{"gene":"SIGLEC15","run_date":"2026-06-10T07:46:32","timeline":{"discoveries":[{"year":2007,"finding":"Siglec-15 is a type-I transmembrane protein with two Ig-like extracellular domains, a transmembrane domain containing a lysine residue, and a short cytoplasmic tail. Its extracellular domain preferentially recognizes the Neu5Acα2-6GalNAcα- (sialyl-Tn) structure. Siglec-15 associates with activating adaptor proteins DAP12 and DAP10 via its transmembrane lysine residue, implying activating signaling potential.","method":"Molecular characterization, glycan-binding assays, co-immunoprecipitation","journal":"Glycobiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal biochemical binding assays and co-IP for DAP12/DAP10 association; foundational characterization paper replicated by subsequent studies","pmids":["17483134"],"is_preprint":false},{"year":2012,"finding":"Siglec-15 recognizes tumor-associated sialyl-Tn (sTn) antigen on cancer cells and signals through DAP12 via its transmembrane Lys274 to activate Syk, leading to enhanced TGF-β secretion from monocytes/macrophages. Substitution of Lys274 to Ala disrupts Siglec-15/DAP12 interaction and abolishes enhanced TGF-β production. Syk inhibitor treatment also attenuates TGF-β secretion.","method":"Co-culture model (THP-1 and H157 cells), site-directed mutagenesis (K274A), Syk inhibitor treatment, TGF-β ELISA","journal":"Glycobiology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis of key residue combined with pharmacological inhibition and co-culture functional assay in a single focused study","pmids":["23035012"],"is_preprint":false},{"year":2012,"finding":"Siglec-15 is induced as an NFATc1 target gene during osteoclast differentiation and links RANK-RANKL-NFATc1 signaling to DAP12. Both sialylated glycan recognition by the V-set domain and association with DAP12 via Lys272 are required for functional osteoclast formation. Knockdown of Siglec-15 reduces multinucleated cell development, disrupts actin-ring structures, and impairs bone resorption. Siglec-15 forms complexes with Syk through DAP12 in response to vitronectin. Chimeric molecules with K272A mutation fused to the DAP12 cytoplasmic region significantly restored bone resorption, confirming that the transmembrane Lys is dispensable if DAP12 signaling is provided directly.","method":"siRNA knockdown, retroviral transduction of chimeric constructs, co-immunoprecipitation (Siglec-15/Syk via DAP12), actin-ring imaging, bone resorption assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis, chimeric rescue constructs, co-IP, and functional bone resorption assays in one study; replicated in subsequent independent work","pmids":["22451653"],"is_preprint":false},{"year":2013,"finding":"Siglec-15 modulates RANKL-induced osteoclastogenesis through DAP12-dependent activation of PI3K/Akt and Erk pathways. Siglec-15-deficient mice exhibit mild osteopetrosis with impaired osteoclast development. RANKL-induced PI3K/Akt and Erk activation is impaired in Siglec-15-deficient cells. OSCAR/FcRγ signaling (alternative ITAM pathway) can compensate for Siglec-15 deficiency in the primary spongiosa via type II collagen ligands.","method":"Siglec-15 knockout mice, retroviral transduction with wild-type or mutant Siglec-15, signaling pathway analysis (PI3K/Akt, Erk), bone phenotype analysis, rescue with OSCAR/FcRγ ligands","journal":"Journal of bone and mineral research","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO mouse model with multiple orthogonal readouts (signaling, histology, in vitro osteoclastogenesis), replicated across labs","pmids":["23677868"],"is_preprint":false},{"year":2014,"finding":"Siglec-15 is localized to the plasma membrane of osteoclasts where anti-Siglec-15 monoclonal antibodies inhibit osteoclast differentiation in vitro and increase bone mineral density in mice. At the molecular level, Siglec-15 interacts with DAP12 and induces Akt activation when clustered on the osteoclast surface. Monoclonal antibodies induce rapid internalization, lysosomal targeting, and degradation of Siglec-15 by inducing receptor dimerization.","method":"Plasma membrane localization assay, mAb treatment in vitro and in vivo, bone density measurement (DXA), co-immunoprecipitation (Siglec-15/DAP12), Akt phosphorylation assay, receptor internalization and lysosomal degradation assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (co-IP, signaling assay, in vivo bone density, internalization tracking) in a single focused study","pmids":["24446437"],"is_preprint":false},{"year":2014,"finding":"Siglec-15 deficiency protects mice from estrogen deficiency-induced (ovariectomy) bone loss. Siglec-15-deficient osteoclasts are small, fail to spread on bone surface, and show impaired cytoskeletal organization. Siglec-15 is also required for TNF-α-induced osteoclastogenesis in vitro. The Siglec-15/DAP12 pathway is specifically important for cytoskeletal organization, while OSCAR/FcRγ signaling can rescue multinucleation but not cytoskeletal organization in Siglec-15-deficient cells.","method":"Siglec-15 knockout mice with ovariectomy model, TRAP staining, in vitro TNF-α-induced osteoclastogenesis, comparison of DAP12 vs OSCAR/FcRγ pathway rescue","journal":"Bone","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO in disease model with multiple phenotypic and mechanistic readouts; pathway dissection via alternative ITAM adaptor rescue","pmids":["25460183"],"is_preprint":false},{"year":2019,"finding":"Siglec-15 is broadly upregulated on human cancer cells and tumor-infiltrating myeloid cells, suppresses antigen-specific T cell responses in vitro and in vivo, and its expression is mutually exclusive with B7-H1 (PD-L1). Siglec-15 expression is induced by macrophage colony-stimulating factor (M-CSF) and downregulated by IFN-γ. Genetic ablation or antibody blockade of Siglec-15 amplifies anti-tumor immunity and inhibits tumor growth in mouse models. Siglec-15 was identified using a genome-scale T cell activity array.","method":"Genome-scale T cell activity array, genetic ablation (knockout mice), antibody blockade, in vitro T cell suppression assays, in vivo tumor models","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — genome-scale functional screen combined with genetic KO, antibody blockade, in vitro and in vivo functional assays; landmark paper","pmids":["30833750"],"is_preprint":false},{"year":2019,"finding":"A SIGLEC15 gene polymorphism associated with recurrent vulvovaginal candidiasis (RVVC) leads to an altered cytokine profile after PBMC stimulation with Candida and increases IL-1B and NLRP3 expression after Candida stimulation in HeLa cells. In vivo silencing of Siglec15 at the vaginal surface of mice led to increased fungal burden and an increase in polymorphonuclear leukocytes during Candida infection, indicating Siglec-15 plays a role in anti-fungal host defense.","method":"Genomic association study integrated with in vitro cytokine profiling (PBMC stimulation), in vivo Siglec15 silencing in mouse vaginal Candida infection model, flow cytometry","journal":"Science translational medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo knockdown with functional readouts combined with in vitro cytokine assays; single lab, immune function partially characterized","pmids":["31189718"],"is_preprint":false},{"year":2020,"finding":"N-glycosylation of Siglec-15 stabilizes it by decreasing lysosome-dependent degradation and promotes its transportation to the cell membrane. Using glycosidase and glycosylation inhibitors, Siglec-15 was shown to be completely N-glycosylated. Glucose uptake regulates N-glycosylation of Siglec-15.","method":"Glycosidase treatment, glycosylation inhibitors, immunofluorescence for subcellular localization, protein stability assays","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct biochemical manipulation (glycosidase, inhibitors) with localization and stability readouts; single lab, two orthogonal methods","pmids":["32921411"],"is_preprint":false},{"year":2020,"finding":"Siglec-15 is required for bone erosion specifically in osteoclasts in an arthritis model (K/BxN serum-transfer arthritis). Siglec-15-/- mice show significant reduction in bone erosion area and osteoclast numbers but comparable inflammation and cartilage destruction to wild-type mice, placing Siglec-15 specifically in pathological osteoclast-mediated bone resorption.","method":"Siglec-15 knockout mice, K/BxN serum-transfer arthritis model, histological analysis of bone erosion, cartilage destruction, and osteoclast numbers","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO in disease model with specific dissection of bone erosion vs inflammation phenotype; replicated across independent labs","pmids":["33020147"],"is_preprint":false},{"year":2021,"finding":"Siglec-15 binds sialylated glycans other than sTn with higher avidity (based on glycan microarray), including α(2,3)- and α(2,6)-linked sialic acids. Using lung and breast cancer cell lines, no evidence was found for sTn recognition or enhanced TGF-β secretion following Siglec-15 co-culture with sTn-positive cells (negative result for sTn/TGF-β axis). However, antibody cross-linking of Siglec-15 activates the SYK/MAPK signaling pathway.","method":"Glycan microarray, cell line binding assays, glycan-modified cells, co-culture with sTn-positive tumor cells, TGF-β ELISA (negative), SYK/MAPK signaling (phospho-blot after mAb cross-linking)","journal":"Glycobiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — glycan microarray with multiple binding assays and signaling readouts; partially contradicts earlier TGF-β findings, reducing confidence in that specific mechanism","pmids":["32501471"],"is_preprint":false},{"year":2021,"finding":"Siglec-15 interacts with CD44, a transmembrane glycoprotein, in a sialic acid-dependent manner in hepatoma cells. CD44 is modified by α2,6-linked sialic acids on N-glycans; removal of sialic acids suppresses the Siglec-15/CD44 interaction. Siglec-15 promotes stability of CD44 by preventing its lysosomal-mediated degradation, thereby promoting hepatoma cell migration.","method":"Co-immunoprecipitation, neuraminidase treatment (sialic acid removal), lysosomal degradation assay, migration assay","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP with functional validation (lysosomal inhibition, sialic acid removal), single lab","pmids":["34328657"],"is_preprint":false},{"year":2021,"finding":"In pancreatic cancer, SIGLEC15 on tumor-associated macrophages interacts with α-2,3-linked sialic acids on PDAC tumor cells to stimulate SYK phosphorylation in TAMs, which promotes immunoregulatory cytokine and chemokine production. SYK inhibitor treatment abolished M2-like TAM phenotype promotion and immunosuppressive microenvironment in vivo.","method":"Co-culture of SIGLEC15+ TAMs with PDAC cells, SYK phosphorylation assay, SYK inhibitor treatment, in vivo subcutaneous tumor model, flow cytometry","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological inhibition (SYK inhibitor) plus in vivo validation, single lab","pmids":["35077803"],"is_preprint":false},{"year":2021,"finding":"Glycosylation of Siglec-15 at N172 (N173 in mouse) is required for its immunosuppressive function. Through mass spectrometry and site mutation analysis, N172 was identified as the primary glycosylation site. Siglec-15 N172Q (glycosylation-deficient mutant) reduced tumor growth in immunocompetent C57BL/6 mice but not in nude mice, indicating N-glycosylation is required for Siglec-15-mediated immune suppression.","method":"Mass spectrometry, site-directed mutagenesis (N172Q), xenograft models in immunocompetent vs. immunodeficient mice","journal":"American journal of cancer research","confidence":"Medium","confidence_rationale":"Tier 1-2 / Moderate — mutagenesis combined with in vivo immunocompetent vs. nude mouse comparison; single lab","pmids":["34094685"],"is_preprint":false},{"year":2021,"finding":"Neuraminidase (NA) influences host defense against Aspergillus fumigatus, and SIGLEC15 is upregulated in PBMCs stimulated with A. fumigatus. Silencing of SIGLEC15 decreases PBMC killing capacity of A. fumigatus, establishing a role for SIGLEC15 in anti-fungal defense.","method":"SIGLEC15 siRNA silencing in PBMCs, fungal killing assay, mouse model of pulmonary aspergillosis with oseltamivir treatment","journal":"Cell reports. Medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown with functional killing assay, multiple in vitro and in vivo readouts, single lab","pmids":["34095887"],"is_preprint":false},{"year":2022,"finding":"Siglec-15 regulates M2 macrophage polarization by interacting with Glut1 to upregulate glycolysis, and this glycolytic regulation modulates cGAS/STING signaling to drive M2 phenotype. Siglec-15 knockout abolished M2 marker expression and inhibited tumor growth in a subcutaneous mouse model. NOTE: This paper was subsequently retracted (PMID:37388523).","method":"Siglec-15 knockout macrophages, co-immunoprecipitation (Siglec-15/Glut1), glycolysis assay, cGAS-STING pathway analysis — RETRACTED","journal":"Oxidative medicine and cellular longevity","confidence":"Low","confidence_rationale":"Tier 3 / Weak — paper was retracted; findings should not be relied upon","pmids":["36105484","37388523"],"is_preprint":false},{"year":2023,"finding":"Crystal structure of Siglec-15 was determined, and its binding epitope was characterized by co-crystallization with an anti-Siglec-15 blocking antibody. STD-NMR and molecular dynamics simulations revealed binding mode to α(2,3)- and α(2,6)-linked sialic acids and STn glycoform. Siglec-15 binding to T cells (which lack STn) depends on α(2,3)- and α(2,6)-linked sialoglycans. The leukocyte integrin CD11b was identified as a Siglec-15 binding partner on human T cells.","method":"X-ray crystallography, co-crystallization with blocking antibody, STD-NMR spectroscopy, molecular dynamics simulations, glycan binding assays, co-immunoprecipitation/pulldown for CD11b","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus NMR and MD simulation with functional validation of binding partner; multiple orthogonal methods in one rigorous study","pmids":["37311743"],"is_preprint":false},{"year":2023,"finding":"Osteoclast-derived apoptotic bodies bearing membranous Siglec15 bind sialylated Toll-like receptor 2 (TLR2) on naive CD8+ T cells, blocking downstream co-stimulatory signaling and inhibiting naive CD8+ T cell activation. Siglec15 neutralizing antibodies significantly reduced secondary breast cancer bone metastases and improved survival in mice.","method":"AB-null MRL/lpr mouse model, co-immunoprecipitation/binding assay (Siglec15 on ABs with sialylated TLR2), T cell activation assay, in vivo antibody neutralization, flow cytometry","journal":"Cell reports. Medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — binding assay between Siglec15 and sialylated TLR2 with functional T cell readout and in vivo validation; single lab","pmids":["37607544"],"is_preprint":false},{"year":2023,"finding":"ETS-1 and ETS-2 transcription factors bind the Siglec-15 promoter to enhance its transcription in hepatocellular carcinoma cells. TGF-β1 upregulates ETS-1 and ETS-2 and facilitates their binding to the Siglec-15 promoter via the Ras/C-Raf/MEK/ERK1/2 signaling pathway, leading to phosphorylation of ETS-1/ETS-2 and increased Siglec-15 transcription.","method":"Chromatin immunoprecipitation (ChIP), promoter-reporter assays, TGF-β1 stimulation, ERK pathway inhibition, ETS-1/ETS-2 knockdown","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP and reporter assays with pathway inhibition; single lab, focused mechanistic study","pmids":["36614238"],"is_preprint":false},{"year":2023,"finding":"Siglec-15 promotes migration of thyroid carcinoma cells by binding to EGFR on cancer cells in a sialic acid-dependent manner and increasing EGFR protein stability (slowing its degradation). Pull-down assay confirmed Siglec-15/EGFR interaction; EGFR pathway inhibition blocked the pro-migratory effect.","method":"Pull-down assay (Siglec-15/EGFR interaction), cycloheximide chase assay (protein stability), wound-healing and transwell migration assays, EGFR pathway inhibitor treatment, sialic acid-dependent interaction confirmed with Siglec-15 mutant co-culture","journal":"Glycobiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pull-down with functional validation (stability assay, inhibitor rescue); single lab","pmids":["37129515"],"is_preprint":false},{"year":2023,"finding":"Siglec-15 overexpression in B-ALL is driven by NFκB activation, which also increases surface localization of Siglec-15. Soluble/secreted Siglec-15 circulates at elevated levels in plasma of children with B-ALL. Genetic inhibition of Siglec-15 in a murine B-ALL model promoted immune clearance with expanded early effector CD8+ T cells and reduced immunosuppressive cytokines.","method":"NFκB pathway inhibition/activation experiments, flow cytometry for surface Siglec-15, ELISA for soluble Siglec-15 in patient plasma, genetic Siglec-15 knockdown/knockout in murine B-ALL model","journal":"Cancer research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pathway inhibition establishing NFκB as transcriptional driver, combined with in vivo genetic KO functional model; single lab","pmids":["37465593"],"is_preprint":false},{"year":2024,"finding":"Siglec-15 activates M-CSF-induced RAP1/RAC1 cytoskeletal remodeling in osteoclasts through formation of a complex with p130CAS and CrkII. Siglec-15-deficient osteoclasts fail to form actin rings. Siglec-15/FcRγ double-deficient mice exhibit severe osteopetrosis versus mild osteopetrosis in Siglec-15-single-deficient mice. TREM-2 and CLEC5A deficient mice show normal bone phenotype, placing Siglec-15 as the dominant DAP12-associated receptor for osteoclast cytoskeletal remodeling.","method":"Knockout mice (single and double KO), bone mass analysis, actin ring staining, biochemical co-immunoprecipitation (Siglec-15/p130CAS/CrkII complex), M-CSF signaling assays (RAP1/RAC1)","journal":"Bone research","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis (multiple KO combinations) combined with biochemical co-IP identifying novel complex; multiple orthogonal methods","pmids":["38849345"],"is_preprint":false},{"year":2024,"finding":"The chromatin remodeling factor Arid1a cooperates with transcription factors Jun/Fos to epigenetically upregulate Siglec-15 expression in osteoclast precursors by increasing chromatin accessibility at the Siglec-15 gene promoter. Loss of Arid1a in BMDMs reprograms chromatin structure to restrict Siglec-15 expression and inhibits osteoclast differentiation.","method":"Conditional knockout of Arid1a in BMDMs, ATAC-seq or chromatin accessibility assay, ChIP for Jun/Fos at Siglec-15 promoter, osteoclast differentiation assay, ovariectomy bone loss model","journal":"Journal of bone and mineral research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — chromatin accessibility and transcription factor binding established for Siglec-15 promoter with functional KO validation; single lab","pmids":["38477755"],"is_preprint":false},{"year":2024,"finding":"CA72-4 (a sialylated glycan antigen secreted by synovial cells) binds directly to Siglec-15 on macrophages, as confirmed by co-immunoprecipitation. This interaction activates the TIGIT/SHP-1 signaling axis in macrophages, inhibiting MSU-induced M1 polarization. Siglec-15 knockdown abolished the CA72-4-mediated activation of TIGIT/SHP-1 and its inhibitory effect on M1 polarization.","method":"Co-immunoprecipitation (CA72-4/Siglec-15), Siglec-15 siRNA knockdown, TIGIT/SHP-1 signaling assays, macrophage M1 polarization assay","journal":"Autoimmunity","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP establishing ligand-receptor interaction combined with siRNA knockdown and downstream signaling validation; single lab","pmids":["41920724"],"is_preprint":false},{"year":2026,"finding":"Using genome-wide knockout screening, St3gal4 (α2-3 sialyltransferase) and other enzymes in sialic acid biosynthesis and N-glycan processing are identified as contributors to Siglec-15 ligand expression, establishing that α2-3-linked sialic acid on N-glycans is the primary glycotope recognized by Siglec-15. LRP1 is identified as a Siglec-15 counter-receptor. The retriever complex (endosome-to-plasma membrane recycling) maintains LRP1 surface expression as a Siglec-15 ligand. RAW264.7 cells deficient in St3gal4, Lrp1, or Vps35l show impaired osteoclast differentiation.","method":"Genome-wide CRISPR knockout screen, Siglec-15 binding assay, glycan structural analysis, functional osteoclast differentiation assay in KO cells","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 1 / Moderate — genome-wide functional screen with direct Siglec-15 binding readout and structural glycan identification, validated by functional osteoclast assays in KO cells; single lab but rigorous","pmids":["41569849"],"is_preprint":false},{"year":2026,"finding":"Siglec-15 promotes M2 polarization of Kupffer cells through the DAP12/IRAK-M axis. Molecular docking and in vitro experiments confirmed DAP12 and IRAK-M as downstream targets. Silencing DAP12 or IRAK-M via siRNA abolished the promoting effect of Siglec-15 on M2 KC polarization. Siglec-15 overexpression reduced acute rejection and improved survival in a rat liver transplantation model.","method":"Co-immunoprecipitation/molecular docking (Siglec-15/DAP12/IRAK-M), siRNA knockdown of DAP12 and IRAK-M, macrophage polarization assay, rat liver transplantation model","journal":"Molecular immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — molecular docking plus siRNA epistasis establishing DAP12/IRAK-M pathway, with in vivo transplant model; single lab","pmids":["42066581"],"is_preprint":false},{"year":2022,"finding":"The 3' UTR of SIGLEC15 mRNA markedly promotes mRNA degradation, reducing protein production, while the 5' UTR has a modest inhibitory effect on translation. A 43-nt stem-loop structure within the 993-1317 region of the 3' UTR has the most robust inhibitory activity in multiple cell lines.","method":"Reporter assays with 5' UTR and 3' UTR constructs, mRNA half-life measurement, shortened 3' UTR fragment analysis in four cell lines","journal":"Molekuliarnaia biologiia","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — systematic reporter assay with multiple deletion constructs and direct mRNA stability measurement; single lab","pmids":["35621101"],"is_preprint":false}],"current_model":"Siglec-15 is a conserved type-I transmembrane sialic acid-binding lectin that associates constitutively with the ITAM-bearing adaptor DAP12 (and DAP10) via a critical transmembrane lysine residue; upon engagement of α2-3- or α2-6-linked sialoglycans (with LRP1 identified as a counter-receptor on osteoclast precursors), it activates Syk and downstream PI3K/Akt, Erk, and RAP1/RAC1 pathways to drive cytoskeletal remodeling and fusion of osteoclast precursors, while in tumor-associated macrophages the same DAP12-Syk-MAPK cascade promotes immunosuppressive TGF-β and IL-10 secretion and M2 polarization; Siglec-15 surface abundance is regulated by N-glycosylation at N172 (which stabilizes the protein and routes it to the plasma membrane), and its transcription is upregulated by M-CSF, RANKL/NFATc1, NFκB (in leukemia), ETS-1/ETS-2/TGF-β signaling, and chromatin remodeling via Arid1a/Jun/Fos, whereas IFN-γ downregulates it; structurally, co-crystallography and NMR reveal a defined sialic-acid binding pocket and glycosylation-dependent interaction with the integrin CD11b on T cells, through which Siglec-15 suppresses antigen-specific T cell responses independently of, and mutually exclusive with, the PD-L1/PD-1 axis."},"narrative":{"mechanistic_narrative":"SIGLEC15 encodes a type-I transmembrane sialic acid-binding immunoglobulin-like lectin that couples recognition of sialylated glycans to ITAM-based activating signaling, functioning both as a driver of osteoclast-mediated bone resorption and as an immune-suppressive checkpoint in the tumor microenvironment [PMID:17483134, PMID:30833750]. Through a transmembrane lysine residue, Siglec-15 associates constitutively with the activating adaptors DAP12 and DAP10, and engagement of its sialoglycan ligands triggers Syk recruitment and downstream activation of PI3K/Akt and Erk signaling [PMID:17483134, PMID:22451653, PMID:23677868]. In osteoclasts, Siglec-15 is induced as an NFATc1 target downstream of RANK-RANKL and links this program to DAP12-dependent cytoskeletal remodeling: it drives M-CSF-induced RAP1/RAC1 activation via a p130CAS/CrkII complex required for actin-ring formation and bone resorption, and is the dominant DAP12-associated receptor in this process, with OSCAR/FcRγ able to compensate for multinucleation but not cytoskeletal organization [PMID:22451653, PMID:25460183, PMID:38849345]. Siglec-15-deficient mice show mild osteopetrosis and are protected from estrogen-deficiency, arthritis-associated, and inflammatory bone loss [PMID:23677868, PMID:25460183, PMID:33020147]. Genome-wide screening establishes α2-3-linked sialic acid on N-glycans as the primary glycotope and identifies LRP1, maintained at the surface by the retriever complex, as a Siglec-15 counter-receptor on osteoclast precursors [PMID:41569849]. In cancer, Siglec-15 is broadly upregulated on tumor cells and myeloid cells, suppresses antigen-specific T cell responses in a manner mutually exclusive with the PD-L1/PD-1 axis, and acts on tumor-associated macrophages through DAP12-Syk-MAPK signaling to promote immunosuppressive cytokine production and M2 polarization [PMID:30833750, PMID:35077803]. Structural and NMR studies define its sialic-acid binding pocket and antibody epitope and identify the integrin CD11b as a Siglec-15 ligand on T cells [PMID:37311743]. Surface abundance is controlled by N-glycosylation at N172, which stabilizes the protein and is required for immune suppression, while transcription is regulated by M-CSF, IFN-γ, ETS-1/ETS-2 downstream of TGF-β, NFκB, and Arid1a/Jun/Fos-mediated chromatin remodeling [PMID:30833750, PMID:32921411, PMID:34094685, PMID:36614238, PMID:37465593, PMID:38477755].","teleology":[{"year":2007,"claim":"Established the basic architecture and signaling potential of Siglec-15, defining it as a sialic acid-binding lectin that could engage activating ITAM adaptors rather than acting alone.","evidence":"Molecular characterization, glycan-binding assays, and co-immunoprecipitation showing two Ig-like domains, sialyl-Tn recognition, and DAP12/DAP10 association via a transmembrane lysine","pmids":["17483134"],"confidence":"High","gaps":["Did not define downstream effectors or cellular function","Glycan specificity restricted to sialyl-Tn at this stage"]},{"year":2012,"claim":"Connected ligand engagement to a defined signaling output, showing the transmembrane lysine and DAP12-Syk axis convert glycan recognition into functional consequences in both immune and bone contexts.","evidence":"Co-culture with sTn-positive cancer cells plus K274A mutagenesis and Syk inhibition for TGF-β secretion (PMID 23035012); siRNA, chimeric rescue constructs, and bone resorption assays placing Siglec-15 downstream of RANKL-NFATc1 (PMID 22451653)","pmids":["23035012","22451653"],"confidence":"High","gaps":["sTn-driven TGF-β axis later contradicted by glycan microarray data","Did not resolve which sialoglycan is the physiological ligand in vivo"]},{"year":2013,"claim":"Demonstrated through genetic loss-of-function that Siglec-15 is physiologically required for osteoclast development and identified PI3K/Akt and Erk as the impaired pathways, while revealing redundancy with OSCAR/FcRγ.","evidence":"Siglec-15 knockout mice, retroviral rescue, and signaling pathway analysis showing mild osteopetrosis and impaired RANKL-induced PI3K/Akt and Erk activation","pmids":["23677868"],"confidence":"High","gaps":["Compensation by alternative ITAM pathway obscured full requirement","Did not pinpoint the osteoclast cytoskeletal effector machinery"]},{"year":2014,"claim":"Defined the surface-localized, antibody-targetable nature of Siglec-15 and showed receptor clustering/internalization controls signaling, validating it as a therapeutic target in bone.","evidence":"Plasma membrane localization, mAb treatment in vitro and in vivo with DXA bone density, Akt phosphorylation, and receptor internalization/lysosomal degradation assays (PMID 24446437); ovariectomy KO model dissecting cytoskeletal organization from multinucleation (PMID 25460183)","pmids":["24446437","25460183"],"confidence":"High","gaps":["Molecular link between Siglec-15 and the actin cytoskeleton not yet identified","Did not resolve the in vivo ligand on bone surfaces"]},{"year":2019,"claim":"Repositioned Siglec-15 from a bone receptor to an immune checkpoint, establishing it as a T-cell-suppressive molecule operating independently of PD-L1 and regulated by M-CSF and IFN-γ.","evidence":"Genome-scale T cell activity array, knockout mice, antibody blockade, and in vitro/in vivo tumor models showing amplified anti-tumor immunity upon ablation","pmids":["30833750"],"confidence":"High","gaps":["T-cell ligand and exact suppressive mechanism not defined at this point","Relationship between bone and immune functions unresolved"]},{"year":2019,"claim":"Extended Siglec-15 function to anti-fungal host defense, indicating its glycan-sensing role contributes to innate immune responses beyond bone and tumor settings.","evidence":"Genomic association study with PBMC cytokine profiling, HeLa stimulation, and in vivo vaginal Candida infection with Siglec15 silencing","pmids":["31189718"],"confidence":"Medium","gaps":["Single lab; mechanism linking Siglec-15 to NLRP3/IL-1β not fully resolved","Polymorphism-function link is associative"]},{"year":2020,"claim":"Clarified post-translational and disease-context determinants of Siglec-15 abundance and showed osteoclast bone erosion can be uncoupled from inflammation.","evidence":"Glycosidase and inhibitor experiments showing N-glycosylation stabilizes Siglec-15 and routes it to the membrane (PMID 32921411); K/BxN arthritis KO model showing reduced bone erosion with intact inflammation (PMID 33020147)","pmids":["32921411","33020147"],"confidence":"Medium","gaps":["Specific N-glycosylation site not yet mapped","Glucose/glycolysis link to glycosylation only correlative"]},{"year":2021,"claim":"Refined ligand specificity beyond sTn and uncovered a sialic-acid-dependent role in stabilizing partner glycoproteins that promote cancer cell behavior and TAM immunosuppression.","evidence":"Glycan microarray showing α2,3/α2,6 preference and negative sTn/TGF-β result (PMID 32501471); co-IP and degradation assays for CD44 (PMID 34328657) and SYK-driven TAM cytokine output in PDAC (PMID 35077803); N172 mapped as the functional glycosylation site (PMID 34094685)","pmids":["32501471","34328657","35077803","34094685"],"confidence":"Medium","gaps":["Conflicting reports on sTn recognition unresolved","Whether CD44/EGFR stabilization is a general or cell-type-specific mechanism unclear"]},{"year":2023,"claim":"Provided structural definition of the sialic-acid binding pocket and antibody epitope and identified CD11b on T cells as a binding partner, giving a molecular basis for immune suppression.","evidence":"X-ray crystallography, co-crystallization with a blocking antibody, STD-NMR, molecular dynamics, and pulldown for CD11b","pmids":["37311743"],"confidence":"High","gaps":["Signaling consequence of CD11b engagement on T cells not fully mapped","Structure of full-length receptor/DAP12 complex not determined"]},{"year":2023,"claim":"Mapped transcriptional and additional cell-cell mechanisms of Siglec-15-mediated immune suppression across cancer contexts, including apoptotic-body delivery and promoter regulation.","evidence":"Apoptotic-body Siglec15 binding sialylated TLR2 on CD8+ T cells (PMID 37607544); ChIP and reporter assays for ETS-1/ETS-2 downstream of TGF-β (PMID 36614238); NFκB-driven overexpression and soluble Siglec-15 in B-ALL (PMID 37465593); EGFR stabilization in thyroid carcinoma (PMID 37129515)","pmids":["37607544","36614238","37465593","37129515"],"confidence":"Medium","gaps":["Multiple ligand/partner mechanisms reported by single labs without cross-validation","Relative contribution of soluble vs membrane Siglec-15 unclear"]},{"year":2024,"claim":"Identified the osteoclast cytoskeletal effector complex and established Siglec-15 as the dominant DAP12-associated receptor for actin-ring formation, and defined chromatin-level control of its expression.","evidence":"Single and double KO genetic epistasis with actin-ring staining and co-IP of the Siglec-15/p130CAS/CrkII complex driving RAP1/RAC1 (PMID 38849345); Arid1a 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Bio","url":"https://pubmed.ncbi.nlm.nih.gov/39687802","citation_count":3,"is_preprint":false},{"pmid":"37388523","id":"PMC_37388523","title":"Retracted: Siglec-15 Regulates the Inflammatory Response and Polarization of Tumor-Associated Macrophages in Pancreatic Cancer by Inhibiting the cGAS-STING Signaling Pathway.","date":"2023","source":"Oxidative medicine and cellular longevity","url":"https://pubmed.ncbi.nlm.nih.gov/37388523","citation_count":3,"is_preprint":false},{"pmid":"39524871","id":"PMC_39524871","title":"Siglec-15 as a potential molecule involved in osteoclast differentiation and bone metabolism.","date":"2024","source":"Heliyon","url":"https://pubmed.ncbi.nlm.nih.gov/39524871","citation_count":2,"is_preprint":false},{"pmid":"39756115","id":"PMC_39756115","title":"Targeting Siglec-15 mediates mitochondrial retrograde regulation of cervical cancer development.","date":"2024","source":"Tissue & cell","url":"https://pubmed.ncbi.nlm.nih.gov/39756115","citation_count":2,"is_preprint":false},{"pmid":"41158758","id":"PMC_41158758","title":"SIGLEC15 modulates the immunosuppressive microenvironment and suppresses malignant phenotypes in triple-negative breast cancer.","date":"2025","source":"Genes & diseases","url":"https://pubmed.ncbi.nlm.nih.gov/41158758","citation_count":1,"is_preprint":false},{"pmid":"40172660","id":"PMC_40172660","title":"Siglec-15 is a putative receptor for porcine epidemic diarrhea virus infection.","date":"2025","source":"Cellular and molecular life sciences : CMLS","url":"https://pubmed.ncbi.nlm.nih.gov/40172660","citation_count":1,"is_preprint":false},{"pmid":"35621101","id":"PMC_35621101","title":"[Mapping Regulatory Elements within 5' and 3' UTRs of SIGLEC15 with a Use of Reporter System].","date":"2022","source":"Molekuliarnaia 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pathology","url":"https://pubmed.ncbi.nlm.nih.gov/37222841","citation_count":1,"is_preprint":false},{"pmid":"41260165","id":"PMC_41260165","title":"Cajanin transcriptionally disrupts the Siglec15/NFATc1 signaling cascade to attenuate osteoclast fusion and bone resorption.","date":"2025","source":"International immunopharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/41260165","citation_count":0,"is_preprint":false},{"pmid":"39434541","id":"PMC_39434541","title":"Siglec-15 expression in diffuse gliomas and its correlation with MRI morphologic features and apparent diffusion coefficient.","date":"2024","source":"Acta radiologica (Stockholm, Sweden : 1987)","url":"https://pubmed.ncbi.nlm.nih.gov/39434541","citation_count":0,"is_preprint":false},{"pmid":"40886986","id":"PMC_40886986","title":"Immunochromatographic assay for rapid detection of SIGLEC15 to evaluate its therapeutic potential in cervical cancer.","date":"2025","source":"International journal of biological 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immunopharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/41558291","citation_count":0,"is_preprint":false},{"pmid":"40833001","id":"PMC_40833001","title":"The Role of Siglec-15 in Tumor Immunity: Mechanisms and Therapy.","date":"2026","source":"Molecular cancer therapeutics","url":"https://pubmed.ncbi.nlm.nih.gov/40833001","citation_count":0,"is_preprint":false},{"pmid":"41349947","id":"PMC_41349947","title":"Investigating the role and mechanism of methionine in different types of skeletal fluorosis based on Siglec-15 methylation.","date":"2025","source":"Environmental pollution (Barking, Essex : 1987)","url":"https://pubmed.ncbi.nlm.nih.gov/41349947","citation_count":0,"is_preprint":false},{"pmid":"42066581","id":"PMC_42066581","title":"Siglec-15 promotes M2 polarization of Kupffer cells via DAP12/IRAK-M axis to alleviate acute rejection in liver transplantation.","date":"2026","source":"Molecular immunology","url":"https://pubmed.ncbi.nlm.nih.gov/42066581","citation_count":0,"is_preprint":false},{"pmid":"41920724","id":"PMC_41920724","title":"CA72-4 derived from synovial cells inhibits monosodium urate-induced macrophage M1 polarization by activating the TIGIT/SHP-1 axis through binding to Siglec-15.","date":"2026","source":"Autoimmunity","url":"https://pubmed.ncbi.nlm.nih.gov/41920724","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":43464,"output_tokens":8138,"usd":0.126231,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":17579,"output_tokens":5176,"usd":0.108647,"stage2_stop_reason":"end_turn"},"total_usd":0.234878,"stage1_batch_id":"msgbatch_013LWZZT6MWaqB9qyTSeQBmU","stage2_batch_id":"msgbatch_0194ZzQaTGNpruoNJBbEMbt3","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2007,\n      \"finding\": \"Siglec-15 is a type-I transmembrane protein with two Ig-like extracellular domains, a transmembrane domain containing a lysine residue, and a short cytoplasmic tail. Its extracellular domain preferentially recognizes the Neu5Acα2-6GalNAcα- (sialyl-Tn) structure. Siglec-15 associates with activating adaptor proteins DAP12 and DAP10 via its transmembrane lysine residue, implying activating signaling potential.\",\n      \"method\": \"Molecular characterization, glycan-binding assays, co-immunoprecipitation\",\n      \"journal\": \"Glycobiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal biochemical binding assays and co-IP for DAP12/DAP10 association; foundational characterization paper replicated by subsequent studies\",\n      \"pmids\": [\"17483134\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Siglec-15 recognizes tumor-associated sialyl-Tn (sTn) antigen on cancer cells and signals through DAP12 via its transmembrane Lys274 to activate Syk, leading to enhanced TGF-β secretion from monocytes/macrophages. Substitution of Lys274 to Ala disrupts Siglec-15/DAP12 interaction and abolishes enhanced TGF-β production. Syk inhibitor treatment also attenuates TGF-β secretion.\",\n      \"method\": \"Co-culture model (THP-1 and H157 cells), site-directed mutagenesis (K274A), Syk inhibitor treatment, TGF-β ELISA\",\n      \"journal\": \"Glycobiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis of key residue combined with pharmacological inhibition and co-culture functional assay in a single focused study\",\n      \"pmids\": [\"23035012\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Siglec-15 is induced as an NFATc1 target gene during osteoclast differentiation and links RANK-RANKL-NFATc1 signaling to DAP12. Both sialylated glycan recognition by the V-set domain and association with DAP12 via Lys272 are required for functional osteoclast formation. Knockdown of Siglec-15 reduces multinucleated cell development, disrupts actin-ring structures, and impairs bone resorption. Siglec-15 forms complexes with Syk through DAP12 in response to vitronectin. Chimeric molecules with K272A mutation fused to the DAP12 cytoplasmic region significantly restored bone resorption, confirming that the transmembrane Lys is dispensable if DAP12 signaling is provided directly.\",\n      \"method\": \"siRNA knockdown, retroviral transduction of chimeric constructs, co-immunoprecipitation (Siglec-15/Syk via DAP12), actin-ring imaging, bone resorption assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis, chimeric rescue constructs, co-IP, and functional bone resorption assays in one study; replicated in subsequent independent work\",\n      \"pmids\": [\"22451653\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Siglec-15 modulates RANKL-induced osteoclastogenesis through DAP12-dependent activation of PI3K/Akt and Erk pathways. Siglec-15-deficient mice exhibit mild osteopetrosis with impaired osteoclast development. RANKL-induced PI3K/Akt and Erk activation is impaired in Siglec-15-deficient cells. OSCAR/FcRγ signaling (alternative ITAM pathway) can compensate for Siglec-15 deficiency in the primary spongiosa via type II collagen ligands.\",\n      \"method\": \"Siglec-15 knockout mice, retroviral transduction with wild-type or mutant Siglec-15, signaling pathway analysis (PI3K/Akt, Erk), bone phenotype analysis, rescue with OSCAR/FcRγ ligands\",\n      \"journal\": \"Journal of bone and mineral research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO mouse model with multiple orthogonal readouts (signaling, histology, in vitro osteoclastogenesis), replicated across labs\",\n      \"pmids\": [\"23677868\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Siglec-15 is localized to the plasma membrane of osteoclasts where anti-Siglec-15 monoclonal antibodies inhibit osteoclast differentiation in vitro and increase bone mineral density in mice. At the molecular level, Siglec-15 interacts with DAP12 and induces Akt activation when clustered on the osteoclast surface. Monoclonal antibodies induce rapid internalization, lysosomal targeting, and degradation of Siglec-15 by inducing receptor dimerization.\",\n      \"method\": \"Plasma membrane localization assay, mAb treatment in vitro and in vivo, bone density measurement (DXA), co-immunoprecipitation (Siglec-15/DAP12), Akt phosphorylation assay, receptor internalization and lysosomal degradation assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (co-IP, signaling assay, in vivo bone density, internalization tracking) in a single focused study\",\n      \"pmids\": [\"24446437\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Siglec-15 deficiency protects mice from estrogen deficiency-induced (ovariectomy) bone loss. Siglec-15-deficient osteoclasts are small, fail to spread on bone surface, and show impaired cytoskeletal organization. Siglec-15 is also required for TNF-α-induced osteoclastogenesis in vitro. The Siglec-15/DAP12 pathway is specifically important for cytoskeletal organization, while OSCAR/FcRγ signaling can rescue multinucleation but not cytoskeletal organization in Siglec-15-deficient cells.\",\n      \"method\": \"Siglec-15 knockout mice with ovariectomy model, TRAP staining, in vitro TNF-α-induced osteoclastogenesis, comparison of DAP12 vs OSCAR/FcRγ pathway rescue\",\n      \"journal\": \"Bone\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO in disease model with multiple phenotypic and mechanistic readouts; pathway dissection via alternative ITAM adaptor rescue\",\n      \"pmids\": [\"25460183\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Siglec-15 is broadly upregulated on human cancer cells and tumor-infiltrating myeloid cells, suppresses antigen-specific T cell responses in vitro and in vivo, and its expression is mutually exclusive with B7-H1 (PD-L1). Siglec-15 expression is induced by macrophage colony-stimulating factor (M-CSF) and downregulated by IFN-γ. Genetic ablation or antibody blockade of Siglec-15 amplifies anti-tumor immunity and inhibits tumor growth in mouse models. Siglec-15 was identified using a genome-scale T cell activity array.\",\n      \"method\": \"Genome-scale T cell activity array, genetic ablation (knockout mice), antibody blockade, in vitro T cell suppression assays, in vivo tumor models\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genome-scale functional screen combined with genetic KO, antibody blockade, in vitro and in vivo functional assays; landmark paper\",\n      \"pmids\": [\"30833750\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"A SIGLEC15 gene polymorphism associated with recurrent vulvovaginal candidiasis (RVVC) leads to an altered cytokine profile after PBMC stimulation with Candida and increases IL-1B and NLRP3 expression after Candida stimulation in HeLa cells. In vivo silencing of Siglec15 at the vaginal surface of mice led to increased fungal burden and an increase in polymorphonuclear leukocytes during Candida infection, indicating Siglec-15 plays a role in anti-fungal host defense.\",\n      \"method\": \"Genomic association study integrated with in vitro cytokine profiling (PBMC stimulation), in vivo Siglec15 silencing in mouse vaginal Candida infection model, flow cytometry\",\n      \"journal\": \"Science translational medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo knockdown with functional readouts combined with in vitro cytokine assays; single lab, immune function partially characterized\",\n      \"pmids\": [\"31189718\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"N-glycosylation of Siglec-15 stabilizes it by decreasing lysosome-dependent degradation and promotes its transportation to the cell membrane. Using glycosidase and glycosylation inhibitors, Siglec-15 was shown to be completely N-glycosylated. Glucose uptake regulates N-glycosylation of Siglec-15.\",\n      \"method\": \"Glycosidase treatment, glycosylation inhibitors, immunofluorescence for subcellular localization, protein stability assays\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct biochemical manipulation (glycosidase, inhibitors) with localization and stability readouts; single lab, two orthogonal methods\",\n      \"pmids\": [\"32921411\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Siglec-15 is required for bone erosion specifically in osteoclasts in an arthritis model (K/BxN serum-transfer arthritis). Siglec-15-/- mice show significant reduction in bone erosion area and osteoclast numbers but comparable inflammation and cartilage destruction to wild-type mice, placing Siglec-15 specifically in pathological osteoclast-mediated bone resorption.\",\n      \"method\": \"Siglec-15 knockout mice, K/BxN serum-transfer arthritis model, histological analysis of bone erosion, cartilage destruction, and osteoclast numbers\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO in disease model with specific dissection of bone erosion vs inflammation phenotype; replicated across independent labs\",\n      \"pmids\": [\"33020147\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Siglec-15 binds sialylated glycans other than sTn with higher avidity (based on glycan microarray), including α(2,3)- and α(2,6)-linked sialic acids. Using lung and breast cancer cell lines, no evidence was found for sTn recognition or enhanced TGF-β secretion following Siglec-15 co-culture with sTn-positive cells (negative result for sTn/TGF-β axis). However, antibody cross-linking of Siglec-15 activates the SYK/MAPK signaling pathway.\",\n      \"method\": \"Glycan microarray, cell line binding assays, glycan-modified cells, co-culture with sTn-positive tumor cells, TGF-β ELISA (negative), SYK/MAPK signaling (phospho-blot after mAb cross-linking)\",\n      \"journal\": \"Glycobiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — glycan microarray with multiple binding assays and signaling readouts; partially contradicts earlier TGF-β findings, reducing confidence in that specific mechanism\",\n      \"pmids\": [\"32501471\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Siglec-15 interacts with CD44, a transmembrane glycoprotein, in a sialic acid-dependent manner in hepatoma cells. CD44 is modified by α2,6-linked sialic acids on N-glycans; removal of sialic acids suppresses the Siglec-15/CD44 interaction. Siglec-15 promotes stability of CD44 by preventing its lysosomal-mediated degradation, thereby promoting hepatoma cell migration.\",\n      \"method\": \"Co-immunoprecipitation, neuraminidase treatment (sialic acid removal), lysosomal degradation assay, migration assay\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP with functional validation (lysosomal inhibition, sialic acid removal), single lab\",\n      \"pmids\": [\"34328657\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"In pancreatic cancer, SIGLEC15 on tumor-associated macrophages interacts with α-2,3-linked sialic acids on PDAC tumor cells to stimulate SYK phosphorylation in TAMs, which promotes immunoregulatory cytokine and chemokine production. SYK inhibitor treatment abolished M2-like TAM phenotype promotion and immunosuppressive microenvironment in vivo.\",\n      \"method\": \"Co-culture of SIGLEC15+ TAMs with PDAC cells, SYK phosphorylation assay, SYK inhibitor treatment, in vivo subcutaneous tumor model, flow cytometry\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological inhibition (SYK inhibitor) plus in vivo validation, single lab\",\n      \"pmids\": [\"35077803\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Glycosylation of Siglec-15 at N172 (N173 in mouse) is required for its immunosuppressive function. Through mass spectrometry and site mutation analysis, N172 was identified as the primary glycosylation site. Siglec-15 N172Q (glycosylation-deficient mutant) reduced tumor growth in immunocompetent C57BL/6 mice but not in nude mice, indicating N-glycosylation is required for Siglec-15-mediated immune suppression.\",\n      \"method\": \"Mass spectrometry, site-directed mutagenesis (N172Q), xenograft models in immunocompetent vs. immunodeficient mice\",\n      \"journal\": \"American journal of cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — mutagenesis combined with in vivo immunocompetent vs. nude mouse comparison; single lab\",\n      \"pmids\": [\"34094685\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Neuraminidase (NA) influences host defense against Aspergillus fumigatus, and SIGLEC15 is upregulated in PBMCs stimulated with A. fumigatus. Silencing of SIGLEC15 decreases PBMC killing capacity of A. fumigatus, establishing a role for SIGLEC15 in anti-fungal defense.\",\n      \"method\": \"SIGLEC15 siRNA silencing in PBMCs, fungal killing assay, mouse model of pulmonary aspergillosis with oseltamivir treatment\",\n      \"journal\": \"Cell reports. Medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown with functional killing assay, multiple in vitro and in vivo readouts, single lab\",\n      \"pmids\": [\"34095887\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Siglec-15 regulates M2 macrophage polarization by interacting with Glut1 to upregulate glycolysis, and this glycolytic regulation modulates cGAS/STING signaling to drive M2 phenotype. Siglec-15 knockout abolished M2 marker expression and inhibited tumor growth in a subcutaneous mouse model. NOTE: This paper was subsequently retracted (PMID:37388523).\",\n      \"method\": \"Siglec-15 knockout macrophages, co-immunoprecipitation (Siglec-15/Glut1), glycolysis assay, cGAS-STING pathway analysis — RETRACTED\",\n      \"journal\": \"Oxidative medicine and cellular longevity\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — paper was retracted; findings should not be relied upon\",\n      \"pmids\": [\"36105484\", \"37388523\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Crystal structure of Siglec-15 was determined, and its binding epitope was characterized by co-crystallization with an anti-Siglec-15 blocking antibody. STD-NMR and molecular dynamics simulations revealed binding mode to α(2,3)- and α(2,6)-linked sialic acids and STn glycoform. Siglec-15 binding to T cells (which lack STn) depends on α(2,3)- and α(2,6)-linked sialoglycans. The leukocyte integrin CD11b was identified as a Siglec-15 binding partner on human T cells.\",\n      \"method\": \"X-ray crystallography, co-crystallization with blocking antibody, STD-NMR spectroscopy, molecular dynamics simulations, glycan binding assays, co-immunoprecipitation/pulldown for CD11b\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus NMR and MD simulation with functional validation of binding partner; multiple orthogonal methods in one rigorous study\",\n      \"pmids\": [\"37311743\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Osteoclast-derived apoptotic bodies bearing membranous Siglec15 bind sialylated Toll-like receptor 2 (TLR2) on naive CD8+ T cells, blocking downstream co-stimulatory signaling and inhibiting naive CD8+ T cell activation. Siglec15 neutralizing antibodies significantly reduced secondary breast cancer bone metastases and improved survival in mice.\",\n      \"method\": \"AB-null MRL/lpr mouse model, co-immunoprecipitation/binding assay (Siglec15 on ABs with sialylated TLR2), T cell activation assay, in vivo antibody neutralization, flow cytometry\",\n      \"journal\": \"Cell reports. Medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — binding assay between Siglec15 and sialylated TLR2 with functional T cell readout and in vivo validation; single lab\",\n      \"pmids\": [\"37607544\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"ETS-1 and ETS-2 transcription factors bind the Siglec-15 promoter to enhance its transcription in hepatocellular carcinoma cells. TGF-β1 upregulates ETS-1 and ETS-2 and facilitates their binding to the Siglec-15 promoter via the Ras/C-Raf/MEK/ERK1/2 signaling pathway, leading to phosphorylation of ETS-1/ETS-2 and increased Siglec-15 transcription.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP), promoter-reporter assays, TGF-β1 stimulation, ERK pathway inhibition, ETS-1/ETS-2 knockdown\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP and reporter assays with pathway inhibition; single lab, focused mechanistic study\",\n      \"pmids\": [\"36614238\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Siglec-15 promotes migration of thyroid carcinoma cells by binding to EGFR on cancer cells in a sialic acid-dependent manner and increasing EGFR protein stability (slowing its degradation). Pull-down assay confirmed Siglec-15/EGFR interaction; EGFR pathway inhibition blocked the pro-migratory effect.\",\n      \"method\": \"Pull-down assay (Siglec-15/EGFR interaction), cycloheximide chase assay (protein stability), wound-healing and transwell migration assays, EGFR pathway inhibitor treatment, sialic acid-dependent interaction confirmed with Siglec-15 mutant co-culture\",\n      \"journal\": \"Glycobiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pull-down with functional validation (stability assay, inhibitor rescue); single lab\",\n      \"pmids\": [\"37129515\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Siglec-15 overexpression in B-ALL is driven by NFκB activation, which also increases surface localization of Siglec-15. Soluble/secreted Siglec-15 circulates at elevated levels in plasma of children with B-ALL. Genetic inhibition of Siglec-15 in a murine B-ALL model promoted immune clearance with expanded early effector CD8+ T cells and reduced immunosuppressive cytokines.\",\n      \"method\": \"NFκB pathway inhibition/activation experiments, flow cytometry for surface Siglec-15, ELISA for soluble Siglec-15 in patient plasma, genetic Siglec-15 knockdown/knockout in murine B-ALL model\",\n      \"journal\": \"Cancer research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pathway inhibition establishing NFκB as transcriptional driver, combined with in vivo genetic KO functional model; single lab\",\n      \"pmids\": [\"37465593\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Siglec-15 activates M-CSF-induced RAP1/RAC1 cytoskeletal remodeling in osteoclasts through formation of a complex with p130CAS and CrkII. Siglec-15-deficient osteoclasts fail to form actin rings. Siglec-15/FcRγ double-deficient mice exhibit severe osteopetrosis versus mild osteopetrosis in Siglec-15-single-deficient mice. TREM-2 and CLEC5A deficient mice show normal bone phenotype, placing Siglec-15 as the dominant DAP12-associated receptor for osteoclast cytoskeletal remodeling.\",\n      \"method\": \"Knockout mice (single and double KO), bone mass analysis, actin ring staining, biochemical co-immunoprecipitation (Siglec-15/p130CAS/CrkII complex), M-CSF signaling assays (RAP1/RAC1)\",\n      \"journal\": \"Bone research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis (multiple KO combinations) combined with biochemical co-IP identifying novel complex; multiple orthogonal methods\",\n      \"pmids\": [\"38849345\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The chromatin remodeling factor Arid1a cooperates with transcription factors Jun/Fos to epigenetically upregulate Siglec-15 expression in osteoclast precursors by increasing chromatin accessibility at the Siglec-15 gene promoter. Loss of Arid1a in BMDMs reprograms chromatin structure to restrict Siglec-15 expression and inhibits osteoclast differentiation.\",\n      \"method\": \"Conditional knockout of Arid1a in BMDMs, ATAC-seq or chromatin accessibility assay, ChIP for Jun/Fos at Siglec-15 promoter, osteoclast differentiation assay, ovariectomy bone loss model\",\n      \"journal\": \"Journal of bone and mineral research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — chromatin accessibility and transcription factor binding established for Siglec-15 promoter with functional KO validation; single lab\",\n      \"pmids\": [\"38477755\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CA72-4 (a sialylated glycan antigen secreted by synovial cells) binds directly to Siglec-15 on macrophages, as confirmed by co-immunoprecipitation. This interaction activates the TIGIT/SHP-1 signaling axis in macrophages, inhibiting MSU-induced M1 polarization. Siglec-15 knockdown abolished the CA72-4-mediated activation of TIGIT/SHP-1 and its inhibitory effect on M1 polarization.\",\n      \"method\": \"Co-immunoprecipitation (CA72-4/Siglec-15), Siglec-15 siRNA knockdown, TIGIT/SHP-1 signaling assays, macrophage M1 polarization assay\",\n      \"journal\": \"Autoimmunity\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP establishing ligand-receptor interaction combined with siRNA knockdown and downstream signaling validation; single lab\",\n      \"pmids\": [\"41920724\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Using genome-wide knockout screening, St3gal4 (α2-3 sialyltransferase) and other enzymes in sialic acid biosynthesis and N-glycan processing are identified as contributors to Siglec-15 ligand expression, establishing that α2-3-linked sialic acid on N-glycans is the primary glycotope recognized by Siglec-15. LRP1 is identified as a Siglec-15 counter-receptor. The retriever complex (endosome-to-plasma membrane recycling) maintains LRP1 surface expression as a Siglec-15 ligand. RAW264.7 cells deficient in St3gal4, Lrp1, or Vps35l show impaired osteoclast differentiation.\",\n      \"method\": \"Genome-wide CRISPR knockout screen, Siglec-15 binding assay, glycan structural analysis, functional osteoclast differentiation assay in KO cells\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — genome-wide functional screen with direct Siglec-15 binding readout and structural glycan identification, validated by functional osteoclast assays in KO cells; single lab but rigorous\",\n      \"pmids\": [\"41569849\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Siglec-15 promotes M2 polarization of Kupffer cells through the DAP12/IRAK-M axis. Molecular docking and in vitro experiments confirmed DAP12 and IRAK-M as downstream targets. Silencing DAP12 or IRAK-M via siRNA abolished the promoting effect of Siglec-15 on M2 KC polarization. Siglec-15 overexpression reduced acute rejection and improved survival in a rat liver transplantation model.\",\n      \"method\": \"Co-immunoprecipitation/molecular docking (Siglec-15/DAP12/IRAK-M), siRNA knockdown of DAP12 and IRAK-M, macrophage polarization assay, rat liver transplantation model\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — molecular docking plus siRNA epistasis establishing DAP12/IRAK-M pathway, with in vivo transplant model; single lab\",\n      \"pmids\": [\"42066581\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The 3' UTR of SIGLEC15 mRNA markedly promotes mRNA degradation, reducing protein production, while the 5' UTR has a modest inhibitory effect on translation. A 43-nt stem-loop structure within the 993-1317 region of the 3' UTR has the most robust inhibitory activity in multiple cell lines.\",\n      \"method\": \"Reporter assays with 5' UTR and 3' UTR constructs, mRNA half-life measurement, shortened 3' UTR fragment analysis in four cell lines\",\n      \"journal\": \"Molekuliarnaia biologiia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — systematic reporter assay with multiple deletion constructs and direct mRNA stability measurement; single lab\",\n      \"pmids\": [\"35621101\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"Siglec-15 is a conserved type-I transmembrane sialic acid-binding lectin that associates constitutively with the ITAM-bearing adaptor DAP12 (and DAP10) via a critical transmembrane lysine residue; upon engagement of α2-3- or α2-6-linked sialoglycans (with LRP1 identified as a counter-receptor on osteoclast precursors), it activates Syk and downstream PI3K/Akt, Erk, and RAP1/RAC1 pathways to drive cytoskeletal remodeling and fusion of osteoclast precursors, while in tumor-associated macrophages the same DAP12-Syk-MAPK cascade promotes immunosuppressive TGF-β and IL-10 secretion and M2 polarization; Siglec-15 surface abundance is regulated by N-glycosylation at N172 (which stabilizes the protein and routes it to the plasma membrane), and its transcription is upregulated by M-CSF, RANKL/NFATc1, NFκB (in leukemia), ETS-1/ETS-2/TGF-β signaling, and chromatin remodeling via Arid1a/Jun/Fos, whereas IFN-γ downregulates it; structurally, co-crystallography and NMR reveal a defined sialic-acid binding pocket and glycosylation-dependent interaction with the integrin CD11b on T cells, through which Siglec-15 suppresses antigen-specific T cell responses independently of, and mutually exclusive with, the PD-L1/PD-1 axis.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SIGLEC15 encodes a type-I transmembrane sialic acid-binding immunoglobulin-like lectin that couples recognition of sialylated glycans to ITAM-based activating signaling, functioning both as a driver of osteoclast-mediated bone resorption and as an immune-suppressive checkpoint in the tumor microenvironment [#0, #6]. Through a transmembrane lysine residue, Siglec-15 associates constitutively with the activating adaptors DAP12 and DAP10, and engagement of its sialoglycan ligands triggers Syk recruitment and downstream activation of PI3K/Akt and Erk signaling [#0, #2, #3]. In osteoclasts, Siglec-15 is induced as an NFATc1 target downstream of RANK-RANKL and links this program to DAP12-dependent cytoskeletal remodeling: it drives M-CSF-induced RAP1/RAC1 activation via a p130CAS/CrkII complex required for actin-ring formation and bone resorption, and is the dominant DAP12-associated receptor in this process, with OSCAR/FcRγ able to compensate for multinucleation but not cytoskeletal organization [#2, #5, #21]. Siglec-15-deficient mice show mild osteopetrosis and are protected from estrogen-deficiency, arthritis-associated, and inflammatory bone loss [#3, #5, #9]. Genome-wide screening establishes α2-3-linked sialic acid on N-glycans as the primary glycotope and identifies LRP1, maintained at the surface by the retriever complex, as a Siglec-15 counter-receptor on osteoclast precursors [#24]. In cancer, Siglec-15 is broadly upregulated on tumor cells and myeloid cells, suppresses antigen-specific T cell responses in a manner mutually exclusive with the PD-L1/PD-1 axis, and acts on tumor-associated macrophages through DAP12-Syk-MAPK signaling to promote immunosuppressive cytokine production and M2 polarization [#6, #12]. Structural and NMR studies define its sialic-acid binding pocket and antibody epitope and identify the integrin CD11b as a Siglec-15 ligand on T cells [#16]. Surface abundance is controlled by N-glycosylation at N172, which stabilizes the protein and is required for immune suppression, while transcription is regulated by M-CSF, IFN-γ, ETS-1/ETS-2 downstream of TGF-β, NFκB, and Arid1a/Jun/Fos-mediated chromatin remodeling [#6, #8, #13, #18, #20, #22].\",\n  \"teleology\": [\n    {\n      \"year\": 2007,\n      \"claim\": \"Established the basic architecture and signaling potential of Siglec-15, defining it as a sialic acid-binding lectin that could engage activating ITAM adaptors rather than acting alone.\",\n      \"evidence\": \"Molecular characterization, glycan-binding assays, and co-immunoprecipitation showing two Ig-like domains, sialyl-Tn recognition, and DAP12/DAP10 association via a transmembrane lysine\",\n      \"pmids\": [\"17483134\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define downstream effectors or cellular function\", \"Glycan specificity restricted to sialyl-Tn at this stage\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Connected ligand engagement to a defined signaling output, showing the transmembrane lysine and DAP12-Syk axis convert glycan recognition into functional consequences in both immune and bone contexts.\",\n      \"evidence\": \"Co-culture with sTn-positive cancer cells plus K274A mutagenesis and Syk inhibition for TGF-β secretion (PMID 23035012); siRNA, chimeric rescue constructs, and bone resorption assays placing Siglec-15 downstream of RANKL-NFATc1 (PMID 22451653)\",\n      \"pmids\": [\"23035012\", \"22451653\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"sTn-driven TGF-β axis later contradicted by glycan microarray data\", \"Did not resolve which sialoglycan is the physiological ligand in vivo\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Demonstrated through genetic loss-of-function that Siglec-15 is physiologically required for osteoclast development and identified PI3K/Akt and Erk as the impaired pathways, while revealing redundancy with OSCAR/FcRγ.\",\n      \"evidence\": \"Siglec-15 knockout mice, retroviral rescue, and signaling pathway analysis showing mild osteopetrosis and impaired RANKL-induced PI3K/Akt and Erk activation\",\n      \"pmids\": [\"23677868\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Compensation by alternative ITAM pathway obscured full requirement\", \"Did not pinpoint the osteoclast cytoskeletal effector machinery\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Defined the surface-localized, antibody-targetable nature of Siglec-15 and showed receptor clustering/internalization controls signaling, validating it as a therapeutic target in bone.\",\n      \"evidence\": \"Plasma membrane localization, mAb treatment in vitro and in vivo with DXA bone density, Akt phosphorylation, and receptor internalization/lysosomal degradation assays (PMID 24446437); ovariectomy KO model dissecting cytoskeletal organization from multinucleation (PMID 25460183)\",\n      \"pmids\": [\"24446437\", \"25460183\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular link between Siglec-15 and the actin cytoskeleton not yet identified\", \"Did not resolve the in vivo ligand on bone surfaces\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Repositioned Siglec-15 from a bone receptor to an immune checkpoint, establishing it as a T-cell-suppressive molecule operating independently of PD-L1 and regulated by M-CSF and IFN-γ.\",\n      \"evidence\": \"Genome-scale T cell activity array, knockout mice, antibody blockade, and in vitro/in vivo tumor models showing amplified anti-tumor immunity upon ablation\",\n      \"pmids\": [\"30833750\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"T-cell ligand and exact suppressive mechanism not defined at this point\", \"Relationship between bone and immune functions unresolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Extended Siglec-15 function to anti-fungal host defense, indicating its glycan-sensing role contributes to innate immune responses beyond bone and tumor settings.\",\n      \"evidence\": \"Genomic association study with PBMC cytokine profiling, HeLa stimulation, and in vivo vaginal Candida infection with Siglec15 silencing\",\n      \"pmids\": [\"31189718\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; mechanism linking Siglec-15 to NLRP3/IL-1β not fully resolved\", \"Polymorphism-function link is associative\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Clarified post-translational and disease-context determinants of Siglec-15 abundance and showed osteoclast bone erosion can be uncoupled from inflammation.\",\n      \"evidence\": \"Glycosidase and inhibitor experiments showing N-glycosylation stabilizes Siglec-15 and routes it to the membrane (PMID 32921411); K/BxN arthritis KO model showing reduced bone erosion with intact inflammation (PMID 33020147)\",\n      \"pmids\": [\"32921411\", \"33020147\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific N-glycosylation site not yet mapped\", \"Glucose/glycolysis link to glycosylation only correlative\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Refined ligand specificity beyond sTn and uncovered a sialic-acid-dependent role in stabilizing partner glycoproteins that promote cancer cell behavior and TAM immunosuppression.\",\n      \"evidence\": \"Glycan microarray showing α2,3/α2,6 preference and negative sTn/TGF-β result (PMID 32501471); co-IP and degradation assays for CD44 (PMID 34328657) and SYK-driven TAM cytokine output in PDAC (PMID 35077803); N172 mapped as the functional glycosylation site (PMID 34094685)\",\n      \"pmids\": [\"32501471\", \"34328657\", \"35077803\", \"34094685\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Conflicting reports on sTn recognition unresolved\", \"Whether CD44/EGFR stabilization is a general or cell-type-specific mechanism unclear\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Provided structural definition of the sialic-acid binding pocket and antibody epitope and identified CD11b on T cells as a binding partner, giving a molecular basis for immune suppression.\",\n      \"evidence\": \"X-ray crystallography, co-crystallization with a blocking antibody, STD-NMR, molecular dynamics, and pulldown for CD11b\",\n      \"pmids\": [\"37311743\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Signaling consequence of CD11b engagement on T cells not fully mapped\", \"Structure of full-length receptor/DAP12 complex not determined\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Mapped transcriptional and additional cell-cell mechanisms of Siglec-15-mediated immune suppression across cancer contexts, including apoptotic-body delivery and promoter regulation.\",\n      \"evidence\": \"Apoptotic-body Siglec15 binding sialylated TLR2 on CD8+ T cells (PMID 37607544); ChIP and reporter assays for ETS-1/ETS-2 downstream of TGF-β (PMID 36614238); NFκB-driven overexpression and soluble Siglec-15 in B-ALL (PMID 37465593); EGFR stabilization in thyroid carcinoma (PMID 37129515)\",\n      \"pmids\": [\"37607544\", \"36614238\", \"37465593\", \"37129515\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Multiple ligand/partner mechanisms reported by single labs without cross-validation\", \"Relative contribution of soluble vs membrane Siglec-15 unclear\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identified the osteoclast cytoskeletal effector complex and established Siglec-15 as the dominant DAP12-associated receptor for actin-ring formation, and defined chromatin-level control of its expression.\",\n      \"evidence\": \"Single and double KO genetic epistasis with actin-ring staining and co-IP of the Siglec-15/p130CAS/CrkII complex driving RAP1/RAC1 (PMID 38849345); Arid1a conditional KO with chromatin accessibility and Jun/Fos ChIP at the promoter (PMID 38477755)\",\n      \"pmids\": [\"38849345\", \"38477755\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How DAP12 signaling assembles the p130CAS/CrkII complex mechanistically not detailed\", \"Arid1a study from a single lab\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Defined the physiological glycotope and counter-receptor for Siglec-15 in osteoclastogenesis, resolving longstanding ambiguity about its in vivo ligand.\",\n      \"evidence\": \"Genome-wide CRISPR knockout screen with Siglec-15 binding readout and glycan structural analysis identifying St3gal4-dependent α2-3 sialic acid on N-glycans and LRP1 (maintained by the retriever complex) as the counter-receptor, validated in KO osteoclast differentiation\",\n      \"pmids\": [\"41569849\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether LRP1 is the relevant ligand in immune/tumor contexts not addressed\", \"Single lab\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Extended the DAP12-dependent immunosuppressive program to liver macrophages, linking Siglec-15 to an IRAK-M axis driving M2 polarization with transplant-relevant outcomes.\",\n      \"evidence\": \"Co-IP/molecular docking and siRNA epistasis for DAP12 and IRAK-M in Kupffer cell polarization, with a rat liver transplantation model\",\n      \"pmids\": [\"42066581\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Docking-based interaction needs biochemical confirmation\", \"Single lab; IRAK-M placement downstream of DAP12 not structurally validated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How Siglec-15 reconciles its activating DAP12-Syk signaling with reported inhibitory outputs (e.g. TIGIT/SHP-1, T-cell suppression), and which ligand-partner pairs dominate in each tissue context, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Mechanism by which an ITAM-coupled receptor produces immunosuppression is not fully reconciled\", \"Many ligand/partner interactions (CD44, EGFR, CD11b, TLR2, CA72-4) are single-lab Co-IP findings lacking cross-validation\", \"No structure of the signaling-competent Siglec-15/DAP12 complex\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 2, 16, 24]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [2, 3, 6, 21]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [5, 21]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [4, 8, 20]},\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [4, 8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [6, 12, 16]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 3, 21]},\n      {\"term_id\": \"R-HSA-1474244\", \"supporting_discovery_ids\": [5, 21]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"DAP12\", \"DAP10\", \"SYK\", \"LRP1\", \"CD11b\", \"CD44\", \"EGFR\", \"p130CAS\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"faith_supported":8,"faith_total":8,"faith_pct":100.0}}