{"gene":"B3GNT5","run_date":"2026-04-28T17:12:37","timeline":{"discoveries":[{"year":2008,"finding":"B3GNT5 (B3gnt5) encodes the Lc3-synthase enzyme that catalyzes formation of the Lc3 (lactotriosylceramide) structure, the core trisaccharide of lactoseries glycosphingolipids; knockout in mouse embryonic stem cells reduced Lc3-synthase activity and lactoseries GSL levels, and germline knockout caused pre-implantation lethality.","method":"Gene knockout in mouse ES cells with enzymatic activity assay for Lc3-synthase; GSL profiling; germline knockout with embryo genotyping; in situ hybridization for expression","journal":"BMC developmental biology","confidence":"High","confidence_rationale":"Tier 1-2 — direct enzymatic assay in knockout ES cells plus multiple orthogonal methods (GSL profiling, embryo genotyping, ISH)","pmids":["19014510"],"is_preprint":false},{"year":2010,"finding":"B3gnt5-encoded Lc3 synthase is required for lacto- and neolacto-series ganglioside biosynthesis; knockout mice lacking lacto-neolacto series gangliosides showed B-cell abnormalities (reduced splenic B-cell numbers, loss of germinal centers, impaired hybridoma fusion), reproductive defects, splenomegaly, and early death, establishing essential physiological roles for these GSLs.","method":"Two independent B3gnt5 gene knockout strategies in mice; histological and flow cytometric analysis of B-cell compartments; phenotypic characterization of homozygous and heterozygous knockouts","journal":"BMC developmental biology","confidence":"High","confidence_rationale":"Tier 2 — two independent knockout strategies with multiple defined cellular/physiological phenotypes replicated across both lines","pmids":["21087515"],"is_preprint":false},{"year":2022,"finding":"B3GNT5 protein is required for surface expression of SSEA-1 (a lacto-series GSL antigen) and cancer stem cell-like properties in basal-like breast cancer cells; B3GNT5 protein itself is heavily N-glycosylated, and this N-glycosylation is critical for its protein stability.","method":"B3GNT5 knockout in BLBC cell lines; flow cytometry for SSEA-1 surface expression; Western blotting for N-glycosylation; mammosphere and colony formation assays; in vivo tumorigenesis model","journal":"Journal of experimental & clinical cancer research : CR","confidence":"Medium","confidence_rationale":"Tier 2 — KO with defined molecular (SSEA-1 loss) and cellular (CSC) phenotypes plus glycosylation mechanism, single lab","pmids":["35526049"],"is_preprint":false},{"year":2025,"finding":"Partial depletion of B3GNT5 in HeLa cells by CRISPR-Cas9 caused accumulation of its upstream substrates glucosylceramide (GlcCer) and lactosylceramide (LacCer) as measured by mass spectrometry, demonstrating that B3GNT5 acts downstream of LacCer in the GSL biosynthetic pathway; depletion also altered EMT marker expression, increased chemoresistance, and reduced RTK activation after serum stimulation.","method":"CRISPR-Cas9 partial depletion; mass spectrometry of GSLs; Western blotting for EMT markers and RTK phosphorylation; chemoresistance assays","journal":"BMC cancer","confidence":"Medium","confidence_rationale":"Tier 1-2 — direct biochemical (MS-confirmed substrate accumulation) plus multiple phenotypic readouts; single lab","pmids":["40847295"],"is_preprint":false},{"year":2020,"finding":"miR-30a-5p directly targets the 3′-UTR of B3GNT5, repressing its expression and downstream ERK and AKT signaling pathway activation, thereby reducing proliferation, invasion, and migration of trophoblast cells.","method":"Dual-luciferase 3′-UTR reporter assay confirming miR-30a-5p binding to B3GNT5; Western blotting for ERK/AKT phosphorylation; functional cell assays with miR-30a mimic/inhibitor in JAR and BeWo cells","journal":"Journal of cellular and molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 — luciferase reporter validates direct miRNA-target interaction; signaling pathway placed by phosphorylation WB; single lab","pmids":["32575164"],"is_preprint":false},{"year":2021,"finding":"The lncRNA MIR4435-2HG acts as a ceRNA to sponge miR-136-5p, which directly targets B3GNT5; this MIR4435-2HG/miR-136-5p/B3GNT5 axis regulates liver cancer cell proliferation, migration, and invasion.","method":"Luciferase reporter assays confirming miR-136-5p binding to MIR4435-2HG and to B3GNT5 3′-UTR; Western blotting for B3GNT5 protein; rescue experiments with miR-136-5p inhibitor upon MIR4435-2HG knockdown","journal":"Molecular medicine reports","confidence":"Medium","confidence_rationale":"Tier 2 — dual luciferase reporters validate both sponge and target interactions; rescue experiment supports pathway axis; single lab","pmids":["34859256"],"is_preprint":false},{"year":2024,"finding":"The transcription factor STAT5B enhances transcriptional activity of the B3GNT5 promoter in pancreatic cancer cells, identifying STAT5B as an upstream transcriptional activator of B3GNT5.","method":"B3GNT5 promoter-luciferase reporter assay with STAT5B overexpression in pancreatic cancer cells","journal":"iScience","confidence":"Low","confidence_rationale":"Tier 3 — single reporter assay, no ChIP or mutagenesis of binding site, single lab","pmids":["39319269"],"is_preprint":false},{"year":2025,"finding":"CircTNFRSF19 directly interacts with B3GNT5 mRNA (confirmed by RIP) and promotes N6-methyladenosine (m6A) modification of B3GNT5; CRISPR knockout of CircTNFRSF19 reduced B3GNT5 m6A levels and slowed TNBC cell growth.","method":"RNA immunoprecipitation (RIP); m6A methylation sequencing; CRISPR/Cas9 knockout of CircTNFRSF19 with m6A level measurement","journal":"SLAS technology","confidence":"Low","confidence_rationale":"Tier 3 — RIP confirms interaction but mechanism linking CircTNFRSF19 to m6A writer is not established; single lab, no mutagenesis","pmids":["40460976"],"is_preprint":false}],"current_model":"B3GNT5 encodes a β-1,3-N-acetylglucosaminyltransferase (Lc3 synthase) that transfers GlcNAc in a β1,3 linkage onto lactosylceramide to generate Lc3-ceramide, the obligate precursor for all lacto- and neolacto-series glycosphingolipids; loss of this activity in mice causes pre-implantation lethality or postnatal multi-system defects including B-cell dysfunction, and in cancer cells depletes SSEA-1 surface expression, disrupts cancer stem cell properties, and alters RTK signaling—with B3GNT5 protein stability itself dependent on N-glycosylation and its transcription regulated by STAT5B upstream and by miRNA-mediated (miR-30a-5p, miR-136-5p) and m6A-dependent post-transcriptional mechanisms."},"narrative":{"teleology":[{"year":2008,"claim":"Identifying B3GNT5 as the gene encoding Lc3 synthase resolved which enzyme initiates lacto-series glycosphingolipid biosynthesis and showed that this activity is essential for pre-implantation embryo survival.","evidence":"Gene knockout in mouse ES cells with enzymatic activity assay, GSL profiling, and germline knockout embryo genotyping","pmids":["19014510"],"confidence":"High","gaps":["Mechanism of pre-implantation lethality not defined at the molecular level","No crystal structure or catalytic-site mutagenesis of B3GNT5","Expression pattern in adult tissues only partially mapped by ISH"]},{"year":2010,"claim":"Two independent knockout strategies demonstrated that lacto/neolacto-series gangliosides generated by B3GNT5 are specifically required for B-cell homeostasis, germinal center formation, and reproductive function, revealing tissue-specific physiological consequences of Lc3 synthase loss.","evidence":"Two independent B3gnt5 knockout mouse lines with flow cytometry, histology, and phenotypic characterization","pmids":["21087515"],"confidence":"High","gaps":["Molecular mechanism by which lacto-series GSLs support B-cell survival or germinal center maintenance is unknown","Whether B-cell defects are cell-intrinsic was not tested by conditional knockout or transplantation","Reproductive failure mechanism undefined"]},{"year":2020,"claim":"Demonstrating that miR-30a-5p directly targets the B3GNT5 3′-UTR established the first post-transcriptional regulatory mechanism for B3GNT5, linking it to ERK/AKT signaling control in trophoblast cells.","evidence":"Dual-luciferase 3′-UTR reporter assay with miR-30a-5p mimic/inhibitor; phosphorylation Western blots in JAR and BeWo cells","pmids":["32575164"],"confidence":"Medium","gaps":["Whether miR-30a-5p regulation of B3GNT5 occurs in non-trophoblast contexts is untested","Pathway between B3GNT5 protein and ERK/AKT activation not delineated"]},{"year":2021,"claim":"Identification of a lncRNA MIR4435-2HG / miR-136-5p / B3GNT5 ceRNA axis in liver cancer revealed a second independent miRNA that represses B3GNT5 and showed that B3GNT5 levels are modulated by competing endogenous RNA networks.","evidence":"Dual luciferase reporters for sponge and target interactions; rescue experiments with miR-136-5p inhibitor in liver cancer cells","pmids":["34859256"],"confidence":"Medium","gaps":["Functional readout limited to proliferation/migration; GSL-level changes not measured","In vivo relevance of ceRNA axis not tested"]},{"year":2022,"claim":"Knockout of B3GNT5 in basal-like breast cancer cells proved that this enzyme is the sole source of SSEA-1 surface antigen and supports cancer stem cell properties, while also revealing that B3GNT5 protein stability is governed by its own N-glycosylation.","evidence":"B3GNT5 knockout in BLBC lines; flow cytometry for SSEA-1; mammosphere/colony formation assays; N-glycosylation site mutagenesis; in vivo tumorigenesis","pmids":["35526049"],"confidence":"Medium","gaps":["Specific N-glycosylation sites critical for stability not fully mapped","Whether SSEA-1 loss itself drives the cancer stem cell phenotype versus other lacto-series GSL changes is not resolved","Single lab finding"]},{"year":2025,"claim":"Mass spectrometry-confirmed accumulation of GlcCer and LacCer upon B3GNT5 depletion in HeLa cells directly validated its position downstream of LacCer in the GSL pathway and linked lacto-series GSL depletion to altered EMT, reduced RTK activation, and chemoresistance.","evidence":"CRISPR partial depletion; mass spectrometry of GSLs; Western blot for EMT markers and RTK phosphorylation; chemoresistance assays in HeLa cells","pmids":["40847295"],"confidence":"Medium","gaps":["Partial rather than complete depletion; residual B3GNT5 activity may complicate interpretation","Whether EMT and chemoresistance phenotypes are directly caused by specific GSL species or by global GSL remodeling is unclear","Single cell line"]},{"year":null,"claim":"The structural basis for B3GNT5 substrate specificity, the identity of the GSL species that mediate B-cell and reproductive phenotypes, and whether B3GNT5 loss-of-function causes human disease remain unknown.","evidence":"","pmids":[],"confidence":"High","gaps":["No crystal or cryo-EM structure of B3GNT5","No conditional knockout to determine cell-intrinsic requirements in specific tissues","No human Mendelian disease linked to B3GNT5 mutations","Mechanism connecting lacto-series GSL loss to RTK signaling and EMT not resolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,1,3]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[0]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0,1,3]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[1]}],"complexes":[],"partners":["MIR-30A-5P","MIR-136-5P"],"other_free_text":[]},"mechanistic_narrative":"B3GNT5 encodes the β-1,3-N-acetylglucosaminyltransferase known as Lc3 synthase, the committed enzyme that transfers GlcNAc in a β1,3 linkage onto lactosylceramide to generate lactotriosylceramide (Lc3Cer), the obligate precursor of all lacto- and neolacto-series glycosphingolipids [PMID:19014510]. Germline knockout in mice causes pre-implantation lethality or, with alternative targeting strategies, postnatal B-cell deficiency with loss of splenic germinal centers, reproductive defects, and early death, establishing that lacto/neolacto-series gangliosides are essential for B-cell development and fertility [PMID:19014510, PMID:21087515]. In cancer cells, B3GNT5 loss abolishes surface SSEA-1 expression and cancer stem cell properties, alters EMT markers and RTK signaling, and increases chemoresistance, while B3GNT5 protein stability itself depends on its own N-glycosylation [PMID:35526049, PMID:40847295]. B3GNT5 expression is post-transcriptionally repressed by miR-30a-5p and miR-136-5p, which directly target its 3′-UTR and modulate downstream ERK/AKT signaling in trophoblast and liver cancer cells [PMID:32575164, PMID:34859256]."},"prefetch_data":{"uniprot":{"accession":"Q9BYG0","full_name":"Lactosylceramide 1,3-N-acetyl-beta-D-glucosaminyltransferase","aliases":["Lactotriaosylceramide synthase","Lc(3)Cer synthase","Lc3 synthase","UDP-GlcNAc:beta-Gal beta-1,3-N-acetylglucosaminyltransferase 5","BGnT-5","Beta-1,3-Gn-T5","Beta-1,3-N-acetylglucosaminyltransferase 5","Beta3Gn-T5"],"length_aa":378,"mass_kda":44.1,"function":"Beta-1,3-N-acetylglucosaminyltransferase that plays a key role in the synthesis of lacto- or neolacto-series carbohydrate chains on glycolipids, notably by participating in biosynthesis of HNK-1 and Lewis X carbohydrate structures. Has strong activity toward lactosylceramide (LacCer) and neolactotetraosylceramide (nLc(4)Cer; paragloboside), resulting in the synthesis of Lc(3)Cer and neolactopentaosylceramide (nLc(5)Cer), respectively. Probably plays a central role in regulating neolacto-series glycolipid synthesis during embryonic development","subcellular_location":"Golgi apparatus membrane","url":"https://www.uniprot.org/uniprotkb/Q9BYG0/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/B3GNT5","classification":"Not Classified","n_dependent_lines":17,"n_total_lines":1208,"dependency_fraction":0.014072847682119206},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/B3GNT5","total_profiled":1310},"omim":[{"mim_id":"615333","title":"BETA-1,3-N-ACETYLGLUCOSAMINYLTRANSFERASE 5; B3GNT5","url":"https://www.omim.org/entry/615333"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoli","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"bone marrow","ntpm":72.3}],"url":"https://www.proteinatlas.org/search/B3GNT5"},"hgnc":{"alias_symbol":["B3GN-T5","beta3Gn-T5"],"prev_symbol":[]},"alphafold":{"accession":"Q9BYG0","domains":[{"cath_id":"3.90.550.10","chopping":"74-298","consensus_level":"high","plddt":96.3163,"start":74,"end":298},{"cath_id":"-","chopping":"312-375","consensus_level":"medium","plddt":93.8595,"start":312,"end":375}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BYG0","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BYG0-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BYG0-F1-predicted_aligned_error_v6.png","plddt_mean":90.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=B3GNT5","jax_strain_url":"https://www.jax.org/strain/search?query=B3GNT5"},"sequence":{"accession":"Q9BYG0","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9BYG0.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9BYG0/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BYG0"}},"corpus_meta":[{"pmid":"19014510","id":"PMC_19014510","title":"The Lc3-synthase gene B3gnt5 is essential to pre-implantation development of the murine embryo.","date":"2008","source":"BMC developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/19014510","citation_count":36,"is_preprint":false},{"pmid":"34859256","id":"PMC_34859256","title":"lncRNA MIR4435‑2HG promotes the progression of liver cancer by upregulating B3GNT5 expression.","date":"2021","source":"Molecular medicine reports","url":"https://pubmed.ncbi.nlm.nih.gov/34859256","citation_count":25,"is_preprint":false},{"pmid":"35526049","id":"PMC_35526049","title":"Elevated transcription and glycosylation of B3GNT5 promotes breast cancer aggressiveness.","date":"2022","source":"Journal of experimental & clinical cancer research : CR","url":"https://pubmed.ncbi.nlm.nih.gov/35526049","citation_count":24,"is_preprint":false},{"pmid":"32677340","id":"PMC_32677340","title":"B3GNT5 is a novel marker correlated with stem-like phenotype and poor clinical outcome in human gliomas.","date":"2020","source":"CNS neuroscience & therapeutics","url":"https://pubmed.ncbi.nlm.nih.gov/32677340","citation_count":20,"is_preprint":false},{"pmid":"21087515","id":"PMC_21087515","title":"Multiple phenotypic changes in mice after knockout of the B3gnt5 gene, encoding Lc3 synthase--a key enzyme in lacto-neolacto ganglioside synthesis.","date":"2010","source":"BMC developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/21087515","citation_count":18,"is_preprint":false},{"pmid":"32575164","id":"PMC_32575164","title":"MiR-30a-5p inhibits proliferation and metastasis of hydatidiform mole by regulating B3GNT5 through ERK/AKT pathways.","date":"2020","source":"Journal of cellular and molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/32575164","citation_count":6,"is_preprint":false},{"pmid":"29416099","id":"PMC_29416099","title":"Generation and characterization of a IgG monoclonal antibody specific for GM3 (NeuGc) ganglioside by immunizing β3Gn-T5 knockout mice.","date":"2018","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/29416099","citation_count":6,"is_preprint":false},{"pmid":"39671359","id":"PMC_39671359","title":"Pan-cancer analysis of B3GNT5 with potential implications for cancer immunotherapy and cancer stem cell stemness.","date":"2024","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/39671359","citation_count":3,"is_preprint":false},{"pmid":"21956797","id":"PMC_21956797","title":"Association of B3GNT5 polymorphisms with susceptibility to ETEC F4ab/ac in the white Duroc × Erhualian intercross and 15 outbred pig breeds.","date":"2011","source":"Biochemical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/21956797","citation_count":3,"is_preprint":false},{"pmid":"21928695","id":"PMC_21928695","title":"Strong antibody reaction against glycosphingolipids injected in liposome-embedded forms in beta3GN-T5 knockout mice.","date":"2011","source":"Nagoya journal of medical science","url":"https://pubmed.ncbi.nlm.nih.gov/21928695","citation_count":2,"is_preprint":false},{"pmid":"40847295","id":"PMC_40847295","title":"Regulation of EMT-MET and chemoresistance by the Lc3Cer-synthase B3GNT5.","date":"2025","source":"BMC cancer","url":"https://pubmed.ncbi.nlm.nih.gov/40847295","citation_count":1,"is_preprint":false},{"pmid":"39319269","id":"PMC_39319269","title":"B3GNT5 is a novel marker correlated with malignant phenotype and poor outcome in pancreatic cancer.","date":"2024","source":"iScience","url":"https://pubmed.ncbi.nlm.nih.gov/39319269","citation_count":1,"is_preprint":false},{"pmid":"40460976","id":"PMC_40460976","title":"CircTNFRSF19 facilitates triple negative breast cancer cell growth by regulating N6-methyladenosine modification of B3GNT5: Medical biological image simulation.","date":"2025","source":"SLAS technology","url":"https://pubmed.ncbi.nlm.nih.gov/40460976","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":8191,"output_tokens":2237,"usd":0.029064},"stage2":{"model":"claude-opus-4-6","input_tokens":5529,"output_tokens":2099,"usd":0.12018},"total_usd":0.149244,"stage1_batch_id":"msgbatch_01TqNM6p6FsoMBT2jzQTwKBr","stage2_batch_id":"msgbatch_01Ya473eco8sTHbvRymQaU8o","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2008,\n      \"finding\": \"B3GNT5 (B3gnt5) encodes the Lc3-synthase enzyme that catalyzes formation of the Lc3 (lactotriosylceramide) structure, the core trisaccharide of lactoseries glycosphingolipids; knockout in mouse embryonic stem cells reduced Lc3-synthase activity and lactoseries GSL levels, and germline knockout caused pre-implantation lethality.\",\n      \"method\": \"Gene knockout in mouse ES cells with enzymatic activity assay for Lc3-synthase; GSL profiling; germline knockout with embryo genotyping; in situ hybridization for expression\",\n      \"journal\": \"BMC developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct enzymatic assay in knockout ES cells plus multiple orthogonal methods (GSL profiling, embryo genotyping, ISH)\",\n      \"pmids\": [\"19014510\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"B3gnt5-encoded Lc3 synthase is required for lacto- and neolacto-series ganglioside biosynthesis; knockout mice lacking lacto-neolacto series gangliosides showed B-cell abnormalities (reduced splenic B-cell numbers, loss of germinal centers, impaired hybridoma fusion), reproductive defects, splenomegaly, and early death, establishing essential physiological roles for these GSLs.\",\n      \"method\": \"Two independent B3gnt5 gene knockout strategies in mice; histological and flow cytometric analysis of B-cell compartments; phenotypic characterization of homozygous and heterozygous knockouts\",\n      \"journal\": \"BMC developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — two independent knockout strategies with multiple defined cellular/physiological phenotypes replicated across both lines\",\n      \"pmids\": [\"21087515\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"B3GNT5 protein is required for surface expression of SSEA-1 (a lacto-series GSL antigen) and cancer stem cell-like properties in basal-like breast cancer cells; B3GNT5 protein itself is heavily N-glycosylated, and this N-glycosylation is critical for its protein stability.\",\n      \"method\": \"B3GNT5 knockout in BLBC cell lines; flow cytometry for SSEA-1 surface expression; Western blotting for N-glycosylation; mammosphere and colony formation assays; in vivo tumorigenesis model\",\n      \"journal\": \"Journal of experimental & clinical cancer research : CR\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO with defined molecular (SSEA-1 loss) and cellular (CSC) phenotypes plus glycosylation mechanism, single lab\",\n      \"pmids\": [\"35526049\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Partial depletion of B3GNT5 in HeLa cells by CRISPR-Cas9 caused accumulation of its upstream substrates glucosylceramide (GlcCer) and lactosylceramide (LacCer) as measured by mass spectrometry, demonstrating that B3GNT5 acts downstream of LacCer in the GSL biosynthetic pathway; depletion also altered EMT marker expression, increased chemoresistance, and reduced RTK activation after serum stimulation.\",\n      \"method\": \"CRISPR-Cas9 partial depletion; mass spectrometry of GSLs; Western blotting for EMT markers and RTK phosphorylation; chemoresistance assays\",\n      \"journal\": \"BMC cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 — direct biochemical (MS-confirmed substrate accumulation) plus multiple phenotypic readouts; single lab\",\n      \"pmids\": [\"40847295\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"miR-30a-5p directly targets the 3′-UTR of B3GNT5, repressing its expression and downstream ERK and AKT signaling pathway activation, thereby reducing proliferation, invasion, and migration of trophoblast cells.\",\n      \"method\": \"Dual-luciferase 3′-UTR reporter assay confirming miR-30a-5p binding to B3GNT5; Western blotting for ERK/AKT phosphorylation; functional cell assays with miR-30a mimic/inhibitor in JAR and BeWo cells\",\n      \"journal\": \"Journal of cellular and molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — luciferase reporter validates direct miRNA-target interaction; signaling pathway placed by phosphorylation WB; single lab\",\n      \"pmids\": [\"32575164\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The lncRNA MIR4435-2HG acts as a ceRNA to sponge miR-136-5p, which directly targets B3GNT5; this MIR4435-2HG/miR-136-5p/B3GNT5 axis regulates liver cancer cell proliferation, migration, and invasion.\",\n      \"method\": \"Luciferase reporter assays confirming miR-136-5p binding to MIR4435-2HG and to B3GNT5 3′-UTR; Western blotting for B3GNT5 protein; rescue experiments with miR-136-5p inhibitor upon MIR4435-2HG knockdown\",\n      \"journal\": \"Molecular medicine reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — dual luciferase reporters validate both sponge and target interactions; rescue experiment supports pathway axis; single lab\",\n      \"pmids\": [\"34859256\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The transcription factor STAT5B enhances transcriptional activity of the B3GNT5 promoter in pancreatic cancer cells, identifying STAT5B as an upstream transcriptional activator of B3GNT5.\",\n      \"method\": \"B3GNT5 promoter-luciferase reporter assay with STAT5B overexpression in pancreatic cancer cells\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single reporter assay, no ChIP or mutagenesis of binding site, single lab\",\n      \"pmids\": [\"39319269\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CircTNFRSF19 directly interacts with B3GNT5 mRNA (confirmed by RIP) and promotes N6-methyladenosine (m6A) modification of B3GNT5; CRISPR knockout of CircTNFRSF19 reduced B3GNT5 m6A levels and slowed TNBC cell growth.\",\n      \"method\": \"RNA immunoprecipitation (RIP); m6A methylation sequencing; CRISPR/Cas9 knockout of CircTNFRSF19 with m6A level measurement\",\n      \"journal\": \"SLAS technology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — RIP confirms interaction but mechanism linking CircTNFRSF19 to m6A writer is not established; single lab, no mutagenesis\",\n      \"pmids\": [\"40460976\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"B3GNT5 encodes a β-1,3-N-acetylglucosaminyltransferase (Lc3 synthase) that transfers GlcNAc in a β1,3 linkage onto lactosylceramide to generate Lc3-ceramide, the obligate precursor for all lacto- and neolacto-series glycosphingolipids; loss of this activity in mice causes pre-implantation lethality or postnatal multi-system defects including B-cell dysfunction, and in cancer cells depletes SSEA-1 surface expression, disrupts cancer stem cell properties, and alters RTK signaling—with B3GNT5 protein stability itself dependent on N-glycosylation and its transcription regulated by STAT5B upstream and by miRNA-mediated (miR-30a-5p, miR-136-5p) and m6A-dependent post-transcriptional mechanisms.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"B3GNT5 encodes the β-1,3-N-acetylglucosaminyltransferase known as Lc3 synthase, the committed enzyme that transfers GlcNAc in a β1,3 linkage onto lactosylceramide to generate lactotriosylceramide (Lc3Cer), the obligate precursor of all lacto- and neolacto-series glycosphingolipids [PMID:19014510]. Germline knockout in mice causes pre-implantation lethality or, with alternative targeting strategies, postnatal B-cell deficiency with loss of splenic germinal centers, reproductive defects, and early death, establishing that lacto/neolacto-series gangliosides are essential for B-cell development and fertility [PMID:19014510, PMID:21087515]. In cancer cells, B3GNT5 loss abolishes surface SSEA-1 expression and cancer stem cell properties, alters EMT markers and RTK signaling, and increases chemoresistance, while B3GNT5 protein stability itself depends on its own N-glycosylation [PMID:35526049, PMID:40847295]. B3GNT5 expression is post-transcriptionally repressed by miR-30a-5p and miR-136-5p, which directly target its 3′-UTR and modulate downstream ERK/AKT signaling in trophoblast and liver cancer cells [PMID:32575164, PMID:34859256].\",\n  \"teleology\": [\n    {\n      \"year\": 2008,\n      \"claim\": \"Identifying B3GNT5 as the gene encoding Lc3 synthase resolved which enzyme initiates lacto-series glycosphingolipid biosynthesis and showed that this activity is essential for pre-implantation embryo survival.\",\n      \"evidence\": \"Gene knockout in mouse ES cells with enzymatic activity assay, GSL profiling, and germline knockout embryo genotyping\",\n      \"pmids\": [\"19014510\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Mechanism of pre-implantation lethality not defined at the molecular level\",\n        \"No crystal structure or catalytic-site mutagenesis of B3GNT5\",\n        \"Expression pattern in adult tissues only partially mapped by ISH\"\n      ]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Two independent knockout strategies demonstrated that lacto/neolacto-series gangliosides generated by B3GNT5 are specifically required for B-cell homeostasis, germinal center formation, and reproductive function, revealing tissue-specific physiological consequences of Lc3 synthase loss.\",\n      \"evidence\": \"Two independent B3gnt5 knockout mouse lines with flow cytometry, histology, and phenotypic characterization\",\n      \"pmids\": [\"21087515\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Molecular mechanism by which lacto-series GSLs support B-cell survival or germinal center maintenance is unknown\",\n        \"Whether B-cell defects are cell-intrinsic was not tested by conditional knockout or transplantation\",\n        \"Reproductive failure mechanism undefined\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Demonstrating that miR-30a-5p directly targets the B3GNT5 3′-UTR established the first post-transcriptional regulatory mechanism for B3GNT5, linking it to ERK/AKT signaling control in trophoblast cells.\",\n      \"evidence\": \"Dual-luciferase 3′-UTR reporter assay with miR-30a-5p mimic/inhibitor; phosphorylation Western blots in JAR and BeWo cells\",\n      \"pmids\": [\"32575164\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether miR-30a-5p regulation of B3GNT5 occurs in non-trophoblast contexts is untested\",\n        \"Pathway between B3GNT5 protein and ERK/AKT activation not delineated\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identification of a lncRNA MIR4435-2HG / miR-136-5p / B3GNT5 ceRNA axis in liver cancer revealed a second independent miRNA that represses B3GNT5 and showed that B3GNT5 levels are modulated by competing endogenous RNA networks.\",\n      \"evidence\": \"Dual luciferase reporters for sponge and target interactions; rescue experiments with miR-136-5p inhibitor in liver cancer cells\",\n      \"pmids\": [\"34859256\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Functional readout limited to proliferation/migration; GSL-level changes not measured\",\n        \"In vivo relevance of ceRNA axis not tested\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Knockout of B3GNT5 in basal-like breast cancer cells proved that this enzyme is the sole source of SSEA-1 surface antigen and supports cancer stem cell properties, while also revealing that B3GNT5 protein stability is governed by its own N-glycosylation.\",\n      \"evidence\": \"B3GNT5 knockout in BLBC lines; flow cytometry for SSEA-1; mammosphere/colony formation assays; N-glycosylation site mutagenesis; in vivo tumorigenesis\",\n      \"pmids\": [\"35526049\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Specific N-glycosylation sites critical for stability not fully mapped\",\n        \"Whether SSEA-1 loss itself drives the cancer stem cell phenotype versus other lacto-series GSL changes is not resolved\",\n        \"Single lab finding\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Mass spectrometry-confirmed accumulation of GlcCer and LacCer upon B3GNT5 depletion in HeLa cells directly validated its position downstream of LacCer in the GSL pathway and linked lacto-series GSL depletion to altered EMT, reduced RTK activation, and chemoresistance.\",\n      \"evidence\": \"CRISPR partial depletion; mass spectrometry of GSLs; Western blot for EMT markers and RTK phosphorylation; chemoresistance assays in HeLa cells\",\n      \"pmids\": [\"40847295\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Partial rather than complete depletion; residual B3GNT5 activity may complicate interpretation\",\n        \"Whether EMT and chemoresistance phenotypes are directly caused by specific GSL species or by global GSL remodeling is unclear\",\n        \"Single cell line\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The structural basis for B3GNT5 substrate specificity, the identity of the GSL species that mediate B-cell and reproductive phenotypes, and whether B3GNT5 loss-of-function causes human disease remain unknown.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No crystal or cryo-EM structure of B3GNT5\",\n        \"No conditional knockout to determine cell-intrinsic requirements in specific tissues\",\n        \"No human Mendelian disease linked to B3GNT5 mutations\",\n        \"Mechanism connecting lacto-series GSL loss to RTK signaling and EMT not resolved\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 1, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0, 1, 3]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"miR-30a-5p\",\n      \"miR-136-5p\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}