{"gene":"USP22","run_date":"2026-04-28T23:00:23","timeline":{"discoveries":[{"year":2008,"finding":"USP22 is a catalytic subunit of the human SAGA transcriptional cofactor complex, where it deubiquitylates histone H2B to enable activator-driven transcription, and is recruited to specific genes by activators such as Myc.","method":"Biochemical subunit identification, in vitro deubiquitylation assay, chromatin immunoprecipitation, loss-of-function with transcriptional readout","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal methods (Co-IP, in vitro assay, ChIP, KD) in a highly-cited foundational paper","pmids":["18206973"],"is_preprint":false},{"year":2008,"finding":"USP22, as part of the hSAGA complex, also deubiquitylates histone H2A in addition to H2B, opposing Polycomb-mediated H2A ubiquitylation.","method":"Biochemical substrate specificity assay with reconstituted histone substrates","journal":"Cell cycle (Georgetown, Tex.)","confidence":"High","confidence_rationale":"Tier 1 — in vitro biochemical assay with defined substrates, independent follow-up of SAGA subunit discovery","pmids":["18469533"],"is_preprint":false},{"year":2012,"finding":"USP22 interacts with and stabilizes SIRT1 by removing polyubiquitin chains from SIRT1, thereby reducing p53 acetylation and suppressing p53-dependent apoptosis; genetic deletion of Usp22 destabilizes SIRT1 and causes early embryonic lethality in mice.","method":"Co-immunoprecipitation, ubiquitination assay, RNAi knockdown, Usp22 knockout mouse model with apoptosis and p53 acetylation readouts","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1–2 — reciprocal Co-IP, in vivo ubiquitination assay, genetic mouse model, multiple orthogonal methods","pmids":["22542455"],"is_preprint":false},{"year":2011,"finding":"USP22 deubiquitinates the transcriptional regulator FBP1, and this deubiquitination does not alter FBP1 stability but instead promotes stable FBP1 occupancy at the p21 gene locus to regulate cell proliferation.","method":"RNAi knockdown, ubiquitination assay, chromatin immunoprecipitation, cell proliferation assays","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (KD, ubiquitination assay, ChIP) with defined molecular mechanism","pmids":["21779003"],"is_preprint":false},{"year":2016,"finding":"Phosphorylation of KDM1A (LSD1) by GSK3β and CK1α induces its binding to USP22, which then deubiquitylates and stabilizes KDM1A, leading to H3K4 demethylation and repression of BMP2, CDKN1A, and GATA6 to promote cancer stem cell self-renewal and glioblastoma tumorigenesis.","method":"Co-immunoprecipitation, ubiquitination assay, mutagenesis of phosphorylation sites, ChIP, in vivo xenograft model","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 1–2 — mechanistic epistasis with mutagenesis, Co-IP, ChIP, and in vivo validation","pmids":["27501329"],"is_preprint":false},{"year":2018,"finding":"USP22 directly deubiquitylates cyclin D1 (CCND1), protecting it from proteasomal degradation independently of the canonical phosphorylation/ubiquitylation pathway, thereby controlling G1 cell cycle progression.","method":"Co-immunoprecipitation, ubiquitination assay, cycloheximide chase, loss-of-function in cancer cell lines and xenograft models","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods with defined substrate and functional cell cycle readout","pmids":["30224477"],"is_preprint":false},{"year":2017,"finding":"USP22 promotes deubiquitination and stabilization of c-Myc in breast cancer cells, increasing c-Myc protein levels and tumorigenic activity.","method":"Co-immunoprecipitation, ubiquitination assay, USP22 knockdown/overexpression with c-Myc protein stability and colony formation readouts","journal":"Journal of cellular physiology","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP and ubiquitination assay with functional readout, single lab","pmids":["28160502"],"is_preprint":false},{"year":2013,"finding":"USP22 is identified as a high-confidence interactor of SIRT1 via its ZnF-UBP domain; USP22 is acetylated on multiple lysines, and acetylation of K129 within the ZnF-UBP domain regulates interaction of the deubiquitinating module (DUBm) with the core SAGA complex; USP22-recruited SIRT1 promotes deacetylation of SAGA components.","method":"Comparative affinity purification-mass spectrometry, Co-IP, domain mapping, mutagenesis (H363Y SIRT1, K129 USP22), in vitro deacetylation assay","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1–2 — AP-MS interactome + mutagenesis + in vitro assay, multiple orthogonal methods","pmids":["23382074"],"is_preprint":false},{"year":2013,"finding":"USP22 is required for embryonic stem cell differentiation; it occupies the Sox2 promoter and deubiquitylates H2Bub to repress Sox2 transcription, enabling the transition from self-renewal to lineage-specific differentiation.","method":"USP22 knockout/knockdown in ESCs, chromatin immunoprecipitation, differentiation assays across three germ layers","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — ChIP with functional differentiation readout, KO model with defined molecular mechanism","pmids":["23760504"],"is_preprint":false},{"year":2018,"finding":"Usp22, the SAGA complex deubiquitinase that removes ubiquitin from H2B-K120, is required for proper DNA break repair during class switch recombination (CSR) and V(D)J recombination; Usp22 ablation in B cells impairs γH2AX formation and classical non-homologous end joining (c-NHEJ), with CSR to IgA being less reliant on Usp22/c-NHEJ than CSR to other isotypes.","method":"Conditional B cell-specific Usp22 knockout, CSR assays, γH2AX detection, NHEJ reporter assay, V(D)J recombination assay","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with multiple orthogonal functional readouts in vivo and in vitro","pmids":["29520062"],"is_preprint":false},{"year":2020,"finding":"Cytoplasmic USP22 promotes nuclear translocation of IRF3 during viral infection by deubiquitinating and stabilizing the importin KPNA2; viral infection induces USP22-IRF3 association in a KPNA2-dependent manner, and USP22 or KPNA2 deficiency impairs IRF3 nuclear translocation and type I IFN production.","method":"Co-immunoprecipitation, ubiquitination assay, USP22/KPNA2 KO cell lines and conditional KO mice, reconstitution of KPNA2 in KO cells, IRF3 nuclear translocation imaging","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods including KO rescue reconstitution and in vivo mouse model","pmids":["32130408"],"is_preprint":false},{"year":2020,"finding":"USP22 controls necroptotic cell death by deubiquitinating RIPK3 at lysines 42, 351, and 518; mutation of RIPK3 K518 reduces necroptosis-associated ubiquitination and amplifies necrosome formation and necroptotic cell death.","method":"Loss-of-function (USP22 KO), ubiquitin remnant profiling by mass spectrometry, RIPK3 site-directed mutagenesis, necroptosis assays in human tumor cell lines","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 1–2 — ubiquitin proteomics + mutagenesis + functional cell death assay","pmids":["33369872"],"is_preprint":false},{"year":2020,"finding":"USP22 directly interacts with and deubiquitinates PD-L1 to inhibit its proteasomal degradation; USP22 also stabilizes CSN5 through deubiquitination, and both USP22 and CSN5 facilitate each other's interaction with PD-L1, removing K6, K11, K27, K29, K33, and K63-linked ubiquitin chains.","method":"Co-immunoprecipitation, ubiquitination assay with linkage-specific analysis, protein half-life assay, flow cytometry, USP22 depletion in tumor cells","journal":"Cell communication and signaling : CCS","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP and ubiquitination assay with multiple linkage types identified, single lab","pmids":["32665011"],"is_preprint":false},{"year":2019,"finding":"USP22 deubiquitinates and stabilizes HIF1α, promoting hypoxia-induced hepatocellular carcinoma stemness and glycolysis; in TP53-mutant HCC, USP22 and HIF1α form a positive feedback loop.","method":"Immunoprecipitation, ubiquitination assay, ChIP assay, loss- and gain-of-function in HCC cells and in vivo mouse model","journal":"Gut","confidence":"High","confidence_rationale":"Tier 2 — Co-IP, ubiquitination assay, ChIP, in vivo validation with multiple orthogonal methods","pmids":["31776228"],"is_preprint":false},{"year":2022,"finding":"USP22 directly interacts with, deubiquitinates (via K48-linked deubiquitination), and stabilizes PPARγ, which in turn increases ACC and ACLY expression to promote de novo fatty acid synthesis in hepatocellular carcinoma.","method":"Co-immunoprecipitation, ubiquitination assay (K48-linkage specific), loss-of-function, in vivo tumorigenesis experiments","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — Co-IP, linkage-specific ubiquitination assay, in vivo validation, multiple orthogonal methods","pmids":["35449157"],"is_preprint":false},{"year":2022,"finding":"USP22 suppresses NLRP3 inflammasome activation by stabilizing ATG5 through decreasing K27- and K48-linked ubiquitination at ATG5 Lys118, thereby promoting ATG5-mediated autophagy and autophagic degradation of NLRP3.","method":"Co-immunoprecipitation, ubiquitination assay (site-specific mutagenesis of ATG5 K118), USP22 KO/knockdown in vivo and in vitro, autophagy/NLRP3 inflammasome readouts","journal":"Autophagy","confidence":"High","confidence_rationale":"Tier 1–2 — site-directed mutagenesis, linkage-specific ubiquitination assay, in vivo KO model","pmids":["35900990"],"is_preprint":false},{"year":2018,"finding":"USP22 deficiency in hematopoietic cells expressing oncogenic Kras promotes AML transformation through impaired myeloid differentiation; USP22 functions as a PU.1 deubiquitylase that positively regulates PU.1 protein stability and PU.1 target gene expression, and PU.1 reconstitution rescues differentiation.","method":"Conditional USP22 KO mouse model with oncogenic Kras, bone marrow transplantation, ubiquitination assay, transcriptome profiling, PU.1 reconstitution rescue experiment","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis with rescue experiment, ubiquitination assay, in vivo model","pmids":["29844011"],"is_preprint":false},{"year":2019,"finding":"USP22 loss in mice causes embryonic lethality due to defects in extra-embryonic placental vasculature; USP22 deletion disrupts TGFβ and receptor tyrosine kinase signaling pathways in endothelial cells and pericytes, impairing cell survival, differentiation, and vessel formation.","method":"Usp22 conditional knockout mice, endothelial/pericyte differentiation from ESCs, vessel formation assays, transcriptome analysis","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with defined developmental phenotype and pathway analysis","pmids":["30718289"],"is_preprint":false},{"year":2011,"finding":"USP22 is required for efficient 3'-end cleavage/polyadenylation of JAK-STAT-inducible genes; USP22 knockdown increases H2Bub levels and reduces Ser2 phosphorylation of RNA Pol II CTD and CPSF73 recruitment, implicating H2B deubiquitination in coupling transcriptional elongation to 3'-end processing.","method":"RNAi knockdown, H2Bub ChIP, RNA Pol II CTD Ser2P ChIP, polyadenylation cleavage assay, USP22 overexpression rescue","journal":"FASEB journal : official publication of the Federation of American Societies for Experimental Biology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple ChIP assays and functional processing assay with rescue, single lab","pmids":["22067483"],"is_preprint":false},{"year":2014,"finding":"USP22 specifically interacts with and deubiquitinates NFATc2, stabilizing its protein levels via its deubiquitinase activity, which is required for IL-2 expression in T cells.","method":"Co-immunoprecipitation, ubiquitination assay, USP22 knockdown in T cells with IL-2 expression readout","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP + ubiquitination assay + functional KD, single lab","pmids":["24561192"],"is_preprint":false},{"year":2019,"finding":"USP22 interacts with and stabilizes BRCA2 and PALB2, is necessary for BRCA2, PALB2, and Rad51 recruitment to DNA double-strand breaks, and promotes homologous recombination; the interaction with PALB2's WD40 domain stimulates USP22 catalytic activity in vitro.","method":"Co-immunoprecipitation, in vitro catalytic activity assay, HR reporter assay, foci formation at DSBs, USP22 knockdown","journal":"Molecular cancer research : MCR","confidence":"Medium","confidence_rationale":"Tier 1–2 — in vitro catalytic assay + Co-IP + functional HR assay, single lab","pmids":["31685642"],"is_preprint":false},{"year":2019,"finding":"USP22 functions as a XPC deubiquitylase; depletion of USP22 sensitizes prostate cancer cells to genotoxic insult, and XPC was identified as a critical mediator of USP22-mediated survival to DNA damage through ubiquitylome analysis.","method":"USP22 overexpression/depletion, ubiquitylome profiling, genotoxic sensitivity assays, mouse adult fibroblast model","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — ubiquitylome proteomics + functional KD with genotoxic readout, single lab","pmids":["31740444"],"is_preprint":false},{"year":2020,"finding":"USP22 directly interacts with STAT1, deubiquitinates it, and improves its stability in melanoma cells; USP22 deficiency impairs IFNγ-JAK1-STAT1 signaling and reduces sensitivity to T cell-mediated killing.","method":"Co-immunoprecipitation, ubiquitination assay, USP22 KO in mouse and human melanoma cells, genome-wide CRISPR screen, T cell killing assay","journal":"Molecular therapy : the journal of the American Society of Gene Therapy","confidence":"Medium","confidence_rationale":"Tier 2 — CRISPR screen + Co-IP + ubiquitination assay + functional T cell killing assay, single lab","pmids":["33601053"],"is_preprint":false},{"year":2020,"finding":"USP22 interacts with Mediator subunit MED1 and deubiquitinates histone H2A (but not H2B) to enhance MED1-dependent transcription of IL-2Rβ and T-bet genes, controlling iNKT cell development and differentiation.","method":"Co-immunoprecipitation, USP22 conditional KO in iNKT cells, H2A/H2Bub ChIP, gene expression analysis","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 — Co-IP + substrate-specific ChIP + genetic KO with defined developmental phenotype, multiple orthogonal methods","pmids":["32069354"],"is_preprint":false},{"year":2022,"finding":"USP22 controls basal STING activation and type III IFN (IFN-λ) signaling in intestinal epithelial cells; USP22-deficient cells show upregulated ISGs, increased IFN-λ secretion, and enhanced STAT1 signaling even without viral stimulation, and are protected from SARS-CoV-2 infection in a STING-dependent manner.","method":"USP22 KO intestinal epithelial cell lines, 2'3'-cGAMP stimulation assays, SARS-CoV-2 infection model, STING reconstitution/rescue experiments","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 — KO with STING rescue and viral infection functional readout, single lab","pmids":["35933402"],"is_preprint":false},{"year":2018,"finding":"USP22 promotes epithelial-mesenchymal transition via the FAK signaling pathway in pancreatic cancer cells, inducing Ezrin redistribution and phosphorylation, cytoskeletal remodeling, and upregulation of Snail and ZEB1.","method":"USP22 overexpression/knockdown, FAK pathway inhibition, invasion/migration assays, EMT marker analysis","journal":"Oncology reports","confidence":"Low","confidence_rationale":"Tier 3 — functional KD/OE with pathway readout but limited molecular mechanism for direct USP22-FAK link","pmids":["25070659"],"is_preprint":false},{"year":2014,"finding":"USP22 interacts with MDMX and promotes its stabilization in NSCLC cells; USP22 silencing downregulates MDMX and activates the p53 pathway, and MDMX overexpression reverses USP22 silencing-induced growth arrest.","method":"Co-immunoprecipitation, USP22 shRNA knockdown, MDMX rescue experiment, p53 pathway analysis","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP + rescue experiment, single lab","pmids":["25547493"],"is_preprint":false},{"year":2015,"finding":"USP22 directly interacts with and stabilizes COX-2 through deubiquitination; USP22 silencing reduces COX-2 protein half-life and inhibits lung carcinoma cell proliferation.","method":"Co-immunoprecipitation, ubiquitination assay, cycloheximide chase, USP22 knockdown","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP + ubiquitination assay + half-life assay, single lab","pmids":["25817787"],"is_preprint":false},{"year":2018,"finding":"USP22 deubiquitinates EGFR localized on late endosomes, preventing ubiquitination-mediated EGFR degradation and enhancing EGFR recycling after EGF stimulation, thereby sustaining activation of STAT3, AKT/mTOR, and MEK/ERK pathways.","method":"Co-immunoprecipitation, ubiquitination assay, EGFR recycling assay, endosomal localization studies, USP22 knockdown with pathway readouts","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP + ubiquitination assay + subcellular localization + functional signaling readout, single lab","pmids":["29981430"],"is_preprint":false},{"year":2017,"finding":"USP22 stabilizes BMI1 protein in gastric cancer cells through deubiquitination, promoting cancer stem cell self-renewal; TAT-BMI1 protein reconstitution rescues the stem cell properties lost upon USP22 knockdown.","method":"USP22 knockdown, BMI1 protein stability assay, TAT-BMI1 rescue experiment, sphere formation assay, xenograft model","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2 — protein stability assay + rescue experiment + in vivo model, single lab","pmids":["28415621"],"is_preprint":false},{"year":2021,"finding":"USP22 deubiquitinates and stabilizes E2F6, leading to transcriptional repression of DUSP1 phosphatase, which in turn strengthens AKT activation in hepatocellular carcinoma cells.","method":"Co-immunoprecipitation, ubiquitination assay, loss-of-function, transcriptional repression and AKT signaling readouts","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP + ubiquitination assay + defined signaling mechanism, single lab","pmids":["34339800"],"is_preprint":false},{"year":2021,"finding":"USP22 deubiquitinates and stabilizes PTEN in pancreatic cancer, which then induces p21 (CDKN1A) expression by interacting with ANKHD1 and inhibiting ANKHD1 binding to the p21 promoter.","method":"Co-immunoprecipitation, ubiquitination assay, USP22 overexpression, ANKHD1 interaction assay, p21 promoter binding assay","journal":"Molecular oncology","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP + ubiquitination assay + mechanistic pathway placement, single lab","pmids":["34743406"],"is_preprint":false},{"year":2015,"finding":"The catalytic deubiquitinase activity of USP22 (abolished by C185S mutation and reduced by Y513C mutation) is necessary for regulating HeLa cell cycle progression and controlling BMI-1, c-Myc, cyclin D2, and p53 levels.","method":"Active-site mutagenesis (C185S, Y513C), cell cycle analysis, western blot of downstream targets","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 1 — active-site mutagenesis establishing catalytic requirement, single lab","pmids":["26143114"],"is_preprint":false},{"year":2018,"finding":"USP22 promotes homologous recombination repair by interacting with PALB2 (via its WD40 domain), which stimulates USP22 catalytic activity in vitro, and by stabilizing BRCA2 and PALB2 to enable Rad51 recruitment to DNA double-strand breaks.","method":"In vitro catalytic activity assay, Co-immunoprecipitation, HR reporter assay, foci formation assay, domain mapping","journal":"Molecular cancer research : MCR","confidence":"Medium","confidence_rationale":"Tier 1–2 — in vitro reconstitution of catalytic stimulation + Co-IP + functional HR assay, single lab","pmids":["31685642"],"is_preprint":false},{"year":2015,"finding":"Reduction of Usp22 in mice impairs intestinal epithelial lineage specification and affects differentiated cell frequencies in the small intestine and brain, demonstrating a physiological role for USP22 in cell differentiation independent of global H2Bub1 changes.","method":"Usp22 hypomorphic mouse model (lacZ knock-in), histological analysis, cell lineage marker staining, H2Bub1 immunostaining","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo genetic mouse model with defined histological phenotype, single lab","pmids":["26431380"],"is_preprint":false},{"year":2023,"finding":"USP22 deubiquitinates and stabilizes Snail1 (an EMT transcription factor) in renal tubular epithelial cells under high-glucose conditions, promoting epithelial-to-mesenchymal transition and renal tubulointerstitial fibrosis in diabetic kidney disease.","method":"Co-immunoprecipitation, ubiquitination assay, USP22 overexpression/knockdown, deubiquitinase activity assay, in vivo db/db mouse model","journal":"European journal of pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP + ubiquitination assay + in vivo KD, single lab","pmids":["37001578"],"is_preprint":false},{"year":2015,"finding":"USP22 positively regulates RCAN1 protein stability by direct interaction and deubiquitination, opposing the actions of FBW7, NEDD4-2, and β-TrCP E3 ligases; interferon-α treatment dissociates RCAN1 from USP22, triggering RCAN1 ubiquitination and degradation.","method":"Co-immunoprecipitation, ubiquitination assay, E3 ligase competition assay, IFN-α treatment","journal":"Journal of cellular physiology","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP + ubiquitination assay with E3 ligase competition, single lab","pmids":["25546086"],"is_preprint":false},{"year":2022,"finding":"PRDM1 enhances USP22 transcription, and USP22 then reduces SPI1 protein degradation through deubiquitination, which enhances PD-L1 transcription in hepatocellular carcinoma, leading to CD8+ T cell exhaustion.","method":"Immunoprecipitation, ubiquitination assay, transcriptional reporter assays, in vivo HCC mouse models, PD-1 mAb combination treatment","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP + ubiquitination assay + in vivo model, single lab","pmids":["36509766"],"is_preprint":false},{"year":2005,"finding":"Human USP22 and mouse Usp22 encode 525-amino acid proteins containing conserved Cys and His catalytic domains of the UBP deubiquitinase family, and biochemical assay confirmed they possess deubiquitinating enzyme activity.","method":"Gene cloning, sequence analysis, biochemical deubiquitinase activity assay","journal":"Gene expression patterns : GEP","confidence":"Medium","confidence_rationale":"Tier 1 — direct enzymatic activity assay establishing USP22 as a functional DUB, foundational paper","pmids":["16378762"],"is_preprint":false},{"year":2021,"finding":"USP22 stabilizes the major ER chaperone HSPA5 in HER2+ breast cancer cells, actively suppressing the unfolded protein response (UPR); loss of USP22 destabilizes HSPA5, induces UPR, and sensitizes tumor cells to apoptosis and ER stress-targeting therapies.","method":"USP22 conditional KO in mouse HER2+-BC model, transcriptome analysis, HSPA5 protein stability assay, ER stress sensitivity assays","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 — genetic KO mouse model + transcriptome + protein stability readout, single lab","pmids":["34007022"],"is_preprint":false},{"year":2023,"finding":"USP22 deubiquitinates and stabilizes ZEB1, and is co-recruited with ZEB1 to the VEGFA promoter where it alters H2Bub1 levels to enhance ZEB1-mediated VEGFA transcription in hepatocellular carcinoma.","method":"Co-immunoprecipitation, ubiquitination assay, ChIP, USP22 knockdown with VEGFA and H2Bub1 readouts, in vivo xenograft model","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP + ubiquitination assay + ChIP with H2Bub1 readout, single lab","pmids":["36906615"],"is_preprint":false},{"year":2024,"finding":"The small molecule demethylzeylasteral (Dem) binds to USP22 and promotes its degradation, resulting in increased ubiquitination and proteasomal degradation of PD-L1; molecular dynamics simulations identified Leu475 and Arg419 as key residues for USP22 inhibitor binding.","method":"Structure-based virtual screening, USP22 binding assay, ubiquitination assay, PD-L1 stability assay, in vivo syngeneic tumor model, molecular dynamics simulation","journal":"Acta pharmaceutica Sinica. B","confidence":"Medium","confidence_rationale":"Tier 1–2 — direct binding assay + ubiquitination assay + molecular dynamics with residue identification + in vivo validation","pmids":["39525573"],"is_preprint":false}],"current_model":"USP22 is a catalytic deubiquitylase subunit of the human SAGA transcriptional cofactor complex that removes monoubiquitin from histones H2A and H2B to regulate transcription and chromatin state, and also acts in the cytoplasm and nucleus on a broad range of non-histone substrates—including SIRT1, cyclin D1, HIF1α, RIPK3, KPNA2, PU.1, KDM1A, PPARγ, PD-L1, PTEN, STAT1, BRCA2/PALB2, ATG5, and others—stabilizing or functionally modulating them through K48/K63/other-linkage deubiquitination to control cell cycle progression, apoptosis, DNA repair, immune signaling, and metabolic pathways."},"narrative":{"teleology":[{"year":2005,"claim":"Establishing that USP22 encodes a functional deubiquitinating enzyme provided the foundational enzymatic identity for the gene product.","evidence":"Gene cloning and biochemical deubiquitinase activity assay on recombinant human and mouse USP22","pmids":["16378762"],"confidence":"Medium","gaps":["No physiological substrate identified","No cellular context established","Catalytic domain residues not yet mapped by mutagenesis"]},{"year":2008,"claim":"Identification of USP22 as the catalytic subunit of the human SAGA complex that deubiquitylates both H2B and H2A established its primary chromatin-level function and connected it to activator-driven transcription.","evidence":"Biochemical subunit identification, in vitro deubiquitylation of defined histone substrates, ChIP showing activator-dependent recruitment, loss-of-function transcriptional assays","pmids":["18206973","18469533"],"confidence":"High","gaps":["Whether H2A and H2B deubiquitylation serve distinct transcriptional outcomes","No structural model of the DUB module on nucleosomes"]},{"year":2011,"claim":"Demonstrating that USP22 deubiquitylates the non-histone substrate FBP1 to regulate its chromatin occupancy rather than its stability, and that USP22 couples H2B deubiquitylation to RNA Pol II elongation and 3'-end processing, expanded USP22's mechanistic repertoire beyond simple histone deubiquitylation.","evidence":"RNAi knockdown with ChIP for FBP1 occupancy and H2Bub at the p21 locus; Pol II CTD Ser2P ChIP and polyadenylation cleavage assays with USP22 rescue","pmids":["21779003","22067483"],"confidence":"High","gaps":["Whether FBP1 deubiquitylation occurs within or outside the SAGA complex context","Mechanism by which H2Bub loss promotes Ser2P and CPSF73 recruitment"]},{"year":2012,"claim":"Discovery that USP22 deubiquitylates and stabilizes SIRT1, modulating p53 acetylation and apoptosis, and that Usp22 knockout causes embryonic lethality, established USP22 as a critical non-histone deubiquitylase with essential developmental roles.","evidence":"Reciprocal Co-IP, in vivo ubiquitination assay, Usp22 knockout mouse with embryonic lethality, p53 acetylation readouts","pmids":["22542455"],"confidence":"High","gaps":["Whether SIRT1 destabilization is the sole cause of lethality or whether histone-level effects contribute","Ubiquitin chain linkage on SIRT1 not defined"]},{"year":2013,"claim":"Mapping the USP22 ZnF-UBP domain as the SIRT1 interaction interface and showing that acetylation of K129 regulates DUB module association with SAGA revealed a post-translational feedback loop governing SAGA integrity.","evidence":"AP-MS interactome, domain mapping, K129 mutagenesis, in vitro deacetylation assay","pmids":["23382074"],"confidence":"High","gaps":["Identity of the acetyltransferase that modifies K129","Whether K129 acetylation status changes in response to specific signaling"]},{"year":2013,"claim":"Showing that USP22 occupies the Sox2 promoter and deubiquitylates H2Bub to repress Sox2 transcription established USP22 as a gatekeeper of the self-renewal–differentiation switch in embryonic stem cells.","evidence":"USP22 knockout/knockdown in ESCs, ChIP at Sox2 locus, differentiation assays across three germ layers","pmids":["23760504"],"confidence":"High","gaps":["How H2B deubiquitylation at Sox2 leads to repression rather than the expected activation","Whether USP22 acts via SAGA or independently at this locus"]},{"year":2015,"claim":"Active-site mutagenesis (C185S, Y513C) confirmed that USP22 catalytic activity is necessary for cell cycle regulation and for controlling levels of BMI-1, c-Myc, cyclin D2, and p53, and in vivo hypomorphic models showed roles in intestinal and neural lineage specification.","evidence":"Catalytic mutant expression in HeLa cells with cell cycle analysis; Usp22 lacZ knock-in hypomorphic mouse with histological lineage analysis","pmids":["26143114","26431380"],"confidence":"Medium","gaps":["Whether BMI-1 and c-Myc are direct substrates or indirectly affected via histone deubiquitylation","Mechanism linking USP22 reduction to altered intestinal lineage frequencies independent of global H2Bub1"]},{"year":2016,"claim":"Discovery that phosphorylated KDM1A is recruited to USP22 for deubiquitylation-dependent stabilization, leading to H3K4 demethylation and cancer stem cell gene repression, revealed a phosphorylation-gated substrate recognition mechanism.","evidence":"Co-IP, phosphorylation-site mutagenesis, ChIP for KDM1A and H3K4me2, in vivo glioblastoma xenograft","pmids":["27501329"],"confidence":"High","gaps":["Whether the GSK3β/CK1α phosphorylation switch operates in non-tumor contexts","No structural basis for phospho-dependent USP22–KDM1A recognition"]},{"year":2018,"claim":"Parallel studies established USP22's direct stabilization of cyclin D1 for G1 progression, its deubiquitylation of PU.1 to maintain myeloid differentiation, and its requirement for γH2AX formation and NHEJ during B cell class switch recombination, broadening USP22 from a transcription-focused enzyme to a regulator of cell cycle, hematopoiesis, and DNA repair.","evidence":"Cyclin D1: Co-IP, cycloheximide chase, cell cycle assays, xenograft; PU.1: conditional KO with Kras, bone marrow transplantation, PU.1 rescue; CSR: B cell-specific Usp22 KO, CSR/V(D)J assays, γH2AX and NHEJ reporters","pmids":["30224477","29844011","29520062"],"confidence":"High","gaps":["Whether cyclin D1 deubiquitylation occurs via K48-linked chains specifically","How USP22-mediated H2B deubiquitylation mechanistically promotes γH2AX and c-NHEJ"]},{"year":2019,"claim":"Identification of PALB2 as both a direct substrate and an allosteric activator of USP22 catalytic activity, together with USP22's roles in stabilizing BRCA2 and recruiting Rad51 to DSBs, placed USP22 as a dedicated facilitator of homologous recombination repair; independently, HIF1α was shown as a USP22 substrate driving HCC stemness.","evidence":"HR: in vitro catalytic stimulation assay with PALB2 WD40, Co-IP, HR reporter; HIF1α: Co-IP, ubiquitination assay, ChIP, in vivo HCC model","pmids":["31685642","31776228"],"confidence":"Medium","gaps":["No structural model for PALB2 WD40-mediated USP22 activation","Whether USP22–PALB2 interaction is regulated by DNA damage signaling","Single-lab status for both HR and HIF1α studies"]},{"year":2019,"claim":"Demonstrating that USP22 controls embryonic lethality through extra-embryonic vasculature defects involving TGFβ and RTK pathways clarified the developmental basis of the previously observed knockout lethality.","evidence":"Conditional Usp22 KO mice, endothelial/pericyte differentiation from ESCs, vessel formation assays, transcriptome analysis","pmids":["30718289"],"confidence":"High","gaps":["Specific TGFβ/RTK pathway components that are direct USP22 substrates in placental development remain unidentified"]},{"year":2020,"claim":"A set of discoveries expanded USP22's role into innate immunity and cell death: USP22 stabilizes importin KPNA2 to enable IRF3 nuclear translocation and type I IFN production, deubiquitylates RIPK3 to restrain necroptosis, interacts with MED1 to deubiquitylate H2A for iNKT cell differentiation, and stabilizes STAT1 to promote IFNγ signaling and tumor immune sensitivity.","evidence":"KPNA2: KO cell lines and conditional KO mice, reconstitution, IRF3 imaging; RIPK3: ubiquitin remnant MS, site-directed mutagenesis, necroptosis assays; MED1/H2A: Co-IP, conditional iNKT KO, substrate-specific ChIP; STAT1: CRISPR screen, Co-IP, T cell killing assay","pmids":["32130408","33369872","32069354","33601053"],"confidence":"High","gaps":["Which ubiquitin linkage on KPNA2 is removed by USP22","Whether RIPK3 deubiquitylation at K518 is K48- or K63-linked","Whether MED1-directed H2A deubiquitylation operates independently of SAGA"]},{"year":2022,"claim":"Further substrate and pathway diversification showed USP22 stabilizes PPARγ via K48-linked deubiquitylation to drive de novo lipogenesis, stabilizes ATG5 via K27/K48-linked deubiquitylation at K118 to promote autophagy and suppress NLRP3 inflammasome activation, and controls basal STING-dependent IFN-λ signaling in intestinal epithelial cells.","evidence":"PPARγ: Co-IP, K48-specific ubiquitination assay, in vivo HCC model; ATG5: K118 mutagenesis, linkage-specific assay, USP22 KO in vivo; STING: USP22 KO IEC lines, cGAMP stimulation, SARS-CoV-2 infection model","pmids":["35449157","35900990","35933402"],"confidence":"High","gaps":["Whether USP22 directly deubiquitylates STING or acts indirectly","Whether the ATG5 K118 mechanism is conserved in non-immune cells","Structural basis for K48 vs K27 linkage selectivity on different substrates"]},{"year":2024,"claim":"Identification of demethylzeylasteral as a small molecule that directly binds USP22 (at Leu475/Arg419) and promotes its degradation, increasing PD-L1 ubiquitination, provided the first chemical tool for pharmacological USP22 targeting.","evidence":"Virtual screening, direct binding assay, ubiquitination and PD-L1 stability assays, syngeneic tumor model, molecular dynamics simulation","pmids":["39525573"],"confidence":"Medium","gaps":["Binding affinity and selectivity over other USPs not rigorously established","Mechanism of USP22 degradation induction unclear","No co-crystal structure"]},{"year":null,"claim":"Despite extensive substrate cataloging, a unifying model for how USP22 substrate selectivity is determined—whether through SAGA-dependent vs. SAGA-independent modes, phosphorylation-gated recognition, or adaptor-mediated recruitment—remains unresolved, and no high-resolution structure of human USP22 or its DUB module on a nucleosome has been reported.","evidence":"","pmids":[],"confidence":"High","gaps":["No structure of human USP22 alone or in complex with nucleosome","Systematic analysis of SAGA-dependent vs. SAGA-independent substrates not performed","Relative contributions of histone vs. non-histone deubiquitylation to developmental and disease phenotypes not deconvolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,1,2,3,4,5,11,14,15,16,20,23,31]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,1,38]},{"term_id":"GO:0042393","term_label":"histone binding","supporting_discovery_ids":[0,1,8,9,18,23,40]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[0,8,18,23]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,1,3,8,9,18,20,23]},{"term_id":"GO:0005694","term_label":"chromosome","supporting_discovery_ids":[0,1,8,9,18,23,40]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[10,11]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[28]}],"pathway":[{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[0,1,8,9,18,23,40]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[0,3,8,18,23]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[5,32]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[9,20,21,33]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[2,11]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[10,19,22,24]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[15]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[8,17,34]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[14]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2,13,28,22]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,1,2,5,11,14,15]}],"complexes":["SAGA complex","SAGA DUB module"],"partners":["SIRT1","PALB2","BRCA2","KPNA2","RIPK3","KDM1A","MED1","ATXN7L3"],"other_free_text":[]},"mechanistic_narrative":"USP22 is a ubiquitin-specific protease that functions as the catalytic deubiquitylase subunit of the human SAGA transcriptional cofactor complex, where it removes monoubiquitin from histones H2A and H2B to regulate activator-driven transcription, chromatin state, RNA polymerase II elongation-coupled 3'-end processing, and DNA repair [PMID:18206973, PMID:18469533, PMID:22067483, PMID:29520062]. Beyond histones, USP22 deubiquitylates and stabilizes a broad spectrum of non-histone substrates—including SIRT1, cyclin D1, HIF1α, KDM1A, RIPK3, KPNA2, PU.1, PPARγ, ATG5, BRCA2/PALB2, and STAT1—thereby controlling cell cycle progression, apoptosis, homologous recombination, necroptosis, autophagy, innate immune signaling, and lipid metabolism [PMID:22542455, PMID:30224477, PMID:31776228, PMID:27501329, PMID:33369872, PMID:32130408, PMID:29844011, PMID:35449157, PMID:35900990, PMID:31685642, PMID:33601053]. Genetic deletion of Usp22 in mice causes embryonic lethality associated with SIRT1 destabilization and defective extra-embryonic vasculature, and conditional ablation reveals essential roles in B cell class switch recombination, iNKT cell development, intestinal lineage specification, and hematopoietic differentiation [PMID:22542455, PMID:30718289, PMID:29520062, PMID:32069354, PMID:26431380, PMID:29844011]. USP22 catalytic activity, dependent on the conserved Cys185 active site, is stimulated by interaction with PALB2's WD40 domain, and its ZnF-UBP domain mediates both SIRT1 binding and acetylation-regulated association with the SAGA core complex [PMID:26143114, PMID:31685642, PMID:23382074]."},"prefetch_data":{"uniprot":{"accession":"Q9UPT9","full_name":"Ubiquitin carboxyl-terminal hydrolase 22","aliases":["Deubiquitinating enzyme 22","Ubiquitin thioesterase 22","Ubiquitin-specific-processing protease 22"],"length_aa":525,"mass_kda":60.0,"function":"Deubiquitinase that plays a role in several cellular processes including transcriptional regulation, cell cycle progression or innate immunity. As part of the transcription regulatory histone acetylation (HAT) complex SAGA, catalyzes the deubiquitination of both histones H2A and H2B, thereby acting as a transcriptional coactivator (PubMed:18206972, PubMed:18206973, PubMed:18469533). Recruited to specific gene promoters by activators such as MYC, where it is required for transcription. Facilitates cell-cycle progression by stabilizing CCNB1 and antagonizing its proteasome-mediated degradation in a cell cycle-specific manner (PubMed:27030811). Modulates cell cycle progression and apoptosis also by antagonizing TP53 transcriptional activation through deacetylase SIRT1 stabilization (PubMed:22542455). Plays multiple roles in immunity and inflammation. Participates in antiviral response by deubiquitinating the importin KPNA2, leading to IRF3 nuclear translocation and subsequent type I interferon production (PubMed:32130408). Acts as a central regulator of type III IFN signaling by negatively regulating STING1 activation and ubiquitination (PubMed:35933402). Inhibits NLRP3 inflammasome activation by promoting NLRP3 degradation through ATG5-dependent autophagy (By similarity). Deubiquitinates CD274 to induce its stabilization and thereby participates in maintenance of immune tolerance to self (PubMed:31399419). Controls necroptotic cell death by regulating RIPK3 phosphorylation and ubiquitination (PubMed:33369872). During bacterial infection, promotes pro-inflammatory response by targeting TRAF6 and removing its 'Lys-48'-linked polyubiquitination (By similarity)","subcellular_location":"Nucleus; Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q9UPT9/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/USP22","classification":"Not Classified","n_dependent_lines":6,"n_total_lines":1208,"dependency_fraction":0.004966887417218543},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000124422","cell_line_id":"CID001774","localizations":[{"compartment":"nucleoplasm","grade":3}],"interactors":[{"gene":"ENY2","stoichiometry":10.0},{"gene":"ACTR3","stoichiometry":10.0},{"gene":"ACTR2","stoichiometry":10.0},{"gene":"ARPC1A","stoichiometry":10.0},{"gene":"ARPC2","stoichiometry":10.0},{"gene":"SUPT7L","stoichiometry":10.0},{"gene":"FAM50A","stoichiometry":4.0},{"gene":"TAF9B","stoichiometry":4.0},{"gene":"CCDC101","stoichiometry":4.0},{"gene":"ARPC5","stoichiometry":4.0}],"url":"https://opencell.sf.czbiohub.org/target/CID001774","total_profiled":1310},"omim":[{"mim_id":"619015","title":"ENY2 TRANSCRIPTION AND EXPORT COMPLEX 2 SUBUNIT; ENY2","url":"https://www.omim.org/entry/619015"},{"mim_id":"619010","title":"ATXN7-LIKE 3; ATXN7L3","url":"https://www.omim.org/entry/619010"},{"mim_id":"612116","title":"UBIQUITIN-SPECIFIC PROTEASE 22; USP22","url":"https://www.omim.org/entry/612116"},{"mim_id":"607699","title":"RING FINGER PROTEIN 20; RNF20","url":"https://www.omim.org/entry/607699"},{"mim_id":"607640","title":"ATAXIN 7; ATXN7","url":"https://www.omim.org/entry/607640"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nuclear speckles","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/USP22"},"hgnc":{"alias_symbol":["KIAA1063"],"prev_symbol":["USP3L"]},"alphafold":{"accession":"Q9UPT9","domains":[{"cath_id":"3.30.40.10","chopping":"26-140","consensus_level":"high","plddt":89.9016,"start":26,"end":140},{"cath_id":"-","chopping":"185-280","consensus_level":"medium","plddt":90.9366,"start":185,"end":280}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UPT9","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UPT9-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UPT9-F1-predicted_aligned_error_v6.png","plddt_mean":83.12},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=USP22","jax_strain_url":"https://www.jax.org/strain/search?query=USP22"},"sequence":{"accession":"Q9UPT9","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9UPT9.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9UPT9/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UPT9"}},"corpus_meta":[{"pmid":"18206973","id":"PMC_18206973","title":"The 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cofactor complex, where it deubiquitylates histone H2B to enable activator-driven transcription, and is recruited to specific genes by activators such as Myc.\",\n      \"method\": \"Biochemical subunit identification, in vitro deubiquitylation assay, chromatin immunoprecipitation, loss-of-function with transcriptional readout\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods (Co-IP, in vitro assay, ChIP, KD) in a highly-cited foundational paper\",\n      \"pmids\": [\"18206973\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"USP22, as part of the hSAGA complex, also deubiquitylates histone H2A in addition to H2B, opposing Polycomb-mediated H2A ubiquitylation.\",\n      \"method\": \"Biochemical substrate specificity assay with reconstituted histone substrates\",\n      \"journal\": \"Cell cycle (Georgetown, Tex.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro biochemical assay with defined substrates, independent follow-up of SAGA subunit discovery\",\n      \"pmids\": [\"18469533\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"USP22 interacts with and stabilizes SIRT1 by removing polyubiquitin chains from SIRT1, thereby reducing p53 acetylation and suppressing p53-dependent apoptosis; genetic deletion of Usp22 destabilizes SIRT1 and causes early embryonic lethality in mice.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, RNAi knockdown, Usp22 knockout mouse model with apoptosis and p53 acetylation readouts\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — reciprocal Co-IP, in vivo ubiquitination assay, genetic mouse model, multiple orthogonal methods\",\n      \"pmids\": [\"22542455\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"USP22 deubiquitinates the transcriptional regulator FBP1, and this deubiquitination does not alter FBP1 stability but instead promotes stable FBP1 occupancy at the p21 gene locus to regulate cell proliferation.\",\n      \"method\": \"RNAi knockdown, ubiquitination assay, chromatin immunoprecipitation, cell proliferation assays\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (KD, ubiquitination assay, ChIP) with defined molecular mechanism\",\n      \"pmids\": [\"21779003\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Phosphorylation of KDM1A (LSD1) by GSK3β and CK1α induces its binding to USP22, which then deubiquitylates and stabilizes KDM1A, leading to H3K4 demethylation and repression of BMP2, CDKN1A, and GATA6 to promote cancer stem cell self-renewal and glioblastoma tumorigenesis.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, mutagenesis of phosphorylation sites, ChIP, in vivo xenograft model\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — mechanistic epistasis with mutagenesis, Co-IP, ChIP, and in vivo validation\",\n      \"pmids\": [\"27501329\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"USP22 directly deubiquitylates cyclin D1 (CCND1), protecting it from proteasomal degradation independently of the canonical phosphorylation/ubiquitylation pathway, thereby controlling G1 cell cycle progression.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, cycloheximide chase, loss-of-function in cancer cell lines and xenograft models\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods with defined substrate and functional cell cycle readout\",\n      \"pmids\": [\"30224477\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"USP22 promotes deubiquitination and stabilization of c-Myc in breast cancer cells, increasing c-Myc protein levels and tumorigenic activity.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, USP22 knockdown/overexpression with c-Myc protein stability and colony formation readouts\",\n      \"journal\": \"Journal of cellular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP and ubiquitination assay with functional readout, single lab\",\n      \"pmids\": [\"28160502\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"USP22 is identified as a high-confidence interactor of SIRT1 via its ZnF-UBP domain; USP22 is acetylated on multiple lysines, and acetylation of K129 within the ZnF-UBP domain regulates interaction of the deubiquitinating module (DUBm) with the core SAGA complex; USP22-recruited SIRT1 promotes deacetylation of SAGA components.\",\n      \"method\": \"Comparative affinity purification-mass spectrometry, Co-IP, domain mapping, mutagenesis (H363Y SIRT1, K129 USP22), in vitro deacetylation assay\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — AP-MS interactome + mutagenesis + in vitro assay, multiple orthogonal methods\",\n      \"pmids\": [\"23382074\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"USP22 is required for embryonic stem cell differentiation; it occupies the Sox2 promoter and deubiquitylates H2Bub to repress Sox2 transcription, enabling the transition from self-renewal to lineage-specific differentiation.\",\n      \"method\": \"USP22 knockout/knockdown in ESCs, chromatin immunoprecipitation, differentiation assays across three germ layers\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — ChIP with functional differentiation readout, KO model with defined molecular mechanism\",\n      \"pmids\": [\"23760504\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Usp22, the SAGA complex deubiquitinase that removes ubiquitin from H2B-K120, is required for proper DNA break repair during class switch recombination (CSR) and V(D)J recombination; Usp22 ablation in B cells impairs γH2AX formation and classical non-homologous end joining (c-NHEJ), with CSR to IgA being less reliant on Usp22/c-NHEJ than CSR to other isotypes.\",\n      \"method\": \"Conditional B cell-specific Usp22 knockout, CSR assays, γH2AX detection, NHEJ reporter assay, V(D)J recombination assay\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with multiple orthogonal functional readouts in vivo and in vitro\",\n      \"pmids\": [\"29520062\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Cytoplasmic USP22 promotes nuclear translocation of IRF3 during viral infection by deubiquitinating and stabilizing the importin KPNA2; viral infection induces USP22-IRF3 association in a KPNA2-dependent manner, and USP22 or KPNA2 deficiency impairs IRF3 nuclear translocation and type I IFN production.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, USP22/KPNA2 KO cell lines and conditional KO mice, reconstitution of KPNA2 in KO cells, IRF3 nuclear translocation imaging\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods including KO rescue reconstitution and in vivo mouse model\",\n      \"pmids\": [\"32130408\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"USP22 controls necroptotic cell death by deubiquitinating RIPK3 at lysines 42, 351, and 518; mutation of RIPK3 K518 reduces necroptosis-associated ubiquitination and amplifies necrosome formation and necroptotic cell death.\",\n      \"method\": \"Loss-of-function (USP22 KO), ubiquitin remnant profiling by mass spectrometry, RIPK3 site-directed mutagenesis, necroptosis assays in human tumor cell lines\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — ubiquitin proteomics + mutagenesis + functional cell death assay\",\n      \"pmids\": [\"33369872\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"USP22 directly interacts with and deubiquitinates PD-L1 to inhibit its proteasomal degradation; USP22 also stabilizes CSN5 through deubiquitination, and both USP22 and CSN5 facilitate each other's interaction with PD-L1, removing K6, K11, K27, K29, K33, and K63-linked ubiquitin chains.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay with linkage-specific analysis, protein half-life assay, flow cytometry, USP22 depletion in tumor cells\",\n      \"journal\": \"Cell communication and signaling : CCS\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP and ubiquitination assay with multiple linkage types identified, single lab\",\n      \"pmids\": [\"32665011\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"USP22 deubiquitinates and stabilizes HIF1α, promoting hypoxia-induced hepatocellular carcinoma stemness and glycolysis; in TP53-mutant HCC, USP22 and HIF1α form a positive feedback loop.\",\n      \"method\": \"Immunoprecipitation, ubiquitination assay, ChIP assay, loss- and gain-of-function in HCC cells and in vivo mouse model\",\n      \"journal\": \"Gut\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP, ubiquitination assay, ChIP, in vivo validation with multiple orthogonal methods\",\n      \"pmids\": [\"31776228\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"USP22 directly interacts with, deubiquitinates (via K48-linked deubiquitination), and stabilizes PPARγ, which in turn increases ACC and ACLY expression to promote de novo fatty acid synthesis in hepatocellular carcinoma.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay (K48-linkage specific), loss-of-function, in vivo tumorigenesis experiments\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP, linkage-specific ubiquitination assay, in vivo validation, multiple orthogonal methods\",\n      \"pmids\": [\"35449157\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"USP22 suppresses NLRP3 inflammasome activation by stabilizing ATG5 through decreasing K27- and K48-linked ubiquitination at ATG5 Lys118, thereby promoting ATG5-mediated autophagy and autophagic degradation of NLRP3.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay (site-specific mutagenesis of ATG5 K118), USP22 KO/knockdown in vivo and in vitro, autophagy/NLRP3 inflammasome readouts\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — site-directed mutagenesis, linkage-specific ubiquitination assay, in vivo KO model\",\n      \"pmids\": [\"35900990\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"USP22 deficiency in hematopoietic cells expressing oncogenic Kras promotes AML transformation through impaired myeloid differentiation; USP22 functions as a PU.1 deubiquitylase that positively regulates PU.1 protein stability and PU.1 target gene expression, and PU.1 reconstitution rescues differentiation.\",\n      \"method\": \"Conditional USP22 KO mouse model with oncogenic Kras, bone marrow transplantation, ubiquitination assay, transcriptome profiling, PU.1 reconstitution rescue experiment\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with rescue experiment, ubiquitination assay, in vivo model\",\n      \"pmids\": [\"29844011\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"USP22 loss in mice causes embryonic lethality due to defects in extra-embryonic placental vasculature; USP22 deletion disrupts TGFβ and receptor tyrosine kinase signaling pathways in endothelial cells and pericytes, impairing cell survival, differentiation, and vessel formation.\",\n      \"method\": \"Usp22 conditional knockout mice, endothelial/pericyte differentiation from ESCs, vessel formation assays, transcriptome analysis\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with defined developmental phenotype and pathway analysis\",\n      \"pmids\": [\"30718289\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"USP22 is required for efficient 3'-end cleavage/polyadenylation of JAK-STAT-inducible genes; USP22 knockdown increases H2Bub levels and reduces Ser2 phosphorylation of RNA Pol II CTD and CPSF73 recruitment, implicating H2B deubiquitination in coupling transcriptional elongation to 3'-end processing.\",\n      \"method\": \"RNAi knockdown, H2Bub ChIP, RNA Pol II CTD Ser2P ChIP, polyadenylation cleavage assay, USP22 overexpression rescue\",\n      \"journal\": \"FASEB journal : official publication of the Federation of American Societies for Experimental Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple ChIP assays and functional processing assay with rescue, single lab\",\n      \"pmids\": [\"22067483\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"USP22 specifically interacts with and deubiquitinates NFATc2, stabilizing its protein levels via its deubiquitinase activity, which is required for IL-2 expression in T cells.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, USP22 knockdown in T cells with IL-2 expression readout\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP + ubiquitination assay + functional KD, single lab\",\n      \"pmids\": [\"24561192\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"USP22 interacts with and stabilizes BRCA2 and PALB2, is necessary for BRCA2, PALB2, and Rad51 recruitment to DNA double-strand breaks, and promotes homologous recombination; the interaction with PALB2's WD40 domain stimulates USP22 catalytic activity in vitro.\",\n      \"method\": \"Co-immunoprecipitation, in vitro catalytic activity assay, HR reporter assay, foci formation at DSBs, USP22 knockdown\",\n      \"journal\": \"Molecular cancer research : MCR\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro catalytic assay + Co-IP + functional HR assay, single lab\",\n      \"pmids\": [\"31685642\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"USP22 functions as a XPC deubiquitylase; depletion of USP22 sensitizes prostate cancer cells to genotoxic insult, and XPC was identified as a critical mediator of USP22-mediated survival to DNA damage through ubiquitylome analysis.\",\n      \"method\": \"USP22 overexpression/depletion, ubiquitylome profiling, genotoxic sensitivity assays, mouse adult fibroblast model\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ubiquitylome proteomics + functional KD with genotoxic readout, single lab\",\n      \"pmids\": [\"31740444\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"USP22 directly interacts with STAT1, deubiquitinates it, and improves its stability in melanoma cells; USP22 deficiency impairs IFNγ-JAK1-STAT1 signaling and reduces sensitivity to T cell-mediated killing.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, USP22 KO in mouse and human melanoma cells, genome-wide CRISPR screen, T cell killing assay\",\n      \"journal\": \"Molecular therapy : the journal of the American Society of Gene Therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — CRISPR screen + Co-IP + ubiquitination assay + functional T cell killing assay, single lab\",\n      \"pmids\": [\"33601053\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"USP22 interacts with Mediator subunit MED1 and deubiquitinates histone H2A (but not H2B) to enhance MED1-dependent transcription of IL-2Rβ and T-bet genes, controlling iNKT cell development and differentiation.\",\n      \"method\": \"Co-immunoprecipitation, USP22 conditional KO in iNKT cells, H2A/H2Bub ChIP, gene expression analysis\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP + substrate-specific ChIP + genetic KO with defined developmental phenotype, multiple orthogonal methods\",\n      \"pmids\": [\"32069354\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"USP22 controls basal STING activation and type III IFN (IFN-λ) signaling in intestinal epithelial cells; USP22-deficient cells show upregulated ISGs, increased IFN-λ secretion, and enhanced STAT1 signaling even without viral stimulation, and are protected from SARS-CoV-2 infection in a STING-dependent manner.\",\n      \"method\": \"USP22 KO intestinal epithelial cell lines, 2'3'-cGAMP stimulation assays, SARS-CoV-2 infection model, STING reconstitution/rescue experiments\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO with STING rescue and viral infection functional readout, single lab\",\n      \"pmids\": [\"35933402\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"USP22 promotes epithelial-mesenchymal transition via the FAK signaling pathway in pancreatic cancer cells, inducing Ezrin redistribution and phosphorylation, cytoskeletal remodeling, and upregulation of Snail and ZEB1.\",\n      \"method\": \"USP22 overexpression/knockdown, FAK pathway inhibition, invasion/migration assays, EMT marker analysis\",\n      \"journal\": \"Oncology reports\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — functional KD/OE with pathway readout but limited molecular mechanism for direct USP22-FAK link\",\n      \"pmids\": [\"25070659\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"USP22 interacts with MDMX and promotes its stabilization in NSCLC cells; USP22 silencing downregulates MDMX and activates the p53 pathway, and MDMX overexpression reverses USP22 silencing-induced growth arrest.\",\n      \"method\": \"Co-immunoprecipitation, USP22 shRNA knockdown, MDMX rescue experiment, p53 pathway analysis\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP + rescue experiment, single lab\",\n      \"pmids\": [\"25547493\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"USP22 directly interacts with and stabilizes COX-2 through deubiquitination; USP22 silencing reduces COX-2 protein half-life and inhibits lung carcinoma cell proliferation.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, cycloheximide chase, USP22 knockdown\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP + ubiquitination assay + half-life assay, single lab\",\n      \"pmids\": [\"25817787\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"USP22 deubiquitinates EGFR localized on late endosomes, preventing ubiquitination-mediated EGFR degradation and enhancing EGFR recycling after EGF stimulation, thereby sustaining activation of STAT3, AKT/mTOR, and MEK/ERK pathways.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, EGFR recycling assay, endosomal localization studies, USP22 knockdown with pathway readouts\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP + ubiquitination assay + subcellular localization + functional signaling readout, single lab\",\n      \"pmids\": [\"29981430\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"USP22 stabilizes BMI1 protein in gastric cancer cells through deubiquitination, promoting cancer stem cell self-renewal; TAT-BMI1 protein reconstitution rescues the stem cell properties lost upon USP22 knockdown.\",\n      \"method\": \"USP22 knockdown, BMI1 protein stability assay, TAT-BMI1 rescue experiment, sphere formation assay, xenograft model\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — protein stability assay + rescue experiment + in vivo model, single lab\",\n      \"pmids\": [\"28415621\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"USP22 deubiquitinates and stabilizes E2F6, leading to transcriptional repression of DUSP1 phosphatase, which in turn strengthens AKT activation in hepatocellular carcinoma cells.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, loss-of-function, transcriptional repression and AKT signaling readouts\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP + ubiquitination assay + defined signaling mechanism, single lab\",\n      \"pmids\": [\"34339800\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"USP22 deubiquitinates and stabilizes PTEN in pancreatic cancer, which then induces p21 (CDKN1A) expression by interacting with ANKHD1 and inhibiting ANKHD1 binding to the p21 promoter.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, USP22 overexpression, ANKHD1 interaction assay, p21 promoter binding assay\",\n      \"journal\": \"Molecular oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP + ubiquitination assay + mechanistic pathway placement, single lab\",\n      \"pmids\": [\"34743406\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The catalytic deubiquitinase activity of USP22 (abolished by C185S mutation and reduced by Y513C mutation) is necessary for regulating HeLa cell cycle progression and controlling BMI-1, c-Myc, cyclin D2, and p53 levels.\",\n      \"method\": \"Active-site mutagenesis (C185S, Y513C), cell cycle analysis, western blot of downstream targets\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — active-site mutagenesis establishing catalytic requirement, single lab\",\n      \"pmids\": [\"26143114\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"USP22 promotes homologous recombination repair by interacting with PALB2 (via its WD40 domain), which stimulates USP22 catalytic activity in vitro, and by stabilizing BRCA2 and PALB2 to enable Rad51 recruitment to DNA double-strand breaks.\",\n      \"method\": \"In vitro catalytic activity assay, Co-immunoprecipitation, HR reporter assay, foci formation assay, domain mapping\",\n      \"journal\": \"Molecular cancer research : MCR\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro reconstitution of catalytic stimulation + Co-IP + functional HR assay, single lab\",\n      \"pmids\": [\"31685642\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Reduction of Usp22 in mice impairs intestinal epithelial lineage specification and affects differentiated cell frequencies in the small intestine and brain, demonstrating a physiological role for USP22 in cell differentiation independent of global H2Bub1 changes.\",\n      \"method\": \"Usp22 hypomorphic mouse model (lacZ knock-in), histological analysis, cell lineage marker staining, H2Bub1 immunostaining\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo genetic mouse model with defined histological phenotype, single lab\",\n      \"pmids\": [\"26431380\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"USP22 deubiquitinates and stabilizes Snail1 (an EMT transcription factor) in renal tubular epithelial cells under high-glucose conditions, promoting epithelial-to-mesenchymal transition and renal tubulointerstitial fibrosis in diabetic kidney disease.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, USP22 overexpression/knockdown, deubiquitinase activity assay, in vivo db/db mouse model\",\n      \"journal\": \"European journal of pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP + ubiquitination assay + in vivo KD, single lab\",\n      \"pmids\": [\"37001578\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"USP22 positively regulates RCAN1 protein stability by direct interaction and deubiquitination, opposing the actions of FBW7, NEDD4-2, and β-TrCP E3 ligases; interferon-α treatment dissociates RCAN1 from USP22, triggering RCAN1 ubiquitination and degradation.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, E3 ligase competition assay, IFN-α treatment\",\n      \"journal\": \"Journal of cellular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP + ubiquitination assay with E3 ligase competition, single lab\",\n      \"pmids\": [\"25546086\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"PRDM1 enhances USP22 transcription, and USP22 then reduces SPI1 protein degradation through deubiquitination, which enhances PD-L1 transcription in hepatocellular carcinoma, leading to CD8+ T cell exhaustion.\",\n      \"method\": \"Immunoprecipitation, ubiquitination assay, transcriptional reporter assays, in vivo HCC mouse models, PD-1 mAb combination treatment\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP + ubiquitination assay + in vivo model, single lab\",\n      \"pmids\": [\"36509766\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Human USP22 and mouse Usp22 encode 525-amino acid proteins containing conserved Cys and His catalytic domains of the UBP deubiquitinase family, and biochemical assay confirmed they possess deubiquitinating enzyme activity.\",\n      \"method\": \"Gene cloning, sequence analysis, biochemical deubiquitinase activity assay\",\n      \"journal\": \"Gene expression patterns : GEP\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — direct enzymatic activity assay establishing USP22 as a functional DUB, foundational paper\",\n      \"pmids\": [\"16378762\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"USP22 stabilizes the major ER chaperone HSPA5 in HER2+ breast cancer cells, actively suppressing the unfolded protein response (UPR); loss of USP22 destabilizes HSPA5, induces UPR, and sensitizes tumor cells to apoptosis and ER stress-targeting therapies.\",\n      \"method\": \"USP22 conditional KO in mouse HER2+-BC model, transcriptome analysis, HSPA5 protein stability assay, ER stress sensitivity assays\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO mouse model + transcriptome + protein stability readout, single lab\",\n      \"pmids\": [\"34007022\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"USP22 deubiquitinates and stabilizes ZEB1, and is co-recruited with ZEB1 to the VEGFA promoter where it alters H2Bub1 levels to enhance ZEB1-mediated VEGFA transcription in hepatocellular carcinoma.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, ChIP, USP22 knockdown with VEGFA and H2Bub1 readouts, in vivo xenograft model\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP + ubiquitination assay + ChIP with H2Bub1 readout, single lab\",\n      \"pmids\": [\"36906615\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The small molecule demethylzeylasteral (Dem) binds to USP22 and promotes its degradation, resulting in increased ubiquitination and proteasomal degradation of PD-L1; molecular dynamics simulations identified Leu475 and Arg419 as key residues for USP22 inhibitor binding.\",\n      \"method\": \"Structure-based virtual screening, USP22 binding assay, ubiquitination assay, PD-L1 stability assay, in vivo syngeneic tumor model, molecular dynamics simulation\",\n      \"journal\": \"Acta pharmaceutica Sinica. B\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — direct binding assay + ubiquitination assay + molecular dynamics with residue identification + in vivo validation\",\n      \"pmids\": [\"39525573\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"USP22 is a catalytic deubiquitylase subunit of the human SAGA transcriptional cofactor complex that removes monoubiquitin from histones H2A and H2B to regulate transcription and chromatin state, and also acts in the cytoplasm and nucleus on a broad range of non-histone substrates—including SIRT1, cyclin D1, HIF1α, RIPK3, KPNA2, PU.1, KDM1A, PPARγ, PD-L1, PTEN, STAT1, BRCA2/PALB2, ATG5, and others—stabilizing or functionally modulating them through K48/K63/other-linkage deubiquitination to control cell cycle progression, apoptosis, DNA repair, immune signaling, and metabolic pathways.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"USP22 is a ubiquitin-specific protease that functions as the catalytic deubiquitylase subunit of the human SAGA transcriptional cofactor complex, where it removes monoubiquitin from histones H2A and H2B to regulate activator-driven transcription, chromatin state, RNA polymerase II elongation-coupled 3'-end processing, and DNA repair [PMID:18206973, PMID:18469533, PMID:22067483, PMID:29520062]. Beyond histones, USP22 deubiquitylates and stabilizes a broad spectrum of non-histone substrates—including SIRT1, cyclin D1, HIF1α, KDM1A, RIPK3, KPNA2, PU.1, PPARγ, ATG5, BRCA2/PALB2, and STAT1—thereby controlling cell cycle progression, apoptosis, homologous recombination, necroptosis, autophagy, innate immune signaling, and lipid metabolism [PMID:22542455, PMID:30224477, PMID:31776228, PMID:27501329, PMID:33369872, PMID:32130408, PMID:29844011, PMID:35449157, PMID:35900990, PMID:31685642, PMID:33601053]. Genetic deletion of Usp22 in mice causes embryonic lethality associated with SIRT1 destabilization and defective extra-embryonic vasculature, and conditional ablation reveals essential roles in B cell class switch recombination, iNKT cell development, intestinal lineage specification, and hematopoietic differentiation [PMID:22542455, PMID:30718289, PMID:29520062, PMID:32069354, PMID:26431380, PMID:29844011]. USP22 catalytic activity, dependent on the conserved Cys185 active site, is stimulated by interaction with PALB2's WD40 domain, and its ZnF-UBP domain mediates both SIRT1 binding and acetylation-regulated association with the SAGA core complex [PMID:26143114, PMID:31685642, PMID:23382074].\",\n  \"teleology\": [\n    {\n      \"year\": 2005,\n      \"claim\": \"Establishing that USP22 encodes a functional deubiquitinating enzyme provided the foundational enzymatic identity for the gene product.\",\n      \"evidence\": \"Gene cloning and biochemical deubiquitinase activity assay on recombinant human and mouse USP22\",\n      \"pmids\": [\"16378762\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No physiological substrate identified\", \"No cellular context established\", \"Catalytic domain residues not yet mapped by mutagenesis\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Identification of USP22 as the catalytic subunit of the human SAGA complex that deubiquitylates both H2B and H2A established its primary chromatin-level function and connected it to activator-driven transcription.\",\n      \"evidence\": \"Biochemical subunit identification, in vitro deubiquitylation of defined histone substrates, ChIP showing activator-dependent recruitment, loss-of-function transcriptional assays\",\n      \"pmids\": [\"18206973\", \"18469533\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether H2A and H2B deubiquitylation serve distinct transcriptional outcomes\", \"No structural model of the DUB module on nucleosomes\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Demonstrating that USP22 deubiquitylates the non-histone substrate FBP1 to regulate its chromatin occupancy rather than its stability, and that USP22 couples H2B deubiquitylation to RNA Pol II elongation and 3'-end processing, expanded USP22's mechanistic repertoire beyond simple histone deubiquitylation.\",\n      \"evidence\": \"RNAi knockdown with ChIP for FBP1 occupancy and H2Bub at the p21 locus; Pol II CTD Ser2P ChIP and polyadenylation cleavage assays with USP22 rescue\",\n      \"pmids\": [\"21779003\", \"22067483\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether FBP1 deubiquitylation occurs within or outside the SAGA complex context\", \"Mechanism by which H2Bub loss promotes Ser2P and CPSF73 recruitment\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Discovery that USP22 deubiquitylates and stabilizes SIRT1, modulating p53 acetylation and apoptosis, and that Usp22 knockout causes embryonic lethality, established USP22 as a critical non-histone deubiquitylase with essential developmental roles.\",\n      \"evidence\": \"Reciprocal Co-IP, in vivo ubiquitination assay, Usp22 knockout mouse with embryonic lethality, p53 acetylation readouts\",\n      \"pmids\": [\"22542455\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SIRT1 destabilization is the sole cause of lethality or whether histone-level effects contribute\", \"Ubiquitin chain linkage on SIRT1 not defined\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Mapping the USP22 ZnF-UBP domain as the SIRT1 interaction interface and showing that acetylation of K129 regulates DUB module association with SAGA revealed a post-translational feedback loop governing SAGA integrity.\",\n      \"evidence\": \"AP-MS interactome, domain mapping, K129 mutagenesis, in vitro deacetylation assay\",\n      \"pmids\": [\"23382074\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the acetyltransferase that modifies K129\", \"Whether K129 acetylation status changes in response to specific signaling\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Showing that USP22 occupies the Sox2 promoter and deubiquitylates H2Bub to repress Sox2 transcription established USP22 as a gatekeeper of the self-renewal–differentiation switch in embryonic stem cells.\",\n      \"evidence\": \"USP22 knockout/knockdown in ESCs, ChIP at Sox2 locus, differentiation assays across three germ layers\",\n      \"pmids\": [\"23760504\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How H2B deubiquitylation at Sox2 leads to repression rather than the expected activation\", \"Whether USP22 acts via SAGA or independently at this locus\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Active-site mutagenesis (C185S, Y513C) confirmed that USP22 catalytic activity is necessary for cell cycle regulation and for controlling levels of BMI-1, c-Myc, cyclin D2, and p53, and in vivo hypomorphic models showed roles in intestinal and neural lineage specification.\",\n      \"evidence\": \"Catalytic mutant expression in HeLa cells with cell cycle analysis; Usp22 lacZ knock-in hypomorphic mouse with histological lineage analysis\",\n      \"pmids\": [\"26143114\", \"26431380\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether BMI-1 and c-Myc are direct substrates or indirectly affected via histone deubiquitylation\", \"Mechanism linking USP22 reduction to altered intestinal lineage frequencies independent of global H2Bub1\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Discovery that phosphorylated KDM1A is recruited to USP22 for deubiquitylation-dependent stabilization, leading to H3K4 demethylation and cancer stem cell gene repression, revealed a phosphorylation-gated substrate recognition mechanism.\",\n      \"evidence\": \"Co-IP, phosphorylation-site mutagenesis, ChIP for KDM1A and H3K4me2, in vivo glioblastoma xenograft\",\n      \"pmids\": [\"27501329\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the GSK3β/CK1α phosphorylation switch operates in non-tumor contexts\", \"No structural basis for phospho-dependent USP22–KDM1A recognition\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Parallel studies established USP22's direct stabilization of cyclin D1 for G1 progression, its deubiquitylation of PU.1 to maintain myeloid differentiation, and its requirement for γH2AX formation and NHEJ during B cell class switch recombination, broadening USP22 from a transcription-focused enzyme to a regulator of cell cycle, hematopoiesis, and DNA repair.\",\n      \"evidence\": \"Cyclin D1: Co-IP, cycloheximide chase, cell cycle assays, xenograft; PU.1: conditional KO with Kras, bone marrow transplantation, PU.1 rescue; CSR: B cell-specific Usp22 KO, CSR/V(D)J assays, γH2AX and NHEJ reporters\",\n      \"pmids\": [\"30224477\", \"29844011\", \"29520062\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether cyclin D1 deubiquitylation occurs via K48-linked chains specifically\", \"How USP22-mediated H2B deubiquitylation mechanistically promotes γH2AX and c-NHEJ\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identification of PALB2 as both a direct substrate and an allosteric activator of USP22 catalytic activity, together with USP22's roles in stabilizing BRCA2 and recruiting Rad51 to DSBs, placed USP22 as a dedicated facilitator of homologous recombination repair; independently, HIF1α was shown as a USP22 substrate driving HCC stemness.\",\n      \"evidence\": \"HR: in vitro catalytic stimulation assay with PALB2 WD40, Co-IP, HR reporter; HIF1α: Co-IP, ubiquitination assay, ChIP, in vivo HCC model\",\n      \"pmids\": [\"31685642\", \"31776228\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model for PALB2 WD40-mediated USP22 activation\", \"Whether USP22–PALB2 interaction is regulated by DNA damage signaling\", \"Single-lab status for both HR and HIF1α studies\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Demonstrating that USP22 controls embryonic lethality through extra-embryonic vasculature defects involving TGFβ and RTK pathways clarified the developmental basis of the previously observed knockout lethality.\",\n      \"evidence\": \"Conditional Usp22 KO mice, endothelial/pericyte differentiation from ESCs, vessel formation assays, transcriptome analysis\",\n      \"pmids\": [\"30718289\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific TGFβ/RTK pathway components that are direct USP22 substrates in placental development remain unidentified\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"A set of discoveries expanded USP22's role into innate immunity and cell death: USP22 stabilizes importin KPNA2 to enable IRF3 nuclear translocation and type I IFN production, deubiquitylates RIPK3 to restrain necroptosis, interacts with MED1 to deubiquitylate H2A for iNKT cell differentiation, and stabilizes STAT1 to promote IFNγ signaling and tumor immune sensitivity.\",\n      \"evidence\": \"KPNA2: KO cell lines and conditional KO mice, reconstitution, IRF3 imaging; RIPK3: ubiquitin remnant MS, site-directed mutagenesis, necroptosis assays; MED1/H2A: Co-IP, conditional iNKT KO, substrate-specific ChIP; STAT1: CRISPR screen, Co-IP, T cell killing assay\",\n      \"pmids\": [\"32130408\", \"33369872\", \"32069354\", \"33601053\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which ubiquitin linkage on KPNA2 is removed by USP22\", \"Whether RIPK3 deubiquitylation at K518 is K48- or K63-linked\", \"Whether MED1-directed H2A deubiquitylation operates independently of SAGA\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Further substrate and pathway diversification showed USP22 stabilizes PPARγ via K48-linked deubiquitylation to drive de novo lipogenesis, stabilizes ATG5 via K27/K48-linked deubiquitylation at K118 to promote autophagy and suppress NLRP3 inflammasome activation, and controls basal STING-dependent IFN-λ signaling in intestinal epithelial cells.\",\n      \"evidence\": \"PPARγ: Co-IP, K48-specific ubiquitination assay, in vivo HCC model; ATG5: K118 mutagenesis, linkage-specific assay, USP22 KO in vivo; STING: USP22 KO IEC lines, cGAMP stimulation, SARS-CoV-2 infection model\",\n      \"pmids\": [\"35449157\", \"35900990\", \"35933402\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether USP22 directly deubiquitylates STING or acts indirectly\", \"Whether the ATG5 K118 mechanism is conserved in non-immune cells\", \"Structural basis for K48 vs K27 linkage selectivity on different substrates\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identification of demethylzeylasteral as a small molecule that directly binds USP22 (at Leu475/Arg419) and promotes its degradation, increasing PD-L1 ubiquitination, provided the first chemical tool for pharmacological USP22 targeting.\",\n      \"evidence\": \"Virtual screening, direct binding assay, ubiquitination and PD-L1 stability assays, syngeneic tumor model, molecular dynamics simulation\",\n      \"pmids\": [\"39525573\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Binding affinity and selectivity over other USPs not rigorously established\", \"Mechanism of USP22 degradation induction unclear\", \"No co-crystal structure\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Despite extensive substrate cataloging, a unifying model for how USP22 substrate selectivity is determined—whether through SAGA-dependent vs. SAGA-independent modes, phosphorylation-gated recognition, or adaptor-mediated recruitment—remains unresolved, and no high-resolution structure of human USP22 or its DUB module on a nucleosome has been reported.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structure of human USP22 alone or in complex with nucleosome\", \"Systematic analysis of SAGA-dependent vs. SAGA-independent substrates not performed\", \"Relative contributions of histone vs. non-histone deubiquitylation to developmental and disease phenotypes not deconvolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 2, 3, 4, 5, 11, 14, 15, 16, 20, 23, 31]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 1, 38]},\n      {\"term_id\": \"GO:0042393\", \"supporting_discovery_ids\": [0, 1, 8, 9, 18, 23, 40]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [0, 8, 18, 23]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 1, 3, 8, 9, 18, 20, 23]},\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [0, 1, 8, 9, 18, 23, 40]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [10, 11]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [28]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [0, 1, 8, 9, 18, 23, 40]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 3, 8, 18, 23]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [5, 32]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [9, 20, 21, 33]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [2, 11]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [10, 19, 22, 24]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [15]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [8, 17, 34]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [14]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 13, 28, 22]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 1, 2, 5, 11, 14, 15]}\n    ],\n    \"complexes\": [\n      \"SAGA complex\",\n      \"SAGA DUB module\"\n    ],\n    \"partners\": [\n      \"SIRT1\",\n      \"PALB2\",\n      \"BRCA2\",\n      \"KPNA2\",\n      \"RIPK3\",\n      \"KDM1A\",\n      \"MED1\",\n      \"ATXN7L3\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}