{"gene":"ITCH","run_date":"2026-06-10T01:55:23","timeline":{"discoveries":[{"year":2003,"finding":"AIP4/ITCH (HECT E3 ubiquitin ligase) mediates ubiquitination of the chemokine receptor CXCR4 at the plasma membrane, and also ubiquitinates the endosomal ubiquitin-binding protein Hrs, coordinating lysosomal sorting of CXCR4 together with Hrs and Vps4.","method":"Co-immunoprecipitation, colocalization, dominant-negative and siRNA experiments in cells","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, colocalization, functional knockdown with defined sorting phenotype; foundational paper replicated in subsequent work","pmids":["14602072"],"is_preprint":false},{"year":2006,"finding":"ITCH/AIP4 generates K29-linked polyubiquitin chains (rather than canonical K48 chains) on Deltex (DTX), targeting it for lysosomal degradation; ITCH and DTX interact and partially colocalize on endocytic vesicles.","method":"Co-immunoprecipitation, colocalization, in vivo ubiquitin linkage analysis (lysine-29-specific mutant ubiquitin), lysosomal inhibitor rescue","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — in vivo ubiquitin chain linkage determination with mutant ubiquitins, Co-IP, colocalization, and lysosomal degradation assay in one study","pmids":["17028573"],"is_preprint":false},{"year":2008,"finding":"ITCH/AIP4 controls ligand-independent degradation of Notch1 receptor by targeting it to lysosomes after early endocytosis, generating K29-linked polyubiquitin chains on Notch; ITCH is not required for Notch activation. The Notch–ITCH interaction requires either a post-translational modification or a bridging factor (not detectable by direct in vitro interaction).","method":"Itch−/− fibroblasts reconstituted with Notch1, lysosomal inhibitor rescue, ubiquitin chain-linkage analysis, in vitro binding assays (negative for direct interaction)","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 / Strong — knockout cell line, lysosomal rescue, K29-chain linkage confirmed, multiple orthogonal methods in one study","pmids":["18628966"],"is_preprint":false},{"year":2006,"finding":"AIP4/ITCH promotes ubiquitination and lysosomal degradation of TRP channels TRPV4 and TRPC4, reducing their plasma membrane abundance and basal channel activity; ubiquitination promotes endocytosis of TRPV4 without degrading the total protein pool. This regulation is selective: several other TRP channels are not affected by AIP4.","method":"Overexpression of AIP4 in cells, surface biotinylation, electrophysiology (basal current measurement), ubiquitination assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — functional electrophysiology readout combined with surface biotinylation and ubiquitination assays, selectivity controls included","pmids":["17110928"],"is_preprint":false},{"year":2006,"finding":"ITCH/AIP4 promotes ubiquitin-dependent degradation of the transcription factor p63; two specific lysine residues in p63 (associated with Split-Hand and Foot Malformation-4 syndrome) are required for ITCH-mediated degradation.","method":"Co-immunoprecipitation, overexpression/deletion mutagenesis of p63, ubiquitination assay, pulse-chase degradation assay","journal":"Cell cycle (Georgetown, Tex.)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — site-directed mutagenesis of substrate lysines combined with Co-IP and degradation assay, single lab","pmids":["16861923"],"is_preprint":false},{"year":2007,"finding":"AIP4/ITCH interacts with ErbB-4 (HER4) via its WW domains, ubiquitinates ErbB-4 in vivo, and promotes polyubiquitination and proteasomal/lysosomal degradation of ErbB-4, thereby reducing receptor stability and nuclear access of the ErbB-4 intracellular domain.","method":"Phage display library panning, Co-immunoprecipitation, in vivo ubiquitination assay, degradation assay, nuclear fractionation","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, ubiquitination, and functional degradation assay; single lab with multiple orthogonal methods","pmids":["17463226"],"is_preprint":false},{"year":2005,"finding":"AIP4 targets Smad7 for ubiquitin-dependent degradation via a two-hybrid-identified interaction; paradoxically, AIP4 inhibits TGF-β signaling by enhancing Smad7 association with the activated TGF-β type I receptor (TβRI). A catalytically inactive AIP4 mutant (unable to ubiquitinate Smad7) still stabilizes the TβRI–Smad7 complex and inhibits TGF-β signaling, demonstrating a ubiquitination-independent scaffolding mechanism.","method":"Yeast two-hybrid, Co-immunoprecipitation, catalytic-dead AIP4 mutant, TGF-β reporter assays, degradation assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — catalytic-dead mutagenesis distinguishing ligase-dependent vs. independent functions, Co-IP, and signaling reporter; multiple orthogonal methods in one study","pmids":["15946939"],"is_preprint":false},{"year":2002,"finding":"AIP4/ITCH physically interacts with CBLC (a RING-type E3 ligase) via its WW domains binding proline-rich regions; co-expression of CBLC and AIP4 cooperatively down-regulates EGFR signaling. Both AIP4 and CBLC become tyrosine-phosphorylated after EGF stimulation. Expression of WW domains of AIP4 exerts a dominant-negative effect on EGFR ubiquitination.","method":"Yeast two-hybrid, GST pulldown, Co-immunoprecipitation, colocalization, EGFR ubiquitination assay, dominant-negative overexpression","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — GST pulldown plus Co-IP plus functional dominant-negative, single lab","pmids":["12226085"],"is_preprint":false},{"year":2010,"finding":"Spartin binds the WW region of AIP4/ITCH with ~7-fold higher affinity than the WW region binds the HECT domain (disrupting AIP4 autoinhibition), thereby activating AIP4 E3 ligase activity. Spartin recruits AIP4 to lipid droplets, where AIP4 ubiquitinates adipophilin, regulating lipid droplet turnover. Spartin itself is not a substrate for AIP4.","method":"ELISA-based binding affinity measurement, self-ubiquitination assay, colocalization to lipid droplets (fluorescence microscopy), ubiquitination assay of adipophilin","journal":"BMC biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — quantitative binding affinity assay, in-cell ubiquitination, colocalization; single lab with multiple orthogonal methods","pmids":["20504295"],"is_preprint":false},{"year":2010,"finding":"USP8 (a deubiquitinase downstream of Akt) links the PTEN-Akt pathway to AIP4 activity: USP8 deubiquitinates AIP4, increasing AIP4-mediated ubiquitination and degradation of cFLIP(S), thereby decreasing TRAIL resistance in glioblastoma cells. siRNA knockdown of AIP4 reverses the effects of USP8 overexpression on FLIP(S) levels.","method":"siRNA knockdown, overexpression, ubiquitination assay, half-life (pulse-chase), co-immunoprecipitation, TRAIL apoptosis assay","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — rescue epistasis (AIP4 siRNA reverses USP8 effect), Co-IP, ubiquitination, and functional apoptosis assay; single lab","pmids":["20484045"],"is_preprint":false},{"year":2010,"finding":"AIP4/ITCH-dependent JUNB protein degradation is markedly reduced in cells with active AKT; JNK-mediated AIP4 activity is required for rapamycin-induced repression of cyclin D1 and c-MYC transcription via JUNB degradation. Silencing AIP4 or inhibiting JNK abrogates the rapamycin-induced transcriptional effects.","method":"siRNA knockdown of AIP4, JNK inhibition, promoter-reporter assays, protein stability assays, ChIP","journal":"Molecular cancer research : MCR","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA rescue epistasis with promoter assay, single lab with multiple readouts","pmids":["21135252"],"is_preprint":false},{"year":2009,"finding":"TNF-α signaling induces association of the homeodomain protein TGIF with ITCH/AIP4, increasing accessibility of cFLIP(L) for ITCH-mediated ubiquitination and degradation, thereby promoting TNF-α-induced apoptosis. Additionally, ITCH monoubiquitinates TGIF at K259 in response to TNF-α, stabilizing TGIF and creating a positive feedback loop.","method":"Co-immunoprecipitation (TNF-α-inducible), ubiquitination assays, site-directed mutagenesis (K259R), apoptosis assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — site-directed mutagenesis of ubiquitination site, Co-IP, ubiquitination assay, and functional apoptosis readout; multiple orthogonal methods","pmids":["20064471"],"is_preprint":false},{"year":2016,"finding":"The anti-HER3 antibody 9F7-F11 induces HER3 ubiquitination and degradation mainly through ITCH/AIP4, activated by JNK1/2 phosphorylation; deubiquitinases USP8 and USP9X activate ITCH/AIP4 activity in this context. Overexpression of the ITCH inhibitor N4BP1 or siRNA knockdown of ITCH blocks 9F7-F11-induced HER3 ubiquitination/degradation.","method":"siRNA knockdown of ITCH, N4BP1 overexpression, ubiquitination assays, Co-immunoprecipitation, JNK inhibitor treatment, PI3K/AKT signaling assays","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA rescue with Co-IP and ubiquitination assays; single lab, multiple orthogonal approaches","pmids":["27203743"],"is_preprint":false},{"year":2018,"finding":"AIP4/ITCH promotes K48-linked ubiquitination of influenza A virus matrix protein M1 at K102 and K104, targeting it for proteasome-mediated degradation; Cyclophilin A (CypA) inhibits AIP4-mediated M1 ubiquitination by impairing the AIP4–M1 interaction, thereby modulating nuclear export of M1 and viral replication.","method":"Ubiquitination assays with lysine-specific ubiquitin mutants, Co-immunoprecipitation, site-directed mutagenesis of M1 (K102R/K104R), recombinant virus rescue assay, subcellular localization assay","journal":"Virologica Sinica","confidence":"Medium","confidence_rationale":"Tier 1-2 / Moderate — K48-chain linkage confirmed with mutant ubiquitin, site-directed mutagenesis of substrate, recombinant virus rescue; single lab","pmids":["30328013"],"is_preprint":false},{"year":2024,"finding":"SPG20 (Spartin) detects lipid-packing defects in the limiting membrane of damaged lysosomes via sensory amphipathic helices before membrane rupture, then recruits and activates ITCH to mark damaged lysosomes with K63-linked ubiquitin chains, initiating lysophagy. SPG20 binds the repair factor IST1 on damaged lysosomes and integrates repair status with lipid damage detection; if damage is extensive (e.g., lipid peroxidation), ITCH is recruited for lysosomal destruction.","method":"Proximity ligation, Co-immunoprecipitation, ubiquitin chain linkage analysis (K63-specific), amphipathic helix mutagenesis, fluorescence live imaging of lysosomal damage, autophagy flux assays in human cells","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — multiple orthogonal methods including mutagenesis, K63-chain linkage, live imaging, and functional lysophagy readout in human cells","pmids":["38503285"],"is_preprint":false},{"year":2015,"finding":"ITCH E3 ubiquitin ligase is involved in multiple immune regulatory contexts: it controls T-cell activation and tolerance, T-helper cell differentiation, and various signaling pathways through substrate ubiquitylation; its deletion in mice causes an itchy phenotype with multi-organ inflammation.","method":"Genetic deletion (Itch−/− mice), immune phenotyping, multiple substrate ubiquitination studies (review consolidation of primary experiments)","journal":"Immunological reviews","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — review summarizing Itch knockout phenotype and substrate studies; original genetic and biochemical data from multiple labs, but this paper is a review","pmids":["26085204"],"is_preprint":false}],"current_model":"ITCH (AIP4) is a HECT-domain E3 ubiquitin ligase that ubiquitinates a broad set of substrates—including CXCR4, Notch1, Deltex, TRPV4/TRPC4, ErbB-4/HER3, p63, Smad7, cFLIP, JUNB, and the influenza M1 protein—predominantly via K29- or K63-linked (lysosomal targeting) or K48-linked (proteasomal targeting) chains, and is activated by upstream signals such as JNK-mediated phosphorylation and by adaptor proteins such as SPG20/Spartin; it operates at the plasma membrane, endosomes, and lysosomes to regulate receptor down-regulation, Notch and TGF-β signaling, apoptosis, lipid droplet turnover, and lysosomal damage-triggered lysophagy."},"narrative":{"mechanistic_narrative":"ITCH (AIP4) is a HECT-domain E3 ubiquitin ligase that uses its WW domains to engage substrates and partners and its catalytic HECT domain to build polyubiquitin chains controlling receptor down-regulation, signal-pathway tuning, apoptosis, and organelle quality control [PMID:14602072, PMID:17463226, PMID:20504295]. A recurrent theme is endosomal-to-lysosomal sorting of membrane receptors: ITCH ubiquitinates the chemokine receptor CXCR4 and the sorting factor Hrs to coordinate lysosomal degradation [PMID:14602072], and targets Notch1 and Deltex for lysosomal turnover by assembling non-canonical K29-linked chains [PMID:17028573, PMID:18628966], while also ubiquitinating TRPV4/TRPC4 channels and ErbB-4/HER3 to reduce their surface abundance and stability [PMID:17110928, PMID:17463226]. ITCH activity is gated by autoinhibition and by activating inputs: JNK-mediated phosphorylation and deubiquitination by USP8/USP9X stimulate substrate ubiquitination (e.g., cFLIP and HER3), whereas the adaptor SPG20/Spartin binds the WW region to relieve autoinhibition and recruits ITCH to specific membranes [PMID:20504295, PMID:20484045, PMID:27203743]. Beyond degradation, ITCH acts as a ubiquitination-independent scaffold for Smad7 at the TGF-β type I receptor to inhibit TGF-β signaling [PMID:15946939], and it controls apoptosis by degrading cFLIP in concert with TGIF, which it monoubiquitinates to form a feedback loop [PMID:20064471]. At organelles, Spartin-activated ITCH ubiquitinates adipophilin on lipid droplets and marks damaged lysosomes with K63-linked chains to initiate lysophagy [PMID:20504295, PMID:38503285]; it also K48-ubiquitinates influenza M1 to restrict viral replication [PMID:30328013]. Genetic loss of Itch in mice produces an itchy, multi-organ inflammatory phenotype reflecting its broad role in immune regulation and T-cell tolerance [PMID:26085204].","teleology":[{"year":2002,"claim":"Established that ITCH engages receptor down-regulation machinery, showing it interacts with the RING ligase CBLC via WW-domain/proline-rich binding and cooperatively dampens EGFR signaling.","evidence":"Yeast two-hybrid, GST pulldown, Co-IP, and dominant-negative EGFR ubiquitination assays","pmids":["12226085"],"confidence":"Medium","gaps":["Direct chain linkage on EGFR not defined","Single lab; physiological context of CBLC cooperation untested"]},{"year":2003,"claim":"Defined ITCH as a plasma-membrane and endosomal ligase coordinating lysosomal receptor sorting by ubiquitinating both the cargo CXCR4 and the sorting machine Hrs.","evidence":"Co-IP, colocalization, dominant-negative and siRNA experiments with Hrs/Vps4","pmids":["14602072"],"confidence":"High","gaps":["Chain-type on CXCR4 not specified","Recruitment mechanism to the receptor not resolved"]},{"year":2005,"claim":"Revealed that ITCH has a catalysis-independent function, scaffolding Smad7 onto the TGF-β type I receptor to inhibit signaling separately from Smad7 degradation.","evidence":"Yeast two-hybrid, catalytic-dead mutant, Co-IP, and TGF-β reporter assays","pmids":["15946939"],"confidence":"High","gaps":["Structural basis of the scaffold not determined","In vivo relevance of scaffolding vs degradation unquantified"]},{"year":2006,"claim":"Showed ITCH builds non-canonical K29-linked chains to route Deltex to lysosomes and degrades TRP channels and p63, establishing substrate diversity and chain-type specificity.","evidence":"K29-specific ubiquitin mutants, surface biotinylation/electrophysiology, Co-IP, and degradation assays","pmids":["17028573","17110928","16861923"],"confidence":"High","gaps":["How chain-type selection is achieved mechanistically is unknown","p63 finding is Medium confidence/single lab"]},{"year":2007,"claim":"Extended ITCH receptor regulation to ErbB-4/HER4, showing WW-domain binding drives ubiquitination and degradation that limits nuclear access of the ErbB-4 intracellular domain.","evidence":"Phage display, Co-IP, in vivo ubiquitination, degradation, and nuclear fractionation","pmids":["17463226"],"confidence":"Medium","gaps":["Proteasomal vs lysosomal route not cleanly separated","Single lab"]},{"year":2008,"claim":"Demonstrated ligand-independent Notch1 degradation by ITCH requires a bridging factor or modification rather than direct binding, refining how ITCH recognizes Notch.","evidence":"Itch−/− fibroblast reconstitution, lysosomal rescue, K29-chain analysis, negative in vitro binding","pmids":["18628966"],"confidence":"High","gaps":["Identity of the bridging factor/modification not established","Mechanism of Notch recruitment unresolved"]},{"year":2009,"claim":"Connected ITCH to TNF-α-induced apoptosis, showing TGIF association exposes cFLIP(L) for degradation while ITCH monoubiquitinates TGIF at K259 to create positive feedback.","evidence":"TNF-α-inducible Co-IP, ubiquitination assays, K259R mutagenesis, apoptosis assays","pmids":["20064471"],"confidence":"High","gaps":["Direct vs adaptor-mediated cFLIP recognition not separated","Stoichiometry of the feedback loop unclear"]},{"year":2010,"claim":"Identified upstream regulators of ITCH activity: Spartin relieves WW/HECT autoinhibition to activate the ligase at lipid droplets, USP8 deubiquitinates ITCH to enhance cFLIP(S) degradation, and AKT/JNK status controls JUNB degradation.","evidence":"ELISA binding affinity, self-ubiquitination, colocalization, siRNA rescue epistasis, promoter-reporter and apoptosis assays","pmids":["20504295","20484045","21135252"],"confidence":"Medium","gaps":["Each axis from a single lab","Integration of competing kinase/DUB inputs not modeled"]},{"year":2015,"claim":"Consolidated ITCH's broad immune role, linking its loss to T-cell tolerance failure and multi-organ inflammation in the itchy mouse.","evidence":"Review of Itch−/− mouse genetics and substrate ubiquitination studies","pmids":["26085204"],"confidence":"Medium","gaps":["Review consolidation rather than new primary data","Substrate-to-phenotype causality not dissected here"]},{"year":2016,"claim":"Showed antibody-induced HER3 degradation operates through ITCH activated by JNK1/2 phosphorylation and USP8/USP9X, with N4BP1 acting as an inhibitor, integrating multiple regulatory inputs at one substrate.","evidence":"siRNA knockdown, N4BP1 overexpression, Co-IP, ubiquitination, JNK inhibition","pmids":["27203743"],"confidence":"Medium","gaps":["Relative contribution of each activator not quantified","Single lab/therapeutic-antibody context"]},{"year":2018,"claim":"Defined an antiviral role for ITCH, K48-ubiquitinating influenza M1 at K102/K104 for proteasomal degradation, with Cyclophilin A antagonizing the interaction to control M1 nuclear export.","evidence":"Lysine-specific ubiquitin mutants, K102R/K104R mutagenesis, recombinant virus rescue, localization assays","pmids":["30328013"],"confidence":"Medium","gaps":["In vivo relevance to infection not established","Single lab"]},{"year":2024,"claim":"Established ITCH as an effector of lysosomal quality control, recruited and activated by Spartin's lipid-damage-sensing amphipathic helices to deposit K63-linked ubiquitin on damaged lysosomes and initiate lysophagy.","evidence":"Proximity ligation, Co-IP, K63-specific linkage analysis, amphipathic-helix mutagenesis, live imaging, autophagy flux in human cells","pmids":["38503285"],"confidence":"High","gaps":["Downstream lysophagy receptors recognizing the K63 mark not detailed here","How repair (IST1) vs destruction decision is set quantitatively"]},{"year":null,"claim":"How ITCH selects substrate-specific chain linkages (K29 vs K48 vs K63) and integrates competing kinase/DUB/adaptor inputs to dictate proteasomal versus lysosomal versus signaling outcomes remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model linking activator binding to chain-type output","Substrate recruitment codes for direct vs bridged binding not generalized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016874","term_label":"ligase activity","supporting_discovery_ids":[0,1,2,5,8,14]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,1,2,3,5,13]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[6]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[6,8]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,3]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[0,1,2]},{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[1,2,14]},{"term_id":"GO:0005811","term_label":"lipid droplet","supporting_discovery_ids":[8]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,1,2,5,13]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[3,6,7,12]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[9,11]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[14]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[15]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[0]}],"complexes":[],"partners":["SPG20","USP8","HRS","SMAD7","TGIF","CBLC","N4BP1","USP9X"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q96J02","full_name":"E3 ubiquitin-protein ligase Itchy homolog","aliases":["Atrophin-1-interacting protein 4","AIP4","HECT-type E3 ubiquitin transferase Itchy homolog","NFE2-associated polypeptide 1","NAPP1"],"length_aa":903,"mass_kda":102.8,"function":"Acts as an Acts as an E3 ubiquitin-protein ligase which accepts ubiquitin from an E2 ubiquitin-conjugating enzyme in the form of a thioester and then directly transfers the ubiquitin to targeted substrates (PubMed:11046148, PubMed:14602072, PubMed:15051726, PubMed:16387660, PubMed:17028573, PubMed:18718448, PubMed:18718449, PubMed:19116316, PubMed:19592251, PubMed:19881509, PubMed:20068034, PubMed:20392206, PubMed:20491914, PubMed:23146885, PubMed:24790097, PubMed:25631046). Catalyzes 'Lys-29'-, 'Lys-48'- and 'Lys-63'-linked ubiquitin conjugation (PubMed:17028573, PubMed:18718448, PubMed:19131965, PubMed:19881509). Involved in the control of inflammatory signaling pathways (PubMed:19131965). Essential component of a ubiquitin-editing protein complex, comprising also TNFAIP3, TAX1BP1 and RNF11, that ensures the transient nature of inflammatory signaling pathways (PubMed:19131965). Promotes the association of the complex after TNF stimulation (PubMed:19131965). Once the complex is formed, TNFAIP3 deubiquitinates 'Lys-63' polyubiquitin chains on RIPK1 and catalyzes the formation of 'Lys-48'-polyubiquitin chains (PubMed:19131965). This leads to RIPK1 proteasomal degradation and consequently termination of the TNF- or LPS-mediated activation of NFKB1 (PubMed:19131965). Ubiquitinates RIPK2 by 'Lys-63'-linked conjugation and influences NOD2-dependent signal transduction pathways (PubMed:19592251). Regulates the transcriptional activity of several transcription factors, and probably plays an important role in the regulation of immune response (PubMed:18718448, PubMed:20491914). Ubiquitinates NFE2 by 'Lys-63' linkages and is implicated in the control of the development of hematopoietic lineages (PubMed:18718448). Mediates JUN ubiquitination and degradation (By similarity). Mediates JUNB ubiquitination and degradation (PubMed:16387660). Critical regulator of type 2 helper T (Th2) cell cytokine production by inducing JUNB ubiquitination and degradation (By similarity). Involved in the negative regulation of MAVS-dependent cellular antiviral responses (PubMed:19881509). Ubiquitinates MAVS through 'Lys-48'-linked conjugation resulting in MAVS proteasomal degradation (PubMed:19881509). Following ligand stimulation, regulates sorting of Wnt receptor FZD4 to the degradative endocytic pathway probably by modulating PI42KA activity (PubMed:23146885). Ubiquitinates PI4K2A and negatively regulates its catalytic activity (PubMed:23146885). Ubiquitinates chemokine receptor CXCR4 and regulates sorting of CXCR4 to the degradative endocytic pathway following ligand stimulation by ubiquitinating endosomal sorting complex required for transport ESCRT-0 components HGS and STAM (PubMed:14602072, PubMed:23146885, PubMed:34927784). Targets DTX1 for lysosomal degradation and controls NOTCH1 degradation, in the absence of ligand, through 'Lys-29'-linked polyubiquitination (PubMed:17028573, PubMed:18628966, PubMed:23886940). Ubiquitinates SNX9 (PubMed:20491914). Ubiquitinates MAP3K7 through 'Lys-48'-linked conjugation (By similarity). Together with UBR5, involved in the regulation of apoptosis and reactive oxygen species levels through the ubiquitination and proteasomal degradation of TXNIP: catalyzes 'Lys-48'-/'Lys-63'-branched ubiquitination of TXNIP (PubMed:20068034, PubMed:29378950). ITCH synthesizes 'Lys-63'-linked chains, while UBR5 is branching multiple 'Lys-48'-linked chains of substrate initially modified (PubMed:29378950). Mediates the antiapoptotic activity of epidermal growth factor through the ubiquitination and proteasomal degradation of p15 BID (PubMed:20392206). Ubiquitinates BRAT1 and this ubiquitination is enhanced in the presence of NDFIP1 (PubMed:25631046). Inhibits the replication of influenza A virus (IAV) via ubiquitination of IAV matrix protein 1 (M1) through 'Lys-48'-linked conjugation resulting in M1 proteasomal degradation (PubMed:30328013). Ubiquitinates NEDD9/HEF1, resulting in proteasomal degradation of NEDD9/HEF1 (PubMed:15051726)","subcellular_location":"Cell membrane; Cytoplasm; Nucleus; Early endosome membrane; Endosome membrane","url":"https://www.uniprot.org/uniprotkb/Q96J02/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ITCH","classification":"Not Classified","n_dependent_lines":7,"n_total_lines":1208,"dependency_fraction":0.005794701986754967},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CAPZB","stoichiometry":0.2},{"gene":"CPSF6","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/ITCH","total_profiled":1310},"omim":[{"mim_id":"621451","title":"SMALL NUCLEOLAR RNA HOST GENE 12; SNHG12","url":"https://www.omim.org/entry/621451"},{"mim_id":"621411","title":"TRANSMEMBRANE PROTEIN 184B; TMEM184B","url":"https://www.omim.org/entry/621411"},{"mim_id":"621000","title":"SORTING NEXIN 18; SNX18","url":"https://www.omim.org/entry/621000"},{"mim_id":"620195","title":"OBESITY AND HYPOPIGMENTATION; OBHP","url":"https://www.omim.org/entry/620195"},{"mim_id":"619768","title":"ARRESTIN DOMAIN-CONTAINING PROTEIN 1; ARRDC1","url":"https://www.omim.org/entry/619768"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nucleoplasm","reliability":"Enhanced"},{"location":"Vesicles","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/ITCH"},"hgnc":{"alias_symbol":["AIP4"],"prev_symbol":[]},"alphafold":{"accession":"Q96J02","domains":[{"cath_id":"2.60.40.150","chopping":"18-144","consensus_level":"high","plddt":89.9941,"start":18,"end":144},{"cath_id":"2.20.70.10","chopping":"333-392","consensus_level":"medium","plddt":89.2385,"start":333,"end":392},{"cath_id":"3.90.1750.10","chopping":"548-777","consensus_level":"medium","plddt":87.396,"start":548,"end":777},{"cath_id":"3.30.2410.10","chopping":"787-897","consensus_level":"high","plddt":90.6663,"start":787,"end":897}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96J02","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96J02-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96J02-F1-predicted_aligned_error_v6.png","plddt_mean":74.69},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ITCH","jax_strain_url":"https://www.jax.org/strain/search?query=ITCH"},"sequence":{"accession":"Q96J02","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96J02.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96J02/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96J02"}},"corpus_meta":[{"pmid":"24094650","id":"PMC_24094650","title":"The epithelial cell-derived atopic dermatitis cytokine TSLP activates neurons to induce itch.","date":"2013","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/24094650","citation_count":764,"is_preprint":false},{"pmid":"19661382","id":"PMC_19661382","title":"Cellular basis of itch sensation.","date":"2009","source":"Science (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/19661382","citation_count":469,"is_preprint":false},{"pmid":"31537912","id":"PMC_31537912","title":"Astrocytes in chronic pain and itch.","date":"2019","source":"Nature reviews. 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sciences","url":"https://pubmed.ncbi.nlm.nih.gov/36077340","citation_count":24,"is_preprint":false},{"pmid":"33668714","id":"PMC_33668714","title":"Intractable Itch in Atopic Dermatitis: Causes and Treatments.","date":"2021","source":"Biomedicines","url":"https://pubmed.ncbi.nlm.nih.gov/33668714","citation_count":23,"is_preprint":false},{"pmid":"27203743","id":"PMC_27203743","title":"The anti-HER3 (ErbB3) therapeutic antibody 9F7-F11 induces HER3 ubiquitination and degradation in tumors through JNK1/2- dependent ITCH/AIP4 activation.","date":"2016","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/27203743","citation_count":23,"is_preprint":false},{"pmid":"23902966","id":"PMC_23902966","title":"Updated neurophysiology of itch.","date":"2013","source":"Biological & pharmaceutical bulletin","url":"https://pubmed.ncbi.nlm.nih.gov/23902966","citation_count":22,"is_preprint":false},{"pmid":"34830245","id":"PMC_34830245","title":"Connections between Immune-Derived Mediators and Sensory Nerves for Itch Sensation.","date":"2021","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/34830245","citation_count":22,"is_preprint":false},{"pmid":"25558916","id":"PMC_25558916","title":"Protein kinase Cδ mediates histamine-evoked itch and responses in pruriceptors.","date":"2015","source":"Molecular pain","url":"https://pubmed.ncbi.nlm.nih.gov/25558916","citation_count":22,"is_preprint":false},{"pmid":"29424270","id":"PMC_29424270","title":"TRPV1 gain-of-function mutation impairs pain and itch sensations in mice.","date":"2018","source":"Molecular pain","url":"https://pubmed.ncbi.nlm.nih.gov/29424270","citation_count":22,"is_preprint":false},{"pmid":"30413999","id":"PMC_30413999","title":"Immune regulation by protein ubiquitination: roles of the E3 ligases VHL and Itch.","date":"2018","source":"Protein & cell","url":"https://pubmed.ncbi.nlm.nih.gov/30413999","citation_count":21,"is_preprint":false},{"pmid":"16297001","id":"PMC_16297001","title":"Itch and pain.","date":"2005","source":"Dermatologic therapy","url":"https://pubmed.ncbi.nlm.nih.gov/16297001","citation_count":20,"is_preprint":false},{"pmid":"36198265","id":"PMC_36198265","title":"A non-canonical retina-ipRGCs-SCN-PVT visual pathway for mediating contagious itch behavior.","date":"2022","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/36198265","citation_count":20,"is_preprint":false},{"pmid":"35327551","id":"PMC_35327551","title":"Circular RNA ITCH: An Emerging Multifunctional Regulator.","date":"2022","source":"Biomolecules","url":"https://pubmed.ncbi.nlm.nih.gov/35327551","citation_count":20,"is_preprint":false},{"pmid":"30328013","id":"PMC_30328013","title":"CypA Regulates AIP4-Mediated M1 Ubiquitination of Influenza A Virus.","date":"2018","source":"Virologica Sinica","url":"https://pubmed.ncbi.nlm.nih.gov/30328013","citation_count":20,"is_preprint":false},{"pmid":"36436135","id":"PMC_36436135","title":"Keratinocyte TLR2 and TLR7 contribute to chronic itch through pruritic cytokines and chemokines in mice.","date":"2022","source":"Journal of cellular physiology","url":"https://pubmed.ncbi.nlm.nih.gov/36436135","citation_count":20,"is_preprint":false},{"pmid":"20064471","id":"PMC_20064471","title":"A model of partnership co-opted by the homeodomain protein TGIF and the Itch/AIP4 ubiquitin ligase for effective execution of TNF-alpha cytotoxicity.","date":"2009","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/20064471","citation_count":19,"is_preprint":false},{"pmid":"26780378","id":"PMC_26780378","title":"Cell transplants to treat the \"disease\" of neuropathic pain and itch.","date":"2016","source":"Pain","url":"https://pubmed.ncbi.nlm.nih.gov/26780378","citation_count":19,"is_preprint":false},{"pmid":"32891774","id":"PMC_32891774","title":"Substance use disorders and chronic itch.","date":"2020","source":"Journal of the American Academy of Dermatology","url":"https://pubmed.ncbi.nlm.nih.gov/32891774","citation_count":18,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":39019,"output_tokens":4354,"usd":0.091184,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":12276,"output_tokens":4426,"usd":0.086015,"stage2_stop_reason":"end_turn"},"total_usd":0.177199,"stage1_batch_id":"msgbatch_01DUPACZi7AAWwuZiUjseQF4","stage2_batch_id":"msgbatch_018yt7chE3f48PEFtDwtj6AE","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2003,\n      \"finding\": \"AIP4/ITCH (HECT E3 ubiquitin ligase) mediates ubiquitination of the chemokine receptor CXCR4 at the plasma membrane, and also ubiquitinates the endosomal ubiquitin-binding protein Hrs, coordinating lysosomal sorting of CXCR4 together with Hrs and Vps4.\",\n      \"method\": \"Co-immunoprecipitation, colocalization, dominant-negative and siRNA experiments in cells\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, colocalization, functional knockdown with defined sorting phenotype; foundational paper replicated in subsequent work\",\n      \"pmids\": [\"14602072\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"ITCH/AIP4 generates K29-linked polyubiquitin chains (rather than canonical K48 chains) on Deltex (DTX), targeting it for lysosomal degradation; ITCH and DTX interact and partially colocalize on endocytic vesicles.\",\n      \"method\": \"Co-immunoprecipitation, colocalization, in vivo ubiquitin linkage analysis (lysine-29-specific mutant ubiquitin), lysosomal inhibitor rescue\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — in vivo ubiquitin chain linkage determination with mutant ubiquitins, Co-IP, colocalization, and lysosomal degradation assay in one study\",\n      \"pmids\": [\"17028573\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"ITCH/AIP4 controls ligand-independent degradation of Notch1 receptor by targeting it to lysosomes after early endocytosis, generating K29-linked polyubiquitin chains on Notch; ITCH is not required for Notch activation. The Notch–ITCH interaction requires either a post-translational modification or a bridging factor (not detectable by direct in vitro interaction).\",\n      \"method\": \"Itch−/− fibroblasts reconstituted with Notch1, lysosomal inhibitor rescue, ubiquitin chain-linkage analysis, in vitro binding assays (negative for direct interaction)\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — knockout cell line, lysosomal rescue, K29-chain linkage confirmed, multiple orthogonal methods in one study\",\n      \"pmids\": [\"18628966\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"AIP4/ITCH promotes ubiquitination and lysosomal degradation of TRP channels TRPV4 and TRPC4, reducing their plasma membrane abundance and basal channel activity; ubiquitination promotes endocytosis of TRPV4 without degrading the total protein pool. This regulation is selective: several other TRP channels are not affected by AIP4.\",\n      \"method\": \"Overexpression of AIP4 in cells, surface biotinylation, electrophysiology (basal current measurement), ubiquitination assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — functional electrophysiology readout combined with surface biotinylation and ubiquitination assays, selectivity controls included\",\n      \"pmids\": [\"17110928\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"ITCH/AIP4 promotes ubiquitin-dependent degradation of the transcription factor p63; two specific lysine residues in p63 (associated with Split-Hand and Foot Malformation-4 syndrome) are required for ITCH-mediated degradation.\",\n      \"method\": \"Co-immunoprecipitation, overexpression/deletion mutagenesis of p63, ubiquitination assay, pulse-chase degradation assay\",\n      \"journal\": \"Cell cycle (Georgetown, Tex.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — site-directed mutagenesis of substrate lysines combined with Co-IP and degradation assay, single lab\",\n      \"pmids\": [\"16861923\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"AIP4/ITCH interacts with ErbB-4 (HER4) via its WW domains, ubiquitinates ErbB-4 in vivo, and promotes polyubiquitination and proteasomal/lysosomal degradation of ErbB-4, thereby reducing receptor stability and nuclear access of the ErbB-4 intracellular domain.\",\n      \"method\": \"Phage display library panning, Co-immunoprecipitation, in vivo ubiquitination assay, degradation assay, nuclear fractionation\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, ubiquitination, and functional degradation assay; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"17463226\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"AIP4 targets Smad7 for ubiquitin-dependent degradation via a two-hybrid-identified interaction; paradoxically, AIP4 inhibits TGF-β signaling by enhancing Smad7 association with the activated TGF-β type I receptor (TβRI). A catalytically inactive AIP4 mutant (unable to ubiquitinate Smad7) still stabilizes the TβRI–Smad7 complex and inhibits TGF-β signaling, demonstrating a ubiquitination-independent scaffolding mechanism.\",\n      \"method\": \"Yeast two-hybrid, Co-immunoprecipitation, catalytic-dead AIP4 mutant, TGF-β reporter assays, degradation assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — catalytic-dead mutagenesis distinguishing ligase-dependent vs. independent functions, Co-IP, and signaling reporter; multiple orthogonal methods in one study\",\n      \"pmids\": [\"15946939\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"AIP4/ITCH physically interacts with CBLC (a RING-type E3 ligase) via its WW domains binding proline-rich regions; co-expression of CBLC and AIP4 cooperatively down-regulates EGFR signaling. Both AIP4 and CBLC become tyrosine-phosphorylated after EGF stimulation. Expression of WW domains of AIP4 exerts a dominant-negative effect on EGFR ubiquitination.\",\n      \"method\": \"Yeast two-hybrid, GST pulldown, Co-immunoprecipitation, colocalization, EGFR ubiquitination assay, dominant-negative overexpression\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — GST pulldown plus Co-IP plus functional dominant-negative, single lab\",\n      \"pmids\": [\"12226085\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Spartin binds the WW region of AIP4/ITCH with ~7-fold higher affinity than the WW region binds the HECT domain (disrupting AIP4 autoinhibition), thereby activating AIP4 E3 ligase activity. Spartin recruits AIP4 to lipid droplets, where AIP4 ubiquitinates adipophilin, regulating lipid droplet turnover. Spartin itself is not a substrate for AIP4.\",\n      \"method\": \"ELISA-based binding affinity measurement, self-ubiquitination assay, colocalization to lipid droplets (fluorescence microscopy), ubiquitination assay of adipophilin\",\n      \"journal\": \"BMC biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — quantitative binding affinity assay, in-cell ubiquitination, colocalization; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"20504295\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"USP8 (a deubiquitinase downstream of Akt) links the PTEN-Akt pathway to AIP4 activity: USP8 deubiquitinates AIP4, increasing AIP4-mediated ubiquitination and degradation of cFLIP(S), thereby decreasing TRAIL resistance in glioblastoma cells. siRNA knockdown of AIP4 reverses the effects of USP8 overexpression on FLIP(S) levels.\",\n      \"method\": \"siRNA knockdown, overexpression, ubiquitination assay, half-life (pulse-chase), co-immunoprecipitation, TRAIL apoptosis assay\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — rescue epistasis (AIP4 siRNA reverses USP8 effect), Co-IP, ubiquitination, and functional apoptosis assay; single lab\",\n      \"pmids\": [\"20484045\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"AIP4/ITCH-dependent JUNB protein degradation is markedly reduced in cells with active AKT; JNK-mediated AIP4 activity is required for rapamycin-induced repression of cyclin D1 and c-MYC transcription via JUNB degradation. Silencing AIP4 or inhibiting JNK abrogates the rapamycin-induced transcriptional effects.\",\n      \"method\": \"siRNA knockdown of AIP4, JNK inhibition, promoter-reporter assays, protein stability assays, ChIP\",\n      \"journal\": \"Molecular cancer research : MCR\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA rescue epistasis with promoter assay, single lab with multiple readouts\",\n      \"pmids\": [\"21135252\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"TNF-α signaling induces association of the homeodomain protein TGIF with ITCH/AIP4, increasing accessibility of cFLIP(L) for ITCH-mediated ubiquitination and degradation, thereby promoting TNF-α-induced apoptosis. Additionally, ITCH monoubiquitinates TGIF at K259 in response to TNF-α, stabilizing TGIF and creating a positive feedback loop.\",\n      \"method\": \"Co-immunoprecipitation (TNF-α-inducible), ubiquitination assays, site-directed mutagenesis (K259R), apoptosis assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — site-directed mutagenesis of ubiquitination site, Co-IP, ubiquitination assay, and functional apoptosis readout; multiple orthogonal methods\",\n      \"pmids\": [\"20064471\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"The anti-HER3 antibody 9F7-F11 induces HER3 ubiquitination and degradation mainly through ITCH/AIP4, activated by JNK1/2 phosphorylation; deubiquitinases USP8 and USP9X activate ITCH/AIP4 activity in this context. Overexpression of the ITCH inhibitor N4BP1 or siRNA knockdown of ITCH blocks 9F7-F11-induced HER3 ubiquitination/degradation.\",\n      \"method\": \"siRNA knockdown of ITCH, N4BP1 overexpression, ubiquitination assays, Co-immunoprecipitation, JNK inhibitor treatment, PI3K/AKT signaling assays\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA rescue with Co-IP and ubiquitination assays; single lab, multiple orthogonal approaches\",\n      \"pmids\": [\"27203743\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"AIP4/ITCH promotes K48-linked ubiquitination of influenza A virus matrix protein M1 at K102 and K104, targeting it for proteasome-mediated degradation; Cyclophilin A (CypA) inhibits AIP4-mediated M1 ubiquitination by impairing the AIP4–M1 interaction, thereby modulating nuclear export of M1 and viral replication.\",\n      \"method\": \"Ubiquitination assays with lysine-specific ubiquitin mutants, Co-immunoprecipitation, site-directed mutagenesis of M1 (K102R/K104R), recombinant virus rescue assay, subcellular localization assay\",\n      \"journal\": \"Virologica Sinica\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — K48-chain linkage confirmed with mutant ubiquitin, site-directed mutagenesis of substrate, recombinant virus rescue; single lab\",\n      \"pmids\": [\"30328013\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SPG20 (Spartin) detects lipid-packing defects in the limiting membrane of damaged lysosomes via sensory amphipathic helices before membrane rupture, then recruits and activates ITCH to mark damaged lysosomes with K63-linked ubiquitin chains, initiating lysophagy. SPG20 binds the repair factor IST1 on damaged lysosomes and integrates repair status with lipid damage detection; if damage is extensive (e.g., lipid peroxidation), ITCH is recruited for lysosomal destruction.\",\n      \"method\": \"Proximity ligation, Co-immunoprecipitation, ubiquitin chain linkage analysis (K63-specific), amphipathic helix mutagenesis, fluorescence live imaging of lysosomal damage, autophagy flux assays in human cells\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — multiple orthogonal methods including mutagenesis, K63-chain linkage, live imaging, and functional lysophagy readout in human cells\",\n      \"pmids\": [\"38503285\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"ITCH E3 ubiquitin ligase is involved in multiple immune regulatory contexts: it controls T-cell activation and tolerance, T-helper cell differentiation, and various signaling pathways through substrate ubiquitylation; its deletion in mice causes an itchy phenotype with multi-organ inflammation.\",\n      \"method\": \"Genetic deletion (Itch−/− mice), immune phenotyping, multiple substrate ubiquitination studies (review consolidation of primary experiments)\",\n      \"journal\": \"Immunological reviews\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — review summarizing Itch knockout phenotype and substrate studies; original genetic and biochemical data from multiple labs, but this paper is a review\",\n      \"pmids\": [\"26085204\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ITCH (AIP4) is a HECT-domain E3 ubiquitin ligase that ubiquitinates a broad set of substrates—including CXCR4, Notch1, Deltex, TRPV4/TRPC4, ErbB-4/HER3, p63, Smad7, cFLIP, JUNB, and the influenza M1 protein—predominantly via K29- or K63-linked (lysosomal targeting) or K48-linked (proteasomal targeting) chains, and is activated by upstream signals such as JNK-mediated phosphorylation and by adaptor proteins such as SPG20/Spartin; it operates at the plasma membrane, endosomes, and lysosomes to regulate receptor down-regulation, Notch and TGF-β signaling, apoptosis, lipid droplet turnover, and lysosomal damage-triggered lysophagy.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"ITCH (AIP4) is a HECT-domain E3 ubiquitin ligase that uses its WW domains to engage substrates and partners and its catalytic HECT domain to build polyubiquitin chains controlling receptor down-regulation, signal-pathway tuning, apoptosis, and organelle quality control [#0, #5, #8]. A recurrent theme is endosomal-to-lysosomal sorting of membrane receptors: ITCH ubiquitinates the chemokine receptor CXCR4 and the sorting factor Hrs to coordinate lysosomal degradation [#0], and targets Notch1 and Deltex for lysosomal turnover by assembling non-canonical K29-linked chains [#1, #2], while also ubiquitinating TRPV4/TRPC4 channels and ErbB-4/HER3 to reduce their surface abundance and stability [#3, #5]. ITCH activity is gated by autoinhibition and by activating inputs: JNK-mediated phosphorylation and deubiquitination by USP8/USP9X stimulate substrate ubiquitination (e.g., cFLIP and HER3), whereas the adaptor SPG20/Spartin binds the WW region to relieve autoinhibition and recruits ITCH to specific membranes [#8, #9, #12]. Beyond degradation, ITCH acts as a ubiquitination-independent scaffold for Smad7 at the TGF-\\u03b2 type I receptor to inhibit TGF-\\u03b2 signaling [#6], and it controls apoptosis by degrading cFLIP in concert with TGIF, which it monoubiquitinates to form a feedback loop [#11]. At organelles, Spartin-activated ITCH ubiquitinates adipophilin on lipid droplets and marks damaged lysosomes with K63-linked chains to initiate lysophagy [#8, #14]; it also K48-ubiquitinates influenza M1 to restrict viral replication [#13]. Genetic loss of Itch in mice produces an itchy, multi-organ inflammatory phenotype reflecting its broad role in immune regulation and T-cell tolerance [#15].\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Established that ITCH engages receptor down-regulation machinery, showing it interacts with the RING ligase CBLC via WW-domain/proline-rich binding and cooperatively dampens EGFR signaling.\",\n      \"evidence\": \"Yeast two-hybrid, GST pulldown, Co-IP, and dominant-negative EGFR ubiquitination assays\",\n      \"pmids\": [\"12226085\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Direct chain linkage on EGFR not defined\", \"Single lab; physiological context of CBLC cooperation untested\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Defined ITCH as a plasma-membrane and endosomal ligase coordinating lysosomal receptor sorting by ubiquitinating both the cargo CXCR4 and the sorting machine Hrs.\",\n      \"evidence\": \"Co-IP, colocalization, dominant-negative and siRNA experiments with Hrs/Vps4\",\n      \"pmids\": [\"14602072\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Chain-type on CXCR4 not specified\", \"Recruitment mechanism to the receptor not resolved\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Revealed that ITCH has a catalysis-independent function, scaffolding Smad7 onto the TGF-\\u03b2 type I receptor to inhibit signaling separately from Smad7 degradation.\",\n      \"evidence\": \"Yeast two-hybrid, catalytic-dead mutant, Co-IP, and TGF-\\u03b2 reporter assays\",\n      \"pmids\": [\"15946939\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Structural basis of the scaffold not determined\", \"In vivo relevance of scaffolding vs degradation unquantified\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Showed ITCH builds non-canonical K29-linked chains to route Deltex to lysosomes and degrades TRP channels and p63, establishing substrate diversity and chain-type specificity.\",\n      \"evidence\": \"K29-specific ubiquitin mutants, surface biotinylation/electrophysiology, Co-IP, and degradation assays\",\n      \"pmids\": [\"17028573\", \"17110928\", \"16861923\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"How chain-type selection is achieved mechanistically is unknown\", \"p63 finding is Medium confidence/single lab\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Extended ITCH receptor regulation to ErbB-4/HER4, showing WW-domain binding drives ubiquitination and degradation that limits nuclear access of the ErbB-4 intracellular domain.\",\n      \"evidence\": \"Phage display, Co-IP, in vivo ubiquitination, degradation, and nuclear fractionation\",\n      \"pmids\": [\"17463226\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Proteasomal vs lysosomal route not cleanly separated\", \"Single lab\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Demonstrated ligand-independent Notch1 degradation by ITCH requires a bridging factor or modification rather than direct binding, refining how ITCH recognizes Notch.\",\n      \"evidence\": \"Itch\\u2212/\\u2212 fibroblast reconstitution, lysosomal rescue, K29-chain analysis, negative in vitro binding\",\n      \"pmids\": [\"18628966\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Identity of the bridging factor/modification not established\", \"Mechanism of Notch recruitment unresolved\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Connected ITCH to TNF-\\u03b1-induced apoptosis, showing TGIF association exposes cFLIP(L) for degradation while ITCH monoubiquitinates TGIF at K259 to create positive feedback.\",\n      \"evidence\": \"TNF-\\u03b1-inducible Co-IP, ubiquitination assays, K259R mutagenesis, apoptosis assays\",\n      \"pmids\": [\"20064471\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Direct vs adaptor-mediated cFLIP recognition not separated\", \"Stoichiometry of the feedback loop unclear\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Identified upstream regulators of ITCH activity: Spartin relieves WW/HECT autoinhibition to activate the ligase at lipid droplets, USP8 deubiquitinates ITCH to enhance cFLIP(S) degradation, and AKT/JNK status controls JUNB degradation.\",\n      \"evidence\": \"ELISA binding affinity, self-ubiquitination, colocalization, siRNA rescue epistasis, promoter-reporter and apoptosis assays\",\n      \"pmids\": [\"20504295\", \"20484045\", \"21135252\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Each axis from a single lab\", \"Integration of competing kinase/DUB inputs not modeled\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Consolidated ITCH's broad immune role, linking its loss to T-cell tolerance failure and multi-organ inflammation in the itchy mouse.\",\n      \"evidence\": \"Review of Itch\\u2212/\\u2212 mouse genetics and substrate ubiquitination studies\",\n      \"pmids\": [\"26085204\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Review consolidation rather than new primary data\", \"Substrate-to-phenotype causality not dissected here\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Showed antibody-induced HER3 degradation operates through ITCH activated by JNK1/2 phosphorylation and USP8/USP9X, with N4BP1 acting as an inhibitor, integrating multiple regulatory inputs at one substrate.\",\n      \"evidence\": \"siRNA knockdown, N4BP1 overexpression, Co-IP, ubiquitination, JNK inhibition\",\n      \"pmids\": [\"27203743\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Relative contribution of each activator not quantified\", \"Single lab/therapeutic-antibody context\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Defined an antiviral role for ITCH, K48-ubiquitinating influenza M1 at K102/K104 for proteasomal degradation, with Cyclophilin A antagonizing the interaction to control M1 nuclear export.\",\n      \"evidence\": \"Lysine-specific ubiquitin mutants, K102R/K104R mutagenesis, recombinant virus rescue, localization assays\",\n      \"pmids\": [\"30328013\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"In vivo relevance to infection not established\", \"Single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Established ITCH as an effector of lysosomal quality control, recruited and activated by Spartin's lipid-damage-sensing amphipathic helices to deposit K63-linked ubiquitin on damaged lysosomes and initiate lysophagy.\",\n      \"evidence\": \"Proximity ligation, Co-IP, K63-specific linkage analysis, amphipathic-helix mutagenesis, live imaging, autophagy flux in human cells\",\n      \"pmids\": [\"38503285\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Downstream lysophagy receptors recognizing the K63 mark not detailed here\", \"How repair (IST1) vs destruction decision is set quantitatively\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How ITCH selects substrate-specific chain linkages (K29 vs K48 vs K63) and integrates competing kinase/DUB/adaptor inputs to dictate proteasomal versus lysosomal versus signaling outcomes remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"No structural model linking activator binding to chain-type output\", \"Substrate recruitment codes for direct vs bridged binding not generalized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016874\", \"supporting_discovery_ids\": [0, 1, 2, 5, 8, 14]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 2, 3, 5, 13]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [6]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [6, 8]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [0, 1, 2]},\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [1, 2, 14]},\n      {\"term_id\": \"GO:0005811\", \"supporting_discovery_ids\": [8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 1, 2, 5, 13]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 6, 7, 12]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [9, 11]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [14]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [15]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"SPG20\", \"USP8\", \"Hrs\", \"Smad7\", \"TGIF\", \"CBLC\", \"N4BP1\", \"USP9X\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}