 to therapy resistance, mapping two cytoplasmic binding sites that engage integrin β1 to activate STAT3 and confer radioresistance in laryngeal cancer.","evidence":"Proteomic Co-IP, peptide-array mapping, MβCD raft disruption, integrin β1 siRNA, STAT3 inhibitor, clonogenic assays","pmids":["30519312","29913153"],"confidence":"Medium","gaps":["Mechanism coupling integrin β1 binding to STAT3 activation not detailed","Single lab"]},{"year":2019,"claim":"Demonstrated an in vivo role for PAG1 in restraining type 2 airway inflammation via both T-cell-intrinsic and -extrinsic control of TH2 differentiation.","evidence":"Pag1-knockout mice with HDM challenge, T cell depletion, OVA-specific adoptive transfer, flow cytometry","pmids":["31321783"],"confidence":"Medium","gaps":["Molecular pathway linking PAG1 loss to epithelial HMGB1 release unresolved","Single lab"]},{"year":2021,"claim":"Placed PAG1 within PD-1 inhibitory signaling, showing it is phosphorylated upon PD-1 ligation and required for PD-1-mediated T cell suppression, with deletion sensitizing tumors to checkpoint blockade.","evidence":"PAG knockdown/overexpression in primary T cells, PD-1 ligation, phospho-assays, MC38/B16 in vivo tumor models","pmids":["34083754"],"confidence":"Medium","gaps":["Direct biochemical link between PD-1 and PAG1 phosphorylation not defined","Single lab"]},{"year":null,"claim":"How PAG1 integrates competing positive and negative inputs across receptor and tissue contexts—and the structural basis and recruitment logic that switch its output—remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of the PAG1 cytoplasmic scaffold bound to its partners","Mechanism determining positive versus negative regulatory polarity not defined","In vivo phosphatase-kinase dynamics governing PAG1 phosphorylation timing not fully reconciled"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,3,5,15]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,1,12]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,20]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,1,12,13,14]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,5,7,18]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[8,9,18]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[11,9]}],"complexes":["PAG/Csk raft complex","PKA-I/Ezrin/EBP50/PAG/Csk complex","PAG-Lyn-STAT3 signalosome (B-NHL rafts)"],"partners":["CSK","FYN","LCK","LYN","EBP50/NHERF1","PTPN22","ITGB1","PDCD1/PD-1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9NWQ8","full_name":"Phosphoprotein associated with glycosphingolipid-enriched microdomains 1","aliases":["Csk-binding protein","Transmembrane adapter protein PAG","Transmembrane phosphoprotein Cbp"],"length_aa":432,"mass_kda":47.0,"function":"Negatively regulates TCR (T-cell antigen receptor)-mediated signaling in T-cells and FCER1 (high affinity immunoglobulin epsilon receptor)-mediated signaling in mast cells. Promotes CSK activation and recruitment to lipid rafts, which results in LCK inhibition. Inhibits immunological synapse formation by preventing dynamic arrangement of lipid raft proteins. May be involved in cell adhesion signaling","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q9NWQ8/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PAG1","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/PAG1","total_profiled":1310},"omim":[{"mim_id":"605767","title":"PHOSPHOPROTEIN ASSOCIATED WITH GLYCOSPHINGOLIPID-ENRICHED MICRODOMAINS 1; PAG1","url":"https://www.omim.org/entry/605767"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Vesicles","reliability":"Supported"},{"location":"Plasma membrane","reliability":"Supported"}],"tissue_specificity":"Low tissue 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reduces formalin-induced pain behavior via PAG in a rat model.","date":"2017","source":"Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/28673711","citation_count":16,"is_preprint":false},{"pmid":"16997391","id":"PMC_16997391","title":"Elevated pCREB in the PAG after exposure to the elevated plus maze in rats previously exposed to a cat.","date":"2006","source":"Behavioural brain research","url":"https://pubmed.ncbi.nlm.nih.gov/16997391","citation_count":16,"is_preprint":false},{"pmid":"14698458","id":"PMC_14698458","title":"Distinct regions of periaqueductal gray (PAG) are involved in freezing behavior in hooded PVG rats on the cat-freezing test apparatus.","date":"2004","source":"Neuroscience letters","url":"https://pubmed.ncbi.nlm.nih.gov/14698458","citation_count":15,"is_preprint":false},{"pmid":"32857187","id":"PMC_32857187","title":"Positive allosteric modulation of the cannabinoid type-1 receptor (CB1R) in periaqueductal gray (PAG) antagonizes anti-nociceptive and cellular effects of a mu-opioid receptor agonist in morphine-withdrawn rats.","date":"2020","source":"Psychopharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/32857187","citation_count":14,"is_preprint":false},{"pmid":"16143214","id":"PMC_16143214","title":"Chorionic mRNA expression and N-glycodiversity of pregnancy-associated glycoprotein family (PAG) of the European bison (Bison bonasus).","date":"2005","source":"Animal reproduction science","url":"https://pubmed.ncbi.nlm.nih.gov/16143214","citation_count":14,"is_preprint":false},{"pmid":"28489932","id":"PMC_28489932","title":"CaMKIIα may modulate fentanyl-induced hyperalgesia via a CeLC-PAG-RVM-spinal cord descending facilitative pain pathway in rats.","date":"2017","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/28489932","citation_count":14,"is_preprint":false},{"pmid":"2331299","id":"PMC_2331299","title":"Immunological reactivity and passive protective activity of monoclonal antibodies against protective antigen (PAg) of Leptospira interrogans serovar lai.","date":"1990","source":"Zentralblatt fur Bakteriologie : international journal of medical microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/2331299","citation_count":14,"is_preprint":false},{"pmid":"17612511","id":"PMC_17612511","title":"Prostaglandin E2 (PGE2) inhibits glutamatergic synaptic transmission in dorsolateral periaqueductal gray (dl-PAG).","date":"2007","source":"Brain research","url":"https://pubmed.ncbi.nlm.nih.gov/17612511","citation_count":14,"is_preprint":false},{"pmid":"31321783","id":"PMC_31321783","title":"PAG1 limits allergen-induced type 2 inflammation in the murine lung.","date":"2019","source":"Allergy","url":"https://pubmed.ncbi.nlm.nih.gov/31321783","citation_count":13,"is_preprint":false},{"pmid":"30116247","id":"PMC_30116247","title":"Positive and Negative Regulatory Roles of C-Terminal Src Kinase (CSK) in FcεRI-Mediated Mast Cell Activation, Independent of the Transmembrane Adaptor PAG/CSK-Binding Protein.","date":"2018","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/30116247","citation_count":13,"is_preprint":false},{"pmid":"19963012","id":"PMC_19963012","title":"Role of homocysteic acid in the guinea pig (Cavia porcellus) anterior cingulate cortex in tonic immobility and the influence of NMDA receptors on the dorsal PAG.","date":"2009","source":"Behavioural brain research","url":"https://pubmed.ncbi.nlm.nih.gov/19963012","citation_count":13,"is_preprint":false},{"pmid":"21543471","id":"PMC_21543471","title":"Heliothis zea nudivirus 1 gene hhi1 induces apoptosis which is blocked by the Hz-iap2 gene and a noncoding gene, pag1.","date":"2011","source":"Journal of virology","url":"https://pubmed.ncbi.nlm.nih.gov/21543471","citation_count":12,"is_preprint":false},{"pmid":"32218734","id":"PMC_32218734","title":"Chronic Fluoxetine Impairs the Effects of 5-HT1A and 5-HT2C Receptors Activation in the PAG and Amygdala on Antinociception Induced by Aversive Situation in Mice.","date":"2020","source":"Frontiers in pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/32218734","citation_count":12,"is_preprint":false},{"pmid":"11275406","id":"PMC_11275406","title":"Lamina I-periaqueductal gray (PAG) projections represent only a limited part of the total spinal and caudal medullary input to the PAG in the cat.","date":"2001","source":"Brain research bulletin","url":"https://pubmed.ncbi.nlm.nih.gov/11275406","citation_count":12,"is_preprint":false},{"pmid":"20656339","id":"PMC_20656339","title":"Pregnancy-associated glycoprotein (PAG) family localized in chorionic cells within the epitheliochorial/diffuse placenta of the alpaca (Lama pacos).","date":"2010","source":"Acta histochemica","url":"https://pubmed.ncbi.nlm.nih.gov/20656339","citation_count":12,"is_preprint":false},{"pmid":"29913153","id":"PMC_29913153","title":"PAG1 promotes the inherent radioresistance of laryngeal cancer cells via activation of STAT3.","date":"2018","source":"Experimental cell research","url":"https://pubmed.ncbi.nlm.nih.gov/29913153","citation_count":11,"is_preprint":false},{"pmid":"37352811","id":"PMC_37352811","title":"PAG neuronal NMDARs activation mediated morphine-induced hyperalgesia by HMGB1-TLR4 dependent microglial inflammation.","date":"2023","source":"Journal of psychiatric research","url":"https://pubmed.ncbi.nlm.nih.gov/37352811","citation_count":11,"is_preprint":false},{"pmid":"30519312","id":"PMC_30519312","title":"Identification of Integrin β1 as a Novel PAG1-Interacting Protein Involved in the Inherent Radioresistance of Human Laryngeal Carcinoma.","date":"2018","source":"Journal of Cancer","url":"https://pubmed.ncbi.nlm.nih.gov/30519312","citation_count":11,"is_preprint":false},{"pmid":"19734952","id":"PMC_19734952","title":"Pregnancy-associated glycoprotein (PAG) family: transcripts and gene amplicons in camelids.","date":"2009","source":"Reproductive biology","url":"https://pubmed.ncbi.nlm.nih.gov/19734952","citation_count":11,"is_preprint":false},{"pmid":"26512138","id":"PMC_26512138","title":"Revisiting the Timing of Action of the PAG Adaptor Using Quantitative Proteomics Analysis of Primary T Cells.","date":"2015","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/26512138","citation_count":11,"is_preprint":false},{"pmid":"23601194","id":"PMC_23601194","title":"PAG/Cbp suppression reveals a contribution of CTLA-4 to setting the activation threshold in T cells.","date":"2013","source":"Cell communication and signaling : CCS","url":"https://pubmed.ncbi.nlm.nih.gov/23601194","citation_count":11,"is_preprint":false},{"pmid":"15975665","id":"PMC_15975665","title":"Expression pattern of adaptor protein PAG: correlation between secondary lymphatic follicle and histogenetically related malignant lymphomas.","date":"2005","source":"Immunology letters","url":"https://pubmed.ncbi.nlm.nih.gov/15975665","citation_count":10,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":50639,"output_tokens":6134,"usd":0.121964,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":14879,"output_tokens":5982,"usd":0.111973,"stage2_stop_reason":"end_turn"},"total_usd":0.233937,"stage1_batch_id":"msgbatch_013a8chtv3AWyTqv4z4sEF4C","stage2_batch_id":"msgbatch_01AHsuW63vinsvuTgzmQ3n62","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2000,\n      \"finding\": \"PAG (PAG1) is a transmembrane adaptor protein constitutively tyrosine-phosphorylated in resting T cells and lymphoid lines; it directly binds the tyrosine kinase Csk via its cytoplasmic tail, recruiting Csk to glycosphingolipid-enriched membrane microdomains (lipid rafts). Expression in COS cells recruits endogenous Csk, alters Src kinase activity, and impairs phosphorylation of Src-specific substrates. Overexpression in Jurkat cells downregulates TCR-mediated NFAT activation.\",\n      \"method\": \"Co-immunoprecipitation, COS-cell overexpression functional assay, Jurkat NFAT reporter assay, primary T cell biochemistry\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, functional overexpression assays in multiple cell systems, replicated across subsequent studies\",\n      \"pmids\": [\"10790433\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"PAG-mediated inhibition of TCR signaling requires tyrosine phosphorylation of PAG and its association with Csk; the inhibitory effect is rescued by a constitutively activated Src-related kinase, confirming that PAG-associated Csk inactivates Src kinases. CD45 transmembrane phosphatase is implicated in PAG dephosphorylation following TCR stimulation, whereas PEP and SHP-1 are not required for this dephosphorylation.\",\n      \"method\": \"Wild-type and phosphorylation-defective PAG overexpression in primary mouse T cells, cell fractionation, analysis of CD45-, PEP-, and SHP-1-deficient mice\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal approaches including dominant-negative mutants, constitutively active kinase rescue, and genetically modified mice in a single study\",\n      \"pmids\": [\"12612075\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"PAG interacts with EBP50 (NHERF) via a C-terminal PDZ-binding motif (TRL sequence of PAG) and the N-terminal PDZ domain(s) of EBP50; since EBP50 binds ERM-family proteins that connect to actin cytoskeleton, this interaction links membrane rafts to the actin cytoskeleton.\",\n      \"method\": \"Yeast two-hybrid screen, domain-mapping with PAG C-terminal truncations\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — yeast two-hybrid plus domain mapping, single lab, not confirmed by reciprocal Co-IP in mammalian cells in this study\",\n      \"pmids\": [\"11684085\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"PAG is constitutively associated with FynT in unstimulated T cells via tyrosines other than Y314; FynT is required for PAG tyrosine phosphorylation and consequent Csk binding. Dissociation of the PAG-FynT complex precedes PAG dephosphorylation after TCR engagement. In anergic T cells, PAG-FynT association is increased. A PAG variant that binds FynT but not Csk enhances TCR-triggered calcium flux and promotes T-cell anergy in a FynT-dependent manner.\",\n      \"method\": \"Co-immunoprecipitation, PAG mutant overexpression, FynT-knockout mice, calcium flux assays, T-cell anergy assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, multiple PAG mutants, FynT-KO validation, functional readouts across orthogonal assays in one study\",\n      \"pmids\": [\"17210649\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"In B-NHL rafts, PAG/Cbp is phosphorylated at Y317 and binds Lyn SH2 via pY299; together with auto-phosphorylated Lyn and phospho-STAT3 (linked via SH2 to Lyn C-terminal regulatory tyrosine), they form a constitutive raft-associated signalosome. Lyn inhibitors prevent Lyn and PAG phosphorylation, dissociate the signalosome, and induce cell death, implicating the PAG-Lyn complex in B-NHL survival.\",\n      \"method\": \"Biochemical fractionation, Co-IP, site-specific phospho-antibodies, Lyn kinase inhibitor treatment, cell viability assays\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, phosphosite-specific antibodies, inhibitor-based functional validation; single lab\",\n      \"pmids\": [\"18070987\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"FynT interacts with PAG via a dual-domain docking mechanism: FynT SH2 domain binds PAG phosphotyrosines and FynT SH3 domain binds the first proline-rich region of PAG. SH3 engagement is required for efficient PAG phosphorylation initiation, while SH2 engagement renders FynT insensitive to Csk negative regulation. This dual-domain binding modulates FynT kinase activity, PAG phosphorylation, and recruitment of FynT and Csk in Jurkat and primary T cells.\",\n      \"method\": \"SPR binding assays, kinase activity assays, SH3/SH2 domain mutant overexpression in Jurkat cells and primary T cells, Co-IP\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — in vitro binding kinetics (SPR), mutagenesis of interaction domains, in-cell kinase assays, and functional TCR signaling readouts\",\n      \"pmids\": [\"18056706\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Protein tyrosine phosphatase alpha (PTPalpha) localizes in part to lipid rafts of thymocytes and regulates raft-associated Fyn activity; in PTPalpha-null thymocytes, Fyn is hyperactivated (increased phosphorylation of Y528 and Y417), which causes hyperphosphorylation of PAG/Cbp and enhanced association of PAG with Csk. PTPalpha is not the phosphatase responsible for PAG dephosphorylation after TCR stimulation.\",\n      \"method\": \"PTPalpha-knockout mouse thymocytes, kinase activity assays, phospho-specific antibodies, lipid raft fractionation\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — knockout mouse model, multiple biochemical readouts; single lab, and the PTPalpha negative result for PAG dephosphorylation is explicitly reported\",\n      \"pmids\": [\"16339530\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"PAG regulates PDGF receptor (PDGFR) partitioning in caveolae and SFK mitogenic signaling through a Csk-independent mechanism. The N-terminal 97 aa of PAG (including extracellular/transmembrane domains, palmitoylation sites, and short cytoplasmic sequence) increase ganglioside GM1 levels at the cell surface via the ganglioside-specific sialidase Neu-3, thereby displacing PDGFR from caveolae.\",\n      \"method\": \"PAG truncation mutants, ganglioside GM1 quantification, PDGFR caveolae fractionation, Csk-deficient cell reconstitution, Neu-3 siRNA knockdown\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple domain mutants and mechanistic dissection (Csk-independence confirmed, Neu-3 requirement shown); single lab\",\n      \"pmids\": [\"18695048\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PAG/Cbp (PAG1) suppresses anchorage-independent growth of c-Src-upregulated NSCLC cells by recruiting c-Src and Csk to lipid rafts, thereby reducing c-Src kinase activity. PAG1 re-expression attenuates tumor formation in nude mice, invasion in vitro, and metastasis in vivo; its expression is markedly downregulated in NSCLC cells.\",\n      \"method\": \"PAG1 ectopic expression in NSCLC cell lines, c-Src kinase assay, lipid raft fractionation, Co-IP, xenograft tumor model, in vitro invasion assay\",\n      \"journal\": \"Molecular cancer research : MCR\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical mechanism (Csk recruitment to rafts) plus in vivo xenograft validation; single lab\",\n      \"pmids\": [\"21156787\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PAG1/Cbp expression is downregulated in Src-transformed cells by epigenetic histone modifications (decreased H4 acetylation and increased H3K27 trimethylation at the cbp promoter) via the MAPK/PI3K pathway; HDAC inhibitors and HDAC1/2 siRNA knockdown restore PAG1 expression. DNA methylation of the cbp promoter CpG islands is not involved.\",\n      \"method\": \"MEK/PI3K inhibitors, HDAC inhibitor treatment, HDAC1/2 siRNA, ChIP for histone modifications, mRNA stability assay, promoter reporter assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP mechanistic evidence plus pharmacological and RNAi confirmation; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"21388951\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Cbp/PAG is phosphorylated by Lyn at Y314 in developing cerebellar growth cones; ganglioside GD3 co-immunoprecipitates with Cbp/PAG and antibody crosslinking of GD3 or GD1b activates Lyn and induces Cbp/PAG tyrosine phosphorylation. Active Lyn and Y314-phosphorylated Cbp/PAG are concentrated in growth cone DRM raft fractions of developing cerebellum.\",\n      \"method\": \"Co-immunoprecipitation with anti-ganglioside antibody, sucrose density gradient fractionation, Lyn/Cbp overexpression in CHO cells, antibody-induced signaling assays\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — Co-IP, ectopic expression kinase assay, antibody crosslinking; single lab\",\n      \"pmids\": [\"23035659\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"A distal hypoxia response element (HRE) 82 kb upstream of PAG1 physically interacts with the PAG1 promoter in a HIF-independent constitutive chromatin loop (shown by 3C); HIF-1 directly binds this HRE to drive hypoxia-induced PAG1 expression. Ablation of the consensus HRE motif by TALEN gene editing abolishes hypoxic PAG1 induction without affecting general oxygen signaling.\",\n      \"method\": \"ChIP, chromosome conformation capture (3C), TALEN gene editing, luciferase reporter assays, RT-qPCR in multiple cell lines and mouse tissues\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — TALEN mutagenesis, 3C conformation capture, ChIP, and reporter assays provide multiple orthogonal mechanistic lines of evidence\",\n      \"pmids\": [\"26007655\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Genetic deletion of PAG enhances effector (but not naive) T cell activation and augments T cell-dependent autoimmunity and resistance to anergy in vivo. In PAG-deficient mice, Csk redistributes to alternative partners PTPN22 and Dok adaptors; combined PAG + PTPN22 or PAG + Dok deficiency further amplifies effector T cell responses, establishing epistatic cooperation.\",\n      \"method\": \"PAG-knockout mice, PTPN22- and Dok-deficient mice, double knockout combinations, T cell activation and autoimmunity assays, Co-IP for Csk partners\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo knockout genetic epistasis with multiple double-KO combinations and orthogonal functional readouts\",\n      \"pmids\": [\"27926878\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PAG-deficient bone marrow-derived mast cells exhibit impaired antigen-induced degranulation, calcium uptake, tyrosine phosphorylation of FcεRI subunits, Syk, and PLCγ, cytokine/chemokine production, and chemotaxis, indicating PAG acts as a positive regulator of FcεRI signaling. Conversely, PAG-deficient BMMCs show enhanced Kit receptor-induced degranulation, indicating PAG acts as a negative regulator of Kit signaling. LYN and FYN kinase activities are increased in non-activated PAG-KO cells, suggesting a negative regulatory loop.\",\n      \"method\": \"PAG-knockout and PAG-knockdown bone marrow-derived mast cells, degranulation assays, calcium flux, phospho-flow cytometry, cytokine ELISA, in vivo passive systemic anaphylaxis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo KO model, multiple orthogonal signaling readouts, in vivo anaphylaxis validation; single lab with comprehensive phenotyping\",\n      \"pmids\": [\"25246632\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PAG is phosphorylated following PD-1 ligation in human T cells and mediates PD-1 inhibitory signaling; PAG knockdown prevents PD-1-mediated inhibition of cytokine secretion, cell adhesion, CD69 expression, and ERK phosphorylation, and enhances SRC527 phosphorylation. PAG overexpression rescues these effects. In vivo, PAG deficiency limits T cell presence in tumors and sensitizes tumors to PD-1 blockade.\",\n      \"method\": \"PAG knockdown/overexpression in primary T cells, PD-1 ligation experiments, phospho-protein assays, in vivo murine tumor models (MC38 and B16) with PAG deletion\",\n      \"journal\": \"Communications biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KD/OE with multiple functional readouts plus in vivo validation; single lab\",\n      \"pmids\": [\"34083754\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PAG participates in a supramolecular signaling complex consisting of PKA type I, Ezrin, EBP50, PAG, and Csk in effector T cell lipid rafts. This Ezrin-EBP50-PAG scaffold spatiotemporally controls cAMP immunomodulation through the PKA-Csk inhibitory pathway.\",\n      \"method\": \"Co-immunoprecipitation, lipid raft fractionation, complex component identification\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — Co-IP and fractionation demonstrating complex assembly; multiple independent labs had previously identified individual interactions\",\n      \"pmids\": [\"20420835\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Quantitative proteomics of tagged-PAG complexes in primary mouse CD4+ T cells reveals PAG has low tyrosine phosphorylation in resting cells that increases after stimulation (peaking at 2 min), contrary to prior biochemical studies showing constitutive phosphorylation in resting cells. PTPN22 and SHIP-1 dynamically associate with PAG following T cell activation, suggesting they cooperate with Csk to terminate T cell activation.\",\n      \"method\": \"Affinity-purification mass spectrometry (AP-MS) with knock-in tagged PAG, quantitative phosphoproteomics, primary thymocytes and CD4+ T cells\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — quantitative AP-MS with endogenous tag knock-in; single lab, contradicts earlier biochemical studies on phosphorylation timing\",\n      \"pmids\": [\"26512138\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PAG knockdown in primary human T cells enhances Src kinase activity and TCR proximal signaling, but rather than causing hyperproliferation, leads to unresponsiveness mediated by Fyn-dependent hyperphosphorylation of CTLA-4, which recruits Shp-1 phosphatase to lipid rafts. Co-suppression of CTLA-4 restores proliferation, identifying a CTLA-4-dependent fail-safe downstream of PAG loss.\",\n      \"method\": \"PAG siRNA knockdown in primary human T cells, CTLA-4 co-knockdown, Src kinase activity assay, CTLA-4 phosphorylation assay, lipid raft fractionation, proliferation assays\",\n      \"journal\": \"Cell communication and signaling : CCS\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RNAi + genetic epistasis (co-knockdown), multiple functional readouts; single lab\",\n      \"pmids\": [\"23601194\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"PAG1 interacts with integrin β1 in lipid rafts of radioresistant laryngeal cancer cells; this interaction can be disrupted by methyl-β-cyclodextrin (lipid raft disruptor). PAG1-integrin β1 complex activates STAT3, and STAT3 activation is required for PAG1-mediated radioresistance; STAT3 inhibition sensitizes cells to radiation. Two binding sites in the PAG1 cytoplasmic domain (Pro216-Arg232 and Asn356-Gly377) mediate interaction with integrin β1.\",\n      \"method\": \"Proteomic Co-IP screen, immunofluorescence co-localization, MβCD disruption, peptide array mapping, integrin β1 siRNA knockdown, STAT3 inhibitor treatment, clonogenic survival assay\",\n      \"journal\": \"Journal of Cancer / Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — proteomic Co-IP plus domain mapping and functional rescue; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"30519312\", \"29913153\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PAG1 deficiency in mice leads to increased airway epithelial HMGB1 translocation/release, expanded ILC2s and monocyte-derived dendritic cells, and enhanced TH2-cell differentiation following allergen challenge, resulting in more severe type 2 airway inflammation. T cell adoptive transfer experiments show that the heightened TH2 differentiation is both T cell-intrinsic and T cell-extrinsic.\",\n      \"method\": \"Pag1-knockout mice, HDM allergen challenge, CD4+ T cell depletion, adoptive transfer of OVA-specific T cells, flow cytometry, cytokine measurements\",\n      \"journal\": \"Allergy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo KO model with adoptive transfer dissection; single lab, multiple orthogonal readouts\",\n      \"pmids\": [\"31321783\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"A palmitoylation-deficient PAG mutant (lacking the CxxC palmitoylation motif) is expressed at the plasma membrane but outside GEM rafts; it still binds Fyn, EBP50, becomes tyrosine-phosphorylated, and recruits Csk, but unlike wild-type PAG does not block proximal TCR signaling. Instead, it depletes Csk from GEM fractions, enhancing CXCL12-induced T cell migration and Src kinase activity in rafts. This demonstrates that raft compartmentalization of PAG is essential for its inhibitory function on TCR signaling.\",\n      \"method\": \"PAG palmitoylation mutant overexpression, lipid raft fractionation, Co-IP, TCR signaling assays, PAG RNAi, migration assays\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — separation-of-function mutant plus RNAi validation with multiple functional readouts; single lab\",\n      \"pmids\": [\"18085663\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PAG1 (PAG/Cbp) is a palmitoylated transmembrane adaptor protein constitutively resident in lipid rafts that acts as a critical negative regulator of Src-family kinase (SFK) signaling by serving as a membrane scaffold for Csk: FynT phosphorylates PAG1 on multiple tyrosines (most critically Y314/Y317), enabling Csk binding and consequent inhibitory phosphorylation of raft-associated SFKs including Lck; TCR stimulation triggers CD45-mediated PAG1 dephosphorylation and Csk release, permitting T cell activation. Raft localization (dependent on palmitoylation) is required for this inhibitory function. Beyond Csk, PAG1 assembles multi-protein complexes including FynT (via dual SH2/SH3 docking), EBP50/Ezrin (linking rafts to actin cytoskeleton), PKA/Csk (cAMP pathway scaffold), PTPN22 and Dok adaptors (cooperative Csk-independent inhibition in effector T cells), integrin β1 (activating STAT3 in cancer), and mediates PD-1 inhibitory signaling; in mast cells PAG1 can function as either positive (FcεRI) or negative (Kit) regulator depending on the receptor context, and its expression is subject to hypoxia-induced transcriptional regulation via a distal HRE and to epigenetic silencing via HDAC-dependent histone modifications in oncogenically transformed cells.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PAG1 (PAG/Cbp) is a palmitoylated transmembrane adaptor that resides constitutively in glycosphingolipid-enriched lipid rafts and functions as a central negative regulator of Src-family kinase signaling by recruiting the inhibitory kinase Csk to the membrane [#0, #1]. In resting T cells PAG1 is tyrosine-phosphorylated by raft-associated FynT, which docks through a dual SH2/SH3 mechanism—its SH3 domain engaging a PAG1 proline-rich region to initiate phosphorylation and its SH2 domain binding PAG1 phosphotyrosines to render FynT resistant to Csk—and this phosphorylation creates the binding site that anchors Csk to inactivate raft SFKs including Lck [#3, #5]. TCR engagement triggers CD45-mediated dephosphorylation of PAG1 and Csk release, relieving the brake and permitting T cell activation [#1]. Localization within rafts, which depends on the palmitoylation (CxxC) motif, is strictly required for the inhibitory function: a non-palmitoylated mutant still binds Fyn and Csk but fails to suppress TCR signaling and instead depletes Csk from rafts [#20]. Genetic loss of PAG1 selectively augments effector T cell activation and autoimmunity, with Csk redistributing to alternative scaffolds PTPN22 and Dok in epistatic cooperation [#12, #16]. PAG1 nucleates additional raft signalosomes, linking rafts to the actin cytoskeleton via an EBP50/Ezrin module and to cAMP control via a PKA-I/Ezrin/EBP50/PAG/Csk complex [#2, #15], and it transmits PD-1 inhibitory signaling in human T cells [#14]. Beyond lymphocytes, PAG1 acts as a tumor suppressor by recruiting c-Src and Csk to rafts in lung cancer [#8], is epigenetically silenced through HDAC-dependent histone modifications in Src-transformed cells [#9], and is transcriptionally induced under hypoxia through a HIF-1-bound distal enhancer that loops to the promoter [#11]. Its regulatory output is context-dependent, acting as a positive regulator of FcεRI but a negative regulator of Kit signaling in mast cells [#13].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Established PAG1 as the membrane anchor that recruits Csk to lipid rafts, answering how the cytosolic inhibitory kinase reaches raft-resident Src kinases.\",\n      \"evidence\": \"Co-IP, COS-cell overexpression, and Jurkat NFAT reporter assays in T cells\",\n      \"pmids\": [\"10790433\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve which kinase phosphorylates PAG1 or which phosphatase reverses it\", \"Specific Src substrates affected not enumerated\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Demonstrated that PAG1 inhibition of TCR signaling requires its phosphorylation and Csk association, and identified CD45 as the phosphatase driving post-TCR PAG1 dephosphorylation.\",\n      \"evidence\": \"Phosphorylation-defective PAG mutants and constitutively active Src rescue in primary mouse T cells, plus CD45-, PEP-, SHP-1-deficient mice\",\n      \"pmids\": [\"12612075\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of CD45 access/specificity to PAG1 not defined\", \"Kinase responsible for PAG1 phosphorylation not yet identified here\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Connected PAG1 rafts to the actin cytoskeleton by mapping a C-terminal PDZ-binding motif that engages EBP50/NHERF.\",\n      \"evidence\": \"Yeast two-hybrid screen with PAG C-terminal truncation domain mapping\",\n      \"pmids\": [\"11684085\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Not confirmed by reciprocal Co-IP in mammalian cells in this study\", \"Functional consequence of raft-actin linkage not tested\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Placed PAG1 phosphorylation downstream of raft Fyn activity by showing PTPalpha loss hyperactivates Fyn and hyperphosphorylates PAG1, while excluding PTPalpha as the TCR-responsive PAG1 phosphatase.\",\n      \"evidence\": \"PTPalpha-knockout thymocytes with kinase assays and raft fractionation\",\n      \"pmids\": [\"16339530\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Identity of the TCR-stimulation phosphatase still open in this study\", \"Single lab\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Defined the dual SH2/SH3 docking mechanism by which FynT binds and phosphorylates PAG1 and showed PAG1-FynT interactions can drive T-cell anergy independently of Csk binding.\",\n      \"evidence\": \"SPR binding kinetics, SH2/SH3 mutants, FynT-KO mice, Co-IP, and calcium/anergy assays\",\n      \"pmids\": [\"18056706\", \"17210649\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Trigger for PAG1-FynT dissociation after TCR engagement not fully resolved\", \"Structural basis of the dual-domain docking not solved\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Extended PAG1 signalosome function to malignancy, showing a constitutive raft PAG-Lyn-STAT3 complex sustains B-NHL survival.\",\n      \"evidence\": \"Biochemical fractionation, phosphosite antibodies, Lyn inhibitor treatment, viability assays\",\n      \"pmids\": [\"18070987\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Direct contribution of PAG1 versus Lyn to survival not genetically separated\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Proved that raft compartmentalization, conferred by palmitoylation, is essential for PAG1's inhibitory function, separating membrane localization from Csk/Fyn binding.\",\n      \"evidence\": \"Palmitoylation-deficient (CxxC) mutant with raft fractionation, Co-IP, TCR/migration assays, RNAi\",\n      \"pmids\": [\"18085663\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Quantitative raft-versus-non-raft Csk pool dynamics not measured in vivo\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Revealed a Csk-independent PAG1 mechanism: an N-terminal segment raises surface GM1 via Neu-3 to displace PDGFR from caveolae and modulate mitogenic SFK signaling.\",\n      \"evidence\": \"PAG truncation mutants, GM1 quantification, caveolae fractionation, Csk-deficient reconstitution, Neu-3 siRNA\",\n      \"pmids\": [\"18695048\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular link between PAG1 N-terminus and Neu-3 activity unresolved\", \"Single lab\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Defined PAG1 as a tumor suppressor in c-Src-driven lung cancer by recruiting c-Src and Csk to rafts and suppressing anchorage-independent growth and metastasis.\",\n      \"evidence\": \"PAG1 ectopic re-expression in NSCLC lines, c-Src kinase assay, raft fractionation, xenograft and invasion assays\",\n      \"pmids\": [\"21156787\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Cause of PAG1 downregulation in NSCLC not yet established here\", \"Single lab\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Identified a higher-order raft scaffold (PKA-I/Ezrin/EBP50/PAG/Csk) coupling cAMP signaling to the Csk inhibitory pathway in effector T cells.\",\n      \"evidence\": \"Co-IP and lipid raft fractionation defining complex composition\",\n      \"pmids\": [\"20420835\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct versus indirect connectivity among complex members not dissected\", \"Single lab\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Explained PAG1 loss in transformed cells as epigenetic silencing through MAPK/PI3K-driven HDAC-dependent histone modifications rather than DNA methylation.\",\n      \"evidence\": \"MEK/PI3K and HDAC inhibitors, HDAC1/2 siRNA, ChIP for histone marks, promoter reporter assays\",\n      \"pmids\": [\"21388951\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct HDAC1/2 recruitment mechanism to the promoter not shown\", \"Single lab\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Extended PAG1/Lyn raft signaling to neural development, showing ganglioside crosslinking activates Lyn to phosphorylate Cbp/PAG at Y314 in cerebellar growth cones.\",\n      \"evidence\": \"Anti-ganglioside Co-IP, density gradient fractionation, Lyn/Cbp ectopic expression and crosslinking assays\",\n      \"pmids\": [\"23035659\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence for axon/growth-cone behavior not established\", \"Single lab\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Uncovered a CTLA-4-dependent fail-safe downstream of PAG loss, where Fyn-driven CTLA-4 hyperphosphorylation recruits Shp-1 and enforces T cell unresponsiveness despite elevated Src activity.\",\n      \"evidence\": \"PAG and CTLA-4 siRNA co-knockdown in primary human T cells, kinase and phosphorylation assays, proliferation readouts\",\n      \"pmids\": [\"23601194\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether this fail-safe operates in vivo not tested here\", \"Single lab\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Showed PAG1 has receptor-context-dependent polarity in mast cells—positive for FcεRI, negative for Kit—rather than a uniform inhibitory role.\",\n      \"evidence\": \"PAG-knockout/knockdown BMMCs, degranulation, calcium flux, phospho-flow, cytokine ELISA, in vivo anaphylaxis\",\n      \"pmids\": [\"25246632\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis distinguishing FcεRI versus Kit outcomes not resolved\", \"Single lab\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identified a HIF-1-bound distal HRE that loops constitutively to the PAG1 promoter to drive hypoxic induction, defining transcriptional control of PAG1.\",\n      \"evidence\": \"ChIP, 3C chromosome conformation capture, TALEN editing, luciferase reporters, RT-qPCR across cell lines and tissues\",\n      \"pmids\": [\"26007655\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological role of hypoxic PAG1 induction not connected to signaling output\", \"Loop-forming factors not identified\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Quantitative endogenous-tag proteomics challenged the constitutive-phosphorylation model, showing low resting PAG1 phosphorylation that rises after stimulation and revealed dynamic recruitment of PTPN22 and SHIP-1.\",\n      \"evidence\": \"AP-MS with knock-in tagged PAG and quantitative phosphoproteomics in primary CD4+ T cells\",\n      \"pmids\": [\"26512138\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Reconciliation with earlier constitutive-phosphorylation biochemistry incomplete\", \"Functional role of SHIP-1 association not tested\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Genetic epistasis defined PAG1 as a selective brake on effector T cells whose loss redistributes Csk to PTPN22 and Dok adaptors in cooperative inhibition.\",\n      \"evidence\": \"PAG, PTPN22, and Dok single and double knockout mice with autoimmunity and Co-IP readouts\",\n      \"pmids\": [\"27926878\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Why effector but not naive T cells depend on PAG not mechanistically resolved\", \"Stoichiometry of Csk redistribution not quantified\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Linked PAG1 to therapy resistance, mapping two cytoplasmic binding sites that engage integrin β1 to activate STAT3 and confer radioresistance in laryngeal cancer.\",\n      \"evidence\": \"Proteomic Co-IP, peptide-array mapping, MβCD raft disruption, integrin β1 siRNA, STAT3 inhibitor, clonogenic assays\",\n      \"pmids\": [\"30519312\", \"29913153\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism coupling integrin β1 binding to STAT3 activation not detailed\", \"Single lab\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Demonstrated an in vivo role for PAG1 in restraining type 2 airway inflammation via both T-cell-intrinsic and -extrinsic control of TH2 differentiation.\",\n      \"evidence\": \"Pag1-knockout mice with HDM challenge, T cell depletion, OVA-specific adoptive transfer, flow cytometry\",\n      \"pmids\": [\"31321783\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular pathway linking PAG1 loss to epithelial HMGB1 release unresolved\", \"Single lab\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Placed PAG1 within PD-1 inhibitory signaling, showing it is phosphorylated upon PD-1 ligation and required for PD-1-mediated T cell suppression, with deletion sensitizing tumors to checkpoint blockade.\",\n      \"evidence\": \"PAG knockdown/overexpression in primary T cells, PD-1 ligation, phospho-assays, MC38/B16 in vivo tumor models\",\n      \"pmids\": [\"34083754\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct biochemical link between PD-1 and PAG1 phosphorylation not defined\", \"Single lab\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How PAG1 integrates competing positive and negative inputs across receptor and tissue contexts—and the structural basis and recruitment logic that switch its output—remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of the PAG1 cytoplasmic scaffold bound to its partners\", \"Mechanism determining positive versus negative regulatory polarity not defined\", \"In vivo phosphatase-kinase dynamics governing PAG1 phosphorylation timing not fully reconciled\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 3, 5, 15]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 12]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 20]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 1, 12, 13, 14]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 5, 7, 18]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [8, 9, 18]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [11, 9]}\n    ],\n    \"complexes\": [\n      \"PAG/Csk raft complex\",\n      \"PKA-I/Ezrin/EBP50/PAG/Csk complex\",\n      \"PAG-Lyn-STAT3 signalosome (B-NHL rafts)\"\n    ],\n    \"partners\": [\n      \"CSK\",\n      \"FYN\",\n      \"LCK\",\n      \"LYN\",\n      \"EBP50/NHERF1\",\n      \"PTPN22\",\n      \"ITGB1\",\n      \"PDCD1/PD-1\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}