{"gene":"SELPLG","run_date":"2026-04-28T20:42:07","timeline":{"discoveries":[{"year":1995,"finding":"A short segment near the amino terminus of PSGL-1 containing a tyrosine sulfation consensus is essential for P-selectin adhesion; mutation of N-terminal tyrosines to phenylalanine abolishes P-selectin binding, and sulfation inhibitors greatly reduce binding.","method":"Site-directed mutagenesis, sulfation inhibitor treatment, rolling adhesion assay on P-selectin-coated coverslips","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis + functional adhesion assay in a high-impact single paper; replicated by multiple subsequent labs","pmids":["7585950"],"is_preprint":false},{"year":1997,"finding":"CLA (cutaneous lymphocyte antigen), the skin-homing receptor on T cells, is an inducible carbohydrate modification (mediated by fucosyltransferase VII) of PSGL-1 that confers E-selectin binding; PSGL-1 without CLA binds P-selectin but not E-selectin, demonstrating independent regulation of selectin-binding phenotypes.","method":"Monoclonal antibody characterization, T cell differentiation assays, selectin-binding functional assays","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods, widely replicated; foundational discovery","pmids":["9353122"],"is_preprint":false},{"year":1998,"finding":"Dimerization of PSGL-1 through a single conserved extracellular cysteine (C320) is essential for functional recognition of P-selectin; a C320A monomeric mutant fails to support rolling or P-selectin chimera binding.","method":"Site-directed mutagenesis, Western blotting under native/denaturing conditions, rolling adhesion assay under physiologic flow, P-selectin chimera binding","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1 — reconstitution with mutagenesis and flow-based functional assay in a single rigorous paper","pmids":["9660879"],"is_preprint":false},{"year":1996,"finding":"PSGL-1 serves as a ligand for L-selectin on neutrophils, mediating neutrophil aggregation; blocking PSGL-1 with Fab fragments of PL1 antibody reduces neutrophil aggregate number and size, consistent with L-selectin–PSGL-1 counter-receptor interaction.","method":"Flow cytometry aggregation assay, blocking antibody (Fab fragments) experiments","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 3 — antibody blocking and flow cytometry, single paper; replicated in later studies","pmids":["8839831"],"is_preprint":false},{"year":1999,"finding":"P-selectin binding to PSGL-1 triggers tyrosine kinase-dependent (Syk-like) signaling that activates CD11b/CD18 (beta2-integrin) on PMN; PSGL-1 engagement with a non-adhesion-blocking antibody was sufficient to trigger beta2-integrin-dependent aggregation and tyrosine phosphorylation.","method":"Mixed cell aggregation assays under shear, blocking antibodies, tyrosine kinase inhibitors (genistein), CHO-P transfectants, P-selectin-IgG fusion protein stimulation","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal approaches (inhibitors, antibodies, transfected cell lines) in a single paper; foundational signaling mechanism","pmids":["9920836"],"is_preprint":false},{"year":2000,"finding":"PSGL-1 is expressed on platelets (at 25–100-fold lower levels than leukocytes) and mediates platelet rolling in mesenteric venules in vivo; anti-PSGL-1 antibody significantly reduced platelet rolling as shown by intravital microscopy.","method":"P-selectin-IgG affinity purification, immunoelectron microscopy, Western blotting, flow cytometry, intravital microscopy","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (biochemical isolation, imaging, in vivo functional assay)","pmids":["10770806"],"is_preprint":false},{"year":2000,"finding":"The human granulocytic ehrlichiosis (HGE) bacterium infects neutrophils by specifically binding to fucosylated PSGL-1; blocking the P-selectin binding domain of PSGL-1 with monoclonal antibodies or enzymatic digestion prevents HGE cell binding and infection, and neoexpression of PSGL-1 with Fuc-TVII in non-susceptible cells confers susceptibility.","method":"Antibody blocking, enzymatic digestion, cDNA co-transfection of PSGL-1 + Fuc-TVII in non-susceptible cells","journal":"Science","confidence":"High","confidence_rationale":"Tier 2 — gain-of-function transfection plus loss-of-function antibody/enzyme approaches, multiple orthogonal methods","pmids":["10834846"],"is_preprint":false},{"year":2002,"finding":"PSGL-1 associates with Syk via the actin-linking ERM proteins moesin and ezrin, which directly interact with Syk in an ITAM-dependent manner; PSGL-1 engagement induces Syk tyrosine phosphorylation and SRE-dependent transcriptional activity, establishing PSGL-1 as a signaling receptor.","method":"Co-immunoprecipitation, Syk inhibitor (piceatannol), dominant-negative Syk and ITAM-mutated moesin overexpression, transcriptional activity reporter assay","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP plus pharmacological and dominant-negative functional validation in a single paper","pmids":["12387735"],"is_preprint":false},{"year":2002,"finding":"Attachment of the PSGL-1 cytoplasmic domain to the actin cytoskeleton via selective interaction with moesin (but not other ERM proteins) is essential for leukocyte rolling on P-selectin; truncation of the cytoplasmic domain abrogates rolling despite intact surface expression and P-selectin binding.","method":"Stable transfectants with truncated PSGL-1, rolling adhesion assays, actin cytoskeletal toxins, co-immunoprecipitation with ERM proteins","journal":"Blood","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis + reconstituted rolling assay + biochemical interaction mapping in one paper","pmids":["12036880"],"is_preprint":false},{"year":2002,"finding":"Core-2 O-glycans on Thr-57 of PSGL-1 and tyrosine sulfation at Tyr-51 (predominant for L-selectin; Tyr-48 predominant for P-selectin) are critical structural determinants for L-selectin binding and leukocyte rolling on PSGL-1.","method":"Site-directed mutagenesis of Thr/Tyr residues, soluble L-selectin binding, leukocyte rolling assays on transfected CHO cells, co-expression of glycosyltransferases","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — systematic mutagenesis combined with functional rolling assays, multiple mutations tested","pmids":["12403782"],"is_preprint":false},{"year":2003,"finding":"P-selectin interaction with PSGL-1 induces formation of procoagulant microparticles from human blood; PSGL-1-deficient mice produce fewer microparticles after P-selectin chimera infusion and fail to increase microparticle count with aging.","method":"P-selectin-Ig chimera infusion, PSGL-1 knockout mice, microparticle quantification, tail-bleeding time in hemophilia A mice","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 2 — genetic KO + chimera infusion + functional hemostasis assay, multiple orthogonal approaches","pmids":["12858167"],"is_preprint":false},{"year":2004,"finding":"Human FucT-IV and FucT-VII both contribute to PSGL-1 selectin-binding activity, with FucT-VII playing the predominant role; core-2 O-glycans on Thr-57 are critical for L- and P-selectin rolling but additional binding sites support >75% of E-selectin-mediated rolling.","method":"CHO cell transfection with FucT-IV and/or FucT-VII, rolling adhesion assays, Thr-57 mutagenesis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — systematic mutagenesis and glycosyltransferase co-expression with functional rolling assays","pmids":["15579466"],"is_preprint":false},{"year":2005,"finding":"P-selectin expressed on thymic endothelium binds PSGL-1 on lymphoid progenitors to mediate thymic homing; PSGL-1-deficient mice have fewer early thymic progenitors and increased empty niches, and the number of resident thymic progenitors controls thymic P-selectin expression.","method":"Parabiosis, competitive thymus reconstitution, short-term homing assays, PSGL-1 knockout mice","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 2 — multiple in vivo assays (parabiosis, competitive reconstitution, homing) with genetic KO","pmids":["15880112"],"is_preprint":false},{"year":2007,"finding":"PSGL-1, ESL-1, and CD44 together constitute all E-selectin ligand activity on neutrophils: PSGL-1 dominates initial capture, ESL-1 is critical for converting tethers to slow rolling, and CD44 controls rolling velocity and mediates E-selectin-dependent redistribution of PSGL-1 and L-selectin to the uropod pole via p38 signaling.","method":"Gene knockout and RNA interference loss-of-function in mice and cells, intravital microscopy, flow chamber assays","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 2 — genetic and siRNA epistasis across multiple ligands with in vivo and in vitro functional readouts","pmids":["17442598"],"is_preprint":false},{"year":2007,"finding":"PSGL-1 mediates an enhanced chemotactic T cell response to homeostatic chemokines CCL21 and CCL19 (but not inflammatory chemokines), facilitating T cell homing to secondary lymphoid organs independently of selectin binding.","method":"PSGL-1-null mice, homing assays, T cell chemotaxis assays","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 2 — genetic KO mice + selective chemotaxis assays demonstrating selectin-independent function","pmids":["17401367"],"is_preprint":false},{"year":2007,"finding":"EphB4 activation upregulates PSGL-1 expression on endothelial progenitor cells (EPCs) and enhances EPC adhesion to E- and P-selectin; PSGL-1 siRNA reverses the proangiogenic and adhesive effects of EphB4 activation, placing PSGL-1 downstream of EphB4 in EPC angiogenic signaling.","method":"siRNA knockdown of EphB4 and PSGL-1, EPC adhesion assays, neutralizing antibodies, mouse hind limb ischemia model","journal":"The Journal of clinical investigation","confidence":"Medium","confidence_rationale":"Tier 2 — siRNA epistasis + functional adhesion assay + in vivo model; single lab","pmids":["17510705"],"is_preprint":false},{"year":2007,"finding":"PSGL-1 engagement in macrophages signals through Akt/mTOR to selectively upregulate translation of preformed ROCK-1 mRNA (not ROCK-2), enabling ROCK-1-dependent chemotaxis and phagocytosis; PSGL-1-deficient macrophages recapitulate effects of mTOR inhibition by rapamycin.","method":"PSGL-1 knockout mouse macrophages, rapamycin inhibition, polysome profiling, ROCK-1 protein detection, chemotaxis and phagocytosis assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — genetic KO + pharmacological inhibition + polysome analysis + functional assays in a single rigorous paper","pmids":["17245434"],"is_preprint":false},{"year":2007,"finding":"Crystal structure of the radixin FERM domain in complex with the PSGL-1 juxtamembrane peptide reveals that the peptide binds the FERM subdomain C groove via a β-strand interaction; PSGL-1 lacks the canonical Motif-1 but compensates with non-conserved large residues (Met9, His8) that stabilize groove binding.","method":"X-ray crystallography of radixin FERM domain–PSGL-1 peptide complex","journal":"Genes to cells : devoted to molecular & cellular mechanisms","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with structural validation of binding mode","pmids":["18076570"],"is_preprint":false},{"year":2008,"finding":"E-selectin engagement of PSGL-1 signals through the Src family kinase Fgr and ITAM-containing adaptor proteins DAP12 and FcRγ to phosphorylate Syk, which is required for slow leukocyte rolling and neutrophil recruitment in vivo.","method":"Gene-deficient mice (fgr-/-, hck-/-lyn-/-fgr-/-, Tyrobp-/-Fcrg-/-), flow chamber assays, intravital microscopy, peritonitis model, Syk and p38 phosphorylation","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 — multiple genetic KO mice with in vitro and in vivo epistasis, replicated across conditions","pmids":["18794338"],"is_preprint":false},{"year":2008,"finding":"The PSGL-1 cytoplasmic domain is dispensable for neutrophil rolling on P-selectin but is essential for activating beta2-integrins (LFA-1) via Syk to induce slow rolling on ICAM-1; DeltaCD mice (cytoplasmic domain-deleted) roll normally on P-selectin but fail to trigger Syk-dependent LFA-1 activation.","method":"DeltaCD knock-in mice, flow chamber assays, OSGE digestion to match PSGL-1 density, Syk phosphorylation assay, intravital microscopy","journal":"Blood","confidence":"High","confidence_rationale":"Tier 1 — knock-in mouse model with mutagenesis strategy, multiple functional readouts separating rolling from signaling","pmids":["18550846"],"is_preprint":false},{"year":2009,"finding":"PSGL-1 interacts with homeostatic chemokines CCL19 and CCL21 to facilitate T-cell chemotaxis; O-glycan modifications that support selectin-mediated rolling interfere with PSGL-1 binding to these homeostatic chemokines, demonstrating that glycosylation reciprocally regulates inflammatory versus homeostatic trafficking functions.","method":"PSGL-1-null mice, chemotaxis assays, glycosyltransferase manipulation (review integrating primary data)","journal":"Immunological reviews","confidence":"Medium","confidence_rationale":"Tier 3 — review integrating prior experimental data; original data from cited primary papers","pmids":["19594630"],"is_preprint":false},{"year":2010,"finding":"E-selectin engagement of PSGL-1 or CD44 triggers slow leukocyte rolling through a common lipid raft-dependent pathway using Src kinases Hck, Lyn, and Fgr, Syk, and Bruton tyrosine kinase (Btk) as intermediates; the PSGL-1 cytoplasmic domain is required to activate SFKs and slow rolling but PI3K is not required.","method":"KO mice (Hck/Lyn/Fgr), Btk-deficient mice, lipid raft disruption, flow chamber and intravital microscopy, phosphorylation assays","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — multiple genetic KOs + pharmacological dissection + in vivo validation","pmids":["20299514"],"is_preprint":false},{"year":2010,"finding":"Tyrosine sulfation at the N-terminus of PSGL-1 (not O-glycosylation at T57) is critical for EV71 binding and infection of leukocytes; sodium chlorate (sulfation inhibitor) blocks PSGL-1–EV71 interaction and viral replication, while T57A mutation does not affect EV71 binding.","method":"PSGL-1 mutant expression in 293T cells, flow cytometry binding assay, sodium chlorate inhibition, viral replication assay in Jurkat cells","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 1 — systematic mutagenesis + pharmacological inhibition + functional infection assay","pmids":["21079683"],"is_preprint":false},{"year":2011,"finding":"Tyrosine sulfation of mouse Psgl-1 is required for optimal P-selectin binding and leukocyte rolling in vivo; hematopoietic reconstitution with Tpst1;Tpst2 double-KO cells (lacking tyrosylprotein sulfotransferase activity) shows reduced P-selectin binding and increased rolling velocity despite equivalent PSGL-1 surface expression.","method":"Bone marrow transplantation with TPST double-KO donors, intravital microscopy, in vitro rolling assay on P-selectin, flow cytometry","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 — genetic loss-of-function reconstitution with in vivo and in vitro functional validation","pmids":["21633705"],"is_preprint":false},{"year":2012,"finding":"The PSGL-1 ERM-binding sequence (EBS), specifically Arg-337 and Lys-338 in the cytoplasmic tail, is critical for leukocyte tethering and rolling on L-, P-, and E-selectin and for activating ERK; however, EBS is dispensable for Syk phosphorylation and E-selectin-induced slow rolling via LFA-1.","method":"Mutagenesis (EBS deletion, Arg/Lys alanine substitution), leukocyte rolling assays on selectin substrates, ERK and Syk phosphorylation assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — systematic mutagenesis with multiple orthogonal signaling and functional readouts","pmids":["22311979"],"is_preprint":false},{"year":2013,"finding":"A subset of PSGL-1 molecules is constitutively associated with L-selectin on neutrophils; this PSGL-1–L-selectin signaling complex signals through Src family kinases and ITAM adaptor proteins to activate LFA-1, with signaling output dependent on the L-selectin cytoplasmic tail.","method":"Co-immunoprecipitation, flow chamber assays, KO mice (L-selectin), neutrophil slow rolling and recruitment by intravital microscopy","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP + genetic KO + in vivo functional validation","pmids":["24127491"],"is_preprint":false},{"year":2013,"finding":"EV71 binds to the N-terminal region of PSGL-1 (sulfated tyrosines) via conserved lysine residues VP1-242 and VP1-244 on the capsid; VP1-145 acts as a molecular switch controlling PSGL-1 binding by modulating the orientation of VP1-244 lysine side chain.","method":"Site-directed mutagenesis (VP1-145, VP1-244, VP1-242), PSGL-1-expressing CHO cell binding assays, Jurkat T-cell infection, crystal structure comparison","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis + structural analysis + functional infection assay","pmids":["23935488"],"is_preprint":false},{"year":2013,"finding":"PSGL-1-mediated EV71 entry proceeds via caveolar (caveolin-1-dependent) endocytosis requiring intact membrane cholesterol and acidification; this is distinct from hSCARB2-mediated entry which uses clathrin-dependent endocytosis.","method":"siRNA knockdown of caveolin-1, specific endocytosis inhibitors, confocal colocalization, pH inhibitors, PSGL-1-expressing L929 cells and Jurkat T cells","journal":"Journal of virology","confidence":"High","confidence_rationale":"Tier 2 — siRNA + pharmacological inhibitors + imaging, receptor-specific entry pathways demonstrated","pmids":["23760234"],"is_preprint":false},{"year":2015,"finding":"The N-termini of PSGL-1 and CCR7 have overlapping and competitive binding sites for CCL19, as determined by NMR chemical shift mapping; the solution structure of CCL19 reveals a canonical chemokine fold, and PSGL-1 competes with CCR7 for CCL19 binding.","method":"NMR solution structure of CCL19, chemical shift mapping, competitive binding assays","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — NMR structure with binding site mapping and competitive binding validation","pmids":["26115234"],"is_preprint":false},{"year":2016,"finding":"PSGL-1 ligation on exhausted CD8+ T cells inhibits TCR and IL-2 signaling and upregulates PD-1, leading to diminished survival upon TCR stimulation; PSGL-1-deficient mice clear chronic virus due to increased survival and multifunctionality of effector T cells with downregulated PD-1.","method":"PSGL-1-deficient mice, chronic viral infection model (LCMV), T cell function assays, receptor expression analysis","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with multiple defined phenotypic readouts and mechanistic pathway placement","pmids":["27192578"],"is_preprint":false},{"year":2018,"finding":"Cooperative PSGL-1 and CXCR2 signaling in rolling neutrophils promotes β2-integrin-dependent arrest and NETosis contributing to deep vein thrombosis; PSGL-1 signaling in DVT uses tyrosine 145 of SLP-76 rather than Y112/Y128, and does not require L-selectin in this context.","method":"Genetically engineered mice, ultrasonography, spinning-disk intravital microscopy, flow restriction DVT model, pharmacological blocking","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — multiple genetic models + live in vivo imaging + mechanistic pathway mapping","pmids":["30068506"],"is_preprint":false},{"year":2019,"finding":"VISTA binds PSGL-1 selectively at acidic pH (as found in tumor microenvironments) via multiple histidine residues along the rim of the VISTA extracellular domain; this interaction suppresses T cells and antibodies that selectively block this interaction at acidic pH reverse VISTA-mediated immune suppression in vivo.","method":"Binding assays, pH titration experiments, histidine mutagenesis, pH-selective blocking antibodies, in vivo tumor models","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1–2 — mutagenesis + pH-selective binding + in vivo functional validation; published in Nature","pmids":["31645726"],"is_preprint":false},{"year":2019,"finding":"HIV-1 Vpu binds PSGL-1 and induces its ubiquitination and proteasomal degradation through the ubiquitin ligase SCFβ-TrCP2; PSGL-1 (induced by IFN-γ) inhibits HIV-1 reverse transcription and blocks virion infectivity by incorporating into progeny virions.","method":"Quantitative mass spectrometry proteomics, co-immunoprecipitation, ubiquitination assays, siRNA knockdown, viral infectivity assays in primary CD4+ T cells","journal":"Nature microbiology","confidence":"High","confidence_rationale":"Tier 2 — MS-based discovery + Co-IP + ubiquitination + functional infection assays, multiple orthogonal methods","pmids":["30833724"],"is_preprint":false},{"year":2020,"finding":"PSGL-1 incorporated into HIV-1 virions blocks virus particle attachment to target cells through its extracellular N-terminal domain; this inhibitory activity is glycoprotein-independent, and Vpu (primarily) and Nef downregulate PSGL-1 from the cell surface to partially escape restriction.","method":"PSGL-1 domain mapping, pseudovirus attachment assays, virus infectivity assays, flow cytometry, siRNA knockdown","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — multiple domain mapping experiments + gain/loss-of-function + mechanistic dissection of escape pathway","pmids":["32273392"],"is_preprint":false},{"year":2020,"finding":"PSGL-1 directly binds cellular F-actin to restrict actin dynamics, inhibiting HIV DNA synthesis; PSGL-1 also binds gp41 and sequesters it at the plasma membrane, blocking Env incorporation into nascent virions, causing loss of envelope spikes and profound defects in viral entry.","method":"F-actin binding assay, gp41 co-immunoprecipitation, cryo-electron microscopy, super-resolution imaging, HIV DNA synthesis assay, Env incorporation assay","journal":"Cell discovery","confidence":"High","confidence_rationale":"Tier 1 — in vitro binding assays + cryo-EM structure + super-resolution imaging + functional virology assays","pmids":["32802403"],"is_preprint":false},{"year":2020,"finding":"Virion-incorporated PSGL-1 (and CD43) inhibits HIV-1 cell-free infection and transinfection by preventing virus-cell attachment; PSGL-1's full-length ectodomain is required for this inhibitory effect, and coclustering with HIV-1 Gag at uropod membranes depends on polybasic sequences in both the PSGL-1 cytoplasmic tail and Gag matrix domain.","method":"Virion incorporation assays, CD4+ and CD4- cell attachment assays, ectodomain truncation mutants, Gag colocalization studies","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — domain mapping + attachment assays + colocalization in primary cells, multiple orthogonal methods","pmids":["32193343"],"is_preprint":false},{"year":2020,"finding":"PSGL-1 impairs SARS-CoV and SARS-CoV-2 spike glycoprotein incorporation into pseudovirions and blocks pseudovirus attachment and infectivity of target cells.","method":"Pseudovirus infectivity assays, Western blotting for spike incorporation, cell attachment assays","journal":"Viruses","confidence":"Medium","confidence_rationale":"Tier 2 — functional pseudovirus assays but single lab; no structural validation","pmids":["33396594"],"is_preprint":false},{"year":2021,"finding":"GALNT4-mediated O-glycosylation of PSGL-1 promotes P-selectin-induced monocyte adhesion and transmigration by activating the Akt/mTOR and IκBα/NFκB pathways; GALNT4 knockdown reduces PSGL-1 O-glycosylation, attenuates Akt/mTOR and NFκB activation, and decreases monocyte adhesion to P-selectin.","method":"VVL pull-down, PSGL-1 immunoprecipitation, GALNT4 shRNA knockdown, GALNT4 overexpression, monocyte flow adhesion assay, mTOR inhibitor (rapamycin), phosphorylation assays","journal":"Journal of molecular and cellular cardiology","confidence":"Medium","confidence_rationale":"Tier 2 — biochemical glycosylation assay + functional adhesion + pharmacological and genetic epistasis; single lab","pmids":["34974060"],"is_preprint":false},{"year":2023,"finding":"PSGL-1 acts upstream of PD-1 and requires co-ligation with the TCR to attenuate early TCR signaling via Zap70 and maintain expression of the Zap70 inhibitor Sts-1, driving terminal CD8+ T cell exhaustion; PSGL-1 deficiency enables responses to low-affinity TCR ligands and sustains an elevated metabolic/glycolytic gene signature.","method":"PSGL-1-deficient mice, chronic infection/tumor models, TCR signaling assays (Zap70 phosphorylation), Sts-1 expression analysis, metabolic gene profiling","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 — genetic KO + signaling pathway dissection + mechanistic epistasis with Zap70/Sts-1 + metabolic readout","pmids":["37115668"],"is_preprint":false},{"year":2008,"finding":"Sorting nexin SLIC-1 (SNX20) directly and specifically interacts with the PSGL-1 cytoplasmic domain and contains a Phox homology domain that targets the PSGL-1/SLIC-1 complex to endosomes, cycling PSGL-1 into the endosomal compartment.","method":"Yeast two-hybrid screen, co-immunoprecipitation, colocalization experiments, motif mapping, SNX20-deficient mice","journal":"European journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 — yeast two-hybrid + Co-IP + functional KO mice; sorting function established but signaling role not found","pmids":["18196517"],"is_preprint":false},{"year":2004,"finding":"Human PSGL-1 interacts with skin-associated chemokine CCL27 via sulfated tyrosines at its amino terminus (not glycans); PSGL-1 expression on CCR10-expressing cells reduces chemotaxis to CCL27, suggesting PSGL-1 regulates chemokine-mediated responses by sequestering CCL27.","method":"rPSGL-Ig binding assays, arylsulfatase and glycosidase treatments, sulfation inhibitor, tyrosine-to-phenylalanine mutagenesis, chemotaxis assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis + enzymatic treatment + functional chemotaxis assay, multiple orthogonal approaches","pmids":["15466853"],"is_preprint":false},{"year":2023,"finding":"P-selectin (CD62P) binding to PSGL-1 on tumor-associated macrophages activates the JNK/STAT1 pathway to induce C5 transcription and C5a release, shifting TAMs toward a pro-tumor phenotype and promoting CRC growth via the C5a/C5aR1 axis.","method":"Western blotting, siRNA knockdown of PSGL-1, JNK/STAT1 pathway inhibitors, dual-luciferase reporter, ChIP assay, in vivo AOM/DSS CRC model","journal":"Theranostics","confidence":"Medium","confidence_rationale":"Tier 2 — genetic/siRNA knockdown + pathway inhibitors + reporter + ChIP; single lab","pmids":["37064877"],"is_preprint":false},{"year":2005,"finding":"PSGL-1 cross-linking in neutrophils triggers tyrosine-phosphorylation-dependent and c-Abl-involved alteration of F-actin cytoskeleton and PSGL-1 polarization; c-Abl redistributes to F-actin-concentrated regions upon PSGL-1 engagement.","method":"Anti-PSGL-1 antibody cross-linking, actin cytoskeleton staining, genistein (tyrosine kinase inhibitor), STI571 (c-Abl inhibitor), cytochalasin B treatment","journal":"Journal of cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 3 — pharmacological inhibition with localization studies; single lab, single paper","pmids":["15526280"],"is_preprint":false},{"year":2009,"finding":"Flotillin-1 and flotillin-2 associate with PSGL-1 in resting and stimulated neutrophils (shown by co-immunoprecipitation and colocalization) and reorganize into uropod domains; flotillin cap formation is PSGL-1-independent as shown by PSGL-1-deficient neutrophils, but PSGL-1 and flotillins redistribute together more rapidly than other uropod proteins.","method":"Co-immunoprecipitation, immunofluorescence, PSGL-1-deficient mice neutrophils, HL-60 differentiated cells","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 3 — Co-IP + immunofluorescence + KO controls, single lab","pmids":["19404397"],"is_preprint":false},{"year":2005,"finding":"PSGL-1 engagement upregulates CSF-1 transcription in a Syk-dependent manner; overexpression of wild-type but not kinase-dead Syk promotes CSF-1 promoter activation downstream of PSGL-1, and Syk inhibitor piceatannol suppresses PSGL-1-induced CSF-1 mRNA upregulation.","method":"Antibody engagement of PSGL-1, CSF-1 promoter reporter assay, Syk dominant-negative overexpression, piceatannol inhibition, RT-PCR","journal":"Cellular immunology","confidence":"Medium","confidence_rationale":"Tier 3 — reporter assay + dominant-negative + pharmacological inhibition; single lab, limited mechanistic depth","pmids":["16289055"],"is_preprint":false}],"current_model":"PSGL-1 is a dimeric, heavily O-glycosylated, tyrosine-sulfated sialomucin on leukocytes that binds P-, E-, and L-selectins via cooperative interaction of its N-terminal sulfated tyrosines (critical: Tyr-48 for P-selectin, Tyr-51 for L-selectin) and core-2 sialyl-Lewis X O-glycans on Thr-57 to mediate leukocyte rolling and tethering; its cytoplasmic domain anchors PSGL-1 to the actin cytoskeleton via moesin/ERM proteins, and upon selectin or co-receptor (L-selectin) engagement signals through Src family kinases (Fgr, Hck, Lyn), ITAM adaptors (DAP12, FcRγ), and Syk to activate β2-integrins for slow rolling and neutrophil recruitment, while also binding homeostatic chemokines CCL19/CCL21 and VISTA (at acidic pH) to regulate T cell trafficking and exhaustion, and acting as an antiviral restriction factor that blocks HIV-1 virion attachment to target cells by its ectodomain and inhibits Env incorporation by sequestering gp41."},"narrative":{"teleology":[{"year":1995,"claim":"Identifying that N-terminal tyrosine sulfation is required for P-selectin binding established the first post-translational modification critical for PSGL-1 adhesive function, moving beyond simple glycoprotein recognition.","evidence":"Site-directed mutagenesis of N-terminal tyrosines and sulfation inhibitor treatment with rolling adhesion assays","pmids":["7585950"],"confidence":"High","gaps":["Relative contributions of individual tyrosine residues not yet resolved","Structural basis of sulfated tyrosine–P-selectin interaction unknown at this point"]},{"year":1997,"claim":"Demonstrating that CLA is an inducible fucosyltransferase VII-dependent carbohydrate modification of PSGL-1 that selectively confers E-selectin binding revealed that the same protein backbone can be differentially glycosylated to regulate distinct selectin interactions.","evidence":"T cell differentiation assays, monoclonal antibody characterization, and selectin-binding functional assays","pmids":["9353122"],"confidence":"High","gaps":["Glycosyltransferase regulation during T cell differentiation not mechanistically defined","Whether other fucosyltransferases contribute was unresolved"]},{"year":1998,"claim":"Showing that Cys-320-mediated disulfide-bonded dimerization is essential for P-selectin rolling established PSGL-1's quaternary structure as a functional requirement, not merely a structural feature.","evidence":"C320A mutagenesis, Western blotting under native conditions, and flow-based rolling assays","pmids":["9660879"],"confidence":"High","gaps":["Whether dimerization is equally required for E- and L-selectin binding was untested"]},{"year":1999,"claim":"Demonstrating that P-selectin engagement of PSGL-1 triggers tyrosine kinase signaling leading to β2-integrin activation transformed PSGL-1 from a passive adhesion molecule into a signaling receptor that couples rolling to firm adhesion.","evidence":"Mixed cell aggregation under shear, tyrosine kinase inhibitors, and P-selectin-IgG stimulation of PMN","pmids":["9920836"],"confidence":"High","gaps":["Identity of the specific kinases downstream of PSGL-1 not yet mapped","Role of the cytoplasmic domain in signaling not defined"]},{"year":2002,"claim":"Defining that the PSGL-1 cytoplasmic tail links to actin via moesin, and that this moesin–Syk axis transduces ITAM-dependent signaling, provided the first molecular bridge between PSGL-1 adhesion and intracellular kinase activation.","evidence":"Co-immunoprecipitation with ERM proteins, cytoplasmic truncation mutants, Syk inhibitors, ITAM-mutated moesin, and SRE reporter assays","pmids":["12036880","12387735"],"confidence":"High","gaps":["How moesin ITAM-like motifs recruit Syk in the absence of classical ITAM adaptors was unclear","Structural details of the PSGL-1–moesin interface not yet resolved"]},{"year":2002,"claim":"Systematic mutagenesis of Thr-57, Tyr-48, and Tyr-51 defined the differential post-translational requirements for L-selectin versus P-selectin binding, establishing that the same N-terminal region uses distinct residues for each selectin.","evidence":"Site-directed mutagenesis with L-selectin binding assays and leukocyte rolling on CHO transfectants co-expressing glycosyltransferases","pmids":["12403782"],"confidence":"High","gaps":["Whether these requirements hold in vivo under inflammatory conditions was not tested"]},{"year":2004,"claim":"Demonstrating that PSGL-1 binds chemokine CCL27 via sulfated tyrosines and attenuates CCL27-mediated chemotaxis uncovered a selectin-independent function as a chemokine-interacting molecule.","evidence":"Tyrosine-to-phenylalanine mutagenesis, arylsulfatase and glycosidase treatment, and chemotaxis assays","pmids":["15466853"],"confidence":"High","gaps":["Physiological significance of CCL27 sequestration in skin homing not confirmed in vivo"]},{"year":2005,"claim":"PSGL-1 on lymphoid progenitors was shown to mediate thymic homing via P-selectin on thymic endothelium, extending its role from inflammatory recruitment to developmental lymphocyte trafficking.","evidence":"Parabiosis, competitive thymus reconstitution, short-term homing assays in PSGL-1 knockout mice","pmids":["15880112"],"confidence":"High","gaps":["Whether PSGL-1 glycosylation is regulated during thymic progenitor development was not explored"]},{"year":2007,"claim":"Multiple discoveries in 2007 consolidated a picture of PSGL-1 as both a dominant capture receptor for E-selectin on neutrophils and a facilitator of homeostatic T cell homing through CCL19/CCL21 binding, independent of selectins, while also signaling through Akt/mTOR to regulate ROCK-1 translation in macrophages.","evidence":"Knockout and siRNA epistasis with intravital microscopy for E-selectin ligand hierarchy; PSGL-1-null T cell chemotaxis assays; polysome profiling and rapamycin inhibition in PSGL-1 KO macrophages","pmids":["17442598","17401367","17245434"],"confidence":"High","gaps":["Structural basis of PSGL-1–CCL19/CCL21 interaction unknown","How PSGL-1 selectively regulates ROCK-1 but not ROCK-2 mRNA translation not mechanistically explained"]},{"year":2007,"claim":"Crystal structure of the radixin FERM domain with the PSGL-1 juxtamembrane peptide revealed β-strand-mediated binding in the subdomain C groove, providing the first atomic-level view of how PSGL-1 connects to the ERM–actin cytoskeleton.","evidence":"X-ray crystallography of radixin FERM domain–PSGL-1 peptide complex","pmids":["18076570"],"confidence":"High","gaps":["Whether the radixin and moesin FERM domains engage PSGL-1 identically was not compared structurally"]},{"year":2008,"claim":"Defining the Fgr/Hck/Lyn → DAP12/FcRγ → Syk signaling cascade downstream of E-selectin–PSGL-1 engagement, and showing the cytoplasmic domain is essential for integrin activation but dispensable for rolling, separated the adhesive and signaling functions of PSGL-1 at the genetic level.","evidence":"Multiple compound-knockout mice (Fgr, Hck/Lyn/Fgr, DAP12/FcRγ), ΔCD knock-in mice, intravital microscopy, and phosphorylation assays","pmids":["18794338","18550846"],"confidence":"High","gaps":["How PSGL-1 cytoplasmic domain recruits SFKs to lipid rafts was mechanistically undefined","Whether DAP12/FcRγ directly bind PSGL-1 or are recruited indirectly was unresolved"]},{"year":2010,"claim":"Identifying that EV71 binds PSGL-1 via sulfated tyrosines (not O-glycans) established PSGL-1 as a viral entry receptor exploiting the same N-terminal motif used by selectins, revealing pathogen hijacking of an adhesion molecule.","evidence":"Systematic mutagenesis (T57A, sulfation inhibitors) with flow cytometry binding and viral replication assays in 293T and Jurkat cells","pmids":["21079683"],"confidence":"High","gaps":["Whether PSGL-1-mediated EV71 entry occurs in vivo not demonstrated","Structural basis of EV71–PSGL-1 interaction not yet solved"]},{"year":2012,"claim":"Fine-mapping of the ERM-binding sequence (Arg-337/Lys-338) showed it is required for tethering/rolling and ERK activation but dispensable for Syk phosphorylation and slow rolling, demonstrating bifurcation of PSGL-1 cytoplasmic signaling into ERM-dependent and ERM-independent arms.","evidence":"Alanine substitution mutagenesis at R337/K338, rolling assays on all three selectins, and parallel measurement of ERK and Syk phosphorylation","pmids":["22311979"],"confidence":"High","gaps":["How PSGL-1 activates Syk independently of ERM linkage was not explained"]},{"year":2013,"claim":"Discovery of a constitutive PSGL-1–L-selectin signaling complex on neutrophils that signals through SFKs and ITAM adaptors to activate LFA-1 revealed a cis-acting receptor complex, distinct from trans selectin–ligand interactions during rolling.","evidence":"Co-immunoprecipitation, L-selectin KO mice, flow chamber and intravital microscopy","pmids":["24127491"],"confidence":"High","gaps":["Stoichiometry and structural basis of the cis PSGL-1–L-selectin complex unresolved","Whether this complex forms in non-neutrophil leukocytes was not tested"]},{"year":2016,"claim":"Showing that PSGL-1 ligation promotes CD8+ T cell exhaustion by upregulating PD-1 and inhibiting TCR/IL-2 signaling—with PSGL-1-deficient mice clearing chronic LCMV—recast PSGL-1 as an immune checkpoint molecule beyond its adhesion function.","evidence":"PSGL-1-deficient mice in chronic LCMV infection model, T cell function and receptor expression analysis","pmids":["27192578"],"confidence":"High","gaps":["Ligand identity for PSGL-1 in the T cell exhaustion context was not established in this study","Mechanism linking PSGL-1 to PD-1 transcription not defined"]},{"year":2019,"claim":"Two major advances established PSGL-1 as both a pH-sensitive receptor for VISTA in the tumor microenvironment and an IFN-γ-induced antiviral restriction factor degraded by HIV-1 Vpu via SCFβ-TrCP2-mediated ubiquitination.","evidence":"Histidine mutagenesis and pH-selective binding/blocking antibodies with in vivo tumor models for VISTA; quantitative mass spectrometry, Co-IP, ubiquitination, and infectivity assays in primary CD4+ T cells for HIV-1","pmids":["31645726","30833724"],"confidence":"High","gaps":["Structural basis of the pH-dependent VISTA–PSGL-1 interaction not solved","Whether PSGL-1 antiviral activity extends to other retroviruses was unexplored"]},{"year":2020,"claim":"Detailed mechanistic dissection showed PSGL-1 restricts HIV-1 through dual mechanisms—blocking virion attachment via its ectodomain and sequestering gp41 to prevent Env incorporation—while also binding F-actin directly to restrict actin dynamics needed for HIV DNA synthesis.","evidence":"Domain mapping, pseudovirus attachment assays, cryo-EM, super-resolution imaging, F-actin binding assays, Env incorporation assays","pmids":["32273392","32802403","32193343"],"confidence":"High","gaps":["Whether F-actin binding by PSGL-1 is relevant to its canonical leukocyte functions was not tested","In vivo relevance of PSGL-1 antiviral restriction not demonstrated in animal models"]},{"year":2023,"claim":"PSGL-1 was positioned upstream of PD-1 in the exhaustion hierarchy: TCR co-ligation with PSGL-1 attenuates Zap70 phosphorylation and maintains the Zap70 inhibitor Sts-1, driving terminal exhaustion, which provided a mechanistic basis for PSGL-1's checkpoint function.","evidence":"PSGL-1-deficient mice in chronic infection and tumor models, Zap70 phosphorylation and Sts-1 expression assays, metabolic gene profiling","pmids":["37115668"],"confidence":"High","gaps":["Direct physical interaction between PSGL-1 and TCR signaling components not demonstrated","Whether PSGL-1-mediated exhaustion involves VISTA as the ligand in these models is not established"]},{"year":null,"claim":"Key unresolved questions include: (1) the structural basis of pH-dependent VISTA–PSGL-1 binding; (2) how PSGL-1 cytoplasmic domain recruits ITAM adaptors and Syk independently of ERM linkage; (3) in vivo validation of PSGL-1 antiviral restriction in animal models; (4) therapeutic targeting of PSGL-1 as an immune checkpoint distinct from PD-1.","evidence":"","pmids":[],"confidence":"Low","gaps":["No full-length PSGL-1 structure available","Therapeutic antibody or small molecule targeting PSGL-1 checkpoint function not yet tested clinically","Integration of PSGL-1 adhesion, signaling, and checkpoint functions into a unified model remains incomplete"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098631","term_label":"cell adhesion mediator activity","supporting_discovery_ids":[0,2,3,9,11,13]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[4,7,18,19,29,38]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[8,17,34]},{"term_id":"GO:0001618","term_label":"virus receptor activity","supporting_discovery_ids":[6,22,26,27]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,2,5,8,33,35]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[8,17,34,42]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[39]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[4,13,18,19,21,25,29,38]},{"term_id":"R-HSA-1500931","term_label":"Cell-Cell communication","supporting_discovery_ids":[0,2,9,11,12]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[7,16,18,21,30,31]},{"term_id":"R-HSA-109582","term_label":"Hemostasis","supporting_discovery_ids":[5,10,30]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[6,22,32,33,36]}],"complexes":["PSGL-1 homodimer","PSGL-1–L-selectin cis signaling complex"],"partners":["SELP","SELE","SELL","MSN","SYK","VISTA","SNX20","DAP12"],"other_free_text":[]},"mechanistic_narrative":"PSGL-1 (P-selectin glycoprotein ligand-1) is a dimeric sialomucin on leukocytes and platelets that serves as the primary counter-receptor for P-, E-, and L-selectins, mediating leukocyte tethering, rolling, and recruitment to activated endothelium, and additionally functions as a signaling receptor that regulates integrin activation, T cell exhaustion, chemokine responsiveness, and antiviral restriction. Selectin recognition requires cooperative engagement of tyrosine-sulfated residues (Tyr-48 for P-selectin, Tyr-51 for L-selectin) and core-2 sialyl-Lewis X O-glycans on Thr-57, with dimerization through Cys-320 essential for P-selectin binding, and fucosyltransferase VII-dependent glycosylation conferring E-selectin specificity [PMID:7585950, PMID:9660879, PMID:12403782, PMID:9353122]. The cytoplasmic tail anchors PSGL-1 to the actin cytoskeleton via ERM proteins (moesin/radixin), and upon selectin engagement signals through Src family kinases (Fgr, Hck, Lyn), ITAM adaptors (DAP12, FcRγ), and Syk to activate β2-integrins for slow rolling and neutrophil arrest, while also modulating T cell exhaustion by attenuating TCR-Zap70 signaling and upregulating PD-1 via interaction with VISTA at acidic pH [PMID:18794338, PMID:12036880, PMID:27192578, PMID:31645726, PMID:37115668]. PSGL-1 also acts as an interferon-induced antiviral restriction factor that blocks HIV-1 virion attachment through its ectodomain, sequesters gp41 to inhibit Env incorporation, and is counteracted by Vpu-mediated ubiquitination and degradation via SCFβ-TrCP2 [PMID:30833724, PMID:32802403, PMID:32273392]."},"prefetch_data":{"uniprot":{"accession":"Q14242","full_name":"P-selectin glycoprotein ligand 1","aliases":["Selectin P ligand"],"length_aa":412,"mass_kda":43.2,"function":"A SLe(x)-type proteoglycan, which through high affinity, calcium-dependent interactions with E-, P- and L-selectins, mediates rapid rolling of leukocytes over vascular surfaces during the initial steps in inflammation. Critical for the initial leukocyte capture (Microbial infection) Acts as a receptor for enterovirus 71","subcellular_location":"Membrane","url":"https://www.uniprot.org/uniprotkb/Q14242/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SELPLG","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/SELPLG","total_profiled":1310},"omim":[{"mim_id":"616627","title":"PODOCALYXIN-LIKE 2; PODXL2","url":"https://www.omim.org/entry/616627"},{"mim_id":"613281","title":"SORTING NEXIN 20; SNX20","url":"https://www.omim.org/entry/613281"},{"mim_id":"601373","title":"CHEMOKINE, CC MOTIF, RECEPTOR 5; CCR5","url":"https://www.omim.org/entry/601373"},{"mim_id":"600751","title":"SIALIC ACID-BINDING IMMUNOGLOBULIN-LIKE LECTIN 1; SIGLEC1","url":"https://www.omim.org/entry/600751"},{"mim_id":"600738","title":"SELECTIN P LIGAND; SELPLG","url":"https://www.omim.org/entry/600738"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Vesicles","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"lymphoid tissue","ntpm":75.0}],"url":"https://www.proteinatlas.org/search/SELPLG"},"hgnc":{"alias_symbol":["PSGL-1","CD162"],"prev_symbol":[]},"alphafold":{"accession":"Q14242","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q14242","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q14242-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q14242-F1-predicted_aligned_error_v6.png","plddt_mean":50.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SELPLG","jax_strain_url":"https://www.jax.org/strain/search?query=SELPLG"},"sequence":{"accession":"Q14242","fasta_url":"https://rest.uniprot.org/uniprotkb/Q14242.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q14242/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q14242"}},"corpus_meta":[{"pmid":"9353122","id":"PMC_9353122","title":"Cutaneous lymphocyte antigen is a specialized form of PSGL-1 expressed on skin-homing T 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P-selectin adhesion; mutation of N-terminal tyrosines to phenylalanine abolishes P-selectin binding, and sulfation inhibitors greatly reduce binding.\",\n      \"method\": \"Site-directed mutagenesis, sulfation inhibitor treatment, rolling adhesion assay on P-selectin-coated coverslips\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis + functional adhesion assay in a high-impact single paper; replicated by multiple subsequent labs\",\n      \"pmids\": [\"7585950\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"CLA (cutaneous lymphocyte antigen), the skin-homing receptor on T cells, is an inducible carbohydrate modification (mediated by fucosyltransferase VII) of PSGL-1 that confers E-selectin binding; PSGL-1 without CLA binds P-selectin but not E-selectin, demonstrating independent regulation of selectin-binding phenotypes.\",\n      \"method\": \"Monoclonal antibody characterization, T cell differentiation assays, selectin-binding functional assays\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods, widely replicated; foundational discovery\",\n      \"pmids\": [\"9353122\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Dimerization of PSGL-1 through a single conserved extracellular cysteine (C320) is essential for functional recognition of P-selectin; a C320A monomeric mutant fails to support rolling or P-selectin chimera binding.\",\n      \"method\": \"Site-directed mutagenesis, Western blotting under native/denaturing conditions, rolling adhesion assay under physiologic flow, P-selectin chimera binding\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution with mutagenesis and flow-based functional assay in a single rigorous paper\",\n      \"pmids\": [\"9660879\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"PSGL-1 serves as a ligand for L-selectin on neutrophils, mediating neutrophil aggregation; blocking PSGL-1 with Fab fragments of PL1 antibody reduces neutrophil aggregate number and size, consistent with L-selectin–PSGL-1 counter-receptor interaction.\",\n      \"method\": \"Flow cytometry aggregation assay, blocking antibody (Fab fragments) experiments\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — antibody blocking and flow cytometry, single paper; replicated in later studies\",\n      \"pmids\": [\"8839831\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"P-selectin binding to PSGL-1 triggers tyrosine kinase-dependent (Syk-like) signaling that activates CD11b/CD18 (beta2-integrin) on PMN; PSGL-1 engagement with a non-adhesion-blocking antibody was sufficient to trigger beta2-integrin-dependent aggregation and tyrosine phosphorylation.\",\n      \"method\": \"Mixed cell aggregation assays under shear, blocking antibodies, tyrosine kinase inhibitors (genistein), CHO-P transfectants, P-selectin-IgG fusion protein stimulation\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal approaches (inhibitors, antibodies, transfected cell lines) in a single paper; foundational signaling mechanism\",\n      \"pmids\": [\"9920836\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"PSGL-1 is expressed on platelets (at 25–100-fold lower levels than leukocytes) and mediates platelet rolling in mesenteric venules in vivo; anti-PSGL-1 antibody significantly reduced platelet rolling as shown by intravital microscopy.\",\n      \"method\": \"P-selectin-IgG affinity purification, immunoelectron microscopy, Western blotting, flow cytometry, intravital microscopy\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (biochemical isolation, imaging, in vivo functional assay)\",\n      \"pmids\": [\"10770806\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"The human granulocytic ehrlichiosis (HGE) bacterium infects neutrophils by specifically binding to fucosylated PSGL-1; blocking the P-selectin binding domain of PSGL-1 with monoclonal antibodies or enzymatic digestion prevents HGE cell binding and infection, and neoexpression of PSGL-1 with Fuc-TVII in non-susceptible cells confers susceptibility.\",\n      \"method\": \"Antibody blocking, enzymatic digestion, cDNA co-transfection of PSGL-1 + Fuc-TVII in non-susceptible cells\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — gain-of-function transfection plus loss-of-function antibody/enzyme approaches, multiple orthogonal methods\",\n      \"pmids\": [\"10834846\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"PSGL-1 associates with Syk via the actin-linking ERM proteins moesin and ezrin, which directly interact with Syk in an ITAM-dependent manner; PSGL-1 engagement induces Syk tyrosine phosphorylation and SRE-dependent transcriptional activity, establishing PSGL-1 as a signaling receptor.\",\n      \"method\": \"Co-immunoprecipitation, Syk inhibitor (piceatannol), dominant-negative Syk and ITAM-mutated moesin overexpression, transcriptional activity reporter assay\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP plus pharmacological and dominant-negative functional validation in a single paper\",\n      \"pmids\": [\"12387735\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Attachment of the PSGL-1 cytoplasmic domain to the actin cytoskeleton via selective interaction with moesin (but not other ERM proteins) is essential for leukocyte rolling on P-selectin; truncation of the cytoplasmic domain abrogates rolling despite intact surface expression and P-selectin binding.\",\n      \"method\": \"Stable transfectants with truncated PSGL-1, rolling adhesion assays, actin cytoskeletal toxins, co-immunoprecipitation with ERM proteins\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis + reconstituted rolling assay + biochemical interaction mapping in one paper\",\n      \"pmids\": [\"12036880\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Core-2 O-glycans on Thr-57 of PSGL-1 and tyrosine sulfation at Tyr-51 (predominant for L-selectin; Tyr-48 predominant for P-selectin) are critical structural determinants for L-selectin binding and leukocyte rolling on PSGL-1.\",\n      \"method\": \"Site-directed mutagenesis of Thr/Tyr residues, soluble L-selectin binding, leukocyte rolling assays on transfected CHO cells, co-expression of glycosyltransferases\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic mutagenesis combined with functional rolling assays, multiple mutations tested\",\n      \"pmids\": [\"12403782\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"P-selectin interaction with PSGL-1 induces formation of procoagulant microparticles from human blood; PSGL-1-deficient mice produce fewer microparticles after P-selectin chimera infusion and fail to increase microparticle count with aging.\",\n      \"method\": \"P-selectin-Ig chimera infusion, PSGL-1 knockout mice, microparticle quantification, tail-bleeding time in hemophilia A mice\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO + chimera infusion + functional hemostasis assay, multiple orthogonal approaches\",\n      \"pmids\": [\"12858167\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Human FucT-IV and FucT-VII both contribute to PSGL-1 selectin-binding activity, with FucT-VII playing the predominant role; core-2 O-glycans on Thr-57 are critical for L- and P-selectin rolling but additional binding sites support >75% of E-selectin-mediated rolling.\",\n      \"method\": \"CHO cell transfection with FucT-IV and/or FucT-VII, rolling adhesion assays, Thr-57 mutagenesis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic mutagenesis and glycosyltransferase co-expression with functional rolling assays\",\n      \"pmids\": [\"15579466\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"P-selectin expressed on thymic endothelium binds PSGL-1 on lymphoid progenitors to mediate thymic homing; PSGL-1-deficient mice have fewer early thymic progenitors and increased empty niches, and the number of resident thymic progenitors controls thymic P-selectin expression.\",\n      \"method\": \"Parabiosis, competitive thymus reconstitution, short-term homing assays, PSGL-1 knockout mice\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple in vivo assays (parabiosis, competitive reconstitution, homing) with genetic KO\",\n      \"pmids\": [\"15880112\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"PSGL-1, ESL-1, and CD44 together constitute all E-selectin ligand activity on neutrophils: PSGL-1 dominates initial capture, ESL-1 is critical for converting tethers to slow rolling, and CD44 controls rolling velocity and mediates E-selectin-dependent redistribution of PSGL-1 and L-selectin to the uropod pole via p38 signaling.\",\n      \"method\": \"Gene knockout and RNA interference loss-of-function in mice and cells, intravital microscopy, flow chamber assays\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic and siRNA epistasis across multiple ligands with in vivo and in vitro functional readouts\",\n      \"pmids\": [\"17442598\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"PSGL-1 mediates an enhanced chemotactic T cell response to homeostatic chemokines CCL21 and CCL19 (but not inflammatory chemokines), facilitating T cell homing to secondary lymphoid organs independently of selectin binding.\",\n      \"method\": \"PSGL-1-null mice, homing assays, T cell chemotaxis assays\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO mice + selective chemotaxis assays demonstrating selectin-independent function\",\n      \"pmids\": [\"17401367\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"EphB4 activation upregulates PSGL-1 expression on endothelial progenitor cells (EPCs) and enhances EPC adhesion to E- and P-selectin; PSGL-1 siRNA reverses the proangiogenic and adhesive effects of EphB4 activation, placing PSGL-1 downstream of EphB4 in EPC angiogenic signaling.\",\n      \"method\": \"siRNA knockdown of EphB4 and PSGL-1, EPC adhesion assays, neutralizing antibodies, mouse hind limb ischemia model\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA epistasis + functional adhesion assay + in vivo model; single lab\",\n      \"pmids\": [\"17510705\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"PSGL-1 engagement in macrophages signals through Akt/mTOR to selectively upregulate translation of preformed ROCK-1 mRNA (not ROCK-2), enabling ROCK-1-dependent chemotaxis and phagocytosis; PSGL-1-deficient macrophages recapitulate effects of mTOR inhibition by rapamycin.\",\n      \"method\": \"PSGL-1 knockout mouse macrophages, rapamycin inhibition, polysome profiling, ROCK-1 protein detection, chemotaxis and phagocytosis assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO + pharmacological inhibition + polysome analysis + functional assays in a single rigorous paper\",\n      \"pmids\": [\"17245434\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Crystal structure of the radixin FERM domain in complex with the PSGL-1 juxtamembrane peptide reveals that the peptide binds the FERM subdomain C groove via a β-strand interaction; PSGL-1 lacks the canonical Motif-1 but compensates with non-conserved large residues (Met9, His8) that stabilize groove binding.\",\n      \"method\": \"X-ray crystallography of radixin FERM domain–PSGL-1 peptide complex\",\n      \"journal\": \"Genes to cells : devoted to molecular & cellular mechanisms\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with structural validation of binding mode\",\n      \"pmids\": [\"18076570\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"E-selectin engagement of PSGL-1 signals through the Src family kinase Fgr and ITAM-containing adaptor proteins DAP12 and FcRγ to phosphorylate Syk, which is required for slow leukocyte rolling and neutrophil recruitment in vivo.\",\n      \"method\": \"Gene-deficient mice (fgr-/-, hck-/-lyn-/-fgr-/-, Tyrobp-/-Fcrg-/-), flow chamber assays, intravital microscopy, peritonitis model, Syk and p38 phosphorylation\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic KO mice with in vitro and in vivo epistasis, replicated across conditions\",\n      \"pmids\": [\"18794338\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The PSGL-1 cytoplasmic domain is dispensable for neutrophil rolling on P-selectin but is essential for activating beta2-integrins (LFA-1) via Syk to induce slow rolling on ICAM-1; DeltaCD mice (cytoplasmic domain-deleted) roll normally on P-selectin but fail to trigger Syk-dependent LFA-1 activation.\",\n      \"method\": \"DeltaCD knock-in mice, flow chamber assays, OSGE digestion to match PSGL-1 density, Syk phosphorylation assay, intravital microscopy\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — knock-in mouse model with mutagenesis strategy, multiple functional readouts separating rolling from signaling\",\n      \"pmids\": [\"18550846\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"PSGL-1 interacts with homeostatic chemokines CCL19 and CCL21 to facilitate T-cell chemotaxis; O-glycan modifications that support selectin-mediated rolling interfere with PSGL-1 binding to these homeostatic chemokines, demonstrating that glycosylation reciprocally regulates inflammatory versus homeostatic trafficking functions.\",\n      \"method\": \"PSGL-1-null mice, chemotaxis assays, glycosyltransferase manipulation (review integrating primary data)\",\n      \"journal\": \"Immunological reviews\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — review integrating prior experimental data; original data from cited primary papers\",\n      \"pmids\": [\"19594630\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"E-selectin engagement of PSGL-1 or CD44 triggers slow leukocyte rolling through a common lipid raft-dependent pathway using Src kinases Hck, Lyn, and Fgr, Syk, and Bruton tyrosine kinase (Btk) as intermediates; the PSGL-1 cytoplasmic domain is required to activate SFKs and slow rolling but PI3K is not required.\",\n      \"method\": \"KO mice (Hck/Lyn/Fgr), Btk-deficient mice, lipid raft disruption, flow chamber and intravital microscopy, phosphorylation assays\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic KOs + pharmacological dissection + in vivo validation\",\n      \"pmids\": [\"20299514\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Tyrosine sulfation at the N-terminus of PSGL-1 (not O-glycosylation at T57) is critical for EV71 binding and infection of leukocytes; sodium chlorate (sulfation inhibitor) blocks PSGL-1–EV71 interaction and viral replication, while T57A mutation does not affect EV71 binding.\",\n      \"method\": \"PSGL-1 mutant expression in 293T cells, flow cytometry binding assay, sodium chlorate inhibition, viral replication assay in Jurkat cells\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic mutagenesis + pharmacological inhibition + functional infection assay\",\n      \"pmids\": [\"21079683\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Tyrosine sulfation of mouse Psgl-1 is required for optimal P-selectin binding and leukocyte rolling in vivo; hematopoietic reconstitution with Tpst1;Tpst2 double-KO cells (lacking tyrosylprotein sulfotransferase activity) shows reduced P-selectin binding and increased rolling velocity despite equivalent PSGL-1 surface expression.\",\n      \"method\": \"Bone marrow transplantation with TPST double-KO donors, intravital microscopy, in vitro rolling assay on P-selectin, flow cytometry\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic loss-of-function reconstitution with in vivo and in vitro functional validation\",\n      \"pmids\": [\"21633705\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The PSGL-1 ERM-binding sequence (EBS), specifically Arg-337 and Lys-338 in the cytoplasmic tail, is critical for leukocyte tethering and rolling on L-, P-, and E-selectin and for activating ERK; however, EBS is dispensable for Syk phosphorylation and E-selectin-induced slow rolling via LFA-1.\",\n      \"method\": \"Mutagenesis (EBS deletion, Arg/Lys alanine substitution), leukocyte rolling assays on selectin substrates, ERK and Syk phosphorylation assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic mutagenesis with multiple orthogonal signaling and functional readouts\",\n      \"pmids\": [\"22311979\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"A subset of PSGL-1 molecules is constitutively associated with L-selectin on neutrophils; this PSGL-1–L-selectin signaling complex signals through Src family kinases and ITAM adaptor proteins to activate LFA-1, with signaling output dependent on the L-selectin cytoplasmic tail.\",\n      \"method\": \"Co-immunoprecipitation, flow chamber assays, KO mice (L-selectin), neutrophil slow rolling and recruitment by intravital microscopy\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP + genetic KO + in vivo functional validation\",\n      \"pmids\": [\"24127491\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"EV71 binds to the N-terminal region of PSGL-1 (sulfated tyrosines) via conserved lysine residues VP1-242 and VP1-244 on the capsid; VP1-145 acts as a molecular switch controlling PSGL-1 binding by modulating the orientation of VP1-244 lysine side chain.\",\n      \"method\": \"Site-directed mutagenesis (VP1-145, VP1-244, VP1-242), PSGL-1-expressing CHO cell binding assays, Jurkat T-cell infection, crystal structure comparison\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis + structural analysis + functional infection assay\",\n      \"pmids\": [\"23935488\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PSGL-1-mediated EV71 entry proceeds via caveolar (caveolin-1-dependent) endocytosis requiring intact membrane cholesterol and acidification; this is distinct from hSCARB2-mediated entry which uses clathrin-dependent endocytosis.\",\n      \"method\": \"siRNA knockdown of caveolin-1, specific endocytosis inhibitors, confocal colocalization, pH inhibitors, PSGL-1-expressing L929 cells and Jurkat T cells\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — siRNA + pharmacological inhibitors + imaging, receptor-specific entry pathways demonstrated\",\n      \"pmids\": [\"23760234\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The N-termini of PSGL-1 and CCR7 have overlapping and competitive binding sites for CCL19, as determined by NMR chemical shift mapping; the solution structure of CCL19 reveals a canonical chemokine fold, and PSGL-1 competes with CCR7 for CCL19 binding.\",\n      \"method\": \"NMR solution structure of CCL19, chemical shift mapping, competitive binding assays\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — NMR structure with binding site mapping and competitive binding validation\",\n      \"pmids\": [\"26115234\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"PSGL-1 ligation on exhausted CD8+ T cells inhibits TCR and IL-2 signaling and upregulates PD-1, leading to diminished survival upon TCR stimulation; PSGL-1-deficient mice clear chronic virus due to increased survival and multifunctionality of effector T cells with downregulated PD-1.\",\n      \"method\": \"PSGL-1-deficient mice, chronic viral infection model (LCMV), T cell function assays, receptor expression analysis\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with multiple defined phenotypic readouts and mechanistic pathway placement\",\n      \"pmids\": [\"27192578\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Cooperative PSGL-1 and CXCR2 signaling in rolling neutrophils promotes β2-integrin-dependent arrest and NETosis contributing to deep vein thrombosis; PSGL-1 signaling in DVT uses tyrosine 145 of SLP-76 rather than Y112/Y128, and does not require L-selectin in this context.\",\n      \"method\": \"Genetically engineered mice, ultrasonography, spinning-disk intravital microscopy, flow restriction DVT model, pharmacological blocking\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic models + live in vivo imaging + mechanistic pathway mapping\",\n      \"pmids\": [\"30068506\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"VISTA binds PSGL-1 selectively at acidic pH (as found in tumor microenvironments) via multiple histidine residues along the rim of the VISTA extracellular domain; this interaction suppresses T cells and antibodies that selectively block this interaction at acidic pH reverse VISTA-mediated immune suppression in vivo.\",\n      \"method\": \"Binding assays, pH titration experiments, histidine mutagenesis, pH-selective blocking antibodies, in vivo tumor models\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — mutagenesis + pH-selective binding + in vivo functional validation; published in Nature\",\n      \"pmids\": [\"31645726\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"HIV-1 Vpu binds PSGL-1 and induces its ubiquitination and proteasomal degradation through the ubiquitin ligase SCFβ-TrCP2; PSGL-1 (induced by IFN-γ) inhibits HIV-1 reverse transcription and blocks virion infectivity by incorporating into progeny virions.\",\n      \"method\": \"Quantitative mass spectrometry proteomics, co-immunoprecipitation, ubiquitination assays, siRNA knockdown, viral infectivity assays in primary CD4+ T cells\",\n      \"journal\": \"Nature microbiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — MS-based discovery + Co-IP + ubiquitination + functional infection assays, multiple orthogonal methods\",\n      \"pmids\": [\"30833724\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PSGL-1 incorporated into HIV-1 virions blocks virus particle attachment to target cells through its extracellular N-terminal domain; this inhibitory activity is glycoprotein-independent, and Vpu (primarily) and Nef downregulate PSGL-1 from the cell surface to partially escape restriction.\",\n      \"method\": \"PSGL-1 domain mapping, pseudovirus attachment assays, virus infectivity assays, flow cytometry, siRNA knockdown\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple domain mapping experiments + gain/loss-of-function + mechanistic dissection of escape pathway\",\n      \"pmids\": [\"32273392\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PSGL-1 directly binds cellular F-actin to restrict actin dynamics, inhibiting HIV DNA synthesis; PSGL-1 also binds gp41 and sequesters it at the plasma membrane, blocking Env incorporation into nascent virions, causing loss of envelope spikes and profound defects in viral entry.\",\n      \"method\": \"F-actin binding assay, gp41 co-immunoprecipitation, cryo-electron microscopy, super-resolution imaging, HIV DNA synthesis assay, Env incorporation assay\",\n      \"journal\": \"Cell discovery\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro binding assays + cryo-EM structure + super-resolution imaging + functional virology assays\",\n      \"pmids\": [\"32802403\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Virion-incorporated PSGL-1 (and CD43) inhibits HIV-1 cell-free infection and transinfection by preventing virus-cell attachment; PSGL-1's full-length ectodomain is required for this inhibitory effect, and coclustering with HIV-1 Gag at uropod membranes depends on polybasic sequences in both the PSGL-1 cytoplasmic tail and Gag matrix domain.\",\n      \"method\": \"Virion incorporation assays, CD4+ and CD4- cell attachment assays, ectodomain truncation mutants, Gag colocalization studies\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — domain mapping + attachment assays + colocalization in primary cells, multiple orthogonal methods\",\n      \"pmids\": [\"32193343\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PSGL-1 impairs SARS-CoV and SARS-CoV-2 spike glycoprotein incorporation into pseudovirions and blocks pseudovirus attachment and infectivity of target cells.\",\n      \"method\": \"Pseudovirus infectivity assays, Western blotting for spike incorporation, cell attachment assays\",\n      \"journal\": \"Viruses\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional pseudovirus assays but single lab; no structural validation\",\n      \"pmids\": [\"33396594\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"GALNT4-mediated O-glycosylation of PSGL-1 promotes P-selectin-induced monocyte adhesion and transmigration by activating the Akt/mTOR and IκBα/NFκB pathways; GALNT4 knockdown reduces PSGL-1 O-glycosylation, attenuates Akt/mTOR and NFκB activation, and decreases monocyte adhesion to P-selectin.\",\n      \"method\": \"VVL pull-down, PSGL-1 immunoprecipitation, GALNT4 shRNA knockdown, GALNT4 overexpression, monocyte flow adhesion assay, mTOR inhibitor (rapamycin), phosphorylation assays\",\n      \"journal\": \"Journal of molecular and cellular cardiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — biochemical glycosylation assay + functional adhesion + pharmacological and genetic epistasis; single lab\",\n      \"pmids\": [\"34974060\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PSGL-1 acts upstream of PD-1 and requires co-ligation with the TCR to attenuate early TCR signaling via Zap70 and maintain expression of the Zap70 inhibitor Sts-1, driving terminal CD8+ T cell exhaustion; PSGL-1 deficiency enables responses to low-affinity TCR ligands and sustains an elevated metabolic/glycolytic gene signature.\",\n      \"method\": \"PSGL-1-deficient mice, chronic infection/tumor models, TCR signaling assays (Zap70 phosphorylation), Sts-1 expression analysis, metabolic gene profiling\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO + signaling pathway dissection + mechanistic epistasis with Zap70/Sts-1 + metabolic readout\",\n      \"pmids\": [\"37115668\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Sorting nexin SLIC-1 (SNX20) directly and specifically interacts with the PSGL-1 cytoplasmic domain and contains a Phox homology domain that targets the PSGL-1/SLIC-1 complex to endosomes, cycling PSGL-1 into the endosomal compartment.\",\n      \"method\": \"Yeast two-hybrid screen, co-immunoprecipitation, colocalization experiments, motif mapping, SNX20-deficient mice\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — yeast two-hybrid + Co-IP + functional KO mice; sorting function established but signaling role not found\",\n      \"pmids\": [\"18196517\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Human PSGL-1 interacts with skin-associated chemokine CCL27 via sulfated tyrosines at its amino terminus (not glycans); PSGL-1 expression on CCR10-expressing cells reduces chemotaxis to CCL27, suggesting PSGL-1 regulates chemokine-mediated responses by sequestering CCL27.\",\n      \"method\": \"rPSGL-Ig binding assays, arylsulfatase and glycosidase treatments, sulfation inhibitor, tyrosine-to-phenylalanine mutagenesis, chemotaxis assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis + enzymatic treatment + functional chemotaxis assay, multiple orthogonal approaches\",\n      \"pmids\": [\"15466853\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"P-selectin (CD62P) binding to PSGL-1 on tumor-associated macrophages activates the JNK/STAT1 pathway to induce C5 transcription and C5a release, shifting TAMs toward a pro-tumor phenotype and promoting CRC growth via the C5a/C5aR1 axis.\",\n      \"method\": \"Western blotting, siRNA knockdown of PSGL-1, JNK/STAT1 pathway inhibitors, dual-luciferase reporter, ChIP assay, in vivo AOM/DSS CRC model\",\n      \"journal\": \"Theranostics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic/siRNA knockdown + pathway inhibitors + reporter + ChIP; single lab\",\n      \"pmids\": [\"37064877\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"PSGL-1 cross-linking in neutrophils triggers tyrosine-phosphorylation-dependent and c-Abl-involved alteration of F-actin cytoskeleton and PSGL-1 polarization; c-Abl redistributes to F-actin-concentrated regions upon PSGL-1 engagement.\",\n      \"method\": \"Anti-PSGL-1 antibody cross-linking, actin cytoskeleton staining, genistein (tyrosine kinase inhibitor), STI571 (c-Abl inhibitor), cytochalasin B treatment\",\n      \"journal\": \"Journal of cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — pharmacological inhibition with localization studies; single lab, single paper\",\n      \"pmids\": [\"15526280\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Flotillin-1 and flotillin-2 associate with PSGL-1 in resting and stimulated neutrophils (shown by co-immunoprecipitation and colocalization) and reorganize into uropod domains; flotillin cap formation is PSGL-1-independent as shown by PSGL-1-deficient neutrophils, but PSGL-1 and flotillins redistribute together more rapidly than other uropod proteins.\",\n      \"method\": \"Co-immunoprecipitation, immunofluorescence, PSGL-1-deficient mice neutrophils, HL-60 differentiated cells\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — Co-IP + immunofluorescence + KO controls, single lab\",\n      \"pmids\": [\"19404397\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"PSGL-1 engagement upregulates CSF-1 transcription in a Syk-dependent manner; overexpression of wild-type but not kinase-dead Syk promotes CSF-1 promoter activation downstream of PSGL-1, and Syk inhibitor piceatannol suppresses PSGL-1-induced CSF-1 mRNA upregulation.\",\n      \"method\": \"Antibody engagement of PSGL-1, CSF-1 promoter reporter assay, Syk dominant-negative overexpression, piceatannol inhibition, RT-PCR\",\n      \"journal\": \"Cellular immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — reporter assay + dominant-negative + pharmacological inhibition; single lab, limited mechanistic depth\",\n      \"pmids\": [\"16289055\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PSGL-1 is a dimeric, heavily O-glycosylated, tyrosine-sulfated sialomucin on leukocytes that binds P-, E-, and L-selectins via cooperative interaction of its N-terminal sulfated tyrosines (critical: Tyr-48 for P-selectin, Tyr-51 for L-selectin) and core-2 sialyl-Lewis X O-glycans on Thr-57 to mediate leukocyte rolling and tethering; its cytoplasmic domain anchors PSGL-1 to the actin cytoskeleton via moesin/ERM proteins, and upon selectin or co-receptor (L-selectin) engagement signals through Src family kinases (Fgr, Hck, Lyn), ITAM adaptors (DAP12, FcRγ), and Syk to activate β2-integrins for slow rolling and neutrophil recruitment, while also binding homeostatic chemokines CCL19/CCL21 and VISTA (at acidic pH) to regulate T cell trafficking and exhaustion, and acting as an antiviral restriction factor that blocks HIV-1 virion attachment to target cells by its ectodomain and inhibits Env incorporation by sequestering gp41.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"PSGL-1 (P-selectin glycoprotein ligand-1) is a dimeric sialomucin on leukocytes and platelets that serves as the primary counter-receptor for P-, E-, and L-selectins, mediating leukocyte tethering, rolling, and recruitment to activated endothelium, and additionally functions as a signaling receptor that regulates integrin activation, T cell exhaustion, chemokine responsiveness, and antiviral restriction. Selectin recognition requires cooperative engagement of tyrosine-sulfated residues (Tyr-48 for P-selectin, Tyr-51 for L-selectin) and core-2 sialyl-Lewis X O-glycans on Thr-57, with dimerization through Cys-320 essential for P-selectin binding, and fucosyltransferase VII-dependent glycosylation conferring E-selectin specificity [PMID:7585950, PMID:9660879, PMID:12403782, PMID:9353122]. The cytoplasmic tail anchors PSGL-1 to the actin cytoskeleton via ERM proteins (moesin/radixin), and upon selectin engagement signals through Src family kinases (Fgr, Hck, Lyn), ITAM adaptors (DAP12, FcRγ), and Syk to activate β2-integrins for slow rolling and neutrophil arrest, while also modulating T cell exhaustion by attenuating TCR-Zap70 signaling and upregulating PD-1 via interaction with VISTA at acidic pH [PMID:18794338, PMID:12036880, PMID:27192578, PMID:31645726, PMID:37115668]. PSGL-1 also acts as an interferon-induced antiviral restriction factor that blocks HIV-1 virion attachment through its ectodomain, sequesters gp41 to inhibit Env incorporation, and is counteracted by Vpu-mediated ubiquitination and degradation via SCFβ-TrCP2 [PMID:30833724, PMID:32802403, PMID:32273392].\",\n  \"teleology\": [\n    {\n      \"year\": 1995,\n      \"claim\": \"Identifying that N-terminal tyrosine sulfation is required for P-selectin binding established the first post-translational modification critical for PSGL-1 adhesive function, moving beyond simple glycoprotein recognition.\",\n      \"evidence\": \"Site-directed mutagenesis of N-terminal tyrosines and sulfation inhibitor treatment with rolling adhesion assays\",\n      \"pmids\": [\"7585950\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contributions of individual tyrosine residues not yet resolved\", \"Structural basis of sulfated tyrosine–P-selectin interaction unknown at this point\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Demonstrating that CLA is an inducible fucosyltransferase VII-dependent carbohydrate modification of PSGL-1 that selectively confers E-selectin binding revealed that the same protein backbone can be differentially glycosylated to regulate distinct selectin interactions.\",\n      \"evidence\": \"T cell differentiation assays, monoclonal antibody characterization, and selectin-binding functional assays\",\n      \"pmids\": [\"9353122\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Glycosyltransferase regulation during T cell differentiation not mechanistically defined\", \"Whether other fucosyltransferases contribute was unresolved\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Showing that Cys-320-mediated disulfide-bonded dimerization is essential for P-selectin rolling established PSGL-1's quaternary structure as a functional requirement, not merely a structural feature.\",\n      \"evidence\": \"C320A mutagenesis, Western blotting under native conditions, and flow-based rolling assays\",\n      \"pmids\": [\"9660879\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether dimerization is equally required for E- and L-selectin binding was untested\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Demonstrating that P-selectin engagement of PSGL-1 triggers tyrosine kinase signaling leading to β2-integrin activation transformed PSGL-1 from a passive adhesion molecule into a signaling receptor that couples rolling to firm adhesion.\",\n      \"evidence\": \"Mixed cell aggregation under shear, tyrosine kinase inhibitors, and P-selectin-IgG stimulation of PMN\",\n      \"pmids\": [\"9920836\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the specific kinases downstream of PSGL-1 not yet mapped\", \"Role of the cytoplasmic domain in signaling not defined\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Defining that the PSGL-1 cytoplasmic tail links to actin via moesin, and that this moesin–Syk axis transduces ITAM-dependent signaling, provided the first molecular bridge between PSGL-1 adhesion and intracellular kinase activation.\",\n      \"evidence\": \"Co-immunoprecipitation with ERM proteins, cytoplasmic truncation mutants, Syk inhibitors, ITAM-mutated moesin, and SRE reporter assays\",\n      \"pmids\": [\"12036880\", \"12387735\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How moesin ITAM-like motifs recruit Syk in the absence of classical ITAM adaptors was unclear\", \"Structural details of the PSGL-1–moesin interface not yet resolved\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Systematic mutagenesis of Thr-57, Tyr-48, and Tyr-51 defined the differential post-translational requirements for L-selectin versus P-selectin binding, establishing that the same N-terminal region uses distinct residues for each selectin.\",\n      \"evidence\": \"Site-directed mutagenesis with L-selectin binding assays and leukocyte rolling on CHO transfectants co-expressing glycosyltransferases\",\n      \"pmids\": [\"12403782\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether these requirements hold in vivo under inflammatory conditions was not tested\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Demonstrating that PSGL-1 binds chemokine CCL27 via sulfated tyrosines and attenuates CCL27-mediated chemotaxis uncovered a selectin-independent function as a chemokine-interacting molecule.\",\n      \"evidence\": \"Tyrosine-to-phenylalanine mutagenesis, arylsulfatase and glycosidase treatment, and chemotaxis assays\",\n      \"pmids\": [\"15466853\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological significance of CCL27 sequestration in skin homing not confirmed in vivo\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"PSGL-1 on lymphoid progenitors was shown to mediate thymic homing via P-selectin on thymic endothelium, extending its role from inflammatory recruitment to developmental lymphocyte trafficking.\",\n      \"evidence\": \"Parabiosis, competitive thymus reconstitution, short-term homing assays in PSGL-1 knockout mice\",\n      \"pmids\": [\"15880112\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PSGL-1 glycosylation is regulated during thymic progenitor development was not explored\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Multiple discoveries in 2007 consolidated a picture of PSGL-1 as both a dominant capture receptor for E-selectin on neutrophils and a facilitator of homeostatic T cell homing through CCL19/CCL21 binding, independent of selectins, while also signaling through Akt/mTOR to regulate ROCK-1 translation in macrophages.\",\n      \"evidence\": \"Knockout and siRNA epistasis with intravital microscopy for E-selectin ligand hierarchy; PSGL-1-null T cell chemotaxis assays; polysome profiling and rapamycin inhibition in PSGL-1 KO macrophages\",\n      \"pmids\": [\"17442598\", \"17401367\", \"17245434\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of PSGL-1–CCL19/CCL21 interaction unknown\", \"How PSGL-1 selectively regulates ROCK-1 but not ROCK-2 mRNA translation not mechanistically explained\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Crystal structure of the radixin FERM domain with the PSGL-1 juxtamembrane peptide revealed β-strand-mediated binding in the subdomain C groove, providing the first atomic-level view of how PSGL-1 connects to the ERM–actin cytoskeleton.\",\n      \"evidence\": \"X-ray crystallography of radixin FERM domain–PSGL-1 peptide complex\",\n      \"pmids\": [\"18076570\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the radixin and moesin FERM domains engage PSGL-1 identically was not compared structurally\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Defining the Fgr/Hck/Lyn → DAP12/FcRγ → Syk signaling cascade downstream of E-selectin–PSGL-1 engagement, and showing the cytoplasmic domain is essential for integrin activation but dispensable for rolling, separated the adhesive and signaling functions of PSGL-1 at the genetic level.\",\n      \"evidence\": \"Multiple compound-knockout mice (Fgr, Hck/Lyn/Fgr, DAP12/FcRγ), ΔCD knock-in mice, intravital microscopy, and phosphorylation assays\",\n      \"pmids\": [\"18794338\", \"18550846\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How PSGL-1 cytoplasmic domain recruits SFKs to lipid rafts was mechanistically undefined\", \"Whether DAP12/FcRγ directly bind PSGL-1 or are recruited indirectly was unresolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Identifying that EV71 binds PSGL-1 via sulfated tyrosines (not O-glycans) established PSGL-1 as a viral entry receptor exploiting the same N-terminal motif used by selectins, revealing pathogen hijacking of an adhesion molecule.\",\n      \"evidence\": \"Systematic mutagenesis (T57A, sulfation inhibitors) with flow cytometry binding and viral replication assays in 293T and Jurkat cells\",\n      \"pmids\": [\"21079683\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PSGL-1-mediated EV71 entry occurs in vivo not demonstrated\", \"Structural basis of EV71–PSGL-1 interaction not yet solved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Fine-mapping of the ERM-binding sequence (Arg-337/Lys-338) showed it is required for tethering/rolling and ERK activation but dispensable for Syk phosphorylation and slow rolling, demonstrating bifurcation of PSGL-1 cytoplasmic signaling into ERM-dependent and ERM-independent arms.\",\n      \"evidence\": \"Alanine substitution mutagenesis at R337/K338, rolling assays on all three selectins, and parallel measurement of ERK and Syk phosphorylation\",\n      \"pmids\": [\"22311979\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How PSGL-1 activates Syk independently of ERM linkage was not explained\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Discovery of a constitutive PSGL-1–L-selectin signaling complex on neutrophils that signals through SFKs and ITAM adaptors to activate LFA-1 revealed a cis-acting receptor complex, distinct from trans selectin–ligand interactions during rolling.\",\n      \"evidence\": \"Co-immunoprecipitation, L-selectin KO mice, flow chamber and intravital microscopy\",\n      \"pmids\": [\"24127491\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and structural basis of the cis PSGL-1–L-selectin complex unresolved\", \"Whether this complex forms in non-neutrophil leukocytes was not tested\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Showing that PSGL-1 ligation promotes CD8+ T cell exhaustion by upregulating PD-1 and inhibiting TCR/IL-2 signaling—with PSGL-1-deficient mice clearing chronic LCMV—recast PSGL-1 as an immune checkpoint molecule beyond its adhesion function.\",\n      \"evidence\": \"PSGL-1-deficient mice in chronic LCMV infection model, T cell function and receptor expression analysis\",\n      \"pmids\": [\"27192578\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Ligand identity for PSGL-1 in the T cell exhaustion context was not established in this study\", \"Mechanism linking PSGL-1 to PD-1 transcription not defined\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Two major advances established PSGL-1 as both a pH-sensitive receptor for VISTA in the tumor microenvironment and an IFN-γ-induced antiviral restriction factor degraded by HIV-1 Vpu via SCFβ-TrCP2-mediated ubiquitination.\",\n      \"evidence\": \"Histidine mutagenesis and pH-selective binding/blocking antibodies with in vivo tumor models for VISTA; quantitative mass spectrometry, Co-IP, ubiquitination, and infectivity assays in primary CD4+ T cells for HIV-1\",\n      \"pmids\": [\"31645726\", \"30833724\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the pH-dependent VISTA–PSGL-1 interaction not solved\", \"Whether PSGL-1 antiviral activity extends to other retroviruses was unexplored\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Detailed mechanistic dissection showed PSGL-1 restricts HIV-1 through dual mechanisms—blocking virion attachment via its ectodomain and sequestering gp41 to prevent Env incorporation—while also binding F-actin directly to restrict actin dynamics needed for HIV DNA synthesis.\",\n      \"evidence\": \"Domain mapping, pseudovirus attachment assays, cryo-EM, super-resolution imaging, F-actin binding assays, Env incorporation assays\",\n      \"pmids\": [\"32273392\", \"32802403\", \"32193343\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether F-actin binding by PSGL-1 is relevant to its canonical leukocyte functions was not tested\", \"In vivo relevance of PSGL-1 antiviral restriction not demonstrated in animal models\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"PSGL-1 was positioned upstream of PD-1 in the exhaustion hierarchy: TCR co-ligation with PSGL-1 attenuates Zap70 phosphorylation and maintains the Zap70 inhibitor Sts-1, driving terminal exhaustion, which provided a mechanistic basis for PSGL-1's checkpoint function.\",\n      \"evidence\": \"PSGL-1-deficient mice in chronic infection and tumor models, Zap70 phosphorylation and Sts-1 expression assays, metabolic gene profiling\",\n      \"pmids\": [\"37115668\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct physical interaction between PSGL-1 and TCR signaling components not demonstrated\", \"Whether PSGL-1-mediated exhaustion involves VISTA as the ligand in these models is not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: (1) the structural basis of pH-dependent VISTA–PSGL-1 binding; (2) how PSGL-1 cytoplasmic domain recruits ITAM adaptors and Syk independently of ERM linkage; (3) in vivo validation of PSGL-1 antiviral restriction in animal models; (4) therapeutic targeting of PSGL-1 as an immune checkpoint distinct from PD-1.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No full-length PSGL-1 structure available\", \"Therapeutic antibody or small molecule targeting PSGL-1 checkpoint function not yet tested clinically\", \"Integration of PSGL-1 adhesion, signaling, and checkpoint functions into a unified model remains incomplete\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098631\", \"supporting_discovery_ids\": [0, 2, 3, 9, 11, 13]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [4, 7, 18, 19, 29, 38]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [8, 17, 34]},\n      {\"term_id\": \"GO:0001618\", \"supporting_discovery_ids\": [6, 22, 26, 27]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 2, 5, 8, 33, 35]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [8, 17, 34, 42]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [39]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [4, 13, 18, 19, 21, 25, 29, 38]},\n      {\"term_id\": \"R-HSA-1500931\", \"supporting_discovery_ids\": [0, 2, 9, 11, 12]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [7, 16, 18, 21, 30, 31]},\n      {\"term_id\": \"R-HSA-109582\", \"supporting_discovery_ids\": [5, 10, 30]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [6, 22, 32, 33, 36]}\n    ],\n    \"complexes\": [\n      \"PSGL-1 homodimer\",\n      \"PSGL-1–L-selectin cis signaling complex\"\n    ],\n    \"partners\": [\n      \"SELP\",\n      \"SELE\",\n      \"SELL\",\n      \"MSN\",\n      \"SYK\",\n      \"VISTA\",\n      \"SNX20\",\n      \"DAP12\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}