{"gene":"XAF1","run_date":"2026-06-11T09:02:06","timeline":{"discoveries":[{"year":2001,"finding":"XAF1 binds directly to XIAP and antagonizes XIAP's anti-caspase activity and anti-apoptotic function. XAF1 expression triggers redistribution of XIAP from the cytosol to the nucleus.","method":"Yeast two-hybrid screening, co-immunoprecipitation, in vitro apoptosis and caspase activity assays, subcellular fractionation/immunofluorescence","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal binding demonstrated, functional caspase antagonism shown in vitro, subcellular redistribution confirmed by direct imaging; foundational study replicated by multiple subsequent labs","pmids":["11175744"],"is_preprint":false},{"year":2000,"finding":"Overexpressed XAF1 blocks both the caspase-inhibiting and anti-apoptotic activities of XIAP. XAF1 encodes a zinc finger protein of ~34 kDa.","method":"Yeast two-hybrid, overexpression in cells with caspase activity and apoptosis assays","journal":"Genomics","confidence":"High","confidence_rationale":"Tier 2 / Strong — functional overexpression assays with multiple readouts, replicated by independent lab (PMID 11175744)","pmids":["11087668"],"is_preprint":false},{"year":2007,"finding":"XAF1 binds XIAP, cIAP1, cIAP2, Livin, TsIAP, and NAIP (but not Survivin directly). The XAF1-XIAP complex activates XIAP's E3 ubiquitin ligase (RING) activity to ubiquitinate and degrade Survivin via the proteasome. IFN-β induction forms an endogenous XIAP-XAF1-Survivin ternary complex facilitating Survivin degradation.","method":"Co-immunoprecipitation, proteasome inhibitor (MG132) rescue, XIAP RING mutant, siRNA knockdown of XIAP, XAF1-/- stable clones, immunoprecipitation of endogenous complex","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods including genetic rescue, dominant-negative mutant, and stable KO lines in a single study","pmids":["17613533"],"is_preprint":false},{"year":2007,"finding":"XAF1 promotes TNF-α-induced apoptosis by translocating to the mitochondria, promoting XIAP inactivation through a mitochondrial pathway. XAF1 overexpression also sensitizes trophoblast cells to Fas-mediated apoptosis.","method":"XAF1 overexpression, subcellular fractionation, apoptosis assays, siRNA knockdown; confocal microscopy for localization","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization experiment with functional consequence, single lab with two orthogonal methods","pmids":["17329253"],"is_preprint":false},{"year":2006,"finding":"XAF1 expression is activated by STAT1 binding to an interferon-stimulated response element (ISRE) located at -55 to -66 nt upstream of the first ATG of XAF1 gene. IFN-β induces XAF1 expression through this STAT1-ISRE interaction; STAT1 knockdown or blockade of its phosphorylation abolishes induction.","method":"Luciferase reporter assay, EMSA, chromatin immunoprecipitation, siRNA knockdown of STAT1","journal":"Cancer letters","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (reporter, EMSA, ChIP, siRNA) in one study establishing the mechanism","pmids":["18035482"],"is_preprint":false},{"year":2006,"finding":"All-trans retinoic acid (ATRA) induces XAF1 expression via IRF-1 binding to an IRF-E element located at -30 to -38 nt upstream of the XAF1 ATG. Site-directed mutagenesis of IRF-E-XAF1 abolishes promoter activity and IRF-1 binding.","method":"Luciferase reporter assay, EMSA, chromatin immunoprecipitation, site-directed mutagenesis","journal":"Gastroenterology","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis combined with EMSA and ChIP confirms the mechanistic element","pmids":["16530516"],"is_preprint":false},{"year":2005,"finding":"HSF1 represses XAF1 transcription by binding to a heat-shock element in the XAF1 promoter (-862/-821 nt region). Inactivation of this element by mutation or HSF1 inhibitor restores XAF1 promoter activity.","method":"Luciferase reporter assay, EMSA, chromatin immunoprecipitation, site-directed mutagenesis, HSF1 overexpression/siRNA","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis + ChIP + EMSA in one study, multiple independent approaches confirm the element","pmids":["16303760"],"is_preprint":false},{"year":2009,"finding":"XAF1 interacts with and activates checkpoint kinase 1 (Chk1), leading to inactivation of Cdc25C and subsequently the Cdc2-cyclin B complex, causing G2/M cell cycle arrest. XAF1 is predominantly expressed in G2/M phase. Chk1 suppression abrogates XAF1-induced G2/M arrest.","method":"Co-immunoprecipitation, kinase assay, immunoblotting, cell cycle synchronization, siRNA knockdown of Chk1, flow cytometry","journal":"Carcinogenesis","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus kinase assay plus epistasis (Chk1 knockdown rescue), single lab","pmids":["19628579"],"is_preprint":false},{"year":2006,"finding":"XAF1 expression elevated p53 protein stability and its target gene expression, and the apoptosis-sensitizing function of XAF1 was markedly impeded by blockade of p53 function, placing XAF1 upstream of p53-mediated apoptotic stress response.","method":"Overexpression, immunoblotting, siRNA/dominant-negative p53 epistasis, flow cytometry for apoptosis","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis established by p53 blockade rescue, single lab with multiple apoptotic readouts","pmids":["16909101"],"is_preprint":false},{"year":2012,"finding":"XAF1 has a distinct domain organization with a compact N-terminal domain (NTD), middle domain (MD), a 42-residue unstructured linker, and a C-terminal domain (CTD). A XIAP RING-binding domain (XAF1 RBD) is located at the C-terminal portion (Thr251-Ser301) with a dissociation constant of ~18 μM for XIAP RING. Interaction of XAF1 RBD with XIAP RING is required for XIAP-mediated ubiquitination of XAF1.","method":"Limited proteolysis, peptide mass fingerprinting, NMR spectroscopy (interaction mapping), in vitro ubiquitination assay","journal":"Protein science","confidence":"High","confidence_rationale":"Tier 1 / Strong — NMR structural mapping combined with in vitro ubiquitination assay and biochemical domain characterization in one study","pmids":["22811387"],"is_preprint":false},{"year":2014,"finding":"XAF1 binds directly to the N-terminal proline-rich domain of p53 via zinc finger domain 6, interfering with MDM2 binding and ubiquitination of p53. XAF1 also stimulates HIPK2-mediated Ser-46 phosphorylation of p53 by blocking Siah2-mediated HIPK2 ubiquitination. XAF1 further activates ZNF313, a p21(WAF1)-targeting ubiquitin E3 ligase, via zinc finger domain 7. XAF1 interacts with p53, Siah2, and ZNF313 through zinc finger domains 5, 6, and 7, respectively.","method":"Co-immunoprecipitation, domain mutagenesis (truncated/domain-deleted XAF1 mutants), in vitro ubiquitination assays, immunoblotting, reporter assays, xenograft tumor studies","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — domain mutagenesis + in vitro ubiquitination + multiple Co-IPs with mechanistic rescue in vivo","pmids":["25313037"],"is_preprint":false},{"year":2018,"finding":"XAF1 forms a positive feedback loop with IRF-1: XAF1 binds to the multifunctional domain 2 (MFD2) of IRF-1 via zinc finger domain 6, blocking CHIP-mediated ubiquitination and degradation of IRF-1, thereby stabilizing and activating IRF-1. XAF1 also functions as a transcriptional coactivator of IRF-1 on proapoptotic gene promoters. Oncogenic Ras/ERK signaling represses XAF1 transcription to disrupt this loop.","method":"Co-immunoprecipitation, domain mutagenesis, ubiquitination assays, chromatin immunoprecipitation, luciferase reporter, IRF-1 knockdown epistasis, xenograft tumor studies","journal":"Cell death & disease","confidence":"High","confidence_rationale":"Tier 1 / Strong — domain mutagenesis + ubiquitination assay + ChIP + epistasis, replicated in vivo","pmids":["30042418"],"is_preprint":false},{"year":2017,"finding":"XAF1 directly interacts with metallothionein 2A (MT2A) and facilitates its lysosomal degradation, raising free intracellular zinc levels and activating p53 and inactivating XIAP. MT2A in turn destabilizes XAF1 protein via lysosomal pathway, establishing mutual antagonism. XAF1 is a transcriptional target of MTF-1. Wild-type but not MT2A binding-deficient mutant XAF1 increases free zinc and drives p53 activation.","method":"Co-immunoprecipitation, domain mutagenesis (MT2A binding-deficient XAF1), lysosomal pathway inhibition, intracellular zinc measurement, p53 activity assays, xenograft studies","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — domain mutant combined with multiple pathway readouts and in vivo validation in one rigorous study","pmids":["28507149"],"is_preprint":false},{"year":2014,"finding":"The XIAP-XAF1 complex degrades Chk1 via K48-linked ubiquitination through a CUL4A/DDB1-based E3 ubiquitin ligase. Without XAF1, XIAP stabilizes Chk1; when XAF1 is present, XIAP facilitates Chk1 degradation. Depletion of CUL4A or DDB1 prevents XIAP-XAF1-mediated Chk1 degradation.","method":"Co-immunoprecipitation, siRNA knockdown of CUL4A/DDB1, ubiquitination assays, immunoblotting, cell viability after irradiation","journal":"Cancer biology & therapy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus siRNA epistasis plus ubiquitination evidence, single lab","pmids":["25535897"],"is_preprint":false},{"year":2011,"finding":"XAF1 induces autophagy through upregulation of Beclin-1 expression and inhibition of the Akt/p70S6K pathway. Beclin-1 knockdown or 3-methyladenine suppressed XAF1-induced autophagy but enhanced XAF1-induced apoptosis, indicating crosstalk between autophagy and apoptosis downstream of XAF1.","method":"Adenovirus-mediated overexpression, siRNA knockdown of Beclin-1, pharmacological inhibition (3-MA, caspase inhibitor), immunoblotting, immunofluorescence, xenograft","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic (siRNA) and pharmacological epistasis, single lab with multiple orthogonal readouts","pmids":["21788101"],"is_preprint":false},{"year":2011,"finding":"XAF1 is a transcriptional target of wild-type p53: p53 binds a responsive element (-95 to -86 nt) in the XAF1 promoter to suppress XAF1 transcription. Reciprocally, overexpressed XAF1 activates wild-type p53 via post-translational modification (enhanced nuclear accumulation and transcriptional activity), forming a feedback loop.","method":"Chromatin immunoprecipitation (ChIP) for p53 binding, site-directed mutagenesis, luciferase reporter assay, siRNA knockdown of p53, immunoblotting","journal":"Molecular carcinogenesis","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP plus mutagenesis establishes direct regulatory interaction, single lab","pmids":["21678496"],"is_preprint":false},{"year":2014,"finding":"p300-dependent acetylation of IRF-1 promotes XAF1 gene activation. IRF-1 binds to the XAF1 promoter and this binding is enhanced by p300-mediated IRF-1 acetylation; two acetylation sites on IRF-1 were identified.","method":"Chromatin immunoprecipitation, in vivo and in vitro acetylation assays, siRNA knockdown of p300/IRF-1/XAF1 in cells and in vivo (Thy-1 nephritis rat model), luciferase reporter assay","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP plus in vivo silencing plus acetylation assay, single lab with multiple orthogonal methods","pmids":["24743731"],"is_preprint":false},{"year":2022,"finding":"XAF1 destabilizes GRP78 (ER stress sensor) through assembly of a ZNF313-mediated destruction complex. XAF1 also destabilizes CHIP ubiquitin E3 ligase, thereby blocking CHIP-mediated K63-linked ubiquitination and subsequent phosphorylation of IRE1α involved in adaptive ER stress response. XAF1 transcription is activated through PERK-Nrf2 signaling. XAF1-/- tumors show reduced response to ER stress inducers.","method":"Co-immunoprecipitation, ubiquitination assays (K63-specific), genetic KO/overexpression, immunoblotting, xenograft tumor assays, correlation in primary breast carcinomas","journal":"Cell death & disease","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple Co-IPs, specific ubiquitin-chain analysis, genetic KO rescue, in vivo validation in one study","pmids":["35902580"],"is_preprint":false},{"year":2023,"finding":"XAF1 functions as an adaptor of valosin-containing protein (VCP) and facilitates VCP-mediated deubiquitination of the E3 ligase RNF114. Stabilized RNF114 promotes K48-linked ubiquitination and degradation of junction plakoglobin (JUP), driving CRC cell migration and metastasis.","method":"Co-immunoprecipitation, ubiquitination assays (K48-specific), protein stability assays, migration/invasion assays, xenograft models, clinical sample correlation","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple Co-IPs with specific ubiquitin-chain analysis, in vivo validation and clinical correlation in one rigorous study","pmids":["38095639"],"is_preprint":false},{"year":2023,"finding":"Upon RNA virus infection, MAVS recruits XAF1 and TBK1; TBK1 phosphorylates XAF1 at serine-252 and promotes its nuclear translocation. Nuclear XAF1 interacts with TRIM28 guided by IRF1 at antiviral gene loci, and XAF1 de-SUMOylates TRIM28 via its PHD domain, increasing chromatin accessibility and inducing antiviral gene transcription. XAF1-deficient mice are susceptible to RNA virus infection.","method":"Co-immunoprecipitation, phosphorylation site mapping, nuclear translocation assays (imaging), SUMO modification assays, chromatin accessibility assays (ATAC-seq type), XAF1-deficient mouse model, domain mutagenesis (PHD domain)","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 2 / Strong — phosphorylation site identified, domain mutagenesis, de-SUMOylation assay, in vivo KO validation, multiple orthogonal methods","pmids":["37595039"],"is_preprint":false},{"year":2022,"finding":"XAF1 stabilizes IRF1 by antagonizing CHIP-mediated degradation of IRF1, forming a positive feedback loop to induce antiviral gene expression (DDX58, DDX60, MX1, OAS2). XAF1 knockout attenuates antiviral innate immunity in vitro and in vivo; XAF1-KO mice show more severe lung injury and higher mortality upon influenza infection.","method":"Co-immunoprecipitation, protein stability assays, XAF1 KO (cell lines and mice), overexpression, immunoblotting, antiviral gene induction assays, in vivo influenza infection model","journal":"Journal of virology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO in vivo plus mechanistic Co-IP and stability assays, replicated concept from PMID 30042418","pmids":["35972291"],"is_preprint":false},{"year":2022,"finding":"XAF1 associates specifically with IRF7 and inhibits XIAP activity. The XAF1-XIAP axis controls the activity of KLHL22, an adaptor of the BTB-CUL3-RBX1 E3 ligase complex via a ubiquitin-dependent pathway. CUL3-KLHL22 directly targets IRF7 for K48-linked ubiquitination and proteasomal degradation, thus preventing hyperproduction of type I IFN. XAF1-KO and XIAP-transgenic mice display resistance to viral infection with elevated IFN-I production.","method":"Co-immunoprecipitation, K48-ubiquitination assays, XAF1-KO mice, XIAP-transgenic mice, viral infection models, immunoblotting","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — Co-IP with K48-specific ubiquitination, multiple mouse genetic models, replicated across KO and transgenic in one study","pmids":["36394357"],"is_preprint":false},{"year":2023,"finding":"XAF1 directly interacts with the N-terminal region of AKT1, blocking K63-linked poly-ubiquitination and subsequent AKT activation. Xaf1 knockout in mice causes AKT activation in muscle and fat tissues and reduces body weight gain and insulin resistance on high-fat diet. FOXO1 transcriptionally activates XAF1, forming a negative feedback loop with AKT1.","method":"Co-immunoprecipitation/pulldown, K63-ubiquitination assays, Xaf1 KO mice, Pten heterozygous mouse model, orthotopic tumorigenesis assay, domain mutant (P277L), luciferase reporter for FOXO1-XAF1 axis","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct binding, K63-ubiquitination assay, multiple in vivo mouse models, cancer-derived mutant used as control, single rigorous study","pmids":["37384528"],"is_preprint":false},{"year":2022,"finding":"XAF1 destabilizes estrogen receptor α (ERα) through assembly of a BRCA1-mediated destruction complex; XAF1 interacts with ERα and BRCA1 via zinc finger domains 5/6 and 4, respectively. Mutants lacking ZF5/6 or ZF4 fail to drive ERα ubiquitination. XAF1 is activated by E2 through a GPER (G protein-coupled estrogen receptor)-mediated non-genomic pathway, and ERα represses XAF1 for E2-driven proliferation.","method":"Co-immunoprecipitation, domain mutagenesis (ZF4/5/6 deletion mutants), ubiquitination assays, XAF1+/+ and XAF1-/- xenograft tumor models, immunoblotting, promoter methylation analysis","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 1 / Strong — domain mutagenesis + ubiquitination assay + genetic KO/restoration in vivo in one rigorous study","pmids":["35430604"],"is_preprint":false},{"year":2022,"finding":"XAF1 is translocated into mitochondria to stimulate ROS production and ATM-AMPK signaling, directing autophagic flux toward apoptosis in response to temozolomide. A mutant XAF1 lacking zinc finger domain 6 fails to localize to mitochondria and cannot activate ROS-ATM-AMPK signaling or autophagy-mediated apoptosis.","method":"Mitochondrial fractionation, domain mutagenesis (ZF6 deletion), ROS measurement, ATM-AMPK pathway immunoblotting, flow cytometry, XAF1-restored xenograft tumors","journal":"Neuro-oncology advances","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — domain mutagenesis plus mitochondrial localization assay with functional readout, single lab","pmids":["35274103"],"is_preprint":false},{"year":2024,"finding":"XAF1 interacts with RING domains of TRIM28 and ZNF313 via zinc finger domains ZF6 and ZF7, respectively, facilitating ZNF313-induced K48-linked ubiquitination and proteasomal degradation of TRIM28. By destabilizing TRIM28, XAF1 blocks TRIM28-mediated ubiquitination of p53 and RLIM, prevents p53-HDAC1 interaction, and blocks TWIST1 stabilization. Conversely, TRIM28 ubiquitinates XAF1 via K48-linked polyubiquitination to protect tumor cells from apoptosis.","method":"Co-immunoprecipitation, domain mutagenesis (ZF6 and ZF7 deletion mutants), K48-ubiquitination assays, immunoblotting, invasion/EMT assays, xenograft tumor studies","journal":"Molecular biomedicine","confidence":"High","confidence_rationale":"Tier 1 / Strong — domain mutagenesis + K48-specific ubiquitination assay + multiple functional readouts + in vivo validation in one rigorous study","pmids":["39532800"],"is_preprint":false},{"year":2024,"finding":"XAF1 depletion in osteoclasts decreases apoptosis by facilitating the interaction between XIAP and caspase-3/7, thereby promoting osteoclastogenesis. Activation of XAF1 with a XIAP inhibitor suppresses osteoclast formation. Global and chimeric Xaf1 KO mouse models show increased osteoclast number and enhanced bone resorption.","method":"Xaf1 global and chimeric KO mouse models (OVX and osteolysis), in vitro osteoclast differentiation, Co-IP of XIAP-caspase-3/7, caspase activity assays, bone histomorphometry","journal":"Journal of orthopaedic translation","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO mouse model in two disease models plus mechanistic Co-IP establishing XIAP-caspase interaction","pmids":["38957269"],"is_preprint":false},{"year":2006,"finding":"XAF1 can induce apoptosis and cooperate with TNF-α via the mitochondrial pathway (cytochrome c release, blocked by Bcl2) independently of XIAP interaction. In Saos-2 cells, no interaction between Xaf1 and XIAP was detected; Xaf1 also sensitizes XIAP-/- fibroblasts to TNF-α.","method":"Inducible overexpression, cytochrome c release assay, Bcl2 overexpression rescue, XIAP-/- fibroblasts (genetic epistasis), no Xaf1-XIAP interaction detected by co-IP","journal":"Molecular and cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with XIAP-KO cells plus cytochrome c release assay, single lab; note negative finding (no XIAP interaction in this cellular context) is mechanistically informative","pmids":["16432762"],"is_preprint":false},{"year":2008,"finding":"JNK1 upregulates XAF1 expression through induction of IRF-1, which then binds to the IRF-E within the XAF1 promoter. Site mutation of IRF-E or IRF-1 siRNA abrogates JNK1-induced XAF1 transcription.","method":"JNK1 wild-type/dominant-negative constructs, siRNA knockdown of IRF-1, luciferase reporter with mutated IRF-E, RT-PCR and immunoblotting","journal":"Carcinogenesis","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis plus reporter mutagenesis, single lab with multiple orthogonal methods","pmids":["19056926"],"is_preprint":false},{"year":2015,"finding":"CTCF binds the XAF1 promoter in a methylation-sensitive manner and maintains open chromatin configuration, inhibiting CpG methylation and repressive histone modifications. Loss of CTCF binding leads to XAF1 epigenetic silencing.","method":"Chromatin immunoprecipitation, transgene reporter assays, methylation-sensitive CTCF binding experiments","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP plus transgene assay, single lab with two orthogonal methods","pmids":["26443201"],"is_preprint":false},{"year":2019,"finding":"SARM1 deficiency leads to strong selective overexpression of XAF1 in prion-infected mice, resulting in increased pro-apoptotic caspase activity and neuronal death, exacerbating prion disease. SARM1 thus acts as a regulator suppressing XAF1-mediated neuronal apoptosis.","method":"SARM1-/- mouse model with prion infection, whole-transcriptome analysis, caspase activity assays, neuronal death quantification","journal":"The Journal of experimental medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO mouse model with transcriptome identification plus functional caspase readout, single study","pmids":["30842236"],"is_preprint":false},{"year":2012,"finding":"XAF1 interacts with XIAP during dengue virus (DENV2) infection as confirmed by co-immunoprecipitation and co-localization by confocal microscopy. XAF1 knockdown reduces caspase-3/8/9 and PARP expression, while XAF1 overexpression upregulates them, establishing a role for XAF1 in promoting apoptosis in DENV2-infected vascular endothelial cells.","method":"Co-immunoprecipitation with anti-XAF1 antibody, confocal microscopy co-localization, siRNA knockdown, overexpression, immunoblotting","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — Co-IP plus confocal localization plus loss/gain-of-function, single lab; co-IP evidence is confirmatory of known interaction","pmids":["23207547"],"is_preprint":false},{"year":2024,"finding":"TRIM47 interacts with XAF1 and promotes its ubiquitination and proteasomal degradation. TRIM47 overexpression causes XAF1-dependent suppression of apoptosis and autophagy in HNSCC cells; XAF1 overexpression reverses the proliferative effect of TRIM47 overexpression.","method":"Co-immunoprecipitation, ubiquitination assays, overexpression/knockdown, autophagy inhibitor rescue, xenograft tumor model","journal":"iScience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus ubiquitination assay plus genetic epistasis (XAF1 overexpression rescue), single lab","pmids":["39834862"],"is_preprint":false},{"year":2024,"finding":"XAF1 is secreted from stressed cancer cells via an unconventional endo-lysosomal trafficking pathway; zinc finger domain 4 (ZF4) is essential for this secretion. Secreted XAF1 is internalized into T cells via clathrin-mediated endocytosis and directly interacts with and phosphorylates Lck (lymphocyte-specific protein tyrosine kinase), activating RAF-MEK-ERK signaling and stimulating T cell proliferation, migration, and tumor infiltration.","method":"Subcellular fractionation, ZF4 domain mutant, clathrin-mediated endocytosis inhibition, Lck co-immunoprecipitation/phosphorylation assay, ERK signaling readouts, Xaf1+/+ vs Xaf1-/- xenograft with IFN-γ and recombinant XAF1 injection","journal":"Neoplasia","confidence":"High","confidence_rationale":"Tier 2 / Strong — domain mutagenesis + direct kinase interaction/phosphorylation assay + genetic KO rescue with recombinant protein in vivo, multiple orthogonal methods in single study","pmids":["39615106"],"is_preprint":false},{"year":2025,"finding":"Xaf1 orchestrates PANoptosis in cochlear hair cells through direct interaction with and transcriptional regulation of ZBP1, placing Xaf1 hierarchically upstream of ZBP1 in the PANoptosis signaling cascade. Xaf1 knockdown via AAV-based gene delivery in cochlear hair cells reduces neomycin-induced ototoxicity.","method":"Single-nucleus RNA sequencing, overexpression and knockdown assays in vitro, AAV-based in vivo Xaf1 knockdown, ZBP1 interaction and transcriptional regulation assays","journal":"Cell proliferation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct interaction + transcriptional regulation assay + in vivo KD with functional rescue, single lab","pmids":["40600354"],"is_preprint":false}],"current_model":"XAF1 is a stress-inducible, multi-functional tumor suppressor and interferon-stimulated gene whose protein product contains seven zinc finger (ZF) domains that mediate distinct protein-protein interactions: it directly binds and antagonizes XIAP (via its C-terminal RING-binding domain), activates XIAP's E3 ubiquitin ligase activity to degrade Survivin, blocks MDM2-mediated ubiquitination and CHIP-mediated degradation of p53 and IRF-1 to form positive feedback loops, facilitates ZNF313-mediated destruction of TRIM28 and GRP78, destabilizes ERα through a BRCA1 destruction complex, acts as a VCP adaptor to stabilize RNF114 and degrade JUP promoting CRC metastasis, blocks K63-linked AKT ubiquitination to inhibit AKT activation, de-SUMOylates TRIM28 in the nucleus to open chromatin at antiviral gene loci, modulates the CUL3-KLHL22-IRF7 axis to prevent IFN-I hyperproduction, and is itself regulated at the transcriptional level by STAT1/ISRE, IRF-1/IRF-E, HSF1, JNK1, ERK, TGF-β1, p53, FOXO1, and CTCF, as well as by promoter CpG methylation; it can also be secreted to activate Lck-ERK signaling in T cells, and is degraded by TRIM28, TRIM47, and XIAP-mediated ubiquitination, collectively placing XAF1 as a multi-valent molecular switch integrating apoptotic, cell cycle, ER stress, autophagy, innate immune, and metabolic stress responses."},"narrative":{"mechanistic_narrative":"XAF1 is a stress-inducible, zinc-finger tumor suppressor that integrates apoptotic, cell-cycle, ER-stress, autophagy, and innate-immune programs by acting as a multivalent scaffold and regulator of protein ubiquitination [PMID:11175744, PMID:25313037, PMID:35902580]. It was first defined as a direct XIAP-binding antagonist that neutralizes XIAP's caspase-inhibitory and anti-apoptotic activity and drives XIAP redistribution from cytosol to nucleus [PMID:11175744, PMID:11087668], with the interaction mapped to a C-terminal XIAP-RING-binding domain [PMID:22811387]; beyond inhibition, XAF1 converts the XIAP-XAF1 complex into an active E3 ligase that ubiquitinates and degrades Survivin and, via a CUL4A/DDB1 complex, Chk1 [PMID:17613533, PMID:25535897]. Its discrete zinc-finger domains confer distinct interactions that reprogram ubiquitin-dependent stability of key regulators: XAF1 binds p53 (ZF6) to block MDM2-mediated ubiquitination and engages Siah2 and ZNF313 (ZF5/ZF7) to stabilize p53 and activate p21 turnover [PMID:25313037], stabilizes IRF-1 by blocking CHIP-mediated degradation while serving as its transcriptional coactivator [PMID:30042418], and uses ZF6/ZF7 to drive ZNF313-mediated K48 degradation of TRIM28, thereby relieving TRIM28-dependent p53 ubiquitination [PMID:39532800]. XAF1 also assembles a BRCA1 destruction complex to degrade ERα via ZF4 and ZF5/6 [PMID:35430604], destabilizes GRP78 and CHIP during ER stress [PMID:35902580], blocks K63-linked ubiquitination and activation of AKT1 [PMID:37384528], and acts as a VCP adaptor stabilizing RNF114 to degrade JUP and promote colorectal metastasis [PMID:38095639]. In innate immunity, MAVS- and TBK1-dependent phosphorylation at Ser252 drives nuclear XAF1, where it de-SUMOylates TRIM28 via its PHD domain to open antiviral chromatin and stabilizes IRF1, while the XAF1-XIAP axis restrains the CUL3-KLHL22-IRF7 module to prevent type-I IFN hyperproduction [PMID:37595039, PMID:35972291, PMID:36394357]. XAF1 transcription is tightly controlled, induced by STAT1/ISRE and IRF-1/IRF-E and repressed by HSF1 and p53 [PMID:18035482, PMID:16530516, PMID:16303760, PMID:21678496]. XAF1 is itself a degradation target of TRIM28 and TRIM47 [PMID:39532800, PMID:39834862]. Functional consequences established in vivo include regulation of apoptosis and metabolic insulin signaling, osteoclastogenesis, and antiviral defense [PMID:37384528, PMID:38957269, PMID:36394357].","teleology":[{"year":2001,"claim":"Established XAF1's founding molecular identity: a direct XIAP-interacting protein that antagonizes XIAP's anti-caspase and anti-apoptotic function, answering what XAF1 does at the protein level.","evidence":"Yeast two-hybrid, co-IP, in vitro caspase/apoptosis assays, subcellular fractionation in cells","pmids":["11175744","11087668"],"confidence":"High","gaps":["Did not map the interaction interface","Mechanism of XIAP nuclear redistribution unresolved"]},{"year":2007,"claim":"Showed XAF1 not only inhibits but reprograms XIAP into an active E3 ligase that degrades Survivin, expanding XAF1 from antagonist to a switch that redirects IAP catalytic activity.","evidence":"Co-IP, MG132 rescue, XIAP RING mutant, siRNA and XAF1-/- clones, endogenous ternary complex IP","pmids":["17613533"],"confidence":"High","gaps":["IAP binding selectivity rules not defined","How XAF1 selects Survivin as substrate unclear"]},{"year":2009,"claim":"Linked XAF1 to cell-cycle control by showing it activates Chk1 to enforce G2/M arrest, broadening its role beyond apoptosis.","evidence":"Co-IP, kinase assay, cell-cycle synchronization, Chk1 siRNA epistasis, flow cytometry","pmids":["19628579"],"confidence":"Medium","gaps":["Single lab","Reconciliation with later XAF1-XIAP-mediated Chk1 degradation not addressed"]},{"year":2012,"claim":"Defined XAF1's domain architecture and mapped a C-terminal XIAP RING-binding domain, providing the structural basis for XIAP engagement and reciprocal XAF1 ubiquitination.","evidence":"Limited proteolysis, NMR interaction mapping, in vitro ubiquitination assay","pmids":["22811387"],"confidence":"High","gaps":["Full-length structure not solved","Functions of individual zinc fingers not yet assigned"]},{"year":2014,"claim":"Resolved how individual zinc fingers confer substrate-specific control of p53 stability and activity, establishing XAF1 as a domain-encoded ubiquitination regulator.","evidence":"Co-IP, domain-deletion mutants, in vitro ubiquitination, reporters, xenografts (p53/Siah2/ZNF313); CUL4A/DDB1 siRNA epistasis for Chk1 degradation","pmids":["25313037","25535897"],"confidence":"High","gaps":["Stoichiometry of multi-partner complexes unknown","Context determining Chk1 stabilization vs degradation undefined"]},{"year":2018,"claim":"Established a XAF1-IRF-1 positive feedback loop in which XAF1 blocks CHIP-mediated IRF-1 degradation and coactivates IRF-1 transcription, repressed by oncogenic Ras/ERK.","evidence":"Co-IP, domain mutagenesis, ubiquitination assays, ChIP, reporters, IRF-1 knockdown epistasis, xenografts","pmids":["30042418"],"confidence":"High","gaps":["Direct coactivator mechanism on chromatin not detailed"]},{"year":2022,"claim":"Demonstrated XAF1's reach across ER stress, estrogen signaling, and antiviral type-I IFN control, showing it tunes diverse substrate degradation programs and prevents IFN hyperproduction.","evidence":"Co-IP, chain-specific ubiquitination assays, domain mutants, genetic KO/transgenic mice, viral infection and xenograft models (GRP78/CHIP, ERα/BRCA1, IRF1, CUL3-KLHL22-IRF7)","pmids":["35902580","35430604","35972291","36394357"],"confidence":"High","gaps":["How a single protein coordinates these distinct complexes in different compartments is unresolved"]},{"year":2023,"claim":"Revealed signal-induced nuclear and metabolic functions: TBK1 phosphorylation drives nuclear XAF1 to de-SUMOylate TRIM28 and open antiviral chromatin, XAF1 blocks K63-ubiquitination of AKT1, and acts as a VCP adaptor controlling metastasis.","evidence":"Phospho-site mapping, de-SUMOylation and ATAC-type assays, K63/K48 ubiquitination assays, VCP adaptor co-IP, multiple KO mouse and xenograft models (TRIM28/IRF1, AKT1/FOXO1, RNF114/JUP)","pmids":["37595039","37384528","38095639"],"confidence":"High","gaps":["Catalytic basis of XAF1 de-SUMOylation activity not characterized","How cytosolic vs nuclear pools are partitioned unclear"]},{"year":2024,"claim":"Extended XAF1 to non-cell-autonomous and tissue-specific roles, including secretion that activates Lck-ERK in T cells, ZNF313-driven TRIM28 degradation, and control of osteoclast apoptosis.","evidence":"ZF-domain mutants, secretion/endocytosis assays, Lck phosphorylation, K48 ubiquitination, global/chimeric Xaf1 KO mice (secreted XAF1, TRIM28, osteoclast XIAP-caspase)","pmids":["39615106","39532800","38957269"],"confidence":"High","gaps":["Mechanism of unconventional secretion incompletely defined","Physiological scope of secreted XAF1 signaling unknown"]},{"year":null,"claim":"How XAF1's seven zinc fingers are dynamically partitioned among its many partners and compartments to specify which program (apoptosis, IFN, ER stress, metabolism) is engaged in a given stress context remains unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No integrated structural model of multi-partner selection","Quantitative rules governing compartment-specific function lacking"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[2,10,17,25,19]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,2,21,22]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[18,11]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[11,34]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,19]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[3,24]}],"pathway":[{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[0,2,27]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[19,20,21]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[17,24]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[14,24]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[7,13]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[22,33]}],"complexes":["XIAP-XAF1 complex","ZNF313-mediated destruction complex","BRCA1 destruction complex"],"partners":["XIAP","TRIM28","IRF1","TP53","ZNF313","AKT1","VCP","ESR1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q6GPH4","full_name":"XIAP-associated factor 1","aliases":["BIRC4-binding protein"],"length_aa":301,"mass_kda":34.6,"function":"Seems to function as a negative regulator of members of the IAP (inhibitor of apoptosis protein) family. Inhibits anti-caspase activity of BIRC4. Induces cleavage and inactivation of BIRC4 independent of caspase activation. Mediates TNF-induced apoptosis and is involved in apoptosis in trophoblast cells. May inhibit BIRC4 indirectly by activating the mitochondrial apoptosis pathway. After translocation to mitochondria, promotes translocation of BAX to mitochondria and cytochrome c release from mitochondria. Seems to promote the redistribution of BIRC4 from the cytoplasm to the nucleus, probably independent of BIRC4 inactivation which seems to occur in the cytoplasm. The BIRC4-XAF1 complex mediates down-regulation of BIRC5/survivin; the process requires the E3 ligase activity of BIRC4. Seems to be involved in cellular sensitivity to the proapoptotic actions of TRAIL. May be a tumor suppressor by mediating apoptosis resistance of cancer cells","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/Q6GPH4/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/XAF1","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/XAF1","total_profiled":1310},"omim":[{"mim_id":"617108","title":"SESSILE SERRATED POLYPOSIS CANCER SYNDROME; SSPCS","url":"https://www.omim.org/entry/617108"},{"mim_id":"607732","title":"STERILE ALPHA AND TIR MOTIFS-CONTAINING PROTEIN 1; SARM1","url":"https://www.omim.org/entry/607732"},{"mim_id":"606717","title":"XIAP-ASSOCIATED FACTOR 1; XAF1","url":"https://www.omim.org/entry/606717"},{"mim_id":"605878","title":"ZINC FINGER- AND BTB DOMAIN-CONTAINING PROTEIN 7A; ZBTB7A","url":"https://www.omim.org/entry/605878"},{"mim_id":"604959","title":"PHORBOL-12-MYRISTATE-13-ACETATE-INDUCED PROTEIN 1; PMAIP1","url":"https://www.omim.org/entry/604959"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Mitochondria","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/XAF1"},"hgnc":{"alias_symbol":["BIRC4BP","XIAPAF1","HSXIAPAF1"],"prev_symbol":[]},"alphafold":{"accession":"Q6GPH4","domains":[{"cath_id":"3.30.40","chopping":"2-55","consensus_level":"medium","plddt":91.5015,"start":2,"end":55},{"cath_id":"-","chopping":"87-136","consensus_level":"medium","plddt":88.5,"start":87,"end":136},{"cath_id":"3.30.160","chopping":"56-83","consensus_level":"medium","plddt":91.4086,"start":56,"end":83}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6GPH4","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q6GPH4-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q6GPH4-F1-predicted_aligned_error_v6.png","plddt_mean":72.69},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=XAF1","jax_strain_url":"https://www.jax.org/strain/search?query=XAF1"},"sequence":{"accession":"Q6GPH4","fasta_url":"https://rest.uniprot.org/uniprotkb/Q6GPH4.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q6GPH4/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6GPH4"}},"corpus_meta":[{"pmid":"11175744","id":"PMC_11175744","title":"Identification 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apoptosis.","date":"2022","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/35430604","citation_count":6,"is_preprint":false},{"pmid":"15843754","id":"PMC_15843754","title":"[Frequent epigenetic inactivation of XAF1 by promotor hypermethylation in human colon cancers].","date":"2005","source":"The Korean journal of gastroenterology = Taehan Sohwagi Hakhoe chi","url":"https://pubmed.ncbi.nlm.nih.gov/15843754","citation_count":6,"is_preprint":false},{"pmid":"37384528","id":"PMC_37384528","title":"Identification of XAF1 as an endogenous AKT inhibitor.","date":"2023","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/37384528","citation_count":5,"is_preprint":false},{"pmid":"35829914","id":"PMC_35829914","title":"XAF1 overexpression exacerbates diabetes by promoting pancreatic β-cell apoptosis.","date":"2022","source":"Acta 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ubiquitination.","date":"2024","source":"iScience","url":"https://pubmed.ncbi.nlm.nih.gov/39834862","citation_count":3,"is_preprint":false},{"pmid":"35517406","id":"PMC_35517406","title":"WZY-321 triggers glioma cell apoptosis via XAF1 up-regulation caused by MTM-mediated miR-873 down-regulation.","date":"2022","source":"Journal of Cancer","url":"https://pubmed.ncbi.nlm.nih.gov/35517406","citation_count":3,"is_preprint":false},{"pmid":"23358741","id":"PMC_23358741","title":"Assessment of XAF1 as A Biomarker to Differentiate Hepatocellular Carcinoma from Nonneoplastic Liver Tissues.","date":"2012","source":"Chinese journal of cancer research = Chung-kuo yen cheng yen chiu","url":"https://pubmed.ncbi.nlm.nih.gov/23358741","citation_count":3,"is_preprint":false},{"pmid":"22944270","id":"PMC_22944270","title":"[Relationship between methylation status of promoter and expression of XAF1 gene in papillary thyroid carcinoma].","date":"2012","source":"Zhonghua yi xue za zhi","url":"https://pubmed.ncbi.nlm.nih.gov/22944270","citation_count":3,"is_preprint":false},{"pmid":"36819813","id":"PMC_36819813","title":"Li-Fraumeni-associated pancreatic neuroendocrine tumour and XAF1 p.Glu134Ter risk modifier variant.","date":"2022","source":"Ecancermedicalscience","url":"https://pubmed.ncbi.nlm.nih.gov/36819813","citation_count":3,"is_preprint":false},{"pmid":"40600354","id":"PMC_40600354","title":"Single-Nucleus Transcriptomics Uncovers Xaf1-Driven PANoptosis as a Therapeutic Target in Aminoglycoside-Induced Hearing Loss.","date":"2025","source":"Cell proliferation","url":"https://pubmed.ncbi.nlm.nih.gov/40600354","citation_count":2,"is_preprint":false},{"pmid":"38520543","id":"PMC_38520543","title":"XAF1 overexpression inhibits the malignant progression and cisplatin resistance of NSCLC by activating endoplasmic reticulum stress.","date":"2024","source":"Molecular biology 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University","url":"https://pubmed.ncbi.nlm.nih.gov/17884799","citation_count":1,"is_preprint":false},{"pmid":"27121136","id":"PMC_27121136","title":"Adenovirus encoding XAF-1 and TNF‑α in the same open reading frame efficiently inhibits hepatocellular cancer cells.","date":"2016","source":"Molecular medicine reports","url":"https://pubmed.ncbi.nlm.nih.gov/27121136","citation_count":1,"is_preprint":false},{"pmid":"41692347","id":"PMC_41692347","title":"Gamabufotalin impedes NSCLC progression by inhibiting the mitochondrial factor CHCHD2 and modulating XAF1 expression.","date":"2026","source":"Biochemical pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/41692347","citation_count":0,"is_preprint":false},{"pmid":"42029946","id":"PMC_42029946","title":"XAF1 nonsense mutation rs117407731 enhances lung adenocarcinoma susceptibility via apoptosis suppression.","date":"2026","source":"Molecular genetics and genomics : 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XAF1 expression triggers redistribution of XIAP from the cytosol to the nucleus.\",\n      \"method\": \"Yeast two-hybrid screening, co-immunoprecipitation, in vitro apoptosis and caspase activity assays, subcellular fractionation/immunofluorescence\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal binding demonstrated, functional caspase antagonism shown in vitro, subcellular redistribution confirmed by direct imaging; foundational study replicated by multiple subsequent labs\",\n      \"pmids\": [\"11175744\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Overexpressed XAF1 blocks both the caspase-inhibiting and anti-apoptotic activities of XIAP. XAF1 encodes a zinc finger protein of ~34 kDa.\",\n      \"method\": \"Yeast two-hybrid, overexpression in cells with caspase activity and apoptosis assays\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — functional overexpression assays with multiple readouts, replicated by independent lab (PMID 11175744)\",\n      \"pmids\": [\"11087668\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"XAF1 binds XIAP, cIAP1, cIAP2, Livin, TsIAP, and NAIP (but not Survivin directly). The XAF1-XIAP complex activates XIAP's E3 ubiquitin ligase (RING) activity to ubiquitinate and degrade Survivin via the proteasome. IFN-β induction forms an endogenous XIAP-XAF1-Survivin ternary complex facilitating Survivin degradation.\",\n      \"method\": \"Co-immunoprecipitation, proteasome inhibitor (MG132) rescue, XIAP RING mutant, siRNA knockdown of XIAP, XAF1-/- stable clones, immunoprecipitation of endogenous complex\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods including genetic rescue, dominant-negative mutant, and stable KO lines in a single study\",\n      \"pmids\": [\"17613533\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"XAF1 promotes TNF-α-induced apoptosis by translocating to the mitochondria, promoting XIAP inactivation through a mitochondrial pathway. XAF1 overexpression also sensitizes trophoblast cells to Fas-mediated apoptosis.\",\n      \"method\": \"XAF1 overexpression, subcellular fractionation, apoptosis assays, siRNA knockdown; confocal microscopy for localization\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization experiment with functional consequence, single lab with two orthogonal methods\",\n      \"pmids\": [\"17329253\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"XAF1 expression is activated by STAT1 binding to an interferon-stimulated response element (ISRE) located at -55 to -66 nt upstream of the first ATG of XAF1 gene. IFN-β induces XAF1 expression through this STAT1-ISRE interaction; STAT1 knockdown or blockade of its phosphorylation abolishes induction.\",\n      \"method\": \"Luciferase reporter assay, EMSA, chromatin immunoprecipitation, siRNA knockdown of STAT1\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (reporter, EMSA, ChIP, siRNA) in one study establishing the mechanism\",\n      \"pmids\": [\"18035482\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"All-trans retinoic acid (ATRA) induces XAF1 expression via IRF-1 binding to an IRF-E element located at -30 to -38 nt upstream of the XAF1 ATG. Site-directed mutagenesis of IRF-E-XAF1 abolishes promoter activity and IRF-1 binding.\",\n      \"method\": \"Luciferase reporter assay, EMSA, chromatin immunoprecipitation, site-directed mutagenesis\",\n      \"journal\": \"Gastroenterology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis combined with EMSA and ChIP confirms the mechanistic element\",\n      \"pmids\": [\"16530516\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"HSF1 represses XAF1 transcription by binding to a heat-shock element in the XAF1 promoter (-862/-821 nt region). Inactivation of this element by mutation or HSF1 inhibitor restores XAF1 promoter activity.\",\n      \"method\": \"Luciferase reporter assay, EMSA, chromatin immunoprecipitation, site-directed mutagenesis, HSF1 overexpression/siRNA\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis + ChIP + EMSA in one study, multiple independent approaches confirm the element\",\n      \"pmids\": [\"16303760\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"XAF1 interacts with and activates checkpoint kinase 1 (Chk1), leading to inactivation of Cdc25C and subsequently the Cdc2-cyclin B complex, causing G2/M cell cycle arrest. XAF1 is predominantly expressed in G2/M phase. Chk1 suppression abrogates XAF1-induced G2/M arrest.\",\n      \"method\": \"Co-immunoprecipitation, kinase assay, immunoblotting, cell cycle synchronization, siRNA knockdown of Chk1, flow cytometry\",\n      \"journal\": \"Carcinogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus kinase assay plus epistasis (Chk1 knockdown rescue), single lab\",\n      \"pmids\": [\"19628579\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"XAF1 expression elevated p53 protein stability and its target gene expression, and the apoptosis-sensitizing function of XAF1 was markedly impeded by blockade of p53 function, placing XAF1 upstream of p53-mediated apoptotic stress response.\",\n      \"method\": \"Overexpression, immunoblotting, siRNA/dominant-negative p53 epistasis, flow cytometry for apoptosis\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis established by p53 blockade rescue, single lab with multiple apoptotic readouts\",\n      \"pmids\": [\"16909101\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"XAF1 has a distinct domain organization with a compact N-terminal domain (NTD), middle domain (MD), a 42-residue unstructured linker, and a C-terminal domain (CTD). A XIAP RING-binding domain (XAF1 RBD) is located at the C-terminal portion (Thr251-Ser301) with a dissociation constant of ~18 μM for XIAP RING. Interaction of XAF1 RBD with XIAP RING is required for XIAP-mediated ubiquitination of XAF1.\",\n      \"method\": \"Limited proteolysis, peptide mass fingerprinting, NMR spectroscopy (interaction mapping), in vitro ubiquitination assay\",\n      \"journal\": \"Protein science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — NMR structural mapping combined with in vitro ubiquitination assay and biochemical domain characterization in one study\",\n      \"pmids\": [\"22811387\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"XAF1 binds directly to the N-terminal proline-rich domain of p53 via zinc finger domain 6, interfering with MDM2 binding and ubiquitination of p53. XAF1 also stimulates HIPK2-mediated Ser-46 phosphorylation of p53 by blocking Siah2-mediated HIPK2 ubiquitination. XAF1 further activates ZNF313, a p21(WAF1)-targeting ubiquitin E3 ligase, via zinc finger domain 7. XAF1 interacts with p53, Siah2, and ZNF313 through zinc finger domains 5, 6, and 7, respectively.\",\n      \"method\": \"Co-immunoprecipitation, domain mutagenesis (truncated/domain-deleted XAF1 mutants), in vitro ubiquitination assays, immunoblotting, reporter assays, xenograft tumor studies\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — domain mutagenesis + in vitro ubiquitination + multiple Co-IPs with mechanistic rescue in vivo\",\n      \"pmids\": [\"25313037\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"XAF1 forms a positive feedback loop with IRF-1: XAF1 binds to the multifunctional domain 2 (MFD2) of IRF-1 via zinc finger domain 6, blocking CHIP-mediated ubiquitination and degradation of IRF-1, thereby stabilizing and activating IRF-1. XAF1 also functions as a transcriptional coactivator of IRF-1 on proapoptotic gene promoters. Oncogenic Ras/ERK signaling represses XAF1 transcription to disrupt this loop.\",\n      \"method\": \"Co-immunoprecipitation, domain mutagenesis, ubiquitination assays, chromatin immunoprecipitation, luciferase reporter, IRF-1 knockdown epistasis, xenograft tumor studies\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — domain mutagenesis + ubiquitination assay + ChIP + epistasis, replicated in vivo\",\n      \"pmids\": [\"30042418\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"XAF1 directly interacts with metallothionein 2A (MT2A) and facilitates its lysosomal degradation, raising free intracellular zinc levels and activating p53 and inactivating XIAP. MT2A in turn destabilizes XAF1 protein via lysosomal pathway, establishing mutual antagonism. XAF1 is a transcriptional target of MTF-1. Wild-type but not MT2A binding-deficient mutant XAF1 increases free zinc and drives p53 activation.\",\n      \"method\": \"Co-immunoprecipitation, domain mutagenesis (MT2A binding-deficient XAF1), lysosomal pathway inhibition, intracellular zinc measurement, p53 activity assays, xenograft studies\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — domain mutant combined with multiple pathway readouts and in vivo validation in one rigorous study\",\n      \"pmids\": [\"28507149\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The XIAP-XAF1 complex degrades Chk1 via K48-linked ubiquitination through a CUL4A/DDB1-based E3 ubiquitin ligase. Without XAF1, XIAP stabilizes Chk1; when XAF1 is present, XIAP facilitates Chk1 degradation. Depletion of CUL4A or DDB1 prevents XIAP-XAF1-mediated Chk1 degradation.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown of CUL4A/DDB1, ubiquitination assays, immunoblotting, cell viability after irradiation\",\n      \"journal\": \"Cancer biology & therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus siRNA epistasis plus ubiquitination evidence, single lab\",\n      \"pmids\": [\"25535897\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"XAF1 induces autophagy through upregulation of Beclin-1 expression and inhibition of the Akt/p70S6K pathway. Beclin-1 knockdown or 3-methyladenine suppressed XAF1-induced autophagy but enhanced XAF1-induced apoptosis, indicating crosstalk between autophagy and apoptosis downstream of XAF1.\",\n      \"method\": \"Adenovirus-mediated overexpression, siRNA knockdown of Beclin-1, pharmacological inhibition (3-MA, caspase inhibitor), immunoblotting, immunofluorescence, xenograft\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic (siRNA) and pharmacological epistasis, single lab with multiple orthogonal readouts\",\n      \"pmids\": [\"21788101\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"XAF1 is a transcriptional target of wild-type p53: p53 binds a responsive element (-95 to -86 nt) in the XAF1 promoter to suppress XAF1 transcription. Reciprocally, overexpressed XAF1 activates wild-type p53 via post-translational modification (enhanced nuclear accumulation and transcriptional activity), forming a feedback loop.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP) for p53 binding, site-directed mutagenesis, luciferase reporter assay, siRNA knockdown of p53, immunoblotting\",\n      \"journal\": \"Molecular carcinogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP plus mutagenesis establishes direct regulatory interaction, single lab\",\n      \"pmids\": [\"21678496\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"p300-dependent acetylation of IRF-1 promotes XAF1 gene activation. IRF-1 binds to the XAF1 promoter and this binding is enhanced by p300-mediated IRF-1 acetylation; two acetylation sites on IRF-1 were identified.\",\n      \"method\": \"Chromatin immunoprecipitation, in vivo and in vitro acetylation assays, siRNA knockdown of p300/IRF-1/XAF1 in cells and in vivo (Thy-1 nephritis rat model), luciferase reporter assay\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP plus in vivo silencing plus acetylation assay, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"24743731\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"XAF1 destabilizes GRP78 (ER stress sensor) through assembly of a ZNF313-mediated destruction complex. XAF1 also destabilizes CHIP ubiquitin E3 ligase, thereby blocking CHIP-mediated K63-linked ubiquitination and subsequent phosphorylation of IRE1α involved in adaptive ER stress response. XAF1 transcription is activated through PERK-Nrf2 signaling. XAF1-/- tumors show reduced response to ER stress inducers.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assays (K63-specific), genetic KO/overexpression, immunoblotting, xenograft tumor assays, correlation in primary breast carcinomas\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple Co-IPs, specific ubiquitin-chain analysis, genetic KO rescue, in vivo validation in one study\",\n      \"pmids\": [\"35902580\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"XAF1 functions as an adaptor of valosin-containing protein (VCP) and facilitates VCP-mediated deubiquitination of the E3 ligase RNF114. Stabilized RNF114 promotes K48-linked ubiquitination and degradation of junction plakoglobin (JUP), driving CRC cell migration and metastasis.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assays (K48-specific), protein stability assays, migration/invasion assays, xenograft models, clinical sample correlation\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple Co-IPs with specific ubiquitin-chain analysis, in vivo validation and clinical correlation in one rigorous study\",\n      \"pmids\": [\"38095639\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Upon RNA virus infection, MAVS recruits XAF1 and TBK1; TBK1 phosphorylates XAF1 at serine-252 and promotes its nuclear translocation. Nuclear XAF1 interacts with TRIM28 guided by IRF1 at antiviral gene loci, and XAF1 de-SUMOylates TRIM28 via its PHD domain, increasing chromatin accessibility and inducing antiviral gene transcription. XAF1-deficient mice are susceptible to RNA virus infection.\",\n      \"method\": \"Co-immunoprecipitation, phosphorylation site mapping, nuclear translocation assays (imaging), SUMO modification assays, chromatin accessibility assays (ATAC-seq type), XAF1-deficient mouse model, domain mutagenesis (PHD domain)\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — phosphorylation site identified, domain mutagenesis, de-SUMOylation assay, in vivo KO validation, multiple orthogonal methods\",\n      \"pmids\": [\"37595039\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"XAF1 stabilizes IRF1 by antagonizing CHIP-mediated degradation of IRF1, forming a positive feedback loop to induce antiviral gene expression (DDX58, DDX60, MX1, OAS2). XAF1 knockout attenuates antiviral innate immunity in vitro and in vivo; XAF1-KO mice show more severe lung injury and higher mortality upon influenza infection.\",\n      \"method\": \"Co-immunoprecipitation, protein stability assays, XAF1 KO (cell lines and mice), overexpression, immunoblotting, antiviral gene induction assays, in vivo influenza infection model\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO in vivo plus mechanistic Co-IP and stability assays, replicated concept from PMID 30042418\",\n      \"pmids\": [\"35972291\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"XAF1 associates specifically with IRF7 and inhibits XIAP activity. The XAF1-XIAP axis controls the activity of KLHL22, an adaptor of the BTB-CUL3-RBX1 E3 ligase complex via a ubiquitin-dependent pathway. CUL3-KLHL22 directly targets IRF7 for K48-linked ubiquitination and proteasomal degradation, thus preventing hyperproduction of type I IFN. XAF1-KO and XIAP-transgenic mice display resistance to viral infection with elevated IFN-I production.\",\n      \"method\": \"Co-immunoprecipitation, K48-ubiquitination assays, XAF1-KO mice, XIAP-transgenic mice, viral infection models, immunoblotting\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — Co-IP with K48-specific ubiquitination, multiple mouse genetic models, replicated across KO and transgenic in one study\",\n      \"pmids\": [\"36394357\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"XAF1 directly interacts with the N-terminal region of AKT1, blocking K63-linked poly-ubiquitination and subsequent AKT activation. Xaf1 knockout in mice causes AKT activation in muscle and fat tissues and reduces body weight gain and insulin resistance on high-fat diet. FOXO1 transcriptionally activates XAF1, forming a negative feedback loop with AKT1.\",\n      \"method\": \"Co-immunoprecipitation/pulldown, K63-ubiquitination assays, Xaf1 KO mice, Pten heterozygous mouse model, orthotopic tumorigenesis assay, domain mutant (P277L), luciferase reporter for FOXO1-XAF1 axis\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct binding, K63-ubiquitination assay, multiple in vivo mouse models, cancer-derived mutant used as control, single rigorous study\",\n      \"pmids\": [\"37384528\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"XAF1 destabilizes estrogen receptor α (ERα) through assembly of a BRCA1-mediated destruction complex; XAF1 interacts with ERα and BRCA1 via zinc finger domains 5/6 and 4, respectively. Mutants lacking ZF5/6 or ZF4 fail to drive ERα ubiquitination. XAF1 is activated by E2 through a GPER (G protein-coupled estrogen receptor)-mediated non-genomic pathway, and ERα represses XAF1 for E2-driven proliferation.\",\n      \"method\": \"Co-immunoprecipitation, domain mutagenesis (ZF4/5/6 deletion mutants), ubiquitination assays, XAF1+/+ and XAF1-/- xenograft tumor models, immunoblotting, promoter methylation analysis\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — domain mutagenesis + ubiquitination assay + genetic KO/restoration in vivo in one rigorous study\",\n      \"pmids\": [\"35430604\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"XAF1 is translocated into mitochondria to stimulate ROS production and ATM-AMPK signaling, directing autophagic flux toward apoptosis in response to temozolomide. A mutant XAF1 lacking zinc finger domain 6 fails to localize to mitochondria and cannot activate ROS-ATM-AMPK signaling or autophagy-mediated apoptosis.\",\n      \"method\": \"Mitochondrial fractionation, domain mutagenesis (ZF6 deletion), ROS measurement, ATM-AMPK pathway immunoblotting, flow cytometry, XAF1-restored xenograft tumors\",\n      \"journal\": \"Neuro-oncology advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — domain mutagenesis plus mitochondrial localization assay with functional readout, single lab\",\n      \"pmids\": [\"35274103\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"XAF1 interacts with RING domains of TRIM28 and ZNF313 via zinc finger domains ZF6 and ZF7, respectively, facilitating ZNF313-induced K48-linked ubiquitination and proteasomal degradation of TRIM28. By destabilizing TRIM28, XAF1 blocks TRIM28-mediated ubiquitination of p53 and RLIM, prevents p53-HDAC1 interaction, and blocks TWIST1 stabilization. Conversely, TRIM28 ubiquitinates XAF1 via K48-linked polyubiquitination to protect tumor cells from apoptosis.\",\n      \"method\": \"Co-immunoprecipitation, domain mutagenesis (ZF6 and ZF7 deletion mutants), K48-ubiquitination assays, immunoblotting, invasion/EMT assays, xenograft tumor studies\",\n      \"journal\": \"Molecular biomedicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — domain mutagenesis + K48-specific ubiquitination assay + multiple functional readouts + in vivo validation in one rigorous study\",\n      \"pmids\": [\"39532800\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"XAF1 depletion in osteoclasts decreases apoptosis by facilitating the interaction between XIAP and caspase-3/7, thereby promoting osteoclastogenesis. Activation of XAF1 with a XIAP inhibitor suppresses osteoclast formation. Global and chimeric Xaf1 KO mouse models show increased osteoclast number and enhanced bone resorption.\",\n      \"method\": \"Xaf1 global and chimeric KO mouse models (OVX and osteolysis), in vitro osteoclast differentiation, Co-IP of XIAP-caspase-3/7, caspase activity assays, bone histomorphometry\",\n      \"journal\": \"Journal of orthopaedic translation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO mouse model in two disease models plus mechanistic Co-IP establishing XIAP-caspase interaction\",\n      \"pmids\": [\"38957269\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"XAF1 can induce apoptosis and cooperate with TNF-α via the mitochondrial pathway (cytochrome c release, blocked by Bcl2) independently of XIAP interaction. In Saos-2 cells, no interaction between Xaf1 and XIAP was detected; Xaf1 also sensitizes XIAP-/- fibroblasts to TNF-α.\",\n      \"method\": \"Inducible overexpression, cytochrome c release assay, Bcl2 overexpression rescue, XIAP-/- fibroblasts (genetic epistasis), no Xaf1-XIAP interaction detected by co-IP\",\n      \"journal\": \"Molecular and cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with XIAP-KO cells plus cytochrome c release assay, single lab; note negative finding (no XIAP interaction in this cellular context) is mechanistically informative\",\n      \"pmids\": [\"16432762\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"JNK1 upregulates XAF1 expression through induction of IRF-1, which then binds to the IRF-E within the XAF1 promoter. Site mutation of IRF-E or IRF-1 siRNA abrogates JNK1-induced XAF1 transcription.\",\n      \"method\": \"JNK1 wild-type/dominant-negative constructs, siRNA knockdown of IRF-1, luciferase reporter with mutated IRF-E, RT-PCR and immunoblotting\",\n      \"journal\": \"Carcinogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis plus reporter mutagenesis, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"19056926\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"CTCF binds the XAF1 promoter in a methylation-sensitive manner and maintains open chromatin configuration, inhibiting CpG methylation and repressive histone modifications. Loss of CTCF binding leads to XAF1 epigenetic silencing.\",\n      \"method\": \"Chromatin immunoprecipitation, transgene reporter assays, methylation-sensitive CTCF binding experiments\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP plus transgene assay, single lab with two orthogonal methods\",\n      \"pmids\": [\"26443201\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SARM1 deficiency leads to strong selective overexpression of XAF1 in prion-infected mice, resulting in increased pro-apoptotic caspase activity and neuronal death, exacerbating prion disease. SARM1 thus acts as a regulator suppressing XAF1-mediated neuronal apoptosis.\",\n      \"method\": \"SARM1-/- mouse model with prion infection, whole-transcriptome analysis, caspase activity assays, neuronal death quantification\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO mouse model with transcriptome identification plus functional caspase readout, single study\",\n      \"pmids\": [\"30842236\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"XAF1 interacts with XIAP during dengue virus (DENV2) infection as confirmed by co-immunoprecipitation and co-localization by confocal microscopy. XAF1 knockdown reduces caspase-3/8/9 and PARP expression, while XAF1 overexpression upregulates them, establishing a role for XAF1 in promoting apoptosis in DENV2-infected vascular endothelial cells.\",\n      \"method\": \"Co-immunoprecipitation with anti-XAF1 antibody, confocal microscopy co-localization, siRNA knockdown, overexpression, immunoblotting\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — Co-IP plus confocal localization plus loss/gain-of-function, single lab; co-IP evidence is confirmatory of known interaction\",\n      \"pmids\": [\"23207547\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"TRIM47 interacts with XAF1 and promotes its ubiquitination and proteasomal degradation. TRIM47 overexpression causes XAF1-dependent suppression of apoptosis and autophagy in HNSCC cells; XAF1 overexpression reverses the proliferative effect of TRIM47 overexpression.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assays, overexpression/knockdown, autophagy inhibitor rescue, xenograft tumor model\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus ubiquitination assay plus genetic epistasis (XAF1 overexpression rescue), single lab\",\n      \"pmids\": [\"39834862\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"XAF1 is secreted from stressed cancer cells via an unconventional endo-lysosomal trafficking pathway; zinc finger domain 4 (ZF4) is essential for this secretion. Secreted XAF1 is internalized into T cells via clathrin-mediated endocytosis and directly interacts with and phosphorylates Lck (lymphocyte-specific protein tyrosine kinase), activating RAF-MEK-ERK signaling and stimulating T cell proliferation, migration, and tumor infiltration.\",\n      \"method\": \"Subcellular fractionation, ZF4 domain mutant, clathrin-mediated endocytosis inhibition, Lck co-immunoprecipitation/phosphorylation assay, ERK signaling readouts, Xaf1+/+ vs Xaf1-/- xenograft with IFN-γ and recombinant XAF1 injection\",\n      \"journal\": \"Neoplasia\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — domain mutagenesis + direct kinase interaction/phosphorylation assay + genetic KO rescue with recombinant protein in vivo, multiple orthogonal methods in single study\",\n      \"pmids\": [\"39615106\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Xaf1 orchestrates PANoptosis in cochlear hair cells through direct interaction with and transcriptional regulation of ZBP1, placing Xaf1 hierarchically upstream of ZBP1 in the PANoptosis signaling cascade. Xaf1 knockdown via AAV-based gene delivery in cochlear hair cells reduces neomycin-induced ototoxicity.\",\n      \"method\": \"Single-nucleus RNA sequencing, overexpression and knockdown assays in vitro, AAV-based in vivo Xaf1 knockdown, ZBP1 interaction and transcriptional regulation assays\",\n      \"journal\": \"Cell proliferation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct interaction + transcriptional regulation assay + in vivo KD with functional rescue, single lab\",\n      \"pmids\": [\"40600354\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"XAF1 is a stress-inducible, multi-functional tumor suppressor and interferon-stimulated gene whose protein product contains seven zinc finger (ZF) domains that mediate distinct protein-protein interactions: it directly binds and antagonizes XIAP (via its C-terminal RING-binding domain), activates XIAP's E3 ubiquitin ligase activity to degrade Survivin, blocks MDM2-mediated ubiquitination and CHIP-mediated degradation of p53 and IRF-1 to form positive feedback loops, facilitates ZNF313-mediated destruction of TRIM28 and GRP78, destabilizes ERα through a BRCA1 destruction complex, acts as a VCP adaptor to stabilize RNF114 and degrade JUP promoting CRC metastasis, blocks K63-linked AKT ubiquitination to inhibit AKT activation, de-SUMOylates TRIM28 in the nucleus to open chromatin at antiviral gene loci, modulates the CUL3-KLHL22-IRF7 axis to prevent IFN-I hyperproduction, and is itself regulated at the transcriptional level by STAT1/ISRE, IRF-1/IRF-E, HSF1, JNK1, ERK, TGF-β1, p53, FOXO1, and CTCF, as well as by promoter CpG methylation; it can also be secreted to activate Lck-ERK signaling in T cells, and is degraded by TRIM28, TRIM47, and XIAP-mediated ubiquitination, collectively placing XAF1 as a multi-valent molecular switch integrating apoptotic, cell cycle, ER stress, autophagy, innate immune, and metabolic stress responses.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"XAF1 is a stress-inducible, zinc-finger tumor suppressor that integrates apoptotic, cell-cycle, ER-stress, autophagy, and innate-immune programs by acting as a multivalent scaffold and regulator of protein ubiquitination [#0, #10, #17]. It was first defined as a direct XIAP-binding antagonist that neutralizes XIAP's caspase-inhibitory and anti-apoptotic activity and drives XIAP redistribution from cytosol to nucleus [#0, #1], with the interaction mapped to a C-terminal XIAP-RING-binding domain [#9]; beyond inhibition, XAF1 converts the XIAP-XAF1 complex into an active E3 ligase that ubiquitinates and degrades Survivin and, via a CUL4A/DDB1 complex, Chk1 [#2, #13]. Its discrete zinc-finger domains confer distinct interactions that reprogram ubiquitin-dependent stability of key regulators: XAF1 binds p53 (ZF6) to block MDM2-mediated ubiquitination and engages Siah2 and ZNF313 (ZF5/ZF7) to stabilize p53 and activate p21 turnover [#10], stabilizes IRF-1 by blocking CHIP-mediated degradation while serving as its transcriptional coactivator [#11], and uses ZF6/ZF7 to drive ZNF313-mediated K48 degradation of TRIM28, thereby relieving TRIM28-dependent p53 ubiquitination [#25]. XAF1 also assembles a BRCA1 destruction complex to degrade ERα via ZF4 and ZF5/6 [#23], destabilizes GRP78 and CHIP during ER stress [#17], blocks K63-linked ubiquitination and activation of AKT1 [#22], and acts as a VCP adaptor stabilizing RNF114 to degrade JUP and promote colorectal metastasis [#18]. In innate immunity, MAVS- and TBK1-dependent phosphorylation at Ser252 drives nuclear XAF1, where it de-SUMOylates TRIM28 via its PHD domain to open antiviral chromatin and stabilizes IRF1, while the XAF1-XIAP axis restrains the CUL3-KLHL22-IRF7 module to prevent type-I IFN hyperproduction [#19, #20, #21]. XAF1 transcription is tightly controlled, induced by STAT1/ISRE and IRF-1/IRF-E and repressed by HSF1 and p53 [#4, #5, #6, #15]. XAF1 is itself a degradation target of TRIM28 and TRIM47 [#25, #32]. Functional consequences established in vivo include regulation of apoptosis and metabolic insulin signaling, osteoclastogenesis, and antiviral defense [#22, #26, #21].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Established XAF1's founding molecular identity: a direct XIAP-interacting protein that antagonizes XIAP's anti-caspase and anti-apoptotic function, answering what XAF1 does at the protein level.\",\n      \"evidence\": \"Yeast two-hybrid, co-IP, in vitro caspase/apoptosis assays, subcellular fractionation in cells\",\n      \"pmids\": [\"11175744\", \"11087668\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not map the interaction interface\", \"Mechanism of XIAP nuclear redistribution unresolved\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Showed XAF1 not only inhibits but reprograms XIAP into an active E3 ligase that degrades Survivin, expanding XAF1 from antagonist to a switch that redirects IAP catalytic activity.\",\n      \"evidence\": \"Co-IP, MG132 rescue, XIAP RING mutant, siRNA and XAF1-/- clones, endogenous ternary complex IP\",\n      \"pmids\": [\"17613533\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"IAP binding selectivity rules not defined\", \"How XAF1 selects Survivin as substrate unclear\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Linked XAF1 to cell-cycle control by showing it activates Chk1 to enforce G2/M arrest, broadening its role beyond apoptosis.\",\n      \"evidence\": \"Co-IP, kinase assay, cell-cycle synchronization, Chk1 siRNA epistasis, flow cytometry\",\n      \"pmids\": [\"19628579\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Reconciliation with later XAF1-XIAP-mediated Chk1 degradation not addressed\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Defined XAF1's domain architecture and mapped a C-terminal XIAP RING-binding domain, providing the structural basis for XIAP engagement and reciprocal XAF1 ubiquitination.\",\n      \"evidence\": \"Limited proteolysis, NMR interaction mapping, in vitro ubiquitination assay\",\n      \"pmids\": [\"22811387\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length structure not solved\", \"Functions of individual zinc fingers not yet assigned\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Resolved how individual zinc fingers confer substrate-specific control of p53 stability and activity, establishing XAF1 as a domain-encoded ubiquitination regulator.\",\n      \"evidence\": \"Co-IP, domain-deletion mutants, in vitro ubiquitination, reporters, xenografts (p53/Siah2/ZNF313); CUL4A/DDB1 siRNA epistasis for Chk1 degradation\",\n      \"pmids\": [\"25313037\", \"25535897\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry of multi-partner complexes unknown\", \"Context determining Chk1 stabilization vs degradation undefined\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Established a XAF1-IRF-1 positive feedback loop in which XAF1 blocks CHIP-mediated IRF-1 degradation and coactivates IRF-1 transcription, repressed by oncogenic Ras/ERK.\",\n      \"evidence\": \"Co-IP, domain mutagenesis, ubiquitination assays, ChIP, reporters, IRF-1 knockdown epistasis, xenografts\",\n      \"pmids\": [\"30042418\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct coactivator mechanism on chromatin not detailed\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstrated XAF1's reach across ER stress, estrogen signaling, and antiviral type-I IFN control, showing it tunes diverse substrate degradation programs and prevents IFN hyperproduction.\",\n      \"evidence\": \"Co-IP, chain-specific ubiquitination assays, domain mutants, genetic KO/transgenic mice, viral infection and xenograft models (GRP78/CHIP, ERα/BRCA1, IRF1, CUL3-KLHL22-IRF7)\",\n      \"pmids\": [\"35902580\", \"35430604\", \"35972291\", \"36394357\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How a single protein coordinates these distinct complexes in different compartments is unresolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Revealed signal-induced nuclear and metabolic functions: TBK1 phosphorylation drives nuclear XAF1 to de-SUMOylate TRIM28 and open antiviral chromatin, XAF1 blocks K63-ubiquitination of AKT1, and acts as a VCP adaptor controlling metastasis.\",\n      \"evidence\": \"Phospho-site mapping, de-SUMOylation and ATAC-type assays, K63/K48 ubiquitination assays, VCP adaptor co-IP, multiple KO mouse and xenograft models (TRIM28/IRF1, AKT1/FOXO1, RNF114/JUP)\",\n      \"pmids\": [\"37595039\", \"37384528\", \"38095639\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Catalytic basis of XAF1 de-SUMOylation activity not characterized\", \"How cytosolic vs nuclear pools are partitioned unclear\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Extended XAF1 to non-cell-autonomous and tissue-specific roles, including secretion that activates Lck-ERK in T cells, ZNF313-driven TRIM28 degradation, and control of osteoclast apoptosis.\",\n      \"evidence\": \"ZF-domain mutants, secretion/endocytosis assays, Lck phosphorylation, K48 ubiquitination, global/chimeric Xaf1 KO mice (secreted XAF1, TRIM28, osteoclast XIAP-caspase)\",\n      \"pmids\": [\"39615106\", \"39532800\", \"38957269\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of unconventional secretion incompletely defined\", \"Physiological scope of secreted XAF1 signaling unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How XAF1's seven zinc fingers are dynamically partitioned among its many partners and compartments to specify which program (apoptosis, IFN, ER stress, metabolism) is engaged in a given stress context remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No integrated structural model of multi-partner selection\", \"Quantitative rules governing compartment-specific function lacking\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [2, 10, 17, 25, 19]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 2, 21, 22]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [18, 11]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [11, 34]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 19]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [3, 24]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [0, 2, 27]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [19, 20, 21]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [17, 24]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [14, 24]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [7, 13]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [22, 33]}\n    ],\n    \"complexes\": [\"XIAP-XAF1 complex\", \"ZNF313-mediated destruction complex\", \"BRCA1 destruction complex\"],\n    \"partners\": [\"XIAP\", \"TRIM28\", \"IRF1\", \"TP53\", \"ZNF313\", \"AKT1\", \"VCP\", \"ESR1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}