{"gene":"LRP2","run_date":"2026-04-28T18:30:27","timeline":{"discoveries":[{"year":1983,"finding":"LRP2/gp330 localizes to clathrin-coated pits on glomerular epithelial cells (podocytes) and proximal tubule cells, where it concentrates and serves as the site of immune complex formation in Heymann nephritis; it is synthesized by glomerular epithelial cells and traffics through ER, Golgi, and multivesicular bodies to coated pits.","method":"Immunoprecipitation of radiolabeled kidney extracts, indirect immunofluorescence, immunoperoxidase electron microscopy on cryostat sections","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (immunoprecipitation + immunofluorescence + immunoelectron microscopy), foundational paper with 500 citations","pmids":["6337231"],"is_preprint":false},{"year":1990,"finding":"A C-terminal domain of gp330 (encoded by clone 14, ~319 amino acids) contains a major pathogenic epitope responsible for antibody binding and subepithelial immune deposit formation in Heymann nephritis; antibodies against this domain induce both passive and active Heymann nephritis in rats.","method":"cDNA library screening with eluted glomerular IgG, expression of fusion protein, passive and active immunization of rats, immunoblotting","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1–2 — in vivo disease model with molecular domain mapping, replicated in both passive and active models","pmids":["2408041"],"is_preprint":false},{"year":1991,"finding":"LRP2/gp330 functions as a receptor for plasminogen; binding is saturable and specifically inhibitable, and is not exclusively through lysine-binding sites, indicating additional interaction sites.","method":"Western blot ligand binding, ELISA saturation and competition assays, cDNA library screening with antibody to purified serum protein","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 — in vitro binding assays with purified components, multiple independent approaches","pmids":["1645711"],"is_preprint":false},{"year":1992,"finding":"LRP2/gp330 acts as a Ca2+-binding endocytic receptor in renal proximal tubule; it binds the 40-kDa RAP protein in a Ca2+-dependent, heparin-sensitive manner, and mediates endocytosis of RAP into lysosomes as demonstrated by in vivo tubular microperfusion.","method":"Ligand blotting, 45Ca2+ blotting, light and electron microscopic autoradiography, in vivo microperfusion of rat proximal tubules with 125I-labeled ligand","journal":"The journal of histochemistry and cytochemistry","confidence":"High","confidence_rationale":"Tier 1–2 — direct endocytosis demonstrated in vivo with multiple methods including microperfusion and subcellular tracking","pmids":["1382088"],"is_preprint":false},{"year":1992,"finding":"LRP2/gp330 shares multiple ligand-binding specificities with LRP1, binding plasminogen activator-inhibitor complexes, lactoferrin, and apolipoprotein E-enriched beta-VLDL; all ligand binding to both receptors is inhibited by the 39-kDa RAP protein, identifying RAP as a universal regulator of ligand binding. Cross-competition shows at least three distinct but overlapping binding sites on LRP.","method":"Nitrocellulose ligand blotting with purified rat kidney gp330, cell-based cholesteryl ester synthesis assay, cross-competition experiments in cultured human fibroblasts","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 — multiple ligands tested with multiple orthogonal methods, replicated across cell and membrane systems; 426 citations","pmids":["1464627"],"is_preprint":false},{"year":1992,"finding":"LRP2/gp330 forms a stable heterodimeric complex with a 44-kDa protein (RAP/alpha2-MRAP) in the rat kidney, constituting the Heymann nephritis antigenic complex (HNAC); the complex is stable to detergent extraction, and RAP shares immunological identity with the C14 fusion protein.","method":"Immunoprecipitation with specific antibodies, immunoblotting, long-term centrifugation stability tests","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — reciprocal immunoprecipitation and immunoblotting confirming stable complex; 150 citations","pmids":["1495959"],"is_preprint":false},{"year":1992,"finding":"Once plasminogen is bound to gp330, urokinase can convert it to plasmin at an accelerated rate; plasmin remains bound to gp330 in an active state and is protected from inactivation by alpha2-antiplasmin while bound.","method":"In vitro enzyme kinetics (Km/Vmax analysis), ELISA binding assays, chromogenic substrate cleavage assays","journal":"Archives of biochemistry and biophysics","confidence":"High","confidence_rationale":"Tier 1 — reconstituted enzymatic assay with kinetic parameters and inhibitor protection data","pmids":["1280065"],"is_preprint":false},{"year":1993,"finding":"LRP2/gp330 and its associated 44-kDa protein (RAP) assemble in the endoplasmic reticulum; the complex forms in two steps: first a Ca2+-dependent 19.3S heterodimer within 30 min of synthesis, then a larger 38.6S heterooligomer >60 min post-synthesis, both steps preceding Golgi processing (Endo H-resistant glycosylation).","method":"Pulse-chase radiolabeling of rat kidney tubule fragments, immunoprecipitation with specific antibodies, sucrose velocity gradient centrifugation, endoglycosidase H digestion","journal":"The American journal of physiology","confidence":"High","confidence_rationale":"Tier 1–2 — pulse-chase biosynthesis with biochemical fractionation and multiple controls; establishes temporal and spatial assembly in ER","pmids":["8322889"],"is_preprint":false},{"year":1993,"finding":"LRP2/gp330 mediates endocytosis of pro-urokinase, PAI-1, and urokinase:PAI-1 complexes in type II pneumocytes; RAP completely inhibits this internalization and degradation, and anti-gp330 antibodies inhibit 30–50%, confirming gp330-dependent clearance of plasminogen activation system components.","method":"Radiolabeled ligand internalization and degradation assays in cultured type II pneumocytes, antibody inhibition, RAP competition","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 — direct cellular endocytosis assay with specific inhibitors and antibody blockade, multiple ligands tested","pmids":["7673355"],"is_preprint":false},{"year":1993,"finding":"LRP2/gp330 binds a distinct 45-kDa protein (RAP) as a separate ligand from plasminogen; gp330 has two separate and non-competing binding sites for plasminogen and the 45-kDa RAP, demonstrating multi-site ligand architecture.","method":"ELISA binding assays, competitive inhibition experiments, cDNA library screening, sequence analysis","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — solid-phase binding with competition assays, but single lab","pmids":["7681839"],"is_preprint":false},{"year":1995,"finding":"Megalin/gp330 localizes primarily to apical coated pits, small and large endocytic vacuoles, and dense apical tubules in proximal tubule cells, with segmental variation; it is also found in lysosomes (especially segments 1 and 2) and brush border microvilli, consistent with a protein scavenger receptor role cycling through the early endocytic pathway.","method":"Light and electron microscope immunocytochemistry on cryosections and Lowicryl sections from rat, rabbit, and human kidney","journal":"European journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — multi-species immunoelectron microscopy with quantitative morphometry; detailed subcellular localization linked to function","pmids":["7656901"],"is_preprint":false},{"year":1989,"finding":"Microtubule integrity is required for polarized apical localization of LRP2/gp330 in proximal tubule cells; colchicine treatment disperses gp330-containing vesicles throughout the cytoplasm, though gp330 is not inserted into the basolateral membrane, indicating microtubules drive apical accumulation but other factors govern membrane fusion.","method":"In vivo colchicine treatment of rats, immunocytochemistry (immunofluorescence and immunoperoxidase), intravenous antibody injection to test basolateral access","journal":"The American journal of physiology","confidence":"High","confidence_rationale":"Tier 2 — direct in vivo perturbation with functional consequence (abrogated apical targeting) confirmed by antibody accessibility test","pmids":["2669509"],"is_preprint":false},{"year":1995,"finding":"Microtubule disruption by colchicine blocks apical endocytosis, impairs endocytic invagination formation, disrupts membrane recycling (dense apical tubules), and redistributes gp330 from the apical endocytic apparatus to dispersed cytoplasmic vesicles, without altering other brush border markers.","method":"In vivo colchicine treatment, electron microscopy, morphometry, immunocytochemistry, functional peroxidase endocytosis assay","journal":"European journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — functional endocytosis assay combined with morphometry and immunoelectron microscopy, confirms role of microtubules in gp330 trafficking","pmids":["7543847"],"is_preprint":false},{"year":1996,"finding":"Complete primary structure of human gp330/LRP2 was determined: 4655 amino acids, single transmembrane domain, 36 LDLR ligand-binding repeats in four domains, 16 EGF-like repeats, two FXNPXY internalization signals in the cytoplasmic tail, and multiple signaling motifs (SH2, SH3, PKC, CKII sites) suggesting potential intracellular signaling capacity.","method":"cDNA cloning, RT-PCR, sequence analysis of human parathyroid, kidney, placenta, epididymis, and lung","journal":"European journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 — complete molecular characterization establishing domain architecture; foundational structural paper","pmids":["8706697"],"is_preprint":false},{"year":1996,"finding":"Megalin/LRP2 knockout mice exhibit holoprosencephaly, loss of olfactory bulbs, forebrain fusion, and perinatal death from respiratory insufficiency, demonstrating that megalin-mediated endocytic uptake (possibly of cholesterol-carrying lipoproteins) in neuroepithelium is essential for forebrain development.","method":"Knockout mouse generation, pathological analysis of brain and epithelial tissues, phenotypic characterization","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — clean KO with defined developmental phenotype; 427 citations, foundational loss-of-function study","pmids":["8710893"],"is_preprint":false},{"year":1997,"finding":"Antibodies that cause passive Heymann nephritis inhibit the binding and internalization of apolipoprotein E-enriched beta-VLDL by megalin/LRP2 in podocytes, causing accumulation of apo E and apo B within subepithelial immune deposits; constitutive lipoprotein uptake via megalin occurs through clathrin-coated pits and multivesicular bodies in normal podocytes.","method":"Immunoelectron microscopy, immunofluorescence, in vitro binding and internalization assays with antibodies eluted from nephritic glomeruli","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 — direct in vivo and in vitro demonstration of functional inhibition of receptor-mediated endocytosis by pathogenic antibodies","pmids":["9410908"],"is_preprint":false},{"year":1998,"finding":"Megalin/gp330 binds thyroglobulin (Tg) with high affinity (Kd ~9.2 nM) in a Ca2+-dependent manner; binding is inhibited by other megalin ligands (lactoferrin, lipoprotein lipase, apolipoprotein J) and by RAP, indicating a shared binding site and suggesting megalin mediates Tg endocytosis in thyroid cells.","method":"Solid-phase binding assays with purified rat megalin and 125I-labeled Tg, EDTA/heparin release, SDS-PAGE, immunoblotting","journal":"Endocrinology","confidence":"High","confidence_rationale":"Tier 1 — direct binding with purified proteins, Kd determination, competition assays; replicated in thyroid cell line","pmids":["9492085"],"is_preprint":false},{"year":1999,"finding":"Megalin/gp330 mediates endocytosis of thyroglobulin in Fisher rat thyroid (FRTL-5) cells; chemical cross-linking and immunoprecipitation confirmed Tg binding to surface megalin, and cell internalization assays showed RAP and anti-megalin antibody inhibited Tg uptake by ~60–80%, demonstrating megalin-dependent endocytosis.","method":"Chemical cross-linking with immunoprecipitation, 125I-Tg binding at 4°C followed by heparin release, ELISA quantification of internalized Tg at 37°C","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods in intact cells demonstrating receptor-mediated endocytosis of a physiologic ligand","pmids":["10212279"],"is_preprint":false},{"year":1999,"finding":"Megalin/gp330 mediates transcytosis of intact thyroglobulin from the apical to basolateral side of thyroid cells; blocking megalin with RAP or anti-megalin antibody redirects Tg to lysosomal degradation (increasing T3 release), while megalin-mediated transcytosis diverts Tg from proteolysis, thus regulating thyroid hormone release.","method":"Polarized FRTL-5 cells on permeable filters in dual-chamber devices, 125I-Tg transcytosis assays, RAP and antibody competition, in vivo goiter model with aminotriazole","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — polarized cell transcytosis assay with specific inhibitors plus in vivo validation in goiter model; defines novel function","pmids":["10702280"],"is_preprint":false},{"year":1999,"finding":"Megalin/gp330 binds and mediates cellular uptake and degradation of lipoprotein(a) in vitro; purified megalin on a sensor chip binds Lp(a) in a Ca2+-dependent manner, and megalin-expressing yolk sac cells show 2-fold higher uptake and degradation of Lp(a) versus megalin-null controls, an effect abolished by RAP.","method":"Surface plasmon resonance with purified megalin, fluorescent DiI-Lp(a) uptake imaging, 125I-Lp(a) internalization/degradation assays comparing megalin-expressing vs. LRP/megalin double-knockout cell lines","journal":"Arteriosclerosis, thrombosis, and vascular biology","confidence":"High","confidence_rationale":"Tier 1 — reconstituted binding with purified receptor + cell-based uptake with genetic knockout controls","pmids":["10073957"],"is_preprint":false},{"year":2005,"finding":"Megalin/LRP2 expression in the neuroepithelium (not the yolk sac) is required for forebrain development; megalin deficiency leads to increased BMP4 expression and signaling in the dorsal neuroepithelium and consequent loss of SHH expression in the ventral forebrain, resulting in loss of oligodendroglial and interneuronal cell populations; megalin mediates endocytic uptake and degradation of BMP4, acting as a BMP4 clearance receptor.","method":"Conditional and complete megalin knockout mice, in situ hybridization for BMP4 and SHH, immunohistochemistry, cell population analysis in forebrain","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 — conditional KO with defined pathway (BMP4/SHH epistasis) and cellular phenotype; multiple genetic models tested","pmids":["15623804"],"is_preprint":false},{"year":2006,"finding":"Megalin/LRP2 and its co-receptor cubilin are conserved in the zebrafish larval pronephros; knockdown of megalin/LRP2 eliminates Rab4-positive endosomes in proximal pronephric duct epithelium and abrogates apical endocytosis; knockdown of the megalin adaptor Disabled-2 (Dab2) also blocks renal clearance, establishing that renal tubular endocytosis is a ligand-induced process requiring megalin activity and its intracellular adaptors.","method":"Morpholino knockdown in zebrafish, fluorescent tracer clearance assays, immunofluorescence for Rab4 endosomes, genetic epistasis with Dab2 knockdown","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 — morpholino KD with functional endocytosis readout and epistasis with adaptor protein; conserved pathway established","pmids":["16638803"],"is_preprint":false},{"year":2010,"finding":"MESD chaperone is required for proper folding of the beta-propeller/EGF domain common to LRP family members and for apical localization of LRP2/megalin in the visceral endoderm; loss of MESD results in mislocalization of megalin and impaired endocytic function in visceral endoderm.","method":"Targeted Mesd knockout mice, immunofluorescence localization of LRP2, in vitro maturation assays for beta-propeller/EGF domains","journal":"Developmental dynamics","confidence":"Medium","confidence_rationale":"Tier 2 — KO with localization readout, but mechanistic link to LRP2 misfolding relies partly on in vitro data","pmids":["21337463"],"is_preprint":false},{"year":2011,"finding":"LRP2/megalin functions as an auxiliary SHH receptor in the rostral diencephalon ventral midline (RDVM) during forebrain development; LRP2 sequesters SHH at the apical surface and controls internalization and cellular trafficking of SHH/patched-1 complexes; LRP2 loss causes failure to respond to SHH despite intact patched-1 and smoothened expression, while LRP2 overexpression increases SHH signaling capacity.","method":"LRP2 knockout mice, cephalic explant assays, overexpression of LRP2 variants in cells, SHH binding assays, epistasis analysis with patched-1 and smoothened","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 2 — loss-of-function and gain-of-function in both in vivo and ex vivo systems with defined pathway position","pmids":["22340494"],"is_preprint":false},{"year":2011,"finding":"LRP2 acts as an endocytic clearance receptor for SHH in the developing retina, preventing spread of SHH activity from central retina into the retinal margin; loss of LRP2 increases sensitivity of retinal margin progenitors to SHH, causing expansion of the progenitor pool and hyperproliferation.","method":"Conditional LRP2 knockout mice (retina-specific), immunohistochemistry, BrdU incorporation assays for proliferation, SHH pathway activity measurements","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 2 — conditional KO with defined cellular and molecular phenotype demonstrating context-dependent receptor function","pmids":["26439398"],"is_preprint":false},{"year":2011,"finding":"LRP2 regulates megalin-mediated hypothalamic clusterin (ApoJ) signaling: LRP2 acts as the primary receptor mediating clusterin endocytosis in hypothalamic neurons; clusterin binding to LRP2 enhances association of LRP2 with the long-form leptin receptor, potentiating leptin-induced STAT3 activation and anorexigenic signaling.","method":"Central administration of clusterin in mice, co-immunoprecipitation of LRP2 with leptin receptor in neurons, siRNA knockdown of LRP2 and leptin receptor, STAT3 phosphorylation assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — Co-IP showing receptor complex + in vivo functional assay + KD phenotype; multiple complementary approaches","pmids":["23673647"],"is_preprint":false},{"year":2014,"finding":"Clusterin/ApoJ enhances leptin receptor endocytosis and STAT3 signaling through LRP2; LRP2-mediated endocytosis of the clusterin-leptin complex is required for full anorexigenic leptin action; inhibition of hypothalamic LRP2 or endocytosis blocks clusterin-enhanced leptin signaling.","method":"Co-administration experiments in cultured neurons, endocytosis inhibition assays, LRP2 siRNA knockdown, STAT3 activation measurements, receptor binding assays","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 2 — mechanistic dissection of receptor-mediated endocytosis in signaling with genetic knockdown and functional pathway readout","pmids":["24825475"],"is_preprint":false},{"year":2019,"finding":"TGF-β1 downregulates megalin/LRP2 expression through the SMAD2/3 pathway; SMAD2/3 transcription factors bind to two SMAD-binding elements (SBEs) in the megalin promoter at positions -57 and -605 and repress transcription; histone deacetylase inhibition (TSA) counteracts TGF-β1-mediated repression.","method":"Site-directed mutagenesis of SBEs, chromatin immunoprecipitation (ChIP), promoter reporter assays, siRNA knockdown, TGF-βRI inhibitor experiments in kidney and gallbladder epithelial cell lines","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1–2 — ChIP + mutagenesis + pharmacological inhibition identifying specific transcriptional repressor mechanism","pmids":["31120873"],"is_preprint":false},{"year":2021,"finding":"LRP2 is required for neural tube closure through two mechanisms: (1) its intracellular domain functions as a hub interacting with Shroom3 and Gipc1 adaptors to orchestrate endocytic membrane removal for apical constriction; (2) LRP2 regulates proper localization of the PCP protein Vangl2, essential for planar cell polarity during neurulation; these functions are conserved between mouse and Xenopus.","method":"Lrp2 loss-of-function in mouse and Xenopus, morphological analysis of neural tube closure, co-immunoprecipitation of LRP2 with Shroom3 and Gipc1, immunofluorescence for Vangl2 and apical constriction markers","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 — cross-species genetic KO with Co-IP of novel intracellular interactors and defined cellular phenotypes (apical constriction, PCP)","pmids":["33500317"],"is_preprint":false},{"year":2022,"finding":"Mettl3-mediated m6A modification of Lrp2 mRNA enhances its stability and translation efficiency through the m6A reader protein Ythdc2, promoting neurogenesis; depletion of Mettl3 reduces m6A abundance and Lrp2 expression; overexpression of Lrp2 rescues neurogenesis defects caused by Mettl3 depletion.","method":"Mettl3/Mettl14 knockout in neural stem cells, Lrp2 overexpression rescue experiments, m6A sequencing, m6A reader (Ythdc2) interaction studies, behavioral analysis","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 — identifies specific writer (Mettl3), reader (Ythdc2), and substrate (Lrp2 mRNA) with rescue validation, single lab","pmids":["35716070"],"is_preprint":false},{"year":2023,"finding":"Cryo-EM structures of LRP2 isolated from mouse kidney at extracellular and endosomal pH reveal that LRP2 functions as a homodimer; at cell-surface pH, LRP2 adopts a conformation for ligand binding; at endosomal pH, conformational transformation mediates ligand shedding; pH-sensitive sites are located at both homodimer and intra-protomer interfaces; a subset of human disease-associated missense variants impairs homodimer assembly.","method":"High-resolution cryo-electron microscopy of native LRP2 isolated from mouse kidney, structural analysis at two pH conditions, correlation of structural findings with human disease missense variants","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 — atomic-resolution cryo-EM structures with functional interpretation at two pH states, directly validated against disease variants","pmids":["36750096"],"is_preprint":false},{"year":2011,"finding":"GSK3 phosphorylates the cytoplasmic domain of megalin/LRP2, and megalin surface availability is regulated by multiple mechanisms: ectodomain shedding at the cell surface, subsequent intramembrane proteolysis by gamma-secretase, and exosome secretion.","method":"Review citing biochemical data on phosphorylation, shedding, and gamma-secretase cleavage from primary literature; described in a review article","journal":"Biological research","confidence":"Low","confidence_rationale":"Tier 3–4 — described as established in a review article without original experimental data presented; mechanism referenced from prior work","pmids":["21720686"],"is_preprint":false},{"year":2016,"finding":"miR-146a directly represses LRP2 translation in SH-SY5Y neuronal cells; overexpression of miR-146a decreases LRP2 protein levels, reducing Akt activation and increasing caspase-3-dependent apoptosis.","method":"miR-146a overexpression in SH-SY5Y cells, Western blot for LRP2 and downstream signaling (Akt, caspase-3), predicted target site analysis","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 3 — overexpression with downstream pathway readout, single lab; direct binding to LRP2 3'UTR not rigorously validated in this paper","pmids":["27241555"],"is_preprint":false},{"year":2020,"finding":"LRP2 is required for cardiomyocyte proliferation and differentiation; siRNA knockdown in human iPSC-derived cardiomyocytes and RNAi in developing Drosophila and zebrafish hearts demonstrates that LRP2 loss reduces cardiomyocyte proliferation, consistent with hypoplastic heart defects.","method":"siRNA knockdown in hiPSC-CMs, RNAi in Drosophila and zebrafish hearts, proliferation assays, cross-species functional platform","journal":"eLife","confidence":"Medium","confidence_rationale":"Tier 2 — multi-species knockdown with defined cellular phenotype (proliferation), but mechanism not fully elucidated","pmids":["33006316"],"is_preprint":false}],"current_model":"LRP2/megalin is a giant homodimeric endocytic receptor (whose pH-dependent conformational change between cell-surface and endosomal states was revealed by cryo-EM) that localizes to clathrin-coated pits on the apical surface of epithelial and neuroepithelial cells, where it binds a broad repertoire of ligands (lipoproteins, plasminogen, thyroglobulin, BMP4, SHH, clusterin/ApoJ, RAP, and others) through multiple Ca2+-dependent extracellular binding domains regulated by RAP; after internalization—directed by FXNPXY motifs and intracellular adaptors including Dab2, Shroom3, and Gipc1—ligands are routed to lysosomes for degradation or transcytosed intact; surface availability is modulated by GSK3 phosphorylation of its cytoplasmic tail, ectodomain shedding, gamma-secretase cleavage, and transcriptional repression via TGF-β1/SMAD2/3; in development, LRP2 acts context-dependently as either a morphogen-activating co-receptor (SHH in the forebrain) or a clearance receptor (BMP4 in neuroepithelium; SHH in retinal margin), and loss of LRP2 causes holoprosencephaly, neural tube defects, and renal Fanconi syndrome in mice and Donnai-Barrow syndrome in humans."},"narrative":{"teleology":[{"year":1983,"claim":"Establishing LRP2/gp330 as a membrane glycoprotein of clathrin-coated pits in kidney epithelial cells resolved the identity of the Heymann nephritis antigen and placed it in the endocytic pathway.","evidence":"Immunoprecipitation, immunofluorescence, and immunoelectron microscopy on rat kidney sections","pmids":["6337231"],"confidence":"High","gaps":["Ligand identity unknown","Molecular structure undetermined","Function beyond immune target not established"]},{"year":1991,"claim":"Identification of plasminogen, RAP, and lipoprotein ligands revealed that LRP2 is a multi-ligand endocytic receptor with distinct but overlapping binding sites, regulated universally by the 39-kDa RAP chaperone.","evidence":"Ligand blotting, ELISA competition, and cross-competition assays with purified gp330 and multiple ligands; in vivo microperfusion demonstrating RAP endocytosis into lysosomes","pmids":["1645711","1464627","1382088","1280065"],"confidence":"High","gaps":["Full ligand-binding domain mapping not achieved","Endocytic trafficking itinerary beyond lysosomes not resolved","RAP mechanism of inhibition not structurally defined"]},{"year":1993,"claim":"Demonstrating that LRP2 and RAP assemble as a heterodimeric complex in the ER through Ca²⁺-dependent steps established that RAP functions as an intracellular chaperone, not merely an extracellular competitor.","evidence":"Pulse-chase radiolabeling, sucrose gradient sedimentation, and endoglycosidase H digestion in rat kidney tubule fragments","pmids":["8322889","1495959"],"confidence":"High","gaps":["Whether RAP dissociates before or upon exit from ER/Golgi not resolved","Structural basis of Ca²⁺-dependent assembly unknown"]},{"year":1995,"claim":"Detailed subcellular mapping by immunoelectron microscopy across species confirmed LRP2 cycles through apical coated pits, endocytic vacuoles, dense apical tubules, and lysosomes, and that microtubule integrity is required for its apical polarization and endocytic function.","evidence":"Multi-species immunoelectron microscopy with morphometry; in vivo colchicine perturbation with functional peroxidase endocytosis assay","pmids":["7656901","7543847","2669509"],"confidence":"High","gaps":["Motor proteins mediating microtubule-dependent transport not identified","Sorting signals for apical targeting beyond FXNPXY motifs not mapped"]},{"year":1996,"claim":"Cloning of the complete human LRP2 sequence revealed its domain architecture (36 ligand-binding repeats, 16 EGF repeats, two FXNPXY motifs, signaling motifs), and LRP2 knockout mice demonstrated that the receptor is essential for forebrain development, linking endocytic receptor function to morphogenesis.","evidence":"Full-length cDNA cloning from human tissues; LRP2 knockout mouse with holoprosencephaly phenotype","pmids":["8706697","8710893"],"confidence":"High","gaps":["Which ligand(s) mediate the forebrain phenotype not determined","Contribution of individual binding domains not dissected"]},{"year":1999,"claim":"Discovery that LRP2 mediates both endocytosis and apical-to-basolateral transcytosis of thyroglobulin in thyroid cells, with transcytosis diverting Tg from lysosomal degradation, established a non-degradative trafficking function that regulates thyroid hormone release.","evidence":"Polarized FRTL-5 transcytosis assays with RAP and antibody inhibition; chemical cross-linking confirming surface Tg–megalin complexes","pmids":["10212279","10702280","9492085"],"confidence":"High","gaps":["Sorting signals distinguishing transcytotic from degradative routing not identified","In vivo thyroid phenotype in megalin-deficient animals not reported"]},{"year":2005,"claim":"Conditional knockout studies resolved the forebrain phenotype mechanism: LRP2 acts as a BMP4 clearance receptor in the dorsal neuroepithelium; its loss elevates BMP4 signaling, which suppresses ventral SHH expression, causing holoprosencephaly.","evidence":"Conditional and complete LRP2 knockout mice with in situ hybridization for BMP4 and SHH, cell population analysis","pmids":["15623804"],"confidence":"High","gaps":["Direct BMP4 binding affinity and stoichiometry not measured","Whether other BMP family members are also cleared not tested"]},{"year":2011,"claim":"A dual role for LRP2 in morphogen signaling was established: it acts as a SHH co-receptor in the forebrain (enhancing SHH/Patched-1 signaling) but as a SHH clearance receptor in the retinal margin, demonstrating context-dependent function.","evidence":"LRP2 knockout mice, cephalic explant assays, overexpression/loss-of-function with SHH pathway readouts; conditional retinal KO with BrdU proliferation assays","pmids":["22340494","26439398"],"confidence":"High","gaps":["Structural determinants of co-receptor vs. clearance mode not identified","Whether LRP2 directly binds SHH or acts via Patched-1 complex not fully resolved"]},{"year":2013,"claim":"LRP2 was shown to function beyond classical endocytosis as a signaling scaffold: clusterin binding to LRP2 promotes its association with the leptin receptor in hypothalamic neurons, potentiating STAT3 activation and anorexigenic signaling.","evidence":"Co-immunoprecipitation of LRP2 with leptin receptor, siRNA knockdown, in vivo central clusterin administration with STAT3 readout","pmids":["23673647","24825475"],"confidence":"High","gaps":["Whether LRP2-leptin receptor interaction is direct or mediated by clusterin bridging not resolved","Downstream intracellular trafficking route of the ternary complex not characterized"]},{"year":2021,"claim":"Identification of Shroom3 and Gipc1 as intracellular binding partners of LRP2's cytoplasmic domain established a non-endocytic structural role: LRP2 orchestrates apical constriction and planar cell polarity (Vangl2 localization) required for neural tube closure.","evidence":"LRP2 loss-of-function in mouse and Xenopus, co-immunoprecipitation with Shroom3/Gipc1, immunofluorescence for Vangl2 and apical markers","pmids":["33500317"],"confidence":"High","gaps":["Whether Shroom3/Gipc1 binding is simultaneous or competitive not resolved","Which cytoplasmic motifs mediate Shroom3 vs. Gipc1 interaction not mapped"]},{"year":2023,"claim":"Cryo-EM structures at two pH states revealed that LRP2 functions as a homodimer with a pH-dependent conformational switch: an open ligand-binding state at neutral pH and a closed ligand-release state at endosomal pH, with disease-associated mutations disrupting dimerization.","evidence":"High-resolution cryo-EM of native LRP2 from mouse kidney at pH 7.4 and pH 5.0; mapping of human Donnai–Barrow syndrome missense variants onto structure","pmids":["36750096"],"confidence":"High","gaps":["Ligand-bound structures not yet solved","How individual domains contribute to multi-ligand binding not structurally resolved","Dynamics of pH transition in intact endosomes not captured"]},{"year":null,"claim":"Key unresolved questions include the structural basis for multi-ligand selectivity across LRP2's four binding domains, the sorting determinants that route LRP2-ligand complexes to transcytosis versus degradation, and the mechanism by which the same receptor switches between morphogen co-receptor and clearance receptor roles in different tissues.","evidence":"","pmids":[],"confidence":"High","gaps":["No ligand-bound cryo-EM structure","Sorting signals for transcytotic vs. degradative pathway not mapped","Tissue-specific co-factors determining co-receptor vs. clearance function unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0038024","term_label":"cargo receptor activity","supporting_discovery_ids":[3,4,8,16,17,19,20,23,24]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[4,15,19]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[25,26,28]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,10,13,30]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[10,12,21]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[0,10,12]},{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[3,10]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[7]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,3,8,10,12,17,21]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[14,20,23,24,28]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[23,25,26]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[15,16,17,18,19]}],"complexes":["LRP2-RAP chaperone complex","LRP2-cubilin receptor complex"],"partners":["LRPAP1","CUBN","SHH","BMP4","SHROOM3","GIPC1","DAB2","CLU"],"other_free_text":[]},"mechanistic_narrative":"LRP2 (megalin) is a giant multi-ligand endocytic receptor of the LDL receptor family that functions as a central mediator of apical endocytosis, transcytosis, and morphogen signaling in polarized epithelial and neuroepithelial cells. The receptor contains 36 complement-type ligand-binding repeats organized into four extracellular domains, a single transmembrane segment, and a cytoplasmic tail with two FXNPXY internalization motifs; it operates as a pH-sensitive homodimer that binds ligands at cell-surface pH and releases them upon endosomal acidification [PMID:36750096, PMID:8706697]. Through Ca²⁺-dependent binding regulated by the chaperone RAP, LRP2 internalizes a broad ligand repertoire—including lipoproteins, thyroglobulin, plasminogen, BMP4, SHH, and clusterin—routing them to lysosomes for degradation or mediating transcytosis, and it acts context-dependently as either a morphogen clearance receptor (BMP4 in dorsal neuroepithelium, SHH in retinal margin) or a signaling co-receptor (SHH in forebrain, clusterin/leptin receptor in hypothalamus) [PMID:15623804, PMID:22340494, PMID:26439398, PMID:23673647, PMID:10702280]. Loss-of-function mutations cause holoprosencephaly and neural tube defects in mice, and Donnai–Barrow syndrome in humans, while its intracellular domain coordinates apical constriction during neurulation through interactions with Shroom3 and Gipc1 adaptors [PMID:8710893, PMID:33500317, PMID:36750096]."},"prefetch_data":{"uniprot":{"accession":"P98164","full_name":"Low-density lipoprotein receptor-related protein 2","aliases":["Glycoprotein 330","gp330","Megalin"],"length_aa":4655,"mass_kda":522.0,"function":"Multiligand endocytic receptor (By similarity). Acts together with CUBN to mediate endocytosis of high-density lipoproteins (By similarity). Mediates receptor-mediated uptake of polybasic drugs such as aprotinin, aminoglycosides and polymyxin B (By similarity). In the kidney, mediates the tubular uptake and clearance of leptin (By similarity). Also mediates transport of leptin across the blood-brain barrier through endocytosis at the choroid plexus epithelium (By similarity). Endocytosis of leptin in neuronal cells is required for hypothalamic leptin signaling and leptin-mediated regulation of feeding and body weight (By similarity). Mediates endocytosis and subsequent lysosomal degradation of CST3 in kidney proximal tubule cells (By similarity). Mediates renal uptake of 25-hydroxyvitamin D3 in complex with the vitamin D3 transporter GC/DBP (By similarity). Mediates renal uptake of metallothionein-bound heavy metals (PubMed:15126248). Together with CUBN, mediates renal reabsorption of myoglobin (By similarity). Mediates renal uptake and subsequent lysosomal degradation of APOM (By similarity). Plays a role in kidney selenium homeostasis by mediating renal endocytosis of selenoprotein SEPP1 (By similarity). Mediates renal uptake of the antiapoptotic protein BIRC5/survivin which may be important for functional integrity of the kidney (PubMed:23825075). Mediates renal uptake of matrix metalloproteinase MMP2 in complex with metalloproteinase inhibitor TIMP1 (By similarity). Mediates endocytosis of Sonic hedgehog protein N-product (ShhN), the active product of SHH (By similarity). Also mediates ShhN transcytosis (By similarity). In the embryonic neuroepithelium, mediates endocytic uptake and degradation of BMP4, is required for correct SHH localization in the ventral neural tube and plays a role in patterning of the ventral telencephalon (By similarity). Required at the onset of neurulation to sequester SHH on the apical surface of neuroepithelial cells of the rostral diencephalon ventral midline and to control PTCH1-dependent uptake and intracellular trafficking of SHH (By similarity). During neurulation, required in neuroepithelial cells for uptake of folate bound to the folate receptor FOLR1 which is necessary for neural tube closure (By similarity). In the adult brain, negatively regulates BMP signaling in the subependymal zone which enables neurogenesis to proceed (By similarity). In astrocytes, mediates endocytosis of ALB which is required for the synthesis of the neurotrophic factor oleic acid (By similarity). Involved in neurite branching (By similarity). During optic nerve development, required for SHH-mediated migration and proliferation of oligodendrocyte precursor cells (By similarity). Mediates endocytic uptake and clearance of SHH in the retinal margin which protects retinal progenitor cells from mitogenic stimuli and keeps them quiescent (By similarity). Plays a role in reproductive organ development by mediating uptake in reproductive tissues of androgen and estrogen bound to the sex hormone binding protein SHBG (By similarity). Mediates endocytosis of angiotensin-2 (By similarity). Also mediates endocytosis of angiotensis 1-7 (By similarity). Binds to the complex composed of beta-amyloid protein 40 and CLU/APOJ and mediates its endocytosis and lysosomal degradation (By similarity). Required for embryonic heart development (By similarity). Required for normal hearing, possibly through interaction with estrogen in the inner ear (By similarity)","subcellular_location":"Apical cell membrane; Endosome lumen; Membrane, coated pit; Cell projection, dendrite; Cell projection, axon","url":"https://www.uniprot.org/uniprotkb/P98164/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/LRP2","classification":"Not Classified","n_dependent_lines":7,"n_total_lines":1208,"dependency_fraction":0.005794701986754967},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/LRP2","total_profiled":1310},"omim":[{"mim_id":"619020","title":"LRP2-BINDING PROTEIN; LRP2BP","url":"https://www.omim.org/entry/619020"},{"mim_id":"618882","title":"IMERSLUND-GRASBECK SYNDROME 2; IGS2","url":"https://www.omim.org/entry/618882"},{"mim_id":"610947","title":"CORONARY ARTERY DISEASE, AUTOSOMAL DOMINANT 2; ADCAD2","url":"https://www.omim.org/entry/610947"},{"mim_id":"605747","title":"LOW DENSITY LIPOPROTEIN RECEPTOR ADAPTOR PROTEIN 1; LDLRAP1","url":"https://www.omim.org/entry/605747"},{"mim_id":"605072","title":"GIPC PDZ DOMAIN-CONTAINING FAMILY, MEMBER 1; GIPC1","url":"https://www.omim.org/entry/605072"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Uncertain","locations":[{"location":"Cell Junctions","reliability":"Uncertain"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"kidney","ntpm":32.5},{"tissue":"parathyroid gland","ntpm":42.1},{"tissue":"retina","ntpm":27.1}],"url":"https://www.proteinatlas.org/search/LRP2"},"hgnc":{"alias_symbol":["gp330","DBS"],"prev_symbol":[]},"alphafold":{"accession":"P98164","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P98164","model_url":"","pae_url":"","plddt_mean":null},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=LRP2","jax_strain_url":"https://www.jax.org/strain/search?query=LRP2"},"sequence":{"accession":"P98164","fasta_url":"https://rest.uniprot.org/uniprotkb/P98164.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P98164/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P98164"}},"corpus_meta":[{"pmid":"6337231","id":"PMC_6337231","title":"Immunocytochemical localization of the Heymann nephritis antigen (GP330) in glomerular epithelial cells of normal Lewis rats.","date":"1983","source":"The Journal of experimental 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The time has come to tailor DBS targets.","date":"2010","source":"Expert review of neurotherapeutics","url":"https://pubmed.ncbi.nlm.nih.gov/21384698","citation_count":116,"is_preprint":false},{"pmid":"10523665","id":"PMC_10523665","title":"Dependence of Dbl and Dbs transformation on MEK and NF-kappaB activation.","date":"1999","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/10523665","citation_count":100,"is_preprint":false},{"pmid":"2408041","id":"PMC_2408041","title":"Molecular cloning of a cDNA encoding a major pathogenic domain of the Heymann nephritis antigen gp330.","date":"1990","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/2408041","citation_count":93,"is_preprint":false},{"pmid":"22934024","id":"PMC_22934024","title":"LRP-1 and LRP-2 receptors function in the membrane neuron. 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it is synthesized by glomerular epithelial cells and traffics through ER, Golgi, and multivesicular bodies to coated pits.\",\n      \"method\": \"Immunoprecipitation of radiolabeled kidney extracts, indirect immunofluorescence, immunoperoxidase electron microscopy on cryostat sections\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (immunoprecipitation + immunofluorescence + immunoelectron microscopy), foundational paper with 500 citations\",\n      \"pmids\": [\"6337231\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1990,\n      \"finding\": \"A C-terminal domain of gp330 (encoded by clone 14, ~319 amino acids) contains a major pathogenic epitope responsible for antibody binding and subepithelial immune deposit formation in Heymann nephritis; antibodies against this domain induce both passive and active Heymann nephritis in rats.\",\n      \"method\": \"cDNA library screening with eluted glomerular IgG, expression of fusion protein, passive and active immunization of rats, immunoblotting\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vivo disease model with molecular domain mapping, replicated in both passive and active models\",\n      \"pmids\": [\"2408041\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"LRP2/gp330 functions as a receptor for plasminogen; binding is saturable and specifically inhibitable, and is not exclusively through lysine-binding sites, indicating additional interaction sites.\",\n      \"method\": \"Western blot ligand binding, ELISA saturation and competition assays, cDNA library screening with antibody to purified serum protein\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro binding assays with purified components, multiple independent approaches\",\n      \"pmids\": [\"1645711\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"LRP2/gp330 acts as a Ca2+-binding endocytic receptor in renal proximal tubule; it binds the 40-kDa RAP protein in a Ca2+-dependent, heparin-sensitive manner, and mediates endocytosis of RAP into lysosomes as demonstrated by in vivo tubular microperfusion.\",\n      \"method\": \"Ligand blotting, 45Ca2+ blotting, light and electron microscopic autoradiography, in vivo microperfusion of rat proximal tubules with 125I-labeled ligand\",\n      \"journal\": \"The journal of histochemistry and cytochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct endocytosis demonstrated in vivo with multiple methods including microperfusion and subcellular tracking\",\n      \"pmids\": [\"1382088\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"LRP2/gp330 shares multiple ligand-binding specificities with LRP1, binding plasminogen activator-inhibitor complexes, lactoferrin, and apolipoprotein E-enriched beta-VLDL; all ligand binding to both receptors is inhibited by the 39-kDa RAP protein, identifying RAP as a universal regulator of ligand binding. Cross-competition shows at least three distinct but overlapping binding sites on LRP.\",\n      \"method\": \"Nitrocellulose ligand blotting with purified rat kidney gp330, cell-based cholesteryl ester synthesis assay, cross-competition experiments in cultured human fibroblasts\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple ligands tested with multiple orthogonal methods, replicated across cell and membrane systems; 426 citations\",\n      \"pmids\": [\"1464627\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"LRP2/gp330 forms a stable heterodimeric complex with a 44-kDa protein (RAP/alpha2-MRAP) in the rat kidney, constituting the Heymann nephritis antigenic complex (HNAC); the complex is stable to detergent extraction, and RAP shares immunological identity with the C14 fusion protein.\",\n      \"method\": \"Immunoprecipitation with specific antibodies, immunoblotting, long-term centrifugation stability tests\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal immunoprecipitation and immunoblotting confirming stable complex; 150 citations\",\n      \"pmids\": [\"1495959\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"Once plasminogen is bound to gp330, urokinase can convert it to plasmin at an accelerated rate; plasmin remains bound to gp330 in an active state and is protected from inactivation by alpha2-antiplasmin while bound.\",\n      \"method\": \"In vitro enzyme kinetics (Km/Vmax analysis), ELISA binding assays, chromogenic substrate cleavage assays\",\n      \"journal\": \"Archives of biochemistry and biophysics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted enzymatic assay with kinetic parameters and inhibitor protection data\",\n      \"pmids\": [\"1280065\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"LRP2/gp330 and its associated 44-kDa protein (RAP) assemble in the endoplasmic reticulum; the complex forms in two steps: first a Ca2+-dependent 19.3S heterodimer within 30 min of synthesis, then a larger 38.6S heterooligomer >60 min post-synthesis, both steps preceding Golgi processing (Endo H-resistant glycosylation).\",\n      \"method\": \"Pulse-chase radiolabeling of rat kidney tubule fragments, immunoprecipitation with specific antibodies, sucrose velocity gradient centrifugation, endoglycosidase H digestion\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — pulse-chase biosynthesis with biochemical fractionation and multiple controls; establishes temporal and spatial assembly in ER\",\n      \"pmids\": [\"8322889\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"LRP2/gp330 mediates endocytosis of pro-urokinase, PAI-1, and urokinase:PAI-1 complexes in type II pneumocytes; RAP completely inhibits this internalization and degradation, and anti-gp330 antibodies inhibit 30–50%, confirming gp330-dependent clearance of plasminogen activation system components.\",\n      \"method\": \"Radiolabeled ligand internalization and degradation assays in cultured type II pneumocytes, antibody inhibition, RAP competition\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct cellular endocytosis assay with specific inhibitors and antibody blockade, multiple ligands tested\",\n      \"pmids\": [\"7673355\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"LRP2/gp330 binds a distinct 45-kDa protein (RAP) as a separate ligand from plasminogen; gp330 has two separate and non-competing binding sites for plasminogen and the 45-kDa RAP, demonstrating multi-site ligand architecture.\",\n      \"method\": \"ELISA binding assays, competitive inhibition experiments, cDNA library screening, sequence analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — solid-phase binding with competition assays, but single lab\",\n      \"pmids\": [\"7681839\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Megalin/gp330 localizes primarily to apical coated pits, small and large endocytic vacuoles, and dense apical tubules in proximal tubule cells, with segmental variation; it is also found in lysosomes (especially segments 1 and 2) and brush border microvilli, consistent with a protein scavenger receptor role cycling through the early endocytic pathway.\",\n      \"method\": \"Light and electron microscope immunocytochemistry on cryosections and Lowicryl sections from rat, rabbit, and human kidney\",\n      \"journal\": \"European journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multi-species immunoelectron microscopy with quantitative morphometry; detailed subcellular localization linked to function\",\n      \"pmids\": [\"7656901\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1989,\n      \"finding\": \"Microtubule integrity is required for polarized apical localization of LRP2/gp330 in proximal tubule cells; colchicine treatment disperses gp330-containing vesicles throughout the cytoplasm, though gp330 is not inserted into the basolateral membrane, indicating microtubules drive apical accumulation but other factors govern membrane fusion.\",\n      \"method\": \"In vivo colchicine treatment of rats, immunocytochemistry (immunofluorescence and immunoperoxidase), intravenous antibody injection to test basolateral access\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct in vivo perturbation with functional consequence (abrogated apical targeting) confirmed by antibody accessibility test\",\n      \"pmids\": [\"2669509\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Microtubule disruption by colchicine blocks apical endocytosis, impairs endocytic invagination formation, disrupts membrane recycling (dense apical tubules), and redistributes gp330 from the apical endocytic apparatus to dispersed cytoplasmic vesicles, without altering other brush border markers.\",\n      \"method\": \"In vivo colchicine treatment, electron microscopy, morphometry, immunocytochemistry, functional peroxidase endocytosis assay\",\n      \"journal\": \"European journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — functional endocytosis assay combined with morphometry and immunoelectron microscopy, confirms role of microtubules in gp330 trafficking\",\n      \"pmids\": [\"7543847\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Complete primary structure of human gp330/LRP2 was determined: 4655 amino acids, single transmembrane domain, 36 LDLR ligand-binding repeats in four domains, 16 EGF-like repeats, two FXNPXY internalization signals in the cytoplasmic tail, and multiple signaling motifs (SH2, SH3, PKC, CKII sites) suggesting potential intracellular signaling capacity.\",\n      \"method\": \"cDNA cloning, RT-PCR, sequence analysis of human parathyroid, kidney, placenta, epididymis, and lung\",\n      \"journal\": \"European journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — complete molecular characterization establishing domain architecture; foundational structural paper\",\n      \"pmids\": [\"8706697\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Megalin/LRP2 knockout mice exhibit holoprosencephaly, loss of olfactory bulbs, forebrain fusion, and perinatal death from respiratory insufficiency, demonstrating that megalin-mediated endocytic uptake (possibly of cholesterol-carrying lipoproteins) in neuroepithelium is essential for forebrain development.\",\n      \"method\": \"Knockout mouse generation, pathological analysis of brain and epithelial tissues, phenotypic characterization\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined developmental phenotype; 427 citations, foundational loss-of-function study\",\n      \"pmids\": [\"8710893\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Antibodies that cause passive Heymann nephritis inhibit the binding and internalization of apolipoprotein E-enriched beta-VLDL by megalin/LRP2 in podocytes, causing accumulation of apo E and apo B within subepithelial immune deposits; constitutive lipoprotein uptake via megalin occurs through clathrin-coated pits and multivesicular bodies in normal podocytes.\",\n      \"method\": \"Immunoelectron microscopy, immunofluorescence, in vitro binding and internalization assays with antibodies eluted from nephritic glomeruli\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct in vivo and in vitro demonstration of functional inhibition of receptor-mediated endocytosis by pathogenic antibodies\",\n      \"pmids\": [\"9410908\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Megalin/gp330 binds thyroglobulin (Tg) with high affinity (Kd ~9.2 nM) in a Ca2+-dependent manner; binding is inhibited by other megalin ligands (lactoferrin, lipoprotein lipase, apolipoprotein J) and by RAP, indicating a shared binding site and suggesting megalin mediates Tg endocytosis in thyroid cells.\",\n      \"method\": \"Solid-phase binding assays with purified rat megalin and 125I-labeled Tg, EDTA/heparin release, SDS-PAGE, immunoblotting\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct binding with purified proteins, Kd determination, competition assays; replicated in thyroid cell line\",\n      \"pmids\": [\"9492085\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Megalin/gp330 mediates endocytosis of thyroglobulin in Fisher rat thyroid (FRTL-5) cells; chemical cross-linking and immunoprecipitation confirmed Tg binding to surface megalin, and cell internalization assays showed RAP and anti-megalin antibody inhibited Tg uptake by ~60–80%, demonstrating megalin-dependent endocytosis.\",\n      \"method\": \"Chemical cross-linking with immunoprecipitation, 125I-Tg binding at 4°C followed by heparin release, ELISA quantification of internalized Tg at 37°C\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods in intact cells demonstrating receptor-mediated endocytosis of a physiologic ligand\",\n      \"pmids\": [\"10212279\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Megalin/gp330 mediates transcytosis of intact thyroglobulin from the apical to basolateral side of thyroid cells; blocking megalin with RAP or anti-megalin antibody redirects Tg to lysosomal degradation (increasing T3 release), while megalin-mediated transcytosis diverts Tg from proteolysis, thus regulating thyroid hormone release.\",\n      \"method\": \"Polarized FRTL-5 cells on permeable filters in dual-chamber devices, 125I-Tg transcytosis assays, RAP and antibody competition, in vivo goiter model with aminotriazole\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — polarized cell transcytosis assay with specific inhibitors plus in vivo validation in goiter model; defines novel function\",\n      \"pmids\": [\"10702280\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Megalin/gp330 binds and mediates cellular uptake and degradation of lipoprotein(a) in vitro; purified megalin on a sensor chip binds Lp(a) in a Ca2+-dependent manner, and megalin-expressing yolk sac cells show 2-fold higher uptake and degradation of Lp(a) versus megalin-null controls, an effect abolished by RAP.\",\n      \"method\": \"Surface plasmon resonance with purified megalin, fluorescent DiI-Lp(a) uptake imaging, 125I-Lp(a) internalization/degradation assays comparing megalin-expressing vs. LRP/megalin double-knockout cell lines\",\n      \"journal\": \"Arteriosclerosis, thrombosis, and vascular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted binding with purified receptor + cell-based uptake with genetic knockout controls\",\n      \"pmids\": [\"10073957\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Megalin/LRP2 expression in the neuroepithelium (not the yolk sac) is required for forebrain development; megalin deficiency leads to increased BMP4 expression and signaling in the dorsal neuroepithelium and consequent loss of SHH expression in the ventral forebrain, resulting in loss of oligodendroglial and interneuronal cell populations; megalin mediates endocytic uptake and degradation of BMP4, acting as a BMP4 clearance receptor.\",\n      \"method\": \"Conditional and complete megalin knockout mice, in situ hybridization for BMP4 and SHH, immunohistochemistry, cell population analysis in forebrain\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO with defined pathway (BMP4/SHH epistasis) and cellular phenotype; multiple genetic models tested\",\n      \"pmids\": [\"15623804\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Megalin/LRP2 and its co-receptor cubilin are conserved in the zebrafish larval pronephros; knockdown of megalin/LRP2 eliminates Rab4-positive endosomes in proximal pronephric duct epithelium and abrogates apical endocytosis; knockdown of the megalin adaptor Disabled-2 (Dab2) also blocks renal clearance, establishing that renal tubular endocytosis is a ligand-induced process requiring megalin activity and its intracellular adaptors.\",\n      \"method\": \"Morpholino knockdown in zebrafish, fluorescent tracer clearance assays, immunofluorescence for Rab4 endosomes, genetic epistasis with Dab2 knockdown\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — morpholino KD with functional endocytosis readout and epistasis with adaptor protein; conserved pathway established\",\n      \"pmids\": [\"16638803\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"MESD chaperone is required for proper folding of the beta-propeller/EGF domain common to LRP family members and for apical localization of LRP2/megalin in the visceral endoderm; loss of MESD results in mislocalization of megalin and impaired endocytic function in visceral endoderm.\",\n      \"method\": \"Targeted Mesd knockout mice, immunofluorescence localization of LRP2, in vitro maturation assays for beta-propeller/EGF domains\",\n      \"journal\": \"Developmental dynamics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO with localization readout, but mechanistic link to LRP2 misfolding relies partly on in vitro data\",\n      \"pmids\": [\"21337463\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"LRP2/megalin functions as an auxiliary SHH receptor in the rostral diencephalon ventral midline (RDVM) during forebrain development; LRP2 sequesters SHH at the apical surface and controls internalization and cellular trafficking of SHH/patched-1 complexes; LRP2 loss causes failure to respond to SHH despite intact patched-1 and smoothened expression, while LRP2 overexpression increases SHH signaling capacity.\",\n      \"method\": \"LRP2 knockout mice, cephalic explant assays, overexpression of LRP2 variants in cells, SHH binding assays, epistasis analysis with patched-1 and smoothened\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function and gain-of-function in both in vivo and ex vivo systems with defined pathway position\",\n      \"pmids\": [\"22340494\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"LRP2 acts as an endocytic clearance receptor for SHH in the developing retina, preventing spread of SHH activity from central retina into the retinal margin; loss of LRP2 increases sensitivity of retinal margin progenitors to SHH, causing expansion of the progenitor pool and hyperproliferation.\",\n      \"method\": \"Conditional LRP2 knockout mice (retina-specific), immunohistochemistry, BrdU incorporation assays for proliferation, SHH pathway activity measurements\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO with defined cellular and molecular phenotype demonstrating context-dependent receptor function\",\n      \"pmids\": [\"26439398\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"LRP2 regulates megalin-mediated hypothalamic clusterin (ApoJ) signaling: LRP2 acts as the primary receptor mediating clusterin endocytosis in hypothalamic neurons; clusterin binding to LRP2 enhances association of LRP2 with the long-form leptin receptor, potentiating leptin-induced STAT3 activation and anorexigenic signaling.\",\n      \"method\": \"Central administration of clusterin in mice, co-immunoprecipitation of LRP2 with leptin receptor in neurons, siRNA knockdown of LRP2 and leptin receptor, STAT3 phosphorylation assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP showing receptor complex + in vivo functional assay + KD phenotype; multiple complementary approaches\",\n      \"pmids\": [\"23673647\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Clusterin/ApoJ enhances leptin receptor endocytosis and STAT3 signaling through LRP2; LRP2-mediated endocytosis of the clusterin-leptin complex is required for full anorexigenic leptin action; inhibition of hypothalamic LRP2 or endocytosis blocks clusterin-enhanced leptin signaling.\",\n      \"method\": \"Co-administration experiments in cultured neurons, endocytosis inhibition assays, LRP2 siRNA knockdown, STAT3 activation measurements, receptor binding assays\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic dissection of receptor-mediated endocytosis in signaling with genetic knockdown and functional pathway readout\",\n      \"pmids\": [\"24825475\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"TGF-β1 downregulates megalin/LRP2 expression through the SMAD2/3 pathway; SMAD2/3 transcription factors bind to two SMAD-binding elements (SBEs) in the megalin promoter at positions -57 and -605 and repress transcription; histone deacetylase inhibition (TSA) counteracts TGF-β1-mediated repression.\",\n      \"method\": \"Site-directed mutagenesis of SBEs, chromatin immunoprecipitation (ChIP), promoter reporter assays, siRNA knockdown, TGF-βRI inhibitor experiments in kidney and gallbladder epithelial cell lines\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — ChIP + mutagenesis + pharmacological inhibition identifying specific transcriptional repressor mechanism\",\n      \"pmids\": [\"31120873\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"LRP2 is required for neural tube closure through two mechanisms: (1) its intracellular domain functions as a hub interacting with Shroom3 and Gipc1 adaptors to orchestrate endocytic membrane removal for apical constriction; (2) LRP2 regulates proper localization of the PCP protein Vangl2, essential for planar cell polarity during neurulation; these functions are conserved between mouse and Xenopus.\",\n      \"method\": \"Lrp2 loss-of-function in mouse and Xenopus, morphological analysis of neural tube closure, co-immunoprecipitation of LRP2 with Shroom3 and Gipc1, immunofluorescence for Vangl2 and apical constriction markers\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — cross-species genetic KO with Co-IP of novel intracellular interactors and defined cellular phenotypes (apical constriction, PCP)\",\n      \"pmids\": [\"33500317\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Mettl3-mediated m6A modification of Lrp2 mRNA enhances its stability and translation efficiency through the m6A reader protein Ythdc2, promoting neurogenesis; depletion of Mettl3 reduces m6A abundance and Lrp2 expression; overexpression of Lrp2 rescues neurogenesis defects caused by Mettl3 depletion.\",\n      \"method\": \"Mettl3/Mettl14 knockout in neural stem cells, Lrp2 overexpression rescue experiments, m6A sequencing, m6A reader (Ythdc2) interaction studies, behavioral analysis\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — identifies specific writer (Mettl3), reader (Ythdc2), and substrate (Lrp2 mRNA) with rescue validation, single lab\",\n      \"pmids\": [\"35716070\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Cryo-EM structures of LRP2 isolated from mouse kidney at extracellular and endosomal pH reveal that LRP2 functions as a homodimer; at cell-surface pH, LRP2 adopts a conformation for ligand binding; at endosomal pH, conformational transformation mediates ligand shedding; pH-sensitive sites are located at both homodimer and intra-protomer interfaces; a subset of human disease-associated missense variants impairs homodimer assembly.\",\n      \"method\": \"High-resolution cryo-electron microscopy of native LRP2 isolated from mouse kidney, structural analysis at two pH conditions, correlation of structural findings with human disease missense variants\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — atomic-resolution cryo-EM structures with functional interpretation at two pH states, directly validated against disease variants\",\n      \"pmids\": [\"36750096\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"GSK3 phosphorylates the cytoplasmic domain of megalin/LRP2, and megalin surface availability is regulated by multiple mechanisms: ectodomain shedding at the cell surface, subsequent intramembrane proteolysis by gamma-secretase, and exosome secretion.\",\n      \"method\": \"Review citing biochemical data on phosphorylation, shedding, and gamma-secretase cleavage from primary literature; described in a review article\",\n      \"journal\": \"Biological research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3–4 — described as established in a review article without original experimental data presented; mechanism referenced from prior work\",\n      \"pmids\": [\"21720686\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"miR-146a directly represses LRP2 translation in SH-SY5Y neuronal cells; overexpression of miR-146a decreases LRP2 protein levels, reducing Akt activation and increasing caspase-3-dependent apoptosis.\",\n      \"method\": \"miR-146a overexpression in SH-SY5Y cells, Western blot for LRP2 and downstream signaling (Akt, caspase-3), predicted target site analysis\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — overexpression with downstream pathway readout, single lab; direct binding to LRP2 3'UTR not rigorously validated in this paper\",\n      \"pmids\": [\"27241555\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"LRP2 is required for cardiomyocyte proliferation and differentiation; siRNA knockdown in human iPSC-derived cardiomyocytes and RNAi in developing Drosophila and zebrafish hearts demonstrates that LRP2 loss reduces cardiomyocyte proliferation, consistent with hypoplastic heart defects.\",\n      \"method\": \"siRNA knockdown in hiPSC-CMs, RNAi in Drosophila and zebrafish hearts, proliferation assays, cross-species functional platform\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multi-species knockdown with defined cellular phenotype (proliferation), but mechanism not fully elucidated\",\n      \"pmids\": [\"33006316\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"LRP2/megalin is a giant homodimeric endocytic receptor (whose pH-dependent conformational change between cell-surface and endosomal states was revealed by cryo-EM) that localizes to clathrin-coated pits on the apical surface of epithelial and neuroepithelial cells, where it binds a broad repertoire of ligands (lipoproteins, plasminogen, thyroglobulin, BMP4, SHH, clusterin/ApoJ, RAP, and others) through multiple Ca2+-dependent extracellular binding domains regulated by RAP; after internalization—directed by FXNPXY motifs and intracellular adaptors including Dab2, Shroom3, and Gipc1—ligands are routed to lysosomes for degradation or transcytosed intact; surface availability is modulated by GSK3 phosphorylation of its cytoplasmic tail, ectodomain shedding, gamma-secretase cleavage, and transcriptional repression via TGF-β1/SMAD2/3; in development, LRP2 acts context-dependently as either a morphogen-activating co-receptor (SHH in the forebrain) or a clearance receptor (BMP4 in neuroepithelium; SHH in retinal margin), and loss of LRP2 causes holoprosencephaly, neural tube defects, and renal Fanconi syndrome in mice and Donnai-Barrow syndrome in humans.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"LRP2 (megalin) is a giant multi-ligand endocytic receptor of the LDL receptor family that functions as a central mediator of apical endocytosis, transcytosis, and morphogen signaling in polarized epithelial and neuroepithelial cells. The receptor contains 36 complement-type ligand-binding repeats organized into four extracellular domains, a single transmembrane segment, and a cytoplasmic tail with two FXNPXY internalization motifs; it operates as a pH-sensitive homodimer that binds ligands at cell-surface pH and releases them upon endosomal acidification [PMID:36750096, PMID:8706697]. Through Ca²⁺-dependent binding regulated by the chaperone RAP, LRP2 internalizes a broad ligand repertoire—including lipoproteins, thyroglobulin, plasminogen, BMP4, SHH, and clusterin—routing them to lysosomes for degradation or mediating transcytosis, and it acts context-dependently as either a morphogen clearance receptor (BMP4 in dorsal neuroepithelium, SHH in retinal margin) or a signaling co-receptor (SHH in forebrain, clusterin/leptin receptor in hypothalamus) [PMID:15623804, PMID:22340494, PMID:26439398, PMID:23673647, PMID:10702280]. Loss-of-function mutations cause holoprosencephaly and neural tube defects in mice, and Donnai–Barrow syndrome in humans, while its intracellular domain coordinates apical constriction during neurulation through interactions with Shroom3 and Gipc1 adaptors [PMID:8710893, PMID:33500317, PMID:36750096].\",\n  \"teleology\": [\n    {\n      \"year\": 1983,\n      \"claim\": \"Establishing LRP2/gp330 as a membrane glycoprotein of clathrin-coated pits in kidney epithelial cells resolved the identity of the Heymann nephritis antigen and placed it in the endocytic pathway.\",\n      \"evidence\": \"Immunoprecipitation, immunofluorescence, and immunoelectron microscopy on rat kidney sections\",\n      \"pmids\": [\"6337231\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Ligand identity unknown\", \"Molecular structure undetermined\", \"Function beyond immune target not established\"]\n    },\n    {\n      \"year\": 1991,\n      \"claim\": \"Identification of plasminogen, RAP, and lipoprotein ligands revealed that LRP2 is a multi-ligand endocytic receptor with distinct but overlapping binding sites, regulated universally by the 39-kDa RAP chaperone.\",\n      \"evidence\": \"Ligand blotting, ELISA competition, and cross-competition assays with purified gp330 and multiple ligands; in vivo microperfusion demonstrating RAP endocytosis into lysosomes\",\n      \"pmids\": [\"1645711\", \"1464627\", \"1382088\", \"1280065\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full ligand-binding domain mapping not achieved\", \"Endocytic trafficking itinerary beyond lysosomes not resolved\", \"RAP mechanism of inhibition not structurally defined\"]\n    },\n    {\n      \"year\": 1993,\n      \"claim\": \"Demonstrating that LRP2 and RAP assemble as a heterodimeric complex in the ER through Ca²⁺-dependent steps established that RAP functions as an intracellular chaperone, not merely an extracellular competitor.\",\n      \"evidence\": \"Pulse-chase radiolabeling, sucrose gradient sedimentation, and endoglycosidase H digestion in rat kidney tubule fragments\",\n      \"pmids\": [\"8322889\", \"1495959\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether RAP dissociates before or upon exit from ER/Golgi not resolved\", \"Structural basis of Ca²⁺-dependent assembly unknown\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Detailed subcellular mapping by immunoelectron microscopy across species confirmed LRP2 cycles through apical coated pits, endocytic vacuoles, dense apical tubules, and lysosomes, and that microtubule integrity is required for its apical polarization and endocytic function.\",\n      \"evidence\": \"Multi-species immunoelectron microscopy with morphometry; in vivo colchicine perturbation with functional peroxidase endocytosis assay\",\n      \"pmids\": [\"7656901\", \"7543847\", \"2669509\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Motor proteins mediating microtubule-dependent transport not identified\", \"Sorting signals for apical targeting beyond FXNPXY motifs not mapped\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Cloning of the complete human LRP2 sequence revealed its domain architecture (36 ligand-binding repeats, 16 EGF repeats, two FXNPXY motifs, signaling motifs), and LRP2 knockout mice demonstrated that the receptor is essential for forebrain development, linking endocytic receptor function to morphogenesis.\",\n      \"evidence\": \"Full-length cDNA cloning from human tissues; LRP2 knockout mouse with holoprosencephaly phenotype\",\n      \"pmids\": [\"8706697\", \"8710893\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which ligand(s) mediate the forebrain phenotype not determined\", \"Contribution of individual binding domains not dissected\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Discovery that LRP2 mediates both endocytosis and apical-to-basolateral transcytosis of thyroglobulin in thyroid cells, with transcytosis diverting Tg from lysosomal degradation, established a non-degradative trafficking function that regulates thyroid hormone release.\",\n      \"evidence\": \"Polarized FRTL-5 transcytosis assays with RAP and antibody inhibition; chemical cross-linking confirming surface Tg–megalin complexes\",\n      \"pmids\": [\"10212279\", \"10702280\", \"9492085\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Sorting signals distinguishing transcytotic from degradative routing not identified\", \"In vivo thyroid phenotype in megalin-deficient animals not reported\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Conditional knockout studies resolved the forebrain phenotype mechanism: LRP2 acts as a BMP4 clearance receptor in the dorsal neuroepithelium; its loss elevates BMP4 signaling, which suppresses ventral SHH expression, causing holoprosencephaly.\",\n      \"evidence\": \"Conditional and complete LRP2 knockout mice with in situ hybridization for BMP4 and SHH, cell population analysis\",\n      \"pmids\": [\"15623804\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct BMP4 binding affinity and stoichiometry not measured\", \"Whether other BMP family members are also cleared not tested\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"A dual role for LRP2 in morphogen signaling was established: it acts as a SHH co-receptor in the forebrain (enhancing SHH/Patched-1 signaling) but as a SHH clearance receptor in the retinal margin, demonstrating context-dependent function.\",\n      \"evidence\": \"LRP2 knockout mice, cephalic explant assays, overexpression/loss-of-function with SHH pathway readouts; conditional retinal KO with BrdU proliferation assays\",\n      \"pmids\": [\"22340494\", \"26439398\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural determinants of co-receptor vs. clearance mode not identified\", \"Whether LRP2 directly binds SHH or acts via Patched-1 complex not fully resolved\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"LRP2 was shown to function beyond classical endocytosis as a signaling scaffold: clusterin binding to LRP2 promotes its association with the leptin receptor in hypothalamic neurons, potentiating STAT3 activation and anorexigenic signaling.\",\n      \"evidence\": \"Co-immunoprecipitation of LRP2 with leptin receptor, siRNA knockdown, in vivo central clusterin administration with STAT3 readout\",\n      \"pmids\": [\"23673647\", \"24825475\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether LRP2-leptin receptor interaction is direct or mediated by clusterin bridging not resolved\", \"Downstream intracellular trafficking route of the ternary complex not characterized\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identification of Shroom3 and Gipc1 as intracellular binding partners of LRP2's cytoplasmic domain established a non-endocytic structural role: LRP2 orchestrates apical constriction and planar cell polarity (Vangl2 localization) required for neural tube closure.\",\n      \"evidence\": \"LRP2 loss-of-function in mouse and Xenopus, co-immunoprecipitation with Shroom3/Gipc1, immunofluorescence for Vangl2 and apical markers\",\n      \"pmids\": [\"33500317\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Shroom3/Gipc1 binding is simultaneous or competitive not resolved\", \"Which cytoplasmic motifs mediate Shroom3 vs. Gipc1 interaction not mapped\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Cryo-EM structures at two pH states revealed that LRP2 functions as a homodimer with a pH-dependent conformational switch: an open ligand-binding state at neutral pH and a closed ligand-release state at endosomal pH, with disease-associated mutations disrupting dimerization.\",\n      \"evidence\": \"High-resolution cryo-EM of native LRP2 from mouse kidney at pH 7.4 and pH 5.0; mapping of human Donnai–Barrow syndrome missense variants onto structure\",\n      \"pmids\": [\"36750096\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Ligand-bound structures not yet solved\", \"How individual domains contribute to multi-ligand binding not structurally resolved\", \"Dynamics of pH transition in intact endosomes not captured\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis for multi-ligand selectivity across LRP2's four binding domains, the sorting determinants that route LRP2-ligand complexes to transcytosis versus degradation, and the mechanism by which the same receptor switches between morphogen co-receptor and clearance receptor roles in different tissues.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No ligand-bound cryo-EM structure\", \"Sorting signals for transcytotic vs. degradative pathway not mapped\", \"Tissue-specific co-factors determining co-receptor vs. clearance function unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0038024\", \"supporting_discovery_ids\": [3, 4, 8, 16, 17, 19, 20, 23, 24]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [4, 15, 19]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [25, 26, 28]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 10, 13, 30]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [10, 12, 21]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [0, 10, 12]},\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [3, 10]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [7]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 3, 8, 10, 12, 17, 21]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [14, 20, 23, 24, 28]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [23, 25, 26]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [15, 16, 17, 18, 19]}\n    ],\n    \"complexes\": [\n      \"LRP2-RAP chaperone complex\",\n      \"LRP2-cubilin receptor complex\"\n    ],\n    \"partners\": [\n      \"LRPAP1\",\n      \"CUBN\",\n      \"SHH\",\n      \"BMP4\",\n      \"SHROOM3\",\n      \"GIPC1\",\n      \"DAB2\",\n      \"CLU\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}