{"gene":"VBP1","run_date":"2026-04-28T23:00:23","timeline":{"discoveries":[{"year":1996,"finding":"VBP1 directly binds to pVHL in vivo, requiring the C-terminal end of pVHL for interaction; co-expression of VBP1 with VHL causes VBP1 to translocate from the cytoplasm to the nucleus, indicating VHL controls VBP1 subcellular localization.","method":"Yeast two-hybrid, immunoprecipitation/Western blotting, epitope-tag co-expression localization studies","journal":"Cancer Research","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP plus two-hybrid plus localization experiments; foundational paper with 106 citations","pmids":["8674032"],"is_preprint":false},{"year":2008,"finding":"VBP1 physically interacts with hepatitis B virus X protein (HBx) and facilitates HBx-induced NF-κB activation and cell proliferation.","method":"Yeast two-hybrid, in vitro and in vivo immunoprecipitation, reporter assays for NF-κB activity, proliferation assays","journal":"BMB Reports","confidence":"Medium","confidence_rationale":"Tier 2–3 — Co-IP confirmed in vitro and in vivo with functional NF-κB readout, single lab","pmids":["18315953"],"is_preprint":false},{"year":2013,"finding":"VBP1 targets hMSH4 for proteasomal and autophagy-mediated degradation via ubiquitination; VBP1 interacts with p97 (AAA+ ATPase) and forms a complex with VHL and p97 on hMSH4, promoting its polyubiquitination and degradation.","method":"Co-immunoprecipitation, ubiquitination assays, proteasome/autophagy inhibitor experiments, knockdown studies in HEK293T cells","journal":"FASEB Journal","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (Co-IP, ubiquitination assay, inhibitor studies) demonstrating mechanistic pathway","pmids":["23964080"],"is_preprint":false},{"year":2017,"finding":"VBP1 enhances the stability of pVHL and facilitates pVHL-mediated ubiquitination and degradation of HIF-1α, thereby suppressing HIF-1α-induced epithelial-mesenchymal transition in vitro and tumor metastasis in vivo.","method":"Co-immunoprecipitation, ubiquitination assays, stability assays, in vitro EMT assays, in vivo metastasis models","journal":"The FEBS Journal","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (Co-IP, ubiquitination, in vivo) in a single study with clear mechanistic readout","pmids":["29121446"],"is_preprint":false},{"year":2020,"finding":"VBP1 directly binds all four TCF/LEF family members and pVHL; either overexpression or knockdown of VBP1 increases the TCF/LEF–pVHL association, leading to proteasomal degradation of TCF/LEFs and reduced Wnt/β-catenin signaling.","method":"Co-immunoprecipitation, proteasome inhibitor experiments, Wnt reporter assays, zebrafish embryo model, knockdown/overexpression in cultured cells","journal":"Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (Co-IP, reporter assay, in vivo zebrafish, pharmacological inhibition) demonstrating mechanistic pathway","pmids":["32989053"],"is_preprint":false},{"year":2023,"finding":"VBP1 negatively regulates HIF-1α (but not HIF-2α) by interacting with ubiquitin ligase CHIP and HSP70; VBP1 promotes CHIP-mediated degradation of HIF-1α in a pVHL-independent manner; vbp1 deletion in zebrafish causes Hif-1α accumulation and upregulation of Hif target genes.","method":"Co-immunoprecipitation, protein degradation assays, zebrafish vbp1 knockout, in vitro cell culture models, CHIP/HSP70 interaction studies","journal":"Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP with new partners (CHIP, HSP70), in vivo zebrafish knockout, and in vitro degradation assays; multiple orthogonal methods","pmids":["37201586"],"is_preprint":false},{"year":2003,"finding":"C. elegans VBP-1 (ortholog) is required for embryonic morphogenesis; RNAi knockdown of VBP-1 arrests embryogenesis at the morula stage.","method":"RNAi (dsRNA interference) in C. elegans, embryo morphology assessment","journal":"Oncology Reports","confidence":"Medium","confidence_rationale":"Tier 2 — clean loss-of-function RNAi with defined developmental phenotype in ortholog; single lab","pmids":["12579260"],"is_preprint":false}],"current_model":"VBP1 is a pVHL-binding protein that acts as a scaffold/co-regulator: it binds pVHL's C-terminal domain and enhances pVHL-mediated ubiquitination and degradation of HIF-1α and TCF/LEF transcription factors, while also promoting pVHL-independent HIF-1α degradation through a CHIP/HSP70 ubiquitin-ligase complex; additionally, VBP1 forms complexes with p97 to target hMSH4 for proteasomal/autophagic degradation, interacts with HBx to facilitate NF-κB activation, and controls the nucleocytoplasmic localization of pVHL-associated proteins."},"narrative":{"teleology":[{"year":1996,"claim":"Identifying VBP1 as a direct pVHL-binding protein established the first molecular link between VBP1 and the VHL tumor suppressor pathway, and revealed that VHL controls VBP1 nucleocytoplasmic localization.","evidence":"Yeast two-hybrid screen and reciprocal co-immunoprecipitation with epitope-tagged localization studies in mammalian cells","pmids":["8674032"],"confidence":"High","gaps":["Functional consequence of VBP1–pVHL interaction on pVHL activity was unknown","Endogenous VBP1 substrates or downstream targets not identified","Structural basis of the C-terminal pVHL–VBP1 interface not resolved"]},{"year":2003,"claim":"Demonstrating that the C. elegans VBP-1 ortholog is required for embryonic morphogenesis established an essential developmental role, moving VBP1 beyond a mere binding partner.","evidence":"RNAi knockdown in C. elegans causing morula-stage arrest","pmids":["12579260"],"confidence":"Medium","gaps":["Mechanism by which VBP-1 loss causes morphogenesis arrest was not defined","Whether developmental role depends on VHL interaction was untested","Single-organism RNAi study; not confirmed in other metazoan models at that time"]},{"year":2008,"claim":"Showing that VBP1 interacts with hepatitis B virus HBx protein and facilitates NF-κB activation expanded VBP1's functional scope to viral pathogenesis and inflammatory signaling.","evidence":"Yeast two-hybrid, in vitro/in vivo co-immunoprecipitation, and NF-κB reporter assays in cultured cells","pmids":["18315953"],"confidence":"Medium","gaps":["Mechanism linking VBP1–HBx interaction to NF-κB activation was not delineated","Whether this involves pVHL or ubiquitination was not tested","Single-lab finding without independent replication"]},{"year":2013,"claim":"Revealing that VBP1 recruits p97 and promotes polyubiquitination and dual proteasomal/autophagic degradation of hMSH4 established VBP1 as an active scaffold for substrate-directed protein turnover beyond the canonical pVHL–HIF axis.","evidence":"Co-immunoprecipitation, ubiquitination assays, proteasome and autophagy inhibitor experiments in HEK293T cells","pmids":["23964080"],"confidence":"High","gaps":["Identity of the E3 ligase responsible for hMSH4 ubiquitination in this complex was not definitively assigned","Physiological consequence of hMSH4 degradation (e.g., meiotic recombination effects) was not tested","Whether p97 interaction is direct or bridged by VHL was unclear"]},{"year":2017,"claim":"Demonstrating that VBP1 stabilizes pVHL and enhances pVHL-mediated HIF-1α ubiquitination and degradation connected VBP1 to the hypoxia response and showed it suppresses epithelial-mesenchymal transition and metastasis in vivo.","evidence":"Co-immunoprecipitation, ubiquitination and stability assays, in vitro EMT assays, and in vivo tumor metastasis models","pmids":["29121446"],"confidence":"High","gaps":["Mechanism by which VBP1 stabilizes pVHL protein was not resolved","Whether VBP1 regulates HIF-2α through pVHL was not addressed","Structural determinants of VBP1-enhanced ubiquitination were unknown"]},{"year":2020,"claim":"Showing that VBP1 directly binds all four TCF/LEF transcription factors and bridges them to pVHL for proteasomal degradation revealed VBP1 as a negative regulator of Wnt/β-catenin signaling.","evidence":"Co-immunoprecipitation, Wnt reporter assays, proteasome inhibitor experiments, zebrafish developmental model, and knockdown/overexpression in cultured cells","pmids":["32989053"],"confidence":"High","gaps":["Paradoxical effect where both overexpression and knockdown enhance TCF/LEF–pVHL association was mechanistically unexplained","Whether VBP1's role in Wnt suppression is relevant to tumorigenesis in vivo was not tested","Stoichiometric versus catalytic role of VBP1 in bridging TCF/LEF to pVHL was unclear"]},{"year":2023,"claim":"Identifying the CHIP/HSP70 complex as a pVHL-independent route by which VBP1 targets HIF-1α (but not HIF-2α) for degradation demonstrated functional specificity among HIF isoforms and expanded VBP1's E3 ligase partnerships.","evidence":"Reciprocal co-immunoprecipitation, protein degradation assays, zebrafish vbp1 knockout with Hif target gene analysis","pmids":["37201586"],"confidence":"High","gaps":["Structural basis for HIF-1α selectivity over HIF-2α in the CHIP/HSP70 pathway was not determined","Relative contribution of VHL-dependent versus CHIP-dependent HIF-1α degradation under physiological conditions is unknown","Whether VBP1 functions as a co-chaperone or adaptor within the CHIP/HSP70 complex was not resolved"]},{"year":null,"claim":"The structural basis of VBP1's multi-partner scaffolding, its potential enzymatic activities, and its roles in human disease beyond cancer remain undefined.","evidence":"","pmids":[],"confidence":"Low","gaps":["No crystal or cryo-EM structure of VBP1 or its complexes is available","Whether VBP1 has intrinsic catalytic activity or functions purely as a scaffold is unresolved","Genetic association of VBP1 mutations with human disease has not been established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,2,3,4,5]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[2,3,4,5]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[4,1]}],"complexes":[],"partners":["VHL","HIF1A","STUB1","HSPA1A","VCP","MSH4","TCF7L2","HBX"],"other_free_text":[]},"mechanistic_narrative":"VBP1 functions as a scaffold protein that coordinates ubiquitin-dependent degradation of multiple substrates, primarily through its interaction with the tumor suppressor pVHL and additional E3 ubiquitin ligase complexes. VBP1 directly binds the C-terminal domain of pVHL and enhances pVHL stability and its ubiquitin ligase activity toward HIF-1α, thereby suppressing HIF-1α-driven epithelial-mesenchymal transition and metastasis; it similarly promotes pVHL-mediated proteasomal degradation of all four TCF/LEF transcription factors, attenuating Wnt/β-catenin signaling [PMID:8674032, PMID:29121446, PMID:32989053]. VBP1 also mediates pVHL-independent HIF-1α degradation by recruiting the CHIP/HSP70 ubiquitin ligase complex, and it cooperates with the AAA+ ATPase p97 to target hMSH4 for proteasomal and autophagic degradation [PMID:37201586, PMID:23964080]. The C. elegans ortholog is essential for embryonic morphogenesis, indicating a conserved role in development [PMID:12579260]."},"prefetch_data":{"uniprot":{"accession":"P61758","full_name":"Prefoldin subunit 3","aliases":["HIBBJ46","von Hippel-Lindau-binding protein 1","VBP-1","VHL-binding protein 1"],"length_aa":197,"mass_kda":22.6,"function":"Binds specifically to cytosolic chaperonin (c-CPN) and transfers target proteins to it. Binds to nascent polypeptide chain and promotes folding in an environment in which there are many competing pathways for nonnative proteins","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/P61758/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/VBP1","classification":"Common Essential","n_dependent_lines":862,"n_total_lines":1208,"dependency_fraction":0.7135761589403974},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"PFDN6","stoichiometry":10.0},{"gene":"CCT2","stoichiometry":0.2},{"gene":"CLINT1","stoichiometry":0.2},{"gene":"GDI1","stoichiometry":0.2},{"gene":"MAP4","stoichiometry":0.2},{"gene":"TUBA1B","stoichiometry":0.2},{"gene":"TUBB4B","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/VBP1","total_profiled":1310},"omim":[{"mim_id":"604897","title":"PREFOLDIN 1; PFDN1","url":"https://www.omim.org/entry/604897"},{"mim_id":"603135","title":"CULLIN 2; CUL2","url":"https://www.omim.org/entry/603135"},{"mim_id":"308300","title":"INCONTINENTIA PIGMENTI; IP","url":"https://www.omim.org/entry/308300"},{"mim_id":"300815","title":"CHROMOSOME Xq28 DUPLICATION SYNDROME","url":"https://www.omim.org/entry/300815"},{"mim_id":"300133","title":"VON HIPPEL-LINDAU BINDING PROTEIN 1; VBP1","url":"https://www.omim.org/entry/300133"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Cytosol","reliability":"Supported"},{"location":"Vesicles","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/VBP1"},"hgnc":{"alias_symbol":["PFD3","PFDN3"],"prev_symbol":[]},"alphafold":{"accession":"P61758","domains":[{"cath_id":"1.10.287.370","chopping":"43-183","consensus_level":"high","plddt":94.0559,"start":43,"end":183}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P61758","model_url":"https://alphafold.ebi.ac.uk/files/AF-P61758-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P61758-F1-predicted_aligned_error_v6.png","plddt_mean":86.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=VBP1","jax_strain_url":"https://www.jax.org/strain/search?query=VBP1"},"sequence":{"accession":"P61758","fasta_url":"https://rest.uniprot.org/uniprotkb/P61758.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P61758/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P61758"}},"corpus_meta":[{"pmid":"8674032","id":"PMC_8674032","title":"Identification of a novel protein (VBP-1) binding to the von Hippel-Lindau (VHL) tumor suppressor gene product.","date":"1996","source":"Cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/8674032","citation_count":106,"is_preprint":false},{"pmid":"18315953","id":"PMC_18315953","title":"Hepatitis B virus X protein enhances NFkappaB activity through cooperating with VBP1.","date":"2008","source":"BMB reports","url":"https://pubmed.ncbi.nlm.nih.gov/18315953","citation_count":40,"is_preprint":false},{"pmid":"29121446","id":"PMC_29121446","title":"VBP1 represses cancer metastasis by enhancing HIF-1α degradation induced by pVHL.","date":"2017","source":"The FEBS journal","url":"https://pubmed.ncbi.nlm.nih.gov/29121446","citation_count":28,"is_preprint":false},{"pmid":"9339366","id":"PMC_9339366","title":"Characterization of the gene (VBP1) and transcript for the von Hippel-Lindau binding protein and isolation of the highly conserved murine homologue.","date":"1997","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/9339366","citation_count":24,"is_preprint":false},{"pmid":"23964080","id":"PMC_23964080","title":"VBP1 facilitates proteasome and autophagy-mediated degradation of MutS homologue hMSH4.","date":"2013","source":"FASEB journal : official publication of the Federation of American Societies for Experimental Biology","url":"https://pubmed.ncbi.nlm.nih.gov/23964080","citation_count":20,"is_preprint":false},{"pmid":"10441001","id":"PMC_10441001","title":"Genomic organization and chromosomal localization of the human CUL2 gene and the role of von Hippel-Lindau tumor suppressor-binding protein (CUL2 and VBP1) mutation and loss in renal-cell carcinoma development.","date":"1999","source":"Genes, chromosomes & cancer","url":"https://pubmed.ncbi.nlm.nih.gov/10441001","citation_count":18,"is_preprint":false},{"pmid":"32989053","id":"PMC_32989053","title":"VBP1 modulates Wnt/β-catenin signaling by mediating the stability of the transcription factors TCF/LEFs.","date":"2020","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/32989053","citation_count":17,"is_preprint":false},{"pmid":"37201586","id":"PMC_37201586","title":"VBP1 negatively regulates CHIP and selectively inhibits the activity of hypoxia-inducible factor (HIF)-1α but not HIF-2α.","date":"2023","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/37201586","citation_count":12,"is_preprint":false},{"pmid":"9931330","id":"PMC_9931330","title":"Expression of the von Hippel-Lindau-binding protein-1 (Vbp1) in fetal and adult mouse tissues.","date":"1999","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/9931330","citation_count":8,"is_preprint":false},{"pmid":"38700744","id":"PMC_38700744","title":"VBP1 promotes tumor proliferation as a part of the hypoxia-related signature in esophageal squamous cell carcinoma.","date":"2024","source":"Human cell","url":"https://pubmed.ncbi.nlm.nih.gov/38700744","citation_count":4,"is_preprint":false},{"pmid":"12579260","id":"PMC_12579260","title":"VBP-1 is necessary for morphogenesis in Caenorhabditis elegans.","date":"2003","source":"Oncology reports","url":"https://pubmed.ncbi.nlm.nih.gov/12579260","citation_count":4,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":6465,"output_tokens":1685,"usd":0.022335},"stage2":{"model":"claude-opus-4-6","input_tokens":4996,"output_tokens":2321,"usd":0.124507},"total_usd":0.146842,"stage1_batch_id":"msgbatch_01BparvgRZ9S2LMidvaoo86K","stage2_batch_id":"msgbatch_01NkBfv9SVZWthhS7j6mU6G3","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1996,\n      \"finding\": \"VBP1 directly binds to pVHL in vivo, requiring the C-terminal end of pVHL for interaction; co-expression of VBP1 with VHL causes VBP1 to translocate from the cytoplasm to the nucleus, indicating VHL controls VBP1 subcellular localization.\",\n      \"method\": \"Yeast two-hybrid, immunoprecipitation/Western blotting, epitope-tag co-expression localization studies\",\n      \"journal\": \"Cancer Research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP plus two-hybrid plus localization experiments; foundational paper with 106 citations\",\n      \"pmids\": [\"8674032\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"VBP1 physically interacts with hepatitis B virus X protein (HBx) and facilitates HBx-induced NF-κB activation and cell proliferation.\",\n      \"method\": \"Yeast two-hybrid, in vitro and in vivo immunoprecipitation, reporter assays for NF-κB activity, proliferation assays\",\n      \"journal\": \"BMB Reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — Co-IP confirmed in vitro and in vivo with functional NF-κB readout, single lab\",\n      \"pmids\": [\"18315953\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"VBP1 targets hMSH4 for proteasomal and autophagy-mediated degradation via ubiquitination; VBP1 interacts with p97 (AAA+ ATPase) and forms a complex with VHL and p97 on hMSH4, promoting its polyubiquitination and degradation.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assays, proteasome/autophagy inhibitor experiments, knockdown studies in HEK293T cells\",\n      \"journal\": \"FASEB Journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (Co-IP, ubiquitination assay, inhibitor studies) demonstrating mechanistic pathway\",\n      \"pmids\": [\"23964080\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"VBP1 enhances the stability of pVHL and facilitates pVHL-mediated ubiquitination and degradation of HIF-1α, thereby suppressing HIF-1α-induced epithelial-mesenchymal transition in vitro and tumor metastasis in vivo.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assays, stability assays, in vitro EMT assays, in vivo metastasis models\",\n      \"journal\": \"The FEBS Journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (Co-IP, ubiquitination, in vivo) in a single study with clear mechanistic readout\",\n      \"pmids\": [\"29121446\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"VBP1 directly binds all four TCF/LEF family members and pVHL; either overexpression or knockdown of VBP1 increases the TCF/LEF–pVHL association, leading to proteasomal degradation of TCF/LEFs and reduced Wnt/β-catenin signaling.\",\n      \"method\": \"Co-immunoprecipitation, proteasome inhibitor experiments, Wnt reporter assays, zebrafish embryo model, knockdown/overexpression in cultured cells\",\n      \"journal\": \"Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (Co-IP, reporter assay, in vivo zebrafish, pharmacological inhibition) demonstrating mechanistic pathway\",\n      \"pmids\": [\"32989053\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"VBP1 negatively regulates HIF-1α (but not HIF-2α) by interacting with ubiquitin ligase CHIP and HSP70; VBP1 promotes CHIP-mediated degradation of HIF-1α in a pVHL-independent manner; vbp1 deletion in zebrafish causes Hif-1α accumulation and upregulation of Hif target genes.\",\n      \"method\": \"Co-immunoprecipitation, protein degradation assays, zebrafish vbp1 knockout, in vitro cell culture models, CHIP/HSP70 interaction studies\",\n      \"journal\": \"Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP with new partners (CHIP, HSP70), in vivo zebrafish knockout, and in vitro degradation assays; multiple orthogonal methods\",\n      \"pmids\": [\"37201586\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"C. elegans VBP-1 (ortholog) is required for embryonic morphogenesis; RNAi knockdown of VBP-1 arrests embryogenesis at the morula stage.\",\n      \"method\": \"RNAi (dsRNA interference) in C. elegans, embryo morphology assessment\",\n      \"journal\": \"Oncology Reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean loss-of-function RNAi with defined developmental phenotype in ortholog; single lab\",\n      \"pmids\": [\"12579260\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"VBP1 is a pVHL-binding protein that acts as a scaffold/co-regulator: it binds pVHL's C-terminal domain and enhances pVHL-mediated ubiquitination and degradation of HIF-1α and TCF/LEF transcription factors, while also promoting pVHL-independent HIF-1α degradation through a CHIP/HSP70 ubiquitin-ligase complex; additionally, VBP1 forms complexes with p97 to target hMSH4 for proteasomal/autophagic degradation, interacts with HBx to facilitate NF-κB activation, and controls the nucleocytoplasmic localization of pVHL-associated proteins.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"VBP1 functions as a scaffold protein that coordinates ubiquitin-dependent degradation of multiple substrates, primarily through its interaction with the tumor suppressor pVHL and additional E3 ubiquitin ligase complexes. VBP1 directly binds the C-terminal domain of pVHL and enhances pVHL stability and its ubiquitin ligase activity toward HIF-1α, thereby suppressing HIF-1α-driven epithelial-mesenchymal transition and metastasis; it similarly promotes pVHL-mediated proteasomal degradation of all four TCF/LEF transcription factors, attenuating Wnt/β-catenin signaling [PMID:8674032, PMID:29121446, PMID:32989053]. VBP1 also mediates pVHL-independent HIF-1α degradation by recruiting the CHIP/HSP70 ubiquitin ligase complex, and it cooperates with the AAA+ ATPase p97 to target hMSH4 for proteasomal and autophagic degradation [PMID:37201586, PMID:23964080]. The C. elegans ortholog is essential for embryonic morphogenesis, indicating a conserved role in development [PMID:12579260].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Identifying VBP1 as a direct pVHL-binding protein established the first molecular link between VBP1 and the VHL tumor suppressor pathway, and revealed that VHL controls VBP1 nucleocytoplasmic localization.\",\n      \"evidence\": \"Yeast two-hybrid screen and reciprocal co-immunoprecipitation with epitope-tagged localization studies in mammalian cells\",\n      \"pmids\": [\"8674032\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Functional consequence of VBP1–pVHL interaction on pVHL activity was unknown\",\n        \"Endogenous VBP1 substrates or downstream targets not identified\",\n        \"Structural basis of the C-terminal pVHL–VBP1 interface not resolved\"\n      ]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Demonstrating that the C. elegans VBP-1 ortholog is required for embryonic morphogenesis established an essential developmental role, moving VBP1 beyond a mere binding partner.\",\n      \"evidence\": \"RNAi knockdown in C. elegans causing morula-stage arrest\",\n      \"pmids\": [\"12579260\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Mechanism by which VBP-1 loss causes morphogenesis arrest was not defined\",\n        \"Whether developmental role depends on VHL interaction was untested\",\n        \"Single-organism RNAi study; not confirmed in other metazoan models at that time\"\n      ]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Showing that VBP1 interacts with hepatitis B virus HBx protein and facilitates NF-κB activation expanded VBP1's functional scope to viral pathogenesis and inflammatory signaling.\",\n      \"evidence\": \"Yeast two-hybrid, in vitro/in vivo co-immunoprecipitation, and NF-κB reporter assays in cultured cells\",\n      \"pmids\": [\"18315953\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Mechanism linking VBP1–HBx interaction to NF-κB activation was not delineated\",\n        \"Whether this involves pVHL or ubiquitination was not tested\",\n        \"Single-lab finding without independent replication\"\n      ]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Revealing that VBP1 recruits p97 and promotes polyubiquitination and dual proteasomal/autophagic degradation of hMSH4 established VBP1 as an active scaffold for substrate-directed protein turnover beyond the canonical pVHL–HIF axis.\",\n      \"evidence\": \"Co-immunoprecipitation, ubiquitination assays, proteasome and autophagy inhibitor experiments in HEK293T cells\",\n      \"pmids\": [\"23964080\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Identity of the E3 ligase responsible for hMSH4 ubiquitination in this complex was not definitively assigned\",\n        \"Physiological consequence of hMSH4 degradation (e.g., meiotic recombination effects) was not tested\",\n        \"Whether p97 interaction is direct or bridged by VHL was unclear\"\n      ]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Demonstrating that VBP1 stabilizes pVHL and enhances pVHL-mediated HIF-1α ubiquitination and degradation connected VBP1 to the hypoxia response and showed it suppresses epithelial-mesenchymal transition and metastasis in vivo.\",\n      \"evidence\": \"Co-immunoprecipitation, ubiquitination and stability assays, in vitro EMT assays, and in vivo tumor metastasis models\",\n      \"pmids\": [\"29121446\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Mechanism by which VBP1 stabilizes pVHL protein was not resolved\",\n        \"Whether VBP1 regulates HIF-2α through pVHL was not addressed\",\n        \"Structural determinants of VBP1-enhanced ubiquitination were unknown\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Showing that VBP1 directly binds all four TCF/LEF transcription factors and bridges them to pVHL for proteasomal degradation revealed VBP1 as a negative regulator of Wnt/β-catenin signaling.\",\n      \"evidence\": \"Co-immunoprecipitation, Wnt reporter assays, proteasome inhibitor experiments, zebrafish developmental model, and knockdown/overexpression in cultured cells\",\n      \"pmids\": [\"32989053\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Paradoxical effect where both overexpression and knockdown enhance TCF/LEF–pVHL association was mechanistically unexplained\",\n        \"Whether VBP1's role in Wnt suppression is relevant to tumorigenesis in vivo was not tested\",\n        \"Stoichiometric versus catalytic role of VBP1 in bridging TCF/LEF to pVHL was unclear\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identifying the CHIP/HSP70 complex as a pVHL-independent route by which VBP1 targets HIF-1α (but not HIF-2α) for degradation demonstrated functional specificity among HIF isoforms and expanded VBP1's E3 ligase partnerships.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation, protein degradation assays, zebrafish vbp1 knockout with Hif target gene analysis\",\n      \"pmids\": [\"37201586\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis for HIF-1α selectivity over HIF-2α in the CHIP/HSP70 pathway was not determined\",\n        \"Relative contribution of VHL-dependent versus CHIP-dependent HIF-1α degradation under physiological conditions is unknown\",\n        \"Whether VBP1 functions as a co-chaperone or adaptor within the CHIP/HSP70 complex was not resolved\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The structural basis of VBP1's multi-partner scaffolding, its potential enzymatic activities, and its roles in human disease beyond cancer remain undefined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No crystal or cryo-EM structure of VBP1 or its complexes is available\",\n        \"Whether VBP1 has intrinsic catalytic activity or functions purely as a scaffold is unresolved\",\n        \"Genetic association of VBP1 mutations with human disease has not been established\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 2, 3, 4, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [2, 3, 4, 5]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [4, 1]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"VHL\",\n      \"HIF1A\",\n      \"STUB1\",\n      \"HSPA1A\",\n      \"VCP\",\n      \"MSH4\",\n      \"TCF7L2\",\n      \"HBX\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}