{"gene":"TPBG","run_date":"2026-06-10T10:51:55","timeline":{"discoveries":[{"year":1990,"finding":"TPBG/5T4 antigen is a 72 kDa glycoprotein with a 42 kDa core protein; extensive N-linked glycosylation accounts for the molecular weight difference; the native molecule is resistant to proteolysis until N-linked sugars are removed or the glycoprotein is denatured and reduced.","method":"Lectin- and immunoaffinity chromatography, gel filtration, SDS-PAGE, N-glycanase treatment, protease digestion assays","journal":"International journal of cancer","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct biochemical characterization with multiple orthogonal methods (chromatographic purification, enzymatic deglycosylation, protease resistance assays) in foundational study","pmids":["2298503"],"is_preprint":false},{"year":1994,"finding":"TPBG/5T4 cDNA encodes a 420 amino acid type I transmembrane protein (46 kDa predicted, 72 kDa glycosylated) with N- and C-terminal hydrophobic signal/transmembrane segments, 8 potential N-glycosylation sites, and leucine-rich repeats (LRRs) in the extracellular domain.","method":"cDNA cloning from human placental library using oligonucleotides based on purified protein sequence; Northern blot analysis; sequence database comparison","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct cDNA isolation, amino acid sequencing of purified protein, and sequence analysis providing the primary structural framework for the protein","pmids":["8132670"],"is_preprint":false},{"year":1995,"finding":"TPBG/5T4 is concentrated at microvillus projections of the plasma membrane in transfected murine L cells (A9 derivative) and in carcinoma cell lines; 5T4 expression in A9 cells is associated with altered cell division, decreased cell-substratum adhesion, and increased cellular motility.","method":"Stable transfection of 5T4 cDNA into L cells; confocal immunofluorescence microscopy; transmission and scanning electron microscopy","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain-of-function transfection with defined morphological and motility phenotype, multiple imaging modalities, single lab","pmids":["7593330"],"is_preprint":false},{"year":1996,"finding":"Transfection of full-length 5T4 cDNA into epithelial cells disrupts actin/cadherin-containing cell-cell contacts and increases motility; deletion of the cytoplasmic domain shows that the cytoplasmic tail is necessary for abrogating actin/cadherin contacts but is not required for the effects on motility, indicating that 5T4 can deliver signals through both extracellular and intracellular domains.","method":"Stable transfection of full-length and cytoplasmic-domain-deleted 5T4 cDNA into CL-S1 murine mammary cells and MDCK epithelial cells; motility assays; morphological analysis","journal":"International journal of cancer","confidence":"High","confidence_rationale":"Tier 1 / Strong — domain-deletion mutagenesis with separable functional readouts (actin/cadherin disruption vs motility), two cell line models","pmids":["8895545"],"is_preprint":false},{"year":2002,"finding":"TPBG/5T4 interacts with TIP-2/GIPC, a cytoplasmic PDZ-domain protein; the interaction requires the C-terminal class I PDZ-binding motif (Ser-Asp-Val) of 5T4, specifically the terminal valine; 5T4 and TIP-2/GIPC co-localize in HeLa cells and can be co-immunoprecipitated, providing the first link between 5T4 and the actin cytoskeleton.","method":"Yeast two-hybrid screen; site-directed mutagenesis of PDZ-binding motif; co-immunoprecipitation from HeLa cell lysates; co-localization by immunofluorescence","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — yeast two-hybrid identification plus reciprocal co-IP validation plus co-localization plus mutagenesis of binding motif, all in single study","pmids":["11798178"],"is_preprint":false},{"year":2002,"finding":"Glycosylation analysis of 5T4 demonstrates all seven consensus N-glycosylation sites are occupied: two predominantly high-mannose chains and five mostly sialylated bi-, tri- and tetra-antennary complex chains with minor core fucose. The mAb5T4 epitope was mapped to the membrane-proximal LRR2 region or its flanking region using deletion/mutation constructs and human-mouse chimeras.","method":"Site-directed mutagenesis; deletion constructs; human-mouse chimeric cDNA constructs; glycan analysis by mass spectrometry/carbohydrate chemistry","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — epitope mapping by mutagenesis/chimeras plus glycan compositional analysis with multiple orthogonal methods","pmids":["11903056"],"is_preprint":false},{"year":2007,"finding":"E-cadherin-mediated cell-cell contact prevents cell surface localization of 5T4 antigen; disruption of E-cadherin contacts (by neutralizing antibody or in E-cadherin knockout ES cells) causes translocation of 5T4 from the cytoplasm to the cell surface in an energy-dependent manner; this cell surface localization of 5T4 is associated with increased cellular motility during epithelial-mesenchymal transition. 5T4 knockout ES cells show significantly decreased motility during EMT.","method":"Mouse ES cell differentiation; E-cadherin neutralizing antibody; E-cadherin knockout ES cells; forced E-cadherin re-expression; 5T4 knockout ES cells; FACS; motility assays; confocal imaging","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple genetic knockout models plus antibody perturbation plus rescue experiments with defined functional readouts (motility, actin cytoskeleton), multiple orthogonal approaches","pmids":["17507657"],"is_preprint":false},{"year":2010,"finding":"TPBG/5T4 is required for optimal functional cell surface expression of CXCR4 and CXCL12-mediated chemotaxis in differentiating mouse embryonic stem cells and embryonic fibroblasts; 5T4 and CXCR4 co-localize at the cell surface; in 5T4 knockout cells CXCR4 is retained intracellularly and CXCL12 chemotaxis is abolished; adenoviral restoration of 5T4 rescues CXCR4 surface expression and chemotaxis; the 5T4 transmembrane domain is sufficient and necessary for CXCR4 membrane expression.","method":"5T4 knockout mouse-derived ES cells and MEFs; adenoviral 5T4 rescue; chimeric 5T4/CD44 domain-swap constructs; CXCL12 chemotaxis assays; co-localization immunofluorescence; FACS","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — knockout + rescue + domain-swap mutagenesis + functional chemotaxis assay, multiple cell types, transmembrane domain identified as necessary and sufficient","pmids":["20376365"],"is_preprint":false},{"year":2011,"finding":"TPBG/5T4 (Waif1) inhibits Wnt/β-catenin signaling and activates non-canonical Wnt pathways; Waif1a binds the Wnt co-receptor LRP6 and inhibits Wnt-induced LRP6 internalization into endocytic vesicles, a process required for canonical Wnt pathway activation; Waif1a also enhances β-catenin-independent Wnt signaling by promoting a non-canonical function of Dickkopf1.","method":"Zebrafish and Xenopus embryo gain/loss-of-function; mammalian cell Wnt reporter assays; co-immunoprecipitation of Waif1a with LRP6; LRP6 internalization assays","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — binding partner identified by Co-IP, mechanistic LRP6 internalization assay, functional validation in three model systems (zebrafish, Xenopus, mammalian cells)","pmids":["22100263"],"is_preprint":false},{"year":2012,"finding":"5T4 glycoprotein regulates activity-dependent dendritic development of specific interneuron subtypes in the mouse olfactory bulb; overexpression of 5T4 facilitates dendritic arborization under sensory-deprived conditions; 5T4 knockdown (RNAi) and 5T4 knockout reduce dendritic arborization of 5T4+ granule cells; the cytoplasmic domain of 5T4 contains the sequence necessary and sufficient for sensory input-dependent dendritic shaping.","method":"5T4 overexpression and RNAi knockdown in newborn OB interneurons; 5T4 knockout mice; cytoplasmic domain deletion/truncation constructs; dendritic morphometry","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — overexpression, RNAi, knockout, and domain-deletion mutants all tested with quantitative dendritic morphology readout; cytoplasmic domain identified as necessary and sufficient","pmids":["22323733"],"is_preprint":false},{"year":2012,"finding":"In the absence of 5T4 expression, CXCL12 signaling through CXCR4 (activating ERK and AKT) is non-functional despite intact pathways; CXCR7 is upregulated and becomes the predominant CXCL12 receptor, activating a distinct pathway involving EGFR transactivation and eliciting proliferation rather than chemotaxis; 5T4 surface expression thus determines receptor preference (CXCR4 vs CXCR7) and hence the biological response to CXCL12.","method":"Wild-type and 5T4 knockout MEFs; CXCR4 antagonist AMD3100; CXCR7 antagonist CCX771; ERK/AKT pathway phosphorylation assays; chemotaxis and proliferation assays; human SCLC cell lines with 5T4/CXCR7 reciprocity","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — knockout genetic model plus pharmacological receptor antagonists plus downstream signaling readouts plus validation in human cancer cells, multiple orthogonal approaches","pmids":["22956548"],"is_preprint":false},{"year":2014,"finding":"Crystal structure of the extracellular domain of 5T4/WAIF1 at 1.8 Å resolution reveals a highly glycosylated rigid core comprising eight leucine-rich repeats (LRRs); conserved surface residues in LRR1, particularly Tyr325 and Phe97, are essential for inhibition of Wnt/β-catenin signaling as determined by structural and cell-based analyses.","method":"X-ray crystallography at 1.8 Å; cell-based Wnt/β-catenin reporter assays; structure-guided mutagenesis of surface residues","journal":"Structure","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus cell-based mutagenesis validation of key residues for Wnt inhibition function","pmids":["24582434"],"is_preprint":false},{"year":2018,"finding":"5T4 interacts with membrane trafficking proteins Rab11, Rab18, and ARF6 as identified by co-immunoprecipitation and mass spectrometry; Rab11 and Rab18 have opposing roles in controlling 5T4 surface expression; endocytosis of 5T4 is strongly Rab11-dependent; 5T4 depletion stabilizes Rab11 protein expression and stimulates transferrin surface labeling, indicating that 5T4 represses Rab11-mediated endocytic activity. 5T4 localizes to focal adhesions in differentiated breast cancer cells.","method":"Co-immunoprecipitation followed by mass spectrometry; flow cytometry; immunofluorescence co-localization; 5T4 siRNA depletion; transferrin surface labeling assay","journal":"The international journal of biochemistry & cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP/MS identification of binding partners plus functional depletion experiments, single lab, multiple orthogonal methods","pmids":["29549047"],"is_preprint":false},{"year":2019,"finding":"TPBG/5T4 expression in adventitial pericyte-like cells is upregulated by hypoxia through the transcriptional modulator CITED2, leading to CXCL12 signaling via CXCR7 and ERK1/2 activation; TPBG silencing downregulates CXCL12, CXCR7, and pERK1/2 and reduces pericyte migratory and proangiogenic capacity; TPBG forced expression induces formation of CXCR7/CXCR4 heterodimers; in vivo, TPBG is essential for angiogenesis (Matrigel plug assay) and perfusion recovery in limb ischemia.","method":"siRNA silencing; forced overexpression; proximity ligation assay for CXCR7/CXCR4 heterodimers; ELISA, Western blot, immunocytochemistry; in vivo Matrigel plug assay; murine limb ischemia model","journal":"Arteriosclerosis, thrombosis, and vascular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — knockdown and overexpression in primary pericytes with multiple molecular and functional readouts plus in vivo validation, multiple orthogonal methods","pmids":["31018661"],"is_preprint":false},{"year":2018,"finding":"siRNA-mediated depletion of 5T4 in most tested cancer cell lines (A549, C33A, DLD-1, MDA-231, PC-3) did not change the CXCL12 receptor usage or subcellular localization of CXCR4/CXCR7 in the majority of lines, failing to replicate the previously reported general organizational role of 5T4 in the CXCL12 system in cancer cells; however, 5T4 inhibition did modulate migration and proliferation per se in some cell lines.","method":"siRNA depletion of 5T4; CXCR4 antagonist AMD3100; CXCR7 antagonist CCX771; chemotaxis and proliferation assays in multiple cancer cell lines","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — negative replication result across multiple cancer cell lines with pharmacological and genetic tools; contradicts generalizability of earlier findings but single lab","pmids":["29408206"],"is_preprint":false},{"year":2015,"finding":"Irradiation of 5T4-expressing DU145 prostate cancer cells induces Hsp70 surface expression; cross-presentation of 5T4 antigen by dendritic cells to CD8+ T cells is predominantly Hsp70-dependent: Hsp70 inhibitor pretreatment robustly prevented antigen cross-presentation and CD86 upregulation on DCs; blocking the Hsp70 receptor CD91 also abolished cross-presentation.","method":"DC-tumor cell co-culture cross-presentation model; Hsp70 inhibitors; CD91 blocking antibody; CD8+ T cell proliferation and IFN-γ production assays; HMGB1 inhibition; TLR4 SNP analysis","journal":"Cancer immunology research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mechanistic dissection of cross-presentation pathway using pharmacological inhibitors and receptor blocking in defined in vitro model, single lab","pmids":["25678582"],"is_preprint":false},{"year":2003,"finding":"Murine 5T4 antigen expression is absent on undifferentiated ES cells but is rapidly upregulated upon differentiation into all three primary germ layer derivatives; 5T4 expression correlates with early differentiation events involving altered motility and morphology; overexpression of mouse 5T4 in B16 F10 melanoma cells and A9 L fibroblasts produces spindle-like morphology, increased motility, and reduced adhesion and proliferation, dependent on integrity of the actin cytoskeleton.","method":"Cell surface FACS, Western blot, RT-PCR on differentiating ES cells; stable transfection of m5T4 in B16 F10 and A9 cells; motility, adhesion, proliferation assays; cytochalasin D actin disruption","journal":"Journal of cell science / The Biochemical journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain-of-function transfection with quantitative functional readouts plus pharmacological actin disruption linking cytoskeleton to phenotype, single lab","pmids":["14576347","12003637"],"is_preprint":false}],"current_model":"TPBG/5T4 is a heavily N-glycosylated type I transmembrane glycoprotein with a leucine-rich repeat extracellular domain (crystal structure resolved at 1.8 Å) that localizes to microvillus/cell surface in a manner controlled by E-cadherin-mediated actin cortical organization; its cytoplasmic tail (containing a PDZ-binding motif that recruits TIP-2/GIPC) mediates disruption of actin/cadherin contacts while its extracellular domain influences cell motility; at the cell surface 5T4 facilitates CXCR4 membrane localization and CXCL12-driven chemotaxis (with the transmembrane domain being sufficient for this function), shifting CXCL12 signaling from a CXCR7/EGFR/proliferation axis to a CXCR4/ERK/AKT/chemotaxis axis; 5T4 also binds LRP6 and inhibits its Wnt-induced endocytosis, thereby suppressing canonical Wnt/β-catenin signaling while promoting non-canonical Wnt pathways, with LRR1 surface residues Tyr325 and Phe97 essential for this inhibitory function; 5T4 additionally interacts with Rab11 to regulate its own endocytic trafficking; collectively these activities underlie its roles in epithelial-mesenchymal transition, cancer metastasis, embryonic development, and activity-dependent dendritic development in the nervous system."},"narrative":{"mechanistic_narrative":"TPBG (5T4/WAIF1) is a heavily N-glycosylated type I transmembrane glycoprotein whose leucine-rich-repeat extracellular domain and short cytoplasmic tail integrate cell-surface signaling with cytoskeletal and membrane-trafficking control, acting as a regulator of cell motility, epithelial-mesenchymal transition (EMT), and developmental signaling [PMID:8132670, PMID:17507657, PMID:22100263]. The mature protein is a ~72 kDa glycoprotein built on a ~42–46 kDa core whose extensive, largely complex N-glycosylation confers protease resistance, and its extracellular region folds into a rigid eight-LRR core resolved by crystallography at 1.8 Å [PMID:2298503, PMID:8132670, PMID:11903056, PMID:24582434]. Surface delivery of 5T4 is gated by E-cadherin-mediated cell-cell adhesion: loss of E-cadherin contacts during EMT drives energy-dependent translocation of 5T4 to the cell surface, where it disrupts actin/cadherin junctions and increases motility, with the cytoplasmic tail required for junction disruption but dispensable for the motility effect [PMID:8895545, PMID:17507657]. The cytoplasmic tail carries a class I PDZ-binding motif (terminal valine) that recruits the PDZ protein TIP-2/GIPC, linking 5T4 to the actin cytoskeleton, while interactions with Rab11, Rab18 and ARF6 control 5T4's own endocytic trafficking and surface levels [PMID:11798178, PMID:29549047]. At the cell surface 5T4 organizes chemokine signaling by promoting functional CXCR4 surface expression and CXCL12-driven chemotaxis—an activity for which the transmembrane domain is necessary and sufficient—thereby steering CXCL12 responses away from a CXCR7/EGFR-transactivation/proliferation axis toward a CXCR4/ERK/AKT/chemotaxis axis [PMID:20376365, PMID:22956548]. As WAIF1, 5T4 binds the Wnt co-receptor LRP6 and blocks its Wnt-induced internalization, suppressing canonical Wnt/β-catenin signaling while promoting non-canonical Wnt output, with LRR1 surface residues Tyr325 and Phe97 essential for this inhibition [PMID:22100263, PMID:24582434]. These activities underlie roles in EMT and metastasis, embryonic differentiation, hypoxia-driven pericyte angiogenic behavior, and activity-dependent dendritic development of olfactory bulb interneurons [PMID:17507657, PMID:22323733, PMID:31018661].","teleology":[{"year":1990,"claim":"Establishing that the 5T4 antigen is a single heavily N-glycosylated glycoprotein defined the molecule biochemically and explained its unusual protease resistance.","evidence":"Lectin/immunoaffinity purification, deglycosylation, and protease assays on the native antigen","pmids":["2298503"],"confidence":"High","gaps":["Primary sequence and domain organization not yet known","No functional role assigned"]},{"year":1994,"claim":"cDNA cloning revealed 5T4 as a type I transmembrane LRR protein, providing the structural framework for all later mechanistic work.","evidence":"cDNA cloning from a human placental library guided by purified-protein sequence, with sequence analysis","pmids":["8132670"],"confidence":"High","gaps":["No interaction partners identified","Function of LRR domain and cytoplasmic tail unknown"]},{"year":1995,"claim":"Forced expression linked 5T4 to a motility/adhesion phenotype, indicating it is not merely a tumor marker but an active modulator of cell behavior.","evidence":"Stable 5T4 transfection into L cells with confocal and electron microscopy of microvillus localization and motility/adhesion assays","pmids":["7593330"],"confidence":"Medium","gaps":["Mechanism connecting surface localization to motility unresolved","Single-lab gain-of-function only"]},{"year":1996,"claim":"Domain-deletion separated 5T4's two outputs—the cytoplasmic tail abrogates actin/cadherin contacts while motility effects map elsewhere—showing the protein signals through distinct domains.","evidence":"Full-length vs cytoplasmic-deleted 5T4 transfected into mammary and MDCK epithelial cells with morphology and motility readouts","pmids":["8895545"],"confidence":"High","gaps":["Cytoplasmic-tail effector not identified","Extracellular determinant of motility undefined"]},{"year":2002,"claim":"Identification of the TIP-2/GIPC PDZ interaction gave the first molecular link between 5T4's tail and the actin cytoskeleton.","evidence":"Yeast two-hybrid, PDZ-motif mutagenesis, co-IP, and co-localization in HeLa cells","pmids":["11798178"],"confidence":"High","gaps":["Functional consequence of GIPC binding for motility/junctions not directly tested","Link to downstream actin regulators unmapped"]},{"year":2002,"claim":"Defining glycan occupancy and mapping the antibody epitope characterized the surface architecture of the extracellular domain.","evidence":"Glycan compositional analysis plus deletion/chimera epitope mapping","pmids":["11903056"],"confidence":"High","gaps":["Functional role of specific glycans not tested","No 3D structure yet"]},{"year":2003,"claim":"Developmental upregulation upon ES cell differentiation tied 5T4 expression to early morphogenetic transitions and confirmed actin-dependence of its phenotype.","evidence":"FACS/RT-PCR on differentiating ES cells plus transfection into melanoma/fibroblast lines with cytochalasin D actin disruption","pmids":["14576347","12003637"],"confidence":"Medium","gaps":["Signaling pathway driving morphology change undefined","Single-lab gain-of-function"]},{"year":2007,"claim":"E-cadherin contacts were shown to gate 5T4 surface localization, embedding 5T4 in the EMT program as an adhesion-controlled surface switch.","evidence":"ES cell EMT models with E-cadherin neutralization, E-cadherin and 5T4 knockouts, and rescue with motility readouts","pmids":["17507657"],"confidence":"High","gaps":["Mechanism of energy-dependent translocation unresolved","Trafficking machinery not yet identified"]},{"year":2010,"claim":"5T4 was found necessary for functional CXCR4 surface expression and CXCL12 chemotaxis, identifying a transmembrane-domain-mediated chemokine-organizing function.","evidence":"5T4 knockout ES cells/MEFs with adenoviral rescue and 5T4/CD44 domain-swap chimeras in chemotaxis and co-localization assays","pmids":["20376365"],"confidence":"High","gaps":["Molecular nature of TM-domain/CXCR4 interaction undefined","Whether 5T4 directly binds CXCR4 unproven"]},{"year":2011,"claim":"As WAIF1, 5T4 was shown to bind LRP6 and block its Wnt-induced internalization, placing 5T4 as a switch between canonical and non-canonical Wnt signaling.","evidence":"Zebrafish/Xenopus gain-loss-of-function, mammalian Wnt reporters, Waif1a–LRP6 co-IP, and LRP6 internalization assays","pmids":["22100263"],"confidence":"High","gaps":["Structural basis of LRP6 binding not yet defined","Mechanism of non-canonical DKK1 enhancement unresolved"]},{"year":2012,"claim":"5T4 was shown to determine CXCL12 receptor preference (CXCR4 vs CXCR7), dictating chemotaxis versus proliferation outcomes.","evidence":"Wild-type vs 5T4 knockout MEFs with CXCR4/CXCR7 antagonists, ERK/AKT readouts, and human SCLC lines","pmids":["22956548"],"confidence":"High","gaps":["How 5T4 represses CXCR7 expression is unknown","Direct receptor contacts not mapped"]},{"year":2012,"claim":"5T4 was assigned a neuronal role in activity-dependent dendritic development, with the cytoplasmic domain necessary and sufficient for sensory-input-dependent shaping.","evidence":"Overexpression, RNAi, knockout, and cytoplasmic-domain truncations in olfactory bulb interneurons with dendritic morphometry","pmids":["22323733"],"confidence":"High","gaps":["Cytoplasmic-tail effectors mediating dendritic shaping unidentified","Link to activity-dependent signaling pathways unmapped"]},{"year":2014,"claim":"The 1.8 Å crystal structure of the LRR ectodomain defined a rigid eight-LRR core and pinpointed LRR1 residues Tyr325/Phe97 as required for Wnt inhibition.","evidence":"X-ray crystallography with structure-guided mutagenesis in Wnt reporter assays","pmids":["24582434"],"confidence":"High","gaps":["Structure of LRP6-bound complex not solved","Structural basis of CXCR4/CXCR7 organization not addressed"]},{"year":2018,"claim":"5T4 was linked to Rab11/Rab18/ARF6 trafficking machinery that controls its own surface levels, revealing a self-regulatory endocytic loop.","evidence":"Co-IP/mass spectrometry, siRNA depletion, transferrin surface labeling, and focal-adhesion localization in breast cancer cells","pmids":["29549047"],"confidence":"Medium","gaps":["Direct vs indirect nature of Rab interactions unclear","Single-lab Co-IP/MS without reciprocal validation"]},{"year":2015,"claim":"5T4 antigen cross-presentation was shown to be predominantly Hsp70/CD91-dependent, relevant to anti-5T4 immune responses.","evidence":"DC–tumor co-culture cross-presentation with Hsp70 inhibitors, CD91 blockade, and CD8+ T-cell readouts","pmids":["25678582"],"confidence":"Medium","gaps":["Concerns 5T4 as an antigen, not its intrinsic molecular function","Single in vitro model"]},{"year":2019,"claim":"In pericytes, hypoxia/CITED2-driven TPBG was shown to act through CXCL12/CXCR7/ERK and induce CXCR7/CXCR4 heterodimers, extending its chemokine-organizing role to angiogenesis in vivo.","evidence":"siRNA/overexpression in primary pericytes, proximity ligation for heterodimers, and Matrigel/limb-ischemia in vivo models","pmids":["31018661"],"confidence":"High","gaps":["Reconciliation with the CXCR4-favoring model from MEFs unresolved","Direct 5T4–receptor contacts not mapped"]},{"year":2018,"claim":"A negative replication challenged the generality of 5T4's CXCL12-organizing role, indicating context-dependence across cancer cell types.","evidence":"siRNA depletion of 5T4 with CXCR4/CXCR7 antagonists across five cancer cell lines failing to alter receptor usage","pmids":["29408206"],"confidence":"Medium","gaps":["Does not exclude the role in non-transformed/ES cell contexts","Mechanistic basis of cell-type dependence unknown"]},{"year":null,"claim":"It remains unresolved how 5T4 physically couples a single LRR ectodomain and short tail to its diverse outputs—CXCR4/CXCR7 organization, LRP6 internalization control, and cytoplasmic-tail-dependent dendritic and junctional effects—within a unified mechanism.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structure of 5T4 bound to CXCR4, CXCR7, or LRP6","Cytoplasmic-tail effectors beyond GIPC for neuronal/junctional roles unidentified","Cell-type determinants of CXCR4 vs CXCR7 preference unexplained"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[8,10,11]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[4,7]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,1,11]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[2,6,7]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[6]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[8,10,13]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[6,9,16]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[12]}],"complexes":[],"partners":["GIPC1","LRP6","CXCR4","CXCR7","RAB11A","ARF6"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q13641","full_name":"Trophoblast glycoprotein","aliases":["5T4 oncofetal antigen","5T4 oncofetal trophoblast glycoprotein","5T4 oncotrophoblast glycoprotein","M6P1","Wnt-activated inhibitory factor 1","WAIF1"],"length_aa":420,"mass_kda":46.0,"function":"May function as an inhibitor of Wnt/beta-catenin signaling by indirectly interacting with LRP6 and blocking Wnt3a-dependent LRP6 internalization","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q13641/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/TPBG","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/TPBG","total_profiled":1310},"omim":[{"mim_id":"190920","title":"TROPHOBLAST GLYCOPROTEIN; TPBG","url":"https://www.omim.org/entry/190920"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/TPBG"},"hgnc":{"alias_symbol":["5T4-AG","5T4"],"prev_symbol":[]},"alphafold":{"accession":"Q13641","domains":[{"cath_id":"3.80.10.10","chopping":"68-342","consensus_level":"medium","plddt":92.328,"start":68,"end":342},{"cath_id":"1.20.5","chopping":"349-398","consensus_level":"medium","plddt":85.5934,"start":349,"end":398}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q13641","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q13641-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q13641-F1-predicted_aligned_error_v6.png","plddt_mean":82.19},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=TPBG","jax_strain_url":"https://www.jax.org/strain/search?query=TPBG"},"sequence":{"accession":"Q13641","fasta_url":"https://rest.uniprot.org/uniprotkb/Q13641.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q13641/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q13641"}},"corpus_meta":[{"pmid":"2404511","id":"PMC_2404511","title":"Immunohistological distribution of 5T4 antigen in normal and malignant tissues.","date":"1990","source":"British journal of cancer","url":"https://pubmed.ncbi.nlm.nih.gov/2404511","citation_count":168,"is_preprint":false},{"pmid":"20881001","id":"PMC_20881001","title":"Vaccination of metastatic renal cancer patients with MVA-5T4: a randomized, double-blind, placebo-controlled phase III study.","date":"2010","source":"Clinical cancer research : an official journal of the American Association for Cancer Research","url":"https://pubmed.ncbi.nlm.nih.gov/20881001","citation_count":144,"is_preprint":false},{"pmid":"17507657","id":"PMC_17507657","title":"E-cadherin inhibits cell surface localization of the pro-migratory 5T4 oncofetal antigen in mouse embryonic stem cells.","date":"2007","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/17507657","citation_count":91,"is_preprint":false},{"pmid":"22100263","id":"PMC_22100263","title":"Waif1/5T4 inhibits Wnt/β-catenin signaling and activates noncanonical Wnt pathways by modifying LRP6 subcellular localization.","date":"2011","source":"Developmental cell","url":"https://pubmed.ncbi.nlm.nih.gov/22100263","citation_count":80,"is_preprint":false},{"pmid":"11578488","id":"PMC_11578488","title":"5T4 oncofetal antigen expression in ovarian carcinoma.","date":"1995","source":"International journal of gynecological cancer : official journal of the International Gynecological Cancer Society","url":"https://pubmed.ncbi.nlm.nih.gov/11578488","citation_count":77,"is_preprint":false},{"pmid":"17671134","id":"PMC_17671134","title":"Vaccination of colorectal cancer patients with modified vaccinia ankara encoding the tumor antigen 5T4 (TroVax) given alongside chemotherapy induces potent immune responses.","date":"2007","source":"Clinical cancer research : an official journal of the American Association for Cancer 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science","url":"https://pubmed.ncbi.nlm.nih.gov/35551574","citation_count":4,"is_preprint":false},{"pmid":"29549047","id":"PMC_29549047","title":"The breast cancer antigen 5T4 interacts with Rab11, and is a target and regulator of Rab11 mediated trafficking.","date":"2018","source":"The international journal of biochemistry & cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/29549047","citation_count":4,"is_preprint":false},{"pmid":"33192298","id":"PMC_33192298","title":"LRR-Containing Oncofetal Trophoblast Glycoprotein 5T4 Shapes Neural Circuits in Olfactory and Visual Systems.","date":"2020","source":"Frontiers in molecular neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/33192298","citation_count":4,"is_preprint":false},{"pmid":"23603858","id":"PMC_23603858","title":"Murine responses to recombinant MVA versus ALVAC vaccines against tumor-associated antigens, gp100 and 5T4.","date":"2013","source":"Journal of immunotherapy (Hagerstown, Md. : 1997)","url":"https://pubmed.ncbi.nlm.nih.gov/23603858","citation_count":4,"is_preprint":false},{"pmid":"17765223","id":"PMC_17765223","title":"Novel vectors for homologous recombination strategies in mouse embryonic stem cells: an ES cell line expressing EGFP under control of the 5T4 promoter.","date":"2007","source":"Experimental cell research","url":"https://pubmed.ncbi.nlm.nih.gov/17765223","citation_count":4,"is_preprint":false},{"pmid":"17484803","id":"PMC_17484803","title":"5T4 oncotrophoblast glycoprotein: janus molecule in life and a novel potential target against tumors.","date":"2007","source":"Cellular & molecular immunology","url":"https://pubmed.ncbi.nlm.nih.gov/17484803","citation_count":3,"is_preprint":false},{"pmid":"39377811","id":"PMC_39377811","title":"Preclinical evaluation and pilot clinical study of [68Ga]Ga-NOTA-H006 for non-invasive PET imaging of 5T4 oncofetal antigen.","date":"2024","source":"European journal of nuclear medicine and molecular imaging","url":"https://pubmed.ncbi.nlm.nih.gov/39377811","citation_count":3,"is_preprint":false},{"pmid":"40836888","id":"PMC_40836888","title":"Preclinical Characterization of XB010: A Novel Antibody-Drug Conjugate for the Treatment of Solid Tumors that Targets Tumor-Associated Antigen 5T4.","date":"2025","source":"Molecular cancer therapeutics","url":"https://pubmed.ncbi.nlm.nih.gov/40836888","citation_count":2,"is_preprint":false},{"pmid":"40443260","id":"PMC_40443260","title":"Development of [18F]AlF-RESCA-H006 as a Novel Molecular Probe for 5T4 Tumor Imaging and Exploration of Its Application in Pancreatic Adenocarcinoma.","date":"2025","source":"Molecular pharmaceutics","url":"https://pubmed.ncbi.nlm.nih.gov/40443260","citation_count":2,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":54243,"output_tokens":5333,"usd":0.121362,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":13513,"output_tokens":5114,"usd":0.097708,"stage2_stop_reason":"end_turn"},"total_usd":0.21907,"stage1_batch_id":"msgbatch_017qqVz33Ga63SCDwzb35XPb","stage2_batch_id":"msgbatch_01Scr2Ei9x4HJMiRGxwrmvLK","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1990,\n      \"finding\": \"TPBG/5T4 antigen is a 72 kDa glycoprotein with a 42 kDa core protein; extensive N-linked glycosylation accounts for the molecular weight difference; the native molecule is resistant to proteolysis until N-linked sugars are removed or the glycoprotein is denatured and reduced.\",\n      \"method\": \"Lectin- and immunoaffinity chromatography, gel filtration, SDS-PAGE, N-glycanase treatment, protease digestion assays\",\n      \"journal\": \"International journal of cancer\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct biochemical characterization with multiple orthogonal methods (chromatographic purification, enzymatic deglycosylation, protease resistance assays) in foundational study\",\n      \"pmids\": [\"2298503\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"TPBG/5T4 cDNA encodes a 420 amino acid type I transmembrane protein (46 kDa predicted, 72 kDa glycosylated) with N- and C-terminal hydrophobic signal/transmembrane segments, 8 potential N-glycosylation sites, and leucine-rich repeats (LRRs) in the extracellular domain.\",\n      \"method\": \"cDNA cloning from human placental library using oligonucleotides based on purified protein sequence; Northern blot analysis; sequence database comparison\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct cDNA isolation, amino acid sequencing of purified protein, and sequence analysis providing the primary structural framework for the protein\",\n      \"pmids\": [\"8132670\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"TPBG/5T4 is concentrated at microvillus projections of the plasma membrane in transfected murine L cells (A9 derivative) and in carcinoma cell lines; 5T4 expression in A9 cells is associated with altered cell division, decreased cell-substratum adhesion, and increased cellular motility.\",\n      \"method\": \"Stable transfection of 5T4 cDNA into L cells; confocal immunofluorescence microscopy; transmission and scanning electron microscopy\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain-of-function transfection with defined morphological and motility phenotype, multiple imaging modalities, single lab\",\n      \"pmids\": [\"7593330\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Transfection of full-length 5T4 cDNA into epithelial cells disrupts actin/cadherin-containing cell-cell contacts and increases motility; deletion of the cytoplasmic domain shows that the cytoplasmic tail is necessary for abrogating actin/cadherin contacts but is not required for the effects on motility, indicating that 5T4 can deliver signals through both extracellular and intracellular domains.\",\n      \"method\": \"Stable transfection of full-length and cytoplasmic-domain-deleted 5T4 cDNA into CL-S1 murine mammary cells and MDCK epithelial cells; motility assays; morphological analysis\",\n      \"journal\": \"International journal of cancer\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — domain-deletion mutagenesis with separable functional readouts (actin/cadherin disruption vs motility), two cell line models\",\n      \"pmids\": [\"8895545\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"TPBG/5T4 interacts with TIP-2/GIPC, a cytoplasmic PDZ-domain protein; the interaction requires the C-terminal class I PDZ-binding motif (Ser-Asp-Val) of 5T4, specifically the terminal valine; 5T4 and TIP-2/GIPC co-localize in HeLa cells and can be co-immunoprecipitated, providing the first link between 5T4 and the actin cytoskeleton.\",\n      \"method\": \"Yeast two-hybrid screen; site-directed mutagenesis of PDZ-binding motif; co-immunoprecipitation from HeLa cell lysates; co-localization by immunofluorescence\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — yeast two-hybrid identification plus reciprocal co-IP validation plus co-localization plus mutagenesis of binding motif, all in single study\",\n      \"pmids\": [\"11798178\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Glycosylation analysis of 5T4 demonstrates all seven consensus N-glycosylation sites are occupied: two predominantly high-mannose chains and five mostly sialylated bi-, tri- and tetra-antennary complex chains with minor core fucose. The mAb5T4 epitope was mapped to the membrane-proximal LRR2 region or its flanking region using deletion/mutation constructs and human-mouse chimeras.\",\n      \"method\": \"Site-directed mutagenesis; deletion constructs; human-mouse chimeric cDNA constructs; glycan analysis by mass spectrometry/carbohydrate chemistry\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — epitope mapping by mutagenesis/chimeras plus glycan compositional analysis with multiple orthogonal methods\",\n      \"pmids\": [\"11903056\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"E-cadherin-mediated cell-cell contact prevents cell surface localization of 5T4 antigen; disruption of E-cadherin contacts (by neutralizing antibody or in E-cadherin knockout ES cells) causes translocation of 5T4 from the cytoplasm to the cell surface in an energy-dependent manner; this cell surface localization of 5T4 is associated with increased cellular motility during epithelial-mesenchymal transition. 5T4 knockout ES cells show significantly decreased motility during EMT.\",\n      \"method\": \"Mouse ES cell differentiation; E-cadherin neutralizing antibody; E-cadherin knockout ES cells; forced E-cadherin re-expression; 5T4 knockout ES cells; FACS; motility assays; confocal imaging\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple genetic knockout models plus antibody perturbation plus rescue experiments with defined functional readouts (motility, actin cytoskeleton), multiple orthogonal approaches\",\n      \"pmids\": [\"17507657\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"TPBG/5T4 is required for optimal functional cell surface expression of CXCR4 and CXCL12-mediated chemotaxis in differentiating mouse embryonic stem cells and embryonic fibroblasts; 5T4 and CXCR4 co-localize at the cell surface; in 5T4 knockout cells CXCR4 is retained intracellularly and CXCL12 chemotaxis is abolished; adenoviral restoration of 5T4 rescues CXCR4 surface expression and chemotaxis; the 5T4 transmembrane domain is sufficient and necessary for CXCR4 membrane expression.\",\n      \"method\": \"5T4 knockout mouse-derived ES cells and MEFs; adenoviral 5T4 rescue; chimeric 5T4/CD44 domain-swap constructs; CXCL12 chemotaxis assays; co-localization immunofluorescence; FACS\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — knockout + rescue + domain-swap mutagenesis + functional chemotaxis assay, multiple cell types, transmembrane domain identified as necessary and sufficient\",\n      \"pmids\": [\"20376365\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"TPBG/5T4 (Waif1) inhibits Wnt/β-catenin signaling and activates non-canonical Wnt pathways; Waif1a binds the Wnt co-receptor LRP6 and inhibits Wnt-induced LRP6 internalization into endocytic vesicles, a process required for canonical Wnt pathway activation; Waif1a also enhances β-catenin-independent Wnt signaling by promoting a non-canonical function of Dickkopf1.\",\n      \"method\": \"Zebrafish and Xenopus embryo gain/loss-of-function; mammalian cell Wnt reporter assays; co-immunoprecipitation of Waif1a with LRP6; LRP6 internalization assays\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — binding partner identified by Co-IP, mechanistic LRP6 internalization assay, functional validation in three model systems (zebrafish, Xenopus, mammalian cells)\",\n      \"pmids\": [\"22100263\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"5T4 glycoprotein regulates activity-dependent dendritic development of specific interneuron subtypes in the mouse olfactory bulb; overexpression of 5T4 facilitates dendritic arborization under sensory-deprived conditions; 5T4 knockdown (RNAi) and 5T4 knockout reduce dendritic arborization of 5T4+ granule cells; the cytoplasmic domain of 5T4 contains the sequence necessary and sufficient for sensory input-dependent dendritic shaping.\",\n      \"method\": \"5T4 overexpression and RNAi knockdown in newborn OB interneurons; 5T4 knockout mice; cytoplasmic domain deletion/truncation constructs; dendritic morphometry\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — overexpression, RNAi, knockout, and domain-deletion mutants all tested with quantitative dendritic morphology readout; cytoplasmic domain identified as necessary and sufficient\",\n      \"pmids\": [\"22323733\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"In the absence of 5T4 expression, CXCL12 signaling through CXCR4 (activating ERK and AKT) is non-functional despite intact pathways; CXCR7 is upregulated and becomes the predominant CXCL12 receptor, activating a distinct pathway involving EGFR transactivation and eliciting proliferation rather than chemotaxis; 5T4 surface expression thus determines receptor preference (CXCR4 vs CXCR7) and hence the biological response to CXCL12.\",\n      \"method\": \"Wild-type and 5T4 knockout MEFs; CXCR4 antagonist AMD3100; CXCR7 antagonist CCX771; ERK/AKT pathway phosphorylation assays; chemotaxis and proliferation assays; human SCLC cell lines with 5T4/CXCR7 reciprocity\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — knockout genetic model plus pharmacological receptor antagonists plus downstream signaling readouts plus validation in human cancer cells, multiple orthogonal approaches\",\n      \"pmids\": [\"22956548\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Crystal structure of the extracellular domain of 5T4/WAIF1 at 1.8 Å resolution reveals a highly glycosylated rigid core comprising eight leucine-rich repeats (LRRs); conserved surface residues in LRR1, particularly Tyr325 and Phe97, are essential for inhibition of Wnt/β-catenin signaling as determined by structural and cell-based analyses.\",\n      \"method\": \"X-ray crystallography at 1.8 Å; cell-based Wnt/β-catenin reporter assays; structure-guided mutagenesis of surface residues\",\n      \"journal\": \"Structure\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus cell-based mutagenesis validation of key residues for Wnt inhibition function\",\n      \"pmids\": [\"24582434\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"5T4 interacts with membrane trafficking proteins Rab11, Rab18, and ARF6 as identified by co-immunoprecipitation and mass spectrometry; Rab11 and Rab18 have opposing roles in controlling 5T4 surface expression; endocytosis of 5T4 is strongly Rab11-dependent; 5T4 depletion stabilizes Rab11 protein expression and stimulates transferrin surface labeling, indicating that 5T4 represses Rab11-mediated endocytic activity. 5T4 localizes to focal adhesions in differentiated breast cancer cells.\",\n      \"method\": \"Co-immunoprecipitation followed by mass spectrometry; flow cytometry; immunofluorescence co-localization; 5T4 siRNA depletion; transferrin surface labeling assay\",\n      \"journal\": \"The international journal of biochemistry & cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP/MS identification of binding partners plus functional depletion experiments, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"29549047\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"TPBG/5T4 expression in adventitial pericyte-like cells is upregulated by hypoxia through the transcriptional modulator CITED2, leading to CXCL12 signaling via CXCR7 and ERK1/2 activation; TPBG silencing downregulates CXCL12, CXCR7, and pERK1/2 and reduces pericyte migratory and proangiogenic capacity; TPBG forced expression induces formation of CXCR7/CXCR4 heterodimers; in vivo, TPBG is essential for angiogenesis (Matrigel plug assay) and perfusion recovery in limb ischemia.\",\n      \"method\": \"siRNA silencing; forced overexpression; proximity ligation assay for CXCR7/CXCR4 heterodimers; ELISA, Western blot, immunocytochemistry; in vivo Matrigel plug assay; murine limb ischemia model\",\n      \"journal\": \"Arteriosclerosis, thrombosis, and vascular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — knockdown and overexpression in primary pericytes with multiple molecular and functional readouts plus in vivo validation, multiple orthogonal methods\",\n      \"pmids\": [\"31018661\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"siRNA-mediated depletion of 5T4 in most tested cancer cell lines (A549, C33A, DLD-1, MDA-231, PC-3) did not change the CXCL12 receptor usage or subcellular localization of CXCR4/CXCR7 in the majority of lines, failing to replicate the previously reported general organizational role of 5T4 in the CXCL12 system in cancer cells; however, 5T4 inhibition did modulate migration and proliferation per se in some cell lines.\",\n      \"method\": \"siRNA depletion of 5T4; CXCR4 antagonist AMD3100; CXCR7 antagonist CCX771; chemotaxis and proliferation assays in multiple cancer cell lines\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — negative replication result across multiple cancer cell lines with pharmacological and genetic tools; contradicts generalizability of earlier findings but single lab\",\n      \"pmids\": [\"29408206\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Irradiation of 5T4-expressing DU145 prostate cancer cells induces Hsp70 surface expression; cross-presentation of 5T4 antigen by dendritic cells to CD8+ T cells is predominantly Hsp70-dependent: Hsp70 inhibitor pretreatment robustly prevented antigen cross-presentation and CD86 upregulation on DCs; blocking the Hsp70 receptor CD91 also abolished cross-presentation.\",\n      \"method\": \"DC-tumor cell co-culture cross-presentation model; Hsp70 inhibitors; CD91 blocking antibody; CD8+ T cell proliferation and IFN-γ production assays; HMGB1 inhibition; TLR4 SNP analysis\",\n      \"journal\": \"Cancer immunology research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mechanistic dissection of cross-presentation pathway using pharmacological inhibitors and receptor blocking in defined in vitro model, single lab\",\n      \"pmids\": [\"25678582\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Murine 5T4 antigen expression is absent on undifferentiated ES cells but is rapidly upregulated upon differentiation into all three primary germ layer derivatives; 5T4 expression correlates with early differentiation events involving altered motility and morphology; overexpression of mouse 5T4 in B16 F10 melanoma cells and A9 L fibroblasts produces spindle-like morphology, increased motility, and reduced adhesion and proliferation, dependent on integrity of the actin cytoskeleton.\",\n      \"method\": \"Cell surface FACS, Western blot, RT-PCR on differentiating ES cells; stable transfection of m5T4 in B16 F10 and A9 cells; motility, adhesion, proliferation assays; cytochalasin D actin disruption\",\n      \"journal\": \"Journal of cell science / The Biochemical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain-of-function transfection with quantitative functional readouts plus pharmacological actin disruption linking cytoskeleton to phenotype, single lab\",\n      \"pmids\": [\"14576347\", \"12003637\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TPBG/5T4 is a heavily N-glycosylated type I transmembrane glycoprotein with a leucine-rich repeat extracellular domain (crystal structure resolved at 1.8 Å) that localizes to microvillus/cell surface in a manner controlled by E-cadherin-mediated actin cortical organization; its cytoplasmic tail (containing a PDZ-binding motif that recruits TIP-2/GIPC) mediates disruption of actin/cadherin contacts while its extracellular domain influences cell motility; at the cell surface 5T4 facilitates CXCR4 membrane localization and CXCL12-driven chemotaxis (with the transmembrane domain being sufficient for this function), shifting CXCL12 signaling from a CXCR7/EGFR/proliferation axis to a CXCR4/ERK/AKT/chemotaxis axis; 5T4 also binds LRP6 and inhibits its Wnt-induced endocytosis, thereby suppressing canonical Wnt/β-catenin signaling while promoting non-canonical Wnt pathways, with LRR1 surface residues Tyr325 and Phe97 essential for this inhibitory function; 5T4 additionally interacts with Rab11 to regulate its own endocytic trafficking; collectively these activities underlie its roles in epithelial-mesenchymal transition, cancer metastasis, embryonic development, and activity-dependent dendritic development in the nervous system.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"TPBG (5T4/WAIF1) is a heavily N-glycosylated type I transmembrane glycoprotein whose leucine-rich-repeat extracellular domain and short cytoplasmic tail integrate cell-surface signaling with cytoskeletal and membrane-trafficking control, acting as a regulator of cell motility, epithelial-mesenchymal transition (EMT), and developmental signaling [#1, #6, #8]. The mature protein is a ~72 kDa glycoprotein built on a ~42–46 kDa core whose extensive, largely complex N-glycosylation confers protease resistance, and its extracellular region folds into a rigid eight-LRR core resolved by crystallography at 1.8 Å [#0, #1, #5, #11]. Surface delivery of 5T4 is gated by E-cadherin-mediated cell-cell adhesion: loss of E-cadherin contacts during EMT drives energy-dependent translocation of 5T4 to the cell surface, where it disrupts actin/cadherin junctions and increases motility, with the cytoplasmic tail required for junction disruption but dispensable for the motility effect [#3, #6]. The cytoplasmic tail carries a class I PDZ-binding motif (terminal valine) that recruits the PDZ protein TIP-2/GIPC, linking 5T4 to the actin cytoskeleton, while interactions with Rab11, Rab18 and ARF6 control 5T4's own endocytic trafficking and surface levels [#4, #12]. At the cell surface 5T4 organizes chemokine signaling by promoting functional CXCR4 surface expression and CXCL12-driven chemotaxis—an activity for which the transmembrane domain is necessary and sufficient—thereby steering CXCL12 responses away from a CXCR7/EGFR-transactivation/proliferation axis toward a CXCR4/ERK/AKT/chemotaxis axis [#7, #10]. As WAIF1, 5T4 binds the Wnt co-receptor LRP6 and blocks its Wnt-induced internalization, suppressing canonical Wnt/β-catenin signaling while promoting non-canonical Wnt output, with LRR1 surface residues Tyr325 and Phe97 essential for this inhibition [#8, #11]. These activities underlie roles in EMT and metastasis, embryonic differentiation, hypoxia-driven pericyte angiogenic behavior, and activity-dependent dendritic development of olfactory bulb interneurons [#6, #9, #13].\",\n  \"teleology\": [\n    {\n      \"year\": 1990,\n      \"claim\": \"Establishing that the 5T4 antigen is a single heavily N-glycosylated glycoprotein defined the molecule biochemically and explained its unusual protease resistance.\",\n      \"evidence\": \"Lectin/immunoaffinity purification, deglycosylation, and protease assays on the native antigen\",\n      \"pmids\": [\"2298503\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Primary sequence and domain organization not yet known\", \"No functional role assigned\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"cDNA cloning revealed 5T4 as a type I transmembrane LRR protein, providing the structural framework for all later mechanistic work.\",\n      \"evidence\": \"cDNA cloning from a human placental library guided by purified-protein sequence, with sequence analysis\",\n      \"pmids\": [\"8132670\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No interaction partners identified\", \"Function of LRR domain and cytoplasmic tail unknown\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Forced expression linked 5T4 to a motility/adhesion phenotype, indicating it is not merely a tumor marker but an active modulator of cell behavior.\",\n      \"evidence\": \"Stable 5T4 transfection into L cells with confocal and electron microscopy of microvillus localization and motility/adhesion assays\",\n      \"pmids\": [\"7593330\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism connecting surface localization to motility unresolved\", \"Single-lab gain-of-function only\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Domain-deletion separated 5T4's two outputs—the cytoplasmic tail abrogates actin/cadherin contacts while motility effects map elsewhere—showing the protein signals through distinct domains.\",\n      \"evidence\": \"Full-length vs cytoplasmic-deleted 5T4 transfected into mammary and MDCK epithelial cells with morphology and motility readouts\",\n      \"pmids\": [\"8895545\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cytoplasmic-tail effector not identified\", \"Extracellular determinant of motility undefined\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Identification of the TIP-2/GIPC PDZ interaction gave the first molecular link between 5T4's tail and the actin cytoskeleton.\",\n      \"evidence\": \"Yeast two-hybrid, PDZ-motif mutagenesis, co-IP, and co-localization in HeLa cells\",\n      \"pmids\": [\"11798178\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of GIPC binding for motility/junctions not directly tested\", \"Link to downstream actin regulators unmapped\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Defining glycan occupancy and mapping the antibody epitope characterized the surface architecture of the extracellular domain.\",\n      \"evidence\": \"Glycan compositional analysis plus deletion/chimera epitope mapping\",\n      \"pmids\": [\"11903056\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional role of specific glycans not tested\", \"No 3D structure yet\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Developmental upregulation upon ES cell differentiation tied 5T4 expression to early morphogenetic transitions and confirmed actin-dependence of its phenotype.\",\n      \"evidence\": \"FACS/RT-PCR on differentiating ES cells plus transfection into melanoma/fibroblast lines with cytochalasin D actin disruption\",\n      \"pmids\": [\"14576347\", \"12003637\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Signaling pathway driving morphology change undefined\", \"Single-lab gain-of-function\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"E-cadherin contacts were shown to gate 5T4 surface localization, embedding 5T4 in the EMT program as an adhesion-controlled surface switch.\",\n      \"evidence\": \"ES cell EMT models with E-cadherin neutralization, E-cadherin and 5T4 knockouts, and rescue with motility readouts\",\n      \"pmids\": [\"17507657\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of energy-dependent translocation unresolved\", \"Trafficking machinery not yet identified\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"5T4 was found necessary for functional CXCR4 surface expression and CXCL12 chemotaxis, identifying a transmembrane-domain-mediated chemokine-organizing function.\",\n      \"evidence\": \"5T4 knockout ES cells/MEFs with adenoviral rescue and 5T4/CD44 domain-swap chimeras in chemotaxis and co-localization assays\",\n      \"pmids\": [\"20376365\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular nature of TM-domain/CXCR4 interaction undefined\", \"Whether 5T4 directly binds CXCR4 unproven\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"As WAIF1, 5T4 was shown to bind LRP6 and block its Wnt-induced internalization, placing 5T4 as a switch between canonical and non-canonical Wnt signaling.\",\n      \"evidence\": \"Zebrafish/Xenopus gain-loss-of-function, mammalian Wnt reporters, Waif1a–LRP6 co-IP, and LRP6 internalization assays\",\n      \"pmids\": [\"22100263\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of LRP6 binding not yet defined\", \"Mechanism of non-canonical DKK1 enhancement unresolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"5T4 was shown to determine CXCL12 receptor preference (CXCR4 vs CXCR7), dictating chemotaxis versus proliferation outcomes.\",\n      \"evidence\": \"Wild-type vs 5T4 knockout MEFs with CXCR4/CXCR7 antagonists, ERK/AKT readouts, and human SCLC lines\",\n      \"pmids\": [\"22956548\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How 5T4 represses CXCR7 expression is unknown\", \"Direct receptor contacts not mapped\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"5T4 was assigned a neuronal role in activity-dependent dendritic development, with the cytoplasmic domain necessary and sufficient for sensory-input-dependent shaping.\",\n      \"evidence\": \"Overexpression, RNAi, knockout, and cytoplasmic-domain truncations in olfactory bulb interneurons with dendritic morphometry\",\n      \"pmids\": [\"22323733\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cytoplasmic-tail effectors mediating dendritic shaping unidentified\", \"Link to activity-dependent signaling pathways unmapped\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"The 1.8 Å crystal structure of the LRR ectodomain defined a rigid eight-LRR core and pinpointed LRR1 residues Tyr325/Phe97 as required for Wnt inhibition.\",\n      \"evidence\": \"X-ray crystallography with structure-guided mutagenesis in Wnt reporter assays\",\n      \"pmids\": [\"24582434\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of LRP6-bound complex not solved\", \"Structural basis of CXCR4/CXCR7 organization not addressed\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"5T4 was linked to Rab11/Rab18/ARF6 trafficking machinery that controls its own surface levels, revealing a self-regulatory endocytic loop.\",\n      \"evidence\": \"Co-IP/mass spectrometry, siRNA depletion, transferrin surface labeling, and focal-adhesion localization in breast cancer cells\",\n      \"pmids\": [\"29549047\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct vs indirect nature of Rab interactions unclear\", \"Single-lab Co-IP/MS without reciprocal validation\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"5T4 antigen cross-presentation was shown to be predominantly Hsp70/CD91-dependent, relevant to anti-5T4 immune responses.\",\n      \"evidence\": \"DC–tumor co-culture cross-presentation with Hsp70 inhibitors, CD91 blockade, and CD8+ T-cell readouts\",\n      \"pmids\": [\"25678582\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Concerns 5T4 as an antigen, not its intrinsic molecular function\", \"Single in vitro model\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"In pericytes, hypoxia/CITED2-driven TPBG was shown to act through CXCL12/CXCR7/ERK and induce CXCR7/CXCR4 heterodimers, extending its chemokine-organizing role to angiogenesis in vivo.\",\n      \"evidence\": \"siRNA/overexpression in primary pericytes, proximity ligation for heterodimers, and Matrigel/limb-ischemia in vivo models\",\n      \"pmids\": [\"31018661\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Reconciliation with the CXCR4-favoring model from MEFs unresolved\", \"Direct 5T4–receptor contacts not mapped\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"A negative replication challenged the generality of 5T4's CXCL12-organizing role, indicating context-dependence across cancer cell types.\",\n      \"evidence\": \"siRNA depletion of 5T4 with CXCR4/CXCR7 antagonists across five cancer cell lines failing to alter receptor usage\",\n      \"pmids\": [\"29408206\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Does not exclude the role in non-transformed/ES cell contexts\", \"Mechanistic basis of cell-type dependence unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved how 5T4 physically couples a single LRR ectodomain and short tail to its diverse outputs—CXCR4/CXCR7 organization, LRP6 internalization control, and cytoplasmic-tail-dependent dendritic and junctional effects—within a unified mechanism.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structure of 5T4 bound to CXCR4, CXCR7, or LRP6\", \"Cytoplasmic-tail effectors beyond GIPC for neuronal/junctional roles unidentified\", \"Cell-type determinants of CXCR4 vs CXCR7 preference unexplained\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [8, 10, 11]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [4, 7]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 1, 11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [2, 6, 7]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [8, 10, 13]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [6, 9, 16]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [12]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"GIPC1\", \"LRP6\", \"CXCR4\", \"CXCR7\", \"RAB11A\", \"ARF6\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}