{"gene":"CHMP4B","run_date":"2026-06-09T22:57:18","timeline":{"discoveries":[{"year":2003,"finding":"CHMP4B was identified as a binding partner of Alix (ALG-2-interacting protein X) through yeast two-hybrid screen, confirmed by GST pull-down and co-immunoprecipitation. CHMP4B co-localizes with Alix in HeLa cells and co-immunoprecipitates with dominant-negative SKD1(E235Q) AAA-ATPase. Overexpression of CHMP4B inhibited endocytosed EGF disappearance and caused accumulation of ubiquitinated proteins, consistent with a role in multivesicular body (MVB) sorting cooperating with SKD1.","method":"Yeast two-hybrid, GST pull-down, co-immunoprecipitation, fluorescence microscopy, overexpression phenotypic assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, GST pull-down, and yeast two-hybrid across multiple orthogonal methods in a single focused study","pmids":["12860994"],"is_preprint":false},{"year":2004,"finding":"Among the three CHMP4 isoforms (CHMP4a, CHMP4b, CHMP4c), CHMP4B is the major binding partner of Alix, showing stronger direct interaction than CHMP4a or CHMP4c as demonstrated by GST pull-down using recombinant proteins and co-immunoprecipitation from cell lysates.","method":"GST pull-down with recombinant proteins, co-immunoprecipitation","journal":"Archives of biochemistry and biophysics","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct in vitro reconstitution with recombinant proteins plus Co-IP, replicated finding from same group with refined isoform specificity","pmids":["14678797"],"is_preprint":false},{"year":2006,"finding":"CHMP7, a novel ESCRT-III-related protein, directly interacts with CHMP4B through its C-terminal SNF7 domain, as shown by pull-down assay. Overexpression of CHMP4B-GFP relocalized FLAG-CHMP7 from diffuse cytoplasm to cytoplasmic puncta, indicating functional interaction.","method":"Pull-down assay (Strep-tagged CHMP7 with GFP-CHMP4b from cell lysates), confocal fluorescence microscopy","journal":"The Biochemical journal","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — single pull-down from cell lysates plus co-localization imaging, two orthogonal methods but not in vitro reconstitution","pmids":["16856878"],"is_preprint":false},{"year":2007,"finding":"Disease-associated mutations in CHMP4B (D129V and E161K) cause autosomal dominant cataracts. Transfection studies showed that truncated D129V-CHMP4B had altered subcellular distribution compared to wild-type and an increased capacity to inhibit virus-like particle release from the cell surface, consistent with gain-of-function dominant negative effects on ESCRT-III.","method":"Transfection of mutant vs. wild-type CHMP4B in cultured cells, subcellular localization imaging, virus-like particle release assay","journal":"American journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — single lab, two orthogonal functional assays (localization and VLP release), but no in vitro reconstitution or structural analysis","pmids":["17701905"],"is_preprint":false},{"year":2009,"finding":"The CHMP4B-docking site and Src-docking site in the Bro1 domain of Alix are autoinhibited in the native cytosolic state of Alix. In HEK-293 cell lysates, these sites are unavailable in cytosolic Alix but available in membrane-bound Alix, indicating that Alix membrane association relieves autoinhibition to enable CHMP4B binding.","method":"Biochemical fractionation, detergent treatment of recombinant Alix, cell lysate binding assays","journal":"The Biochemical journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean biochemical fractionation combined with cell lysate binding studies, single lab with two orthogonal approaches","pmids":["19016654"],"is_preprint":false},{"year":2012,"finding":"CC2D1A and CC2D1B are direct regulators of CHMP4B, binding with nanomolar affinity in a 1:1 complex. The binding site on CC2D1A was mapped to the third DM14 domain, and the CC2D1A binding site on CHMP4B was mapped to the N-terminal helical hairpin. A crystal structure of the CHMP4B helical hairpin identified two surface patches involved in CC2D1A interaction. CC2D1A binding to CHMP4B prevents CHMP4B polymerization in vitro. Mutations at the CC2D1A-binding surface of CHMP4B abolished its dominant negative effect on HIV-1 budding, suggesting this surface is required for CHMP4B polymerization.","method":"Crystal structure of CHMP4B helical hairpin, surface plasmon resonance (nanomolar affinity measurement), deletion mapping, in vitro polymerization assay, HIV-1 budding assay with CHMP4B mutants","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure combined with SPR, in vitro polymerization assay, and functional mutagenesis in a single study with multiple orthogonal methods","pmids":["22406677"],"is_preprint":false},{"year":2012,"finding":"Hydrophobic residues in the CHMP4B C-terminal amphipathic α-helix bind a concave surface of Brox (a mammalian Alix paralog). Crystal/structural analysis showed the CHMP4B C-terminal tail adopts an α-helical conformation when bound to Brox, at the same site used by CHMP5 (which binds via a β-hairpin). This defines a shared but conformationally distinct binding surface on Brox for ESCRT-III proteins.","method":"Crystal structure of Brox:CHMP4B complex, mutagenesis, binding assays","journal":"Structure (London, England : 1993)","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure with functional binding validation, single rigorous study with structural and biochemical orthogonal methods","pmids":["22484091"],"is_preprint":false},{"year":2014,"finding":"Anillin-septin complex is required for the recruitment of CHMP4B to the abscission site during cytokinesis. Using live imaging and subdiffraction microscopy, the anillin-septin cytoskeleton drives intercellular bridge elongation and maturation, which primes the bridge for CHMP4B assembly at the abscission site.","method":"Live cell imaging, subdiffraction microscopy, anillin/septin depletion (loss-of-function with CHMP4B localization readout)","journal":"Open biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic depletion with direct localization imaging of CHMP4B, single lab but using two orthogonal microscopy methods","pmids":["24451548"],"is_preprint":false},{"year":2014,"finding":"CHMP4B not only localizes to cytokinetic bridges but also to chromosome bridges and micronuclei (the latter surrounded by lysosomes and autophagosomes), and can be co-immunoprecipitated with chromatin. A cataract-associated CHMP4B mutation abolishes its ability to localize to micronuclei, suggesting this localization is mutation-sensitive.","method":"Immunofluorescence localization, co-immunoprecipitation with chromatin, comparison of wild-type vs. cataract mutant CHMP4B","journal":"BioMed research international","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct localization imaging with functional comparison of mutant vs. wild-type, co-IP with chromatin, but single lab and no mechanistic reconstitution","pmids":["24741567"],"is_preprint":false},{"year":2019,"finding":"Conditional knockdown of CHMP4B in mouse lens results in arrest of lens growth and differentiation, with lens fiber cell degeneration (shown by AQP0 immunolocalization) and cell death (TUNEL). Homozygous knock-in of the cataract-associated D129V mutation causes embryonic lethality by E15.5 with abnormal eye and brain histology, indicating CHMP4B is essential for lens development.","method":"Conditional knockout/knockdown mouse model, knock-in mouse model, immunolocalization (AQP0, CD68), TUNEL assay, in situ hybridization","journal":"Differentiation; research in biological diversity","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple clean genetic models (CKD + knock-in) with multiple cellular readouts (localization, TUNEL, histology) in a single study","pmids":["31404815"],"is_preprint":false},{"year":2019,"finding":"CHMP4B localizes to primary cilia in mammalian cells and is required for cilium assembly and maintenance of ciliary structural integrity. Knockdown of CHMP4B caused defective cilium assembly and fragmentation of pre-existing cilia. Morpholino-mediated depletion in zebrafish induced ciliopathy phenotypes (curved body axis, hydrocephalus, otolith malformation, kidney cysts), independently of ESCRT-dependent endocytic degradation.","method":"Immunofluorescence localization to primary cilia, siRNA knockdown in mammalian cells, morpholino depletion in zebrafish, phenotypic analysis","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct localization plus loss-of-function in two organisms (mammalian cells and zebrafish) with specific ciliary phenotypes, multiple orthogonal methods","pmids":["31914703"],"is_preprint":false},{"year":2021,"finding":"In ALS neurons, neither CHMP4B nor CHMP2B show increased nuclear accumulation (in contrast to CHMP7 and VPS4), indicating that CHMP4B is not a primary driver of nuclear pore complex injury in ALS despite CHMP7's known role in recruiting ESCRT-III subunits for nuclear envelope/NPC repair.","method":"Super-resolution structured illumination microscopy (SIM) of neuronal nuclei from ALS patients and models","journal":"Acta neuropathologica communications","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — super-resolution imaging is high quality, but this is a negative finding in a single study (CHMP4B is NOT elevated in ALS nuclei)","pmids":["34281622"],"is_preprint":false},{"year":2023,"finding":"HSP90β directly interacts with CHMP4B as a client protein. HSP90β silencing causes upregulation of CHMP4B and p53; CHMP4B upregulation/overexpression induces excessive division of lens epithelial cells without differentiation, triggering apoptosis via the p53/Bak-Bim pathway and causing cataractogenesis and microphthalmia in zebrafish. Simultaneous silencing of both HSP90β and CHMP4B restored the normal eye phenotype.","method":"Co-immunoprecipitation (direct interaction), zebrafish knockdown/rescue experiment, overexpression phenotypic analysis, epistasis (double knockdown)","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct interaction demonstrated by Co-IP, genetic epistasis via double knockdown rescue in zebrafish, and functional overexpression analysis with specific molecular pathway readouts","pmids":["37487085"],"is_preprint":false},{"year":2023,"finding":"CHMP4B interacts with GSDMD (gasdermin D) and VPS4A, as shown by co-immunoprecipitation. CHMP4B and VPS4A puncta co-localize at injured plasma membranes in GSDMD-N-terminus-expressing cells. Depletion of CHMP4B enhanced pyroptotic indicators (PI-positive cells, Ca2+ efflux, IL-1β, LDH release), while overexpression attenuated them, demonstrating CHMP4B mediates membrane repair to reverse GSDMD-induced pyroptosis.","method":"Co-immunoprecipitation, fluorescence confocal microscopy, electron microscopy of membrane perforations, siRNA knockdown and overexpression with pyroptosis readouts (LDH, IL-1β, Ca2+ flux, FITC-Annexin V/PI)","journal":"Biochimica et biophysica acta. General subjects","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus electron microscopy plus multiple functional readouts, single lab but with several orthogonal methods","pmids":["37931722"],"is_preprint":false},{"year":2025,"finding":"PRP4K kinase controls splicing of CHMP4B pre-mRNA; loss of PRP4K causes mis-splicing and reduced expression of CHMP4B in human cells. CHMP4B is required for autophagosome-lysosome fusion; re-expression of CHMP4B cDNA in PRP4K-deficient cells restores normal autophagosome-lysosome fusion, placing CHMP4B downstream of PRP4K in an evolutionarily conserved splicing circuit regulating autophagy.","method":"Genetic epistasis (CHMP4B cDNA rescue in PRP4K knockout cells), autophagosome-lysosome fusion assay, mRNA splicing analysis","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic epistasis via cDNA rescue experiment with specific autophagy functional readout, replicated in two organisms (human cells and Dictyostelium)","pmids":["40531620"],"is_preprint":false},{"year":2025,"finding":"GAS2L3 localizes to the midbody and recruits CHMP4B to the abscission site. GAS2L3 undergoes liquid-liquid phase separation (LLPS) via its intrinsically disordered region (IDR) and scaffolds CHMP4B condensate formation at the midbody through phase separation. GAS2L3 knockdown or IDR deletion leads to defective CHMP4B recruitment, defective cytokinesis, and G1 arrest.","method":"Live cell imaging, structured illumination microscopy, FRAP, in vitro droplet formation assay, GAS2L3 knockdown/IDR deletion with CHMP4B localization and cytokinesis readouts","journal":"Journal of advanced research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — FRAP and in vitro droplet assays plus genetic loss-of-function with CHMP4B localization readout, single lab but multiple orthogonal methods","pmids":["41177429"],"is_preprint":false},{"year":2026,"finding":"CHMP4B binds PI(3,5)P2 (a lysosomal phosphoinositide) as demonstrated by liposome sedimentation assay. Forced recruitment of Pikfyve (the PI(3,5)P2-generating kinase) to early endosomes recruits a fraction of CHMP4B to early endosomes. A CHMP4B mutant defective in PI(3,5)P2 binding cannot restore microautophagic STING degradation or resolution of STING signaling in Chmp4b-depleted cells, establishing a PI(3,5)P2/CHMP4B axis on lysosomes as essential for STING encapsulation by lysosomes.","method":"Liposome sedimentation assay (direct lipid binding), forced Pikfyve recruitment assay, CHMP4B mutant rescue experiment, STING degradation/signaling assay in Chmp4b-depleted cells","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro liposome sedimentation demonstrates direct binding, combined with forced recruitment assay and mutagenesis rescue experiment with specific functional readout","pmids":["42203786"],"is_preprint":false},{"year":2025,"finding":"CHMP4B displays progressively severe spatial organization defects at the cytokinetic abscission site when CHMP2A is depleted, as visualized by SIM and CLEM. Dual-protein imaging revealed disrupted coordination between CHMP4B and other ESCRT-III subunits in CHMP2A-deficient cells, supporting an ordered/hierarchical assembly of ESCRT-III subunits in which CHMP2A acts upstream of CHMP4B during abscission.","method":"CHMP2A knockout, live cell imaging, structured illumination microscopy (SIM), correlative light-electron microscopy (CLEM), dual-protein co-imaging","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean genetic KO with super-resolution imaging and CLEM, multiple orthogonal microscopy methods, but preprint not yet peer-reviewed","pmids":["bio_10.1101_2025.06.24.661003"],"is_preprint":true},{"year":2024,"finding":"CHMP4B associates with specific lipid species in dividing HeLa cells (identified by lipid-trap mass spectrometry using GFP-tagged CHMP4B immunoprecipitation followed by lipidomic analysis), with the lipid association enriched in dividing compared to non-dividing cells.","method":"Lipid-trap mass spectrometry (GFP immunoprecipitation + lipidomics)","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 / Weak — novel single-method pulldown from cells without in vitro reconstitution, preprint only, specific lipid species not detailed in abstract","pmids":["bio_10.1101_2024.12.13.627510"],"is_preprint":true}],"current_model":"CHMP4B is a core ESCRT-III subunit that forms a direct complex with Alix (via the Alix Bro1 domain, subject to membrane-dependent autoinhibition) and with CC2D1A/CC2D1B (via its N-terminal helical hairpin), polymerizes at membranes to drive scission, binds PI(3,5)P2 on lysosomes to mediate microautophagic encapsulation of STING, is recruited to cytokinetic abscission sites downstream of anillin-septin and CHMP2A in a hierarchical ESCRT-III assembly, localizes to primary cilia to maintain ciliary membrane integrity, undergoes HSP90β-dependent regulation to control lens cell division and differentiation, and functions in plasma membrane repair to counteract GSDMD-mediated pyroptosis."},"narrative":{"mechanistic_narrative":"CHMP4B is a core ESCRT-III subunit that polymerizes at membranes to drive membrane remodeling and scission across multivesicular body sorting, cytokinetic abscission, plasma membrane repair, and lysosomal microautophagy [PMID:12860994, PMID:22406677, PMID:42203786]. It was first defined as the dominant Alix-binding CHMP4 isoform, cooperating with the AAA-ATPase SKD1 in MVB sorting of ubiquitinated cargo and endocytosed EGF [PMID:12860994, PMID:14678797]; Alix engagement is gated by membrane-dependent relief of autoinhibition at the Bro1 docking site [PMID:19016654], and CHMP4B is also bound by the Alix paralog Brox through its C-terminal amphipathic helix [PMID:22484091] and by the ESCRT-III-related protein CHMP7 [PMID:16856878]. Polymerization is directly controlled by CC2D1A/CC2D1B, which bind the N-terminal helical hairpin of CHMP4B with nanomolar affinity and block filament assembly; the same surface is required for CHMP4B's dominant-negative effect on HIV-1 budding [PMID:22406677]. During cytokinesis, CHMP4B is recruited to the abscission site downstream of the anillin-septin cytoskeleton and the GAS2L3 midbody scaffold, which nucleates CHMP4B condensates via phase separation, and its spatial organization depends on CHMP2A, establishing a hierarchical ESCRT-III assembly [PMID:24451548, PMID:41177429]. Beyond division, CHMP4B maintains primary cilium integrity independently of endocytic degradation [PMID:31914703], mediates plasma membrane repair to counteract GSDMD-driven pyroptosis together with VPS4A [PMID:37931722], supports autophagosome-lysosome fusion downstream of the PRP4K splicing circuit [PMID:40531620], and binds the lysosomal phosphoinositide PI(3,5)P2 to drive microautophagic encapsulation and degradation of STING [PMID:42203786]. Dominant CHMP4B mutations (D129V, E161K) cause autosomal dominant cataract, and CHMP4B is essential for lens development, with its dysregulation by HSP90β triggering p53/Bak-Bim apoptosis in lens epithelial cells [PMID:17701905, PMID:31404815, PMID:37487085].","teleology":[{"year":2003,"claim":"Established CHMP4B's foundational identity as an ESCRT-III component by linking it physically and functionally to the Alix adaptor and the SKD1 AAA-ATPase in MVB cargo sorting.","evidence":"Yeast two-hybrid, GST pull-down, co-IP, and overexpression EGF/ubiquitin-sorting assays in HeLa cells","pmids":["12860994","14678797"],"confidence":"High","gaps":["Did not resolve the structural basis of the Alix interaction","Isoform-specific functional differences among CHMP4a/b/c beyond binding strength not defined"]},{"year":2006,"claim":"Extended the CHMP4B interaction network to the ESCRT-III-related protein CHMP7 via its SNF7 domain, indicating CHMP4B partners with multiple ESCRT-III-family proteins.","evidence":"Strep-tag pull-down from cell lysates and confocal relocalization imaging","pmids":["16856878"],"confidence":"Medium","gaps":["Single pull-down from lysates without in vitro reconstitution","Functional consequence of the CHMP4B-CHMP7 interaction not tested"]},{"year":2007,"claim":"Connected CHMP4B to human disease by showing dominant cataract-causing mutations act as gain-of-function dominant negatives on ESCRT-III-mediated membrane budding.","evidence":"Transfection of D129V/E161K mutants with subcellular localization and virus-like particle release assays","pmids":["17701905"],"confidence":"Medium","gaps":["No in vitro or structural analysis of mutant polymerization","Mechanism connecting ESCRT defect to lens pathology not established"]},{"year":2009,"claim":"Resolved how Alix-CHMP4B engagement is regulated, showing the Bro1 docking site is autoinhibited in cytosol and unmasked only upon Alix membrane association.","evidence":"Biochemical fractionation and cell-lysate binding assays of cytosolic vs. membrane-bound Alix","pmids":["19016654"],"confidence":"Medium","gaps":["Structural conformational change underlying autoinhibition not directly visualized","In vivo trigger for membrane recruitment unresolved"]},{"year":2012,"claim":"Defined the structural and biochemical control of CHMP4B polymerization, identifying CC2D1A/B as direct high-affinity negative regulators and mapping the polymerization surface, plus a distinct Brox-binding mode.","evidence":"Crystal structures of the CHMP4B helical hairpin and Brox:CHMP4B complex, SPR, in vitro polymerization, and HIV-1 budding mutagenesis","pmids":["22406677","22484091"],"confidence":"High","gaps":["In vivo conditions that relieve CC2D1A inhibition not defined","Full-length CHMP4B polymer architecture not solved"]},{"year":2014,"claim":"Placed CHMP4B in the cytokinetic abscission pathway downstream of the anillin-septin cytoskeleton and revealed its localization to chromosome bridges and micronuclei.","evidence":"Live and subdiffraction imaging with anillin/septin depletion; immunofluorescence and chromatin co-IP with mutant comparison","pmids":["24451548","24741567"],"confidence":"Medium","gaps":["Molecular link from septins to CHMP4B recruitment not defined","Functional role of chromatin/micronuclear localization unresolved"]},{"year":2019,"claim":"Demonstrated CHMP4B is essential for lens development and for primary cilium assembly/integrity, the latter independent of ESCRT endocytic degradation.","evidence":"Conditional knockout and D129V knock-in mouse models with TUNEL/histology; siRNA and zebrafish morpholino with ciliary phenotyping","pmids":["31404815","31914703"],"confidence":"High","gaps":["Mechanism of ciliary membrane maintenance by CHMP4B not defined","How D129V causes embryonic lethality vs. dominant cataract not reconciled"]},{"year":2021,"claim":"Distinguished CHMP4B from CHMP7 in disease context by showing CHMP4B does not abnormally accumulate in ALS neuronal nuclei, arguing against a primary role in ALS NPC injury.","evidence":"Super-resolution SIM of neuronal nuclei from ALS patients and models","pmids":["34281622"],"confidence":"Medium","gaps":["Negative finding in a single study","Does not exclude CHMP4B in nuclear envelope repair under other conditions"]},{"year":2023,"claim":"Uncovered an HSP90β chaperone relationship governing CHMP4B levels in the lens and a membrane-repair function antagonizing GSDMD-mediated pyroptosis.","evidence":"Co-IP with zebrafish epistasis/rescue and p53/Bak-Bim readouts; Co-IP, EM, and pyroptosis assays with VPS4A co-localization","pmids":["37487085","37931722"],"confidence":"Medium","gaps":["How HSP90β mechanistically sets CHMP4B/p53 levels not fully defined","Whether membrane repair uses the canonical ESCRT-III scission machinery not dissected"]},{"year":2025,"claim":"Embedded CHMP4B in additional remodeling pathways: a PRP4K splicing circuit controlling autophagosome-lysosome fusion, and GAS2L3 phase separation nucleating CHMP4B condensates at the midbody within a CHMP2A-dependent assembly hierarchy.","evidence":"CHMP4B cDNA rescue in PRP4K-null cells with autophagy assay; GAS2L3 LLPS/FRAP/droplet and IDR-deletion imaging; CHMP2A KO SIM/CLEM (preprint)","pmids":["40531620","41177429","bio_10.1101_2025.06.24.661003"],"confidence":"Medium","gaps":["Direct mechanistic role of CHMP4B in fusion vs. scission during autophagy unclear","Biophysical relationship between GAS2L3 condensates and CHMP4B filament formation not fully resolved"]},{"year":2026,"claim":"Identified a direct PI(3,5)P2-binding activity on lysosomes that targets CHMP4B for microautophagic encapsulation and degradation of STING, defining a phosphoinositide-driven recruitment axis.","evidence":"Liposome sedimentation, forced Pikfyve recruitment, and PI(3,5)P2-binding-deficient mutant rescue of STING degradation in Chmp4b-depleted cells","pmids":["42203786"],"confidence":"High","gaps":["Structural basis of CHMP4B PI(3,5)P2 recognition not solved","Generality of phosphoinositide-directed recruitment to other CHMP4B functions untested"]},{"year":null,"claim":"How CHMP4B's single polymerization machinery is differentially licensed across MVB sorting, abscission, ciliary maintenance, membrane repair, autophagy, and microautophagy remains the central open question.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model for how distinct adaptors/lipids select CHMP4B function","Specific lipid species bound during division (lipid-trap MS, preprint) not structurally defined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,5]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[16]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[5]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[13]},{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[10]},{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[16]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[4]}],"pathway":[{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[7,17]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[14,16]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[13]}],"complexes":["ESCRT-III"],"partners":["PDCD6IP","CC2D1A","CC2D1B","CHMP7","VPS4A","GSDMD","GAS2L3","HSP90AB1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9H444","full_name":"Charged multivesicular body protein 4b","aliases":["Chromatin-modifying protein 4b","CHMP4b","SNF7 homolog associated with Alix 1","SNF7-2","hSnf7-2","Vacuolar protein sorting-associated protein 32-2","Vps32-2","hVps32-2"],"length_aa":224,"mass_kda":24.9,"function":"Probable core component of the endosomal sorting required for transport complex III (ESCRT-III) which is involved in multivesicular bodies (MVBs) formation and sorting of endosomal cargo proteins into MVBs. MVBs contain intraluminal vesicles (ILVs) that are generated by invagination and scission from the limiting membrane of the endosome and mostly are delivered to lysosomes enabling degradation of membrane proteins, such as stimulated growth factor receptors, lysosomal enzymes and lipids. The MVB pathway appears to require the sequential function of ESCRT-O, -I,-II and -III complexes. ESCRT-III proteins mostly dissociate from the invaginating membrane before the ILV is released (PubMed:12860994, PubMed:18209100). The ESCRT machinery also functions in topologically equivalent membrane fission events, such as the terminal stages of cytokinesis (PubMed:21310966). Together with SPAST, the ESCRT-III complex promotes nuclear envelope sealing and mitotic spindle disassembly during late anaphase (PubMed:26040712). Plays a role in the endosomal sorting pathway. ESCRT-III proteins are believed to mediate the necessary vesicle extrusion and/or membrane fission activities, possibly in conjunction with the AAA ATPase VPS4. When overexpressed, membrane-assembled circular arrays of CHMP4B filaments can promote or stabilize negative curvature and outward budding. CHMP4A/B/C are required for the exosomal release of SDCBP, CD63 and syndecan (PubMed:22660413). Majority of the protein exists in a folded closed conformation (PubMed:33349255) (Microbial infection) The ESCRT machinery also functions in topologically equivalent membrane fission events, such as the budding of enveloped viruses (HIV-1 and other lentiviruses). Via its interaction with PDCD6IP involved in HIV-1 p6- and p9-dependent virus release","subcellular_location":"Cytoplasm, cytosol; Late endosome membrane; Midbody; Nucleus envelope","url":"https://www.uniprot.org/uniprotkb/Q9H444/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/CHMP4B","classification":"Common Essential","n_dependent_lines":1057,"n_total_lines":1208,"dependency_fraction":0.875},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000101421","cell_line_id":"CID000776","localizations":[{"compartment":"vesicles","grade":3}],"interactors":[{"gene":"CBX1","stoichiometry":0.2},{"gene":"CC2D1A","stoichiometry":0.2},{"gene":"CC2D1B","stoichiometry":0.2},{"gene":"CLTA","stoichiometry":0.2},{"gene":"CLTB","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID000776","total_profiled":1310},"omim":[{"mim_id":"621486","title":"MICROTUBULE-INTERACTING AND TRAFFICKING DOMAIN-CONTAINING PROTEIN 1; MITD1","url":"https://www.omim.org/entry/621486"},{"mim_id":"611130","title":"CHARGED MULTIVESICULAR BODY PROTEIN 7; CHMP7","url":"https://www.omim.org/entry/611130"},{"mim_id":"610907","title":"VACUOLAR PROTEIN SORTING 25 HOMOLOG; VPS25","url":"https://www.omim.org/entry/610907"},{"mim_id":"610901","title":"CHARGED MULTIVESICULAR BODY PROTEIN 6; CHMP6","url":"https://www.omim.org/entry/610901"},{"mim_id":"610900","title":"CHARGED MULTIVESICULAR BODY PROTEIN 5; CHMP5","url":"https://www.omim.org/entry/610900"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/CHMP4B"},"hgnc":{"alias_symbol":["dJ553F4.4","Shax1","SNF7-2","VPS32B"],"prev_symbol":["C20orf178"]},"alphafold":{"accession":"Q9H444","domains":[{"cath_id":"1.10.287.1060","chopping":"21-121","consensus_level":"high","plddt":95.5773,"start":21,"end":121}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H444","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H444-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H444-F1-predicted_aligned_error_v6.png","plddt_mean":78.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CHMP4B","jax_strain_url":"https://www.jax.org/strain/search?query=CHMP4B"},"sequence":{"accession":"Q9H444","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9H444.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9H444/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H444"}},"corpus_meta":[{"pmid":"12860994","id":"PMC_12860994","title":"The ALG-2-interacting protein Alix associates with CHMP4b, a human homologue of yeast Snf7 that is involved in multivesicular body sorting.","date":"2003","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12860994","citation_count":184,"is_preprint":false},{"pmid":"17701905","id":"PMC_17701905","title":"CHMP4B, a novel gene for autosomal dominant cataracts linked to chromosome 20q.","date":"2007","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/17701905","citation_count":107,"is_preprint":false},{"pmid":"24451548","id":"PMC_24451548","title":"Anillin-dependent organization of septin filaments promotes intercellular bridge elongation and Chmp4B targeting to the abscission site.","date":"2014","source":"Open biology","url":"https://pubmed.ncbi.nlm.nih.gov/24451548","citation_count":66,"is_preprint":false},{"pmid":"16856878","id":"PMC_16856878","title":"CHMP7, a novel ESCRT-III-related protein, associates with CHMP4b and functions in the endosomal sorting pathway.","date":"2006","source":"The Biochemical journal","url":"https://pubmed.ncbi.nlm.nih.gov/16856878","citation_count":61,"is_preprint":false},{"pmid":"24741567","id":"PMC_24741567","title":"Association of CHMP4B and autophagy with micronuclei: implications for cataract formation.","date":"2014","source":"BioMed research international","url":"https://pubmed.ncbi.nlm.nih.gov/24741567","citation_count":55,"is_preprint":false},{"pmid":"14678797","id":"PMC_14678797","title":"CHMP4b is a major binding partner of the ALG-2-interacting protein Alix among the three CHMP4 isoforms.","date":"2004","source":"Archives of biochemistry and biophysics","url":"https://pubmed.ncbi.nlm.nih.gov/14678797","citation_count":55,"is_preprint":false},{"pmid":"22406677","id":"PMC_22406677","title":"CC2D1A is a regulator of ESCRT-III CHMP4B.","date":"2012","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/22406677","citation_count":51,"is_preprint":false},{"pmid":"32585748","id":"PMC_32585748","title":"Up-regulation of CHMP4B alleviates microglial necroptosis induced by traumatic brain injury.","date":"2020","source":"Journal of cellular and molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/32585748","citation_count":25,"is_preprint":false},{"pmid":"31404815","id":"PMC_31404815","title":"A charged multivesicular body protein (CHMP4B) is required for lens growth and differentiation.","date":"2019","source":"Differentiation; research in biological diversity","url":"https://pubmed.ncbi.nlm.nih.gov/31404815","citation_count":23,"is_preprint":false},{"pmid":"19016654","id":"PMC_19016654","title":"The CHMP4b- and Src-docking sites in the Bro1 domain are autoinhibited in the native state of Alix.","date":"2009","source":"The Biochemical journal","url":"https://pubmed.ncbi.nlm.nih.gov/19016654","citation_count":23,"is_preprint":false},{"pmid":"22484091","id":"PMC_22484091","title":"Two distinct binding modes define the interaction of Brox with the C-terminal tails of CHMP5 and CHMP4B.","date":"2012","source":"Structure (London, England : 1993)","url":"https://pubmed.ncbi.nlm.nih.gov/22484091","citation_count":20,"is_preprint":false},{"pmid":"25874485","id":"PMC_25874485","title":"High CHMP4B expression is associated with accelerated cell proliferation and resistance to doxorubicin in hepatocellular carcinoma.","date":"2015","source":"Tumour biology : the journal of the International Society for Oncodevelopmental Biology and Medicine","url":"https://pubmed.ncbi.nlm.nih.gov/25874485","citation_count":19,"is_preprint":false},{"pmid":"34281622","id":"PMC_34281622","title":"The ESCRT-III protein VPS4, but not CHMP4B or CHMP2B, is pathologically increased in familial and sporadic ALS neuronal nuclei.","date":"2021","source":"Acta neuropathologica communications","url":"https://pubmed.ncbi.nlm.nih.gov/34281622","citation_count":18,"is_preprint":false},{"pmid":"31914703","id":"PMC_31914703","title":"ESCRT subunit CHMP4B localizes to primary cilia and is required for the structural integrity of the ciliary membrane.","date":"2019","source":"FASEB journal : official publication of the Federation of American Societies for Experimental Biology","url":"https://pubmed.ncbi.nlm.nih.gov/31914703","citation_count":15,"is_preprint":false},{"pmid":"35147915","id":"PMC_35147915","title":"BMP4 preserves the developmental potential of mESCs through Ube2s- and Chmp4b-mediated chromosomal stability safeguarding.","date":"2022","source":"Protein & cell","url":"https://pubmed.ncbi.nlm.nih.gov/35147915","citation_count":15,"is_preprint":false},{"pmid":"37931722","id":"PMC_37931722","title":"CHMP4B and VSP4A reverse GSDMD-mediated pyroptosis by cell membrane remodeling in endometrial carcinoma.","date":"2023","source":"Biochimica et biophysica acta. General subjects","url":"https://pubmed.ncbi.nlm.nih.gov/37931722","citation_count":13,"is_preprint":false},{"pmid":"25478783","id":"PMC_25478783","title":"CHMP4B, ESCRT-III associating protein, associated with neuronal apoptosis following intracerebral hemorrhage.","date":"2014","source":"Brain research","url":"https://pubmed.ncbi.nlm.nih.gov/25478783","citation_count":13,"is_preprint":false},{"pmid":"34722561","id":"PMC_34722561","title":"Broadening the Mutation Spectrum in GJA8 and CHMP4B: Novel Missense Variants and the Associated Phenotypes in Six Chinese Han Congenital Cataracts Families.","date":"2021","source":"Frontiers in medicine","url":"https://pubmed.ncbi.nlm.nih.gov/34722561","citation_count":11,"is_preprint":false},{"pmid":"35690225","id":"PMC_35690225","title":"Long noncoding RNA Sh2d3c promotes manganese-induced neuronal apoptosis through the mmu-miR-675-5p/Chmp4b/Bax axis.","date":"2022","source":"Toxicology 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of biological sciences","url":"https://pubmed.ncbi.nlm.nih.gov/40384863","citation_count":4,"is_preprint":false},{"pmid":"40715737","id":"PMC_40715737","title":"Aerobic Exercise Attenuates Autophagy-Lysosomal Flux Deficits via β2-AR-Mediated ESCRT-III Subunit CHMP4B in Mice With Human MAPT P301L.","date":"2025","source":"Aging cell","url":"https://pubmed.ncbi.nlm.nih.gov/40715737","citation_count":4,"is_preprint":false},{"pmid":"40705827","id":"PMC_40705827","title":"KIF4A Inhibits Ferroptosis in Glioblastoma via the CHMP4B/GPX4 Axis and Promotes Temozolomide Resistance.","date":"2025","source":"Molecular carcinogenesis","url":"https://pubmed.ncbi.nlm.nih.gov/40705827","citation_count":3,"is_preprint":false},{"pmid":"41177429","id":"PMC_41177429","title":"IDR-driven LLPS of GAS2L3 scaffolds CHMP4B condensates to accelerate cytokinesis in hepatocellular carcinoma cells.","date":"2025","source":"Journal of advanced research","url":"https://pubmed.ncbi.nlm.nih.gov/41177429","citation_count":2,"is_preprint":false},{"pmid":"38895958","id":"PMC_38895958","title":"CHMP4B contributes to maintaining the follicular cells integrity in the panoistic ovary of the cockroach Blattella germanica.","date":"2024","source":"Biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/38895958","citation_count":1,"is_preprint":false},{"pmid":"40531620","id":"PMC_40531620","title":"The evolutionarily conserved PRP4K-CHMP4B/vps32 splicing circuit regulates autophagy.","date":"2025","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/40531620","citation_count":0,"is_preprint":false},{"pmid":"42203786","id":"PMC_42203786","title":"A PI(3,5)P2/CHMP4B axis on lysosomes is essential for microautophagic degradation of STING.","date":"2026","source":"Nature 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partner of Alix (ALG-2-interacting protein X) through yeast two-hybrid screen, confirmed by GST pull-down and co-immunoprecipitation. CHMP4B co-localizes with Alix in HeLa cells and co-immunoprecipitates with dominant-negative SKD1(E235Q) AAA-ATPase. Overexpression of CHMP4B inhibited endocytosed EGF disappearance and caused accumulation of ubiquitinated proteins, consistent with a role in multivesicular body (MVB) sorting cooperating with SKD1.\",\n      \"method\": \"Yeast two-hybrid, GST pull-down, co-immunoprecipitation, fluorescence microscopy, overexpression phenotypic assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, GST pull-down, and yeast two-hybrid across multiple orthogonal methods in a single focused study\",\n      \"pmids\": [\"12860994\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Among the three CHMP4 isoforms (CHMP4a, CHMP4b, CHMP4c), CHMP4B is the major binding partner of Alix, showing stronger direct interaction than CHMP4a or CHMP4c as demonstrated by GST pull-down using recombinant proteins and co-immunoprecipitation from cell lysates.\",\n      \"method\": \"GST pull-down with recombinant proteins, co-immunoprecipitation\",\n      \"journal\": \"Archives of biochemistry and biophysics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct in vitro reconstitution with recombinant proteins plus Co-IP, replicated finding from same group with refined isoform specificity\",\n      \"pmids\": [\"14678797\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"CHMP7, a novel ESCRT-III-related protein, directly interacts with CHMP4B through its C-terminal SNF7 domain, as shown by pull-down assay. Overexpression of CHMP4B-GFP relocalized FLAG-CHMP7 from diffuse cytoplasm to cytoplasmic puncta, indicating functional interaction.\",\n      \"method\": \"Pull-down assay (Strep-tagged CHMP7 with GFP-CHMP4b from cell lysates), confocal fluorescence microscopy\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — single pull-down from cell lysates plus co-localization imaging, two orthogonal methods but not in vitro reconstitution\",\n      \"pmids\": [\"16856878\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Disease-associated mutations in CHMP4B (D129V and E161K) cause autosomal dominant cataracts. Transfection studies showed that truncated D129V-CHMP4B had altered subcellular distribution compared to wild-type and an increased capacity to inhibit virus-like particle release from the cell surface, consistent with gain-of-function dominant negative effects on ESCRT-III.\",\n      \"method\": \"Transfection of mutant vs. wild-type CHMP4B in cultured cells, subcellular localization imaging, virus-like particle release assay\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — single lab, two orthogonal functional assays (localization and VLP release), but no in vitro reconstitution or structural analysis\",\n      \"pmids\": [\"17701905\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The CHMP4B-docking site and Src-docking site in the Bro1 domain of Alix are autoinhibited in the native cytosolic state of Alix. In HEK-293 cell lysates, these sites are unavailable in cytosolic Alix but available in membrane-bound Alix, indicating that Alix membrane association relieves autoinhibition to enable CHMP4B binding.\",\n      \"method\": \"Biochemical fractionation, detergent treatment of recombinant Alix, cell lysate binding assays\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean biochemical fractionation combined with cell lysate binding studies, single lab with two orthogonal approaches\",\n      \"pmids\": [\"19016654\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CC2D1A and CC2D1B are direct regulators of CHMP4B, binding with nanomolar affinity in a 1:1 complex. The binding site on CC2D1A was mapped to the third DM14 domain, and the CC2D1A binding site on CHMP4B was mapped to the N-terminal helical hairpin. A crystal structure of the CHMP4B helical hairpin identified two surface patches involved in CC2D1A interaction. CC2D1A binding to CHMP4B prevents CHMP4B polymerization in vitro. Mutations at the CC2D1A-binding surface of CHMP4B abolished its dominant negative effect on HIV-1 budding, suggesting this surface is required for CHMP4B polymerization.\",\n      \"method\": \"Crystal structure of CHMP4B helical hairpin, surface plasmon resonance (nanomolar affinity measurement), deletion mapping, in vitro polymerization assay, HIV-1 budding assay with CHMP4B mutants\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure combined with SPR, in vitro polymerization assay, and functional mutagenesis in a single study with multiple orthogonal methods\",\n      \"pmids\": [\"22406677\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Hydrophobic residues in the CHMP4B C-terminal amphipathic α-helix bind a concave surface of Brox (a mammalian Alix paralog). Crystal/structural analysis showed the CHMP4B C-terminal tail adopts an α-helical conformation when bound to Brox, at the same site used by CHMP5 (which binds via a β-hairpin). This defines a shared but conformationally distinct binding surface on Brox for ESCRT-III proteins.\",\n      \"method\": \"Crystal structure of Brox:CHMP4B complex, mutagenesis, binding assays\",\n      \"journal\": \"Structure (London, England : 1993)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure with functional binding validation, single rigorous study with structural and biochemical orthogonal methods\",\n      \"pmids\": [\"22484091\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Anillin-septin complex is required for the recruitment of CHMP4B to the abscission site during cytokinesis. Using live imaging and subdiffraction microscopy, the anillin-septin cytoskeleton drives intercellular bridge elongation and maturation, which primes the bridge for CHMP4B assembly at the abscission site.\",\n      \"method\": \"Live cell imaging, subdiffraction microscopy, anillin/septin depletion (loss-of-function with CHMP4B localization readout)\",\n      \"journal\": \"Open biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic depletion with direct localization imaging of CHMP4B, single lab but using two orthogonal microscopy methods\",\n      \"pmids\": [\"24451548\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"CHMP4B not only localizes to cytokinetic bridges but also to chromosome bridges and micronuclei (the latter surrounded by lysosomes and autophagosomes), and can be co-immunoprecipitated with chromatin. A cataract-associated CHMP4B mutation abolishes its ability to localize to micronuclei, suggesting this localization is mutation-sensitive.\",\n      \"method\": \"Immunofluorescence localization, co-immunoprecipitation with chromatin, comparison of wild-type vs. cataract mutant CHMP4B\",\n      \"journal\": \"BioMed research international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct localization imaging with functional comparison of mutant vs. wild-type, co-IP with chromatin, but single lab and no mechanistic reconstitution\",\n      \"pmids\": [\"24741567\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Conditional knockdown of CHMP4B in mouse lens results in arrest of lens growth and differentiation, with lens fiber cell degeneration (shown by AQP0 immunolocalization) and cell death (TUNEL). Homozygous knock-in of the cataract-associated D129V mutation causes embryonic lethality by E15.5 with abnormal eye and brain histology, indicating CHMP4B is essential for lens development.\",\n      \"method\": \"Conditional knockout/knockdown mouse model, knock-in mouse model, immunolocalization (AQP0, CD68), TUNEL assay, in situ hybridization\",\n      \"journal\": \"Differentiation; research in biological diversity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple clean genetic models (CKD + knock-in) with multiple cellular readouts (localization, TUNEL, histology) in a single study\",\n      \"pmids\": [\"31404815\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CHMP4B localizes to primary cilia in mammalian cells and is required for cilium assembly and maintenance of ciliary structural integrity. Knockdown of CHMP4B caused defective cilium assembly and fragmentation of pre-existing cilia. Morpholino-mediated depletion in zebrafish induced ciliopathy phenotypes (curved body axis, hydrocephalus, otolith malformation, kidney cysts), independently of ESCRT-dependent endocytic degradation.\",\n      \"method\": \"Immunofluorescence localization to primary cilia, siRNA knockdown in mammalian cells, morpholino depletion in zebrafish, phenotypic analysis\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct localization plus loss-of-function in two organisms (mammalian cells and zebrafish) with specific ciliary phenotypes, multiple orthogonal methods\",\n      \"pmids\": [\"31914703\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"In ALS neurons, neither CHMP4B nor CHMP2B show increased nuclear accumulation (in contrast to CHMP7 and VPS4), indicating that CHMP4B is not a primary driver of nuclear pore complex injury in ALS despite CHMP7's known role in recruiting ESCRT-III subunits for nuclear envelope/NPC repair.\",\n      \"method\": \"Super-resolution structured illumination microscopy (SIM) of neuronal nuclei from ALS patients and models\",\n      \"journal\": \"Acta neuropathologica communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — super-resolution imaging is high quality, but this is a negative finding in a single study (CHMP4B is NOT elevated in ALS nuclei)\",\n      \"pmids\": [\"34281622\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"HSP90β directly interacts with CHMP4B as a client protein. HSP90β silencing causes upregulation of CHMP4B and p53; CHMP4B upregulation/overexpression induces excessive division of lens epithelial cells without differentiation, triggering apoptosis via the p53/Bak-Bim pathway and causing cataractogenesis and microphthalmia in zebrafish. Simultaneous silencing of both HSP90β and CHMP4B restored the normal eye phenotype.\",\n      \"method\": \"Co-immunoprecipitation (direct interaction), zebrafish knockdown/rescue experiment, overexpression phenotypic analysis, epistasis (double knockdown)\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct interaction demonstrated by Co-IP, genetic epistasis via double knockdown rescue in zebrafish, and functional overexpression analysis with specific molecular pathway readouts\",\n      \"pmids\": [\"37487085\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CHMP4B interacts with GSDMD (gasdermin D) and VPS4A, as shown by co-immunoprecipitation. CHMP4B and VPS4A puncta co-localize at injured plasma membranes in GSDMD-N-terminus-expressing cells. Depletion of CHMP4B enhanced pyroptotic indicators (PI-positive cells, Ca2+ efflux, IL-1β, LDH release), while overexpression attenuated them, demonstrating CHMP4B mediates membrane repair to reverse GSDMD-induced pyroptosis.\",\n      \"method\": \"Co-immunoprecipitation, fluorescence confocal microscopy, electron microscopy of membrane perforations, siRNA knockdown and overexpression with pyroptosis readouts (LDH, IL-1β, Ca2+ flux, FITC-Annexin V/PI)\",\n      \"journal\": \"Biochimica et biophysica acta. General subjects\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus electron microscopy plus multiple functional readouts, single lab but with several orthogonal methods\",\n      \"pmids\": [\"37931722\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PRP4K kinase controls splicing of CHMP4B pre-mRNA; loss of PRP4K causes mis-splicing and reduced expression of CHMP4B in human cells. CHMP4B is required for autophagosome-lysosome fusion; re-expression of CHMP4B cDNA in PRP4K-deficient cells restores normal autophagosome-lysosome fusion, placing CHMP4B downstream of PRP4K in an evolutionarily conserved splicing circuit regulating autophagy.\",\n      \"method\": \"Genetic epistasis (CHMP4B cDNA rescue in PRP4K knockout cells), autophagosome-lysosome fusion assay, mRNA splicing analysis\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic epistasis via cDNA rescue experiment with specific autophagy functional readout, replicated in two organisms (human cells and Dictyostelium)\",\n      \"pmids\": [\"40531620\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"GAS2L3 localizes to the midbody and recruits CHMP4B to the abscission site. GAS2L3 undergoes liquid-liquid phase separation (LLPS) via its intrinsically disordered region (IDR) and scaffolds CHMP4B condensate formation at the midbody through phase separation. GAS2L3 knockdown or IDR deletion leads to defective CHMP4B recruitment, defective cytokinesis, and G1 arrest.\",\n      \"method\": \"Live cell imaging, structured illumination microscopy, FRAP, in vitro droplet formation assay, GAS2L3 knockdown/IDR deletion with CHMP4B localization and cytokinesis readouts\",\n      \"journal\": \"Journal of advanced research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — FRAP and in vitro droplet assays plus genetic loss-of-function with CHMP4B localization readout, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"41177429\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"CHMP4B binds PI(3,5)P2 (a lysosomal phosphoinositide) as demonstrated by liposome sedimentation assay. Forced recruitment of Pikfyve (the PI(3,5)P2-generating kinase) to early endosomes recruits a fraction of CHMP4B to early endosomes. A CHMP4B mutant defective in PI(3,5)P2 binding cannot restore microautophagic STING degradation or resolution of STING signaling in Chmp4b-depleted cells, establishing a PI(3,5)P2/CHMP4B axis on lysosomes as essential for STING encapsulation by lysosomes.\",\n      \"method\": \"Liposome sedimentation assay (direct lipid binding), forced Pikfyve recruitment assay, CHMP4B mutant rescue experiment, STING degradation/signaling assay in Chmp4b-depleted cells\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro liposome sedimentation demonstrates direct binding, combined with forced recruitment assay and mutagenesis rescue experiment with specific functional readout\",\n      \"pmids\": [\"42203786\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CHMP4B displays progressively severe spatial organization defects at the cytokinetic abscission site when CHMP2A is depleted, as visualized by SIM and CLEM. Dual-protein imaging revealed disrupted coordination between CHMP4B and other ESCRT-III subunits in CHMP2A-deficient cells, supporting an ordered/hierarchical assembly of ESCRT-III subunits in which CHMP2A acts upstream of CHMP4B during abscission.\",\n      \"method\": \"CHMP2A knockout, live cell imaging, structured illumination microscopy (SIM), correlative light-electron microscopy (CLEM), dual-protein co-imaging\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean genetic KO with super-resolution imaging and CLEM, multiple orthogonal microscopy methods, but preprint not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.06.24.661003\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CHMP4B associates with specific lipid species in dividing HeLa cells (identified by lipid-trap mass spectrometry using GFP-tagged CHMP4B immunoprecipitation followed by lipidomic analysis), with the lipid association enriched in dividing compared to non-dividing cells.\",\n      \"method\": \"Lipid-trap mass spectrometry (GFP immunoprecipitation + lipidomics)\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — novel single-method pulldown from cells without in vitro reconstitution, preprint only, specific lipid species not detailed in abstract\",\n      \"pmids\": [\"bio_10.1101_2024.12.13.627510\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"CHMP4B is a core ESCRT-III subunit that forms a direct complex with Alix (via the Alix Bro1 domain, subject to membrane-dependent autoinhibition) and with CC2D1A/CC2D1B (via its N-terminal helical hairpin), polymerizes at membranes to drive scission, binds PI(3,5)P2 on lysosomes to mediate microautophagic encapsulation of STING, is recruited to cytokinetic abscission sites downstream of anillin-septin and CHMP2A in a hierarchical ESCRT-III assembly, localizes to primary cilia to maintain ciliary membrane integrity, undergoes HSP90β-dependent regulation to control lens cell division and differentiation, and functions in plasma membrane repair to counteract GSDMD-mediated pyroptosis.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CHMP4B is a core ESCRT-III subunit that polymerizes at membranes to drive membrane remodeling and scission across multivesicular body sorting, cytokinetic abscission, plasma membrane repair, and lysosomal microautophagy [#0, #5, #16]. It was first defined as the dominant Alix-binding CHMP4 isoform, cooperating with the AAA-ATPase SKD1 in MVB sorting of ubiquitinated cargo and endocytosed EGF [#0, #1]; Alix engagement is gated by membrane-dependent relief of autoinhibition at the Bro1 docking site [#4], and CHMP4B is also bound by the Alix paralog Brox through its C-terminal amphipathic helix [#6] and by the ESCRT-III-related protein CHMP7 [#2]. Polymerization is directly controlled by CC2D1A/CC2D1B, which bind the N-terminal helical hairpin of CHMP4B with nanomolar affinity and block filament assembly; the same surface is required for CHMP4B's dominant-negative effect on HIV-1 budding [#5]. During cytokinesis, CHMP4B is recruited to the abscission site downstream of the anillin-septin cytoskeleton and the GAS2L3 midbody scaffold, which nucleates CHMP4B condensates via phase separation, and its spatial organization depends on CHMP2A, establishing a hierarchical ESCRT-III assembly [#7, #15]. Beyond division, CHMP4B maintains primary cilium integrity independently of endocytic degradation [#10], mediates plasma membrane repair to counteract GSDMD-driven pyroptosis together with VPS4A [#13], supports autophagosome-lysosome fusion downstream of the PRP4K splicing circuit [#14], and binds the lysosomal phosphoinositide PI(3,5)P2 to drive microautophagic encapsulation and degradation of STING [#16]. Dominant CHMP4B mutations (D129V, E161K) cause autosomal dominant cataract, and CHMP4B is essential for lens development, with its dysregulation by HSP90\\u03b2 triggering p53/Bak-Bim apoptosis in lens epithelial cells [#3, #9, #12].\",\n  \"teleology\": [\n    {\n      \"year\": 2003,\n      \"claim\": \"Established CHMP4B's foundational identity as an ESCRT-III component by linking it physically and functionally to the Alix adaptor and the SKD1 AAA-ATPase in MVB cargo sorting.\",\n      \"evidence\": \"Yeast two-hybrid, GST pull-down, co-IP, and overexpression EGF/ubiquitin-sorting assays in HeLa cells\",\n      \"pmids\": [\"12860994\", \"14678797\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve the structural basis of the Alix interaction\", \"Isoform-specific functional differences among CHMP4a/b/c beyond binding strength not defined\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Extended the CHMP4B interaction network to the ESCRT-III-related protein CHMP7 via its SNF7 domain, indicating CHMP4B partners with multiple ESCRT-III-family proteins.\",\n      \"evidence\": \"Strep-tag pull-down from cell lysates and confocal relocalization imaging\",\n      \"pmids\": [\"16856878\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single pull-down from lysates without in vitro reconstitution\", \"Functional consequence of the CHMP4B-CHMP7 interaction not tested\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Connected CHMP4B to human disease by showing dominant cataract-causing mutations act as gain-of-function dominant negatives on ESCRT-III-mediated membrane budding.\",\n      \"evidence\": \"Transfection of D129V/E161K mutants with subcellular localization and virus-like particle release assays\",\n      \"pmids\": [\"17701905\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No in vitro or structural analysis of mutant polymerization\", \"Mechanism connecting ESCRT defect to lens pathology not established\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Resolved how Alix-CHMP4B engagement is regulated, showing the Bro1 docking site is autoinhibited in cytosol and unmasked only upon Alix membrane association.\",\n      \"evidence\": \"Biochemical fractionation and cell-lysate binding assays of cytosolic vs. membrane-bound Alix\",\n      \"pmids\": [\"19016654\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural conformational change underlying autoinhibition not directly visualized\", \"In vivo trigger for membrane recruitment unresolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Defined the structural and biochemical control of CHMP4B polymerization, identifying CC2D1A/B as direct high-affinity negative regulators and mapping the polymerization surface, plus a distinct Brox-binding mode.\",\n      \"evidence\": \"Crystal structures of the CHMP4B helical hairpin and Brox:CHMP4B complex, SPR, in vitro polymerization, and HIV-1 budding mutagenesis\",\n      \"pmids\": [\"22406677\", \"22484091\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo conditions that relieve CC2D1A inhibition not defined\", \"Full-length CHMP4B polymer architecture not solved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Placed CHMP4B in the cytokinetic abscission pathway downstream of the anillin-septin cytoskeleton and revealed its localization to chromosome bridges and micronuclei.\",\n      \"evidence\": \"Live and subdiffraction imaging with anillin/septin depletion; immunofluorescence and chromatin co-IP with mutant comparison\",\n      \"pmids\": [\"24451548\", \"24741567\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular link from septins to CHMP4B recruitment not defined\", \"Functional role of chromatin/micronuclear localization unresolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Demonstrated CHMP4B is essential for lens development and for primary cilium assembly/integrity, the latter independent of ESCRT endocytic degradation.\",\n      \"evidence\": \"Conditional knockout and D129V knock-in mouse models with TUNEL/histology; siRNA and zebrafish morpholino with ciliary phenotyping\",\n      \"pmids\": [\"31404815\", \"31914703\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of ciliary membrane maintenance by CHMP4B not defined\", \"How D129V causes embryonic lethality vs. dominant cataract not reconciled\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Distinguished CHMP4B from CHMP7 in disease context by showing CHMP4B does not abnormally accumulate in ALS neuronal nuclei, arguing against a primary role in ALS NPC injury.\",\n      \"evidence\": \"Super-resolution SIM of neuronal nuclei from ALS patients and models\",\n      \"pmids\": [\"34281622\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Negative finding in a single study\", \"Does not exclude CHMP4B in nuclear envelope repair under other conditions\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Uncovered an HSP90\\u03b2 chaperone relationship governing CHMP4B levels in the lens and a membrane-repair function antagonizing GSDMD-mediated pyroptosis.\",\n      \"evidence\": \"Co-IP with zebrafish epistasis/rescue and p53/Bak-Bim readouts; Co-IP, EM, and pyroptosis assays with VPS4A co-localization\",\n      \"pmids\": [\"37487085\", \"37931722\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How HSP90\\u03b2 mechanistically sets CHMP4B/p53 levels not fully defined\", \"Whether membrane repair uses the canonical ESCRT-III scission machinery not dissected\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Embedded CHMP4B in additional remodeling pathways: a PRP4K splicing circuit controlling autophagosome-lysosome fusion, and GAS2L3 phase separation nucleating CHMP4B condensates at the midbody within a CHMP2A-dependent assembly hierarchy.\",\n      \"evidence\": \"CHMP4B cDNA rescue in PRP4K-null cells with autophagy assay; GAS2L3 LLPS/FRAP/droplet and IDR-deletion imaging; CHMP2A KO SIM/CLEM (preprint)\",\n      \"pmids\": [\"40531620\", \"41177429\", \"bio_10.1101_2025.06.24.661003\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct mechanistic role of CHMP4B in fusion vs. scission during autophagy unclear\", \"Biophysical relationship between GAS2L3 condensates and CHMP4B filament formation not fully resolved\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Identified a direct PI(3,5)P2-binding activity on lysosomes that targets CHMP4B for microautophagic encapsulation and degradation of STING, defining a phosphoinositide-driven recruitment axis.\",\n      \"evidence\": \"Liposome sedimentation, forced Pikfyve recruitment, and PI(3,5)P2-binding-deficient mutant rescue of STING degradation in Chmp4b-depleted cells\",\n      \"pmids\": [\"42203786\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of CHMP4B PI(3,5)P2 recognition not solved\", \"Generality of phosphoinositide-directed recruitment to other CHMP4B functions untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How CHMP4B's single polymerization machinery is differentially licensed across MVB sorting, abscission, ciliary maintenance, membrane repair, autophagy, and microautophagy remains the central open question.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model for how distinct adaptors/lipids select CHMP4B function\", \"Specific lipid species bound during division (lipid-trap MS, preprint) not structurally defined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 5]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [16]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [13]},\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [10]},\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [16]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [7, 17]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [14, 16]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [13]}\n    ],\n    \"complexes\": [\"ESCRT-III\"],\n    \"partners\": [\"PDCD6IP\", \"CC2D1A\", \"CC2D1B\", \"CHMP7\", \"VPS4A\", \"GSDMD\", \"GAS2L3\", \"HSP90AB1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}