{"gene":"USP4","run_date":"2026-06-11T09:02:06","timeline":{"discoveries":[{"year":1993,"finding":"The mouse Unp (USP4 ortholog) protein contains a putative nuclear localization signal and consensus sequences for binding to the retinoblastoma gene product (pRb), and its overexpression causes tumorigenic transformation of NIH3T3 cells.","method":"cDNA cloning, sequence analysis, NIH3T3 transformation assay","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — sequence prediction for NLS and Rb-binding motifs, functional transformation assay; two methods but no direct biochemical binding confirmation in this paper","pmids":["8336951"],"is_preprint":false},{"year":1994,"finding":"The Unp (USP4) protein is localized in the nucleus, as demonstrated by expression of the protein product and subcellular localization analysis.","method":"Subcellular localization/immunofluorescence of expressed protein","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 3 / Weak — direct localization experiment but single method, single lab, contradicted by later studies","pmids":["8183569"],"is_preprint":false},{"year":1998,"finding":"Human UNP/USP4 encodes two cytoplasmic isoforms with deubiquitinating activity; mutation of the conserved catalytic cysteine to alanine abolishes deubiquitination activity. Endogenous protein localizes primarily to the cytoplasm.","method":"Deubiquitination assay, site-directed mutagenesis, cellular fractionation, immunocytochemistry","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 1 / Moderate — catalytic activity demonstrated in vitro with mutagenesis confirmation, direct fractionation for localization; multiple orthogonal methods in one study","pmids":["9464533"],"is_preprint":false},{"year":2000,"finding":"Mouse Unp and human Unph (USP4) are active deubiquitinating enzymes that cleave ubiquitin from natural and engineered linear ubiquitin-protein fusions including polyubiquitin precursors; mutation of conserved Cys and His residues abolishes activity; USP4 does not generally disrupt ubiquitin-dependent proteolysis of N-end rule or non-N-end rule substrates in yeast.","method":"In vitro deubiquitination assay, site-directed mutagenesis, yeast degradation assay","journal":"Biochimica et biophysica acta","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstituted in vitro enzymatic activity with mutagenesis of both Cys and His catalytic residues; negative result for global ubiquitin-pathway disruption also established","pmids":["11018721"],"is_preprint":false},{"year":2001,"finding":"USP4 (Unp) specifically interacts with the retinoblastoma protein (pRb) in cells; this interaction is sensitive to site-directed mutations analogous to those in viral oncoproteins that disrupt Rb binding.","method":"Co-immunoprecipitation, in vitro binding, site-directed mutagenesis","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP plus in vitro binding plus mutagenesis confirmation; replicated in two independent papers (PMID 11571651 and 11571652)","pmids":["11571651","11571652"],"is_preprint":false},{"year":2001,"finding":"USP4 (Unp) also associates with the pocket proteins p107 and p130 in addition to pRb; these associations are detectable in vitro and in cells.","method":"Co-immunoprecipitation, in vitro binding assay","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — Co-IP and in vitro binding, single lab","pmids":["11571651"],"is_preprint":false},{"year":2004,"finding":"USP4 undergoes nucleocytoplasmic shuttling: it contains a functional nuclear export signal (133VEVYLLELKL142) and a nuclear import signal (766QPQKKKK772) recognized by importin α/β. Inhibition of nuclear export with leptomycin B causes nuclear accumulation of both exogenous and endogenous USP4. The equilibrium of USP4 localization varies between cell types.","method":"Live-cell fluorescence imaging (RFP-USP4), leptomycin B treatment, Rev-GFP export assay, importin binding assay, highly specific antibodies distinguishing USP4 from USP15","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (live imaging, pharmacological export inhibition, functional export assay, importin binding), exogenous and endogenous protein validated","pmids":["15494318"],"is_preprint":false},{"year":2005,"finding":"USP4 binds to the C-terminus of the A2A adenosine receptor (A2AR), deubiquitinates it, and thereby enhances its cell surface expression by relaxing ER quality control. This effect is specific to the A2AR C-terminus and is not seen with USP14 or the metabotropic glutamate receptor-5.","method":"Co-immunoprecipitation, cell surface expression assay, ubiquitination assay, C-terminal truncation mutants","journal":"Molecular pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, functional surface expression assay, specificity controls with truncation mutants and alternative DUB; single lab","pmids":["16339847"],"is_preprint":false},{"year":2006,"finding":"USP4 (UnpEL) functions as a deubiquitinating enzyme in human cells and specifically deconjugates ubiquitin from the interacting protein Ro52 via its isopeptidase activity. USP4 co-localizes with Ro52 in cytoplasmic rod-like structures when Ro52 is overexpressed.","method":"Co-immunoprecipitation, deubiquitination assay in HEK293T cells, immunofluorescence co-localization","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — Co-IP and in-cell deubiquitination assay with co-localization; single lab, single paper","pmids":["16316627"],"is_preprint":false},{"year":2009,"finding":"USP4 suppresses canonical Wnt signaling; its knockdown activates β-catenin-dependent transcription. USP4 has dual hydrolysing activity for K48- and K63-conjugated polyubiquitin chains, interacts with Nemo-like kinase (NLK) and TCF4, and deubiquitinates TCF4. Overexpression of catalytically active NLK promotes nuclear accumulation of USP4.","method":"RNAi screen, luciferase reporter assay, co-immunoprecipitation, ubiquitin chain hydrolysis assay","journal":"Journal of cellular and molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RNAi functional screen, biochemical chain-specificity assay, Co-IP, reporter assay; multiple methods, single lab","pmids":["20141612"],"is_preprint":false},{"year":2011,"finding":"USP4 deubiquitinates TAK1 by removing K63-linked polyubiquitin chains both in vitro and in vivo; TNFα induces USP4-TAK1 association; overexpression of catalytically active USP4 but not the C311A catalytic mutant inhibits TAK1 polyubiquitination and NF-κB activation; knockdown of USP4 enhances TAK1 polyubiquitination and downstream NF-κB signaling. USP4 also negatively regulates IL-1β-, LPS-, and TGFβ-induced NF-κB activation.","method":"In vitro deubiquitination assay, co-immunoprecipitation, NF-κB reporter assay, siRNA knockdown, catalytic mutant (C311A)","journal":"Cell death and differentiation","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro deubiquitination, catalytic mutant controls, Co-IP, siRNA knockdown with specific signaling readouts; replicated partially in multiple subsequent papers","pmids":["21331078"],"is_preprint":false},{"year":2011,"finding":"USP4 directly interacts with and deubiquitinates ARF-BP1, leading to ARF-BP1 stabilization and subsequent reduction of p53 levels. Usp4 knockout mice show enhanced apoptosis in thymus and spleen after ionizing radiation, and Usp4−/− MEFs exhibit retarded growth, premature senescence, resistance to oncogenic transformation, and hyperactive DNA damage checkpoints consistent with elevated p53.","method":"Co-immunoprecipitation, in vitro deubiquitination, Usp4 knockout mouse analysis, MEF functional assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro deubiquitination, genetic KO with multiple phenotypic readouts, Co-IP; multiple orthogonal methods in one study","pmids":["21522127"],"is_preprint":false},{"year":2012,"finding":"USP4 directly interacts with TGF-β type I receptor (TβRI) and acts as a deubiquitylating enzyme to stabilize TβRI at the plasma membrane, counteracting SMAD7-SMURF2-mediated ubiquitylation and degradation. AKT directly associates with and phosphorylates USP4, relocating nuclear USP4 to the cytoplasm and membrane and maintaining its protein stability. USP4 depletion mitigates TGF-β-induced EMT and metastasis. AKT-induced breast cancer cell migration is inhibited by USP4 depletion.","method":"Genome-wide gain-of-function screen, co-immunoprecipitation, in vitro deubiquitylation assay, AKT kinase assay, subcellular fractionation, siRNA knockdown, metastasis assays","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — genome-wide screen, in vitro DUB assay, AKT kinase assay, Co-IP, fractionation; multiple orthogonal methods in one highly cited study","pmids":["22706160"],"is_preprint":false},{"year":2012,"finding":"USP4 specifically interacts with TRAF2 and TRAF6 (but not TRAF3) and deubiquitinates both in vitro and in vivo in a deubiquitinase activity-dependent manner. The USP domain of USP4 mediates interaction with TRAF6 independently of deubiquitinase activity. USP4 negatively regulates TNFα- and IL-1β-induced NF-κB activation and cancer cell migration.","method":"Co-immunoprecipitation, in vitro deubiquitination assay, NF-κB reporter, domain mapping, cell migration assay","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro deubiquitination, reciprocal Co-IP, domain mapping, functional NF-κB and migration assays; multiple orthogonal methods","pmids":["22029577"],"is_preprint":false},{"year":2012,"finding":"USP4 interacts with the S9/Rpn6 subunit of the 26S proteasome via an internal ubiquitin-like (UBL) domain.","method":"Co-immunoprecipitation, domain mapping","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 3 / Weak — single Co-IP with domain identification; single lab, single method","pmids":["23022198"],"is_preprint":false},{"year":2013,"finding":"USP4 interacts with RIG-I and removes K48-linked polyubiquitination chains from RIG-I, thereby stabilizing RIG-I protein and positively regulating RIG-I-mediated IFN-β signaling and antiviral response. USP4 expression is attenuated after virus-induced RIG-I activation.","method":"Co-immunoprecipitation, ubiquitin chain-linkage-specific deubiquitination assay, siRNA knockdown, IFN-β reporter assay, viral replication assay","journal":"Journal of virology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — Co-IP, chain-specific in-cell DUB assay, functional IFN signaling and viral replication readouts; multiple orthogonal methods","pmids":["23388719"],"is_preprint":false},{"year":2014,"finding":"USP4 has its catalytic triad in a productive conformation but requires its N-terminal DUSP-Ubl domain for full catalytic turnover. The DUSP-Ubl domain enhances ubiquitin dissociation after substrate hydrolysis ('product discharge'), and binding of the DUSP-Ubl domain promotes a conformational change in a switching loop near the active site.","method":"Pre-steady-state kinetics, structural analysis, domain deletion/mutation experiments","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — pre-steady-state kinetics with defined mechanistic model, domain deletions, structural/conformational analysis; rigorous biochemical characterization","pmids":["25404403"],"is_preprint":false},{"year":2015,"finding":"USP4 promotes DNA-end resection and homologous recombination (HR) by interacting with CtIP and the MRE11-RAD50-NBS1 (MRN) complex and is required for CtIP recruitment to DNA damage sites. USP4 itself is ubiquitylated on multiple sites including cysteine residues, and auto-deubiquitylation of these sites is required for USP4 to interact with CtIP/MRN and to promote HR.","method":"Co-immunoprecipitation, HR reporter assay, DNA damage sensitivity assay, mass spectrometry identification of ubiquitylation sites, catalytic mutant analysis","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — Co-IP with CtIP and MRN, functional HR assay, MS identification of modification sites, catalytic mutant analysis; multiple orthogonal methods, replicated in independent Cell Reports paper (PMID 26387952)","pmids":["26455393","26387952"],"is_preprint":false},{"year":2015,"finding":"USP4 interacts directly with and deubiquitinates HDAC2, stabilizing HDAC2 and leading to compromised p53 acetylation, impaired p53 transcriptional activation, and downregulation of TNFα-induced NF-κB activation.","method":"Co-immunoprecipitation, in vitro deubiquitination assay, p53 acetylation assay, NF-κB reporter assay","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, in vitro DUB assay, functional p53 and NF-κB readouts; single lab, multiple methods","pmids":["26411366"],"is_preprint":false},{"year":2016,"finding":"The crystal structure of the SART3 HAT repeat domain in complex with the DUSP-UBL domains of USP4 was determined. USP4 binds SART3 at the β-structured linker between DUSP and UBL domains (Kd ~0.9 μM). SART3 recruits USP4 to the nucleus via its NLS; removal of SART3 NLS prevents nuclear entry of USP4 and abrogates its deubiquitinase activity toward spliceosomal substrates.","method":"X-ray crystallography, binding affinity measurement, nuclear localization assay, deubiquitinase activity assay with SART3 NLS mutants","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure with functional validation (localization and activity assays), binding affinity quantified; rigorous multi-method study","pmids":["27060135"],"is_preprint":false},{"year":2017,"finding":"USP4 deubiquitinates SMAD4 by removing inhibitory monoubiquitination, thereby strongly inducing activin/BMP signaling. SMURF2 is recruited to SMAD4 upon ligand stimulation and triggers SMAD4 monoubiquitination. Depletion of USP4 in mouse embryonic stem cells increases monoubiquitinated SMAD4 and decreases BMP- and activin-induced cell fate changes. USP4 depletion in zebrafish causes defective cell migration and epiboly, both rescued by SMAD4.","method":"Co-immunoprecipitation, in vitro deubiquitination, mESC differentiation assay, zebrafish morpholino knockdown with rescue","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro DUB assay, genetic rescue in zebrafish, mESC functional assays, Co-IP; multiple orthogonal systems and methods","pmids":["28468752"],"is_preprint":false},{"year":2017,"finding":"USP4 preferentially removes monoubiquitination from HAS2 (hyaluronan synthase 2), interacts with HAS2 in membrane preparations, and suppression of USP4 increases hyaluronan synthesis.","method":"DUB screen, co-immunoprecipitation from membrane fractions, ubiquitination assay, siRNA knockdown with hyaluronan production measurement","journal":"Oncogenesis","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — DUB screen followed by Co-IP and functional assay; multiple methods, single lab","pmids":["28604766"],"is_preprint":false},{"year":2017,"finding":"USP4 physically interacts with IRF8 and stabilizes it via K48-linked deubiquitination in regulatory T cells, thereby promoting the suppressive function of Treg cells.","method":"Co-immunoprecipitation, ubiquitination assay (K48-linkage specific), USP4 inhibitor treatment, Treg functional suppression assay","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, linkage-specific ubiquitination assay, functional Treg assay; single lab, multiple methods","pmids":["28477415"],"is_preprint":false},{"year":2017,"finding":"USP4 suppresses myoblast differentiation by downregulating MyoD activity in a catalytic-independent manner. USP4 knockdown enhances myogenesis and reduces HDAC1 and HDAC4 activity/protein levels. The effect on myogenesis involves AKT and p38 MAPK signaling pathways.","method":"siRNA knockdown, overexpression with catalytic mutant, C2C12 differentiation assay, immunoblot for myogenic markers","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — catalytic mutant demonstrates mechanism is independent of DUB activity, siRNA KD with multiple readouts, pathway inhibitor experiments; single lab","pmids":["28336234"],"is_preprint":false},{"year":2018,"finding":"USP4 interacts with TRAF6 and positively regulates RLR-induced NF-κB signaling by removing K48-linked ubiquitin chains from TRAF6, preventing TRAF6 degradation. Overexpression of USP4 suppresses EV71 replication.","method":"Co-immunoprecipitation, K48-linkage-specific deubiquitination assay, NF-κB reporter, viral replication assay","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, chain-specific DUB assay, functional signaling and viral replication readouts; single lab","pmids":["30194441"],"is_preprint":false},{"year":2019,"finding":"USP4 co-immunoprecipitates with AQP2 from mpkCCD14 cells and mouse kidney; USP4 can deubiquitylate AQP2 in vitro; shRNA knockdown of USP4 decreases AQP2 protein abundance and reduces VP-induced AQP2 membrane accumulation, associated with higher levels of ubiquitylated AQP2, without affecting AQP2 mRNA levels. AQP2 protein half-life is reduced in USP4 knockdown cells.","method":"Co-immunoprecipitation, in vitro deubiquitylation assay, shRNA knockdown, VP-stimulation membrane accumulation assay, protein half-life assay","journal":"Cells","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro DUB assay, Co-IP from endogenous tissue, functional membrane accumulation and protein stability assays; multiple orthogonal methods, single lab","pmids":["30901874"],"is_preprint":false},{"year":2019,"finding":"USP4 deficiency exacerbates hepatic ischaemia/reperfusion injury by inducing activation of TAK1/JNK signaling pathways; TAK1 inhibition abolishes USP4 protective function in vitro, placing USP4 upstream of TAK1 in this context.","method":"USP4 knockout mouse model, TAK1 pharmacological inhibition, hepatic I/R model, pathway analysis","journal":"Clinical science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with defined pathway readout, pharmacological epistasis; single lab","pmids":["30622220"],"is_preprint":false},{"year":2019,"finding":"USP4 was identified as a downstream target of PAK5-DNPEP pathway; DNPEP mediates USP4 downregulation and PAK5 decreases DNPEP abundance via the ubiquitin-proteasome pathway, thereby indirectly stabilizing USP4.","method":"Co-immunoprecipitation, ubiquitination assay, overexpression/knockdown, in vivo xenograft","journal":"International journal of cancer","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, ubiquitination assays, in vivo model; single lab, pathway epistasis established","pmids":["31219614"],"is_preprint":false},{"year":2019,"finding":"Phosphorylation status of USP4 (analogous to USP15 Thr149/Thr219) regulates its nuclear-cytoplasmic distribution and deubiquitinase activity. Treatment with cyclin-dependent kinase inhibitor purvalanol A causes changes in USP4 localization and activity, dependent on phosphorylation.","method":"Nuclear-cytoplasmic fractionation, mass spectrometry, CDK inhibitor treatment, activity assay","journal":"Journal of molecular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — fractionation, MS-identified phosphosites, pharmacological perturbation; single lab, functional consequence shown","pmids":["31330151"],"is_preprint":false},{"year":2020,"finding":"USP4 binds to, deubiquitinates, and stabilizes Twist1 protein. Silencing USP4 reduces Oct4, Sox2, and CD133+ cell population and inhibits tumorsphere formation in lung cancer cells. USP4-promoted stemness is effectively rescued by simultaneous silencing of Twist1.","method":"Co-immunoprecipitation, ubiquitination assay, siRNA knockdown, tumorsphere formation, rescue experiment","journal":"Cancers","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, ubiquitination assay, genetic rescue; single lab, multiple methods","pmids":["32549341"],"is_preprint":false},{"year":2022,"finding":"USP4 deubiquitinates PDGFRβ (removing both K63 and K48-linked chains), does not affect receptor stability but alters the speed of PDGFRβ trafficking toward early endosomes, and leads to prolonged/shifted STAT3 activation in response to PDGF-BB. Deletion of USP4 leads to decreased proliferative response to PDGF-BB stimulation.","method":"DUB overexpression screen, co-immunoprecipitation, receptor trafficking assay, STAT3 activation assay, USP4 knockout","journal":"Cellular and molecular life sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — DUB screen, Co-IP, functional trafficking and signaling assays, KO phenotype; single lab, multiple methods","pmids":["35064336"],"is_preprint":false},{"year":2022,"finding":"USP4 and its paralog USP15 regulate alternative splicing of SRSF1; depletion of USP4 impairs SRSF1 splicing, promoting an alternative isoform (SRSF1-3) subject to nonsense-mediated mRNA decay, and thereby impairs lung cancer cell proliferation.","method":"siRNA knockdown, RT-PCR for alternative splicing, rescue with SRSF1 overexpression, proliferation assay","journal":"Cell death discovery","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional splicing assay, genetic rescue, proliferation readout; single lab, multiple methods","pmids":["35027535"],"is_preprint":false},{"year":2023,"finding":"USP4 interacts with cortactin (CTTN) via proximal labeling in HCT116 cells, and this interaction promotes cell migration independently of USP4 deubiquitinase activity on cortactin; USP4 overexpression increases cortactin phosphorylation by regulating Src/FAK binding to cortactin.","method":"Proximity labeling (BioID), co-immunoprecipitation, cortactin phosphorylation assay, migration assay, CTTN knockdown rescue","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — proximity labeling plus Co-IP, functional migration assay with CTTN knockdown rescue; single lab, multiple orthogonal methods","pmids":["37039823"],"is_preprint":false},{"year":2023,"finding":"USP4 stabilizes TAK1 protein via deubiquitination in esophageal squamous cell carcinoma cells, and promotes ESCC proliferation, migration, and invasion via the MEK/ERK signaling pathway.","method":"Co-immunoprecipitation, deubiquitination assay, MEK/ERK pathway inhibition (U0126), loss/gain-of-function, in vivo xenograft","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, DUB assay, pathway inhibitor epistasis; single lab, multiple methods","pmids":["37949874"],"is_preprint":false},{"year":2023,"finding":"USP4 interacts with and deubiquitinates PKM2, stabilizing it and promoting cell proliferation and glycolysis (glucose uptake and lactate production) in gastric cancer cells.","method":"Co-immunoprecipitation, ubiquitination assay, overexpression/knockdown, metabolic assays (glucose uptake, lactate production), MTT proliferation assay","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, ubiquitination assay, functional metabolic readouts; single lab, multiple methods","pmids":["37624791"],"is_preprint":false},{"year":2023,"finding":"Vialinin A inhibits USP4 deubiquitinating enzyme activity, leading to enhanced K48-ubiquitination and proteasomal degradation of Keap1, thereby activating Nrf2-dependent antioxidant response; overexpression of USP4 reverses these neuroprotective effects.","method":"USP4 enzymatic inhibition assay, co-immunoprecipitation, ubiquitination assay, luciferase reporter, USP4 overexpression rescue in vivo (MCAO model)","journal":"Phytomedicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — inhibitor-activity assay, Co-IP, in vivo rescue; single lab, multiple methods","pmids":["38176274"],"is_preprint":false},{"year":2024,"finding":"USP4 interacts with SART3 and deubiquitinates TUT1 (terminal uridylyl transferase 1), a key U4/U6 spliceosome regulator; SART3 enhances USP4 deubiquitinating activity toward TUT1; USP4 orchestrates subnuclear relocalization of TUT1 from the nucleolus to the nucleoplasm and facilitates stability of U6 snRNA.","method":"Co-immunoprecipitation, ubiquitination assay, immunofluorescence for TUT1 localization, U6 snRNA stability assay","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, ubiquitination assay, localization experiment with functional RNA stability readout; single lab, multiple methods","pmids":["38310689"],"is_preprint":false},{"year":2024,"finding":"USP4 interacts with, deubiquitinates and stabilizes BRCA1, maintaining its protein level. USP4 knockdown decreases BRCA1, impairs homologous recombination-mediated DSB repair, increases genome instability, and confers resistance to DNA damage agents and PARP inhibitors.","method":"Co-immunoprecipitation, ubiquitination assay, HR reporter assay, DNA damage sensitivity assay, genome instability assay","journal":"NPJ breast cancer","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, DUB assay, functional HR and genome stability readouts; single lab, multiple methods","pmids":["38734703"],"is_preprint":false},{"year":2024,"finding":"USP4 deubiquitinates RAB7A; reduced USP4 levels in periodontitis lead to RAB7A ubiquitination, impairing autophagosome-lysosome fusion and lysosomal trafficking. Upregulation of USP4 attenuates periodontitis in vivo.","method":"Proteomics analysis, co-immunoprecipitation, ubiquitination assay, autophagy flux assay, in vivo periodontitis model","journal":"Autophagy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — proteomics identification, Co-IP, DUB assay, in vivo functional outcome; single lab, multiple methods","pmids":["39663592"],"is_preprint":false},{"year":2024,"finding":"USP4 deubiquitinates and stabilizes PES1, facilitating ribosome biogenesis and protein synthesis in proliferating hematopoietic stem cells and leukemic cells; Usp4 deletion decreases protein synthesis and HSC reconstitution capacity.","method":"Co-immunoprecipitation, ubiquitination assay, ribosome biogenesis assay, protein synthesis measurement, Usp4 conditional knockout mouse","journal":"Leukemia","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, DUB assay, functional ribosome and protein synthesis assays, genetic KO; single lab, multiple methods","pmids":["39266638"],"is_preprint":false},{"year":2024,"finding":"USP4 impedes the nuclear localization of IRF3 by deubiquitinating the K63-polyubiquitin chain of both TRAF6 and IRF3, thereby suppressing the tumor-intrinsic interferon response and antitumor immunity in colorectal cancer.","method":"Co-immunoprecipitation, K63-specific deubiquitination assay, IRF3 nuclear localization assay, siRNA knockdown, syngeneic mouse model","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — K63-specific DUB assay, nuclear localization assay, in vivo syngeneic model; single lab, multiple methods","pmids":["38556105"],"is_preprint":false},{"year":2024,"finding":"USP4 deubiquitinates MAVS by removing K48-linked ubiquitin chains at Lys461, stabilizing MAVS and promoting antiviral innate immunity. This activity is activated through the p53-USP4-MAVS signaling axis downstream of PBLD.","method":"Co-immunoprecipitation, site-specific ubiquitination assay (K48 chains, Lys461 of MAVS), PBLD knockout mouse, IFN-I response assay","journal":"Proceedings of the National Academy of Sciences","confidence":"High","confidence_rationale":"Tier 1 / Strong — site-specific ubiquitination mapping (K461), K48-linkage DUB assay, Co-IP, in vivo KO mouse with viral challenge; multiple orthogonal methods","pmids":["39589880"],"is_preprint":false},{"year":2024,"finding":"USP4 interacts with, deubiquitinates and stabilizes CARM1, promoting its activity; CARM1 stabilization by USP4 upregulates SLC7A11 expression, contributing to breast cancer cell malignancy.","method":"Co-immunoprecipitation, cycloheximide chase assay, ubiquitination assay, rescue experiment","journal":"Clinical breast cancer","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, protein stability assay, DUB assay; single lab, multiple methods","pmids":["39500657"],"is_preprint":false},{"year":2025,"finding":"USP4 directly cleaves both Lys48- and Lys63-linked polyubiquitin chains of ANXA2, with the Lys63-linked chains at K28 mediating ANXA2 Y24 phosphorylation. K10 acetylation of ANXA2 enhances its interaction with USP4. USP4 stabilizes ANXA2 and promotes glioblastoma stem cell maintenance and radioresistance via BMX-mediated STAT3 activation.","method":"Co-immunoprecipitation, chain-specific ubiquitination assay, phosphorylation assay, acetylation assay, siRNA knockdown, tumorsphere assay, radioresistance assay","journal":"Cell death and differentiation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — K48/K63 chain-specific DUB assay, multiple PTM characterizations, functional GSC assays; single lab, multiple methods","pmids":["40185997"],"is_preprint":false},{"year":2025,"finding":"FBXO3 binds to and stabilizes USP4 by disrupting the interaction between USP4 and DNPEP (which mediates USP4 degradation), thereby stabilizing Twist1 via USP4 deubiquitinase activity and promoting breast cancer metastasis. PI3K/p110αH1047R facilitates phosphorylation and stabilization of FBXO3 via ERK1.","method":"Co-immunoprecipitation, protein stability assay, ubiquitination assay, siRNA knockdown, in vivo breast cancer metastasis model","journal":"PLoS biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, ubiquitination/stability assays, in vivo model; single lab, multiple methods","pmids":["38134227"],"is_preprint":false},{"year":2025,"finding":"USP4 interacts with and stabilizes PGAM5 by removing K48-linked ubiquitin chains, thereby regulating mitochondrial dynamics and promoting mitophagy in esophageal squamous cell carcinoma.","method":"Co-immunoprecipitation, K48-specific ubiquitination assay, mitochondrial function assays (MMP, mtROS), in vivo tumor model","journal":"Molecular carcinogenesis","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, K48 chain-specific DUB assay, mitochondrial functional assays; single lab, multiple methods","pmids":["41176636"],"is_preprint":false},{"year":2025,"finding":"USP4 interacts with, deubiquitinates, and stabilizes LDHA protein in papillary thyroid carcinoma cells, and promotes PTC proliferation by modulating MAPK and AKT signaling pathways.","method":"Co-immunoprecipitation, deubiquitination assay, MAPK/AKT pathway analysis, siRNA knockdown, proliferation assay","journal":"Aging","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, DUB assay, pathway readout; single lab","pmids":["39393052"],"is_preprint":false},{"year":2025,"finding":"USP4 modulates ZBP1 ubiquitination: USP4 interacts with, deubiquitinates, and stabilizes ZBP1 in microglia. AKT-mediated phosphorylation is required to maintain USP4 protein stability. Pharmacological inhibition of USP4 with Vialinin A leads to ZBP1 degradation and reduces microglial PANoptosis after traumatic brain injury.","method":"Co-immunoprecipitation, deubiquitination assay, AKT phosphorylation analysis, Vialinin A inhibitor treatment, TBI mouse model","journal":"Cell death and differentiation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, DUB assay, AKT phosphorylation assay, in vivo inhibitor treatment; single lab, multiple methods","pmids":["42091674"],"is_preprint":false},{"year":2025,"finding":"USP4 stabilizes β-catenin and Twist1 proteins in colorectal cancer cells by deubiquitinating them; a novel small molecule inhibitor U4-I05 binds the catalytic C311 site of USP4 and triggers proteasomal degradation of β-catenin and Twist1, inhibiting cancer stemness.","method":"Virtual screening, co-immunoprecipitation, ubiquitination assay, catalytic site binding assay, cancer stemness assay (organoids, xenograft), site-specific mutant (C311)","journal":"Journal of translational medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — catalytic site mutagenesis, Co-IP, DUB assay, functional stemness readouts, in vivo model; single lab but mechanistically comprehensive","pmids":["39856683"],"is_preprint":false},{"year":2025,"finding":"USP4 deubiquitinates and stabilizes NR4A1, protecting it from ubiquitination-mediated degradation; MEF2A transcriptionally activates USP4 expression by binding its promoter; the MEF2A-USP4-NR4A1 axis suppresses ER stress and apoptosis in multiple myeloma cells.","method":"Co-immunoprecipitation, ubiquitination assay, ChIP assay, luciferase reporter, siRNA knockdown, xenograft model","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, DUB assay, ChIP and reporter for transcriptional regulation, in vivo model; single lab, multiple methods","pmids":["41186214"],"is_preprint":false},{"year":2025,"finding":"USP4 deubiquitinates and stabilizes KLF2 protein; KLF2 transcriptionally regulates HMGA2; the USP4/KLF2/HMGA2 cascade regulates cell growth, apoptosis, and bortezomib sensitivity in drug-resistant multiple myeloma cells.","method":"Co-immunoprecipitation, protein stability assay, luciferase reporter, ChIP assay, functional growth and apoptosis assays","journal":"Journal of orthopaedic surgery and research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, stability assay, ChIP/reporter for downstream target; single lab","pmids":["40022160"],"is_preprint":false},{"year":2025,"finding":"USP4 deubiquitinates and stabilizes SRC-1, enhancing its protein stability; the USP4-SRC-1 axis inhibits M2 macrophage polarization via the NF-κB pathway and is validated in an OVA-induced asthma model in vivo.","method":"Co-immunoprecipitation, ubiquitination assay, flow cytometry for macrophage polarization, NF-κB pathway analysis, in vivo OVA model","journal":"Experimental lung research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, DUB assay, functional macrophage assay, in vivo model; single lab, multiple methods","pmids":["40493388"],"is_preprint":false},{"year":2025,"finding":"USP4 stabilizes PAF1 by directly binding and reducing its K48-linked polyubiquitination, counteracting CNOT4-mediated PAF1 degradation and promoting NSCLC cell proliferation in vitro and tumor growth in vivo.","method":"Co-immunoprecipitation, K48-ubiquitination assay, rescue assay, CCK-8 proliferation, xenograft model","journal":"Respiratory research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, chain-specific DUB assay, genetic rescue in vivo; single lab, multiple methods","pmids":["41857610"],"is_preprint":false},{"year":2025,"finding":"USP4 removes Lys48-linked polyubiquitin chains from the A2A receptor (A2AR) via deubiquitination at the C311 site in gastric cancer cells, stabilizing A2AR, modulating autophagy, and inhibiting ferroptosis.","method":"Co-immunoprecipitation, K48-specific ubiquitination assay, catalytic mutant (C311), autophagy and ferroptosis assays","journal":"Cellular and molecular life sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, site-specific mutant, chain-specific DUB assay, functional autophagy/ferroptosis assays; single lab","pmids":["41051500"],"is_preprint":false},{"year":2026,"finding":"USP4 interacts with and stabilizes CENPF via deubiquitination in colorectal cancer; USP4 expression positively correlates with CENPF protein (but not mRNA) levels in clinical samples; USP4-mediated CENPF upregulation is a critical regulator of CRC metastasis.","method":"Co-immunoprecipitation, deubiquitination assay, siRNA knockdown, in vivo metastasis model, clinical sample correlation","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, DUB assay, in vivo model; single lab","pmids":["39922805"],"is_preprint":false},{"year":2026,"finding":"USP4, enriched in melatonin-preconditioned exosomes, directly interacts with and deubiquitinates ARNTL (a core circadian regulator), stabilizing its protein levels and suppressing ferroptosis in skin flap cells. H3K18 lactylation upregulates USP4 mRNA, enhancing USP4 translation within exosomes.","method":"Co-immunoprecipitation, deubiquitination assay, m6A modification analysis, ferroptosis assay, in vivo flap model","journal":"Clinical and translational medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, DUB assay, in vivo model; single lab, novel substrate","pmids":["41482632"],"is_preprint":false}],"current_model":"USP4 is a nucleocytoplasmic-shuttling cysteine deubiquitylase whose DUSP-Ubl domain allosterically promotes ubiquitin product discharge and whose catalytic C311 residue removes K48- and/or K63-linked polyubiquitin (and monoubiquitin) from a broad array of substrates—including TβRI, SMAD4, TAK1, TRAF2/6, RIG-I, MAVS, IRF3, CtIP/MRN, BRCA1, ARF-BP1, HDAC2, AQP2, Twist1, PES1, RAB7A, PKM2, ANXA2, and others—to regulate TGF-β/SMAD, NF-κB, antiviral interferon, DNA repair, Wnt/β-catenin, spliceosome, and metabolic signaling; its activity and localization are in turn controlled by AKT-mediated phosphorylation and by nuclear import/export mediated through the SART3 scaffold."},"narrative":{"mechanistic_narrative":"USP4 is a nucleocytoplasmic-shuttling ubiquitin-specific protease (cysteine deubiquitylase) that controls the stability and activity of a broad set of signaling proteins by cleaving K48- and K63-linked polyubiquitin and monoubiquitin from its substrates [PMID:9464533, PMID:11018721, PMID:20141612]. Catalysis depends on the active-site cysteine (C311), and its full turnover is governed allosterically by the N-terminal DUSP-Ubl domain, which promotes ubiquitin product discharge through a conformational change near the active site [PMID:21331078, PMID:25404403]. USP4 moves between nucleus and cytoplasm via a defined nuclear export signal and an importin-recognized nuclear import signal [PMID:15494318], with nuclear entry and spliceosomal substrate access supplied by binding to the SART3 HAT-repeat scaffold; AKT-mediated phosphorylation drives nuclear-to-cytoplasmic/membrane relocalization and stabilizes the enzyme [PMID:22706160, PMID:27060135, PMID:42091674]. Through these activities USP4 acts as a hinge across multiple pathways: it stabilizes the TGF-β type I receptor and deubiquitylates SMAD4 to potentiate TGF-β/activin/BMP signaling [PMID:22706160, PMID:28468752]; it deubiquitylates TAK1, TRAF2/TRAF6, and IRF3 to tune NF-κB and interferon responses [PMID:21331078, PMID:22029577, PMID:38556105]; it stabilizes RIG-I and MAVS to promote antiviral innate immunity [PMID:23388719, PMID:39589880]; and it promotes DNA-end resection and homologous recombination through CtIP/MRN and BRCA1, requiring auto-deubiquitylation for these interactions [PMID:26455393, PMID:26387952, PMID:38734703]. USP4 also engages the p53 axis by stabilizing the E3 ligase ARF-BP1 to lower p53, a role corroborated by Usp4-knockout mice showing elevated p53-dependent phenotypes [PMID:21522127]. In cancer contexts USP4 stabilizes pro-tumorigenic substrates including Twist1, β-catenin, PKM2, and PES1 to drive stemness, metabolism, and proliferation [PMID:32549341, PMID:39266638, PMID:39856683].","teleology":[{"year":1998,"claim":"Establishing that USP4 is a bona fide enzyme answered whether the gene encodes catalytic activity rather than merely a sequence motif, defining it as a cysteine-dependent deubiquitylase.","evidence":"in vitro deubiquitination assay with catalytic-cysteine-to-alanine mutagenesis and cellular fractionation","pmids":["9464533","11018721"],"confidence":"High","gaps":["No physiological substrate identified at this stage","Chain-linkage preference not yet defined"]},{"year":2001,"claim":"Identifying pRb and pocket-protein binding addressed how the originally oncogenic USP4 might connect to growth control, linking it physically to the Rb tumor-suppressor pathway.","evidence":"reciprocal Co-IP, in vitro binding, and motif mutagenesis","pmids":["11571651","11571652"],"confidence":"High","gaps":["Whether USP4 deubiquitylates pRb was not shown","Functional consequence of the interaction for Rb activity unresolved"]},{"year":2004,"claim":"Mapping functional export and import signals answered how USP4 localization is determined, establishing it as an actively shuttling enzyme with cell-type-dependent distribution.","evidence":"live-cell imaging, leptomycin B export inhibition, Rev-GFP export assay, importin binding, USP4-specific antibodies","pmids":["15494318"],"confidence":"High","gaps":["Signals controlling the shuttling equilibrium not identified here","Functional importance of nuclear versus cytoplasmic pools undefined"]},{"year":2009,"claim":"Demonstrating dual K48/K63 chain hydrolysis and Wnt suppression via NLK/TCF4 defined USP4's biochemical breadth and its first signaling pathway role.","evidence":"RNAi screen, luciferase reporter, Co-IP, ubiquitin chain hydrolysis assay","pmids":["20141612"],"confidence":"Medium","gaps":["Direct TCF4 deubiquitylation in vitro not fully resolved","Mechanism of NLK-driven nuclear accumulation unclear"]},{"year":2011,"claim":"Linking USP4 to TAK1 and to ARF-BP1/p53 answered how it represses NF-κB and modulates apoptosis/senescence, providing the first in vivo genetic evidence of its role.","evidence":"in vitro deubiquitination with C311A mutant, Co-IP, NF-κB reporter, Usp4 knockout mouse and MEF assays","pmids":["21331078","21522127"],"confidence":"High","gaps":["Context-dependent positive versus negative NF-κB regulation not reconciled","Whether p53 and NF-κB effects share a common pathway unresolved"]},{"year":2012,"claim":"Identifying TβRI stabilization and AKT-mediated regulation answered how USP4 promotes TGF-β-driven EMT and how upstream kinase signaling controls USP4 localization and stability.","evidence":"genome-wide gain-of-function screen, in vitro DUB assay, AKT kinase assay, fractionation, metastasis assays","pmids":["22706160"],"confidence":"High","gaps":["Phosphosites on USP4 not exhaustively mapped here","How phosphorylation alters catalytic activity vs trafficking not separated"]},{"year":2014,"claim":"Defining the DUSP-Ubl domain's allosteric role answered the long-standing question of why full-length USP4 turns over substrate efficiently, revealing product-discharge acceleration as the mechanism.","evidence":"pre-steady-state kinetics, structural analysis, domain deletion/mutation","pmids":["25404403"],"confidence":"High","gaps":["Whether substrate-specific partners modulate this allostery in cells untested","Structure of full-length enzyme with substrate not solved"]},{"year":2016,"claim":"Solving the SART3-DUSP/UBL structure answered how USP4 is delivered to the nucleus and to spliceosomal substrates, coupling scaffold binding to localization and activity.","evidence":"X-ray crystallography, affinity measurement, NLS-mutant localization and activity assays","pmids":["27060135"],"confidence":"High","gaps":["Spliceosomal substrate identity not defined in this study","Whether AKT phosphorylation competes with SART3 binding unknown"]},{"year":2017,"claim":"Showing SMAD4 deubiquitylation and CtIP/MRN-dependent HR established two mechanistically distinct roles—developmental TGF-β signaling and DNA-end resection—and revealed auto-deubiquitylation as a prerequisite for HR engagement.","evidence":"in vitro DUB assays, zebrafish/mESC functional rescue, MS mapping of USP4 ubiquitylation sites, HR reporter","pmids":["28468752","26455393","26387952"],"confidence":"High","gaps":["How USP4 is recruited to DNA damage sites mechanistically undefined","Relationship between SMAD4 monoubiquitin removal and receptor-level TGF-β regulation not integrated"]},{"year":2017,"claim":"Identifying RIG-I substrate stabilization positioned USP4 as a positive regulator of antiviral interferon signaling, distinct from its NF-κB-suppressing roles.","evidence":"Co-IP, K48-linkage-specific DUB assay, IFN-β reporter, viral replication assay","pmids":["23388719"],"confidence":"High","gaps":["Why USP4 expression falls after RIG-I activation mechanistically unclear","Linkage-specificity determinants at substrate level undefined"]},{"year":2024,"claim":"Mapping site-specific MAVS (K461) and IRF3 regulation refined how USP4 sets the threshold of innate immune signaling, including a p53-PBLD-USP4-MAVS axis and an interferon-suppressive role in cancer.","evidence":"site-specific ubiquitination mapping, K48/K63-specific DUB assays, PBLD knockout mouse, IRF3 nuclear localization, syngeneic model","pmids":["39589880","38556105"],"confidence":"High","gaps":["How USP4 selects opposing pro- versus anti-interferon outcomes across tissues unresolved","Coordination with the RIG-I/TRAF6 arms not unified"]},{"year":2024,"claim":"Expanding the substrate set to BRCA1, PES1, RAB7A and others demonstrated USP4's reach into HR repair, ribosome biogenesis, and autophagic trafficking, broadening its cellular footprint.","evidence":"Co-IP, chain-specific ubiquitination assays, HR/ribosome/autophagy functional readouts, conditional knockout mice","pmids":["38734703","39266638","39663592"],"confidence":"Medium","gaps":["Most substrate relationships rest on single-lab studies without reciprocal cross-validation","Whether localization gating determines which substrates are engaged not established"]},{"year":null,"claim":"How USP4 selects among its many substrates and reconciles opposing roles (tumor suppressor via p53/Rb versus oncogenic stabilizer of Twist1/β-catenin/PKM2) in a context-dependent manner remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unifying model linking localization, phosphorylation state, and substrate choice","Substrate-specificity determinants of K48 vs K63 vs monoubiquitin cleavage undefined","In vivo substrate hierarchy across tissues not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[2,3,10,16]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[2,3]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[12,15,41]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[2,6]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[1,6,19]},{"term_id":"GO:0005654","term_label":"nucleoplasm","supporting_discovery_ids":[19,36]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[12]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[12,20,30]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[10,13,15,41,40]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[17,37]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[19,31,36]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[2,3,12]}],"complexes":["MRE11-RAD50-NBS1 (MRN) complex"],"partners":["SART3","TAK1","TRAF6","RIG-I","MAVS","SMAD4","CTIP","ARF-BP1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q13107","full_name":"Ubiquitin carboxyl-terminal hydrolase 4","aliases":["Deubiquitinating enzyme 4","Ubiquitin thioesterase 4","Ubiquitin-specific-processing protease 4","Ubiquitous nuclear protein homolog"],"length_aa":963,"mass_kda":108.6,"function":"Deubiquitinating enzyme that removes conjugated ubiquitin from target proteins (PubMed:16316627, PubMed:16339847, PubMed:16472766, PubMed:20595234, PubMed:22347420, PubMed:25404403, PubMed:28604766, PubMed:30514904). Deubiquitinates PDPK1 (PubMed:22347420). Deubiquitinates TRIM21 (PubMed:16316627). Deubiquitinates receptor ADORA2A which increases the amount of functional receptor at the cell surface (PubMed:16339847). Deubiquitinates HAS2 (PubMed:28604766). Deubiquitinates MAVs leading to maintain MAVS protein stability, resulting in increased production of type I interferons (IFN-I) and enhanced antiviral innate immune responses against viral infections (PubMed:39589880). Deubiquitinates RHEB in response to EGF signaling, promoting mTORC1 signaling (PubMed:30514904). May regulate mRNA splicing through deubiquitination of the U4 spliceosomal protein PRPF3 (PubMed:20595234). This may prevent its recognition by the U5 component PRPF8 thereby destabilizing interactions within the U4/U6.U5 snRNP (PubMed:20595234). May also play a role in the regulation of quality control in the ER (PubMed:16339847)","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/Q13107/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/USP4","classification":"Not Classified","n_dependent_lines":12,"n_total_lines":1208,"dependency_fraction":0.009933774834437087},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/USP4","total_profiled":1310},"omim":[{"mim_id":"618493","title":"HYPOTONIA, HYPOVENTILATION, IMPAIRED INTELLECTUAL DEVELOPMENT, DYSAUTONOMIA, EPILEPSY, AND EYE ABNORMALITIES; HIDEA","url":"https://www.omim.org/entry/618493"},{"mim_id":"614584","title":"PROLYL 4-HYDROXYLASE, TRANSMEMBRANE; P4HTM","url":"https://www.omim.org/entry/614584"},{"mim_id":"614471","title":"UBIQUITIN-SPECIFIC PROTEASE 19; USP19","url":"https://www.omim.org/entry/614471"},{"mim_id":"604731","title":"UBIQUITIN-SPECIFIC PROTEASE 15; USP15","url":"https://www.omim.org/entry/604731"},{"mim_id":"604728","title":"UBIQUITIN-SPECIFIC PROTEASE 3; USP3","url":"https://www.omim.org/entry/604728"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Vesicles","reliability":"Additional"},{"location":"Basal body","reliability":"Additional"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/USP4"},"hgnc":{"alias_symbol":["Unph"],"prev_symbol":["UNP"]},"alphafold":{"accession":"Q13107","domains":[{"cath_id":"3.30.2230.10","chopping":"12-133","consensus_level":"high","plddt":84.4241,"start":12,"end":133},{"cath_id":"3.10.20.90","chopping":"137-216","consensus_level":"medium","plddt":84.6172,"start":137,"end":216},{"cath_id":"3.10.20.90","chopping":"485-590_597-632_705-764","consensus_level":"high","plddt":82.2559,"start":485,"end":764}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q13107","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q13107-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q13107-F1-predicted_aligned_error_v6.png","plddt_mean":75.94},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=USP4","jax_strain_url":"https://www.jax.org/strain/search?query=USP4"},"sequence":{"accession":"Q13107","fasta_url":"https://rest.uniprot.org/uniprotkb/Q13107.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q13107/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q13107"}},"corpus_meta":[{"pmid":"22706160","id":"PMC_22706160","title":"USP4 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assay\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — sequence prediction for NLS and Rb-binding motifs, functional transformation assay; two methods but no direct biochemical binding confirmation in this paper\",\n      \"pmids\": [\"8336951\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"The Unp (USP4) protein is localized in the nucleus, as demonstrated by expression of the protein product and subcellular localization analysis.\",\n      \"method\": \"Subcellular localization/immunofluorescence of expressed protein\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Weak — direct localization experiment but single method, single lab, contradicted by later studies\",\n      \"pmids\": [\"8183569\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Human UNP/USP4 encodes two cytoplasmic isoforms with deubiquitinating activity; mutation of the conserved catalytic cysteine to alanine abolishes deubiquitination activity. Endogenous protein localizes primarily to the cytoplasm.\",\n      \"method\": \"Deubiquitination assay, site-directed mutagenesis, cellular fractionation, immunocytochemistry\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — catalytic activity demonstrated in vitro with mutagenesis confirmation, direct fractionation for localization; multiple orthogonal methods in one study\",\n      \"pmids\": [\"9464533\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Mouse Unp and human Unph (USP4) are active deubiquitinating enzymes that cleave ubiquitin from natural and engineered linear ubiquitin-protein fusions including polyubiquitin precursors; mutation of conserved Cys and His residues abolishes activity; USP4 does not generally disrupt ubiquitin-dependent proteolysis of N-end rule or non-N-end rule substrates in yeast.\",\n      \"method\": \"In vitro deubiquitination assay, site-directed mutagenesis, yeast degradation assay\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstituted in vitro enzymatic activity with mutagenesis of both Cys and His catalytic residues; negative result for global ubiquitin-pathway disruption also established\",\n      \"pmids\": [\"11018721\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"USP4 (Unp) specifically interacts with the retinoblastoma protein (pRb) in cells; this interaction is sensitive to site-directed mutations analogous to those in viral oncoproteins that disrupt Rb binding.\",\n      \"method\": \"Co-immunoprecipitation, in vitro binding, site-directed mutagenesis\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP plus in vitro binding plus mutagenesis confirmation; replicated in two independent papers (PMID 11571651 and 11571652)\",\n      \"pmids\": [\"11571651\", \"11571652\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"USP4 (Unp) also associates with the pocket proteins p107 and p130 in addition to pRb; these associations are detectable in vitro and in cells.\",\n      \"method\": \"Co-immunoprecipitation, in vitro binding assay\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — Co-IP and in vitro binding, single lab\",\n      \"pmids\": [\"11571651\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"USP4 undergoes nucleocytoplasmic shuttling: it contains a functional nuclear export signal (133VEVYLLELKL142) and a nuclear import signal (766QPQKKKK772) recognized by importin α/β. Inhibition of nuclear export with leptomycin B causes nuclear accumulation of both exogenous and endogenous USP4. The equilibrium of USP4 localization varies between cell types.\",\n      \"method\": \"Live-cell fluorescence imaging (RFP-USP4), leptomycin B treatment, Rev-GFP export assay, importin binding assay, highly specific antibodies distinguishing USP4 from USP15\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (live imaging, pharmacological export inhibition, functional export assay, importin binding), exogenous and endogenous protein validated\",\n      \"pmids\": [\"15494318\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"USP4 binds to the C-terminus of the A2A adenosine receptor (A2AR), deubiquitinates it, and thereby enhances its cell surface expression by relaxing ER quality control. This effect is specific to the A2AR C-terminus and is not seen with USP14 or the metabotropic glutamate receptor-5.\",\n      \"method\": \"Co-immunoprecipitation, cell surface expression assay, ubiquitination assay, C-terminal truncation mutants\",\n      \"journal\": \"Molecular pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, functional surface expression assay, specificity controls with truncation mutants and alternative DUB; single lab\",\n      \"pmids\": [\"16339847\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"USP4 (UnpEL) functions as a deubiquitinating enzyme in human cells and specifically deconjugates ubiquitin from the interacting protein Ro52 via its isopeptidase activity. USP4 co-localizes with Ro52 in cytoplasmic rod-like structures when Ro52 is overexpressed.\",\n      \"method\": \"Co-immunoprecipitation, deubiquitination assay in HEK293T cells, immunofluorescence co-localization\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — Co-IP and in-cell deubiquitination assay with co-localization; single lab, single paper\",\n      \"pmids\": [\"16316627\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"USP4 suppresses canonical Wnt signaling; its knockdown activates β-catenin-dependent transcription. USP4 has dual hydrolysing activity for K48- and K63-conjugated polyubiquitin chains, interacts with Nemo-like kinase (NLK) and TCF4, and deubiquitinates TCF4. Overexpression of catalytically active NLK promotes nuclear accumulation of USP4.\",\n      \"method\": \"RNAi screen, luciferase reporter assay, co-immunoprecipitation, ubiquitin chain hydrolysis assay\",\n      \"journal\": \"Journal of cellular and molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RNAi functional screen, biochemical chain-specificity assay, Co-IP, reporter assay; multiple methods, single lab\",\n      \"pmids\": [\"20141612\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"USP4 deubiquitinates TAK1 by removing K63-linked polyubiquitin chains both in vitro and in vivo; TNFα induces USP4-TAK1 association; overexpression of catalytically active USP4 but not the C311A catalytic mutant inhibits TAK1 polyubiquitination and NF-κB activation; knockdown of USP4 enhances TAK1 polyubiquitination and downstream NF-κB signaling. USP4 also negatively regulates IL-1β-, LPS-, and TGFβ-induced NF-κB activation.\",\n      \"method\": \"In vitro deubiquitination assay, co-immunoprecipitation, NF-κB reporter assay, siRNA knockdown, catalytic mutant (C311A)\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro deubiquitination, catalytic mutant controls, Co-IP, siRNA knockdown with specific signaling readouts; replicated partially in multiple subsequent papers\",\n      \"pmids\": [\"21331078\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"USP4 directly interacts with and deubiquitinates ARF-BP1, leading to ARF-BP1 stabilization and subsequent reduction of p53 levels. Usp4 knockout mice show enhanced apoptosis in thymus and spleen after ionizing radiation, and Usp4−/− MEFs exhibit retarded growth, premature senescence, resistance to oncogenic transformation, and hyperactive DNA damage checkpoints consistent with elevated p53.\",\n      \"method\": \"Co-immunoprecipitation, in vitro deubiquitination, Usp4 knockout mouse analysis, MEF functional assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro deubiquitination, genetic KO with multiple phenotypic readouts, Co-IP; multiple orthogonal methods in one study\",\n      \"pmids\": [\"21522127\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"USP4 directly interacts with TGF-β type I receptor (TβRI) and acts as a deubiquitylating enzyme to stabilize TβRI at the plasma membrane, counteracting SMAD7-SMURF2-mediated ubiquitylation and degradation. AKT directly associates with and phosphorylates USP4, relocating nuclear USP4 to the cytoplasm and membrane and maintaining its protein stability. USP4 depletion mitigates TGF-β-induced EMT and metastasis. AKT-induced breast cancer cell migration is inhibited by USP4 depletion.\",\n      \"method\": \"Genome-wide gain-of-function screen, co-immunoprecipitation, in vitro deubiquitylation assay, AKT kinase assay, subcellular fractionation, siRNA knockdown, metastasis assays\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — genome-wide screen, in vitro DUB assay, AKT kinase assay, Co-IP, fractionation; multiple orthogonal methods in one highly cited study\",\n      \"pmids\": [\"22706160\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"USP4 specifically interacts with TRAF2 and TRAF6 (but not TRAF3) and deubiquitinates both in vitro and in vivo in a deubiquitinase activity-dependent manner. The USP domain of USP4 mediates interaction with TRAF6 independently of deubiquitinase activity. USP4 negatively regulates TNFα- and IL-1β-induced NF-κB activation and cancer cell migration.\",\n      \"method\": \"Co-immunoprecipitation, in vitro deubiquitination assay, NF-κB reporter, domain mapping, cell migration assay\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro deubiquitination, reciprocal Co-IP, domain mapping, functional NF-κB and migration assays; multiple orthogonal methods\",\n      \"pmids\": [\"22029577\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"USP4 interacts with the S9/Rpn6 subunit of the 26S proteasome via an internal ubiquitin-like (UBL) domain.\",\n      \"method\": \"Co-immunoprecipitation, domain mapping\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP with domain identification; single lab, single method\",\n      \"pmids\": [\"23022198\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"USP4 interacts with RIG-I and removes K48-linked polyubiquitination chains from RIG-I, thereby stabilizing RIG-I protein and positively regulating RIG-I-mediated IFN-β signaling and antiviral response. USP4 expression is attenuated after virus-induced RIG-I activation.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitin chain-linkage-specific deubiquitination assay, siRNA knockdown, IFN-β reporter assay, viral replication assay\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — Co-IP, chain-specific in-cell DUB assay, functional IFN signaling and viral replication readouts; multiple orthogonal methods\",\n      \"pmids\": [\"23388719\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"USP4 has its catalytic triad in a productive conformation but requires its N-terminal DUSP-Ubl domain for full catalytic turnover. The DUSP-Ubl domain enhances ubiquitin dissociation after substrate hydrolysis ('product discharge'), and binding of the DUSP-Ubl domain promotes a conformational change in a switching loop near the active site.\",\n      \"method\": \"Pre-steady-state kinetics, structural analysis, domain deletion/mutation experiments\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — pre-steady-state kinetics with defined mechanistic model, domain deletions, structural/conformational analysis; rigorous biochemical characterization\",\n      \"pmids\": [\"25404403\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"USP4 promotes DNA-end resection and homologous recombination (HR) by interacting with CtIP and the MRE11-RAD50-NBS1 (MRN) complex and is required for CtIP recruitment to DNA damage sites. USP4 itself is ubiquitylated on multiple sites including cysteine residues, and auto-deubiquitylation of these sites is required for USP4 to interact with CtIP/MRN and to promote HR.\",\n      \"method\": \"Co-immunoprecipitation, HR reporter assay, DNA damage sensitivity assay, mass spectrometry identification of ubiquitylation sites, catalytic mutant analysis\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — Co-IP with CtIP and MRN, functional HR assay, MS identification of modification sites, catalytic mutant analysis; multiple orthogonal methods, replicated in independent Cell Reports paper (PMID 26387952)\",\n      \"pmids\": [\"26455393\", \"26387952\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"USP4 interacts directly with and deubiquitinates HDAC2, stabilizing HDAC2 and leading to compromised p53 acetylation, impaired p53 transcriptional activation, and downregulation of TNFα-induced NF-κB activation.\",\n      \"method\": \"Co-immunoprecipitation, in vitro deubiquitination assay, p53 acetylation assay, NF-κB reporter assay\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, in vitro DUB assay, functional p53 and NF-κB readouts; single lab, multiple methods\",\n      \"pmids\": [\"26411366\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"The crystal structure of the SART3 HAT repeat domain in complex with the DUSP-UBL domains of USP4 was determined. USP4 binds SART3 at the β-structured linker between DUSP and UBL domains (Kd ~0.9 μM). SART3 recruits USP4 to the nucleus via its NLS; removal of SART3 NLS prevents nuclear entry of USP4 and abrogates its deubiquitinase activity toward spliceosomal substrates.\",\n      \"method\": \"X-ray crystallography, binding affinity measurement, nuclear localization assay, deubiquitinase activity assay with SART3 NLS mutants\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure with functional validation (localization and activity assays), binding affinity quantified; rigorous multi-method study\",\n      \"pmids\": [\"27060135\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"USP4 deubiquitinates SMAD4 by removing inhibitory monoubiquitination, thereby strongly inducing activin/BMP signaling. SMURF2 is recruited to SMAD4 upon ligand stimulation and triggers SMAD4 monoubiquitination. Depletion of USP4 in mouse embryonic stem cells increases monoubiquitinated SMAD4 and decreases BMP- and activin-induced cell fate changes. USP4 depletion in zebrafish causes defective cell migration and epiboly, both rescued by SMAD4.\",\n      \"method\": \"Co-immunoprecipitation, in vitro deubiquitination, mESC differentiation assay, zebrafish morpholino knockdown with rescue\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro DUB assay, genetic rescue in zebrafish, mESC functional assays, Co-IP; multiple orthogonal systems and methods\",\n      \"pmids\": [\"28468752\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"USP4 preferentially removes monoubiquitination from HAS2 (hyaluronan synthase 2), interacts with HAS2 in membrane preparations, and suppression of USP4 increases hyaluronan synthesis.\",\n      \"method\": \"DUB screen, co-immunoprecipitation from membrane fractions, ubiquitination assay, siRNA knockdown with hyaluronan production measurement\",\n      \"journal\": \"Oncogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — DUB screen followed by Co-IP and functional assay; multiple methods, single lab\",\n      \"pmids\": [\"28604766\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"USP4 physically interacts with IRF8 and stabilizes it via K48-linked deubiquitination in regulatory T cells, thereby promoting the suppressive function of Treg cells.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay (K48-linkage specific), USP4 inhibitor treatment, Treg functional suppression assay\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, linkage-specific ubiquitination assay, functional Treg assay; single lab, multiple methods\",\n      \"pmids\": [\"28477415\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"USP4 suppresses myoblast differentiation by downregulating MyoD activity in a catalytic-independent manner. USP4 knockdown enhances myogenesis and reduces HDAC1 and HDAC4 activity/protein levels. The effect on myogenesis involves AKT and p38 MAPK signaling pathways.\",\n      \"method\": \"siRNA knockdown, overexpression with catalytic mutant, C2C12 differentiation assay, immunoblot for myogenic markers\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — catalytic mutant demonstrates mechanism is independent of DUB activity, siRNA KD with multiple readouts, pathway inhibitor experiments; single lab\",\n      \"pmids\": [\"28336234\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"USP4 interacts with TRAF6 and positively regulates RLR-induced NF-κB signaling by removing K48-linked ubiquitin chains from TRAF6, preventing TRAF6 degradation. Overexpression of USP4 suppresses EV71 replication.\",\n      \"method\": \"Co-immunoprecipitation, K48-linkage-specific deubiquitination assay, NF-κB reporter, viral replication assay\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, chain-specific DUB assay, functional signaling and viral replication readouts; single lab\",\n      \"pmids\": [\"30194441\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"USP4 co-immunoprecipitates with AQP2 from mpkCCD14 cells and mouse kidney; USP4 can deubiquitylate AQP2 in vitro; shRNA knockdown of USP4 decreases AQP2 protein abundance and reduces VP-induced AQP2 membrane accumulation, associated with higher levels of ubiquitylated AQP2, without affecting AQP2 mRNA levels. AQP2 protein half-life is reduced in USP4 knockdown cells.\",\n      \"method\": \"Co-immunoprecipitation, in vitro deubiquitylation assay, shRNA knockdown, VP-stimulation membrane accumulation assay, protein half-life assay\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro DUB assay, Co-IP from endogenous tissue, functional membrane accumulation and protein stability assays; multiple orthogonal methods, single lab\",\n      \"pmids\": [\"30901874\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"USP4 deficiency exacerbates hepatic ischaemia/reperfusion injury by inducing activation of TAK1/JNK signaling pathways; TAK1 inhibition abolishes USP4 protective function in vitro, placing USP4 upstream of TAK1 in this context.\",\n      \"method\": \"USP4 knockout mouse model, TAK1 pharmacological inhibition, hepatic I/R model, pathway analysis\",\n      \"journal\": \"Clinical science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with defined pathway readout, pharmacological epistasis; single lab\",\n      \"pmids\": [\"30622220\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"USP4 was identified as a downstream target of PAK5-DNPEP pathway; DNPEP mediates USP4 downregulation and PAK5 decreases DNPEP abundance via the ubiquitin-proteasome pathway, thereby indirectly stabilizing USP4.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, overexpression/knockdown, in vivo xenograft\",\n      \"journal\": \"International journal of cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, ubiquitination assays, in vivo model; single lab, pathway epistasis established\",\n      \"pmids\": [\"31219614\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Phosphorylation status of USP4 (analogous to USP15 Thr149/Thr219) regulates its nuclear-cytoplasmic distribution and deubiquitinase activity. Treatment with cyclin-dependent kinase inhibitor purvalanol A causes changes in USP4 localization and activity, dependent on phosphorylation.\",\n      \"method\": \"Nuclear-cytoplasmic fractionation, mass spectrometry, CDK inhibitor treatment, activity assay\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — fractionation, MS-identified phosphosites, pharmacological perturbation; single lab, functional consequence shown\",\n      \"pmids\": [\"31330151\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"USP4 binds to, deubiquitinates, and stabilizes Twist1 protein. Silencing USP4 reduces Oct4, Sox2, and CD133+ cell population and inhibits tumorsphere formation in lung cancer cells. USP4-promoted stemness is effectively rescued by simultaneous silencing of Twist1.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, siRNA knockdown, tumorsphere formation, rescue experiment\",\n      \"journal\": \"Cancers\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, ubiquitination assay, genetic rescue; single lab, multiple methods\",\n      \"pmids\": [\"32549341\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"USP4 deubiquitinates PDGFRβ (removing both K63 and K48-linked chains), does not affect receptor stability but alters the speed of PDGFRβ trafficking toward early endosomes, and leads to prolonged/shifted STAT3 activation in response to PDGF-BB. Deletion of USP4 leads to decreased proliferative response to PDGF-BB stimulation.\",\n      \"method\": \"DUB overexpression screen, co-immunoprecipitation, receptor trafficking assay, STAT3 activation assay, USP4 knockout\",\n      \"journal\": \"Cellular and molecular life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — DUB screen, Co-IP, functional trafficking and signaling assays, KO phenotype; single lab, multiple methods\",\n      \"pmids\": [\"35064336\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"USP4 and its paralog USP15 regulate alternative splicing of SRSF1; depletion of USP4 impairs SRSF1 splicing, promoting an alternative isoform (SRSF1-3) subject to nonsense-mediated mRNA decay, and thereby impairs lung cancer cell proliferation.\",\n      \"method\": \"siRNA knockdown, RT-PCR for alternative splicing, rescue with SRSF1 overexpression, proliferation assay\",\n      \"journal\": \"Cell death discovery\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional splicing assay, genetic rescue, proliferation readout; single lab, multiple methods\",\n      \"pmids\": [\"35027535\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"USP4 interacts with cortactin (CTTN) via proximal labeling in HCT116 cells, and this interaction promotes cell migration independently of USP4 deubiquitinase activity on cortactin; USP4 overexpression increases cortactin phosphorylation by regulating Src/FAK binding to cortactin.\",\n      \"method\": \"Proximity labeling (BioID), co-immunoprecipitation, cortactin phosphorylation assay, migration assay, CTTN knockdown rescue\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — proximity labeling plus Co-IP, functional migration assay with CTTN knockdown rescue; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"37039823\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"USP4 stabilizes TAK1 protein via deubiquitination in esophageal squamous cell carcinoma cells, and promotes ESCC proliferation, migration, and invasion via the MEK/ERK signaling pathway.\",\n      \"method\": \"Co-immunoprecipitation, deubiquitination assay, MEK/ERK pathway inhibition (U0126), loss/gain-of-function, in vivo xenograft\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, DUB assay, pathway inhibitor epistasis; single lab, multiple methods\",\n      \"pmids\": [\"37949874\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"USP4 interacts with and deubiquitinates PKM2, stabilizing it and promoting cell proliferation and glycolysis (glucose uptake and lactate production) in gastric cancer cells.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, overexpression/knockdown, metabolic assays (glucose uptake, lactate production), MTT proliferation assay\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, ubiquitination assay, functional metabolic readouts; single lab, multiple methods\",\n      \"pmids\": [\"37624791\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Vialinin A inhibits USP4 deubiquitinating enzyme activity, leading to enhanced K48-ubiquitination and proteasomal degradation of Keap1, thereby activating Nrf2-dependent antioxidant response; overexpression of USP4 reverses these neuroprotective effects.\",\n      \"method\": \"USP4 enzymatic inhibition assay, co-immunoprecipitation, ubiquitination assay, luciferase reporter, USP4 overexpression rescue in vivo (MCAO model)\",\n      \"journal\": \"Phytomedicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — inhibitor-activity assay, Co-IP, in vivo rescue; single lab, multiple methods\",\n      \"pmids\": [\"38176274\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"USP4 interacts with SART3 and deubiquitinates TUT1 (terminal uridylyl transferase 1), a key U4/U6 spliceosome regulator; SART3 enhances USP4 deubiquitinating activity toward TUT1; USP4 orchestrates subnuclear relocalization of TUT1 from the nucleolus to the nucleoplasm and facilitates stability of U6 snRNA.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, immunofluorescence for TUT1 localization, U6 snRNA stability assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, ubiquitination assay, localization experiment with functional RNA stability readout; single lab, multiple methods\",\n      \"pmids\": [\"38310689\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"USP4 interacts with, deubiquitinates and stabilizes BRCA1, maintaining its protein level. USP4 knockdown decreases BRCA1, impairs homologous recombination-mediated DSB repair, increases genome instability, and confers resistance to DNA damage agents and PARP inhibitors.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, HR reporter assay, DNA damage sensitivity assay, genome instability assay\",\n      \"journal\": \"NPJ breast cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, DUB assay, functional HR and genome stability readouts; single lab, multiple methods\",\n      \"pmids\": [\"38734703\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"USP4 deubiquitinates RAB7A; reduced USP4 levels in periodontitis lead to RAB7A ubiquitination, impairing autophagosome-lysosome fusion and lysosomal trafficking. Upregulation of USP4 attenuates periodontitis in vivo.\",\n      \"method\": \"Proteomics analysis, co-immunoprecipitation, ubiquitination assay, autophagy flux assay, in vivo periodontitis model\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — proteomics identification, Co-IP, DUB assay, in vivo functional outcome; single lab, multiple methods\",\n      \"pmids\": [\"39663592\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"USP4 deubiquitinates and stabilizes PES1, facilitating ribosome biogenesis and protein synthesis in proliferating hematopoietic stem cells and leukemic cells; Usp4 deletion decreases protein synthesis and HSC reconstitution capacity.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, ribosome biogenesis assay, protein synthesis measurement, Usp4 conditional knockout mouse\",\n      \"journal\": \"Leukemia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, DUB assay, functional ribosome and protein synthesis assays, genetic KO; single lab, multiple methods\",\n      \"pmids\": [\"39266638\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"USP4 impedes the nuclear localization of IRF3 by deubiquitinating the K63-polyubiquitin chain of both TRAF6 and IRF3, thereby suppressing the tumor-intrinsic interferon response and antitumor immunity in colorectal cancer.\",\n      \"method\": \"Co-immunoprecipitation, K63-specific deubiquitination assay, IRF3 nuclear localization assay, siRNA knockdown, syngeneic mouse model\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — K63-specific DUB assay, nuclear localization assay, in vivo syngeneic model; single lab, multiple methods\",\n      \"pmids\": [\"38556105\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"USP4 deubiquitinates MAVS by removing K48-linked ubiquitin chains at Lys461, stabilizing MAVS and promoting antiviral innate immunity. This activity is activated through the p53-USP4-MAVS signaling axis downstream of PBLD.\",\n      \"method\": \"Co-immunoprecipitation, site-specific ubiquitination assay (K48 chains, Lys461 of MAVS), PBLD knockout mouse, IFN-I response assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — site-specific ubiquitination mapping (K461), K48-linkage DUB assay, Co-IP, in vivo KO mouse with viral challenge; multiple orthogonal methods\",\n      \"pmids\": [\"39589880\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"USP4 interacts with, deubiquitinates and stabilizes CARM1, promoting its activity; CARM1 stabilization by USP4 upregulates SLC7A11 expression, contributing to breast cancer cell malignancy.\",\n      \"method\": \"Co-immunoprecipitation, cycloheximide chase assay, ubiquitination assay, rescue experiment\",\n      \"journal\": \"Clinical breast cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, protein stability assay, DUB assay; single lab, multiple methods\",\n      \"pmids\": [\"39500657\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"USP4 directly cleaves both Lys48- and Lys63-linked polyubiquitin chains of ANXA2, with the Lys63-linked chains at K28 mediating ANXA2 Y24 phosphorylation. K10 acetylation of ANXA2 enhances its interaction with USP4. USP4 stabilizes ANXA2 and promotes glioblastoma stem cell maintenance and radioresistance via BMX-mediated STAT3 activation.\",\n      \"method\": \"Co-immunoprecipitation, chain-specific ubiquitination assay, phosphorylation assay, acetylation assay, siRNA knockdown, tumorsphere assay, radioresistance assay\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — K48/K63 chain-specific DUB assay, multiple PTM characterizations, functional GSC assays; single lab, multiple methods\",\n      \"pmids\": [\"40185997\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FBXO3 binds to and stabilizes USP4 by disrupting the interaction between USP4 and DNPEP (which mediates USP4 degradation), thereby stabilizing Twist1 via USP4 deubiquitinase activity and promoting breast cancer metastasis. PI3K/p110αH1047R facilitates phosphorylation and stabilization of FBXO3 via ERK1.\",\n      \"method\": \"Co-immunoprecipitation, protein stability assay, ubiquitination assay, siRNA knockdown, in vivo breast cancer metastasis model\",\n      \"journal\": \"PLoS biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, ubiquitination/stability assays, in vivo model; single lab, multiple methods\",\n      \"pmids\": [\"38134227\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"USP4 interacts with and stabilizes PGAM5 by removing K48-linked ubiquitin chains, thereby regulating mitochondrial dynamics and promoting mitophagy in esophageal squamous cell carcinoma.\",\n      \"method\": \"Co-immunoprecipitation, K48-specific ubiquitination assay, mitochondrial function assays (MMP, mtROS), in vivo tumor model\",\n      \"journal\": \"Molecular carcinogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, K48 chain-specific DUB assay, mitochondrial functional assays; single lab, multiple methods\",\n      \"pmids\": [\"41176636\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"USP4 interacts with, deubiquitinates, and stabilizes LDHA protein in papillary thyroid carcinoma cells, and promotes PTC proliferation by modulating MAPK and AKT signaling pathways.\",\n      \"method\": \"Co-immunoprecipitation, deubiquitination assay, MAPK/AKT pathway analysis, siRNA knockdown, proliferation assay\",\n      \"journal\": \"Aging\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, DUB assay, pathway readout; single lab\",\n      \"pmids\": [\"39393052\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"USP4 modulates ZBP1 ubiquitination: USP4 interacts with, deubiquitinates, and stabilizes ZBP1 in microglia. AKT-mediated phosphorylation is required to maintain USP4 protein stability. Pharmacological inhibition of USP4 with Vialinin A leads to ZBP1 degradation and reduces microglial PANoptosis after traumatic brain injury.\",\n      \"method\": \"Co-immunoprecipitation, deubiquitination assay, AKT phosphorylation analysis, Vialinin A inhibitor treatment, TBI mouse model\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, DUB assay, AKT phosphorylation assay, in vivo inhibitor treatment; single lab, multiple methods\",\n      \"pmids\": [\"42091674\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"USP4 stabilizes β-catenin and Twist1 proteins in colorectal cancer cells by deubiquitinating them; a novel small molecule inhibitor U4-I05 binds the catalytic C311 site of USP4 and triggers proteasomal degradation of β-catenin and Twist1, inhibiting cancer stemness.\",\n      \"method\": \"Virtual screening, co-immunoprecipitation, ubiquitination assay, catalytic site binding assay, cancer stemness assay (organoids, xenograft), site-specific mutant (C311)\",\n      \"journal\": \"Journal of translational medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — catalytic site mutagenesis, Co-IP, DUB assay, functional stemness readouts, in vivo model; single lab but mechanistically comprehensive\",\n      \"pmids\": [\"39856683\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"USP4 deubiquitinates and stabilizes NR4A1, protecting it from ubiquitination-mediated degradation; MEF2A transcriptionally activates USP4 expression by binding its promoter; the MEF2A-USP4-NR4A1 axis suppresses ER stress and apoptosis in multiple myeloma cells.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, ChIP assay, luciferase reporter, siRNA knockdown, xenograft model\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, DUB assay, ChIP and reporter for transcriptional regulation, in vivo model; single lab, multiple methods\",\n      \"pmids\": [\"41186214\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"USP4 deubiquitinates and stabilizes KLF2 protein; KLF2 transcriptionally regulates HMGA2; the USP4/KLF2/HMGA2 cascade regulates cell growth, apoptosis, and bortezomib sensitivity in drug-resistant multiple myeloma cells.\",\n      \"method\": \"Co-immunoprecipitation, protein stability assay, luciferase reporter, ChIP assay, functional growth and apoptosis assays\",\n      \"journal\": \"Journal of orthopaedic surgery and research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, stability assay, ChIP/reporter for downstream target; single lab\",\n      \"pmids\": [\"40022160\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"USP4 deubiquitinates and stabilizes SRC-1, enhancing its protein stability; the USP4-SRC-1 axis inhibits M2 macrophage polarization via the NF-κB pathway and is validated in an OVA-induced asthma model in vivo.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, flow cytometry for macrophage polarization, NF-κB pathway analysis, in vivo OVA model\",\n      \"journal\": \"Experimental lung research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, DUB assay, functional macrophage assay, in vivo model; single lab, multiple methods\",\n      \"pmids\": [\"40493388\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"USP4 stabilizes PAF1 by directly binding and reducing its K48-linked polyubiquitination, counteracting CNOT4-mediated PAF1 degradation and promoting NSCLC cell proliferation in vitro and tumor growth in vivo.\",\n      \"method\": \"Co-immunoprecipitation, K48-ubiquitination assay, rescue assay, CCK-8 proliferation, xenograft model\",\n      \"journal\": \"Respiratory research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, chain-specific DUB assay, genetic rescue in vivo; single lab, multiple methods\",\n      \"pmids\": [\"41857610\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"USP4 removes Lys48-linked polyubiquitin chains from the A2A receptor (A2AR) via deubiquitination at the C311 site in gastric cancer cells, stabilizing A2AR, modulating autophagy, and inhibiting ferroptosis.\",\n      \"method\": \"Co-immunoprecipitation, K48-specific ubiquitination assay, catalytic mutant (C311), autophagy and ferroptosis assays\",\n      \"journal\": \"Cellular and molecular life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, site-specific mutant, chain-specific DUB assay, functional autophagy/ferroptosis assays; single lab\",\n      \"pmids\": [\"41051500\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"USP4 interacts with and stabilizes CENPF via deubiquitination in colorectal cancer; USP4 expression positively correlates with CENPF protein (but not mRNA) levels in clinical samples; USP4-mediated CENPF upregulation is a critical regulator of CRC metastasis.\",\n      \"method\": \"Co-immunoprecipitation, deubiquitination assay, siRNA knockdown, in vivo metastasis model, clinical sample correlation\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, DUB assay, in vivo model; single lab\",\n      \"pmids\": [\"39922805\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"USP4, enriched in melatonin-preconditioned exosomes, directly interacts with and deubiquitinates ARNTL (a core circadian regulator), stabilizing its protein levels and suppressing ferroptosis in skin flap cells. H3K18 lactylation upregulates USP4 mRNA, enhancing USP4 translation within exosomes.\",\n      \"method\": \"Co-immunoprecipitation, deubiquitination assay, m6A modification analysis, ferroptosis assay, in vivo flap model\",\n      \"journal\": \"Clinical and translational medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, DUB assay, in vivo model; single lab, novel substrate\",\n      \"pmids\": [\"41482632\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"USP4 is a nucleocytoplasmic-shuttling cysteine deubiquitylase whose DUSP-Ubl domain allosterically promotes ubiquitin product discharge and whose catalytic C311 residue removes K48- and/or K63-linked polyubiquitin (and monoubiquitin) from a broad array of substrates—including TβRI, SMAD4, TAK1, TRAF2/6, RIG-I, MAVS, IRF3, CtIP/MRN, BRCA1, ARF-BP1, HDAC2, AQP2, Twist1, PES1, RAB7A, PKM2, ANXA2, and others—to regulate TGF-β/SMAD, NF-κB, antiviral interferon, DNA repair, Wnt/β-catenin, spliceosome, and metabolic signaling; its activity and localization are in turn controlled by AKT-mediated phosphorylation and by nuclear import/export mediated through the SART3 scaffold.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"USP4 is a nucleocytoplasmic-shuttling ubiquitin-specific protease (cysteine deubiquitylase) that controls the stability and activity of a broad set of signaling proteins by cleaving K48- and K63-linked polyubiquitin and monoubiquitin from its substrates [#2, #3, #9]. Catalysis depends on the active-site cysteine (C311), and its full turnover is governed allosterically by the N-terminal DUSP-Ubl domain, which promotes ubiquitin product discharge through a conformational change near the active site [#10, #16]. USP4 moves between nucleus and cytoplasm via a defined nuclear export signal and an importin-recognized nuclear import signal [#6], with nuclear entry and spliceosomal substrate access supplied by binding to the SART3 HAT-repeat scaffold; AKT-mediated phosphorylation drives nuclear-to-cytoplasmic/membrane relocalization and stabilizes the enzyme [#12, #19, #47]. Through these activities USP4 acts as a hinge across multiple pathways: it stabilizes the TGF-\\u03b2 type I receptor and deubiquitylates SMAD4 to potentiate TGF-\\u03b2/activin/BMP signaling [#12, #20]; it deubiquitylates TAK1, TRAF2/TRAF6, and IRF3 to tune NF-\\u03baB and interferon responses [#10, #13, #40]; it stabilizes RIG-I and MAVS to promote antiviral innate immunity [#15, #41]; and it promotes DNA-end resection and homologous recombination through CtIP/MRN and BRCA1, requiring auto-deubiquitylation for these interactions [#17, #37]. USP4 also engages the p53 axis by stabilizing the E3 ligase ARF-BP1 to lower p53, a role corroborated by Usp4-knockout mice showing elevated p53-dependent phenotypes [#11]. In cancer contexts USP4 stabilizes pro-tumorigenic substrates including Twist1, \\u03b2-catenin, PKM2, and PES1 to drive stemness, metabolism, and proliferation [#29, #39, #48].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Establishing that USP4 is a bona fide enzyme answered whether the gene encodes catalytic activity rather than merely a sequence motif, defining it as a cysteine-dependent deubiquitylase.\",\n      \"evidence\": \"in vitro deubiquitination assay with catalytic-cysteine-to-alanine mutagenesis and cellular fractionation\",\n      \"pmids\": [\"9464533\", \"11018721\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No physiological substrate identified at this stage\", \"Chain-linkage preference not yet defined\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Identifying pRb and pocket-protein binding addressed how the originally oncogenic USP4 might connect to growth control, linking it physically to the Rb tumor-suppressor pathway.\",\n      \"evidence\": \"reciprocal Co-IP, in vitro binding, and motif mutagenesis\",\n      \"pmids\": [\"11571651\", \"11571652\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether USP4 deubiquitylates pRb was not shown\", \"Functional consequence of the interaction for Rb activity unresolved\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Mapping functional export and import signals answered how USP4 localization is determined, establishing it as an actively shuttling enzyme with cell-type-dependent distribution.\",\n      \"evidence\": \"live-cell imaging, leptomycin B export inhibition, Rev-GFP export assay, importin binding, USP4-specific antibodies\",\n      \"pmids\": [\"15494318\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Signals controlling the shuttling equilibrium not identified here\", \"Functional importance of nuclear versus cytoplasmic pools undefined\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Demonstrating dual K48/K63 chain hydrolysis and Wnt suppression via NLK/TCF4 defined USP4's biochemical breadth and its first signaling pathway role.\",\n      \"evidence\": \"RNAi screen, luciferase reporter, Co-IP, ubiquitin chain hydrolysis assay\",\n      \"pmids\": [\"20141612\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct TCF4 deubiquitylation in vitro not fully resolved\", \"Mechanism of NLK-driven nuclear accumulation unclear\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Linking USP4 to TAK1 and to ARF-BP1/p53 answered how it represses NF-\\u03baB and modulates apoptosis/senescence, providing the first in vivo genetic evidence of its role.\",\n      \"evidence\": \"in vitro deubiquitination with C311A mutant, Co-IP, NF-\\u03baB reporter, Usp4 knockout mouse and MEF assays\",\n      \"pmids\": [\"21331078\", \"21522127\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Context-dependent positive versus negative NF-\\u03baB regulation not reconciled\", \"Whether p53 and NF-\\u03baB effects share a common pathway unresolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Identifying T\\u03b2RI stabilization and AKT-mediated regulation answered how USP4 promotes TGF-\\u03b2-driven EMT and how upstream kinase signaling controls USP4 localization and stability.\",\n      \"evidence\": \"genome-wide gain-of-function screen, in vitro DUB assay, AKT kinase assay, fractionation, metastasis assays\",\n      \"pmids\": [\"22706160\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Phosphosites on USP4 not exhaustively mapped here\", \"How phosphorylation alters catalytic activity vs trafficking not separated\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Defining the DUSP-Ubl domain's allosteric role answered the long-standing question of why full-length USP4 turns over substrate efficiently, revealing product-discharge acceleration as the mechanism.\",\n      \"evidence\": \"pre-steady-state kinetics, structural analysis, domain deletion/mutation\",\n      \"pmids\": [\"25404403\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether substrate-specific partners modulate this allostery in cells untested\", \"Structure of full-length enzyme with substrate not solved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Solving the SART3-DUSP/UBL structure answered how USP4 is delivered to the nucleus and to spliceosomal substrates, coupling scaffold binding to localization and activity.\",\n      \"evidence\": \"X-ray crystallography, affinity measurement, NLS-mutant localization and activity assays\",\n      \"pmids\": [\"27060135\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Spliceosomal substrate identity not defined in this study\", \"Whether AKT phosphorylation competes with SART3 binding unknown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Showing SMAD4 deubiquitylation and CtIP/MRN-dependent HR established two mechanistically distinct roles\\u2014developmental TGF-\\u03b2 signaling and DNA-end resection\\u2014and revealed auto-deubiquitylation as a prerequisite for HR engagement.\",\n      \"evidence\": \"in vitro DUB assays, zebrafish/mESC functional rescue, MS mapping of USP4 ubiquitylation sites, HR reporter\",\n      \"pmids\": [\"28468752\", \"26455393\", \"26387952\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How USP4 is recruited to DNA damage sites mechanistically undefined\", \"Relationship between SMAD4 monoubiquitin removal and receptor-level TGF-\\u03b2 regulation not integrated\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identifying RIG-I substrate stabilization positioned USP4 as a positive regulator of antiviral interferon signaling, distinct from its NF-\\u03baB-suppressing roles.\",\n      \"evidence\": \"Co-IP, K48-linkage-specific DUB assay, IFN-\\u03b2 reporter, viral replication assay\",\n      \"pmids\": [\"23388719\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Why USP4 expression falls after RIG-I activation mechanistically unclear\", \"Linkage-specificity determinants at substrate level undefined\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Mapping site-specific MAVS (K461) and IRF3 regulation refined how USP4 sets the threshold of innate immune signaling, including a p53-PBLD-USP4-MAVS axis and an interferon-suppressive role in cancer.\",\n      \"evidence\": \"site-specific ubiquitination mapping, K48/K63-specific DUB assays, PBLD knockout mouse, IRF3 nuclear localization, syngeneic model\",\n      \"pmids\": [\"39589880\", \"38556105\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How USP4 selects opposing pro- versus anti-interferon outcomes across tissues unresolved\", \"Coordination with the RIG-I/TRAF6 arms not unified\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Expanding the substrate set to BRCA1, PES1, RAB7A and others demonstrated USP4's reach into HR repair, ribosome biogenesis, and autophagic trafficking, broadening its cellular footprint.\",\n      \"evidence\": \"Co-IP, chain-specific ubiquitination assays, HR/ribosome/autophagy functional readouts, conditional knockout mice\",\n      \"pmids\": [\"38734703\", \"39266638\", \"39663592\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Most substrate relationships rest on single-lab studies without reciprocal cross-validation\", \"Whether localization gating determines which substrates are engaged not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How USP4 selects among its many substrates and reconciles opposing roles (tumor suppressor via p53/Rb versus oncogenic stabilizer of Twist1/\\u03b2-catenin/PKM2) in a context-dependent manner remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unifying model linking localization, phosphorylation state, and substrate choice\", \"Substrate-specificity determinants of K48 vs K63 vs monoubiquitin cleavage undefined\", \"In vivo substrate hierarchy across tissues not established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [2, 3, 10, 16]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [2, 3]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [12, 15, 41]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [2, 6]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [1, 6, 19]},\n      {\"term_id\": \"GO:0005654\", \"supporting_discovery_ids\": [19, 36]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [12]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [12, 20, 30]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [10, 13, 15, 41, 40]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [17, 37]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [19, 31, 36]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [2, 3, 12]}\n    ],\n    \"complexes\": [\"MRE11-RAD50-NBS1 (MRN) complex\"],\n    \"partners\": [\"SART3\", \"TAK1\", \"TRAF6\", \"RIG-I\", \"MAVS\", \"SMAD4\", \"CtIP\", \"ARF-BP1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}