{"gene":"GPC1","run_date":"2026-06-10T01:55:21","timeline":{"discoveries":[{"year":2001,"finding":"GPC1 (glypican-1) binds Slit-2 protein via its heparan sulfate chains with high affinity (Kd ~80-110 nM); the glycanated proteoglycan binds with ~10-fold higher affinity than the core protein alone; O-sulfate groups on heparan sulfate chains are critical for this interaction; co-immunoprecipitation confirmed the interaction in vivo after co-transfection of 293 cells, and colocalization was demonstrated immunocytochemically in the embryonic and adult CNS.","method":"ELISA binding assay with glypican-Fc fusion protein and recombinant Slit-2; co-immunoprecipitation after co-transfection; heparinase treatment and desulfated heparin competition; immunocytochemistry","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro binding assay with defined Kd values, enzymatic removal of HS chains, sulfation inhibition, and in vivo co-IP with immunolocalization; multiple orthogonal methods in one study","pmids":["11375980"],"is_preprint":false},{"year":2006,"finding":"GPC1 is the principal alpha4(V) collagen-binding heparan sulfate proteoglycan on the Schwann cell surface. siRNA-mediated knockdown of GPC1 reduced binding of alpha4(V) collagen N-terminal domain to Schwann cells, decreased Schwann cell adhesion and spreading on alpha4(V)-NTD, impaired incorporation of alpha4(V) collagen into ECM, and significantly inhibited myelination in Schwann cell–DRG neuron co-cultures.","method":"siRNA knockdown; adhesion/spreading assays; ECM incorporation assay; Schwann cell–DRG neuron co-culture myelination assay","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Moderate — clean siRNA loss-of-function with multiple orthogonal cellular phenotype readouts (binding, adhesion, ECM, myelination) in a single study","pmids":["16407548"],"is_preprint":false},{"year":2008,"finding":"Both cancer cell-derived and host-derived GPC1 are required for efficient tumor growth, metastasis, and angiogenesis. Antisense-mediated GPC1 downregulation in PANC-1 cells prolonged doubling times, decreased anchorage-independent growth in vitro, and attenuated tumor growth, angiogenesis, and metastasis in athymic mice. GPC1-null host mice showed decreased tumor angiogenesis, metastasis, and fewer pulmonary metastases with multiple cancer cell lines; hepatic endothelial cells from GPC1-null mice had an attenuated mitogenic response to VEGF-A.","method":"Antisense knockdown; xenograft tumor implantation; GPC1 knockout mouse; in vitro proliferation and soft-agar assays; metastasis quantification; VEGF-A mitogenesis assay on isolated endothelial cells","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — both cell-intrinsic and host-derived GPC1 tested with antisense and genetic knockout, multiple cancer models and orthogonal readouts (growth, metastasis, angiogenesis, VEGF response)","pmids":["18064304"],"is_preprint":false},{"year":2009,"finding":"GPC1 mediates lipid raft association of the cellular prion protein (PrPc) and facilitates conversion to the disease isoform (PrPSc). Depletion of GPC1 (the major neuronal GPI-anchored HSPG) displaced PrPc from rafts and promoted its endocytosis. Both PrPc and PrPSc co-immunoprecipitated with GPC1. Critically, GPC1 siRNA knockdown in scrapie-infected N2a cells significantly reduced PrPSc formation.","method":"siRNA knockdown; co-immunoprecipitation; detergent-resistant raft fractionation; confocal immunofluorescence; scrapie-infected cell model","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP, raft fractionation, siRNA loss-of-function with functional PrPSc formation readout, multiple orthogonal methods in one study","pmids":["19936054"],"is_preprint":false},{"year":2006,"finding":"GPC1 controls copper-dependent co-internalization of PrPc from the cell surface to perinuclear compartments. PrPc provides the Cu2+ ions required to nitrosylate thiol groups in the GPC1 core protein, enabling GPC1 recycling via a caveolin-associated pathway and heparan sulfate autoprocessing. A PrPc construct lacking the copper-binding domain failed to drive GPC1 internalization and abrogated GPC1 autoprocessing. GPC1 silencing had no effect on copper-stimulated PrPc endocytosis.","method":"Confocal immunofluorescence; immunomagnetic isolation; siRNA silencing; copper treatment; dominant-negative PrPc construct lacking Cu-binding domain","journal":"Journal of neurochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (confocal co-localization, immunomagnetic pull-down, genetic silencing, domain-deletion construct), single lab","pmids":["16923158"],"is_preprint":false},{"year":2011,"finding":"GPC1 overexpression in brain endothelial cells inactivates the G1/S checkpoint by activating the mitogen-independent Skp2 autoinduction loop: GPC1 suppresses CDK inhibitors (p21, p27, p16, p19) and D cyclins, induces CDK2 and Skp2, and activates ERK/MAPK, Wnt, and BMP signaling pathways. p21 knockdown by RNAi phenocopied GPC1 effects on cell cycle regulators.","method":"GPC1 overexpression and RNAi knockdown; immunoblotting for cell cycle regulators; luciferase reporter assays for signaling pathways; flow cytometry for cell cycle phasing","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain- and loss-of-function with multiple molecular readouts and epistasis (p21 RNAi rescue), single lab","pmids":["22203671"],"is_preprint":false},{"year":2013,"finding":"GPC1 expression strongly stimulates S phase entry, DNA replication, and causes DNA rereplication and damage in glioma cells and normal astrocytes; it downregulates pRb, Cip/Kip CKIs, and CDH1, upregulates cyclin E, CDK2, Skp2, and Cdt1, and constitutively activates ERK/MAPK and PI3K/Akt pathways. Knockdown of Skp2, CDK2, or cyclin E reduced S phase and aneuploid fractions, confirming their role downstream of GPC1.","method":"GPC1 overexpression and siRNA knockdown; BrdU/EdU incorporation; flow cytometry; immunoblotting; PI3K/Akt and ERK pathway inhibitors","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — bidirectional manipulation, epistasis via secondary knockdowns, multiple orthogonal readouts, single lab","pmids":["24019070"],"is_preprint":false},{"year":2013,"finding":"GPC1 acts as a susceptibility gene for biliary atresia and regulates Hedgehog signaling in biliary development. Morpholino knockdown of gpc1 in zebrafish caused developmental biliary defects; partial rescue by a Hedgehog antagonist (cyclopamine) and induction of biliary defects by recombinant Sonic Hedgehog injection phenocopying the morphant established GPC1 as a positive regulator of Hh signaling in this context.","method":"Morpholino antisense knockdown in zebrafish; cyclopamine rescue; recombinant Sonic Hedgehog injection; biliary morphology analysis; copy number variant analysis in BA patients","journal":"Gastroenterology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis by pharmacological rescue and ligand injection in vivo zebrafish model, supported by human genetic data; single lab","pmids":["23336978"],"is_preprint":false},{"year":2014,"finding":"GPC1 mediates shear stress-induced eNOS activation in endothelial cells. RNA silencing of GPC1 (but not syndecan-1) blocked flow-induced eNOS activation, while SDC1 knockdown (but not GPC1) attenuated cell elongation and alignment. GPC1 is localized to caveolae where eNOS resides, consistent with its role as a centralized mechanotransmission agent.","method":"siRNA silencing of GPC1 or SDC1; heparinase III treatment; shear stress application to EC monolayers; eNOS activity measurement; cell morphology analysis","journal":"Integrative biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean siRNA knockdown with specific functional readout (eNOS activation) and specificity control (SDC1), single lab","pmids":["24480876"],"is_preprint":false},{"year":2013,"finding":"GPC1 and GPC3 physically interact with BMP2 and inhibit BMP2, BMP4, and BMP7 activities in cranial suture mesenchymal cells. Immunoblockade of endogenous GPC1 and GPC3 potentiated BMP2 activity; overexpression or addition of recombinant GPC1/GPC3 protein inhibited BMP2 signaling and BMP2-mediated osteogenesis. GPC1 and GPC3 inhibit both SMAD-dependent and SMAD-independent BMP2 signaling pathways.","method":"Recombinant protein binding (physical interaction assay); antibody blockade of endogenous glypicans; overexpression; SMAD phosphorylation immunoblotting; osteogenesis assay in primary suture mesenchymal cells","journal":"Bone","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct physical interaction assay, bidirectional manipulation (blockade and overexpression), functional osteogenesis readout; single lab","pmids":["23624389"],"is_preprint":false},{"year":2021,"finding":"GPC1 is the principal and rate-limiting factor that drives unconventional secretion of FGF2. Among all heparan sulfate proteoglycan subclasses (syndecans, perlecans, glypicans), only GPC1 knockdown substantially reduced FGF2 secretion. Disaccharides with N-linked sulfate groups are enriched in GPC1 heparan sulfate chains and mediate high-affinity FGF2 binding. GPC1 was dispensable for FGF2 signaling into cells.","method":"siRNA knockdown of specific HSPG subclasses; FGF2 secretion assay; heparan sulfate chain structural analysis; FGF2 binding affinity measurements; FGF2 signaling assay","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — systematic subclass knockdown, HS structural characterization, binding assay, and signaling assay in one study; multiple orthogonal methods establishing specificity of GPC1","pmids":["35348113"],"is_preprint":false},{"year":2021,"finding":"GPC1 is required for VEGF- and HGF-induced angiogenesis in human dermal microvascular endothelial cells (HDMEC). GPC1 siRNA transfection completely abrogated pseudotube formation induced by keratinocyte-conditioned media. Cleavage of GPC1 from the cell surface by phospholipase C promoted HDMEC proliferation. GPC1 was shown to interact directly with VEGFR2 and c-Met to regulate angiogenesis.","method":"siRNA knockdown; phospholipase C cleavage; pseudotube formation assay; co-immunoprecipitation/direct interaction assay for GPC1-VEGFR2 and GPC1-c-Met","journal":"Frontiers in cell and developmental biology","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — siRNA loss-of-function with functional angiogenesis readout and direct GPC1-receptor interaction assays; single lab","pmids":["34957110"],"is_preprint":false},{"year":2021,"finding":"GPC1 protects endothelial cells from stiffness-mediated dysfunction. On stiff substrates (10 kPa), GPC1 gene and protein expression were reduced; GPC1 siRNA silencing on soft substrates recapitulated stiffness-induced EC dysfunction (inflammation, proliferation, EndMT); GPC1 overexpression reversed these effects. GPC1 knockout mice (GPC1-/-) showed exacerbated endothelial dysfunction in young but not old mice (where GPC1 is already low).","method":"Polyacrylamide gel substrates of defined stiffness; siRNA silencing and plasmid overexpression; GPC1 knockout mouse model; monocyte adhesion assay; NO measurement; gene expression analysis","journal":"Cardiovascular research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — bidirectional manipulation in vitro and in vivo KO mouse, multiple functional EC dysfunction readouts; single lab","pmids":["32647868"],"is_preprint":false},{"year":2022,"finding":"GPC1 promotes colorectal cancer cell growth and migration through the TGF-β1/SMAD2 signaling pathway. GPC1 knockdown in CRC cell lines inhibited proliferation, migration, and promoted apoptosis; it suppressed TGF-β1 levels and p-SMAD2 while increasing total SMAD2, placing GPC1 upstream of TGF-β1/SMAD2 signaling in CRC.","method":"siRNA knockdown; CCK-8 proliferation assay; Transwell migration assay; apoptosis assay; western blotting for TGF-β1, SMAD2, and p-SMAD2","journal":"PloS one","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, siRNA knockdown with downstream pathway readout but no rescue or overexpression confirmation","pmids":["35671267"],"is_preprint":false},{"year":2006,"finding":"GPC1 downregulation in pancreatic cancer cells reduces anchorage-independent growth and slightly modifies TGF-β1, activin-A, and BMP-2 signaling (growth, p21 induction, Smad2 phosphorylation). GPC1 mRNA correlates with activin and BMP receptor expression in pancreatic tissues.","method":"Stable antisense transfection of GPC1; MTT and soft agar growth assays; immunoblotting for p-Smad1, p-Smad2, p21; quantitative RT-PCR for receptors","journal":"International journal of oncology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, antisense knockdown with modest and partial signaling readouts; correlation data only for receptor associations","pmids":["17016645"],"is_preprint":false},{"year":2000,"finding":"GPC1 (glypican) biosynthesis involves GPI-anchor attachment and heparan sulfate chain assembly on serine residues in consensus sequences. Chain-truncated GPC1 formed by endoheparanase cleavage at GlcNH2 residues followed by NO-derived nitrite deaminative cleavage can serve as a precursor for reformation of full-length proteoglycan, establishing a recycling pathway for GPC1 heparan sulfate chains.","method":"Biochemical characterization; in vitro enzymatic assays; GlcNH2 identification; NO/nitrite deaminative cleavage assay","journal":"Matrix biology","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro biochemical reconstitution of chain cleavage and recycling, but single lab and limited structural validation","pmids":["10963998"],"is_preprint":false},{"year":2019,"finding":"GPC1 overexpression in colon cancer cells activates epithelial-mesenchymal transition (EMT), increasing invasion and migration; GPC1 silencing inactivated EMT and decreased invasion and migration. miR-96-5p and miR-149 were shown to regulate GPC1 expression, and their overexpression decreased GPC1 levels, GPC1+ exosome secretion, and tumor growth.","method":"GPC1 overexpression and siRNA knockdown; EMT marker immunoblotting; invasion/migration Transwell assays; adenoviral miRNA overexpression; xenograft tumor model","journal":"Oncotarget","confidence":"Low","confidence_rationale":"Tier 3 / Weak — bidirectional manipulation but EMT pathway placement is indirect; single lab","pmids":["29254156"],"is_preprint":false}],"current_model":"GPC1 (glypican-1) is a GPI-anchored heparan sulfate proteoglycan that functions as a co-receptor and regulatory scaffold at the cell surface: its heparan sulfate chains (particularly N-sulfated disaccharides) bind ligands including Slit-2, FGF2, VEGF, and HGF with high affinity, making it the principal driver of unconventional FGF2 secretion and a required co-receptor for VEGF/HGF-induced angiogenesis; in caveolae it transmits fluid shear stress to eNOS for nitric oxide production; it facilitates PrPc–PrPSc conversion in lipid rafts by scaffolding both isoforms; it promotes G1/S cell cycle progression via the Skp2 autoinduction loop and activation of ERK/MAPK, Wnt, and BMP signaling; it supports Schwann cell myelination through interaction with alpha4(V) collagen; and it regulates BMP2/4/7 signaling in osteogenesis; collectively, loss-of-function studies in cells and in vivo models establish GPC1 as a broadly acting heparan-sulfate-dependent co-receptor that amplifies growth factor and morphogen signaling to promote cell proliferation, angiogenesis, and metastasis."},"narrative":{"mechanistic_narrative":"GPC1 (glypican-1) is a GPI-anchored, heparan-sulfate-bearing cell-surface proteoglycan that acts as a heparan-sulfate-dependent co-receptor and scaffold, concentrating and presenting secreted ligands and morphogens to amplify growth-factor and developmental signaling [PMID:11375980, PMID:35348113]. Its heparan sulfate chains, particularly N-sulfated disaccharides, mediate high-affinity ligand binding—including Slit-2 and FGF2—and the glycanated proteoglycan binds substantially more avidly than the core protein alone [PMID:11375980, PMID:35348113]; among heparan sulfate proteoglycan subclasses, GPC1 is the principal, rate-limiting driver of unconventional FGF2 secretion while being dispensable for FGF2 signaling into cells [PMID:35348113]. At the cell surface GPC1 functions as a required co-receptor for angiogenesis, interacting directly with VEGFR2 and c-Met and acting cell-intrinsically and from the host vasculature to support VEGF-A-driven endothelial mitogenesis, tumor growth, and metastasis [PMID:18064304, PMID:34957110]. In endothelial caveolae it serves as a mechanotransducer that is specifically required for shear-stress-induced eNOS activation and protects against substrate-stiffness-induced endothelial dysfunction [PMID:24480876, PMID:32647868]. GPC1 modulates multiple morphogen pathways in a context-dependent manner: it is the principal alpha4(V)-collagen-binding proteoglycan on Schwann cells and is required for myelination [PMID:16407548], positively regulates Hedgehog signaling during biliary development [PMID:23336978], and physically binds BMP2 to inhibit BMP2/4/7 signaling and osteogenesis [PMID:23624389]. In proliferating cells GPC1 drives G1/S progression and DNA replication by engaging the Skp2 autoinduction loop—suppressing CDK inhibitors and inducing Skp2, CDK2, and cyclin E—while activating ERK/MAPK, PI3K/Akt, Wnt, and BMP signaling [PMID:22203671, PMID:24019070]. GPC1 also scaffolds the cellular prion protein in lipid rafts, mediating its raft association and copper-dependent internalization and facilitating PrPc-to-PrPSc conversion [PMID:19936054, PMID:16923158].","teleology":[{"year":2000,"claim":"Establishing the biosynthetic and recycling logic of GPC1 was needed to understand how its heparan sulfate chains are assembled and regenerated, the basis for its ligand-binding function.","evidence":"Biochemical reconstitution of GPI-anchor attachment, HS chain assembly, and endoheparanase/NO-driven deaminative cleavage and reformation in vitro","pmids":["10963998"],"confidence":"Medium","gaps":["Single-lab in vitro reconstitution with limited structural validation","Physiological relevance of the recycling pathway not tested in cells"]},{"year":2001,"claim":"Demonstrating high-affinity, sulfation-dependent binding of Slit-2 to GPC1 heparan sulfate chains established GPC1 as a ligand-binding co-receptor rather than an inert structural proteoglycan.","evidence":"ELISA binding with glypican-Fc, heparinase and desulfated-heparin competition, co-IP after co-transfection, and CNS immunolocalization","pmids":["11375980"],"confidence":"High","gaps":["Functional consequence of GPC1-Slit-2 binding on axon guidance not tested","Does not establish whether GPC1 presents Slit-2 to a signaling receptor"]},{"year":2006,"claim":"Identifying GPC1 as the principal alpha4(V)-collagen-binding proteoglycan on Schwann cells linked it to ECM assembly and peripheral myelination.","evidence":"siRNA knockdown with adhesion, ECM incorporation, and Schwann cell–DRG co-culture myelination assays","pmids":["16407548"],"confidence":"High","gaps":["Whether HS chains or core protein mediate alpha4(V) binding not resolved","No in vivo myelination phenotype"]},{"year":2006,"claim":"Defining a copper- and PrPc-dependent route for GPC1 internalization connected GPC1 trafficking to prion protein biology in lipid rafts.","evidence":"Confocal co-localization, immunomagnetic isolation, siRNA silencing, and a Cu-binding-domain-deletion PrPc construct","pmids":["16923158"],"confidence":"Medium","gaps":["Single lab","Mechanism of nitrosylation-driven autoprocessing not biochemically resolved"]},{"year":2008,"claim":"Genetic and antisense loss-of-function across cancer and host compartments established GPC1 as both cell-intrinsic and stromal driver of tumor growth, angiogenesis, and metastasis.","evidence":"Antisense knockdown in PANC-1, xenografts in athymic and GPC1-null host mice, metastasis quantification, and VEGF-A mitogenesis on isolated endothelial cells","pmids":["18064304"],"confidence":"High","gaps":["Direct ligand/receptor mechanism for the angiogenic defect not defined in this study","Does not identify the GPC1-dependent signaling axis"]},{"year":2009,"claim":"Showing GPC1 scaffolds both PrPc and PrPSc in rafts and is required for PrPSc formation gave GPC1 a mechanistic role in prion conversion.","evidence":"Reciprocal co-IP, detergent-resistant raft fractionation, confocal IF, and siRNA in scrapie-infected N2a cells","pmids":["19936054"],"confidence":"High","gaps":["Whether GPC1 directly catalyzes or merely co-localizes the isoforms unresolved","No structural model of the scaffold"]},{"year":2011,"claim":"Linking GPC1 to the mitogen-independent Skp2 autoinduction loop explained how it inactivates the G1/S checkpoint to drive proliferation.","evidence":"GPC1 overexpression/RNAi, cell-cycle regulator immunoblotting, signaling reporter assays, and p21 RNAi epistasis in brain endothelial cells","pmids":["22203671"],"confidence":"Medium","gaps":["Single lab","How surface GPC1 transmits signal to the Skp2 loop mechanistically unclear"]},{"year":2013,"claim":"Demonstrating that GPC1 drives S-phase entry, DNA rereplication, and damage via Skp2/CDK2/cyclin E extended its proliferative role to genomic instability in glioma and astrocytes.","evidence":"Bidirectional manipulation, BrdU/EdU incorporation, flow cytometry, and Skp2/CDK2/cyclin E knockdown epistasis with PI3K/ERK inhibitors","pmids":["24019070"],"confidence":"Medium","gaps":["Single lab","Upstream receptor coupling to ERK/Akt not defined"]},{"year":2013,"claim":"Establishing GPC1 as a positive Hedgehog regulator in biliary development and a biliary atresia susceptibility gene linked GPC1 to a morphogen pathway in vivo.","evidence":"Zebrafish morpholino knockdown with cyclopamine rescue and Sonic Hedgehog injection phenocopy, plus copy-number analysis in patients","pmids":["23336978"],"confidence":"Medium","gaps":["Single lab","Molecular mechanism of GPC1 Hh modulation not defined"]},{"year":2013,"claim":"Identifying direct GPC1-BMP2 binding and BMP inhibition showed GPC1 can negatively, not only positively, regulate morphogen signaling in a context-dependent manner.","evidence":"Recombinant-protein physical interaction, antibody blockade, overexpression, SMAD phosphorylation, and osteogenesis assays in cranial suture mesenchyme","pmids":["23624389"],"confidence":"Medium","gaps":["Single lab","Whether HS chains or core protein mediate BMP2 binding not resolved"]},{"year":2014,"claim":"Pinpointing GPC1 (and not syndecan-1) as the specific mediator of shear-stress-induced eNOS activation defined a distinct mechanotransduction role in caveolae.","evidence":"siRNA of GPC1 vs SDC1, heparinase III, shear stress on EC monolayers, and eNOS activity and morphology readouts","pmids":["24480876"],"confidence":"Medium","gaps":["Single lab","Physical coupling between GPC1 and eNOS not directly demonstrated"]},{"year":2021,"claim":"Systematic subclass comparison established GPC1 as the principal, rate-limiting heparan sulfate proteoglycan for unconventional FGF2 secretion while being dispensable for FGF2 signaling into cells.","evidence":"siRNA across HSPG subclasses, FGF2 secretion assay, HS structural analysis, and FGF2 binding/signaling assays","pmids":["35348113"],"confidence":"High","gaps":["Mechanism by which GPC1 carries FGF2 across the membrane not resolved","Whether N-sulfated disaccharide enrichment is GPC1-specific in vivo untested"]},{"year":2021,"claim":"Showing GPC1 is required for VEGF/HGF-induced angiogenesis and interacts with VEGFR2 and c-Met provided the receptor-level basis for its pro-angiogenic function.","evidence":"siRNA knockdown, PLC cleavage, pseudotube formation, and GPC1-VEGFR2/c-Met interaction assays in HDMEC","pmids":["34957110"],"confidence":"Medium","gaps":["Single lab","Whether interactions are HS-mediated and direct in vivo not established"]},{"year":2021,"claim":"Linking GPC1 expression to substrate stiffness and endothelial protection extended its mechanobiology beyond shear flow to matrix-stiffness sensing.","evidence":"Defined-stiffness substrates, bidirectional manipulation, GPC1-/- mice, and EC dysfunction readouts (inflammation, EndMT, NO)","pmids":["32647868"],"confidence":"Medium","gaps":["Single lab","Signaling intermediates between GPC1 and EndMT not defined"]},{"year":null,"claim":"How a single GPI-anchored proteoglycan can act as both positive (FGF2, VEGF, Hedgehog, proliferation) and negative (BMP2) regulator across tissues—and what determines which receptor or ligand it couples to in a given context—remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structural model of GPC1-receptor complexes","Determinants of context-specific positive vs negative regulation unknown","In vivo HS-chain dependence of most interactions untested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0038024","term_label":"cargo receptor activity","supporting_discovery_ids":[2,11]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[0,10]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[5,9,10]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[8,12]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[1]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,8,11]},{"term_id":"GO:0031012","term_label":"extracellular matrix","supporting_discovery_ids":[1]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[9,11,5]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[1,7,9]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[5,6]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[2,3]}],"complexes":["caveolae"],"partners":["SLIT2","FGF2","BMP2","VEGFR2","MET","PRNP","COL5A3"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P35052","full_name":"Glypican-1","aliases":[],"length_aa":558,"mass_kda":61.7,"function":"Cell surface proteoglycan that bears heparan sulfate. Binds, via the heparan sulfate side chains, alpha-4 (V) collagen and participates in Schwann cell myelination (By similarity). May act as a catalyst in increasing the rate of conversion of prion protein PRPN(C) to PRNP(Sc) via associating (via the heparan sulfate side chains) with both forms of PRPN, targeting them to lipid rafts and facilitating their interaction. Required for proper skeletal muscle differentiation by sequestering FGF2 in lipid rafts preventing its binding to receptors (FGFRs) and inhibiting the FGF-mediated signaling","subcellular_location":"Secreted, extracellular space","url":"https://www.uniprot.org/uniprotkb/P35052/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/GPC1","classification":"Not Classified","n_dependent_lines":12,"n_total_lines":1208,"dependency_fraction":0.009933774834437087},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"SRP9","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/GPC1","total_profiled":1310},"omim":[{"mim_id":"618940","title":"OCULOPHARYNGODISTAL MYOPATHY 2; OPDM2","url":"https://www.omim.org/entry/618940"},{"mim_id":"615209","title":"MICRO RNA 149; MIR149","url":"https://www.omim.org/entry/615209"},{"mim_id":"604472","title":"TUMOR NECROSIS FACTOR LIGAND SUPERFAMILY, MEMBER 13; TNFSF13","url":"https://www.omim.org/entry/604472"},{"mim_id":"602446","title":"GLYPICAN 5; GPC5","url":"https://www.omim.org/entry/602446"},{"mim_id":"600395","title":"GLYPICAN 1; GPC1","url":"https://www.omim.org/entry/600395"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Plasma membrane","reliability":"Supported"},{"location":"Cytosol","reliability":"Supported"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"skin 1","ntpm":213.4}],"url":"https://www.proteinatlas.org/search/GPC1"},"hgnc":{"alias_symbol":["glypican"],"prev_symbol":[]},"alphafold":{"accession":"P35052","domains":[{"cath_id":"-","chopping":"92-349_371-434","consensus_level":"high","plddt":93.1075,"start":92,"end":434}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P35052","model_url":"https://alphafold.ebi.ac.uk/files/AF-P35052-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P35052-F1-predicted_aligned_error_v6.png","plddt_mean":82.5},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=GPC1","jax_strain_url":"https://www.jax.org/strain/search?query=GPC1"},"sequence":{"accession":"P35052","fasta_url":"https://rest.uniprot.org/uniprotkb/P35052.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P35052/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P35052"}},"corpus_meta":[{"pmid":"26106858","id":"PMC_26106858","title":"Glypican-1 identifies cancer exosomes and 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biology","url":"https://pubmed.ncbi.nlm.nih.gov/34591076","citation_count":17,"is_preprint":false},{"pmid":"18813128","id":"PMC_18813128","title":"Frequent expression of glypican-3 in Merkel cell carcinoma: an immunohistochemical study of 55 cases.","date":"2009","source":"Applied immunohistochemistry & molecular morphology : AIMM","url":"https://pubmed.ncbi.nlm.nih.gov/18813128","citation_count":16,"is_preprint":false},{"pmid":"35946078","id":"PMC_35946078","title":"Frequently expressed glypican-3 as a promising novel therapeutic target for osteosarcomas.","date":"2022","source":"Cancer science","url":"https://pubmed.ncbi.nlm.nih.gov/35946078","citation_count":16,"is_preprint":false},{"pmid":"33992682","id":"PMC_33992682","title":"Advances in immunotherapeutic targets for childhood cancers: A focus on glypican-2 and B7-H3.","date":"2021","source":"Pharmacology & therapeutics","url":"https://pubmed.ncbi.nlm.nih.gov/33992682","citation_count":16,"is_preprint":false},{"pmid":"27373597","id":"PMC_27373597","title":"Common genetic variants of GPC1 gene reduce risk of biliary atresia in a Chinese population.","date":"2016","source":"Journal of pediatric surgery","url":"https://pubmed.ncbi.nlm.nih.gov/27373597","citation_count":15,"is_preprint":false},{"pmid":"35142364","id":"PMC_35142364","title":"Hedgehog pathway modulation by glypican 3-conjugated heparan sulfate.","date":"2022","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/35142364","citation_count":15,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":52054,"output_tokens":5198,"usd":0.117066,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":13441,"output_tokens":4710,"usd":0.092478,"stage2_stop_reason":"end_turn"},"total_usd":0.209544,"stage1_batch_id":"msgbatch_01DUPACZi7AAWwuZiUjseQF4","stage2_batch_id":"msgbatch_018yt7chE3f48PEFtDwtj6AE","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2001,\n      \"finding\": \"GPC1 (glypican-1) binds Slit-2 protein via its heparan sulfate chains with high affinity (Kd ~80-110 nM); the glycanated proteoglycan binds with ~10-fold higher affinity than the core protein alone; O-sulfate groups on heparan sulfate chains are critical for this interaction; co-immunoprecipitation confirmed the interaction in vivo after co-transfection of 293 cells, and colocalization was demonstrated immunocytochemically in the embryonic and adult CNS.\",\n      \"method\": \"ELISA binding assay with glypican-Fc fusion protein and recombinant Slit-2; co-immunoprecipitation after co-transfection; heparinase treatment and desulfated heparin competition; immunocytochemistry\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro binding assay with defined Kd values, enzymatic removal of HS chains, sulfation inhibition, and in vivo co-IP with immunolocalization; multiple orthogonal methods in one study\",\n      \"pmids\": [\"11375980\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"GPC1 is the principal alpha4(V) collagen-binding heparan sulfate proteoglycan on the Schwann cell surface. siRNA-mediated knockdown of GPC1 reduced binding of alpha4(V) collagen N-terminal domain to Schwann cells, decreased Schwann cell adhesion and spreading on alpha4(V)-NTD, impaired incorporation of alpha4(V) collagen into ECM, and significantly inhibited myelination in Schwann cell–DRG neuron co-cultures.\",\n      \"method\": \"siRNA knockdown; adhesion/spreading assays; ECM incorporation assay; Schwann cell–DRG neuron co-culture myelination assay\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean siRNA loss-of-function with multiple orthogonal cellular phenotype readouts (binding, adhesion, ECM, myelination) in a single study\",\n      \"pmids\": [\"16407548\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Both cancer cell-derived and host-derived GPC1 are required for efficient tumor growth, metastasis, and angiogenesis. Antisense-mediated GPC1 downregulation in PANC-1 cells prolonged doubling times, decreased anchorage-independent growth in vitro, and attenuated tumor growth, angiogenesis, and metastasis in athymic mice. GPC1-null host mice showed decreased tumor angiogenesis, metastasis, and fewer pulmonary metastases with multiple cancer cell lines; hepatic endothelial cells from GPC1-null mice had an attenuated mitogenic response to VEGF-A.\",\n      \"method\": \"Antisense knockdown; xenograft tumor implantation; GPC1 knockout mouse; in vitro proliferation and soft-agar assays; metastasis quantification; VEGF-A mitogenesis assay on isolated endothelial cells\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — both cell-intrinsic and host-derived GPC1 tested with antisense and genetic knockout, multiple cancer models and orthogonal readouts (growth, metastasis, angiogenesis, VEGF response)\",\n      \"pmids\": [\"18064304\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"GPC1 mediates lipid raft association of the cellular prion protein (PrPc) and facilitates conversion to the disease isoform (PrPSc). Depletion of GPC1 (the major neuronal GPI-anchored HSPG) displaced PrPc from rafts and promoted its endocytosis. Both PrPc and PrPSc co-immunoprecipitated with GPC1. Critically, GPC1 siRNA knockdown in scrapie-infected N2a cells significantly reduced PrPSc formation.\",\n      \"method\": \"siRNA knockdown; co-immunoprecipitation; detergent-resistant raft fractionation; confocal immunofluorescence; scrapie-infected cell model\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP, raft fractionation, siRNA loss-of-function with functional PrPSc formation readout, multiple orthogonal methods in one study\",\n      \"pmids\": [\"19936054\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"GPC1 controls copper-dependent co-internalization of PrPc from the cell surface to perinuclear compartments. PrPc provides the Cu2+ ions required to nitrosylate thiol groups in the GPC1 core protein, enabling GPC1 recycling via a caveolin-associated pathway and heparan sulfate autoprocessing. A PrPc construct lacking the copper-binding domain failed to drive GPC1 internalization and abrogated GPC1 autoprocessing. GPC1 silencing had no effect on copper-stimulated PrPc endocytosis.\",\n      \"method\": \"Confocal immunofluorescence; immunomagnetic isolation; siRNA silencing; copper treatment; dominant-negative PrPc construct lacking Cu-binding domain\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (confocal co-localization, immunomagnetic pull-down, genetic silencing, domain-deletion construct), single lab\",\n      \"pmids\": [\"16923158\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"GPC1 overexpression in brain endothelial cells inactivates the G1/S checkpoint by activating the mitogen-independent Skp2 autoinduction loop: GPC1 suppresses CDK inhibitors (p21, p27, p16, p19) and D cyclins, induces CDK2 and Skp2, and activates ERK/MAPK, Wnt, and BMP signaling pathways. p21 knockdown by RNAi phenocopied GPC1 effects on cell cycle regulators.\",\n      \"method\": \"GPC1 overexpression and RNAi knockdown; immunoblotting for cell cycle regulators; luciferase reporter assays for signaling pathways; flow cytometry for cell cycle phasing\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain- and loss-of-function with multiple molecular readouts and epistasis (p21 RNAi rescue), single lab\",\n      \"pmids\": [\"22203671\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"GPC1 expression strongly stimulates S phase entry, DNA replication, and causes DNA rereplication and damage in glioma cells and normal astrocytes; it downregulates pRb, Cip/Kip CKIs, and CDH1, upregulates cyclin E, CDK2, Skp2, and Cdt1, and constitutively activates ERK/MAPK and PI3K/Akt pathways. Knockdown of Skp2, CDK2, or cyclin E reduced S phase and aneuploid fractions, confirming their role downstream of GPC1.\",\n      \"method\": \"GPC1 overexpression and siRNA knockdown; BrdU/EdU incorporation; flow cytometry; immunoblotting; PI3K/Akt and ERK pathway inhibitors\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — bidirectional manipulation, epistasis via secondary knockdowns, multiple orthogonal readouts, single lab\",\n      \"pmids\": [\"24019070\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"GPC1 acts as a susceptibility gene for biliary atresia and regulates Hedgehog signaling in biliary development. Morpholino knockdown of gpc1 in zebrafish caused developmental biliary defects; partial rescue by a Hedgehog antagonist (cyclopamine) and induction of biliary defects by recombinant Sonic Hedgehog injection phenocopying the morphant established GPC1 as a positive regulator of Hh signaling in this context.\",\n      \"method\": \"Morpholino antisense knockdown in zebrafish; cyclopamine rescue; recombinant Sonic Hedgehog injection; biliary morphology analysis; copy number variant analysis in BA patients\",\n      \"journal\": \"Gastroenterology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis by pharmacological rescue and ligand injection in vivo zebrafish model, supported by human genetic data; single lab\",\n      \"pmids\": [\"23336978\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"GPC1 mediates shear stress-induced eNOS activation in endothelial cells. RNA silencing of GPC1 (but not syndecan-1) blocked flow-induced eNOS activation, while SDC1 knockdown (but not GPC1) attenuated cell elongation and alignment. GPC1 is localized to caveolae where eNOS resides, consistent with its role as a centralized mechanotransmission agent.\",\n      \"method\": \"siRNA silencing of GPC1 or SDC1; heparinase III treatment; shear stress application to EC monolayers; eNOS activity measurement; cell morphology analysis\",\n      \"journal\": \"Integrative biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean siRNA knockdown with specific functional readout (eNOS activation) and specificity control (SDC1), single lab\",\n      \"pmids\": [\"24480876\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"GPC1 and GPC3 physically interact with BMP2 and inhibit BMP2, BMP4, and BMP7 activities in cranial suture mesenchymal cells. Immunoblockade of endogenous GPC1 and GPC3 potentiated BMP2 activity; overexpression or addition of recombinant GPC1/GPC3 protein inhibited BMP2 signaling and BMP2-mediated osteogenesis. GPC1 and GPC3 inhibit both SMAD-dependent and SMAD-independent BMP2 signaling pathways.\",\n      \"method\": \"Recombinant protein binding (physical interaction assay); antibody blockade of endogenous glypicans; overexpression; SMAD phosphorylation immunoblotting; osteogenesis assay in primary suture mesenchymal cells\",\n      \"journal\": \"Bone\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct physical interaction assay, bidirectional manipulation (blockade and overexpression), functional osteogenesis readout; single lab\",\n      \"pmids\": [\"23624389\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"GPC1 is the principal and rate-limiting factor that drives unconventional secretion of FGF2. Among all heparan sulfate proteoglycan subclasses (syndecans, perlecans, glypicans), only GPC1 knockdown substantially reduced FGF2 secretion. Disaccharides with N-linked sulfate groups are enriched in GPC1 heparan sulfate chains and mediate high-affinity FGF2 binding. GPC1 was dispensable for FGF2 signaling into cells.\",\n      \"method\": \"siRNA knockdown of specific HSPG subclasses; FGF2 secretion assay; heparan sulfate chain structural analysis; FGF2 binding affinity measurements; FGF2 signaling assay\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — systematic subclass knockdown, HS structural characterization, binding assay, and signaling assay in one study; multiple orthogonal methods establishing specificity of GPC1\",\n      \"pmids\": [\"35348113\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"GPC1 is required for VEGF- and HGF-induced angiogenesis in human dermal microvascular endothelial cells (HDMEC). GPC1 siRNA transfection completely abrogated pseudotube formation induced by keratinocyte-conditioned media. Cleavage of GPC1 from the cell surface by phospholipase C promoted HDMEC proliferation. GPC1 was shown to interact directly with VEGFR2 and c-Met to regulate angiogenesis.\",\n      \"method\": \"siRNA knockdown; phospholipase C cleavage; pseudotube formation assay; co-immunoprecipitation/direct interaction assay for GPC1-VEGFR2 and GPC1-c-Met\",\n      \"journal\": \"Frontiers in cell and developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — siRNA loss-of-function with functional angiogenesis readout and direct GPC1-receptor interaction assays; single lab\",\n      \"pmids\": [\"34957110\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"GPC1 protects endothelial cells from stiffness-mediated dysfunction. On stiff substrates (10 kPa), GPC1 gene and protein expression were reduced; GPC1 siRNA silencing on soft substrates recapitulated stiffness-induced EC dysfunction (inflammation, proliferation, EndMT); GPC1 overexpression reversed these effects. GPC1 knockout mice (GPC1-/-) showed exacerbated endothelial dysfunction in young but not old mice (where GPC1 is already low).\",\n      \"method\": \"Polyacrylamide gel substrates of defined stiffness; siRNA silencing and plasmid overexpression; GPC1 knockout mouse model; monocyte adhesion assay; NO measurement; gene expression analysis\",\n      \"journal\": \"Cardiovascular research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — bidirectional manipulation in vitro and in vivo KO mouse, multiple functional EC dysfunction readouts; single lab\",\n      \"pmids\": [\"32647868\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"GPC1 promotes colorectal cancer cell growth and migration through the TGF-β1/SMAD2 signaling pathway. GPC1 knockdown in CRC cell lines inhibited proliferation, migration, and promoted apoptosis; it suppressed TGF-β1 levels and p-SMAD2 while increasing total SMAD2, placing GPC1 upstream of TGF-β1/SMAD2 signaling in CRC.\",\n      \"method\": \"siRNA knockdown; CCK-8 proliferation assay; Transwell migration assay; apoptosis assay; western blotting for TGF-β1, SMAD2, and p-SMAD2\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, siRNA knockdown with downstream pathway readout but no rescue or overexpression confirmation\",\n      \"pmids\": [\"35671267\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"GPC1 downregulation in pancreatic cancer cells reduces anchorage-independent growth and slightly modifies TGF-β1, activin-A, and BMP-2 signaling (growth, p21 induction, Smad2 phosphorylation). GPC1 mRNA correlates with activin and BMP receptor expression in pancreatic tissues.\",\n      \"method\": \"Stable antisense transfection of GPC1; MTT and soft agar growth assays; immunoblotting for p-Smad1, p-Smad2, p21; quantitative RT-PCR for receptors\",\n      \"journal\": \"International journal of oncology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, antisense knockdown with modest and partial signaling readouts; correlation data only for receptor associations\",\n      \"pmids\": [\"17016645\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"GPC1 (glypican) biosynthesis involves GPI-anchor attachment and heparan sulfate chain assembly on serine residues in consensus sequences. Chain-truncated GPC1 formed by endoheparanase cleavage at GlcNH2 residues followed by NO-derived nitrite deaminative cleavage can serve as a precursor for reformation of full-length proteoglycan, establishing a recycling pathway for GPC1 heparan sulfate chains.\",\n      \"method\": \"Biochemical characterization; in vitro enzymatic assays; GlcNH2 identification; NO/nitrite deaminative cleavage assay\",\n      \"journal\": \"Matrix biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro biochemical reconstitution of chain cleavage and recycling, but single lab and limited structural validation\",\n      \"pmids\": [\"10963998\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"GPC1 overexpression in colon cancer cells activates epithelial-mesenchymal transition (EMT), increasing invasion and migration; GPC1 silencing inactivated EMT and decreased invasion and migration. miR-96-5p and miR-149 were shown to regulate GPC1 expression, and their overexpression decreased GPC1 levels, GPC1+ exosome secretion, and tumor growth.\",\n      \"method\": \"GPC1 overexpression and siRNA knockdown; EMT marker immunoblotting; invasion/migration Transwell assays; adenoviral miRNA overexpression; xenograft tumor model\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — bidirectional manipulation but EMT pathway placement is indirect; single lab\",\n      \"pmids\": [\"29254156\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"GPC1 (glypican-1) is a GPI-anchored heparan sulfate proteoglycan that functions as a co-receptor and regulatory scaffold at the cell surface: its heparan sulfate chains (particularly N-sulfated disaccharides) bind ligands including Slit-2, FGF2, VEGF, and HGF with high affinity, making it the principal driver of unconventional FGF2 secretion and a required co-receptor for VEGF/HGF-induced angiogenesis; in caveolae it transmits fluid shear stress to eNOS for nitric oxide production; it facilitates PrPc–PrPSc conversion in lipid rafts by scaffolding both isoforms; it promotes G1/S cell cycle progression via the Skp2 autoinduction loop and activation of ERK/MAPK, Wnt, and BMP signaling; it supports Schwann cell myelination through interaction with alpha4(V) collagen; and it regulates BMP2/4/7 signaling in osteogenesis; collectively, loss-of-function studies in cells and in vivo models establish GPC1 as a broadly acting heparan-sulfate-dependent co-receptor that amplifies growth factor and morphogen signaling to promote cell proliferation, angiogenesis, and metastasis.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"GPC1 (glypican-1) is a GPI-anchored, heparan-sulfate-bearing cell-surface proteoglycan that acts as a heparan-sulfate-dependent co-receptor and scaffold, concentrating and presenting secreted ligands and morphogens to amplify growth-factor and developmental signaling [#0, #10]. Its heparan sulfate chains, particularly N-sulfated disaccharides, mediate high-affinity ligand binding—including Slit-2 and FGF2—and the glycanated proteoglycan binds substantially more avidly than the core protein alone [#0, #10]; among heparan sulfate proteoglycan subclasses, GPC1 is the principal, rate-limiting driver of unconventional FGF2 secretion while being dispensable for FGF2 signaling into cells [#10]. At the cell surface GPC1 functions as a required co-receptor for angiogenesis, interacting directly with VEGFR2 and c-Met and acting cell-intrinsically and from the host vasculature to support VEGF-A-driven endothelial mitogenesis, tumor growth, and metastasis [#2, #11]. In endothelial caveolae it serves as a mechanotransducer that is specifically required for shear-stress-induced eNOS activation and protects against substrate-stiffness-induced endothelial dysfunction [#8, #12]. GPC1 modulates multiple morphogen pathways in a context-dependent manner: it is the principal alpha4(V)-collagen-binding proteoglycan on Schwann cells and is required for myelination [#1], positively regulates Hedgehog signaling during biliary development [#7], and physically binds BMP2 to inhibit BMP2/4/7 signaling and osteogenesis [#9]. In proliferating cells GPC1 drives G1/S progression and DNA replication by engaging the Skp2 autoinduction loop—suppressing CDK inhibitors and inducing Skp2, CDK2, and cyclin E—while activating ERK/MAPK, PI3K/Akt, Wnt, and BMP signaling [#5, #6]. GPC1 also scaffolds the cellular prion protein in lipid rafts, mediating its raft association and copper-dependent internalization and facilitating PrPc-to-PrPSc conversion [#3, #4].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Establishing the biosynthetic and recycling logic of GPC1 was needed to understand how its heparan sulfate chains are assembled and regenerated, the basis for its ligand-binding function.\",\n      \"evidence\": \"Biochemical reconstitution of GPI-anchor attachment, HS chain assembly, and endoheparanase/NO-driven deaminative cleavage and reformation in vitro\",\n      \"pmids\": [\"10963998\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab in vitro reconstitution with limited structural validation\", \"Physiological relevance of the recycling pathway not tested in cells\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Demonstrating high-affinity, sulfation-dependent binding of Slit-2 to GPC1 heparan sulfate chains established GPC1 as a ligand-binding co-receptor rather than an inert structural proteoglycan.\",\n      \"evidence\": \"ELISA binding with glypican-Fc, heparinase and desulfated-heparin competition, co-IP after co-transfection, and CNS immunolocalization\",\n      \"pmids\": [\"11375980\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of GPC1-Slit-2 binding on axon guidance not tested\", \"Does not establish whether GPC1 presents Slit-2 to a signaling receptor\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Identifying GPC1 as the principal alpha4(V)-collagen-binding proteoglycan on Schwann cells linked it to ECM assembly and peripheral myelination.\",\n      \"evidence\": \"siRNA knockdown with adhesion, ECM incorporation, and Schwann cell–DRG co-culture myelination assays\",\n      \"pmids\": [\"16407548\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether HS chains or core protein mediate alpha4(V) binding not resolved\", \"No in vivo myelination phenotype\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Defining a copper- and PrPc-dependent route for GPC1 internalization connected GPC1 trafficking to prion protein biology in lipid rafts.\",\n      \"evidence\": \"Confocal co-localization, immunomagnetic isolation, siRNA silencing, and a Cu-binding-domain-deletion PrPc construct\",\n      \"pmids\": [\"16923158\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Mechanism of nitrosylation-driven autoprocessing not biochemically resolved\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Genetic and antisense loss-of-function across cancer and host compartments established GPC1 as both cell-intrinsic and stromal driver of tumor growth, angiogenesis, and metastasis.\",\n      \"evidence\": \"Antisense knockdown in PANC-1, xenografts in athymic and GPC1-null host mice, metastasis quantification, and VEGF-A mitogenesis on isolated endothelial cells\",\n      \"pmids\": [\"18064304\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct ligand/receptor mechanism for the angiogenic defect not defined in this study\", \"Does not identify the GPC1-dependent signaling axis\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Showing GPC1 scaffolds both PrPc and PrPSc in rafts and is required for PrPSc formation gave GPC1 a mechanistic role in prion conversion.\",\n      \"evidence\": \"Reciprocal co-IP, detergent-resistant raft fractionation, confocal IF, and siRNA in scrapie-infected N2a cells\",\n      \"pmids\": [\"19936054\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether GPC1 directly catalyzes or merely co-localizes the isoforms unresolved\", \"No structural model of the scaffold\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Linking GPC1 to the mitogen-independent Skp2 autoinduction loop explained how it inactivates the G1/S checkpoint to drive proliferation.\",\n      \"evidence\": \"GPC1 overexpression/RNAi, cell-cycle regulator immunoblotting, signaling reporter assays, and p21 RNAi epistasis in brain endothelial cells\",\n      \"pmids\": [\"22203671\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"How surface GPC1 transmits signal to the Skp2 loop mechanistically unclear\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Demonstrating that GPC1 drives S-phase entry, DNA rereplication, and damage via Skp2/CDK2/cyclin E extended its proliferative role to genomic instability in glioma and astrocytes.\",\n      \"evidence\": \"Bidirectional manipulation, BrdU/EdU incorporation, flow cytometry, and Skp2/CDK2/cyclin E knockdown epistasis with PI3K/ERK inhibitors\",\n      \"pmids\": [\"24019070\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Upstream receptor coupling to ERK/Akt not defined\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Establishing GPC1 as a positive Hedgehog regulator in biliary development and a biliary atresia susceptibility gene linked GPC1 to a morphogen pathway in vivo.\",\n      \"evidence\": \"Zebrafish morpholino knockdown with cyclopamine rescue and Sonic Hedgehog injection phenocopy, plus copy-number analysis in patients\",\n      \"pmids\": [\"23336978\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Molecular mechanism of GPC1 Hh modulation not defined\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identifying direct GPC1-BMP2 binding and BMP inhibition showed GPC1 can negatively, not only positively, regulate morphogen signaling in a context-dependent manner.\",\n      \"evidence\": \"Recombinant-protein physical interaction, antibody blockade, overexpression, SMAD phosphorylation, and osteogenesis assays in cranial suture mesenchyme\",\n      \"pmids\": [\"23624389\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Whether HS chains or core protein mediate BMP2 binding not resolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Pinpointing GPC1 (and not syndecan-1) as the specific mediator of shear-stress-induced eNOS activation defined a distinct mechanotransduction role in caveolae.\",\n      \"evidence\": \"siRNA of GPC1 vs SDC1, heparinase III, shear stress on EC monolayers, and eNOS activity and morphology readouts\",\n      \"pmids\": [\"24480876\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Physical coupling between GPC1 and eNOS not directly demonstrated\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Systematic subclass comparison established GPC1 as the principal, rate-limiting heparan sulfate proteoglycan for unconventional FGF2 secretion while being dispensable for FGF2 signaling into cells.\",\n      \"evidence\": \"siRNA across HSPG subclasses, FGF2 secretion assay, HS structural analysis, and FGF2 binding/signaling assays\",\n      \"pmids\": [\"35348113\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which GPC1 carries FGF2 across the membrane not resolved\", \"Whether N-sulfated disaccharide enrichment is GPC1-specific in vivo untested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showing GPC1 is required for VEGF/HGF-induced angiogenesis and interacts with VEGFR2 and c-Met provided the receptor-level basis for its pro-angiogenic function.\",\n      \"evidence\": \"siRNA knockdown, PLC cleavage, pseudotube formation, and GPC1-VEGFR2/c-Met interaction assays in HDMEC\",\n      \"pmids\": [\"34957110\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Whether interactions are HS-mediated and direct in vivo not established\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Linking GPC1 expression to substrate stiffness and endothelial protection extended its mechanobiology beyond shear flow to matrix-stiffness sensing.\",\n      \"evidence\": \"Defined-stiffness substrates, bidirectional manipulation, GPC1-/- mice, and EC dysfunction readouts (inflammation, EndMT, NO)\",\n      \"pmids\": [\"32647868\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Signaling intermediates between GPC1 and EndMT not defined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How a single GPI-anchored proteoglycan can act as both positive (FGF2, VEGF, Hedgehog, proliferation) and negative (BMP2) regulator across tissues—and what determines which receptor or ligand it couples to in a given context—remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structural model of GPC1-receptor complexes\", \"Determinants of context-specific positive vs negative regulation unknown\", \"In vivo HS-chain dependence of most interactions untested\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0038024\", \"supporting_discovery_ids\": [2, 11]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [0, 10]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [5, 9, 10]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [8, 12]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 8, 11]},\n      {\"term_id\": \"GO:0031012\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [9, 11, 5]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [1, 7, 9]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [5, 6]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [2, 3]}\n    ],\n    \"complexes\": [\"caveolae\"],\n    \"partners\": [\"SLIT2\", \"FGF2\", \"BMP2\", \"VEGFR2\", \"MET\", \"PRNP\", \"COL5A3\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}