{"gene":"SKIL","run_date":"2026-04-28T20:42:07","timeline":{"discoveries":[{"year":1999,"finding":"SnoN (SKIL) interacts directly with Smad2 and Smad4, repressing their transcriptional activity through recruitment of the transcriptional corepressor N-CoR, thereby maintaining TGF-β target genes in a repressed state in the absence of ligand.","method":"Co-immunoprecipitation, transcriptional reporter assays, protein interaction studies","journal":"Science","confidence":"High","confidence_rationale":"Tier 2 — reciprocal binding demonstrated, functional transcriptional repression assays, foundational paper with >400 citations replicated across many subsequent studies","pmids":["10531062"],"is_preprint":false},{"year":1999,"finding":"Upon TGF-β stimulation, nuclear accumulation of Smad3 triggers rapid proteasome-dependent degradation of SnoN, allowing activation of TGF-β target genes; SnoN then participates in a negative feedback loop as TGF-β subsequently induces SnoN re-expression to terminate Smad-mediated transactivation.","method":"Western blot, reporter assays, pulse-chase degradation experiments","journal":"Science","confidence":"High","confidence_rationale":"Tier 2 — functional dissection of degradation kinetics and feedback loop, replicated in multiple independent studies","pmids":["10531062"],"is_preprint":false},{"year":2001,"finding":"Smad3 recruits the anaphase-promoting complex (APC) with UbcH5 ubiquitin-conjugating enzymes to SnoN, leading to its ubiquitination in a destruction box (D box)-dependent manner and subsequent proteasomal degradation; both the Smad3-binding site in SnoN and key lysine ubiquitin-attachment residues are required for efficient degradation.","method":"In vitro ubiquitination assay, co-immunoprecipitation, site-directed mutagenesis, proteasome inhibitor experiments","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution of ubiquitination with mutagenesis validation, replicated concept in multiple subsequent studies","pmids":["11691834"],"is_preprint":false},{"year":2000,"finding":"SnoN is a component of a macromolecular repressor complex containing N-CoR/SMRT, mSin3, and histone deacetylase, through which it mediates transcriptional repression and inhibits TGF-β signaling by recruiting this complex to Smad proteins.","method":"Biochemical fractionation, co-immunoprecipitation, genetic knockout mouse model","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — complex composition defined by biochemical fractionation and co-IP; mouse genetic data supports in vivo relevance","pmids":["10811619"],"is_preprint":false},{"year":2003,"finding":"The transforming activity of SnoN requires its ability to bind and repress both receptor-regulated Smads (Smad2/Smad3) and Smad4; Smad2/3 and Smad4 bind to distinct regions of SnoN, and mutation of both binding sites (but not each alone) abolishes TGF-β transcriptional repression, cell cycle arrest resistance, and oncogenic transformation of chicken embryo fibroblasts.","method":"Site-directed mutagenesis, co-immunoprecipitation, transcriptional reporter assay, transformation assay (focus formation/soft agar)","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis with multiple functional readouts (binding, transcription, transformation)","pmids":["12764135"],"is_preprint":false},{"year":2005,"finding":"In normal tissues and nontumorigenic epithelial cells, SnoN is predominantly cytoplasmic and antagonizes TGF-β signaling by sequestering Smad proteins in the cytoplasm; upon morphological differentiation or cell-cycle arrest, SnoN translocates to the nucleus. Cytoplasmic SnoN is resistant to TGF-β-induced degradation. In cancer cells, SnoN is exclusively nuclear.","method":"Immunofluorescence, subcellular fractionation, co-immunoprecipitation, TGF-β treatment/degradation assays in primary vs. cancer cell lines","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — direct localization experiments in multiple cell types with functional consequence (Smad sequestration vs. transcriptional repression), mechanistic distinction established","pmids":["16109768"],"is_preprint":false},{"year":2007,"finding":"Arkadia (an E3 ubiquitin ligase) is absolutely required for TGF-β-induced SnoN degradation; Arkadia interacts with SnoN and constitutively ubiquitinates it, but efficient degradation only occurs when SnoN forms a complex with both Arkadia and phosphorylated Smad2 or Smad3, activating Smad3/Smad4-dependent transcription.","method":"siRNA knockdown, dominant-negative mutant, ubiquitination assay, co-immunoprecipitation, luciferase reporter assay, reconstitution in cancer cell line lacking Arkadia","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods including loss-of-function, rescue, ubiquitination assay, and mechanistic epistasis; independently replicated in companion paper","pmids":["17591695"],"is_preprint":false},{"year":2007,"finding":"Arkadia induces ubiquitin-dependent degradation of both SnoN and c-Ski (in addition to Smad7) through its RING domain, interacting with these proteins both in their free forms and when bound to Smad proteins, thereby enhancing TGF-β signaling.","method":"Co-immunoprecipitation, ubiquitination assay, western blot degradation assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — biochemical mechanism established with binding and ubiquitination assays, consistent with companion paper (PMID:17591695)","pmids":["17510063"],"is_preprint":false},{"year":2007,"finding":"TAK1 (MAP3K7) interacts with and phosphorylates SnoN, and this phosphorylation regulates SnoN stability; TAK1 inactivation prevents TGF-β-induced SnoN degradation and impairs induction of TGF-β-responsive genes.","method":"Co-immunoprecipitation, in vitro kinase assay, TAK1 loss-of-function, western blot","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — kinase assay plus loss-of-function phenotype, single lab","pmids":["17276978"],"is_preprint":false},{"year":2006,"finding":"SnoN is a substrate of Cdh1-APC (anaphase-promoting complex with Cdh1) in neurons; Cdh1 forms a physical complex with SnoN and stimulates its ubiquitin-dependent proteasomal degradation, and SnoN knockdown reduces axonal growth, placing SnoN as a key Cdh1-APC target that promotes axonal morphogenesis in a transcription-dependent manner.","method":"Co-immunoprecipitation, ubiquitination assay, shRNA knockdown in neurons, in vivo cerebellar cortex analysis","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 2 — biochemical complex formation, ubiquitination assay, in vivo and in vitro loss-of-function with specific morphogenic phenotype; replicated in multiple follow-up papers","pmids":["16675394"],"is_preprint":false},{"year":2008,"finding":"Smad2 is constitutively phosphorylated and nuclear in cerebellar granule neurons where it forms a physical complex with endogenous SnoN; Smad2 acts upstream of SnoN in the Cdh1-APC pathway to control axonal growth, and Smad2 knockdown stimulates axonal growth and overrides myelin-induced axon growth inhibition.","method":"Co-immunoprecipitation of endogenous proteins, genetic epistasis (double knockdown), shRNA in neurons, in vitro axon growth assay","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 — endogenous co-IP plus genetic epistasis with defined cellular phenotype","pmids":["18287512"],"is_preprint":false},{"year":2009,"finding":"SnoN interacts with the transcriptional coactivator p300, and p300 is required for SnoN-induced axon growth in neurons; SnoN activates transcription of Ccd1 (a signaling scaffold enriched at axon terminals that activates JNK kinase), and Ccd1 knockdown suppresses SnoN-dependent axonal growth in vivo.","method":"Gene expression profiling, co-immunoprecipitation, shRNA knockdown in neurons, in vivo parallel fiber analysis in rat cerebellum","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 — target gene identification by profiling, binding partner confirmed by co-IP, in vivo loss-of-function with specific neuronal phenotype","pmids":["19339625"],"is_preprint":false},{"year":1999,"finding":"Ski and SnoN preferentially form heterodimers over homodimers when co-expressed; tethered Ski:SnoN heterodimers lacking TR/LZ domains are more active in transcriptional repression and cellular transformation than homodimers or monomers. Efficient SnoN homodimerization requires both the TR/LZ domain and an upstream region unique to SnoN, unlike Ski.","method":"In vitro co-translation, co-immunoprecipitation, electrophoretic mobility shift assay (DNA binding), transformation assay","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro and in vivo dimerization with functional readouts, single lab","pmids":["9927733"],"is_preprint":false},{"year":2002,"finding":"Two short segments of Smad3 — the 'SE' sequence in the C-terminal MH2 domain and the adjacent 'QPSMT' sequence — are required for specific interaction with c-Ski and SnoN; these sequences are conserved in Smad2 but absent in Smad1, explaining preferential binding to Smad2/3 over Smad1. Smurf2 induces ubiquitin-dependent degradation of SnoN by positioning it close to the Smad2 linker region.","method":"Mutagenesis, co-immunoprecipitation, structural mapping using known Smad MH2 crystal structure","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — mutagenesis mapping of interaction surfaces with structural context, functional degradation assay","pmids":["12426322"],"is_preprint":false},{"year":2006,"finding":"Smurf2 (an E3 ubiquitin ligase) is induced in obstructed kidneys and forms a complex with SnoN, promoting its ubiquitination and proteasomal degradation in vivo; immunodepletion of Smurf2 reduces SnoN ubiquitination in kidney extracts.","method":"Immunodepletion, co-immunoprecipitation, ubiquitination assay in kidney extracts, immunohistochemistry","journal":"Kidney international","confidence":"Medium","confidence_rationale":"Tier 2 — endogenous complex in tissue extracts with functional ubiquitination assay, single study","pmids":["16625151"],"is_preprint":false},{"year":2007,"finding":"SnoN sumoylation occurs primarily at lysine 50 (Lys-50) and is mediated by E3 SUMO ligases PIAS1 and PIASx, which physically interact with SnoN. SUMO modification does not alter SnoN stability or TGF-β repression, but loss of sumoylation at Lys-50 potently activates muscle-specific gene expression and enhances myotube formation, revealing a TGF-β-independent function of SnoN in myogenesis.","method":"In vivo sumoylation assay, site-directed mutagenesis (K50R), co-immunoprecipitation, muscle differentiation assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — PTM characterized biochemically, specific site identified by mutagenesis, writer identified (PIAS1/PIASx), functional consequence established","pmids":["17202138"],"is_preprint":false},{"year":2012,"finding":"The SNON-SMAD4 complex directly binds the TGF-β response element (TRE) in the SKIL gene proximal promoter and recruits histone deacetylases to repress basal SKIL gene expression; upon TGF-β signaling, SNON is removed from the promoter allowing SMAD complexes to induce SKIL transcription, and the re-expressed SNON-SMAD4 complex then represses its own gene as a negative feedback loop.","method":"ChIP assay, sequential ChIP, promoter-reporter (luciferase), cloning of human SKIL promoter","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — ChIP and sequential ChIP establish in vivo binding; functional promoter assays demonstrate repression mechanism; negative feedback loop confirmed","pmids":["22674574"],"is_preprint":false},{"year":2012,"finding":"SNON (SKIL) is expressed in human embryonic stem cells (hESCs) and associates with SMAD2 at promoters of primitive streak and early definitive endoderm marker genes; SNON knockdown causes premature activation of these genes and loss of hESC morphology, while enforced SNON expression inhibits endoderm formation and diverts hESCs toward extraembryonic fate.","method":"ChIP assay, siRNA knockdown, overexpression, analysis of hESC differentiation markers","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 — ChIP demonstrates in vivo binding at target promoters; gain- and loss-of-function establish specific developmental role","pmids":["23154981"],"is_preprint":false},{"year":2016,"finding":"SnoN interacts with multiple components of the Hippo pathway (including Lats2) to inhibit Lats2 binding to TAZ and subsequent TAZ phosphorylation, leading to TAZ stabilization and enhanced TAZ transcriptional and oncogenic activities; SnoN itself is downregulated by Lats2 activated by the basolateral polarity protein Scribble.","method":"Co-immunoprecipitation, kinase assay, shRNA knockdown, TAZ phosphorylation/stability assays, breast cancer cell models","journal":"Developmental cell","confidence":"Medium","confidence_rationale":"Tier 2 — multiple binding partners identified by co-IP, functional phosphorylation assay, loss-of-function phenotype; single lab","pmids":["27237790"],"is_preprint":false},{"year":2021,"finding":"Arkadia (RNF111) promotes iTreg cell differentiation in CD4+ T cells by inducing degradation of SKI and SnoN; genetic ablation of both SKI and SnoN rescues Arkadia-deficient iTreg differentiation in vitro and in vivo, demonstrating that SKI/SnoN are the critical Arkadia substrates mediating TGF-β-dependent iTreg induction.","method":"Conditional knockout mouse (Arkadia in CD4+ T cells), in vitro differentiation assay, double-knockout epistasis, flow cytometry","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 — clean genetic epistasis in mouse with defined cellular phenotype (iTreg differentiation); in vivo and in vitro concordance","pmids":["34473197"],"is_preprint":false},{"year":2013,"finding":"SKIL (SnoN) is a driver gene at the 3q26 amplicon; elevated SKIL expression induces cell invasion in immortalized human mammary epithelial cells through upregulation of SLUG (SNAI2), and combined TLOC1 + SKIL expression induces subcutaneous tumor growth in vivo.","method":"Gain-of-function genetic screen, shRNA loss-of-function, invasion assay, xenograft mouse model, proteomic studies","journal":"Cancer discovery","confidence":"Medium","confidence_rationale":"Tier 2 — functional genomic screen with in vivo validation and pathway identification (SLUG upregulation), single lab","pmids":["23764425"],"is_preprint":false},{"year":2012,"finding":"SnoN suppresses BMP-induced hypertrophic maturation of chondrocytes by inhibiting BMP signaling downstream of Smad1/5/8 activation, specifically by suppressing Id1 expression; SnoN expression is highest in articular cartilage of adult mice and co-localizes with phospho-Smad2/3 in prehypertrophic chondrocytes.","method":"siRNA knockdown, overexpression, BMP-responsive reporter assay, expression analysis in mouse growth plate and human OA cartilage","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — gain- and loss-of-function with pathway reporter and in vivo expression pattern; single lab","pmids":["22767605"],"is_preprint":false},{"year":2012,"finding":"SnoN coordinates TGF-β and prolactin signaling in mammary epithelial cells by enhancing Stat5 protein stability; SnoN-/- mice display severe defects in alveologenesis and lactogenesis that can be rescued by active Stat5, demonstrating SnoN promotes Stat5 signaling to control lactation.","method":"Knockout mouse model, rescue by active Stat5, mammary gland morphogenesis analysis","journal":"Development","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with specific morphogenic phenotype and molecular rescue defines pathway position","pmids":["22833129"],"is_preprint":false},{"year":2003,"finding":"Sno-deficient T cells show augmented TGF-β sensitivity; Sno-dependent suppression of TGF-β signaling is required for normal T-cell proliferation following receptor ligation, as the proliferation defect in Sno hypomorph and null mice is reversed by anti-TGF-β antibodies or exogenous IL-2. IL-2 and IL-4 production is reduced in mutant T cells.","method":"Targeted gene deletion (hypomorph and null mice), T-cell proliferation assay, anti-TGF-β rescue, cytokine measurement","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with specific immune phenotype and pharmacological rescue establishing TGF-β pathway epistasis","pmids":["12861029"],"is_preprint":false},{"year":2024,"finding":"NSUN2 promotes m5C methylation of SKIL mRNA, which is recognized by YBX1 to stabilize SKIL transcripts; elevated SKIL increases TAZ activation to promote colorectal cancer progression.","method":"m5C-methylated RNA immunoprecipitation, RNA stability assay, bisulfite sequencing, NSUN2 knockout mouse, YBX1 interaction studies","journal":"Clinical and translational medicine","confidence":"Medium","confidence_rationale":"Tier 2 — m5C modification of SKIL mapped, reader (YBX1) identified, functional mRNA stability consequence demonstrated; single lab","pmids":["38468490"],"is_preprint":false},{"year":2020,"finding":"SKIL promotes tumorigenesis and immune escape of NSCLC by interacting with TAZ (co-immunoprecipitation), upregulating TAZ to activate autophagy and suppress the STING pathway; silencing TAZ cancels the effects of SKIL overexpression.","method":"Co-immunoprecipitation, lentiviral overexpression/knockdown, colony formation assay, xenograft and syngeneic mouse models, flow cytometry for T cell infiltration","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 — co-IP demonstrates physical interaction, epistasis experiment (TAZ KD rescues SKIL OE phenotype) places pathway position; single lab","pmids":["33268765"],"is_preprint":false},{"year":1998,"finding":"SnoN binds a specific DNA sequence (GTCTAGAC) and represses transcription through a tripartite repression domain; subdomain II interacts with TAF(II)110 via a quenching mechanism of transcriptional repression. Two subdomains (II and III) are required for DNA binding and cellular transformation.","method":"Electrophoretic mobility shift assay, Gal4 fusion reporter assay, deletion mutagenesis, transformation assay, GST pulldown with TAF(II)110","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 — DNA binding, repression domain mapping by mutagenesis, and interaction with basal transcription factor identified; single lab with multiple assays","pmids":["9824161"],"is_preprint":false},{"year":2018,"finding":"FMRP directly interacts with lncRNA TUG1 and decreases its stability; TUG1 binds to SnoN and negatively modulates the SnoN-Ccd1 pathway to control axonal development in neurons.","method":"RNA immunoprecipitation, co-immunoprecipitation, axon growth assay in FMRP-deficient neurons","journal":"Human molecular genetics","confidence":"Low","confidence_rationale":"Tier 3 — single pulldown/co-IP, limited mechanistic follow-up of SnoN involvement specifically","pmids":["29211876"],"is_preprint":false}],"current_model":"SKIL (SnoN) functions as a transcriptional corepressor that binds Smad2, Smad3, and Smad4 to repress TGF-β target genes by recruiting histone deacetylase complexes (N-CoR/SMRT/mSin3); upon TGF-β stimulation, SnoN is rapidly degraded via multiple E3 ubiquitin ligases (APC/Cdh1, Arkadia, Smurf2) recruited by activated Smads, allowing target gene activation, after which re-expressed SnoN-SMAD4 complexes bind the SKIL promoter to terminate signaling in a negative feedback loop; additionally, SnoN interacts with Hippo pathway components to stabilize TAZ, interacts with p300 to activate neuronal transcription programs (including Ccd1) that promote axonal growth, is modified by SUMO-1 at Lys-50 (via PIAS1/PIASx) to regulate myogenesis independently of TGF-β, and its subcellular localization (cytoplasmic in normal cells vs. nuclear in cancer cells) determines whether it sequesters Smads in the cytoplasm or represses their transcriptional activity in the nucleus."},"narrative":{"teleology":[{"year":1998,"claim":"Establishing that SnoN directly binds DNA and represses transcription through a tripartite domain that interacts with basal transcription factor TAF(II)110 defined SnoN as an active transcriptional repressor rather than a passive binding partner.","evidence":"EMSA, Gal4 fusion reporter, deletion mutagenesis, GST pulldown with TAF(II)110","pmids":["9824161"],"confidence":"Medium","gaps":["Physiological relevance of direct DNA binding versus Smad-mediated recruitment unclear","TAF(II)110 interaction not validated in vivo"]},{"year":1999,"claim":"Demonstrating that SnoN binds Smad2/Smad4, recruits N-CoR, and is rapidly degraded upon TGF-β stimulation—then re-expressed to shut off signaling—established the core model of SnoN as both a gatekeeper and feedback terminator of TGF-β transcription.","evidence":"Co-immunoprecipitation, transcriptional reporter assays, pulse-chase degradation experiments in multiple cell lines","pmids":["10531062","9927733"],"confidence":"High","gaps":["Identity of the E3 ligase mediating degradation was unknown","Mechanism of SnoN nuclear export/import not resolved"]},{"year":2000,"claim":"Biochemical isolation of a macromolecular SnoN–N-CoR/SMRT–mSin3–HDAC repressor complex defined the enzymatic basis of SnoN-mediated silencing as histone deacetylation.","evidence":"Biochemical fractionation, co-immunoprecipitation, knockout mouse model","pmids":["10811619"],"confidence":"High","gaps":["Specific HDAC isoform(s) required not identified","Genome-wide target gene repertoire not mapped"]},{"year":2001,"claim":"Reconstitution of Smad3-dependent recruitment of APC/UbcH5 to SnoN's destruction box identified the first E3 ligase responsible for TGF-β-induced SnoN degradation, resolving how ligand signaling removes the repressor.","evidence":"In vitro ubiquitination assay with reconstituted components, site-directed mutagenesis of D-box and lysine residues","pmids":["11691834"],"confidence":"High","gaps":["Relative contribution of APC versus other E3 ligases in different cell types not resolved","Cell-cycle phase dependence of APC-mediated degradation not clarified"]},{"year":2002,"claim":"Mapping the Smad3 interaction surfaces (SE and QPSMT motifs in MH2 domain) and showing Smurf2 induces SnoN ubiquitination revealed a second E3 ligase and explained the specificity of SnoN for TGF-β/activin Smads over BMP Smads.","evidence":"Mutagenesis of Smad3, co-immunoprecipitation, structural mapping using known crystal structure","pmids":["12426322"],"confidence":"Medium","gaps":["Crystal structure of the SnoN–Smad complex not solved","Smurf2-mediated degradation not reconstituted in vitro with purified components"]},{"year":2003,"claim":"Demonstrating that oncogenic transformation by SnoN requires simultaneous repression of both R-Smads and Smad4, and that SnoN deficiency in T cells causes augmented TGF-β sensitivity, established in vivo physiological consequences of SnoN-mediated TGF-β repression.","evidence":"Double Smad-binding-site mutagenesis with transformation assays; SnoN-null/hypomorph mouse T cells with anti-TGF-β rescue","pmids":["12764135","12861029"],"confidence":"High","gaps":["Whether Smad4 and R-Smad binding are simultaneously occupied on chromatin unknown","T-cell-intrinsic versus microenvironment contributions not fully separated"]},{"year":2005,"claim":"Showing that SnoN is cytoplasmic in normal epithelial cells (where it sequesters Smads) but nuclear in cancer cells resolved a longstanding paradox about how SnoN can be both a tumor suppressor and an oncogene depending on context.","evidence":"Immunofluorescence and subcellular fractionation across primary and cancer cell lines, TGF-β degradation assays","pmids":["16109768"],"confidence":"High","gaps":["Signals controlling nuclear import/export not identified","Whether cytoplasmic SnoN is degradation-resistant in vivo not confirmed"]},{"year":2006,"claim":"Identifying SnoN as a Cdh1-APC substrate in neurons whose degradation restricts axonal growth revealed a TGF-β-independent function for SnoN in neuronal morphogenesis.","evidence":"Co-immunoprecipitation, ubiquitination assay, shRNA knockdown in granule neurons, in vivo cerebellar analysis","pmids":["16675394","14585991"],"confidence":"High","gaps":["Transcriptional targets of SnoN in neurons not yet identified at this point","Whether Cdh1-APC acts on SnoN in non-neuronal tissues unclear"]},{"year":2007,"claim":"Establishing Arkadia (RNF111) as the essential E3 ligase for TGF-β-induced SnoN degradation, requiring a ternary complex with phospho-Smad2/3, resolved the hierarchy among the three known SnoN-targeting E3 ligases and explained signal-dependent gating of degradation.","evidence":"siRNA, dominant-negative mutant, ubiquitination assay, reconstitution in Arkadia-null cancer cells","pmids":["17591695","17510063"],"confidence":"High","gaps":["Relative tissue-specific contributions of APC, Arkadia, and Smurf2 not systematically compared","Structural basis of ternary complex formation unknown"]},{"year":2007,"claim":"Demonstrating that SUMO modification of SnoN at Lys-50 by PIAS1/PIASx regulates muscle-specific gene expression independently of TGF-β signaling uncovered a post-translational switch controlling a non-canonical SnoN function in myogenesis.","evidence":"In vivo sumoylation assay, K50R mutagenesis, muscle differentiation assay","pmids":["17202138"],"confidence":"High","gaps":["Identity of SUMO-dependent SnoN interactors in myogenesis unknown","Whether SUMO modification alters chromatin targeting not tested"]},{"year":2009,"claim":"Identifying p300 as a SnoN coactivator and Ccd1 as a direct transcriptional target in neurons provided the molecular mechanism by which SnoN promotes axonal growth—switching from repressor to activator function via coactivator choice.","evidence":"Gene expression profiling, co-immunoprecipitation with p300, Ccd1 shRNA in rat cerebellum in vivo","pmids":["19339625"],"confidence":"High","gaps":["How SnoN switches from N-CoR to p300 recruitment is mechanistically unresolved","Additional neuronal transcription targets not comprehensively mapped"]},{"year":2012,"claim":"ChIP and promoter analysis showing that SNON-SMAD4 directly occupies the SKIL promoter TRE to repress its own gene closed the negative feedback loop at the chromatin level and explained signal termination kinetics.","evidence":"ChIP, sequential ChIP, cloned human SKIL promoter-reporter assays","pmids":["22674574"],"confidence":"High","gaps":["Kinetics of SNON re-occupancy after TGF-β pulse not measured genome-wide","Whether other TGF-β target promoters use identical autorepression unclear"]},{"year":2012,"claim":"Demonstrating that SnoN occupies primitive streak gene promoters with SMAD2 in hESCs, and that its loss causes premature endoderm specification, extended SnoN's gatekeeper role to human pluripotency and early lineage commitment.","evidence":"ChIP in hESCs, siRNA knockdown and overexpression with differentiation marker analysis","pmids":["23154981"],"confidence":"High","gaps":["Whether SnoN acts similarly in mouse ESCs not tested","Mechanism of SnoN downregulation during normal endoderm specification unknown"]},{"year":2012,"claim":"Showing that SnoN-null mice have severe lactation defects rescued by active Stat5 revealed that SnoN enhances Stat5 protein stability, linking SnoN to JAK-STAT signaling in mammary gland development.","evidence":"Knockout mouse, Stat5 rescue, mammary gland histology","pmids":["22833129"],"confidence":"High","gaps":["Mechanism by which SnoN stabilizes Stat5 (direct binding or indirect) not defined","Whether this function is TGF-β-dependent not resolved"]},{"year":2016,"claim":"Discovering that SnoN interacts with Hippo pathway components to inhibit Lats2-mediated TAZ phosphorylation and degradation revealed a TGF-β-independent oncogenic mechanism operating through cross-pathway regulation.","evidence":"Co-immunoprecipitation, kinase assay, shRNA knockdown, TAZ stability assays in breast cancer cells","pmids":["27237790"],"confidence":"Medium","gaps":["Structural basis of SnoN–Lats2 interaction unknown","Whether SnoN also regulates YAP not tested","Single-lab finding awaiting independent confirmation"]},{"year":2021,"claim":"Genetic epistasis showing that double knockout of SKI and SnoN rescues Arkadia-deficient iTreg differentiation established that SnoN (and SKI) are the critical Arkadia substrates gating TGF-β-dependent regulatory T cell induction in vivo.","evidence":"Conditional knockout mice, in vitro/in vivo iTreg differentiation, flow cytometry","pmids":["34473197"],"confidence":"High","gaps":["Whether SnoN and SKI have redundant or distinct roles in iTreg specification unclear","SnoN targets in Treg-specific gene programs not identified"]},{"year":null,"claim":"Key unresolved questions include the structural basis of SnoN's cofactor switching (N-CoR versus p300), the signals controlling SnoN nuclear-cytoplasmic shuttling, and the relative tissue-specific contributions of the three E3 ligases (APC, Arkadia, Smurf2) to SnoN turnover.","evidence":"","pmids":[],"confidence":"High","gaps":["No crystal or cryo-EM structure of SnoN in complex with any partner","Genome-wide direct target gene maps across tissues lacking","Mechanism of cofactor switching between repression and activation unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[0,3,4,16,17,26]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,1,18,22]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,5,16,17]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[5]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,2,4,6,18,19,23]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[0,3,16,17,26]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[2,6,7,9,14,15]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[9,11,17,22]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[19,23]}],"complexes":["N-CoR/SMRT/mSin3/HDAC repressor complex","APC/Cdh1"],"partners":["SMAD2","SMAD3","SMAD4","SKI","RNF111","EP300","SMURF2","LATS2"],"other_free_text":[]},"mechanistic_narrative":"SKIL (SnoN) is a transcriptional corepressor that negatively regulates TGF-β signaling by binding Smad2, Smad3, and Smad4 and recruiting histone deacetylase complexes containing N-CoR/SMRT, mSin3, and HDAC to maintain target genes in a repressed state [PMID:10531062, PMID:10811619]. Upon TGF-β stimulation, SnoN is rapidly degraded via the ubiquitin–proteasome pathway through multiple E3 ligases—APC/Cdh1, Arkadia (RNF111), and Smurf2—that are recruited by activated Smads, allowing transient target gene activation; SnoN is subsequently re-expressed and binds its own promoter with SMAD4 to terminate signaling in a negative feedback loop [PMID:11691834, PMID:17591695, PMID:22674574]. Beyond TGF-β, SnoN functions in neuronal axon growth by interacting with p300 to activate transcription of Ccd1, is regulated by Cdh1-APC in neurons, controls Hippo pathway output by stabilizing TAZ through inhibition of Lats2, promotes Stat5 stability during mammary alveologenesis, and undergoes SUMO modification at Lys-50 by PIAS1/PIASx to regulate myogenesis independently of TGF-β [PMID:16675394, PMID:19339625, PMID:27237790, PMID:22833129, PMID:17202138]. SnoN subcellular localization—cytoplasmic in normal cells versus nuclear in cancer cells—determines whether it sequesters Smads in the cytoplasm or represses their transcriptional activity in the nucleus [PMID:16109768]."},"prefetch_data":{"uniprot":{"accession":"P12757","full_name":"Ski-like protein","aliases":["Ski-related oncogene","Ski-related protein"],"length_aa":684,"mass_kda":77.0,"function":"May have regulatory role in cell division or differentiation in response to extracellular signals","subcellular_location":"","url":"https://www.uniprot.org/uniprotkb/P12757/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SKIL","classification":"Not 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research","url":"https://pubmed.ncbi.nlm.nih.gov/20460516","citation_count":26,"is_preprint":false},{"pmid":"31471872","id":"PMC_31471872","title":"SNHG14 promotes the tumorigenesis and metastasis of colorectal cancer through miR-32-5p/SKIL axis.","date":"2019","source":"In vitro cellular & developmental biology. Animal","url":"https://pubmed.ncbi.nlm.nih.gov/31471872","citation_count":25,"is_preprint":false},{"pmid":"18261624","id":"PMC_18261624","title":"Ski/SnoN expression in the sequence metaplasia-dysplasia-adenocarcinoma of Barrett's esophagus.","date":"2008","source":"Human pathology","url":"https://pubmed.ncbi.nlm.nih.gov/18261624","citation_count":25,"is_preprint":false},{"pmid":"27956242","id":"PMC_27956242","title":"Fusaric acid induces oxidative stress and apoptosis in human cancerous oesophageal SNO cells.","date":"2016","source":"Toxicon : official journal of the International Society on Toxinology","url":"https://pubmed.ncbi.nlm.nih.gov/27956242","citation_count":25,"is_preprint":false},{"pmid":"28382204","id":"PMC_28382204","title":"Nitrosopersulfide (SSNO-) decomposes in the presence of sulfide, cyanide or glutathione to give HSNO/SNO-: consequences for the assumed role in cell signalling.","date":"2017","source":"Interface focus","url":"https://pubmed.ncbi.nlm.nih.gov/28382204","citation_count":24,"is_preprint":false},{"pmid":"22833129","id":"PMC_22833129","title":"SnoN regulates mammary gland alveologenesis and onset of lactation by promoting prolactin/Stat5 signaling.","date":"2012","source":"Development (Cambridge, England)","url":"https://pubmed.ncbi.nlm.nih.gov/22833129","citation_count":24,"is_preprint":false},{"pmid":"23154181","id":"PMC_23154181","title":"SnoN/SKIL modulates proliferation through control of hsa-miR-720 transcription in esophageal cancer cells.","date":"2012","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/23154181","citation_count":23,"is_preprint":false},{"pmid":"23621864","id":"PMC_23621864","title":"Phospholipid Scramblase 1, an interferon-regulated gene located at 3q23, is regulated by SnoN/SkiL in ovarian cancer cells.","date":"2013","source":"Molecular cancer","url":"https://pubmed.ncbi.nlm.nih.gov/23621864","citation_count":22,"is_preprint":false},{"pmid":"19383336","id":"PMC_19383336","title":"Overexpression of SnoN/SkiL, amplified at the 3q26.2 locus, in ovarian cancers: a role in ovarian pathogenesis.","date":"2008","source":"Molecular oncology","url":"https://pubmed.ncbi.nlm.nih.gov/19383336","citation_count":22,"is_preprint":false},{"pmid":"9824161","id":"PMC_9824161","title":"A domain necessary for the transforming activity of SnoN is required for specific DNA binding, transcriptional repression and interaction with TAF(II)110.","date":"1998","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/9824161","citation_count":22,"is_preprint":false},{"pmid":"12861029","id":"PMC_12861029","title":"Defective T-cell activation is associated with augmented transforming growth factor Beta sensitivity in mice with mutations in the Sno gene.","date":"2003","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/12861029","citation_count":22,"is_preprint":false},{"pmid":"25749039","id":"PMC_25749039","title":"Recurrent SKIL-activating rearrangements in ETS-negative prostate cancer.","date":"2015","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/25749039","citation_count":22,"is_preprint":false},{"pmid":"22710173","id":"PMC_22710173","title":"SnoN signaling in proliferating cells and postmitotic neurons.","date":"2012","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/22710173","citation_count":20,"is_preprint":false},{"pmid":"29211876","id":"PMC_29211876","title":"Interplay between FMRP and lncRNA TUG1 regulates axonal development through mediating SnoN-Ccd1 pathway.","date":"2018","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/29211876","citation_count":20,"is_preprint":false},{"pmid":"28115165","id":"PMC_28115165","title":"Repression of Smad3 by Stat3 and c-Ski/SnoN induces gefitinib resistance in lung adenocarcinoma.","date":"2017","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/28115165","citation_count":20,"is_preprint":false},{"pmid":"15927266","id":"PMC_15927266","title":"Light-induced inhibition of papain by a {Mn-NO}6 nitrosyl: identification of papain-SNO adduct by mass spectrometry.","date":"2005","source":"Journal of inorganic biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/15927266","citation_count":20,"is_preprint":false},{"pmid":"18782659","id":"PMC_18782659","title":"Clinical significance of the expression of c-Ski and SnoN, possible mediators in TGF-beta resistance, in primary cutaneous melanoma.","date":"2008","source":"Journal of dermatological science","url":"https://pubmed.ncbi.nlm.nih.gov/18782659","citation_count":20,"is_preprint":false},{"pmid":"31917288","id":"PMC_31917288","title":"Smad2 and Smad3 play antagonistic roles in high glucose-induced renal tubular fibrosis via the regulation of SnoN.","date":"2020","source":"Experimental and molecular pathology","url":"https://pubmed.ncbi.nlm.nih.gov/31917288","citation_count":20,"is_preprint":false},{"pmid":"17202138","id":"PMC_17202138","title":"Transforming growth factor-beta-independent regulation of myogenesis by SnoN sumoylation.","date":"2007","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/17202138","citation_count":19,"is_preprint":false},{"pmid":"26743567","id":"PMC_26743567","title":"The downregulation of SnoN expression in human renal proximal tubule epithelial cells under high-glucose conditions is mediated by an increase in Smurf2 expression through TGF-β1 signaling.","date":"2015","source":"International journal of molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/26743567","citation_count":18,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":47913,"output_tokens":6636,"usd":0.121639},"stage2":{"model":"claude-opus-4-6","input_tokens":10402,"output_tokens":3975,"usd":0.227077},"total_usd":0.348716,"stage1_batch_id":"msgbatch_011rkcQdVV1RaFq9XhcG6df6","stage2_batch_id":"msgbatch_01RzgrJafdF4EWHhj5mNi6dh","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1999,\n      \"finding\": \"SnoN (SKIL) interacts directly with Smad2 and Smad4, repressing their transcriptional activity through recruitment of the transcriptional corepressor N-CoR, thereby maintaining TGF-β target genes in a repressed state in the absence of ligand.\",\n      \"method\": \"Co-immunoprecipitation, transcriptional reporter assays, protein interaction studies\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal binding demonstrated, functional transcriptional repression assays, foundational paper with >400 citations replicated across many subsequent studies\",\n      \"pmids\": [\"10531062\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Upon TGF-β stimulation, nuclear accumulation of Smad3 triggers rapid proteasome-dependent degradation of SnoN, allowing activation of TGF-β target genes; SnoN then participates in a negative feedback loop as TGF-β subsequently induces SnoN re-expression to terminate Smad-mediated transactivation.\",\n      \"method\": \"Western blot, reporter assays, pulse-chase degradation experiments\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — functional dissection of degradation kinetics and feedback loop, replicated in multiple independent studies\",\n      \"pmids\": [\"10531062\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Smad3 recruits the anaphase-promoting complex (APC) with UbcH5 ubiquitin-conjugating enzymes to SnoN, leading to its ubiquitination in a destruction box (D box)-dependent manner and subsequent proteasomal degradation; both the Smad3-binding site in SnoN and key lysine ubiquitin-attachment residues are required for efficient degradation.\",\n      \"method\": \"In vitro ubiquitination assay, co-immunoprecipitation, site-directed mutagenesis, proteasome inhibitor experiments\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution of ubiquitination with mutagenesis validation, replicated concept in multiple subsequent studies\",\n      \"pmids\": [\"11691834\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"SnoN is a component of a macromolecular repressor complex containing N-CoR/SMRT, mSin3, and histone deacetylase, through which it mediates transcriptional repression and inhibits TGF-β signaling by recruiting this complex to Smad proteins.\",\n      \"method\": \"Biochemical fractionation, co-immunoprecipitation, genetic knockout mouse model\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — complex composition defined by biochemical fractionation and co-IP; mouse genetic data supports in vivo relevance\",\n      \"pmids\": [\"10811619\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The transforming activity of SnoN requires its ability to bind and repress both receptor-regulated Smads (Smad2/Smad3) and Smad4; Smad2/3 and Smad4 bind to distinct regions of SnoN, and mutation of both binding sites (but not each alone) abolishes TGF-β transcriptional repression, cell cycle arrest resistance, and oncogenic transformation of chicken embryo fibroblasts.\",\n      \"method\": \"Site-directed mutagenesis, co-immunoprecipitation, transcriptional reporter assay, transformation assay (focus formation/soft agar)\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis with multiple functional readouts (binding, transcription, transformation)\",\n      \"pmids\": [\"12764135\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"In normal tissues and nontumorigenic epithelial cells, SnoN is predominantly cytoplasmic and antagonizes TGF-β signaling by sequestering Smad proteins in the cytoplasm; upon morphological differentiation or cell-cycle arrest, SnoN translocates to the nucleus. Cytoplasmic SnoN is resistant to TGF-β-induced degradation. In cancer cells, SnoN is exclusively nuclear.\",\n      \"method\": \"Immunofluorescence, subcellular fractionation, co-immunoprecipitation, TGF-β treatment/degradation assays in primary vs. cancer cell lines\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct localization experiments in multiple cell types with functional consequence (Smad sequestration vs. transcriptional repression), mechanistic distinction established\",\n      \"pmids\": [\"16109768\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Arkadia (an E3 ubiquitin ligase) is absolutely required for TGF-β-induced SnoN degradation; Arkadia interacts with SnoN and constitutively ubiquitinates it, but efficient degradation only occurs when SnoN forms a complex with both Arkadia and phosphorylated Smad2 or Smad3, activating Smad3/Smad4-dependent transcription.\",\n      \"method\": \"siRNA knockdown, dominant-negative mutant, ubiquitination assay, co-immunoprecipitation, luciferase reporter assay, reconstitution in cancer cell line lacking Arkadia\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods including loss-of-function, rescue, ubiquitination assay, and mechanistic epistasis; independently replicated in companion paper\",\n      \"pmids\": [\"17591695\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Arkadia induces ubiquitin-dependent degradation of both SnoN and c-Ski (in addition to Smad7) through its RING domain, interacting with these proteins both in their free forms and when bound to Smad proteins, thereby enhancing TGF-β signaling.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, western blot degradation assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — biochemical mechanism established with binding and ubiquitination assays, consistent with companion paper (PMID:17591695)\",\n      \"pmids\": [\"17510063\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"TAK1 (MAP3K7) interacts with and phosphorylates SnoN, and this phosphorylation regulates SnoN stability; TAK1 inactivation prevents TGF-β-induced SnoN degradation and impairs induction of TGF-β-responsive genes.\",\n      \"method\": \"Co-immunoprecipitation, in vitro kinase assay, TAK1 loss-of-function, western blot\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — kinase assay plus loss-of-function phenotype, single lab\",\n      \"pmids\": [\"17276978\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"SnoN is a substrate of Cdh1-APC (anaphase-promoting complex with Cdh1) in neurons; Cdh1 forms a physical complex with SnoN and stimulates its ubiquitin-dependent proteasomal degradation, and SnoN knockdown reduces axonal growth, placing SnoN as a key Cdh1-APC target that promotes axonal morphogenesis in a transcription-dependent manner.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, shRNA knockdown in neurons, in vivo cerebellar cortex analysis\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — biochemical complex formation, ubiquitination assay, in vivo and in vitro loss-of-function with specific morphogenic phenotype; replicated in multiple follow-up papers\",\n      \"pmids\": [\"16675394\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Smad2 is constitutively phosphorylated and nuclear in cerebellar granule neurons where it forms a physical complex with endogenous SnoN; Smad2 acts upstream of SnoN in the Cdh1-APC pathway to control axonal growth, and Smad2 knockdown stimulates axonal growth and overrides myelin-induced axon growth inhibition.\",\n      \"method\": \"Co-immunoprecipitation of endogenous proteins, genetic epistasis (double knockdown), shRNA in neurons, in vitro axon growth assay\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — endogenous co-IP plus genetic epistasis with defined cellular phenotype\",\n      \"pmids\": [\"18287512\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"SnoN interacts with the transcriptional coactivator p300, and p300 is required for SnoN-induced axon growth in neurons; SnoN activates transcription of Ccd1 (a signaling scaffold enriched at axon terminals that activates JNK kinase), and Ccd1 knockdown suppresses SnoN-dependent axonal growth in vivo.\",\n      \"method\": \"Gene expression profiling, co-immunoprecipitation, shRNA knockdown in neurons, in vivo parallel fiber analysis in rat cerebellum\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — target gene identification by profiling, binding partner confirmed by co-IP, in vivo loss-of-function with specific neuronal phenotype\",\n      \"pmids\": [\"19339625\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Ski and SnoN preferentially form heterodimers over homodimers when co-expressed; tethered Ski:SnoN heterodimers lacking TR/LZ domains are more active in transcriptional repression and cellular transformation than homodimers or monomers. Efficient SnoN homodimerization requires both the TR/LZ domain and an upstream region unique to SnoN, unlike Ski.\",\n      \"method\": \"In vitro co-translation, co-immunoprecipitation, electrophoretic mobility shift assay (DNA binding), transformation assay\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro and in vivo dimerization with functional readouts, single lab\",\n      \"pmids\": [\"9927733\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Two short segments of Smad3 — the 'SE' sequence in the C-terminal MH2 domain and the adjacent 'QPSMT' sequence — are required for specific interaction with c-Ski and SnoN; these sequences are conserved in Smad2 but absent in Smad1, explaining preferential binding to Smad2/3 over Smad1. Smurf2 induces ubiquitin-dependent degradation of SnoN by positioning it close to the Smad2 linker region.\",\n      \"method\": \"Mutagenesis, co-immunoprecipitation, structural mapping using known Smad MH2 crystal structure\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mutagenesis mapping of interaction surfaces with structural context, functional degradation assay\",\n      \"pmids\": [\"12426322\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Smurf2 (an E3 ubiquitin ligase) is induced in obstructed kidneys and forms a complex with SnoN, promoting its ubiquitination and proteasomal degradation in vivo; immunodepletion of Smurf2 reduces SnoN ubiquitination in kidney extracts.\",\n      \"method\": \"Immunodepletion, co-immunoprecipitation, ubiquitination assay in kidney extracts, immunohistochemistry\",\n      \"journal\": \"Kidney international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — endogenous complex in tissue extracts with functional ubiquitination assay, single study\",\n      \"pmids\": [\"16625151\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"SnoN sumoylation occurs primarily at lysine 50 (Lys-50) and is mediated by E3 SUMO ligases PIAS1 and PIASx, which physically interact with SnoN. SUMO modification does not alter SnoN stability or TGF-β repression, but loss of sumoylation at Lys-50 potently activates muscle-specific gene expression and enhances myotube formation, revealing a TGF-β-independent function of SnoN in myogenesis.\",\n      \"method\": \"In vivo sumoylation assay, site-directed mutagenesis (K50R), co-immunoprecipitation, muscle differentiation assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — PTM characterized biochemically, specific site identified by mutagenesis, writer identified (PIAS1/PIASx), functional consequence established\",\n      \"pmids\": [\"17202138\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The SNON-SMAD4 complex directly binds the TGF-β response element (TRE) in the SKIL gene proximal promoter and recruits histone deacetylases to repress basal SKIL gene expression; upon TGF-β signaling, SNON is removed from the promoter allowing SMAD complexes to induce SKIL transcription, and the re-expressed SNON-SMAD4 complex then represses its own gene as a negative feedback loop.\",\n      \"method\": \"ChIP assay, sequential ChIP, promoter-reporter (luciferase), cloning of human SKIL promoter\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — ChIP and sequential ChIP establish in vivo binding; functional promoter assays demonstrate repression mechanism; negative feedback loop confirmed\",\n      \"pmids\": [\"22674574\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"SNON (SKIL) is expressed in human embryonic stem cells (hESCs) and associates with SMAD2 at promoters of primitive streak and early definitive endoderm marker genes; SNON knockdown causes premature activation of these genes and loss of hESC morphology, while enforced SNON expression inhibits endoderm formation and diverts hESCs toward extraembryonic fate.\",\n      \"method\": \"ChIP assay, siRNA knockdown, overexpression, analysis of hESC differentiation markers\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — ChIP demonstrates in vivo binding at target promoters; gain- and loss-of-function establish specific developmental role\",\n      \"pmids\": [\"23154981\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"SnoN interacts with multiple components of the Hippo pathway (including Lats2) to inhibit Lats2 binding to TAZ and subsequent TAZ phosphorylation, leading to TAZ stabilization and enhanced TAZ transcriptional and oncogenic activities; SnoN itself is downregulated by Lats2 activated by the basolateral polarity protein Scribble.\",\n      \"method\": \"Co-immunoprecipitation, kinase assay, shRNA knockdown, TAZ phosphorylation/stability assays, breast cancer cell models\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple binding partners identified by co-IP, functional phosphorylation assay, loss-of-function phenotype; single lab\",\n      \"pmids\": [\"27237790\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Arkadia (RNF111) promotes iTreg cell differentiation in CD4+ T cells by inducing degradation of SKI and SnoN; genetic ablation of both SKI and SnoN rescues Arkadia-deficient iTreg differentiation in vitro and in vivo, demonstrating that SKI/SnoN are the critical Arkadia substrates mediating TGF-β-dependent iTreg induction.\",\n      \"method\": \"Conditional knockout mouse (Arkadia in CD4+ T cells), in vitro differentiation assay, double-knockout epistasis, flow cytometry\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic epistasis in mouse with defined cellular phenotype (iTreg differentiation); in vivo and in vitro concordance\",\n      \"pmids\": [\"34473197\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SKIL (SnoN) is a driver gene at the 3q26 amplicon; elevated SKIL expression induces cell invasion in immortalized human mammary epithelial cells through upregulation of SLUG (SNAI2), and combined TLOC1 + SKIL expression induces subcutaneous tumor growth in vivo.\",\n      \"method\": \"Gain-of-function genetic screen, shRNA loss-of-function, invasion assay, xenograft mouse model, proteomic studies\",\n      \"journal\": \"Cancer discovery\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional genomic screen with in vivo validation and pathway identification (SLUG upregulation), single lab\",\n      \"pmids\": [\"23764425\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"SnoN suppresses BMP-induced hypertrophic maturation of chondrocytes by inhibiting BMP signaling downstream of Smad1/5/8 activation, specifically by suppressing Id1 expression; SnoN expression is highest in articular cartilage of adult mice and co-localizes with phospho-Smad2/3 in prehypertrophic chondrocytes.\",\n      \"method\": \"siRNA knockdown, overexpression, BMP-responsive reporter assay, expression analysis in mouse growth plate and human OA cartilage\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — gain- and loss-of-function with pathway reporter and in vivo expression pattern; single lab\",\n      \"pmids\": [\"22767605\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"SnoN coordinates TGF-β and prolactin signaling in mammary epithelial cells by enhancing Stat5 protein stability; SnoN-/- mice display severe defects in alveologenesis and lactogenesis that can be rescued by active Stat5, demonstrating SnoN promotes Stat5 signaling to control lactation.\",\n      \"method\": \"Knockout mouse model, rescue by active Stat5, mammary gland morphogenesis analysis\",\n      \"journal\": \"Development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with specific morphogenic phenotype and molecular rescue defines pathway position\",\n      \"pmids\": [\"22833129\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Sno-deficient T cells show augmented TGF-β sensitivity; Sno-dependent suppression of TGF-β signaling is required for normal T-cell proliferation following receptor ligation, as the proliferation defect in Sno hypomorph and null mice is reversed by anti-TGF-β antibodies or exogenous IL-2. IL-2 and IL-4 production is reduced in mutant T cells.\",\n      \"method\": \"Targeted gene deletion (hypomorph and null mice), T-cell proliferation assay, anti-TGF-β rescue, cytokine measurement\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with specific immune phenotype and pharmacological rescue establishing TGF-β pathway epistasis\",\n      \"pmids\": [\"12861029\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"NSUN2 promotes m5C methylation of SKIL mRNA, which is recognized by YBX1 to stabilize SKIL transcripts; elevated SKIL increases TAZ activation to promote colorectal cancer progression.\",\n      \"method\": \"m5C-methylated RNA immunoprecipitation, RNA stability assay, bisulfite sequencing, NSUN2 knockout mouse, YBX1 interaction studies\",\n      \"journal\": \"Clinical and translational medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — m5C modification of SKIL mapped, reader (YBX1) identified, functional mRNA stability consequence demonstrated; single lab\",\n      \"pmids\": [\"38468490\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SKIL promotes tumorigenesis and immune escape of NSCLC by interacting with TAZ (co-immunoprecipitation), upregulating TAZ to activate autophagy and suppress the STING pathway; silencing TAZ cancels the effects of SKIL overexpression.\",\n      \"method\": \"Co-immunoprecipitation, lentiviral overexpression/knockdown, colony formation assay, xenograft and syngeneic mouse models, flow cytometry for T cell infiltration\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP demonstrates physical interaction, epistasis experiment (TAZ KD rescues SKIL OE phenotype) places pathway position; single lab\",\n      \"pmids\": [\"33268765\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"SnoN binds a specific DNA sequence (GTCTAGAC) and represses transcription through a tripartite repression domain; subdomain II interacts with TAF(II)110 via a quenching mechanism of transcriptional repression. Two subdomains (II and III) are required for DNA binding and cellular transformation.\",\n      \"method\": \"Electrophoretic mobility shift assay, Gal4 fusion reporter assay, deletion mutagenesis, transformation assay, GST pulldown with TAF(II)110\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — DNA binding, repression domain mapping by mutagenesis, and interaction with basal transcription factor identified; single lab with multiple assays\",\n      \"pmids\": [\"9824161\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"FMRP directly interacts with lncRNA TUG1 and decreases its stability; TUG1 binds to SnoN and negatively modulates the SnoN-Ccd1 pathway to control axonal development in neurons.\",\n      \"method\": \"RNA immunoprecipitation, co-immunoprecipitation, axon growth assay in FMRP-deficient neurons\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single pulldown/co-IP, limited mechanistic follow-up of SnoN involvement specifically\",\n      \"pmids\": [\"29211876\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SKIL (SnoN) functions as a transcriptional corepressor that binds Smad2, Smad3, and Smad4 to repress TGF-β target genes by recruiting histone deacetylase complexes (N-CoR/SMRT/mSin3); upon TGF-β stimulation, SnoN is rapidly degraded via multiple E3 ubiquitin ligases (APC/Cdh1, Arkadia, Smurf2) recruited by activated Smads, allowing target gene activation, after which re-expressed SnoN-SMAD4 complexes bind the SKIL promoter to terminate signaling in a negative feedback loop; additionally, SnoN interacts with Hippo pathway components to stabilize TAZ, interacts with p300 to activate neuronal transcription programs (including Ccd1) that promote axonal growth, is modified by SUMO-1 at Lys-50 (via PIAS1/PIASx) to regulate myogenesis independently of TGF-β, and its subcellular localization (cytoplasmic in normal cells vs. nuclear in cancer cells) determines whether it sequesters Smads in the cytoplasm or represses their transcriptional activity in the nucleus.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"SKIL (SnoN) is a transcriptional corepressor that negatively regulates TGF-β signaling by binding Smad2, Smad3, and Smad4 and recruiting histone deacetylase complexes containing N-CoR/SMRT, mSin3, and HDAC to maintain target genes in a repressed state [PMID:10531062, PMID:10811619]. Upon TGF-β stimulation, SnoN is rapidly degraded via the ubiquitin–proteasome pathway through multiple E3 ligases—APC/Cdh1, Arkadia (RNF111), and Smurf2—that are recruited by activated Smads, allowing transient target gene activation; SnoN is subsequently re-expressed and binds its own promoter with SMAD4 to terminate signaling in a negative feedback loop [PMID:11691834, PMID:17591695, PMID:22674574]. Beyond TGF-β, SnoN functions in neuronal axon growth by interacting with p300 to activate transcription of Ccd1, is regulated by Cdh1-APC in neurons, controls Hippo pathway output by stabilizing TAZ through inhibition of Lats2, promotes Stat5 stability during mammary alveologenesis, and undergoes SUMO modification at Lys-50 by PIAS1/PIASx to regulate myogenesis independently of TGF-β [PMID:16675394, PMID:19339625, PMID:27237790, PMID:22833129, PMID:17202138]. SnoN subcellular localization—cytoplasmic in normal cells versus nuclear in cancer cells—determines whether it sequesters Smads in the cytoplasm or represses their transcriptional activity in the nucleus [PMID:16109768].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Establishing that SnoN directly binds DNA and represses transcription through a tripartite domain that interacts with basal transcription factor TAF(II)110 defined SnoN as an active transcriptional repressor rather than a passive binding partner.\",\n      \"evidence\": \"EMSA, Gal4 fusion reporter, deletion mutagenesis, GST pulldown with TAF(II)110\",\n      \"pmids\": [\"9824161\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological relevance of direct DNA binding versus Smad-mediated recruitment unclear\", \"TAF(II)110 interaction not validated in vivo\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Demonstrating that SnoN binds Smad2/Smad4, recruits N-CoR, and is rapidly degraded upon TGF-β stimulation—then re-expressed to shut off signaling—established the core model of SnoN as both a gatekeeper and feedback terminator of TGF-β transcription.\",\n      \"evidence\": \"Co-immunoprecipitation, transcriptional reporter assays, pulse-chase degradation experiments in multiple cell lines\",\n      \"pmids\": [\"10531062\", \"9927733\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the E3 ligase mediating degradation was unknown\", \"Mechanism of SnoN nuclear export/import not resolved\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Biochemical isolation of a macromolecular SnoN–N-CoR/SMRT–mSin3–HDAC repressor complex defined the enzymatic basis of SnoN-mediated silencing as histone deacetylation.\",\n      \"evidence\": \"Biochemical fractionation, co-immunoprecipitation, knockout mouse model\",\n      \"pmids\": [\"10811619\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific HDAC isoform(s) required not identified\", \"Genome-wide target gene repertoire not mapped\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Reconstitution of Smad3-dependent recruitment of APC/UbcH5 to SnoN's destruction box identified the first E3 ligase responsible for TGF-β-induced SnoN degradation, resolving how ligand signaling removes the repressor.\",\n      \"evidence\": \"In vitro ubiquitination assay with reconstituted components, site-directed mutagenesis of D-box and lysine residues\",\n      \"pmids\": [\"11691834\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of APC versus other E3 ligases in different cell types not resolved\", \"Cell-cycle phase dependence of APC-mediated degradation not clarified\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Mapping the Smad3 interaction surfaces (SE and QPSMT motifs in MH2 domain) and showing Smurf2 induces SnoN ubiquitination revealed a second E3 ligase and explained the specificity of SnoN for TGF-β/activin Smads over BMP Smads.\",\n      \"evidence\": \"Mutagenesis of Smad3, co-immunoprecipitation, structural mapping using known crystal structure\",\n      \"pmids\": [\"12426322\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Crystal structure of the SnoN–Smad complex not solved\", \"Smurf2-mediated degradation not reconstituted in vitro with purified components\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Demonstrating that oncogenic transformation by SnoN requires simultaneous repression of both R-Smads and Smad4, and that SnoN deficiency in T cells causes augmented TGF-β sensitivity, established in vivo physiological consequences of SnoN-mediated TGF-β repression.\",\n      \"evidence\": \"Double Smad-binding-site mutagenesis with transformation assays; SnoN-null/hypomorph mouse T cells with anti-TGF-β rescue\",\n      \"pmids\": [\"12764135\", \"12861029\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Smad4 and R-Smad binding are simultaneously occupied on chromatin unknown\", \"T-cell-intrinsic versus microenvironment contributions not fully separated\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Showing that SnoN is cytoplasmic in normal epithelial cells (where it sequesters Smads) but nuclear in cancer cells resolved a longstanding paradox about how SnoN can be both a tumor suppressor and an oncogene depending on context.\",\n      \"evidence\": \"Immunofluorescence and subcellular fractionation across primary and cancer cell lines, TGF-β degradation assays\",\n      \"pmids\": [\"16109768\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Signals controlling nuclear import/export not identified\", \"Whether cytoplasmic SnoN is degradation-resistant in vivo not confirmed\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Identifying SnoN as a Cdh1-APC substrate in neurons whose degradation restricts axonal growth revealed a TGF-β-independent function for SnoN in neuronal morphogenesis.\",\n      \"evidence\": \"Co-immunoprecipitation, ubiquitination assay, shRNA knockdown in granule neurons, in vivo cerebellar analysis\",\n      \"pmids\": [\"16675394\", \"14585991\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Transcriptional targets of SnoN in neurons not yet identified at this point\", \"Whether Cdh1-APC acts on SnoN in non-neuronal tissues unclear\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Establishing Arkadia (RNF111) as the essential E3 ligase for TGF-β-induced SnoN degradation, requiring a ternary complex with phospho-Smad2/3, resolved the hierarchy among the three known SnoN-targeting E3 ligases and explained signal-dependent gating of degradation.\",\n      \"evidence\": \"siRNA, dominant-negative mutant, ubiquitination assay, reconstitution in Arkadia-null cancer cells\",\n      \"pmids\": [\"17591695\", \"17510063\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative tissue-specific contributions of APC, Arkadia, and Smurf2 not systematically compared\", \"Structural basis of ternary complex formation unknown\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Demonstrating that SUMO modification of SnoN at Lys-50 by PIAS1/PIASx regulates muscle-specific gene expression independently of TGF-β signaling uncovered a post-translational switch controlling a non-canonical SnoN function in myogenesis.\",\n      \"evidence\": \"In vivo sumoylation assay, K50R mutagenesis, muscle differentiation assay\",\n      \"pmids\": [\"17202138\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of SUMO-dependent SnoN interactors in myogenesis unknown\", \"Whether SUMO modification alters chromatin targeting not tested\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Identifying p300 as a SnoN coactivator and Ccd1 as a direct transcriptional target in neurons provided the molecular mechanism by which SnoN promotes axonal growth—switching from repressor to activator function via coactivator choice.\",\n      \"evidence\": \"Gene expression profiling, co-immunoprecipitation with p300, Ccd1 shRNA in rat cerebellum in vivo\",\n      \"pmids\": [\"19339625\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How SnoN switches from N-CoR to p300 recruitment is mechanistically unresolved\", \"Additional neuronal transcription targets not comprehensively mapped\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"ChIP and promoter analysis showing that SNON-SMAD4 directly occupies the SKIL promoter TRE to repress its own gene closed the negative feedback loop at the chromatin level and explained signal termination kinetics.\",\n      \"evidence\": \"ChIP, sequential ChIP, cloned human SKIL promoter-reporter assays\",\n      \"pmids\": [\"22674574\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinetics of SNON re-occupancy after TGF-β pulse not measured genome-wide\", \"Whether other TGF-β target promoters use identical autorepression unclear\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Demonstrating that SnoN occupies primitive streak gene promoters with SMAD2 in hESCs, and that its loss causes premature endoderm specification, extended SnoN's gatekeeper role to human pluripotency and early lineage commitment.\",\n      \"evidence\": \"ChIP in hESCs, siRNA knockdown and overexpression with differentiation marker analysis\",\n      \"pmids\": [\"23154981\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SnoN acts similarly in mouse ESCs not tested\", \"Mechanism of SnoN downregulation during normal endoderm specification unknown\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Showing that SnoN-null mice have severe lactation defects rescued by active Stat5 revealed that SnoN enhances Stat5 protein stability, linking SnoN to JAK-STAT signaling in mammary gland development.\",\n      \"evidence\": \"Knockout mouse, Stat5 rescue, mammary gland histology\",\n      \"pmids\": [\"22833129\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which SnoN stabilizes Stat5 (direct binding or indirect) not defined\", \"Whether this function is TGF-β-dependent not resolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Discovering that SnoN interacts with Hippo pathway components to inhibit Lats2-mediated TAZ phosphorylation and degradation revealed a TGF-β-independent oncogenic mechanism operating through cross-pathway regulation.\",\n      \"evidence\": \"Co-immunoprecipitation, kinase assay, shRNA knockdown, TAZ stability assays in breast cancer cells\",\n      \"pmids\": [\"27237790\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis of SnoN–Lats2 interaction unknown\", \"Whether SnoN also regulates YAP not tested\", \"Single-lab finding awaiting independent confirmation\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Genetic epistasis showing that double knockout of SKI and SnoN rescues Arkadia-deficient iTreg differentiation established that SnoN (and SKI) are the critical Arkadia substrates gating TGF-β-dependent regulatory T cell induction in vivo.\",\n      \"evidence\": \"Conditional knockout mice, in vitro/in vivo iTreg differentiation, flow cytometry\",\n      \"pmids\": [\"34473197\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SnoN and SKI have redundant or distinct roles in iTreg specification unclear\", \"SnoN targets in Treg-specific gene programs not identified\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis of SnoN's cofactor switching (N-CoR versus p300), the signals controlling SnoN nuclear-cytoplasmic shuttling, and the relative tissue-specific contributions of the three E3 ligases (APC, Arkadia, Smurf2) to SnoN turnover.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No crystal or cryo-EM structure of SnoN in complex with any partner\", \"Genome-wide direct target gene maps across tissues lacking\", \"Mechanism of cofactor switching between repression and activation unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [0, 3, 4, 16, 17, 26]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 18, 22]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 5, 16, 17]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 2, 4, 6, 18, 19, 23]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 3, 16, 17, 26]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [2, 6, 7, 9, 14, 15]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [9, 11, 17, 22]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [19, 23]}\n    ],\n    \"complexes\": [\n      \"N-CoR/SMRT/mSin3/HDAC repressor complex\",\n      \"APC/Cdh1\"\n    ],\n    \"partners\": [\n      \"SMAD2\",\n      \"SMAD3\",\n      \"SMAD4\",\n      \"SKI\",\n      \"RNF111\",\n      \"EP300\",\n      \"SMURF2\",\n      \"LATS2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}