{"gene":"MVB12B","run_date":"2026-04-29T11:37:56","timeline":{"discoveries":[{"year":2007,"finding":"MVB12A and MVB12B are identified as the fourth class of metazoan ESCRT-I subunits, associating with the core TSG101-VPS37 binary complex through conserved C-terminal sequence elements; hydrodynamic studies show soluble human ESCRT-I contains one copy of each of the four subunit types. Depletion or overexpression of MVB12 subunits inhibits HIV-1 infectivity and induces aberrant virion morphologies and altered viral Gag protein processing.","method":"Co-immunoprecipitation, hydrodynamic sedimentation, siRNA knockdown, HIV budding infectivity assays","journal":"Cell host & microbe","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, hydrodynamic analysis, functional depletion/overexpression with defined phenotypes; strong evidence from multiple orthogonal approaches","pmids":["18005716"],"is_preprint":false},{"year":2012,"finding":"The MVB12B MABP (MVB12-associated β-prism) domain has a β-prism fold with a hydrophobic membrane-anchoring loop and an electropositive phosphoinositide-binding patch that binds in vitro to liposomes containing acidic lipids in a charge-density-dependent (but not stereoselective) manner; the MABP domain autonomously localizes to subcellular puncta and the plasma membrane.","method":"1.3-Å crystal structure, in vitro liposome-binding assay, subcellular localization by fluorescence microscopy","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — atomic-resolution crystal structure combined with in vitro biochemical assay and cell-based localization; single paper but multiple orthogonal methods with rigorous controls","pmids":["22232651"],"is_preprint":false},{"year":2010,"finding":"MVB12B is ubiquitinated at Lys264 and Lys290, leading to its instability and inclusion body formation; these ubiquitinations are induced by EGF stimulation and regulated by phosphorylation of Tyr241 and Tyr243 of MVB12B. MVB12A also participates in the aggregation of MVB12B, suggesting cross-regulation of the two paralogs within ESCRT-I.","method":"Mass spectrometry-based PTM identification, site-directed mutagenesis, co-immunoprecipitation, EGF stimulation assays","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — PTM site mapping with mutagenesis and functional consequence, but single lab study","pmids":["20654576"],"is_preprint":false},{"year":2013,"finding":"MVB12A and MVB12B (but not UBAP1) are selectively incorporated into ESCRT-I complexes; siRNA-mediated depletion of UBAP1, but not MVB12A/MVB12B, disrupts ubiquitin-dependent cargo sorting at the multivesicular body, demonstrating functional specialization among MVB12 family members in endosomal sorting.","method":"siRNA knockdown, co-immunoprecipitation, cargo sorting assays (EGF receptor degradation)","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 — selective depletion with defined cargo-sorting phenotype, but single lab","pmids":["24284069"],"is_preprint":false},{"year":2019,"finding":"MVB12B is a substrate of TANK-binding kinase 1 (TBK1): TBK1-mediated phosphorylation of MVB12B is essential for sorting of bacterial DNA into extracellular vesicles (EVs) in Listeria monocytogenes-infected cells; EVs carrying bacterial DNA are delivered to bystander cells to activate the cGAS-STING pathway and inhibit T-cell proliferation.","method":"Phosphoproteomics/MS identification of TBK1 substrate, siRNA knockdown, EV isolation, bystander-cell stimulation assays, T-cell proliferation assays","journal":"Nature microbiology","confidence":"High","confidence_rationale":"Tier 2 — substrate identification by MS with functional validation via knockdown and multiple readouts; replicated across three bacterial pathogens","pmids":["30804548"],"is_preprint":false},{"year":2018,"finding":"MVB12B is required for unconventional secretion of CFTRΔF508: siRNA knockdown of MVB12B inhibits stress-induced cell-surface trafficking of CFTRΔF508 from the ER via the MVB/ESCRT pathway, bypassing the Golgi; MVB12B overexpression partially rescues CFTRΔF508 cell-surface expression and Cl− channel function.","method":"siRNA screen of ESCRT components, overexpression rescue, cell-surface expression assay, Cl− channel functional assay","journal":"Autophagy","confidence":"Medium","confidence_rationale":"Tier 2 — loss-of-function and gain-of-function with functional readout (channel activity), but single lab","pmids":["29969945"],"is_preprint":false},{"year":2025,"finding":"MVB12B overexpression suppresses BLCA (bladder urothelial carcinoma) cell proliferation and migration in vitro; PPI network analysis links MVB12B to ESCRT components, and GSEA implicates keratinization and intermediate filament organization pathways.","method":"Overexpression functional assays (proliferation, migration) in T24 and UM-UC-3 cell lines, immunohistochemistry, qRT-PCR, GSEA","journal":"Translational cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — defined cellular phenotypes with gain-of-function, but single lab, no pathway placement beyond descriptive GSEA","pmids":["41510117"],"is_preprint":false}],"current_model":"MVB12B is the fourth subunit of the human ESCRT-I complex, associating with the TSG101-VPS37 core via conserved C-terminal elements; its MABP domain confers charge-dependent membrane targeting; it is phosphorylated by TBK1 downstream of STING activation to sort bacterial DNA into extracellular vesicles, ubiquitinated at Lys264/Lys290 in an EGF-regulated manner that promotes its proteasomal degradation, and required for ESCRT-dependent unconventional secretion of CFTR and for HIV budding."},"narrative":{"teleology":[{"year":2007,"claim":"The identity of the fourth ESCRT-I subunit class in metazoans was unknown; identification of MVB12A/MVB12B as stoichiometric ESCRT-I components established the heterotetrameric architecture and linked these subunits to HIV-1 budding.","evidence":"Reciprocal co-immunoprecipitation, hydrodynamic sedimentation, siRNA knockdown and overexpression with HIV infectivity readouts in human cells","pmids":["18005716"],"confidence":"High","gaps":["Structural basis for MVB12B incorporation into the ESCRT-I core not resolved","Functional distinction between MVB12A and MVB12B paralogs unclear","Role in endogenous cargo sorting not tested"]},{"year":2010,"claim":"How MVB12B stability is regulated post-translationally was unknown; EGF-stimulated ubiquitination at Lys264/Lys290, modulated by phosphorylation at Tyr241/Tyr243, was shown to destabilize MVB12B and promote inclusion body formation, establishing an EGFR-linked regulatory circuit.","evidence":"Mass spectrometry PTM mapping, site-directed mutagenesis, EGF stimulation in human cells","pmids":["20654576"],"confidence":"Medium","gaps":["The E3 ubiquitin ligase responsible was not identified","Kinase phosphorylating Tyr241/Tyr243 not determined","Physiological consequence of MVB12B destabilization on cargo sorting not measured"]},{"year":2012,"claim":"How MVB12B engages membranes was structurally undefined; the 1.3-Å crystal structure of the MABP domain revealed a β-prism fold with a hydrophobic anchoring loop and an electropositive patch, establishing a charge-density-dependent (not stereoselective) lipid-binding mechanism.","evidence":"X-ray crystallography at 1.3 Å, in vitro liposome-binding assays, fluorescence microscopy localization","pmids":["22232651"],"confidence":"High","gaps":["Which specific endosomal phosphoinositide species are preferred in vivo not determined","Whether MABP-mediated membrane binding is required for ESCRT-I function in cells not tested"]},{"year":2013,"claim":"Whether MVB12A/MVB12B and UBAP1 subunits are functionally interchangeable within ESCRT-I was unclear; depletion experiments showed that UBAP1, but not MVB12A/MVB12B, is required for ubiquitin-dependent EGF receptor sorting, revealing functional specialization among ESCRT-I fourth-subunit variants.","evidence":"siRNA knockdown of individual subunits with EGF receptor degradation as cargo-sorting readout","pmids":["24284069"],"confidence":"Medium","gaps":["The specific cargo class sorted by MVB12B-containing ESCRT-I complexes remained unidentified","Whether MVB12A and MVB12B are truly redundant or have distinct cargo selectivities was not resolved"]},{"year":2018,"claim":"Whether ESCRT-I participates in unconventional ER-to-plasma-membrane secretion was unknown; MVB12B was shown to be required for stress-induced, Golgi-bypassing surface trafficking of CFTRΔF508, with its overexpression partially rescuing chloride channel function.","evidence":"siRNA screen of ESCRT components, overexpression rescue, cell-surface expression and Cl⁻ channel functional assays","pmids":["29969945"],"confidence":"Medium","gaps":["Mechanism by which MVB12B recognizes CFTRΔF508 as cargo not defined","Whether this pathway operates for wild-type CFTR or other misfolded clients not tested"]},{"year":2019,"claim":"How innate immune signaling intersects with ESCRT-mediated vesicle biogenesis was undefined; TBK1-dependent phosphorylation of MVB12B was shown to be essential for packaging bacterial DNA into extracellular vesicles, which activate cGAS-STING in bystander cells and suppress T-cell proliferation.","evidence":"Phosphoproteomics, siRNA knockdown, EV isolation, bystander cGAS-STING activation, T-cell proliferation assays across three bacterial pathogens","pmids":["30804548"],"confidence":"High","gaps":["Specific phosphorylation site(s) on MVB12B required for this function not mapped","Whether MVB12B directly binds DNA cargo or acts indirectly through adaptor proteins unknown","Relevance to viral DNA sorting into EVs not tested"]},{"year":2025,"claim":"Whether MVB12B has tumor-suppressive activity was unexplored; overexpression in bladder cancer cell lines suppressed proliferation and migration, suggesting a growth-inhibitory role linked to ESCRT function.","evidence":"Overexpression in T24 and UM-UC-3 bladder cancer lines, proliferation and migration assays, GSEA pathway analysis","pmids":["41510117"],"confidence":"Medium","gaps":["Mechanism by which MVB12B suppresses proliferation not elucidated","No in vivo tumor model used","Loss-of-function genetic evidence (knockout, mutations in tumors) not provided"]},{"year":null,"claim":"Key unresolved questions include: which specific cargo molecules are selectively sorted by MVB12B-containing versus MVB12A-containing ESCRT-I complexes; the identity of the TBK1 phosphorylation site(s) on MVB12B; whether the MABP domain is required for ESCRT-I function in vivo; and how EGF-regulated ubiquitination feeds back onto MVB12B's sorting activities.","evidence":"","pmids":[],"confidence":"Low","gaps":["No cargo-selectivity model distinguishing MVB12B- from MVB12A-containing ESCRT-I","No reconstitution of TBK1–MVB12B–DNA sorting in a minimal system","No structural model of full-length MVB12B within the ESCRT-I heterotetramer"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[1]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[0,3]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[4,5]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,3,4,5]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[4]}],"complexes":["ESCRT-I"],"partners":["TSG101","VPS37A","MVB12A","UBAP1","TBK1"],"other_free_text":[]},"mechanistic_narrative":"MVB12B is a dedicated subunit of the metazoan ESCRT-I complex, incorporating into the TSG101–VPS37 core through conserved C-terminal elements and contributing to membrane-associated cargo sorting and vesicle biogenesis [PMID:18005716]. Its N-terminal MABP domain adopts a β-prism fold with a hydrophobic membrane-anchoring loop and an electropositive patch that binds acidic lipids in a charge-density-dependent manner, enabling autonomous membrane targeting [PMID:22232651]. MVB12B is phosphorylated by TBK1 downstream of STING activation, which is essential for sorting bacterial DNA into extracellular vesicles during intracellular infection, linking ESCRT-I to innate immune signaling [PMID:30804548]. MVB12B is also required for ESCRT-dependent unconventional secretion of CFTRΔF508 from the ER to the cell surface, and its perturbation impairs HIV-1 budding [PMID:29969945, PMID:18005716]."},"prefetch_data":{"uniprot":{"accession":"Q9H7P6","full_name":"Multivesicular body subunit 12B","aliases":["ESCRT-I complex subunit MVB12B","Protein FAM125B"],"length_aa":319,"mass_kda":35.6,"function":"Component of the ESCRT-I complex, a regulator of vesicular trafficking process. Required for the sorting of endocytic ubiquitinated cargos into multivesicular bodies","subcellular_location":"Endosome; Late endosome membrane","url":"https://www.uniprot.org/uniprotkb/Q9H7P6/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MVB12B","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"VPS37B","stoichiometry":10.0},{"gene":"TSG101","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/MVB12B","total_profiled":1310},"omim":[{"mim_id":"621543","title":"UBIQUITIN-ASSOCIATED PROTEIN 1-LIKE PROTEIN; UBAP1L","url":"https://www.omim.org/entry/621543"},{"mim_id":"621454","title":"MULTIVESICULAR BODY SUBUNIT 12B; MVB12B","url":"https://www.omim.org/entry/621454"},{"mim_id":"621453","title":"MULTIVESICULAR BODY SUBUNIT 12A; MVB12A","url":"https://www.omim.org/entry/621453"},{"mim_id":"609787","title":"UBIQUITIN-ASSOCIATED PROTEIN 1; UBAP1","url":"https://www.omim.org/entry/609787"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Vesicles","reliability":"Supported"},{"location":"Primary cilium","reliability":"Additional"},{"location":"Primary cilium tip","reliability":"Additional"},{"location":"Primary cilium transition zone","reliability":"Additional"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"brain","ntpm":110.8}],"url":"https://www.proteinatlas.org/search/MVB12B"},"hgnc":{"alias_symbol":["FLJ00001"],"prev_symbol":["C9orf28","FAM125B"]},"alphafold":{"accession":"Q9H7P6","domains":[{"cath_id":"2.100.10.50","chopping":"51-192","consensus_level":"high","plddt":95.0068,"start":51,"end":192}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H7P6","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H7P6-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H7P6-F1-predicted_aligned_error_v6.png","plddt_mean":76.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MVB12B","jax_strain_url":"https://www.jax.org/strain/search?query=MVB12B"},"sequence":{"accession":"Q9H7P6","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9H7P6.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9H7P6/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H7P6"}},"corpus_meta":[{"pmid":"30804548","id":"PMC_30804548","title":"Intracellular bacteria engage a STING-TBK1-MVB12b pathway to enable paracrine cGAS-STING signalling.","date":"2019","source":"Nature microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/30804548","citation_count":107,"is_preprint":false},{"pmid":"18005716","id":"PMC_18005716","title":"Identification of human MVB12 proteins as ESCRT-I subunits that function in HIV budding.","date":"2007","source":"Cell host & microbe","url":"https://pubmed.ncbi.nlm.nih.gov/18005716","citation_count":98,"is_preprint":false},{"pmid":"29969945","id":"PMC_29969945","title":"Specific autophagy and ESCRT components participate in the unconventional secretion of CFTR.","date":"2018","source":"Autophagy","url":"https://pubmed.ncbi.nlm.nih.gov/29969945","citation_count":54,"is_preprint":false},{"pmid":"22232651","id":"PMC_22232651","title":"Structural basis for membrane targeting by the MVB12-associated β-prism domain of the human ESCRT-I MVB12 subunit.","date":"2012","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/22232651","citation_count":43,"is_preprint":false},{"pmid":"24518671","id":"PMC_24518671","title":"A genome-wide association study of intra-ocular pressure suggests a novel association in the gene FAM125B in the TwinsUK cohort.","date":"2014","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/24518671","citation_count":37,"is_preprint":false},{"pmid":"27363808","id":"PMC_27363808","title":"Indexing Effects of Copy Number Variation on Genes Involved in Developmental Delay.","date":"2016","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/27363808","citation_count":31,"is_preprint":false},{"pmid":"24284069","id":"PMC_24284069","title":"The molecular basis for selective assembly of the UBAP1-containing endosome-specific ESCRT-I complex.","date":"2013","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/24284069","citation_count":29,"is_preprint":false},{"pmid":"20654576","id":"PMC_20654576","title":"Distinct functions of human MVB12A and MVB12B in the ESCRT-I dependent on their posttranslational modifications.","date":"2010","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/20654576","citation_count":25,"is_preprint":false},{"pmid":"33504897","id":"PMC_33504897","title":"Transcriptome-wide Mendelian randomization study prioritising novel tissue-dependent genes for glioma susceptibility.","date":"2021","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/33504897","citation_count":11,"is_preprint":false},{"pmid":"24899618","id":"PMC_24899618","title":"Protective effect of ischaemic preconditioning in total knee arthroplasty.","date":"2014","source":"European review for medical and pharmacological sciences","url":"https://pubmed.ncbi.nlm.nih.gov/24899618","citation_count":9,"is_preprint":false},{"pmid":"38339094","id":"PMC_38339094","title":"Genetic Factors Associated with the Development of Neuropathy in Type 2 Diabetes.","date":"2024","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/38339094","citation_count":5,"is_preprint":false},{"pmid":"33163277","id":"PMC_33163277","title":"Novel genetic variants of PIP5K1C and MVB12B of the endosome-related pathway predict cutaneous melanoma-specific survival.","date":"2020","source":"American journal of cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/33163277","citation_count":4,"is_preprint":false},{"pmid":"38255187","id":"PMC_38255187","title":"Cell-Free Genic Extrachromosomal Circular DNA Profiles of DNase Knockouts Associated with Systemic Lupus Erythematosus and Relation with Common Fragile Sites.","date":"2023","source":"Biomedicines","url":"https://pubmed.ncbi.nlm.nih.gov/38255187","citation_count":4,"is_preprint":false},{"pmid":"41510117","id":"PMC_41510117","title":"Multivesicular body subunit 12B (MVB12B) overexpression represses proliferation and migration in bladder urothelial carcinoma.","date":"2025","source":"Translational cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/41510117","citation_count":0,"is_preprint":false},{"pmid":"41404738","id":"PMC_41404738","title":"Identification of Biomarkers for Right Ventricular Dysfunction in Idiopathic Dilated Cardiomyopathy Via Urinary Proteomics and Machine Learning.","date":"2025","source":"Journal of the American Heart Association","url":"https://pubmed.ncbi.nlm.nih.gov/41404738","citation_count":0,"is_preprint":false},{"pmid":"39967738","id":"PMC_39967738","title":"Transcriptome analysis of 3D4/21 cells expressing CSFV NS4B.","date":"2025","source":"Frontiers in microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/39967738","citation_count":0,"is_preprint":false},{"pmid":"40493586","id":"PMC_40493586","title":"Leveraging molecular-QTL co-association to predict novel disease-associated genetic loci using a graph convolutional neural network.","date":"2025","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/40493586","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":10727,"output_tokens":1846,"usd":0.029936},"stage2":{"model":"claude-opus-4-6","input_tokens":5128,"output_tokens":2302,"usd":0.124785},"total_usd":0.154721,"stage1_batch_id":"msgbatch_012ZiiCUBfB62NCTQd4Bk1Jo","stage2_batch_id":"msgbatch_01Xuqq9aUHoQouS7UVGZNStZ","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2007,\n      \"finding\": \"MVB12A and MVB12B are identified as the fourth class of metazoan ESCRT-I subunits, associating with the core TSG101-VPS37 binary complex through conserved C-terminal sequence elements; hydrodynamic studies show soluble human ESCRT-I contains one copy of each of the four subunit types. Depletion or overexpression of MVB12 subunits inhibits HIV-1 infectivity and induces aberrant virion morphologies and altered viral Gag protein processing.\",\n      \"method\": \"Co-immunoprecipitation, hydrodynamic sedimentation, siRNA knockdown, HIV budding infectivity assays\",\n      \"journal\": \"Cell host & microbe\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, hydrodynamic analysis, functional depletion/overexpression with defined phenotypes; strong evidence from multiple orthogonal approaches\",\n      \"pmids\": [\"18005716\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The MVB12B MABP (MVB12-associated β-prism) domain has a β-prism fold with a hydrophobic membrane-anchoring loop and an electropositive phosphoinositide-binding patch that binds in vitro to liposomes containing acidic lipids in a charge-density-dependent (but not stereoselective) manner; the MABP domain autonomously localizes to subcellular puncta and the plasma membrane.\",\n      \"method\": \"1.3-Å crystal structure, in vitro liposome-binding assay, subcellular localization by fluorescence microscopy\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — atomic-resolution crystal structure combined with in vitro biochemical assay and cell-based localization; single paper but multiple orthogonal methods with rigorous controls\",\n      \"pmids\": [\"22232651\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"MVB12B is ubiquitinated at Lys264 and Lys290, leading to its instability and inclusion body formation; these ubiquitinations are induced by EGF stimulation and regulated by phosphorylation of Tyr241 and Tyr243 of MVB12B. MVB12A also participates in the aggregation of MVB12B, suggesting cross-regulation of the two paralogs within ESCRT-I.\",\n      \"method\": \"Mass spectrometry-based PTM identification, site-directed mutagenesis, co-immunoprecipitation, EGF stimulation assays\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — PTM site mapping with mutagenesis and functional consequence, but single lab study\",\n      \"pmids\": [\"20654576\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"MVB12A and MVB12B (but not UBAP1) are selectively incorporated into ESCRT-I complexes; siRNA-mediated depletion of UBAP1, but not MVB12A/MVB12B, disrupts ubiquitin-dependent cargo sorting at the multivesicular body, demonstrating functional specialization among MVB12 family members in endosomal sorting.\",\n      \"method\": \"siRNA knockdown, co-immunoprecipitation, cargo sorting assays (EGF receptor degradation)\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — selective depletion with defined cargo-sorting phenotype, but single lab\",\n      \"pmids\": [\"24284069\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"MVB12B is a substrate of TANK-binding kinase 1 (TBK1): TBK1-mediated phosphorylation of MVB12B is essential for sorting of bacterial DNA into extracellular vesicles (EVs) in Listeria monocytogenes-infected cells; EVs carrying bacterial DNA are delivered to bystander cells to activate the cGAS-STING pathway and inhibit T-cell proliferation.\",\n      \"method\": \"Phosphoproteomics/MS identification of TBK1 substrate, siRNA knockdown, EV isolation, bystander-cell stimulation assays, T-cell proliferation assays\",\n      \"journal\": \"Nature microbiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — substrate identification by MS with functional validation via knockdown and multiple readouts; replicated across three bacterial pathogens\",\n      \"pmids\": [\"30804548\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"MVB12B is required for unconventional secretion of CFTRΔF508: siRNA knockdown of MVB12B inhibits stress-induced cell-surface trafficking of CFTRΔF508 from the ER via the MVB/ESCRT pathway, bypassing the Golgi; MVB12B overexpression partially rescues CFTRΔF508 cell-surface expression and Cl− channel function.\",\n      \"method\": \"siRNA screen of ESCRT components, overexpression rescue, cell-surface expression assay, Cl− channel functional assay\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function and gain-of-function with functional readout (channel activity), but single lab\",\n      \"pmids\": [\"29969945\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"MVB12B overexpression suppresses BLCA (bladder urothelial carcinoma) cell proliferation and migration in vitro; PPI network analysis links MVB12B to ESCRT components, and GSEA implicates keratinization and intermediate filament organization pathways.\",\n      \"method\": \"Overexpression functional assays (proliferation, migration) in T24 and UM-UC-3 cell lines, immunohistochemistry, qRT-PCR, GSEA\",\n      \"journal\": \"Translational cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — defined cellular phenotypes with gain-of-function, but single lab, no pathway placement beyond descriptive GSEA\",\n      \"pmids\": [\"41510117\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MVB12B is the fourth subunit of the human ESCRT-I complex, associating with the TSG101-VPS37 core via conserved C-terminal elements; its MABP domain confers charge-dependent membrane targeting; it is phosphorylated by TBK1 downstream of STING activation to sort bacterial DNA into extracellular vesicles, ubiquitinated at Lys264/Lys290 in an EGF-regulated manner that promotes its proteasomal degradation, and required for ESCRT-dependent unconventional secretion of CFTR and for HIV budding.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"MVB12B is a dedicated subunit of the metazoan ESCRT-I complex, incorporating into the TSG101–VPS37 core through conserved C-terminal elements and contributing to membrane-associated cargo sorting and vesicle biogenesis [PMID:18005716]. Its N-terminal MABP domain adopts a β-prism fold with a hydrophobic membrane-anchoring loop and an electropositive patch that binds acidic lipids in a charge-density-dependent manner, enabling autonomous membrane targeting [PMID:22232651]. MVB12B is phosphorylated by TBK1 downstream of STING activation, which is essential for sorting bacterial DNA into extracellular vesicles during intracellular infection, linking ESCRT-I to innate immune signaling [PMID:30804548]. MVB12B is also required for ESCRT-dependent unconventional secretion of CFTRΔF508 from the ER to the cell surface, and its perturbation impairs HIV-1 budding [PMID:29969945, PMID:18005716].\",\n  \"teleology\": [\n    {\n      \"year\": 2007,\n      \"claim\": \"The identity of the fourth ESCRT-I subunit class in metazoans was unknown; identification of MVB12A/MVB12B as stoichiometric ESCRT-I components established the heterotetrameric architecture and linked these subunits to HIV-1 budding.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation, hydrodynamic sedimentation, siRNA knockdown and overexpression with HIV infectivity readouts in human cells\",\n      \"pmids\": [\"18005716\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis for MVB12B incorporation into the ESCRT-I core not resolved\",\n        \"Functional distinction between MVB12A and MVB12B paralogs unclear\",\n        \"Role in endogenous cargo sorting not tested\"\n      ]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"How MVB12B stability is regulated post-translationally was unknown; EGF-stimulated ubiquitination at Lys264/Lys290, modulated by phosphorylation at Tyr241/Tyr243, was shown to destabilize MVB12B and promote inclusion body formation, establishing an EGFR-linked regulatory circuit.\",\n      \"evidence\": \"Mass spectrometry PTM mapping, site-directed mutagenesis, EGF stimulation in human cells\",\n      \"pmids\": [\"20654576\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"The E3 ubiquitin ligase responsible was not identified\",\n        \"Kinase phosphorylating Tyr241/Tyr243 not determined\",\n        \"Physiological consequence of MVB12B destabilization on cargo sorting not measured\"\n      ]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"How MVB12B engages membranes was structurally undefined; the 1.3-Å crystal structure of the MABP domain revealed a β-prism fold with a hydrophobic anchoring loop and an electropositive patch, establishing a charge-density-dependent (not stereoselective) lipid-binding mechanism.\",\n      \"evidence\": \"X-ray crystallography at 1.3 Å, in vitro liposome-binding assays, fluorescence microscopy localization\",\n      \"pmids\": [\"22232651\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Which specific endosomal phosphoinositide species are preferred in vivo not determined\",\n        \"Whether MABP-mediated membrane binding is required for ESCRT-I function in cells not tested\"\n      ]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Whether MVB12A/MVB12B and UBAP1 subunits are functionally interchangeable within ESCRT-I was unclear; depletion experiments showed that UBAP1, but not MVB12A/MVB12B, is required for ubiquitin-dependent EGF receptor sorting, revealing functional specialization among ESCRT-I fourth-subunit variants.\",\n      \"evidence\": \"siRNA knockdown of individual subunits with EGF receptor degradation as cargo-sorting readout\",\n      \"pmids\": [\"24284069\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"The specific cargo class sorted by MVB12B-containing ESCRT-I complexes remained unidentified\",\n        \"Whether MVB12A and MVB12B are truly redundant or have distinct cargo selectivities was not resolved\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Whether ESCRT-I participates in unconventional ER-to-plasma-membrane secretion was unknown; MVB12B was shown to be required for stress-induced, Golgi-bypassing surface trafficking of CFTRΔF508, with its overexpression partially rescuing chloride channel function.\",\n      \"evidence\": \"siRNA screen of ESCRT components, overexpression rescue, cell-surface expression and Cl⁻ channel functional assays\",\n      \"pmids\": [\"29969945\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Mechanism by which MVB12B recognizes CFTRΔF508 as cargo not defined\",\n        \"Whether this pathway operates for wild-type CFTR or other misfolded clients not tested\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"How innate immune signaling intersects with ESCRT-mediated vesicle biogenesis was undefined; TBK1-dependent phosphorylation of MVB12B was shown to be essential for packaging bacterial DNA into extracellular vesicles, which activate cGAS-STING in bystander cells and suppress T-cell proliferation.\",\n      \"evidence\": \"Phosphoproteomics, siRNA knockdown, EV isolation, bystander cGAS-STING activation, T-cell proliferation assays across three bacterial pathogens\",\n      \"pmids\": [\"30804548\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Specific phosphorylation site(s) on MVB12B required for this function not mapped\",\n        \"Whether MVB12B directly binds DNA cargo or acts indirectly through adaptor proteins unknown\",\n        \"Relevance to viral DNA sorting into EVs not tested\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Whether MVB12B has tumor-suppressive activity was unexplored; overexpression in bladder cancer cell lines suppressed proliferation and migration, suggesting a growth-inhibitory role linked to ESCRT function.\",\n      \"evidence\": \"Overexpression in T24 and UM-UC-3 bladder cancer lines, proliferation and migration assays, GSEA pathway analysis\",\n      \"pmids\": [\"41510117\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Mechanism by which MVB12B suppresses proliferation not elucidated\",\n        \"No in vivo tumor model used\",\n        \"Loss-of-function genetic evidence (knockout, mutations in tumors) not provided\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: which specific cargo molecules are selectively sorted by MVB12B-containing versus MVB12A-containing ESCRT-I complexes; the identity of the TBK1 phosphorylation site(s) on MVB12B; whether the MABP domain is required for ESCRT-I function in vivo; and how EGF-regulated ubiquitination feeds back onto MVB12B's sorting activities.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No cargo-selectivity model distinguishing MVB12B- from MVB12A-containing ESCRT-I\",\n        \"No reconstitution of TBK1–MVB12B–DNA sorting in a minimal system\",\n        \"No structural model of full-length MVB12B within the ESCRT-I heterotetramer\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [4, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 3, 4, 5]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"complexes\": [\n      \"ESCRT-I\"\n    ],\n    \"partners\": [\n      \"TSG101\",\n      \"VPS37A\",\n      \"MVB12A\",\n      \"UBAP1\",\n      \"TBK1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}